Hydrophilic compositions, methods for their production, and substrates coated with such compositions
Liquid compositions are disclosed that include a photocatalytic material and a hydrophilic binder that includes an essentially completely hydrolyzed organosilicate. Also disclosed are methods of making such compositions, methods of coating a substrate with a hydrophilic composition, and substrates coated with such compositions. The compositions may, for example, be embodied as stable one-pack compositions.
1. A method of coating a substrate comprising:
(a) applying to the substrate a liquid composition comprising (1) a photocatalytic material present in an amount ranging from 0.1 to 0.75 percent by weight of the composition, (2) a hydrophilic essentially completely hydrolyzed organosilicate comprising silanol groups present in the liquid composition in an amount ranging from 0.1 to 2 percent by weight calculated as SiO 2 , based on the total weight of the composition, and (3) water present in an amount sufficient to prevent a condensation reaction of the silanol groups, and
(b) curing the composition applied in step (a) to provide a coating layer that has a dry film thickness of 10 to 100 nanometers.
2. The method of claim 1 , wherein the composition is cured by exposing the composition to air for at least two hours at 25° C.
3. The method of claim 1 , wherein the substrate comprises cement.
4. The method of claim 1 , wherein the substrate comprises glass.
5. The method of claim 1 , wherein the liquid composition further comprises an antimicrobial agent.
6. The method of claim 5 , wherein the antimicrobial agent comprises silver.
7. The method of claim 1 , wherein at least a portion of the photocatalytic material is present in the form of particles having an average crystalline diameter of 3 to 35 nanometers.
8. The method of claim 1 , wherein the photocatalytic material is selected from the group consisting of the brookite form of titanium dioxide, titanium dioxide chemically modified by flame pyrolysis, nitrogen doped titanium dioxide, plasma treated titanium dioxide, and mixtures thereof.
9. The method of claim 1 , wherein the pH of the liquid composition is no more than 3.5.
10. The method of claim 1 , wherein the dry film thickness of the coating layer is 20 to 60 nanometers.
11. The method of claim 1 , wherein the coating layer exhibits an initial water contact angle of no more than 10° prior to photoexcitation of the photocatalytic material.
12. The method of claim 1 , wherein, following excitation of the photocatalytic material, the coating layer exhibits a contact angle with water of less than 5°.