Classification of Dyes

Dyes may be classified according to their chemical structure or the method by which they are applied to the substrate. The dye manufacturers and dye chemists prefer the former approach of classifying dyes according to the chemical type. The dye users, however, prefer the latter approach of classification according to the application method. 

Classification by application or usage is the principal system adopted by the color index (Cl) [6]. The classification of dyes according to their usage is summarized in Table 8.1, which is arranged according to the Cl apphcation classification. It shows the principal substrates, the methods of apphcation, and the representative chemical t5q es for each apphcation class [7, 8]. 

The definition, chemical nature, the type of substrate best suited for each class, and the mechanism by which the dye is retained by the substrate of the various apphcation classes are discussed in the following sections. 

Acid dyes. Acid dyes are water-soluble anionic dyes, containing one or more sulfonic acid substituent or other acidic groups. An example of the class is acid yellow 36. 

Class Principal substrates Method of application Chemical types 

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Azo Dyes. The Colourindex classifications of dyes depend more on their historical eady use than on their stmctures, eg. Oil Orange is named Solvent Yellow 14, and a yellow for synthetic fibers is Disperse Yellow 23. 

Usage Glassification. It is advantageous to consider the classification of dyes by use or method of appHcation before considering chemical stmctures in detail because of dye nomenclature and jargon that arises from this system. 

The surfactants used as textile auxiliaries can be divided into four major groups, depending on the type and distribution of the polar forces, an arrangement broadly resembling the ionic classification of dyes. The general scheme is shown in Table 8.1. 

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