GB676721A - Dyestuff powders - Google Patents

Abstract

Disperse dyes are made in powder form to readily yield an aqueous dispersion of the dye on mixing with water by reducing to fine droplets a milled aqueous paste of the dye, a water-soluble salt of a lignin-sulphonic acid, and a water-soluble neutral or alkaline inorganic salt of which the cation is incapable of forming a water-insoluble soap, and drying the droplets by contact with heated air. Preferably the air is at 212-300 DEG F. and the particle size on drying is 25-100 microns. Specified salts are sodium sulphate, phosphate, chloride, pyrophosphate and carbonate, potassium pyrophosphate, chloride and thiocyanate and lithium nitrate. Advantageously the slurry to be milled contains from about 1 to about 4 parts by weight of lignin sulphonate and about 1 to about 4 parts by weight of the salt to each 2 parts of dyestuff with water to give a total solids content of the slurry of about 30 to about 50 per cent. Reduction to droplets may be effected by feeding the composition on to a disc rotating at a high peripheral speed, e.g. 4,500-10,000 ft. per sec. and a diagram is provided showing an apparatus for this technique, or by spraying through an atomizing nozzle. Preferably the powder contains about 2 to about 5 per cent of moisture. In examples powders are made from (1) 2-chlor-4-nitro-6-brom - benzene - azo - di - hydroxyethyl - metachlor-anilin, and (2) 1-hydroxy-4-amino-anthraquinone with potassium pyrophosphate and a lignin sulphonate.