To obtain the subject composite aqueous sol improved in water resistance of the coating film therefrom after applied to a plastic base such as lens and cured with no discoloration of such a coating film due to UV irradiation, and suppressed in discoloration and transparency drop, by reaction between a titanium salt, a cerium salt and metallic tin in the presence of hydrogen peroxide in an aqueous medium.
This composite aqueous sol is obtained through the following three consecutive processes: (a) hydrogen peroxide and metallic tin are added either simultaneously or alternately to an aqueous solution of a mixture of a titanium salt and cerium salt while keeping the molar ratio: H2O2/Sn at 2-3 to form an aqueous solution of a titanium-cerium-tin basic salt with the molar ratio for the Ti-component, Ce-component and tin component at 0.01-0.5 in terms of CeO2/TiO2 and 0.25-10 in terms of TiO2/(CeO2+SnO2) and the total concentration at 5-50wt.% in terms of TiO2+CeO2+SnO2, (b) the aqueous solution of the basic salt is kept at 50-100°C for 0.1-100h to form a composite colloid flocculate, and (c) elecrolytes in the above flocculate slurry is removed.
SUZUKI KEITARO
KOYAMA KINYA
IIJIMA MOTOKO
