JP2002047558A - Metal sheet having photocatalytic activity, and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal sheet combining deformability with workability while exhibiting, more effectively and continuously, a decomposing and removing action on the environmental pollutant and also deodorizing, soil-resisting and germicidal actions owing to the photocatalytic action of titanium oxide and also to provide its manufacturing method. SOLUTION: The metal sheet having photocatalytic activity has a film of 0.5-5.0 μm thick on the surface. Moreover, the film consists of the following layers formed from the metal-sheet side toward the surface in the order named: an inner layer consisting of titanium metal layer; an intermediate layer consisting of titanium metal and titanium oxide and having a chemical composition composed of a gradient composition from titanium metal layer to titanium oxide layer; and an outer layer consisting of titanium oxide layer. The method for manufacturing the metal sheet is also provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal plate having a photocatalytic activity imparted to the surface of the metal plate and a method for producing the same.

[0002]

2. Description of the Related Art Titanium oxide exhibits excellent photocatalytic activity when irradiated with light of a specific wavelength in the ultraviolet region.
It is known that a strong oxidation reaction derived from photocatalysis exerts decomposition and removal of environmental pollutants, deodorization, antifouling, and bactericidal action, and application to various materials and practical application thereof are being studied. For example, Japanese Patent Application Laid-Open No. 3-69695 describes that a titanium oxide photocatalyst or the like is coated on paper to have a deodorizing property, an antibacterial property and the like. Further, in JP-A-2-280818 and JP-A-3-94814, as one method of preventing the carrier from collapsing, ceramic fibers or the like are used. However, since this method is a post-processing of the ceramic fiber sheet, the manufacturing equipment is special, the material is not flexible, etc.
There are many practical issues.

[0003] If the material has flexibility and workability, the user can perform processing such as bending, cutting, and drilling according to the intended use, and the range of application is dramatically expanded. Metal plates are easier to perform secondary processing than glass or ceramic materials, but if a hard and thick film such as titanium oxide is formed on the surface,
The titanium oxide cannot follow the deformation of the metal plate, and usually peels off at the interface between the metal plate and the titanium oxide or the titanium oxide itself collapses. For this reason, a method of forming a titanium oxide film on a finished product after processing is generally used. At this time, depending on the shape of the base material after processing, there were various problems, such as uneven formation of the film and the necessity of a large film forming apparatus. In addition, since the thermal expansion coefficient and the Young's modulus of titanium oxide and the metal plate are significantly different from each other, there is a problem that the interface is apt to be separated when environmental factors such as temperature and stress change. In order to solve such problems, it has been considered to disperse titanium oxide particles in an organic substance such as a resin, but the photocatalytic activity is extremely reduced,
Due to the strong oxidizing power of titanium oxide, problems such as decomposition of organic substances in contact with titanium oxide cannot be avoided. In general, it has not been possible to make a metal plate having photocatalytic activity compatible with flexibility and processability and high photocatalytic activity.

[0004] The most common method of coating titanium oxide is a method of applying a hydrolysis product of an alkoxide of titanium, that is, a sol-gel method. No. 83537, a method in which an amide and / or glycol is added to a titanium alkoxide and the reaction product is used,
As disclosed in JP-A-7-100378, there is a method of adding an alcoholamine to a titanium alkoxide and using a reaction product thereof as a coating component. But the above sol
-In the gel method, the thickness of the formed film tends to change depending on the viscosity of the paint and the application conditions, and if the film is thickened to improve the performance of the film, the film shrinks greatly during drying,
There are problems that the adhesion between the film and the substrate surface is lowered, and the film is easily peeled off. Furthermore, in order to enhance the crystallinity of the titanium oxide film, three steps of drying after coating and firing are essential, and in order to stably form an anatase phase, which is considered to have high photocatalytic activity, in titanium oxide. In general, it was necessary to perform the firing at a high temperature of 500 ° C. or more in the atmosphere. Furthermore, the film thickness obtained by one coating is often about 0.1 μm, and in order to obtain a thick film, it is necessary to go through complicated steps such as repeating the above-mentioned coating, drying and baking several times. Was. When fired many times in air at high temperature, the diffusion of elements from the substrate is unavoidable. Particularly in the case of a film with a thickness of about 1 μm, the elements in the substrate diffuse into the entire film and oxidation occurs. There were problems such as a reduction in the photocatalytic activity of titanium. For example, for stainless steel, Cr
Is known to diffuse into the titanium oxide film.

[0005] As described above, the conventional metal plate on which a titanium oxide film is formed is poor in deformability and workability due to poor adhesion between the film and the metal plate. There is a problem that hinders widespread practical application. Also,
As for the film forming method, there is a limit in improving the homogeneity and adhesion of the film, the processing steps are complicated, and an efficient manufacturing method has been desired.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been developed to decompose and remove environmental pollutants derived from the photocatalytic action of titanium oxide.
It is an object of the present invention to provide a metal plate having both deformation and workability while exhibiting deodorizing, antifouling, and sterilizing effects more effectively and continuously, and a method for manufacturing the same.

[0007]

Means for Solving the Problems The inventor of the present invention has conducted intensive studies in order to achieve the above object, and as a result, the intermediate between the titanium oxide film and the metal plate has a graded chemical composition at the interface. The present inventors have found that by forming a layer, physical properties are given continuity and adhesion is improved, and the present invention has been accomplished.

That is, a metal plate having a coating having a thickness of 0.5 to 5.0 μm on its surface, wherein the coating is formed from a metal titanium layer to an inner layer, a metal titanium layer and a titanium oxide layer. A metal plate having photocatalytic activity, characterized in that the intermediate layer has a chemical composition having a gradient composition from a metal titanium layer to a titanium oxide layer, and a coating formed in the order of an outer layer made of a titanium oxide layer. is there. further,
The thickness of the inner layer is 0.05-1.0 μm, and the thickness of the middle layer is 0.05-1.
Preferably, the outer layer has a thickness of 0.4 to 3.0 μm, and the outer layer further contains at least 80% by volume of anatase type titanium oxide. It is also desirable that the metal plate be stainless steel, or titanium or a titanium-based alloy.

In the above-mentioned method for forming a metal plate having photocatalytic activity, during the formation of a film from an inner layer to an outer layer, titanium vapor or ionized titanium vapor and oxygen are released under reduced pressure without ever opening to the atmosphere. That separately control the partial pressure of
A method for producing a metal plate having photocatalytic activity, wherein the method is a method of forming a film on a metal plate at a temperature of 500 ° C. or less by using Method D. Furthermore, that the PVD method is sputtering or ion plating,
preferable.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a conceptual diagram showing the structure of a film and the chemical composition of an intermediate layer. An inner layer made of titanium metal (Ti) is formed on the surface of the metal plate. If it does not contain any impurities, it is represented by Ti in the chemical formula, and the Ti content is
It becomes 100% by mass. The outer layer is a titanium oxide layer, the most active being anatase-type titanium oxide, and when it contains no impurities, it can be described as TiO _{2 in} the chemical formula. In this case, the Ti content is about 59.9% by mass.
In the intermediate layer, the content of titanium changes almost continuously from the content of the inner layer to the content of the outer layer, and is characterized by having no large discontinuous points, and the change is almost linear. Preferably, there is. This will be referred to as a gradient composition for convenience.

The intermediate layer is composed of titanium metal and titanium oxide.
Even if the individual grains are dispersed and mixed
Alternatively, a solid solution may be formed. Even if it ’s crystalline,
It may be amorphous. The crystal phase of titanium oxide is Ti
_TwoO, TiO, Ti_TwoO_Three, Ti_TwoO_Five, Ti _ThreeO_Five, Ti_nO_2n-1(n = 4 〜
10), TiO_TwoA crystal phase with a composition that can be described as
It may be formed of a mixed layer of each crystal phase.

By eliminating discontinuities in the chemical composition, discontinuities in physical properties such as thermal expansion coefficient and Young's modulus can be minimized. A metal plate having photocatalytic activity may be used for a long time in various environments. Temperature change may be large or external force may be applied,
For these environmental factors, long-term durability such as adhesion of the film and photocatalytic activity is required. For this purpose, continuity of physical properties between the film and the metal plate substrate is required, and the intermediate layer is important. For example, if there is a discontinuity in the coefficient of thermal expansion, stress concentrates here and becomes a starting point of peeling of the film. Specifically, when an anatase layer is formed directly on the surface of an 18Cr-8Ni stainless steel substrate, the linear expansion coefficient of the substrate is 14.7 × 10
^-6 / deg (20 ° C), whereas anatase is 10.2 × 10
^-6 / deg (20 ° C). When anatase-coated stainless steel plate manufactured at 500 ° C is cooled to 20 ° C, for example, 1m x 1m
Assuming that a building material is used, a stress is generated that causes a displacement of about 2.5 μm in the linear direction (estimated from the difference in linear expansion between stainless steel and anatase).

This stress concentrates between the anatase and the stainless steel substrate, and peels off when the combined force of the residual stress at the interface and the external force exceeds the adhesion between the two. In other words, even if the external force is equal to or less than the adhesion between anatase and stainless steel, if there is residual stress at the interface, the anatase will be easily peeled off. As described above, the difference in the coefficient of linear expansion correlates with the magnitude of the residual stress at the interface. Therefore, it is important to reduce the difference in the coefficient of linear expansion at each interface in order to avoid stress concentration. Stress may remain in the outer titanium oxide layer depending on the film forming method, and the intermediate layer also serves as a stress relieving layer. In order to exert the above function effectively, the thickness of the intermediate layer is desirably 0.05 to 1.0 μm.
If the thickness is less than 0.05 μm, the effect is small, and even if the thickness is more than 1.0 μm, the effect is not changed, which is uneconomical.

The outer titanium oxide layer preferably has a thickness of 0.4 μm or more, efficiently absorbs light, and functions as a photocatalyst. More than 1.0 μm is more desirable for the most efficient light absorption. When the thickness of the titanium oxide layer exceeds 3.0 μm, deformation and bending workability are inferior. Therefore, the thickness is preferably 3.0 μm or less. Most preferably, it is 2.0 μm or less. The crystal phase of the outer titanium oxide layer is preferably mainly composed of anatase from the viewpoint of photocatalytic activity. Anatase, rutile, and brookite are known as titanium oxides having a TiO ₂ composition. Anatase-type titanium oxide has the highest photocatalytic activity, and its content is preferably increased. Most preferably, the content of anatase-type titanium oxide in the outer layer is 80%.
When the content is at least% by volume, high photocatalytic activity can be obtained. Depending on the purpose, a platinum group metal is supported on the surface of the outer layer,
Further, the catalytic activity may be increased. At this time, the metal layer to be supported is desirably 10% or less of the thickness of the film, and within this range, the deformation and bending workability are not impaired.

The inner titanium layer is important for improving the adhesion between the metal plate and the titanium oxide. Advantageously, the thickness is between 0.05 and 1.0 μm. If the thickness is less than 0.05 μm, the effect is small, and if the thickness is greater than 1.0 μm, the effect does not change.
As the metal plate, stainless steel, titanium, or a titanium-based alloy excellent in versatility, corrosion resistance, designability, workability, and functionality is preferable. These are already used as various members used for building materials, air conditioning equipment, exhaust gas equipment, water purification equipment, and the like, and have a proven track record, so that they are easy to apply.

The metal plate having photocatalytic activity as described above can be manufactured by forming a film on the surface of the metal plate by a PVD (Physical Vapor Deposition) method or the like. The PVD method is characterized in that the load on the substrate due to the temperature is small, and a dense, fine-grained crystalline film can be formed. As the PVD method suitable for the above film formation, specifically, vacuum deposition,
Various techniques such as sputtering and ion plating are suitable. In order to avoid problems such as deformation of the metal plate base material due to heat and deterioration of photocatalytic activity due to diffusion of elements from the metal plate base material to the film, the temperature of the base material at the time of film formation is 500 ° C. or less. All of the above three methods can form a film at a substrate temperature of 500 ° C or lower, provide sufficient film adhesion and film crystallinity, deform the metal plate substrate due to heat, and Problems such as deterioration of photocatalytic activity due to diffusion of elements into the film are unlikely to occur. In the above three methods, the deposition rate is
0.02 to 0.2 μm, for example, to obtain a 1 μm film
It is practical for 5 to 50 minutes.

When the PVD method is applied to the formation of the above-mentioned film,
A method of evaporating metallic titanium under reduced pressure and introducing oxygen as a reaction gas is suitable because of excellent controllability of the composition of titanium oxide. The gradient composition of the intermediate layer of the film is also formed by continuously changing the ratio between the amount of titanium to be evaporated and the oxygen partial pressure or flow rate of the reaction gas. In other words, to form the inner layer, oxygen gas is not introduced, and the film is formed only by titanium vapor.However, to form the intermediate layer, oxygen gas is gradually introduced into the reaction chamber, and the introduced amount gradually increases with time. It can be formed in a process of increasing the amount of oxygen gas to be introduced when forming the outer layer. In this process, the inner layer, the intermediate layer, and the outer layer can be continuously formed in the same chamber without ever opening to the atmosphere. In addition, the formed crystal phase can be easily controlled, and no post heat treatment or the like is required. For example, when the substrate temperature during film formation is 490 ° C., the electron beam current for evaporating metallic titanium is 200 mA (acceleration voltage 20 kV), and the oxygen pressure is 0.
When the ionization was performed at 40 V and 10 A with an arc discharge activated ion plating device at 05 Pa, when the stainless steel SUS304 sample placed 45 cm above the titanium evaporation source was used as the substrate and the film was formed for 10 minutes. , 0.8 μm rutile-based coatings. On the other hand, when a film is formed at a substrate temperature of 300 ° C. for 20 minutes using the same apparatus and sample, a film mainly composed of anatase of about 1.5 μm can be formed. As described above, in the PVD method, the crystal phase and the film thickness can be adjusted to the desired values by controlling the temperature of the base material, the film formation time, and the like while keeping the ionization and the atmospheric pressure at an appropriate level. Since the film formation rate is high, there is no need to repeat the same process, and compared to the conventional sol-gel method, it is simple, easy, and easy to manage, and the production cost can be reduced.

Film formation under reduced pressure is important for promoting the formation reaction of titanium oxide. Further, it is preferable to heat the metal plate base material at 500 ° C. or lower during the film formation because the adhesion and the crystallinity of the film are improved while suppressing the deterioration of the base material due to the temperature. Since the heating of the substrate is performed under reduced pressure, the surface of the substrate is less oxidized than in the case of firing in the air. By reducing the pressure, the titanium metal can be efficiently evaporated.

Vacuum deposition is a method in which metallic titanium is melted under vacuum using a heat source such as an electron beam to generate titanium vapor, and the titanium vapor is deposited on a substrate. The equipment configuration is relatively simple, and the film formation cost is the lowest of the above three methods. Sputtering is a method in which a target titanium is irradiated with a gas component such as ionized argon or the like, and a titanium component hit from the target is deposited on a substrate. Ion plating is a method of dissolving using a heat source such as an electron beam, generating titanium vapor, and reacting the titanium component ionized by plasma on the substrate to form a film. Attract ions with
This is advantageous for forming a dense film, and high adhesion can be obtained even when the substrate temperature is low. In the ion plating method, it is easy to form a film composed of fine-grained crystals. For example, an arc discharge activated ion plating method, which is a type of the ion plating method, is used.
In a 1 μm-thick anatase film formed at Pa, the crystal grains become fine grains of about 0.01 μm.

As described above, a film forming method can be selected according to the characteristics of a target film. Of the above three methods, the sputtering and ion plating methods use titanium to ionize or excite titanium vapor by plasma, so that they are highly reactive and have high film crystallinity and adhesion even at low substrate temperatures. The film obtained is dense and composed of fine grains. From the viewpoint of the film formation rate, vacuum evaporation or ion plating using an electron gun evaporation source is advantageous.
Furthermore, in order to form a film mainly composed of anatase phase at a practical film forming rate, the substrate temperature is set to 200 to 450 ° C., the titanium evaporation rate is set to 0.06 to 0.15 μm per minute, and the oxygen atmosphere pressure is increased. Is preferably 3 to 5 × 10 ⁻⁴ Torr.

[0021]

EXAMPLES Examples of the present invention and comparative examples are shown below.
Using a pure titanium plate for industrial use and a stainless steel plate (SUS304) as a metal plate substrate, forming a film by PVD method or the like, and for the obtained sample, the properties of the film (configuration, film thickness, anatase type titanium oxide content, Each sample was evaluated for its photocatalytic activity (degree of potassium iodide decomposition, deodorizing effect, antibacterial activity). Table 1 shows the conditions for film formation and the evaluation results. Titanium-based alloys are Al, Zr, H
f, V, Nb, Ta, Mn, Fe, Co, Ni, Cr, etc. 0.5 to 5 mass%
In general, the Al content is 0.5% by mass.
A titanium-based alloy was used.

The composition, thickness and anatase type titanium oxide content of the film were determined by Auger electron spectroscopy, X-ray photoelectron spectroscopy,
It was determined by glow discharge emission analysis, Raman scattering analysis, and X-ray diffraction. The adhesion was evaluated by a 90 ° bending test. As a substrate for evaluation of adhesion, a disk-shaped substrate of SUS304 having a diameter of 30 mm and a thickness of 0.3 mm was used, and a film was formed on the surface. This sample was deformed to a bending angle of 90 °, and the part with the largest deformation (bent part) was magnified using a reflection microscope.
Observed at 100x. When the film was completely peeled, the adhesion was evaluated as X. When the film was partially peeled and the film was partially adhered, the adhesion was evaluated. ○

The evaluation of the photocatalytic activity was carried out by the following sol-gel method by using a titanium oxide film on a SUS304 stainless steel plate (40 mm).
At a corner and a thickness of 1 mm), and a relative evaluation of the photocatalytic activity was performed. The sol-gel method was used according to the method of flower making (Sol-gel method science, Agne Shofusha, 1988). Specifically, titanium tetraisopropoxide was diluted to a concentration of 284 g / l with 100 ml of absolute ethanol, and while stirring, a transparent sol was prepared by adding dropwise to a solution of 2 ml of 2N hydrochloric acid diluted with 100 ml of absolute ethanol. Next, dip coating
-The process of drying (100 ° C) was repeated to generate a gel compound on the substrate, and baked in an electric furnace at 600 ° C for 5 hours. After repeating four times, the thickness of the formed film was 0.5 μm.

The degree of decomposition of potassium iodide was evaluated by immersing each sample in an aqueous solution of potassium iodide and irradiating the sample with black light (3 mw / cm ² ) having a high ultraviolet intensity to evaluate the amount of iodine produced. Based on the amount of iodine produced by the above method using the film formed by the sol-gel method,
When the iodine generation amount tested in each sample was less than 0.5 times the reference amount, the evaluation was x, when 0.5 to less than 1.5 times was Δ, and when 1.5 or more times was ○.

Regarding the deodorizing effect, a constant intensity of ultraviolet light (black light: 3 w / cm) was applied from the outside of the quartz tube where each sample was placed.
^The evaluation was performed by flowing a constant flow of aldehyde while irradiating ² ) and measuring the residual aldehyde concentration at the outlet. Based on the residual aldehyde concentration tested by the above method using the film formed by the sol-gel method, the residual concentration tested in each sample was evaluated when the concentration was at least twice the reference concentration.
0.5 to less than 2 times was rated as △, and less than 0.5 times was rated as ○.

With respect to the antibacterial activity, a physiological saline in which Escherichia coli is suspended at a constant concentration is dropped on the surface of each sample, and ultraviolet rays are irradiated.
Evaluated by viability of E. coli after 1 hour irradiation.
Based on the survival rate of Escherichia coli tested by the above method using the film formed by the sol-gel method, the survival rate of the Escherichia coli tested in each sample was evaluated as 1.5 times or more the reference concentration.
5 times to less than 1.5 times were rated as △, and less than 0.5 times were rated as ○.

Nos. 1 to 8 in Table 1 are comparative examples, and Nos. 9 to 18 are examples. In the examples, the same or better characteristics were observed in both adhesion and photocatalytic activity as compared with the sol-gel method. No. 1 is the evaluation result of the blank substrate itself on which no film was formed. In the film formation method, the following two methods were tried as a sputtering method. SP used metallic titanium as a target and introduced oxygen gas as a reaction gas. SP
In Section 2, the plasma was activated with argon gas using titanium dioxide (for forming the outer layer) and titanium metal (for forming the inner layer) as targets. In SP2, when the intermediate layer was formed, titanium dioxide and metallic titanium were simultaneously used as targets to form a film.However, since the titanium vapor and oxygen gas partial pressures could not be individually controlled, the intermediate layer could not have a graded composition. Was.
The gas pressure of both SP and SP2 was 2.7 Pa.

In forming the outer layer by vacuum deposition and ion plating, metal titanium was evaporated by an electron gun under an oxygen atmosphere under a pressure of 0.05 Pa. For the formation of the inner layer, without introducing oxygen gas, performed at a pressure of 0.05 Pa or less,
The formation of the intermediate layer was controlled by keeping the evaporation rate of metallic titanium constant and gradually increasing the oxygen gas flow rate. The thicknesses of the inner layer, the intermediate layer and the outer layer were controlled by changing the deposition time. The film thickness increases linearly with increasing deposition time. The deposition rate was, for example, 0.05 μm / min in the ion plating of No. 17, which was almost the same as the evaporation rate of titanium metal.

For the thermal spraying, titanium oxide particles were irradiated with plasma. In order to avoid an increase in the temperature of the substrate, the substrate was sprayed quickly with compressed air while cooling from the rear of the substrate. There is a limit to creating a gradient composition with good controllability by thermal spraying
(No. 3), sufficient adhesion could not be obtained. As is clear from the examples in Table 1 (Nos. 9 to 18),
~ 5.0 μm thick, an inner layer consisting of a metallic titanium layer,
Forming an intermediate layer composed of titanium metal and titanium oxide and having a chemical composition graded from a titanium metal layer to a titanium oxide layer, and an outer layer composed of a titanium oxide layer to a composition according to the purpose. Thus, a metal plate having excellent adhesion and photocatalytic activity can be obtained. It can be seen that these can be efficiently and effectively produced by the PVD method of separately controlling the partial pressures of titanium vapor or ionized titanium vapor and oxygen.

[0030]

[Table 1]

[0031]

According to the present invention, a metal plate having photocatalytic activity can be put to practical use in a wide range. By providing an intermediate layer having a gradient composition in the film, a film having excellent adhesiveness can be obtained, which can be deformed and processed, and can provide a metal plate having sustained catalytic activity even when used for a long time. Further, since the film can be formed by a single process, the process can be easily controlled, which is advantageous for reducing the manufacturing cost and improving the working efficiency. Furthermore, since the temperature of the metal plate base material at the time of forming the film is low, deformation of the metal plate, a change in design due to heat, a decrease in the photocatalytic activity of the film, and the like can be avoided.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of the chemical structure of a film structure and an intermediate layer according to the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C23C 14/34 C23C 14/34 U 28/00 28/00 BF Term (Reference) 4G069 AA03 BA04A BA04B BA17 BA18 BA48A BC50A DA06 EA11 EC22X EC22Y FA04 FB02 4K029 AA01 BA17 BA48 BB02 BC07 BD00 CA02 CA04 CA05 DC03 DC05 DC16 EA03 4K044 AA03 AA06 AB02 BA02 BA12 BB03 BB04 BC02 BC05 CA13

Claims (6)

[Claims] 1. A metal plate having on its surface a coating having a thickness of 0.5 to 5.0 μm, said coating comprising, from the metal plate to the surface, an inner layer comprising a titanium metal layer; A metal plate having photocatalytic activity, comprising: an intermediate layer having a gradient composition from a metal titanium layer to a titanium oxide layer, and an outer layer comprising a titanium oxide layer. 2. The thickness of the inner layer is 0.05 to 1.0 μm, the thickness of the intermediate layer is 0.05 to 1.0 μm, and the thickness of the outer layer is 0.4 to 1.0 μm.
2. The metal plate having photocatalytic activity according to claim 1, which has a thickness of 3.0 μm. 3. The method according to claim 1, wherein the outer layer comprises anatase-type titanium oxide.
Claim 1 or 2 characterized by containing at least 80% by volume.
4. The metal plate having photocatalytic activity according to claim 1. 4. The metal plate having photocatalytic activity according to claim 1, wherein the metal plate is made of stainless steel, titanium, or a titanium-based alloy. 5. The method for forming a metal plate having photocatalytic activity according to any one of claims 1 to 4, wherein the film is not exposed to the air even once during the formation of a film from an inner layer to an outer layer.
Under reduced pressure, with titanium vapor or ionized titanium vapor,
A method for producing a metal plate having photocatalytic activity, wherein a film is formed on a metal plate at a temperature of 500 ° C or less by using a PVD method in which oxygen partial pressures are separately controlled. 6. The method for producing a metal plate having photocatalytic activity according to claim 5, wherein the PVD method is sputtering or ion plating.