Application, Manufacture of Dye Intermediates and Dyes

There are, of course, many varieties in each of these chemical classifications, so that the result is hundreds of individual dyes each with its own specific characteristics for hue and use on substrates. Dyers have arranged this very complex and large group of chemical products into ten categories arranged by the method of application to the fiber or substrate acid dyes, azoic dyes, basic dyes, direct dyes, disperse dyes, reactive dyes, solvent dyes, sulfur dyes, vat dyes, and mordant dyes. It is in these categories that dyestuffs are discussed in the trade. 

Colour Index, a publication sponsored by the Society of Dyers and Colourists (England) and the American Association of Textile Chemists Colorists, is the most widely recognized source for the classification of dyes. The dyes are classified by usage class and hue, and the chemical class usually is disclosed. When known, the chemical constitution of the dye is identified by a five-digit constitution number. 

The two major types of colorants produced today are dyestuffs and pigments. The difference between these products is evident from the definitions a dyestuff is normally a water-soluble or water-dispersible compound that, is capable of being absorbed into the substrate, whereas a pigment is normally a water-insoluble compound that requires a binder or is entrapped within the matrix of the substrate. The majority of pigments are soluble in solvents and plastics, and both dyes and pigments impart very high tinctorial value for the amount used to color a product. The major end use for dyes is in the textile, leather, and paper industries. Pigments find major uses in paint, ink, and plastic industries. 

The textile industry uses a large number of dyestuffs from each of the dye categories, the choice depending on the shade, fiber used, dyeing process, end use of the textile product, requirement for fastness, and economic considerations. To provide an understanding of the interrelationships that exist among the various dye classes and fiber types, a brief survey of the major textile fibers follows. 

In this survey, commercially important textile fibers are grouped by their origin. First there are the natural fibers from plant sources, cotton and flax, and those from animal sources, wool and silk. A second group consists of those fibers that are regenerated or chemically modified natural materials—the rayon and acetate fibers. The final group consists of the synthetic fibers, which include nylon, polyester, acrylics, polyolefins, and spandex. 

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