INORGANIC POWDER HAVING MODIFIED SURFACE

摘要

PURPOSE:To provide the titled inorg. powder which has excellent water repellency and is smooth to the touch and suitable for use as cosmetic powder, water repellency agent and lubricant, by treating clay mineral powder having an acidity point of a specified value or above with a dialkylphosphoric acid. CONSTITUTION:A clay mineral powder (e.g. kaolin or sericite powder contg. an aluminum element) having 2X10<-5>mol or above/g of an acidity point having an acidity (pKa) of +3.3 or below is prepd. The clay mineral powder is treated with a dialkylphosphoric acid of the formula (wherein R1, R2 are each a 14-22C straight-chain alkyl) such as dicetylphosphoric acid or distearylphosphoric acid to modify the surface of the powder. The proportion of the acidity point having acidity (pKa) of +3.3 or below can be determined by titrating the powder dispersed in benzene with n-butylamine by using r-dimethylaminoazobenzene as an indicator.