GB805494A - Improvements in or relating to alumina-silica pigments and their preparation - Google Patents

Abstract

A finely-divided, amorphous alumina-silica pigment containing at least six mols. of SiO2 per mol. of Al2O3, the ratio of SiO2 to metal oxide being in excess of 2 and the ratio of mols. of Al2O3 per mol. of other metal oxides if present, being not less than 0.2, said pigment having an ultimate particle size below 0.1 microns, may be prepared by reacting in aqueous medium an alkaline earth metal silicate having an average ultimate particle size below 0.1 micron with an amount of an aluminium salt sufficient to react with at least 20 per cent of the alkaline earth metal silicate. In one modification of the method the alkaline earth metal silicate is reacted with an aluminium salt and an acid so that a portion of the alkaline earth metal is extracted from the reaction mixture before reaction with the aluminium salt. A second modification of the method produces a finely divided aluminasilica pigment by simultaneously reacting together, in aqueous solution, a water soluble, alkaline earth metal salt, an alkali metal silicate and an aluminium salt. Alternatively, the pigment may be produced by reacting an aluminium salt with silica, said silica having been precipitated from aqueous sodium silicate solution in pigmentry form and having an average ultimate particle size below 0.1 microns. The alkaline earth metal salt formed in the reaction may be insoluble and may be left in the precipitate or can be washed out. Aluminium salts used include chloride, bromide, nitrate, sulphate or aluminate while the preferred metal salt is calcium chloride. The pigments may be treated with a coating agent before use. Specification 745,822 is referred to.ALSO:A finely-divided, amophous alumina-silica pegment containing at least six mols. of SiO2 per mol. of Al2O3, the ratio of SiO2 to metal oxide being in excess of 2 and the ratio of mols. of Al2O3 per mol. of other metal oxides if present being not less than 0.2, said pigment having an ultimate particle size below 0.1 microns, may be prepared by reacting in aqueous medium an alkaline earth metal silicate having an average ultimate particle size below 0.1 micron with an amount of an aluminium salt sufficient to react with at least 20 per cent of the alkaline earth metal silicate. In one modification of the method the alkaline earth metal silicate is reacted with an aluminium salt and an acid so that a portion of the alkaline earth metal is extracted from thereaction mixture before reaction with the aluminium salt. A second modification of the method produces a finely-divided aluminasilica pigment by simultaneously reacting together, in aqueous solution, a water soluble, alkaline earth metal salt, an alkali metal silicate and an aluminium salt. Alternatively, the pigment may be produced by reacting an aluminium salt with silica, said silica having been precipitated from aqueous sodium silicate solution in pigmentry form and having an average ultimate particle size below 0.1 microns. The alkaline earth metal salt formed in the reaction may be insoluble and may be left in the precipitate or can be washed out. Aluminium salts used include chloride, bromide, nitrate, sulphate or aluminate while the preferred metal salt is calcium chloride. The pigments may be treated with a coating agent before use. The finely-divided alumina-silica pigment which can be used as fillers for natural and synthetic rubbers such as butadienestyrene copolymers known as GR-S rubber, butadiene-acrylonitrile polymers, chloroprene rubber, butyl rubber, and like polymers of butadiene - 1,3, isoprene, 2 - chlorobutadiene-1,3, and 2,3-dimethyl butadiene-1,3 as well as polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, and mixtures of natural and synthetic rubbers, the amount of such pigment incorporated in these rubbers being about 10 to 100 parts by weight per 100 part by weight of elastomer or rubber compositions. Specification 745,822, [Group III], is referred to.