Tioxide Specialties Limited

Tioxide House

Carole A Tapley

Iain Michael Harper

Philip Laurence Lyth

A stabilised aqueous dispersion of particulate zinc oxide comprises water, a stabilising agent and zinc oxide, the particles of which are coated with dense amorphous silica. Useful stabilising agents include cellulose ethers which contain quaternary ammonium groups and polyalkylene glycols. The dispersions have excellent stability at high concentrations of zinc oxide and are useful for preparing sunscreen formulations, cosmetics and veterinary products.

Zinc oxide dispersions

A method of preparing sunscreens in which a dispersion of zinc oxide particles in an oil is formed by milling in the presence of a particulate grinding medium and mixed with cosmetically acceptable materials is claimed. The particles of zinc oxide have an average size of from 0.005 to 0.15 micron and the dispersion is substantially transparent to visible light but with an extinction coefficient at 308 nm (E(308)) and at 360 nm (E(360)) of at least 9 liters per gram per centimeter. The ratio E(360):E(308) is in the range 0.75:1 to 1.5:1. In a preferred method a mixed dispersion containing titanium dioxide and zinc oxide, having E(308) at least 15 liters per gram per centimeter, E(360) at least 10 liters per gram per centimeter and the ratio E(360):E(308) in the range 0.3:1 to 1.5:1 is used. The mixed dispersion is also claimed. The sunscreens prepared have a good balance of absorption for UVA and UVB radiation and better SPF values than those prepared from titanium dioxide and/or zinc oxide powders.

Method of preparing sunscreens

An oil dispersion which is substantially transparent to visible light comprises an oil, particles of zinc oxide having an average size of from 0.005 to 0.15 micron and an organic dispersing agent. The solids content of the dispersion is at least 30 weight percent, its extinction coefficients at 308 nm (E(308)) and 360 nm (E(360)) wavelengths are both at least 9 liters per gram per centimeter and the ratio E(360):E(308) is in the range 0.75:1 to 1.5:1. A method of preparing the dispersion is also described in which the ingredients are milled together in the presence of a particulate grinding medium until the required particle size and optical properties are obtained. The dispersions are useful in sun-screening preparations and especially those products designed to provide a balanced protection from UVA and UVB radiation.

Growing community of inventors

Stockton on Tees, United Kingdom

Carole A Tapley