Decolourising baths used to dye or rinse oxidised aluminium

摘要

Spent aq. Al dyebath or rinsing bath contg. anionic dyes is treated by adding a water-soluble organic, N-contg., basic or cationic polymer (I), opt. together with an inorganic pptn. agent. The resulting ppte. is removed by sedimentation and/or filtration. Pref. (I) has MW 1000-1million (10000-0.5 million) and is the reaction prod. of (a) dicyandiamide with HCHO(or homologue); diethylene triamine (and opt. epichlorohydrin) or dimethylol dihydroxyethylene urea; (b) HNMe2 with epichlorohydrin or (c) adipic acid with diethylene triamine.