JPH09230810A - Outdoor display board and its cleaning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an outdoor display board which exhibits a high degree of hydrophilicity according to the photoexcitation of a photocatalyst, is self cleaned by rainfall, is cleanable by mere water spraying and rinsing and hardly allows the adhesion of the combustion products and soot rendered by the rain water by providing the surface of an outdoor display board base material with a surface layer contg. photocatalyst particles. SOLUTION: A layer contg. the photocatalyst is formed on the surface of the base material. The surface of the outdoor display board is made more highly hydrophilic than lipophilic according to the photoexcitation of the photocatalyst by having such surface structure. As a result, the deposits and/or contaminants adhered to the surface of the outdoor display board are flushed away by rain drops when the surface of the outdoor display board is exposed to the rainfall. The adhesion of the contaminants on the surface when the rain water contg. the contaminants flows down on the surface of the outdoor display board is prevented. Further, the washing of the surface of the outdoor display board with water is made easy. If the surface layer consists of the photocatalyst alone, the photocatalyst is preferably an oxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a traffic sign, an advertising sign, an electric signboard, an aurora vision, a neon sign,
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to outdoor signboards for storefronts, nameplates, etc.

[0002]

2. Description of the Related Art Outdoor display panels are contaminated by the combustion products in the exhaust gas of automobiles and the accumulation of soot and dust floating in the atmosphere. Furthermore, in rainy weather, suspended dust is carried by the rain,
When the surface of the outdoor display board flows down, contaminants adhere to the surface of the outdoor display board along the path of rainwater, and when the surface dries, stripes of dirt are formed.

[0003]

Such dirt on the outdoor display board makes it difficult to see the displayed contents and disturbs the aesthetic landscape of the city. In addition, since many outdoor display boards are located at a high place, cleaning work is dangerous and time-consuming. An object of the present invention is to provide an outdoor display panel having a surface that is self-cleaning (self-cleaning) by rainfall and a cleaning method thereof, which does not involve dangerous cleaning work. Another object of the present invention is to provide an outdoor display panel having a surface that can be cleaned by watering or rinsing without dangerous cleaning work, and a method for cleaning the same. Another object of the present invention is to provide an outdoor display panel having a surface on which combustion products and soot and dust are unlikely to adhere.

[0004]

SUMMARY OF THE INVENTION The present invention is based on the discovery that, in a member having a surface layer containing a photocatalyst formed thereon, when the photocatalyst is photoexcited, the surface of the member is highly hydrophilized. This phenomenon is considered to proceed by the following mechanism. That is, when the photocatalyst is irradiated with light having an energy larger than the energy gap between the valence band upper end and the conduction band lower end of the photocatalyst, the electrons in the valence band of the photocatalyst are excited to generate conduction electrons and holes. The action of either or both of them probably imparts polarity to the surface and collects polar components such as water and hydroxyl groups. Then, one or both of conduction electrons and holes and the above-mentioned polar component cooperate with each other to cut off a chemical bond between the surface and the contaminant chemically adsorbed on the surface, and to cause a chemical adsorbed water on the surface. Is adsorbed, and a physically adsorbed water layer is formed thereon. Further, once the surface of the member is highly hydrophilized, the hydrophilicity of the surface is maintained for a certain period even if the member is kept in a dark place.

The present invention provides a self-cleaning outdoor display panel having a surface layer containing photocatalyst particles on the surface of an outdoor display panel substrate. By providing the surface layer containing the photocatalyst, the surface of the surface layer exhibits hydrophilicity in response to the photoexcitation of the photocatalyst, so that when the surface of the outdoor display panel is exposed to rainfall, adhered deposits and / or contaminants are not generated. It can be washed away by raindrops.

The present invention provides an antifouling outdoor display panel having a surface layer containing photocatalyst particles on the surface of an outdoor display panel substrate. By providing the surface layer containing the photocatalyst, the surface of the surface layer exhibits hydrophilicity in response to the photoexcitation of the photocatalyst, so that when the rainwater containing the contaminant flows down the surface of the outdoor display panel, the contaminant becomes Is prevented from adhering to.

The present invention provides an easily-cleanable outdoor display panel having a surface layer containing photocatalyst particles on the surface of the outdoor display panel substrate. By providing the surface layer containing the photocatalyst, the surface of the surface layer exhibits hydrophilicity in response to photoexcitation of the photocatalyst, so that the surface of the outdoor display panel can be easily washed with water.

In a preferred embodiment of the present invention, the surface layer further contains silica. By containing silica, the surface is likely to exhibit a high degree of hydrophilicity near 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.

In a preferred embodiment of the present invention, the surface layer further contains a solid superacid.
By containing a super strong acid, the surface is likely to exhibit a high degree of hydrophilicity close to a water wetting angle of 0 °, and at the same time, the hydrophilicity maintaining property when kept in a dark place is improved. The reason is that when the surface layer contains a super strong acid, the polarity of the surface is extremely large irrespective of the presence or absence of light, so that water molecules, which are polar molecules, are selectively adsorbed over hydrophobic molecules. Easy to make. Therefore, a stable physically adsorbed water layer is easily formed, and even if the layer is kept in a dark place, the hydrophilicity of the surface can be maintained at a high level for a considerably long period.

In a preferred embodiment of the present invention, the surface layer further contains silicone.
By containing silicone, by photoexcitation of the photocatalyst, at least a part of the organic group bonded to the silicon atom in the silicone is replaced with a hydroxyl group, and a physically adsorbed water layer is formed on the organic group, so that the surface is It exhibits a high degree of hydrophilicity close to a water wetting angle of 0 °, and improves the hydrophilicity maintaining ability when kept in a dark place.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a specific structure of the present invention will be described. On the surface of the outdoor display board in the present invention,
As shown in FIG. 1 or FIG. 2, a layer containing a photocatalyst is formed on the surface of the substrate. By taking such a surface structure, the surface of the outdoor display panel is highly hydrophilized in response to photoexcitation of the photocatalyst. Thereby, the hydrophilicity of the surface becomes stronger than the lipophilicity. As a result, when the surface of the outdoor display board is exposed to rainfall, the adhered deposits and / or contaminants are washed away by raindrops. In addition, when rainwater containing contaminants flows down the surface of the outdoor display board, the contaminants are prevented from adhering to the surface. Further, it becomes easy to wash the surface of the outdoor display board with water.

In FIG. 1, when the surface layer is composed of only the photocatalyst, the photocatalyst is preferably an oxide.
By doing so, the oxide shows hydrophilicity in the state where the pollutants in the environment are not adsorbed, so that the pollutants are rejected by the photoexcitation action and the adsorbed water layer is formed, so that the oxides easily exhibit hydrophilicity. A uniform water film can be formed. In FIG. 2, M represents a metal element. Therefore, in the case of FIG. 2, the outermost surface is made of a general inorganic oxide. Again,
Since the oxide shows hydrophilicity in a state where the pollutant in the environment is not adsorbed, the pollutant is rejected by a photoexcitation effect of a photocatalyst mixed into the surface layer other than the inorganic oxide,
By forming the adsorbed water layer, a uniform water film can be formed.

The outdoor display board according to the present invention includes a traffic sign,
Signboards for advertising, electronic bulletin boards, aurora vision, neon signs, signboards for storefronts, nameplates, etc. are shown. Materials are plastic base materials such as polycarbonate, acrylic or its coated plate, hard coat plate; fluorescent display is glass, plastic etc. A plate covered with the transparent body can be preferably used.

The photocatalyst means an electron in the valence band when irradiated with light (excitation light) having an energy (that is, a short wavelength) larger than the energy gap between the conduction band and the valence band of the crystal. A substance that is excited (photoexcited) to generate conduction electrons and holes. For example, anatase-type titanium oxide, rutile-type titanium oxide, tin oxide, zinc oxide, dibismuth trioxide, tungsten trioxide, and oxide oxide. Diiron, strontium titanate and the like can be preferably used. Here, as the light source used for the photoexcitation of the photocatalyst, sunlight; a light source in the environment such as a street lamp or a night light; Here, as the electric lamp, a light source such as a fluorescent lamp, an incandescent lamp, a metal halide lamp, a mercury lamp, a xenon lamp can be preferably used. In order to make the surface of the base material highly hydrophilic by photoexcitation of the photocatalyst, the illuminance of the excitation light is 0.001 mW /
cm ² suffices above, but preferably that it 0.01 mW / cm ² or more, and more preferably it 0.1 mW / cm ² or more.

The thickness of the surface layer containing the photocatalyst is 0.4
It is preferable that the thickness is less than or equal to μm. Then, white turbidity due to irregular reflection of light can be prevented, and the surface layer becomes substantially transparent. More preferably, the thickness of the surface layer containing the photocatalyst is 0.2 μm or less. Then, it is possible to prevent the surface layer from being colored by light interference. Also, the thinner the surface layer, the better its transparency.
Further, when the film thickness is reduced, the wear resistance of the surface layer is improved. The surface of the surface layer may be further provided with a wear-resistant or corrosion-resistant protective layer capable of being made hydrophilic and other functional films.

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 fungi attached to the surface even in a dark place.

On the surface layer, Pt, Pd, Ru, R
A platinum group metal such as h, Ir, Os can be added. The surface layer to which the metal is added can enhance the oxidation-reduction activity of the photocatalyst and improve the deodorizing and purifying action and the like. Further, when a solid superacid other than the photocatalyst is added, since the acidity of the solid superacid is improved by the addition of the platinum group metal, the hydrophilicity maintenance property is also improved and the formation of a water film of the adhered water is further promoted. Also, the hydrophilicity maintaining property is improved when the photocatalyst is not irradiated with the excitation light for a certain period of time.

When the substrate is a glass containing alkali network modifying ions such as sodium (soda lime glass, parallel plate glass, etc.), an intermediate layer such as silica may be formed between the substrate and the surface layer. Good. Then, the diffusion of the alkali network modifying ions from the base material to the surface layer during the firing is prevented, and the photocatalytic function is more effectively exhibited.

The term "hydrophilic" refers to the property of easily fitting into the surface when water is dropped, and generally means a state where the water wetting angle is less than 90 °. The term “high hydrophilicity” in the present invention refers to a property that is highly compatible when water is dropped on the surface, and more specifically, a state where the water wetting angle is about 10 ° or less. In particular, self-cleanability, easy cleaning with water,
PCT / JP96 / 00 for prevention of dirt adhesion due to rainfall
As disclosed in 734, the water wetting angle is preferably 10 ° or less, more preferably 5 ° or less.

The solid superacid in the present invention refers to a strong acid containing a solid oxide having a Hammett acidity function Ho ≦ -11.93 as a constituent, and specifically, sulfuric acid-supporting Al.
₂ O ₃ , sulfuric acid supported TiO ₂ , sulfuric acid supported ZrO ₂ , sulfuric acid supported SnO ₂ , sulfuric acid supported Fe ₂ O ₃ , sulfuric acid supported SiO ₂ ,
Sulfuric acid supporting HfO ₂ , TiO ₂ / WO ₃ , WO ₃ / SnO
₂ , WO ₃ / ZrO ₂ , WO ₃ / Fe ₂ O ₃ , SiO ₂
-Al ₂ O ₃ or the like can be suitably used.

Next, a method for forming the surface layer will be described. First, the production method in the case where the surface layer is composed of only the photocatalyst will be described by taking the case where the photocatalyst is anatase type titanium oxide as an example. In this case, there are roughly three methods. One method is a sol coating and firing method, the other method is an organic titanate method, and the other method is an electron beam evaporation method. (1) Sol-coating and firing method Anatase-type titanium oxide sol is applied to the surface of a substrate by a method such as spray coating, dip coating, flow coating, spin coating, or roll coating, and then fired. (2) Organic titanate method Titanium alkoxide (tetraethoxy titanium, tetramethoxy titanium, tetrapropoxy titanium, tetrabutoxy titanium, etc.), titanium acetate, titanium chelate, etc. are added with a hydrolysis inhibitor (hydrochloric acid, ethylamine, etc.). , After diluting with a non-aqueous solvent such as alcohol (ethanol, propanol, butanol, etc.), while partially or completely proceeding the hydrolysis, the mixture is spray-coated, dip-coated, Apply by methods such as flow coating method, spin coating method, roll coating method,
dry. By drying, the hydrolysis of the organic titanate is completed to produce titanium hydroxide, and a layer of amorphous titanium oxide is formed on the surface of the base material by dehydration-condensation polymerization of the titanium hydroxide. Thereafter, the amorphous titanium oxide is calcined at a temperature equal to or higher than the crystallization temperature of anatase to cause a phase transition from the amorphous titanium oxide to the anatase titanium oxide. (3) Electron beam evaporation method An amorphous titanium oxide layer is formed on the surface of a substrate by irradiating a titanium oxide target with an electron beam. After that, firing at a temperature higher than the crystallization temperature of anatase,
Phase transition of amorphous titanium oxide to anatase titanium oxide.

Next, the case where the surface layer is composed of a photocatalyst 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 is the organic titanate method, the other is 4
This is a functional silane method. (1) Sol coating and baking method A mixture of anatase-type titanium oxide sol and silica sol is applied to the substrate surface by a method such as a spray coating method, a dip coating method, a flow coating method, a spin coating method, and a roll coating method, and then fired. I do. (2) Organic titanate method Titanium alkoxides (tetraethoxytitanium, tetramethoxytitanium, tetrapropoxytitanium, tetrabutoxytitanium, etc.), titanium acetate, titanium chelate, and other organic titanates are added with a hydrolysis inhibitor (hydrochloric acid, ethylamine, etc.) and silica sol. Add alcohol (ethanol,
After diluting with a non-aqueous solvent such as propanol, butanol, etc., and then allowing the hydrolysis to proceed partially or completely, the mixture is spray-coated, dip-coated, flow-coated,
It is applied by a method such as spin coating or roll coating and dried. By drying, the hydrolysis of the organic titanate is completed to produce titanium hydroxide, and a layer of amorphous titanium oxide is formed on the surface of the base material by dehydration-condensation polymerization of the titanium hydroxide. Thereafter, the amorphous titanium oxide is calcined at a temperature equal to or higher than the crystallization temperature of anatase to cause a phase transition from the amorphous titanium oxide to the anatase titanium oxide. (3) Tetrafunctional silane method A mixture of tetraalkoxysilane (tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, tetramethoxysilane, etc.) and anatase type titanium oxide sol is spray-coated or dip-coated on the surface of a substrate. , A flow coating method, a spin coating method, a roll coating method, or the like, and if necessary, hydrolyzing to form silanol, and then silanol is subjected to dehydration condensation polymerization by a method such as heating.

Next, the case where the surface layer is composed of a photocatalyst and a solid superacid is described by taking as an example the case where the photocatalyst is anatase type titanium oxide and the solid superacid is TiO ₂ / WO ₃ . In this case, a method of mixing an ammonia solution of tungstic acid and an anatase-type titanium oxide sol and, if necessary, diluting the mixture with a diluting liquid (water, ethanol, etc.) on the surface of the base material by spray coating, dip coating, or the like. It is applied by a method such as a flow coating method, a spin coating method, and a roll coating method, and is baked.

Next, the case where the surface layer is composed of a photocatalyst and silicone will be described by taking the case where the photocatalyst is anatase type titanium oxide as an example. The method in this case is to mix a coating composed of uncured or partially cured silicone or a precursor of silicone and anatase type titanium oxide sol, and hydrolyze the precursor of silicone as needed, and then mix the mixture. Spray coating method on the surface of the substrate,
It is applied by a method such as a dip coating method, a flow coating method, a spin coating method, a roll coating method, etc., and a hydrolyzate of a silicone precursor is subjected to dehydration polycondensation by a method such as heating to obtain anatase type titanium oxide particles. A surface layer made of silicone is formed. The formed surface layer, by photoexcitation of anatase type titanium oxide by irradiation with light including ultraviolet rays, at least a part of the organic group bonded to the silicon atom in the silicone molecule is substituted with a hydroxyl group, and further on it. A physically adsorbed water layer is formed,
It exhibits a high degree of hydrophilicity. Here, the precursor of silicone includes methyltrimethoxysilane, methyltriethoxysilane, methyltributoxysilane, methyltripropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltributoxysilane, ethyltripropoxysilane, and phenyl. Trimethoxysilane, phenyltriethoxysilane, phenyltributoxysilane,
Phenyltripropoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldibutoxysilane, dimethyldipropoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, diethyldibutoxysilane, diethyldipropoxysilane, phenylmethyldimethoxysilane, phenylmethyl Diethoxysilane, phenylmethyldibutoxysilane, phenylmethyldipropoxysilane, γ-glycidoxypropyltrimethoxysilane, a hydrolyzate thereof, and a mixture thereof can be suitably used.

[0025]

[Example] First, a primer coating (Toshiba silicone, a coating in which PH93 was diluted 6 times with a toluene solvent) was applied to a 10 cm square PMMA plate surface by a spray coating method, and then dried at room temperature to apply a primer resin to a substrate. Coated with layers. Next, a silicone-based hard coating agent (Toshiba Silicone, Tosgard) was applied by a flow coating method and dried at 90 ° C. for 3 hours to form a hard coat layer on the primer resin layer. Furthermore, the surface of the hard coat layer was treated with a corona surface treatment device (Kasuga Denki) using a wire electrode as an electrode, the gap between the electrode tip and the sample surface was 2 mm, the voltage was 26 kV, the frequency was 39 kHz, and the sample feed rate was 4.2 m / min. A high frequency corona discharge treatment was performed under the conditions to obtain a # 1 sample. On the other hand, 56 parts by weight of anatase-type titanium oxide sol (TA-15, average particle size 12n
m) and 33 parts by weight of silica sol (Nippon Synthetic Rubber, Glasca A liquid) are mixed and diluted with ethanol, and then 11 parts by weight of methyltrimethoxysilane (Nippon Synthetic Rubber, Grasca B).
Liquid) was added to prepare a titanium oxide-containing coating composition.
The above coating composition was applied to the # 1 sample by the flow coating method, and heat-treated at 90 ° C. for 3 hours to be cured.
A sample was obtained. This # 2 sample was used as an ultraviolet light source (Sankyo Denki,
A # 3 sample was obtained by irradiating the surface of the sample with ultraviolet light at a UV illuminance of 0.6 mW / cm ² for about 48 hours using a black light blue (BLB) fluorescent lamp. 10c for comparison
An m-square PMMA plate sample was also prepared. First, # 3 sample and P
A water drop was dropped on the MMA plate sample, and the state after the drop was observed and the contact angle with water was measured. Here, the contact angle with water is measured using a contact angle measuring device (Kyowa Interface Science, CA-X150).
Evaluation was made based on the contact angle with water 30 seconds after dropping. as a result#
When water droplets were dropped on the surface of the three samples from the microsyringe, it was observed that the water droplets spread uniformly on the surface of the sample in the form of a water film. Further, the contact angle with water after 30 seconds was highly hydrophilized to about 0 °. On the other hand, in the case of the PMMA plate sample, when water droplets were dropped from the microsyringe on the surface of the sample, the water droplets were somewhat adapted to the surface, but did not form a uniform water film. The contact angle with water after 30 seconds was 60 °.

Next, 1 part by weight of hydrophobic carbon black,
A slurry was prepared by suspending a powder mixture consisting of 1 part by weight of hydrophilic carbon black in water at a concentration of 1.05 g / liter. # 3 sample and PMMA tilted at 45 degrees
The plate sample was allowed to flow down with 150 ml of the above slurry for 15 minutes and then with 150 ml of distilled water for 15 minutes to dry, and this cycle was repeated 25 times. The color difference change before and after the test was measured using a color difference meter (Tokyo Denshoku).
Color difference is ΔE according to Japanese Industrial Standard (JIS) H0201
* Indication used. As a result, the PMMA plate sample had a large color difference change of 22, while the # 3 sample had a color difference change of only 0.6.

[0026]

According to the present invention, the surface of the outdoor display board substrate is
By providing a surface layer containing photocatalyst particles, the surface of the outdoor display panel exhibits a high degree of hydrophilicity in response to photoexcitation of the photocatalyst, and is self-cleaning (self-cleaning) by rainfall or watering or rinsing with water. It can be cleaned to a certain extent, or combustion products and soot dust caused by rainwater are less likely to adhere.

[Brief description of drawings]

FIG. 1 is a diagram showing a surface structure of an outdoor display panel according to the present invention.

FIG. 2 is a diagram showing another surface structure of the outdoor display panel according to the present invention.

Claims (16)

[Claims] 1. A surface layer containing photocatalyst particles is provided on the surface of an outdoor display board substrate, and in response to photoexcitation of the photocatalyst,
A self-cleaning outdoor display panel, wherein the surface of the layer exhibits hydrophilicity, thus allowing the deposited deposits and / or contaminants to be washed away by raindrops when the layer of the outdoor display panel is exposed to rainfall. 2. A surface layer containing photocatalyst particles is provided on the surface of an outdoor display board substrate, and in response to photoexcitation of the photocatalyst,
The antifouling outdoor display panel, wherein the surface of the layer exhibits hydrophilicity, and thus prevents contaminants from adhering to the surface when rainwater containing the contaminant flows down the surface of the layer of the outdoor display panel. 3. A surface layer containing photocatalyst particles is provided on the surface of an outdoor display board substrate, and in response to photoexcitation of the photocatalyst,
The easily-cleanable outdoor display panel, wherein the surface of the layer exhibits hydrophilicity, and thus the surface of the layer of the outdoor display panel can be easily washed with water. 4. The outdoor display panel according to claim 1, wherein the surface layer further contains silica. 5. The outdoor display panel according to claim 1, wherein the surface layer further contains a solid strong acid. 6. The outdoor display panel according to claim 1, wherein the surface layer further contains silicone. 7. The surface of the surface layer exhibits hydrophilicity of 10 ° or less in terms of contact angle with water in response to photoexcitation of the photocatalyst. Outdoor display board. 8. The surface of the surface layer exhibits hydrophilicity of 5 ° or less in terms of contact angle with water in response to photoexcitation of the photocatalyst. Outdoor display board. 9. The outdoor display panel according to claim 1, wherein the thickness of the surface layer is 0.4 μm or less. 10. The outdoor display panel according to claim 1, wherein the surface layer has a thickness of 0.2 μm or less. 11. The surface of the surface layer is further provided with a hydrophilic protective layer.
The outdoor display board according to any one of claims 1 to 6. 12. The outdoor display board according to claim 1, wherein the outdoor display board is a traffic sign. 13. The outdoor display board according to claim 1, wherein the outdoor display board is an advertising signboard. 14. The outdoor display board according to claim 1, wherein the outdoor display board is an electronic bulletin board. 15. A step of preparing the outdoor display panel according to claim 1; a step of arranging the outdoor display panel outdoors; and a photocatalyst contained in a surface layer of the outdoor display panel being photoexcited. The step of making the surface of the layer hydrophilic; the step of exposing the outdoor display panel to rainfall to wash away the deposits and / or contaminants adhering to the surface of the layer with raindrops. Cleaning method. 16. A step of preparing the outdoor display panel according to claim 1; and a step of making a surface of the layer hydrophilic by photoexciting a photocatalyst contained in a surface layer of the outdoor display panel. A method for cleaning an outdoor display panel, comprising the steps of rinsing the outdoor display panel with water to release deposits and / or contaminants adhering to the surface of the layer from the surface and rinse with water.