SILICA-COATED PIGMENTS

摘要

1470374 Coated lead chromate pigments FERRO (GREAT BRITAIN) Ltd 2 July 1974 [3 July 1973] 31642/73 Heading C4A [Also in Division C1 Dense, amorphous SiO 2 is precipitated from solution on to lead chromate pigment particles at a temperature below 60‹ C. and pH at least 7 in the presence of an alkali metal or ammonium salt of a mineral acid as electrolyte. The pigment is defined as one in which lead chromate is a major ingredient, and includes solid solutions of lead chromate, molybdate and sulphate as well as monoclonic or rhombic lead chromate. Specified electrolytes are aqueous NaCl NaNO 3 , KCl or NH 4 Cl in 2À5-30% w./w. concentration. The amount of SiO 2 , forming a continuous film on the pigment base, may be 2-50 wt. per cent of the coated particles. The products may be further coated with wax, rosin acid salt, long chain fatty acid salt or alumina. A procedure for coating with polyethylene wax is described.