Synthesis of Novel Cosmetic White Pigment by Condensed Phosphoric Acid Treatment of Zinc Oxide

Abstract

Zinc oxide is used as a white pigment in cosmetics, but has the disadvantage of having photocatalytic activity. A certain amount of sebum on the skin is decomposed by ultraviolet rays in sunlight due to the photocatalytic activity of this cosmetic, causing damage to the skin. In this study, a new white pigment for cosmetics was prepared by shaking a mixture of zinc oxide and various condensed phosphate solutions or condensed phosphoric acid to react the surface of zinc oxide to phosphate. The chemical composition, particle size distribution, photocatalytic activity, hue, and smoothness of the resulting powder materials were examined. The condensed phosphoric acid treatment caused some of the zinc oxide to react with the zinc phosphate. The reaction was relatively advanced in the samples prepared in a protonated solution. Most of the sample powders were of a size suitable for white pigments for cosmetics. The condensed phosphoric acid treatment suppressed the photocatalytic activity of the zinc oxide. The obtained samples had sufficiently high reflectance in the visible light range. Judging from the particle size and the photocatalytic activity, the sample prepared with polyphosphoric acid is most suitable as a white pigment for cosmetics.