Process for Producing Hydrophobic Silica Powder

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PURPOSE : A method for efficiently producing a hydrophobic silica powder with excellent re-dispersibility in an organic solvent is provided. CONSTITUTION : A method for producing a hydrophobic silica powder comprises a hydrophobic treatment process comprising : adding a disilazane compound to a mixed solvent silica sol with a silica concentration of 5 to 50 mass%% in an amount of 0.1 to 20 mmol per 100 m^2 of surface area of the hydrophilic colloidal silica; and heating the mixture at a temperature of 50 to 100 deg.C, thereby aging the mixture to obtain a slurry dispersion of hydrophobic treated colloidal silica, wherein the mixed solvent silica sol is obtained by mixing a hydrophilic organic solvent with an aqueous silica sol containing hydrophilic colloidal silica having a specific surface area of 5.5 to 550 m^2/g in a hydrophilic organic solvent to water in the aqueous silica sol mass ratio of 0.12 to 2.5, and the disilazane compound is represented by the formula, (R^1 3Si)2NH, wherein each R^1 is an independently selected alkyl group or phenyl group having 1 to 6 carbon atoms. © KIPO 2007