Water-based inorganic coating agent and coating method

Abstract

Provided are an aqueous inorganic coating agent capable of forming a coating film having excellent adhesion to a substrate, and a coating method using this aqueous inorganic coating agent. The aqueous inorganic coating agent includes alkaline colloidal silica, at least one of a sodium phosphate compound and a potassium phosphate compound, boric acid, and an inorganic abrasive.

Description

[Technical Field]

[0001] The present invention relates to a water-based inorganic coating agent and a coating method. [Background technology]

[0002] Coating agents intended to prevent substrate contamination have been known. For example, Patent Document 1 discloses an aqueous inorganic coating agent that is applied to the surface of an organic or inorganic substrate to form a superhydrophilic, transparent inorganic coating. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4658093 Summary of the Invention [Problem to be solved by the invention]

[0004] Before applying a coating agent, the surface of the substrate is usually polished, but it has been found that water-based coating agents have difficulty adhering to polished substrates.

[0005] An object of the present disclosure is to provide an aqueous inorganic coating agent capable of forming a coating film having excellent adhesion to a substrate, and a coating method using this aqueous inorganic coating agent. [Means for solving the problem]

[0006] The present disclosure includes the following aspects. [1] alkaline colloidal silica; At least one of a sodium phosphate compound and a potassium phosphate compound; Boric acid, An aqueous inorganic coating agent comprising: an inorganic abrasive; [2] The aqueous inorganic coating agent according to [1] above, wherein the inorganic abrasive comprises one or more selected from the group consisting of aluminum oxide, cerium oxide and mesoporous silica. [3] The aqueous inorganic coating agent according to the above [1] or [2] further comprises an inorganic curing agent containing a metal element. [4] The aqueous inorganic coating agent according to [3] above, wherein the inorganic curing agent contains a metal stannate. [5] The aqueous inorganic coating agent according to [3] or [4] above, wherein the inorganic curing agent comprises one or more selected from the group consisting of potassium stannate, sodium stannate, zinc stannate, zinc hydroxide, and indium tin oxide. [6] (i) applying any one of the aqueous inorganic coating agents [1] to [5] above to the surface of a substrate, and then polishing the surface of the substrate with an electric polisher or an electric sander; or (ii) polishing the surface of the substrate with an electric polisher or an electric sander equipped with a buff impregnated with any one of the aqueous inorganic coating agents [1] to [5] above, and applying the aqueous inorganic coating agent at the same time; and removing the inorganic abrasive with water. [Effects of the Invention]

[0007] According to the present disclosure, there are provided an aqueous inorganic coating agent capable of forming a coating film having excellent adhesion to a substrate, and a coating method using this aqueous inorganic coating agent. [Brief explanation of the drawings]

[0008] [Figure 1A] 1 is a photograph of a portion of a solar panel (Application Example 1) coated with the aqueous inorganic coating agent of Example 2. [Figure 1B] 1 is a probe scanning microscope image (size: 1 μm×1 μm) of a portion of a solar panel (Application Example 1) coated with the water-based inorganic coating agent of Example 2. [Figure 1C]1 is a nano-search microscope (size: 500 nm x 400 nm) of a portion of the cross section of a solar panel (Application Example 1) coated with the aqueous inorganic coating agent of Example 2. [Figure 1D] 1 shows the results of elemental analysis of an arbitrary point on the cross-sectional surface of a solar panel (Application Example 1) coated with the aqueous inorganic coating agent of Example 2, using an SEM-EDX analyzer (FE-SEM S-4800, manufactured by Hitachi HT). [Figure 1E] 10 is a photograph of a solar panel (Installation Example 1) coated with the water-based inorganic coating agent of Example 2 after being installed for a certain period of time and then sprayed with water. [Figure 2A] 1 is a photograph of a portion of a solar panel (Comparative Application Example 1) coated with the aqueous inorganic coating agent of Comparative Example 1. [Figure 2B] 1 is a probe scanning microscope image (size: 1 μm×1 μm) of a portion of a solar panel (Comparative Application Example 1) applied with the aqueous inorganic coating agent of Comparative Example 1. [Figure 3] 1 is a photograph of a portion of a bathroom tile (Application Example 2) applied with the aqueous inorganic coating agent of Example 4. [Figure 4] 1 is a photograph of a portion of a bathroom tile (Comparative Application Example 2) applied with the aqueous inorganic coating agent of Comparative Example 1. [Figure 5] 1 is a photograph of an automobile windshield (Application Example 3) coated with the water-based inorganic coating agent of Example 1 on a snowy day after 6 months. [Figure 6] 1 is a photograph of a portion of a mirror (Application Example 4) in a super public bathhouse that was applied with the aqueous inorganic coating agent of Example 1. [Figure 7] 1 is a photograph of a portion of a wall glass of an outdoor building coated with the water-based inorganic coating agent of Example 1 (Application Example 5). [Figure 8A] 1 is a photograph of a portion of a stainless steel door of an elevator (Application Example 6) coated with the water-based inorganic coating agent of Example 3. [Figure 8B] 10 is a photograph of a portion of the inside of a stainless steel cage of an elevator (Application Example 6) coated with the water-based inorganic coating agent of Example 3. [Figure 9]10 is a photograph of a portion of a resin tape (Application Example 7) applied inside a railway vehicle using the aqueous inorganic coating agent of Example 4. [Figure 10A] 1 is a photograph showing the state of the surface of a glass plate before water is sprayed onto it in Experimental Example 1. [Figure 10B] 1 is a photograph showing the state of the surface of a glass plate when water is sprayed onto it in Experimental Example 1. [Figure 10C] 10 is a photograph showing the state of the surface of the glass plate when water is further sprayed on it in Experimental Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Water-based inorganic coating agent] The water-based inorganic coating agent of the present disclosure contains alkaline colloidal silica, at least one of a sodium phosphate compound and a potassium phosphate compound, boric acid, and an abrasive.

[0010] "Aqueous" means that the solvent is water. "Inorganic" means that the substance is not organic. "Organic substance" means a compound containing carbon atom (C). "Aqueous inorganic coating agent" means a coating agent that uses water as the solvent and does not contain any organic substances. However, it is acceptable for aqueous inorganic coating agents to contain unavoidable organic substances. It is acceptable for aqueous inorganic coating agents to contain organic substances below the detection limit.

[0011] The reasons why conventional water-based coating agents are difficult to adhere to polished substrates are thought to be as follows: Polishing not only removes dirt but also activates the surface of the substrate, generating hydroxyl groups (OH groups) on the surface of the substrate. These OH groups react with oxygen atoms in the air to form an oxide film on the surface of the substrate. Because the oxide film exhibits water-repellent properties, it is thought to hinder adhesion between the water-based coating agent applied thereafter and the substrate.

[0012] The aqueous inorganic coating agent of the present disclosure contains an abrasive together with alkaline colloidal silica. Therefore, when the aqueous inorganic coating agent of the present disclosure is applied and polished, the surface of the substrate is activated while avoiding contact with the atmosphere, and the OH groups generated by activation can quickly chemically bond with the colloidal silica. In addition, the abrasive removes dirt from the substrate surface. This improves adhesion between the coating agent and the substrate.

[0013] As described above, polishing and coating are performed simultaneously, resulting in a uniform coating with few pinholes. This improves the strength of the coating and allows it to be made thinner.

[0014] Furthermore, the coating formed by the aqueous inorganic coating agent of the present disclosure (hereinafter, sometimes referred to as an "anti-fouling coating") exhibits superhydrophilicity. As a result, dirt adhering to the substrate is easily washed away with water. The removal of dirt by water is called a self-cleaning effect. The self-cleaning effect is exerted, for example, by rainfall or washing with water. In the present disclosure, anti-fouling property refers to the performance resulting from the self-cleaning effect in addition to the antistatic effect inherent in the aqueous inorganic coating agent.

[0015] "Superhydrophilic" means that the contact angle of water is 15 degrees or less (particularly 10 degrees or less). The contact angle of water can be measured in accordance with JIS R 3257, Test method for wettability of substrate glass surfaces (sessile drop method).

[0016] Superhydrophilicity is achieved by sodium phosphate compounds and potassium phosphate compounds (hereinafter sometimes collectively referred to as "alkali metal phosphates"). Alkali metal phosphates have hygroscopic or water-retentive properties. When moisture in the air is attracted to the alkali metal phosphate, it is absorbed by the hydrophilic groups (SiOH groups) and hydroxide ions (OH) of the alkaline colloidal silica. -)) and is retained as a trace amount of moisture on the coating formed by the aqueous inorganic coating agent. This makes the antifouling coating exhibit superhydrophilicity. The moisture may be that contained in the atmosphere. Even with such a trace amount of moisture, superhydrophilicity is exhibited.

[0017] That is, the aqueous inorganic coating agent of the present disclosure can provide an antifouling coating that is superhydrophilic, has high adhesion, and is highly durable.

[0018] While photocatalysts conventionally used in antifouling coating agents exhibit hydrophilicity when exposed to ultraviolet light, the coating agent of the present disclosure can exhibit superhydrophilicity upon contact with the atmosphere, even in the absence of ultraviolet light.

[0019] Organic fluorine compounds (PFAS, PFOA, etc.), such as fluororesins, are also used in antifouling coating agents. However, in recent years, concerns have arisen about the environmental impact of PFAS, PFOA, etc. The coating agent of the present disclosure can exhibit excellent antifouling properties without using organic fluorine compounds.

[0020] Typically, the substrate surface is washed and rinsed with water, then polished and rinsed with water, and then a coating agent is applied. However, with the aqueous inorganic coating agent of the present disclosure, polishing (removal of dirt and activation) of the substrate surface and antifouling coating can be performed with a single material. This simplifies the application process and offers significant cost benefits.

[0021] The aqueous inorganic coating agent and the coating method using this aqueous inorganic coating agent according to the embodiment of the present disclosure will be described in detail below, but the present invention is not limited to this embodiment.

[0022] The solids concentration of the aqueous inorganic coating agent is not particularly limited and is set appropriately depending on the application and purpose. The solids concentration of the aqueous inorganic coating agent may be 0.1 to 25% by mass, since this can suppress variations in film thickness. When used on inorganic substrates requiring smoothness and transparency, the solids concentration of the aqueous inorganic coating agent may be 5.0 to 25.0% by mass, 10.0 to 25.0% by mass, or 15.0 to 22.0% by mass. When used on organic substrates, the solids concentration of the aqueous inorganic coating agent may be 5.0 to 25.0% by mass, 10.0 to 22.0% by mass, or 15.0 to 20.0% by mass.

[0023] The solid content is also called the non-volatile content. The solid content of an aqueous inorganic coating agent is the heating residue. The solid content concentration can be calculated from the residue when the aqueous inorganic coating agent is heated at 200°C for 20 minutes, according to JIS K 5601-1-2 Heating Residue Measurement Method.

[0024] The content of each component is the ratio of the solid concentration (heating residue) of that component to the total solid concentration (heating residue) of the aqueous inorganic coating agent.

[0025] The pH of the aqueous inorganic coating agent is not particularly limited and may be in the neutral range, for example, 5.0 to 9.0, or 6.0 to 8.0.

[0026] The specific gravity of water-based inorganic coating agents excluding inorganic abrasives is about the same as that of water. The specific gravity of water-based inorganic coating agents excluding inorganic abrasives is about 1.05 to 1.08. The viscosity of water-based inorganic coating agents excluding inorganic abrasives is also about the same as that of water. The viscosity of water-based inorganic coating agents excluding inorganic abrasives is about 1.0 mPa·s at 20°C.

[0027] (Alkaline colloidal silica) The alkaline colloidal silica crosslinks to form a coating on the substrate. Alkaline colloidal silica is negatively charged colloidal silica. In the aqueous inorganic coating agent of the present disclosure, the colloidal silica is usually negatively charged and exists as alkaline colloidal silica. Colloidal silica is also called silica sol.

[0028] Colloidal silica is a colloidal particle that contains silicic acid (SiO2) or silicic acid hydrate as its main component. In aqueous inorganic coating agents, the surface of colloidal silica contains SiOH groups and OH groups. - There are many particles. Therefore, an electric double layer is formed, which suppresses aggregation of the colloidal silica particles, and the colloidal silica is stably dispersed in the aqueous inorganic coating agent. The colloidal silica may be amorphous. The particle shape is not particularly limited, and may be spherical or crushed.

[0029] The average particle size of alkaline colloidal silica (hereinafter sometimes simply referred to as "colloidal silica") is not particularly limited and is appropriately selected depending on the application and purpose. The average particle size of colloidal silica may be, for example, 3 to 100 nm, 5 to 70 nm, or 5 to 30 nm. Multiple types of colloidal silica with different average particle sizes may be used in combination.

[0030] The average particle size of colloidal silica is the particle size (D50) at which the volumetric integrated value is 50% as measured by a laser diffraction particle size distribution analyzer.

[0031] The colloidal silica may be one in which one type of silica particles or a plurality of types of silica particles having different average particle sizes are dispersed in water and stabilized with sodium dioxide.

[0032] Examples of commercially available colloidal silica products include the "Snowtex (registered trademark)" series from Nissan Chemical Industries, Ltd., the "Quartron (registered trademark)" PL series from Fuso Chemical Co., Ltd., the "Cataloid (registered trademark)" series from JGC Catalysts and Chemicals, Ltd., the "Adelite" series from ADEKA Corporation, the "Syton" series from Remet Corporation, "Nalcoag-1060" and "Nalcoag-ID21-64" from Nalco Chem Corporation, and the "Ludox (registered trademark)" series from W.R. Grace Corporation.

[0033] Colloidal silica content W Si The colloidal silica content W is set appropriately depending on the application and purpose. Si The content may be, for example, 20 to 80 mass % or 30 to 70 mass % relative to 100 mass % of the solid content of the aqueous inorganic coating agent.

[0034] (Sodium phosphate compound) As described above, the sodium phosphate compound contributes to the development of superhydrophilicity. Examples of sodium phosphate compounds include anhydrous sodium dihydrogen phosphate (NaH2PO4), sodium dihydrogen phosphate crystal (NaH2PO4·2H2O), disodium hydrogen phosphate crystal (Na2HPO4·12H2O), anhydrous trisodium phosphate (Na3PO4), trisodium phosphate crystal (Na3PO4·12H2O), tetrasodium pyrophosphate crystal (Na4P2O7), tetrasodium pyrophosphate crystal (Na4P2O7·10H2O), sodium dihydrogen pyrophosphate (Na2H2P2O7), sodium tripolyphosphate (Na5P3O 10 ), sodium tetrapolyphosphate (Na6P4O 13 ), sodium hexamenthol (NaPO3) n ), sodium hexametaphosphate ([Na x H y (PO3) x+y ] n These may be used alone or in combination of two or more.

[0035] (potassium phosphate compound) As described above, the potassium phosphate compound contributes to the development of superhydrophilicity. Examples of potassium phosphate compounds include potassium dihydrogen phosphate (KH2PO4), dipotassium hydrogen phosphate (K2HPO4), and potassium metaphosphate, which may be used alone or in combination of two or more.

[0036] Total alkali metal phosphate content W P is set appropriately depending on the application and purpose. The content of alkali metal phosphate W P The degree of hydrophilicity can be adjusted by adjusting the content of alkali metal phosphate W. P may be, for example, 0.5 to 60.0 mass%, 0.5 to 58.0 mass%, 0.5 to 20.0 mass%, or 0.5 to 10.0 mass% relative to 100 mass% of the solid content of the aqueous inorganic coating agent.

[0037] At least one of sodium dihydrogen phosphate and dipotassium hydrogen phosphate may be used, as they are easily soluble in water.

[0038] (boric acid) Boric acid (H3BO3) improves adhesion between colloidal silica and the substrate. Boric acid also acts as a pH adjuster.

[0039] Boric acid content W B The content of boric acid W is set appropriately depending on the application and purpose. B may be, for example, 0.5 to 35.0 mass%, 0.6 to 30.0 mass%, 0.6 to 10.0 mass%, or 0.6 to 5.0 mass% relative to 100 mass% of the solid content of the aqueous inorganic coating agent.

[0040] Alkali metal phosphate content W P is the boric acid content W B and colloidal silica content W Si More is better (W P >WB ,W Si In this case, the adhesion between the aqueous inorganic coating agent and the organic substrate can be further improved. This is because the viscosity of the aqueous inorganic coating agent is increased by the alkali metal phosphate, and the anchoring effect makes it easier for the aqueous inorganic coating agent to adhere to the organic substrate.

[0041] Colloidal silica content W Si is the boric acid content W B and alkali metal phosphate content W P More, W B and W P may be comparable to (W Si >W B ≒W P In this case, the adhesion between the aqueous inorganic coating agent and the inorganic substrate can be further improved, because the inorganic substrate has OH groups on its surface, which easily react with colloidal silica.

[0042] (inorganic abrasives) Inorganic abrasives contribute to improving the adhesion between the anti-fouling coating and the substrate. Inorganic abrasives do not contain carbon atoms. Inorganic abrasives function best when blended into coating agents that contain water as a solvent and no organic substances. Water has low viscosity, which prevents inorganic abrasive particles from adhering to each other, and the abrasive function of the inorganic abrasive is not impaired.

[0043] The inorganic abrasive is not particularly limited and is appropriately selected depending on the substrate. Examples of inorganic abrasives include aluminum oxide, cerium oxide, mesoporous silica, kaolin, and bentonite. These can be used alone or in combination of two or more. Aluminum oxide is suitable for stainless steel, fiber-reinforced plastic (FRP), ceramics, and marble, for example. Cerium oxide is suitable for glass in general, for example. Mesoporous silica is suitable for glass, stainless steel, FRP, ceramics, and marble, for example.

[0044] Mesoporous silica may be blended with other inorganic abrasives. Mesoporous silica absorbs pressure from a polisher or the like to prevent damage to the substrate, and also adsorbs dirt detached from the substrate, enhancing the cleaning effect.

[0045] The content of the inorganic abrasive is appropriately set depending on the application and purpose, and may be, for example, 2 to 85 mass %, 5 to 80 mass %, or 10 to 80 mass % relative to 100 mass % of the solid content of the aqueous inorganic coating agent.

[0046] The average particle size or particle size of the inorganic abrasive is not particularly limited and may be appropriately selected depending on the type of substrate. The following table shows an example of the correspondence between the substrate and the average particle size or particle size of the inorganic abrasive.

[0047] [Table 1]

[0048] The average particle size of inorganic abrasives is the particle size (D50) at which the cumulative volume equivalent is 50% as measured using a laser diffraction particle size distribution analyzer. The particle size of inorganic abrasives is a value in accordance with JIS R 6001-1 2017 and JIS R 6001-2 2017.

[0049] (inorganic hardener) The aqueous inorganic coating agent may contain an inorganic curing agent. The inorganic curing agent contains a metal element. In the aqueous inorganic coating agent, the inorganic curing agent ionizes to generate metal ions. The metal ions are adsorbed onto the surface of the colloidal silica, promoting aggregation of the colloidal silica particles. This facilitates crosslinking (hardening) between the colloidal silica particles, improving the strength of the coating film.

[0050] The inorganic curing agent is not particularly limited as long as it contains a metal element. The metal element is not particularly limited. The inorganic curing agent is not particularly limited as long as it generates an ionized metal in water. The inorganic curing agent may be water-soluble and colorless.

[0051] The inorganic hardener may contain a metal element other than a heavy metal, such as an alkali metal or an alkaline earth metal, because it easily generates ionized metals.The inorganic hardener may be, for example, zinc hydroxide or indium tin oxide (ITO), because it inhibits discoloration of the antifouling coating.

[0052] The alkali metal may be at least one selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). The alkaline earth metal may be at least one selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

[0053] The inorganic hardener may include a metal stannate, such as zinc stannate (Zn2SnO4), barium stannate (BaSnO3), sodium stannate (Na2SnO3), or potassium stannate (K2SnO3).

[0054] The inorganic hardener may include one or more selected from the group consisting of potassium stannate, sodium stannate, zinc stannate, zinc hydroxide, and indium tin oxide, which dissolve in water to form a colorless, transparent aqueous solution.

[0055] The content of the inorganic curing agent is appropriately set depending on the application and purpose. The content of the inorganic curing agent may be 10 to 40 mass % or 15 to 35 mass % relative to 100 mass % of the solid content of the aqueous inorganic coating agent, in order to suppress aggregation and precipitation.

[0056] (solvent) The aqueous inorganic coating agent contains water as a solvent. Examples of water include purified water, pure water, tap water, and ion-exchanged water. Since water is not easily volatilized during storage, it is possible to suppress changes in the physical properties of the aqueous inorganic coating agent over time. Furthermore, since water is not easily volatilized during application, the polishing function of the inorganic abrasive can be fully exerted.

[0057] (others) The aqueous inorganic coating agent may contain sodium silicate (also called sodium silicate or water glass). Sodium silicate improves the adhesion between the antifouling coating and the inorganic substrate. Sodium silicate is a mixture of silicon dioxide (SiO2), sodium oxide (Na2O), and water (H2O). The molar ratio of SiO2 to Na2O is not particularly limited. The content of sodium silicate is not particularly limited.

[0058] (Preparation method) The aqueous inorganic coating agent is prepared, for example, as follows. First, a predetermined amount of alkali metal silicate and boric acid are mixed. The raw material boric acid may be in the form of a powder or an aqueous solution. Water is added to the mixture, which is then heated and stirred to dissolve the ingredients, thereby obtaining an aqueous additive solution. Separately, a predetermined amount of water and colloidal silica are thoroughly stirred at room temperature, or while heated as needed. Furthermore, the aqueous additive solution and, if necessary, an inorganic curing agent are added and stirred. Finally, a predetermined amount of inorganic abrasive is added and stirred to obtain an aqueous inorganic coating agent.

[0059] [Coating method] The coating method of the present disclosure comprises: (i) applying the above-mentioned aqueous inorganic coating agent to the surface of a substrate, and then polishing the surface of the substrate with an electric polisher or an electric sander; or (ii) applying the above-mentioned aqueous inorganic coating agent to the surface of a substrate and polishing the surface of the substrate with an electric polisher or an electric sander, and then removing the inorganic abrasive with water.

[0060] (base material) The substrate to be treated with the aqueous inorganic coating agent is not particularly limited. The surface of the substrate may be formed of an organic material or an inorganic material. For convenience, a substrate having a surface formed at least by an organic material will be referred to as an organic substrate, and a substrate having a surface formed at least by an inorganic material will be referred to as an inorganic substrate.

[0061] Examples of inorganic materials include metals, stone, glass, mirrors, ceramics, and marble. Examples of metals include stainless steel, titanium, aluminum, and copper. Metal surfaces may be formed with a plating layer. Examples of organic materials include various thermoplastic resins, thermosetting resins, FRP, and hard films.

[0062] (1) Application of water-based inorganic coating agent and polishing (i) After applying the aqueous inorganic coating agent to the surface of the substrate, the surface of the substrate is polished with an electric sander, or (ii) the surface of the substrate is polished with an electric polisher equipped with a buff impregnated with the aqueous inorganic coating agent, and the aqueous inorganic coating agent is applied. If the inorganic abrasive has settled, the aqueous inorganic coating agent may be thoroughly stirred before use to disperse the inorganic abrasive.

[0063] Method (i) In the method (i), the aqueous inorganic coating agent is applied by, for example, a sprayer, a semi-automatic mobile coating machine, a fully automatic or semi-automatic indoor coating machine, an electric sander equipped with a buff, or an electric polisher. The amount of the aqueous inorganic coating agent to be applied is not particularly limited.

[0064] The surface of the substrate is then polished with an electric polisher or an electric sander. The electric polisher or the electric sander used for coating and polishing may be the same or different.

[0065] The electric sander is not particularly limited. Examples of the electric sander include an orbital sander and a disc sander. Commercially available electric sanders include a random orbit sander (product number: BO06050) manufactured by Makita Corporation, a rechargeable random orbital sander (product number: BO1800), and a square orbital sander (product number: NS-3250M) manufactured by Kyocera (formerly Ryobi).

[0066] The electric polisher is not particularly limited. Examples of the electric polisher include double action, single action, and gear action polishers. An example of a commercially available electric polisher is the electric sander polisher (product number: PE-2100) manufactured by Kyocera (formerly Ryobi).

[0067] The buff is not particularly limited, and for example, a short wool buff or a sponge buff can be used.

[0068] Method (ii) In method (ii), the aqueous inorganic coating agent is first impregnated into, for example, a buff. The buff is attached to an electric polisher or an electric sander. By using this electric polisher or electric sander, the substrate surface is polished and the aqueous inorganic coating agent is applied. The amount of the aqueous inorganic coating agent impregnated is not particularly limited.

[0069] (2) Removal of inorganic abrasives Since the inorganic abrasive does not participate in the curing system and the aqueous inorganic coating agent has low viscosity, it can be easily removed with water. If necessary, the substrate surface may be rubbed or squeegeeed while or after spraying water. In this way, an antifouling coating is formed on the substrate surface.

[0070] (Application) Water-based inorganic coating agents can be used for a variety of purposes. They can be applied to both outdoor and indoor facilities. The anti-fouling film formed by the water-based inorganic coating agent makes it easy to remove dirt by rain or washing with water.

[0071] Water-based inorganic coating agents form superhydrophilic antifouling coatings and are used, for example, to prevent fogging on mirrors, glass, and paint films, or to prevent static electricity, oil film, and fingerprint adhesion on car windows, mobile phone screens, TV and computer screens, and elevator button panels.

[0072] Aqueous inorganic coating agents form highly adhesive antifouling coatings that are resistant to friction and maintain superhydrophilic properties for a long period of time, making them suitable for coating substrates that are subject to friction during maintenance, such as exterior walls, windows, solar panels, sanitary ware, show windows, glass showcases, windows in buildings and ordinary homes, and automobile windshields.

[0073] Water-based inorganic coating agents polish the substrate surface and provide an anti-fouling coating using a single material. This eliminates the need for detergents containing surfactants, contributing to a reduction in environmental impact. Furthermore, because no water is required except for the final removal of the inorganic abrasive, water-based inorganic coating agents are suitable for use in locations where large amounts of water are required or where transporting water is difficult.

[0074] The aqueous inorganic coating agent is used, for example, to coat the cover glass of several thousand solar panels in mega solar power plants. 2 The amount of water used when coating the substrate is about 1.5 L, which is the amount required for the final removal of the inorganic abrasive. In contrast, the amount of water used in the conventional method, in which different materials are used for removing dirt from the substrate surface, polishing, and anti-fouling coating, is about 4 L. When using the aqueous inorganic coating agent of the present disclosure, coating is possible for 45 to 60 solar panels per person per day. On the other hand, when using the above-mentioned conventional method, coating can be done on 18 to 22 solar panels per person per day. [Example]

[0075] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. In the examples, "%" means % by mass.

[0076] Details of the materials used in the examples are as follows: Colloidal silica (SiO2) Nissan Chemical Co., Ltd., product name "Snowtex 40", average particle size 10-20nm, solid content 40.5% Alkali metal phosphates Sodium dihydrogen phosphate anhydrous, manufactured by Taihei Chemical Industry Co., Ltd., powder form Boric acid Taiyo Chemical Industry Co., Ltd., purified boric acid, powder Sodium silicate Osaka Silica Co., Ltd., product name "Special 1 Sodium Silicate", molar ratio (SiO2 / Na2O) = 2.14 Inorganic abrasives Cerium oxide, average particle size 2μm Alumina, grain size #3000 Mesoporous silica, average particle size 100 μm Inorganic hardener Potassium stannate aqueous solution, solids concentration approximately 35% by mass

[0077] [Example 1] 10 g of anhydrous sodium dihydrogen phosphate powder and 10 g of purified boric acid powder were placed in a stainless steel heating vessel, and approximately 100 g of water was then added. The mixture was heated until the mixture became colorless and transparent, dissolving the powders. Further water was added to bring the total amount to 100 g, and an aqueous additive solution was obtained.

[0078] Separately, 100g of colloidal silica (Snowtex 40) was added to 3973g of water and stirred thoroughly at room temperature. The entire 100g of the additive aqueous solution was added thereto and stirred thoroughly to obtain a mixture. 150g of an inorganic hardener (potassium stannate aqueous solution) was added to 850g of the obtained mixture and stirred thoroughly to obtain 1000g of a hardener-blended aqueous solution.

[0079] To 900 g of the curing agent-blended aqueous solution, 70 g of cerium oxide and 30 g of mesoporous silica were added as inorganic abrasives to obtain 1000 g of a water-based inorganic coating agent.

[0080] [Example 2] An aqueous inorganic coating agent was obtained in the same manner as in Example 1, except that no inorganic curing agent was added.

[0081] [Examples 3 to 4] An aqueous inorganic coating agent was obtained in the same manner as in Example 1, except that the blending amounts of each component were as shown in Table 2.

[0082] The aqueous inorganic coating agents obtained in Examples 1 to 4 had a pH of 6.0 to 8.5 and a specific gravity excluding abrasives of 1.07. Example 1 is suitable for general glass and mirrors. Example 2 is suitable for solar panels. Example 3 is suitable for organic substrates (FRP, films). Example 4 is suitable for stainless steel and ceramics, and hardens at room temperature and with heat.

[0083] [Table 2]

[0084] [Comparative Example 1] An aqueous inorganic coating agent was prepared in the same manner as in Example 1, except that no inorganic abrasive was added.

[0085] [Installation Example 1] Installation on solar panels (glass) A buff (manufactured by Monotaro) attached to a single polisher (KYOCERA (formerly Ryobi) electric sander-polisher, product number PE-2100) was impregnated with 10 g of the water-based inorganic coating agent of Example 2. Next, the surface (cover glass) of a solar panel was polished with the single polisher. After that, water was sprayed onto the surface to remove the inorganic abrasive, and an antifouling coating was obtained.

[0086] 1A is a photograph of a portion of a solar panel coated with the aqueous inorganic coating agent of Example 2. As can be seen from FIG. 1A, the aqueous inorganic coating agent containing the inorganic abrasive of the present disclosure coated the solar panel surface evenly.

[0087] 1B is a probe scanning microscope image (size: 1 μm × 1 μm) of a portion of a solar panel coated with the aqueous inorganic coating agent of Example 2. As can be seen from FIG. 1B, the aqueous inorganic coating agent containing the inorganic abrasive of the present disclosure formed a dense coating with unevenness (texture) on the substrate.

[0088] Figure 1C is a nanosearch microscope image (size: 500 nm × 400 nm) of a portion of the cross section of a solar panel coated with the aqueous inorganic coating agent of Example 2. Figure 1D shows the results of elemental analysis of an arbitrary point on the surface of the cross section using an SEM-EDX analyzer (FE-SEM S-4800, manufactured by Hitachi HT). From Figures 1C and 1D, it is inferred that a single layer of SiOx film approximately 50 nm thick is formed on the surface.

[0089] Figure 1E is a photograph of a solar panel coated with the water-based inorganic coating agent of Example 2 after it had been installed for a certain period of time and then watered. Water was only poured on the right half of the photograph. As can be seen from Figure 1E, the dirt washed away by the water, demonstrating that the antifouling properties were maintained for a long period of time.

[0090] [Comparative Installation Example 1] Installation on solar panels (glass) An antifouling coating was formed on a solar panel in the same manner as in Construction Example 1, except that 10 g of the water-based inorganic coating agent of Comparative Example 1 was impregnated.

[0091] Figure 2A is a photograph of a solar panel coated with the water-based inorganic coating agent of Comparative Example 1. White unevenness in the coating can be seen.

[0092] 2B is a probe scanning microscope image (size: 1 μm×1 μm) of a portion of a solar panel coated with the water-based inorganic coating agent of Comparative Example 1. It can be seen that an uneven coating was formed.

[0093] [Installation Example 2] Installation on bathroom tiles (ceramics) A buff (manufactured by Monotaro) attached to a single polisher (KYOCERA (formerly Ryobi) electric sander-polisher, product number PE-2100) was impregnated with 10 g of the aqueous inorganic coating agent of Example 4. The surface of the tile was then polished with the single polisher. After that, water was sprayed onto the surface to remove the inorganic abrasive (alumina, etc.), and an antifouling coating was obtained.

[0094] FIG. 3 is a photograph of a portion of a bathroom tile coated with the water-based inorganic coating agent of Example 4.

[0095] [Comparative Installation Example 2] Installation on bathroom tiles (ceramics) An antifouling coating was formed on a bathroom tile in the same manner as in Construction Example 1, except that 10 g of the aqueous inorganic coating agent of Comparative Example 1 was impregnated.

[0096] Figure 4 is a photograph of a portion of a bathroom tile coated with the aqueous inorganic coating agent of Comparative Example 1. As can be seen from Figures 3 and 4, the aqueous inorganic coating agent containing the inorganic abrasive of the present disclosure can polish and coat even small areas such as joints. As a result, a coating with superhydrophilic properties is formed uniformly over the entire substrate, demonstrating excellent stain resistance. We have provided examples using comparative coating agents.

[0097] [Comparative Installation Example 2] Installation on bathroom tiles (ceramics) An antifouling coating was formed on a bathroom tile in the same manner as in Construction Example 1, except that 10 g of the aqueous inorganic coating agent of Comparative Example 1 was impregnated.

[0098] Figure 4 is a photograph of a portion of a bathroom tile coated with the aqueous inorganic coating agent of Comparative Example 1. As can be seen from Figures 3 and 4, the aqueous inorganic coating agent containing the inorganic abrasive of the present disclosure can polish and coat even small areas such as joints. As a result, a coating with superhydrophilic properties is formed uniformly over the entire substrate, demonstrating excellent stain resistance.

[0099] [Installation Example 3] Installation on automobile windshield A buff (manufactured by Monotaro Co., Ltd.) attached to a single polisher (KYOCERA (formerly Ryobi) electric sander-polisher, product number PE-2100) was impregnated with 10 g of the aqueous inorganic coating agent of Example 1. After spraying water onto the outer surface of the left half of an automobile windshield (in front of the driver's seat), the surface was polished with the single polisher for about 1 minute. After that, water was poured onto the surface to remove the inorganic abrasive, and an antifouling coating was obtained.

[0100] [Comparative Installation Example 3] Installation on automobile windshield First, water, cerium oxide, and mesoporous silica were mixed in a ratio of water:cerium oxide:mesoporous silica=90% by mass:7% by mass:3% by mass to prepare a polishing liquid. Next, water was sprayed onto the outer surface of the right half (in front of the passenger seat) of the same automobile windshield used in Application Example 3. Thereafter, the outer surface of the right half was polished with a single polisher for about 1 minute in the same manner as Application Example 3, except that the above-mentioned polishing liquid was used. Water was sprayed onto the surface to remove the inorganic abrasive, and then the surface was left for 10 minutes. Finally, the aqueous inorganic coating agent of Comparative Example 1 was sprayed onto the surface to form a coating.

[0101] Figure 5 is a photograph of a windshield taken on a snowy day six months after the above coating was formed. It can be seen that the left half (in front of the driver's seat) is highly transparent. This is thought to be because the coating was formed on the glass surface activated by the inorganic abrasive without coming into contact with oxygen in the air, resulting in the formation of a uniform, pinhole-free anti-fouling coating. Such a uniform, pinhole-free anti-fouling coating exhibits superhydrophilicity.

[0102] On the other hand, on the right half (in front of the passenger seat), streaks or small water droplets remained on the glass. This is thought to be due to the glass surface coming into contact with the atmosphere after being activated by polishing. When oxygen atoms in the atmosphere react with the activated glass surface, a water-repellent oxide film is formed on the glass surface. This oxide film reduces the adhesion between the glass surface and the aqueous inorganic coating agent that is applied later, resulting in the formation of pinholes. As a result, the coating does not exhibit superhydrophilicity, and it is thought that this is why water droplets remain, as shown in Figure 5.

[0103] [Installation Example 4] Installation on a mirror in a super public bath An antifouling coating was formed on a mirror in a super public bath in the same manner as in Construction Example 1, except that 10 g of the aqueous inorganic coating agent of Example 1 was impregnated.

[0104] Figure 6 is a photograph of a portion of a mirror in a public bathhouse that was treated with the water-based inorganic coating agent of Example 1. Facing the mirror, the left side is before treatment (current state), and the right side is after treatment. After treatment, the mirror was free of dirt and no water droplets adhered to it even with steam in the bathroom, demonstrating its superhydrophilicity.

[0105] [Installation Example 5] Installation on wall glass of outdoor building (arena) An antifouling coating was formed on the wall glass of the arena in the same manner as in Construction Example 1, except that 10 g of the water-based inorganic coating agent of Example 1 was impregnated.

[0106] 7 is a photograph of a portion of the wall glass of an outdoor building (arena) coated with the water-based inorganic coating agent of Example 1. After coating, fingerprint stains were removed from the wall glass, and it was confirmed that the transparency was improved.

[0107] [Installation Example 6] Installation on stainless steel elevator doors and inside stainless steel elevator cages An antifouling coating was formed on the stainless steel door and the inside of the stainless steel cage of an elevator in the same manner as in Construction Example 1, except that 10 g of the water-based inorganic coating agent of Example 3 was impregnated.

[0108] Figure 8A is a photograph of a portion of a stainless steel elevator door coated with the water-based inorganic coating agent of Example 3. Figure 8B is a photograph of a portion of the inside of a stainless steel elevator car coated with the water-based inorganic coating agent of Example 3. It was confirmed that dirt had been completely removed from the door and the inside of the car after coating. Furthermore, when a mark was made on the coated surface with an oil-based pen, the mark was removed by pouring water on it and lightly rubbing it.

[0109] [Example 7] Installation on resin tape inside railway vehicles An antifouling coating was formed on a resin tape inside a railway vehicle in the same manner as in Construction Example 1, except that 10 g of the aqueous inorganic coating agent of Example 4 was impregnated.

[0110] 9 is a photograph of a portion of the resin tape inside a railway vehicle that was coated with the water-based inorganic coating agent of Example 3. It was confirmed that the dirt on the tape after coating had been completely removed.

[0111] [Experimental Example 1] Coating on glass plate An antifouling coating was formed on the right half of a glass plate in the same manner as in Application Example 3, except that the aqueous inorganic coating agent of Example 2 was used. A coating was formed on the left half of the same glass plate in the same manner as in Comparative Application Example 3.

[0112] After confirming that the entire surface of the glass plate was dry, a pattern was drawn on it with an oil-based pen (see Figure 10A) and the plate was exposed outdoors. After one week, it was confirmed that dirt had accumulated on the surface of the glass plate. When water was sprayed onto the glass plate, the oil-based ink on the right half rose to the surface and ran off. On the other hand, no change was observed in the oil-based ink on the left half. Figure 10B is a photograph showing the state of the glass plate surface when water was sprayed on it in Experimental Example 1.

[0113] When water was sprayed onto the entire surface of the glass plate, almost all of the oil-based ink on the right half of the plate rose to the surface. However, no change was observed on the left half of the plate. Figure 10C is a photograph showing the state of the glass plate surface after water was sprayed onto the glass plate in Experimental Example 1. [Industrial Applicability]

[0114] The aqueous inorganic coating agent of the present disclosure can impart durable antifouling properties to various substrates.

Claims

1. alkaline colloidal silica; At least one of a sodium phosphate compound and a potassium phosphate compound; Boric acid, an inorganic abrasive; The aqueous inorganic coating agent further comprises an inorganic curing agent containing a metal stannate.

2. 2. The aqueous inorganic coating agent according to claim 1, wherein the inorganic abrasive comprises one or more selected from the group consisting of aluminum oxide, cerium oxide, and mesoporous silica.

3. 2. The water-based inorganic coating agent according to claim 1, wherein the metal stannate comprises one or more selected from the group consisting of potassium stannate, sodium stannate, and zinc stannate.

4. (i) applying the aqueous inorganic coating agent according to claim 1 to a surface of a substrate, and then polishing the surface of the substrate with an electric polisher or an electric sander; or (ii) polishing the surface of the substrate with an electric polisher or an electric sander equipped with a buff impregnated with the aqueous inorganic coating agent according to claim 1 while applying the aqueous inorganic coating agent; and removing the inorganic abrasive with water.

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