Hydrophilic Element

Abstract

Hydrophilic element (10) comprising a structure in which a TiO2 layer (14) provides photocatalysis such that it has a density of 3.33 to 3.75 g / cm³ 3 exhibits, is formed on a surface of a base material (12), and a porous SiO2 layer (16) is formed as an outermost surface layer on the TiO2 layer (14) such that the porous SiO2 layer (16) has a thickness of not less than 10 nm and not more than 50 nm and covers the entire surface of the TiO2 layer (14).

Description

Technical area

[0001] The present invention relates to a hydrophilic element comprising a structure in which a TiO2 (photocatalytic TiO2) layer providing photocatalysis and a porous SiO2 layer are stacked on a surface of a base material. Specifically, the present invention enables an easily formed porous SiO2 layer that is thin and has a uniform film thickness distribution, allowing the porous SiO2 layer to cover the entire surface of the photocatalytic TiO2 layer, and improving the durability of the porous SiO2 layer. State of the art

[0002] Examples of a hydrophilic element comprising a structure in which a photocatalytic TiO2 layer and a porous SiO2 layer are stacked on a surface of a base material are described in Patent Documents 1 and 2. The hydrophilic element described in each of Patent Documents 1 and 2 is a hydrophilic element that ensures hydrophilicity by means of the porous SiO2 layer at an outermost surface, decomposes organic matter and the like adhered to the porous SiO2 layer by means of photocatalysis provided by the photocatalytic TiO2 layer below the porous SiO2 layer, and thereby enables the hydrophilicity of the porous SiO2 layer to be maintained for a long period of time. Document listPatent documents Patent document 1: JP H10 - 36 144 A Patent document 2: JP 2000 - 53 449 A Summary of the inventionTechnical problem

[0003] In a hydrophilic element comprising the above-mentioned structure, in order to ensure uniformity (i.e., no irregularity in all areas of a hydrophilic surface of the hydrophilic element) and preferably hydrophilicity in every part of the hydrophilic surface, it is necessary to form a porous SiO2 layer that is thin and has a uniform film thickness distribution, which allows the porous SiO2 layer to cover the entire surface of a photocatalytic TiO2 layer when the film thickness of the porous SiO2 layer is not more than 50 nm (preferably not more than 20 nm). However, it is not easy to form a porous SiO2 layer that is thin and has a uniform film thickness distribution on a photocatalytic TiO2 layer. In other words, to form a porous SiO2 layer on a photocatalytic TiO2 layer, for example,By vapor deposition, it is necessary to vapor-deposit SiO2 with an increased gas pressure (partial pressure of oxygen gas) in a vapor-deposition atmosphere, compared to the gas pressure in cases where a non-porous vapor-deposited SiO2 layer is formed. However, vapor deposition with an increased gas pressure in a vapor-deposition atmosphere causes instability in the flight of SiO2 vapor-deposited molecules. Consequently, irregularity in the film thickness distribution occurs in some areas of the hydrophilic surface, resulting in the partial exposure of the photocatalytic TiO2 layer. Therefore, to form a SiO2 layer having a uniform film thickness distribution, some ingenuity (e.g.,when arranging a correction plate and / or limiting the number of elements that are subjected to the film formation process at one time).

[0004] The present invention is intended to solve the above-mentioned problems. In other words, the present invention is intended to provide a hydrophilic element having an easily formed porous SiO2 layer that is thin and has a uniform film thickness distribution, allowing the porous SiO2 layer to cover the entire surface of a photocatalytic TiO2 layer, thereby preventing the photocatalytic TiO2 layer from being partially exposed and improving the durability of the porous SiO2 layer. Solution to the problem

[0005] The Fig.Figure 2 shows the results of a test for measuring the hydrophilicity recovery time of a hydrophilic element. The hydrophilic element used in this test is a hydrophilic element formed by forming a photocatalytic TiO2 layer on the surface of a flat and smooth base material and forming a SiO2 layer with a film thickness of no more than 50 nm, which was obtained by vapor-depositing SiO2 molecules, on the photocatalytic TiO2 layer at a low gas pressure that allows stable flight of the SiO2 molecules.Samples of the hydrophilic element with respective photocatalytic TiO2 layers having different densities were prepared, and for each sample, the time from a state where hydrophilicity was lost due to adhesion of organic matter to a surface thereof to the recovery of hydrophilicity due to ultraviolet irradiation (hydrophilicity recovery time) was measured. In this test, a surface of the SiO2 layer of each sample was contaminated with an oil, causing the surface's hydrophilicity to be lost, and then the surface was irradiated with ultraviolet radiation at an intensity of 1 mW / cm. 2irradiated using black light. The recovery of hydrophilicity was determined when the water droplet contact angle was reduced to a value comparable to an initial value before contamination (no more than five degrees). Furthermore, whether SiO2 vapor deposition molecules fly stably during sample preparation can be determined based on whether, for example, the current value (emission current value) of an electron beam or the vapor deposition rate is stable during vapor deposition. In this case, the vapor deposition rate can be measured, for example, as a derivative value of the oscillation frequency of a quartz crystal film thickness gauge. Furthermore, the density of the photocatalytic TiO2 layer of each sample can be adjusted by the film formation conditions (e.g., the temperature of the base material, the film formation rate, and / or the gas pressure), and the density can be determined, for example, bymeasured using glancing angle X-ray diffraction. As shown in the . Fig. 2, the hydrophilicity recovery time is shorter at a lower density of the photocatalytic TiO2 layer, and when the density is 3.68 g / cm 3 the hydrophilicity recovery time increases dramatically, and when the density exceeds 3.75 g / cm 3exceeds, the hydrophilicity recovery time becomes too long and the photocatalytic TiO2 layer becomes unsuitable for practical use. A short hydrophilicity recovery time means that the photocatalysis provided by the photocatalytic TiO2 layer easily reaches the surface of the SiO2 layer because the SiO2 layer is porous. A long hydrophilicity recovery time means that the photocatalysis provided by the photocatalytic TiO2 layer hardly reaches the surface of the SiO2 layer because the SiO2 layer is non-porous. The results of this test show that the formation of a photocatalytic TiO2 layer such that it has a density of no more than 3.75 g / cm 3 (preferably not more than 3.72 g / cm 3 , more preferably not more than 3.68 g / cm 3 ), which is a lower value than 3.90 g / cm 3which is a typical density of anatase crystal structures, enables the formation of a porous SiO2 layer even when SiO2 vapor deposition molecules are subjected to vapor deposition on the photocatalytic TiO2 layer at a low gas pressure, which enables stable flight of the SiO2 vapor deposition molecules. Since the vapor deposition can be carried out at a low gas pressure, a porous SiO2 layer that is thin and has a uniform film thickness distribution can be easily formed without any special ingenuity in the film formation process. The test conducted by the present inventors shows that when a photocatalytic TiO2 layer having a density of not more than 3.75 g / cm 3is formed, and SiO2 vapor deposition molecules are vapor-deposited on the photocatalytic TiO2 layer at a low gas pressure that allows stable flight of the SiO2 vapor deposition molecules, a porous SiO2 layer is formed. Furthermore, when the porous SiO2 layer has a thickness of not less than 10 nm, the entire surface of the photocatalytic TiO2 layer can be covered by the porous SiO2 layer (i.e., partial exposure of the photocatalytic TiO2 layer can be prevented).

[0006] The Fig. Figure 3 shows the results of a test in which for each of the samples similar to those used in the test in the Fig.2 were used (samples of a hydrophilic element formed by forming a photocatalytic TiO2 layer on a surface of a flat and smooth base material and forming an SiO2 layer with a film thickness of not more than 50 nm, which was obtained by vapor deposition of SiO2 vapor deposition molecules on the photocatalytic TiO2 layer with a low gas pressure that allows stable flight of the SiO2 vapor deposition molecules, the samples comprising respective photocatalytic TiO2 layers having different densities), the scratch load for the SiO2 layer was measured. This test was carried out according to a method similar to that of a pencil hardness test, using an iron rod instead of a pencil, by measuring a load with different weights, respectively. Fig.Figure 3 shows that at a lower density of the photocatalytic TiO2 layer, the SiO2 layer formed on the photocatalytic TiO2 layer is more brittle, and that at a higher density of the photocatalytic TiO2 layer, the SiO2 layer is harder.

[0007] The Fig. Figure 4 shows results of a test in which for each of samples similar to those used in each of the tests in the Fig. 2 and Fig. 3, the acid resistance of the SiO2 layer was measured. This test was conducted by dropping H2SO4, which has a normal concentration of 0.1 N, onto a surface of the SiO2 layer and determining the condition of the surface after standing for 24 hours. In this test, when the density of the photocatalytic TiO2 layer was less than 3.33 g / cm 3, the color of a part onto which H2SO4 was dropped faded more than the color of a part surrounding that part. This is because the base material was exposed as a result of the SiO2 layer and the photocatalytic TiO2 layer being peeled off at that part, resulting in no interference color generated by the SiO2 layer and the photocatalytic TiO2 layer. On the other hand, when the density of the photocatalytic TiO2 layer is not less than 3.33 g / cm 3 , no fading occurred on the part where H2SO4 was dropped, and the SiO2 layer and the photocatalytic TiO2 layer were not peeled off. Therefore, the test results in the Fig. 4, that when the density of the photocatalytic TiO2 layer is less than 3.33 g / cm 3the acid resistance is low, and if the density of the photocatalytic TiO2 layer is not less than 3.33 g / cm 3 is, the acid resistance is high.

[0008] The test results in the Fig. 3 and Fig. 4 show that the formation of a photocatalytic TiO2 layer having a density of not less than 3.33 g / cm 3 (preferably not less than 3.47 g / cm 3 , more preferably not less than 3.54 g / cm 3 ), in practice enables the provision of long-term resistance (scratch resistance and acid resistance).

[0009] Accordingly, the results of the tests in the Fig. 2 to 4, that the formation of a photocatalytic TiO2 layer having a density of 3.33 to 3.75 g / cm 3 (preferably 3.47 to 3.72 g / cm 3 , more preferably 3.54 to 3.68 g / cm 3), enables easy formation of a porous SiO2 layer that is thin and has a uniform film thickness distribution, which allows the porous SiO2 layer to cover the entire surface of the photocatalytic TiO2 layer and increases the durability of the porous SiO2 layer.

[0010] Therefore, in the present invention, a photocatalytic TiO2 layer having a density of 3.33 to 3.75 g / cm 3 (preferably 3.47 to 3.72 g / cm 3 , more preferably 3.54 to 3.68 g / cm 3) is formed on a surface of a base material, and as the outermost surface layer, a porous SiO2 layer having a film thickness of not less than 10 nm and not more than 50 nm (preferably not less than 15 nm and not more than 20 nm) is formed on the TiO2 layer such that the porous SiO2 layer covers the entire surface of the TiO2 layer. Consequently, a thin porous SiO2 layer can be formed on a photocatalytic TiO2 layer, and it can also be formed to have a uniform film thickness distribution, allowing the porous SiO2 layer to cover the entire surface of the photocatalytic TiO2 layer, whereby favorable and uniform photocatalysis can be provided by the photocatalytic TiO2 layer. Furthermore, the durability of the porous SiO2 layer can also be increased. Short description of the drawings [ Fig. 1] Fig. 1 is a schematic cross-sectional diagram showing an embodiment of a hydrophilic element of the present invention. [ Fig. 2] Fig.2 is a graph showing results of a test in which, for each of samples of a hydrophilic element (samples of a hydrophilic element formed by forming a photocatalytic TiO2 layer on a surface of a flat and smooth base material and forming an SiO2 layer having a film thickness of not more than 50 nm obtained by vapor-depositing SiO2 vapor-deposited molecules on the photocatalytic TiO2 layer with a low gas pressure that allows stable flight of the SiO2 vapor-deposited molecules, the samples comprising respective photocatalytic TiO2 layers having different densities), the time from a state where hydrophilicity was lost due to adhesion of organic matter to a surface thereof to recovery of hydrophilicity due to ultraviolet irradiation was measured. [ Fig. 3] Fig.Figure 3 is a graph showing results of a test in which, for each of samples similar to those used in the test in the Fig. 2 were used, the scratch load for the SiO2 layer was measured. [ Fig. 4] Fig. 4 is a table showing results of a test in which, for each of samples similar to those used in the tests in the Fig. 2 and Fig. 3 were used, the acid resistance of the SiO2 layer was measured. [ Fig. 5] Fig. Fig. 5 is a schematic diagram showing an example of a vacuum vapor deposition apparatus 18 for producing the hydrophilic member 10 in the Fig. 1 shows. Description of an embodiment

[0011] The Fig.Figure 1 is a schematic cross-sectional diagram of one embodiment of a hydrophilic element of the present invention. A hydrophilic element 10 is formed by forming a photocatalytic TiO2 layer 14 on a flat and smooth surface of a base material 12 and forming a porous SiO2 layer 16 as the outermost layer on the photocatalytic TiO2 layer 14. The porous SiO2 layer 16 is formed to have a uniform film thickness distribution, allowing the porous SiO2 layer 16 to cover the entire surface of the photocatalytic TiO2 layer. The density of the photocatalytic TiO2 layer 14 is 3.33 to 3.75 g / cm 3 (preferably 3.47 to not more than 3.72 g / cm 3 , more preferably 3.54 to 3.68 g / cm 3). The film thickness of the photocatalytic TiO2 layer 14 is 50 to 500 nm. The film thickness of the porous SiO2 layer 16 is not less than 10 nm and not more than 50 nm (preferably not less than 15 nm and not more than 25 nm).

[0012] The hydrophilic member 10 enables, for example, the provision of an automobile windshield or a window glass for buildings by forming the base material 12 using a transparent glass plate or a transparent resin or plastic plate. The hydrophilic member 10 also enables, for example, the provision of a rear surface mirror type exterior mirror for a vehicle or a rear surface mirror such as a bathroom mirror by forming the base material 12 using a transparent glass plate or a transparent resin or plastic plate and forming a reflective film on a rear surface of the base material 12. Furthermore, the hydrophilic member 10 enables, for example, the provision of a front surface mirror such as a front surface mirror type exterior mirror for an automobile by forming the base material 12 using a glass plate or a resin or plastic plate.A plastic plate, and forming a reflective film between the base material 12 and the photocatalytic TiO2 layer 14. Furthermore, the hydrophilic element 10 enables the provision of a fog-resistant optical element by forming the base material 12 using an optical element such as a lens. When the base material 12 is a glass plate, a barrier layer made of, for example, SiO2 may be additionally disposed between the base material 12 and the photocatalytic TiO2 layer 14, so that the diffusion of alkali ions in the base material 12 into the photocatalytic TiO2 layer 14 is prevented.

[0013] An example of a method for producing the hydrophilic element 10 in the Fig.1. Here, the base material 12 is formed using a glass plate, and each of the photocatalytic TiO2 layer 14 and the porous SiO2 layer 16 is formed by vapor deposition.

[0014] The Fig.5 shows an example of a 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 is a base material for the hydrophilic member 10, is held by the substrate holder 26 with a film-forming surface facing downward. The substrate holder 26 is heated by a heater 28, and the glass plate 12 is maintained at a desired temperature by the substrate holder 26. A crucible 30 is arranged at a position below the glass plate 12, and a vapor deposition material (precursor for vapor deposition) 32 is placed in the crucible 30. Examples of the vapor deposition material 32 for forming a TiO2 layer 14 include, for example, TiO2, Ti2O3, and Ti.Examples of the vapor deposition material 32 for forming a SiO2 layer 16 include, for example, SiO2 and SiO.

[0015] The vapor deposition material 32 is evaporated as a result of irradiation with an electron beam 36 emitted from a hot cathode 34. Oxygen gas 42 is introduced into the vacuum chamber 20 from an oxygen tank 40 as a reactive gas. The evaporated vapor deposition material 32 reacts with the oxygen gas 42 to produce TiO2 or SiO2. The resulting TiO2 or SiO2 is deposited on a surface of the glass plate 12, forming a TiO2 layer 14 or a SiO2 layer 16. The film thickness during film formation is monitored by a film thickness monitor 44, and the vapor deposition is stopped when a desired film thickness is reached.

[0016] The film properties of the film deposited by vapor deposition vary depending, for example, on the temperature of the glass plate 12, the vapor deposition rate and the partial pressure of the oxygen gas 42 in the vacuum chamber 20. An example of film formation conditions for forming a photocatalytic TiO2 layer having a density of 3.33 to 3.75 g / cm 3 and for forming a porous SiO2 layer 16 on the photocatalytic TiO2 layer 14 having a uniform film thickness distribution that allows the SiO2 layer 16 to cover the entire surface of the photocatalytic TiO2 layer when the film thickness of the porous SiO2 layer 16 is not less than 10 nm, is given in the following table. Photocatalytic TiO2 layer 14 Porous SiO2 layer 16 Temperature of the glass plate 12 300 °C 300 °C Vapor deposition rate 0.5 nm / second 0.2 nm / second Partial pressure of oxygen gas 42 0.016 Pa 0.016 Pa

[0017] An example of a method for forming a photocatalytic TiO2 layer 14 and a porous SiO2 layer 16 using the vacuum vapor deposition apparatus 18 in the Fig. 5. A photocatalytic TiO2 layer is formed, for example, according to the following procedure. (1) Holding a glass plate 12 in the substrate holder 26, arranging, for example, Ti2O3 as a vapor deposition material 32 in the crucible 30 and closing the vacuum chamber 20. (2) Operating the rotary pump 24 and the diffusion pump 22 to evacuate the vacuum chamber 20. (3) Operating the heating device 28 to heat the glass plate 12 to a predetermined temperature by means of the substrate holder 26. (4) Introducing oxygen gas 42 from the oxygen tank 40 into the vacuum chamber 20. (5) Operating the hot cathode 34 to irradiate the Ti2O3, which is a vapor deposition material 32, with an electron beam 36 to evaporate the Ti2O3. (6) The evaporated Ti2O3 reacts with the oxygen gas 42 to form TiO2. The generated TiO2 is deposited on the glass plate 12, forming a TiO2 film. (7) Stop film formation when about 100 nm of TiO2 has been deposited.

[0018] After the formation of the photocatalytic TiO2 layer 14 is completed, a porous SiO2 layer 16 is subsequently formed. A porous SiO2 layer 16 is formed, for example, according to the following method. (1) Arranging, for example, SiO2 as the vapor deposition material 32 in the crucible 30 and closing the vacuum chamber 20. (2) Operating the rotary pump 24 and the diffusion pump 22 to evacuate the vacuum chamber 20. (3) Operating the heating device 28 to heat the glass plate 12 to a desired temperature by means of the substrate holder 26. (4) Introducing oxygen gas 42 from the oxygen tank 40 into the vacuum chamber 20. (5) Operating the hot cathode 34 to irradiate the SiO2, which is a vapor deposition material 32, with an electron beam 36 to evaporate the SiO2. (6) The evaporated SiO2 is deposited on the photocatalytic TiO2 layer 14 on the glass plate 12, thereby forming a SiO2 film. (7) Stop film formation when about 15 nm of SiO2 has been deposited.

[0019] Since an outermost surface of the hydrophilic member 10 manufactured by the above-described method comprises only the porous SiO2 layer 16, the hydrophilic member 10 exerts excellent effects in surface hardness and hydrophilicity maintenance, compared with cases where the outermost surface comprises only a photocatalytic TiO2 layer or a layer of a mixture of photocatalytic TiO2 and SiO2.

[0020] Although the above embodiment has been described with respect to a case where a photocatalytic TiO2 layer and a porous SiO2 layer are formed by vapor deposition, it can be understood that the effects of the invention according to the present application can also be expected when both layers or one of the layers are formed by another thin film forming method (e.g., sputtering). List of reference symbols

[0021] 10 ... hydrophilic element, 12 ... base material, 14 ... photocatalytic TiO2 layer, 16 ... porous SiO2 layer

Claims

[1] Hydrophilic element (10) comprising a structure in which a TiO2 layer (14) providing photocatalysis is formed such that it has a density of 3.33 to 3.75 g / cm 3 formed on a surface of a base material (12), and a porous SiO2 layer (16) is formed as an outermost surface layer on the TiO2 layer (14) such that the porous SiO2 layer (16) has a thickness of not less than 10 nm and not more than 50 nm and covers the entire surface of the TiO2 layer (14). [2] Hydrophilic element (10) according to claim 1, wherein the density of the TiO2 layer (14) is 3.47 to 3.72 g / cm 3 amounts. [3] Hydrophilic element (10) according to claim 2, wherein the density of the TiO2 layer (14) is 3.54 to 3.68 g / cm 3 amounts. [4] The hydrophilic element (10) according to claim 1, wherein the thickness of the porous SiO2 layer (16) is not less than 15 nm and not more than 20 nm. [5] A hydrophilic element (10) according to claim 2, wherein the thickness of the porous SiO2 layer (16) is not less than 15 nm and not more than 20 nm. [6] A hydrophilic element (10) according to claim 3, wherein the thickness of the porous SiO2 layer (16) is not less than 15 nm and not more than 20 nm.

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