Oxidn. of reduced vat or sulphur dyes - with alkali-metal chlorite(s) in presence of chelating agents

摘要

Dyeings produced by the application of the reduced forms of vat or sulpur-dyes are oxidised by alkali metal chlorites, e.g. Na chloride in acid medium, to which chelating agents have been added. Oxidn. of vat or sulphur dyes is usually carried out with alkali peroxides, oxygenated water or alkali dichromates. The first two tend to lead to 'suroxidn.' with certain sulphur dyes, and dichromates often cau se dulling of shades, as well as causing pollution. No such problems arises with chlorites but they must normally be applied at a relatively alkaline pH and high temp. than normal (80 degrees C). It has now be found that they can be applied at acid pH if chelating agents are added to the bath, they do not affect the tinctorial character of the oxidised dyeings.