Photocatalyst member and method for producing photocatalyst member

Abstract

A photocatalyst member according to the present invention comprises a substrate, an underlayer, and a photocatalyst layer formed in contact with the underlayer, in this order. The photocatalyst member is characterized in that the underlayer is constituted by a composite oxide of cerium and zinc, and the photocatalyst layer contains titanium oxide.

Description

Photocatalytic member and method for manufacturing the same

[0001] The present invention relates to a photocatalytic member and a method for manufacturing a photocatalytic member.

[0002] Photocatalysts, which undergo catalytic action when exposed to light such as ultraviolet or visible light, are currently attracting attention due to their various effects. Known photocatalytic effects include the generation of hydrogen and oxygen through the photolysis of water, as seen in the Honda-Fujishima effect, strong oxidizing properties due to the generation of active oxygen on the surface, and superhydrophilicity due to the generation of numerous hydroxyl groups on the surface. Photocatalysts have a wide range of potential applications, including the sterilization of viruses and pathogens such as coronaviruses, which have become particularly prevalent in recent years, through light irradiation, the decomposition of formaldehyde, which causes sick building syndrome, and the application of superhydrophilicity to anti-fog films.

[0003] Furthermore, when photocatalysts are applied to anti-reflective coatings, they are expected to be effective in decomposing fingerprints that adhere to the surface of the anti-reflective coating. In particular, anti-reflective coatings made of dielectric multilayer films, which are made by alternately stacking inorganic materials with different refractive indices and each having a thickness of 1 μm or less, use light interference. Therefore, even the slightest transparent contaminant, such as a fingerprint, adhering to the surface disrupts the interference effect, making the transparent contaminant easily visible. Conventionally, anti-reflective coatings have been covered with low-surface-energy substances, such as fluorine compounds, to prevent the adhesion of transparent contaminants such as fingerprints. However, this method was not effective enough, and cleaning, such as wiping, was also required. If photocatalysts could address these issues by decomposing organic transparent contaminants, eliminating the need for cleaning, photocatalysts are highly anticipated.

[0004] Titanium oxide is known as a material with photocatalytic properties. Vacuum thin-film deposition techniques, such as sputtering, are known as methods for forming titanium oxide on the surface of a substrate. However, for titanium oxide to exhibit photocatalytic properties, it must be crystallized into anatase or rutile forms, and this requires heat treatment at 300°C or higher during or after film formation. This makes it difficult to apply photocatalysis to components with low heat resistance, such as plastics. Another proposed method involves applying crystallized titanium oxide fine powder to a substrate together with a binder to fix it. This coating method is widely used because it does not require processing such as heating and allows for large-area treatment, and most currently commercially available photocatalysts are produced using this coating method.

[0005] Japanese Patent Publication No. 2007-308729 Japanese Patent Publication No. 2007-314835 Japanese Patent Publication No. 5217023 Japanese Patent Publication No. 2000-345320 Japanese Patent Publication No. 4460537

[0006] However, the binder used to fix the substrate is often an organic substance, and when it comes into contact with the photocatalyst, it decomposes, a phenomenon known as chalking, which can cause the photocatalyst itself to fall off. Another issue is that increasing the binder ratio to strengthen the bond between the substrate and the photocatalyst reduces the photocatalyst ratio relative to the binder, resulting in poor catalytic performance.

[0007] Therefore, it is desirable to form titanium oxide thin films using a vacuum thin film formation method that does not contain binders, but the challenge is how to achieve photocatalytic performance when forming films at room temperature.

[0008] As a method for obtaining crystallized titanium oxide at room temperature, Patent Document 1 discloses a method in which a single cathode or dual cathode is used and the duty ratio of the applied voltage is set to a certain value or less. Patent Document 1 describes that crystallized titanium oxide can be obtained by this method, but when the inventors conducted a reproduction experiment, they were unable to confirm crystallization, and it is possible that the method depends on the configuration of the equipment, etc.

[0009] Furthermore, Patent Documents 2 and 3 disclose methods for promoting crystallization by performing the deposition of a titanium metal film and the oxidation treatment separately, but this requires a complex equipment configuration and is difficult to implement with a general-purpose sputtering device.

[0010] As an example of using a general-purpose sputtering device, a method has been attempted in which water is added during film formation and heat treatment is performed at a relatively low temperature (200°C or higher) to crystallize the film, as shown in Patent Document 4. However, even though it is low-temperature crystallization, heating at 200°C or higher is required, which results in deformation of many plastic substrates. This results in a problem of lack of versatility.

[0011] One method for obtaining photocatalytic performance through room temperature film formation using a general-purpose sputtering device is to form a film of zirconium oxide (zirconia) as an underlayer, followed by formation of a titanium oxide film, as shown in Patent Document 5. This method is an excellent method for achieving photocatalytic performance without heat treatment of titanium oxide.

[0012] However, due to the low degree of crystallization of zirconium oxide, a certain film thickness is required to function as a sufficient underlayer, resulting in low productivity. Furthermore, because zirconium oxide itself is insulating, sputtering requires techniques such as radio frequency (RF) sputtering to form a film, but the slow film formation rate and difficulty in achieving large areas result in significantly low productivity. Another method for achieving photocatalytic performance without a high-temperature environment is to convert metallic zirconium into zirconium oxide by DC reactive sputtering in an inert gas and reactive gas environment. However, since the sputtering conditions vary significantly depending on the surface oxidation state of the zirconium oxide target, it is extremely difficult to achieve stable production. The present invention has been made to solve these problems, and its purpose is to explore underlayers other than zirconium oxide and provide photocatalysts with high industrial productivity.

[0013] The present inventors have conducted extensive research to address these issues and have arrived at the present invention. ２They found that by using a composite oxide target made by mixing and sintering titanium dioxide (TiO2) and zinc oxide (ZnO) to give the target electrical conductivity, and then forming a film as a base layer by sputtering using this target, and then forming a film of titanium oxide, the titanium oxide in the resulting photocatalytic component exhibits photocatalytic performance without heat treatment.

[0014] Furthermore, cerium oxide (CeO ２ They discovered that by using a target formed by mixing titanium dioxide (TiO) and zinc oxide (ZnO) in a molar ratio of 3:1 to 3:2, it is possible to perform DC sputtering, and by forming a base layer using this target and then depositing a titanium oxide layer without heating, it is possible to produce a photocatalytic component that exhibits particularly good photocatalytic performance.

[0015] The underlayer is preferably a composite oxide of cerium and zinc, but may contain other elements. For example, gallium (Ga) or aluminum (Al) may be contained to increase the conductivity of zinc oxide. Furthermore, conductivity is merely necessary for direct current (DC) sputtering, and the underlayer does not need to be conductive. It has been found that a photocatalytic layer obtained with a thickness of even 10 nm can exhibit photocatalytic performance, but in the case of plastic films, etc., a thickness of 20 nm or more is desirable from the viewpoint of ensuring surface smoothness. While a thickness of 20 nm or more can maintain sufficient crystallinity, forming a film with a thickness of 100 nm or more not only places a thermal load on the substrate but is also industrially inefficient, so a thickness of 100 nm or less is desirable.

[0016] The photocatalytic layer in the photocatalytic member of the present invention is made of titanium oxide (TiO ２) as its main component, but other elements may be included as long as photocatalytic performance is exhibited. For example, titanium oxide has a band gap in the ultraviolet region and requires ultraviolet light to function as a photocatalyst, but there are examples in which nitrogen has been added to make it responsive to visible light. In the present invention, nitrogen can also be added to create a visible-responsive photocatalyst. Furthermore, a metal element, such as niobium, may be added to increase the electrical conductivity of the photocatalyst layer. Furthermore, in the present invention, titanium oxide does not need to exhibit crystallinity. The thickness of the photocatalyst layer is sufficient as long as it is thick enough to exhibit photocatalytic performance, for example, 40 nm or more. Furthermore, although the effects of the present invention are exhibited even when the photocatalyst layer is thick, it is desirable for the thickness to be 200 nm or less from an industrial perspective.

[0017] Furthermore, the substrate may have a layer other than the underlayer and the photocatalytic layer. For example, a silicon oxide film may be formed on the surface of the photocatalytic layer in order to maintain the superhydrophilicity of the photocatalyst. Furthermore, as seen in the Honda-Fujishima effect, a conductive layer may be formed on the substrate before forming the underlayer in order to use the present invention as a photocatalytic electrode. In either case, the present invention is completed by forming a titanium oxide film on the surface of the underlayer composed of a composite oxide of cerium oxide and zinc oxide, opposite the substrate.

[0018] That is, the present invention provides the following means: (1) A photocatalytic member according to one aspect of the present invention is a photocatalytic member including, in this order, a substrate, an underlayer, and a photocatalytic layer formed in contact with the underlayer, wherein the underlayer is a composite oxide of cerium and zinc, and the photocatalytic layer contains titanium oxide.

[0019] (2) In the photocatalytic member of (1) above, the ratio of the amounts of cerium oxide and zinc oxide contained in the underlayer may be within the range of 3:1 to 1:1.

[0020] (3) In the photocatalytic member of (1) or (2) above, the element ratio of elements other than titanium oxide contained in the photocatalytic layer may be 10% or less.

[0021] (4) In the photocatalytic member according to any one of (1) to (3) above, the thickness of the underlayer may be 10 nm or more.

[0022] (5) In the photocatalytic members according to (1) to (4) above, the photocatalytic layer may have a thickness of 40 nm or more.

[0023] (6) The photocatalytic members of (1) to (5) above may further comprise a hydrophilicity retaining layer on the photocatalytic layer, and the hydrophilicity retaining layer may contain silicon oxide or a complex oxide of silicon and another metal.

[0024] (7) In the photocatalytic members described above in (1) to (6), the substrate may be a transparent substrate.

[0025] (8) In the photocatalytic members described above in (1) to (7), the substrate may be a polymer film.

[0026] (9) In the photocatalytic members of (1) to (8) above, the underlayer may further contain a group III element, and the total amount of the group III element contained in the underlayer may be 10% or less in terms of substance amount ratio.

[0027] (10) A method for manufacturing a photocatalytic member according to one aspect of the present invention includes a base layer forming step of forming a base layer on a substrate and a photocatalytic layer forming step of forming a photocatalytic layer containing titanium oxide on the base layer, and in the base layer forming step, sputtering is performed on the substrate using a composite target containing a mixture of cerium oxide and zinc oxide.

[0028] (11) In the method for producing a photocatalytic member according to (10) above, the mixture ratio of cerium oxide and zinc oxide in the composite target may be within the range of 3:1 to 3:2 in terms of substance amount ratio.

[0029] (12) In the method for producing a photocatalytic member according to (10) or (11) above, the composite target may be electrically conductive.

[0030] (13) In the method for producing a photocatalytic member according to any one of (10) to (12) above, the underlayer forming step may be performed by DC discharge sputtering or AC discharge sputtering.

[0031] (14) In the method for producing a photocatalytic member according to any one of (10) to (13), in the photocatalytic layer forming step, the photocatalytic layer may be formed by sputtering using a target containing any one of titanium, a titanium alloy, and oxygen-deficient titanium oxide.

[0032] (15) In the method for producing a photocatalytic member according to any one of (10) to (14) above, the substrate may be a polymer film.

[0033] According to the present invention, it is possible to provide a photocatalyst with high industrial productivity. For example, it is possible to provide a photocatalyst member that exhibits photocatalytic performance without high-temperature heat treatment, and a method for manufacturing a photocatalyst member that can use a substrate with low heat resistance, can increase the film formation rate, and can produce a photocatalyst member that exhibits photocatalytic performance.

[0034] 1 is a cross-sectional view showing an example of the configuration of a photocatalytic member according to one embodiment of the present invention. It is a cross-sectional view showing the configuration of a photocatalytic member according to a modified example of Fig. 1. It is a graph showing the XRD spectrum of an underlayer formed on an alkali-free glass substrate in Example 1.

[0035] The drawings used in the following description may show characteristic portions enlarged for convenience in order to make the features of the present invention easier to understand, and the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. The present invention can be implemented by making appropriate changes within the scope of its effects. Furthermore, the upper and / or lower limit values ​​of the numerical ranges described in this specification can be arbitrarily combined to define a preferred range. For example, the upper and lower limit values ​​of the numerical ranges can be arbitrarily combined to define a preferred range.

[0036] [Photocatalytic Member] Fig. 1 is a cross-sectional view showing an example of the configuration of a photocatalytic member according to one embodiment of the present invention. The photocatalytic member 1 shown in Fig. 1 comprises, in this order, a substrate 2, an underlayer 3, and a photocatalytic layer 4 formed in contact with the underlayer 3, with the underlayer 3 made of a composite oxide of cerium and zinc, and the photocatalytic layer 4 containing titanium oxide. In this embodiment, the number of underlayers 3 and the number of photocatalytic layers 4 are typically one each, and in the example shown in Fig. 1, the photocatalytic layer 4 is the outermost layer of the laminate.

[0037] <Substrate> The substrate 2 may be made of any material. Examples of materials for the substrate 2 include glass, metal, resin, and ceramics. Examples of resins that can be used for the substrate 2 include resin films such as polymer films. In particular, resin films with thin resin thickness have many advantages, such as being lightweight and being able to be attached to various locations. Furthermore, for industrial mass production, they have the advantage of being able to perform continuous film formation processing using a roll-to-roll sputtering device. Furthermore, transparent resin (polymer) films may be used when used in places where light transmission is required, such as window glass and displays.

[0038] The material for the transparent resin film is not particularly limited, but examples that can be used include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyaramid, polyimide, polycarbonate, polyethylene, polypropylene, triacetyl cellulose (TAC), and polycycloolefin (COC, COP).

[0039] The substrate 2 is preferably a transparent substrate. The transparent substrate may be made of a transparent material that can transmit light in the visible light range. The transmittance of the transparent substrate for light in the visible light range is, for example, 80% or more.

[0040] The thickness of the substrate 2 is not particularly limited, but when the substrate 2 is a resin film, it is desirable to set the thickness to 20 μm or more and 200 μm or less, taking into consideration ease of handling during manufacturing and thinning of the component. From the viewpoint of improving the abrasion resistance of the substrate 2, a coating of, for example, an acrylic resin may be formed on at least one surface of the substrate 2 by, for example, solution coating. Furthermore, the acrylic resin may have organic or inorganic particles dispersed therein in order to improve the haze and film running properties.

[0041] <Underlayer> The underlayer 3 is a composite oxide of cerium and zinc. The cerium and zinc content in the underlayer 3 is, for example, in a range of Ce (cerium):Zn (zinc) = 9:1 to 1:1 in terms of the mass ratio. That is, the cerium and zinc content in the underlayer 3 is, for example, in a range of Ce:Zn = 9:1 or more and 1:1 or less in terms of the mass ratio. The cerium and zinc content in the underlayer 3 is, for example, in a range of Ce:Zn = 3:1 to 13:12 in terms of the mass ratio, preferably 3:1 to 1:1, or alternatively 3:1 to 1:1, or alternatively 7:3 to 3:2, or alternatively 2:1 to 3:2, or alternatively 62:38 to 52:48. When the mass ratio of cerium to zinc in the underlayer 3 is in this range, the photocatalytic layer 4 formed directly thereon exhibits particularly good photocatalytic performance.

[0042] The underlayer 3 is preferably made of a composite oxide containing only cerium and zinc as metal elements. That is, the underlayer 3 preferably has a 0% content of a third element, which will be described later. On the other hand, the underlayer 3 may contain one or more elements other than cerium, zinc, and oxygen. In this embodiment, a metal element other than cerium and zinc contained in the underlayer 3 is referred to as a third element. Examples of the third element include gallium (Ga), aluminum (Al), and indium (In), which are added to zinc oxide to enhance its conductivity. Thus, the third element is, for example, a Group III element. The content of the third element other than cerium, zinc, and oxygen in the underlayer 3 is preferably 10% or less. The composition of the underlayer 3 corresponds to the composition of the composite target used in the manufacturing process, which will be described later. The elements contained in the underlayer 3 can be measured, for example, by an X-ray microanalyzer (XMA) or X-ray photoelectron spectroscopy (ESCA). This measurement can also determine the ratio of the amounts of substance of the cerium and zinc contents. In the underlayer 3, the total amount of third elements other than cerium and zinc is, for example, 10% or less, preferably 5% or less, and more preferably 2% or less, in element ratio (ratio of substance amount). The total amount of third elements may be 0, 0.5% or more, or 1% or more.

[0043] The resistance value of the target used to form the underlayer 3 is preferably 100 Ω cm or less, and more preferably 1 Ω cm or less, when DC sputtering is performed in the manufacturing process. In this embodiment, when direct current (DC) sputtering is performed in the manufacturing process, the target material needs to be conductive, but the underlayer 3 formed by sputtering it does not need to be conductive.

[0044] The thickness of the underlayer 3 is, for example, 8 nm or more, preferably 10 nm or more. When the substrate 2 is a plastic film or the like, the surface may not be smooth, so a thickness of 20 nm or more is more preferable from the viewpoint of ensuring a sufficient amount of complex oxide at all locations in the in-plane direction. Furthermore, a thickness of 20 nm or more of the underlayer 3 can be said to maintain sufficient crystallinity. The thickness of the underlayer 3 is preferably 100 nm or less from the viewpoint of suppressing the thermal load on the substrate 2 during the manufacturing process and from the viewpoint that, if the underlayer 3 is sufficiently thick, the crystallinity improvement sufficient for the photocatalytic layer 4 to exhibit sufficient catalytic performance is saturated. The thickness of the underlayer 3 may be 50 nm or less. The thickness of the underlayer 3 can be measured, for example, by preparing a cross-sectional section of the sample by microtome method and measuring it with a transmission electron microscope.

[0045] <Photocatalytic Layer> The photocatalytic layer 4 is a layer that functions as a photocatalyst. The photocatalytic layer 4 contains titanium oxide as a photocatalyst. More specifically, the photocatalytic layer 4 is composed of only titanium oxide, or titanium oxide and at least one other element with a total titanium element ratio of 10 atomic % or less. Titanium oxide has a band gap in the ultraviolet region and typically requires ultraviolet light to function as a photocatalyst. However, adding nitrogen can make it responsive to visible light. In the present invention, nitrogen can be added to titanium oxide in the photocatalytic layer 4 to create a visible-responsive photocatalyst. In this case, the nitrogen content in the photocatalytic layer 4 is also 10 atomic % or less relative to the titanium oxide and titanium element. Furthermore, the photocatalytic layer may contain a metal element, such as niobium (Nb), to enhance its electrical conductivity.

[0046] However, this configuration is merely an example, and it is sufficient that the photocatalytic layer 4 contains titanium oxide to an extent that the effects of this embodiment can be obtained. The elements contained in the photocatalytic layer 4 can be measured by, for example, an X-ray microanalyzer (XMA) or X-ray fluorescence analysis (XRF).

[0047] The thickness of the photocatalyst layer 4 is desirably at least 40 nm or more in order for the photocatalyst layer 4 to function as a photocatalyst. The thicker the photocatalyst layer 4, the better. However, titanium oxide also has a slow film formation rate, and from an industrial productivity perspective, the thickness of the photocatalyst layer 4 is desirably 200 nm or less. The thickness of the photocatalyst layer 4 can be measured, for example, by preparing a cross-sectional slice of the sample by microtome method and using a transmission electron microscope. Furthermore, in the photodecomposition performance evaluation, no further improvement in decomposition performance was observed even when the thickness of the titanium oxide was made greater than 200 nm.

[0048] The photocatalytic member according to this embodiment is not limited to one consisting of a substrate 2, an underlayer 3, and a photocatalytic layer 4 as shown in FIG. 1 , but may further have other layers between the substrate 2 and the underlayer 3 or on the photocatalytic layer 4.

[0049] For example, one or more layers of conductive material may be laminated between the substrate 2 and the underlayer 3 in order to impart conductivity to the photocatalytic member 1. Examples of such conductive materials include indium-tin composite oxide (ITO) and aluminum-zinc composite oxide (AZO). Alternatively, a metal material may be laminated. Furthermore, a different oxide may be laminated on the metal material to suppress oxidation by plasma when depositing the underlayer 3. Furthermore, an adhesion layer may be formed to ensure adhesion between the substrate 2 and the underlayer 3. Furthermore, if the substrate 2 is a transparent substrate, a transparent material may be deposited to enhance the transparency of the photocatalytic member 1. Furthermore, a smoothing layer may be formed to smooth the surface of the substrate 2.

[0050] A transparent material may also be formed on the surface of the photocatalytic layer 4. In particular, a hydrophilicity retaining layer containing silicon oxide or a composite oxide of silicon oxide and another metal may be formed on the photocatalytic layer 4 so that superhydrophilicity can be maintained for a long period of time even in a dark place. FIG. 2 is a cross-sectional view showing the configuration of such a photocatalytic member according to a modification of FIG. 1. The photocatalytic member 1A shown in FIG. 2 further includes a hydrophilicity retaining layer 5 on the photocatalytic layer 4 of the photocatalytic member 1 shown in FIG. 1. When the hydrophilicity retaining layer 5 contains a composite oxide, the contained metal is, for example, Na or Al. Furthermore, since titanium oxide used in the photocatalytic layer is a high refractive index material, a layer of a low refractive index material, such as silicon oxide, may be laminated on the photocatalytic layer to reduce the surface reflectance. For example, a low refractive index material layer may be formed instead of the hydrophilicity retaining layer 5 at the position where the hydrophilicity retaining layer 5 is to be formed in FIG. 2. A low refractive index material layer may also be formed between the photocatalytic layer 4 and the hydrophilicity retaining layer 5.

[0051] 1 and 2 can be manufactured by, for example, the method described below. A method for manufacturing the photocatalyst member 1, 1A according to one embodiment of the present invention includes a base layer forming step of forming a base layer 3 on a substrate 2 and a photocatalyst layer forming step of forming a photocatalyst layer 4 containing titanium oxide on the base layer 3. In the base layer forming step, sputtering is performed on the substrate 2 using a composite target containing a mixture of cerium oxide and zinc oxide. When manufacturing a photocatalyst member by roll-to-roll manufacturing, first, the substrate 2 wound around an unwinding roll is unwound.

[0052] (Underlayer Formation Process) Next, the underlayer 3 is formed on the unwound substrate 2, which has been appropriately treated. Any method may be used to form the underlayer 3. However, sputtering is effective from the perspective of stacking different materials to form a multilayer film. There are various sputtering methods, including radio frequency (RF) sputtering, alternating current (AC) sputtering, and direct current (DC) sputtering. However, AC sputtering or DC sputtering is primarily used for high-speed, large-area film formation and long-length film formation using a continuous winding device. When using radio frequency (RF) sputtering, there are almost no restrictions on the target material, and various substances can be sputtered. However, as mentioned above, it is not suitable for high-speed, large-area, and long-length film formation. While AC sputtering or DC sputtering requires the target material to be conductive, it is suitable for high-speed, large-area, and long-length film formation. The underlayer forming step is performed, for example, in a reduced pressure environment in which the chamber containing the substrate and the composite target is filled with oxygen and an inert gas atmosphere.

[0053] From the viewpoint of producing a photocatalytic member that exhibits photocatalytic performance without high-temperature heat treatment, the underlayer formation step is preferably performed by DC sputtering or AC sputtering among the above methods. When forming the underlayer by DC sputtering or AC sputtering, a conductive composite target is used. In this embodiment, being conductive means, for example, that the resistance is 100 Ω cm or less. The resistance of the composite target is preferably 100 Ω cm or less.

[0054] The composite target used in the underlayer formation process is a mixture of cerium oxide and zinc oxide. The composition of the underlayer 3 formed in the underlayer formation process depends on the composition of the composite target. Therefore, an underlayer of any composition can be produced by first examining the correlation between the substance ratio of the cerium and zinc contents in the composite target and the substance ratio of the cerium and zinc contents in the underlayer 3. That is, to form an underlayer having a substance ratio of cerium oxide and zinc oxide within a predetermined range, the substance ratio of cerium and zinc in the composite target is, for example, Ce (cerium):Zn (zinc) = 9:1 to 1:1. From the viewpoint of film formation by DC sputtering, the content of cerium and zinc is preferably within the range of 3:1 to 3:2, more preferably within the range of 18:7 to 13:7, and may be within the range of 7:3 to 13:7. Furthermore, when forming an underlayer 3 containing a third element other than cerium, zinc, and oxygen, the composite target also contains the corresponding third element. That is, the composite target can contain the same third element as the underlayer 3. For example, the composite target can contain a third element such as gallium, aluminum, or indium, which is added to increase the conductivity of zinc oxide. If the target material does not contain a third element, the composition of the formed underlayer 3 will be approximately the same as that of the target material. The third element contributes as a dopant to zinc oxide, lowering the target resistance and increasing the film formation rate of the composite target. However, it is estimated that the increase in the rate of zinc oxide is greater than the increase in the rate of cerium oxide, resulting in a deviation in composition.

[0055] The underlayer forming step is carried out, for example, at a pressure (ultimate vacuum) of 10 －２ Sputtering can be performed under the conditions of 50 Pa and 50 Pa. The sputtering power can be set to, for example, 50 to 300 W.

[0056] The composite target used in the underlayer formation step can be produced, for example, by weighing and mixing the above-mentioned raw material powders and then sintering, powder molding, or the like. When producing a composite target by mixing the raw material powders and then sintering them, the heating temperature can be, for example, 1000 to 1400°C, and the heating time can be, for example, 2 to 6 hours. When producing a composite target by powder molding, the raw material powders can be placed in a die and pressed with an upper punch and a lower punch to form the composite target.

[0057] (Photocatalyst Layer Forming Step) Next, the photocatalyst layer 4 is formed on the underlayer 3. Any method may be used to form the photocatalyst layer 4. However, from the viewpoint of laminating different materials to form a multilayer film, a sputtering method is effective.

[0058] When forming the photocatalytic layer 4 on the underlayer 3 by sputtering, the target can be, for example, titanium, a titanium alloy, oxygen-deficient titanium oxide, or a composite oxide containing oxygen-deficient titanium oxide. Titanium alloys that contain niobium, copper, tungsten, or the like in addition to titanium element can be used. Oxygen-deficient titanium oxide is a titanium oxide represented by the general formula TiOx, where x is a value less than 2.

[0059] In the photocatalytic layer forming step, for example, oxygen and argon gas are sealed in a chamber accommodating the substrate 2 on the surface of which the underlayer 3 is formed and the target, and sputtering is performed in a reduced pressure environment.

[0060] According to the photocatalytic member manufacturing method and the photocatalytic member of the above embodiment, a photocatalyst with high industrial productivity can be realized by using a composite oxide of cerium and zinc for the underlayer 3. For example, after forming the photocatalytic layer 4, the photocatalytic function can be exhibited even without heating the photocatalytic layer 4.

[0061] Cerium oxide and zirconium oxide are insulators. Therefore, while they can be deposited using radio frequency (RF) sputtering, they cannot be deposited using conventional direct current (DC) sputtering. RF sputtering is an excellent technique for depositing films on insulators, but its deposition rate is significantly slower than that of DC sputtering. Furthermore, because RF sputtering uses the same frequency band as radio waves, leakage during high-power deposition may cause serious radio interference in the surrounding area, making it unsuitable for high-speed, large-area production, which is important for industrial applications. In particular, when using a roll-to-roll deposition method in which an underlayer and a photocatalytic layer are deposited consecutively on a film, deposition methods such as vapor deposition may be considered, but it is considered preferable to deposit both the underlayer and the photocatalytic layer using sputtering.

[0062] In the above embodiment, the composite target of cerium oxide and zinc oxide used to form the underlayer of cerium and zinc composite oxide exhibits electrical conductivity that cerium oxide does not exhibit, so the underlayer can be formed by DC sputtering without RF sputtering.

[0063] Therefore, according to the above embodiment, it is possible to provide a photocatalytic member that exhibits photocatalytic performance without high-temperature heat treatment, a photocatalytic member that can use a substrate with low heat resistance, and a method for manufacturing a photocatalytic member that can increase the film formation rate and produce a photocatalytic member that exhibits photocatalytic performance. Furthermore, since the sputtering conditions do not change significantly depending on the surface oxidation state of the target, stable production can be easily achieved.

[0064] Furthermore, in the photocatalytic members 1 and 1A according to the above-described embodiments, it is believed that good photocatalytic performance is exhibited by forming a crystal lattice by the underlayer 3, and titanium oxide crystals grow to fit the crystallites. Furthermore, when forming the underlayer 3 using the sol-gel method, it is difficult to uniformly form a thin film of approximately 100 nm or less, especially on a film, and therefore it is believed to be difficult to form a photocatalytic layer 4 that exhibits good photocatalytic performance without heating.

[0065] EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0066] [Example 1] First, as a preparation step, cerium oxide (CeO ２ A target for the underlayer (composite target) was prepared by mixing powders of gallium-doped zinc oxide (GZO) and gallium-doped zinc oxide (GZO) in a mass ratio of 7:3, and then heating at 1400°C for 4 hours to sinter the mixture. The resistivity of the prepared composite target was measured using a Loresta GP MCP-T610 (Nitto Seiko Analytech Co., Ltd.).

[0067] Next, alkali-free glass (OA-10G manufactured by Nippon Electric Glass Co., Ltd.) was prepared as a substrate. The substrate was washed with a neutral detergent, then subjected to ultrasonic cleaning in pure water for 10 minutes. After being pulled out of the liquid, droplets were immediately removed with an air gun and the substrate was dried. The substrate was set in a four-source sputtering device (manufactured by Toei Scientific Industry Co., Ltd., model number: SPV-420), and after exhausting, film formation was carried out. The sputtering device used was capable of using both DC discharge and RF discharge with a selector switch. In Example 1, the underlayer formation process was carried out using DC discharge.

[0068] Detailed conditions for the underlayer forming step are shown below: (Sputtering conditions) Target dimensions: diameter 2 inches, thickness 4 mm Distance between target and substrate: 80 mm Ultimate vacuum: <1×10 －３ Pa Substrate temperature: room temperature Sputtering power: DC 100 W

[0069] As described above, a 50 nm thick underlayer was formed by DC sputtering. A 150 nm thick titanium oxide (TiO2) photocatalytic layer was then deposited on top of the underlayer under the following film formation conditions, and the sample was then removed to prepare a sample. The photocatalytic layer was formed using oxygen-deficient titanium oxide TiOx as the target. (Sputtering conditions) Target dimensions: diameter 2 inches, thickness 4 mm Distance between target and substrate: 80 mm Ultimate vacuum: <1 x 10 －３ Pa Substrate temperature: room temperature Sputtering power: RF 200 W

[0070] [Example 2] In preparing a composite target used in the underlayer forming step, cerium oxide (CeO ２ A sample was prepared under the same conditions as in Example 1, except that powders of gallium-doped zinc oxide (GZO) and gallium-doped zinc oxide (GZO) were mixed in a material ratio of 3:1.

[0071] [Example 3] In preparing a composite target used in the underlayer forming step, cerium oxide (CeO ２ A sample was prepared under the same conditions as in Example 1, except that powders of gallium-doped zinc oxide (GZO) and gallium-doped zinc oxide (GZO) were mixed in a material ratio of 3:2.

[0072] Example 4 A sample was prepared under the same conditions as in Example 1, except that the thickness of the underlayer film was set to 10 nm.

[0073] Example 5 A sample was prepared under the same conditions as in Example 1, except that the thickness of the photocatalytic layer was set to 40 nm.

[0074] [Example 6] In preparing a composite target used in the underlayer forming step, cerium oxide (CeO ２ A sample was prepared under the same conditions as in Example 1, except that powders of zinc oxide (ZnO) and zinc carbide (CuO) were mixed in a material ratio of 7:3.

[0075] [Example 7] In preparing a composite target used in the underlayer forming step, cerium oxide (CeO ２ A sample was prepared under the same conditions as in Example 1, except that powders of aluminum-doped zinc oxide (AZO) and aluminum-doped zinc oxide (AZO) were mixed in a material ratio of 7:3.

[0076] (Sputtering conditions) Target dimensions: diameter 2 inches, thickness 4 mm Distance between target and substrate: 80 mm Ultimate vacuum: <1×10 －３ Pa Substrate temperature: room temperature Sputtering power: RF 200W

[0077] Comparative Example 1 A sample was prepared by laminating titanium oxide to a thickness of 150 nm as a photocatalytic layer without forming an underlayer. That is, in Comparative Example 1, a TiO 2 photocatalytic layer was formed on a non-alkali glass substrate. ２ was directly formed. ２The layer composed of the above was formed by sputtering using the same target as in Example 1.

[0078] Comparative Example 2 A sample was prepared under the same conditions as in Example 1, except that oxygen-deficient niobium pentoxide (NbOx) was used as the target for the underlayer.

[0079] Reference Example 1 As a composite target, cerium oxide (CeO ２ A target for the underlayer was prepared by mixing powders of gallium-doped zinc oxide (GZO) and gallium-doped zinc oxide (GZO) in a material ratio of 4:1, followed by sintering under the same conditions as in Example 1. When DC sputtering was attempted on an alkali-free glass substrate using this composite target under the same conditions as in Example 1, discharge was not possible in the DC sputtering device, and a sample having an underlayer formed on the substrate could not be prepared.

[0080] [Evaluation] The photocatalytic performance of the prepared samples was evaluated. The photocatalytic performance was evaluated in accordance with JIS R 1703-1 (Fine ceramics - Self-cleaning test method for photocatalytic materials - Part 1: Measurement of water contact angle). Specifically, the sample was exposed to a black light with an irradiance of 2.0 mW / cm. ２ The sample was placed in a position adjusted to 100 cm and left to stand for 24 hours or more. ２ The contact angle at this point was taken as the initial contact angle. After measuring the initial contact angle, the contact angle was measured under black light with an irradiance of 2.0 mW / cm. ２ The sample was left at this position for 24 hours, then removed and the contact angle was measured again to determine the contact angle after UV irradiation. According to the photocatalytic performance evaluation criteria of the Photocatalyst Industry Association, a contact angle of 30° or less after UV irradiation can be said to have good photocatalytic performance.

[0081] The thickness of the underlayer of each sample immediately after the underlayer formation process was evaluated using a spectroscopic ellipsometry (M-2000, manufactured by J.A. Woollam). Ellipsometry provides the amplitude ratio Ψ and phase difference Δ of p-polarized and s-polarized light for each wavelength. Applying an appropriate optical model to these values ​​and performing fitting with the film thickness as a parameter yields the film thickness along with the optical constants. The film thickness was determined based on the measurement results at the center of the substrate.

[0082] The sample preparation conditions, the resistivity of the composite target for preparing the underlayer, and the evaluation results regarding the photocatalytic performance are summarized in Table 1. In Table 1, the entry "OK" in the "Discharge" column of the underlayer indicates that discharge was possible using a DC sputtering device under the same sputtering conditions as in Example 1, and the entry "NG" indicates that discharge was not possible. "Infinity" in the target resistance column indicates that the value was above the measurement limit.

[0083]

[0084] [Evaluation Results] <Examples 1 to 3> As is clear from Table 1, CeO ２Discharge was possible when the mass ratio of oleic acid to GZO was between 3:1 and 3:2. Furthermore, when the prepared sample was irradiated with UV light for 24 hours after application of oleic acid, the contact angle was 30° or less, demonstrating sufficient self-cleaning performance and good photocatalytic performance. Example 4: In contrast to Example 1, even when the underlayer was formed to a thickness of 10 nm, the contact angle was 30° or less when oleic acid was applied and UV light was irradiated for 24 hours, demonstrating sufficient self-cleaning performance and good photocatalytic performance. Example 5: In contrast to Example 1, even when the titanium oxide photocatalytic layer was formed to a thickness of 40 nm, the contact angle was 30° or less when oleic acid was applied and UV light was irradiated for 24 hours, demonstrating sufficient self-cleaning performance and good photocatalytic performance. Example 6: Discharge was also possible when a composite target for the underlayer was prepared using zinc oxide (ZnO) instead of GZO in Example 1. Furthermore, when the prepared sample was coated with oleic acid and then irradiated with UV light for 24 hours, the contact angle was 30° or less, indicating sufficient self-cleaning performance and good photocatalytic performance. Example 7: Discharge was also possible when a composite target for the underlayer was prepared using aluminum-doped zinc oxide (AZO) instead of GZO in Example 1. Furthermore, when the prepared sample was coated with oleic acid and then irradiated with UV light for 24 hours, the contact angle was 30° or less, indicating sufficient self-cleaning performance and good photocatalytic performance.

[0085] <Comparative Examples 1 and 2> When titanium oxide was formed directly on a substrate without forming an underlayer (Comparative Example 1), or when a metal oxide other than a composite oxide of cerium and zinc was formed as an underlayer and then titanium oxide was formed thereon (Comparative Example 2), the contact angle after 24 hours of irradiation with UV light after application of oleic acid did not become 30° or less, and it was confirmed that the titanium oxide did not exhibit self-cleaning performance and did not have photocatalytic performance. Thus, a titanium oxide layer formed without an underlying layer, or a layer formed directly on a layer other than a composite oxide of cerium and zinc as underlayer 3, did not have photocatalytic performance.

[0086] [Composition of Underlayer] To investigate the composition of the underlayer, underlayers were formed using each target under the same conditions as in the Examples, Reference Examples, and Comparative Examples. The underlayers were then removed without forming a photocatalytic layer, and the elemental ratio of Ce to Zn was evaluated by X-ray photoelectron spectroscopy (ESA). The results are shown in Table 1. [Evaluation of Crystallinity] In Example 1, the samples immediately after underlayer formation were evaluated by XRD. XRD measurements were performed using an X'Pert PRO MPD (manufactured by PANalytical) with Cuα as the radiation source at an incident angle of 1°. The XRD results are shown in Figure 3. For comparison, Figure 3 also shows XRD spectra of zinc oxide, cerium oxide, and zirconium oxide. The XRD spectra of zinc oxide, cerium oxide, and zirconium oxide are shown for samples formed by RF sputtering on a 50 nm thick film on the same alkali-free glass substrate as in Example 1.

[0087] As shown in Figure 3, a cerium oxide peak can be seen near the zirconium oxide peak, and its narrow half-width suggests the presence of larger crystallites than those of zirconium oxide. This suggests that cerium oxide crystallizes more easily. In contrast, a thin film deposited using a composite target of cerium oxide and gallium-doped zinc oxide exhibits an XRD pattern similar to that of cerium oxide, and the crystallite size is presumed to be about the same as that of cerium oxide. The graph also shows the XRD pattern of zinc oxide, and a comparison of the peak positions suggests that the crystals observed in the cerium oxide-gallium-doped zinc oxide are cerium oxide crystallites.

[0088] Partial heteroepitaxial growth is thought to be the reason why forming an underlayer composed of a composite oxide of cerium and zinc gives the titanium oxide formed on the underlayer photocatalytic performance. The underlayer forms a crystal lattice, and titanium oxide grows to fit the crystallites. Therefore, if the underlayer side is thin and clearly crystallized, it is thought that the titanium oxide in the photocatalytic layer formed later will also promote crystallization.

[0089] 1, 1A: photocatalytic member, 2: substrate, 3: underlayer, 4: photocatalytic layer, 5: hydrophilic retaining layer

Claims

1. A photocatalytic member comprising, in this order, a substrate, an underlayer, and a photocatalytic layer formed in contact with the underlayer, characterized in that the underlayer is a composite oxide of cerium and zinc, and the photocatalytic layer contains titanium oxide.

2. The photocatalytic member according to claim 1, wherein the mass ratio of cerium oxide and zinc oxide contained in said underlayer is within the range of 3:1 to 1:

1.

3. The photocatalytic member according to claim 1, wherein the element ratio of elements other than titanium oxide contained in the photocatalytic layer is 10% or less.

4. The photocatalytic member according to claim 1, wherein the thickness of the underlayer is 10 nm or more.

5. The photocatalytic member according to claim 1, wherein the thickness of the photocatalytic layer is 40 nm or more.

6. The photocatalytic member according to claim 1, further comprising a hydrophilic retaining layer on said photocatalytic layer, said hydrophilic retaining layer containing silicon oxide or a complex oxide of silicon and another metal.

7. The photocatalytic member according to claim 1, wherein the substrate is a transparent substrate.

8. The photocatalytic member according to claim 1, wherein the substrate is a polymer film.

9. The photocatalytic member according to claim 1, wherein the underlayer further contains a group III element, and the total amount of the group III element contained in the underlayer is 10% or less in terms of substance amount ratio.

10. A method for producing a photocatalytic member, comprising: a base layer forming step of forming a base layer on a substrate; and a photocatalytic layer forming step of forming a photocatalytic layer containing titanium oxide on the base layer, wherein in the base layer forming step, sputtering is performed on the substrate using a composite target containing a mixture of cerium oxide and zinc oxide.

11. The method for producing a photocatalytic member according to claim 10, wherein the mixture ratio of cerium oxide and zinc oxide in the composite target is within the range of 3:1 to 3:2 in terms of substance amount ratio.

12. The method for producing a photocatalytic member according to claim 10, wherein the composite target has electrical conductivity.

13. The method for producing a photocatalytic member according to claim 10, wherein the underlayer forming step is performed by DC discharge sputtering or AC discharge sputtering.

14. The method for manufacturing a photocatalytic member described in claim 10, characterized in that in the photocatalytic layer formation process, the photocatalytic layer is formed by sputtering using a target containing any one of titanium, a titanium alloy, and oxygen-deficient titanium oxide.

15. The method for producing a photocatalytic member according to claim 10, wherein the substrate is a polymer film.

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