Organic pigment

Organic pigments are used to color and/or cover a substrate. They have gained importance because the use of some inorganic pigments containing heavy metals has been legally restricted. 

The most important class of organic pigments in terms of production are the azo pigments. Other important pigment classes include metal-complex pigments (e.g., copper phthalocyanine) and higher polycyclic compounds (e.g., anthraquinone, quinacridone, isoindolinone, and perylene). 

Properties. Lightfastness and weather resistance are the most important properties of paint pigments. The organic pigments should be colorfast and stable towards radiation, heat, and atmospheric substances. Pigments may also be partially responsible for photochemical or thermal degradation of the binder which leads to deterioration of optical film properties (e.g., gloss). 

Migration should not occur when organic pigments are used in paints that are applied in differently colored layers on top of each other. Resistance to migration depends on the pigment, binder, and solvent. 

The pigment should be heat stable because it may be subject to increasing temperature during dispersion, stoving, or use. 

Organic pigments generally provide higher intensity and brightness of 

Organic pigments are shown in Table 4.2. For selected pigments, the chemical names are shown in Table 4.3 

The color index (C.I.) is a reference database held jointly by the Society of Dyers and Colourists and the American Association of Textile Chemists and Colorists (18). 

Preferably, a coloring material for inkjet printing has an average particle diameter of 10-100 nm. When the average particle diameter is 200 nm or less, color reproducibility is favorable and the droplet ejecting properties are favorable. Further, when the average particle diameter is 10 nm or more, light resistance is favorable. The particle 

Pigment Black 1 C.l. Pigment Black 6 C.l. Pigment Black 7 

2-[4-[4-(l-anilino-l,3-dioxobutan-2-yl)diazenyl-3-chlorophenyl]-2-chlorophenyl]diazenyl-3-oxo-N-phenylbutanamide Yellow 128 79953-85-8 

The latest category of special-effect pigments is diffractive pigments, in which interference is produced by diffraction technology. These pigments are produced by vacuum deposition on specially patterned surfaces. 

Organic pigments are synthesized from different petrochemical intermediates therefore, thousands of molecules are possible due to wide latitude in selection of petrochemicals, but only a few hundred are commercially produced that have balanced price and performance. Discussing all the pigments individually is outside the scope of this book therefore, selected important organic pigment families are briefly discussed here. 

There is a large number of organic pigments. They are carbon black,s, phthalo-cyanines, quinacridones, perylenes, basic and acid colorants, anthraquinones, diazines, isoindolidones, azo and azo condensation pigments [2,10]. 

Carbon blacks are the most used among all pigments. They have a high pigmentation power and they improve many of the physical properties of polymers, such as light stability, processibility, and mechanical properties. Channel black has been banned in the United States since 1976 only all gas-fired channel black is still permissible in food contact applications. Other carbon blacks, mainly thermal and lamp carbon blacks, are used in rubber reinforcement acetylene carbon black is interesting for its electrical conductivity and is used as an antistatic agent. Activated carbon is also used in some cases. 

Pyrazolone reds are used to color PVC and rubbers because of their light stability, but they tend to exude and have low thermal stability. 

Perylenes form a group of pigments with shades going from yellow to brown  

Basic and acidic dyes offer only a narrow selection of colors. Their overall quality is low and their use is very limited in the plastics industry. 

Carbon blacks Iron chromite Iron oxide 

Orange Azos Benzimidalones Pyrazolones Quinacridones Cadmium sulfide Cadmium sulfoselenides Lead chromates Lead molybdate 

Red Benzimidalones Disazo s Quinacridones Pyrazolones Cadmium sulfoselenides Iron oxide 

Yellow Benzimidalones Disazo s Cadmium sulfide Chrome titanate 

Iron oxide Lead chromate Nickel titanate Zinc chromate 

Trade names include Sicorin RZ (BASF, Germany) Alkophor 827 (Henkel, Germany) and Irgakor 252 (Ciba-Geigy, Switzerland). 

The zinc salt of 5-nitroisophthalic acid [60580-61-2] [5.49] is produced as an easily dispersible pigment by a wet chemical process from 5-nitroisophthalic acid and zinc oxide [5.180]. It has the following properties  

A less expensive replacement for zinc chromate is obtained by combining the zinc salt of 5-nitroisophthalic acid with zinc phosphate pigments (Section 5.2.2.5) [5.65], [5.67], [5.181]. A concentration of 0.5-2.0% based on the liquid coating is recommended. 

The electrochemical anticorrosive action of the zinc salt of 5-nitroisophthalic acid is comparable with that of zinc potassium chromate [5.182]. 

Other Organic Anticorrosive Pigments. The following organic anticorrosive pigments are either commercial products or have been reported in the literature  

Naturally occurring dyestuff, for example, indigo shrub, madder root, cochineal insects, Persian berries, and the like, have been known and used for centuries. These soluble dyes were rendered insoluble in water by treatment with suitable precipitating agents and used as lakes. With the increase in the variety of synthetic dyes available and multiplicity 

Red pigments. Toluidine red, barium lithol red, and BON red are the three widely used organic red pigments. 

Barium lithol red (Fig. 7.4) is bright red in color and is suitable for interior use only because of its relatively poor light-fastness and poor chemical resistance [10]. 

Yellow pigments. The most common organic yellow pigments are members of the insoluble azo class of pigments and they belong to four main classes monoarylide yellows, diarylide yellows, benzimidiazolone yellows, and heterocyclic yellows. 

The Hansa yellow (Fig. 7.6) is a bright monoarylide often used in trade sales and emulsion paints. They have low opacity in paint films and are soluble in aromatic solvents [10]. 

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Materials. Beside inorganic materials (eg, barium chloride/fluoride crystals, doped with 0.05% samarium), transparent thermoplasts are preferred for the PHB technique, eg, poly (methyl methacrylate) (PMAIA), polycarbonate, and polybutyral doped with small amounts of suitable organic dyes, organic pigments like phthalocyanines, 9-arninoacridine, 1,4-dihydroxyanthraquinone [81-64-1] (quinizarin) (1), and 2,3-dihydroporphyrin (chlorin) (2). 

Metallic Powders. These are usually either aluminum or bronze flakes and vary ia shades from silver to gold, depending on the composition of the metal used. The silver powders can also be toned with organic pigments to produce golds or copper shades usiag transparent yellow or red pigments. 

Phthalocyanine pigments account for approximately 23% of the total worldwide organic pigment consumption of 225,000 tons. Approximately 20,000 t are used in printing inks, 10,000 t in paints, 9,000 t in plastics, 3,000 t in textiles, 7,000 t in dyes, and 2,000 t in specialty uses. Table 1 shows the worldwide distribution of cmde phthalocyanine capacity. The production history of phthalocyanine in the United States from 1980 to 1990 is given in Table 2 (161). The 1990 prices of phthalocyanine blue and green pigments were ca 11—22/kg and 21—27/kg, respectively. 

W. Herbst and K. Hunger, Industrial Organic Pigments, VCH, Weinhekn, Germany, 1993. 

Table 1. Selected Commercial Synthetic Organic Pigments...

Lakes are either dry toner pigments that are extended with a soHd diluent, or an organic pigment obtained by precipitation of a water-soluble dye, frequendy a sulfonic acid, by an inorganic cation or an inorganic substrate such as aluminum hydrate. 

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