Benzimidazolone pigments

DFG-Farbstoffkommission (Dyestuff Commission) / Ringbuch - Kosmetische Farbemittel, Colours for Cosmetics (1991), C-Rot 12. 

Benzimidazolone pigments [1, 2] derive their name from the 5-aminocarbonyl benzimidazolone group (22), which is common to all pigments within this group  

Although, strictly speaking, it would be more precise to refer to such compounds as benzimidazolone azo pigments, the convention of listing them as benzimidazolone pigments will be followed. 

Basically, there are two ways of improving the solvent and migration fastness of an organic pigment  

Initially, pigments had been found which could be rendered insoluble in organic media if they were converted into polar structures molecules containing sulfo or carboxylic acid groups form insoluble salts with alkaline earth metals or manganese ( lakes , Sec. 2.7). 

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Benzil, 3 594 14 594 Benzilonium bromide, 4 359t Benzimidazoles, microwave-assisted synthesis of, 16 574-575 Benzimidazolethiols, 25 197 Benzimidazolone dioxazine, 19 446 Benzimidazolone pigments, 19 432 433 Benzimidazolone Violet, pigment for plastics, 7 367t Benzine, 3 597... 

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 Where sterilization fastness is required, P.R.146 is superseded by P.R.185, a benzimidazolone pigment, which is its coloristically closest neighbor. 

A few years ago the pigment was withdrawn from the market.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 colored 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 coloristically related maroon the difference is 2 to 3 steps on the Blue Scale. 

The chemistry and manufacture of the coupling components for yellow/orange and red benzimidazolone pigments are treated separately. 

Yellow and Orange Benzimidazolone Pigments -Coupling Component... 

Red benzimidazolone pigments, which cover the entire range of shades in the red and brown part of the spectrum, are based on the following general structure ... 

Coupling reactions, which are commonly carried out in aqueous media, afford benzimidazolone pigments, usually in the form of hard particles. Thermal after-treatment is necessary to adapt these crude products to the demands of technical application (Sec. 2.2.3). 

Single crystals [3-5] of a yellow (27) and a red (28) benzimidazolone pigment have been studied by X-ray diffraction analysis. 

In the red pigment, these bands consist of a sequence of individual molecules which are interlocked with each other (30). In terms of molecular structure, benzimidazolone pigments thus represent an entirely new type of azo pigment. 

The benzimidazolone moiety, a fundamental feature of all benzimidazolone pigments, is responsible for the high fastness of these pigments to the solvents which are typically found in application media. In this respect, benzimidazolone pigments perform much better than their counterparts in the monoazo yellow and... 

Naphthol AS pigment series. Excellent fastness to solvents and chemicals is accompanied by good migration fastness. Benzimidazolone pigments do not bloom, and most of them show good and some even excellent bleed fastness and fastness to overcoating. All benzimidazolone pigments, with one exception (P.Y.151), are inert to alkali and acid. Most of them disperse easily in the common application media. 

Polymorphism is a common phenomenon in benzimidazolone pigments. However, each pigment is marketed in only one of its crystal modifications. 

Benzimidazolone pigments are used throughout the paint industry to lend color to all types of industrial finishes. 

Several benzimidazolone pigments are suitable candidates for use in powder coatings based on polyester, acrylic, or polyurethane resin. These pigments satisfy the heat requirements of this application and do not plate out in these media (Sec. 1.6.4.1). Various benzimidazolone pigments even meet the particularly high thermal standards of coil coating. These pigments are also suitable for use in architectural and emulsion paints. 

Benzimidazolone pigments, especially those covering the red range of the spectrum, were originally developed and used mostly for plastics. None of them were found to adversely affect the physical characteristics of their host medium. Benzimidazolone pigments do not bloom in plasticized PVC and other polymers. They are usually bleed resistant under typical application conditions. 

In PVC, most benzimidazolone pigments are heat stable up to 220°C. They have excellent to outstanding lightfastness. Some representatives are very weather-fast in impact resistant PVC types and in rigid PVC and even withstand long-term weathering. Various benzimidazolone pigments are used, for instance by the automobile industry, in PVC plastisols to lend color to synthetic leather. 

Benzimidazolone pigments are also used to color polystyrene, ABS, and other polymers which are processed at high temperature. A number of grades show excellent lightfastness and also satisfy the heat requirements for use in unsaturated polyester without affecting the hardening of the polymer. 

Various benzimidazolone pigments are heat stable enough to be used in polypropylene spin dyeing. Several types find extensive use in the spin dyeing of other fibers, such as polyacrylonitrile, viscose reyon, and vicose cellulose, or secondary acetate. 

Commercial types of benzimidazolone pigments are also sold for use in solvent-based wood stains and other special-purpose media which have not been mentioned previously. 

Table 23 lists commercially available benzimidazolone pigments. It should be noted that pigments in the red range are often derived from a diazonium component carrying a methoxy group in ortho position to the azo group. 

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