Hydrophilic member and method for manufacturing same

Abstract

In a hydrophilic member including a structure in which a photocatalytic TiO.sub.2 layer and a porous SiO.sub.2 layer are stacked on a surface of a base material, easy forming of the porous SiO.sub.2 layer so as to be thin and have a uniform film thickness distribution that enables the porous SiO.sub.2 layer to cover an entire surface of the photocatalytic TiO.sub.2 layer, and enhancement in durability of the porous SiO.sub.2 layer are enabled. A photocatalytic TiO.sub.2 layer is formed so as to have a density of 3.33 to 3.75 g/cm.sup.3 (preferably 3.47 to 3.72 g/cm.sup.3, more preferably 3.54 to 3.68 g/cm.sup.3) on a surface of a base material. As an outermost surface layer, a porous SiO.sub.2 layer is formed on the photocatalytic TiO.sub.2 layer in such a manner that the porous SiO.sub.2 layer has a film thickness of no less than 10 nm and no more than 50 nm.

Claims

1. A hydrophilic member comprising a structure in which a layer consisting of TiO.sub.2 and having an anatase crystal structure and providing photocatalysis is formed so as to have a density of 3.33 to 3.75 g/cm.sup.3 on a surface of a base material, and a porous SiO.sub.2 layer is formed as an outermost surface layer on the TiO.sub.2 layer in such a manner that the porous SiO.sub.2 layer has a thickness of no less than 10 nm and no more than 50 nm and covers an entire surface of the TiO.sub.2 layer.

2. The hydrophilic member according to claim 1, wherein the density of the TiO.sub.2 layer is 3.47 to 3.72 g/cm.sup.3.

3. The hydrophilic member according to claim 2, wherein the density of the TiO.sub.2 layer is 3.54 to 3.68 g/cm.sup.3.

4. The hydrophilic member according to claim 1, wherein the film thickness of the porous SiO.sub.2 layer is no less than 15 nm and no more than 20 nm.

5. The hydrophilic member according to claim 2, wherein the film thickness of the porous SiO.sub.2 layer is no less than 15 nm and no more than 20 nm.

6. The hydrophilic member according to claim 3, wherein the film thickness of the porous SiO.sub.2 layer is no less than 15 nm and no more than 20 nm.

7. A hydrophilic member manufacturing method comprising the steps of: forming a layer consisting of TiO.sub.2 that provides photocatalysis, so as to have a density of 3.33 to 3.75 g/cm.sup.3 on a surface of a base material; and forming a porous SiO.sub.2 layer as an outermost surface layer on the TiO.sub.2 layer in such a manner that the porous SiO.sub.2 layer has a thickness of no less than 10 nm and no more than 50 nm and covers an entire surface of the TiO.sub.2 layer.

8. The hydrophilic layer of claim 1, wherein the density of the TiO.sub.2 layer is 3.33 to 3.54 g/cm.sup.3.

9. A hydrophilic member comprising a structure in which a layer consisting of TiO.sub.2 that provides photocatalysis is formed so as to have a density of 3.33 to 3.54 g/cm.sup.3 on a surface of a base material, and a porous SiO.sub.2 layer is formed as an outermost surface layer on the TiO.sub.2 layer in such a manner that the porous SiO.sub.2 layer has a thickness of no less than 10 nm and no more than 50 nm and covers an entire surface of the TiO.sub.2 layer.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic cross-sectional diagram illustrating an embodiment of a hydrophilic member of the present invention.

(2) FIG. 2 is a diagram indicating results of a test in which for each of samples of a hydrophilic member (samples of a hydrophilic member formed by forming a photocatalytic TiO.sub.2 layer on a surface of a flat and smooth base material and forming an SiO.sub.2 layer having a film thickness of no more than 50 nm obtained by vapor-depositing SiO.sub.2 vapor deposition molecules on the photocatalytic TiO.sub.2 layer with a low gas pressure that enables stable flight of the SiO.sub.2 vapor deposition molecules, the samples including respective photocatalytic TiO.sub.2 layers having different densities), time from a state in which hydrophilicity had been lost due to adherence of organic matter to a surface thereof to recovery of hydrophilicity due to ultraviolet irradiation was measured.

(3) FIG. 3 is a diagram indicating results of a test in which for each of samples that are similar to those used in the test in FIG. 2, a scratching load for the SiO.sub.2 layer was measured.

(4) FIG. 4 is a chart indicating results of a test in which for each of samples that are similar to those used in each of the tests in FIGS. 2 and 3, an acid-resistance of the SiO.sub.2 layer was measured.

(5) FIG. 5 is a schematic diagram illustrating an example of a vacuum vapor deposition apparatus 18 for manufacturing the hydrophilic member 10 in FIG. 1.

DESCRIPTION OF EMBODIMENT

(6) FIG. 1 is a schematic cross-sectional diagram of an embodiment of a hydrophilic member of the present invention. A hydrophilic member 10 is configured by forming a photocatalytic TiO.sub.2 layer 14 on a flat and smooth surface of a base material 12 and, as an outermost surface layer, forming a porous SiO.sub.2 layer 16 on the photocatalytic TiO.sub.2 layer 14. The porous SiO.sub.2 layer 16 is formed so as to have a uniform film thickness distribution that enables the porous SiO.sub.2 layer 16 to cover an entire surface of the photocatalytic TiO.sub.2 layer. A density of the photocatalytic TiO.sub.2 layer 14 is 3.33 to 3.75 g/cm.sup.3 (preferably 3.47 to 3.72 g/cm.sup.3, more preferably 3.54 to 3.68 g/cm.sup.3). A film thickness of the photocatalytic TiO.sub.2 layer 14 is 50 to 500 nm. A film thickness of the porous SiO.sub.2 layer 16 is no less than 10 nm and no more than 50 nm (preferably no less than 15 nm and no more than 25 nm).

(7) The hydrophilic member 10 enables provision of, for example, an automobile window, or building window glass by forming the base material 12 using a transparent glass plate or a transparent resin plate. Also, the hydrophilic member 10 enables provision of, for example, a back surface mirror-type outer mirror for a vehicle or a back surface mirror such as a bathroom mirror by forming the base material 12 using a transparent glass plate or a transparent resin plate and forming a reflective film on a back surface of the base material 12. Also, the hydrophilic member 10 enables provision of, for example, a front surface mirror such as a front surface mirror-type outer mirror for an automobile by forming the base material 12 using a glass plate or a resin plate and forming a reflective film between the base material 12 and the photocatalytic TiO.sub.2 layer 14. Also, the hydrophilic member 10 enables provision of a fog-resistant optical element by forming the base material 12 using an optical element such as a lens. If the base material 12 is a glass plate, a block layer (barrier layer) of, e.g., SiO.sub.2 can additionally be arranged between the base material 12 and the photocatalytic TiO.sub.2 layer 14 in order to prevent diffusion of alkali ions in the base material 12 into the photocatalytic TiO.sub.2 layer 14.

(8) An example of a method for manufacturing the hydrophilic member 10 in FIG. 1 will be described. Here, the base material 12 is formed using a glass plate, and each of the photocatalytic TiO.sub.2 layer 14 and the porous SiO.sub.2 layer 16 is formed by means of vapor deposition.

(9) FIG. 5 illustrates an example of a vacuum vapor deposition apparatus 18. A vacuum chamber 20 is evacuated by a diffusion pump 22 and a rotary pump 24. In an upper portion of the vacuum chamber 20, a substrate holder 26 is arranged, and a glass plate 12, which forms a base material for the hydrophilic member 10, is held by the substrate holder 26, with a film-forming surface directed downward. The substrate holder 26 is heated by a heater 28 and the glass plate 12 is kept at a desired temperature via the substrate holder 26. A crucible 30 is arranged at a position below the glass plate 12, and a vapor deposition material (starting substance for vapor deposition) 32 is placed in the crucible 30. Examples of the vapor deposition material 32 for forming a TiO.sub.2 layer 14 include, e.g., TiO.sub.2, Ti.sub.2O.sub.3 and Ti. Examples of the vapor deposition material 32 for forming an SiO.sub.2 layer 16 include, e.g., SiO.sub.2 and SiO.

(10) The vapor deposition material 32 is evaporated as a result of being irradiated with an electron beam 36 emitted from a hot cathode 34. As a reactive gas, an oxygen gas 42 is introduced from an oxygen tank 40 into the vacuum chamber 20. The evaporated vapor deposition material 32 reacts with the oxygen gas 42 to produce TiO.sub.2 or SiO.sub.2. The produced TiO.sub.2 or SiO.sub.2 is deposited on a surface of the glass plate 12, whereby a TiO.sub.2 layer 14 or an SiO.sub.2 layer 16 is formed. A film thickness during the film forming is monitored by a film thickness monitoring apparatus 44, and the vapor deposition is stopped when a desired film thickness is reached.

(11) Film properties of the vapor-deposited film vary depending on, e.g., the temperature of the glass plate 12, the vapor deposition speed and the partial pressure of the oxygen gas 42 in the vacuum chamber 20. An example of film forming conditions for forming a photocatalytic TiO.sub.2 layer having a density of 3.33 to 3.75 g/cm.sup.3 and forming a porous SiO.sub.2 layer 16 on the photocatalytic TiO.sub.2 layer 14 having a uniform film thickness distribution that enables the SiO.sub.2 layer 16 to cover an entire surface of the photocatalytic TiO.sub.2 layer if the film thickness of the porous SiO.sub.2 layer 16 is no less than 10 nm is indicated in the following table.

(12) TABLE-US-00001 Photocatalytic Porous SiO.sub.2 TiO.sub.2 layer 14 layer 16 Temperature of 300 degrees centigrade 300 degrees centigrade glass plate 12 Vapor 0.5 nm/sec. 0.2 nm/sec. deposition speed Partial pressure 0.016 Pa 0.016 Pa of oxygen gas 42

(13) An example of a procedure for forming a photocatalytic TiO.sub.2 layer 14 and a porous SiO.sub.2 layer 16 using the vacuum vapor deposition apparatus 18 in FIG. 5 will be described below. A photocatalytic TiO.sub.2 layer 14 is formed, for example, according to the following procedure. (1) Hold a glass plate 12 in the substrate holder 26, place, for example, Ti.sub.2O.sub.3 as a vapor deposition material 32 in the crucible 30, and close the vacuum chamber 20. (2) Drive the rotary pump 24 and the diffusion pump 22 to evacuate the vacuum chamber 20. (3) Drive the heater 28 to heat the glass plate 12 to a predetermined temperature through the substrate holder 26. (4) Introduce an oxygen gas 42 from the oxygen tank 40 into the vacuum chamber 20. (5) Drive the hot cathode 34 to irradiate the Ti.sub.2O.sub.3, which is a vapor deposition material 32, with an electron beam 36 to evaporate the Ti.sub.2O.sub.3. (6) The evaporated Ti.sub.2O.sub.3 reacts with the oxygen gas 42 to produce TiO.sub.2. The produced TiO.sub.2 is deposited on the glass plate 12, whereby a TiO.sub.2 film is formed. (7) End the film forming when approximately 100 nm of TiO.sub.2 is deposited.

(14) Upon the end of the forming of the photocatalytic TiO.sub.2 layer 14, subsequently, a porous SiO.sub.2 layer 16 is formed. A porous SiO.sub.2 layer 16 is formed, for example, according to the following procedure. (1) Place, for example, SiO.sub.2 as a vapor deposition material 32 in the crucible 30 and close the vacuum chamber 20. (2) Drive the rotary pump 24 and the diffusion pump 22 to evacuate the vacuum chamber 20. (3) Drive the heater 28 to heat the glass plate 12 to a desired temperature through the substrate holder 26. (4) Introduce an oxygen gas 42 from the oxygen tank 40 to the vacuum chamber 20. (5) Drive the hot cathode 34 to irradiate the SiO.sub.2, which is a vapor deposition material 32, with an electron beam 36 to evaporate the SiO.sub.2. (6) The evaporated SiO.sub.2 is deposited on the photocatalytic TiO.sub.2 layer 14 on the glass plate 12, whereby a SiO.sub.2 film is formed. (7) End the film forming when approximately 15 nm of SiO.sub.2 is deposited.

(15) Since an outermost surface of the hydrophilic member 10 produced by the above process include the porous SiO.sub.2 layer 16 alone, the hydrophilic member 10 exerts excellent effects in surface hardness and hydrophilicity maintenance compared to cases where the outermost surface includes a photocatalytic TiO.sub.2 layer alone or a layer of a mixture of photocatalytic TiO.sub.2 and SiO.sub.2.

(16) Although the above embodiment has been described in terms of a case where a photocatalytic TiO.sub.2 layer and a porous SiO.sub.2 layer are formed by means of vapor deposition, it can be considered that the effects of the invention according to the present application can also be expected where both or one of the layers is formed by means of another thin film forming method (for example, sputtering).