Abstract
Cationic (or basic) dye complex pigments are classical organic pigments obtained from water-soluble cationic dyes for textiles, mainly of triarylmethine (arylcarbonium ion) types, which are precipitated using large inorganic counterions, especially those derived from heteropolyacids such as phosphotungstomolybdic acid or, to a certain extent, using the counteranion derived from copper ferrocyanide. This range of pigments includes red, violet, blue and green products, offering brilliant shades, high color strength and good transparency. They are well suited to printing ink applications, although they provide only moderate levels of fastness properties. The pigments are synthesized by treating aqueous solutions of the dyes under highly controlled conditions with solutions of the heteropolyacids, prepared in situ. The copper ferrocyanide salts are obtained by treatment of potassium ferrocyanide with sodium sulfite in water, and subsequently with solutions of the cationic dye and copper (II) sulfate. The pigments are primarily used in inks for packaging and advertising materials. However, they have little use outside printing inks. Reflex or alkali blue pigments are structurally related cationic dye derivatives which are inner salts of the dye structures and are also used in printing inks.
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