JPH10122671A - Antifouling transparent cover for solar collector - Google Patents

Abstract

(57) [Abstract] [Problem] To prevent contamination of a transparent cover of a solar heat collector,
Maintain high heat collection efficiency of solar heat collector over a long period of time. A substantially transparent surface layer containing photocatalytic oxide particles, silicone and a water-repellent fluororesin is formed on the surface of a transparent cover of a solar heat collector, or A substantially transparent surface layer containing oxide particles, amorphous silica and a water-repellent fluororesin is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solar heat collector such as a solar water heater, and more particularly to a transparent cover for a solar heat collector.

[0002]

2. Description of the Related Art The heat collector of a solar heat collector is covered by a transparent cover. Japanese Industrial Standards require that the transparent cover of the solar collector be made of polycarbonate, glass (plain glass,
Float glass, polished glass or tempered glass),
It is recommended to be formed of glass fiber reinforced polyester or a material having the same or better quality (JI
S, A4111). With long-term use, the transparent cover for the solar heat collector is contaminated with dust and the light transmittance is reduced, so that the heat collection efficiency of the solar heat collector is reduced. In recent years, stains on the transparent cover have become remarkable due to environmental pollution. Therefore, it is desirable to clean the transparent cover for the solar heat collector periodically or as needed.

[0003]

However, since the solar heat collector is installed on the roof, it is not easy to clean the cover. Therefore, an object of the present invention is to provide a transparent cover for a solar heat collector in which the cover surface is less likely to become dirty.

[0004]

According to the present invention, in order to solve the above-mentioned problems, the surface of a transparent cover for a solar heat collector contains substantially photocatalytic oxide particles, silicone and a water-repellent fluororesin. Provided is a solar cell provided with an antifouling transparent cover for a solar heat collector, wherein a transparent surface layer is formed. With such a configuration,
When the photocatalyst is photoexcited, the organic group bonded to the silicon atom in the silicone molecule is at least partially replaced by a hydroxyl group by the photocatalysis, so that the photocatalyst becomes hydrophilic,
Both the hydrophilic part exposed to the outside air and the water-repellent fluororesin exposed to the outside have a microscopically dispersed structure on the surface. further,
Due to the presence of the photocatalyst, the silicone in which the organic group bonded to the silicon atom in the silicone molecule is at least partially substituted with a hydroxyl group in response to the photoexcitation of the photocatalyst permanently maintains hydrophilicity. The structure in which both the presenting portion and the water-repellent portion are microscopically dispersed on the surface is maintained. In such a structure, since the hydrophilic surface and the water-repellent surface are adjacent to each other, the hydrophilic adherent that easily adapts to the hydrophilic surface does not adapt to the adjacent water-repellent portion. Conversely, hydrophobic deposits that are easily adapted to the water-repellent surface do not adapt to adjacent hydrophilic portions. Therefore, neither the hydrophilic deposit nor the hydrophobic deposit is fixed to the member surface, and the surface is maintained in a clean state.

In the present invention, a substantially transparent surface layer containing photocatalytic oxide particles, amorphous silica and a water-repellent fluororesin is formed on the surface of a transparent cover for a solar heat collector. An antifouling transparent cover for a solar heat collector is provided. With this configuration, both the amorphous silica in the surface layer and the water-repellent portion where the water-repellent fluororesin is exposed to the outside are exposed on the surface. It becomes the structure distributed in. Further, the presence of the photocatalyst allows the amorphous silica to maintain its hydrophilicity permanently in response to the photoexcitation of the photocatalyst, so that both the hydrophilic portion and the water-repellent portion are microscopically visible on the surface. The distributed structure is maintained. In such a structure, since the hydrophilic surface and the water-repellent surface are adjacent to each other, the hydrophilic adherent that easily adapts to the hydrophilic surface does not adapt to the adjacent water-repellent portion. Conversely, hydrophobic deposits that are easily adapted to the water-repellent surface do not adapt to adjacent hydrophilic portions. Therefore, neither the hydrophilic deposit nor the hydrophobic deposit is fixed to the member surface, and the surface is maintained in a clean state.

[0006]

FIG. 1 shows an embodiment of a solar heat collector according to the present invention. The solar heat collector 10 is of a natural circulation type, and includes a plurality of heat collectors 12 and a hot water storage tank 14.
Are covered by a transparent cover 16. In the illustrated embodiment, the solar heat collector 10 is of the natural circulation type,
The present invention can also be applied to a pump-type solar collector. The transparent cover 16 can be formed of plastic such as polycarbonate or glass fiber reinforced polyester, or glass.

Next, the surface structure of the transparent cover 16 will be described. In one embodiment of the present invention, as shown in FIG. 2, a surface layer containing photocatalyst particles, silicone, and a water-repellent fluororesin is formed on the surface of the protective cover 20. In FIG. 2, when light capable of photoexciting the photocatalyst is irradiated, at least a part of the silicone exposed to the outside air becomes at least partially converted to a hydroxyl group by an organic group bonded to a silicon atom in the silicone molecule by a photocatalytic action. As a result of the substitution, it became hydrophilic, and both the silicone-exposed hydrophilic part exposed to the outside air and the water-repellent fluororesin exposed to the outside air were both microscopically dispersed on the surface. Structure. Further, the presence of the photocatalyst allows the amorphous silica to maintain its hydrophilicity permanently in response to the photoexcitation of the photocatalyst, so that both the hydrophilic portion and the water-repellent portion are microscopically visible on the surface. The distributed structure is maintained. With such a structure, neither the hydrophilic deposit nor the hydrophobic deposit is fixed to the member surface, and the surface is maintained in a clean state.

In another embodiment of the present invention, as shown in FIG. 3, a surface layer containing photocatalyst particles, amorphous silica, and a water-repellent fluororesin is formed on the surface of the protective cover 20. With this configuration, both the amorphous silica in the surface layer and the water-repellent portion where the water-repellent fluororesin is exposed to the outside are exposed on the surface. It becomes the structure distributed in. Furthermore, the presence of the photocatalyst allows the amorphous silica to remain permanently hydrophilic in response to the photoexcitation of the photocatalyst,
The structure in which both the hydrophilic part and the water-repellent part are microscopically dispersed on the surface is maintained. With such a structure, neither the hydrophilic deposit nor the hydrophobic deposit is fixed to the member surface, and the surface is maintained in a clean state.

A photocatalyst is a device that emits light (excitation light) having an energy (ie, shorter wavelength) larger than the energy gap between the conduction band and the valence band of a crystal when the electrons in the valence band are irradiated. A substance capable of generating conduction electrons and holes by excitation (photoexcitation). Photocatalytic oxides include, for example, anatase-type titanium oxide, rutile-type titanium oxide, zinc oxide, tin oxide, and ferric oxide. And oxides such as bismuth trioxide, tungsten trioxide and strontium titanate.

When the solar cell 10 has a peak sensitivity in the visible light band, it is preferable to adopt a photocatalyst having a band gap energy such that it is photoexcited by ultraviolet rays. Then, since the photocatalyst layer 22 does not absorb light in the visible light band, good sensitivity of the solar cell can be secured. Examples of photocatalysts that can be photoexcited by ultraviolet light include anatase-type titanium oxide (excitation wavelength 387).
nm), zinc oxide (excitation wavelength 387 nm), strontium titanate (excitation wavelength 387 nm), tin oxide (excitation wavelength 344 nm), rutile type titanium oxide (excitation wavelength 413
nm).

The light source used for photoexcitation of the photocatalyst is exposed to sunlight during the day, so that sunlight can be used. Also,
At night, road lighting or the like can be used as a light source. In order for the substrate surface to be highly hydrophilic by photoexcitation of the photocatalyst,
Illuminance of the excitation light may be at 0.001 mW / cm ² or more, but preferably that it 0.01 mW / cm ² or more, 0.1 m
More preferably, it is W / cm ² or more.

The silicone has an average composition formula R _p SiO _{(4-p) / 2} (where R is a functional group comprising one or more monovalent organic groups, or a monovalent organic group) Wherein X is an alkoxy group or a halogen atom, and p is a number satisfying 0 <p <2). it can.

As the water-repellent fluororesin, polytetrafluoroethylene, polychlorotrifluoroethylene, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer and the like can be suitably used.

The thickness of the surface layer is preferably set to 0.4 μm or less. Then, cloudiness due to irregular reflection of light can be prevented, and the surface layer becomes substantially transparent. Further, it is more preferable that the thickness of the surface layer be 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.

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.

Pt, Pd, Ru, Rh, I
A platinum group metal such as r or Os can be added.
The surface layer to which the metal is added can enhance the redox activity of the photocatalyst, and can improve the decomposability of organic contaminants and the decomposability of harmful gases and odors.

Next, a method for producing an antifouling member in which a surface layer containing photocatalytic oxide particles, silicone and a water-repellent fluororesin is formed on the surface of a substrate will be described. The production method in this case is basically based on applying a coating composition to the surface of a substrate and curing the composition.

Here, the coating composition contains, as essential components, a silicone precursor in addition to the photocatalyst particles and the water-repellent fluororesin, and a solvent such as water, ethanol, propanol, hydrochloric acid, nitric acid, sulfuric acid, acetic acid, or the like. Catalysts that promote the hydrolysis of silicone precursors such as maleic acid, and basic compounds such as tributylamine and hexylamine,
A catalyst for curing a silicone precursor such as acidic compounds such as aluminum triisopropoxide and tetraisopropyl titanate, and a surfactant for improving dispersibility of a coating solution such as a silane coupling agent may be added. .

Here, the precursor of the silicone includes an average composition formula R _p SiX _q O _{(4-pq) / 2} (where R is a functional group comprising one or more monovalent organic groups, Or, it is a functional group consisting of two or more kinds selected from a monovalent organic group and a hydrogen group, X is an alkoxy group or a halogen atom, and p and q are 0 <p <2, 0 <
a film-forming element composed of a siloxane represented by the following formula: q <4) or a general formula R _p SiX _4-p (where R is one or more monovalent organic groups) Wherein X is an alkoxy group or a halogen atom, and p is 1 or 2. A film-forming element comprising a hydrolyzable silane derivative to be
Can be suitably used.

Here, as the coating film forming element comprising the hydrolyzable silane derivative, methyltrimethoxysilane,
Methyltriethoxysilane, methyltripropoxysilane, methyltributoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltripropoxysilane, ethyltributoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltripropoxysilane, Phenyltributoxysilane,
Dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldipropoxysilane, dimethyldibutoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, diethyldipropoxysilane, diethyldibutoxysilane, phenylmethyldimethoxysilane, phenylmethyldiethoxysilane, phenyl Methyldipropoxysilane, phenylmethyldibutoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, n-propyltripropoxysilane, n-propyltributoxysilane, γ-glycoxydoxypropyltrimethoxysilane, γ -Acryloxypropyltrimethoxysilane and the like can be suitably used.

The film-forming element composed of the siloxane includes partial hydrolysis and dehydration-condensation polymerization of the hydrolyzable silane derivative, or partial hydrolyzate of the hydrolyzable silane derivative, tetramethoxysilane, tetramethoxysilane and tetramethoxysilane. It can be produced by dehydration polycondensation with a partial hydrolyzate such as ethoxysilane, tetrapropoxysilane, tetrabutoxysilane, diethoxydimethoxysilane and the like.

As the method for applying the coating composition, methods such as spray coating, dip coating, flow coating, spin coating, roll coating, brush coating, and sponge coating can be suitably used. As a curing method, it can be carried out by polymerizing by heat treatment, standing at room temperature, ultraviolet irradiation, or the like.

Next, a method for producing an antifouling member in which a surface layer containing photocatalyst particles, amorphous silica and a water-repellent fluororesin is formed on the surface of a substrate will be described. The production method in this case is basically based on applying a coating composition to the surface of a substrate and curing the composition.

Here, the coating composition contains silica particles or a silica precursor in addition to photocatalyst particles and water-repellent fluororesin as essential components, and in addition, a solvent such as water, ethanol, propanol, hydrochloric acid, nitric acid, and sulfuric acid. , Acetic acid, catalysts that promote the hydrolysis of silica precursors such as maleic acid, and silica such as basic compounds such as tributylamine and hexylamine, and acidic compounds such as aluminum triisopropoxide and tetraisopropyl titanate. A catalyst for curing the precursor or a surfactant for improving the dispersibility of the coating liquid such as a silane coupling agent may be added.

The silicone precursor used herein has an average composition formula of SiX _q O _{(4-q) / 2} (where X is an alkoxy group or a halogen atom, and q satisfies 0 <q <4). A film-forming element composed of a silicate represented by the following formula: or a general formula SiX ₄ (wherein R is a functional group composed of one or more monovalent organic groups, or a monovalent organic group) Is a functional group consisting of two or more selected from an organic group and a hydrogen group, wherein X is an alkoxy group,
Alternatively, a film-forming element made of a tetrafunctional hydrolyzable silane derivative represented by a halogen atom) can be suitably used.

Here, the coating film forming element comprising the above-mentioned tetrafunctional hydrolyzable silane derivative includes tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane,
Tetrabutoxysilane, diethoxydimethoxysilane and the like can be suitably used.

The film-forming element composed of the silicate can be prepared by partial hydrolysis, dehydration-condensation polymerization or the like of the tetrafunctional hydrolyzable silane derivative.

As the method for applying the above coating composition, methods such as spray coating, dip coating, flow coating, spin coating, roll coating, brush coating, and sponge coating can be suitably used. As a curing method, it can be carried out by polymerizing by heat treatment, standing at room temperature, ultraviolet irradiation, or the like.

[0029]

【Example】

Reference example. Anatase type titanium oxide sol (Nissan Chemical, TA
-15, nitric acid peptizer, pH = 1), silica sol (Nippon Synthetic Rubber, Glasca A solution, pH = 4), methyltrimethoxysilane (Nippon Synthetic Rubber, Glasca B solution) and ethanol, The coating liquid obtained by stirring for about 3 minutes is applied to a 10 cm square soda lime glass substrate by a spray coating method, and heat-treated at 200 ° C. for 15 minutes to obtain 11 parts by weight of anatase type titanium oxide particles and silica 6 A # 1 sample having a surface layer composed of 5 parts by weight of silicone and 5 parts by weight of silicone was obtained. The contact angle of the # 1 sample with water was 85 °. Here, the contact angle with water was evaluated using a contact angle measuring device (Kyowa Interface Science, CA-X150) by the contact angle with water 30 seconds after a water droplet was dropped from the micro syringe.
Next, 0.3 mW was applied to the surface of the # 1 sample using an ultraviolet light source (Sankyo Electric, black light blue (BLB) fluorescent lamp).
The sample was irradiated for 1 day with an ultraviolet illuminance of / cm2 to obtain a # 2 sample.
As a result, the contact angle with water of the # 2 sample was hydrophilized to 0 °. Next, a mercury lamp was used for the sample # 1 and the sample # 2 for 22.8.
The surface of each of the # 3 samples obtained by irradiating with an ultraviolet illuminance of mW / cm ² for 2 hours was subjected to Raman spectroscopic analysis. as a result,#
The peak of the methyl group observed on the surface of one sample was not observed in the # 3 sample, but a broad peak of the hydroxyl group was observed instead. From the above, the organic group bonded to the silicon atom in the silicone molecule on the surface of the coating in response to the photoexcitation of the photocatalytic anatase-type titanium oxide is replaced with a hydroxyl group by photocatalysis, and is hydrophilized. I understand.

Embodiment 1 Anatase type titanium oxide sol (Nissan Chemical, TA-15) and silica sol (Nippon Synthetic Rubber,
(Glaska A solution), methyltrimethoxysilane (Nippon Synthetic Rubber, Glasca B solution), polytetrafluoroethylene (PTFE) particles (Daikin Industries, Lubron L-5) and ethanol are mixed and stirred for 2-3 hours. The obtained coating liquid is applied on a 10 cm square soda lime glass plate by a spray coating method, and is heat-treated at 200 ° C. for 15 minutes to obtain 33 parts by weight of anatase type titanium oxide particles, 66 parts by weight of polytetrafluoroethylene particles, # 4 having a surface layer composed of 6 parts by weight of silica and 5 parts by weight of silicone
A sample was obtained. The contact angle of the # 4 sample with water was 110 °. Next, the surface of the sample # 4 was coated with an ultraviolet light source (Sankyo Electric Co., Ltd., black light blue (BLB) fluorescent lamp) by 0.3%.
Irradiation was performed for one day at an ultraviolet irradiance of mW / cm ² to obtain a # 5 sample. As a result, the contact angle of the # 5 sample with water was 97.2 °, and did not change much. According to the above reference example, the portion where the silicone is exposed to the outside air is supposed to be replaced by a hydroxyl group by a photocatalytic action and the organic group bonded to the silicon atom in the silicone molecule to be hydrophilized. It is considered that the contact angle with the film slightly decreased. In other words, the surface of the # 5 sample has both a hydrophilic portion where the hydroxyl group is substituted by the photocatalytic action and the hydrophilicized silicone is exposed to the outside air and a water-repellent portion where the water-repellent fluororesin is exposed to the outside air. It is assumed that the structure is microscopically dispersed on the surface.

Next, the # 5 sample and a soda lime glass plate for comparison were placed outdoors, and the cleanliness of the surface against deposits and contaminants was examined. The cleanliness of the surface against sediment and contaminants was determined by placing the sample as shown in FIG. 4 below the rooftop of the building and exposing it for 4 months. As a result, some stains were observed on the soda lime glass plate, whereas no stain was observed on the # 5 sample.

[0032]

According to the present invention, since the transparent cover of the solar heat collector is less likely to become dirty, the heat collection efficiency of the solar heat collector can be kept high for a long period of time.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view of a solar heat collector of the present invention.

FIG. 2 is a diagram showing a surface structure of a transparent cover of the solar heat collector according to the present invention.

FIG. 3 is a diagram showing a surface structure of a transparent cover of the solar heat collector according to the present invention.

FIG. 4 is a diagram showing a method for setting a test sample according to the embodiment of the present invention.

[Explanation of symbols]

 10: Solar heat collector 16: Transparent cover

Claims (2)

[Claims] 1. A transparent cover for a solar heat collector,
An antifouling transparent cover for a solar heat collector, wherein a substantially transparent surface layer containing photocatalytic oxide particles, silicone and a water-repellent fluororesin is formed on the surface of the transparent cover. 2. A transparent cover for a solar heat collector,
A substantially transparent surface layer containing photocatalytic oxide particles, amorphous silica, and a water-repellent fluororesin is formed on the surface of the transparent cover, wherein the antifouling transparent for a solar heat collector is provided. cover.