Colouration cationic direct dyes

The earliest polymeric cationic aftertreatments stemmed from the development of crease-resist finishes for cellulosic fibres. One such, promoted specifically for its colour fastness improvements when applied as an aftertreatment to direct dyeings, was a condensation product of formaldehyde with dicyandiamide (Scheme 10.82). Many similar compounds followed, such as condensation products of formaldehyde with melamine (10.212), polyethylene imine) with cyanuric chloride (10.213) and alkyl chlorides with polyethylene imine) (10.214 R = alkyl). 

There are many direct dyes of which the wet-fastness is improved by after-treatment with a copper salt such as copper sulphate or, alternatively, spedally prepared mixtures of copper salts and cationic resin-fixing scents. Some of the dyes which have been specifically developed for this treatment are the Cuprofix, the Cuprophenyl, and the Coprantine colours, as well as many others not necessarily classified in distinctive groups. Examples of mixtures of copper salts and cationic products for after-treatment are Resofix C and Ct rantex B. 

Direct dyes like the acid ones belong to strong electrolytes and are completely dissociated in water baths into coloured anions and sodium cations ... 

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