Paper Organic Pigments

Statistics for the production of basic dyes include those products hsted as cationic dyes, eg, cyanines, for dyeing polyacrylonitrile fibers and the classical triaryhnethane dyes, eg, malachite green, for coloring paper and other office apphcations (2,53). Moreover, statistics for triaryhnethane dyes are also hidden in the production figures for acid, solvent, mordant, and food dyes, and also organic pigments. Between 1975 and 1984, the aimual production of basic dyes in the United States varied from 5000—7700 t. However, from 1985—1990, aimual production of basic dyes varied from 5000—5700 t, and the annual sales value increased from 56 to 73 million per year. 

Present usage of triaryknethane dyes, ca 1996, is confined mainly to nontextile appkcations. Substantial quantities ate used in the preparation of organic pigments for printing inks, pastes, and for the paper printing trade, where cost and brilliance of shade are more important than lightfastness. 

Organic pigments are used to color a variety of media. It is useful to distinguish between three primary fields of application the coatings and paints industry, the printing inks industry, and the plastics and fibers industry. Besides, organic pigments are used for special purposes, for instance in office materials and in the mass coloration of paper. 

Typically the chromophores used are pH sensitive, i.e. acidochromic or ionochromic (see section 1.4), and the medium is one whose pH varies with temperature. A variety of pH sensitive chromophores are known that are readily synthesised and can be modified to provide a wide range of shades. Application of these pH sensitive dyes in pressure and thermally sensitive papers for digital printing, e.g. fax papers, where the whole object is for the process to be irreversible, will be covered under ionochromism. The main area of application for reversible indirect thermochromic materials is as thermochromic organic pigments, as will be described below (section 1.3.4.1). 

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