GB449805A - Process for colouring paper and similar products derived from paper pulp - Google Patents

Abstract

Paper, cardboard, and similar products derived from paper pulp are coloured by incorporating in the pulp a copper phthalocyanine (cf. Specifications 322,169, [Class 2 (iii)], 389,842, 410,814, and 418,367) dispersed to a particle size of 8 to 24 microns. In an example, a copper phthalocyanine, obtained from phthalonitrile and copper according to example 2 or from phthalonitrile and cupric chloride according to example 3 of Specification 410,814, is made into a grindable paste with water, sand and the condensation product from formaldehyde and naphthalenesulphonic acid, the mixture is stirred for 24 hours and the finely divided pigment is separated from the sand by decantation, precipitated from the suspension by acidifying with hydrochloric acid, filtered, washed free from acid and re-dispersed by making faintly alkaline with caustic soda; the resulting paste is added to a 4 to 6 per cent unbleached sulphite pulp which is then worked in the beater for \ba1/2\be hour, whereupon rosin size and aluminium sulphate are successively incorporated and the pulp is converted into paper in the usual way; the resulting paper is coloured, on both sides equally, a full bright shade of blue.