Aftertreatment with Cationic Auxiliaries

Aftertreatment of substantive dyeings with cationic organic substances has lately begun to gain in importance. Improvements are obtained in particular in wetfastness properties, especially fastness to water, washing, and wet pressing, as well as fastness to perspiration and cross-dyeing. 

The cationic compounds precipitate the (anionic) dyes from their aqueous solutions and on the fiber form higher molecular mass, sparingly soluble, saltlike compounds with the dyes. Removal of the latter from the fiber is thus made more difficult. A number of companies have compiled their own ranges of this type of aftertreatment agent. 

Cationic textile auxiliaries can be divided into two groups quaternary ammonium compounds and cationic formaldehyde condensation resins. 

Quaternary Ammo nium Compounds. These contain aliphatic and/or cycloaliphatic radicals (R1 -R4 in Eq. 1), of which at least one is a long-chain alkyl radical (with more than five C atoms). The compounds react with the dyes in accordance with the following pattern  

Use is made, for example, of cetyldimethylbenzylammonium chloride and pyridinium compounds of the type 

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The group of direct dyes with aftertreatment includes direct dyes that, after being applied to the fiber by the usual method, are subjected one of the following aftertreatments (1) Aftertreatment with cationic auxiliaries, (2) aftertreatment with formaldehyde, 3) diazotization of the dye on the fiber and coupling with suitable components (diazotization dyes), and (4) aftertreatment with metal salts. 

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