Water-repellent fine particles and making method

Abstract

Silicone elastomer spherical particles having a volume mean particle size of 0.1-100 μm are coated with a polyorganosilsesquioxane and washed with alcohol or a mixture of alcohol and water. The coated fine particles are water repellent so that they are non-dispersible in water and float on water.

1 . Water repellent fine particles comprising 100 parts by weight of silicone elastomer spherical particles having a volume mean particle size of 0.1 to 100 μm, which are coated with 0.5 to 0.25 parts by weight of a polyorganosilsesquioxane, the fine particles being non-dispersible in water and floatable on water. 
     
     
         2 . The fine particles of  claim 1  wherein trimethylsilyl groups are pendant to the surface of the polyorganosilsesquioxane coating. 
     
     
         3 . The fine particles of  claim 1  wherein hydrolytic condensation reaction between a tetraalkoxysilane and at least one silylating agent selected from trimethylalkoxysilane, trimethylsilanol and hexamethyldisilazane has been carried out on the surface of the polyorganosilsesquioxane coating. 
     
     
         4 . A method for preparing water repellent fine particles comprising the steps of
 providing a dispersion of silicone elastomer spherical particles having a volume mean particle size of 0.1 to 100 μm in water using a surfactant,   adding an organotrialkoxysilane to the water dispersion and effecting hydrolytic condensation reaction thereof in the dispersion in the presence of an alkaline substance for coating the silicone elastomer particles with polyorganosilsesquioxane, and   washing the coated particles with alcohol or a mixture of alcohol and water to remove the surfactant.   
     
     
         5 . A method for preparing water repellent fine particles comprising the steps of
 providing a dispersion of silicone elastomer spherical particles having a volume mean particle size of 0.1 to 100 μm in water using a surfactant,   adding an organotrialkoxysilane to the dispersion and effecting hydrolytic condensation reaction thereof in the dispersion in the presence of an alkaline substance for coating the silicone elastomer particles with polyorganosilsesquioxane,   adding a tetraalkoxysilane and at least one silylating agent selected from trimethylalkoxysilane, trimethylsilanol and hexamethyldisilazane to the dispersion and effecting hydrolytic condensation reaction thereof in the dispersion, and   washing the coated particles with alcohol or a mixture of alcohol and water to remove the surfactant.