JP3384930B2 - Method for producing photocatalyst-coated metal plate - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a photocatalyst-coated metal plate exhibiting a photocatalytic action effective for decomposing organic substances and water. 2. Description of the Related Art When photocatalytic particles are irradiated with light having a wavelength having energy equal to or greater than the band gap, electrons are generated in a conduction band and holes are generated in a valence band by photoexcitation. The strong oxidizing power of holes generated by the photoexcitation is used for decomposition of organic substances and water. However, using the photocatalyst in a particulate state makes its handling and recovery difficult,
Outflow and scattering are inevitable. Therefore, the photocatalyst is used by being fixed to a substrate such as a metal. As such a metal plate, one in which a photocatalyst is directly coated on a metal plate is disclosed in JP-A-3-8448, after a light-transmissive charge-separation layer is provided on a carrier having a high reflectance surface. One supporting photocatalyst particles is introduced in JP-A-7-88367. For fixing the photocatalyst to the substrate, a method of sintering and baking the photocatalyst particles at a temperature of 400 ° C. or more on the substrate,
A method of spraying a substance which becomes a photocatalyst by thermal decomposition onto a substrate heated to a temperature of about 400 ° C. or the like is employed. Further, a method of laminating and pressing a mixture of photocatalyst particles and a fluoropolymer on a substrate, a method of attaching a resin paint in which the photocatalyst particles are suspended, and the like are also known. [0003] When a photocatalyst layer is provided by a conventional method, a photocatalyst-coated metal plate exhibiting sufficient photocatalytic activity cannot be obtained. For example, when the photocatalyst particles are applied by being mixed with a resin or the like, a part of the photocatalyst surface is covered with the resin or the like, so that the entire surface of the photocatalyst particles cannot be used as a catalytic surface. On the other hand, the metal plate can be coated with only the photocatalyst by heating and baking, but in this method, the catalytic activity of the formed photocatalyst coating layer is significantly reduced. Further, when a high-reflectance metal plate such as a metal plate having a mirror finish is used for a substrate as disclosed in Japanese Patent Application Laid-Open No. 7-88367, the metal plate can be used only for special purposes such as decomposition of ethylene and the like. Since the cost of finishing is considerably high, it cannot be applied to ordinary metal plates used for building materials and the like. SUMMARY OF THE INVENTION The present invention has been devised to solve such a problem, and requires a mirror finish by forming an SiO ₂ base layer. An object of the present invention is to obtain a photocatalyst-coated metal plate exhibiting sufficient catalytic activity without using a normal metal plate as a substrate. According to the production method of the present invention, X-Si (OR) ₃ (where X represents a group having a vinyl group, an epoxy group, an amino group or a mercapto group or a methyl group, A silane coupling agent or a SiO ₂ sol having a structure of (a) represents an alkyl group) is applied to the surface of the metal plate, and an SiO ₂ precursor or a titania sol is applied after forming an SiO ₂ precursor or an SiO ₂ underlayer by heat treatment. Then, heat treatment is performed at 400 to 850 ° C., and TiO ₂ is baked on the metal plate while diffusion of the metal from the metal plate is suppressed by the SiO ₂ underlayer. As the organic titanium compound, titanium alkoxide or titanium β-diketonate is used. When a silane compound or a SiO ₂ sol is applied to the surface of a metal plate and then heat-treated at preferably 150 to 850 ° C., a hydrophilic or lipophilic coating layer having a Si—O network structure is formed on the surface of the metal plate. Formed. When the TiO ₂ layer is formed using this SiO ₂ -based coating layer as a base, the photocatalytic coating layer is formed without lowering the catalytic activity. Silane compound, SiO ₂ sol, organic titanium compound, TiO ₂
The sol or the like is applied to the surface of the base metal plate by a method such as dipping, spraying, or electrophoresis. The present inventors have conducted various investigations on the cause of a decrease in catalytic activity when a TiO ₂ layer is directly formed on a metal plate. As a result, it was concluded that during heat treatment for forming the TiO ₂ layer, the metal is diffused from the metal plate to form recombination centers of electrons and holes in the TiO ₂ layer. . That is, in the TiO ₂ -based photocatalyst, excitation by light is greatly affected by impurities. The adverse effect due to impurities varies depending on the type of metal, but appears even at 0.1 mol% or less. Therefore, in the present invention, in order to suppress metal diffusion from the metal plate, SiO 2
_Two layers are formed. The SiO ₂ layer slows down the diffusion rate of the metal diffused from the substrate during the heat treatment, and favorably maintains the photocatalytic action inherent to the photocatalytic layer formed thereon. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A hydrophilic SiO ₂ film is formed on the surface of a metal plate by using a substrate having a hydrophilic group as a reactive group in a silane compound and subjecting it to heat treatment at 150 to 400 ° C. I do. When a TiO ₂ coating is applied on the SiO ₂ underlayer using an aqueous TiO ₂ sol, a uniform coating with good wettability can be applied. 600-85
When heat treatment is performed at 0 ° C., the adhesion of the TiO ₂ -based film is improved, and at the same time, the organic substances contained in the underlayer disappear, and
_A homogeneous underlayer consisting of ₂ is formed. On the other hand, when a silane compound having a lipophilic group is used as a reactive group,
A film having a lipophilic group is formed on the surface by the heat treatment at 400 ° C. When a TiO ₂ coating is applied on the underlayer using a solution in which an organic titanium compound such as titanium alkoxide is dissolved in an organic solvent, a uniform coating with good wettability is applied. When the coating is heated at 400 to 850 ° C. after the coating, the adhesion of the TiO ₂ -based film is improved, and the organic substances contained in the underlayer disappear, so that a uniform underlayer made of SiO ₂ is formed. If the heat treatment is performed at a temperature exceeding 850 ° C. during the formation of the underlayer, cracks tend to occur in the formed SiO ₂ layer. When cracks are formed in the SiO ₂ layer, the film is easily peeled off, and stable oil decomposition characteristics are not maintained for a long period of time. At a heat treatment temperature of not higher than 150 ° C., the adhesion to the metal plate is poor, and the coating layer is easily peeled off from the metal plate by impact or contact with foreign matter. If heat treatment is performed at a temperature exceeding 850 ° C. during the formation of the surface layer, the TiO ₂ layer changes from an anatase structure to a rutile structure, and the function as a photocatalyst is impaired. However, if the heat treatment temperature does not reach 400 ° C., the adhesion is inferior, and the coating layer is easily peeled off from the metal plate by contact with impact or foreign matter. In this regard, in the method disclosed in Japanese Patent Application Laid-Open No. 7-88367, the silica layer is dried at 150 ° C. for 3 hours, and the TiO ₂ layer is formed not by TiO ₂ alone but by silica binder.
It contains 0%, is dried at 150 ° C. for 3 to 6 hours, and is sometimes baked at 500 ° C. for 1 hour. In this method, a long-time treatment is required, and a silica binder for improving the adhesion of the TiO ₂ layer is required, so that the catalytic activity is lower than that of TiO ₂ alone. EXAMPLE 1 A SUS430 stainless steel sheet having a thickness of 0.6 mm was used as a substrate and immersed in a silane coupling solution to obtain a SUS430 stainless steel sheet having a thickness of 0.1 mm.
It was pulled up at a speed of m / sec and heated at 100 to 900 ° C. for 10 minutes. As a result, a SiO ₂ layer having a thickness of 0.15 μm was formed on the substrate surface. As the silane coupling solution, N-silane as a silane coupling agent having a hydrophilic group was used.
β- (N-vinylbenzylaminoethyl) -γ-aminopropyltrimethoxysilane hydrochloride was used and its concentration was adjusted to 20% using ethanol. Next, it was immersed in an aqueous TiO ₂ sol, pulled up at a speed of 0.5 m / sec, dried, and baked at 600 to 900 ° C. for 2 minutes. The formed TiO ₂ layer had a thickness of 1.2 μm. For each of the treated samples, the adhesiveness and oil decomposition characteristics of the film were investigated. Adhesion was evaluated by a cross-cut tape peeling test. A sample that did not peel at all was evaluated as ○, and a sample that slightly peeled was evaluated as ×. In the oil decomposition property test, 2
After applying mg / cm ² of salad oil, it was irradiated with black light to decompose oil at a UV intensity of 8 mW / cm ^{2 and} the change in weight was measured. Then, show the same oil breakdown characteristics as TiO ₂ film on a glass substrate, ○ those TiO ₂ film has an anatase structure, while indicating same oil breakdown characteristics as TiO ₂ film on a glass substrate, is TiO ₂ film rutile Those having a structure were evaluated as Δ, and those having a lower oil decomposition property than the TiO ₂ film on the glass substrate were evaluated as ×. As an example, test number 4
Was coated with ² mg / cm ² of salad oil, and then irradiated with black light having an ultraviolet intensity of 8 mW / cm ² to investigate the relationship between irradiation time and oil decomposition rate. As a result, in Test No. 4, as shown in FIG. 1, the same oil decomposition characteristics as those obtained by forming TiO ₂ to a thickness of 1.2 μm on a glass substrate were exhibited. [0012] EXAMPLE 2 A SUS430 stainless steel plate having a thickness of 0.6 mm was used as a substrate and immersed in a silane coupling bath.
It was pulled up at a speed of 1 m / sec and heated at 100 to 900 ° C. for 10 minutes. As the coupling bath, one prepared by using vinyltrimethoxysilane as a silane coupling agent having a lipophilic group and adjusting the concentration to 20% with isopropanol was used. Then immersed in 1M titanium tetraisopropoxide _{-0.2M HCl-0.5M H 2 O-} 15M ethanol solution, pulled up at 0.2 m / min, 30
It baked at 0-900 degreeC for 1 minute. Observation of the surface of the test piece after sintering revealed that the SiO ₂ layer had a thickness of 0.15 μm and a thickness of 0.3.
A μm TiO ₂ layer was formed. Table 2 shows the adhesion and oil decomposition characteristics of the obtained film in relation to the processing conditions. The oil decomposition characteristics in Table 2 were evaluated in the same manner as in Table 1. [0014] EXAMPLE 3 Using a SUS430 stainless steel plate having a thickness of 0.4 mm as a substrate, a SiO ₂ sol was spray-coated and then baked at 500 ° C. for 5 minutes to form an SiO ₂ layer. Next, the aqueous TiO ₂ sol was spray-coated and dried, and then baked at 700 ° C. for 2 minutes. In the obtained coating material, the SiO ₂ layer had a thickness of 0.3 μm and the TiO ₂ layer had a thickness of 4 μm. As a result of examining oil decomposition characteristics using the coated metal plate under the same conditions as in Example 1,
It exhibited the same oil decomposition characteristics as those obtained by coating a glass substrate with a 4 μm-thick TiO ₂ layer. Example 4 A hot-dip aluminum-plated steel sheet having a thickness of 0.5 mm was used as a metal substrate and immersed in a silane coupling agent of methyltrimethoxysilane. 0.1 from the coupling solution.
It was pulled up at a speed of 1 m / sec and dried at 200 ° C. for 20 minutes. After that, 1M titanium acetylacetonate-0.
Immersed in _{2M HCl-0.5M H 2 O-} 15M ethanol solution, pulled up at 0.2 m / min, and baked for 1 minute at 500 ° C.. The obtained coating material has 0.15 μm S
It had an TiO ₂ layer and a 0.3 μm TiO ₂ layer. Using this coated metal plate, the oil decomposition characteristics were examined under the same conditions as in Example 1. As a result, the oil decomposition characteristics were the same as those obtained by coating a glass substrate with a TiO ₂ layer having a thickness of 0.3 μm. . [0017] Comparative Example 1: aqueous TiO ₂ sol was immersed SUS430 stainless steel, TiO ₂ by pulling up at a speed of 0.5 m / sec
Coating was applied. Then, after drying, 2
It was baked for minutes to prepare a photocatalyst-coated metal plate. To investigate the catalytic activity of this photocatalyst-coated metal plate, 2 mg of salad oil
/ Cm ² was applied to an oil decomposition experiment in which black light was irradiated. As a result, as shown in FIG. 1, the oil decomposition characteristics were significantly reduced as compared with the TiO ₂ layer of the same thickness coated on the glass substrate. Comparative Example 2: 1 M titanium tetraisopropoxide-0.2 M HCl
Immersing the SUS430 stainless steel in the sol-gel bath having a composition of -0.5M H ₂ O-15M ethanol, 0.2 m
The TiO ₂ coating was applied by pulling up at a rate of / s. Then, after drying, baking was performed at 700 ° C. for 2 minutes to prepare a photocatalyst-coated metal plate. In order to investigate the catalytic activity of this photocatalyst-coated metal plate, it was subjected to an oil decomposition experiment in which black light was irradiated with ² mg / cm ² of salad oil applied. As a result, as shown in FIG. 1, the oil decomposition characteristics were significantly reduced as compared with the TiO ₂ layer of the same thickness coated on the glass substrate. As described above, according to the present invention, S
Because through the iO ₂ layers to form a TiO ₂ layer, TiO
Metal diffusion during _two layers formed from base metal plate be high temperature heating to TiO ₂ layer is suppressed by the SiO ₂ layer, decrease in catalytic activity is not TiO ₂ layer is formed on the metal plate surface. The photocatalyst-coated metal plate obtained in this way has a high and stable catalytic activity for a long period of time, and is used for applications requiring high sanitary requirements, such as kitchen appliances and building materials for buildings where many people enter and leave. used.

BRIEF DESCRIPTION OF THE DRAWINGS] [Figure 1] metal plate surface oil breakdown characteristics but coated with TiO ₂ layer through the SiO ₂ layer, the oil degradation properties of the metal plate and the glass substrate to the direct TiO ₂ layer and Graph compared

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Setsuko Koura 7-1 Takayashinmachi, Ichikawa-shi, Chiba Nisshin Steel Co., Ltd. Technical Research Institute (56) References JP-A-7-171408 (JP, A) Kaihei 6-278241 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B32B 1/00-35/00 C09D 1/00-201/10 B01J 21/00-35/02

Claims (1)

(57) [Claims 1] X-Si (OR) ₃ (where X is a group having a vinyl group, an epoxy group, an amino group or a mercapto group)
Or a methyl group, R represents SiO ₂ precursor or Si by applying a heat treatment with a silane coupling agent or SiO ₂ sol having a structure of an alkyl group) in the metal plate surface
After forming a base layer made of O ₂ , an organic titanium compound or titania sol is applied and heat-treated at 400 to 850 ° C., and TiO ₂ is baked on the metal plate while suppressing metal diffusion from the metal plate with the SiO ₂ base layer. A method for producing a photocatalyst-coated metal plate, comprising: