GB354696A - Manufacture of pigments in high state of dispersion - Google Patents

Abstract

Pigments in a highly dispersed state are formed by producing the pigment in the presence of an aqueous solution of a cellulose derivative which coagulates when heated. Suitable cellulose derivatives are methyl celluloses, aqueous solutions of which coagulate between 50 and 80 DEG C. and some ethyl celluloses which are soluble in ice-water but which coagulate at room temperature. The pigments may be made by double decomposition with metal salt solutions, by coupling diazo-compounds with suitable components, by oxidizing bases which form pigments or by oxidizing leuco-compounds. The flocks of coloured coagulated cellulose derivatives may be washed and dried and used to produce coloured varnishes by solution in solvents such as alcohols or hydrocarbons with or without usual varnish constituents. Aqueous pastes of the coloured cellulose derivative may be mixed with non-aqueous solutions of cellulose derivatives. In examples: (1) Ferric ammonium sulphate in aqueous solution is precipitated with potassium ferrocyanide in the presence of a 5 per cent aqueous solution of methyl cellulose. The blue solution is coagulated by heat, and the coagulum washed with water until free from salts. (2) A similar process is effected, interaction occurring between aqueous solutions of cadmium sulphate and ammonium sulphydrate to produce the pigment. (3) An aqueous solution of sodium chromate and methyl cellulose is mixed with an aqueous solution of lead nitrate and methyl cellulose. The yellow solution is coagulated by heating and the coagulum washed with hot water. The coagulum may be heated and used liquid as an "aquarell" colour or as a printing colour. It may be worked up with softening agents, resins, solutions of cellulose esters or ethers, &c. to form varnishes.ALSO:Pigments in a highly dispersed state are formed by producing the pigment in the presence of an aqueous solution of a cellulose derivative which coagulates when heated. Suitable cellulose derivatives are methyl celluloses, aqueous solutions of which coagulate between 50 DEG and 80 DEG C. and some ethyl celluloses which are soluble in ice-water but which coagulate at room temperature. The pigments may be made by double decomposition with metal salt solutions, by coupling diazo-compounds with suitable components, by oxidizing bases which form pigments or by oxidizing leuco-compounds. The flocks of coloured coagulated cellulose derivatives may be washed and dried and used to produce coloured varnishes by solution in solvents such as alcohols or hydrocarbons with or without usual varnish constituents. Aqueous pastes of the coloured cellulose derivative may be mixed with non-aqueous solutions of cellulose derivatives. In example (1) Ferric ammonium sulphate in aqueous solution is precipitated with potassium ferrocyanide in the presence of a 5 per cent aqueous solution of methyl cellulose. The blue solution is coagulated by heat and the coagulum washed with water until free from salts. (2) A similar process is effected, interaction occurring between aqeuous solutions of cadmium sulphate and ammonium sulphydrate to produce the pigment. (3) An aqueous solution of sodium chromate and methyl cellulose is mixed with a aqueous solution of lead nitrate and methyl cellulose. The yellow solution is coagulated by heating and the coagulum washed with hot water. The coagulum may be heated and used liquid as an "aquarell" colour.