Multi-layer coatings and related methods

• US 20050266248A1
• 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, Millero, Edward R.
• Granted Patent: US 7,354,624 B2
• Time in Patent Office: Days
• US Class Current: 428/411.100
• CPC Class Codes: C08K 3/22 of metals
• CPC Class Codes: C08L 2666/54 Inorganic substances
• CPC Class Codes: C09D 183/02 Polysilicates
• CPC Class Codes: C09D 5/1675 Polyorganosiloxane-containing compositions
• CPC Class Codes: C09D 7/61 inorganic
• CPC Class Codes: Y10T 428/25 Web or sheet containing structurally defined element or component and including a second component containing structurally defined particles
• CPC Class Codes: Y10T 428/26 Web or sheet containing structurally defined element or component, the element or component having a specified physical dimension
• CPC Class Codes: Y10T 428/31504 Composite [nonstructural laminate]

Abstract

Multi-layer coatings are disclosed that include (a) a first layer deposited from at least one composition that includes a polymeric composition, and (b) a second layer applied over at least a portion of the first layer in which the second layer is deposited from at least one liquid composition that includes (i) a photocatalytic material, and (ii) a binder that is hydrophilic and comprises an essentially completely hydrolyzed organosilicate. Also disclosed are substrates coated with such multi-layer coatings, methods of applying such multi-layer coatings to a substrate and methods of making a painted surface easy-to-clean.

Claims

1. A multi-layer coating comprising:

(a) a first layer deposited from at least one composition that comprises a polymeric composition, and

(b) a second layer applied over at least a portion of the first layer in which the second layer is deposited from at least one liquid composition that comprises (i) a photocatalytic material, and (ii) a binder that is hydrophilic and comprises an essentially completely hydrolyzed organosilicate.

2. The multi-layer coating of claim 1, wherein the average crystalline diameter is 3 to 35 nanometers.

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

7. The multi-layer coating 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 multi-layer coating 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 multi-layer coating of claim 1, wherein the pH of the liquid composition from which the second layer is deposited is no more than 3.5.

10. The multi-layer coating of claim 1, wherein the pH of the liquid composition from which the second layer is deposited is from 7.0 to 8.5.

11. A substrate coated with the multi-layer coating of claim 1.

12. The multi-layer coating of claim 1, wherein the second layer is applied directly over at least a portion of the first layer such that there is no protective layer between the first layer and the second layer.

13. The multi-layer coating of claim 1, wherein the second layer is applied at a dry film thickness of 20 to 40 nanometers.

14. The multi-layer coating of claim 1, wherein, following excitation of the photocatalyst, the multi-layer coating exhibits a water angle with water of less than 5°

.

15. The multi-layer coating 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.

16. The multi-layer coating of claim 15, wherein the binder is prepared by the multi-stage process.

17. The multi-layer coating of claim 16, 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.

18. The multi-layer coating of claim 17, 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.

19. The multi-layer coating of claim 18, 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.

20. A method for improving the anti-fouling and/or self-cleaning properties of a painted article, wherein the article comprises a surface having a polymeric composition deposited thereon, the method comprising

(a) applying a liquid composition comprising (i) a photocatalytic material, and (ii) a binder that is hydrophilic and comprises an essentially completely hydrolyzed organosilicate on the polymeric composition;

and

(b) curing the composition applied in step (a).

21. The method of claim 20, wherein step (b) comprises air drying the composition of the second layer.

22. The method of claim 20, wherein, following step (b), the cured composition applied in step (b) exhibits an initial water contact angle of no more than 10°

prior to photoexcitation of the photocatalytic material.

23. The method of claim 20, wherein the liquid composition applied in step (a) is applied directly over at least a portion of the polymeric composition such that there is no protective layer between the polymeric composition and the composition applied in step (a).