| 摘要 |
PROBLEM TO BE SOLVED: To suppress the radical generation when zinc oxide absorbs UV rays by treating zinc oxide particulates in a phosphoric acid solution to allow a phosphoric acid group to exist as zinc phosphate on particulate surfaces. SOLUTION: The zinc oxide particulates of <=1μm in major axis are immersed in the dilute solution of phosphoric acid and are heated to about 80 deg.C, following which the solution is stirred and held for 1 to 5 hours. The solution is baked for 10 to 24 hours at 250 to 350 deg.C after filtering and washing with water, by which the zinc oxide particulates coated with the phosphoric acid group as zinc phosphate on the particulate surfaces at a thickness of 0.003 to 0.1μm are obtained. The radical generation is suppressed without the impairment of the UV absorption characteristic and optical effect of the zinc oxide by this treatment. The surface treated zinc oxide particulates are preferably applied to materials used under exposure of light as cosmetics. The applications to cosmetics for sun care and makeup cosmetics, such as foundation, are preferable. The particulates are also adequate for use with persons having the sensitive skin.
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