Aqueous coating solution containing titanium peroxide and method of forming photocatalytic layer using the same

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention is an aqueous coating liquid for forming an undercoat layer used for protecting a substrate when forming a photocatalyst layer effectively used for water purification, air purification, deodorization, decomposition of oil, and the like. , And a method for forming a photocatalyst layer using this coating liquid.

【0002】

[Conventional technology]

Conventionally, TiO₂, ZnO, WO₃, Fe₂O₃, SrTiO₃Metal oxides such as these are widely used as photocatalysts for water purification, air purification, deodorization, oil decomposition, etc. Such a photocatalyst is usually used in the form of powder, and is used by being stirred and dispersed in a liquid such as water to be purified or deodorized. However, with such a powdery photocatalyst, it is troublesome to recover after use, and recovery may be difficult.

【0003】

On the other hand, in order to prevent contamination of the substrate (base material) itself of a structure such as a building or a plant, it is necessary to immobilize a powdery photocatalyst on the surface of the substrate, and such a powdery photocatalyst is fixed. As a method of forming the photocatalyst layer, a method of adhering titanium dioxide to a substrate such as glass by sputtering or the like to form a photocatalyst layer, or a method of applying anatase-type titanium dioxide sol and heating (100 ° C) to form the photocatalyst layer is known. ing.

【0004】

However, when the substrate is made of an organic compound such as an organic polymer, there is a problem that the catalytic action of titanium dioxide or the like extends to the substrate, and the substrate is oxidized and / or reduced to be decomposed. In order to prevent such decomposition, it is disclosed in Japanese Patent Application Laid-Open No. 10-53437 that an amorphous titanium peroxide layer is provided between the substrate and the photocatalyst layer.

【0005】

As a result, the catalytic action of titanium dioxide or the like does not extend to the substrate. However, the undercoat layer and the photocatalyst layer such as the amorphous titanium peroxide layer usually need to be transparent or translucent in order to design the substrate to be coated. Moreover, these layers are extremely thin layers of several μm for the same reason. Therefore, it is extremely difficult to confirm whether or not these layers are covered with the object to be coated. That is, if there is an uncoated portion of the undercoat layer, the photocatalyst layer comes into direct contact with the object to be coated, and the object to be coated is decomposed and damaged. Further, if there is a portion where the photocatalyst layer is not coated, the photocatalyst function in that portion cannot be obtained.

【0006】

As a method for easily finding an uncoated portion, a photocatalyst layer is provided in WO00 / 33977 by using a photocatalyst coating solution containing an organic dye or a persistent binder coating solution containing an organic dye. Alternatively, a method is disclosed in which an undercoat layer is formed, the coated portion is colored, and the uncoated portion is not colored, thereby distinguishing the uncoated portion. The dye is decomposed by the catalytic action of the photocatalytic layer and is decolorized, so that the transparency of each layer can be maintained.

【0007】

[Problems to be Solved by the Invention]

According to the study of the present inventor, in the photocatalyst coating layer containing the organic dye in WO00 / 33977, the dye is decomposed and decolorized by its photocatalytic function, but the dye in the persistent undercoat layer is It depends on the photocatalyst function of the photocatalyst coating layer on it, and depending on the properties and layer thickness of the photocatalyst coating layer, decolorization may not be sufficiently performed or may not be performed in a short period of time.

【0008】

Further, regarding whether the photocatalyst layer should be colored or the undercoat layer should be colored, it is important to color the undercoat layer. That is, if the undercoat layer is defective, the substrate itself is damaged, which has a great effect on the structure itself. Therefore, it is important to inspect whether the substrate is completely covered with the undercoat layer. The present inventors also paid attention to the fact that it is clear.

【0009】

Therefore, an object of the present invention made in view of such a point is to provide an aqueous coating liquid for forming an undercoat layer for protecting a substrate, which can be inspected for coating by coloring and can be easily decolorized. To provide.

【0010】

Another object of the present invention is to provide a method for forming an undercoat layer using the above coating liquid and forming a photocatalyst layer on the undercoat layer without damaging the substrate.

【0011】

[Means for solving problems]

The present invention is an aqueous coating solution containing titanium peroxide and a dye that is decolorized by irradiation with visible light, and the dye is colored by irradiation with ultraviolet rays.

【0012】

The coating liquid is a coating liquid for forming a substrate protective undercoat layer provided between a photocatalyst layer containing a metal oxide having a photocatalytic function and a substrate. It is preferable that the compound having this photocatalytic function is anatase-type titanium oxide (generally anatase-type titanium dioxide). It is preferable that the titanium peroxide in the undercoat layer is an amorphous type.

【0013】

The dye is preferably a dye that is also decolorized by blocking light or heating. It is advantageous in use that the dye is a dye that absorbs visible light and decolorizes it. In particular, a dye that absorbs light having a wavelength of 500 to 700 nm (preferably having an absorbance of 0.5 or more) and decolorizes is preferable because the decoloring speed is high. It is preferable that the visible light decolorizing dye is a spiropyran dye, a flugide dye or a diallyl ether dye, particularly a spiropyran dye.

【0014】

It is advantageous that the substrate is made of an organic polymer.

【0015】

The present invention protects a substrate from the photocatalytic layer by applying the above-mentioned aqueous coating liquid on the substrate and drying it before forming a photocatalyst layer containing a metal oxide having a photocatalytic function on the substrate. Another method for forming a photocatalyst layer is to form a substrate protective undercoat layer for the purpose of forming a photocatalyst layer, and then to form the photocatalyst layer on the undercoat layer.

【0016】

BEST MODE FOR CARRYING OUT THE INVENTION

The aqueous coating liquid of the present invention is an aqueous coating liquid containing titanium peroxide and a dye that is colored with ultraviolet rays and decolorized by visible light as a main component, and is particularly provided between a photocatalyst layer and a substrate for protecting a substrate. It can be advantageously used as a coating liquid for forming a coating layer.

【0017】

FIG. 1 shows a schematic cross-sectional view of a laminate including a photocatalyst layer for explaining the present invention. In FIG. 1, a colored substrate protective undercoat layer 12 and a photocatalyst layer 13 are formed on the substrate 11. Since the undercoat layer 12 immediately after coating is colored during coating, if there is a coating defect, only that portion is not colored. By repairing the uncolored portion again, an undercoat layer without coating defects can be formed. Further, the coloring of the undercoat layer 12, which is a characteristic requirement of the present invention, is a dye in a colored state in which a dye that is colored by ultraviolet rays and decolorized by visible light is irradiated with ultraviolet rays, and therefore, a substrate (structure) having a photocatalytic layer. By placing it outdoors, its color disappears completely due to sunlight in a short period of time. That is, since the dye contained in the undercoat layer undergoes a structural change due to visible light, it can be reliably decolorized in a short period of time by irradiation with sunlight or the like. It is uncertain that it depends on the catalytic action of the conventional upper photocatalytic layer, and it is difficult to completely decolorize it. Further, since the undercoat layer of the present invention naturally also receives the catalytic action of the photocatalytic layer, it is possible to improve the decolorization speed accordingly. In addition, the colored dye of the present invention may be decolorized by blocking light or heating, in which case the decolorization is further accelerated, which is preferable.

【0018】

The aqueous coating liquid for forming an undercoat layer of the present invention is a coating liquid containing titanium peroxide and the above-mentioned visible light decolorizing dye in a colored state. For example, it is used by adding the above dye to an amorphous titanium peroxide sol. This sol can be produced, for example, as follows. Titanium tetrachloride TiCl₄Ammonia water or alkali hydroxide such as sodium hydroxide is added to the aqueous titanium salt solution as described above, and the mixture is reacted at pH 6 to 7. The resulting pale bluish white, amorphous titanium hydroxide Ti (OH)₄(Orthotitanium acid H₄TiO₄Also called. ) Is washed and separated, and then treated with hydrogen peroxide solution to obtain a morphous form of titanium peroxide sol.

【0019】

The amorphous titanium peroxide sol thus obtained has a pH of 6 to 7 and a particle size of 8 to 20 nm, and its appearance is a transparent yellow liquid, which is stable even when stored at room temperature for a long period of time. The sol concentration is usually adjusted to 1.4 to 1.6% by mass, but the concentration can be adjusted as needed. When using at a low concentration, dilute with distilled water or the like before use.

【0020】

In addition, this amorphous titanium peroxide sol is amorphous at room temperature and has not yet crystallized into anatase-type titanium oxide, so it is possible to create a uniform and flat thin film with excellent adhesion and film formation. It can be formed, and the dry film has the property of being insoluble in water. When the amorphous titanium peroxide sol is heated at 100 ° C or higher for several hours, it becomes anatase type titanium oxide sol. For the amorphous titanium peroxide sol coated on the substrate and then dried and fixed, 250 to 940 ° C. It becomes anatase type titanium oxide by heating. Therefore, in these cases, it does not function as an undercoat layer, but it can be used as a photocatalyst layer.

【0021】

As the aqueous coating liquid for forming an undercoat layer of the present invention, for example, a visible light decolorizing dye can be added to a viscous amorphous titanium peroxide and used. The viscous amorphous titanium peroxide can be produced, for example, as follows. Titanium tetrachloride TiCl₄ Ammonia water or an alkali hydroxide such as sodium hydroxide is added to the aqueous titanium salt solution as described above, and the reaction is carried out at pH in an acidic region, preferably pH 2 to 6, particularly preferably pH 2. Precipitated pale bluish white, amorphous titanium hydroxide Ti (OH)₄(Orthotitanium acid H₄TiO₄Also called. ) Is washed and separated, treated with hydrogen peroxide solution, reacted at low temperature, preferably at 15 ° C or lower, particularly preferably at 5 to 8 ° C with stirring, and then cured at room temperature for 7 to 10 days. Obtained by

【0022】

The viscous amorphous titanium peroxide thus obtained has a pH of 2 to 4 and a particle size of about 8 to 20 nm, and its appearance is a yellow transparent, slightly viscous sol to semi-jelly-like, that is, various viscosities. It has a very strong adhesive force and is stable even when stored at room temperature for a long period of time. The solid content concentration is usually adjusted to 0.2 to 0.6% by mass, preferably 0.3% by mass, but the concentration can be adjusted as needed.

【0023】

The above-mentioned viscous amorphous titanium peroxide is Titanium tetrachloride TiCl in the manufacturing process.₄By changing the pH at the time of reaction between the aqueous titanium salt solution such as, and aqueous ammonia or alkali hydroxide such as sodium hydroxide within the acidic range, preferably within the range of pH 2 to 6, and by changing the solid content concentration to 0.2. By changing the value within the range of ~ 0.6% by mass, those having various viscosities can be obtained, and various uses can be considered depending on the viscosity. However, for the purpose of forming a thin film having a uniform film thickness, it is homogeneous. It is desirable that the viscosity is about semi-jelly.

【0024】

When the pH of the above reaction exceeds 6, it becomes an amorphous titanium peroxide sol with low viscosity, and hydrophilic treatment with a surfactant or the like is required when coating the surface of a substrate such as a metal or plastic having strong water repellency. If the pH is less than 2, the precipitation of orthotitanic acid is extremely reduced, which is a disadvantage. Further, if the solid content concentration exceeds 0.6% by mass, there arises a problem that it becomes inhomogeneous semi-jelly and it becomes difficult to form a thin film having a uniform film thickness. On the other hand, if it is less than 0.2% by mass, the surface of the substrate At the time of coating, there is a disadvantage that hydrophilic treatment due to surface activity or the like is required.

【0025】

Therefore, the viscous amorphous titanium peroxide is a yellow transparent and viscous substance, and has not yet crystallized into anatase-type titanium oxide in an amorphous state at room temperature, and its adhesion and adhesion are repellent. It is extremely excellent in substrates of all grades including aqueous substrates. In addition, it has a high film-forming property, a uniform and flat thin film can be easily formed, and the dry film has a property of being insoluble in water.

【0026】

When this viscous amorphous titanium peroxide is coated on a substrate, dried and fired at room temperature to 250 ° C., an amorphous titanium peroxide layer having a very strong adhesive force is formed. Further, when dried and fired at 250 to 940 ° C, anatase-type titanium oxide layer is formed, and when heated at 940 ° C or higher, a rutile-type titanium oxide layer is formed, and the function of the photocatalyst is extremely deteriorated. Therefore, in these cases, the function as the undercoat layer is not fulfilled. The former can be used as a photocatalytic layer.

【0027】

The aqueous coating liquid for forming the undercoat layer of the present invention may be any liquid as long as it can prevent the decomposition action of the photocatalyst on the substrate. In addition to the above examples, for example, water glass, colloidal silica, polyorganosiloxane, etc. Silicon compounds such as zinc phosphate, phosphates such as aluminum phosphate; inorganic binders such as heavy phosphate and cement; coating liquids containing organic binders such as fluororesin and silicon resin can be mentioned. These are described in, for example, Japanese Patent Application Laid-Open No. 7-171408. Among these coating liquids for forming an undercoat layer, those that become transparent after film formation, such as the amorphous titanium peroxide sol, are preferable.

【0028】

The visible light decolorizing dye contained in the aqueous coating liquid for forming an undercoat layer of the present invention is a dye that is used in a state of being colored by irradiating with ultraviolet rays, and after being applied, absorbs visible light and decolorizes. is there. The visible light decolorizing dye is particularly preferably a dye that can be decolorized by blocking light or heating, and further, a dye that absorbs light having a wavelength of 500 to 700 nm (preferably having an absorbance of 0.5 or more) to decolorize. Is preferable from the viewpoint of quick decolorization. The visible light decolorizing dye absorbs visible light and decolorizes as described above, but it is clear that the decolorization is further promoted because it is naturally catalyzed by the photocatalytic layer which is the upper layer. Moreover, since the color is directly erased by light, the color can be surely and completely lost.

【0029】

The visible light decolorizing dye is preferably a spiropyran dye, a flugide dye or a diallyl ether dye, particularly a spiropyran dye. Preferred spiropyran dyes have the following formula (I): [0030]

[Chemical 1]

<img file="JP2003268262A_D0001.tif" />【0031】

In the above formula (I), X represents CH or a nitrogen atom, and R¹But hydrogen atom, NO₂Or represents halogen (especially Br), R²Represents a hydrogen atom, an alkoxy (especially methoxy) with 1 to 4 carbon atoms, and R³Represents a hydrogen atom, or R¹And R³Bond to each other to form a benzene ring with the carbon-carbon double bonds in which they are present.

【0032】

Preferred examples of spiropyran dyes are 1,3,3-trimethylindolinobenzopyrylospiran, 1,3,3-trimethylindolinobenzopyrylospiran, 1,3,3-trimethylindolinobenzopyrylospiran, 1,3,3-trimethylindolino-8'-methoxybenzopyrrilopyran, 1,3,3-trimethylindolino-β-naphthpyrrilopyran, 1,3,3-trimethylindolinonaphthospiroxazine and 1 , 3,3-trimethylindolino-6'-nitrobenzopyrrilospiran can be mentioned.

【0033】

It is preferable that the dye is generally contained in the coating liquid in an amount of 0.05 to 10% by mass, particularly preferably 0.1 to 5% by mass. With respect to 100 parts by mass of titanium peroxide, it is generally preferable to contain 1 to 100 parts by mass, particularly 5 to 80 parts by mass.

【0034】

In the present invention, as the material of the substrate (base material), an inorganic material such as ceramics and glass, an organic material such as organic polymer (plastic), rubber, wood and paper, and a metal material such as aluminum and steel are used. Can be done. Among these, in particular, for application to substrates such as films of organic polymer materials such as acrylonitrile resin, vinyl chloride resin, polycarbonate resin, acrylic resin (eg, polymethylmethacrylate), polyester resin (eg, polyethylene terephthalate), and polyurethane resin. The undercoat layer of the present invention is effective in the distance. Further, the size and shape of the substrate are not limited, and a film shape, a honeycomb shape, a fiber shape, a filtration sheet shape, a bead shape, a foam shape, or a product obtained by accumulating them may be used. Further, as the substrate of the present invention, surface portions of various products, members, structures and the like can be regarded as substrates. For example, building materials such as windowpanes, blocks, unit baths, lighting fixtures; structures such as outer walls, roofs, pillars, windows, signals; heavy transportation equipment (body, inner wall) such as automobiles, trains, jets, cranes, etc. The surface portion can be regarded as a substrate. Furthermore, if it is a substrate that allows ultraviolet rays to pass through, it can be applied to the inner surface thereof, and it can also be applied to a painted article.

【0035】

A known method such as dipping or spray spray is used to apply and coat an amorphous titanium peroxide sol or a viscous amorphous titanium peroxide in which the visible light decolorizing dye is dissolved on a substrate. be able to.

【0036】

After coating by coating or spraying as described above, the substrate having the undercoat layer of the amorphous titanium peroxide layer of the present invention can be produced by drying, firing and solidifying at less than 250 ° C. Since the dye itself is usually colorless, the visible light decolorizing dye is dissolved in water or an organic solvent, and the solution is irradiated with ultraviolet rays to obtain a colored dye, which is mixed and dissolved in the titanium sol or the like. Use by letting. The wavelength of the irradiated ultraviolet rays is generally in the range of 1 to 400 nm, particularly in the range of 200 to 400 nm.

【0037】

The coating composition composed of the amorphous titanium peroxide sol or the viscous amorphous titanium peroxide has a feature that a predetermined thickness can be obtained by one coating. The thickness of these titanium peroxide layers formed by the coating is also adjusted by the concentration (mass%) of titanium peroxide in the viscous amorphous titanium peroxide and the like, the viscosity, and the coating thickness before drying. can do. If necessary, the above coating materials can be applied in layers.

【0038】

The substrate having the undercoat layer of the amorphous titanium peroxide layer has excellent weather resistance and can protect the substrate made of an organic polymer material or the like from ultraviolet rays or the like, and when a photocatalytic semiconductor layer is provided on the substrate, It can protect substrates such as organic polymer materials that are easily decomposed by the photocatalytic function.

【0039】

The undercoat layer containing the amorphous titanium peroxide and the visible light decolorizing dye formed by the coating liquid of the present invention generally has a layer thickness of 0.5 to 20 μm, particularly 1 to 10 μm.

【0040】

The photocatalytic layer of the present invention is generally a layer containing a photocatalytic semiconductor. An example is TiO₂, ZnO, SrTiO₃, CdS, Cd0, CaP, InP, In₂O₃, CaAs, BaTiO₃, K₂NbO₃, Fe₂O₃, Ta₂O₅, WO₃, SaO₂, Bi₂O₃, NiO, Cu₂O, SiC, SiO₂, MoS₂, MoS₃, InPb, RuO₂, CeO₂Among these, titanium oxide TiO₂(Especially anatase-type titanium dioxide) is preferable. The photocatalytic semiconductor is used in the form of fine particles or fine powder or a sol having a diameter of about 0.001 to 20 μm. Examples of the photocatalytic semiconductor include product name: ST-01 (manufactured by Ishihara Techno Co., Ltd.), product name: ST-31 (manufactured by Ishihara Techno Co., Ltd.), and product name: anatase-type titanium oxide sol TAK70 (TAO Co., Ltd.). (Made) can be mentioned.

【0041】

As the coating liquid for forming the photocatalyst layer, any conventional coating liquid for forming a photocatalyst layer can be used. A coating liquid that forms a transparent coating layer after film formation is preferable. Examples of such a coating liquid include a suspension containing the above-mentioned photocatalytic semiconductor metal fine particles and a binder (for example, a silane coupling agent such as aminosilane). Among these, those capable of forming a film by heating at room temperature to 120 ° C. are preferable. Some films require heating at 300 to 500 ° C, for example, but the dye in the undercoat layer may be decomposed and decolorized, so it is necessary to select the dye in consideration of this point.

【0042】

Also, Pt, Ag, Rh, RuO for complementing photocatalytic function₂, Nb, Cu, Sn, NiO and the like can also be used as additives.

【0043】

A preferable example of the suspension containing the photocatalytic semiconductor metal fine particles and the binder is a mixed solution of an amorphous titanium peroxide sol and anatase type titanium oxide sol. This amorphous titanium peroxide sol can be obtained in the same manner as described in the coating liquid for forming an undercoat layer. Amorphous titanium peroxide sol (aqueous solution) is in an amorphous state at room temperature and has not yet crystallized into anatase-type titanium oxide. Since it contains ultrafine particles, it has excellent adhesion, is highly film-formed, and is uniform and flat. A thin film can be formed, and the dry film has the property of not being soluble in water. Anatase-type titanium oxide sol can be prepared by heating amorphous titanium peroxide sol at 100 ° C. or higher for several hours.

【0044】

Next, the method for forming the photocatalyst layer of the present invention will be described with reference to FIG. First, the substrate 11 that has been subjected to hydrophilic treatment with a surfactant or the like is coated with a dye-containing amorphous titanium peroxide sol as an aqueous coating liquid for forming an undercoat layer, or the substrate is directly dyed without being subjected to hydrophilic treatment. Containing Viscous Amorphous titanium peroxide is coated with an aqueous coating solution to form an undercoat layer 12 which is an amorphous titanium peroxide layer, while the amorphous titanium peroxide layer has adhesiveness (usually). A method of forming a photocatalyst layer by applying a suspension containing the photocatalyst semiconductor metal fine particles and a binder to (within 1 to 10 minutes at room temperature after coating) and drying; or the amorphous titanium peroxide layer While having adhesiveness (usually within 1 to 10 minutes at room temperature after coating), the fine particles of the photocatalyst semiconductor are uniformly scattered in the gas using a closed / atmospheric container, and naturally adhere or flow. Examples thereof include a method of adhering to an amorphous titanium peroxide layer by pressure adhesion to remove excess fine particles. Further, by fixing the photocatalytic semiconductor to the amorphous titanium peroxide layer (undercoat layer) and then applying pressure, the adhesiveness between the layers is remarkably improved. In this way, a homogeneous thin film can be made.

【0045】

By forming a photocatalytic thin layer of such a photocatalytic semiconductor, it is possible to achieve miniaturization and weight reduction and miniaturization capacity of electronic devices and the like. Further, as the photocatalyst functional substrate, the laminated thin film of the photocatalyst semiconductor has an effect of eliminating the functional deterioration due to mutual interference of the particle surfaces due to electron transfer and the economic loss due to the film thickness during the redox of the photocatalyst semiconductor.

【0046】

In the substrate having a photocatalyst layer made of a titanium oxide film or the like obtained as described above, the photocatalyst is excited by irradiating the photocatalyst layer with light, and exerts actions such as pollution prevention, sterilization, and deodorization. ..

【0047】

[Example]

Examples are shown below, and the present invention will be described in more detail.

【0048】

[Example 1] &lt;Formation of dye-containing undercoat layer&gt; A 5% by mass aqueous solution of a spiropyran dye (1,3,3-trimethylindolino-8'-methoxybenzopyrrilospiran, manufactured by Tokyo Chemical Industry Co., Ltd.) is applied to the center with ultraviolet rays. It was introduced into a reactor having a lamp, the lamp was turned on, and the aqueous solution was stirred for 3 minutes. As a result, a black aqueous solution was obtained.

【0049】

95 parts by mass of amorphous titanium peroxide 0.85 mass% solution (TK100, manufactured by TAO Co., Ltd.) and 5 parts by mass of the above spiropyran dye (5 mass% aqueous solution) are uniformly mixed to form a dye-containing undercoat layer. An aqueous coating solution was obtained. This aqueous coating solution was applied to a white FRP slab plate using a spray gun FS-G05-1 (manufactured by Meiji Machine Co., Ltd.) having a round blowout nozzle with a diameter of 0.5 mm. Application amount 0.4g / 100cm²And dried to form a dye-containing undercoat layer.

【0050】

&lt;Formation of photocatalyst layer&gt; Amorphous titanium peroxide 0.85 mass% solution (TK100, manufactured by TAO Co., Ltd.) and anatase type titanium oxide 0.85 mass% solution (TA100, manufactured by TAO Co., Ltd.) are uniformly used in equal amounts. The mixture was mixed to obtain an aqueous coating solution for forming a photocatalyst layer. This aqueous coating liquid is applied to the undercoat layer on a white FRP slab plate using a spray gun FS-G05-1 (manufactured by Meiji Machine Co., Ltd.) having a round blow-out nozzle with a diameter of 0.5 mm. Amount 0.8g / 100cm²After coating at room temperature and drying at room temperature, the film was formed by heating to 100 ° C with an infrared heater. As a result, a photocatalyst layer was formed.

【0051】

An undercoat layer and a photocatalyst layer were formed on the substrate as described above.

【0052】

[Example 2] In Example 1, 1,3,3-trimethylindolinobenzopyrrilospiran, manufactured by Tokyo Chemical Industry Co., Ltd., was used as a spiropyran-based dye used in the aqueous coating liquid for forming a dye-containing undercoat layer. An undercoat layer and a photocatalyst layer were formed on the substrate in the same manner except that the same amount was used.

【0053】

[Comparative Example 1] In Example 1, the same amount of the trade name Volx Yellow PM-L5G was used in place of the spiropyran dye used in the aqueous coating liquid for forming the dye-containing undercoat layer, but the same was applied on the substrate. , An undercoat layer and a photocatalyst layer were formed.

【0054】

Next, the photocatalyst laminates of the undercoat layer and the photocatalyst layer obtained in Examples 1 and 2 and Comparative Example 1 were evaluated.

【0055】

(1) Discrimination of the coating area of the undercoat layer a) While the aqueous coating liquid for forming the undercoat layer was being applied, it was visually inspected whether or not the unapplied portion on the substrate surface could be easily identified. b) After coating, as judged visually, it was inspected whether or not the undercoat layer was completely formed on the substrate surface.

【0056】

(2) Color reduction of the undercoat layer (pigment) The photocatalyst laminate provided with the undercoat layer and the photocatalyst layer on the substrate was exposed outdoors and inspected whether it became colorless and transparent after 1 month.

【0057】

The results of the above inspection are as follows. (1) Discrimination of the coating area of the undercoat layer a) In Examples 1 and 2, since the coated state of the undercoat layer can be easily known, it was easy to find the uncoated portion. Comparative Example 1 was more difficult than Example. b) In Examples 1 and 2, there were no coating defects as judged at the time of coating. On the other hand, in Comparative Example 1, although the coating was completely applied, there were some coating defects.

【0058】

(2) Color reduction of the undercoat layer (pigment) The coloring of the undercoat layers of Examples 1 and 2 completely disappeared within 1 month. On the other hand, the undercoat layer of Comparative Example 1 remained slightly colored even after one month.

[Simple explanation of drawings]

[Figure 1]

It is the schematic sectional drawing of the laminated body including the photocatalyst layer for demonstrating the present invention.

[Explanation of symbols]

11 board 12 Undercoat layer 13 Photocatalytic layer