Method for making member hydrophilic and preventing deterioration by ultraviolet ray, hydrophilic ultraviolet resistant member and its manufacture

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a method for preventing ultraviolet deterioration of a resin material or the like and making the surface of the member hydrophilic, and a member exhibiting hydrophilicity to which such an ultraviolet deterioration prevention treatment is applied.

【0002】

[Conventional technology]

Titanium oxide (TiO), which is a typical photosemiconductor (photocatalyst)₂ ) Is excited by absorbing ultraviolet rays because the band gap is in the energy range of ultraviolet rays. Taking advantage of this property, titanium oxide is mixed in cosmetics and used as an ultraviolet blocking agent.

【0003】

[Problems to be Solved by the Invention]

When exposed to ultraviolet rays, many resin materials have their molecular structures cut off and their strength decreases. Such a phenomenon is called ultraviolet deterioration of the material. Although many techniques have been proposed for preventing UV deterioration of materials, none of them utilize the UV absorbing action of optical semiconductors and make the surface of the material hydrophilic. An object of the present invention is to provide a method for hydrophilizing a member and preventing ultraviolet deterioration and a hydrophilic ultraviolet resistant member based on a new mechanism.

【0004】

[Means for solving problems]

In order to solve the above problems, in the method for hydrophilizing a member and preventing ultraviolet deterioration of the member, a layer containing an optical semiconductor excited by ultraviolet rays is arranged in the surface layer region of the member, and a photooxidation-reduction reaction of the optical semiconductor is performed. It is characterized in that measures are taken to prevent deterioration of the member due to the above, the surface of the member is made hydrophilic, and ultraviolet rays hitting the member are absorbed by the optical semiconductor. Further, the hydrophilic ultraviolet resistant member of the present invention has a layer containing an optical semiconductor excited by ultraviolet rays in the surface layer region of the member, and is subjected to measures to prevent deterioration of the member due to a photooxidation-reduction reaction of the optical semiconductor. It is characterized in that the surface of the member exhibits hydrophilicity and the optical semiconductor absorbs ultraviolet rays that hit the member.

【0005】

In the present invention, the surface of the layer containing the optical semiconductor can be made hydrophilic by the principle and method described later. In that case, it is possible to obtain a member having excellent cleanliness, which is difficult for dirt to adhere to and is easy to remove the attached dirt by a water stream.

【0006】

In the present invention, measures are taken to prevent deterioration of members due to the photooxidation-reduction reaction of the photosemiconductor. The photocatalytic action of the photosemiconductor may promote the oxidation / reduction reaction, which will be described in detail later. However, a specific photosemiconductor may be selected, the contact between the photosemiconductor and air may be restricted, or the photosemiconductor may be used. By adding a substance that weakens the photocatalytic action of the photosemiconductor, the photooxidation-reduction reaction of the photosemiconductor can be suppressed. Even in that case, the optical semiconductor absorbs ultraviolet rays.

【0007】

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, the thickness of the layer containing the optical semiconductor is preferably 0.1 μm or more, more preferably 1 μm or more. With this thickness, it is possible to sufficiently prevent the transmission of ultraviolet rays.

【0008】

In the present invention, the above-mentioned member is composed of a base material, an intermediate layer formed on the base material having a photooxidation-reduction reaction protective function, and a surface layer containing a photosemiconductor formed on the intermediate layer. Can be configured. As the intermediate layer, a film of a substance having a high binding energy of the main chain such as fluororesin or silicone can be used. The main chain (structure) of these is not cleaved by electrons or radicals generated by photocatalysis. Therefore, by placing these between the photosemiconductor and the base material, it is possible to suppress adverse effects such as the photooxidation-reduction reaction of the base material while maintaining the photocatalytic activity of the photosemiconductor. The thickness of this intermediate layer is preferably 1 μm or more.

【0009】

In the present invention, an ultraviolet absorber and / or a blocking agent may be mixed with the intermediate layer. As such an absorbent / blocking agent, organic arbutin: hydroquinone-β-D-glucopyranoside or the like, inorganic ZnO or the like can be used.

【0010】

In the present invention, an ultraviolet reflective layer may be arranged between the base material and the intermediate layer, or between the intermediate layer and the surface layer. As the ultraviolet reflective layer, a metal vapor deposition film such as cuprous chloride or Al can be used.

【0011】

In the present invention, an antioxidant may be mixed in the base material, the intermediate layer, or the surface layer. Deterioration of the base material can be more strongly prevented by the antioxidant. It is particularly preferable that the antioxidant is mixed in the surface of the base material or the intermediate layer. Examples of the antioxidant include aluminum compounds, aldehyde compounds, and phenol compounds. These antioxidant mechanisms are so-called sacrificial oxidation. It is further preferable to reduce the water absorption rate of either the surface layer or the intermediate layer to 1% by volume or less. Ultraviolet deterioration tends to be promoted by the presence of oxygen species, but if the water absorption rate is low, it becomes difficult for oxygen species such as oxygen and water to permeate to the base material.

【0012】

One aspect of the method for producing a hydrophilic ultraviolet-resistant member of the present invention is to disperse a photosemiconductor having a photooxidation-reduction-reactive coating layer in the member and remove only the coating layer around the photosemiconductor on the surface of the member. The optical semiconductor is exposed to the air, and the optical semiconductor absorbs ultraviolet rays.

【0013】

Specific embodiments of the present invention include the following. TiO₂ Powder or TiO₂ The supported glass fiber or the like is coated with siloxane, mixed with the resin as a filler, molded, and then the surface is treated with alkali to treat the surface with TiO.₂ Activate only. Make resin products using silicone, fluororesin, etc. as a base material. For example, TiO from the beginning on the silicone nipple of a feeding bottle₂ Is kneaded and molded. TiO mixed uniformly with Na compound by coprecipitation method etc.₂ The powder is kneaded into the resin and molded.

【0014】

Examples of products to which the present invention can be applied include resin pipes, rubber hoses, toy plastics, automobile plastics, transmission line coating resins, tires, and building materials decorated with resins (laminated steel plates, vinyl chloride steel plates, painted plates, etc.). Can be mentioned.

【0015】

Next, the relationship between the photosemiconductor (photocatalyst) and hydrophilicity will be described. The present inventor has discovered that when a photosemiconductor is photoexcited, the surface of the photosemiconductor becomes highly hydrophilic. That is, when light semi-conducting titania is photoexcited with ultraviolet rays, the surface becomes highly hydrophilic to the extent that the contact angle with water is 10 ° or less, more specifically 5 ° or less, especially about 0 °. It was discovered that the high degree of hydrophilicity is maintained and restored by irradiation with light, and that the highly hydrophilic state is maintained even in the dark for 3 weeks or more under specific conditions.

【0016】

When light having a wavelength higher than the band gap energy of the optical semiconductor is irradiated with sufficient illuminance for a sufficient time, the surface of the optical semiconductor-containing layer becomes superhydrophilic. At present, the superhydrophilic phenomenon of the surface caused by photoexcitation of an optical semiconductor cannot always be clearly explained. The superhydrophilic phenomenon caused by photosemiconductors does not seem to be necessarily the same as the photodecomposition of substances by photocatalytic redox reactions conventionally known in the field of application of photosemiconductors to chemical reactions. In this regard, the conventional theory regarding photocatalytic redox reactions is that electron-hole pairs are generated by photoexcitation, and the generated electrons reduce surface oxygen to superoxide ions (O).₂^-), The holes oxidize the surface hydroxyl groups to generate hydroxide radicals ( OH), and these highly reactive reactive oxygen species (O)₂^-The substance was decomposed by the redox reaction of OH).

【0017】

However, the phenomenon of superhydrophilization by photosemiconductors is inconsistent with conventional findings regarding photocatalytic decomposition of materials in at least two respects. First, according to the conventional wisdom, photosemiconductors such as rutyl and tin oxide do not have a sufficiently high energy level of the conductor, so that the reduction reaction does not proceed, and as a result, the electrons photoexcited by the conductor. Was excessive, and it was thought that the electron-hole pairs generated by photoexcitation recombine without participating in the redox reaction. On the other hand, it was confirmed that the hydrophilization phenomenon caused by optical semiconductors also occurs in optical semiconductors such as rutile and tin oxide.

【0018】

Secondly, conventionally, it is considered that decomposition of a substance by a photocatalytic redox reaction does not occur unless the film thickness of the photosemiconductor layer is at least 100 nm or more. On the other hand, it was observed that superhydrophilization by photosemiconductors occurs even when the film thickness of the photocatalyst-containing layer is on the order of several nm.

【0019】

Therefore, although it cannot be clearly concluded, the superhydrophilic phenomenon caused by photosemiconductors is considered to be a phenomenon slightly different from the photodecomposition of substances by photocatalytic redox reaction. However, it was confirmed that superhydrophilicization of the surface does not occur unless light with an energy higher than the bandgap energy of the optical semiconductor is irradiated. Presumably, the conduction electrons and holes generated by the excitation of the photo-semiconductor impart polarity to the surface of the photo-semiconductor-containing layer, and water becomes a hydroxyl group (OH).^- ) Is chemically adsorbed, and a physically adsorbed aqueous layer is formed on the chemisorbent, and the surface becomes superhydrophilic.

【0020】

Once the surface of the photo-semiconductor-containing layer is highly hydrophilic by photoexcitation, the surface hydrophilicity remains to some extent even when the substrate is held in the dark. When pollutants are adsorbed on the surface hydroxyl groups with the passage of time and the surface gradually loses its superhydrophilicity, the superhydrophilicity is restored by photoexcitation again.

【0021】

In order to first hydrophilize the optical semiconductor-containing layer, an arbitrary light source having a wavelength having an energy higher than the bandgap energy of the optical semiconductor can be used. In the case of an optical semiconductor whose photoexcitation wavelength is located in the ultraviolet region such as titania, the ultraviolet rays contained in the sunlight are preferably used under the condition that the substrate coated with the optical semiconductor-containing layer is exposed to sunlight. be able to. An optical semiconductor can be photoexcited by an artificial light source indoors or at night. As will be described later, when the optical semiconductor-containing layer is made of silica-blended titania, it can be easily hydrophilized even with weak ultraviolet rays contained in a fluorescent lamp.

【0022】

Once the surface of the optical semiconductor-containing layer is superhydrophilic, the superhydrophilicity can be maintained or restored by relatively weak light. For example, in the case of titania, the maintenance and restoration of hydrophilicity can be sufficiently performed even with weak ultraviolet rays contained in indoor lighting such as fluorescent lamps.

【0023】

The photosemiconductor-containing layer exhibits hydrophilicity even if it is very thin, and in particular, the photocatalytic semiconductor material made of a metal oxide has sufficient hardness, so that the photosemiconductor-containing layer has sufficient durability and abrasion resistance.

【0024】

Opto-semiconductor: As an opto-semiconductor used for the hydrophilic fiber of the present invention, titania (TiO)₂ ) Is the most preferable. Titania is harmless, chemically stable, and inexpensively available. Furthermore, titania has a high bandgap energy, and therefore requires ultraviolet rays for photoexcitation and does not absorb visible light in the process of photoexcitation, so that color development due to complementary color components does not occur.

【0025】

Both anatase and rutile can be used as titania. The advantage of anatase-type titania is that a sol in which very fine particles are dispersed is easily available on the market, and a very thin thin film can be easily formed. Although rutile-type titania has a lower conduction band level than anatase-type, it can be used for the purpose of hydrophilization by photosemiconductors. When the base material is coated with a photo-semiconductor coating made of titania and the titania is photoexcited by ultraviolet rays, water becomes a hydroxyl group (OH) due to the photo-semiconductor action.^- ) Is chemically adsorbed on the surface, and as a result, the surface is considered to be hydrophilic.

【0026】

Other optical semiconductors that can be used in the present invention include ZnO and SnO.₂ , SrTiO₃, WO₃ , Bi₂ O₃ , Fe₂ O₃ There are metal oxides such as. Similar to titania, these metal oxides have metal elements and oxygen on their surface, so they have surface hydroxyl groups (OH).^- ) Is considered to be easily adsorbed. Further, the particles of the optical semiconductor may be mixed with a metal oxide that is not an optical semiconductor such as silica. In particular, when an optical semiconductor is blended with silica or tin oxide, the surface can be highly hydrophilic.

【0027】

Silicone paint containing optical semiconductor Yet another preferred method of forming a photo-semiconductor coating that exhibits hydrophilicity with a contact angle of 0 ° with water is from uncured or partially cured silicone (organopolysiloxane) or a precursor of silicone. A coating composition in which optical semiconductor particles are dispersed in a coating film-forming element is used. When this coating composition is applied to the surface of the base material, the coating film-forming element is cured, and then the photosemiconductor is photoexcited, the organic group bonded to the silicon atom of the silicone molecule is replaced with a hydroxyl group by the action of the photosemiconductor. The surface of the opto-semiconductor coating is highly hydrophilic.

【0028】

This approach has several advantages. Since the opto-semiconductor-containing silicone paint can be cured at room temperature or relatively low temperature, it can be applied to non-heat-resistant materials such as plastics and organic substances. This coating composition containing an opto-semiconductor can be applied to an existing base material that requires superhydrophilicization of the surface at any time by dipping, brush coating, spray coating, roll coating or the like. Superhydrophilicization of an optical semiconductor by photoexcitation can be easily performed even with a light source such as sunlight.

【0029】

Since the photosemiconductor-containing silicone composition has a siloxane bond, it has sufficient resistance to the photooxidizing action of the photosemiconductor (photocatalyst). Yet another advantage of the photo-semiconductor coating consisting of a photo-semiconductor-containing silicone paint is that once the surface is superhydrophilic, it remains hydrophilic for a long period of time even when kept in the dark, like a fluorescent lamp. It is to restore hydrophilicity even with the light of a simple indoor lighting lamp.

【0030】

The coating film-forming elements include methyltrichlorosilane, methyltribromsilane, methyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane, methyltrit-butoxysilane; ethyltrichlorosilane, ethyltribromsilane, and ethyltrimethoxy. Silane, ethyltriethoxysilane, ethyltriisopropoxysilane, ethyltri t-butoxysilane; n-propyltrichlorosilane, n-propyltribromsilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, n-propyltri Isopropoxysilane, n-propyltrit-butoxysilane; n-hexyltrichlorosilane, n-hexyltribromsilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, n-hexyltriisopropoxysilane, n- Hexyltri t-butoxysilane; n-decyltrichlorosilane, n-decyltribromsilane, n-decyltrimethoxysilane, n-decyltriethoxysilane, n-decyltriisopropoxysilane, n-decyltri t-butoxysilane; n -Octadecyltrichlorosilane, n-octadecyltribromsilane, n-octadecyltrimethoxysilane, n-octadecyltriethoxysilane, n-octadecyltriisopropoxysilane, n-octadecyltri t-butoxysilane; Silane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltriisopropoxysilane, phenyltrit-butoxysilane; tetrachlorosilane, tetrabromsilane, tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane, dimethoxydiethoxysilane; Didimethyldichlorosilane, dimethyldibromosilane, dimethyldimethoxysilane, dimethyldiethoxysilane; diphenyldichlorosilane, diphenyldiblomsilane, diphenyldimethoxysilane, diphenyldiethoxysilane;Phenylmethyldichlorosilane, phenylmethyldibromsilane, phenylmethyldimethoxysilane, phenylmethyldiethoxysilane; trichlorohydrosilane, tribromhydrosilane, trimethoxyhydrosilane, triethoxyhydrosilane, triisopropoxyhydrosilane, trit-butoxyhydrosilane; vinyl Trichlorosilane, Vinyltribromsilane, Vinyltrimethoxysilane, Vinyltriethoxysilane, Vinyltriisopropoxysilane, Vinyltrit-butoxysilane; Trifluoropropyltrichlorosilane, Trifluoropropyltribromsilane, Trifluoropropyltrimethoxysilane, Trifluoropropyltriethoxysilane, trifluoropropyltriisopropoxysilane, trifluoropropyltrit-butoxysilane; γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxy Propyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltriisopropoxysilane, γ-glycidoxypropyltri t-butoxysilane; γ-methacryloxipropylmethyldimethoxysilane, γ- Metaacryloxypropylmethyldiethoxysilane, γ-metaacryloxypropyltrimethoxysilane, γ-metaacryloxypropyltriethoxysilane, γ-methacryloxypropyltriisopropoxysilane, γ-methacryloxypropyltri t-butoxy Silane; γ-aminopropylmethyldimethoxysilane, γ-aminopropylmethyldiethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltriisopropoxysilane, γ-aminopropyltrit -Butoxysilane;γ-Mercaptopropylmethyldimethoxysilane, γ-mercaptopropylmethyldiethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropyltriisopropoxysilane, γ-mercaptopropyltri t-butoxy Silanes; β- (3,4-epylcyclohexyl) ethyltrimethoxysilane, β- (3,4-epylcyclohexyl) ethyltriethoxysilane; and partial hydrolysates thereof; and mixtures thereof can be used. it can.

【0031】

In order to ensure good hardness and smoothness of the silicone coating film, it is preferable to contain 10 mol% or more of the three-dimensional crosslinked siloxane. Further, in order to provide sufficient flexibility of the coating film while ensuring good hardness and smoothness, it is preferable to contain 60 mol% or less of the two-dimensional crosslinked siloxane. Further, in order to increase the rate at which the organic group bonded to the silicon atom of the silicone molecule is replaced with the hydroxyl group by photoexcitation, a silicone in which the organic group bonded to the silicon atom of the silicone molecule is composed of an n-propyl group or a phenyl group is used. Is preferable. It is also possible to use an organopolysilazane compound having a silazane bond instead of the silicone having a siloxane bond.

【0032】

Photoexcitation / UV irradiation In the present invention, it is preferable to form a photosemiconductor coating with a photocatalyst having a high bandgap energy and being photoexcited only by ultraviolet rays, such as titania. Then, the visible light is not absorbed by the opto-semiconductor coating, and the glass, the lens, and the mirror are not colored by the complementary color component. Anatase-type titania can be photoexcited with ultraviolet rays having a wavelength of 387 nm or less, rutile-type titania having a wavelength of 431 nm or less, tin oxide having a wavelength of 344 nm or less, and zinc oxide having a wavelength of 387 nm or less.

【0033】

As the ultraviolet light source, indoor lighting such as a fluorescent lamp, an incandescent lamp, a metal halide lamp, and a mercury lamp can be used. Under conditions of exposure to sunlight, the optical semiconductor is naturally photoexcited by the ultraviolet rays contained in the sunlight.

【0034】

Photoexcitation can be performed or allowed to occur until the surface contact angle with water is about 10 ° or less, preferably about 5 ° or less, particularly about 0 °. Generally 0.001 mW / cm²If it is photoexcited with the ultraviolet illuminance of, it can be superhydrophilicized until the contact angle with water becomes about 0 ° in a few days. The illuminance of ultraviolet rays contained in the sunlight falling on the surface of the earth is about 0.1 to 1 mW / cm.²Therefore, the surface can be superhydrophilicized in a shorter time by exposing it to sunlight.

【0035】

When the opto-semiconductor coating is made of titania-containing silicone, it is preferable to photoexcite the opto-semiconductor with sufficient illuminance to replace the surface organic groups bonded to the silicon atoms of the silicone molecule with hydroxyl groups in a sufficient amount. .. The most advantageous way to do this is to use sunlight. Once the surface is highly hydrophilic, the hydrophilicity persists even at night. Hydrophilicity is restored and maintained each time it is exposed to sunlight again.

【0036】

In the present invention, it is preferable that the member is subjected to protective measures for protecting the member from the photooxidation-reduction reaction of the photosemiconductor. Such an idea (weak redox hydrophilicization) is based on the discovery that the hydrophilization phenomenon of the member surface by a photosemiconductor and the photooxidation-reduction reaction by a photosemiconductor are basically different phenomena. Based on this discovery, the present inventor has found that there is a configuration showing a hydrophilization phenomenon, although the photooxidation-reduction reaction is hardly shown in the design of the optical semiconductor thin film.

【0037】

The first aspect of weak oxidation-reducing hydrophilicization is to set the energy level of the conduction band of the photosemiconductor to a positive value when the hydrogen production level is 0 eV. The conventional theory regarding photooxidation-reduction reaction is that conduction electron-hole pairs are generated by photoexcitation, and then the reduction reaction by the generated conduction electrons and the oxidation reaction by holes are promoted and proceed at the same time. Therefore, tin oxide and rutile, whose lower end of the energy level of the conduction band of the optical semiconductor is not sufficiently high on the negative side, have 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, conduction electrons become excessive, and electron-hole pairs generated by photoexcitation are recombined without participating in the redox reaction, so that the oxidation reaction and the reduction reaction hardly occur in reality. However, the hydrophilization phenomenon due to photoexcitation progresses.

【0038】

When the photooxidation-reduction reaction of an optical semiconductor is used for the decomposition of organic substances, the decomposition reaction is carried out using water or oxygen in the environment. That is, the conduction electrons generated by photoexcitation reduce oxygen to superoxide ions (O).₂^-), The holes oxidize the hydroxyl groups to generate hydroxide radicals ( OH), and these highly reactive reactive oxygen species (O)₂^-Organic matter is decomposed by the redox reaction of OH). Therefore, in order to effectively photooxidize and reduce organic substances, the energy level at the upper end of the valence band that generates holes is located on the positive side of the oxygen generation level (+0.82 eV) at which the hydroxyl band emits electrons. In addition, the energy level at the lower end of the conduction band generated by conduction electrons should be located on the negative side of the hydrogen generation level (0eV) at which hydrogen emits electrons and donates them to the oxygen side. Therefore, conversely, in order not to effectively photooxidize-reduce and decompose organic substances, the energy level at the upper end of the valence band should be located on the negative side of the oxygen generation level (+0.82 eV), or the energy at the lower end of the conduction band should be located. The level should be located on the positive side of the hydrogen generation level (0eV).

【0039】

When the photooxidation-reduction reaction of a photo-semiconductor is used for the precipitation of metal ions in water, the metal ions are reduced and precipitated by the conduction electrons generated by photoexcitation (at the same time, the holes oxidize the hydroxyl groups in the water to form a hydroxide. It is thought to generate radicals ( OH).) Therefore, for example, in order to effectively precipitate and remove iron ions from water, the energy level at the lower end of the conduction band generated by conduction electrons must be located on the negative side of the iron generation level (-0.44 eV). Therefore, conversely, in order to prevent metal ions from precipitating from water, the energy level at the lower end of the conduction band should be positioned on the positive side of the metal formation level. Excluding precious metals, the metal formation level is on the negative side of the hydrogen production level, so in the end, the energy level at the lower end of the conduction band should be located on the positive side of the hydrogen generation level (0eV). Become. Examples of optical semiconductors in which the lower end of the energy level of the conduction band that can be used for this is a positive value when the hydrogen generation level is 0 eV include tin oxide, tungsten trioxide, dibismuth trioxide, and second oxide. Examples thereof include metal oxides such as iron and rutile-type titanium oxide.

【0040】

From the above, as one method of photohydrophilization while suppressing the decomposition of the resin and the precipitation of dissolved metal ions in water, when the energy level of the conduction band of the optical semiconductor is set to 0 eV and the hydrogen generation level is set to 0 eV, It turns out that there is a method that is located at a positive value.

【0041】

The second aspect of the weak oxidation-reducing hydrophilicization is to form a layer containing a photosemiconductor and a hydrophilic substance that is not a photosemiconductor on the surface of the base material, and the photosemiconductor is hardly in contact with the outside air. In such a state, most of the conduction electrons and holes generated by photoexcitation of the photosemiconductor do not diffuse to the surface, and the probability of contact with surface reactive species such as water, oxygen, and metal ions is drastically reduced, and therefore photooxidation. The reduction reaction is suppressed. And the excitation light illuminance 1mW / cm²Almost photooxidation-reduction reaction under the amount of conduction electrons and holes generated in a coating film with a thin film thickness and / or a low content of photosemiconductor particles to the extent that sufficient wear resistance can be exhibited. Can be suppressed to the extent that Nevertheless, the photohydrophilization reaction proceeds.

【0042】

The third aspect of weak redox hydrophilicization is to form a layer on the surface of the substrate containing a photosemiconductor and a substance that inhibits the photooxidation-reduction reaction of the photosemiconductor. Although the mechanism is not clear, alkali metals, alkaline earth metals, alumina, zirconia, silica, antimony oxide, atypical titanium oxide, aluminum, manganese, etc. weaken the photooxidation-reduction performance of opto-semiconductors (titanium oxide, Gihodo (1991)). And the excitation light illuminance 1mW / cm²Below, and under the amount of conduction electrons and holes generated in a coating film that is thin enough to exhibit sufficient wear resistance and / or has a low photosemiconductor particle content, the photooxidation-reduction reaction is almost non-existent. It can be suppressed to the extent that it does not occur. However, even if these substances are contained in the layer, the photohydrophilization reaction proceeds.

【0043】

In the second and third aspects of weakly oxidative-reducing hydrophilicization, it is preferable that the film thickness is thin. It is preferably 1 μm or less, more preferably 0.2 μm or less. By doing so, the absolute amount of the optical semiconductor fixed to the base material can be reduced, and the photooxidation-reducing property can be further lowered. It also improves wear resistance. Further, especially when the thickness is 0.2 μm or less, it is easy to secure the transparency of the thin film containing the optical semiconductor, and the design and transparency of the substrate can be maintained.

【0044】

In the second aspect of the weak oxidation-reducing hydrophilicization, the optical semiconductor content is preferably about 5 to 80% by weight, more preferably about 10 to 50% by weight, based on the optical semiconductor-containing layer. This is because the smaller the content of the photosemiconductor, the lower the photooxidation-reduction property. However, since the photohydrophilicization phenomenon is also a phenomenon based on the photoexcitation phenomenon of photosemiconductors, it is necessary that about 5% or more is contained.

【0045】

In the second and third aspects of weak oxidation-reducing hydrophilicization, the illuminance of light having a wavelength below the excitation wavelength is preferably 0.0001 to 1 mW / cm.², More preferably 0.001 ~ 1mW / cm²The degree is good. This is because the lower the illuminance of the light having a wavelength equal to or lower than the excitation wavelength, the smaller the amount of electron-hole pairs generated, so that the photooxidation-reduction property can be lowered. However, since the photohydrophilicization phenomenon is also a phenomenon based on the photoexcitation phenomenon of optical semiconductors, it is approximately 0.0001 mW / cm.²The above excitation light illuminance is required.

【0046】

In the present invention, an intermediate layer may be provided between the base material and the optical semiconductor-containing layer. As a result, the adhesion to the base material is increased and the wear resistance is improved.

【0047】

An optical semiconductor in which the energy level of the conduction band is a positive value when the hydrogen generation level is 0 eV on a substrate that requires surface hydrophilicity, which is the first aspect of weak oxidation-reducing hydrophilicization. For example, there are the following methods for forming a thin film containing particles. (1) The above photosemiconductor particles are applied to the surface of the base material and fired. (2) On the surface of the base material, an organic compound (alkoxide, chelate, acetate, etc.) containing the constituent element of the photo-semiconductor metal oxide, or an inorganic compound (chloride, sulfate, etc.) that is not an oxide is hydrolyzed. It is applied to a base material and dehydrated by a method such as heating. If the metal oxide is not crystallized like titanium oxide by this process, it is further heated to crystallize the metal oxide. (3) After fixing the constituent element metal of the semiconductor metal oxide on the surface of the base material by sputtering or the like, it is oxidized by a method such as heating or electrode reaction. If the metal oxide is not crystallized like titanium oxide by this process, it is further heated to crystallize the metal oxide.

【0048】

The method of forming a thin film containing photosemiconductor particles and a hydrophilic substance that is not a photosemiconductor on a substrate that requires surface hydrophilicity, which is the second aspect of weak oxidation-reducing hydrophilicity, is a type of hydrophilic substance that is not a photosemiconductor. The method differs depending on the type. (I) When the hydrophilic substance that is not a photosemiconductor is an inorganic oxide such as silica or alumina (1) Photosemiconductor particles and the above-mentioned inorganic oxide particles are coated on the surface of the base material and fired. (2) Addition of photo-semiconductor particles and an organic compound (alkoxide, chelate, acetate, etc.) containing the constituent element metal species of the inorganic oxide or an inorganic compound (chloride, sulfate, etc.) that is not an oxide on the surface of the substrate. The decomposition product is applied to a base material and subjected to a dehydration reaction by a method such as heating. (3) On the surface of the base material, an organic compound (alkoxide, chelate, acetate, etc.) containing the above-mentioned inorganic oxide particles and the constituent element metal species of the photo-semiconductor particles or an inorganic compound (chloride, sulfated product, etc.) that is not an oxide. The hydrolyzate is applied to a base material and dehydrated by a method such as heating. If the metal oxide is not crystallized like titanium oxide by this process, it is further heated to crystallize the metal oxide. (II) In the case of a silicone resin in which at least a part of the organogroup in which a hydrophilic substance other than a photosemiconductor is bonded to a silicon atom is substituted with a hydroxyl group. Photo-semiconductor particles and silicone resin and / or a precursor thereof (organoalkoxysilane and its hydrolyzate) are applied to a substrate and heated. As a result, it is hydrolyzed as needed, then dehydrated and polycondensed and cured to fix the photosemiconductor particles and the silicone resin on the substrate. Then, the optical semiconductor is irradiated with light having a wavelength equal to or lower than the excitation wavelength to replace at least a part of the organogroup bonded to the silicon atom in the silicone resin with a hydroxyl group.

【0049】

A method for forming a thin film containing photosemiconductor particles and a substance that inhibits the photooxidation-reduction reaction of the photosemiconductor on a substrate that requires surface hydrophilization, which is the third aspect of weak redox hydrophilicity, is, for example, as follows. There is a method. (1) A compound containing photosemiconductor particles and the constituent metal species in the above-mentioned inhibitory substance is applied to the surface of the base material and fired. (2) On the surface of the base material, a compound containing a constituent element metal species in an inhibitory substance and an organic compound (alkoxide, chelate, acetate, etc.) containing a constituent element metal species of photo-semiconductor particles or an inorganic compound (chloride) that is not an oxide. A hydrolyzate of a substance, alkoxide, etc.) is applied to a base material and dehydrated by a method such as heating. If the metal oxide is not crystallized like titanium oxide by this process, it is further heated to crystallize the metal oxide.

【0050】

[Example]

Example 1 (titanium oxide + silicone, film thickness change) First, a 10 cm square aluminum substrate was previously coated with a silicone layer in order to smooth the surface of the substrate. For this reason, solution A (silica sol) and solution B (trimethoxymethylsilane) of the Japanese synthetic rubber paint composition "Grasca" are mixed so that the weight ratio is 3, and this mixed solution is applied to the aluminum substrate. Then, it was cured at a temperature of 150 ° C. to obtain a plurality of aluminum substrates (# 1 sample) coated with a silicone base coat having a film thickness of 3 μm.

【0051】

Next, a thin film made of an optical semiconductor and a silicone resin was formed on the surface of the # 1 sample. More specifically, anatase-type titania sol (manufactured by Nissan Chemical Industries, Ltd., TA-15) and the above-mentioned "Grasca" solution A are mixed, diluted with ethanol, and then the above-mentioned "Grasca" solution B is added to form a titanium oxide-containing silicone paint. The composition for use was adjusted. Here, the weight ratio of liquid A and liquid B of "Grasca" was set to 3.

【0052】

This coating composition was applied to the surface of # 1 sample and cured at a temperature of 150 ° C. to form a top coat composed of anatase-type titania particles and a silicone resin to obtain # 2 to # 6 samples. Topcoat film thickness of # 2 sample is 0.03 μm, topcoat film thickness of # 3 sample is 0.1 μm, topcoat film thickness of # 4 sample is 0.2 μm, topcoat film thickness of # 5 sample is 0.6 μm, # 6 The topcoat film thickness of the sample was 2.5 μm. In each sample, the total weight of silica and silicone resin was set to 1 with respect to 1 part by weight of anatase-type titania particles.

【0053】

0.5mW / cm for each sample using a 20W BLB fluorescent lamp (manufactured by Sankyo Electric)²The time change of the contact angle of the sample surface with water was investigated using a contact angle measuring device (made by ERMA, model G-1-1000) while irradiating with ultraviolet rays with the ultraviolet illuminance of. The contact angle was measured 30 seconds after dropping water droplets on the sample surface from the microsyringe. The results are shown in the graph in Fig. 1. As can be seen from the graph in FIG. 1, the surface of each sample was highly hydrophilized within 50 hours of irradiation, and the contact angle with water was less than 3 °, regardless of the film thickness.

【0054】

Example 2 SK Kaken's "Lenacast" (undercoat is Lenacast, topcoat is urethane color, white) is deposited on the asbestos slate board. A silicone resin was formed on the silicone resin at 120 ° C. for 30 minutes so that the film thickness was 0.1 μm, and the siding material of Example 2 was prepared.

【0055】

Comparative example "Lenacast" (undercoat is Lenacast, topcoat is urethane color, white) manufactured by SK Kaken Co., Ltd. was formed on an asbestos slate board to prepare a siding material of a comparative example.

【0056】

The siding materials of Example 2 and Comparative Example were subjected to an accelerated weather resistance test (63 ° C, 18 minutes of rain in 120 minutes, 3,000 hr) by a sunshine weather meter, and the appearance was evaluated. As a result, Example 2 was normal. On the other hand, the comparative example was yellowed and cracked. Therefore, it is considered that the weather resistance of the surface of the siding material is improved by forming the photocatalytic coating film of the present invention. As a result of exposing Example 2 and Comparative Example to the outdoors for 3 months, Example 2 did not produce stains, whereas Comparative Example produced black and streaky stains. At this time, when the contact angle of each siding material surface with water was measured, it was 0 ° in Example 2 and 70 ° in Comparative Example. Therefore, it is considered that the surface of the siding material is made hydrophilic and the antifouling property is improved by forming the photocatalytic coating film of the present invention.

【0057】

[Effect of the invention]

As is clear from the above description, in the present invention, since the optical semiconductor of the member surface layer absorbs ultraviolet rays, the member does not undergo ultraviolet deterioration. Further, it is possible to make the surface of the member less likely to be soiled by making the member surface hydrophilic by the optical semiconductor.

[Simple explanation of drawings]

[Figure 1]

It is a graph which investigated the time change of the contact angle with water of the surface of the sample in Example 1.