Patent GB-471829-A (GB)
Title: Improvements in or relating to the production of composite pigments
IPC: C09C1/00
Filed: 1936-08-22
Abstract: Composite pigments are prepared by effecting co-flocculation in a mixture of suspensions of the component pigments, separating the co-flocculated deposit, and washing and drying it.  Separate suspensions of the component pigments may be prepared with the aid of dispersing agents, the suspensions mixed, and co-flocculation effected by the addition of a coagulating agent, or as a result of interaction between the different dispersing agents used.  In the latter case it is preferred to use substantially stoichiometric proportions of the antipathetic dispersing agents.  Specified dispersing agents are the carbonates and hydroxides of alkali metals, alkali metal silicates, sulphides, e.g. hydrogen sulphide, lead and barium chlorides, acidic halides of tri- and tetravalent elements, metallic soaps, the ammonium soap of sulphonated castor oil, turkey red oil, alkyl-substituted aryl sulphonic acids or salts, saponin and trihydroxyethylamine, and specified coagulating agents are magnesium sulphate, sulphuric acid and sodium hydroxide.  According to examples: (1) titanium dioxide is milled with an equal weight of water and 1 per cent of aluminium chloride; barium sulphate is milled with an equal weight of water and \ba1/2\be--\ba3/4\be per cent of sodium silicate; the two suspensions are mixed, and co-flocculation results through interaction of the aluminium chloride and sodium silicate; the co-flocculated pigment particles are separated from the liquor, washed, dried and pulverized; (2) titanium dioxide and barium sulphate are separately milled with water and sodium silicate, and the suspensions mixed; co-flocculation is effected by the addition of an aqueous solution of magnesium sulphate; (3) zinc sulphide is dispersed in water saturated with hydrogen sulphide, and barium sulphate is dispersed in an aqueous solution of sodium silicate; co-flocculation occurs when the two dispersions are mixed; (4) zinc sulphide and barium sulphate are separately milled with water containing sodium silicate, the dispersions mixed, and an aqueous solution of magnesium sulphate added; (5) a composite titanium dioxide-barium sulphate pigment is dispersed in water in the presence of sodium silicate, and basic lead carbonate is dispersed in water in the presence of lead chloride; on mixing the two dispersions, co-floccuation results, with the formation of a tertiary titanium dioxide-barium sulphate-basic lead carbonate pigment; (6) a co-precipitated, mutually calcined, titanium dioxide-barium sulphate composite pigment is dispersed in water containing sodium hydroxide, and basic lead carbonate is dispersed in water containing barium hydroxide; the suspensions are mixed, and co-flocculation effected by adding sulphuric acid; (7) titanium dioxide is dispersed in water containing sodium hydroxide; barium sulphate and basic lead carbonate are separately dispersed in water containing sodium silicate; the three separately prepared suspensions are mixed and co-flocculation effected by adding an aqueous solution of magnesium sulphate. Coloured or tinted composite pigments may be prepared by a suitable choice of starting pigments, e.g. by co-flocculating dispersions of chrome yellow and of Prussian blue.