Exterior wall building material

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a building material for an outer wall that can be self-cleaned by rainfall, and a building material for an outer wall that can be easily cleaned by washing with water.

【0002】

[Conventional technology]

The outer walls of high-rise buildings are polluted by combustion products such as soot and exhaust gas contained in the air, dirt eluted from the sealant above, and hydrophobic dirt such as pollutants discharged from the exhaust port of the building. .. These hydrophobic stains are light black and significantly spoil the aesthetics of the building. Furthermore, if an attempt is made to clean the outer wall of a high-rise building, the cleaning is a high-altitude work, which is both heavy labor and dangerous.

【0003】

[Problems to be Solved by the Invention]

An object of the present invention is to provide a building material for an outer wall that can be cleaned by rainfall or water washing.

【0004】

[Means for solving problems]

The present invention is based on the discovery that in a member having a surface layer containing a photocatalyst, when the photocatalyst is photoexcited, the surface of the member becomes highly hydrophilic. This phenomenon is considered to proceed by the mechanism shown below. That is, when the photocatalyst is irradiated with light having an energy equal to or greater than the energy gap between the upper end of the valence band of the photocatalyst and the lower end of the conduction band, the electrons in the valence band of the photocatalyst are excited to generate conduction electrons and holes. , Either or both of them will probably impart polarity to the surface and collect polar components such as water and hydroxyl bands. Then, by the cooperative action of either or both of conduction electrons and holes and the polar component, the chemical bond between the surface and the pollutant chemically adsorbed on the surface is broken, and the chemically adsorbed water on the surface. Is adsorbed, and a physically adsorbed aqueous layer is formed on it. Further, once the surface of the member is highly hydrophilic, the hydrophilicity of the surface is maintained for a certain period of time even if the member is held in a dark place.

【0005】

The present invention provides a self-cleaning outer wall building material provided with a surface layer containing substantially transparent photocatalytic oxide particles on the surface of the outer wall building material substrate. By providing a surface layer containing photocatalytic oxide particles, the surface of the surface layer becomes hydrophilic in response to photoexcitation of the photocatalyst, and when the surface of the building material for the outer wall is exposed to rainfall, adherent deposits and / Alternatively, the contaminants will be washed away by the raindrops.

【0006】

The present invention provides an easy-to-clean exterior wall building material provided with a surface layer containing substantially transparent photocatalytic oxide particles on the surface of the exterior wall building material substrate. By providing a surface layer containing photocatalytic oxide particles, the surface of the surface layer becomes hydrophilic in response to photoexcitation of the photocatalyst, and the surface of the building material for the outer wall can be easily washed with water and rinsed with water. It can be cleaned with a simple wipe.

【0007】

In a preferred embodiment of the present invention, the surface layer is further contained with silica. By containing silica, the surface tends to exhibit a high degree of hydrophilicity close to a water wetting angle of 0 °, and the hydrophilicity retention when held in a dark place is improved. The reason seems to be related to the ability of silica to store water in its structure.

【0008】

In a preferred embodiment of the present invention, the surface layer is further contained with silicone. Due to the inclusion of silicone, at least a part of the organic groups bonded to the silicon atoms in the silicone is replaced with hydroxyl groups by the photoexcitation of the photocatalyst, and a physically adsorbed aqueous layer is formed on the hydroxyl groups, so that the surface is surfaced. It exhibits a high degree of hydrophilicity close to a water wetting angle of 0 °, and improves hydrophilicity retention when held in a dark place.

【0009】

BEST MODE FOR CARRYING OUT THE INVENTION

Next, a specific configuration of the present invention will be described. As shown in FIG. 1 or 2, a layer containing a photocatalytic (crystalline) oxide or the like is formed on the surface of the base material on the surface of the building material for the outer wall in the present invention. By adopting such a surface structure, the surface of the building material for the outer wall becomes highly hydrophilic in response to the photoexcitation of the photocatalyst. As a result, the deposits and / or contaminants adhering to the surface of the surface layer due to precipitation are washed away by raindrops. Further, when the above surface structure is provided on the surface of the building material for the outer wall, the deposits and / or contaminants adhering to the surface of the surface layer can be easily washed with water, and the sunny day continues. However, it will be cleaned by rinsing or sprinkling water.

【0010】

In FIG. 1, the surface layer is composed only of photocatalytic oxide particles. In this case, since the photocatalyst is composed of oxides, the oxides are hydrophilic when the pollutants in the environment are not adsorbed. Therefore, the pollutants are excluded by the photoexcitation action to form an adsorbed aqueous layer. Therefore, it is easy to exhibit hydrophilicity, and a uniform water film can be formed. In FIG. 2, M represents a metallic element. Therefore, in the case of FIG. 2, the outermost surface is made of a general inorganic oxide. In this case as well, since the oxide exhibits hydrophilicity when the pollutants in the environment are not adsorbed, the pollutants are eliminated by the photoexciting action of the photocatalytic oxide mixed in the surface layer in addition to the above-mentioned inorganic oxides. By forming an adsorbed aqueous layer, a uniform aqueous film can be formed.

【0011】

Building material substrates for exterior walls for which the present invention can be used include glazed tiles, non-glazed tiles, bricks, crystallized glass, glass blocks, concrete, stones, wood; lightweight cellular concrete plates, asbestos cement calcium silicate plates, precast reinforced concrete plates, Cosmetic inorganic building materials in which resin paints such as acrylic resin, urethane resin, polyester, silicone, fluororesin, and acrylic silicon resin are applied to the surface layer of inorganic base materials such as asbestos slate board, pulp cement board, and plaster board board; aluminum, stainless steel. , Painted steel plate with resin paint such as acrylic resin, urethane resin, polyester, silicone, fluororesin, acrylic silicon resin coated on the surface layer of metal base material such as steel; plastic plate such as acrylic plate, polycarbonate plate or its coating Etc. can be preferably used.

【0012】

A photocatalyst is an excitation (photoexcitation) of electrons in the valence band when irradiated with light (excitation light) having an energy larger than the energy gap between the conduction band and the valence band of the crystal (that is, a short wavelength). ) Is generated to generate conduction electrons and holes, and the photocatalytic titanium oxide refers to crystalline titanium oxide such as anatase-type titanium oxide and rutile-type titanium oxide. Here, sunlight can be preferably used as the light source used for photoexcitation of the photocatalyst. In order for the surface of the substrate to be highly hydrophilic by photoexcitation of the photocatalyst, the illuminance of the excitation light is 0.001 mW / cm.²More than that is fine, but 0.01mW / cm²Above is preferable, 0.1mW / cm²The above is more preferable.

【0013】

The film thickness of the surface layer containing photocatalytic titanium oxide is preferably 0.4 μm or less. By doing so, it is possible to prevent white turbidity due to diffused reflection of light, and the surface layer becomes substantially transparent. Further, it is more preferable that the film thickness of the surface layer containing photocatalytic titanium oxide is 0.2 μm or less. By doing so, it is possible to prevent color development of the surface layer due to light interference. Further, the thinner the surface layer, the higher the transparency. Further, if the film thickness is reduced, the wear resistance of the surface layer is improved. A wear-resistant or corrosion-resistant protective layer or other functional film that can be hydrophilized may be further provided on the surface of the surface layer.

【0014】

It is preferable that the surface layer does not have a high refractive index as compared with the base material. Preferably, the refractive index of the surface layer is 2 or less. Then, the reflection of light at the interface between the base material and the surface layer and the interface between the surface layer and the air can be suppressed. To reduce the refractive index of the surface layer to 2 or less, a photocatalytic titanium oxide is added with another substance having a refractive index of 2 or less. Here, examples of other substances having a refractive index of 2 or less include calcium carbonate (refractive index 1.6), calcium hydroxide (refractive index 1.6), magnesium carbonate (refractive index 1.5), strontium carbonate (refractive index 1.5), and dolomite. (Refractive index 1.7), Calcium fluoride (Refractive index 1.4), Magnesium fluoride (Refractive index 1.4), Silica (Refractive index 1.5), Alumina (Refractive index 1.6), Silica sand (Refractive index 1.6), Montmorillonite (Refractive index 1.6) 1.5), kaolin (refractive index 1.6), sericite (refractive index 1.6), zeolite (refractive index 1.5), tin oxide (refractive index 1.9) and the like can be added to the surface layer.

【0015】

Metals such as Ag, Cu and Zn can be added to the surface layer. The surface layer to which the metal is added can kill bacteria and mold adhering to the surface even in a dark place.

【0016】

Platinum group metals such as Pt, Pd, Ru, Rh, Ir and Os can be added to the surface layer. The surface layer to which the metal is added can enhance the redox activity of the photocatalyst, and the deodorizing and purifying action and the like are improved. In addition, when a solid acid is added in addition to the photocatalyst, the acidity of the solid acid is improved by the addition of the platinum group metal, so that the hydrophilicity retention property is also improved, the water film formation of the adhered water is further promoted, and to some extent. The hydrophilicity retention property is also improved when the photocatalyst is not irradiated with excitation light for a long period of time. Mo may be added to the surface layer. In this case as well, the acidity of the solid acid is improved by the addition, so that the hydrophilicity retention property is also improved, the water film formation of the adhered water is further promoted, and the hydrophilicity retention property when the photocatalyst is not irradiated with the excitation light for a certain period of time. Also improves.

【0017】

When the base material is glass containing alkaline network-modifying ions such as sodium (soda lime glass, parallel plate glass, etc.), an intermediate layer such as silica may be formed between the base material and the surface layer. By doing so, the alkali network-modifying ions are prevented from diffusing from the base material to the surface layer during firing, and the photocatalytic function is better exhibited.

【0018】

Hydrophilicity refers to the property of being easily adapted when water is dropped on the surface, and generally refers to a state in which the water wetting angle is less than 90 °. The high degree of hydrophilicity in the present invention means a property that is very familiar when water is dropped on the surface, and more specifically, a state in which the water wetting angle is about 10 ° or less. In particular, as disclosed in PCT / JP96 / 00734, the antifogging property preferably has a water wetting angle of 10 ° or less, and more preferably 5 ° or less.

【0019】

The solid acid in the present invention includes sulfuric acid-supported Al.₂O₃, Sulfuric acid supported TiO₂, Sulfuric acid-supported ZrO₂, Sulfuric acid-supported SnO₂, Sulfuric acid supported Fe₂O₃, Sulfuric acid supported SiO₂, Sulfuric acid-supported HfO₂, TiO₂/ WO₃, WO₃/ SnO₂, WO₃/ ZrO₂, WO₃/ Fe₂O₃, SiO₂ Al₂O₃, TiO₂/ SiO₂, TiO₂/ Al₂O₃, TiO₂/ ZrO₂Etc. can be preferably used.

【0020】

Next, a method of forming the surface layer will be described. First, a production method when the surface layer is composed of only a photocatalytic oxide will be described by taking the case where the photocatalyst is anatase-type titanium oxide as an example. The method in this case is roughly divided into three methods. One method is a sol coating firing method, the other method is an organic titanate method, and the other method is an electron beam deposition method. (1) Sol coating and firing method Anatase-type titanium oxide sol is applied to the surface of a base material by a method such as a spray coating method, a dip coating method, a flow coating method, a spin coating method, or a roll coating method, and fired. (2) Organic titanate method Add a hydrolysis inhibitor (hydrolysis, ethylamine, etc.) to organic titanates such as titanium alkoxide (tetraethoxytitanium, tetramethoxytitanium, tetrapropoxytitanium, tetrabutoxytitanium, etc.), titanium acetate, titanium chelate, etc. After diluting with a non-aqueous solvent such as alcohol (ethanol, propanol, butanol, etc.), the mixture is spray-coated, dip-coated, with partial or complete hydrolysis. Apply by a method such as flow coating method, spin coating method, roll coating method, etc., and dry. Drying completes the hydrolysis of organic titanate to produce titanium hydroxide, and dehydration polycondensation of titanium hydroxide forms a layer of amorphous titanium oxide on the surface of the substrate. Then, it is fired at a temperature equal to or higher than the crystallization temperature of anatase to perform a phase transition of amorphous titanium oxide to anatase-type titanium oxide. (3) Electron beam vapor deposition method By irradiating the target of titanium oxide with an electron beam, an amorphous titanium oxide layer is formed on the surface of the base material. Then, it is fired at a temperature equal to or higher than the crystallization temperature of anatase to perform a phase transition of amorphous titanium oxide to anatase-type titanium oxide.

【0021】

Next, the case where the surface layer is composed of a photocatalytic oxide and silica will be described by taking the case where the photocatalyst is anatase-type titanium oxide as an example. In this case, for example, there are the following three methods. One method is the sol coating firing method, the other method is the organic titanate method, and the other method is the tetrafunctional silane method. (1) Sol coating and firing method A mixed solution of anatase-type titanium oxide sol and silica sol is applied to the surface of the substrate by a spray coating method, dip coating method, flow coating method, spin coating method, roll coating method, etc., and fired. To do. (2) Organic titanate method Add hydrolysis inhibitor (hydrolysis, ethylamine, etc.) and silica sol to organic titanates such as titanium alkoxide (tetraethoxytitanium, tetramethoxytitanium, tetrapropoxytitanium, tetrabutoxytitanium, etc.), titanium acetate, titanium chelate, etc. After adding and diluting with a non-aqueous solvent such as alcohol (ethanol, propanol, butanol, etc.), the mixture is spray-coated or dip-coated with partial or complete hydrolysis. Apply by method, flow coating method, spin coating method, roll coating method, etc. and dry. Drying completes the hydrolysis of organic titanate to produce titanium hydroxide, and dehydration polycondensation of titanium hydroxide forms a layer of amorphous titanium oxide on the surface of the substrate. Then, it is fired at a temperature equal to or higher than the crystallization temperature of anatase to perform a phase transition of amorphous titanium oxide to anatase-type titanium oxide. (3) 4-Functional Silane Method A mixture of tetraalkoxysilane (tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, tetramethoxysilane, etc.) and anatase-type titanium oxide sol is spray-coated on the surface of the substrate, and a dip coating method is used. , Flow coating method, spin coating method, roll coating method, etc. are applied, and if necessary, silanol is formed by hydrolysis, and then silanol is subjected to dehydration shrink polymerization by a method such as heating.

【0022】

Next, when the surface layer is composed of a photocatalytic oxide and a solid acid, the photocatalyst is anatase-type titanium oxide and the solid acid is TiO.₂/ WO₃The case of is described as an example. In this case, the method is to mix an ammonia solution of tungstic acid and anatase-type titanium oxide sol, and if necessary, spray-coat the surface of the substrate with a mixture diluted with a diluent (water, ethanol, etc.) or dip-coat. It is applied and fired by a method such as a method, a flow coating method, a spin coating method, or a roll coating method. In another method, an amorphous titanium oxide film is formed by electron beam deposition, hydrolysis of an organic titanate such as titanium alkoxide, titanium acetate, or titanium chelate, and dehydration polycondensation, and then tungonic acid is applied, and then amorphous. Titanium oxide crystallizes and TiO₂/ WO₃Heat treat at the temperature at which the composite oxide is formed.

【0023】

Next, the case where the surface layer is composed of a photocatalytic oxide and silicone will be described by taking the case where the photocatalyst is anatase-type titanium oxide as an example. In this case, the method is to mix a paint consisting of uncured or partially cured silicone or a silicone precursor with anatase-type titanium oxide sol, hydrolyze the silicone precursor if necessary, and then mix. Is applied to the surface of the base material by a method such as a spray coating method, a dip coating method, a flow coating method, a spin coating method, or a roll coating method, and the hydrolyzate of the silicone precursor is subjected to dehydration polycondensation by a method such as heating. To form a surface layer composed of anatase-type titanium oxide particles and silicone. In the formed surface layer, at least a part of the organic group bonded to the silicon atom in the silicone molecule is replaced with a hydroxyl group by photoexciting the anatase-type titanium oxide by irradiation with light including ultraviolet rays, and further on the surface layer. A physically adsorbed aqueous layer is formed to exhibit a high degree of hydrophilicity. Here, the precursors of silicone include methyltrimethoxysilane, methyltriethoxysilane, methyltributoxysilane, methyltripropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltributoxysilane, ethyltripropoxysilane, and phenyl. Trimethoxysilane, phenyltriethoxysilane, phenyltributoxysilane, phenyltripropoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldibutoxysilane, dimethyldipropoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, diethyldibutoxy Silane, diethyldipropoxysilane, phenylmethyldimethoxysilane, phenylmethyldiethoxysilane, phenylmethyldibutoxysilane, phenylmethyldipropoxysilane, γ-glycidoxypropyltrimethoxysilane, and their hydrolyzates, mixtures thereof. Can be preferably used.

【0024】

In addition, a film coated with the above coating may be attached to the surface of the base material with a transparent adhesive such as soapy water. Here, as the film base material, a plastic film such as polyethylene terephthalate, polyester, or polyethylene can be preferably used.

【0025】

[Example]

Example 1. Anatase type titanium oxide sol (Nissan Kagaku, TA-15, solid content 15% by weight, nitrate defibration type, pH = 1) 16 parts by weight and silica sol (Nippon Synthetic Rubber, Grasca A solution, solid content 13% by weight) %, pH = 4) After mixing 9 parts by weight, add 3 parts by weight of methyltrimethoxysilane (Nippon Synthetic Rubber, Grasca B solution) and 452 parts by weight of ethanol, and stir for another 2 hours to partially add methyltrimethoxysilane. A coating solution was prepared by subjecting the mixture to a hydrolysis reaction and a dehydration polycondensation reaction. This coating liquid is applied by a flow coating method to a decorative inorganic building material (Daiken Kogyo, Cerastar, WK1002-113, Ivory White, plate thickness 4 mm; autoclaved cement calcium silicate plate surface is adjusted, and then a silicone resin-based material is used. After applying it to the surface of a decorative inorganic building material coated with a colored paint, it was heated at 150 ° C for 30 minutes. Next, 0.5 mW / cm using an ultraviolet light source ((Sankyo Electric, Black Light Blue (BLB) fluorescent lamp)) on the surface coated with the coating liquid.²The # 1 sample was obtained by irradiating with ultraviolet rays for about 3 days with the ultraviolet illuminance of. For comparison, # 2 samples of decorative inorganic building materials (Daiken Corporation, Cerastar, WK1002-113, ivory white, plate thickness 4 mm) were also prepared. Water droplets were dropped on the # 1 sample and the # 2 sample, and the contact angle with water was measured. Here, the contact angle with water was evaluated using a contact angle measuring device (Kyowa Interface Science, CA-X150) based on the contact angle with water 30 seconds after dropping. As a result, the # 2 sample showed a hydrophobic contact angle of 90 °, while the # 1 sample showed a high degree of hydrophilicity with a water contact angle of 0 °.

【0026】

Next, # 1 sample and # 2 sample were installed outdoors, and the self-cleaning property due to rainfall was investigated. The self-cleaning property due to rainfall was tested as follows. That is, the outdoor dirt acceleration test equipment shown in Fig. 3 and Fig. 4 was installed on the roof of the building located in Chigasaki City. With reference to FIGS. 3 and 4, the device comprises an inclined sample support surface 22 supported by a frame 20 and is adapted to mount the sample 24. A roof 26 that slopes forward is fixed to the top of the frame. The roof is made of corrugated plastic plates, and the collected rain flows down in a streak on the surface of the sample 24 attached to the sample support surface 22. Samples # 1 and # 2 were attached to the sample support surface 22 of this device and exposed to weather conditions for one month from June 12, 1995. During this time, it rained frequently due to the rainy season. When observed one month later, vertical streaks were noticeably observed on the sample surface in the # 2 sample without the photocatalytic coating. On the other hand, no stain was observed in the # 1 sample with the photocatalytic coating. The situation was investigated by the color difference change of the most prominently soiled part before and after the installation of the accelerated test device. Here, the color difference was examined using a color difference meter (Tokyo Denshoku) and using the ΔE * display in accordance with Japanese Industrial Standards (JIS) H0201. As a result, in the # 2 sample without the photocatalyst film, the color difference change was very large at 7.2 and the stain was remarkable, whereas in the # 1 sample with the photocatalyst film, the color difference change was very small at 0.8.

【0027】

Example 2. A coating solution obtained by mixing 0.69 g of tetraethoxysilane (Wako Pure Chemical Industries, Ltd.), 1.07 g of anatase-type titanium oxide sol (Nissan Chemical, TA-15, average particle size 10 nm), 29.88 g of ethanol, and 0.36 g of pure water. Was prepared. This coating liquid was applied onto a 5 × 10 cm square crystallized glass substrate by a flow coating method. By holding this crystallized glass plate at a temperature of about 150 ° C for about 20 minutes, tetraethoxysilane is subjected to hydrolysis and dehydration-condensation polymerization, and anatase-type titanium oxide particles are bound with amorphous silica. Was formed on the surface of the crystallized glass plate. The weight ratio of titanium oxide to silica in this coating was 1. After leaving this crystallized glass plate in the dark for several days, 0.5 mW / cm on the surface of the sample using an ultraviolet light source (Sankyo Electric, Black Light Blue (BLB) fluorescent lamp).²A # 3 sample was obtained by irradiating with ultraviolet rays for about 1 hour under the ultraviolet illuminance of. For comparison, a # 4 sample in which a 10 cm square crystallized glass plate was left in the dark for several days was also prepared. First, water droplets were dropped on the # 3 sample and the # 4 sample, and the state after the drops was observed and the contact angle with water was measured. Here, the contact angle with water was evaluated using a contact angle measuring device (Kyowa Interface Science, CA-X150) based on the contact angle with water 30 seconds after dropping. As a result, when water droplets were dropped on the sample surface from the microsyringe of the # 3 sample, it was observed that the water droplets uniformly spread on the sample surface in the form of a water film. The contact angle with water after 30 seconds was highly hydrophilic to about 0 °. On the other hand, in the # 4 sample, when water droplets were dropped from the microsyringe onto the sample surface, the water droplets became familiar with the surface, but did not reach a uniform water film shape. The contact angle with water after 30 seconds was 30 °.

【0028】

Next, a slurry was prepared by suspending a powder mixture consisting of 1 part by weight of hydrophobic carbon black and 1 part by weight of hydrophilic carbon black in water at a concentration of 1.05 g / liter. 150 ml of the above slurry was allowed to flow down to a # 1 sample tilted at 45 degrees and dried for 15 minutes, then 150 ml of distilled water was allowed to flow down and dried for 15 minutes, and this cycle was repeated 25 times. The change in color difference before and after the test was measured using a color difference meter (Tokyo Denshoku). The color difference was evaluated using the ΔE * display in accordance with Japanese Industrial Standards (JIS) H0201. As a result, the color difference change of the # 1 sample before and after the test was 0.6, which was almost unchanged.

【0029】

Example 3. 1 g of ammonia defibrated anatase-type titanium oxide sol (Ishihara Sangyo, STS-11) and tungstic acid dissolved in 2 g of 25% ammonia water are mixed, and 2 g of distilled water is further added to the coating liquid. The molar ratio of titanium oxide particles to tungstic acid was set to 10: 1. Next, the above coating liquid was applied to a 5 × 10 cm square glazed tile plate (Toto, AB02E11) and fired at a temperature of 700 ° C for 30 minutes to produce anatase-type titanium oxide and TiO.₂/ WO₃A # 5 sample consisting of was obtained. No color development was observed due to the surface layer. Next, after leaving this # 5 sample in the dark for several days, 0.5 mW / cm on the surface of the sample using a BLB fluorescent lamp.²A # 6 sample was obtained by irradiating with ultraviolet rays for about 1 hour under the ultraviolet illuminance of. For comparison, a # 7 sample in which a 5 x 10 cm square glazed tile plate (Toto, AB02E11) was left in the dark for several days was also prepared. First, water droplets were dropped on the # 6 sample and the # 7 sample, and the state after the drops was observed and the contact angle with water was measured. As a result, it was observed that when water droplets were dropped on the sample surface of the # 6 sample from the microsyringe, the water droplets uniformly spread on the sample surface in the form of a water film. The contact angle with water after 30 seconds was highly hydrophilic to about 0 °. On the other hand, in the # 7 sample, when water droplets were dropped from the microsyringe onto the sample surface, the water droplets became familiar with the surface, but did not reach a uniform water film shape. The contact angle with water after 30 seconds was 30 °. Further, the # 6 sample was left in a dark place for 2 days thereafter to obtain a # 8 sample. Then, for the # 8 sample, the contact angle with water was similarly measured with a contact angle measuring device. As a result, when water droplets were dropped on the sample surface from the microsyringe on the # 8 sample, it was observed that the water droplets uniformly spread on the sample surface in the form of a water film, similar to the # 6 sample. The contact angle with water was maintained at about 1 °.

【0030】

Next, oleic acid was applied to the surface of the # 8 sample, and each sample was immersed in water filled in a water tank while keeping the sample surface in a horizontal position. As a result, the oleic acid was rounded and, when lightly rubbed, came off the surface.

【0031】

Next, a slurry was prepared by suspending a powder mixture consisting of 1 part by weight of hydrophobic carbon black and 1 part by weight of hydrophilic carbon black in water at a concentration of 1.05 g / liter. 150 ml of the above slurry was allowed to flow down to a # 8 sample tilted at 45 degrees and dried for 15 minutes, then 150 ml of distilled water was allowed to flow down and dried for 15 minutes, and this cycle was repeated 25 times. The change in color difference before and after the test was measured using a color difference meter (Tokyo Denshoku). The color difference was evaluated using the ΔE * display in accordance with Japanese Industrial Standards (JIS) H0201. As a result, the color difference change of the # 8 sample before and after the test was 0.4, which was almost unchanged.

【0032】

[Effect of the invention]

In the present invention, by providing a surface layer containing substantially transparent photocatalytic oxide particles on the surface of the building material for the outer wall, the surface of the surface layer exhibits hydrophilicity in response to photoexcitation of the photocatalyst. As a result, the surface of the surface layer is self-cleaned by rainfall. Further, the surface of the surface layer will be cleaned only by rinsing with water or sprinkling water.

[Simple explanation of drawings]

[Figure 1]

The figure which shows the surface structure of the building material for an outer wall which concerns on this invention.

[Figure 2]

The figure which shows the other surface structure of the building material for an outer wall which concerns on this invention.

[Fig. 3]

The front view of the outdoor dirt acceleration test apparatus which concerns on embodiment of this invention.

[Fig. 4]

The side view of the outdoor dirt acceleration test apparatus which concerns on embodiment of this invention.