Hydrophilic compositions, methods for their production, and substrates coated with such compositions

• US 20050266981A1
• Filed: 05/18/2005
• Published: 12/01/2005
• Est. Priority Date: 05/28/2004
• Status: Active Grant

• Current Assignee: PPG Industries Ohio Incorporated (Nouryon BV)
• Original Assignee: PPG Industries Ohio Incorporated (Nouryon BV)
• Inventors: Cheng, Shan, Lin, Chia-Cheng, Colton, James P., Nakajima, Masayuki
• Granted Patent: US 7,959,980 B2
• Time in Patent Office: Days
• US Class Current: 502/150
• CPC Class Codes: C09D 183/02 Polysilicates
• CPC Class Codes: C09D 5/1618 inorganic
• CPC Class Codes: C09D 7/61 inorganic
• CPC Class Codes: C09D 7/67 Particle size smaller than 100 nm

Abstract

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.

Claims

1. A liquid composition comprising:

(a) a photocatalytic material, and

(b) a hydrophilic binder comprising an essentially completely hydrolyzed organosilicate.

2. The liquid composition of claim 1 wherein at least apportion of the photocatalytic material is present in the form of particles having an average crystalline diameter of 3 to 35 nanometers.

3. The liquid composition 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.

4. The liquid composition of claim 1, wherein the photocatalytic material is provided in the form of a sol comprising particles of photocatalytic material dispersed in water.

5. The liquid composition of claim 1, wherein the photocatalytic material is present in the liquid composition in an amount ranging from 0.1 to 0.75 percent by weight based on the total weight of the composition.

6. The liquid composition of claim 1, wherein the organosilicate is selected from the group consisting of organoxysilanes, organoxysiloxanes, and mixtures thereof, wherein the organoxysilanes are selected from the group consisting of tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetraisopropoxysilane, tetra-n-butoxysilane, tetraisobutoxysilane, tetra-sec-butoxysilane, tetra-t-butoxysilane, tetraphenoxysilane, dimethoxydiethoxysilane, and mixtures there of.

7. The liquid composition of claim 1, wherein the organosilicate is present in the liquid composition in an amount ranging from 0.1 to 2 percent by weight calculated as SiO₂, based on the total weight of the composition.

8. The liquid composition of claim 1, wherein the photocatalytic material and the organosilicate are present in the liquid composition at a ratio of 0.05:

0.95 to 5;

0.3 by weight.

9. The liquid composition of claim 1, wherein the pH of the composition is no more than 3.5.

10. The liquid composition of claim 1, wherein the pH of the composition is from 7.0 to 8.5.

11. A substrate coated with a cured film formed from the liquid composition of claim 1.

12. The substrate of claim 11, wherein the film has a dry film thickness of 20 to 60 nanometers.

13. The substrate of claim 11, wherein the film exhibits an initial water contact angle, of no more than 10°

prior to photoexcitation of the photocatalytic material.

14. The substrate of claim 11, wherein, following excitation of the photocatalyst, the film exhibits a water angle with water of less than 5°

.

15. A method for making the liquid composition of claim 1, the method comprising the steps of:

(a) providing a hydrophilic material comprising an essentially completely hydrolyzed organosilicate, wherein the pH of the hydrophilic material is no more than 3.5;

(b) providing a sol or paste comprising a photocatalytic material dispersed in a diluent, wherein the pH of the sol or paste is no more than 3.5; and

(c) mixing the hydrophilic material provided in (a) with the sol or paste provided in (b) to disperse the photocatalytic material in the hydrophilic material.

16. The method of claim 15, wherein the hydrophilic material provided in step (a) is obtained by (1) providing a hydrophilic material comprising an essentially completely hydrolyzed organosilicate, wherein the pH of the hydrophilic material is greater than the desired pH, and (2) adding acid to the hydrophilic material until the desired pH is achieved.

17. The method of claim 15, wherein the sol or paste provided in step (b) is obtained by (1 )providing a sol or paste comprising a photocatalytic material dispersed in a diluent, wherein the pH of sol or paste is greater than the desired pH, and (2) adding acid to the sol or paste until the desired pH is achieved.

18. A method for making the liquid composition of claim 1, the method comprising the steps of:

(a) providing a hydrophilic material comprising an essentially completely hydrolyzed organosilicate, wherein the pH of the hydrophilic material is from 7.0to 8.5;

(b) providing a sol or paste comprising a photocatalytic material dispersed in a diluent, wherein the pH of the sol or paste is from 7.0 to 8.5; and

(c) mixing the hydrophilic material provided in (a) with the sol or paste provided in (b) to disperse the photocatalytic material in the hydrophilic material.

19. The method of claim 18, wherein the hydrophilic material provided in step (a) is obtained by (1 ) providing a hydrophilic material comprising an essentially completely hydrolyzed organosilicate, wherein the pH of the hydrophilic material is less than the desired pH, and (2) adding a base to the hydrophilic material until the desired pH is achieved.

20. The method of claim 18, wherein the sol or paste provided in step (b) is obtained by (1) providing a sol or paste comprising a photocatalytic material dispersed in a diluent, wherein the pH of sol or paste is less than the desired pH, and (2) adding a base to the sol or paste until the desired pH is achieved.

21. The liquid composition of claim 1, wherein the liquid composition is in the form of a one-pack liquid composition having a shelf-life of at least 3 months.

22. The composition of claim 21, wherein the one-pack liquid composition has a shelf-life of at least 6 months.

23. The composition of claim 22, wherein the one-pack liquid composition has a shelf-life of at least 12 months.

24. The composition of claim 23, wherein the composition has a turbidity of no more than 600 NTU after 3 months.

25. A method of coating a substrate comprising the steps of:

(a) applying to the substrate the liquid composition of claim 1, and

(b) curing the composition.

26. The method of claim 25, wherein the composition is cured by exposing the composition to air for at least two hours at 25°

C.

27. The liquid composition of claim 1, wherein the photocatalytic material is present in the liquid composition in an amount sufficient to produce a coating that maintains its initial water contact angle after exposure to a Cleveland Condensation Chamber for 4000 hours, wherein the CCC chamber is operated at a vapor temperature of 140°

F. (60°

C.) in an indoor ambient environment which results in constant water condensation on the test surface.

28. The liquid composition of claim 1, wherein the photocatalytic material is present in the liquid composition in an amount sufficient to produce a coating that maintain a contact angle of less than 10 degrees after exposure to a Cleveland Condensation Chamber for 4000 hours, wherein the CCC chamber is operated at a vapor temperature of 140°

F. (60°

C.) in an indoor ambient environment which results in constant water condensation on the test surface.

29. The liquid composition of claim 1 , wherein the binder is prepared by a process selected from:

(a) a multi-stage process comprising a first stage wherein a partial hydrolysis polycondensation reaction product is formed by reacting an organosilicate water in the presence of an acid hydrolysis catalyst, wherein the water is present in an amount that is less than the stoichiometric amount capable of hydrolyzing the organoxy groups of the organosilicate, and a second stage wherein the partial hydrolysis polycondensation reaction product is contacted with a large amount of water to form an essentially completely hydrolyzed organosilicate, and

(b) reacting a tetraalkoxysilane oligomer with water in the presence of an organic acid hydrolysis catalyst and/or an organic solvent, wherein the water is present in an amount that is considerably greater than the stoichiometric amount capable of hydrolyzing organoxy groups of the alkoxysilane to form an essentially completely hydrolyzed organosilicate.

30. The liquid composition of claim 29, wherein the binder is prepared by the multi-stage process.

31. The liquid composition of claim 30, wherein the water is present during the first stage in a stoichiometric amount capable of hydrolyzing 50 percent of the organoxy groups of the organosilicate.

32. The liquid composition of claim 30, wherein the first stage is conducted at conditions that limit the degree of condensation of Si—

OH groups formed as a result of the hydrolysis reaction.

33. The liquid composition of claim 32, wherein the conditions that limit the degree of condensation of Si—

OH groups formed as a result of the hydrolysis, reaction are selected from controlling the reaction exotherm by external cooling, controlling the rate of addition of the acid catalyst, and/or conducting the first stage hydrolysis in the substantial absence of any organic cosolvent.