Coating composition and photocatalytic coating film

Abstract

To provide a photocatalytic coating film that exhibits excellent durability regardless of the surface condition of various products, and a coating composition used therefor. [Solution] The coating composition containing the photocatalyst contains peroxotitanic acid and ammonium ions, titanium oxide microparticles dispersed in water, and an emulsion-type acrylic adhesive in which an acrylic copolymer having a weight average molecular weight of 300,000 or more and 800,000 or less is dispersed in water, in a proportion of 0.15% by weight to 3.0% by weight relative to the total weight of the coating composition.

Description

[Technical Field]

[0001] The present invention relates to a coating composition containing a photocatalyst and a photocatalytic coating film using the same. [Background technology]

[0002] Photocatalysts are substances that exhibit catalytic activity when irradiated with light, and the active oxygen and hydroxyl radicals generated by the catalytic activity decompose organic matter such as bacteria and viruses. Focusing on this, photocatalytic coating films containing photocatalysts are sometimes formed on the surfaces of various products that come into contact with human fingers (hereinafter also referred to as "substrate surfaces"). Known coating compositions used to form photocatalytic coating films include those described in Patent Document 1, for example.

[0003] In this coating composition, titanium oxide fine particles serving as a photocatalyst are dispersed in water, and a binder that binds the titanium oxide fine particles to the substrate surface is not included. Therefore, if the substrate surface has minute irregularities, when the coating composition is applied to the substrate surface, the titanium oxide fine particles will enter the recesses and harden in this state (i.e., by the anchoring effect), thereby adhering to the substrate surface. On the other hand, if the product portion is made of, for example, resin and the substrate surface is smooth, the titanium oxide fine particles cannot be effectively adhered, resulting in the photocatalytic coating film being easily peeled off and having poor durability. In addition, to improve the adhesion of the titanium oxide fine particles to the substrate surface, a base film containing, for example, a binder can be formed on the substrate surface, and then a coating composition containing titanium oxide fine particles can be applied on this base film to form a photocatalytic coating film, but this makes the coating process complicated. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 2875993 Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above, an object of the present invention is to provide a photocatalytic coating film that exhibits excellent durability regardless of the surface condition of various products, and a coating composition to be used therefor. [Means for solving the problem]

[0006] To solve the above problems, the photocatalyst-containing coating composition of the present invention is characterized by containing peroxotitanic acid and ammonium ions, titanium oxide fine particles dispersed in water, and an emulsion-type acrylic pressure-sensitive adhesive in which an acrylic copolymer having a weight-average molecular weight of 300,000 or more and 800,000 or less is dispersed in water, in a proportion of 0.15% to 3.0% by weight based on the total weight of the coating composition. Note that in the present invention, titanium oxide fine particles refer to those having an average particle size of 50 nm or less (typically 4 nm to 20 nm).

[0007] In addition, in order to solve the above problems, the coating composition containing the photocatalyst of the present invention is characterized by containing peroxotitanic acid and ammonium ions, titanium oxide microparticles dispersed in water, and an emulsion-type acrylic adhesive in which an acrylic copolymer having a polymerization average molecular weight of 300,000 or more and 800,000 or less is dispersed in water, in a ratio of 0.01 to 7.5 parts by weight per 1 part by weight of titanium oxide.

[0008] The photocatalytic coating film of the present invention is characterized by being formed from the above-mentioned coating composition. As a result of intensive research, the present inventors have discovered the following: Specifically, the inventors discovered that a photocatalytic coating film obtained by blending a coating composition containing peroxotitanic acid and ammonium ions, in which titanium oxide microparticles are dispersed, with an emulsion-type acrylic pressure-sensitive adhesive, in which an acrylic copolymer having a weight-average molecular weight of 300,000 or more and 800,000 or less is dispersed in water, at 0.15 to 3.0 wt % based on the total weight of the coating composition, and then applying the blended composition exhibits improved compactness. Based on this finding, the photocatalytic coating film obtained by applying the above-mentioned coating composition exhibits enhanced adhesion between titanium oxide microparticles and improved adhesion of the titanium oxide microparticles to the substrate surface, resulting in a dramatic improvement in the hardness of the photocatalytic coating film, compared to a coating film that does not contain the acrylic pressure-sensitive adhesive. The photocatalytic coating film of the present invention, even when applied to a resin substrate surface, exhibits a hardness of 4H or more in the scratch hardness (pencil method) test based on JIS K 5600-5-4, demonstrating excellent durability. Furthermore, if the coating composition of the present invention is applied directly to the surface of a substrate, a photocatalytic coating film having the above-mentioned hardness can be obtained, eliminating the need to form a base film, etc., and making the coating process less complicated. Note that the acrylic adhesive contained in the coating composition of the present invention does not bond the titanium oxide fine particles to the surface of the substrate, but rather serves to increase the strength of the titanium oxide fine particles themselves and to harden them more firmly.

[0009] Furthermore, the photocatalytic coating film of the present invention does not suffer from the problem of titanium oxide fine particles in the photocatalytic coating film being buried in the binder, and the titanium oxide fine particles are exposed to the coating film surface. As a result, the surface of the titanium oxide fine particles is more susceptible to light irradiation, and the contact area between the surface of the titanium oxide fine particles and organic matter such as bacteria and viruses is increased, thereby improving the photocatalytic activity of the photocatalytic coating film. Furthermore, the photocatalytic coating film of the present invention is a transparent film with a visible light transmittance of 88% or more, and even when applied to a substrate surface that has been printed or colored, the visibility of the printing or the like on the substrate surface is not impaired. In this invention, the binder refers to an organic binder whose main component is an organic material such as acrylic, epoxy, or urethane, or an inorganic binder whose main component is an inorganic material such as silica, alumina, or zinc oxide.

[0010] The coating composition of the present invention preferably further contains at least one of a metal other than titanium oxide, a metal compound, and a metal ion. In this case, for example, the metal compound may be a copper compound such as copper oxide (CuO), or the metal ion may be a silver ion (Ag + A photocatalytic coating film obtained by applying a coating composition containing titanium dioxide can decompose organic matter such as bacteria and viruses by copper compounds and silver ions even when not exposed to light. Furthermore, by including a metal or metal compound other than titanium dioxide, the photocatalytic activity of titanium dioxide can be enhanced in the visible light region. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a spectrum showing the visible light transmittance of the photocatalytic coating film of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described using as an example a coating composition containing titanium oxide fine particles dispersed in water as a photocatalyst and a photocatalytic coating film obtained by applying the same. Titanium oxide fine particles refer to particles having an average particle size of 50 nm or less (typical particle size is 4 nm to 20 nm). If the particle size of titanium oxide fine particles exceeds 50 nm, problems such as the titanium oxide fine particles becoming more likely to aggregate and precipitate will occur. Furthermore, the average particle size of titanium oxide fine particles can be determined by known methods, such as capturing and analyzing images of titanium oxide fine particles using a transmission electron microscope, and therefore a detailed description thereof will be omitted.

[0013] To obtain the coating composition, a titanium oxide microparticle dispersion containing peroxotitanic acid and ammonium ions and containing dispersed titanium oxide microparticles is first prepared. The titanium oxide microparticle dispersion can be prepared, for example, using the method described in the above-mentioned patent document (Japanese Patent No. 2875993). However, the titanium oxide microparticle dispersion is not limited to this method; other methods or commercially available titanium oxide microparticle dispersions can also be used. Examples of titanium-containing materials that can be used as the raw material for titanium oxide microparticles include dispersions containing dispersed microparticles such as titanium hydroxide, titanium oxide, and titanium hydroxide gel. When titanium hydroxide gel is used as the raw material, it can be prepared by reacting an aqueous solution of an inorganic titanium compound such as titanium chloride or titanium sulfate with ammonia or sodium hydroxide. The titanium hydroxide gel and titanium oxide microparticles in the dispersion are then separated, and the suspension containing these microparticles is mixed with aqueous hydrogen peroxide to react with the titanium hydroxide and titanium oxide, thereby preparing a peroxotitanic acid solution.

[0014] After decomposing the unreacted hydrogen peroxide in the solution, the solution is heated at 95°C to 100°C for 4 to 8 hours. This generates crystal nuclei of anatase-type titanium oxide having peroxo groups, resulting in a titanium oxide microparticle dispersion in which anatase-type titanium oxide microparticles whose surfaces are modified with peroxo groups are dispersed in water. The pH (e.g., 7 to 8.6) and ionic strength (e.g., so that the ammonium ion concentration is in the range of 100 ppm to 500 ppm) of the titanium oxide microparticle dispersion are adjusted as appropriate. The resulting titanium oxide microparticle dispersion contains peroxotitanic acid and ammonium ions, with at least a portion of the peroxotitanic acid present as a peroxotitanic acid complex coordinated with ammonium ions. This peroxotitanic acid complex carries an overall positive charge, and this charge causes the titanium oxide microparticles to which the peroxotitanic acid complex is adsorbed to repel each other, preventing the titanium oxide microparticles from aggregating and ensuring stable dispersion in water. Therefore, when preparing a titanium oxide microparticle dispersion using the above method, auxiliary agents such as dispersants and organic solvents for dispersing titanium oxide microparticles in water are not required (in other words, the titanium oxide microparticle dispersion obtained by the above method does not contain any special auxiliary agents other than water.) Furthermore, the coating composition of the present invention obtained using the titanium oxide microparticle dispersion preferably contains peroxotitanic acid in the range of 0.09 wt % to 0.4 wt % based on the total weight of the coating composition, and preferably contains titanium oxide microparticles (titanium oxide) in the range of 0.4 wt % to 13.4 wt % based on the total weight of the coating composition.

[0015] Next, an acrylic adhesive is mixed with the titanium oxide microparticle dispersion to obtain a coating composition. Examples of acrylic adhesives that can be used include emulsion-type acrylic adhesives in which an acrylic copolymer is dispersed in a solvent such as an aqueous medium (e.g., Fujikura Kasei Co., Ltd., product names "LKG-1101," "LKG-1102," "LKG-1104," and "LKG-1202A"; DIC Corporation, product names "Boncoat W-26" and "Boncoat W-386"; Toagosei Co., Ltd., product name "HV-C9500"). In this case, the molecular weight (weight average molecular weight) of the acrylic copolymer contained in the acrylic adhesive is preferably in the range of 300,000 to 800,000. If the molecular weight of the acrylic copolymer is less than 300,000, sufficient adhesion is not obtained, and the strength between the titanium oxide microparticles is not enhanced. Consequently, the hardness of the photocatalytic coating film obtained by applying this is less than 4H. On the other hand, if the molecular weight of the acrylic copolymer exceeds 800,000, the titanium dioxide particles in the coating composition are more likely to condense and precipitate, resulting in a photocatalytic coating film with a hardness of no more than 4H. Furthermore, polyacrylates, such as sodium polyacrylate and potassium polyacrylate, are preferred as the acrylic copolymers contained in the acrylic adhesive. The pH of emulsion-type acrylic adhesives is preferably in the neutral range (7 to 8.6). When using emulsion-type acrylic adhesives containing cationic or anionic acrylic copolymers, or emulsion-type acrylic adhesives based on styrene-acrylic acid copolymers or acrylic esters, which are more polar than polyacrylates, or emulsion-type acrylic adhesives containing organic solvents such as alcohols or dispersants, mixing the acrylic adhesive may induce precipitation of titanium dioxide particles.

[0016] Furthermore, the concentration of the acrylic adhesive in the coating composition is preferably in the range of 0.15 wt% to 3.0 wt% based on the total weight of the coating composition. If the concentration of the acrylic adhesive is less than 0.15 wt% based on the total weight of the coating composition, the hardness of the photocatalytic coating film obtained by applying this coating composition will not be 4H or higher. On the other hand, if the concentration of the acrylic adhesive exceeds 3.0 wt% based on the total weight of the coating composition, condensation and precipitation of the titanium oxide fine particles in the coating composition will occur, and the hardness of the photocatalytic coating film obtained by applying this coating composition will not be 4H or higher. Furthermore, the photocatalytic coating film obtained by applying this coating composition will have the disadvantage of becoming cloudy.

[0017] When mixing the titanium dioxide microparticle dispersion with an acrylic pressure-sensitive adhesive, additives such as insoluble solid particles, metals and metal compounds other than titanium dioxide, metal ions, and surfactants for improving wettability with the substrate surface can be added. Examples of metals and metal compounds that can be added include at least one of titanium nitride (TiN), titanium carbide (TiC), copper (Cu), silver (Ag), gold (Au), aluminum (Al), iron (Fe), zinc (Zn), nickel (Ni), niobium (Nb), cobalt (Co), manganese (Mn), and zirconium (Zr), as well as metal compounds such as oxides, nitrides, and carbonates of these metals. Examples of metal ions that can be added include at least one of copper ions, silver ions, gold ions, aluminum ions, iron ions, zinc ions, nickel ions, niobium ions, cobalt ions, manganese ions, and zirconium ions, as well as complexes containing these metal ions. These additives can be added to and mixed with the titanium oxide fine particle dispersion before mixing with the acrylic adhesive or with the coating composition already mixed with the acrylic adhesive.

[0018] When the coating composition containing the acrylic adhesive is obtained as described above, it can be applied to the surface of a substrate to obtain a photocatalytic coating film. Specifically, the coating composition containing the acrylic adhesive is applied to the surface of a substrate at a rate of 20 ml / m. 2 ~40ml / m 2The coating composition is applied to the surface of the substrate so that the coating composition is uniform. For example, a spray coater is used to apply the coating composition, but the application method is not limited to this. After the coating composition is applied to the surface of the substrate, the coating composition is dried to form a photocatalytic coating film on the surface of the substrate. The photocatalytic coating film thus obtained has a hardness of 4H or more in the scratch hardness (pencil method) test based on JIS K 5600-5-4. The drying method may be a known method such as drying at room temperature or using a dryer.

[0019] As explained above, according to this embodiment, the emulsion-type acrylic pressure-sensitive adhesive, in which an acrylic copolymer having a polymerization average molecular weight of 300,000 or more and 800,000 or less is dispersed in water, is contained in a proportion of 0.15 wt % to 3.0 wt % relative to the total weight of the coating composition, and the photocatalytic coating film obtained by applying the coating composition of this embodiment has a hardness of 4H or more and exhibits excellent durability, regardless of the surface condition of the coated product. Furthermore, if the coating composition is applied directly to the surface of a substrate, a photocatalytic coating film having a hardness of 4H or more can be obtained, so the coating process does not become complicated.

[0020] Furthermore, the coating composition of this embodiment and the photocatalytic coating film obtained by applying the same do not contain a binder, and the surface of the titanium oxide fine particles is exposed. This makes the surface of the titanium oxide fine particles more susceptible to light irradiation, and increases the contact area between the surface of the titanium oxide fine particles and organic matter such as bacteria and viruses, thereby improving the photocatalytic action of the photocatalytic coating film. Furthermore, because this photocatalytic coating film is a transparent film with a visible light transmittance of 88% or more, the visibility of the printing, etc. on the substrate surface is not impaired even when the photocatalytic coating film is applied to the surface of a substrate that has been printed, colored, etc.

[0021] In addition, the coating composition contains silver ions (Ag +), the photocatalytic coating film obtained by applying the coating composition can decompose organic matter such as bacteria and viruses by silver ions, etc., even when not exposed to light. Furthermore, by including a metal or metal compound other than titanium oxide, the photocatalytic action of titanium oxide can be enhanced in the visible light region. Examples and comparative examples of the present invention will be described below.

[0022] [Example 1] 110 ml of 2.5 wt. % ammonia water was added dropwise to 1000 ml of 0.6 wt. % titanium tetrachloride aqueous solution, and the precipitated titanium hydroxide was separated. The separated titanium hydroxide was suspended in 180 ml of distilled water, and 20 ml of 30 wt. % hydrogen peroxide was added to this suspension to obtain peroxotitanic acid. After decomposing the unreacted hydrogen peroxide in the solution, the solution was heated at 100°C for 6 hours. At this time, ammonia water was added dropwise as needed to adjust the pH and ammonium ion concentration. This resulted in a titanium oxide microparticle dispersion containing 1.11 wt. % titanium oxide by solids, with a peroxotitanic acid concentration of 0.23 wt. %, an ammonium ion concentration of 300 ppm, and an average particle size of titanium oxide microparticles of 20 nm or less. Next, 18 ml of distilled water was added to 72 ml of this titanium oxide microparticle dispersion, and 10 ml of emulsion-type acrylic adhesive (manufactured by Fujikura Kasei Co., Ltd., product name "LKG-1101", an acrylic copolymer solution with a weight average molecular weight of 430,000) adjusted to 20% by weight with distilled water was mixed to prepare a coating composition containing 0.17% by weight of peroxotitanic acid and 0.8% by weight of titanium oxide in solid content relative to the total weight of the coating composition, and also containing 2.0% by weight of emulsion-type acrylic adhesive relative to the total weight of the coating composition. Then, a 5 cm square ABS resin substrate was used as the base material, and the above coating composition was applied to one side of the substrate at 30 ml / m. 2After coating so that the coating was as follows, it was dried at room temperature for 2 hours to obtain a photocatalytic coating film with a thickness of approximately 0.1 μm. A plurality of ABS resin substrates with the photocatalytic coating film thus formed were prepared, and these were used as test pieces to evaluate the pencil hardness (Uni, Mitsubishi Pencil Co., Ltd.) according to JIS K 5600-5-4. The hardness of the photocatalytic coating film was found to be 4H.

[0023] The coating composition was applied to one side of a white tempered glass plate (thickness: 0.1 cm) at 30 ml / m 2 After coating so that the coating composition was applied, the glass plate was dried at room temperature for 2 hours to obtain a photocatalytic coating film with a thickness of approximately 0.1 μm. The visible light transmittance of the glass plate on which this photocatalytic coating film was formed was measured. The measured spectrum is shown by the solid line in Figure 1. The average transmittance of visible light (380 nm to 780 nm) obtained from the spectrum in Figure 1 was 88%. The spectrum of the visible light transmittance of a white tempered glass plate before application of the coating composition is shown by the dashed-dotted line in Figure 1. The average transmittance of visible light (380 nm to 780 nm) obtained from the spectrum in Figure 1 was 90%.

[0024] [Example 2] 72 ml of titanium oxide microparticle dispersion was mixed with 0.28 wt. % silver ions (Ag + A coating composition was prepared in the same manner as in Example 1 above, except that 10 ml of an emulsion-type acrylic adhesive (20 wt%) was mixed with 18 ml of water (i.e., the silver ion concentration in the coating composition was 0.05 wt%). Furthermore, using this coating composition, test pieces were prepared in the same manner as in Example 1 above, and the pencil hardness was evaluated, resulting in a hardness of 4H. Furthermore, using this coating composition, glass plates on which a photocatalytic coating film was formed were prepared in the same manner as in Example 1 above, and their visible light transmittance was measured, resulting in an average transmittance of 88% or more. Furthermore, the test pieces were evaluated for antibacterial and antiviral properties under the following conditions. <Antibacterial test> The antibacterial test was carried out by a film adhesion method in accordance with the antibacterial test method of JIS Z 2801:2010. Specifically, E. coli solution was dropped onto the test piece and onto an ABS resin substrate not coated with the coating composition, respectively, as a test bacterial solution, and then cultured for 24 hours. Then, the "log (per 1 cm of the ABS resin substrate not coated with the coating composition)" was calculated. 2 Number of viable bacteria after incubation per 1cm test piece) - log( 2 The antibacterial activity value of the test piece was calculated from the formula "number of viable bacteria after incubation per sample," and was found to be 6.1. Note that an antibacterial activity value of 2.0 or higher is considered to have antibacterial properties. <Antiviral activity test> The antiviral activity test was carried out by the film adhesion method in accordance with the antibacterial test method of ISO 21702. Specifically, an influenza virus suspension was dropped onto the test piece and onto an ABS resin substrate not coated with the coating composition, respectively, as a test virus solution, and then the test pieces were left to stand for 24 hours. The virus infectivity (PFU / cm) of the ABS resin substrate not coated with the coating composition after standing for 24 hours was measured. 2 ) and the virus infectivity (PFU / cm) after leaving the test piece for 24 hours 2 The antiviral activity value of the test piece was calculated from the difference between the average of the common logarithm of the value of the antiviral activity value of the test piece and the value of the common logarithm of the value of the antiviral activity value of the test piece. The antiviral activity value of the test piece was 4.3. An antiviral activity value of 2.0 or higher is considered to have antiviral properties.

[0025] [Comparative Example 1] A coating composition was prepared in the same manner as in Example 1 above, except that 10 ml of distilled water was mixed with 72 ml of titanium oxide microparticle dispersion liquid to which 18 ml of distilled water was added instead of the emulsion-type acrylic adhesive (i.e., the coating composition did not contain an emulsion-type acrylic adhesive). Furthermore, using this coating composition, test pieces were prepared in the same manner as in Example 1 above, and the pencil hardness was evaluated, resulting in a hardness of 2H.

[0026] Comparative Example 2 A coating composition was prepared in the same manner as in Example 1 above, except that 0.6 ml of an emulsion-type acrylic adhesive adjusted to 2.0 wt % with distilled water was mixed with 72 ml of titanium oxide microparticle dispersion liquid and 22 ml of distilled water (i.e., the emulsion-type acrylic adhesive was contained in an amount of 0.12 wt % based on the total weight of the coating composition). Furthermore, a test piece was prepared using this coating composition in the same manner as in Example 1 above, and the pencil hardness was evaluated, resulting in a hardness of 2H.

[0027] [Example 3] A coating composition was prepared in the same manner as in Example 1 above, except that 7.5 ml of an emulsion-type acrylic adhesive adjusted to 2.0 wt % with distilled water was mixed with 72 ml of titanium oxide microparticle dispersion liquid and 20.5 ml of distilled water (i.e., the emulsion-type acrylic adhesive was contained in an amount of 0.15 wt % based on the total weight of the coating composition). Furthermore, using this coating composition, test pieces were prepared in the same manner as in Example 1 above, and the pencil hardness was evaluated, resulting in a hardness of 4H. Furthermore, using this coating composition, a glass plate on which a photocatalytic coating film was formed was prepared in the same manner as in Example 1 above, and its visible light transmittance was measured, resulting in an average transmittance of 88% or more.

[0028] [Example 4] A coating composition was prepared in the same manner as in Example 1 above, except that 2.5 ml of an emulsion-type acrylic adhesive (20 wt %) was mixed with 72 ml of titanium oxide microparticle dispersion and 25.5 ml of distilled water (i.e., the emulsion-type acrylic adhesive was contained in an amount of 0.5 wt % based on the total weight of the coating composition). Furthermore, a test piece was prepared using this coating composition in the same manner as in Example 1 above, and the pencil hardness was evaluated; the hardness was found to be 4H.

[0029] [Example 5] A coating composition was prepared in the same manner as in Example 1 above, except that 15 ml of an emulsion-type acrylic adhesive (20 wt %) was mixed with 72 ml of titanium oxide microparticle dispersion and 13 ml of distilled water (i.e., the emulsion-type acrylic adhesive was contained in an amount of 3.0 wt % based on the total weight of the coating composition). Furthermore, a test piece was prepared using this coating composition in the same manner as in Example 1 above, and the pencil hardness was evaluated; the hardness was found to be 4H.

[0030] Comparative Example 3 A coating composition was prepared in the same manner as in Example 1 above, except that 16 ml of a 20 wt % emulsion-type acrylic adhesive was mixed with 72 ml of titanium oxide microparticle dispersion and 12 ml of distilled water (i.e., the emulsion-type acrylic adhesive was contained in an amount of 3.2 wt % based on the total weight of the coating composition). It was confirmed that the titanium oxide microparticles in the coating composition aggregated and precipitated. Furthermore, when a test piece was prepared using this coating composition in the same manner as in Example 1 above, the resulting photocatalytic coating film was opaque, and when its pencil hardness was evaluated, it was found to have a hardness of 2H.

[0031] Comparative Example 4 A coating composition was prepared in the same manner as in Example 1 above, except that an emulsion-type acrylic adhesive (manufactured by Taisei Fine Chemical Co., Ltd., product name "1HY-3025", an acrylic copolymer solution with a weight average molecular weight of 250,000) adjusted to 20% by weight with distilled water was used as the emulsion-type acrylic adhesive. Furthermore, a test piece was prepared using this coating composition in the same manner as in Example 1 above, and the pencil hardness was evaluated; the hardness was found to be 2H.

[0032] [Example 6] A coating composition was prepared in the same manner as in Example 1 above, except that an emulsion-type acrylic adhesive (manufactured by Fujikura Kasei Co., Ltd., product name "LKG-1104", an acrylic copolymer solution with a weight average molecular weight of 300,000) adjusted to 20% by weight with distilled water was used as the emulsion-type acrylic adhesive. A coating composition was prepared in the same manner as in Example 1 above. Furthermore, a test piece was prepared using this coating composition in the same manner as in Example 1 above, and the pencil hardness was evaluated; the hardness was 4H.

[0033] [Example 7] A coating composition was prepared in the same manner as in Example 1 above, except that an emulsion-type acrylic adhesive (manufactured by Fujikura Kasei Co., Ltd., product name "LKG-1202A", an acrylic copolymer solution with a weight average molecular weight of 600,000) adjusted to 20% by weight with distilled water was used as the emulsion-type acrylic adhesive. A coating composition was prepared in the same manner as in Example 1 above. Furthermore, a test piece was prepared using this coating composition in the same manner as in Example 1 above, and the pencil hardness was evaluated; the hardness was 4H.

[0034] [Example 8] A coating composition was prepared in the same manner as in Example 1 above, except that an emulsion-type acrylic pressure-sensitive adhesive (manufactured by Fujikura Kasei Co., Ltd., product name "LKG-1102", an acrylic copolymer solution with a weight average molecular weight of 770,000) adjusted to 20% by weight with distilled water was used as the emulsion-type acrylic pressure-sensitive adhesive. A coating composition was prepared in the same manner as in Example 1 above. Furthermore, a test piece was prepared using this coating composition in the same manner as in Example 1 above, and the pencil hardness was evaluated; the hardness was found to be 4H.

[0035] Comparative Example 5 A coating composition was prepared in the same manner as in Example 1 above, except that an emulsion-type acrylic adhesive (manufactured by Fujikura Kasei Co., Ltd., product name "LKG-1008A," an acrylic copolymer solution with a weight average molecular weight of 1,000,000) adjusted to 20% by weight with distilled water was used as the emulsion-type acrylic adhesive. It was confirmed that titanium oxide fine particles in the coating composition aggregated and precipitated. Furthermore, when a test piece was prepared using this coating composition in the same manner as in Example 1 above, the resulting photocatalytic coating film was opaque, and when its pencil hardness was evaluated, it was found to have a hardness of 2H.

[0036] [Example 9] A coating composition was prepared in the same manner as in Example 1 above, except that 10 ml of an emulsion-type acrylic adhesive (20 wt%) was mixed with 40 ml of titanium oxide microparticle dispersion and 50 ml of distilled water (i.e., containing 0.09 wt% peroxotitanic acid in solids relative to the total weight of the coating composition and 0.4 wt% titanium oxide in solids relative to the total weight of the coating composition). Furthermore, using this coating composition, test pieces were prepared in the same manner as in Example 1 above, and the pencil hardness was evaluated. The hardness was 4H. Furthermore, using this coating composition, a glass plate on which a photocatalytic coating film was formed was prepared in the same manner as in Example 1 above, and its visible light transmittance was measured. The average transmittance was 88% or more.

[0037] [Example 10] A coating composition was prepared in the same manner as in Example 1 above, except that 10 ml of an emulsion-type acrylic adhesive (20 wt %) was mixed with 90 ml of the titanium oxide microparticle dispersion (i.e., the coating composition contained 0.2 wt % of peroxotitanic acid in terms of solid content relative to the total weight of the coating composition and 1.0 wt % of titanium oxide in terms of solid content relative to the total weight of the coating composition). Furthermore, a test piece was prepared using this coating composition in the same manner as in Example 1 above, and the hardness was 4H.

[0038] [Example 11] A titanium oxide fine particle dispersion (peroxotitanic acid concentration 0.2 wt%, ammonium ion concentration 300 ppm) containing 1.0 wt% titanium oxide by solids content relative to the total weight of the dispersion was prepared using titanium oxide powder (manufactured by Teika Corporation, product name "AMT-100", average particle diameter of titanium oxide fine particles 6 nm). 10 ml of emulsion-type acrylic pressure-sensitive adhesive (acrylic copolymer solution with a weight average molecular weight of 430,000) adjusted to 20 wt% with distilled water as in Example 1 above was mixed with 90 ml of this dispersion, and a coating composition was prepared in the same manner as in Example 1 above. Furthermore, test pieces were prepared using this coating composition in the same manner as in Example 1 above, and the pencil hardness was evaluated. The hardness was 4H.

[0039] [Example 12] A coating composition was prepared in the same manner as in Example 1 above, except that 18 ml of a 0.28 wt % copper oxide (CuO) solution was added to 72 ml of titanium oxide microparticle dispersion liquid instead of distilled water, and 10 ml of an emulsion-type acrylic adhesive was mixed with this (i.e., the copper oxide concentration in the coating composition was 0.05 wt %). Furthermore, using this coating composition, test pieces were prepared in the same manner as in Example 1 above, and the pencil hardness was evaluated, resulting in a hardness of 4H. Furthermore, using this coating composition, a glass plate on which a photocatalytic coating film was formed was prepared in the same manner as in Example 1 above, and its visible light transmittance was measured, resulting in an average transmittance of 88% or more.

[0040] Comparative Example 6 A coating composition was prepared in the same manner as in Example 2 above, except that 10 ml of a 1.2 wt % silicon oxide solution was mixed as an inorganic binder instead of the emulsion-type acrylic adhesive. Furthermore, using this coating composition, test pieces were prepared in the same manner as in Example 2 above, and the antibacterial and antiviral properties were evaluated. Both the antibacterial activity value and the antiviral activity value showed lower values ​​than those of the photocatalytic coating film obtained in Example 2 above.

[0041] Table 1 summarizes the outline of each coating composition in Examples 1 to 12 and Comparative Examples 1 to 6, as well as the hardness of the photocatalytic coating films obtained by applying these compositions. In Examples 1 to 12, when the coating composition contained an emulsion-type acrylic pressure-sensitive adhesive, in which an acrylic copolymer having a weight-average molecular weight of 300,000 or more and 800,000 or less was dispersed in water, at a concentration of 0.15 wt % to 3.0 wt % relative to the total weight of the coating composition, a photocatalytic coating film having a hardness of 4H or more was obtained. In contrast, in Comparative Examples 1 and 2, which did not contain an emulsion-type acrylic pressure-sensitive adhesive or contained an emulsion-type acrylic pressure-sensitive adhesive but had an acrylic pressure-sensitive adhesive concentration of less than 0.15 wt % relative to the total weight of the coating composition, and in Comparative Example 4, in which the molecular weight of the acrylic copolymer contained in the acrylic pressure-sensitive adhesive was less than 300,000, a hardness of 4H or more was not obtained. These results demonstrate that photocatalytic coatings obtained by coating with an emulsion-type acrylic pressure-sensitive adhesive containing an acrylic copolymer with a polymerization average molecular weight of 300,000 or more dispersed in water at a concentration of 0.15 wt% or more relative to the total weight of the coating composition exhibit excellent durability. On the other hand, in Comparative Example 3, where the emulsion-type acrylic pressure-sensitive adhesive exceeded 3.0 wt% relative to the total weight of the coating composition, and Comparative Example 5, where the acrylic copolymer contained in the acrylic pressure-sensitive adhesive had a polymerization average molecular weight of over 800,000, aggregation and precipitation of the titanium oxide particles in the coating composition occurred, preventing a hardness of 4H or higher. Therefore, it is preferable for the emulsion-type acrylic pressure-sensitive adhesive to contain an acrylic copolymer with a polymerization average molecular weight of 300,000 or more and 800,000 or less, and for the emulsion-type acrylic pressure-sensitive adhesive to be present in an amount ranging from 0.15 wt% to 3.0 wt% relative to the total weight of the coating composition.

[0042] [Table 1]

[0043] Furthermore, from Examples 9 to 12 above, it was found that even if the type of titanium oxide microparticles in the coating composition, the amount of titanium oxide microparticles (titanium oxide concentration), the peroxotitanic acid concentration, or the ammonium ion concentration changes, as long as the coating composition contains an emulsion-type acrylic adhesive in the range of 0.15 wt % to 3.0 wt % relative to the total weight of the coating composition, the photocatalytic coating film obtained by applying these will exhibit a hardness of 4H or more.

[0044] The coating composition of the present invention contains 0.01 to 7.5 parts by weight of emulsion-type acrylic adhesive per 1 part by weight of titanium oxide. In the present invention, if the proportion of emulsion-type acrylic adhesive in the coating composition exceeds 7.5 parts by weight per 1 part by weight of titanium oxide, the photocatalytic coating film obtained by applying this composition is prone to film cracking and has poor durability. Furthermore, since the resulting photocatalytic coating film becomes cloudy, when applied to a substrate surface on which printing or the like has been applied, the visibility of the printing or the like on the substrate surface is impaired.

[0045] Furthermore, Examples 2 and 12 above demonstrated that even when silver ions or copper oxide were added as additives other than titanium dioxide microparticles and an emulsion-type acrylic adhesive, these additives did not affect the hardness of the photocatalytic coating film. Furthermore, as long as the emulsion-type acrylic adhesive was present in an amount ranging from 0.15 wt % to 3.0 wt % relative to the total weight of the coating composition, the photocatalytic coating film obtained by applying this composition exhibited a hardness of 4H or higher. The photocatalytic coating films of Examples 2 and 12 above were capable of decomposing organic matter such as bacteria and viruses due to the silver ions and copper oxide contained in the photocatalytic coating film, even when not exposed to light. Furthermore, the photocatalytic coating film obtained in Example 2 above had higher antibacterial and antiviral activity values ​​than the photocatalytic coating film containing a binder (Comparative Example 6 above). It was confirmed that the absence of a binder improved the antibacterial and antiviral activity values.

[0046] The present invention is not limited to the above-described embodiments and examples. In the above examples, titanium oxide particles were described as being dispersed in anatase-type titanium oxide particles whose surfaces are modified with peroxo groups, titanium oxide nanoparticles whose surfaces are modified with acidic phosphate esters, or rutile-type titanium oxide particles, but the titanium oxide particles are not limited to these. Supports such as iron ions, copper, and halides can also be used as titanium oxide particles.

[0047] Furthermore, in the above examples, an example was described in which an ABS resin substrate was used as the resin substrate, but this is not limited to this, and the present invention can also be applied when painting on resin substrates such as PBT resin, POM resin, acrylic resin, and PC resin.

Claims

1. A coating composition comprising a photocatalyst, A dispersion of titanium oxide fine particles in water containing peroxotitanic acid and ammonium ions, A coating composition characterized by containing an emulsion-type acrylic pressure-sensitive adhesive in which an acrylic copolymer having a weight average molecular weight of 300,000 or more and 800,000 or less is dispersed in water, in a proportion of 0.15% by weight to 3.0% by weight relative to the total weight of the coating composition.

2. A coating composition comprising a photocatalyst, A dispersion of titanium oxide fine particles in water containing peroxotitanic acid and ammonium ions, A coating composition comprising an emulsion-type acrylic pressure-sensitive adhesive in which an acrylic copolymer having a weight average molecular weight of 300,000 or more and 800,000 or less is dispersed in water, in a ratio of 0.01 to 7.5 parts by weight per part by weight of titanium oxide.

3. 3. The coating composition according to claim 1, further comprising at least one of a metal other than titanium oxide, a metal compound, and a metal ion.

4. A photocatalytic coating film formed from the coating composition according to claim 1 or 2.

5. A photocatalytic coating film formed from the coating composition according to claim 3.

Images