Photocatalyst-coated metallic sheet and its production

Description: TECHNICAL FIELD [Detailed description of the invention]

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INDUSTRIAL APPLICABILITY The present invention relates to a photocatalytic coated metal plate exhibiting a photocatalytic action effective for decomposition of organic substances and water, and a method for producing the same.

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PROBLEM TO BE SOLVED: When a photocatalyst particle is irradiated with light having a wavelength having an energy equal to or larger than a band gap, electrons are generated in the conduction band and holes are generated in the valence band by photoexcitation. The strong oxidizing power of holes generated by this photoexcitation is used for decomposition of organic substances and water. However, using the photocatalyst in the state of particles makes it difficult to handle and recover it, and outflow and scattering are unavoidable. Therefore, the photocatalyst is used by being fixed to a substrate such as metal. As such a metal plate, a metal plate directly coated with a photocatalyst is described in JP-A-3-8448, in which a charge separation tank having good light transmittance is provided on a carrier having a high reflectance surface and then a photocatalyst. Those bearing particles are introduced in Japanese Patent Application Laid-Open No. 7-88367. For fixing the photocatalyst to the substrate, there are a method of sintering and baking the photocatalyst particles on the substrate at a temperature of 400 ° C. or higher, a method of spraying a substance that becomes a photocatalyst by thermal decomposition onto the substrate heated to a temperature of about 400 ° C., etc. It has been adopted. Further, a method of laminating and pressure-bonding a mixture of photocatalyst particles and a fluoropolymer on a substrate, a method of adhering a resin paint in which photocatalyst particles are suspended, and the like are also known.

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PROBLEM TO BE SOLVED: To obtain a photocatalyst-coated metal plate exhibiting sufficient photocatalytic activity when a photocatalyst layer is provided by a conventional method. For example, when the photocatalyst particles are applied by mixing with a resin or the like, the entire surface of the photocatalyst particles 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 only with the photocatalyst by heat baking, but in this method, the catalytic activity of the formed photocatalyst coating layer is significantly reduced. Further, a metal plate having a high reflectance such as a mirror-finished metal plate as in JP-A-7-88367 can only be used for special purposes such as ethylene decomposition, and the metal plate can be mirror-finished. Since it is quite costly to finish, it cannot be applied to ordinary metal plates used for building materials and the like. The present invention has been devised to solve such a problem, and SiO₂ By forming the base layer of the system, it is an object of the present invention to obtain a photocatalyst-coated metal plate exhibiting sufficient catalytic activity by using a normal metal plate as a substrate without requiring a mirror finish.

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PROBLEM TO BE SOLVED: To achieve the object of the photocatalyst-coated metal plate of the present invention, SiO for suppressing metal diffusion on the surface of the metal plate.₂ TiO via the base layer₂ It is characterized in that a layer is formed. This photocatalyst-coated metal plate is a silane compound or SiO coated on the surface of the metal plate.₂ Heat-treat the sol and put SiO on the surface of the metal plate₂ Precursor or SiO₂ After forming a base layer made of, an organic titanium compound or titania sol is applied and heat-treated to diffuse metal from the metal plate.₂ TIO while suppressing with the base layer₂ Is manufactured by baking on a metal plate. As a silane compound, X-Si (OR)₃ The one with the structure of is used. In the formula, X represents a vinyl group, an epoxy group, an amino group, a methacryl group or a mercapto group, and R represents an alkyl group. Titanium alkoxide or titanium β-diketonate is used as the organic titanium compound.

Silane compound or SiO₂ When the sol is applied to the surface of the metal plate and then heat-treated, preferably at 150 to 850 ° C., a hydrophilic or lipophilic coating layer having a SiO network structure is formed on the surface of the metal plate. This SiO₂ TiO with the system coating layer as the base₂When forming the layer, the photocatalytic coating layer is formed without reducing the catalytic activity. The photocatalyst coating layer is formed by applying, for example, an organic titanium compound or titania sol and then heat-treating at 400 to 850 ° C. Silane compound, SiO₂ Sol, organic titanium compound, TiO₂ The sol or the like is applied to the surface of the metal plate of the substrate by a method such as immersion, spraying, or electrophoretic electrodeposition.

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[Action] The present inventors have TiO on a metal plate.₂ Various causes of the decrease in catalytic activity when the layer was directly formed were investigated. As a result, TiO₂ During the heat treatment to form the layer, the metal diffuses from the metal plate, causing the electron and hole recombination centers to become TiO.₂ It was concluded that the cause was the formation in the layers. That is, TiO₂ In the photocatalyst of the system, the excitation by light is greatly affected by impurities. The adverse effect of impurities varies depending on the type of metal, but appears even at 0.1 mol% or less. Therefore, in the present invention, SiO is placed on the surface of the metal plate in order to suppress metal diffusion from the metal plate.₂ Forming a layer. SiO₂ The layer slows down the diffusion rate of the metal diffused from the substrate during the heat treatment, and maintains the photocatalytic action inherent in the photocatalytic layer formed on the layer.

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[Embodiment] A SiO having a hydrophilic group is used as a reactive group in the silane compound of the base layer, and the surface of the metal plate is hydrophilic by heat treatment at 150 to 400 ° C.₂ Form a film. Water-based TiO₂ TIO on top of this base layer with sol₂ When the coating is applied, the wettability is good and a uniform coating can be applied. When heat-treated at 600-850 ° C, TiO₂ As the adhesion of the system film is improved, the organic substances contained in the base layer disappear, and SiO₂ A homogeneous base layer consisting of is formed. On the other hand, when a silane compound having a lipophilic group is used as the reactive group, a film having a lipophilic group is formed on the surface by heat treatment at 150 to 400 ° C. TIO on the base layer using a solution of an organic titanium compound such as titanium alkoxide in an organic solvent.₂ When the coating is applied, a uniform coating with good wettability is applied. After coating, heat treatment at 400-850 ° C₂ As the adhesion of the system film is improved, the organic substances contained in the base layer disappear, and SiO₂ A homogeneous base layer consisting of is formed.

When the base layer is formed by heat treatment at a temperature exceeding 850 ° C., the formed SiO₂ The layer is prone to cracking. SiO₂ When cracks are formed in the layer, the film is easily peeled off, and stable oil decomposition characteristics are not maintained for a long period of time. Further, at a heat treatment temperature of less than 150 ° C., the adhesion to the metal plate is inferior, and the coating layer is easily peeled off from the metal plate by impact or contact with foreign matter. When heat-treated at a temperature exceeding 850 ° C. when forming the surface layer, TiO₂ The layer changes from an anatase structure to a rutile structure, impairing its function as a photocatalyst. However, at a heat treatment temperature of less than 400 ° C., the adhesion is poor, and the coating layer is easily peeled off from the metal plate due to impact or contact with foreign matter. In this regard, in the method disclosed in Japanese Patent Application Laid-Open No. 7-88367, when the silica layer is formed, it is dried at 150 ° C. for 3 hours and TIO.₂ TIO at the time of layer formation₂ It contains 20% of silica binder, not alone, is dried at 150 ° C. for 3 to 6 hours, and is baked at 500 ° C. for 1 hour in some cases. This method requires a long time of processing and is also TIO.₂ Catalytic activity is TiO because a silica binder is required to improve the adhesion of the layer.₂ Lower than alone.

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[Example]

Example 1: A SUS430 stainless steel plate having a thickness of 0.6 mm was used as a substrate, immersed in a silane coupling liquid, pulled up at a speed of 0.1 m / sec, and heated at 100 to 900 ° C. for 10 minutes. As a result, SiO with a film thickness of 0.15 μm is formed on the surface of the substrate.₂ A layer was formed. As the silane coupling solution, N-β- (N-vinylbenzylaminoethyl) -γ-aminopropyltrimethoxysilane hydrochloride was used as a silane coupling agent having a hydrophilic group, and ethanol was used to make a concentration of 20. The one prepared to% was used. Next, water-based TiO₂ It was immersed in a sol, pulled up at a rate of 0.5 m / sec, dried and calcined at 600 to 900 ° C. for 2 minutes. Formed TiO₂ The layer had a thickness of 1.2 μm.

The adhesion and oil decomposition characteristics of the membrane were investigated for each treated sample. Adhesion was investigated by a grid tape peeling test, and those that did not peel at all were evaluated as , and those that peeled even slightly were evaluated as x. 2 mg / cm in oil decomposition property test² After applying the salad oil of, irradiate with black light and 8mW / cm² The oil was decomposed by the UV intensity of the above, and the weight change was measured. And TIO on the glass substrate₂ Shows the same oil decomposition characteristics as the membrane, and TIO₂ If the membrane has an anatase structure, , TIO on the glass substrate₂ Although it exhibits the same oil decomposition properties as the membrane, it is TiO.₂ A film having a rutile structure is Δ, and TIO on a glass substrate₂ Those having lower oil decomposition characteristics than the membrane were evaluated as x. As an example, 2 mg / cm of vegetable oil was added to the test piece of test number 4.² After application, UV intensity 8mW / cm² The relationship between the irradiation time and the oil decomposition rate was investigated by irradiating with black light. As a result, in test number 4, TiO on the glass substrate as shown in FIG.₂ Exhibited almost the same oil decomposition characteristics as those formed with a film thickness of 1.2 μm.

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Example 2: A SUS430 stainless steel plate having a thickness of 0.6 mm was used as a substrate, immersed in a silane coupling bath, pulled up at a speed of 0.1 m / sec, and heated at 100 to 900 ° C. for 10 minutes. As the coupling bath, vinyltrimethoxysilane was used as a silane coupling agent having a lipophilic group, and a solution prepared with isopropanol to a concentration of 20% was used. Then 1M Titanium Tetraisopropoxide-0.2M HCl-0.5MH₂ It was immersed in an O-15M ethanol solution, pulled up at a rate of 0.2 m / min, and calcined at 300 to 900 ° C. for 1 minute. When observing the surface of the test piece after firing, SiO with a film thickness of 0.15 μm is observed.₂ TiO with a layer and a film thickness of 0.3 μm₂ Layers were formed. The adhesion and oil decomposition characteristics of the obtained film are shown in Table 2 in relation to the treatment conditions. The oil decomposition characteristics in Table 2 were evaluated in the same manner as in Table 1.

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Example 3: Using a SUS430 stainless steel plate having a thickness of 0.4 mm as a substrate, SiO₂ After spray coating the sol, bake at 500 ° C for 5 minutes to SiO₂Formed a layer. Next, water-based TiO₂ The sol was spray coated and dried, and then calcined at 700 ° C. for 2 minutes. The obtained coating material is SiO₂ The layer has a film thickness of 0.3 μm, TiO₂The layer had a film thickness of 4 μm. As a result of investigating the oil decomposition characteristics using this coated metal plate under the same conditions as in Example 1, a TIO having a film thickness of 4 μm on a glass substrate.₂It showed the same oil decomposition properties as those coated with a 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. It was pulled up from the coupling solution at a rate of 0.1 m / sec and dried at 200 ° C. for 20 minutes. Then 1M Titanium Acetylacetone-0.2M HCl-0.5MH₂ It was immersed in an O-15M ethanol solution, pulled up at a rate of 0.2 m / min, and calcined at 500 ° C. for 1 minute. The obtained coating material is 0.15 μm SiO.₂ Layer and 0.3 μm TiO₂ Had a layer. As a result of investigating the oil decomposition characteristics using this coated metal plate under the same conditions as in Example 1, a TIO having a film thickness of 0.3 μm on a glass substrate.₂ It exhibited the same oil decomposition properties as those coated with a layer.

Comparative Example 1: Water-based TiO₂ TIO by immersing SUS430 stainless steel in the sol and pulling it up at a speed of 0.5 m / sec.₂ It was coated. Then, after drying, it was fired at 700 ° C. for 2 minutes to prepare a photocatalyst-coated metal plate. In order to investigate the catalytic activity of this photocatalytic coated metal plate, salad oil 2 mg / cm² Was applied to an oil decomposition experiment in which black light was irradiated. As a result, as shown in FIG. 1, TiO of the same film thickness coated on the glass substrate₂ The oil decomposition characteristics were significantly reduced compared to the layer.

Comparative Example 2: 1M Titanium Tetraisopropoxide-0.2M HCl-0.5M H₂ TIO by immersing SUS430 stainless steel in a sol-gel bath having a composition of O-15M ethanol and pulling it up at a rate of 0.2 m / sec.₂ It was coated. Then, after drying, it was fired at 700 ° C. for 2 minutes to prepare a photocatalyst-coated metal plate. In order to investigate the catalytic activity of this photocatalytic coated metal plate, salad oil 2 mg / cm² Was applied to an oil decomposition experiment in which black light was irradiated. As a result, as shown in FIG. 1, TiO of the same film thickness coated on the glass substrate₂ The oil decomposition characteristics were significantly reduced compared to the layer.

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[Effect of the Invention] As described above, the photocatalyst-coated metal plate of the present invention is a SiO.₂ TiO through layers₂ Since the layer is formed, the metal elements from the base metal plate diffuse during firing.₂ TIO that is suppressed by the layer and does not reduce catalytic activity₂ A layer is formed on the surface of the metal plate. The photocatalyst-coated metal plate thus obtained maintains a high level of stable catalytic activity for a long period of time, and is used for applications with high hygiene requirements such as kitchen appliances and building materials for buildings where many people come and go. used.

[Simple explanation of drawings]

FIG. 1 is a SiO on the surface of a metal plate.₂ TiO through layers₂ The oil decomposition characteristics of the layer-coated material can be directly checked by TIO.₂ Graph comparing with oil decomposition characteristics of layered metal plate and glass substrate

Continuation of front page (72) Inventor Setsuko Koura 7-1 Koyashinmachi, Ichikawa City, Chiba Prefecture Nissin Steel Co., Ltd. Technical Research Institute