Method for photocatalytically rendering a surface of a substrate superhydrophilic, a substrate with superhydrophilic photocatalytic surface, and method of making thereof

• US 7,294,365 B2
• Filed: 08/23/2004
• Issued: 11/13/2007
• Est. Priority Date: 03/20/1995
• Status: Expired due to Fees

• Current Assignee: Toto Limited
• Original Assignee: Toto Limited
• Inventors: Fujishima, Akira, Hashimoto, Kazuhito, Hayakawa, Makoto, Watanabe, Toshiya, Kitamura, Atsushi, Kojima, Eiichi, Machida, Mitsuyoshi, Chikuni, Makoto, Norimoto, Keiichiro
• Primary Examiner(s): PADGETT, MARIANNE L
• Application Number:
  US10/924,158
• Publication Number:
  US 20050019700A1
• Time in Patent Office: 1,177 Days
• Field of Search: None
• US Class Current: 427/553
• CPC Class Codes: C03C 17/23 Oxides C03C17/02 takes precedence
• CPC Class Codes: C03C 17/2456 Coating containing TiO2
• CPC Class Codes: C03C 17/256 Coating containing TiO2
• CPC Class Codes: C03C 2217/212 TiO2
• CPC Class Codes: C03C 2217/229 Non-specific enumeration
• CPC Class Codes: C03C 2217/23 Mixtures
• CPC Class Codes: C03C 2217/71 Photocatalytic coatings
• CPC Class Codes: C03C 2218/113 by sol-gel processes
• CPC Class Codes: C03C 2218/151 by vacuum evaporation
• CPC Class Codes: C03C 2218/32 After-treatment
• CPC Class Codes: C09K 3/18 for application to surfaces to minimize adherence of ice, mist or water thereto rendering particulate materials free flowing, in general, e.g. making them hydrophobic B01J2/30; Thawing or antifreeze materials for application to surfaces used in liquids for heat-transfer, heat-exchange or heat-storage or for the production of heat or cold other than by combustion, e.g. radiator liquids, C09K5/00
• CPC Class Codes: G02B 1/18 Coatings for keeping optical surfaces clean, e.g. hydrophobic or photo-catalytic films G02B1/16 takes precedence

Abstract

A method of preventing or reducing fogging of a surface of a composite when subjected to humid conditions includes providing a composite with a surface. The composite includes a substrate and a photocatalytic surface layer. The photocatalytic surface layer includes a photocatalyst. The method further includes subjecting the photocatalyst to photoexcitation to render the surface of the composite hydrophilic, wherein, after the photoexcitation, the surface of the composite has a water wettability of less than 10° in terms of the contact angle with water. The method further includes subjecting the composite to humidity that is sufficient to induce fogging of the substrate if the photocatalytic surface layer were absent.

Claims

1. A method of preventing or reducing fogging of a surface of a composite when subjected to humid conditions, comprising:

providing a composite with a surface, said composite comprising a substrate and a photocatalytic surface layer, said photocatalytic surface layer comprising a photocatalyst;

subjecting the photocatalyst to photoexcitation by exposing the composite to light from an indoor illumination lamp having a UV intensity from about 0.001 to about 1 mW/cm², to render the surface of the composite hydrophilic, wherein, after said photoexcitation, the surface of the composite has a water wettability of less than 10°

in terms of the contact angle with water; and

subjecting the composite to humidity that is sufficient to induce fogging of said substrate if said photocatalytic surface layer were absent.

2. The method of claim 1, wherein, after said photoexcitation, the surface of the composite has a water wettability of less than 5°

in terms of the contact angle with water.

3. The method of claim 1, wherein, after said photoexcitation, the surface of the composite has a water wettability of about 0°

in terms of the contact angle with water.

4. The method of claim 1, wherein said photocatalyst is selected from the group consisting of TiO₂, ZnO, SnO₂, SrTiO₃, WO₃, Bi₂O₃ and Fe₂O₃.

5. The method of claim 4, wherein said photocatalytic surface layer further comprises a metal selected from the group consisting of Ag, Cu and Zn.

6. The method of claim 4, wherein said photocatalytic surface layer further comprises a metal selected from the group consisting of Pt, Pd, Rh, Ru, Os and Ir.

7. The method of claim 1, wherein said substrate comprises glass.

8. The method of claim 1, wherein, said substrate comprises glass containing alkaline network modifier ions, and wherein said composite further comprises a film disposed between said substrate and said photocatalytic surface layer, said film preventing ions from diffusing from said substrate into said photocatalytic surface layer.

9. The method of claim 8, wherein said film comprises silica.

10. The method of claim 1, wherein said photocatalytic surface layer further comprises silica or silicone.

11. The method of claim 1, wherein said photocatalytic surface layer consists essentially of said photocatalyst.

12. A method for maintaining a surface of a composite in a clean state when subjected to dirt in air and precipitation, comprising:

providing a composite with a surface, said composite comprising a substrate and a photocatalytic surface layer, said photocatalytic surface layer comprising a photocatalyst;

subjecting the photocatalyst to photoexcitation by exposing the composite to light from an indoor illumination lamp having a UV intensity from about 0.001 to about 1 mW/cm2, to render the surface of the composite hydrophilic, wherein, after said photoexcitation, the surface of the composite has a water wettability of less than about 20°

in terms of the contact angle with water;

subjecting said composite to dirt in air or precipitation; and

washing away the dirt on the surface of the composite by occasional contact with water.

13. The method of claim 12, wherein, after said photoexcitation, the surface of the composite has a water wetrability of less than 10°

in terms of the contact angle with water.

14. The method of claim 12, wherein, after said photoexcitation, the surface of the composite has a water wettability of less than 5°

in terms of the contact angle with water.

15. The method of claim 12, wherein, after said photoexcitation, the surface of the composite has a water wettability of about 0°

in terms of the contact angle with water.

16. The method of claim 12, wherein said photocatalyst is selected from the group consisting of TiO₂, ZnO, SnO₂, SrTiO₃, WO₃, Bi₂O₃ and Fe₂O₃.

17. The method of claim 16, wherein said photocatalytic surface layer further comprises a metal selected from group consisting of Ag, Cu and Zn.

18. The method of claim 16, wherein said photocatalytic surface layer further comprises a metal selected from the group consisting of Pt, Pd, Rh, Ru, Os and Ir.

19. The method of claim 12, wherein said substrate comprises glass containing alkaline network modifier ions, and wherein said composite further comprises a film disposed between said substrate and said photocatalytic surface layer, said film preventing ions from diffusing from said substrate and photocatalytic surface layer.

20. The method of claim 19, wherein said film comprises silica.

21. The method of claim 12, wherein said substrate is a tile, a portion of the body of a motor vehicle, an inner panel of a building, or an outer panel of a building.

22. The method of claim 12, wherein said photocatalytic surface layer further comprises silica.

23. The method of claim 12, wherein said photocatalytic surface layer consists essentially of said photocatalyst.