GB565029A - Process for dyeing of suede leather - Google Patents

Abstract

Azo dyes, forming on the material.-A process for the production of an azo dye on suede leather comprises the steps of applying thereto a diazo component in alkaline solution, adding a strong mineral acid in one or more stages to produce a pH sufficiently acid to exhaust the component on the leather and employing the same acid in conjunction with a nitrite to form the nitrous acid for the diazotization. The deleterious effect upon the subsequently added coupling component of the excess of nitrous acid remaining after the diazotization may be eliminated by addition to the bath, prior to the addition of the coupling component thereto, of a reagent capable of neutralizing or destroying the nitrous acid. Specified reagents for this purpose are ammonium hydroxide, primary aliphatic amines or carboxylic acid amides, urea, sulphamic acid and ammonium sulphamate. The diazo component is advantageously an aminoazo dyestuff such as Developed black BH, Diazamine blue BR, Diazo black RS, Diazine brown M, Diazine dark green G, Diazo fast yellow 2G and Direct green G. Specified coupling components are b -naphthol, p-aminodiphenylamine, 2 : 8 : 6-aminonaphtholsulphonic acid, N - ethyl - b - naphthylamine, m - phenylenediamine, m - toluylenediamine, resorcinol, 3-nitro-4 : 41-diaminodiphenyl, 1-phenyl-3-methyl-5-pyrazolone, 2 : 3-hydroxynaphthoic acid and the benzidide and p-phenetidide of acetoacetic acid. In examples: (1) chrome-tanned calfskins are treated in a rotary drum with an aqueous solution at 55 DEG F. containing Developed black BH, Direct green G, ammonia and soda ash, hydrochloric acid is added, followed by an aqueous solution of sodium nitrite run in during 20 minutes, whereafter an aqueous solution of ammonium sulphamate is run in, followed by an ammoniacal solution of m-toluylenediamine, the skins being then washed and fat-liquored with a solution containing sulphonated cod liver oil; (2) the coupling component in (1) is replaced by the p-phenetidide of acetoacetic acid applied with the aminoazo dyestuff, the step of adding the ammonium sulphamate solution being omitted; (3) and (4), tanned kid skins are treated in a rotary drum with an aqueous solution cooled to 70 DEG F. containing Developed black BH, Direct green G, ammonia and soda ash, hydrochloric acid is added, followed by sodium nitrite, whereafter (3) aqueous ammonium hydroxide; (4) an aqueous solution of methylamine is added to neutralise or destroy the excess nitrous acid, followed by an ammoniacal solution of m-toluylenediamine, the skins being then washed and fat-liquored as in (1).