To impart sustained release characterisitcs to water at a low cost by covering water drops with a hydrophobic ultrafine silicon oxide powder which has been coated with at least one compd. selected from among an organosilicon compd., an organofluorine compd., and an organotitanium compd.
A hydrophobic ultrafine silicon oxide powder used here is prepd. by subjecting an ultrafine silicon oxide powder known as vapor-phase colloidal silica or fumed silica, obtd. by the vapor-phase oxidation of a silicon halide (e.g. silicon tetrachloride), and having an average primary particle size of 0.007-0.05μm to hydrophobizing treatment. The treatment comprises covering fumed silica with e.g. an organosilicon compd. (e.g. dimethyldichlorosilane or a dimethylsilicone). These examples of the organosilicon compd. are liq. at room temp. However, in the case of an organosilicon compd. solid at room temp., it is used as a soln. in a suitable volatile solvent. The amt. of the hydrophobizing agent attached is 5-30wt.% of fumed silica. The ratio of water to the hydrophobic ultrafine silicon oxide powder is usally (50:50)-(90:10).
HIGO AYAKO
AZUMA AKIKO
HONDA TSUNETOSHI
