Method for photocatalytically hydrophilifying surface and composite material with photocatalytically hydrophilifiable surface

• US 6,090,489 A
• Filed: 06/19/1998
• Issued: 07/18/2000
• Est. Priority Date: 12/22/1995
• Status: Expired due to Term

• 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): Meeks, Timothy
• Assistant Examiner(s): Strain, Paul D.
• Application Number:
  US09/091,692
• Time in Patent Office: 760 Days
• Field of Search: 427/301, 427/333, 428/409, 428/403, 428/411.1
• US Class Current: 428/409
• CPC Class Codes: C03C 17/23 Oxides C03C17/02 takes precedence
• 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 2217/71 Photocatalytic coatings
• CPC Class Codes: C03C 2218/113 by sol-gel processes
• 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
• CPC Class Codes: Y10T 428/31 Surface property or characteristic of web, sheet or block
• CPC Class Codes: Y10T 428/31504 Composite [nonstructural laminate]

Abstract

A method for hydrophilifying the surface of a substrate by taking advantage of photocatalytic action. The substrate has a photocatalytic titania coating (10). The surface of the photocatalytic coating (10) bears the solid acid that increases a hydrogen bond component (γ_S^h) in the surface energy in the solid/gas interface of the coating. Photoexcitation of the photocatalyst enhances the hydrogen bond component (γ_S^h) in the surface energy of the photocatalytic coating (10), accelerating the physical adsorption of molecules of water in the atmosphere through a hydrogen bond (16) onto hydrogen atoms in a terminal OH group (12), bonded to a titanium atom, and a bridge OH group (14) on the surface of the coating. This results in the formation of a high density, physically adsorbed water layer (18) on the surface of the photocatalytic coating (10), thus permitting the surface of the substrate to be easily hydrophilified. The method is applicable to antifogging, antifouling, selfcleaning and cleaning of articles.

Claims

1. A method for hydrophilifying the surface of a substrates comprising the steps of:

providing a substrate coated with a solid layer having an interface with air, and containing a photoatalyst; and

photoexciting the photocatalyst to permit molecules of water to be physically adsorbed onto the surface of said layer under the photocatalytic action of said photoctalyst, thereby hydrophilifying the surface of said substrate.

4. The method according to any one of claims 1 to 3, wherein said layer further comprises an enhancing agent for increasing the hydrogen bond component, γ

_S^h, in the surface energy at the interface between said layer and air.

5. The method according to claim 4, wherein said solid layer has a high hydrogen bond component in the surface energy at said interface.

6. The method according to claim 5, wherein the material that increases a hydrogen bond component in the surface energy comprises a solid acid.

7. The method according to claim 6, wherein the solid acid is a metal oxide bearing sulfuric acid.

8. The method according to claim 6, wherein the solid acid is a metal oxide bearing nitric acid.

9. The method according to claim 6, wherein the solid acid is a compound oxide of metals.

10. The method according to claim 9, wherein the compound oxide of metals is an oxide superstrong acid.

11. The method according to claim 9, wherein the metal oxide composite is selected from the group consisting of TiO₂ /WO₃,WO₃ /ZrO₂, and WO₃ /SnO₂.

12. The method according to claim 6, wherein the solid acid is Al₂ O₃.SiO₂.

13. The method according to claim 5, wherein the material that increases said hydrogen bond component in the surface energy is a solid base.

2. A method for hydrophilifying the surface of a substrate, comprising the steps of:

providing a substrate coated with a solid layer having an interface with air, said layer containing a photocatalyst, and, at said interface, a hydrogen bond component, γ

_S^h ; and

photoexciting the photocatalyst to increase said hydrogen bond component under the photocatalytic action of said photocatalyst.

3. A method for hydrophilifying the surface of a substrate, comprising the steps of:

providing a substrate coated with a solid layer having an interface with air, said layer containing a photocatalyst, and having, at said interface, a hydrogen bond component, γ

_S^h ; and

photoexciting the photocatalyst to increase said hydrogen bond component under the photocatalytic action of said photocatalyst, thereby accelerating the physical adsorption of molecules of water onto the surface of said layer.

14. A method for enhancing the oil repellency of the surface of a the substrate in water, comprising the steps of:

providing a substrate coated with a solid layer having an interface with air, and containing a photocatalyst; and

photoexciting the photocatalyst to increase a hydrogen bond component, in the surface energy in the solid/gas interface of said layer under the photocatalytic action of said photocatalyst, thereby enhancing the oil repellency of the surface of the substrate when placed in water.

15. A method for cleaning a substrate, comprising the steps of:

providing a substrate coated with a solid layer having an interface with air, and containing a photocatalytic semiconductor material;

photoexciting the photoctalyst to enhance a hydrogen bond component, γ

₅^h, in the surface energy in the solid/gas interface of said layer tinder the photoctalytic action of said photocatalyst, thereby enhancing the oil repellency of the surface of the substrate when placed in water; and

immersing the substrate in water or wetting the substrate with water to release an oil stain adhering on the surface of the substrate.

16. A composite with a hydroplilifiable surface, comprising:

a substrate;

a solid layer provided on the surface of the substrate and having an interface with air, said layer containing a photocatalyst; and

a layer of molecules of water physically adsorbed onto the surface of said layer containing a photocatalyst in response to the photoexcitation of the photocatalyst.

21. The method according to any one of claims 16 to 20, wherein said layer further comprises an enhancing agent for increasing the hydrogen bond component, γ

_S^h, in the surface energy at the interface between said layer and air.

22. The composite according to claim 21, wherein the agent that increases a hydrogen bond component in the surface energy comprises a solid acid.

23. The composite according to claim 22, wherein the solid acid is a metal oxide bearing sulfuric acid.

24. The composite according to claim 22, wherein the solid acid is a metal oxide bearing nitric acid.

25. The composite according to claim 22, wherein the solid acid is a compound oxide of metals.

26. The composite according to claim 25, wherein the compound oxide of metals is an oxide superstrong acid.

27. The composite according to claim 25, wherein the compound oxide of metals is selected from the group consisting of TiO₂ /WO₃, WO₃ /ZrO₂, and WO₃ /SnO₂.

28. The composite according to claim 22, wherein the solid acid is Al₂ O₃.SiO₂.

29. The composite according to claim 21, wherein the agent that increases a hydrogen bond component in the surface energy is a solid base.

17. A composite with a hydrophilifiable surface, comprising:

a substrate; and

a solid layer provided on the surface of the substrate and having an interface with air, said layer containing a photocatalyst and adapted to increase the hydrogen bond component, γ

_S^h, in the surface energy at said interface in response to the photoexcitation of said photocatalyst.

18. A composite with a hydrophilifiable surface, comprising:

a substrate;

a solid layer provided on the surface of the substrate and having an interface with air, said layer containing a photocatalyst and adapted to increase the hydrogen bond component, γ

_S^h, in the surface energy at said interface in response to photoexcitation of said photocatalyst; and

a layer of molecules of water physically adsorbed onto the surface of said layer containing a photocatalyst in response to the photoexcitation of the photocatalyst.

19. A composite with a surface adapted to be rendered oil repellent in water, comprising:

a substrate;

a solid layer provided on the surface of the substrate and having an interface with air, said layer containing a photocatalyst and adapted to increase the hydrogen bond component, γ

_S^h, in the surface energy at said interface in response to photoexcitation of said photocatalyst, thereby increasing the oil repellency of the surface of the composite in water.

20. A composite with an easily cleanable surface, comprising:

a substrate; and

a solid layer provided on the surface of the substrate and having an interface with air, said layer containing a photocatalyst,

said layer operating to increase the hydrogen bond component, γ

_S^h, in the surface energy at said interface in response to photoexcitation of the photocatalyst, thereby enhancing the oil repellency of the surface of the composite in water, whereby, upon immersion of the composite in water or wetting of the composite with water, an oil stain adhering on the surface of said layer is released therefrom.