PURPOSE: To manufacture a stable metal powder pigment composition which is excellent in chemical resistance, weather resistance, corrosion resistance, heat resistance, etc., by coating the surface of a metal powder pigment which has been subjected to a surface treatment using a B compound and/or a hexavalent Cr compound together with a degreasing agent with fine amorphous silica.
CONSTITUTION: A metal powder pigment is subjected to a surface treatment in which the pigment is dipped in an aqueous solution containing 0W50wt% (as B2O5) B compound, e.g., boric acid, borax, etc., and/or 0.2W3wt% (as CrO3) Cr compound, e.g., chromic anhydride, K2Cr2O7, etc., together with a degreasing agent. Then, the pigment so treated is dispersed in a water of pH 8W11 to prepare a 50W300g/l concentration of aqueous slurry, and the slurry kept at 60°C or more and pH 8W11 is mixed with an aqueous alkali silicate solution of an SiO2/M2O molal ratio of 2W4 (M is Na, K, etc.), hydrochloric acid, and a watersoluble inorganic compound, e.g., CaCl2, etc., to cause reaction for 2W4hr, whereupon silica sol of a grain size of less than 200mμ is formed and then deposited on the surfaces of the pigment particles.
KANAMARU KIYOSHI
YOKOYAMA MINORU
TOHO GANRIYOU KOGYO KK