GB813453A - Silica pigments - Google Patents

Abstract

A silica pigment for rubber reinforcement is prepared by mixing an ethylenically or acetylenically unsaturated organopolysiloxane with finely divided hydrated silica-containing pigment having an ultimate particle size below 0.1 m and a surface area of 25-250 sq. m/grm., which pigment contains at least 75 per cent SiO2 and bound water in an amount corresponding to the formula H2O(SiO2)x, where x is 3-85. The organopolysiloxane, in amount 1-20 per cent, should have an R/Si ratio of at least 0.5, where R is an aliphatically unsaturated hydrocarbon or corresponding halogen substituted hydrocarbon radical, e.g. vinyl-, allyl-, methallyl-, 2-chloroallyl-, divinyl-, diallyl-, vinyl phenyl-, allyl phenyl-, cyclohexenyl-and propargyl-polysiloxane, polymers of vinyl ethoxysilanol, or copolymers with dimethyl silanol. The silica-pigment may be coated with the organopolysiloxane before incorporation in the rubber, in which case it is stated that the silica has a chemically bound coating of polysiloxane. The silica may be treated by adding the polysiloxane resin to a slurry of silica and water or organic solvent, e.g. benzene or toluene, or by tumbling the silica while a gas, e.g. nitrogen, containing volatile polysiloxane is passed through, or by adding a small amount of silica to a large amount of polysiloxane and blending with untreated silica, or by spraying liquid polysiloxane or a solution of polysiloxane in a volatile solvent on to silica with agitation and drying at 110 DEG C. Alternatively, the silica and polysiloxane may be milled together with the rubber composition. The silica may contain less than 2 per cent Na2O, and up to 1 mol. per 3 mols. SiO2 of oxides of Ca, Ba, Sr, Mg, Al or Zn, e.g. calcium silicate CaO(SiO2)3.3 and sodium aluminium silicate containing at least 75 per cent SiO2. The silica may be produced by precipitation from sodium silicate solution at 25 DEG C. in the presence of sodium chloride by an acid or acid salt, e.g. carbon dioxide, ammonium or sodium bicarbonate, hydrochloric, sulphuric, phosphoric, sulphurous, or nitric acids, sodium acid sulphate or disodium acid phosphate. Alternatively, the silica may be produced by reacting acid with calcium silicate prepared from sodium silicate and calcium chloride in an aqueous medium containing sodium chloride. Magnesium, barium, strontium, or zinc silicates may alternatively be used in silica preparation. In examples: (4) aqueous silica slurry is homogenized with a toluene solution of vinyl polysiloxane and dried, and the dry pigment is mixed with natural rubber, zinc oxide, sulphur, stearic acid, phenyl-b -naphthylamine, benzothiazyl disulphide, di-o-tolyl guanidine, and triethanolamine; (5) silica is mixed into a paste with toluene, vinyl polysiloxane dissolved in toluene, and n-butanol containing triethanolamine are then added, solvents are evaporated on a steam bath, and the resulting pigment is mixed with the composition of Example (4) or with butadiene-styrene copolymer GR/S, zinc oxide, sulphur, di-o-tolyl guanidine, and 2-mercaptothiazoline.ALSO:A silica pigment for rubber reinforcement is prepared by mixing an ethylenically or acetylenically unsaturated organopolysiloxane with finely-divided hydrated silica-containing pigment having an ultimate particle size below 0.1 m and a surface area of 25-250 sq. m./g., which pigment contains at least 75 per cent of SiO2, and bound water in an amount corresponding to the formula H2O(SiO2)x, where x is 3-85. The organopolysiloxane, in amount 1-20 per cent, should have an R/Si ratio of at least 0.5, where R is an aliphatically unsaturated hydrocarbon or corresponding halogen substituted hydrocarbon radical, e.g. vinyl-, allyl-, methallyl-, 2-chloroallyl-, divinyl-, di-allyl-, vinyl phenyl-, allyl phenyl-, cyclo-hexenyl- and propargyl-polysiloxane, polymers of vinyl ethoxysilonol, or copolymers with dimethyl silanol. The silica pigment may be coated with the organopolysiloxane before incorporation in the rubber, in which case it is stated that the silica has a chemicallybound coating of polysiloxane. The silica may be treated by adding the polysiloxane resin to a slurry of silica and water or organic solvent, e.g. benzene or toluene, or by tumbling the silica while a gas, e.g. nitrogen, containing volatile polysiloxane is passed through, or by adding a small amount of silica to a large amount of polysiloxane and blending with untreated silica, or by spraying liquid polysiloxane or a solution of polysiloxane in a volatile solvent on to silica with agitation and drying at 110 DEG C. Alternatively, the silica and polysiloxane may be milled together with the rubber composition. The silica may contain less than 2 per cent of Na2O, and up to 1 mol. per 3 mols. SiO2 of oxides of Ca, Ba, Sr, Mg. Al or Zn, e.g. calcium silicate CaO(SiO2)3.3 and sodium aluminium silicate containing at least 75 per cent of SiO2. In examples: (4) aqueous silica slurry is homogenized with a toluene solution of vinyl polysiloxane and dried, and the dry pigment is mixed with natural rubber, zinc oxide, sulphur, stearic acid, phenyl-b -naphthylamine, benzothiazyl disulphide, di-o-tolyl guanidine, and triethanolamine; (5) silica is mixed into a paste with toluene, vinyl polysiloxane dissolved in toluene, and n-butanol containing triethanolamine are then added, solvents are evaporated on a stream bath, and the resulting pigment is mixed with the composition of Example (4) or with butadiene-styrene copolymer GR-S, zinc oxide, sulphur, di-o-tolyl guanidine, and 2-mercaptothiazoline.