Method for dyeing synthetic materials with vat dyestuffs

Abstract

A method is provided for dyeing a non-cellulosic organic material with a dye, preferably a vat dye, comprising (a) treating the material with a dye in the presence of a reducing agent and an alkali and (b) oxidising the treated material produced in step (a) characterised in that the concentration of reducing agent used in step (a) is increased above that used for conventional vat dyeing such that the resultant dyed material has a lightfastness of 5 or more by BS 1006 B01 and B02 (1978) and/or has a washfastness or 5 or more by British Standard Test BS 1006 C06.C2 (1981). Preferably the step (a) is carried out in the presence of an alkali in concentration of at least 0.5 molar, more preferably 1 molar or more and most preferably 1 to 4 molar. The method provides vat dyed non-cellulosic organic materials having a reflectance of infrared light of wavelength 400 nm to 680 nm of less than 15%.

Dependencies are inferred from the claim text.