Photocatalytic coating

Abstract

To provide photocatalytic coatings with excellent weather resistance. [Solution] A photocatalytic coating comprising a substrate, a first layer containing an organic resin on the surface of the substrate, and a second layer containing a photocatalyst on the side of the first layer opposite to the substrate side, wherein the first layer further contains cerium oxide (CeO2) and hydrophilic inorganic particles, and the particle size of the hydrophilic inorganic particles is larger than the film thickness of the first layer.

Description

[Technical Field]

[0001] This invention relates to a photocatalytic coating suitable for exterior applications of buildings and the like. [Background technology]

[0002] Coated bodies comprising a substrate and a photocatalytic layer are widely used. While photocatalysts impart advantageous effects such as antifouling and antibacterial properties to coated bodies through their oxidative decomposition and hydrophilic functions, the manifestation of these functions can also cause unfavorable effects (side effects) such as deterioration of the durability (adhesion between the substrate and the photocatalytic layer) and weather resistance of the coated body. For this reason, one configuration of a coated body that can suppress unfavorable effects while maintaining the advantageous effects of photocatalysis is to provide an intermediate layer between the substrate and the photocatalytic layer.

[0003] For example, Japanese Patent Publication No. 2019-181455 (Patent Document 1) discloses that by including cerium oxide (CeO2) in the intermediate layer, a photocatalytic coating was realized in which deterioration of durability and weather resistance was suppressed while maintaining photocatalytic activity. Furthermore, Patent Document 1 states that the intermediate layer may contain inorganic particles, and these inorganic particles are added to the intermediate layer to form an uneven surface, to control gloss, or as a filler.

[0004] Furthermore, Japanese Patent Publication No. 2011-104988 (Patent Document 2) discloses that by including water-repellent fine particles having a particle size larger than the film thickness of the intermediate layer in the intermediate layer, a photocatalytic coating has been realized that makes it difficult for cracks to occur in the photocatalytic layer and prevents a deterioration in aesthetics due to interference colors, etc., of the photocatalytic layer. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2019-181455 [Patent Document 2] Japanese Patent Publication No. 2011-104988

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present inventors have now found a novel configuration that can further improve the weather resistance of a photocatalytic coating body including a base material, an intermediate layer containing cerium oxide, and a photocatalytic layer. That is, in a photocatalytic coating body including a base material, an intermediate layer containing cerium oxide, and a photocatalytic layer, by including hydrophilic inorganic particles having a particle diameter larger than the film thickness of the intermediate layer together with cerium oxide in the intermediate layer, the deterioration of the weather resistance of the photocatalytic coating body exhibited by cerium oxide can be suppressed (hereinafter referred to as "weather resistance deterioration suppression effect"), and the effect can be further enhanced, that is, the knowledge that the weather resistance of the photocatalytic coating body can be further improved has been obtained. The present invention is based on such knowledge.

[0007] Therefore, an object of the present invention is to provide a photocatalytic coating body with an even higher weather resistance deterioration suppression effect, that is, with even better weather resistance.

Means for Solving the Problems

[0008] And the photocatalytic coating body according to the present invention is a photocatalytic coating body comprising a base material, a first layer containing an organic resin on the surface of the base material, and a second layer containing a photocatalyst on the side opposite to the surface of the first layer on the base material side, wherein the first layer further contains cerium oxide (CeO2) and hydrophilic inorganic particles, and the particle diameter of the hydrophilic inorganic particles is larger than the film thickness of the first layer and is characterized by this.

Brief Description of the Drawings

[0009] [Figure 1] It is a schematic diagram for explaining the basic configuration of the photocatalytic coating body according to the present invention. [Figure 2] It is a scanning electron microscope (SEM) photograph of the cross section of the photocatalytic coating body of Example 3. [Figure 3] This is an SEM image of a cross-section of the photocatalytic coated material in Example 9. [Modes for carrying out the invention]

[0010] Photocatalytic coating according to the present invention The basic structure of the photocatalytic coating according to the present invention will be described with reference to Figure 1. In the following, the symbols in parentheses correspond to the symbols shown in Figure 1. The photocatalytic coating according to the present invention comprises a first layer (2) containing an organic resin on the surface of a substrate (1), and a second layer (3) containing a photocatalyst provided on the opposite side of the first layer from the substrate side, preferably in contact with the opposite side. The first layer (2) further contains cerium oxide (CeO2) (4) and hydrophilic inorganic particles (5), and the particle size of the hydrophilic inorganic particles (5) is larger than the film thickness of the first layer (2). By having such a structure, the photocatalytic coating according to the present invention exhibits even better weather resistance while maintaining photocatalytic activity over a long period of time. Specifically, the photocatalytic coating according to the present invention has the effect that the second layer (3) containing the photocatalyst adheres stably to the substrate (1) over a long period of time without peeling off, and is also less susceptible to deterioration such as discoloration. Therefore, it is preferably used, for example, for exterior applications of buildings and the like.

[0011] The mechanism (action) by which weather-resistant degradation suppression is achieved. The mechanism by which the photocatalytic coating body according to the present invention exhibits excellent weather resistance degradation suppression is thought to be as follows. In other words, in the present invention, the presence of cerium oxide (4) contained in the first layer (2) results in the manifestation of excellent weather resistance. Specifically, the cerium oxide (4) contained in the first layer (2) suppresses degradation by capturing and neutralizing reactive oxygen species, which are generated from the photocatalyst contained in the second layer (3) and cause the deterioration of the weather resistance of the photocatalytic coating body, particularly the deterioration of the first and second layers (hereinafter sometimes referred to as "coating film"). Furthermore, because the first layer (2) containing cerium oxide (4) contains hydrophilic inorganic particles (5) having a particle size larger than its film thickness, the surface of the hydrophilic inorganic particles (5) can be exposed and / or come into close proximity to the interface between the first and second layers, for example, thereby newly creating interfaces (6) from the interface between the first and second layers to the interior of the first layer and the interior of the second layer. As a result, the reactive oxygen species generated by the photocatalyst are promoted to efficiently penetrate the first layer (2) by traveling through the newly formed interface (6) inside the second layer and then through the newly formed interface (6) inside the first layer, increasing the probability that cerium oxide will capture the reactive oxygen species, thereby further improving the weather resistance degradation suppression effect of cerium oxide. It should be noted that the mechanism described above is merely a hypothesis, and the present invention is not limited in any way by this hypothesis. Furthermore, if the first layer contains hydrophobic inorganic particles instead of hydrophilic inorganic particles, the aforementioned penetration will be hindered, and the weather resistance degradation suppression effect will not be obtained.

[0012] Base material The substrate used in the present invention can be any material, whether inorganic or organic, as long as a first layer containing an organic resin can be formed on it, and its shape is not limited. Preferred examples of substrates from a material standpoint include metals, ceramics, glass, plastics, rubber, stone, cement, concrete, fibers, fabrics, wood, paper, combinations thereof, laminates thereof, and those having at least one coating on their surface. Preferred examples of substrates from an application standpoint include building materials, building exteriors, window frames, window glass, structural members, vehicle exteriors and coatings, exteriors of machinery and articles, dust covers and coatings, traffic signs, various display devices, advertising towers, road sound barriers, railway sound barriers, bridges, guardrail exteriors and coatings, tunnel interiors and coatings, insulators, solar cell covers, solar water heater collector covers, greenhouses, vehicle lighting covers, outdoor lighting fixtures, stands, and films, sheets, seals, etc., for attaching to the surface of the above articles.

[0013] First layer containing organic resin In the present invention, the first layer containing an organic resin is provided between the substrate and the second layer, which is a photocatalytic layer, and functions as a protective layer to prevent the substrate from degrading due to the photocatalyst. Incidentally, it may also be used to aesthetically modify the surface of the substrate.

[0014] In the present invention, the organic resin constituting the first layer is not particularly limited as long as it ensures adhesion to the substrate and allows for the provision of a photocatalyst layer on the side opposite to the substrate-side surface of the first layer, preferably in contact with the opposite side. Examples include fluororesin, silicone, acrylic silicone, vinyl acetate, vinyl acetate acrylic, acrylic urethane, acrylic, epoxy, vinyl chloride vinyl acetate, vinylidene chloride, SBR, alkyd, melamine, polyester, nylon, polyolefin, and polycarbonate.

[0015] Furthermore, according to another aspect of the present invention, the organic resin may be applied to the substrate in the form of a composition such as an aqueous dispersion, emulsion, or dispersion to form the first layer. Therefore, the method for forming the first layer containing the organic resin is not particularly limited in the present invention, but it may be formed by appropriately applying a paint or coating composition containing the organic resin to the substrate. Alternatively, a dispersion of the organic resin in a solvent may be formed and applied to the substrate.

[0016] According to a preferred embodiment of the present invention, it is preferable to make the first layer of organic resin a silicone-based resin such as polysiloxane or silicone resin, which is a material that is difficult to decompose, in order to obtain high weather resistance. According to a preferred embodiment of the present invention, a resin having a Si content of 2% by mass or more can be used.

[0017] Cerium oxide In the present invention, the first layer containing the organic resin contains cerium oxide. The form of the cerium oxide is not particularly limited as long as it can be added to the first layer containing the organic resin, but it is preferably added to the organic resin composition in the form of a sol dispersed in water.

[0018] In this invention, cerium oxide is preferably in the form of particles. Furthermore, the particle size of the cerium oxide particles is preferably smaller than the particle size of the hydrophilic inorganic particles. This allows for more contact points between the cerium oxide particles and the hydrophilic inorganic particles, increasing the probability that cerium oxide will capture reactive oxygen species and further improving the weather resistance degradation suppression effect of cerium oxide. From the viewpoint of degradation suppression, the particle size of the cerium oxide particles is preferably less than 1 μm, and more preferably 0.1 μm or less.

[0019] Method for determining the presence or absence of cerium oxide, and for measuring the particle size of cerium oxide particles. In the present invention, the determination of whether or not the first layer contains cerium oxide, and the measurement of the particle size of the cerium oxide particles, are carried out by the following method. The presence or absence of cerium oxide is determined by scanning electron microscopy (SEM) and EDX elemental analysis using energy-dispersive X-ray fluorescence spectroscopy (EDX). When performing EDX elemental analysis, the acceleration voltage should be 15 kV. For observations at high magnifications of 50,000x or more, it is preferable to use a field emission scanning electron microscope (FE-SEM).

[0020] Discrimination of the presence or absence of cerium oxide particles when the particle size of the cerium oxide particles is 1 μm or larger. The cerium oxide particles are observed at a magnification that allows them to be seen (for example, 10,000x for 1-3 μm, 5,000x for 3-10 μm, 1,000x for 10-50 μm, and 500x for particles larger than 50 μm), and EDX elemental analysis is performed to confirm whether the particles contain Ce and O. The length in the longitudinal direction of the observed particles is defined as the particle diameter, and the smallest particle diameter observed in five fields of view is defined as the particle diameter of the cerium oxide particle.

[0021] Discrimination of the presence or absence of cerium oxide particles when the particle size of the cerium oxide particles is less than 1 μm. The backscattered electron images of cerium oxide particles are observed at a magnification (50,000x) and an accelerating voltage (3.0kV), and EDX analysis is performed to confirm whether the particles contain Ce and O. The length of the observed particle in the longitudinal direction is defined as the particle diameter, and the smallest particle diameter observed in five fields of view is defined as the particle diameter of the cerium oxide particle. Furthermore, if cerium oxide particles cannot be visually detected by SEM, the presence of cerium oxide particles in the first layer will be confirmed by detecting CeO2 by XRD of the photocatalytic coating. In other words, even if cerium oxide particles cannot be visually detected by SEM, if CeO2 can be detected by in-plane XRD measurement, it will be considered that the first layer contains cerium oxide particles with a particle size smaller than the smallest particle size measured for cerium oxide particles visually detected by SEM. In that case, the particle size of the cerium oxide particles will be judged to be smaller than the smallest measured particle size of cerium oxide particles visually detected by SEM.

[0022] The amount of cerium oxide contained in the first layer is preferably in the range of 0.1% to 2% by mass, more preferably in the range of 0.3% to 2% by mass, and even more preferably about 0.5% by mass, relative to the solid content of the organic resin. Maintaining a cerium oxide concentration within the above range allows for higher weather resistance.

[0023] Hydrophilic inorganic particles In the present invention, the first layer containing an organic resin comprises hydrophilic inorganic particles. From a materials standpoint, preferred examples of hydrophilic inorganic particles include those whose surface or entirety is made of a metal oxide. Those made of organic polymers such as synthetic resins, or those in which metal oxides are coated with organic polymers, are not included in the hydrophilic inorganic particles of the present invention. Therefore, for example, a metal oxide surface-treated with a surfactant containing a silane coupling agent is included in the hydrophilic inorganic particles of the present invention. The absence of a coating of organic polymers on the metal oxide can be confirmed by SEM observation or EDX elemental analysis of the cross-section of the target (metal oxide).

[0024] How to tell if there is "covering" or not. Whether or not a metal oxide is coated with an organic polymer can be confirmed, for example, by the following method. • Sample preparation: A cross-section of the coating film is cut out, fixed with resin or the like, and then the cross-section is polished using a polishing device to obtain the sample. Observation method: The sample cross-section is observed using a field emission scanning electron microscope (FE-SEM) or by EDX elemental analysis to confirm whether or not there is a layer around the nucleus of the inorganic particles. • Measurement conditions such as magnification: When performing FE-SEM observation, it is preferable to magnify up to a maximum of 100,000 times (allowing observation down to the order of tens of nanometers), and when performing EDX elemental analysis, it is preferable to set the acceleration voltage to 15kV. • Criteria for determination: A "covered" layer is defined as one in which a clear structural difference between the nucleus and the surface can be confirmed by FE-SEM observation or EDX elemental analysis.

[0025] Specific examples of hydrophilic inorganic particles include silica sand, quartz, glass (natural or synthetic), celben, silicon dioxide, aluminum oxide, zirconium oxide and other metal oxide particles, and their hollow or solid forms.

[0026] Particle size of hydrophilic inorganic particles In this invention, the hydrophilic inorganic particles have a particle size larger than the film thickness of the first layer. The effects of this have already been described in the explanation of "Mechanism (Effect) that Provides Weather Resistance Degradation Suppression." The presence or absence of hydrophilic inorganic particles and their particle size can be measured by the following method and conditions. A cross-section of the coating film is cut out, fixed with resin embedding or the like, and then polished using a polishing device. A scanning electron microscope (SEM) is used to observe the entire polished cross-section at a magnification that allows the first layer to be seen (for example, 5000x for film thickness of 3-10 μm, 1000x for 10-50 μm, and 500x for thickness of 50 μm or more). The vertical length of the observed particles is defined as the particle diameter. If particles satisfying the condition of particle diameter > film thickness of the first layer are observed in any field of view, the first layer is determined to contain hydrophilic inorganic particles with a particle diameter larger than that film thickness. The largest particle diameter observed is then defined as the particle diameter of the hydrophilic inorganic particles.

[0027] In the present invention, hydrophilic inorganic particles having a particle diameter larger than the film thickness of the first layer may be primary particles or secondary particles formed by the aggregation of primary particles. Furthermore, the present invention does not exclude embodiments in which the first layer includes hydrophilic inorganic particles having a particle diameter smaller than the film thickness of the first layer, insofar as the first layer includes hydrophilic inorganic particles having a particle diameter larger than its film thickness.

[0028] Suitable range of particle size In the present invention, the particle size of the hydrophilic inorganic particles is not particularly limited as long as it is larger than the film thickness of the first layer, but the upper limit is preferably 20 times, 10 times, 5 times, 4 times, 3 times, or 2 times the film thickness of the first layer.

[0029] Concentration of hydrophilic inorganic particles contained in the coating film In the present invention, the concentration (by weight) of hydrophilic inorganic particles contained in the coating film is preferably more than 10% by mass and 50% by mass or less. More preferably, it is preferably 20% by mass or more and 50% by mass or less, and even more preferably 30% by mass or more and 50% by mass or less. As a result, the photocatalytic coating body according to the present invention can have a weather-resistant degradation suppression effect, as well as coating film strength, coating film hardness, water permeability, scratch resistance, and the like.

[0030] According to a preferred embodiment of the present invention, the first layer may contain an inorganic pigment. The inorganic pigment is added as an extender pigment or as a coloring pigment. The first layer may also contain inorganic particles other than hydrophilic inorganic particles having a particle size larger than the film thickness of the first layer as described above. These inorganic particles are added to form an uneven surface, for gloss control, or as a filler.

[0031] Film thickness of the first layer In the present invention, the film thickness of the first layer is not particularly limited, but is preferably 3 μm to 100 μm, more preferably 5 μm to 100 μm, and even more preferably 5 μm to 40 μm. By having a film thickness of 3 μm or more of the first layer, deterioration of the substrate due to reactive oxygen species generated from the photocatalyst and deterioration of the substrate due to ultraviolet rays can be prevented, and the photocatalytic coated body can maintain high weather resistance. Furthermore, by having a film thickness of 100 μm or less of the first layer, it is possible to prevent the occurrence of (mud) cracks and appearance defects such as clouding.

[0032] Method and conditions for measuring the film thickness of the first layer In this invention, the film thickness of the first layer is measured by the following method. Specifically, a cross-section of the coating film is cut out and polished using a polishing device. During polishing, the section may be fixed with resin or other materials as needed. A scanning electron microscope (SEM) is used, set to a magnification that allows the first layer to be observed (for example, 5000x for film thickness of 3-10 μm, 1000x for 10-50 μm, and 500x for thickness of 50 μm or more). Four fields of view are randomly selected from the entire polished cross-section and observed. Each of the four selected fields of view is divided horizontally into four equal parts, and the film thickness at the thinnest point in each of the four resulting blocks is measured and taken as the film thickness of each block. In this way, the film thickness is measured at a total of four points in each field of view, meaning that ultimately, the film thickness is measured at a total of 16 points across four fields of view. The average value of these measurements is taken as the film thickness of the first layer.

[0033] Method for forming the first layer In the present invention, the method for forming the first layer is not particularly limited as long as a stable layer can be formed on the substrate. For example, a coating composition may be prepared containing an organic resin, cerium oxide, hydrophilic inorganic particles having a particle size larger than the film thickness of the first layer, a solvent, and an optional additive, and this can be applied to the substrate and allowed to solidify and dry. The method for applying the coating composition can be appropriately selected, and for example, methods such as roller, spray, roll coater, flow coater, dip coat, pour coating, screen printing, electrodeposition, and vapor deposition can be used.

[0034] Second layer containing photocatalyst In the present invention, the second layer is a photocatalytic layer, which may be a photocatalytic layer already known. According to a preferred embodiment of the present invention, the photocatalytic activity of the second layer is preferably 5 nmol / L / min or more, as determined by the methylene blue decomposition activity measurement method specified in JIS R 1703-2:2014, in order to have sufficient activity and practical antifouling properties, and is more preferably 10 nmol / L / min or more, in order to have even higher antifouling properties. Furthermore, the upper limit of the photocatalytic activity of the second layer is preferably 30 nmol / L / min or less, as determined by the methylene blue decomposition activity measurement method specified in JIS R 1703-2:2014. In the present invention, the photocatalytic activity of the second layer is preferably 5 nmol / L / min or more and 30 nmol / L / min or less, as determined by the methylene blue decomposition activity measurement method specified in JIS R 1703-2:2014, and more preferably 5 nmol / L / min or more and 23 nmol / L / min or less.

[0035] In the present invention, the photocatalyst constituting the second layer is not limited as long as it is usable as a photocatalyst, but titanium dioxide is preferably used. In the present invention, titanium dioxide is available in various forms such as powder, sol, and solution, but any form is usable as long as it exhibits photocatalytic activity. In a preferred embodiment of the present invention, the photocatalytic particles preferably have an average particle size of 10 nm to 100 nm, and more preferably 10 nm to 60 nm. Within this range, weather resistance, harmful gas decomposition ability, and various desired film properties (ultraviolet absorption, transparency, film strength, etc.) are efficiently exhibited. Furthermore, by using a commercially available photocatalyst in sol form and reducing the particle size to 30 nm or less, preferably 20 nm or less, it is possible to obtain a photocatalytic layer with good transparency.

[0036] In this invention, the particle size of the photocatalyst is calculated as the average length of any 100 particles that fit within a 200,000x magnification field of view using a scanning electron microscope. While a perfect sphere is most preferred as the particle shape, approximately circular or elliptical shapes are also preferred, in which case the particle length is approximately calculated as ((major axis + minor axis) / 2).

[0037] In the present invention, the second layer may be formed by preparing a coating composition containing a photocatalyst, applying it to the first layer, and allowing it to solidify and dry. The method of applying the coating composition may be appropriately selected, and for example, methods such as roller, spray, roll coater, flow coater, dip coat, pour coating, screen printing, electrodeposition, and vapor deposition can be used.

[0038] The thickness of the second layer is not particularly limited, but is preferably 0.1 μm to 3 μm, and more preferably 0.5 μm to 1.5 μm.

[0039] According to a preferred embodiment of the present invention, the second layer contains inorganic particles. Suitable inorganic particles include single oxides such as silica, alumina, zirconia, ceria, yttria, boronia, magnesia, calcia, ferrite, amorphous titania, and hafnia, as well as composite oxides such as barium titanate and calcium silicate, with silica particles being particularly suitable. These inorganic oxides are preferably in the form of an aqueous colloid with water as the dispersion medium, or an organosol in which they are colloidally dispersed in a hydrophilic solvent such as ethyl alcohol, isopropyl alcohol, or ethylene glycol, with colloidal silica being particularly preferred. The particle size of the inorganic particles is preferably 10 nm or more and less than 40 nm in average particle size when in the form of an aqueous colloid or organosol, and more preferably 10 nm or more and 30 nm or less.

[0040] Here, the average particle size is calculated as the average length of any 100 particles that fit within the field of view at 200,000x magnification using a scanning electron microscope. A perfect sphere is most preferred as the particle shape, but approximately circular or elliptical shapes are also acceptable, in which case the particle length is approximately calculated as ((major axis + minor axis) / 2).

[0041] Furthermore, the second layer may contain a water-soluble inorganic amorphous substance, such as one or more selected from the group consisting of alkali silicates, alkali borosilicates, alkali zirconates, and alkali phosphates. These substances readily form a chemiadsorbent aqueous layer in the presence of water and can exhibit high and long-term hydrophilicity. Among these, alkali silicates are preferred, and more preferably, at least one of sodium silicate, potassium silicate, lithium silicate, and ammonium silicate. Generally, adhesion is considered to be strongest in the order of sodium silicate and potassium silicate, and water resistance is considered to be strongest in the order of ammonium silicate and lithium silicate, but considering film-forming properties, film hardness, water resistance, etc., it is more preferable to include lithium silicate.

[0042] The second layer may also contain other inorganic binders, such as hydrolyzable silicones. Hydrolyzable silicones are a general term for organosiloxanes having alkoxy groups and / or partially hydrolyzed condensates thereof. Tetrafunctional silicone compounds are commonly used as hydrolyzable silicones and are commercially available in the form of ethyl silicate 40 (oligomer, R is an ethyl group), ethyl silicate 48 (oligomer, R is an ethyl group), and methyl silicate 51 (oligomer, R is a methyl group) (all manufactured by Colcoat).

[0043] In the present invention, the content of photocatalytic particles in the second layer and the coating composition for forming it is generally preferably 1 part by mass or more and less than 50 parts by mass per 100 parts by mass of the total amount of photocatalytic particles and inorganic oxide particles, but can be appropriately selected considering performance such as photocatalytic activity, appearance, and durability. [Examples]

[0044] The present invention will be further described by the following examples, but the present invention is not limited to these examples.

[0045] material The following materials were prepared for the preparation of the photocatalytic coated body. The following materials were prepared for the first layer coating composition. (1) Organic resins • Resin 1: A water-based emulsion silicone-modified acrylic resin (solid content 35.0%) with a silicon content of 30% by mass relative to the solid content of the resin. • Resin 2: Silicon-free, water-based emulsion polyurethane resin (solids content 50.0%) (2) Cerium oxide (CeO2) • Ceria 1: Cerium oxide microparticle sol (a transparent sol in which microparticles with a primary particle size of 8 nm are highly dispersed, with a solid content of 10.0%) • Ceria 2: A suspension containing aggregates of Ceria 1 (2.0g of 1% dilute sulfuric acid was added to 20g of Ceria 1. The resulting precipitate was centrifuged at 2000 rpm for 10 minutes, the supernatant was removed, and it was mixed with 50g of deionized water. The above centrifugation, supernatant removal, and mixing with 50g of deionized water were repeated twice for washing, and a third centrifugation was performed to remove the supernatant, and 38g of deionized water was added to disperse the mixture. Solid content: 5.0%) • Ceria 3: Cerium oxide microparticle sol (a sol containing dispersed microparticles with an average particle size of 150 nm, determined by a laser diffraction particle size analyzer; solid content 10.0%) • Ceria 4: Cerium oxide microparticle suspension (a suspension containing microparticles with an average particle size of 300 nm, determined by a laser diffraction particle size analyzer, with a solid content of 10.0%) (3) Dispersion medium: Ion-exchanged water (4) Hydrophilic inorganic particles and hydrophobic organic particles (Hereafter, "hydrophilic inorganic particles" and "hydrophobic organic particles" may also be referred to as "hydrophilic inorganic particles" and "hydrophobic organic particles.") • Hydrophilic inorganic particles 1 Product name: Silica sand No. 8 (manufactured by Yamamori Tsuchimoto Mining Co., Ltd.) • Hydrophilic inorganic particles 2 Product name: Coarse silica powder (manufactured by Yamamori Tsuchimoto Mining Co., Ltd.) • Hydrophilic inorganic particles 3. Aluminum hydroxide. Product name: Low-soda aluminum hydroxide BW53 (manufactured by Nippon Light Metal Co., Ltd.) • Hydrophilic inorganic particles 4 Diatomaceous earth Product name: Diatomaceous earth FW-60 (manufactured by Tomoe Kogyo) • Hydrophilic inorganic particles 5 Talc Product name: Crown Talc DR (manufactured by Matsumura Sangyo Co., Ltd.) • Hydrophobic organic particles 1 Acrylic beads Product name: Art Pearl SE050T (manufactured by Negami Kogyo) (5) UV absorber: Hydroxyphenyltriazine-based UV absorber (UVA) (Solid content 40.0%) (6) Thickening agent: Alkaline swelling type viscosity modifier (solids content 25.0%) (7) Curing agent: Hydrolyzable silicone compound (solids content 100%)

[0046] The following materials were prepared for the coating composition for the second layer. (1) Photocatalyst: Titanium dioxide aqueous dispersion (anatase type, particle size: X90 = 72.5 nm by laser diffraction / scattering method (JIS Z 8825:2013), basic, solid content 17.5%) (2) Binder: Water-dispersible colloidal silica (manufactured by Nissan Chemical Industries, Ltd., product name: Snowtex 50T, solids content 50%) (3) Dispersion medium: Ion-exchanged water (4) Additives: Polyether-modified silicone surfactant (surfactant content 100%)

[0047] Preparation of the coating composition for the first layer Coating compositions 1 to 30 for the first layer were prepared by mixing (1) the organic resin, (2) cerium oxide, (3) the dispersion medium, (4) one of the hydrophilic inorganic particles 1 to 5 and hydrophobic organic particle 1, and the various additives (5) to (7) to the proportions shown in Table 1. (The "concentration of materials" shown in Table 1 refers to the proportion of each material to the total composition.) The total solid content concentration of materials (1) to (7) in each composition was set to 27% by mass for compositions 1 to 10 and to 26.5% by mass for compositions 11 to 30. Here, the solid content concentration refers to the mass % when the coating composition is dried at 105 to 110°C and reaches a constant weight. [Table 1]

[0048] Preparation of the coating composition for the second layer The above-mentioned (1) photocatalyst, (2) binder, (3) dispersion medium, and (4) additive were mixed to obtain the second layer coating compositions T1, T2, and T3 in the proportions shown in Table 2. (The "concentration of materials" shown in Table 2 refers to the proportion of each material to the total composition.) The total solid content concentration of the photocatalyst and binder in the second layer coating compositions T1, T2, and T3 was set to 5.5% by mass. Here, the total solid content concentration of the photocatalyst and binder refers to the mass % when the photocatalyst and binder are dried at 105-110°C and reach a constant weight, and the concentration in the composition calculated from their respective proportions. [Table 2]

[0049] Preparation of substrate I obtained siding boards that had been coated with epoxy sealer, painted them with acrylic silicone black enamel, and allowed them to dry completely to obtain the base material.

[0050] Fabrication of photocatalytic coated bodies The substrate obtained above is heated to a plate temperature of 60°C, and the first layer coating compositions 1-20 and 23-30 are applied to its surface at a rate of 150±50 g / m². 2 The coating was applied using an air spray at the specified amount and dried at 80°C for 5 minutes to form a first layer with a film thickness of 25 μm on the substrate. The substrate obtained above was then heated to a plate temperature of 60°C, and the first layer coating compositions 21 and 22 were applied to its surface at a rate of 60 ± 20 g / m². 2 The coating was applied using an air spray at the specified amount, and dried at 80°C for 5 minutes to form a first layer with a film thickness of 12 μm on the substrate.

[0051] Next, the substrate coated with the first layer is heated to a plate temperature of 60°C, and the coating composition for the second layer is applied to the surface of the first layer at a rate of 12.5±2.5 g / m². 2 The coating was applied using an air spray with the specified amount, and then allowed to air dry to form the second layer on top of the first layer. In this way, the photocatalytic coated bodies of Examples 1 to 35, as shown in Table 3, were obtained.

[0052] Measurement of particle size of hydrophilic inorganic particles or hydrophobic organic particles Hydrophilic inorganic particles contained in photocatalytic coatings in Examples 1-35 or hydrophobic organic particles The particle size was measured by the following method. Each photocatalytic coated material was cut into 1 cm square sections to obtain cross-sections that included the cross-sections of the first and second layers. After fixing these sections with resin embedding, the cross-sections were polished using a polishing device. A scanning electron microscope (SEM) was used to observe the entire polished cross-section at a magnification that allowed the first layer to be observed (5000x for film thicknesses of 3-10 μm, 1000x for 10-50 μm, and 500x for thicknesses of 50 μm or more). The vertical length of the observed particles was defined as the particle diameter, and the largest particle diameter observed was identified as the hydrophilic inorganic particle. or hydrophobic organic particles The particle size was set to [specify particle size]. The results are shown in Table 3.

[0053] Measurement of the film thickness of the first layer The film thickness of the first layer of the photocatalytic coated bodies in Examples 1-35 was measured by the following method. Each photocatalytic coated body was cut out to include cross-sections of the first and second layers, and sections were obtained. The cross-sections of the obtained sections were polished using a polishing device. A scanning electron microscope (SEM) was used, set to a magnification that allowed the first layer to be observed (5000x for film thicknesses of 3-10 μm, 1000x for 10-50 μm, and 500x for thicknesses of 50 μm or more). Four fields of view were randomly extracted from the entire polished cross-section and observed. Each of the four extracted fields of view was divided horizontally into four equal parts, and the film thickness at the thinnest point in each of the four resulting blocks was measured and taken as the film thickness of each block. In this way, the film thickness was measured at a total of four points in each field of view, and ultimately, the film thickness was measured at a total of 16 points across the four fields of view. The average value of these measurements was taken as the film thickness of the first layer. The results are shown in Table 3.

[0054] Measurement of the particle size of cerium oxide contained in the first layer The particle size of cerium oxide contained in the first layer of the photocatalytic coated bodies in Examples 1-35 was measured by the following method. Each photocatalytic coated material was cut into 1 cm square sections to obtain cross-sections, including the cross-sections of the first and second layers. The cross-sections of the obtained sections were polished using a polishing apparatus and an ion milling apparatus. The backscattered electron images of these cross-sections were observed using a scanning electron microscope (SEM) at a magnification that allowed for the observation of cerium oxide particles (50,000x or higher for particles less than 1 μm, 10,000x for particles between 1 and 3 μm, 5,000x for particles between 3 and 10 μm, 1,000x for particles between 10 and 50 μm, and 500x for particles larger than 50 μm) and at an accelerating voltage (3.0 kV). EDX analysis was performed to confirm whether the particles contained Ce and O. The length in the longitudinal direction of the observed particles was defined as the particle diameter, and the smallest particle diameter observed in five fields of view was defined as the particle diameter of the cerium oxide particles. If cerium oxide particles could not be visually observed by SEM, the presence of cerium oxide particles in the first layer was determined by detecting CeO2 by XRD in-plane measurement of the photocatalytic coating (2θ=28.46°, surface index (111)), and the particle size was judged to be smaller than the minimum cerium oxide particle size of 70 nm that could be measured in this example (less than 70 nm).

[0055] XRD was performed under conditions that allowed for the detection of substrate components in layers below the first layer, while obtaining a clear peak for cerium oxide in the first layer. The detailed measurement conditions are shown below. Analyzer: Rigaku SmartLAB X-ray source: CuKα (45kV, 200mA) Input optical system: CBO Detector: HyPix-3000 Incident angle: 0.2° In-plane incidence parallel slit: 1.0° Long side limiting slit: 10mm In-plane light-receiving parallel slit: 0.0114° Scan axis: 2θχ / φ Scan range: 10-70° Scan speed: 0.2°min ―1 Step width: 0.048°

[0056] The results are shown in Table 3. In the photocatalytic coated bodies of Examples 15, 20, and 25 containing ceria 4, the particle size of cerium oxide was 70 nm. In the photocatalytic coated bodies of the examples containing ceria 1 to 3, although cerium oxide particles could not be visually recognized by SEM, CeO2 could be detected by XRD in-plane measurement. Therefore, as described above, it was determined that the particle size of cerium oxide was smaller than 70 nm (less than 70 nm).

[0057] Evaluation of weather resistance of photocatalytic coatings The weather resistance (degree of discoloration) of the photocatalytic coated bodies of Examples 1 to 35 was evaluated by the following procedures 1 to 5. 1. Color difference measurement (initial): Using the SCE method, for the photocatalytic coated bodies of Examples 1 to 35, the data of the L * a * b * color space, that is, L * (initial), a * (initial), and b * (initial) were obtained. 2. Conducting the weather resistance test and preparing the test specimens: The photocatalytic coated bodies of Examples 1 to 10 and Examples 26 to 35 were left standing at 23 ± 1°C and 50 ± 5% RH for 24 hours or more, and the cycle of irradiation and rainfall was repeated using a metal halide weather meter (manufactured by Suga Test Instruments Co., Ltd.) to prepare Test Specimens 1 to 10 and Test Specimens 26 to 35 with an integrated energy of 1080 MJ / m 2 . Also, the photocatalytic coated bodies of Examples 11 to 25 were left standing at 23 ± 1°C and 50 ± 5% RH for 24 hours or more, and the cycle of irradiation and rainfall was repeated using a xenon weather meter (manufactured by Toyo Seiki Seisakusho Co., Ltd.) to prepare Test Specimens 11 to 25 with an integrated energy of 115.2 MJ / m 2 . 3. Color difference measurement (after the weather resistance test): Using the SCE method, for Test Specimens 1 to 20, the data of the L* a* b* color space, that is, L * (after the weather resistance test), a * (after the weather resistance test), and b * (after the weather resistance test) were obtained. 4. Calculation of the degree of discoloration: The value of the color difference ΔE * ab was calculated using the following calculation formula.

Equation

[0058] ΔE of the photocatalytic coated material in Example 1 * ab (with Ce) and ΔE of the photocatalytic coating in Example 2 * Comparison with ab (without Ce); Comparison of ΔE*ab (with Ce) of the photocatalytic coating in Example 3 and ΔE*ab (without Ce) of the photocatalytic coating in Example 4; ΔE of the photocatalytic coating in Example 5 * ab (with Ce) and ΔE of the photocatalytic coating in Example 6* Comparison with ab (without Ce); ΔE of the photocatalytic coated body in Example 7 * ab (with Ce) and ΔE of the photocatalytic coating in Example 8 * Comparison with ab (without Ce); ΔE of the photocatalytic coated body in Example 9 * ab (with Ce) and ΔE of the photocatalytic coating in Example 10 * The same procedure was followed for comparison with ab(without Ce), and the determination was made accordingly. ΔE of photocatalytic coated bodies in Examples 12-15 * ab (with Ce) and ΔE of the photocatalytic coating in Example 11 * Comparison with ab (without Ce); ΔE of photocatalytic coated bodies in Examples 17-20 * ab (with Ce) and ΔE of the photocatalytic coating in Example 16 * Comparison with ab (without Ce); ΔE of photocatalytic coated bodies in Examples 22-25 * ab (with Ce) and ΔE of the photocatalytic coating in Example 21 * The same procedure was followed for comparison with ab(without Ce), and the determination was made accordingly. ΔE of the photocatalytic coated material in Example 26 * ab (with Ce) and ΔE of the photocatalytic coating in Example 27 * Comparison with ab (without Ce); Comparison of ΔE*ab (with Ce) of the photocatalytic coating in Example 28 and ΔE*ab (without Ce) of the photocatalytic coating in Example 29; ΔE of the photocatalytic coating in Example 30 * ab (with Ce) and ΔE of the photocatalytic coating in Example 31 * Comparison with ab (without Ce); ΔE of the photocatalytic coated body in Example 32 * ab (with Ce) and ΔE of the photocatalytic coating in Example 33 * Comparison with ab (without Ce); ΔE of the photocatalytic coated body in Example 34 * ab (with Ce) and ΔE of the photocatalytic coating in Example 35 * The same procedure was followed for comparison with ab(without Ce), and the determination was made accordingly. The results are shown in Table 3.

[0059] [Table 3]

[0060] Evaluation results The results shown in Table 3 confirm that adding hydrophilic inorganic particles with a particle size larger than the film thickness to the first layer further improves the weather resistance effect brought about by the addition of cerium oxide. This remarkable effect will be discussed with reference to Figures 2 and 3. Figure 2 shows a scanning electron microscope (SEM) image of the cross-section of the photocatalytic coating in Example 3, and Figure 3 shows an SEM image of the cross-section of the photocatalytic coating in Example 9. In the photocatalytic coating of Example 3, which includes hydrophilic inorganic particles 1 (indicated by reference numeral 5 in Figure 2) having a particle size larger than the film thickness of the first layer (25 μm), the inorganic particles extend into the interior of both the first and second layers. Therefore, at the interface formed between the inorganic particles and the second layer, it is considered that the inorganic particles and the second layer are in almost complete contact. As a result, it is thought that reactive oxygen species generated in the second layer travel through the interface to the interior of the first layer, and their capture and detoxification by cerium oxide are promoted. On the other hand, in the photocatalytic coating of Example 9, which includes hydrophilic inorganic particles 2 (indicated by reference numeral 5 in Figure 3) having a particle size smaller than the film thickness of the first layer (25 μm) in the first layer, the inorganic particles do not extend into the interior of the second layer, resulting in a structure where the inorganic particles and the second layer are not in contact. As a result, no interface is created that allows the reactive oxygen species generated in the second layer to reach the interior of the first layer, and their capture and detoxification by cerium oxide only occurs near the surface of the first layer. Therefore, it is considered that the weather resistance improvement effect, i.e., the weather resistance degradation suppression effect, is smaller compared to the photocatalytic coating of Example 3. [Explanation of Symbols]

[0061] 1: Base material 2: 1st layer 3:Second layer 4: Cerium oxide 5: Hydrophilic inorganic particles 6: Newly generated interface

Claims

1. A photocatalytic coating comprising a substrate, a first layer containing an organic resin on the surface of the substrate, and a second layer containing a photocatalyst on the side of the first layer opposite to the substrate side, The first layer is made of cerium oxide (CeO ２ ) and further containing hydrophilic inorganic particles, The particle size of the hydrophilic inorganic particles is larger than the film thickness of the first layer. A photocatalytic coated body characterized by the above features.

2. The photocatalytic coating according to claim 1, wherein the cerium oxide is in the form of particles, and its particle size is smaller than that of the hydrophilic inorganic particles.

3. The photocatalytic coating according to claim 1 or 2, wherein the amount of cerium oxide contained in the first layer is 0.1 to 2% by mass relative to the solid content of the organic resin.

4. The photocatalytic coating according to claim 1 or 2, wherein the thickness of the first layer is 3 to 100 μm.

5. The photocatalytic coating according to claim 3, wherein the thickness of the first layer is 3 to 100 μm.

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