Surface-coated titanium dioxide sol, process for producing the same and coating compositions containing the same
AssigneeTayca Corporation
InventorNobuyuki Yokoyama
Life of this patent
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Abstract
A transparent titanium oxide in which the titanium oxide particles have been coated with a hydrated metal oxide having no photocatalytic activity in order to block photocatalytic activity. Hydrous titanium oxide sol particles are coated with a layer comprising a hydrated oxide of silicon. The coating layer can further contain a hydrated oxide of at least one metal selected among tin, aluminum, and zirconium and a hydrated oxide of antimony. Also provided are a process for producing a sol of surface-coated transparent titanium oxide and a coating composition containing a sol of surface-coated transparent titanium oxide.
Claims16
A titanium dioxide sol composition comprising titanium dioxide sol particles having a coating layer thereon and a liquid dispersion medium of the sol, said coating layer comprising, in the following radially-inner to radially-outer order:
- (i) hydrated silica in a proportion calculated as SiO2 from 10 to 40% by weight of said titanium dioxide sol particles calculated as TiO2, and
- (ii) at least one hydrated metal oxide selected from the group consisting of tin oxide, aluminum oxide and zirconium oxide in a proportion calculated as sum of SnO2, Al2O3 and ZrO2 from 2 to 40% by weight of said titanium dioxide sol particles calculated as TiO2.
A process for producing a stable titanium dioxide sol composition comprising the steps of:
- (a) providing a titanium dioxide hydrosol;
- (b) adding to said titanium oxide hydrosol a stabilizer selected from the group consisting of hydrogen peroxide, an aliphatic or aromatic hydroxy-carboxylic acid, and an alkoxysilane compound of the formula:
- R1nSiX4-n
- wherein R1 is C1-C8 alkyl, glycidoxylated C1-C8 alkyl or C2-C8 alkenyl, X is alkoxy, and n is 0 or 1;
- (c) adding the stabilized titanium dioxide hydrosol prepared in step (b) to a solution of a water-soluble silicate salt or silica sol containing an amount of alkali sufficient to keep the mixture alkaline at a pH higher than 9 after said titanium dioxide hydrosol has been added;
- (d) adding to the mixture at least one oxide or water-soluble salt of a metal selected from the group consisting of tin, aluminum and zirconium after said stabilized titanium dioxide hydrosol has been added in step (c) while keeping the pH of the mixture above 9;
- (e) adjusting the pH of the mixture lower than 8, and
- (f) removing electrolytic contaminants from the mixture.
Dependencies are inferred from the claim text.