GB451419A - Improvements in or relating to the manufacture of vat colour powders - Google Patents

Abstract

Vat colour powders for dyeing paper are obtained by drying a vat colour paste containing dextrine and a water-soluble salt of a condensation product of a naphthalene sulphonic acid and formaldehyde. Small quantities of alkaline substances may be added to assist in the dispersion of powders containing acidic impurities. Specifications 272,896 and 276,100, [both in Class 2 (iii)], are referred to. According to examples, N-dihydro-1 : 2 : 2<1> : 1<1>-anthraquinone azine, dichlorisoviolanthrone, flavanthrone, Sulphanthrene orange R, Sulphanthrene pink FF, and 5 : 7 : 5<1> : 7<1>-tetrabromindigo are mixed in paste form with dextrine and an aqueous solution of the sodium salt of the condensation product of naphthalene sulphonic acid and formaldehyde. The mixtures are dried and ground, and used to dye paper by incorporating into the paper beater, with the bleached sulphite pulp, resin soap size and aluminium sulphate, in the customary manner. Formaldehyde-naphthalene sulphonates are prepared by heating naphthalene with sulphuric acid monohydrate for 10 hours at 160 DEG C., diluting, and heating for 6 hours with 40 per cent formaldehyde at 95 DEG to 100 DEG C. The mass is cooled, diluted, treated with lime and the sodium, potassium or ammonium salt prepared from the calcium salt by the use of the appropriate carbonate. Specifications 195,619, [Class 2 (ii)], 224,502, and 241,854, [both in Class 120 (iii)], and 246,609, [Class 15 (ii)], also are referred to.