2.2.1.2.1 Direct Diazotization

An aqueous sodium nitrite solution is added to a cold solution or suspension of the primary aromatic amine in an excess of hydrochloric or sulfuric acid. A temperature of 0–5 °C is maintained by adding ice directly to the reaction mixture.

2.2.1.2.2 Indirect Diazotization Method

This method is particularly useful for aromatic aminocarboxylic and aminosulfonic acids, which are often only sparingly soluble in dilute acid. The amino compound is dissolved in water or in weak alkali and combined with a stoichiometric amount of sodium nitrite, upon which the resulting solution is poured into a mixture of acid and ice. Alternatively, the process may be reversed by pouring the acid into the amine–nitrite mixture.

2.2.1.2.3 Diazotization of Weakly Basic Amines

Amines of very low basicity undergo diazotization after being dissolved in concentrated sulfuric acid. The nitrosating agent is provided by nitrosylsulfuric acid, which is either purchased commercially or easily prepared by dissolving solid sodium nitrite in concentrated sulfuric acid.

Sulfuric acid as a reaction medium may be replaced by glacial acetic acid or by a mixture of glacial acetic acid/nitrosylsulfuric acid. In the former case, half-concentrated hydrochloric acid is added, and diazotization proceeds in an aqueous sodium nitrite solution. The combination of glacial acetic acid/nitrosylsulfuric acid is a particularly useful medium for the bisdiazotization of 1,2-, 1,3- or 1,4-diaminobenzenes (phenylenediamines).

2.2.1.2.4 Diazotization in Organic Solvents

Amines that are considerably or entirely insoluble in water are dissolved in glacial acetic acid or in other organic media, possibly mixed with water; for example alcohols or aprotic solvents. Addition of acid is followed by a typical diazotization reaction in an aqueous sodium nitrite solution. Other possible sources of the nitrosating species NO include nitrosylsulfuric acid, nitrosyl chloride, alkyl nitrite and nitrous gases.

The outcome of a diazotization reaction is largely controlled by the temperature, the pH and the concentration of the medium in which the reaction is carried out. Reactions involving sparingly soluble amines are also dependent on physical parameters, such as distribution and particle size, as well as on the possible presence of emulsifiers or dispersion agents.

A newer diazotization technique using masked diazonium compounds is described in connection with the different coupling methods (Section 2.2.2.1).

In aqueous media, most diazonium salts are only stable at low temperature. Heating frequently leads to decomposition; as a result, nitrogen and the corresponding phenol are formed. The stability of a diazonium compound is a function of the substitution pattern of the aromatic ring system. Electronegative (electron withdrawing) substituents (electron acceptors), such as halogens or nitro functions, render their host structure more sensitive to decomposition than do electron donors such as -CH₃, -OCH₃, -OC₂H₅. Some amines can even be diazotized up to a temperature of 50 °C. Other factors that affect the stability of a diazonium compound are visible light or heavy metal ions.

On an industrial scale, diazotization reactions are chiefly carried out in cast iron kettles that are lined with brick or rubber as a protection against acid. Wooden vats also continue to be used.

In most cases, diazonium salts are unstable in the dry state and are sensitive to heat and impact. Since isolation is not necessary for hydrazone pigment production, the diazonium compound is coupled with the coupling component as it is formed in solution or suspension.

2.2.2.1.1 Direct Coupling

The coupling component is dissolved in an alkaline solution and, after adding a clarifying agent and possibly charcoal to the solution, it is filtered through a sparkler filter or a filter press.

The solution is then transferred into the coupling vessel equipped with a mechanical stirrer and, possibly in the presence of a surfactant, precipitated with acetic acid, hydrochloric acid or phosphoric acid. The coupling component may also be precipitated ‘indirectly’; that is, the appropriate mixture of acid and emulsifier is filled into the kettle first and the alkaline solution of the coupling component is then added gradually to the clear solution by gravity flow. The clarified solution of the diazonium compound is then introduced into or onto this coupling suspension.

Precipitating the coupling component with acetic acid or phosphoric acid often automatically provides the buffer that is necessary to maintain a certain pH throughout the coupling reaction. Otherwise, buffers such as sodium acetate, sodium phosphate or calcium carbonate (‘chalk coupling’) must be added.

2.2.2.1.2 Indirect Coupling

The clarified acidic diazonium salt solution is first transferred to a coupling vat equipped with a mechanical agitator, and the clarified alkaline coupling component solution is then added above or under the surface of the diazonium salt solution. Constant agitation is essential.

2.2.2.1.3 ‘Pendulum’ Technique

If a coupling reaction is carried out in the absence of a buffer system, a constant pH is maintained throughout the coupling process by continuously adding dilute sodium hydroxide solution (‘pendulum solution’) to the reaction mixture.

2.2.2.1.4 Organic Solvents as Coupling Media

Starting materials that are only sparingly soluble in water may require solvents that are either partially or entirely organic. Diazotization can either be carried out as usual with an aqueous sodium nitrite solution, or alternatively with nitrosylsulfuric acid or an organic nitrite. Appropriate solvents must be stable to the reactants. Examples include aromatic hydrocarbons, chlorohydrocarbons, glycol ethers, nitriles, esters, and dipolar aprotic solvents, such as dimethylformamide, dimethyl sulfone, tetramethylene sulfone, tetramethylurea and N-methylpyrrolidone.

A special type of azo bridge formation is observed in aprotic polar media (solvents with a dielectric constant below 15). In these solvents, the reaction proceeds via an aprotic diazotization–coupling mechanism [11], which unites both diazotization and coupling in one step. The process involves adding a volatile alkyl nitrite to a slightly acidic suspension of a combined solution of diazo and coupling component. Organic solvents have the double advantage of being almost completely accessible to recycling and of producing only very small amounts of contaminants that affect the wastewater.

2.2.2.1.5 Coupling with ‘Masked’ Diazonium Compound

Coupling reactions in organic solvents are occasionally carried out with ‘masked’ diazonium compounds; for example, with special diazonium moieties that are incorporated into a larger organic structure [12], for instance in a diazoamino compound (15) or a benzotriazinone (16):

The diazonium compound itself is liberated by adding a strong organic acid, such as halogenated acetic acid, after the coupling component has been introduced into the reaction mixture:

Hydrazone pigments are difficult to purify, because they emerge from the manufacturing process as almost insoluble substances. The purity of the starting materials is therefore of major concern to the producer. However, contamination is not the only factor to influence the outcome of pigment synthesis: the following factors have a much greater impact on pigment production than on the synthesis of dyes:

• coupling technique, for example sequence and rate of reactant addition;
• concentrations of the reactants;
• temperature of the reaction mixture;
• choice of organic solvent added;
• technical and operational parameters: shape and size of the reaction vats and the agitator, as well as the speed of agitation.

2.3.4.2.1 Pigment Yellow 1

This compound has entered pigment history as ‘Hansa Yellow G'. The commercial varieties are products with comparatively coarse particle sizes and specific surface areas of approximately 8–30 m² g⁻¹. P.Y.1 provides good hiding power, it is used primarily in air drying paints as well as in packaging and textile printing.

Decreasing the particle size produces more transparent, more greenish and cleaner pigment types; the tinctorial strength frequently improves. This advantageous trend is compromised by a considerable decrease in lightfastness and resistance to organic solvents. In several application media, the tendency to recrystallize is also enhanced (Section 1.7.7). Pigment Yellow 1 types with very fine particle sizes lose the advantage of superior lightfastness compared to diarylide yellow pigments with comparable shades, whose solvent resistance is much better and whose tinctorial strength is almost twice as high as that of P.Y.1.

Although inferior fastness to organic solvents, involving unsatisfactory migration properties, excludes P.Y.1 from important areas of application, such as baking enamels, there are certain conditions under which it may be applied in such media. The user must in this case observe a certain concentration limit beyond which the pigment may bloom. The pigment is stable up to 140 °C.

For decades, P.Y.1 represented the standard source of yellow for all printing purposes. Today, however, P.Y.1 has been replaced in this field by the stronger diarylide yellow pigments.

The tinctorial strength of a printing ink is measured in terms of the pigment concentration in a standardized ink film that will produce a certain depth of shade in letterpress proof-prints. Depending on the type, inks made from P.Y.1 must contain about 8–11 wt% pigment to produce 1/3 SD films; while inks made from the similarly shaded diarylide yellow pigment P.Y.14 require only between 4% and 6% pigment. The lightfastness of such a printed P.Y.1 sample equals approximately step 5 on the Blue Scale, while the corresponding P.Y.14 specimen only reaches step 3. The corresponding values for 1/1 SD prints are 6–7 and 3 on the Blue Scale, respectively.

P.Y.1 prints are comparatively sensitive to most common organic solvents, such as esters, ketones, and aromatic hydrocarbons, but completely fast to alcohols and aliphatic hydrocarbons. The prints are also resistant to soap, alkali and acid.

In the printing ink industry, P.Y.1 is used especially to replace diarylide yellow pigments in areas where the latter are not sufficiently lightfast to meet the technical standards. This is especially true for the packaging printing industry, which particularly appreciates the good hiding power of most types of P.Y.1. Since they are sensitive to organic solvents, such grades are mainly used in alcohol-based nitrocellulose (NC) printing inks and in waterborne inks. Poor migration resistance and heat stability largely precludes the use of P.Y.1 in plastics.

In general, P.Y.1 is used extensively in various applications, including those generally mentioned in connection with monohydrazone yellow pigments. As a result of its good lightfastness, this pigment is particularly interesting for textile printing; however, its fastness to dry-cleaning solvents and to dry heat setting (fixation) is poor. P.Y.1 is easily dispersed in most media, irrespective of the dispersion equipment.

2.3.4.2.2 Pigment Yellow 2

This pigment has little impact on the market today and is only occasionally found in printing inks or in office articles, for instance in coloured pencils. Its shade is more reddish and its tinctorial strength superior to that of P.Y.1. The low specific surface area of the types which are still commercially available makes for good hiding in print. Solvent resistance and other fastness properties equal those of P.Y.1; P.Y.2 is only slightly less lightfast than P.Y.1.

2.3.4.2.3 Pigment Yellow 3

P.Y.3 grades produce a pure, much greener yellow than the Pigment Yellow 1 types. Pigment Yellow 3 can easily be combined with blue pigments to produce shades of green; it may also be used to modify the hue of a green pigment, such as Copper Phthalocyanine Green. The commercial types exhibit low specific surface areas and confer good hiding power on paints, coatings and prints.

P.Y.3 is even less stable to most organic solvents than P.Y.1; it migrates in baking enamels and is applied in this context only rarely and at a pigment concentration below the concentration limit above which blooming occurs (Section 1.6.3.1). As a comparison, the concentration limit beyond which P.Y.3 blooms in a certain urea/alkyd resin paint at a temperature of 120 °C (30 min) is 1%; at 140 °C, the limit increases to 2.5%. Higher temperatures always cause blooming, irrespective of the concentration. Any pigment that is to be applied in a baking enamel should be submitted to a test run in the specific material. There are commercially available grades which recrystallize considerably less in alkyd resin paints.

P.Y.3 is completely water, acid and alkali resistant. Alkali fastness is a major prerequisite for several applications, especially in aqueous media.

The pigment exhibits excellent lightfastness and durability; its performance in this respect is superior to that of P.Y.1, especially if it is reduced with titanium dioxide. Compared to P.Y.98, which exhibits a similar hue but is much stronger, P.Y.3 grades have the advantage of being more reasonable in terms of cost but less fast to solvents and migration. In air drying paints, for instance, medium white reductions of P.Y.3 are somewhat less lightfast but more durable than comparable P.Y.98 grades.

P.Y.3 and P.Y.1 are used in similar applications. The paint industry employs these pigments in air drying, cellulose nitrate, polyurethane, acid hardening and similar paints. P.Y.3 may lend colour to emulsion paints, and its full and medium shades even comply with the industrial standards for exterior house paints. In the printing inks field, the pigment is primarily used in various packaging inks. P.Y.3 also plays a role in textile printing, office articles, artists' paints, and several special purposes. It is, however, not used in plastics; a certain exception is the colouration of unsaturated polyester resins, whose hardening process by peroxide is not influenced by P.Y.3 and in which the pigment exhibits good lightfastness.

Single crystal data and X-ray powder patterns were reported by Whitaker [34, 35].

2.3.4.2.4 Pigment Yellow 5

Over the last few decades, commercial recognition of Pigment Yellow 5 has decreased considerably. Two crystal modifications of the pigment are available [36]; both show practically identical shades. P.Y.5 is a greenish yellow pigment, applied mainly in printing inks and occasionally also in air drying systems. Although its hue is considerably redder than that of P.Y.3, its application properties parallel that of P.Y.3. It is slightly less lightfast and in this respect similar to the more reddish P.Y.1.

2.3.4.2.5 Pigment Yellow 6

This representative is only of limited regional importance. Its shade is a medium yellow, which places it in a competitive position with several similar colourants of the same class, which it also resembles in its fastness properties.

Crystal data are described by A. Whitaker [22, 37].

2.3.4.2.6 Pigment Yellow 10

P.Y.10 provides clean, reddish yellow hues. Its very good lightfastness makes it almost as fast as P.Y.97. However, its solvent fastness is poor and in this respect inferior to most other monohydrazone yellow pigments; it shares this deficiency with P.O.1. Its migration resistance is also poor and considerably less satisfactory than that of the slightly greener P.Y.65. In the face of increasingly stringent application requirements, P.Y.10 has almost vanished from the European market in recent years. Originally, it was used in special printing inks and in air drying paints. In the USA, it is still applied in traffic marking paints.

2.3.4.2.7 Pigment Yellow 49

This very lightfast pigment has a clean greenish yellow shade and is used for viscose spin dyeing and for the mass colouration of viscose foils, sponges, and so on. It is commercially available in the form of aqueous pigment preparations, in which the pigment is predispersed. In 1/1 to 1/3 SD, the lightfastness equals step 8, in 1/12 SD it reaches a value of 7–8 on the Blue Scale. The pigment performs excellently on textiles, but its fastness to wet and dry crocking is not always satisfactory.

2.3.4.2.8 Pigment Yellow 60

This colourant is produced in the USA, where it also plays a minor role on the market. Its shade is a reddish yellow. P.Y.60 is used in trade sales paints and in emulsion paints. Poor resistance to organic solvents, lack of overcoating fastnesss, and a lightfastness that deteriorates rapidly with the degree of reduction with TiO₂ are reasons for the limited commercial interest in this pigment. Crystal data have been published by A. Whitaker, who described it already as a hydrazone pigment [38].

2.3.4.2.9 Pigment Yellow 65

Pigment Yellow 65 provides reddish yellow shades. Although its importance as a colourant on the European and Asian market has diminished over the last years, there is still some demand for it in the USA. The types which are still commercially available consist of pigments with comparatively coarse particle sizes and with specific surface areas of approximately 6–20 m² g⁻¹. The pigment thus provides excellent hiding power. There is some resemblance between Pigment Yellow 65 and P.Y.74 types with high hiding power in that they perform equally well in terms of solvent resistance, recrystallization fastness in solvent containing media, lightfastness, and durability. Tinctorially, however, P.Y.65 is considerably inferior, which precludes its application in printing inks. Opaque varieties of the slightly more greenish diarylide yellow pigment P.Y.83, for instance, are more than three times as strong as P.Y.65, yet provide similar lightfastness. Media in which P.Y.65 grades are applied include air drying and emulsion paints. Combinations of the positional isomers P.Y.65 and 74 are also commercially available. Crystal data have been reported by A. Whitaker [23, 39].

2.3.4.2.10 Pigment Yellow 73

Depending on particle size distribution and the application medium, this pigment more or less bears some resemblance to P.Y.1 as far as shade and tinctorial strength are concerned. At equal tinctorial strength, however, P.Y.73 is more lightfast and durable. Compared to P.Y.1, it is also considerably more insoluble in various organic solvents, such as aliphatic and aromatic hydrocarbons, and thus also less prone to recrystallize. This facilitates its incorporation into solvent containing media, such as air drying systems and emulsion paints, as well as in nitrocellulose systems and so on throughout the printing inks field. Compared to P.Y.1, Pigment Yellow 73 grades generally afford more transparent prints and are also somewhat redder than the P.Y.74 types with fine grains, which provide a tinctorial strength which is about twice as high. P.Y.73 representatives are more lightfast and durable than the tinctorially similar dihydrazone yellow pigments, which are also very stable to solvents.

2.3.4.2.11 Pigment Yellow 74

P.Y.74, a commercial pigment of considerable significance, is used primarily in the printing ink and paint industries. Its greenish yellow shades are somewhere between those of P.Y.3 and P.Y.1. The pigment is considerably stronger than and superior to all comparable monohydrazone yellow pigments. P.Y.74 grades with very different particle sizes are commercially available. Varieties with fine particle sizes, that is, pigments with specific surface areas between approximately 30 and 70 m² g⁻¹, are used primarily in the printing ink industry. They provide brilliant prints, which are brighter and more transparent than those of other monohydrazone yellow pigments. In terms of tinctorial strength, these P.Y.74 varieties reach the level of the similarly coloured dihydrazone yellow pigments, such as the slightly redder P.Y.12. The pigment concentration that is necessary to produce a 1/3 SD P.Y.12 proof-print is 4.5%, compared to 4.2% in the case of P.Y.74. In letterpress application, P.Y.74 has a yellow hue, which corresponds to the DIN 16508 standard for letterpress; in offset printing, it matches not only the DIN 16509 standard in the yellow section of the DIN Scale for process colour printing (Section 1.8.1.1), but also the standard yellow on the Kodak scale. On the European Scale (Section 1.8.1.1), P.Y.74 is somewhat more greenish than the standard yellow. Its shade can be adjusted with suitable reddish yellow pigments.

The lightfastness of types with fine particle sizes exceeds that of colouristically similar dihydrazone yellow pigments (P.Y.12) by 2 to 3 steps on the Blue Scale. This explains why types with fine particle sizes are preferred where excellent lightfastness is required, such as in packaging printing. P.Y.74 is not different from other yellow pigments of this class in that it performs poorly in solvents. The prints are not very suitable for calendering and are not colourfast to sterilization. As typical monohydrazone yellow pigments, P.Y.74 specimens are fast to alkali, acid and soap. Other aspects of their fastness in print, such as butter resistance and fastness to the solvent mixture described in DIN 16 524 (Section 1.6.2.1), are not convincing. However, like other pigments of their class, P.Y.74 varieties with comparatively fine particle sizes are also used in the paint industry, where they lend colour to air drying and emulsion paints. Excellent tinctorial strength, especially in pastel shades, that is in white reductions, make P.Y.74 more advantageous on a cost/performance basis than the somewhat redder P.Y.1. A strong tendency to bloom, however, precludes the use of P.Y.74 in baking enamels.

For some years, the paint industry in particular has focussed increasingly on P.Y.74 types with very low specific surface areas between about 12 and 20 m² g⁻¹ and correspondingly very large particle sizes. Such materials exhibit good hiding power and are particularly interesting as replacements for Chrome Yellows in air drying systems. As a result of favourable pigment rheology, P.Y.74 concentrations in paints can be increased to even improve the hiding power without affecting the rheology, that is, the flow properties, the ease of processing, or the brilliance of the product (Section 1.7.8). Compared to transparent types with fine particle sizes, the more opaque varieties are less brilliant, more reddish, and more lightfast and durable. They are also faster to various organic solvents; but their tendency to migrate is similar. The crystal structure was determined by Whitaker [40] and more accurately by Paulus [24].

2.3.4.2.12 Pigment Yellow 75

Although it is sold in the USA, this pigment has failed to gain commercial importance. Its hue is a reddish yellow, much redder than that of P.Y.74 but greener than that of P.Y.65. In full shade and in white reductions, it resembles the shade of the pigment which is produced by mixed coupling between the two, or plain mixtures of the positional isomers, which are also marketed in the USA. P.Y.75 is somewhat more lightfast than the above-mentioned mixture. Its lightfastness in full shade (5%) corresponds to step 7–8 in an air-dried alkyd resin paint, in reductions (1:5 TiO₂), it matches step 7 on the Blue Scale. Its tinctorial strength is poor, and it is used mainly in traffic marking paints.

2.3.4.2.13 Pigment Yellow 97

Pigment Yellow 97 provides a medium yellow shade with properties that are somewhat of an exception compared to other monohydrazone yellow pigments. Its hue is similar to that of P.Y.1. P.Y.97 is considerably more resistant to most organic solvents than the other representatives of this group, its migration fastness properties are also superior. In baking enamels, for instance, the pigment resists blooming up to about 180 °C. However, its fastness to overpainting in such coatings is not always sufficient. In a white baking enamel on alkyd-melamine resin basis, P.Y.97 does not bleed after 30 min at 120 °C, but very slight bleeding is observed at 160 °C. Its high quality in terms of fastness to clear lacquer overcoatings and sterilization (Section 1.6.2.3), which are important aspects in the printing inks field, is very unusual for a monohydrazone yellow pigment.

In contrast to most other representatives of its class, P.Y.97 is also much more heat resistant. In a performance test, in which prints formulated at 5% pigment concentration are applied to sheet metal covered with white paint, most monohydrazone yellow pigments clearly change colour after 30 min exposure to a temperature up to 140 °C (Section 1.6.7). P.Y.97, however, being very heat stable, retains its colour for 30 min at 180 °C or for 10 min at 200 °C.

P.Y.97 is very lightfast and durable; in this respect it excels over P.Y.1, especially in white reductions. In various systems (air drying and baking paints), P.Y.97 exhibits a lightfastness that corresponds to step 6–7 on the Blue Scale, even if it is reduced by as much as 1:140 TiO₂.

Its tinctorial strength is average and comparable to that of other monohydrazone yellow pigments, except P.Y.74. P.Y.97 disperses easily in all application media.

P.Y.97 is used in various fields. Even in pastel shades, it is used in industrial finishes; while its full shades lend colour to automobile refinishes. In emulsion paints, both its medium and full shades are suited to exterior application. The printing ink industry uses P.Y.97 in high grade printing products, especially where excellent fastness is required, such as in stable posters, and so on. It lends itself without difficulty to all printing techniques. However, lack of fastness to monostyrene and acetone and therefore a certain tendency to bleed in these media precludes its application in deco printing inks, that is, for decorative laminates.

P.Y.97 can also be applied in plastics. In rigid PVC, for instance, its lightfastness is excellent, both in transparent and in opaque shades with TiO₂. Depending on its concentration, the lightfastness reaches values between steps 6–7 and 8 on the Blue Scale. In tests designed to determine the colour fastness in rigid PVC films containing 0.5% pigment, coconut fat, for instance, is not stained. In plasticized PVC, however, the pigment tends to migrate at low concentrations. P.Y.97 exhibits good thermal stability in polyolefins; in 1/3 and 1/25 SD HDPE foils, for instance, it is stable up to 240 °C for 5 min. In HDPE extrusion the pigment does not affect shrinkage. P.Y.97 performs similarly in polystyrene and PE as far as thermal stability is concerned. At common colouration concentrations, the pigment dissolves almost completely at temperatures above 200 °C. The lightfastness of transparent polystyrene colourations is excellent (step 7–8 on the Blue Scale); its opaque shades show good lightfastness (0.1% pigment/0.5% TiO₂) (step 5). In ABS, the lightfastness is superior even in reduction with TiO₂ (step 7 on the Blue Scale). If polymethacrylate is used as a medium, the pigment changes colour only after 5 min at 280 °C; in transparent and opaque colourations; the colour change is 1 CIELAB unit in the system of colour difference. The lightfastness of transparent colourations in such media corresponds to step 8 on the Blue Scale.

P.Y.97 is also used to lend colour to cast epoxy resins and to unsaturated polyester resins; it considerably accelerates the hardening process in the latter (Section 1.8.3.7).

Basically, P.Y.97 can also be applied in other areas, such as in pigmented water-based paints. However, various more economical organic pigments covering the same range of hues, such as P.Y.1, frequently compete with P.Y.97 in this area.

2.3.4.2.14 Pigment Yellow 98

This pigment has been removed from the market worldwide because one of the intermediates for its production is no longer available. P.Y.98 resembles P.Y.3 in shade, that is, it provides clean greenish shades of yellow. P.Y.98, like P.Y.3, is a particularly suitable pigment for clean green mixtures. No perfect replacement for P.Y.98 is commercially available. A mixture of P.Y.3 and P.Y. 111 has been introduced to the market which approaches the colouristic, application and fastness properties of P.Y.98 in printing inks. However, this mixture is not quite as lightfast as P.Y.98. In the paint field, P.Y.3 can replace P.Y.98 in many areas of application. Compared to P.Y.98, however, P.Y.3 is much less resistant to organic solvents. The interval in which blooming occurs in baking enamels is consequently much wider for P.Y.3, which is why this pigment is unsuitable for such applications.

The crystal data and powder pattern were reported by A. Whitaker [41].

2.3.4.2.15 Pigment Yellow 111

P.Y.111 has been commercially available since the 1970s. It is much redder and somewhat duller than P.Y.98, but considerably greener than P.Y.74. In printing inks it is tinctorially stronger than the more greenish P.Y.98 and less lightfast than the latter; the difference between printing inks containing the same amount of P.Y.74 and 98, respectively, equals one step on the Blue Scale. Prints that exhibit the same depth of shade are even more different in their lightfastness. Packaging gravure and flexographic inks, some of which are based on alcohol-soluble nitrocellulose, are much less subject to differences in tinctorial strength than are letterpress or offset inks. The commercially available version of P.Y.111 is considerably more opaque than P.Y.98 and 74 types with fine particle sizes.

2.3.4.2.16 Pigment Yellow 116

Pigment Yellow 116 is a product of somewhat less commercial importance. Its shade is a medium to reddish yellow. The commercial types with their low specific surface area (about 15–18 m² g⁻¹) exhibit good hiding power.

Areas of application include coatings, printing inks, and plastics. Compared to other representatives of its class, P.Y.116 is exceptionally resistant to common organic solvents. Its fastness to overpainting in baking systems, however, is not satisfactory at baking temperatures which are typically around 150 °C. The pigment is acid and alkali resistant and thermally stable up to 180 °C. It is very lightfast; in a medium-oil alkyd resin paint, its full shades (5% pigment) are equal to step 7–8 on the Blue Scale, while in 1/3 SD formulations it equals step 7 on the Blue Scale. P.Y.116 is also very weatherfast. It is applied especially in combination with inorganic yellow pigments and also in baking enamels that are baked at high temperature, such as 200 °C (30 min); and in automobile repair finishes. The pigment is also found in emulsion paints; exterior use is possible if the demands are not too high.

P.Y.116 generally exhibits good fastness properties in printing inks. In letterpress and offset application, for instance, it resists several organic solvents, such as the standard DIN 16 524/1 solvent mixture (Section 1.6.2.1), paraffins, butter, soap, alkali, and acid. Its thermostability is good up to 180 °C. The pigment is also recommended for metal deco printing. The lightfastness of 1/1 to 1/3 SD letterpress proof-prints is equal to step 6 on the Blue Scale. Its good solvent resistance qualifies P.Y.116 as a colourant for packaging gravure inks. The pigment can, for instance, be applied in mixed polymers based on vinyl chloride/vinyl acetate for PVC films.

P.Y.116 is also used in plastics. In plasticized PVC, it shows little tendency to bleed and is thermally stable up to 180 °C. The lightfastness of transparent PVC colourations (0.1% pigment) equals step 7–8; in 1/3 SD (with 5% TiO₂), it corresponds to step 6 on the Blue Scale. Insufficient heat resistance limits the application of P.Y.116 in polyolefins, polystyrene, and other polymers which are processed at high temperature.

2.3.4.2.17 Pigment Yellow 130

This pigment is not marketed in Europe and enjoys only limited commercial importance in other parts of the world. As one of the less resistant representatives of its class, its lightfastness and resistance to organic solvents are particularly deficient. It is recommended to be used for air-drying paints.

2.3.4.2.18 Pigment Yellow 165

Its chemical constitution is identical with Pigment Yellow 10. The pigment enjoys limited commercial success, mainly in the Japanese market. Its hue is reddish yellow, its lightfastness is almost as good as the much greener and tinctorially stronger P.Y.97. P.Y.165 is recommended for use in paints.

2.3.4.2.19 Pigment Yellow 167

The constitution of this pigment differs from that of common monohydrazone yellow pigments, since it is synthesized from aminophthalic imide as a diazonium compound.

P.Y.167 enjoys only regional importance and is recommended for application in paints. The currently available type provides medium hiding power. In full shade and in similar deep shades, it shows a medium yellow; white reductions are greenish yellow and very clean. Its fastness properties correspond to those of other monohydrazone yellow pigments; P.Y.167 is not alkali resistant.

2.3.4.2.20 Pigment Yellow 203

This monohydrazone pigment exhibits a yellow shade. It is recommended for use in paints and printing inks as a substitute for lead containing pigments. P.Y.203 is scarcely found on the European market.

2.3.4.2.21 Pigment Orange 1

P.O.1 has lost most of its commercial significance. Its shade is a very reddish yellow; the Colour Index classifies it as a yellowish orange. Resistance to organic solvents is very low. P.O.1 dissolves more easily in common organic solvents than do other monohydrazone orange pigments, and it is also less lightfast.

P.O.1 is not entirely acid resistant; acids change its colour to a more reddish shade. The pigment has not been able to meet the increasingly stringent requirements of the printing ink and paint industry in recent years. It is now limited in scope to air drying paints and has largely been replaced by mixtures of P.O.5 or others with other monohydrazone yellow pigments.

2.3.4.2.22 Pigment Orange 6

P.O.6 has also suffered considerable loss of interest throughout the European market and is rarely sold today. It provides a very reddish yellow shade. Its lightfastness is very good and almost reaches the level of that of P.Y.1.

2.3.4.3.1 Pigment Yellow 61

This calcium pigment lake is of little commercial value. It is used to lend colour to plastics and to spin dyeing of polypropylene. Its shade is a greenish yellow, and 1/3 SD formulations in polyolefin are thermally stable up to 250 °C. Its tinctorial strength, however, is not satisfactory. 1/3 SD HDPE colourations (1% TiO₂), for instance, require 0.7% pigment. The more costly but colouristically identical hydrazone condensation pigment P.Y.94 requires only 0.44% pigment in order to afford the same depth of shade, and only 0.13% of the somewhat redder diarylide yellow pigment P.Y.17 suffice for this purpose. In partially crystalline polymers, P.Y.61 has a considerable influence on the shrinkage during polymer extrusion. The pigment provides good lightfastness; in HDPE, transparent and opaque 1/3 SD colourations are equal to step 5–6 on the Blue Scale. Its lightfastness is even better in rigid and in plasticized PVC, but the pigment also exhibits very poor tinctorial strength in these media. 1/3 SD colourations require a 3.6% pigment concentration. Its migration resistance in plasticized PVC is good.

P.Y.61 is also used for industrial and trade sales paints. Its full shade and close to deep shades, frequently in combination with inorganic yellow pigments (especially Nickel Titanium Yellow), exhibit good-to-excellent lightfastness and durability. However, the pigment is technically unsuitable for exterior application. Its hiding power and its fastness to overpainting are good. However, P.Y.61 is of little overall importance to the paint industry.

2.3.4.3.2 Pigment Yellow 62

There is equally little commercial interest in the calcium pigment lake P.Y.62. Its use is in the plastics industry, where it produces colours in the medium to reddish yellow range. Although its solvent resistance is only average, P.Y.62 shows better fastness to plasticizers, such as dioctyl phthalate and dioctyl adipate, and consequently exhibits good bleeding fastness in plasticized PVC. It is also thermally stable. Transparent colourations and white reductions up to 1/3 SD equal step 7 on the Blue Scale for lightfastness. At 1/25 SD, the lightfastness drops to step 5–6.

P.Y.62 exhibits comparably low tinctorial strength. A 0.5% pigment concentration in HDPE is necessary to produce 1/3 SD colourations (containing 1% TiO₂), compared to the 0.17% pigment concentration required to afford equal depth of shade with the somewhat more reddish diarylide yellow pigment P.Y.13.

P.Y.62 is thermally stable up to 250 °C. It has a considerable effect on the shrinkage of HDPE and other partially crystalline polymers. The pigment is an equally suitable colourant for polystyrene and polyurethane and lends colour to polypropylene spin dyeing products with minimal application requirements.

2.3.4.3.3 Pigment Yellow 100

This pigment is of little technical importance, except in the USA, where it is sometimes used to lend colour to NC-based flexographic inks and has also some usage in plastics. Owing to its heat stability of 280 °C it is used in food containers, for example HDPE milk bottles. P.Y.100 provides greenish yellow shades of little alkali and soap fastness. It also performs poorly in organic solvents and even water and exhibits little fastness to overcoating. Its tinctorial strength is inferior to that of other organic pigments, and it provides poor lightfastness.

As long as it complies with certain purity requirements, the pigment is approved as a colourant for food and cosmetics in the USA under FD&C Yellow 5 and in Europe under E102.

2.3.4.3.4 Pigment Yellow 133

This pigment is of regional commercial importance in East Asia. It is a strontium lake of a monohydrazone yellow pigment, which provides greenish to medium yellow shades and is used in plastics and for the spin dyeing of polyolefins. Its tinctorial strength is poor. 1/3 SD HDPE colourations (1% TiO₂), for instance, require 0.85% pigment. In this medium, the pigment is thermally stable up to 260 °C.

2.3.4.3.5 Pigment Yellow 142

The pigment is of regional importance in East Asia. P.Y.142 provides a bright yellow shade and is used for the colouration of plastics.

2.3.4.3.6 Pigment Yellow 168

P.Y.168 is a calcium pigment lake and chemically closely related to the P.Y.61 and 62:1 lakes. It has been commercially available for some years, but has as yet gained only regional importance. It provides a clean, somewhat greenish yellow shade somewhere between the shades of P.Y.1 and 3. P.Y.168 is used in paints and plastics.

The pigment exhibits good fastness to aliphatic and aromatic hydrocarbons; but it shows only limited resistance to alcohols, esters and ketones. It is largely acid and alkali resistant. P.Y.168 is not fast to overpainting. It is used in inexpensive industrial finishes wherever the application requirements, especially as far as lightfastness and durability are concerned, are not high.

P.Y.168 shows good migration resistance in plasticized PVC, but its tinctorial strength is relatively poor. In transparent colourations, its lightfastness (0.1% pigment) is equal to step 6 on the Blue Scale; at 1/3 SD it corresponds to step 5. In HDPE, the pigment affects the shrinkage of extrusion products, which is typical of hydrazone pigment lakes of this class. P.Y.168 is recommended especially for use in LDPE.

2.3.4.3.7 Pigment Yellow 169

P.Y.169 is another calcium monohydrazone yellow pigment lake, which has been available for some years. Its hue is a reddish yellow. Its properties and application are similar to those of the much greener P.Y.168.

2.3.4.3.8 Pigment Yellow 183

P.Y.183 entered the market a few years ago and is considered a speciality product for the colouration of plastics.

This monohydrazone yellow calcium pigment lake affords reddish, somewhat dull yellow shades with poor tinctorial strength. 1/3 SD HDPE colourations (1% TiO₂) require 0.32% pigment. In such media, the pigment is thermally stable up to 300 °C. Polymer shrinkage is practically unaffected. The pigment provides very good lightfastness; 1/3 SD colourations equal step 7–8 on the Blue Scale. P.Y.183 is also recommended for other high temperature processed plastics. In ABS, for example, it is thermally stable up to 300 °C.

P.Y.183 is bleed resistant in plasticized PVC, where its poor tinctorial strength is of some disadvantage. 1/3 SD samples (5% TiO₂) require 1.64% pigment. Such systems provide a lightfastness which is equal to step 6 on the Blue Scale; 1/3 SD transparent colourations correspond to step 6–7 on the Blue Scale.

2.3.4.3.9 Pigment Yellow 190

The monohydrazone calcium pigment lake P.Y.190 is considered a speciality product for the colouration of plastics, but it has been removed from the market.

The commercially available type is tinctorially very weak. 0.66% pigment are required to produce 1/3 SD HDPE colourations (1% TiO₂). P.Y.190 provides medium shades of yellow. In HDPE, the pigment resists heat up to 300 °C.

In polyamide, P.Y.190 is heat stable up to 270 °C. In this medium, the pigment has a somewhat redder shade and demonstrates noticeably higher tinctorial strength than in HDPE. 0.3% of the commercially available type are sufficient to produce 1/3 SD colourations.

This commercial grade is slightly soluble in water, which may cause problems during extrusion.

2.3.4.3.10 Pigment Yellow 191

The Monohydrazone calcium pigment lake P.Y.191 produces reddish shades of yellow, covering the same range of shades as the diarylide yellow pigment P.Y.83. P.Y.191, however, exhibits distinctly less tinctorial strength than P.Y.83. 0.32% P.Y.191 are needed to produce 1/3 SD colourations (1% TiO₂) in HDPE. These colourations are heat stable up to 300 °C, while 1/3 SD colourations without TiO₂ resist heat up to 290 °C. The pigment does not affect the shrinkage of the polymer. P.Y.191 shows good lightfastness: 1/3 SD colourations containing 1% TiO₂ equal step 6–7 on the Blue Scale, while 1/3 SD colourations without TiO₂ equal step 8. In media such as polystyrene and ABS, P.Y.191 shows similar values in terms of tinctorial strength, heat stability, and lightfastness. In polycarbonate, 1/3 SD colourations (containing 1% TiO₂) are heat stable up to 330 °C; such colourations equal step 4–5 on the Blue Scale for lightfastness. P.Y.191 is migration resistant in plasticized PVC; up to a concentration limit of 0.005%, the pigment can be used at 180 °C and in rigid PVC up to a concentration limit of 0.005% at 200 °C.

P.Y.191 displays excellent solvent fastness in aliphatic and in aromatic hydrocarbons, as well as in the commonly used plasticizers. The pigment is almost completely fast to alcohols and esters but not to water, ketones and methyl-glycol.

P.Y.191 is also used for hot melting traffic paints in the USA.

The usual crystal phase of P.Y.191 is the α-phase. Four new crystal modifications of P.Y.191 (β, γ, δ, ɛ) have been described [42], which are obtained for example by recrystallization from different solvents. Phase conversions were achieved by solvation of the α-phase in high boiling organic solvents with subsequent cooling: the β-phase by recrystallizing from NMP (N-methylpyrrolidone) (180 °C), DMAA (dimethylacetamide) or DMSO (dimethyl sulfoxide); the γ-phase from diethylene-glycol dimethyl ether (150–170 °C), the δ-phase from ethylene-glycol (170–200 °C) and the ɛ-product from DMF (N,N-dimethylformamide. The β- and γ- phases can also be obtained by varying the synthetic procedure; correspondingly they are also found in commercial products.

2.3.4.3.11 Pigment Yellow 191:1

The Monohydrazone ammonium lake is a recent product and differs in its colouristic and fastness properties scarcely from the calcium lake types. Therefore, the recommended application media for the two lakes are the same. 0.34% P.Y.191:1 are required to produce 1/3 SD colourations (1% TiO₂) in HDPE. Such colourations are heat stable up to 300 °C.

2.3.4.3.12 Pigment Yellow 205

This is a metallized hydrazone pigment with the exact chemical constitution remaining unpublished. The pigment exhibits very good heat stability in polyolefins where it can be used to 285 °C in masstone and in tint tone. The pigment is almost exclusively developed for plastic applications where lightfastness and weatherfastness are not important requirements. It is used in packaging and in disposable plastic items. Its relatively strong mid-shade tone allows concentrate manufacturers and moulders to replace diarylide yellows P.Y.14 and P.Y.17 where diarylides are restricted. P.Y.205 has been especially useful where P.Y.62 is tinctorially too weak to gain the intensity of colour and chroma required. P.Y.205 exhibits approximately 2–2.5 times the tinctorial strength of P.Y.62. By virtue of this increased strength, P.Y.205 is arguably the best valued alternative to diarylide yellows P.Y.14 and P.Y.17 for plastic applications where temperatures of 200 °C or higher will be reached.

2.3.4.3.13 Pigment Yellow 206

A pigment of the metallized hydrazone class in which the exact chemical constitution remains unpublished. P.Y.206 exhibits excellent heat stability in polyolefins and good compatibility and highly chromatic colour in polyester and polycarbonates as well as styrene. The heat stability reaches 285 °C in both masstone and tint tone. P.Y.206, although used mostly in plastics, exhibits good lightfastness in coatings as well, and can be used as shading pigment for many maintenance paints. In plastics it is a strong red shade yellow, almost yellow shade orange in masstone and a bright red shade yellow in tints. By virtue of this wide shift from almost orange masstone to red shade yellow tint-tone, the formulator gains a wide colour space of coverage and possibilities. The colour strength of P.Y.206 makes it a high value as a diarylide yellow P.Y.83 alternative where P.Y.83 is restricted.

2.3.4.3.14 Pigment Yellow 209 and 209:1

Both of these pigments are of the metallized hydrazone pyrazolone class. Pigment Yellow 209, the calcium salt, is the redder shade of the two pigments with Pigment Yellow 209:1, the strontium salt, being a more mid-red shade yellow. Both yellows exhibit good resin compatibility in plastics and excellent heat stability to 285 °C in polyolefins. These pigments were developed for the plastic packaging market segment as alternatives to diarylides and as products that comply with the FDA requirements for food contact under the conditions of use (A) through (H) as described in Table 2 of 21 CFR Part 176.170(c), where the pigments are allowed to be used at levels up to 1% by weight of the polymer subject to the provisions and definitions described in Title 21 CFR part 178.3297. Both pigments exhibit excellent colour strength and good dimensional stability in moulding applications. Owing to marginal lightfastness and weatherfastness these products are limited to use in interior applications.

2.3.4.3.15 Pigment Yellow 212

P.Y.212 is a metallized hydrazone pyrazolone pigment exhibiting excellent heat stability in polyolefins, HDPE and polypropylenes exceeding 312 °C in masstone and tint. It is a bright medium shade yellow and provides an excellent alternative to diarylides and other yellows in this shade range. The pigment complies with the FDA requirements for food contact under the conditions of use (A) through (H) as described in Table 2 of 21 CFR Part 176.170(c), where this pigment is allowed to be used at levels up to 1% by weight of the polymer subject to the provisions and definitions described in Title 21 CFR Part 178.3297.

P.Y.212 is not recommended for exterior use, but provides an excellent value for interior applications such as packaging and household durables of all types. It is tinctorially quite strong as metallized hydrazones go and exhibits very good dimensional stability, making it very useful in moulded items such as blow moulded containers.

2.4.1.1.1 Crystal Structures

The crystal structures of P.Y1.2, P.Y.13, P.Y.14, P.Y.63 and P.Y.83 have been determined by single-crystal structure analysis and by X-ray powder diffraction [49–53]:

Although these five compounds differ only in the substitution on their terminal phenyl rings, their molecular conformation and the arrangement of molecules in the crystal vary considerably. In the commercial α-phase of P.Y.12, the central biphenyl fragment is not planar, but the phenyl rings form an interplanar angle of 22°. One of the terminal phenyl rings is nearly coplanar with the adjacent acetoacetyl fragment, the other one is rotated by 29° (Figure 2.17). The molecules are arranged in a complicated interdigitated herringbone pattern (Figure 2.18) [50].

Lattice-energy calculations [53] show that this pattern is the optimal one for P.Y.12, but any additional substituent would cause steric hindrance with the neighbouring molecules, leading to an energetically unfavourable structure. Correspondingly, this structure is found for P.Y.12 only.

P.Y.13, P.Y.14 and P.Y.63 crystallize in a layer structure built from planar molecules (Figures 2.19 and 2.20) [51]. Such a layer structure is less sensitive to variations of the substitution pattern. P.Y.83 forms a herringbone arrangement of planar molecules (Figure 2.21) [52].

According to quantum-mechanical calculations the preferred conformation of an individual molecule exhibits a mutual rotation of the two phenyl rings of the biphenyl fragment by about 40° [53]. The planar conformation of P.Y.13, P.Y.14, P.Y.63 and P.Y.83 is a packing effect. With a twisted conformation, an energetically favourable molecular arrangement is not possible, as is shown by lattice-energy calculations. Therefore, the molecules adopt a planar conformation, which easily allows a good and dense molecular packing. The planarization enhances the conjugation between the chromophoric systems of the two halves of the molecules. Apparently, this has no effect on the hue. The colour strength increases considerably, as shown by quantum-mechanical calculations [54]. Correspondingly, the intrinsic colour strength of P.Y.13 is about 50% higher than that of P.Y.12. The additional methyl groups in P.Y.13 have no electronic influence on the chromophoric system, but lead to a planar conformation in the solid state. Hence the increased colour strength of P.Y.13 (and P.Y.14, P.Y.63 and P.Y.83, too) is a packing effect.

Solid solutions of P.Y.13 and P.Y.14, as well as solid solutions of P.Y.12 with P.Y.13 or P.Y.14 also adopt the layer structure of P.Y.13, resulting in pigments with high colour strengths. Hence the crystal structure of P.Y.13 can be ‘diluted' with the cheaper P.Y.12 without changing the optical properties – an excellent example for crystal engineering [53].

2.4.1.4.1 General

Diarylide yellow pigments entered the market in 1935, when P.Y.13 was introduced by IG Farben in Germany. Sold as Vulcan-Echtgelb GR, this pigment was designed to lend colour to natural rubber articles. P.Y.12, which was produced and offered a few years later in the USA, replaced the P.Y.1 type monohydrazone yellow pigments, which up until then had dominated the yellow pigment market in most parts of the world. In subsequent years, methods for diarylide yellow pigment synthesis advanced steadily and resulted in a broad range of products, many of which have since then either vanished from the market or are now only regionally important. This is true for diarylide yellow pigments based on 3,3′-dimethoxy, 3,3′-dimethyl, or 2,2′-dimethoxy-5,5′-dichlorobenzidine as a bisdiazo component instead of the most commonly used 3,3′-dichlorobenzidine. P.O.15, 16 and 44 are the only species that have maintained a somewhat important position in the American and Japanese markets.

Table 2.5 lists the commercially significant diarylide yellow pigments. Notably, the acetoacetarylides in the aromatic moiety possess mostly methoxy or methyl substituents.

C.I. Name	C.I. Constitution Number	X	Y				Shade
P.Y.12	21090	Cl	H	H	H	H	yellow
P.Y.13	21100	Cl	H	CH3	CH3	H	yellow
P.Y.14	21095	Cl	H	CH3	H	H	yellow
P.Y.17	21105	Cl	H	OCH3	H	H	greenish yellow
P.Y.55	21096	Cl	H	H	CH3	H	reddish yellow
P.Y.63	21091	Cl	H	Cl	H	H	yellow
P.Y.81	21127	Cl	Cl	CH3	CH3	H	very greenish yellow
P.Y.83	21108	Cl	H	OCH3	Cl	OCH3	reddish yellow
P.Y.87	21107:1a)	Cl	H	OCH3	H	OCH3	reddish yellow
P.Y.90	—	—	—	H	H	H	reddish yellow
P.Y.106	—	Cl	H	CH3	CH3	H	greenish yellow
				OCH3	H	H
P.Y.113	21126	Cl	Cl	CH3,	Cl	H	very greenish yellow
P.Y.114	21092	Cl	H	H	H	H	reddish yellow
				H	CH3	H
P.Y.121	21091	Cl	H	Cl	H	H	yellow
P.Y.124	21107a)	Cl	H	OCH3	OCH3	H	yellow
P.Y.126	21101	Cl	H	H	H	H	yellow
				H	OCH3	H
P.Y.127	21102	Cl	H	CH3	CH3	H	yellow
				OCH3	H	H
P.Y.136	—	Cl	H	—	—	—	yellow
P.Y.152	21111	Cl	H	H	OC2H5	H	reddish yellow
P.Y.170	21104	Cl	H	H	OCH3	H	yellowish orange
P.Y.171	21106	Cl	H	CH3	Cl	H	yellow
P.Y.172	21109	Cl	H	OCH3	H	Cl	yellow
P.Y.174	21098	Cl	H	CH3	CH3	H	yellow
				CH3	H	H
P.Y.176	21103	Cl	H	CH3	CH3	H	yellow
				OCH3	Cl	OCH3
P.Y.188	21094	Cl	H	CH3	CH3	H	yellow
				H	H	H
P.O.15	21130	CH3	H	H	H	H	yellowish orange
P.O.16	21160	OCH3	H	H	H	H	yellowish orange
P.O.44	21162	OCH3	H	H	Cl	H	reddish orange
P.O.47	—	CH3	H	CH3	Cl	H	yellowish orange
a) CoIour Index constitution numbers 21107 (P.Y.124) and 21107:1 (P.Y.87) are misleading since both pigments exhibit different chemical structures.

2.4.1.4.2 Pigment Yellow 12

P.Y.12 is a commercially important product; it makes up a large portion of the worldwide pigment production. The unsubstituted skeleton of the acetoacetanilide as coupling component makes P.Y.12 chemically the simplest representative of diarylide yellow pigments. The fastness properties of P.Y.12 are somewhat lower than those of the substituted derivatives. This is particularly true for the lightfastness. 1/1 to 1/3 SD letterpress proof prints exhibit a lightfastness around step 3 on the Blue Scale; in 1/5 SD, the lightfastness decreases to about step 2. At equal depth of shade, P.Y.12 is thus 1–2 steps less fast to light than other diarylide yellow pigments, such as P.Y.13, 83, 127 or 176, which cover the medium to reddish yellow range. The only exception is P.Y.14, whose lightfastness is about the same.

At equal pigment concentration, P.Y.12 is as much as 2–3 steps less lightfast than its counterparts. In other words, to achieve the same depth of shade, the tinctorially stronger diarylide yellow pigments in the medium to reddish yellow range require much lower pigment concentrations than a comparative P.Y.12 sample, which has to be more highly pigmented. Since the lightfastness of a pigment in an application medium increases with its concentration, differences between pigments become more obvious as the pigment level increases. Printed in equally thick layers (1 µm) and provided the particle sizes of the two samples are similar, a 1/1 SD P.Y.12 letterpress proof print requires a 10% pigment concentration, while a P.Y.13 sample will afford the same depth of shade if it is formulated at only about 7%.

P.Y.12 has a medium yellow hue, which is used to a large extent in letterpress and offset printing inks as the yellow component in three- and four-colour printing. To adjust P.Y.12 to the standard yellow of the European standard (Section 1.8.1.1), the hue may be shaded with traces of a redder component, such as one of the orange pigments P.O.13 or 34. No such shading is necessary for P.Y.12 to match the yellow on the Kodak scale.

The transparency of P.Y.12 can be optimized to meet various application requirements. The product line ranges from fairly opaque versions, which are targeted for packaging and newspaper printing inks, to semitransparent and highly transparent, typically resinated types. As the pigment particle size is reduced for the more transparent versions, the hue shifts increasingly towards more clean, greenish shades; fine pigment particles also render the resulting products more sensitive to light. In this respect, P.Y.12 types are satisfactory only in areas where fastness to light is of less concern. High gloss has its advantage for types that are to be used in the uppermost and very thin layer of a three- or four-colour print. Common printing techniques (Section 1.8.1.1) for letterpress and offset application produce roughly 1 µm ink films. This requirement explains why good dispersibility and optimized ink formulation are of major importance to the manufacturer.

While in Europe P.Y.13 and its derivatives are preferred to P.Y.12 for offset printing inks, the reverse is true in the USA, where P.Y.12 is almost exclusively used. In America, most oil-based inks are manufactured from pigment presscake with a fine particle size, which is transferred directly into the flush paste and then converted into the printing ink, avoiding agglomeration and, to a large extent, recrystallization (Section 1.6.5.8). This technique has become practically obsolete in Europe, considering the easy dispersibility of pigment powders for process colours, that is, colours for three- or four-colour printing in letterpress and offset application.

Compared to other diarylide yellow pigments, P.Y.12 is only moderately fast to organic solvents. Its tendency to recrystallize is particularly detrimental to modern agitated ball mills that are used to disperse pigments in Web offset printing vehicles. Under these processing conditions, highly transparent P.Y.12 types are inferior to the corresponding P.Y.13 types; improved reddish varieties of P.Y.12 with distinctly improved recrystallization stability have recently been introduced.

P.Y.12 is a typical diarylide yellow pigment in that its prints are fast to clear lacquer overcoating, which is used to protect tin prints against scratching and scrubbing. They are also fast to sterilization (Section 1.6.2.3), which is one of the major requirements of an ink to be printed on food cans.

Offset and letterpress inks are usually formulated at high pigment concentrations; most contain more than 15% pigment. This is a particular challenge to highly transparent products with very fine particle sizes. These depend on good rheology, which determines the flow behaviour of a material in a high-speed printing press.

Yellow shades for publication gravure printing inks are produced almost exclusively by speciality types of P.Y.12. These types have the additional advantage of providing extra depth of shade. A side reaction takes place between the aliphatic amines that are used to prepare the pigment, in which a portion of the pigment reacts to form ketimines (Section 2.4.1.1). The reaction products dissolve in the media commonly used to formulate publication gravure printing inks, shifting the colour of the ink to a dark red. Toluene is more effective than benzene in this respect. The result is a seemingly deeper colour in print. At equal pigment concentration, printing inks containing such speciality pigments also exhibit much better flow behaviour than inks made from traditional types.

Recently, amine-treated pigments have been developed that show less of a tendency to penetrate low-cost gravure paper (Section 1.8.1.2). In certain circumstances, the storage stability of a gravure printing ink is a major concern. This is particularly true for the transportation of such inks in summertime, when products are exposed to high temperature and agitation. The resins that are commonly used to formulate these printing inks are frequently unable to prevent a pigment from changing its colouristic properties in an ink. Ketimine formation is reversed and the previously dissolved compound precipitates as a crystalline pigment. The result is a shift towards a greener shade, reduced tinctorial strength and viscosity increase, owing to the formation of additional pigment surface [46]. The storage stability of a given publication gravure printing ink may be improved considerably by choosing appropriate resins for the product. Notably, in contrast to calcium resinates, the commonly used zinc resinates shorten the shelf life of an ink. However, the underlying mechanisms are not yet entirely known.

P.Y.12 types are used in packaging gravure and flexographic inks for their reasonable price, but they can also be utilized in aqueous printing inks, provided they are sufficiently fast to light. They cannot be applied as decorative printing inks to laminated paper.

The paint industry shows little interest in P.Y.12, since it is not sufficiently fast to overcoating for use in baking enamels. In air drying paints, lightfastness of P.Y.12 in white reduction (with 1:5 TiO₂) only equals step 2 on the Blue Scale.

There is also little demand for P.Y.12 as a colourant for polymers. Although a certain tendency to migrate precludes its use in plasticized PVC, rigid PVC somewhat enhances its performance. Transparent varieties become sufficiently fast to light to equal step 6 on the Blue Scale; opaque types afford values between 2 and 5, depending on the pigment concentration and amount of TiO₂ or depth of shade. Good heat resistance also qualifies P.Y.12 for use in polyurethane foam; aromatic polyurethanes themselves are not very fast to light.

Like modified P.Y.12 (P.Y.126), P.Y.12 is selected to lend colour to various speciality products, such as cleaning agents or office articles. Where better lightfastness is required, P.Y.12 is replaced by less intense and less solvent resistant monohydrazone yellow pigments, especially by P.Y.1 types, which provide a similar hue.

P.Y.12 exists in at least four crystal phases (α, β, γ, X). The α-phase is the usual phase. The metastable β-phase is claimed to be formed during special milling processes [56]. The γ-phase is obtained with additives such as dodecyldipropylenetriamine [57], and the X-phase is obtained with an additive formed by the coupling of diazotized dichlorobenzidine with acetoacetylated 5-amino-2-hydroxybenzoic acid (i.e. with the substituents in the coupling component) [58].

2.4.1.4.3 Pigment Yellow 13

P.Y.13 is also a frequent choice throughout the printing ink industry, especially in offset application. Its hue corresponds to the standard yellow on the European Scale for three- and four-colour printing, and it also matches the yellow on the Kodak Scale (Section 1.8.1.1). High transparency is a major asset to a yellow pigment that is to be used as the uppermost layer in the multicolour printing sequence. P.Y.13 types, as well as their derivatives P.Y.127 and 176, are therefore surface coated with hard resins. At comparable specific surface area and particle size distribution and consequently similar transparency, prints containing P.Y.13 or its modifications are up to 25% stronger than those formulated with P.Y.12 or 126.

Although P.Y.13 types, especially the resinated, highly transparent versions, are generally easy to disperse, problems may arise with low shear equipment like agitated ball mills. Incompletely dispersed pigment may appear to recrystallize during dispersion, affecting both the transparency and the tinctorial strength of the product.

P.Y.13 is not only more resistant to solvents, but also shows less of a tendency to recrystallize than P.Y.12. This makes it much more advantageous to incorporate such pigments in offset vehicles containing large amounts of mineral oil by using agitated ball mills like the ones mentioned above (Section 1.8.1.1). P.Y.127 and 176 are even more recrystallization resistant than P.Y.13.

At equal depth of shade, the lightfastness of P.Y.13 exceeds that of similarly transparent types of P.Y.12 by one to two steps on the Blue Scale.

P.Y.13 is supplied as a wide selection of different types, ranging from highly transparent systems to semi-transparent and semi-opaque versions to highly opaque varieties.

P.Y.13 and its chemically modified derivatives, due to their higher solvent fastness compared to P.Y.12, are used in much greater volume in packaging gravure inks. P.Y.13 is also fast to protective clear lacquer overcoatings and may be sterilized and calendared.

P.Y.13 is not used in publication gravure printing inks based on toluene or toluene–benzene mixtures; amine-treated grades are not commercially available at present.

The paint industry shows only limited interest in either P.Y.13 or 12. Although the redder varieties of P.Y.13 are more lightfast than the P.Y.12 types by a few steps on the Blue Scale, they do not reach the lightfastness of Hansa Yellow type monohydrazone pigments. P.Y.13 is not fast to overpainting.

P.Y.13 is used to a more appreciable extent in plastics, where it meets average standards. Depending on the choice and the amount of plasticizer and processing temperature, a P.Y.13 content below 0.05% in plasticized PVC may cause some blooming (Section 1.6.3.1). Fastness to bleeding in plasticized PVC is much better than for P.Y.12; regarding bleed resistance, P.Y.13 is in fact more comparable to the more greenish P.Y.17. In 1/3 SD, which corresponds to a pigment concentration of about 0.3% with 5% TiO₂, the lightfastness (daylight) of P.Y.13 in plasticized PVC is equal to step 6–7 on the Blue Scale; the pigment behaves similarly in rigid PVC, in which it does not migrate. In cable insulations made of plasticized PVC, P.Y.13 is used to match the standards according to DIN 47 002, RAL 1021 and RAL 2003 (Section 1.6.1.3); it is also used in PVC-based floor covering.

As a result of the discovered thermal decomposition of diarylide yellow pigments (Section 2.4.1.3), the use of P.Y.13 in HDPE must be limited to 200 °C, even though the pigment was previously said to survive a 5 min exposure to 200–260 °C (depending on the depth of shade and the commercial grade). Since P.Y.13 is a product with a high tinctorial strength, a pigment concentration of about 0.12% in HDPE will produce a 1/3 SD sample (1% TiO₂ content). The shrinkage of plastics extrusion products is only affected if the processing temperature is low. In these materials, P.Y.13 is as lightfast as in PVC. P.Y.13 is used to an appreciable extent – usually in the form of pigment preparations – in rubber and other elastomers and in aromatic polyurethane foams. The spin dyeing market employs P.Y.13 to colour viscose rayon and synthetic wool.

2.4.1.4.4 Pigment Yellow 14

Although P.Y.14 is less important than P.Y.12 and 13, the packaging and textiles printing ink industries use it in large volume. P.Y.14 is somewhat greener than P.Y.12 and considerably more so in comparison with P.Y.13. A number of the P.Y.14 types are appreciably greener than the standard yellow on the European Scale. P.Y.14 is not only weaker than comparable P.Y.13 varieties with similar physical characteristics, such as specific surface area, but it is also less lightfast by 1 to 2 steps on the Blue Scale. Its resistance to solvents is also comparatively poor. This somewhat limits its use for process inks in offset and letterpress application to special cases, which is equally true for P.Y.14 blends with reddish pigments. Types with fine particle sizes, which match highly transparent versions of P.Y.12 and 13, are not available in Europe.

P.Y.14 is more resistant to solvents than P.Y.12. In contrast to P.Y.12, it is resistant to paraffin, which makes it a useful product for packaging inks. This is one of the reasons why P.Y.14 is used so much more widely throughout the USA, where it is produced in considerably larger volumes than P.Y.13. Where P.Y.12 is not fast enough to meet the requirements, P.Y.14 is usually the second choice in the USA; while most other countries replace P.Y.12 by P.Y.13.

Suitable P.Y.14 preparation with amines affords speciality types for publication gravure inks. Compared with corresponding varieties of P.Y.12, P.Y.14 speciality types provide a clean, particularly greenish hue; they are also colouristically somewhat weaker. However, the graphics industry currently prefers reddish shades for publication gravure printing inks, which explains why P.Y.14 speciality types currently have no value. However, untreated P.Y.14 is of regional importance as a colourant in publication gravure printing inks. The resulting inks exhibit poor rheology.

P.Y.14 is not utilized by the paint industry, and the interest of the plastics area varies according to the region. The pigment is more important in the USA, where it is used in polyolefins. It is thermally stable up to 200 °C, which makes it a useful colourant for elastomers, especially rubber. Whenever P.Y.14 is worked into plasticized PVC, there is a certain concentration threshold beyond which the pigment will bloom. P.Y.14 is also used for spin dyeing viscose rayon and viscose cellulose, and it is an especially important product for the mass colouration of viscose sponges. It is not particularly lightfast in these applications: in 1/1 to 1/9 SD, it equals only step 4 to step 5–6 on the Blue Scale. The important textile fastnesses are good.

2.4.1.4.5 Pigment Yellow 17

Used primarily in the printing ink field, this pigment is considerably greener than P.Y.14 and much more greenish than P.Y.12. At equal depth of shade, P.Y.17 is more lightfast than P.Y.14 by 1–2 steps on the Blue Scale. P.Y.17 is tinctorially weaker than P.Y.14. Printed in a standard layer (1 µm) on a letterpress proof printer, a P.Y.17 ink must be formulated at about 7.5% pigment to afford 1/3 SD prints; while an equally deep P.Y.14 ink only requires 3.7% pigment. In comparing the lightfastness of prints containing P.Y.17 and 13, respectively, it should be remembered that accelerated exposure to light with high pressure xenon lamps destroys P.Y.17 distinctly faster than P.Y.13. The reverse is true for daylight exposure, to which P.Y.17 is more resistant than P.Y.13. P.Y.17 is also more resistant to most organic solvents than P.Y.14.

Most commercially available P.Y.17 types are highly transparent, often resinated pigments, which have gained recognition in packaging inks. Combination with equally transparent, very reddish varieties of P.Y.83 affords a range of intermediate shades which exhibit good transparency and are very lightfast.

P.Y.17 is suitable for all printing techniques. It is somewhat more greenish than the standard yellow for offset and letterpress application on the European Scale. Shading with traces of P.Y.83, however, alleviates the problem. P.Y.17 is also applied in various packaging printing inks. The choice ranges from nitrocellulose and polyamide based inks to vinyl chloride/vinyl acetate mixed polymers on a ketone/ester basis for PVC or aluminium foil. In ester-based NC colours and in other media, the pigment, particularly in its fine particle size, highly transparent varieties, tends to exhibit poor flow properties and is highly viscous. It may also thicken, but this is rare. Publication gravure printing inks do not normally contain P.Y.17 but are mostly based on speciality types of P.Y.12 and 14. Reliable heat stability at temperatures up to 200 °C makes P.Y.17 suitable for metal deco printing.

P.Y.17 is only rarely employed in paints. It is used in interior linings of cans and other products for its high transparency. In air drying paints, its more opaque versions (organic pigment : TiO₂  1:5) equal step 5 on the Blue Scale for lightfastness; full shades correspond to step 7. P.Y.17 is not completely fast to overpainting when employed in baking enamels.

The plastics industry, however, uses P.Y.17 extensively, although problems may occur in plasticized PVC, where blooming is observed if pigment concentrations are low. P.Y.17 is almost as lightfast as the somewhat redder P.Y.13 (step 6–7 at 1/3 SD). Likewise, both pigments are almost equally lightfast in rigid PVC. In polymers, as in other materials, P.Y.17 is also considerably weaker than P.Y.13.

P.Y.17 may be used for mass colouration and also to print PVC film. For these purposes, P.Y.17 is frequently prepared on a VC/VAc (vinyl chloride/vinyl acetate) mixed polymer basis. Good dispersibility in plastics makes these preparations suitable even for thin films. The dielectric properties of P.Y.17 allow its application in PVC cable insulations.

P.Y.17 is also frequently used in polyolefins, sometimes in the form of pigment preparations. Its heat stability in these media was said to be about 220–240 °C, but must now, as a result of the detected thermal decomposition of diarylide yellow pigments in plastics, be limited to 200 °C. This tendency to decompose excludes P.Y.17 from recommendation for use in polystyrene, in which the pigment largely dissolves under the processing conditions. The same is true for ABS.

Aromatic polyurethane foams are equally suitable media for P.Y.17, which is extremely lightfast in various cast resins. In 3 mm thick methyl methacrylate resins containing 0.025% pigment, P.Y.17 equals step 7–8 on the Blue Scale for lightfastness. Similar values are found for unsaturated polyester resins, whose hardening is not affected by the pigment (Section 1.8.3.5). In heat setting plastics such as melamine or urea/formaldehyde types, however, P.Y.17 is one to two steps on the Blue Scale less lightfast, which is true both for transparent and opaque versions. P.Y.17 is also used for the colouration of rubber.

The textiles printing industry has an appreciable interest in P.Y.17 and applies it in the form of pigment preparations. Where its fastness properties satisfy the specifications and where the use requirements are not too demanding, the pigment is also utilized for spin dyeing purposes. Manufacturer recommendations include media such as polyacrylonitrile and cellulose acetate fibres, on which 1/3 SD pigment prints exhibit a lightfastness which is equal to step 5 on the Blue Scale.

2.4.1.4.6 Pigment Yellow 55

P.Y.55 is less important than some other diarylide yellow pigments, especially the P.Y.12, 13, and 83 types. It affords a very reddish yellow, which is not quite as red as P.Y.83 or 114.

The main area of application for P.Y.55 is in the printing ink industry, where it is used particularly in speciality products for packaging inks. Various types are available with different specific surface areas to satisfy customer specifications regarding transparency or opacity. The flow properties are considerably different, especially in oil-based and aqueous systems, which are the most common media for P.Y.55. According to expectation, types with lower specific surface areas are redder, more opaque, show less tinctorial strength, and are less viscous than types with fine particle sizes. The pigment is occasionally highly resinated to enhance the transparency of the product. Most P.Y.55 types are distinctly weaker than comparable diarylide yellow pigments covering the reddish and medium yellow range. In 1/3 SD letterpress proof prints, P.Y.55 equals step 4 on the Blue Scale: it is as lightfast as the chemically and tinctorially similar diarylide yellow pigment P.Y.114.

The paints market shows only limited interest in P.Y.55, although the pigment is occasionally used to lend colour to low quality industrial paints. In 1/3 SD white reductions, the pigment matches the lightfastness of P.Y.13 samples; its full shades are more lightfast. Addition of TiO₂ decreases its resistance to light.

P.Y.55 is suitable for application in polymers such as PVC and rubber. In plasticized PVC, it exhibits a certain tendency to bleed; its tinctorial strength is good-to-average. 0.7% pigment, incorporated in plasticized PVC, will produce a 1/3 SD sample (5% TiO₂); while only 0.28% Pigment Yellow 83 is sufficient to afford the same depth of shade. The lightfastness equals step 7 on the Blue Scale. P.Y.55 is also used throughout the textiles printing ink industry.

2.4.1.4.7 Pigment Yellow 63

P.Y.63 continues to be manufactured in Japan, where it enjoys only limited regional importance. It provides a greenish to medium yellow hue with a lightfastness that is much inferior to that of other diarylide yellow pigments. Under standardized conditions, 1/1 SD letterpress proof prints equal only step 2 on the Blue Scale. Fastness to various organic solvents that are common in printing inks is good, and the pigment shows no tendency to recrystallize. Preparation with amines considerably shifts the hue of publication gravure printing inks towards greener shades, which is also observed with P.Y.14.

2.4.1.4.8 Pigment Yellow 81

This pigment affords a very greenish yellow. Its hue is similar to that of the monohydrazone yellow pigment P.Y.3, but white reductions are much stronger exhibiting considerably improved solvent and migration resistance. Although P.Y.81 shows satisfactory lightfastness, it is not quite as lightfast as P.Y.3. P.Y.81 resembles P.Y.113 as far as shade and fastness properties are concerned, although P.Y.113 is more resistant to solvents and also more migration resistant.

P.Y.81 is found in various media. It is equally suited to all printing purposes, including textile printing. Good resistance to many organic solvents facilitates its use in various solvent-containing printing inks, such as mixed polymer paints on ketone/ester basis for PVC. Its heat resistance qualifies the pigment for application in metal deco printing inks. The prints are resistant to clear lacquer coatings, sterilization, and calendering. In 1/3 SD, the lightfastness is equal to step 5–6 on the Blue Scale. Comparative values are: P.Y.3: step 6–7, P.Y.113: step 5–6.

P.Y.81 is recognized throughout the paint industry for its fastness to overcoating and very good solvent fastness in industrial application. Most types exhibit good hiding power. In an alkyd-melamine paint, the pigment equals step 7–8 on the Blue Scale in full shades and step 6–7 in white reduction (1:4 TiO₂) for lightfastness. In paints, P.Y.81 provides a tinctorial strength which is similar to that of P.Y.3 of comparable shade, but it is not quite as lightfast and weatherfast.

At low pigment concentrations in plasticized PVC, the pigment may bloom, depending on the processing conditions and formulation of the polymer. In rigid PVC, however, P.Y.81 performs well, irrespective of its concentration. Its daylight fastness in 1/3 SD is equal to step 7 on the Blue Scale, in which it equals the distinctly stronger P.Y.113. At exposure to light from a xenon lamp, P.Y.113 is much more lightfast than P.Y.81, especially in transparent types. The difference is sometimes more than one step on the Blue Scale. P.Y.81 is very resistant to bleeding, provided the appropriate concentration limits are observed. Its heat resistance makes it a useful colourant for polyolefins. P.Y.81 was said to be heat stable up to 260 °C for 5 min, depending on the depth of shade. The pigment was thus much more heat resistant than other diarylide yellow pigments. As a consequence of new insight into the thermal decomposition of diarylide yellow pigments in the presence of plastics (Section 2.4.1.3), the heat stability of P.Y.81 must now be limited to 200 °C. The pigment hardly affects the shrinkage of preformed HDPE articles and those made from similar, partially crystalline plastics. It is also useful in other plastics and for spin dyeing of materials such as secondary acetate.

2.4.1.4.9 Pigment Yellow 83

P.Y.83 possesses excellent fastness properties, which make it almost universally applicable. It provides a reddish yellow hue, which is considerably more reddish than that of P.Y.13 and at the same time very strong.

P.Y.83 can be used for all printing techniques and purposes. The printing ink industry often prefers highly transparent, mostly resinated types. Printing such types on aluminium foil or on metal sheets produces brilliant shades of gold. Combining P.Y.83 with transparent versions of the greenish P.Y.17 affords transparent prints with good lightfastness, which cover the range of intermediate shades. Both pigments are similar in that their varieties with fine pigment particles afford transparent 1/3 SD prints whose lightfastness equals step 5 on the Blue Scale. For comparison, P.Y.12 equals step 2; P.Y.13 reaches step 3–4.

P.Y.83 is the standard pigment within the reddish yellow range. The similarly shaded monohydrazone yellow pigment P.Y.10 (see Table 2.4, Section 2.3.4.1.6) is only about half as strong as P.Y.83, but more lightfast (about 1.5 steps on the Blue Scale). At the same time, it is less transparent and considerably less solvent resistant, which may cause significant recrystallization problems during pigment incorporation into the medium of application.

P.Y.83 shows good-to-very good resistance to most solvents that are typically found in application media. Recrystallization is therefore rare under common processing conditions, even in highly transparent types. Resistance to clear lacquers, calendering and sterilization is consequently excellent.

P.Y.83 is also used to an appreciable extent in plastics. Because of its good solvent resistance, migration is no problem in plasticized PVC even at low pigment levels; it does not bleed or bloom. Its daylight fastness at 1/3 SD equals step 8 on the Blue Scale; at 1/25 SD, it still reaches step 7. The results in rigid PVC are similar. P.Y.83 is also very strong in polyolefins. The pigment concentration required for 1/3 SD HDPE colouration (1% TiO₂) is only 0.08%. A considerable variety of pigment preparations is available for colouring several plastics. The choice ranges from pigment formulations on VC/VAc copolymer basis to pigment plasticizer pastes for PVC mass colouration, including application in thin films or cable insulations and printing on PVC films. Certain preparations are recommended for polyolefins or other plastics. The pigment has so far, on the basis of application tests in polyolefins, been said to be heat stable up to 250 °C. As a result of new insight into the thermal decomposition of diarylide yellow pigments in monohydrazone colourants and aromatic amines (Section 2.4.1.3), this heat stability must now be limited to 200 °C.

P.Y. 83 shows excellent lightfastness, even in methyl methacrylate or unsaturated polyester cast resins. The pigment does not effect the hardening of the latter.

The high quality of the fastness properties is the basis for frequent pigment use in textile printing. Dry cleaning with perchloroethylene or washing has almost no effect on the colour. P.Y.83, sometimes in the form of a preparation, is used for viscose spin dyeing, secondary acetate, and polyacrylonitrile.

In the paint industry, P.Y.83 types with fine particle sizes are intended for use in transparent and metallic finishes and are also generally employed in industrial coatings and emulsion paints, provided the demands on the light stability of the pigment are not too stringent. In full shades, the pigment reaches step 6–7 on the Blue Scale; some darkening is observed as a consequence of exposure to light. Opaque finishes with TiO₂ (1:10) are equal to step 6 and mixtures of (1:125) correspond to step 4–5. P.Y.83 is fast to overcoating in baking enamels.

One of the P.Y.83 types is an extremely opaque form. It provides finishes with good flow properties and makes it easy to increase the pigment concentration, which in turn improves the hiding power. This special opaque type is considerably more weatherfast than its more transparent counterparts, which makes its full shades useful colourants for an original automobile finishes (O.E.M.). The product also lends itself to paints for automobile refinishes and tractor and implement finishes. It is found in various high grade industrial finishes.

Good overall fastness and considerable tinctorial strength broaden the scope of P.Y.83 application. The list includes office articles, artists' colours, and solvent based wood stains, in which the pigment is frequently combined with red pigments and carbon black to produce shades of brown.

2.4.1.4.10 Pigment Yellow 87

Although this pigment has recently been offered by several manufacturers throughout the USA and Japan, it is not produced in Europe. Its colour is a reddish yellow, similar to that of the chemically closely related P.Y.83. Although both provide almost equal strength, P.Y.87 shows very poor fastness to overcoating in baking enamels and plasticized PVC. It is also less lightfast. Under standard conditions, 1/1 SD letterpress proof prints are equal only to step 4 on the Blue Scale, while corresponding P.Y.83 prints reach step 5. The pigment is used to a certain extent in textile printing.

2.4.1.4.11 Pigment Yellow 90

P.Y.90 has little commercial impact, it is a regional product. The pigment provides very reddish yellow shades, similar to those of the much light-faster P.Y.114. 1/1 SD and 1/3 SD letterpress proof prints equal only step 3 on the Blue Scale, while corresponding P.Y.114 specimens reach step 4–5 and 4, respectively.

2.4.1.4.12 Pigment Yellow 106

The shade of P.Y.106 is greenish, somewhat redder than P.Y.17, and its tinctorial strength is greater than that of P.Y.17. Standard films of 1/1 SD letterpress proof prints are made with only 12% P.Y.106, while the necessary P.Y.17 content exceeds 25%. The required pigment concentrations for 1/3 SD proof prints are 6% and 7.5%, respectively. At equal SD, the lightfastness of P.Y.106 is inferior to that of P.Y.17; the difference is about 1/2 step on the Blue Scale. Both pigments lend themselves to similar purposes, mainly in the area of printing inks. P.Y.106 is thermally stable up to 200 °C (10 min); in prints, it is bleed resistant toward clear lacquer coatings and sterilization, which qualifies it for metal deco printing.

P.Y.106 has recently been removed from the market.

2.4.1.4.13 Pigment Yellow 113

A few years ago P.Y.113 has been removed from the market worldwide because one of the intermediates for its production is no longer internationally available. P.Y.113 is a yellow pigment with a very greenish shade. In its colouristic and application properties, the pigment largely resembles P.Y.81, by which it must widely be replaced. In contrast to P.Y.81, however, P.Y.113 is completely migration resistant in plasticized PVC. Even at very low pigment concentrations, P.Y.113 does not bloom in this medium and has no limitation in this respect. Both pigments display approximately equal lightfastness.

2.4.1.4.14 Pigment Yellow 114

P.Y.114 affords very reddish yellow shades which closely resemble those of P.Y.83, although the level of the fastness properties of P.Y.114 is lower; it is somewhere between those of P.Y.12 and 13. In print, P.Y.114 is less lightfast than P.Y.83; the difference is ½ to 2 steps on the Blue Scale, depending on the depth of shade; but P.Y.114 does not achieve the tinctorial strength of P.Y.83.

P.Y.114 is primarily supplied to the printing ink industry, where it is used especially for packaging inks. The pigment is utilized to produce prints at reasonable cost, especially where exceptional fastness, as provided by P.Y.83, is a minor consideration. Prints made from P.Y.114 are not entirely resistant to a number of organic solvents, including the standard DIN 16 524 solvent mixture, paraffin and butter; however, P.Y.114 prints are soap, alkali and acid resistant. The fact that the pigment does not withstand a temperature of 140 °C and is not stable to sterilization excludes P.Y.114 from use in metal deco printing.

2.4.1.4.15 Pigment Yellow 121

The pigment enjoys a certain regional importance and lends itself to various printing inks. It produces a medium yellow shade, which is somewhat less green than the standard yellow on the European Scale CIE 12-66 for process printing (Section 1.8.1.1). Commercial types show medium transparency. The pigment is weaker than similarly coloured diarylide yellow pigments, such as P.Y.126 or 176. P.Y.121 is fast to several organic solvents, which are commonly used in printing inks; the pigment does not recrystallize in these media. The list includes aromatic hydrocarbons, especially toluene, which qualifies the pigment for use in publication gravure printing inks. This is especially true for amine preparations, which shift the colour to a much greener shade. A similar colour trend is observed with P.Y.14.

2.4.1.4.16 Pigment Yellow 124

Its distribution is limited to the USA, where it enjoys little importance. The pigment affords a medium yellow shade.

2.4.1.4.17 Pigment Yellow 126

This pigment is roughly as fast as the chemically related P.Y.12. In types with a similar specific surface area, P.Y.126 is somewhat redder. In contrast to P.Y.12, printing inks containing P.Y.126 require little, if any, modification with reddish components to attain the European Standard Yellow (Section 1.8.1.1) for process printing. This feature makes P.Y.126 a suitable process colour pigment for offset printing. Highly transparent versions are designed for use as the uppermost layer in four colour printing.

P.Y.126 is tinctorially stronger than P.Y.12; to produce standard films of highly transparent 1/1 SD proof prints, 9% P.Y.126 is needed, as opposed to 10% P.Y.12. P.Y.126 prints are more resistant to light; the difference is one step on the Blue Scale. In 1/1 to 1/25 SD prints, the lightfastness of P.Y.126 and P.Y.12 equals step 4 and 3, respectively. Heat stability up to 200 °C (10 min) and complete resistance to clear lacquer coatings and sterilization facilitate its use in metal deco printing. In aqueous or water/alcohol-based printing inks P.Y.126 is also stronger and more lightfast than P.Y.12. Treatment with aliphatic amines leads to ketimine formation, which is also true for P.Y.12 (Section 2.4.1.1). The resulting products afford high tinctorial strength and prints with a comparatively reddish shade. Its storage stability and penetration characteristics parallel those of P.Y.12.

P.Y.126 is generally applied wherever P.Y.12 types suit the purpose, such as in office articles and cleaning agents.

2.4.1.4.18 Pigment Yellow 127

This pigment performs like the chemically related P.Y.13. Its commercial types are highly transparent, resinated materials. P.Y.127 is principally used in offset printing inks; in Europe it is considered a standard product for this purpose. The pigment provides a yellow shade, which matches the standard yellow for process printing according to CIE 12-66 (Section 1.8.1.1). P.Y.127 has a very high tinctorial strength. 1/1 SD letterpress proof prints require 6.5% pigment, 1/3 SD proof prints contain 3.3% pigment. Comparative values for several other pigments covering the same range of colours are listed under the respective name.

The fact that P.Y.127 recrystallizes only very slightly facilitates its dispersion in modern agitated ball mills. The pigment is easy to disperse and its heat stability parallels that of P.Y.13. Its fastness to clear lacquer coatings and to sterilization are excellent, which is why the pigment is suitable for metal deco printing.

P.Y.127 is also used to an appreciable extent in packaging gravure printing inks. Highly transparent inks lend gloss especially to nitrocellulose inks. P.Y.127 prints are very fast, in which they largely parallel P.Y.13 prints.

2.4.1.4.19 Pigment Yellow 136

This pigment has been commercially available for several years. Chemically, it is a modified version of P.Y.13 and 14. Its colouristic and application properties are comparable to those of P.Y.13 and 14 mixtures. P.Y.136 is supplied to the printing ink industry, primarily for the production of oil-based inks, that is, offset inks. Both its hue and its tinctorial strength are somewhere between those of P.Y.13 and 14.

2.4.1.4.20 Pigment Yellow 152

Although P.Y.152 enjoys little appreciation in Europe, it is used to a considerable extent in the USA. It produces a reddish, somewhat dull yellow shade. Most of the commercial varieties are very opaque versions with good hiding power, which frequently displace Chrome Yellows in paints. P.Y.152 types are more viscous than opaque varieties of the much greener P.Y.83. The pigment is only moderately fast to overcoating: the tendency to bleed is very strong in an alkyd-melamine resin paint at a baking temperature of 120 °C. Its lightfastness is average. White reductions (1:5 TiO₂) equal step 5 on the Blue Scale, while the corresponding P.Y.83 paint reaches step 7–8. In full and deep shades, there is some darkening, as with P.Y.83; the lightfastness of such shades equals step 7. White reductions of P.Y.152 in air drying alkyd resin systems are almost twice as strong as the somewhat more greenish yellow monohydrazone pigment P.Y.65; full shades are considerably more opaque.

2.4.1.4.21 Pigment Yellow 170

P.Y.170 is produced in Japan and in Europe. Its hue is yellowish orange or very reddish yellow. The commercial products with a coarse particle size exhibit good hiding power and correspondingly little tinctorial strength in white reductions. It is considerably weaker than the more yellowish benzimidazolone pigment P.O.62, which is also far superior in light and weather resistance. P.Y.170 withstands overcoating in baking enamels at commonly used temperatures. Its prints are thermally stable up to 200 °C, are fast to clear lacquer coatings, and may be sterilized.

2.4.1.4.22 Pigment Yellow 171

The only manufacturer of this pigment has recently cancelled its production.

P.Y.171 was found in the Japanese market. Its prints are considerably redder than those made from P.Y.13; besides, its colour is off the fastness limits for yellows on the European colour scales for offset and letterpress application. P.Y.171 has a dull hue and is weaker than P.Y.13. The pigment is targeted for the colouration of plastics, such as PVC and PE.

2.4.1.4.23 Pigment Yellow 172

P.Y.172, like P.Y.171, was produced in Japan. The two pigments were not only colouristically alike but also possessed similar application properties. P.Y.172 is no longer found on the market.

2.4.1.4.24 Pigment Yellow 174

P.Y.174 joined the market a few years ago and bears some resemblance to P.Y.13. The commercially available varieties are very strong, highly resinated products which are correspondingly transparent. They are of great interest to the offset printing industry.

P.Y.174 provides a yellow shade that matches the CIE 12-66 standard yellow for process colour printing. The excellent tinctorial strength of the commercial products is accompanied by the high viscosity of the ink.

2.4.1.4.25 Pigment Yellow 176

P.Y.176 exhibits application properties which are similar to those of the chemically related P.Y.13. Only highly transparent varieties are available. The hue of P.Y.176 is somewhat redder than that of P.Y.13.

P.Y.176 finds extensive use in offset printing, where it matches the CIE 12-66 standard yellow for process colour printing (Section 1.8.1.1). It is a particularly strong pigment. Standardized 1/1 SD proof prints are made from inks containing only 6% pigment, while 1/3 SD samples require 3% pigment. P.Y.176 is stronger than P.Y.13 and 127. In certain vehicle systems, however, this advantage can be compromised by increased viscosity and poor flow behaviour, respectively. Fastness in prints, including lightfastness, heat stability, and resistance to clear lacquer coatings and sterilization, common organic solvents, and the DIN 16 524 solvent mixture are good-to-excellent. In this respect, P.Y.176 largely parallels P.Y.13.

2.4.1.4.26 Pigment Yellow 188

P.Y.188, which was released onto the market only a few years ago, is closely related to Pigment Yellow 13 in both its chemical and application properties.

The commercially available, highly transparent type is primarily applied in offset printing inks. In this field, P.Y.188 matches the CIE 12-66 standard yellow shade for process printing (Section 1.8.1.1). The commercially available type of P.Y.188 is highly resinated and shows very good tinctorial strength. It displays good flow behaviour.

2.4.1.4.27 Pigment Orange 15

P.O.15 produces yellowish orange shades, which resemble those of P.O.13. Compared to P.O.13, however, P.O.15 has largely lost its importance. Currently, it is only produced in the USA. Although the pigment is less lightfast and less stable to organic solvents than P.O.13, P.O.15 is used to lend colour to printing inks and rubber.

2.4.1.4.28 Pigment Orange 16

Structurally based on 3,3′-dimethoxybenzidine (o-dianisidine) as a diazo component, P.O.16 is also known as Dianisidine Orange. At present, the pigment only enjoys some importance in Europe, the USA and in Japan.

Its colour is a yellowish orange, which is considerably redder than P.O.13 and 34. Increasingly stringent application requirements regarding lightfastness and durability, solvent and migration resistance present a considerable challenge to P.Y.16 and have largely eliminated the pigment from the market.

The largest area of application for P.Y.16 is in the printing ink industry. The pigment is used particularly to adjust the shades of P.Y.12 type diarylide yellow pigments, to which it is most closely related as far as application performance is concerned. Such blends are employed in low-cost packaging and speciality inks. Resinated types are produced to provide higher transparency. There is a certain disadvantage to the poor rheology of several P.Y.16 types, which makes it difficult to formulate highly pigmented systems.

P.O.16 is not lightfast and durable enough to be used in paints. In this respect, it performs even more poorly than P.Y.12. Low-cost production, however, makes it a suitable colourant for rubber and for textile printing.

2.4.1.4.29 Pigment Orange 44

P.O.44 has lost most of its commercial importance and is at present only applied to a limited extent. This is also true for other pigments whose synthetic route involves 3,3′-dimethoxybenzidine as a diazo component. P.O.44 provides a very reddish orange shade, which is much redder than the colour of the β-naphthol pigment P.O.5. Although P.O.44 is more resistant to solvents than P.O.5, the reverse is true for lightfastness. Standardized letterpress proof prints containing P.O.44, for instance, equal step 3 on the Blue Scale, while equally deeply shaded P.O.5 prints equal step 6 on the Blue Scale.

The main area of application for P.O.44 is in the field of textile printing, although it is less lightfast than P.O.5. 1/1 SD prints containing P.O.44 equal step 5–6, as opposed to step 7 for P.O.5 prints; 1/3 SD P.O.44 samples equal step 4–5, again as opposed to step 7; and 1/6 SD P.O.44 prints only reach step 3–4 on the Blue Scale, while P.O.5 still scores as high as step 6–7.

The application fastness of the pigment, however, is more satisfactory. P.O.44 may be dry cleaned and resists dry heat up to 210 °C for 30 s; while P.O.5 and also the somewhat redder Naphthol AS pigment P.R.10 are less fast. P.O.44 is also used in PVC coatings.

2.4.1.4.30 Pigment Orange 47

Pigment orange 47 is one of the few diarylide yellow pigments which is based on 3,3′-dimethylbenzidine instead of 3,3′-dichlorobenzidine as disazo component. The coupling compound is the same as in P.Y.171. The replacement of 3,3′ dichlorobenzidine by 3,3′dimethylbenzidine results in a colour shift from yellow (P.Y.171) to a bright yellowish orange (P.O.47).

P.O.47 is mainly produced in the USA. Specific applications are not reported.

2.4.2.3.1 Pigment Yellow 16

P.Y.16 covers the medium yellow range. Increasingly stringent industrial requirements in some areas are slowly restricting the use of this originally versatile product.

P.Y.16 shows good-to-very good resistance to various organic solvents, including alcohols and esters; however, it exhibits no fastness to some other solvents, such as xylene and other aromatic hydrocarbons. Recrystallization may be a problem if the pigment is to be processed in systems containing aromatic solvents, such as some baking enamels and packaging gravure printing inks, resulting in a considerable shift toward red shades. By thermic treatment P.Y.16 undergoes a similar colour shift in the presence of certain solvents in the medium of application, owing to a change of crystal modification. Different solvent treatment has led to three more crystal modifications. Compared with the β-form, the γ-modification is greener, the δ-form considerably redder and the ɛ-form somewhat redder and cleaner in shade. The results have been confirmed by X-ray diffraction studies [61]. Both the δ- and ɛ-modifications exhibit improved lightfastness compared with the α- or β-form.

In the paint field P.Y.16 is primarily used in industrial finishes. The similarity to P.Y.1 is limited to a likeness in shade; but P.Y.16 is fast to overcoating and shows no tendency to bleed in baking enamels. Although its full shade lightfastness equals step 7–8 on the Blue Scale, types that are only slightly reduced with TiO₂ (1:5) reach only step 5. Only full shades provide good weatherfastness.

To produce chromium-free full shade finishes with good hiding power, special opaque P.Y.16 types are available. Their good rheology makes it possible to further increase the hiding power by increasing the pigment concentration without adversely affecting flow, gloss or other inherent features of the paint. Although the weatherfastness of such opaque versions with coarse particle sizes is somewhat better than that of traditional types, it is frequently insufficient for long-term exterior application. The opaque varieties are faster to aromatic solvents and solvents other than the standard types, and they recrystallize less readily.

P.Y.16 is supplied as a pigment preparation to the emulsion paint industry.

P.Y.16 is suitable for all printing techniques used in the printing ink industry. In some systems, however, it tends to recrystallize. P.Y.16 shows high tinctorial strength and relatively good resistance to light. The pigment is as lightfast as the good lightfast diarylide yellow pigments. 1/1 SD printed samples equal step 5 on the Blue Scale, 1/3 SD prints reach step 4–5. Very opaque types are even faster to light; depending on the depth of shade, these score ½ to 1 step higher on the Blue Scale. The prints are resistant to clear lacquer (Section 1.6.2.1) and stable to calendering and sterilization. Heat stability at 30 min exposure up to 200 °C makes P.Y.16 a suitable pigment for metal deco printing. Similarly, it is utilized for textile printing purposes. Application in the plastics field has diminished considerably. P.Y.16 migrates in PVC, which leads to blooming and bleeding. Moreover, its heat resistance in plasticized PVC is unsatisfactory, due to recrystallization. The pigment shows good tinctorial strength in polyolefins. Its heat stability in this medium has been said to equal approximately 230–240 °C for 5 min, depending on the depth of shade. But as a result of the thermal decomposition (Section 2.4.1.3) the heat stability is to be limited to 200 °C.

Besides its use in cast resin, such as methyl methacrylate mixtures, P.Y.16 has gained recognition as a colourant for felt-tip pens, watercolours and several related applications. It lends colour to leather, mass and surface paper colouration, and paper pulp.

2.4.2.3.2 Pigment Yellow 155

P.Y.155 provides clean, somewhat greenish yellow shades and is characterized by high tinctorial strength, good solvent resistance, and fastness to alkali and acid.

The pigment is recommended for use in paints, plastics and printing inks. P.Y.155 is one of the most important yellow pigments for laser printers. It shows excellent fastness to overcoating in baking enamels: in alkyd-melamine systems, it withstands 30 min of exposure to up to 140 °C without bleeding. P.Y.155 is characterized by good lightfastness; its full shades are as fast as P.Y.16. In full shades and in white reductions, P.Y.155 is more weatherfast than P.Y.16, but it is not as weather resistant as the somewhat greener monohydrazone yellow pigment P.Y.97. A new type consisting of coarser particles, which provides better weatherfastness, has recently been introduced to the market. This type is recommended as a replacement for Chrome Yellow pigments for its higher hiding power.

P.Y.155 is used to an appreciable extent in industrial finishes that are targeted for commercial vehicles, tractors and farm implements. In paints, it resists temperatures up to 160 °C.

Incorporated in plasticized PVC, P.Y.155 withstands temperatures up to 180 °C, but it shows a certain tendency to bleed under common processing conditions. Its tinctorial strength is good-to-average. 1/3 SD colourations (5% TiO₂) require 0.7% pigment. In PVC, the ability of both transparent (0.1%) and opaque (0.1% pigment +0.5% TiO₂) versions to withstand light is equal to step 7–8 on the Blue Scale, while such types are less weather resistant. In HDPE, 1/3 SD P.Y.155 colourations (1% TiO₂) may be exposed to temperatures up to 260 °C for 5 min without changing colour. As in PVC, the tinctorial strength in HDPE is average. Recommendations for application include polypropylene and styrene, but exclude polyesters.

In printing inks, P.Y.155 lends itself to all printing techniques. The prints provide good fastness properties; they are even soap and butter resistant. P.Y.155 is one of the most important pigments for inkjet printing and laser printing.

2.4.2.3.3 Pigment Yellow 198

The pigment was recently introduced to the market.

P.Y.198 is primarily recommended for packaging gravure printing, in particular for printing inks based on nitrocellulose with alcohols and esters as solvents and for water-based printing inks as well. The lightfastness of the corresponding prints in 1/1 SD with 4.7% of pigment equals step 5, in 1/3 SD with 2.5% of pigment it matches step 4 of the Blue Scale.

Although fast to bleeding in petroleum ether and dibutyl phthalate, very little bleeding is found in ethanol and methoxypropanol and a slight bleeding occurs in toluene, ethyl acetate, paraffin and the solvent mixture according to DIN 16 524.

2.4.2.3.4 Pigment Yellow 212

A metallized bisacetoacetarylide pigment with a chemical constitution is as yet unpublished. This pigment exhibits excellent heat stability in polyolefins, HDPE and polypropylenes exceeding 310°C in masstone and tint. It is a bright medium shade yellow and provides an excellent alternative to diarylides and other yellows in this shade range. The pigment complies with the FDA requirements for food contact under the conditions of use (A) through (H) as described in Table 2 of 21 CFR Part 176.170(c) where this pigment is allowed to be used at levels up to 1% by weight of the polymer subject to the provisions and definitions described in Title 21 CFR Part 178.3297.

P.Y.212 is not recommended for exterior use, but provides an excellent value for interior applications such as packaging and household durables of all types. Pigment Yellow 212 is tinctorially quite strong as metallized azos go and exhibits very good dimensional stability, making it very useful in moulded items such as blow moulded containers.

2.4.2.3.5 Pigment Yellow 219

A rather new development is P.Y.219, exhibiting a particularly bright greenish yellow shade, high colour strength and good opacity. The pigment is suitable for automotive paints and all kinds of industrial paints, both for water-based as well as solvent-based coatings. It is ideal for combinations with bismuth vanadate, as the colour does not change over a wide array of mixture ratios.

It can also be used in plastics, toners and inks. The lightfastness (DIN EN 105-B01) in deep shade is 7–8, in 1/25 SD 6–7; weatherfastness in deep shade is 4–5 and shows 4 in 1/25 SD.

Six different crystal modifications of the pigment could be obtained by heat treatment with organic solvents/water. The amorphous crude pigment suspended in dimethylformamide/water at 140 °C yields the β-polymorph. If this modification is heat-treated with N-methylpyrrolidone, dimethyl sulfoxide, long-chain alcohols, 1,2-dichlorobenzene, pyridine and/or nitrobenzene, the α, γ, δ, ɛ, ξ, and η modifications are obtained [62].

2.4.3.4.1 General

P.O.34 and 13 are the two most frequently used dihydrazonepyrazolone pigments obtained by bisdiazotization of 3,3′-dichlorobenzidine. P.O.13 comprises the largest portion of dihydrazonepyrazolone pigment production and also reigns supreme amongst organic orange pigments in general. P.R.38 and 37 have less of an impact on the pigment industry. Both were introduced around the same time as P.O.13. P.R.37 and 41 are obtained with 3,3′-dimethoxybenzidine as bisdiazonium component. Table 2.6 lists the commercially available dihydrazonepyrazolone pigments.

C.I. Name	C.I. Constitution Number	X	R1	R2	Shade
P.O.13	21110	Cl	CH3	H	yellowish orange
P.O.34	21115	Cl	CH3	CH3	yellowish orange
P.R.37	21205	OCH3	CH3	CH3	yellowish red
P.R.38	21120	Cl	COOC2H5	H	Red
P.R.41	21200	OCH3	H	H	Red
P.R.111	—	—	—	—	Red

2.4.3.4.2 Pigment Orange 13

P.O.13, sold in the USA as pyrazolone orange, comes in semi-transparent types with specific surface areas between about 35 and 50 m² g⁻¹. It is colouristically very similar to P.O.34, but generally somewhat yellower. Occasionally weaker than P.O.34, it is also slightly less fast in many media. Considering its tendency to migrate, incorporation into plasticized PVC is not recommended. The pigment blooms over a large concentration range and bleeds considerably. At concentrations below about 0.1%, neither P.O.34 nor 13 are suited for use in rigid PVC.

Application of P.O.13 in polyolefins is limited. It is recommended for use at temperatures up to 200 °C (Section 2.4.1.3). This is equally true for polystyrene and other plastic materials that are processed above 200 °C, such as polymethacrylate, in which P.O.13 is used. P.O.13 is one of the pigments that do not affect the extrusion shrinkage of HDPE, but it is nevertheless rarely employed to colour such materials. In LDPE, there is some danger of blooming.

P.Y.13 is extensively used in the rubber industry. It is fast to vulcanization and bleeding in natural rubber. Owing to its excellent fastness to water the pigment can be applied for bathing articles, sponges and sealing rubbers for preservation glasses.

The pigment is very fast to detergents. It is also employed in viscose spin dyeing and in mass dyeing, for example for cellulose sponges and foils. In full shades (1/1 SD) the lightfastness equals step 6–7 of the Blue Scale and decreases with reduction (1/12 SD) to step 4. The most important fastness properties for textile printing are excellent or very good.

P.O.13 shows less stability in paints than P.O.34 types of similar particle size. This includes both fastness to overpainting in baking enamels and lightfastness in air drying paints. The volume of trade sales for this purpose is accordingly limited.

The graphics industry, on the other hand, uses P.O.13 to an appreciable extent for packaging printing inks. Its fastness to light is average and corresponds to that of the diarylide yellow pigment P.Y.12, with which it is frequently combined as a shading component. The stability of pigmented prints to several organic solvents is excellent or almost perfect. Similarly, the prints are fast to paraffin, butter and soap. They withstand heat very well and are stable up to 200 °C. P.O.13 thus lends itself to metal deco printing, provided its lightfastness suits the purpose. Likewise, its resistance to clear lacquer coatings and to sterilization are excellent.

2.4.3.4.3 Pigment Orange 34

P.O.34 is supplied in various types, which differ considerably in their particle size distributions. Specific surface areas range from 15 m² g⁻¹ in highly opaque versions to about 75 m² g⁻¹ in transparent types. It is these physical characteristics that determine the colouristic and fastness properties of each type. Even varieties of P.O.34 with fine particle sizes are generally not resinated.

Transparent P.O.34 versions represent the most frequent choice for printing inks. They provide a clean, yellowish orange hue and high tinctorial strength. Standardized 1/1 SD letterpress proof prints require inks formulated at 7.6% pigment. The same is true for corresponding yellow shades produced by the tinctorially strong diarylide yellow pigment P.Y.13. P.O.34 is somewhat redder than the similarly strong P.O.13. At equal depth of shade, prints obtained from P.O.34 tolerate light better than do prints containing P.O.13; the difference is about 1 step on the Blue Scale. The lightfastness of 1/1 and 1/3 SD prints equals step 4 on the Blue Scale, which makes the pigment almost as fast as P.Y.13.

P.O.34 shows good solvent resistance to several organic solvents. Its prints are more stable in this respect than those made from P.O.13, which is also true for the standard DIN 16 524 solvent mixture (Section 1.6.2.1). Despite these comparatively good fastness properties, P.O.34 may recrystallize in various printing inks, depending on the processing conditions. P.O.34 prints are fast to paraffin and dioctyl phthalate; likewise, they tolerate clear lacquer coatings and may be sterilized.

Transparent P.O.34 is somewhat sensitive to heat and generally only withstands temperatures up to 100–140 °C. Higher sterilization or metal deco printing temperatures may produce a colour shift towards a redder orange.

P.O.34 is used for all printing techniques. Packaging printing inks, especially nitrocellulose inks, often use the orange version of the cheaper and more lightfast P.O.5 in areas where fastness to organic solvents is unimportant. The shade of the product may have to be modified accordingly. P.O.34, as do diarylide yellow pigments, exhibits insufficient solvent fastness to be used in decorative printing inks; it is particularly not fast enough to monostyrene and acetone (Section 1.8.1.2). The pigment also performs poorly as far as lightfastness is concerned, and it bleeds into solutions of melamine resins, which precludes its use in such fields.

The textiles printing industry, however, uses P.O.34 to an appreciable extent. The pigment provides average lightfastness (at 1/3 SD, it equals step 5–6 on the Blue Scale); its dry cleaning solvent resistance is excellent, and it withstands exposure to dry heat up to 200 °C. P.O.34 performs similarly in connection with spin dyeing of polyacrylonitrile.

Throughout the plastics industry, P.O.34 is used to colour plasticized PVC, although a certain tendency to bloom precludes its application at levels below about 0.1%. At higher concentrations, the pigment tends to bleed in plasticized PVC, but it is considerably more stable to light than the weaker P.O.13. At equal depth of shade, 1/3 SD samples equal step 6 on the Blue Scale, while the corresponding P.O.13 sample reaches only step 4. Transparent P.O.34 colourations in rigid PVC are even more resistant to light. Pigment concentrations of less than about 0.1% are likewise unsuitable, due to the necessity to avoid blooming. The pigment is also used in vinyl floor coverings and in cable insulations.

P.O.34 is rarely used in polyolefins. In such media, it only withstands exposure to 200 °C, and its opaque colourations show insufficient lightfastness. P.O.34 tends to bloom, especially in extrusion products made of low molecular weight LDPE types. The pigment is, however, recommended for various other media. These range from aromatic polyurethane foams to cast resins of unsaturated polyester, in which the pigment slightly delays the hardening process.

In the paint industry, transparent types are used only to a limited extent. In air drying systems, P.O.34 equals step 6–7 on the Blue Scale in full shades, while opaque colourations with TiO₂ (1:5) only reach step 3 for lightfastness. In baking enamels, the pigment is not fast to overpainting.

Highly opaque versions of P.O.34 with coarse particle sizes and specific surface areas between about 15 and 25 m² g⁻¹, however, are gaining recognition within the paint field. Excellent flow properties make it possible to further increase the pigment level and the opacity, in which P.O.34 affords exceptionally good results for an organic pigment. Even at equal pigment concentration, P.O.34 is more opaque than commercially available Molybdate Red pigments which cover the same range of hues. Full shades of this very opaque type are very fast to light and weather, and they have a much better ability to tolerate solvents and migration. This makes P.O.34 attractive as a partial or complete replacement for Molybdate Red in industrial finishes, tractor and agricultural implement finishes, house paints, and so on. Its temperature stability is similarly superior. This is also true for application in print, where P.O.34 exhibits an increase in thermal stability from less than 120 °C in transparent prints to 200 °C in specialized opaque varieties. Opaque types are also much more reddish, which changes the DIN colour (Section 1.6.1.4) of 1/3 SD prints from 4.06 to 5.93. Combinations with other coloured pigments, such as iron oxides or titanium mixed oxides, such as nickel titanium yellow and colourations that are reduced with TiO₂ are much less fast.

2.4.3.4.4 Pigment Red 37

P.R.37 is a yellowish red pigment that performs poorly in many applications and is largely restricted to the colouration of rubber and plastics.

Lightfastness in rubber, which meets almost all requirements, is accompanied by good curing properties and migration resistance. The resulting pigmented articles are very resistant to water and detergent solutions.

P.R.37 is a very strong pigment in PVC, but deficient in its fastness to light. 1/3 SD coloured samples equal step 2–3 on the Blue Scale, while 1/25 SD specimens only reach step 1. In its fastness to light, the pigment thus performs much poorer by several steps on the Blue Scale than diarylide yellow pigments, such as P.Y.13 or P.Y.17. Its fastness to bleeding in plasticized PVC (at 1/3 SD), however, parallels that of these yellows. Pigment preparations of P.R.37 are also available. Owing to its good dielectric characteristics, P.R.37 is frequently selected for use in cable insulations. However, application recommendations exclude polyolefins.

2.4.3.4.5 Pigment Red 38

P.R.38 affords a medium red shade. It is used primarily in rubber and plastics. Much faster to several organic solvents than P.R.37, rubber colourations are very fast to light and are used under almost any application conditions. P.R.38 is completely resistant to curing and bleeding into natural rubber and fabric backing (Section 1.8.3.6). The coloured articles are resistant to water, soap and detergent solutions, and equally fast to various organic solvents, including gasoline. P.R.38 shows high tinctorial strength in PVC, but tends to bloom at low pigment levels. In contrast to P.R.37, low P.R.38 levels in rigid PVC are equally prone to bloom. However, P.R.38 is much more lightfast than P.R.37: in 1/3 SD, it reaches step 6 on the Blue Scale, in which it parallels the properties of P.Y.13. Combinations of the two are frequently used to produce intermediate shades. In PVC, the pigment withstands temperatures up to 180 °C; its good dielectric properties make it a useful colourant for PVC cable insulations.

In polyethylene, the pigment tolerates temperatures up to 200 °C; such systems are used to make films. Higher processing temperatures carry the risk of inducing blooming and decomposition by heat in LDPE types. Depending on the depth of shade, its lightfastness in HDPE equals between step 3 and step 6 on the Blue Scale. In this medium, it does not affect the shrinkage of the plastic. Especially throughout the USA, P.R.38 is primarily used for paper coatings, mass colouration of paper, artists' colours, crayons, and similar specialized media, and also in specialized printing inks.

2.4.3.4.6 Pigment Red 41

P.R.41 is also known as pyrazolone red. It has lost most of its commercial importance in recent years. P.R.41 production is now limited to the USA, where it is mostly employed to lend colour to rubber. To a lesser extent, P.R.41 is found in PVC; excellent dielectric properties make it a suitable candidate for PVC cable insulations. The pigment provides a medium to bluish red; of limited brilliance, it is much bluer than P.R.38. P.R.41 is somewhat less fast than P.R.38, which is also true for its stability to various organic solvents. However, it parallels P.R.38 in its alkali and acid resistance. P.R.41 is very lightfast in rubber; 1% pigment concentrations equal step 6–7 on the Blue Scale, which meets practically any requirement. The pigment also withstands migration, that is, it does not bleed into natural rubber or fabric backing (Section 1.8.3.6). P.R.41 is also completely resistant to curing conditions. Coloured rubber articles tolerate boiling water, acid and soap.

2.4.3.4.7 Pigment Red 111

P.R.111 is chemically related to the pyrazolone pigments P.O.34 and P.R.37. Its hue is somewhat bluer than that of its pyrazolone counterparts; it equals that of Signal Red (RAL 3000). The lightfastness of P.R.111 is somewhere between that of P.O.34 and of P.R.37. P.R.111 performs similarly as far as other fastness properties are concerned. The pigment lends itself particularly to the colouration of rubber and PVC; excellent dielectric properties also render it suitable for cable insulations. Thermally, P.R.111 is not sufficiently stable to be used in polyolefins, styrene, ABS and similar plastics.

2.6.4.2.1 Pigment Red 2

P.R.2 provides a medium red shade, which is somewhat yellower than the Naphthol AS pigment P.R.112. Its main area of application is the printing inks field. In some systems, P.R.2 is even slightly stronger than P.R.112, although it does not quite achieve the same lightfastness. 1/1 SD letterpress proof prints equal step 5 on the Blue Scale, 1/25 SD prints reach step 4. The corresponding values for P.R.112 are ½ to 1 step higher. Most of the commercially available products have specific surface areas between about 20 and 30 m² g⁻¹. They afford prints with correspondingly poor transparency. The types with comparatively coarse grains, on the other hand, which are frequently used to formulate highly pigmented printing inks, show good flow properties and satisfy the requirements for corresponding application. The prints exhibit good gloss.

P.R.2 does not show perfect performance in special applications (Section 1.6.2.3) in prints, which is also true for several other members of this class. In this respect, P.R.2 is inferior to P.R.112. This may have a particular impact on marginal areas of pigment applicability. P.R.112 letterpress proof prints, for instance, tolerate mineral spirits and soap, while P.R.2 prints only reach step 4 on the 5 step fastness scale. P.R.2 specimens are also sensitive to clear lacquer coatings and to sterilization.

P.R.2 is primarily used in offset and packaging gravure and flexo printing inks. The pigment also lends itself to textile printing. Besides, P.R.2 also functions as a pigment in connection with the spin dyeing of viscose rayon and viscose cellulose and in the mass colouration of viscose sponges and films. Leather coverings are also frequently coloured with P.R.2.

The paint industry has little demand for P.R.2. The pigment finds some use in household paints, especially in air drying systems.

2.6.4.2.2 Pigment Red 7

P.R.7 provides bluish red shades and is used in various media in the printing inks, paints and plastics field. Only one or two decades ago, P.R.7 was considered the leading Naphthol AS pigment. The pigment has been removed from the market altogether, because the starting materials for its synthesis were no longer available. There are other Naphthol AS pigments covering the same range of shades, such as P.R.170, which may replace P.R.7.

2.6.4.2.3 Pigment Red 8

Pigment Red 8 affords clean, bluish shades of red. It is primarily used in the printing ink industry. P.R.8 exhibits high tinctorial strength and produces brilliant prints. Commercially available types with specific surface areas between about 50 and 60 m² g⁻¹ afford transparent prints. P.R.8 is used in prints that require no particular solvent resistance. However, the pigment tolerates solvents much better than the yellower P.R.7; in this respect, P.R.8 matches the yellower, but more lightfast P.R.5. The prints are fast to soap but not entirely stable to butter and paraffin. P.R.8 is sensitive to clear lacquers coatings and to sterilization. It tolerates exposure to 140 °C for 30 min.

The lightfastness (such as in letterpress proof prints) deteriorates drastically with decreasing pigment area concentration. 1/1 SD prints equal step 5, while 1/25 SD specimens only reach step 3 on the Blue Scale. P.R.8 is used in letterpress and offset inks, in packaging gravure printing inks and in various flexo inks. Types with finer particle sizes, dispersed in vehicles for various printing techniques, may recrystallize and drastically deteriorate in tinctorial strength and transparency. P.R.8 is also used in textile printing, although its lightfastness does not satisfy high demands.

P.R.8 is used in various special media outside the paints, printing inks and plastics field, which is also true for other members of this class of pigments. One such application is in the paper industry, where the pigment is used for mass colouration and surface coating formulations. It also lends itself to application in artists' colours and office articles.

2.6.4.2.4 Pigment Red 9

P.R.9 affords clean, yellowish shades of red, which show very good lightfastness. The fact that the pigment is supplied in the form of an unstable crystal modification, which is very sensitive to aromatic hydrocarbons and some other organic solvents, restricts its use to media that do not contain aromatic solvents. P.R.9 is therefore used in letterpress and offset printing and aqueous flexo inks. Although the prints are comparatively sensitive to several solvents, they are soap and butter fast and almost fast to paraffin, dibutyl phthalate and mineral spirits. Compared to the slightly yellower P.R.10, P.R.9 is more lightfast if the pigment area concentration is low. In comparison with the slightly bluer 1/3 SD P.R.53:1 prints, P.R.9 is more lightfast by a few steps on the Blue Scale; it is also alkali and acid resistant. Commercial types with low specific surface areas around 20 m² g⁻¹ afford little transparency in print.

The paints field is another area in which P.R.9 is restricted to media containing aliphatic hydrocarbons only. Application in systems containing aromatic hydrocarbons, ketones, esters or glycol ethers changes the crystal modification and causes recrystallization, shifts the colour considerably, and drastically reduces the tinctorial strength. In suitable finishes, however, P.R.9 demonstrates very good stability to light, even in white reduction. This qualifies it for use in emulsion paints, where it shows equal perfection in lightfastness and weatherfastness. Even its full shades, however, are frequently not fast enough for exterior application.

Applications outside the above-mentioned areas include coloured pencils.

2.6.4.2.5 Pigment Red 10

This pigment exhibits a clean, yellowish red shade, similar to that of P.R.9. It is supplied as a stable crystal modification and is thus not as sensitive to aggressive solvents as P.R.9. This broadens its scope to include packaging gravure and flexo printing inks containing solvents. The pigment provides good lightfastness. 1/3 or 1/25 SD letterpress proof prints, however, score ½ to 1 step less on the Blue Scale than corresponding P.R.9 prints. P.R.10 prints are not suitable for clear lacquer coatings and may not be sterilized; their heat stability is low.

Textile prints score poorly in dry cleaning tests involving agents such as perchloroethylene, a feature that is typical of Naphthol AS pigments. P.R.10 is affected by dry heat and is equally unsuitable for PVC coatings. The prints equal step 6–7 on the Blue Scale for lightfastness, depending on the depth of shade.

P.R.10 is used to a certain extent in office articles, artists' colours and cleaners.

2.6.4.2.6 Pigment Red 11

P.R.11 has largely been replaced by other products. Its hue is a bluish red that resembles the colour of ruby; P.R.11 is more bluish than its positional isomer P.R.7. Both pigments behave similarly as far as fastness properties are concerned, which includes fastness to most of the solvents that are used in paints and printing inks, fastness to overlacquering, heat stability and so on. However, P.R.11 is much less lightfast than P.R.7; incorporated in medium-oil alkyd systems at 1/3 SD, P.R.11 scores 2 steps less on the Blue Scale (step 4).

2.6.4.2.7 Pigment Red 12

P.R.12 is one of the more significant bordeaux coloured pigments. Two crystal modifications are known, of which only the thermodynamically unstable bordeaux one is commercially used. Little activation energy is required to convert the bordeaux modification into the stable red modification. Conversion is, for instance, initiated as the pigment is dispersed in an oily binder containing zinc oxide using low shear equipment, such as a Hoover muller. Change of crystal modification may also occur if P.R.12 is milled in dry state with dry baryte. The transition occurs also very rapidly in the presence of chlorohydrocarbons or ketones in the dispersion medium. Exceptionally large pigment crystals are formed as the crystal modification changes, considerably reducing the viscosity of the dispersion medium. Poor lightfastness renders the stable red modification unsuitable for commercial application.

The graphic industry uses P.R.12 in offset inks, for packaging gravure and flexo printing inks. The pigment is comparatively lightfast; 1/1 to 1/25 SD letterpress proof prints equal step 5–6 to step 4 on the Blue Scale. P.R.12 demonstrates very high tinctorial strength; the fastness of the prints to solvents and other media is, however, moderate. The prints are affected by paraffin, butter and other fats. P.R.12 is similarly sensitive to alkali.

P.R.12 textile prints are excellently lightfast; 1/1 to 1/6 SD prints equal step 7 and 6–7, respectively, on the Blue Scale. However, the pigment fails dry cleaning tests and migrates considerably in PVC coatings. P.R.12 tolerates dry heat up to 150 °C; at 180 °C, the pigment still largely retains its initial colour value.

The paint industry uses P.R.12 primarily in air drying paints. Baking may be a problem, since a pigment concentration of less than 1% will cause blooming between 140 and 180 °C; at 200 °C, the concentration limit is 2.5%. P.R.12 is therefore only used in highly concentrated formulations, especially in full and related shades. Ketones and other aggressive solvents induce a change of the crystal modification, accompanied by a drastic colour change.

However, P.R.12 demonstrates a satisfactory degree of lightfastness. Air drying paints equal step 6 on the Blue Scale in full shade, while baking enamels reach step 6–7, but show some darkening. In white reductions (1:10 TiO₂), the pigmented systems equal step 4–5 and 5–6, respectively. In baking enamels, P.R.12 bleeds considerably, irrespective of the temperature. The pigment is, however, occasionally used in emulsion paints wherever its fastness properties satisfy the specifications.

P.R.12 is also employed in a series of special applications, such as automotive cleaners, floor polish, shoe polish and so on, and it is frequently used to colour office articles and leather.

2.6.4.2.8 Pigment Red 13

Produced in China, this pigment is of limited commercial interest. Its colour is a bluish red.

2.6.4.2.9 Pigment Red 14

P.R.14 provides an intense, lightfast bordeaux shade, which is much yellower than that of P.R.12. Like P.R.12, it also possesses two crystal modifications. Again, the commercially available form is thermodynamically unstable, but, in contrast to P.R.12, conversion into the stable modification, which is technically less interesting because of its poor lightfastness, requires something of an effort. It is facilitated, for instance, by aromatic hydrocarbon and ketone solvents.

The main market for P.R.14 is in the paint industry, but the pigment is also used in printing inks and in some other applications.

Apart from air drying systems, P.R.14 is also used in baking enamels; however, it blooms beyond certain concentration limits. In an alkyd-melamine resin system, for instance, the pigment shows resistance to blooming up to 160 °C, independent of the concentration; the concentration limit at 180 °C is 0.2%, and at 200 °C it is 1%. Blooming is accompanied by considerable bleeding.

P.R.14 is very lightfast; its full shade lightfastness in air drying systems equals step 6–7 on the Blue Scale; in baking enamels, it reaches step 7–8. In white reductions (1:7 TiO₂), the lightfastness of the same systems equals step 5–6 and 6–7, respectively.

Very lightfast red shades can be produced by combining P.R.14 with Molybdate Red. P.R.112 is a member of the same class of pigments, behaves similarly and is particularly suitable as a partner for P.R.14 in blends that approach the colours of Toluidine Red (P.R.3) but provide much improved lightfastness and weatherfastness.

In applications where the pigment is fast enough to solvents to satisfy the requirements, it may also be used for offset, packaging gravure and flexo printing inks. The resulting prints are soap, alkali and acid resistant. They are not completely fast to paraffin and quite sensitive to butter and several other fats. P.R.14 prints are not fast to clear lacquer coatings and may not be sterilized. Heat stability is less than 140 °C. 1/1 SD letterpress proof prints equal step 6 on the Blue Scale for lightfastness, 1/3 SD prints equal step 5–6 and 1/25 SD prints reach step 4.

2.6.4.2.10 Pigment Red 15

P.R.15 continues to be offered in the Japanese market, but is of limited commercial value. Its hue is a brilliant medium maroon.

2.6.4.2.11 Pigment Red 16

The bluish bordeaux crystal modification of this polymorphous pigment is produced in Japan and China. It is used in printing inks wherever tolerance to solvents is unimportant. Although the pigment exhibits average lightfastness, it fails to meet current industrial standards. The shade can be adjusted by tinting P.R.12, which is a member of the same pigment family.

2.6.4.2.12 Pigment Red 17

P.R.17 provides medium reddish shades. As a result of poor fastness properties, its commercial significance is somewhat limited and it is sold only in small volume. P.R.17 has the advantage of being fast to acid, alkali and soap. It is therefore used in offset, gravure and flexo printing inks wherever tolerance to alkali and soap is a major concern. Moreover, P.R.17 is also employed in connection with mass colouration and surface colouration of paper.

2.6.4.2.13 Pigment Red 18

P.R.18, a positional isomer of P.R.114, is currently unavailable in Europe. Production abroad, especially in Japan and Central America, is limited. P.R.18 produces shades of maroon, with properties that parallel those of other members of its class with somewhat poorer fastness levels. The pigment is registered in the USA as D&C Red No. 38.

2.6.4.2.14 Pigment Red 21

P.R.21 is produced and sold in the USA and in Japan. It affords yellowish shades of red. Since it fails to meet the increasingly stringent industrial requirements, P.R.21 is no longer extensively used.

2.6.4.2.15 Pigment Red 22

P.R.22 affords yellowish shades of red. Its commercial significance varies considerably with the region. Less common in Europe, the pigment maintains an important position in the USA and especially in Japan. Its main market is in textile printing, but it is also used throughout the graphics field, such as in offset and gravure printing, especially in NC-based inks. P.R.22 is advantageous where soap and alkali resistance are required. A pigment with high tinctorial strength, it is somewhat lighter than P.R.9 in high pigment area concentrations, while at lower pigment area concentrations it is yellower. Compared to P.R.2, P.R.22 is distinctly yellower and less lightfast; this tendency is even more pronounced in comparison with P.R.112. As opposed to Lake Red C pigments (P.R.53:1), P.R.22 is bluer to yellower, depending on the choice of printing ink, but its lightfastness is better by about 1 step on the Blue Scale.

The paint industry employs P.R.22 in air drying systems, in emulsion paints and occasionally in industrial finishes, although there is some danger of blooming, and the appropriate limit has to be observed. Again, P.R.22 is much less lightfast in these media than P.R.112. Areas of application include paper mass and surface colouration, coloured pencils, artists' colours and other purposes.

2.6.4.2.16 Pigment Red 23

P.R.23 provides bluish, dull red shades, yellower and much duller than P.R.146. Its commercial significance, like that of P.R.22, varies considerably with the region. Fastness to solvents and application performance are mostly inferior, which is also true for lightfastness: 1/1 SD letterpress proof prints equal step 3 on the Blue Scale, while P.R.146, at equal depth, reaches step 5. Commercial P.R.23 types usually have smaller particles than P.R.146; they are stronger and more transparent, but at the same time provide higher viscosity in ink. Inadequate solvent resistance and, as a result, a tendency to recrystallize is a disadvantage, especially in packaging gravure printing inks. Compared to P.R.146, P.R.23 will produce more opaque, weaker prints. The pigment lends itself to application in aqueous printing inks and NC-based inks. It is also used for textile printing.

P.R.23 is recommended for use in industrial paints, although this is one of the markets where it competes primarily with P.R.146. Despite being tinctorially stronger and somewhat yellower, P.R.23 is also less fast to overpainting than P.R.146 and is considerably less lightfast.

2.6.4.2.17 Rigment Red 95

P.R.95 produces a bluish red, a carmine.

The pigment is used for printing inks and paints, where it satisfies average requirements. 1/1 SD letterpress proof prints equal step 4–5 on the Blue Scale for lightfastness; the prints are not fast to butter and various fats. They are acid and alkali fast but not entirely so to soap. They are also not completely resistant to the DIN 16 524/1 standard solvent mixture. The pigment tolerates heat up to 180 °C for 10 min, but it is not entirely stable to calendering and sterilization, a feature that is typical of its class.

P.R.95 is suitable for various printing techniques. Poor migration resistance and insufficient fastness to plasticizers render the pigment unsuitable as a colourant in special gravure inks for plasticized PVC.

The paint industry employs P.R.95 primarily in various industrial finishes and in paints. Relatively lightfast in full shade, its fastness to light rapidly deteriorates upon reduction of the shade with TiO₂. The 5% full shade finishes (medium-oil alkyd resin) equal step 6–7 on the Blue Scale; 1/3 SD coatings reach step 4–5, and 1/25 SD samples afford step 3. P.R.95 is also frequently used in blends with Molybdate Red. The commercial variety shows good transparency and is therefore suited to purposes such as metallic coatings and ‘hammertone finish'. These systems, however, do not satisfy the stringent requirements with regard to lightfastness; besides, they are not fast to overcoating. At high temperature and low pigment concentration, blooming is observed. Incorporated in an alkyd-melamine resin system, for instance, at a pigment concentration below 0.1%, blooming may be observed above 140 °C. P.R.95 is heat stable up to 140 °C for 30 min.

2.6.4.2.18 Pigment Red 112

P.R.112 produces highly brilliant medium red shades. Patented as early as 1939, it has only been marketed for a few decades. However, production has increased rapidly due to its superior application properties. Its main market is in printing inks, finishes and paints, but it is also used in various other areas.

The printing inks field employs P.R.112 primarily in letterpress and offset inks, in packaging gravure inks and in flexo inks. It is tinctorially very strong. At standard thickness of layer, 1/1 SD letterpress proof prints are formulated at 17% pigment concentration, but, in practice, the amount is often much higher. The prints show excellent lightfastness. 1/1 to 1/25 SD letterpress proof prints, which, after all, cover a wide range of pigment concentrations per surface area unit, uniformly equal step 5–6 or step 6 on the Blue Scale. The fastness to light increases with increasing pigment concentration, until it reaches step 6–7 on the Blue Scale (25% printing inks). The prints are fast to soap, although they do not completely tolerate paraffin and are only moderately fast to butter and other fats (step 3). They are also affected by clear lacquer coatings and sterilization. The pigment demonstrates poor heat stability; the prints do not withstand exposure to 140 °C.

P.R.112 is very lightfast on textiles; 1/1 to 1/3 SD (deep shade) prints equal step 7 on the Blue Scale. Exposure to dry heat at 150 and 180 °C has no effect. However, like other members of its class, P.R.112 fails the dry cleaning test with perchloroethylene. The pigment may not be brought into contact with PVC coatings, into which it bleeds.

In paints, P.R.112 produces a shade that is referred to as signal red. It may be used not only in air drying paints but also in baking enamels, provided appropriate conditions are maintained to avoid blooming. At baking temperatures between 140 and 160 °C, the concentration threshold is 0.1%; between 180 and 200 °C, the limit is 2.5%. However, the fastness to overcoating is unsatisfactory. Lightfastness and weatherfastness are excellent, even in white reductions. Air drying finishes in full shade equal step 7–8 on the Blue Scale, while baking enamels reach step 8. There is not much difference in white reduction: 1:10 reductions with TiO₂ afford step 6–7 and step 7, respectively.

The shade of P.R.112 approaches that of Toluidine Red (P.R.3), which it may consequently replace in applications with demanding requirements. P.R.112 may also be combined with the bordeaux P.R.12, which behaves similarly, to provide a broad range of colours. It is somewhat bluer than P.R.9 and considerably more lightfast and weatherfast. Types that provide optimized flow are used particularly in opaque full shade finishes. Excellent fastness properties make P.R.112 suitable for high grade paints, such as automotive finishes and general industrial coatings. Electrophoretic painting is one of its special applications; the pigment is also found in emulsion paints, despite the disadvantage of comparatively poor fastness in exterior application.

Rigid PVC is one of the polymers that are sometimes coloured by P.R.112. Transparent systems (0.1% pigment) equal step 8 on the Blue Scale for lightfastness, while the lightfastness of white reductions is only step 5–6. The spin dyeing industry employs P.R.142 for viscose rayon and viscose cellulose, in which the pigment exhibits excellent lightfastness and performs, if not perfectly, then almost satisfactorily.

In addition, P.R.112 is also used in various special media and applications. It is encountered in aqueous wood stains, in which it may also be combined with yellow pigments, such as P.Y.83, or with violet colours, such as P.V.23, or with carbon black to produce shades of brown. In these media, its lightfastness equals approximately step 5 on the Blue Scale. However, the pigment bleeds when oversprayed by a white nitrocellulose combination paint; it may, though, be coated with a nitro or acid hardening varnish or a polyester varnish. The list of special applications includes office articles and artists' colours, such as pigmented felt-tip pen inks, watercolours and coloured pencils, poster paints, as well as cleaning agents and detergents. In paper mass colouration, optimum lightfastness is only realized in full shade.

2.6.4.2.19 Pigment Red 114

P.R.114, an isomer of P.R.18, is sold only in Japan, where it is of minor importance. It produces a bluish red shade, carmine. The pigment largely parallels P.R.22 in terms of application properties, especially in its fastness properties.

2.6.4.2.20 Pigment Red 119

Although it is considered a member of the Naphthol AS pigment series, the exact chemical constitution of P.R.119 has not yet been published. The pigment used to be marketed, but its production has recently been discontinued. It affords a brilliant yellowish red shade and is used throughout the paint and printing ink industry. A typical representative of group I Naphthol AS pigments as far as application performance goes, the pigment exhibits very good lightfastness in finishes. Incorporated in medium-oil alkyd varnishes, for instance, or in alkyd-melamine resin systems, the full shade lightfastness of a 5% formulation equals step 7–8 on the Blue Scale, although some darkening is observed. In white reduction, at 1/25 SD, the pigment still scores step 5 on the Blue Scale for lightfastness, in which it resembles the somewhat bluer P.R.112. Comparisons of the weatherfastness, however, are in favour of P.R.112.

P.R.119 is not resistant to overcoating; however, no blooming has been observed at low pigment concentrations and typical baking conditions. The pigment is also used in emulsion paints, although exterior application is not recommended.

Throughout the printing ink industry, P.R.119 is in direct competition with other members of the Naphthol AS pigment series. Its shade, for instance, closely resembles that of P.R.10, although it is somewhat weaker. Regarding fastness to light, P.R.119 scores ½ to 1 step less on the Blue Scale than P.R.112. P.R.119 is mainly used in flexo and wallpaper inks. It migrates in gravure inks printed on plasticized PVC, a typical feature of members of the Naphthol AS series. P.R.119 is resistant to clear lacquer coatings, may be sterilized and is highly suitable for metal deco printing. The pigment is heat stable up to 180 °C for 10 min. It is also found in crayons and artists' colours.

2.6.4.2.21 Pigment Red 136

Although P.R.136 is a Naphthol AS pigment, its exact chemical constitution remains to be published. The pigment is currently not being marketed. Two versions have been commercially available. The transparent type has a specific surface area of almost 70 m² g⁻¹ and shows a considerable degree of structural viscosity. Its shade is a cherry red. The bordeaux grade, on the other hand, has a specific surface area of about 25 m² g⁻¹, is much more opaque and exhibits a more favourable flow behaviour. It is used primarily in close to full shade colourations, for applications where hiding power is an issue. The shade of RAL 3004 is matched by adding appropriate amounts of TiO₂.

Both types, however, enjoyed limited commercial success. They were found in paints, in which they are heat stable up to 160 °C. The fastness of the pigment to solvents is typical of a member of the Naphthol AS pigment series, which includes inadequate fastness to overcoating. At low pigment concentrations, high baking temperatures may induce blooming. The pigment will bloom, for instance, at 160 °C in an alkyd-melamine resin baking enamel formulated at less than 0.05% pigment concentration. Both P.R.136 types demonstrate good lightfastness and weatherfastness, but darken in full shade. The more opaque version is more lightfast and weatherfast and is recommended for automotive refinishes.

2.6.4.2.22 Pigment Red 148

A few years ago P.R.148 was withdrawn from the market. It used to be employed in printing inks, paints, coloured pencils and also for the spin dyeing of viscose rayon and viscose cellulose. Although P.R.148 is lightfast, its behaviour towards solvents and its corresponding fastness properties, such as migration resistance, fail to meet current industrial standards. The pigment is very heat stable, but shows a strong tendency to bloom, which precludes its use even in rigid PVC. It affords a very yellowish red or reddish orange shade, which may also be produced by appropriate blends of other Naphthol AS pigments.

2.6.4.2.23 Pigment Orange 22

A reddish orange pigment, P.O.22 is used for spin dyeing viscose rayon and viscose cellulose, for which it is sold in the form of a pigment preparation. Properties that have a bearing on textile printing and colouration, such as fastness to light, as well as fastness to wet and dry rubbing, dry cleaning, and bleaching with peroxide, are excellent.

2.6.4.2.24 Pigment Orange 24

P.O.24 is manufactured exclusively in Japan and enjoys only minor recognition. Its resistance to organic solvents is inferior to that of other Naphthol AS pigments. The pigment fails to meet most lightfastness requirements.

2.6.4.2.25 Pigment Brown 1

P.Br.1 is a neutral brown pigment of very good lightfastness. However, it has lost most of its importance in recent years; therefore, production has currently been discontinued. The pigment is not stable to organic solvents. Its main market is in printing inks wherever solvent resistance is not required. The prints are not fast to soap and butter, do not tolerate clear lacquer coatings, and cannot be calendered or sterilized without colour change. The 1/1 to 1/25 letterpress proof prints equal step 6–7 on the Blue Scale for lightfastness. In high grade prints, P.Br.1 is being displaced successively by newer pigments, such as P.Br.23 and 25, which have much better application properties and are calender and sterilization resistant. P.Br.1 is also falling prey to blends of orange, red and yellow pigments with carbon black, which show more acceptable performance.

The pigment is not used in paints. Rigid PVC is one of the few polymers in which it is employed. P.Br.1 is found in bottles, in which its transparent formulations (0.1%) equal step 7 on the Blue Scale for lightfastness, while opaque versions reach step 6–7.

P.Br.1 is also used in polystyrene, in which it produces an orange shade as it dissolves. P.Br.1 used to play a role in the spin dyeing of viscose rayon and viscose cellulose. The pigment continues to be employed in connection with textile printing, where it exhibits excellent lightfastness and durability. Its lightfastness in full shade (1/1 SD) equals step 8 on the Blue Scale, while in white reduction (1/6 SD) it reaches step 7. Although the pigment does not tolerate dry cleaning with tetrachloroethylene, other facets of its performance are excellent or almost excellent. The pigment also lends colour to coloured pencils.

2.6.4.3.1 Pigment Red 5

P.R.5 affords a bluish red shade, somewhat similar to that of P.R.8, although the former is much more lightfast. Its commercial significance and its primary use depend on the region: In Europe it is primarily employed in printing inks, while the American and Japanese markets mainly utilize the pigment in the paint field.

Compared to other members of its class, P.R.5 exhibits good fastness to solvents.

In the printing inks field, P.R.5 is in direct competition with the much more bluish P.R.146, which provides more brilliant prints and is considerably more solvent resistant. P.R.146, on the other hand, is less lightfast. P.R.5 letterpress proof prints score between step 6–7 and step 5 on the Blue Scale for lightfastness, depending on the depth of shade (1/1 to 1/25 SD). The corresponding values for P.R.146 are 5 and 4, respectively. Prints made from P.R.5 are fast to soap and resistant to clear lacquer coatings, but are not entirely stable to butter and paraffin wax.

Since the prints do not tolerate calendering, the pigment is primarily used in offset inks, as well as in packaging gravure inks and in flexo inks.

In finishes, P.R.5 does not bloom under normal processing conditions, but it bleeds in baking enamels. The pigment is lightfast in full shade and in white reductions. Full shade lightfastness equals step 7 on the Blue Scale, while some darkening is observed. At 1:6 reduction with TiO₂, the lightfastness equals step 6 in air drying systems and step 7 in baking enamels. At 1:60 TiO₂ reduction, the values are step 4–5 and step 5 on the Blue Scale, respectively. P.R.5 is generally used in industrial and in trade sales paints. It may be blended with Molybdate Orange to produce opaque shades of red.

Types containing comparatively large particles and therefore featuring very low specific surface areas produce duller shades; these varieties are used mainly in Japan. They are employed to formulate dark red shades for automotive finishes, in which they compete with more opaque types of P.R.170, which produce a cleaner shade, tolerate solvents better and are fast to overlacquering.

Owing to the disadvantage of comparatively poor migration resistance, P.R.5 is not used in plasticized PVC, but it can be applied in rigid PVC. Its lightfastness is excellent in this medium, transparent and opaque colourations (up to 0.01% pigment + 0.5% TiO₂) equal step 7 and, respectively, step 6–7 on the Blue Scale. Dispersed pigment preparations are available for the mass colouration of viscose films as well as for spin dyeing of viscose rayon and viscose cellulose.

The pigment performs satisfactorily on textiles, it shows good lightfastness. Depending on the SD, its lightfastness equals step 5 to step 7 on the Blue Scale (1/12 and 1/1 SD).

P.R.5 also lends itself to various special applications. The list includes (decorative) cosmetics such as lipstick, eye shadow, powder, nail polish and others. Application in this area depends on special purity requirements, and the commercially available types are tested accordingly. The pigment is listed in the European Cosmetics List.

2.6.4.3.2 Pigment Red 31

The pigment enjoys regional significance on the North American Continent and in Japan, but has vanished from the European market. It provides bluish shades of red, bordeaux. Its principal application is in rubber, in which it shows good lightfastness. No bleeding into natural rubber or into the fabric backing is observed (Section 1.8.3.6). The pigmented products resist cold and boiling water, soap, detergent solutions, 5% aqueous acetic acid, and 50% aqueous ethanol.

In polystyrene (PS), polymethacrylate (PMA), unsaturated polyester resins or similar media, P.R.31 affords highly transparent colourations of medium red shades, which are used as automobile tail lights and for other signalling purposes. Its heat stability in PS and PMA extrusion products (5 min) is good up to about 280 °C. P.R.31 is stable to the usual peroxide catalysts. The pigment is lightfast (0.025% formulations in PMA, 1.5 mm thickness of layer: step 7 on the Blue Scale). P.R.31 is also used in textile printing.

2.6.4.3.3 Pigment Red 32

P.R.32 is made in Japan and South America and enjoys only limited local significance. Its fastness properties and application performance largely parallel those of the chemically related Naphthol AS pigment P.R.31.

2.6.4.3.4 Pigment Red 146

P.R.146 is a bluish red pigment with very good solvent resistance, even compared to other group II Naphthol AS pigments. It is primarily used in printing inks, coatings and paints.

The printing ink industry uses P.R.146 for letterpress and offset inks and also in packaging gravure and flexo printing inks. The pigment lends itself to various special applications: it is used, for instance, to print bank notes and securities. A certain tendency to migrate, however, precludes its use in print on plasticized PVC films.

P.R.146 is somewhat yellower than P.R.57:1; it therefore fails to match the standard magenta for three- and four-colour printing. However, P.R.146 prints have the advantage of good application performance (Section 1.6.2.3), corresponding to the above-mentioned solvent fastnesses.

The prints tolerate white spirit, dibutyl phthalate, butter, soap, alkali and acid. Moreover, they are also stable to clear lacquer coating; their fastness to sterilization, on the other hand, exceeds that of P.R.57:1, but is not perfect. Where sterilization fastness is required, P.R.146 is superseded by P.R.185, a benzimidazolone pigment, which is its colouristically closest neighbour.

As far as heat stability goes, P.R.146 retains its colour value for 10 min at 200 °C or for 30 min at 180 °C; it thus scores 20 °C higher than P.R.57:1. The 1/1 and 1/3 SD letterpress proof prints equal step 5 on the Blue Scale for lightfastness, while 1/25 SD specimens match step 4. P.R.146 is thus ½ to 1 step on the Blue Scale more lightfast than P.R.57:1. Prints made from commercially available types are semi-transparent.

P.R.146 also shows good lightfastness in textile printing. 1/1 SD prints equal step 7 on the Blue Scale, while 1/3 SD samples score step 6–7 and are therefore somewhat less lightfast than those of the yellower P.R.7, but superior to the likewise yellower P.R.170. Weatherfastness in print, however, is much inferior to that of P.R.7 and 170. P.R.146 prints are not entirely stable to dry cleaning and dry heat; they match step 4 on the 5 step evaluation scale.

P.R.146, which is also used in paints, is primarily applied in emulsion and architectural paints; it also lends colour to general industrial paints in applications where durability is unimportant.

In air drying systems, its full shade lightfastness equals step 5–6 on the Blue Scale; in baking enamels, the lightfastness equals step 6 and some darkening is observed. In white reduction, at 1:7 reduction with TiO₂, however, fastness to light drops to step 3–4. The pigment thus satisfies most requirements for emulsion paints in interior application. As far as durability is concerned, full shade paints only score step 2 to 3 (Section 1.6.6) on the 5 step scale. P.R.146 exhibits high tinctorial strength and does not bloom in baking enamels. Its fastness to overcoating is much superior to that of group I Naphthol AS pigments, but it is not perfect. P.R.146 may be used in combination with Molybdate Orange pigments to produce bright opaque shades of red.

In polymers, P.R.146 is only used to colour rigid PVC. Transparent colourations (0.1%) afford a lightfastness that matches step 8 on the Blue Scale, while opaque specimens equal between step 6–7 and step 6, depending on the standard depth of shade and on the TiO₂ content. Insufficient heat resistance in polyolefins (less than 200 °C) precludes its use in such media.

P.R.146 is a suitable candidate for various special applications. The list includes wood stains, in which it is frequently blended with yellow pigments, especially with P.Y.83, and also with black to afford shades of brown. The products are fast to overcoating and stable to nitro and acid catalysed and polyester varnishes. Intense shades match step 5 on the Blue Scale for lightfastness. Other areas of application include office articles and artists' colours, cleaning agents, paper mass colouration, laundry markers and so on. In connection with cosmetics, the pigment frequently lends colour to soaps.

2.6.4.3.5 Pigment Red 147

P.R.147 produces a very bluish, clean red, a pink. Its main field of application is in printing inks. Inks formulated at ca 15% pigment concentration afford the standard magenta for multicolour printing on the European Scale CIE 12-66. As far as fastness to solvents is concerned, the pigment may be compared to the yellower P.R.184 or to the even yellower P.R.146. The prints are correspondingly fast to soap, paraffin, dibutyl phthalate, white spirit and toluene, but are not entirely fast to butter and other fats. They are suitable for clear lacquer coatings, but may not be sterilized. The heat stability of the pigment equals 200 °C for 10 min or 190 °C for 30 min, which is considered excellent.

Compared to P.R.146, lower pigment area concentrations of P.R.147 are less lightfast. 1/1 SD letterpress proof prints equal step 5 on the Blue Scale for lightfastness, and 1/3 SD specimens match step 4, while 1/25 SD prints are equal to step 3. P.R.147 is used in offset inks, in packaging gravure printing inks and in various flexo inks. Like other Naphthol AS pigments, P.R.147 is also employed in a series of special applications.

2.6.4.3.6 Pigment Red 150

P.R.150 is of limited regional significance. Depending on the area of application and on the reduction ratio, the pigment affords shades from bluish purple to carmine. P.R.150 is used in textile printing. In PVC colouration, which used to be its main market, it has been superseded by other products. P.R.213 is identical to P.R.150.

2.6.4.3.7 Pigment Red 164

This dihydrazone pigment on a Naphthol AS basis provides a somewhat dull, yellowish red shade of little strength. P.Y.164 was withdrawn from the market a few years ago. Used in printing inks, paints and plastics, the pigment was produced only in small volume. Lack of lightfastness generally precluded its use in exterior application. Incorporated in air drying alkyd paint, its full shade lightfastness (5%) equals step 6–7 on the Blue Scale, while addition of TiO₂ (1:5 TiO₂) reduces this value to 5–6.

P.R.164 is heat stable up to 200 °C, which made it a suitable candidate for applications where good temperature resistance is required. At baking temperatures of 140–160 °C and higher, the fastness to overcoating begins to decrease.

Letterpress proof prints with 30% P.R.164 in the inks reach step 5–6 on the Blue Scale for lightfastness. The prints are inert to paraffin and butter, as well as to various other fats, but they do not tolerate acid and alkali. The same is true for soap. P.R.164, however, is stable to sterilization.

Good heat stability made P.R.164 an interesting colourant for a series of polymers. It was being worked into polystyrene, in which full shades retain their colour value up to 270 °C before turning yellow; white reductions are stable up to 250 °C. The pigment shows average lightfastness. P.R.164 also lends itself to the colouration of rigid PVC. Its heat stability in PE is only 200–220 °C. A tendency to bloom made it necessary to observe certain concentration limits.

P.R.164 was also found in cast resin composed of methacrylate and unsaturated polyester. The pigment does not affect the hardening process of such media, which may be carried out, for instance, by using peroxides. An important field of application was in the colouration of various polyurethanes, for which the pigment was also sold in the form of a pigment preparation.

2.6.4.3.8 Pigment Red 170

P.R.170 provides medium shades of red, which in tints are somewhat bluish. Developed in the 1960s, excellence in application performance soon made this one of the most recognized pigments.

Like some other Naphthol AS pigments, P.R.170 is polymorphous (α-, β- and γ-phases); the shades of the commercial β- and γ-modifications are within the same range of colours. The α-phase is obtained from synthesis; finishing in water results in the β- or γ- phases.

Commercially available types, which are made from the β- or γ- phases, differ primarily in terms of opacity. The more transparent version (β-phase) is also somewhat more bluish. The very opaque modification (γ-phase) is much more stable to a variety of agents than the more transparent type. The opaque type is, for instance, slightly more resistant to organic solvents than the transparent one. Notably, however, even transparent varieties are very resistant to solvents, compared to other members of this class of pigments. They are not affected by white spirit and are largely inert to alcohol, esters, xylene and other solvents. The stability of the more transparent version to ethyl-glycol and methyl ethyl ketone equals step 3 on the 5 step scale, while the opaque variety matches step 4.

As a result of its excellent fastness properties, P.R.170 is used in high grade industrial paints. The pigment lends colour to finishes for tools, to implements, agricultural machinery, and commercial vehicles; the opaque varieties are also used for automotive finishes, such as automotive refinishes. Thorough testing is necessary before a product can be used in original automotive finishes, for which full shades of P.R.170 are sometimes employed.

P.R.170 does not bloom in stoving enamels, but it does bleed. Opaque varieties show better overcoating fastness than the more transparent ones. Very pure shades of red, which exhibit good hiding power, are produced by blending P.R.170 with Molybdate Orange. Combinations with quinacridone pigments afford bluer red shades. P.R.170 may, as a result of its excellent lightfastness and durability, be incorporated into high grade systems. The standard transparent type, for instance, equals step 6 on the Blue Scale in full shade, while the opaque version matches step 7–8 for lightfastness. Full shades show some darkening upon exposure to light and weathering. Opaque types have been introduced to the market which are characterized by noticeably improved weatherfastness compared to previously available grades. P.R.170 is less costly than similarly coloured perylene tetracarbonic acid pigments or diketopyrrolopyrrole pigments such as P.R.254, which are completely fast to overpainting and also more weatherfast. The opaque versions exhibit good flow behaviour, which makes it possible to enhance the hiding power of a product by increasing the pigment concentration without affecting the gloss.

The transparent type is preferred for printing inks. It is tinctorially very strong and lends itself to use in various high grade formulations. Inks formulated at only 15% pigment concentration will under standardized conditions produce 1/1 SD letterpress proof prints; the resulting prints are very lightfast. 1/1 to 1/3 SD letterpress samples equal step 6 on the Blue Scale. The opaque, yellower and somewhat weaker version is more lightfast than the transparent one; the difference is about 1/2 step on the Blue Scale.

P.R.170 and 5 are closely related as far as hue is concerned: 1/1 SD prints made from the bluish crystal modification (β-phase) resemble each other colouristically. The fact that P.R.5, depending on the depth of shade, is more lightfast by ½ to 1 step on the Blue Scale is somewhat compromised by its considerably inferior fastness in application and by its appreciably lower tinctorial strength. The slightly bluer P.R.8 is much less lightfast and solvent resistant than P.R.170; prints made from P.R.170 also have the advantage of being fast to butter, soap, alkali, and acid. Fastness to clear lacquer coatings and stability to sterilization are almost perfect (step 4–5). P.R.170 is also very heat stable; it retains its colour strength for 10 min at 200 °C or for 30 min at 180 °C, which makes it a valuable pigment for metal deco printing.

P.R.170 is also found in decorative printing inks for polyester films. It is almost completely inert to styrene monomer; in this respect, it matches step 4–5 on a 5 step scale. Gravure prints made from 8% pigment formulations almost equal step 7 on the Blue Scale, which indicates excellent lightfastness. There is no danger of plate-out during the production of laminated films (Section 1.6.4.1). Another area of application is in textile printing, in which the pigment shows very good fastness properties to a number of agents. It is almost completely fast to dry cleaning with tetrachloroethylene or white spirit, to washing with peroxide at 95 °C, and to alkali.

The plastics industry uses P.R.170 almost exclusively to colour rigid PVC. Transparent variations (0.1%) equal step 8 on the Blue Scale for lightfastness, while opaque types (1/1 to 1/25 SD) equal step 8 to step 6–7, depending on depth of shade and reduction with TiO₂. In plasticized PVC, the pigment is also very lightfast, although it does tend to bleed. At low pigment concentrations, less than 0.01% pigment, P.R.170 may not be used in plasticized PVC. However, it is suitable for printing on films made of plasticized PVC or on PVC or PUR simulated leather, such as in automobiles.

P.R.170 is not always heat stable enough to allow application in polyolefins. In HDPE systems formulated at 1/3 SD, the pigment tolerates exposure to 220–240 °C for one minute. Its tinctorial strength, on the other hand, is excellent. P.R.170 is also occasionally used in polypropylene and polyacrylonitrile spin dyeing; in the latter medium, it satisfies the specifications of the clothing and home textiles industries. Besides, P.R.170 lends colour to viscose rayon and viscose cellulose; it is used for the mass colouration of semisynthetic fibres made of cellulose; last but not least, it colours yarns, fibres, and films made of secondary acetate.

P.R.170 is broad in scope. It is found in wood stains, including solvent-based stains; it is blended with carbon black and yellows to produce various interesting shades of brown. The colourations are fast to overcoating in these media and resist nitro and acid hardening varnishes and polyester coatings. Its lightfastness in these media equals step 7 on the Blue Scale.

2.6.4.3.9 Pigment Red 184

P.R.184 affords a red which is somewhat on the bluish side of P.R.146, to which it is closely related in terms of chemical constitution. Both products also behave very similarly in application. Their prints are fast to soap, butter, paraffin, dibutyl phthalate, white spirit, and toluene. P.R.184 produces a shade which matches that of the standard magenta for multicolour printing on the European Colour Scale CIE 12-66. This shade results from formulating an ink at 15% pigment concentration and printing the ink in a standard layer (1 µm).

P.R.184 is used especially in applications where P.R.57:1 fails the requirements for alkali, acid, or soap fastness, or where the pigment lake is not lightfast enough to satisfy the demand. Depending on the standard depth of shade, the lightfastness of P.R.184 exceeds that of P.R.57:1 by approximately one step on the Blue Scale. Excellent fastness to solvents makes P.R.184 a suitable candidate for letterpress and offset application, as well as for packaging gravure printing inks and flexo inks. Its metal deco prints tolerate clear lacquer coatings, but not sterilization. The pigment is heat stable up to 170 °C for 10 min or up to 160 °C for 30 min. P.R.184 is also employed in rubber.

2.6.4.3.10 Pigment Red 187

Two crystal modifications are known, which differ considerably in terms of shade and fastness properties. Only the bluish red form continues to be commercially available. Its high specific surface area (about 75 m² g⁻¹) makes it a transparent pigment.

The main market for P.R.187 is in the plastics field. The pigment does not migrate in plasticized PVC and shows very good lightfastness: depending on the depth of shade and on the amount of TiO₂, it equals step 6 to step 8 on the Blue Scale. However, in PVC its white reductions are frequently replaced by the yellower and brighter benzimidazolone pigment P.R.208. P.R.187 exhibits high heat stability in polyolefins; in HDPE, 1/3 SD samples, reduced with 1% TiO₂, retain their colour upon exposure to 250 °C for 5 min; in LDPE, the temperature may be raised to 270 °C, and the heat stability of 1/25 SD colourations is 10 °C higher. The shrinkage of the polymer is only slightly affected by the pigment. As a result, P.R.187 may be used in polyolefin extrusion products which do not show rotational symmetry, such as bottle crates. The pigment exhibits equally satisfactory lightfastness in polyolefins: at 1/3 SD, transparent and opaque versions equal step 7 on the Blue Scale.

Good thermostability is an asset in media like polystyrene. P.R.187 is a very interesting product for polypropylene spin dyeing, for which it is available as a special preparation. 1/3 SD colourations tolerate temperatures up to 290 °C for 5 min. The pigment is also very lightfast in polyacrylonitrile spin dyeing: 1/3 SD specimens equal step 6–7 on the Blue Scale. Dry and wet crocking fastness is satisfactory and makes it a suitable pigment for home textiles, such as upholstery and carpeting.

The printing industry uses P.R.187 inks for all printing techniques. Although its shade is somewhat more bluish, its lightfastness in print equals that of P.R.208, which is stronger and also much less transparent. The thermostability of P.R.187 is about 20 °C higher: it is stable at 220 °C for 10 min and at 200 °C for 30 min. The pigment is very fast to chemicals and to clear lacquer coatings and may be sterilized, which makes it a useful transparent product for metal deco printing. Likewise, P.R.187 offers some advantage in paper lamination, that is, in decorative prints. Fastness to light and other fastness properties in compression moulded melamine sheets are comparable. The pigment is also used to colour polyester films.

In paints, P.R.187 is fast to overcoating, even at high baking temperatures. This is another application in which high thermostability is an asset, which is especially true for coil coating (Section 1.8.2.2). The pigment lends colour to industrial paints in general; its high transparency facilitates application in transparent paints, such as in films or bicycle paints, and in metallic finishes. P.R.187 tolerates exposure to light very well; incorporated in an alkyd-melamine system, full shades equal step 7–8 on the Blue Scale, while 1:600 TiO₂ reductions still reach step 6–7. Pigment weatherfastness is equally excellent, which makes P.R.187 a suitable candidate for automotive refinishes. The fact that the pigment is chemically inert makes it an interesting product for application in various powder coatings, such as amine accelerated epoxy powders. The list of applications also includes artists' colours, especially wax colours.

2.6.4.3.11 Pigment Red 188

P.R.188 is an intense yellowish red pigment with very good fastness properties.

Its main fields of application are in printing inks and paints; the pigment is suited to all printing techniques. 1/1 to 1/25 SD letterpress proof prints equal step 5–6 to step 5 on the Blue Scale for lightfastness. The pigment shows relatively poor tinctorial strength. However, the prints are very fast to organic solvents, fats, paraffin, soap, alkali, and acid. They are also fast to clear lacquer coatings and may be sterilized. Fastness to the DIN 16 524/1 solvent mixture, however, is not perfect. Regarding heat stability, P.R.188 prints tolerate exposure to up to 220 °C for 10 min or to 180 °C for 30 min. Similarly shaded but somewhat duller Toluidine Red pigments are less lightfast by one step on the Blue Scale, and they are considerably inferior in terms of solvent and heat stability, as well as other special application requirements.

The paints industry uses P.R.188 for its excellent fastness properties in high grade industrial finishes. Although some darkening is observed upon exposure to light, its full shades equal step 7 on the Blue Scale for lightfastness. TiO₂ reductions up to 1:5 exhibit the same fastness to light. Pigment weatherfastness is equally excellent in full shade and related deep shades. The pigment does not bleed at baking temperatures of 160 °C or less, and it retains its colour in a coating up to 200 °C. P.R.188 is frequently found in decorative paints, an area in which it is used to a great extent in the USA.

A highly opaque P.R.188 grade has been introduced to the market. It provides brilliant, still yellower shades of red than the previously known types. It also shows improved lightfastness and weatherfastness, as well as very good rheological properties and high gloss, compared to these types. The pigment is mainly used to produce lead-free, clean shades of red in automotive and industrial paints.

In plasticized PVC systems, P.R.188 blooms at low concentrations, which is also true for rigid PVC. Its thermostability in polyolefins is only about 220 °C, which makes it an unsuitable pigment for most polymers. However, the pigment is used to some extent in PVC and PUR plastisols.

P.R.188 is also employed in paper mass colouration, paper surface colouration, paper pulp, and paper spread-coating formulations, as well as in wallpaper and wax crayons.

2.6.4.3.12 Pigment Red 210

P.R.210, a mixed coupling of P.R.170 and P.R.266, is used primarily in printing inks. Its hue is considerably bluer than that of P.R.170.

P.R.210 is inferior to P.R.170 in various aspects of pigment performance. 1/3 SD and 1/25 SD letterpress proof prints, for instance, score ½ to 1 step less on the Blue Scale for lightfastness. In contrast to P.R.170, which is almost entirely fast to clear lacquer coatings and sterilization, P.R.210 is very sensitive in this respect. The two pigments behave similarly in print; P.R.210 prints are equally fast to several organic solvents, paraffin, soap, alkali, and acid. They are also heat stable up to 200 °C.

Besides printing inks, P.R.210 is primarily found in aquarelle colours.

2.6.4.3.13 Pigment Red 212

A few years ago the pigment was withdrawn from the market. P.R.212 was rarely sold outside Japan. It produces considerably bluish shades of red, which might be considered pink. Compared to the similarly coloured quinacridone pigment P.R.122, P.R.212 is duller, weaker, and less fast. 1/3 SD letterpress proof prints, for instance, equal step 2–3 on the Blue Scale for lightfastness; while prints containing P.R.122 equal step 6–7. P.R.212 is also less lightfast than the somewhat more bluish and duller benzimidazolone pigment P.V.32, a colouristically related maroon; the difference is 2–3 steps on the Blue Scale.

P.R.212 was used throughout the graphics industry and for textile printing, as well as in specialized media, such as coloured pencils.

2.6.4.3.14 Pigment Red 213

P.R.213 is a product rarely encountered outside Japan.

The pigment affords very bluish shades of red, which are too much on the blue side to match the standard magenta for three- and four-colour printing. The commercially available type is considerably opaque but not very lightfast compared to other Naphthol AS pigments. 1/3 SD letterpress proof prints, for instance, equal only step 3–4 on the Blue Scale for lightfastness; while 1/25 SD specimens match step 3. P.R.150 is identical with P.R.213.

2.6.4.3.15 Pigment Red 222

Since recently the pigment is not offered to the market anymore, but it is still in use. It affords a bluish red shade, which may be considered magenta or ruby; it is very transparent.

Its main market was in printing inks, where it was used in three and four colour printing. P.R.222 is heat stable up to 180 °C, which made it a suitable candidate for metal deco printing. It also tolerates organic solvents well. Prints containing P.R.222 are fast to overcoating but may not be sterilized. Gravure prints on plasticized PVC films show a slight tendency to migrate.

The plastics industry uses P.R.222 primarily in polyurethane. The pigment exhibits average tinctorial strength. 1/3 SD colourations in HDPE, for instance (1% TiO₂), are formulated at 0.23% pigment concentration.

P.R.222 is heat stable up to 240 °C; above this temperature, the colour shifts appreciably towards the bluish side of the spectrum. P.R.222 bleeds in plasticized PVC.

2.6.4.3.16 Pigment Red 223

P.R.223 used to have some commercial importance before it was withdrawn from the market. The pigment produces a bluish red shade, bluer even than P.R.170. Its main market was in high grade industrial finishes. Good lightfastness and durability in full shades and the fact that it met certain specifications made it suitable for use on public transportation vehicles. However, the pigment is not fast to overpainting.

2.6.4.3.17 Pigment Red 238

This pigment, which was introduced to the market a few years ago, enjoys only limited regional importance; its chemical constitution is identical with Pigment Red 269. It is recommended for printing inks and for industrial paints. Its shade in print is much bluer than the CIE 12-66 standard magenta for three colour printing on the European Colour Scale (Section 1.8.1.1). A pigment of low tinctorial strength, P.R.238 is neither fast to clear lacquer coatings, nor does it tolerate sterilization. In paints, P.R.238 is of average tinctorial strength and it bleeds.

The pigment is recommended for textile printing.

2.6.4.3.18 Pigment Red 245

P.R.245 is of little commercial significance and is rarely encountered in Europe. It provides bluish shades of red, ruby, and carmine. P.R.245 is used in printing inks, particularly in packaging inks. Suitable inks contain nitrocellulose polyamide-based polymers or VC/VAc copolymers; in these media, the pigment exhibits high tinctorial strength, but only average to poor lightfastness.

2.6.4.3.19 Pigment Red 253

P.R.253, which was introduced to the market a few years ago, provides medium red shades, which are considerably yellower than those of P.R.170. The commercial grade of P.R.253 exhibits good transparency. The pigment is recommended especially for use in paints.

Its fastness to organic solvents and chemicals corresponds to that of other representatives of group II Naphthol AS pigments (Section 2.6.2). Consequently, P.R.253 is almost completely fast to overpainting.

In full shade and in similarly deep shades, P.R.253 shows good lightfastness and weatherfastness with some darkening. White reductions with TiO₂, however, exhibit noticeably less weatherfastness.

P.R.253 is used in packaging printing inks. For a pigment of its class, it shows medium tinctorial strength. The prints demonstrate good fastness to organic solvents, but they are not completely fast to the DIN 16524 solvent mixture (Section 1.6.2.1) (step 4–5). 1/1 SD letterpress proof prints show a lightfastness corresponding to step 5 on the Blue Scale.

2.6.4.3.20 Pigment Red 256

P.R.256 is used especially for industrial and decorative paints in applications where fastness to overcoating is not required. The pigment provides a yellowish red shade, a scarlet. Compared to other pigments covering the same range of shades and fastness properties, P.R.256 shows medium tinctorial strength. It exhibits good lightfastness; its full shade and similarly deep shades reach step 7 on the Blue Scale. Similar values are found for reduced shades with TiO₂, up to a ratio of approximately 1 : 4.

P.R.256 is also recommended for paste, solvent and water based packaging inks, as well as for wall coverings. It exhibits limited migration- and heat-resistance and is therefore not recommended for tin printing.

2.6.4.3.21 Pigment Red 258

This pigment was reported to the Colour Index by a Japanese producer. The chemical constitution has been disclosed. P.R.258 has not yet been introduced into the market.

2.6.4.3.22 Pigment Red 261

A few years ago P.R.261, together with its chemical constitution, was reported to the Colour Index by an American manufacturer. It has not yet been met in the market.

2.6.4.3.23 Pigment Red 266

P.R.266 is a product affording a bluish red shade. The pigment is primarily used in packaging gravure and flexo printing inks, for which a special grade is offered. Its hue is considerably bluer than that of P.R.170 and bluer than that of P.R.210. In various aspects of pigment performance P.R.266 is inferior to P.R.170. So, for instance, the lightfastness of proof prints is ½ to 1 step less on the Blue Scale. It is sensitive to clear lacquer coatings and sterilization. In other application properties the commercially available grades of P.R.170 and P.R.210 behave very similar. Tinctorial strength, transparency and gloss of the prints of both pigments are comparable as well as the fastness to organic solvents used for printing inks, and to paraffin, soap, alkali and acid.

2.6.4.3.24 Pigment Red 267

The pigment provides slightly dull yellowish red shades. Commercially available grades of P.R.267 have as yet not been met on the market. In Japan the pigment is primarily recommended for the use in printing inks.

2.6.4.3.25 Pigment Red 268

The pigment is recommended in the USA for printing inks. It provides bluish shades of red.

2.6.4.3.26 Pigment Red 269

As for P.R.268 the pigment is recommended for printing inks. In prints it provides a very bluish red.

2.6.4.3.27 Pigment Orange 38

P.O.38, a clear yellowish red, is mainly used in printing inks and in plastics.

In printing inks, P.O.38 shows good fastness properties. 1/1 SD to 1/25 SD letterpress proof prints, for example, equal step 6 to step 5 on the Blue Scale for lightfastness, depending on the depth of shade. The prints are stable to the standard DIN 16 524 solvent mixture, to paraffin, fats, oils, soap, alkali, and acid; they also tolerate clear lacquer coatings and sterilization. They are heat stable up to 220 °C for 10 min or to 200 °C for 30 min. P.O.38 is therefore suitable for offset printing inks as well as for metal deco printing; it is used in special printing inks for substrates such as plasticized PVC and in various flexo inks.

Besides, P.O.38 lends colour to decorative inks for laminated sheets. Inks formulated at a pigment concentration of 8% and printed in 20 µm cell melamine sheets equal step 6–7 on the Blue Scale for lightfastness; at 40 µm, they match step 7. Laminated sheets do not exhibit plate-out.

P.O.38 is stable to styrene monomer, but not entirely fast to acetone, which occasionally leads to bleeding if the pigment is processed according to the diallyl phthalate method (Section 1.8.1.2). This is also true if the pigment is treated with a melamine resin solution.

The plastics industry uses P.O.38 primarily to colour PVC, polyolefins, and polystyrene. In plasticized PVC, the pigment does not bleed at concentrations up to about 0.3%. Its lightfastness is good. Transparent colourations in rigid PVC(0.1%) equal step 7–8 on the Blue Scale; while opaque versions (0.1% pigment + 0.5% TiO₂) equal step 7.

P.O.38 is frequently employed in combination with P.Y.83 to provide brilliant and very lightfast shades of orange. P.O.38 is particularly useful to produce shades of brown in PVC and PUR imitation leather. 1/3 SD HDPE formulations containing 1% TiO₂ withstand temperatures up to 240 °C for 5 min. At this temperature, the pigment does not noticeably affect the polymer shrinkage. Transparent specimens equal step 6 on the Blue Scale in terms of lightfastness; while opaque versions equal step 5–6.

P.O.38 is also used in spin dyeing, where it colours filament, fibres, and films made of secondary acetate. The pigment possesses excellent fastness properties in this medium.

P.O.38 is especially lightfast in unsaturated polyester resins. Transparent samples equal step 8 on the Blue Scale, opaque versions (0.1% pigment–0.5% TiO₂) equal step 7; however, notably, the hardening of the resin is slowed down considerably.

As far as the paints field is concerned, P.O.38 is solvent resistant enough to qualify for application in high grade industrial paints wherever lightfastness and durability requirements are not too stringent. The lightfastness of close to full strength shades in an alkyd-melamine resin system, for instance, equals step 6–7 on the Blue Scale (1:1 TiO₂); further addition of white pigment reduces the lightfastness to step 5–6. The pigment does not bloom; however, it ceases to be completely fast to overcoating as the baking temperatures rise. It is heat stable up to 180 °C.

P.O.38 is broad in scope. The list of applications includes special media, such as wax crayons, artists' colours, and wood stains, including those that are solvent based. The products are very lightfast (step 7 on the Blue Scale) and fast to overcoating. Blends of P.O.38 with yellow pigments, such as P.Y.83 or P.Y.120, or with carbon black produce useful shades of brown.

2.6.4.3.28 Pigment Orange 74

P.O.74 [76] is recommended for the paint industry. In full shades and in tints it exhibits clean reddish orange shades, with good tinctorial strength in white reductions. The commercial grade shows good hiding power. The viscosity of the mill base is rather high, P.O.74 tends to flocculate.

The pigment is not resistant to different organic solvents, thus coatings, for instance based on alkyd melamine resin systems, are not fast to overpainting.

In printing inks P.O.74 exhibits also a clean reddish orange shade with good light and weather fastness properties. The semi-transparent version is recommended for paste inks as well as for solvent- and water-based packaging gravure and flexographic printing inks. The high opaque version is recommended for printing on special substrates, for example Kraft paper or for packaging inks where very good light fastness properties are required.

2.6.4.3.29 Pigment Violet 13

The marketing of this pigment has recently been discontinued. P.V.13 produces clean shades of violet. Compared to other group I Naphthol AS pigments, P.V.13 shows poor general fastness properties. 1/1 SD letterpress proof prints only equal step 3 on the Blue Scale for lightfastness, while 1/3 SD specimens reach step 2. The prints tolerate acid but not alkali or soap. Similarly, they are not fast to overlacquering and may not be sterilized, which renders the pigment unsuitable for metal deco printing and for printing on PVC or polyolefin foils.

2.6.4.3.30 Pigment Violet 25

P.V.25 is only produced in Japan and enjoys limited regional significance. It is used in printing inks.

2.6.4.3.31 Pigment Violet 44

A Japanese product like P.V.50, the pigment is registered in the Colour Index as P.V.44. The two pigments are extremely similar, both colouristically and in terms of performance in application, even in detail. It is very likely that the products are chemically identical and listed twice in the Colour Index, although exhibiting different CAS numbers.

2.6.4.3.32 Pigment Violet 50

P.V.50, produced in Japan, is only of limited regional importance, since it fails to satisfy the increasingly stringent application requirements for organic pigments. Its fastness to light, for instance, is particularly poor: 1/3 SD and 1/1 SD letterpress proof prints equal only step 2 on the Blue Scale. Compared to P.V.23, Dioxazine Violet, P.V.50 is redder at greater depth of shade, while samples which are further reduced with TiO₂ appear bluer and considerably duller. P.V.50 is tinctorially weaker than P.V.23, which in some media is as much as twice as strong as the former.

P.V.50 is used in printing inks and in office articles. Poor lightfastness and a strong tendency to migrate makes it an inadequate product for most plastics materials. Lack of lightfastness also precludes its use in paints (see also P.V.44).

2.6.4.3.33 Pigment Blue 25

P.Bl.25 is only produced in small volume in Europe, Japan, and the USA. It is used for the spin dyeing of secondary acetate, lends colour to rubber, and is found in inks for packaging purposes.

Its hue is a somewhat reddish navy blue, which varies considerably if the pigment is chemically modified.

P.Bl.25 is very fast in application; it is fast to fats, oils, soap, and paraffin, which makes it a suitable candidate for packaging inks. Its lightfastness, however, is not excellent. In natural rubber, P.Bl.25 tolerates curing very well, and it bleeds neither into the rubber nor into the fabric backing (Section 1.8.3.6). In rubber, the pigment is fast to cold and hot water, to soap, soda, and alkali solutions, and to acetic acid.

In spin dyed secondary acetate threads, fibres and films, P.Bl.25 exhibits good textile fastness properties; the only problem is a certain lack of fastness to bleaching with sodium hypochlorite (Section 1.6.2.4). Its fastness to light in 0.1% spin dyed specimens equals step 3–4 on the Blue Scale, while 1% samples equal step 5.

2.7.1.4.1 General

Table 2.10 lists the currently available β-Naphthol pigment lakes.

General chemical structure:
C.I. Name	C.I. Constitution Number	DC	M/2	Shade
P.O.17	15510:1		Ba	orange
P.O.17:1	15510:2		Al	reddish orange
P.O.46	15602		Ba	yellowish red
P.R.49	15630		2 Na	yellowish red
P.R.49:1	15630:1		Ba	yellowish red
P.R.49:2	15630:2		Ca	bluish red or maroon
P.R.49:3	15630:3		Sr	red
P.R.50:1	15500:1		Ba	scarlet
P.R.51	15580		Ba	scarlet
P.R.53	15585		2 Na	scarlet
P.R.53:1	15585:1		Ba	scarlet
P.R.53:2	15585:2		Ca	reddish orange
P.R.53:3	15585:3		Sr	yellowish red
P.R.68	15525		Ca	yellowish red

Pigment Red 53 has for some time dominated the β-naphthol pigment lake market in Europe and Japan and is still an important product. Pigment Red 49, employed especially as the barium and less frequently as the calcium salt, is mainly used in the USA. Other pigments of this type are less important.

A certain amount of emphasis is placed on Pigment Red 68, with its two acidic groups available for salt formation.

2.7.1.4.2 Pigment Orange 17

Besides being offered as a barium salt, P.O.17 is also available as a precipitate onto aluminium oxide hydrate. These types, especially in the USA, are referred to as Persian Orange. The products have been discontinued in Europe, but play a certain role in the Japanese market. P.O.17 affords brilliant, orange–red shades. Commercial types are tinctorially strong and highly transparent. They are used in inexpensive packaging prints, including metal deco printing. Varieties that contain a large amount of aluminium oxide hydrate often adversely affect the drying properties of oily media, such as offset printing inks. In a highly acidic binder, the pigment may lose its metal ion as it reverts to the free acid and consequently undergoes considerable colour shift. In the past, P.O.17 was also used in large volume to colour natural rubber.

2.7.1.4.3 Pigment Orange 17:1

Aluminium lakes of P.O.17:1 are available in the USA. Properties that are pertinent to the colouristics and application of the pigment parallel those of the barium lakes. P.O.17:1, an equally high strength pigment, also affords brilliant shades and is used in packaging prints, especially for paraffin-based wrapping paper for bread.

2.7.1.4.4 Pigment Orange 46

P.O.46, which is gaining commercial recognition in Europe, plays a certain role in the US market. The application properties of the pigment are quite similar to those of the Lake Red C types, P.R.53:1. P.O.46 produces a shade that is appreciably yellower than that of conventional P.R.53:1 types. Its shade is much more comparable to the colour of the second crystal modification of the barium salt of Lake Red C.

Commercially available P.O.46 types are usually quite transparent. They are employed primarily in packaging printing inks, also in offset and metal deco printing. Publication gravure inks, plastics, especially PVC, LDPE, and elastomers, as well as general industrial paints are suitable media for pigment application. P.O.46 is less solvent resistant than P.R.53:1, but it is faster to alkali and acid. In terms of lightfastness, P.O.46 performs poorly: 1/3 and 1/25 SD prints equal only step 1 on the Blue Scale.

2.7.1.4.5 Pigment Red 49 Types

Products of the Pigment Red 49 range differ considerably in their commercial importance, depending on the region in which they are marketed. Although of little importance in Europe and Japan, P.R.49 types play a major role in the USA. The pigments are supplied as sodium (P.R.49) or as calcium salts (P.R.49:2); but the largest fraction is sold as barium salts (P.R.49:1). The product line has been extended to include the strontium salt (P.R.49:3). The shade of the barium lake is yellower than that of P.R.57:1 and bluer than that of P.R.53:1. Calcium types are somewhat bluer than P.R.49:1, while the sodium salt is more yellowish.

Pigment Red 49 types are often referred to as Lithol Red pigments, especially in the USA. They are used in all types of printing inks. Throughout the USA, Pigment Red 49 grades are frequently employed to lend red shades to publication gravure printing inks targeted for three- or four-colour printing. P.R.49:1 is slightly too yellow to match the CIE 12-66 standard for process printing inks on the European Colour Scale for offset printing.

2.7.1.4.6 Pigment Red 50:1

P.R.50:1, patented as early as 1905 by Meister Lucius & Brüning, is only of regional importance today; its sale has been discontinued in Europe. Marketed first as a sodium lake (P.R.50) to be transformed into the barium salt by the consumer, the barium lake (P.R.50:1) is now exclusively used. This salt affords clean shades of scarlet.

P.R.50:1 is used primarily in packaging printing inks, which mostly afford bronzing prints with good fastness to organic solvents. Weak alkaline agents induce a colour shift to blue shades, while acids have a yellowing effect. In the presence of drying agents based on cobalt salts, the pigment undergoes a reformulation of its salt form to produce shades of brown. P.R.50:1 has accordingly lost its importance in offset inks, which used to be its major market. The pigment fails to meet modern requirements.

2.7.1.4.7 Pigment Red 51

P.R.51, a barium pigment lake, affords shades of scarlet similar to those of Pigment Red 53:1. P.R.51 performs like P.R.49 in terms of fastness, but it is particularly sensitive to alkaline agents. P.R.51, which used to be quite important, especially in printing inks and rubber, has largely been replaced by other products. It continues to be used in typewriter and printer ribbons for its shade.

2.7.1.4.8 Pigment Red 53 Types

Barium and sodium lakes are commercially available (P.R.53:1 and 53). Calcium salts (P.R.53:2) have only enjoyed commercial success for a limited time; they have largely vanished from the market; however, strontium lakes (P.R.53:3) are being used commercially.

2.7.1.4.9 Pigment Red 68

P.R.68 is supplied as a calcium salt. It produces a yellowish red shade, referred to as scarlet, which at equal depth of shade is slightly bluer than P.R.53:1, a member of the same class of pigments. P.R.68 has gained considerably less commercial recognition than the widely used Lake Red C pigments.

The main area of application for P.R.68 is in the colouration of plastics. The pigment, whose tinctorial strength is average, is fast to blooming but not quite bleed resistant in plasticized PVC. Its lightfastness, especially in white reduction, fails to satisfy more stringent requirements. 1/3 SD samples that contain 5% TiO₂ equal step 4 on the Blue Scale for fastness to daylight, while 1/25 SD specimens are equal to step 3. P.R.68 is heat stable enough to be applied safely in polyolefins. Incorporated in HDPE, for instance, it is stable up to 300 °C. The pigment exhibits average tinctorial strength. P.R.68 does not affect the shrinkage of injection-moulded polymers. The lightfastness of 1/3 to 1/25 SD specimens equals between step 2–3 and step 3 on the Blue Scale. P.R.68 is also found in polystyrene.

The pigment is also used as a colourant for printing inks, but its importance in this area has diminished considerably. P.R.68 is somewhat weaker than P.R.53:1, but more lightfast. 1/3 SD letterpress proof prints equal step 4 (2) on the Blue Scale for lightfastness, while 1/25 SD specimens equal step 3 (1). The values in brackets represent the lightfastness of P.R.53:1. In print, P.R.68 shows excellent fastness to several organic solvents, including the standard DIN 16 524 solvent blend. Its resistance to soap, alkali and acid, however, is unsatisfactory. P.R.68, in contrast to P.R.53:1, is completely fast to sterilization. Since P.R.68 also provides excellent heat stability (1/3 SD samples withstand exposure to 220 °C for 10 min), it lends itself to metal deco printing, although it is not fast to clear lacquer coatings. As in other application media, insufficient fastness of P.R.68 inks to water may affect the results of offset printing.

P.R.68 is used in paints for applications where it performs well, especially in terms of lightfastness. Incorporated in an air drying alkyd resin vehicle, full shades equal step 5 on the Blue Scale for lightfastness. The 1:5 TiO₂ reductions, however, only score as high as step 2. P.R.68 exhibits excellent resistance to numerous organic solvents, while it is quite sensitive to alkali and acid, as well as to water.

P.R.68 is also recommended for use in decorative cosmetics, such as nail polish, lipstick, powders and shading creams. For these purposes, types are supplied that fulfil legal purity standards and are tested accordingly.

2.7.2.4.1 General

As with β-naphthol pigment lakes, only a few BONA pigment lakes are marketed in large volume. Two of these pigments, however, maintain an important position within the pigments industry. Table 2.11 lists the currently available BONA pigment lakes.

C.I. Name	C.I. Constitution Number				M	Shade
P.R.48:1	15865:1		CH3	Cl	Ba	red
P.R.48:2	15865:2		CH3	Cl	Ca	bluish red
P.R.48:3	15865:3		CH3	Cl	Sr	red
P.R.48:4	15865:4		CH3	Cl	Mn	bluish red
P.R.48:5	15865:5		CH3	Cl	Mg	red
P.R.52:1	15860:1		Cl	CH3	Ca	ruby
P.R.52:2	15860:2		Cl	CH3	Mn	maroon
P.R.57:1	15850:1		CH3	H	Ca	bluish red (magenta, ruby)
P.R.58:2	15825:2	H	Cl		Ca	bluish red
P.R.58:4	15825:4	H	Cl		Mn	medium red
P.R.63:1 P.R.63.2	15880:1 15880:2		Ca Mn	bordeaux bordeaux
P.R.64	15800	H	H	H	Ba/2	red
P.R.64:1	15800:1	H	H	H	Ca/2	yellowish red
P.R.200	15867		Cl	C2H5	Ca	bluish red
P.Br.5	15800:2	H	H	H	Cu/2	brown

All pigments within this series, with the exception of P.R.64 and P.Br.5, contain two acidic functions: a sulfonic acid group and a carboxylic acid moiety. Precipitation is accomplished primarily with calcium or manganese, more rarely with barium, strontium or magnesium. The sulfonic acid function is found almost invariably in the ortho position relative to the hydrazone group. Commercially important pigments, including Pigment Red 48 and 57, also bear a methyl group in para position relative to the hydrazone bridge. Manganese lakes are always bluer than the strontium or barium lakes. They often appear even more bluish than the calcium salts.

2.7.2.4.2 Pigment Red 48 Types

Amongst the commercially available types are ‘lakes' with various metals, including barium (P.R.48:1), calcium (P.R.48:2), strontium (P.R.48:3), manganese (P.R.48:4) and magnesium salts (P.R.48:5). There are also types, such as barium/calcium salts, which are obtained by ‘mixed' laking. Commercial interest in each type depends on the area of application, but the pigments enjoy overall importance. Pigments of this type are known under various common names, especially in the English language. The best known designation, ‘2B toner', is clearly derived from the name under which the pigment was first marketed, namely as Permanent Red 2B, a sodium salt.

2.7.2.4.3 Pigment Red 52 Types

Both calcium and manganese salts are commercially available. The US market also offers strontium salts and mixed barium/calcium lakes. Although they are important pigments in the USA, P.R.52 types generally have little commercial importance in Europe. These types are referred to in the USA as IBB toners.

2.7.2.4.4 Pigment Red 57:1

P.R.57:1 is known under various names, the most common amongst which is 4B toner. P.R.57:1, the calcium salt, ranks high amongst organic pigments in production volume and use. The pigment is used primarily in printing inks. Its shade matches the standard magenta of several colour scales for three- and four-colour printing, including the CIE 12-66 European Colour Scale (Section 1.8.1.1). Even the printed edition of this book is printed with P.R.57:1.

There are enough commercially available grades of P.R.57:1 to cover a comparatively wide range of shades. Adding particular mixed coupling components, for instance to the diazonium component, will produce any desired hue within this range. A similar effect is achieved by varying the particle size distribution. If Tobias acid (2-aminonaphthalene-1-sulfonic acid) is added as diazo component, the resulting molecules of P.R.63:1 are incorporated in the crystal lattice of P.R.57:1. The resulting blue shift is attributed to an expansion of the crystal lattice through the comparatively large diazo compound. The rate of crystal growth is also inhibited, which also contributes to the colour shift.

P.R.57:1 is a pigment with high tinctorial strength. Approximately 19% pigment is needed to formulate offset and letterpress inks, which produce 1/1 SD proof prints at standard film thickness. 1/3 SD prints, on the other hand, require 7.8% pigment, and 1/25 SD specimens are made with 2.1% pigment. Comparative values are listed under the respective pigments. Inks for prints that satisfy the specifications of the so-called European Standard are prepared under standardized conditions at pigment concentrations of about 14%.

The lightfastness of 1/1 SD P.R.57:1 letterpress proof prints equals step 4–5 on the Blue Scale, while 1/3 and 1/25 SD specimens match step 4 and step 3, respectively. In print, P.R.57:1 is fast to many of the most common organic solvents, including the DIN 16 524 standard solvent mixture, but it performs poorly in terms of soap, alkali and acid resistance. The pigment is equally sensitive to clear lacquer coatings. Wherever prints are expected to be fast to such media, P.R.57:1 is frequently replaced by the colouristically closely related Naphthol AS pigment P.R.184, which has the added advantage of being more lightfast. However, prints made from P.R.184 are as sensitive to sterilization as those obtained from P.R.57:1. P.R.57:1 is heat stable enough to withstand exposure to 180 °C for 10 min or to 160 °C for 30 min.

Several resinated grades are produced to provide higher transparency and to optimize other aspects of pigment properties in application. For reasons connected with process engineering, the resin is typically incorporated as a metal (calcium) resinate. In the past, types of P.R.57:1 additionally contained certain amounts of barium sulfate.

P.R.57:1 is found in all types of printing inks. Like with other pigment lakes, however, there is a certain possibility that storage problems may arise, a fault that is independent of the resination of a pigment. The viscosity of an alkaline printing ink often increases more or less upon storage, that is, the ink thickens. This problem is largely attributed to the interaction between the pigment lake and the cation of the base and leads to an exchange of the metal ion. Reprecipitation also plays a certain role. This phenomenon is based on the fact that the pigment lake, being a salt, is somewhat soluble in water. In an aqueous alcoholic medium, the binder converts dissociated metal ions (calcium ions) into similarly sparingly soluble metal/binder salts, forming the partially soluble sodium pigment lake. The process is repeated as more of the calcium lake dissolves, until the solubility product is reached. In the face of these problems, P.R.184 is also a suitable alternative to P.R.57:1.

Temperatures of up to 100 °C and higher may be observed as P.R.57:1 is dispersed in offset printing inks, especially in Web offset inks by means of modern dispersion equipment. This is especially true for agitating pearl mills. Printing inks and prints may undergo colour shifts if they are exposed to these conditions. The process, which is reversible, is caused by release of the water of crystallization from the pigment.

The different grades of P.R.57:1 vary considerably, not only in their colouristics but also in their rheological behaviour. Individual grades are frequently optimized for special printing inks, for instance for publication gravure inks. In contrast to corresponding diarylide yellow pigments, amine treated types of P.R.57:1 are not available for publication gravure printing inks.

The plastics industry uses P.R.57:1 primarily wherever performance in application is a minor concern, especially with respect to lightfastness. In plasticized PVC, for instance, transparent colouration (0.1% pigment) of P.R.57:1 equals only step 2 on the Blue Scale, while samples containing TiO₂ never score higher than step 3. The exact value depends on the standard depth of shade and on the pigment concentration. P.R.57:1 is not suitable for use in concentrations below approximately 0.03%.

P.R.57:1 is employed in cable insulations because of its good dielectric properties. It is much more lightfast in rigid PVC: transparent colourations (0.1% pigment) equal step 6 on the Blue Scale, while white reductions with TiO₂ match between step 4 and step 2, depending on the standard depth of shade and on the TiO₂ content.

P.R.57:1 is heat stable up to about 250 °C, which makes it a suitable candidate for use in polyethylene, particularly in LDPE types. Incorporated in LDPE, the pigment only slightly affects the shrinkage of extruded articles (Section 1.6.4.3). However, the lightfastness of such products is below expectation, which considerably restricts the versatility of the pigment. The same is true for PP spin dyeing. Apart from being used in these areas, P.R.57:1 also lends colour to polystyrene.

P.R.57:1 is also used for PUR foam products. Problems arise with steam vulcanization, because some colour is transferred to the wrapper as the pigment is worked into rubber (Section 1.8.3.6). The pigmented rubber articles are not completely fast to a number of organic solvents, to soap and sodium carbonate solutions, and to acids and SO₂ (Section 1.6.2.2).

Poor lightfastness considerably restricts the use of P.R.57:1 in coatings and emulsion paints. The pigment is, however, occasionally found in industrial paints.

P.R.57:1 is a useful colourant for various special purpose media, including coloured pencils and crayons. Several countries have legally defined purity regulations concerning the use in decorative cosmetics articles, such as face powder and lipstick. The same is true for cheese casings [94]. Suitable grades are commercially available, they are registered in the USA as D & C Red 7, in Japan as Red No. 202.

2.7.2.4.5 Pigment Red 58 Types

The following salts have been produced: the sodium salt (P.R.58), the barium salt (P.R.58:1), the calcium salt (P.R.58:2), the strontium salt (P.R.58:3) and the manganese lake (P.R.58:4). The commercial success of each type varies considerably by region but has generally decreased considerably as the pigments have been replaced by other lakes. P.R.58:4 is unique in that it is the only representative to have remained in the European market.

2.7.2.4.6 Pigment Red 63 Types

The following cations have been used for salt formation: sodium, calcium, barium and manganese, as well as blends of calcium and manganese. European manufacturers continue to supply the calcium and manganese lakes, while the Japanese market also provides a barium lake. The latter, however, is of limited regional importance.

2.7.2.4.7 Pigment Red 64 Types

Several metal lakes have been prepared from this parent structure of all β-oxynaphthoic acid pigments. The list includes the barium salt (P.R.64), the calcium salt (P.R.64:1) and the copper lake, which is registered as Pigment Brown 5. The pigments are rarely used in Europe, and their impact on the market in Japan and the USA has also decreased considerably.

2.7.2.4.8 Pigment Red 200

P.R.200, which was first introduced in the USA, is as yet only supplied in the form of its calcium salt. It produces a clean bluish shade of red, which is close to that of P.R.57:1. The two pigments are also similar in their resistance to organic solvents. P.R.200 shows average fastness to overcoating. It is recommended for use in air drying and heat drying systems, in which it only exhibits moderate lightfastness. P.R.200 is also found in various different types of printing inks, especially those for offset and gravure printing. The pigment is used to lend colour to plastics wherever lightfastness is a minor issue. The pigment is not fast to acid, alkali or soap.

2.7.2.4.9 Pigment Brown 5

Production of P.Br.5 seems to be discontinued. It enjoyed only limited regional importance. The pigment is the poorest performer of all pigments within its class. P.Br.5 is used in special applications, such as flexographic printing inks, textile inks and wood stains.

2.7.3.2.1 General

There is no common structural principle to these pigments beyond the basic Naphthol AS pigment skeleton. Table 2.12 lists the commercially available Naphthol AS pigment lakes.

C.I. Name	C.I. Constitution Number						M	Shade
P.R.151	15892		H	H	H		Ba	red
P.R.211	—		CH3	Cl	OCH3	H	Ca/2	scarlet red
P.R.237a)	—	—	—	—	—	—	—	yellowish red
P.R.239	—	—	—	—	—	—	—	bluish red
P.R.240	—	—	—	—	—	—	—	maroon
P.R.243	15910		CH3	Cl	OCH3	H	Ba/2	red
P.R.247	15915	CH3	H	CONHC6H4 (p)	H	OCH3	Ca/2	bluish red/redb)
a) Apparently identical with P.R.243, see text. b) Different crystal modifications.

2.7.3.2.2 Pigment Red 151

P.R.151, a barium lake, which is produced in Japan, affords a bluish red colour that may be referred to as carmine. Of medium tinctorial strength, the pigment is used primarily in plastics.

P.R.151 is completely migration resistant in plasticized PVC. Transparent colourations (0.1% pigment) equal step 6 on the Blue Scale for lightfastness, while the pigment only matches step 3–4 in white reduction (0.01% pigment + 0.5% TiO₂). Pigmented rigid PVC systems are appreciably more lightfast, the corresponding values are 7 and 6, respectively. P.R.151 is frequently used for the colouration of synthetic leather made of PVC. However, the pigment is not fast to acid or alkali. Good dielectric properties make it a suitable candidate for PVC cable insulations.

Incorporated in PE, P.R.151 shows only average tinctorial strength. Some 0.24% pigment is required to produce 1/3 SD colourations in PE containing 1% TiO₂. In HDPE, the pigment is heat stable up to 290 °C, but this advantage is somewhat compromised by the fact that it affects the shrinkage to a considerable extent. Caution should therefore be exercised if P.R.151 is to be used in larger, non-symmetrical injection-moulded objects. The lightfastness of P.R.151 in PE equals that in rigid PVC.

One of the primary fields of application for P.R.151 is in polystyrene, although there is a slight colour change at temperatures above 260 °C, at which the pigment partially dissolves. It is also used to a considerable extent in ABS. Cast resins based on methyl methacrylate and unsaturated polyesters are also frequently coloured with P.R.151, which is resistant to the peroxide catalysts that are used to harden the plastic. The lightfastness in these media is good – it equals step 6–7 on the Blue Scale.

2.7.3.2.3 Pigment Red 211

P.R.211 is offered only in the Japanese market. It is the calcium salt of a monohydrazone pigment. P.R.211 affords shades of scarlet that resemble those provided by Lake Red C types (P.R.53:1). The list of suitable media includes plastics and printing inks. Incorporated in these media, P.R.211 presents application and fastness properties that are very close to those of P.R.53:1. HDPE samples containing P.R.211, for instance, like those based on P.R.53:1, are heat stable up to approx. 260 °C. Both pigments are fast to bleeding in plasticized PVC. In prints, however, the commercial grade of P.R.211 is tinctorially weaker than similarly coloured Lake Red C types. Depending on the application medium, P.R.211 is weaker by 5–50%.

2.7.3.2.4 Pigment Red 237

P.R.237, introduced some years ago, enjoys only limited regional importance. Its chemical constitution has not yet been published but several test results indicate chemical identity with P.R.243, C.I. No. 15910. The pigment affords a yellowish red shade, referred to as scarlet. P.R.237 is particularly recommended as a colourant for PVC, in which it shows good bleed resistance. Its colouristic properties in this medium parallel those of the β-naphthol pigment lake P.R.68. P.R.237 is only of average tinctorial strength: 0.36% pigment is needed to formulate a 1/3 SD sample (1% TiO₂). The pigment is heat stable up to 260 °C. Good fastness to overlacquering makes it a suitable candidate for industrial finishes.

2.7.3.2.5 Pigment Red 239

P.R.239 enjoys limited regional impact and is used very little in Europe. Its exact chemical constitution remains to be published. P.R.239 affords dull, bluish shades of red. Its main application media are plastics. The pigment is bleed resistant in plasticized PVC. Its shade in this medium equals that of P.R.247, a member of the same class of pigments, which, however, has the advantage of providing a much cleaner shade. Incorporated in HDPE, P.R.239 is of average tinctorial strength and is heat stable up to 270 °C.

2.7.3.2.6 Pigment Red 240

The exact chemical constitution of this pigment, which was introduced to the Japanese market some years ago, has not yet been published. P.R.240 enjoys only limited regional importance. Its dull bluish shades of red are referred to as maroon. P.R.240 is recommended for use in industrial finishes for its good lightfastness and weatherfastness as well as for its bleed resistance. The commercial type is quite transparent and lacks tinctorial strength. P.R.240 is equally weak in plastics: 0.42% pigment is needed, for instance, to afford 1/3 SD HDPE samples (1% TiO₂). In this medium the pigment withstands temperatures up to 300 °C.

2.7.3.2.7 Pigment Red 243

P.R.243, the barium salt of a Naphthol AS pigment, affords a dull, yellowish to medium red. The pigment is somewhat sensitive to solvents. P.R.243 is recommended for use in plastics. It is almost completely bleed resistant in plasticized PVC, but fails to satisfy more stringent lightfastness requirements. Transparent samples (0.1% pigment) equal merely step 4 on the Blue Scale, while opaque formulations (1/3 SD) match only step 3. Incorporated in HDPE, the pigment affects the shrinkage of the polymer. It is recommended specifically for use in LDPE.

2.7.3.2.8 Pigment Red 247

The primary area of application for P.R.247 is in plastics, in which it produces medium to bluish, brilliant and opaques shades or red. Its tinctorial strength is moderate: 0.28% pigment is needed, for instance, to formulate 1/3 SD HDPE samples containing 1% TiO₂. Such samples equal step 6–7 on the Blue Scale for lightfastness.

P.R.247 exhibits excellent heat stability as it withstands temperatures up to 300 °C. The shrinkage of such partially crystalline plastics is not noticeably affected. P.R.247 is not completely bleed resistant in plasticized PVC, but it shows good lightfastness. Transparent (0.1% pigment) and opaque colourations (0.01% pigment + 0.5% TiO₂) equal step 6–7 on the Blue Scale for lightfastness. The same values apply if the pigment is incorporated in rigid PVC. P.R.247 is also used to colour PS, ABS and polyacetal. Excellent heat stability makes it a suitable candidate for PP spin dyeing.

Some time ago a different crystal modification [95] of the same chemical structure became commercially available. Originally listed in the Colour Index with the C.I. Generic Name Pigment Red 247:1, this name has now been changed to P.R.247. The new designation is in accordance with other pigments equally existing in different crystal modifications, such as the quinacridone pigment P.V.19, but are listed under the same C.I. Generic Name and C.I. Constitution Number.

The main application area of the new β-crystal modification is also in plastics. It affords a much yellower shade than the other α-crystal phase and shows similar tinctorial strength. 1/3 SD HDPE samples (1% TiO₂), for instance, are formulated with 0.32% pigment. These samples equal step 5–6 on the Blue Scale for lightfastness, which is about one step less than the other modification. The heat stability is excellent, the new type equally withstands temperatures up to 300 °C in HDPE. Partially crystalline plastics show no noticeable shrinkage through the incorporation of this pigment. It is almost completely bleed resistant and in this respect superior to the other modification. The pigment exhibits good lightfastness but is not quite as lightfast as the first type.

This more yellowish grade is also recommended for use in rigid PVC, PS and ABS. In polycarbonate 0.64% pigment is needed to afford 1/3 SD (1% TiO₂). These samples withstand temperatures up to 310 °C and equal step 5–6 on the Blue Scale for lightfastness. In PP spin dyeing this more yellowish modification is also heat stable up to 300 °C. The lightfastness of colourations containing 0.3% pigment equals step 4–5 on the Blue Scale, while those with 2% pigment equal step 6.

2.7.4.2.1 General

These pigments have the following general structures:

Table 2.13 shows the monohydrazone pigment lakes that are based on naphthalene sulfonic acid.

(a) Coupling at the 1-position:
C.I. Name	C.I. Constitution Number						m	M	Shade
P.Y.104	15985:1	H		H	H	H	3	2 Al	reddish yellow
P.O.19	15990	Cl	H	H	H	H	2	Ba	orange
P.O.79	—	H	COO−	H	H	H	1	Sr	orange [96]
P.R.60	16105	COO−	H	H		H	2	3 Ba	bluish red
P.R.273	16035:1	OCH3		CH3	H	H	3	2 Al	yellowish red
P.R.274	16255:1	DC: 1-amino naphthalene-4-sulfonate			H		1	Al	bright red
P.R.276	—	Solid solution of:							scarlet
			Cl	C2H5	H	H	1	Sr
			CH3	Cl	H	H	1	Sr
P.R.277	—	Solid solution of:							bluish red [97]
			Cl	C2H5	H	H	1	Sr
		DC: 2-amino naphthalene-1-sulfonate			H	H	1	Sr
P.V.52	—		OCH3	H	H	H	1	Sr	violet [98]
(b) Coupling at the 7-position:
C.I. Name	C.I. Constitution Number					X	m	M	Shade
P.R.66	18000:1	H		CH3		H	2	Ba, 2Na	red
P.R.67	18025:1	OCH3		H		Cl	2	Ba, 2Na	bluish red

2.7.4.2.2 Pigment Yellow 104³⁾

P.Y.104, an aluminium salt, has been approved for use in food, pharmaceuticals and cosmetics, and appropriate purity standards have been developed. The pigment is known under the designation E 110 throughout the European Community and as FD&C Yellow No. 6 in the USA. It produces reddish shades of yellow. Like several other aluminium lakes of simple dyes, P.Y.104 exhibits poor fastness to organic solvents and limited bleeding fastness. Similarly, it is not fast to soap and alkali. P.Y.104 exhibits very little tinctorial strength in various media and is not lightfast.

2.7.4.2.3 Pigment Orange 19

P.O.19 has stimulated only limited industrial interest and is rarely used in Europe. It provides a shade that in white reductions resembles that of P.O.34, but which is much duller. Its full shade is noticeably yellower than that of P.O.34. P.O.19, incorporated in medium-oil alkyd resin systems, is less lightfast, both in full shade and in white reductions, than opaque P.O.34 types. The commercially available type exhibits poor rheological behaviour.

2.7.4.2.4 Pigment Orange 79

Pigment Orange 79, CAS 250640, is a bright orange pigment of the class of hydrazone naphthalene sulfonic acid pigment lakes (strontium lake) [99].

This pigment has been adopted as the preferred orange pigment for food packaging and containers due to its extremely low warpage and shrinkage. It is heat stable up to 285 °C and is compatible with a wide variety of polymers including ABS, PET, PC, polyolefins and styrenics. This product has been in the market since 1995 and in that time has replaced other oranges for food packaging applications. Pigment Orange 79 complies with the FDA requirements for food contact under the conditions of use (A) through (H) as described in Table 2 of 21 CFR Part 196.170(c) where this pigment is allowed to be used at levels up to 1% by weight of the polymer subject to the provisions and definitions described in Title 21 CFR Part 178.3297.

P.O.79 has exhibited very low distortion and warpage characteristics when moulded in polyolefins.

2.7.4.2.5 Pigment Red 60

P.R.60, which was patented as early as 1902 by Meister Lucius & Brüning, has lost much of its importance in recent years. Today, it is mostly used throughout the USA and Japan. P.R.60 affords bright bluish red shades, which are referred to as shades of scarlet. Its tinctorial strength is poor compared to that of other pigment lakes with similar shades. P.R.60 shows limited fastness to acid, alkali and soap, and exhibits poor lightfastness. Several commercial types, which feature the pigment as a barium salt laked onto aluminium oxide hydrate, provide improved colouristic and fastness properties. Zinc oxide, added as the pigment precipitates, affects only the colouristic properties of the pigment. The exact chemical composition of such types is therefore very complex.

P.R.60 is used throughout the printing ink industry, especially for inexpensive packaging and metal deco printing inks. It does not bronze. Since the pigment is sensitive to water, problems may occur in offset printing. P.R.60 is used increasingly as a colourant for plastics, such as PVC, polyethylene, and especially for LDPE and polystyrene. Its lightfastness is satisfactory in these media.

P.R.60 is also used for emulsion paints and in paper mass colouration.

2.7.4.2.6 Pigment Red 66

P.R.66, a barium salt, is sold only in the USA. The pigment is also available as an aluminium oxide hydrate precipitate. Its shade is considered a brilliant medium red, which is somewhat yellower than that of the chemically related P.R.67. Commercial types of P.R.66 are very transparent. The pigment is highly sensitive to acid, alkali and soap. Its fastness to organic solvents is poor, as it its fastness to overcoating. P.R.66 exhibits limited lightfastness. Its main application is in metal deco printing.

2.7.4.2.7 Pigment Red 67

P.R.67, a barium salt, is also available in the form of an aluminium oxide hydrate precipitate. Its shade is bluer than the chemically related P.R.66; it is referred to as a bright bluish red. Commercial types are transparent and tinctorially strong. P.R.67 is used especially in metal deco printing. The prints do not tolerate acid, alkali or soap. They show only limited fastness to organic solvents and to clear lacquer coatings. P.R.67 prints are not fast to sterilization and only poorly lightfast. The pigment is also used for the colouration of rubber. It exhibits good resistance to common oxidants and does not tend to migrate.

2.7.4.2.8 Pigment Red 276

This is a solid solution of two pigments (CAS No. 197566-90-8 and CAS No. 197566-87-3) [100]. P.R.276 exhibits a bright scarlet shade and is predominantly useful in plastic applications that do not require exterior weatherfastness.

Pigment Red 276 is FDA compliant under 21 CFR Part 176.170(c) at 2% by weight of the polymer subject to provisions and definitions described in Title 21 CFR Part 178.3297. It is primarily used in food packaging applications and in mouldings when its superior warpage characteristics to DPP chemistry is needed. The heat stability of P.R.276 approaches 285 °C in masstone and all tint levels. Although the pigment is of modest colour strength in light tints, it has steadily gained in acceptance since its inception in the mid-1990s due to its excellent value in the above applications.

2.7.4.2.9 Pigment Red 277

Like P.R.276, this is a solid solution of two pigments (CAS No. 197566-90-8 and CAS No. 250639-69-1) [101]. The bluish red pigment was developed in mid-1990s as a heat stable pigment specifically for the plastics packaging market. Pigment Red 277 has very little use in applications where weatherability is needed, but fills an essential position in plastic packaging and other interior plastic durable goods. The pigment is heat stable up to 285 °C in masstone and tint, and although of modest colour strength in light tints, it delivers good economic value in the masstone and near masstone levels.

P.R.277 is FDA compliant under 21 CFR Part 176.170(c) at 2% by weight of the polymer subject to the provisions and definitions described in Title 21 CFR Part 178.3297. By virtue of this compliance, P.R.277 finds its way into many food-packaging applications. In moulding, P.R.277 has desirable low-warpage characteristics.

2.7.4.2.10 Pigment Violet 52 [102]

This laked violet hydrazone pigment has excellent heat stability of above 310 °C. P.V.52 has been developed for the plastics industry where it brings good value to the packaging and interior household durables segments. Tinctorially it is quite strong and similar in colour to quinacridone violet and can be used as cost-effective diluent, but its use is restricted to the interior due to its low fastness properties. Pigment Violet 52 is redder than Pigment Violet 51 (Section 4.4.9) and is in compliance with the FDA requirements for food contact under the conditions of use, (A) through (H) as described in Table 2 of 21 CFR Part 176.170(c), where the pigments are allowed to be used at levels of up to 2% by weight of the polymer subject to the provisions and definitions described in Title 21 CFR part 178.3297. The pigment exhibits very low warpage characteristics in polyolefin mouldings.

2.8.4.1.1 Pigment Yellow 120

P.Y.120 affords a medium yellow shade. The pigment powder shows good fastness to solvents, in which it is similar to other yellow pigments within this class.

P.Y.120 is primarily applied in plastics, especially in PVC. A pigment preparation is available for this purpose. P.Y.120 is very bleed resistant in plasticized PVC and has excellent lightfastness in both plasticized and rigid PVC. 1/1 to 1/25 SD samples (5% TiO₂) as well as transparent formulations equal step 8 on the Blue Scale for fastness to daylight. The pigment, however, is much less weatherfast in lead/cadmium stabilized rigid PVC than other representatives of its class, which precludes its use in exterior application. P.Y.120 is heat stable enough in HDPE for 1/3 SD samples (1% TiO₂) to tolerate exposure to 270 °C for 5 min. The shrinkage of the polymer is not affected. Incorporated in LDPE, P.Y.120 withstands approximately 220 °C, in polystyrene 240 °C. Transparent HDPE colourations (0.1%) equal step 8 on the Blue Scale for lightfastness, while opaque samples (0.01% pigment + 0.5% TiO₂) match step 6–7.

The printing ink industry uses P.Y.120 primarily for decorative printing inks on laminated melamine and polyester resin sheets. In terms of lightfastness, 8% gravure prints in 20 and 40 µm cells on such plates correspond to step 8 on the Blue Scale. Plate-out is not observed. P.Y.120 is insoluble in monostyrene and acetone (Section 1.8.1.2).

P.Y.120 lends itself to all printing methods. Its lightfastness in letterpress and offset prints is also very good. Depending on the depth of shade, prints equal step 7 to step 6 on the Blue Scale. P.Y.120 thus scores approximately 1 step higher than the similarly coloured P.Y.97.

P.Y.120 is used primarily to colour high grade gravure inks for posters, metal sheets and packaging purposes. The pigment has gained particular recognition in gravure inks for plasticized PVC. The prints are completely resistant to the DIN 16524 standard solvent mixture, as well as to various organic solvents and media, including toluene, mineral spirits, methyl ethyl ketone, ethyl acetate, paraffin, butter, soap, alkali, and acid. Moreover, the prints are fast to clear lacquer coatings and may safely be sterilized. They are heat stable up to 200 °C for 30 min.

P.Y.120 has less of an impact on the paint industry. In contrast to the similarly coloured P.Y.97, P.Y.120 is fast to overcoating. Moreover, it exhibits noticeably higher durability. White reductions, reduced 1:1 to about 1:5, are approximately as durable as P.Y.151 systems. P.Y.120 is recommended for general industrial finishes, including automotive refinishes, and it is also suitable for use in architectural paints. P.Y.120 is completely fast to alkali.

2.8.4.1.2 Pigment Yellow 151

P.Y.151, available since 1971, affords a clean greenish yellow shade. Its hue is somewhat greener than that of P.Y.154 and distinctly redder than that of P.Y.175. The type which features a specific surface area of less than 20 m² g⁻¹ provides good hiding power.

P.Y.151 maintains an important position throughout the pigment industry. Its main area of application is in the paint industry, which uses P.Y.151 particularly for high grade industrial finishes. Good rheological properties make it possible to incorporate up to approximately 30% pigment in a paint without affecting the gloss of the coating. The percentage value is given relative to the amount of solid binder. For comparison, full shade paints containing other pigments are usually restricted to a pigment concentration of 10–15%. P.Y.151 is frequently used in combination with TiO₂ and/or inorganic yellow pigments. Very lightfast and weatherfast P.Y.151/phthalocyanine green pigment combinations are equally important; they are sometimes used in conjunction with the above-mentioned inorganic pigments. As a rule, P.Y.151 is employed to produce deeper shades, which makes it an interesting product for manufacturers of automobile (O.E.M) finishes and automotive refinishes and paints for commercial vehicles.

Coatings containing P.Y.151 are very lightfast and durable. Systems based on acrylic melamine resin, for instance, were exposed to the Florida climate for one year and then evaluated. 1:1 reductions with TiO₂ equalled step 5 on the Grey Scale for weatherfastness, while 1:3 TiO₂ reductions matched step 4, and 1:35 reduced samples coincided with step 3–4. Comparative values for P.Y.154 and 175 are listed for the respective pigments. P.Y.151 is fast to overcoating up to 160 °C.

P.Y.151 is heat stable up to a maximum of 200 °C and withstands acid, but is affected by alkali under certain test conditions. Although the pigment tolerates weak bases, it will undergo a distinct colour change towards reddish yellow shades if it is exposed to strong alkali. P.Y.151 is also affected by lime (Section 1.6.2.2), which almost entirely precludes its use in emulsion paints.

The plastics industry uses P.Y.151 to colour PVC, polyolefins, and other polymers. The pigment shows excellent migration fastness in plasticized PVC. Plasticized PVC samples up to 1/25 SD equal step 8 on the Blue Scale for lightfastness. The pigment exhibits good weatherability in rigid PVC, but performs distinctly poorer in this respect than P.Y.154 and 175, and it is therefore usually unacceptable for long-term exposure. 1/3 SD P.Y.151 samples in HDPE (with 1% TiO₂) show a heat stability of 260 °C for 5 min. Temperatures in excess of this value shift the colour towards the reddish side of the spectrum and decrease its brightness. The shrinkage of the polymer is only slightly affected at processing temperatures between 220 and 280 °C. P.Y.151 is equally heat stable in polystyrene, as long as the processing temperature does not exceed 260–280 °C. The pigment is very lightfast in this medium (step 8).

P.Y.151 is employed for printing inks wherever lightfastness is a prime consideration. 1/1 SD letterpress proof prints equal step 7 on the Blue Scale for lightfastness, while 1/3 SD prints match step 6–7. The prints are fast to soap but not sufficiently alkali resistant. They are fast to clear lacquer coatings, but not fast to sterilization. P.Y.151 finds extensive use in offset and letterpress applications, as well as in packaging gravure inks for PVC substrates. It is equally suitable for decorative printing inks for laminated plastic sheets based on polyester resin. P.Y.151 is insoluble in monostyrene and acetone. In terms of lightfastness, 8% gravure prints (etching depth 20 and 40 µm) equal step 8 on the Blue Scale. P.Y.151 should not be used for laminated melamine resin sheets. It is not compatible with aqueous melamine resin solutions, in which it dissolves to a certain extent.

2.8.4.1.3 Pigment Yellow 154

P.Y.154, which was introduced in the mid-1970s, affords a somewhat greenish yellow shade of very high lightfastness and weatherfastness. Its shade is distinctly redder than that of P.Y.175 and noticeably redder than that of P.Y.151, both of which are also members of the benzimidazolone series. P.Y.154 is completely or at least almost completely resistant to the major organic solvents. The list includes alcohols, esters, such as butyl acetate, aliphatic and aromatic hydrocarbons, such as mineral spirits or xylene, and dibutyl phthalate.

P.Y.154 is primarily applied in paints, in which it is one of the most weatherfast organic yellow pigments. Incorporated in the same system and tested and evaluated under the same conditions as P.Y.151, for instance, after one year of outdoor exposure in Florida, TiO₂ reductions up to 1:3 were found to equal step 5 on the Grey Scale, while 1:30 TiO₂ reductions matched step 4–5.

P.Y.154 is thus also a suitable shading component for other hues and may be used to tone reduced clean yellow and green shades.

Irrespective of the concentration, P.Y.154 is recommended for all high grade industrial paints, including automobile (O.E.M.) finishes. Incorporated in baking enamels, it may safely be overcoated up to 130 °C. Temperatures in excess of this value will increase its tendency to bleed, which is only slightly noticeable at 140 °C. The pigment is heat stable up to 160 °C. Its good rheology makes it possible to increase the pigment concentration in a paint without affecting the gloss of the coating. P.Y.154 disperses easily. Areas of application also include other common media throughout the coatings and paints industry, such as architectural paints and emulsion paints. P.Y.154 is employed wherever high lightfastness and weatherfastness are required.

Its principal application within the plastics area is in PVC. P.Y.154 reigns supreme in terms of lightfastness and durability in rigid PVC and in impact resistant PVC types, which makes it a suitable product for exterior use. P.Y.154 also has excellent lightfastness and weatherfastness in PVC plastisols which are coil coated onto steel. Systems of this kind are frequently applied to the exterior of houses. P.Y.154, however, exhibits inferior tinctorial strength. 2.5% pigment is required to formulate 1/3 SD colourations with 5% TiO₂ in plasticized PVC. Only 1.4% are needed of the slightly redder P.Y.120, which is also a member of the benzimidazolone pigment series. P.Y.154 has excellent bleeding fastness in plasticized PVC. The heat stability of 1/3 SD samples in HDPE (with 1% TiO₂) is only up to 210 °C for 5 min, which practically precludes its use in this polymer. The pigment is equally unsuitable for polypropylene spin dyeing.

P.Y.154 is a useful pigment for the printing ink industry wherever high lightfastness is required. Letterpress proof prints up to 1/25 SD equal step 6–7 on the Blue Scale for lightfastness, which is at least 1 1/2 to 2 steps above that of similarly coloured diarylide yellow pigments or representatives of the monohydrazone yellow pigment series. In print, however, like in plastics, P.Y.154 lacks tinctorial strength. 1/3 SD standardized letterpress proof prints are prepared from inks which contain 25% pigment. For comparison, equally deep samples are prepared from inks which contain 3.5% P.Y.13 or 8.8% P.Y.1, respectively. P.Y.154 prints are not fast to clear lacquer coatings or to sterilization.

The list of applications also includes other media, such as oil colours for artists, in which P.Y.154 is used for its high lightfastness.

2.8.4.1.4 Pigment Yellow 175

P.Y.175, a clean, very greenish yellow pigment, is a comparatively recent product. It has only gained limited commercial recognition. The shade of the commercially available modification is somewhat greener than that of other benzimidazolone pigments and greener than corresponding pigments of other types, such as P.Y.109, 128 or 138.

P.Y.175 is primarily used in the paint field, where it is used especially to colour high grade systems, such as automobile (O.E.M.) and automotive refinishes. The products are used for brilliant yellow or green shades. Shades of green are accessible, for instance, by combining P.Y.175 with phthalocyanine pigments. Despite its comparatively low specific surface area (approx. 20 m² g⁻¹), the commercially available type exhibits good transparency. However, it is not weatherfast enough to be used in metallic finishes. On the other hand, both lightfastness and durability are excellent in solid shades. In medium white reductions with TiO₂, P.Y.175 shows excellent weatherfastness, but this fastness deteriorates rapidly as more white pigment is added. In this respect, P.Y.175 is inferior to the somewhat redder P.Y.154, which is also a member of the benzimidazolone pigment series. Incorporated in an acrylic melamine resin system and exposed to the Florida weather for one year, for instance, P.Y.175 samples which are reduced 1:1 with TiO₂ equal step 5 on the Grey Scale, while 1:2.5 samples coincide with step 4, and 1:30 reductions match step 3–4.

P.Y.175 does not bloom. It may safely be overcoated up to 140 °C. At higher temperatures, bleeding is observed to a small extent in various systems. The pigment is heat stable up to 180 °C. The commercially available type exhibits good rheological properties in paints and may therefore be used at higher concentrations.

P.Y.175 is of interest to the plastics industry wherever high lightfastness and weatherfastness are a prime concern. It is, for instance, frequently used for long-term exposure in rigid PVC in white reductions containing little TiO₂. The pigment is, however, less durable than P.Y.154. 1/3 SD HDPE samples (with 1% TiO₂) are heat stable up to 270 °C. The shrinkage of the polymer is not affected at processing temperatures between 220 and 270 °C (Section 1.6.4.3). However, P.Y.175 is comparatively weak. 0.55% pigment is needed to produce a 1/3 SD sample with 1% TiO₂, while only 0.13% is required of the less lightfast, still somewhat greener diarylide yellow pigment P.Y.17. 0.27% of the somewhat redder P.Y.16, on the other hand, is sufficient to achieve the same purpose, although the two latter pigments are considerably less heat stable and lightfast than P.Y.175.

The printing ink industry uses P.Y.175 only for high grade products. Up to 1/25 SD, its lightfastness equals step 6–7 on the Blue Scale. Its limited tinctorial strength, however, is somewhat of a disadvantage. The prints are fast to paraffin, butter, soap, dibutyl phthalate, toluene, mineral spirit, and other media. They are also fast to clear lacquer coatings but may not be sterilized. Prints containing P.Y.175 are heat stable up to 200 °C for 10 min or up to 180 °C for 30 min.

2.8.4.1.5 Pigment Yellow 180

P.Y.180, a greenish to medium yellow shade pigment, was introduced a few years ago. It is a dihydrazone yellow pigment and is of particular interest to the plastics industry and for laser printing.

In HDPE, P.Y.180 is heat stable up to 290 °C. P.Y.180, like P.Y.181, does not affect the shrinkage of the plastics, so that there is no limitation to its use in injection-moulded articles. It is, however, less fast to light than the redder P.Y.181. 1/3 SD colourations (1% TiO₂), for instance, equal step 6 on the Blue Scale. 1/3 SD specimens are formulated at a pigment concentration of 0.15%, which indicates good tinctorial strength. P.Y.180 is also used for PP spin dyeing, since it has excellent heat stability and affords clean hues. A special pigment preparation is available for this purpose. Redder shades are accessible through combination with the very reddish P.Y.181. Deep colours have excellent lightfastness: 1/1 to 1/3 SD samples equal step 7 on the Blue Scale. The fastness to light decreases rapidly, however, as more white pigment is added: 1/25 SD specimens match only step 5 on the Blue Scale. P.Y.180 performs excellently in terms of textile fastness properties.

P.Y.180 is becoming increasingly important and is utilized in printing inks to suit particular applications where diarylide yellow pigments cannot be used. Diarylide yellow pigments decompose at temperatures in excess of 200 °C (Section 2.4.1.3), which precludes their use in certain inks for metal deco which are baked at temperatures above 200 °C.

P.Y.180 is an equally important pigment for PVC. It does not migrate in plasticized PVC. Depending on the standard depth of shade and on the TiO₂ content, its lightfastness in rigid and in plasticized PVC equals step 5 (0.01% pigment + 0.5% TiO₂) to step 6–7 on the Blue Scale (0.1% pigment + 0.5% TiO₂). P.Y.180 is also used to colour other plastics which are processed at high temperature. Technical polymers, such as polycarbonate, PS, ABS, and polyester, are particularly common media for P.Y.180. The pigment is also used to colour injection-moulded and extrusion-made polyamide – in contrast to P.Y.181, which is not suitable for this purpose. These plastics melts are slightly basic and have a reducing effect, in contrast to other polymer melts which are neutral.

A special grade is also commercially available which is recommended for the colouration of solvent and water based packaging gravure and flexo printing inks, respectively, and for metal deco printing as well. The grade exhibits good dispersibility and flocculation stability and is especially being employed where the use of diarylide yellow pigments is limited due to their thermal decomposition above 200 °C (Section 2.4.1.3).

2.8.4.1.6 Pigment Yellow 181

P.Y.181, a reddish yellow pigment, was introduced to the market a few years ago. Its main area of application is in plastics, especially in polyolefins. In these media, P.Y.181 is heat stable up to 300 °C and very lightfast. 1/3 SD HDPE samples (1% TiO₂), for instance, equal step 8 on the Blue Scale. The pigment does not affect the shrinkage of the partially crystalline polymer. Its tinctorial strength, however, is poor.

P.Y.181 does not migrate in plasticized PVC. Besides, it shows excellent lightfastness in this medium. Both transparent samples (0.1% pigment) and white reduced samples (0.1% pigment + 0.5% TiO₂) equal step 8 on the Blue Scale. Even plasticized and rigid PVC samples which contain a higher concentration of white pigment (0.01% pigment + 0.5% TiO₂) still match step 7–8 on the Blue Scale.

P.Y.181 is extremely heat stable, which makes it a suitable pigment for other polymers which are processed at high or very high temperature. The list includes PS, ABS, polyester, polyacetal, and various other technical plastics. The pigment is equally interesting in connection with PP spin dyeing. The 0.3% and 3% PP samples equal step 7 and step 7–8 on the Blue Scale, respectively. A special pigment preparation is available for this purpose. P.Y.181 also frequently colours spin dyed viscose rayon and viscose cellulose. In these media, the pigment satisfies the particularly stringent specifications regarding lightfastness and weatherfastness for use in automobile interiors. This is a purpose to which only very few organic yellow pigments are suited.

P.Y.181 is also recommended for use in paints, but in this area it is in direct competition with numerous similarly shaded pigments within the same class as well as from different pigment classes. Inferior tinctorial strength makes P.Y.181 a less important product in this field.

2.8.4.1.7 Pigment Yellow 194

The pigment affords medium yellow shades. Regarding shades and performance it competes with some other pigments, such as the monohydrazone pigment P.Y.97 and the bisacetoacetarylide pigment P.Y.16.

P.Y.194 is gaining increasing importance in liquid industrial coatings and in powder coatings as well. Owing to its solvent fastness in baking enamels it is fast to overpainting at 120 °C, shows a slight bleeding at 140 °C (after 30 min baking time) and is heat stable up to 200 °C. High hiding power and correspondingly a specific surface area of 20 m² g⁻¹ favour its use for lead free coatings.

The pigment is also employed in the plastics field. A special grade features good tinctorial strength and particularly a good dispersibility. Pigmentation of HDPE in 1/3 SD (1% TiO₂) requires 0.17% of pigment. The colourations are heat stable up to 240 °C and the lightfastness corresponds with step 5 on the Blue Scale. The pigment is preferentially used in LDPE.

It is bleeding in plasticized PVC. Dependent on the standard depth of shade in this medium the lightfastness equals step 5–6 on the Blue Scale. The pigment is equally employed for cable insulation, since it influences the specific electrical resistance only negligibly.

2.8.4.1.8 Pigment Orange 36

P.O.36 is a reddish, somewhat dull orange pigment which provides very good lightfastness and weatherfastness. It is a highly important pigment. The commercially available types differ considerably in their hiding power/transparency. Different types vary even in terms of shade – the opaque version is redder and noticeably cleaner – and other properties, as well as fastness properties.

In the production, P.O.36 is obtained upon coupling as a brown α-phase. A subsequent finishing process is needed to gain the desired orange β-phase.

P.O.36 is broad in scope, its main area of application is in paints. Masstone and similar deep shades have excellent lightfastness. The opaque variety, which was introduced in the mid-1970s, performs much better in this respect than the standard grade. In deep shades, P.O.36 meets the requirements for use in automobile (O.E.M.) finishes. The opaque version is the current standard grade in this range of shades for applications which require lead free pigmentation. To suit this purpose, P.O.36 is frequently used in combination with quinacridone pigments to produce paints which feature, for instance, lightfast and durable RAL shades 3000 (fire engine red), 3002 (carmine), 3003 (ruby), and 3013 (tomato red). Small amounts of TiO₂ may be added. Very good rheological behaviour in paints makes it possible to increase the concentration of opaque pigment without affecting the gloss. The opaque version of P.O.36 is also used in combination with chromate pigments. Coatings which are pigmented in full and similarly deep shades do not darken as they are exposed to light and weather. The list of applications also includes automotive repair finishes, paints for commercial vehicles and agricultural machines, as well as for general industrial finishes. P.O.36 is used extensively in these areas.

P.O.36 is completely fast to overcoating. Bleeding into a white overcoat is only observed at baking temperatures above 160 °C. P.O.36 is heat stable up to 160 °C. In dispersing the opaque type, it is important to avoid excessive shearing forces and to closely monitor the temperature, especially if agitated ball mills are used. Faulty temperature control may lead to a dull colour.

P.O.36 is used throughout the printing ink industry for letterpress and offset inks, all types of packaging gravure and flexographic inks, and for metal deco printing. The prints are very lightfast. Depending on the grade and on the standard depth of shade, letterpress proof prints up to 1/25 SD equal step 6–7 to step 5 on the Blue Scale. The prints are excellently fast to chemicals and resistant to solvents such as toluene, mineral spirit, methyl ethyl ketone, and to the DIN 16 524 standard solvent blend. They withstand clear lacquer coatings and may safely be sterilized. Prints made from P.O.36 tolerate exposure to 220 °C for 30 min. At equal standard depth, their shade is noticeably duller than that of the somewhat redder P.O.34 and also duller than that of other less fast pigments covering the same range of shades.

The plastics industry uses P.O.36 to colour PVC. 1/3 to 1/25 SD plasticized PVC samples containing 5% TiO₂ equal step 8 and step 7, respectively, for lightfastness, while transparent specimens (0.1% pigment) equal step 8 on the Blue Scale. The pigment does not migrate, for example, it is practically resistant to bleeding and blooming. Combinations with carbon black are frequently used to create shades of brown for furniture films. Suitable media include PVC plastisols.

Incorporated in rigid PVC, P.O.36 lacks lightfastness at low concentrations. Barium/cadmium stabilized 1/3 SD colourations in rigid PVC show good durability but are frequently not weatherfast enough to satisfy the requirements for plastics materials in respect of long-term exposure. Heat stability, tested in HDPE at 1/3 SD, is to 220 °C. The pigment does not affect the shrinkage of the plastic. P.O.36 is normally, however, not heat stable enough to meet the standards of practical pigment application in polyolefins.

P.O.36 is also used to colour unsaturated polyester resins. Both transparent and opaque samples exhibit a lightfastness in these media that equals step 7 on the Blue Scale. The pigment does not affect the shrinkage of the plastic.

2.8.4.1.9 Pigment Orange 60

Introduced some years ago the production of this pigment has been discontinued. P.O.60 is a yellowish orange pigment with excellent lightfastness and durability.

Its main area of application was in paints, in which it was used primarily to colour high grade industrial finishes, such as automotive finishes, especially automobile O.E.M. finishes. P.O.60 was used to advantage in white reductions and as a shading pigment. Its response to accelerated weathering under a xenon arc lamp is much inferior to its actual weatherfastness in outdoor exposure, for instance in Florida. The commercially available grade was transparent and exhibited a low specific surface area (less than 20 m² g⁻¹). This is what made P.O.60 a suitable candidate to produce orange shades in metallic finishes. There is a certain disadvantage to its lack of tinctorial strength, which is attributed to the low specific surface area.

P.O.60 is one of the organic orange pigments with the highest fastness standards. Its durability – even in metallic finishes – equals that of P.Y.154. After one year of outdoor exposure in Florida, acrylic melamine resin systems containing up to 1:25 TiO₂ equal step 5 on the Grey Scale for durability. Metallic finishes containing 60% pigment and 40% aluminium paste (65%) and also 40:60 blends equal step 4–5 on the same scale. Comparative values are listed with some other representatives of this class.

P.O.60 is heat stable up to 160 °C. Baking temperatures in excess of this value will in some paint systems cause a decrease in fastness to overcoating.

P.O.60 was basically also used in printing inks and plastics, provided the requirements concerning lightfastness and durability were high. Adding small amounts of TiO₂ confers long-term weatherfastness on the pigment, although this advantage is compromised by its poor tinctorial strength. Wherever the requirements are appropriate, P.O.60 was also employed in other application media, such as artists' colours, poster colours and so on.

2.8.4.1.10 Pigment Orange 62

P.O.62 affords a clean, very yellowish shade of orange. The commercially available grade exhibits a low specific surface area of approximately 12 m² g⁻¹ and has, accordingly, coarse particles that make for good hiding power.

P.O.62 is utilized mostly to colour paints, especially to produce very clean yellowish shades of red or reddish shades of yellow in full and similarly deep shades. Good rheological properties make it possible to employ the pigment at higher concentrations without affecting the gloss. The pigment concentration may reach up to 30% relative to the content of solid binder. Deep shades are very lightfast and weatherfast. Full and related shades of P.O.62 are also recommended for use in automotive finishes. The list of applications includes automotive refinishes, commercial vehicles, agricultural machinery, and other high grade and general industrial paints. This is especially true for areas where intense shades of red are required and Molybdate Red is to be avoided or its use restricted. At higher baking temperatures (160 °C), P.O.62 is not completely fast to overcoating. The pigment is heat stable up to 180 °C.

P.O.62 is frequently used in the printing inks field to produce lightfast offset and aqueous flexographic inks. Its lightfastness in these media equals step 5 to step 6 on the Blue Scale, depending on the standard depth of shade. The prints are not completely fast to alkali and do not tolerate clear lacquer coatings and sterilization.

P.O.62 is interesting to the plastics field because it is very lightfast and durable in rigid PVC. However, it fails to meet higher standards regarding long-term weathering.

P.O.62 also lends itself to polypropylene spin dyeing, especially at temperatures up to approximately 230 °C. This makes it a suitable colourant for PP types that exhibit good flow behaviour.

2.8.4.1.11 Pigment Orange 72

P.O.72 is polymorphic: the red α-phase is obtained upon synthesis. During finishing in solvents it transforms into an orange β-phase. Additionally, two brown phases (γ and δ) are known. The commercial product contains only the orange β-phase.

Providing a bright yellowish orange, P.O.72 is particularly useful for the colouration of plastics. Incorporation in HDPE in 1/3 SD (1% TiO₂) requires 0.2% of pigment – the respective heat stability reaches 290 °C and the lightfastness corresponds with step 8 on the Blue Scale. The pigment does not affect the shrinkage of this partially crystalline polymer and can therefore be used in injection moulding without restriction.

P.O.72 is as well suitable for the application in polystyrene and ABS. Colorations of PS in 1/3 SD, requiring only 0.15% pigment, exhibit a heat stability of 280 °C, colourations of ABS are stable up to 290 °C. In these media the lightfastness equals step 8 on the Blue Scale. Pigment concentration of less than 0.1% in polyoxymethylene (POM, polyacetals) may lead to coating of the manufacturing equipment (see plate out, Section 1.6.4.1).

P.O.72 is used for melt spin dyeing of polypropylene, in which 1/3 SD (1% TiO₂) affords 0.2% pigment. The lightfastness of PP colourations with 0.3% pigment equals step 7, such with 2% pigment step 7–8 on the Blue Scale. Owing to its heat stability the pigment is equally suitable for powder coatings.

P.O.72 is also recommended for paste- and liquid packaging inks as well as for decorative inks. It exhibits a clean yellowish orange shade, excellent fastness properties and very high heat resistance.

2.8.4.2.1 Pigment Red 171

P.R.171 affords a dull, very bluish red, referred to as maroon. The pigment generally provides good fastness properties. The commercially available types are highly transparent.

P.R.171 is used in plastics and in paints. Its lightfastness in PVC equals step 7 to step 8 on the Blue Scale, depending on the exact composition of the tested system, the pigment concentration and the TiO₂ content. When incorporated in plasticized PVC, P.O.171 is migration resistant and heat stable up to 180 °C. It is used in conjunction with organic yellow pigments, frequently also with iron oxides, to produce shades of brown. Shades of bordeaux are accessible in deep transparent colourations.

P.R.171 exhibits excellent tinctorial strength. Only 0.46% pigment is required to formulate 1/3 SD samples containing 5% TiO₂. 1/3 SD samples (with 1% TiO₂) in PE are heat stable up to approximately 240 °C. P.R.171 application is accordingly restricted to LDPE, which is processed at low temperature. Transparent samples (0.1% pigment) equal step 6–7 on the Blue Scale for lightfastness, while reduced colourations (0.01% pigment + 0.5% TiO₂) match step 6. Used in polyacrylonitrile spin dyeing, P.R.171 affords very lightfast products. In the concentration range between 0.1% and 3%, its lightfastness equals step 7–8 on the Blue Scale. The products are completely fast to dry rubbing but do not entirely withstand wet rubbing. Incorporated in unsaturated polyester resins, P.R.171 accelerates the hardening of the plastic. It shows very good lightfastness in this medium, too.

Paints containing P.R.171 may be safely oversprayed and exhibit excellent lightfastness and weatherfastness. Its good fastness properties make P.R.171 a suitable candidate for high grade industrial paints, including automotive repair finishes. Its high transparency in paint films is used to advantage in a host of applications, such as in transparent foil coatings and metallic finishes.

P.R.171 lends maroon shades to printing inks wherever it suits the required fastness standards.

2.8.4.2.2 Pigment Red 175

P.R.175, a somewhat dull red pigment, exhibits very good fastness properties. It is completely or almost completely insoluble in common organic solvents. The commercially available types exhibit high specific surface areas and are therefore very transparent.

The paint industry uses P.R.175 primarily to colour industrial paints and also automobile repair finishes. High transparency makes the pigment an important product for transparent and metallic effect finishes. The pigment is suited to two-coat metallic automobile (O.E.M.) finishes, also referred to as base coat/clear coat finishes, especially if the clear coat contains UV absorbants. Its lightfastness and weatherfastness are excellent. P.R.175 does not bloom, is completely fast to overpainting and is heat stable up to 200 °C.

In plastics, P.R.175 is also very lightfast and weatherfast. Its lightfastness in plasticized and rigid PVC, for instance, equals step 7 to step 8 on the Blue Scale, depending on the composition of the polymer, the type of stabilization, the depth of shade and possibly on the TiO₂ content. In these media, P.R.175 is frequently applied in conjunction with carbon black to afford shades of brown for furniture laminates. The pigment is migration resistant in plasticized PVC – bleeding or blooming is practically never observed. P.R.175 is also applied in PVC and PUR plastisols for synthetic leather, which is used in markets such as automobile interiors. The pigment is very durable. P.R.175, combined with carbon black but containing no TiO₂, is used in window frames made of impact resistant PVC.

In white reductions, P.R.175 does not quite satisfy the requirements of long-term outdoor exposure. PVC plastisols, coil coated onto steel plates, also provide good fastness to light and weather. 1/3 SD HDPE samples (with 1% TiO₂) tolerate exposure to up to 270 °C for 5 min. The pigment only affects the shrinkage of HDPE to a negligible extent. Transparent (0.1% pigment) and opaque colourations (0.01% pigment + 0.5% TiO₂) equal step 6–7 on the Blue Scale for lightfastness.

P.R.175 is also used in polypropylene spin dyeing, where it satisfies the lightfastness requirements. The pigment is an interesting colourant for polystyrene and for polyester (PETP). These systems are utilized to make bottles and other products.

P.R.175 has stimulated interest throughout the printing ink industry wherever high lightfastness, excellent solvent fastness, fastness to sterilization and very high heat stability (up to 220 °C) are required.

2.8.4.2.3 Pigment Red 176

P.R.176 provides a bluish red shade, which is somewhat bluer than those of P.R.187 and 208 and somewhat yellower than that of P.R.185.

P.R.176 is primarily applied in plastics and in laminated papers. The pigment exhibits very good migration fastness in plasticized PVC. 1/3 SD samples containing 5% TiO₂ equal step 6–7 on the Blue Scale for lightfastness, 1/25 SD specimens match step 6, and transparent colourations (0.1% pigment) equal step 7. Transparent rigid PVC colourations match step 7–8. P.R.176 is heat stable up to 200 °C, and it is a suitable colourant for PVC cable insulations and synthetic leather. The pigment is also used in polyolefins and in polystyrene, where its lightfastness is equally good. Transparent polystyrene samples (0.1%) are heat stable up to 280 °C, addition of large amounts of TiO₂ reduces this stability to 220 °C.

The list of applications includes decorative prints for laminated plastic sheets. P.R.176, like P.R.187 and 208, is insoluble in styrene monomer and acetone, exhibits no plate-out onto the plastic sheets, and does not bleed if it is soaked with a melamine resin solution. This is what makes P.R.176 an interesting pigment for both melamine and polyester resin sheets. Its lightfastness is inferior to that of these other pigments covering the same colour range; it scores one step less on the Blue Scale. P.R.176 affords a shade that closely approaches the standard magenta for three- and four-colour printing.

P.R.176 provides very lightfast polyacrylonitrile spin dyeing products. The samples equal step 6–7 on the Blue Scale. Dry and wet crocking may affect the objects to a certain extent. P.R.176 is also used in polypropylene spin dyeing, especially for coarse textiles, such as carpet fibres, split fibres, filaments, bristles or tape, and also for finer denier yarns. A special pigment preparation for this purpose is commercially available. 1/3 SD samples tolerate exposure to up to 300 °C for 1 min or up to 290 °C for 5 min. In terms of lightfastness, 0.1% colourations equal step 5–6 on the Blue Scale, while 2% samples match step 7.

2.8.4.2.4 Pigment Red 185

The commercially available types of this polymorphous pigment afford very clean, bluish shades of red. P.R.185 is completely or almost completely insoluble in common solvents.

Its main area of application is in graphics printing and in the mass colouration of plastics.

The printing ink industry uses P.R.185 for all printing techniques. The prints show very good solvent fastness, for instance towards the standard DIN 16524 solvent mixture and towards clear lacquer coatings. They may safely be sterilized. P.R.185 prints are heat stable up to 220 °C for 10 min or to 200 °C for 30 min, which makes the pigment a suitable product for metal deco printing. In terms of lightfastness, 1/1 SD prints equal step 6–7 on the Blue Scale, while 1/3 to 1/25 SD specimens match step 5. P.R.185 affords a colour that closely approaches the DIN 16524 standard magenta for three- and four-colour printing (Section 1.8.1.1). Consequently, the pigment is used in process colours wherever P.R.57:1 and 184 are not fast enough to meet the standards. This is true for applications such as metal deco printing. Moreover, P.R.185 also lends itself to use in laminated polyester products.

P.R.185 is employed throughout the plastics industry to colour PVC, poly(vinylidene) chloride, and polyolefins. In plasticized PVC, the pigment is migration resistant at concentrations down to 0.005%. Under standardized conditions, the extent of bleeding into a white plasticized PVC sheet that is in contact with a 1/3 SD coloured plasticized PVC sheet (Section 1.6.3.2) is only 0.2 CIELAB units. 1/3 SD samples (5% TiO₂) equal step 6–7 on the Blue Scale for lightfastness, while 1/25 SD samples match step 6. Similar values are measured for rigid PVC. In deeper shades, P.R.185 is also found in several types of synthetic leather, including materials based on PVC and PUR for use in automobiles. In terms of heat stability, 1/3 SD P.R.185 samples in PE (1% TiO₂) withstand less than 200 °C, which restricts its use to low temperature LDPE. P.R.185 is also well suited to polypropylene spin dyeing, provided the polymer can be processed at low temperature. P.R.185 is used by the paint industry to colour general industrial finishes.

2.8.4.2.5 Pigment Red 208

Incorporated in its application medium, P.R.208 affords medium shades of red. The pigment exhibits good fastness to chemicals and solvents. Its main area of application is in the mass colouration of plastics and in packaging gravure printing inks.

P.R.208 worked into PVC provides medium shades of red. Pigment blends with compounds such as P.Y.83 or with carbon black are frequently employed to produce shades of brown. P.Y.208 is an interesting product for synthetic leather based on PVC, which is targeted for use in automobiles. The pigment does not bloom in plasticized PVC, provided it is used at concentrations above 0.005%. It shows excellent bleed resistance. Samples in the range between 1/3 and 1/25 SD (with 5% TiO₂) equal step 6–7 on the Blue Scale for lightfastness. The pigment is heat stable up to approximately 200 °C and exhibits high tinctorial strength. Some 0.6% pigment is required to formulate 1/3 SD PVC samples with 5% TiO₂. Good dielectric properties make the pigment a suitable candidate for use in PVC cable insulations.

In white reductions, P.R.208/polyolefin systems only withstand temperatures below 200 °C, while transparent specimens (0.1%) are stable up to approximately 240 °C. Thus the pigment is a suitable and economical candidate for polypropylene spin dyeing, provided the temperature is kept below 200 °C. It is also possible to apply higher temperatures if a colour shift towards more yellowish shades is acceptable. In terms of lightfastness, P.R.208 meets the common standards for interior application.

P.R.208 is also used in polyacrylonitrile spin dyeing. It exhibits excellent textile fastness properties and shows good lightfastness. Full shades (3% pigment concentration) equal step 7 on the Blue Scale, while very light (0.1% pigment) red specimens match step 5. The list of applications includes secondary acetate spin dyeing and mass colouration of polyurethane foam and elastomers. P.R.208 is inert to peroxides.

P.R.208 is recommended for all printing methods and is very lightfast in print. The prints exhibit very good resistance to solvents and clear lacquer coatings and may safely be sterilized. Moreover, they are heat stable up to 200 °C for 10 min or 180 °C for 30 min. For comparison, notably, the cleaner, somewhat yellower P.R.112 is less lightfast, less fast to solvents and chemicals, and less heat stable. Shades of brown are accessible by blending P.R.208 with yellow pigments and with carbon black, frequently in printing inks based on vinyl chloride/acetate mixed polymer. Such materials are used especially to produce wood imitations. P.R.208 is particularly suited to use in decorative printing inks. The lightfastness of 8% gravure prints at 20 and 40 µm cell depth in laminated melamine sheets equals step 8 on the Blue Scale. Plate-out, that is colouration of the printing plates, is not observed. The pigment does not bleed if the print is soaked with a melamine resin solution. It is also completely inert to styrene monomer and acetone, which makes it an equally interesting candidate for polyester sheets.

The paint industry recommends P.R.208 primarily for general industrial finishes, in which it is used to a limited extent. Its lightfastness and weatherfastness do not satisfy the standards of several applications.

P.R.208 is also applied in various speciality media besides the three main groups mentioned, such as in crayons and laundry inks, as well as in solvent-based wood stains. Applied onto a surface, these products may safely be overcoated and are resistant towards nitro varnish, acid hardening varnish and polyester varnish. The lightfastness in these media equals step 7 on the Blue Scale, which is excellent.

2.8.4.2.6 Pigment Violet 32

P.V.32 is a somewhat dull, very bluish red pigment, referred to as a bordeaux. It is completely fast to numerous organic solvents and is used in paints, plastics and printing inks, as well as in spin dyeing.

Paints containing P.V.32 are totally resistant to overpainting. However, the pigment exhibits only moderate lightfastness. Full shade samples in an alkyd-melamine resin equal step 5–6 on the Blue Scale and darken, while 1:10 TiO₂ reductions match step 5–6 and 1:100 reductions coincide with step 3–4. The pigment is utilized in general industrial finishes wherever its lightfastness and weatherfastness satisfy the requirements. The similarly coloured P.R.12, on the other hand, a Naphthol AS pigment, bleeds and blooms in baking enamels.

High transparency makes P.V.32 an interesting colourant for transparent foil coatings and similar purposes. Like P.R.171 and 175, P.V.32 shows excellent heat stability, even in long-term exposure. Incorporated in a silicone resin coating, even more reduced colourations (1:50 TiO₂) withstand up to 200 °C for 120 h and 180 °C for 1000 h. No colour change is observed. However, the lightfastness deteriorates during exposure by approximately ½ step on the Blue Scale.

Transparent P.V.32 colourations in PVC equal step 7–8 on the Blue Scale for lightfastness, while opaque types (1/3 SD; 5% TiO₂) match step 6–7. The pigment is completely bleed resistant in plasticized PVC. P.V.32 exhibits high tinctorial strength. Only 0.44% pigment is required to produce 1/3 SD colouration in PVC (5% TiO₂). The similarly coloured but not bleed resistant tetrachlorothioindigo pigment P.R.88 is only about half as strong (Section 3.6.2.3). P.V.32 is frequently used in combination with Molybdate Red. Its heat stability in polyolefins is somewhat below 200 °C, although the colour change, as in many other cases, is not so noticeable as to absolutely preclude pigment application at a higher temperature. Therefore, P.V.32 is generally recommended only for use in LDPE at low processing temperatures. It is also suitable for spin dyeing, for instance for secondary acetate, viscose rayon or viscose cellulose. Its lightfastness in these media is good: 1/1 SD samples equal step 7 on the Blue Scale and 1/12 SD specimens match step 6. The textile fastnesses are excellent, although the pigment is not entirely fast to wet crocking and only poorly vat resistant.

Incorporated in printing inks, P.V.32 affords clean, highly transparent bluish shades of bordeaux. The pigment is used to produce high grade printing inks wherever fastness to calendering and other fastness properties are required. Moreover, P.V.32 is employed in laminated plastic sheets. Prints made from 8% gravure printing inks in 20 µm cells correspond to step 7 on the Blue Scale for lightfastness. The pigment is suitable both for polyester and for melamine sheets. Bleeding, however, may occur to a very slight extent if prints are soaked with a melamine resin solution. Notably, the pigment is not entirely fast to acetone (Section 1.8.1.2). P.V.32 is frequently used in printing inks based on vinyl chloride/vinyl acetate copolymer.

Apart from these areas of application, P.V.32 is also used in solvent-based wood stains. The lightfastness of the products equals step 6 on the Blue Scale, which is very good. These systems may safely be overcoated. Pigment blends with yellow pigments, such as with P.Y.83, and blends with black provide interesting shades of brown.

2.8.4.2.7 Pigment Brown 25

The pigment affords a reddish shade of brown. The commercially available types feature a high specific surface area of approximately 80 m² g⁻¹ and are therefore highly transparent. P.Br.25 is somewhat less fast to some solvents than other pigments of the same class. It is used in paints, plastics, and printing inks and is in these areas in direct competition with the colouristically closely related but somewhat yellower and more opaque P.Br.23.

The paint industry uses P.Br.25 primarily as a colourant for high grade industrial paints, such as automobile O.E.M. and repair finishes. High transparency makes it a suitable product wherever transparent or metallic effects are to be created, especially in two-coat (base coat/clear coat) metallic automotive finishes. For these purposes, P.Br.25 is frequently used in pigment blends with transparent iron oxides or with carbon black to afford shades of brown or maroon that are not accessible by using iron oxide pigments alone. P.Br.25 is completely fast to overcoating and is heat stable up to 200 °C. Its lightfastness and weatherfastness are equally excellent. Even in white reductions, alkyd-melamine resins systems reduced 1:300 with TiO₂ equal step 7–8 on the Blue Scale. White reductions of acrylic/melamine resin, reduced 1:1 with TiO₂ and exposed to Florida weather for one year, match step 5 on the Grey Scale for durability, while 1:6 reductions equal step 4–5 and 1:60 specimens correspond to step 4 on the Grey Scale.

P.Br.25 is a frequently used pigment in plastics. It exhibits very good but not perfect migration fastness in plasticized PVC. At concentrations down to 0.005%, P.Br.25 is heat stable up to 200 °C. It exhibits high tinctorial strength: only 0.77% pigment is required to produce 1/3 SD colourations in PVC with 5% TiO₂. Its lightfastness in PVC equals step 8 on the Blue Scale, and step 7–8 if considerable amounts of white pigment are added. P.Br.25 shows excellent weatherfastness in rigid PVC and in impact resistant PVC, which is also true for reductions with TiO₂. The pigment even satisfies the requirements of long-term exposure. It is used, for instance, in window frames made of impact resistant PVC. PVC plastisols that are coil coated onto steel plates exhibit excellent lightfastness and durability. P.Br.25 is also found in PVC and PUR leather targeted for use in automobiles.

1/3 SD HDPE colourations containing 1% TiO₂ are heat stable up to 290 °C. The shrinkage of injection-moulded articles is noticeably affected in the direction of flow if the processing temperature is low (220 °C). This influence, however, is already very slight at 260 °C.

P.Br.25 also shows excellent lightfastness in polyolefins. Transparent polystyrene samples are heat stable up to 280 °C, while specimens reduced considerably with TiO₂ withstand up to 240 °C. P.Br.25 is also used in polyester, in which it provides an interesting raw material for the manufacture of bottles.

Excellent fastness properties make P.Br.25 a suitable product for polypropylene spin dyeing. It is also very lightfast in polyacrylonitrile spin dyeing: 1/3 SD samples equal step 7 on the Blue Scale for lightfastness. Pigment weatherfastness is equally excellent, which qualifies P.Br.25 for use in awnings and so on. The pigment is completely fast to dry rubbing and almost completely fast to wet crocking. Moreover, P.Br.25 is also interesting as a pigment for polyurethane foam.

The printing ink industry uses P.Br.25 for all printing methods. The prints show excellent lightfastness. 1/1 to 1/25 SD letterpress proof prints, for instance, equal step 7 to step 6–7 on the Blue Scale. Prints made from P.Br.25 are fast to the DIN 16 524 standard solvent mixture, to paraffin, butter, soap and acid, but they are not entirely fast to alkali. The products are fast to clear lacquer coatings and may safely be sterilized. The temperature stability is up to 240 °C for 10 min or 220 °C for up to 30 min, which makes P.Br.25 a suitable candidate for metal deco printing inks. It is also frequently applied in printing inks for PVC.

Moreover, P.Br.25 is used in various speciality media, for instance in oil colours for artists and in watercolours. It lends itself to solvent-based wood stains. The products are very lightfast (step 7) and fast to overcoating.

2.9.4.2.1 Pigment Yellow 93

P.Y.93 affords a light greenish to medium yellow shade similar to that of P.Y.16.

The pigment is primarily used to colour plastics, including PP spin dyeing. Incorporated in plasticized PVC, P.Y.93 shows good-to-average tinctorial strength and good bleed resistance. Approximately 0.85% pigment is required to formulate a 1/3 SD samples with 5% TiO₂. P.Y.93 demonstrates very good lightfastness. In PVC, it is as lightfast as P.Y.94 and in this respect even slightly superior to P.Y.95, but it is less stable to light than the greener P.Y.128.

1/3 SD pigment formulations in rigid PVC and in PVC plastisols that are intended for coil coating lose weatherfastness much more rapidly as more TiO₂ is added than do P.Y.94 and 128. There is no difference in the response of the respective pigmented systems to weather, as long as they contain only 1% TiO₂, while a TiO₂ content of 5% renders the P.Y.93 system considerably less durable than its counterparts.

1/3 SD P.Y.93 formulations in HDPE (1% TiO₂) withstand exposure to up to 290 °C for 1 min or up to 270 °C for 5 min. The pigment causes distortion at processing temperatures between 220 and 280 °C. This effect, however, is so minor as to be tolerable for most purposes. Distortion phenomena therefore rarely restrict the extent of pigment application. In terms of lightfastness, 1/3 to 1/25 SD samples (1% TiO₂) equal step 7 on the Blue Scale. Good heat fastness makes P.Y.93 a suitable candidate for polypropylene spin dyeing. The pigment is also very lightfast in this medium. P.Y.93 shows good-to-excellent textile fastnesses in textile printing.

P.Y.93 has no importance in the paint industry. The graphic ink field uses P.Y.93 only where fastness standards are high, such as in high grade packaging and metal deco inks.

2.9.4.2.2 Pigment Yellow 94

P.Y.94 is the greenest one of all available yellow dihydrazone condensation pigments. It was only recently withdrawn from the market. With approximately equal cleanness, it is somewhat greener than P.Y.128, which is a member of the same class of pigments. However, P.Y.94 is only about half as strong tinctorially. Some 0.44% P.Y.94 is required to produce a 1/3 SD HDPE sample containing 1% TiO₂, while the same end result is achieved by using only either 0.22% P.Y.128 or 0.2% of the somewhat redder P.Y.93.

P.Y.94 shows excellent heat stability. 1/3 SD to 1/25 SD samples in HDPE (1% TiO₂) withstand up to 300 °C. The shrinkage of the plastic, however, is considerably affected. P.Y.94 is equally weak in PVC. Some 2.1% pigment is needed to formulate 1/3 SD samples containing 5% TiO₂. P.Y.94 exhibits excellent lightfastness and weatherfastness, which is also true for PVC plastisols targeted for coil coating. The pigment is completely fast to migration, even in highly plasticized PVC. Its excellent heat stability makes it a suitable candidate for PP spin dyeing. In addition, P.Y.94 is also used in polyacrylonitrile spin dyeing.

The printing ink industry uses P.Y.94, like other dihydrazone condensation pigments, only for high grade printed products, especially in metal deco printing. Economical pigment formulation is compromised by somewhat poor tinctorial strength. The commercial type, which features a comparatively low specific surface area of approximately 35 m² g⁻¹, is consequently less transparent than other products in this class of pigments. P.Y.94 is noticeably less lightfast than P.Y.128, which has a finer particle size; the difference is approximately one step on the Blue Scale. In this respect, P.Y.94 resembles the diarylide yellow pigment P.Y.113, which is somewhat greener and distinctly stronger tinctorially. P.Y.94 exhibits plate-out on the metal plates if it is used in decorative printing, that is, on laminated papers for laminated plastic sheets (Section 1.6.4.1).

2.9.4.2.3 Pigment Yellow 95

P.Y.95 affords reddish shades of yellow. At 1/3 SD, its shade may be located somewhere between those of the diarylide yellow pigments P.Y.13 and 83.

Its main field of application is in plastics and in spin dyeing, which is also true for other members of this class of pigments. P.Y.95 is a pigment with high tinctorial strength, it is the strongest yellow dihydrazone condensation pigment. Some 0.7% pigment is required to formulate a 1/3 SD sample in plasticized PVC containing 5% TiO₂. For comparison, 0.8% is needed of the greener P.Y.93 and 2.1% of P.Y.94, which is even greener at 1/3 SD.

Some 0.35% must be added of the similarly shaded, but generally less fast P.Y.13 to achieve the same result. P.Y.95 is very lightfast. However, incorporated in plasticized or in rigid PVC, P.Y.95 is less lightfast than P.Y.93.

The pigment shows excellent heat stability in polyolefins. 1/3 SD samples may safely be exposed to 290 °C, while 1/25 SD specimens (1% TiO₂) withstand 270 °C. Incorporated in polyolefins, P.Y.95 demonstrates much higher tinctorial strength than most other yellow pigments within its class. Tested in HDPE, the pigment was found to influence the shrinkage of the polymer in injection moulding only to a very negligible extent. In terms of lightfastness, 1/3 SD colourations (1% TiO₂) of this medium equal step 6 on the Blue Scale.

P.Y.95 is also used for PUR as well as for polypropylene spin dyeing, where it is employed for its good heat stability and its high tinctorial strength. However, the pigment is not lightfast and durable enough to meet the standards for application in polyacrylonitrile spin dyeing products, such as canvas awnings (Section 1.8.3.8). P.Y.95 is also utilized in textile printing.

Like other representatives of its class, P.Y.95 has only limited impact on the printing ink industry. It is only used in special-purpose printing inks for high grade prints. Its lightfastness in offset and in metal deco printing corresponds to that of P.Y.93. P.Y.95 exhibits good heat stability. The prints are fast to overcoating and sterilization and in most cases show excellent fastness in special applications (Section 1.6.2). P.Y.95 therefore lends itself to metal deco printing and packaging gravure printing inks, that is, printing inks based on nitrocellulose, polyamide and vinyl chloride copolymers.

2.9.4.2.4 Pigment Yellow 128

At medium tinctorial strength, P.Y.128, after P.Y.94, is the second greenest pigment in the dihydrazone condensation range, and it exhibits very good general fastness properties. The pigment is completely or at least almost completely fast to almost all organic solvents that are used in colouristically important media. The pigment possesses excellent lightfastness and weatherfastness, and it is completely fast to overcoating. This makes it a suitable product for automotive paints, even for original automotive (O.E.M) finishes. The commercial type features a relatively high specific surface area of approximately 70 m² g⁻¹ and is correspondingly transparent. It is mainly used in high grade industrial paints, on which it confers good tinctorial strength and high gloss, and also in architectural paints, for instance in green shades. P.Y.128 is, however, also used in emulsion paints.

The plastics industry uses P.Y.128 mainly in PVC, in which the pigment exhibits average tinctorial strength. 1/3 SD colourations containing 5% TiO₂, for instance, are formulated at 1.35% pigment. The lightfastness is very good and equals step 7–8 on the Blue Scale for 1/3 SD samples. Pigment durability is equally very good in this medium and also in PVC plastisols for coil coating. P.Y.128 also lends colour to elastomers. 1/3 to 1/25 SD colourations in HDPE (1% TiO₂) withstand exposure to 250 °C for 5 min. The shrinkage of polyethylene is only slightly affected. P.Y.128 can also be used for polyacrylonitrile spin dyeing, an area in which it exhibits very good lightfastness and performs excellently in terms of the more important textile fastnesses. Its weatherfastness, however, does not satisfy the requirements for outdoor application. P.Y.128 is therefore used particularly in home textiles such as upholstery.

The printing ink industry uses P.Y.128 particularly in high quality products. The resulting prints, like those made from other dihydrazone condensation pigments, are fast to calendering and sterilization. P.Y.128 lends itself particularly to metal deco printing. It shows good lightfastness. In this respect, it scores approximately one step higher under comparable conditions than the greener P.Y.94 and the somewhat redder P.Y.93, which are members of the same class of pigments.

2.9.4.2.5 Pigment Yellow 166

P.Y.166 is available in Japan. The pigment has generally a better performance as compared with P.Y. 93, 94 or 95. P.Y.166 is used for the colouration of PVC and polyolefines.

2.9.4.3.1 Pigment Orange 31

This pigment is no longer listed as a sales product. It affords a reddish, somewhat dull orange shade. It was recommended particularly for brown shades.

P.O.31 was a useful colourant for plastics and was employed especially in polypropylene spin dyeing. Compared to other members of its class, the pigment exhibits good-to-average tinctorial strength.

P.O.31 is not completely fast to bleeding in plasticized PVC. Its lightfastness in this medium is only satisfactory at higher pigment concentrations, but the pigment possesses excellent heat stability. 1/3 SD HDPE samples (1% TiO₂) are fast up to 300 °C. P.O.31 considerably affects the shrinkage of polyolefins in injection moulding (Section 1.8.3.2). 1/3 SD specimens equal step 6 on the Blue Scale for lightfastness. Good heat fastness made the pigment a suitable candidate especially for polypropylene spin dyeing, mainly to produce shades of brown and beige. P.O.31 was also used in textile printing, most of its textile fastnesses are very good.

2.9.4.3.2 Pigment Red 144

P.R.144 is a medium to slightly bluish red pigment, which probably reigns supreme within its class. It is broad in scope and is mainly used to colour plastics, including spin dyeing products. The commercially available types of the acicular pigment differ considerably in terms of particle size, consequently demonstrating a range of colouristic properties. This is especially true for the tinctorial strength. P.R.144 is less stable to various organic solvents than other dihydrazone condensation pigments of its class, such as P.R.166.

P.R.144 is almost completely fast to migration in plasticized PVC. One of the most tinctorially strong dihydrazone condensation pigments, only about 0.7% P.R.144 is needed to produce a 1/3 SD PVC sample containing 5% TiO₂. Comparative values are listed for other pigments within the same class and also in other classes. P.R.144 is very fast to light. Its weatherfastness in rigid PVC is less satisfactory, it fails to meet the standards of long-term exposure.

Within this group of pigments, P.R.144, incorporated in PE, ranks second only to P.R.221 regarding tinctorial strength. Some 0.13% pigment is required to produce 1/3 SD specimens containing 1% TiO₂. In HDPE, P.R.144 withstands temperatures up to 300 °C at 1/3 to 1/25 SD, both with and without TiO₂. It considerably affects the shrinkage of the plastic at processing temperatures between 220 and 280 °C, which should be taken into consideration if the pigment is to be used in injection moulding. P.R.144 has excellent lightfastness: 1/3 SD colourations in HDPE containing 1% TiO₂ equal step 7–8 on the Blue Scale, while transparent samples even reach step 8.

P.R.144 is also suited to use in other plastics, such as polystyrene, polyurethane, elastomers or cast resins, including those made from unsaturated polyester.

Good heat stability and lightfastness make P.R.144 a suitable candidate especially for polypropylene spin dyeing. It is equally important for polyacrylonitrile spin dyeing, but does not satisfy the demands for use in canvasses. The more important textile fastnesses are very good, but the pigment is not completely stable to dry and wet crocking. In this respect, it scores as high as step 4 on the 5 step Grey Scale.

The printing ink industry uses P.R.144, like other pigments of its class, primarily in high quality products. The commercial types exhibit specific surface areas between approximately 50 and 90 m² g⁻¹, which makes for more or less transparent prints. Numerous fastnesses that are important for packaging purposes (Section 1.6.2), such as resistance to soap, butter, cheese, paraffin, acid and alkali, are perfect. P.R.144 is fast to clear lacquer coatings and sterilization, which makes it suitable for metal deco printing. The pigment has very good lightfastness; letterpress proof prints equal step 6 to step 7 on the Blue Scale, depending on the pigment area concentration. In this respect, P.R.144 (at low pigment area concentrations such as 1/25 SD) is somewhat inferior to P.R.166.

Throughout the paint industry, P.R.144 functions as a pigment in general industrial coatings, automotive finishes and architectural paints.

2.9.4.3.3 Pigment Red 166

P.R.166 affords clean yellowish shades of red. It is broad in scope and in this respect resembles the somewhat bluer dihydrazone condensation pigment P.R.144. Its main area of application, however, is in plastics and in spin dyeing.

In the plastics sector, P.R.166 is used primarily to colour PVC and polyolefins. The pigment is almost completely fast to bleeding in plasticized PVC. Similarly coloured pigments of other classes perform poorer in terms of migration and lightfastness and also regarding heat stability. These pigments are considered suitable alternatives to P.R.166 only where the application requirements are less stringent.

P.R.166 exhibits medium-to-good tinctorial strength compared to other pigments covering the same range of shades. Between 0.9% and 1.2% pigment is needed, for instance, to produce 1/3 SD PVC samples containing 5% TiO₂. The exact amount depends on the grade. Commercial types of this pigment provide medium to high hiding power. The lightfastness and weatherfastness of P.R.166 in PVC are very good. However, its weatherfastness is often not sufficient to meet the standards of long-term outdoor exposure.

P.R.166 shows excellent heat stability in polyolefins, for instance in HDPE. 1/3 SD samples containing 1% TiO₂, for instance, are fast up to 300 °C. This high heat stability in HDPE is compromised by the fact that P.R.166 causes considerable distortion in this medium, irrespective of the processing temperature. Transparent HDPE samples equal step 8 on the Blue Scale for lightfastness, while corresponding polypropylene colourations match step 7. 1/3 SD colourations containing 1% TiO₂ reach step 6–7 and step 7, respectively. High lightfastness makes P.R.166 a suitable candidate for polypropylene spin dyeing. Its application in polyacrylonitrile spin dyeing is restricted by the fact that it fails to satisfy the high lightfastness and durability standards of materials such as canvasses. P.R.166 exhibits perfect or almost perfect textile fastnesses. It is also used in polystyrene, rubber and other elastomers. P.R.166 is encountered in polyurethane that is intended for use in coatings, and applied in cast resins made from unsaturated polyester or aminoplast resins.

P.R.166 is recommended in the paint field for use in high grade industrial paints, for original automotive finishes, and for automobile refinishes, as well as for architectural paints and emulsion paints. Incorporated in baking enamels, deep shades (1:1 TiO₂) and white reductions (1:20 TiO₂) exhibit good weatherability. However, P.R.166 is not quite as weatherfast in these media as the somewhat yellower and considerably cleaner Anthanthrone pigment P.R.168 (Section 3.7.4.2). Dispersed in an alkyd-melamine resin that is baked at 120 °C, the pigment is almost completely fast to overcoating.

Like other members of its class, P.R.166 is used throughout the printing ink industry for high grade prints, especially for packaging purposes. It basically possesses all-round suitability for various printing techniques. P.R.166 is fast to clear lacquer coatings and to sterilization, which qualifies it particularly for use in metal deco printing. It provides very lightfast prints: 1/1 to 1/3 SD letterpress proof prints equal step 7 on the Blue Scale. P.R.166 is thus faster to light than the somewhat bluer dihydrazone condensation pigment P.R.144. P.R.166 shows excellent fastness to agents such as alkali, acids, soap, fats, paraffin and others, which are frequently encountered in packaging printing inks. The pigment is also used in textile printing.

2.9.4.3.4 Pigment Red 214

P.R.214 affords a medium to bluish shade of red. It exhibits average stability to organic solvents, an aspect in which it resembles other members of its class. P.R.214 is very lightfast and fast to overcoating. Its weatherfastness, however, does not quite reach the standards of other types of pigments within its class: it is somewhat inferior, for instance, to that of P.R.242.

The paint industry uses P.R.214 primarily for various types of industrial finishes. The pigment demonstrates very good tinctorial strength in plastics. Some 0.13% pigment is required, for instance, to produce 1/3 SD HDPE colouration containing 1% TiO₂. P.R.214 produces a shade which, although cleaner, is very similar to that of P.R.144, a member of the same class of pigments. The two pigments also show similar tinctorial strength. The fact that P.R.214 considerably affects the shrinkage of the plastic makes it less important in injection moulding. It should be emphasized that P.R.214 possesses excellent heat stability. 1/3 to 1/25 SD HDPE samples containing 1% TiO₂, as well as transparent specimens of the same depth of shade, are fast to temperatures up to 300 °C. P.R.214 is also used in PP spin dyeing. It shows good textile fastness. A pigment with high tinctorial strength in plasticized PVC, P.R.214 is not completely fast to bleeding in this medium. The pigment is also recommended for use in polystyrene and in several engineering plastics.

Like other representatives of its class, P.R.214 lends itself particularly to use in high grade printing inks that are targeted for purposes such as posters, packaging gravure printing inks for PVC films, and metal deco printing. The prints exhibit good fastness properties, they are stable to soap, alkali and acids and withstand temperatures up to 200 °C. They are also fast to clear lacquer coatings and to calendering.

2.9.4.3.5 Pigment Red 220

P.R.220 affords a yellowish red shade, which is somewhat bluer than that of P.R.166 and slightly yellower than that of P.R.144. P.R.220 is considerably weaker, however, than the latter: 0.31% pigment is required to produce 1/3 SD HDPE samples containing 1% TiO₂. Although P.R.220 affects the shrinkage of injection-moulded HDPE at processing temperatures of 220 °C, it does this to an extent that is acceptable for most purposes. The effect is negligible at 260 °C. 1/3 SD specimens are fast to temperatures up to 300 °C and equal step 7 on the Blue Scale for lightfastness. P.R.220 is thus a suitable candidate for polypropylene spin dyeing and is also used in polyacrylonitrile spin dyeing.

2.9.4.3.6 Pigment Red 221

P.R.221 is a slightly bluish red pigment. Its main field of application is also in plastics, especially in PVC and in PUR. P.R.221 is sufficiently fast to migration in plasticized PVC to satisfy the requirements for most applications. The pigment demonstrates very high tinctorial strength in plasticized PVC; its full shade and related shades are the strongest in its class. Only 0.58% pigment is needed to produce a 1/3 SD sample containing 5% TiO₂. The tinctorial strength of lighter shades corresponds to that of other dihydrazone condensation pigments in the red range. On the other hand, P.R.221 is less lightfast than many other types. The pigment does not exhibit plate-out in PVC.

P.R.221 is not recommended for use in polyolefins, since it also causes considerable distortion. It has, however, gained recognition as a pigment for high grade printing inks, especially for metal deco printing.

2.9.4.3.7 Pigment Red 242

P.R.242 affords a yellowish red shade, referred to as scarlet. It exhibits good-to-excellent resistance to organic solvents, such as alcohols, esters, ketones and aliphatic hydrocarbons. The pigment is more soluble in aromatic hydrocarbons. P.R.242, like other members of its class, is fast to alkali and acid.

P.R.242 is used throughout the plastics industry as a colourant for PVC as well as for polyolefins, polystyrene and other engineering plastics. It exhibits average tinctorial strength: 0.2% pigment is required to formulate 1/3 SD HDPE samples containing 1% TiO₂. P.R.242 is heat stable up to 300 °C. 1/25 SD specimens containing 1% TiO₂, as well as transparent samples at 1/3 to 1/25 SD, are stable to temperatures up to 280 °C. The pigment has a considerable effect on the shrinkage of the plastic. It is of interest to PP spin dyeing, for which a special-purpose pigment preparation is available.

In plasticized PVC, P.R.242 shows good fastness to bleeding and provides average tinctorial strength. 1/3 SD colourations containing 5% TiO₂ require 1.1% pigment. Good heat stability makes P.R.242 a suitable candidate for use in polystyrene, ABS, PMMA and polyester.

P.R.242 is an equally valuable product for paints, especially for various types of industrial paints. It is also recommended for use in automotive finishes. Both lightfastness and weatherfastness are excellent, but do not quite reach the levels of the appreciably yellower anthanthrone P.R.168. P.R.242 is fast to overcoating and heat stable above 180 °C. It is also employed in emulsion paints based on synthetic resin.

In the printing ink field P.R.242 is utilized to colour high grade systems, such as printing inks for PVC films or metal deco printing. P.R.242 exhibits good fastness properties in application. It shows some bleeding in styrene monomer, which makes the pigment unsuitable for decorative printing for laminated plastic sheets based on styrene/polyester.

2.9.4.3.8 Pigment Red 248

P.R.248 was introduced to the market a few years ago, but marketing has already been discontinued. It was used to colour plastics, especially polyolefins and polystyrene. It provides bluish shades of red.

1/3 SD HDPE samples containing 1% TiO₂ are heat stable up to 290 °C. The distortion problem in injection-moulded HDPE gains significance as the processing temperature increases. While at 220 °C the material is distorted to a still acceptable degree, considerable shrinkage is observed at 250 °C and higher temperatures. P.R.248 is one of the types in its class that provides high tinctorial strength. Its strength is comparable to that of P.R.166: 1/3 SD systems containing 1% TiO₂ are formulated at 0.16% pigment. 1/3 SD HDPE samples equal step 7 on the Blue Scale for lightfastness. P.R.248 was not recommended for polypropylene spin dyeing.

P.R.248 exhibits excellent bleed resistance in plasticized PVC. Transparent specimens equal step 8 on the Blue Scale for lightfastness, while 1/3 SD samples match step 7. The pigment does not perform as well in terms of weatherfastness, for instance in PVC plastisols for coil coating. P.R.248 was also recommended for use in elastomers, polyurethane and unsaturated polyester.

2.9.4.3.9 Pigment Red 262

P.R.262 is a comparatively recent product that affords bluish shades of red. P.R.262 is recommended for polypropylene spin dyeing, but possesses all-round suitability for other applications, as long as the requirements do not exceed the fastness properties of this class of pigments.

2.9.4.3.10 Pigment Brown 23

P.Br.23 confers reddish shades of brown on its application media. In numerous areas, this pigment is in direct competition with the colouristically similar, somewhat redder and more transparent P.Br.25.

In terms of stability to organic solvents, P.Br.23 performs like other red pigments within its class. It is thus somewhat inferior to the yellow products. Regarding fastness to various ketones, esters and alcohols, as well as to dioctyl phthalate and dibutyl phthalate, P.Br.23 equals step 3–4 and step 4, respectively, on the 5 step scale. P.Br.23 is broad in scope, but its main field of application is in plastics.

Incorporated in plasticized PVC, P.Br.23 exhibits average to good tinctorial strength: 0.75% pigment is required to produce 1/3 SD samples containing 5% TiO₂. The pigment is not entirely bleed resistant (step 4), but exhibits excellent lightfastness and weatherfastness. In rigid PVC, for instance, P.Br.23 is fast to long-term exposure. It is primarily used to colour window frames and similar articles.

P.Br.23 shows excellent heat stability in polyolefins. 1/3 SD samples containing 1% TiO₂, as well as transparent colourations at 1/3 SD in HDPE, are stable to exposure to 300 °C for 5 min. In injection moulding, P.Br.23 considerably affects the shrinkage of the plastic at 220 °C, an effect that diminishes with increasing temperature (Section 1.8.3.2).

P.Br.23, like other members of this series of pigments, is a suitable colourant for elastomers. However, due to the low fastness of rubber itself, P.Br.23 is only used in high grade elastomers. The pigment is also recommended for use in polystyrene. Transparent polystyrene samples are fast to exposure to 280 °C for 5 min, while light shades containing TiO₂ (0.01% pigment + 0.5% TiO₂) are only stable up to 240 °C. In terms of lightfastness, these samples equal step 7 and step 5, respectively, on the Blue Scale. Good fastness properties make P.Br.23 a suitable candidate for polyacrylonitrile spin dyeing, although its lightfastness and weatherfastness do not satisfy the stringent requirements for use in applications such as canvasses.

The paint industry utilizes P.Br.23 particularly in industrial paints. As a result of its lack of solvent fastness, P.Br.23 is not completely fast to overcoating if it is used in baking enamels at a curing temperature of 120 °C. It is, however, very fast to light and weather. In deep shades (1:1 TiO₂), P.Br.23 equals step 8 on the Blue Scale for lightfastness, while light shades (1:20 TiO₂) match step 7–8. To assess their weatherfastness, baking enamels containing P.Br.23 were subjected to two years of outdoor exposure. The colourations were found to equal step 4–5 and step 3–4 on the Grey Scale, respectively (Section 1.6.6). In the automotive industry, P.Br.23 is recommended for use in original automotive and repair finishes. The list of applications also includes emulsion paints and high grade architectural paints. Moreover, the pigment is also found in various types of wood stains and other special-purpose media.

P.Br.23 possesses all-round suitability for all printing applications. Its shade and its fastness properties make it particularly suitable for printing imitation wood, for instance on PVC. The prints show good fastness to clear lacquer coatings. Sterilization causes somewhat of a yellow shift. P.Br.23 prints demonstrate good lightfastness: under standardized conditions, 1/1 to 1/25 SD letterpress proof prints equal step 6–7 and step 6 on the Blue Scale, respectively, depending on the substrate.

2.9.4.3.11 Pigment Brown 41

This dihydrazone condensation pigment affords very yellowish shades of brown, covering the range of the displaced benzimidazolone pigment P.Br.32.

Incorporated in PVC, P.Br.41 provides medium tinctorial strength and good hiding power. The pigment is not completely fast to bleeding in plasticized PVC. In polyolefins, P.Br.41 also exhibits medium tinctorial strength: 0.21% pigment is required to formulate 1/3 SD HDPE samples containing 1% TiO₂. Such specimens are stable up to 300 °C. P.Br.41 shows excellent weather fastness in rigid PVC and in impact-resistant PVC, which is also true for reductions with TiO₂. The pigment even satisfies the requirements of long-term exposure. It is used, for instance, in window frames made of impact-resistant PVC.

Incorporated in paints, P.Br.41 exhibits equally high hiding power, which makes it a less attractive product for use in metallic finishes. Its tinctorial strength in these media is comparatively poor. However, P.Br.41 is completely fast to overcoating. The commercial grade shows considerable flocculation in various paint systems.

2.9.4.3.12 Pigment Brown 42

P.Br.42 provides yellowish shades of brown, which are on the yellowish side of P.Br.41. The pigment is particularly recommended for use in rigid PVC, in which it exhibits medium tinctorial strength: 0.85% pigment is required to produce 1/3 SD samples containing 5% TiO₂. P.Br.42 is very lightfast and weatherfast, a quality that makes it suitable for long-term exposure. Incorporated in plasticized PVC, P.Br.42, like other brown pigments within its class, is not completely bleed resistant (step 3–4).

1/3 SD P.Br.42 samples in HDPE containing 1% TiO₂ are stable up to 280 °C for 5 min, which indicates very good heat stability. Some 0.22% pigment is needed to formulate such 1/3 SD samples.

P.Br.42 affords somewhat dull, yellowish shades of brown in industrial finishes, such as alkyd melamine resin systems. The coating shows a certain opacity; the pigment, however, is recommended to be used in metallics and as opaque pigment as well.