JPH09225392A - Automobile and coating method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect and prevent the coated face of an automobile from deterioration by forming a top coat layer which comprises a photo-semiconductor layer and of which the surface has a specified value of wettability to water corresponding to photo- excitation by irradiation with light on a designed base coat layer on the surface of a metal substrate composing an automotive body of an automobile. SOLUTION: A top coat layer, of which the surface is made to have wettability to water not more than 10-degrees based on the contact angle to water responding to photo-excitation by irradiation with light rays with wavelength to excite a photo- semiconducting oxide or shorter and which comprises a photo-semiconductor layer or a layer containing a photo-semiconductor, is formed on a substrate surface of a vehicle through a designed base coat layer, and a layer containing a hardly decomposable substance is further formed between the base coat layer and the top coat layer. The top coat layer is formed by combining a photo-semiconductor and silicone resin and a substance to inhibit photolytic redox reaction of the photo-semiconductor is added to the photo-semiconductor layer, so that the surface of the coating is changed to be hydrophilic by photo-excitation by irradiation with light rays having wavelength to excite the photo-semiconductor or shorter and at 1mW/cm<2> illuminance or weaker.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides an automobile that is hard to stain and easy to clean by making the surface of the automobile body highly hydrophilic and maintaining it. Also, the surface of the car body is made highly hydrophilic, and
A method of painting a motor vehicle that can be maintained.

[0002]

The purpose of painting automobiles is to protect the metal body from rust and corrosion and to enhance its aesthetic and design elements. However, the coating of automobiles running under natural environment cannot always maintain the same performance and aesthetics as new cars, and gradually deteriorates, discoloration, fading, chalking, chalking,
It begins to show phenomena such as blister and crack. These deterioration phenomena are caused by the chemical destruction of the chain-like or net-like macromolecular structure that forms the coating film, or when these molecules become even larger molecules and become hard and brittle. This is the process in which the tackiness of the film disappears. Specific causes of this deterioration phenomenon include oxygen, sunlight, solar heat, moisture, dust, asphalt pitch, and body fluids of animals and plants. Therefore, with respect to the factors that cause these deteriorations, it has been customary in the past to use a cur wax for the purpose of well removing stains adhering to the surface and forming a thin film on the surface of the film to protect it. (Washing design, 25 volumes, p. 63-80 (1985)).

[0003]

However, regarding the use of carwax, it is difficult to form a uniform thin film that needs to be sufficiently washed and dried before use, and the effect of time and effort is prolonged. It is not permanent and needs to be used frequently. The type must be selected properly according to the type, color and usage conditions of the coating film. The user's hands get dirty during use. Environmental pollution due to cleaning and dumping of tools used during use. However, there were various problems such as the above, and as a result, it was not sufficient to protect the coating film.

The present invention has been made in view of the above problems in the prior art, and it is an object of the present invention to protect a coating film on a vehicle body of an automobile to prevent deterioration.

[0005]

[Means for Solving the Problems] The present invention has been variously studied in order to solve the above-mentioned problems, and it has been found that by making a coated surface of an automobile hydrophilic, stains are less likely to occur and cleaning is facilitated. Then, the present invention was conceived.

The present invention is based on the phenomenon of hydrophilization of the surface of a metal substrate by an optical semiconductor. That is, in order to solve the above problems, the automobile according to claim 1 comprises an optical semiconductor layer or a layer containing an optical semiconductor on the surface of a metal base material with a design base coat layer interposed. And forming a topcoat layer having a surface wettability of 10 ° or less in terms of a contact angle with water in response to photoexcitation by irradiation with light having a wavelength not longer than the excitation wavelength of the photosemiconductor oxide. And

The automobile according to claim 2 is the automobile according to claim 1, characterized in that a layer made of a hardly decomposable substance is interposed between the designable base coat layer and the top coat layer. .

According to a third aspect of the present invention, in the vehicle according to the first or second aspect, the topcoat layer is a combination of an optical semiconductor and a silicone resin. To do.

A vehicle according to a fourth aspect is the vehicle according to any one of the first to third aspects, wherein the lower level of the energy of the conduction band of the optical semiconductor is the hydrogen production level. It is characterized by being located at a positive value when the position is 0 eV.

A vehicle according to a fifth aspect is the vehicle according to any one of the first to third aspects, in which the photo-semiconductor layer is a photo-oxidation-reduction of the photo-semiconductor layer or the layer containing the photo-semiconductor layer. A substance that inhibits the reaction is added, and the illuminance of light having an excitation wavelength of the photo-semiconductor or less is hydrophilized in response to photoexcitation by irradiation with light having a light intensity of 1 mW / cm ² or less, but a photoredox reaction hardly occurs. It is characterized by having only the photocatalytic activity of.

According to a sixth aspect of the invention, in the vehicle according to the fifth aspect, the substance that inhibits the photoredox reaction is an alkali metal, an alkaline earth metal, alumina, zirconia, silica, antimony oxide, One or more substances selected from amorphous titanium oxide, aluminum, and manganese.

According to a seventh aspect of the present invention, there is provided an automobile coating method, wherein a metallic base material surface is provided with a design base coat layer.
An optical semiconductor layer or a topcoat layer containing an optical semiconductor,
It is formed such that the water wettability of the surface of the topcoat layer is converted into a contact angle with water of 10 ° or less in response to photoexcitation by irradiation with light having a wavelength not longer than the excitation wavelength of the photosemiconductor oxide. And

According to the eighth aspect of the present invention, in the automobile coating method according to the seventh aspect, the topcoat layer is formed by combining an optical semiconductor and a silicone resin. Is characterized by.

The method for coating a vehicle according to claim 9 is the method for coating a vehicle according to claim 7 or 8, wherein the lower level of the energy of the conduction band of the optical semiconductor is hydrogen. It is characterized by being located at a positive value when the generation level is 0 eV.

A method for coating a vehicle according to claim 10 is the method for coating a vehicle according to any one of claims 7 and 8, wherein the optical semiconductor layer or the layer containing an optical semiconductor is:
A substance that inhibits the photo-oxidation / reduction reaction of a photo-semiconductor is added, and it is hydrophilized by photo-excitation by irradiation with light having an excitation wavelength of the photo-semiconductor or less and an illuminance of 1 mW / cm 2 or less. It is characterized by forming a topcoat layer which does not occur.

The method for coating an automobile according to claim 11 is the same as the method for coating an automobile according to claim 10.
One or more kinds of substances that inhibit the photo-oxidation / reduction reaction are selected from alkali metals, alkaline earth metals, alumina, zirconia, silica, antimony oxide, amorphous titanium oxide, aluminum and manganese.

The automotive coating composition according to claim 12 is characterized in that it is composed of an optical semiconductor or is prepared by adding and mixing an optical semiconductor to a base material.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION

According to a first aspect of the present invention, a layer of an optical semiconductor or a layer containing an optical semiconductor is formed as a top coat layer on a coated surface of an automobile, and light having an excitation wavelength of the optical semiconductor or less is irradiated,
The surface is made hydrophilic in response to photoexcitation.

The term "hydrophilization" as used herein means a phenomenon in which the water wettability of the surface is increased by an external factor and the contact angle with water is reduced. The photohydrophilization is a case where the external factor is light in the above. Highly hydrophilic and superhydrophilic means that the contact angle with water is 10 ° or less, preferably 5 ° or less. In this way, not only hydrophobic substances such as carbon but also hydrophilic substances do not easily adhere to the highly hydrophilic surface, and even if they adhere, they can be easily washed away by washing with water (including rainfall). It is thought that the surface is kept clean. In addition, the base coat layer plays a role in designing, which is another functional aspect of coating. In the second structure of the present invention, silica is further provided between the base coat layer and the top coat layer,
A layer made of a hardly decomposable substance such as silicone resin or fluororesin can be interposed. According to this method, a hydrophilic top coat can be applied to an already painted automobile without impairing its design.

A third structure of the present invention is an optical semiconductor and a silicon-based semiconductor.
A combination with a resin is used as the top coat layer.

The silicone resin is easily available, safe and easy to handle. In addition, since it has transparency,
The top coat layer can be formed without impairing the color tone of the coat layer.

Further, as a means for forming the top coat layer, a method of low time and low cost is desirable, and one of the methods is cation electrodeposition coating. In this case, it can be dealt with by using a structure having an amino group (—NH ⁺ ) in the side chain of the silicone resin.

A fourth structure of the present invention is such that the energy level of the conduction band of the optical semiconductor is located at a positive value when the hydrogen generation level is 0 eV. The conventional theory regarding the photooxidation / reduction reaction is that a conduction electron-hole pair is generated by photoexcitation, and then the reduction reaction by the conduction electron and the oxidation reaction by the hole are simultaneously promoted and proceed. Therefore, tin oxide or rutile whose energy level in the conduction band of the optical semiconductor is not sufficiently high on the negative side has a structure in which the reduction reaction by conduction electrons is difficult to proceed and only the oxidation reaction by holes is easily promoted. In such a structure, the conduction electrons become excessive, and the electron-hole pairs generated by photoexcitation recombine without participating in the redox reaction, so that in reality, almost no oxidation reaction or reduction reaction occurs.
However, as described later, the hydrophilization phenomenon by photoexcitation progresses.

When the photo-oxidation / reduction reaction of an optical semiconductor is used for decomposing an organic substance, the decomposition reaction is carried out by utilizing water and oxygen in the environment. That is, the conduction electrons generated by photoexcitation reduce oxygen and superoxide oxide (O
₂ ^-) to generate the hole is to oxidize the hydroxyl group to generate a hydroxyl radical (· OH), these highly reactive oxygen species (O ₂ ^- organics by oxidation-reduction reaction of and · OH) Is decomposed. Therefore, in order to effectively photooxidatively decompose organic substances, the energy level in the upper valence band for generating holes is the oxygen generation level (+ 0.82e) at which the hydroxyl group releases electrons.
V) is located on the positive side, and the energy level at the bottom of the conduction band generated by conduction electrons is located on the negative side of the hydrogen generation level (0 eV) at which hydrogen releases electrons to donate to the oxygen side. It will be good. Therefore, conversely, in order to prevent the photooxidation-reduction decomposition of organic matter effectively, the energy level in the upper valence band should be located on the negative side of the oxygen production level (+0.82 eV) or the lower end of the conduction band. The energy level of is to be located on the positive side of the hydrogen generation level (0 eV).

When the photo-oxidation / reduction reaction of the photo-semiconductor is used for the precipitation of metal ions in water, the conduction electrons generated by photoexcitation cause the reduction and precipitation of metal ions. (At the same time, the holes oxidize the hydroxyl groups in the water to cause hydroxyl radicals (.O
H). ) Therefore, for example, in order to effectively remove iron ions from water, the energy level at the lower end of the conduction band in which conduction electrons are generated is the iron generation level (-
It must be located on the negative side of 0.44 eV). Therefore,
On the contrary, in order to prevent metal ions from precipitating from water, the energy level at the lower end of the conduction band should be located on the positive side of the metal production level. Excluding noble metals, the metal production level is on the negative side of the hydrogen production level, so the energy level at the bottom of the conduction band should be positioned on the positive side of the hydrogen production level (0 eV). become.

From the above, the decomposition of resin (basic
(1) deterioration of the coating film of the coating layer, discoloration, etc.), and precipitation of dissolved metal ions in water (precipitation and adhesion of colored metal, rusting, etc.), and photohydrophilization as one method of making the energy of the conduction band of the optical semiconductor It can be seen that there is a method in which the level is located at a positive value when the hydrogen generation level is 0 eV.

Further, a fifth constitution of the present invention is to form a thin film containing photo-semiconductor particles and a substance which inhibits photo-oxidation-reduction reaction of the photo-semiconductor as a top coat layer of a coating film of an automobile. Further, the illuminance of light having an excitation wavelength of the photo-semiconductor or less is hydrophilized in response to photo-excitation by irradiation with light having a wavelength of 1 mW / cm ² or less, but the photocatalytic activity of the photo-oxidation-reduction reaction hardly occurs. As in the previous section, the decomposition of the resin and the precipitation of dissolved metal ions in water are suppressed.

The photo-semiconductor which can be preferably used in the present invention includes anatase type titanium oxide, rutile type titanium oxide, zinc oxide, tin oxide, strontium titanate, tungsten trioxide, dibismuth trioxide and second oxide. Examples thereof include metal oxides such as iron.

The optical semiconductors that can be preferably used in the present invention and have a positive energy level in the conduction band when the hydrogen generation level is 0 eV include tin oxide, tungsten trioxide, and ditrioxide. Examples thereof include metal oxides such as bismuth, ferric oxide and rutile type titanium oxide.

Known substances that inhibit the photo-oxidation / reduction reaction of optical semiconductors are alkali metals, alkaline earth metals, alumina, zirconia, silica, antimony oxide, amorphous titanium oxide, aluminum and manganese.

In the fifth structure of the present invention, it is preferable to make the thickness of the top coat layer as thin as possible. 1 μm or less,
More preferably, it is 0.2 μm or less. Then, the absolute amount of the optical semiconductor fixed on the base material can be reduced, and the photo-oxidation / reduction property can be further reduced. Also, the wear resistance is improved. Especially when the thickness is 0.2 μm or less, the transparency of the thin film containing the optical semiconductor can be easily ensured, and the design and transparency of the base can be maintained. Further, the refractive index of the top coat layer is preferably 2 or less. This is because the design of the base is less likely to be impaired by the reflection of the top coat layer. Since titanium oxide has a refractive index of 2.5 to 2.7, it is preferable to add a substance having a refractive index lower than 2 when using titanium oxide as an optical semiconductor. For substances with a refractive index lower than 2, silica (1.4
8), alumina (1.63), silicone (1.4-
1.6), tin oxide (1.9), and magnesium fluoride, which can be preferably used.

In the present invention, the content of the optical semiconductor in the top coat layer is preferably 5 to 5 with respect to the optical semiconductor-containing layer.
The amount is preferably 80% by weight, more preferably 10 to 50% by weight. This is because the photooxidation / reduction property can be lowered as the content of the optical semiconductor is reduced. However, since the photohydrophilization phenomenon is also a phenomenon based on the photoexcitation phenomenon of the optical semiconductor, it is necessary to contain about 5% or more.

[0034] In the present invention, the illuminance of the following wavelength excitation wavelength, preferably 0.0001~1mW / cm ^2, more preferably from about 0.001~1mW / cm ^2. This is because the lower the illuminance of light having a wavelength equal to or shorter than the excitation wavelength is, the more the amount of generated electron-hole pairs is generated, so that the photooxidation / reduction property can be lowered. However, since the photohydrophilization phenomenon is also a phenomenon based on the photoexcitation phenomenon of an optical semiconductor, it is about 0.0001 mW / cm ²
The above excitation light illuminance is required.

In the present invention, the light source for exciting the optical semiconductor may be any light source capable of emitting illuminance of light having a wavelength not more than the above excitation wavelength, such as sunlight, fluorescent lamps, incandescent lamps, metal hydrate lamps, and mercury. Interior lighting such as lamps can be used.

In the fourth structure of the present invention, the top coat of the thin film containing the photo-semiconductor particles, which has a positive energy level of 0 eV when the hydrogen generation level is 0 eV, on the coated surface of the automobile. For example, the following method is available as a method for forming the coating layer. (1) The above-mentioned optical semiconductor particles are applied to the surface of the base coat layer and baked. (2) On the surface of the base coat layer, an organic salt compound (alkoxide, containing an element metal species of the above-mentioned photo-semiconductor metal oxide).
A chelate, acetate, etc.) or an inorganic compound that is not an oxide (chloride, sulfate, etc.) is hydrolyzed, applied to a substrate, and dehydrated by a method such as heating. If the metal oxide is not crystallized up to this process like titanium oxide, it is further heated to crystallize the metal oxide. (3) After the constituent element metal of the semiconductor metal oxide is fixed on the surface of the base coat layer by sputtering or the like, it is oxidized by a method such as heating or electrode reaction. If the metal oxide is not crystallized up to this process like titanium oxide, it is further heated to crystallize the metal oxide.

The method for forming a thin-film topcoat layer containing photo-semiconductor particles and a substance that inhibits the photo-oxidation / reduction reaction of the photo-semiconductor on the coating surface of an automobile, which is the fifth constitution of the present invention, is, for example, as follows. There is a method. (1) A photo-semiconductor particle and a compound containing a constituent metal species in the inhibiting substance are applied to the surface of the base coat layer and baked. (2) On the surface of the base coat layer, a compound containing the constituent element metal species in the inhibiting substance and an organic compound containing the constituent element metal species of the optical semiconductor particles (alkoxide, chelate, acetate, etc.) Alternatively, a hydrolyzate of an inorganic compound that is not an oxide (chloride, sulfate, etc.) is applied to a metal substrate and dehydrated by a method such as heating. If the metal oxide is not crystallized up to this process like titanium oxide, it is further heated to crystallize the metal oxide.

[0038]

Example 1 First, a sample coated on a 10 cm square iron substrate was prepared, washed, and precoated with a silicone layer in order to smooth the substrate surface. For this reason, liquid A (silica sol) and liquid B (trimethoxymethylsilane) of the Japanese synthetic rubber coating composition "GLASCA" are mixed in a weight ratio of 3, and the mixed liquid is applied to an iron substrate. The sample was cured at a temperature of 150 ° C. to obtain a sample coated with silicon and having a thickness of 3 μm. Next, on the surface of the iron plate, a thin-film top coat layer made of an optical semiconductor (1 part by weight) and a silicone resin (1 part by weight) was formed. 1 was obtained. More specifically, anatase-type titania sol (TA-
15) and the above-mentioned "grasca" solution A were mixed and diluted with ethanol, and then "grasca" solution B was added to prepare a titanium oxide-containing silicone coating composition. Here, the liquids A and B of "grasca" were adjusted to have a weight ratio of 3. This coating composition is applied to the surface of the iron plate,
After curing at a temperature of 0 ° C., a 5 μm thick top coat layer composed of anatase-type titania particles and silicone resin was formed to form a sample No. 1 was obtained. This sample No. 20W for 1
0.5mW / c using BLB fluorescent lamp (manufactured by Sankyo Denki)
After irradiating with ultraviolet rays with an ultraviolet illuminance of m ² , the contact angle between the sample and water was measured using a contact angle measuring device (ERMA, model GI-1000). The contact angle was measured 30 seconds after a water drop was dropped on the sample surface from the micro syringe. The measurement result at this time was 2 °, and the surface of the topcoat layer showed a high degree of hydrophilicity.

(Embodiment 2) A coated iron substrate of 10 cm square was washed, and a film thickness of 3 μm was obtained in the same manner as in Embodiment 1.
A sample coated with silicone was obtained. Next, the above
On the surface of the coat layer, a 0.2 μm top coat layer containing a photo-semiconductor, a silicone resin, and a substance that inhibits the photo-oxidation / reduction reaction was formed to form a sample No. 2 was obtained. More specifically, a new paint product prepared by adding sodium nitrate, which is a substance that inhibits the photoredox reaction, to the paint product prepared in Example 1 is applied to the surface of the base coat layer and then cured. , UV irradiation. Then, the contact angle on the surface was measured in the same manner as in Example 1. As a result, the contact angle is 3
At 0 °, the surface of the topcoat layer again showed a high degree of hydrophilicity.

(Example 3) The following samples were prepared as comparative examples of Example 1 and Example 2. Two 10 cm square coated iron substrates were washed, and in the same manner as in Example 1,
A sample coated with silicon having a film thickness of 3 μm was obtained. On one side, a 10 μm acrylic resin was formed as a top coat, and a sample No. No. 3 was obtained, and on the other side, 1 μm automotive wax was formed as a top coat, and sample No.
4 was obtained. The contact angle of the surface of each of these two samples was measured by the same method as in Example 1. As a result, the sample No. No. 3 is 70 °, and sample No. No. 4 was 100 °, and both were found to be poor in hydrophilicity.

(Example 4) The outdoor stain accelerator shown in FIGS. 1 and 2 was installed on the roof of a building located in Chigasaki City. FIG.
2 and FIG. 2, the apparatus comprises an inclined sample support surface 2 supported by a frame 1 for mounting a sample 3. A roof 4 inclined forward is fixed to the top of the frame. This roof is made of a corrugated plastic plate so that the collected rain flows down in a streak on the surface of the sample 3 attached to the sample support surface 2. No. No. 1 to No. Each of the four samples was attached and exposed outdoors for about one month.

After that, the appearance was observed. 1 and No. 1 The samples of No. 2 all had a beautiful appearance. On the other hand, No. 3 and No. 3 The surface of each of the samples of No. 4 was dirty. Therefore, it was found that the sample having the photosemiconductor coating has excellent stain resistance.

(Example 5) No. 2 to No. 2 Each of the samples of No. 4 was attached to a sunshine weather meter (WEL-SUN-HC, manufactured by Suga Test Instruments Co., Ltd.), and light was irradiated by a carbon arc lamp for 12 minutes of rain spraying for 60 minutes and a temperature of 40. An accelerated weather resistance test was performed for 240 hours under the condition of ° C, and then color difference measurement and appearance observation were performed. The color difference measurement was performed using a color difference meter (Tokyo Denshoku).

[0044]

[Table 1]

[0045]

INDUSTRIAL APPLICABILITY According to the present invention, when a layer containing an optical semiconductor is formed on a coated surface of an automobile and (1) the hydrogen generation level of the optical semiconductor is set to 0 eV, the energy of the conduction band decreases. The lower end of the level is set to a positive value, or (2) the surface further contains a substance that inhibits the photo-redox reaction of the photo-semiconductor, so that It is possible to obtain an automobile paint and a method for cleaning a paint surface, which has a photocatalytic activity that is hydrophilized in response to photoexcitation by irradiation but hardly causes a photoredox reaction. According to such a technology, a vehicle which is not deteriorated by photooxidation and is made superhydrophilic to be antifouling, antifogging, easy to clean only with water and rainfall, has excellent biocompatibility, and has little deterioration to the environment Outer panels, tire wheels, electrodeposition coated products, etc. can be obtained. Furthermore, when used in an aqueous environment, it does not undergo photoreductive deposition of colored metal ions and is rendered superhydrophilic to prevent stains, fogging, rust, and is easy to clean with water and rainfall, and has excellent biocompatibility. Car outer panel, tire wheel,
Electrodeposited products etc. can be obtained.

[Brief description of drawings]

FIG. 1 is a front view of an outdoor dirt acceleration test device.

[Fig. 2] Side view of an outdoor dirt acceleration test device

[Explanation of symbols]

 1-Frame 2-Sample support surface 3-Sample 4-Roof

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Makoto Senkoku 2-1, 1-1 Nakajima, Kokurakita-ku, Kitakyushu, Fukuoka Prefecture Totoki Kikai Co., Ltd. (72) Toshiya Watanabe Nakajima, Kokurakita-ku, Kitakyushu, Fukuoka 2-1-1 1-1 Totoki Co., Ltd. (72) Inventor Atsushi Kitamura 2-1-1 1-1 Nakajima, Kokurakita-ku, Kitakyushu, Fukuoka Prefecture

Claims (12)

[Claims] 1. A metal base material constituting a car body,
It is composed of a photosemiconductor layer or a layer containing a photosemiconductor through a design base coat layer, and has a surface water wettability in response to photoexcitation by irradiation with light having a wavelength equal to or shorter than the excitation wavelength of the photosemiconductor oxide. An automobile comprising a topcoat layer having a contact angle with water of 10 ° or less. 2. The automobile according to claim 1, wherein a layer made of a hardly decomposable substance is interposed between the designable base coat layer and the top coat layer. 3. The automobile according to claim 1 or 2, wherein the top coat layer is a combination of an optical semiconductor and a silicone resin. 4. The lower level of the energy of the conduction band of the optical semiconductor is located at a positive value when the hydrogen production level is 0 eV. The automobile according to any one of 1. 5. A substance which inhibits a photo-oxidation reduction reaction of an optical semiconductor is added to the optical semiconductor layer or a layer containing the optical semiconductor, and an illuminance of light having an excitation wavelength of the optical semiconductor or less is 1 mW /
It becomes hydrophilic in response to photoexcitation by irradiation with light of cm ² or less, but has only a photocatalytic activity to such an extent that a photoredox reaction hardly occurs, according to any one of claims 1 to 3. The listed car. 6. The substance which inhibits the photoredox reaction is an alkali metal, an alkaline earth metal, alumina, zirconia,
The vehicle according to claim 5, which is one or more kinds of substances selected from silica, antimony oxide, amorphous titanium oxide, aluminum and manganese. 7. A surface of a metal base material constituting a car body of an automobile,
A top coat layer containing a photosemiconductor layer or a photosemiconductor via a design-based base coat layer is provided in response to photoexcitation by irradiation with light having a wavelength not longer than the excitation wavelength of the photosemiconductor oxide. The water wettability of the surface is 10 in terms of contact angle with water.
A coating method for automobiles, which is characterized in that it is formed so as to be below 8. The method of coating an automobile according to claim 7, wherein the top coat layer is formed by combining an optical semiconductor and a silicone resin. 9. The lower level of the energy of the conduction band of the optical semiconductor is located at a positive value when the hydrogen generation level is 0 eV. The car painting method described in. 10. A substance which inhibits a photo-oxidation / reduction reaction of an optical semiconductor is added to the optical semiconductor layer or a layer containing the optical semiconductor, and the illuminance is 1 mW / c or less at an excitation wavelength of the optical semiconductor or less.
9. The automobile according to claim 7 or 8, which forms a topcoat layer which is hydrophilized in response to photoexcitation by irradiation with light of m ² or less, but hardly causes photoredox reaction. How to paint. 11. The substance which inhibits the photoredox reaction is selected from at least one selected from alkali metals, alkaline earth metals, alumina, zirconia, silica, antimony oxide, amorphous titanium oxide, aluminum and manganese. The method for coating an automobile according to claim 10. 12. A coating material for automobiles, which is composed of an optical semiconductor or is prepared by adding and mixing an optical semiconductor to a base material.