Application of Azo Dyes

For stretch cord and similar articles made of PA-CEL blends, metal-complex dyes that are resistant to reducing agents are added to dye the PA fibers, because only a few sulfur dyes stain PA sufficiently. Water-soluble sulfur dyes can be combined with selected reactive dyes. In this manner, more brilliant shades are obtained. 

An azo dye is formed from a Naphtol AS coupling component and a diazotized base (developing component) under suitable conditions (see Section 3.7). This coupling is carried out on the fiber itself. If components without solubilizing groups are used, the dye formed is an insoluble pigment, and dyeings with excellent fastness properties are achieved. Today, azoics are used primarily for deep clear shades, like red and purple. 

On cellulose acetate, developing dyes are still used, but for black only. Although dyeings are produced that are especially fast to wet treatments, the process is more tedious than dyeing with direct disperse dyes. 

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The application of azo dyes to proteins is complicated by the fact that the diazo compound can enter into combination with the fibre itself (Everkst AND Wallwork, 1934, 50, 37). The only practical application... 

The extensive patent literature describing the production and application of azo dyes based on amino-l,2,4-thiadiazoles is briefly summarized below under a separate heading. 

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