Water-based inorganic coating agent and coating method

Abstract

Provided is a water-based inorganic coating agent capable of forming a coating film having high antifouling properties and excellent abrasion resistance. The aqueous inorganic coating agent includes colloidal silica, at least one of a sodium phosphate compound and a potassium phosphate compound, boric acid, aluminum monophosphate, and water.

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] An object of the present disclosure is to provide an aqueous inorganic coating agent that can form a coating film having high antifouling properties and excellent abrasion resistance. [Means for solving the problem]

[0005] The present disclosure includes the following aspects. [1] Colloidal silica and At least one of a sodium phosphate compound and a potassium phosphate compound; Boric acid, Monoaluminum phosphate, and water. [2] The aqueous inorganic coating agent according to [1] above, which has a pH of 5.0 to 8.0. [3] The aqueous inorganic coating agent according to the above [1] or [2], having a solid content concentration of 0.1 to 25.0% by mass. [4] The aqueous inorganic coating agent according to any one of the above [1] to [3] further contains an alkali metal silicate. [5] Applying any one of the aqueous inorganic coating agents [1] to [4] above to the surface of a substrate; and Thereafter, the surface of the substrate is rubbed while spraying water on it, or the surface of the substrate is rubbed after spraying water on it, thereby forming a coating. [6] A coating method comprising applying any one of the aqueous inorganic coating agents [1] to [4] above to the surface of a substrate while applying pressure to form a coating. [7] The coating method according to [5] or [6] above, further comprising heating the coating at 80 to 250°C for 8 to 30 minutes after the coating is formed. [Effects of the Invention]

[0006] According to the present disclosure, there are provided an aqueous inorganic coating agent capable of forming a coating film having high antifouling properties and excellent abrasion resistance, and a coating method using this aqueous inorganic coating agent. [Brief explanation of the drawings]

[0007] [Figure 1A] 10 is a photograph showing the state of the tile surface before water is sprayed onto it in Application Example 2. [Figure 1B] 10 is a photograph showing the state of the tile surface immediately after spraying water in Application Example 2. [Figure 1C] 10 is a photograph showing the state of the tile surface 1.5 minutes after spraying water on it in Application Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Water-based inorganic coating agent] The aqueous inorganic coating agent of the present disclosure contains colloidal silica, at least one of a sodium phosphate compound and a potassium phosphate compound, boric acid, aluminum monophosphate, and water, and forms a coating film having high antifouling and abrasion resistance.

[0009] "Aqueous" means that the solvent is water. "Inorganic" means that the substance is not organic. "Organic substance" means a compound containing a carbon atom (C). "Aqueous inorganic coating agent" means a coating agent that uses water as the solvent and does not contain any organic substances. Because the aqueous inorganic coating agent of the present disclosure does not contain any organic substances, the resulting coating film is less susceptible to deterioration (especially UV deterioration). However, it is acceptable for the aqueous inorganic coating agent to contain unavoidable organic substances. It is acceptable for the aqueous inorganic coating agent to contain organic substances below the detection limit.

[0010] The aqueous inorganic coating agent of the present disclosure contains aluminum monophosphate together with colloidal silica. Aluminum monophosphate densifies the coating film, increasing its hardness, while suppressing shrinkage of the coating layer during curing. Aluminum monophosphate is particularly effective in suppressing shrinkage of the coating layer during heat curing. Therefore, the coating film (hereinafter sometimes referred to as an antifouling coating film) formed by the aqueous inorganic coating agent of the present disclosure has a uniform thickness and excellent abrasion resistance. The antifouling coating film can exhibit excellent antifouling properties for a long period of time.

[0011] The antifouling properties are achieved by the superhydrophilicity of the antifouling coating. Superhydrophilicity is achieved by sodium phosphate compounds or 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.

[0012] Due to the superhydrophilicity of the substrate, dirt adhering to the substrate can be easily washed away with water. The removal of dirt by water is called the self-cleaning effect. The self-cleaning effect can be achieved, for example, by rainfall or washing with water.

[0013] "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).

[0014] Conventionally, anti-fouling coating agents have used organic fluorine compounds (PFAS, PFOA, etc.) such as fluororesins or surfactants. In recent years, the U.S. Environmental Protection Agency (EPA) published a PFAS Strategic Roadmap, and the Food and Drug Administration (FDA) announced that it will verify the amount of PFAS contained in food. As can be seen from these findings, there are concerns about the environmental and health effects of organic fluorine compounds. Furthermore, surfactants have poor abrasion resistance and easily peel off when the surface is rubbed. The coating agent disclosed herein can achieve high anti-fouling and abrasion resistance without the need for organic fluorine compounds or surfactants.

[0015] The 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.

[0016] The solid content concentration of the aqueous inorganic coating agent is not particularly limited and is appropriately set depending on the application and purpose. In order to suppress variations in film thickness, the solid content concentration of the aqueous inorganic coating agent may be 0.1 to 25.0 mass %, or may be 0.3 to 8.0 mass %.

[0017] 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.

[0018] 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.

[0019] The pH of the aqueous inorganic coating agent is not particularly limited and may be in the neutral range, for example, 5.0 to 8.0, or 6.0 to 8.0.

[0020] (colloidal silica) The colloidal silica crosslinks to form a coating on the substrate.

[0021] Colloidal silica is also called silica sol. Colloidal silica is a colloidal particle containing silicic acid (SiO2) or silicic acid hydrate as a main component. Colloidal silica can be amorphous. The particle shape is not particularly limited and may be spherical or crushed.

[0022] The average particle size of the colloidal silica is not particularly limited and may be appropriately selected depending on the application and purpose. The average particle size of the colloidal silica may be, for example, 3.0 to 100.0 nm. A combination of several types of colloidal silica with different average particle sizes may be used.

[0023] 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.

[0024] Examples of colloidal silica include at least one of alkaline colloidal silica and neutral colloidal silica. Both alkaline colloidal silica and neutral colloidal silica may be included, or alkaline colloidal silica may be included alone.

[0025] In particular, alkaline colloidal silica and neutral colloidal silica may be used in combination. The use of alkaline and neutral colloidal silica allows for easy adjustment of the pH of the inorganic coating agent. For example, when applying an inorganic coating agent to glass, the pH is preferably slightly alkaline, since glass is prone to alkali burn. Additionally, the use of alkaline and neutral colloidal silica allows for easier adjustment of the amount of water adsorption in the resulting antifouling coating, thereby preventing condensation or fogging of the substrate. This is because alkaline colloidal silica adsorbs water more easily than neutral colloidal silica.

[0026] The ratio of the alkaline colloidal silica content to the neutral colloidal silica content is appropriately set depending on the application and purpose. The alkaline colloidal silica content is, for example, 0.8 to 1.5 times the neutral colloidal silica content. The alkaline colloidal silica content may be 0.9 times or more the neutral colloidal silica content. The alkaline colloidal silica content may be 1.3 times or less the neutral colloidal silica content. The alkaline colloidal silica content may be 0.9 to 1.3 times the neutral colloidal silica content.

[0027] The alkaline colloidal silica is negatively charged colloidal silica, and may be, for example, silica particles dispersed in water and stabilized with sodium dioxide or the like.

[0028] Neutral colloidal silica has a pH in the neutral range of about 7.3. Neutral colloidal silica is produced, for example, by the sol-gel method. The pH can be adjusted, for example, by adding an acidic or alkaline substance.

[0029] In aqueous inorganic coating agents, the surface of alkaline colloidal silica contains SiOH groups and OH groups. -There are many of these particles. This creates an electric double layer, which prevents the alkaline colloidal silica particles from flocculating. Neutral colloidal silica has a stable surface charge, which creates a moderate electrostatic repulsion between particles, preventing flocculation. In aqueous inorganic coating agents, colloidal silica is stably dispersed.

[0030] 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.

[0031] The content of colloidal silica is appropriately set depending on the application and purpose. The content of colloidal silica may be, for example, 20.0 to 90.0 mass% relative to 100 mass% of the solid content of the aqueous inorganic coating agent. The content of colloidal silica may be 50.0 mass% or more, or 60.0 mass% or more. The content of colloidal silica may be 85.0 mass% or less. The content of colloidal silica may be 50.0 to 90.0 mass% or 60.0 to 85.0 mass%.

[0032] (aluminum monophosphate) Monoaluminum phosphate is expressed as Al2O3·3P2O5·6H2O. Monoaluminum phosphate densifies the coating while suppressing shrinkage of the coating layer during hardening.

[0033] Commercially available aluminum monophosphate products include, for example, liquid aluminum monophosphate manufactured by Taki Chemical Co., Ltd. under the trade names "50L," "50LH," "100L," and "100P," and powdered aluminum monophosphate products such as "Acidophos (registered trademark) 37," "Acidophos (registered trademark) 75," and "Acidophos (registered trademark) 120M."

[0034] The content of aluminum monophosphate is appropriately set depending on the application, the desired hardness, etc. The content of aluminum monophosphate may be, for example, 0.5 to 5.0% by mass relative to 100% by mass of the solids content of the aqueous inorganic coating agent. The content of aluminum monophosphate may be 0.8% by mass or more, or may be 1.0% by mass or more. The content of aluminum monophosphate may be 4.0% by mass or less, or may be 3.0% by mass or less. The content of aluminum monophosphate may be 0.8 to 4.0% by mass, or may be 1.0 to 3.0% by mass.

[0035] (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.

[0036] (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.

[0037] The total content of alkali metal phosphates is appropriately set depending on the application and purpose. The degree of hydrophilicity can be adjusted by the content of alkali metal phosphates. The content of alkali metal phosphates may be, for example, 0.5 to 60.0 mass% relative to 100 mass% of the solids content of the aqueous inorganic coating agent. The content of alkali metal phosphates may be 1.0 mass% or more, 5.0 mass% or more, or 10.0 mass% or more. The content of alkali metal phosphates may be 40.0 mass% or less, or 20.0 mass% or less. The content of alkali metal phosphates may be 1.0 to 40.0 mass%, 5.0 to 20.0 mass%, or 10.0 to 20.0 mass%.

[0038] At least one of sodium dihydrogen phosphate and dipotassium hydrogen phosphate may be used, as they are easily soluble in water.

[0039] (boric acid) Boric acid (H3BO3) improves adhesion between colloidal silica and the substrate. Boric acid also acts as a pH adjuster.

[0040] The content of boric acid is appropriately set depending on the application and purpose. The content of boric acid may be, for example, 0.5 to 35.0% by mass relative to 100% by mass of the solids content of the aqueous inorganic coating agent. The content of boric acid may be 1.0% by mass or more, 2.0% by mass or more, or 3.0% by mass or more. The content of boric acid may be 30.0% by mass or less, 20.0% by mass or less, or 15.0% by mass or less. The content of boric acid may be 1.0 to 30.0% by mass, 2.0 to 20.0% by mass, or 3.0 to 15.0% by mass.

[0041] (alkali metal silicates) The aqueous inorganic coating agent may contain an alkali metal silicate. The alkali metal silicate is added depending on the substrate, purpose, application, etc. The alkali metal silicate further increases the strength of the coating, especially after firing.

[0042] The alkali metal includes at least one selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).

[0043] Examples of alkali metal silicates include sodium silicate, potassium silicate, and lithium silicate. These may be used alone or in combination of two or more. Of these, sodium silicate is particularly preferred.

[0044] Sodium silicate is also called sodium silicate or water glass. 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.

[0045] The content of the alkali metal silicate is appropriately set depending on the application and purpose, and may be 0.5 to 8.0 mass % or 2.0 to 4.0 mass % relative to 100 mass % of the solid content of the alkali metal silicate.

[0046] (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. Water is unlikely to volatilize during storage, so that changes in the physical properties of the aqueous inorganic coating agent over time can be suppressed.

[0047] Specific examples of components contained in the aqueous inorganic coating agent of the present disclosure are as follows. (1) Colloidal silica (alkaline alone or a combination of alkaline and neutral), monoaluminum phosphate, sodium phosphate compound, boric acid, and water (2) Colloidal silica (alkaline alone or a combination of alkaline and neutral), monoaluminum phosphate, potassium phosphate compound, boric acid, and water (3) Colloidal silica (alkaline alone or a combination of alkaline and neutral), monoaluminum phosphate, sodium phosphate compound, potassium phosphate compound, boric acid, and water (4) The above component (1), (2), or (3), and an alkali metal silicate

[0048] (Preparation method) The aqueous inorganic coating agent is prepared, for example, as follows. First, boric acid and an alkali metal phosphate are added to water. The mixture is heated and dissolved until transparent to prepare an additive solution. The boric acid and alkali metal phosphate may be in the form of powder or an aqueous solution. Next, predetermined amounts of water, the additive solution, aluminum monophosphate, and colloidal silica are mixed and stirred.

[0049] (Application) Aqueous inorganic coating agents can be used for a variety of purposes. For example, they are suitable for coating glass used in smartphones, eyeglasses, VR goggles, surveillance cameras, automobiles, etc., and ceramics such as tiles. Aqueous inorganic coating agents are particularly suitable for coating optical glass. This is because the antifouling coatings formed by aqueous inorganic coating agents are dense and do not easily impair the properties of the optical glass.

[0050] The water-based inorganic coating agent can be used for the purpose of maintaining existing buildings and their accessories, vehicles, etc. The water-based inorganic coating agent can also be used in coating processes that involve heat curing during the manufacturing process of industrial products. Monoaluminum phosphate is particularly effective in suppressing the shrinkage of the coating layer during heat curing.

[0051] (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 of an organic material will be referred to as an organic substrate, and a substrate having a surface formed at least of an inorganic material will be referred to as an inorganic substrate. When heat curing is performed, an inorganic substrate is preferred.

[0052] Examples of inorganic materials include metals, stone, glass, mirrors, ceramics, and marble. Examples of metals include stainless steel, titanium, aluminum, and copper. The metal surface may be formed by a plating layer.

[0053] Examples of organic materials include various thermoplastic resins, thermosetting resins, FRP, and hard films. The organic substrate may be surface-treated. In particular, a surface treatment to impart hydrophilic groups (OH groups) may be performed. Examples of surface treatments include corona treatment, plasma treatment, and SiO2 sputtering.

[0054] [Coating method] First embodiment The coating method according to the first embodiment of the present disclosure comprises applying the aqueous inorganic coating agent of the present disclosure to the surface of a substrate, and then rubbing the surface of the substrate while spraying water on it, or rubbing the surface of the substrate after spraying water on it, to form a coating. "Rubbing" refers to moving an object against the surface of the substrate. The surface of the substrate may be rubbed while applying pressure.

[0055] After application of the aqueous inorganic coating agent, the surface of the substrate is rubbed in the presence of water, whereby the active ingredients such as colloidal silica are fixed to the surface of the substrate, resulting in a dense, strong coating.

[0056] The aqueous inorganic coating agent can be applied, for example, by a spray, a semi-automatic mobile coating machine, a fully automatic or semi-automatic indoor coating machine, or an electric sander or polisher equipped with a buff.

[0057] The object for rubbing the surface of the substrate is not particularly limited, and may be, for example, a cloth or a buff. Rubbing may also be performed by an electric polisher or the like.

[0058] The amount of the aqueous inorganic coating agent to be applied and the amount of water are not particularly limited.

[0059] Second embodiment A coating method according to a second embodiment of the present disclosure includes applying the aqueous inorganic coating agent of the present disclosure to the surface of a substrate while applying pressure to form a coating.

[0060] By applying pressure to the aqueous inorganic coating agent, the active ingredients such as colloidal silica are fixed to the surface of the substrate, resulting in a dense, strong coating.

[0061] Examples of methods for applying pressure include air spray coating, airless spray coating, electrodeposition coating, roll coater coating, die coater coating, and silk screen printing. The pressure to be applied is not limited and can be set appropriately depending on the substrate, etc.

[0062] The amount of the aqueous inorganic coating agent to be applied is not particularly limited.

[0063] In the first and second embodiments, the method may include heating the coating at 80 to 250°C for 8 to 30 minutes after the coating is formed. Heating can further improve abrasion resistance. The heating temperature may be 100°C or higher. The heating temperature may be 200°C or lower. The heating temperature may be 100 to 200°C. The heating time may be 10 minutes or longer, or 12 minutes or longer. The heating time may be 25 minutes or less, or 20 minutes or less. The heating time may be 10 to 25 minutes, or 12 to 20 minutes.

[0064] By using the aqueous inorganic coating agent of the present disclosure, a coating having high hardness (i.e., a coating having excellent abrasion resistance) can be formed even when cured at room temperature (20 to 25°C). For example, an antifouling coating having a pencil hardness of 3 to 4H can be obtained by leaving it at 20 to 25°C (room temperature) for 3 to 4 days. For example, an antifouling coating having a pencil hardness of 3 to 4H can be obtained by heating at 100°C for 10 to 15 minutes. For example, an antifouling coating having a pencil hardness of 9H can be obtained by heating at 250°C for 25 minutes. Pencil hardness is evaluated in accordance with JIS K5600-5-4 (1999) Scratch Hardness (Pencil Method). [Example]

[0065] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the examples, "%" means % by mass. The blending ratio (solid content) of each component is shown in Table 1.

[0066] Details of the materials used in the examples are as follows: Colloidal silica Nissan Chemical Co., Ltd., product name "Snowtex XS", alkaline, average particle size (Sears method, catalog value) 5 nm, solid content concentration 20 mass%, sodium dioxide stabilized Alkali metal phosphates Potassium dihydrogen phosphate, manufactured by Taihei Chemical Industry Co., Ltd., powder form Boric acid Taiyo Chemical Industry Co., Ltd., purified boric acid, powder Monobasic aluminum phosphate Manufactured by Taki Chemical Co., Ltd., product name "100L", liquid

[0067] [Example 1] 9.5 g of anhydrous potassium dihydrogen phosphate powder and 7.14 g of purified boric acid powder were placed in a stainless steel heating vessel, and approximately 191.36 g of water was then added. The mixture was heated until it became colorless and transparent, dissolving the powders. Further water was added to bring the total volume to 208 g, and an aqueous additive solution was obtained.

[0068] Separately, 236 g of colloidal silica and 3 g of aluminum monophosphate solution (50% solids concentration) were added to 1530 g of water and stirred thoroughly at room temperature. The entire 208 g of the additive aqueous solution was added thereto and stirred thoroughly to obtain 2060 g of an aqueous inorganic coating agent (solids concentration 3.94 mass%, pH 7.8).

[0069] [Comparative Example 1] An aqueous inorganic coating agent (solid content concentration: 3.87% by mass, pH 7.75) was prepared in the same manner as in Example 1, except that no aluminum monophosphate solution was added.

[0070] [Table 1]

[0071] [Application example 1] Application to tiles The aqueous inorganic coating agent of Example 1 was applied to the surface of a tile, and after splashing water on the surface, it was rubbed with a cloth. It was then left to stand at room temperature (23°C) for 3 to 4 days to form a coating. The pencil hardness of the resulting coating, evaluated in accordance with JIS K5600-5-4 (1999) scratch hardness (pencil method), was 3H.

[0072] [Comparative application example 1] Application to tiles A coating film was formed in the same manner as in Application Example 1, except that the aqueous inorganic coating agent of Comparative Example 1 was used. The pencil hardness of the resulting coating film, evaluated in accordance with JIS K5600-5-4 (1999) scratch hardness (pencil method), was immeasurable.

[0073] [Application example 2] Application to tiles The aqueous inorganic coating agent of Example 1 was applied to the surface of the tile, water was poured onto the surface, and the surface was rubbed with a cloth. Then, the surface was left to stand at room temperature (23°C) for 3 to 4 days to form a coating.

[0074] After drawing a pattern on the coating with an oil-based pen (see Figure 1A), water was sprayed on it, and the oil-based ink was immediately seen to float up (see Figure 1B). After 1.5 minutes, the oil-based ink had completely floated up and could be easily removed (see Figure 1C). This result indicates high stain resistance. [Industrial Applicability]

[0075] The aqueous inorganic coating agent of the present disclosure can impart high stain resistance and abrasion resistance to various substrates.

Claims

1. Colloidal silica and At least one of a sodium phosphate compound and a potassium phosphate compound; Boric acid, Monoaluminum phosphate, and water.

2. 2. The aqueous inorganic coating agent according to claim 1, which has a pH of 5.0 to 8.

0.

3. 3. The aqueous inorganic coating agent according to claim 1, wherein the solid content concentration is 0.1 to 25.0% by mass.

4. The water-based inorganic coating agent according to claim 1 or 2, further comprising an alkali metal silicate.

5. Applying the aqueous inorganic coating agent of claim 1 to the surface of a substrate; and Thereafter, the surface of the substrate is rubbed while spraying water on it, or the surface of the substrate is rubbed after spraying water on it, thereby forming a coating.

6. A coating method comprising applying the aqueous inorganic coating agent of claim 1 to a surface of a substrate while applying pressure to form a coating.

7. 7. The coating method according to claim 5, further comprising heating the coating at 80 to 250° C. for 8 to 30 minutes after forming the coating.

Images