PURPOSE: To obtain a silica-coated ultramarine composition having excellent chemical resistance, weather resistance, heat resistance, etc., by forming an aerosol of an aqueous solution of an acid and contacting the sol together with an alkali silicate to an aqueous slurry of ultramarine, thereby depositing silica on the surface of the ultramarine particle.
CONSTITUTION: The objective composition can be produced by keeping (A) an aqueous slurry of ultramarine to e.g. 90W95°C and 9W11pH and contacting the slurry with (B) 9W15wt% (based on the ultramarine pigment) alkali silicate (e.g. aqueous solution of sodium silicate) and (C) and aerosol of an aqueous solution of an acid (e.g. aqueous solution of an inorganic acid such as sulfuric acid having a concentration of 1W10%).
MORITA KAZUO
YAMASHITA MORIYUKI
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