Photocatalyst-containing water-based curable coating compositions and process for production thereof

A method for producing a photocatalyst-containing water-based curable coating composition, the method comprising the following (1) to (4):

• (1) subjecting a polymer (a′), and organoalkoxysilane (b) and/or a hydrolytic condensation product thereof (b-1) to a hydrolytic condensation process and thereby obtaining a composite resin (A′B), the polymer (a′) having a combination of an acid group, a hydroxyl group bonded to a silicon atom, and/or a hydrolyzable group bonded to a silicon atom, the composite resin (A′B) being formed by a chemical bonding between a polymer segment (A′) derived from the polymer (a′) and a polysiloxane segment (B) derived from the organoalkoxysilane (b);
• (2) subjecting the obtained composite resin (A′B) and an alkyltrialkoxysilane condensate (c) with an alkyl group of 1 to 3 carbon atoms to a hydrolytic condensation process and thereby obtaining a composite resin (A′BC), the composite resin (A′BC) being formed by the coupling between a polysiloxane segment (C), which is derived from the alkyltrialkoxysilane condensate (c) with an alkyl group of 1 to 3 carbon atoms, and the polysiloxane segment (B) in the composite resin (A′B) via a silicon-oxygen bond, followed by the neutralization of an acid group within the composite resin (A′BC) by a basic compound to obtain a composite resin (ABC), or
• neutralizing an acid group within the obtained composite resin (A′B) by a basic compound and thereby obtaining a composite resin (AB), and then hydrolytically condensing an alkyltrialkoxysilane condensate (c) with an alkyl group of 1 to 3 carbon atoms to obtain a composite resin (ABC), the composite resin (ABC) being formed by the coupling between a polysiloxane segment (C), which is derived from the alkyltrialkoxysilane condensate (c) with an alkyl group of 1 to 3 carbon atoms, and the polysiloxane segment (B) in the composite resin (AB) via a silicon-oxygen bond;
• (3) mixing the obtained composite resin (ABC) with a water-based medium and thereby dispersing or dissolving the composite resin (ABC), followed by the mixing of fine particles of a photocatalytic oxide (D) or a water-based dispersion thereof so that the amount of the fine particles of a photocatalytic oxide (D) is within the range of 0.1 to 10 parts by weight with respect to 100 parts by weight of the composite resin (ABC), to obtain a water-based dispersion (X1), the water-based dispersion (X1) in which the composite resin (ABC) is dispersed or dissolved and the fine particles of a photocatalytic oxide (D) are dispersed;
• and
• (4) mixing the obtained water-based dispersion, which is formed of the composite resin (ABC) and the fine particles of a photocatalytic oxide (D), with a curing agent (E) that cures the composite resin (ABC);
• or the method comprising:
• above steps (1) and (2) as well as step (3′):
• (3′) mixing the composite resin (ABC) obtained by the aforementioned (2) with a water-based medium and thereby obtaining a water-based dispersion in which resin particles composed of the composite resin (ABC) are dispersed;
• and the method also includes, before the aforementioned (3′) for dispersing the composite resin (ABC) by mixing the composite resin (ABC) with a water-based medium, mixing fine particles of a photocatalytic oxide (D) with the composite resin (ABC) or a precursor thereof so that the amount of the photocatalytic oxide (D) is within the range of 0.1 to 10 parts by weight with respect to 100 parts by weight of the composite resin (ABC).