Aqueous inorganic coating agent and coating method

Abstract

The present invention provides an aqueous inorganic coating agent capable of forming a highly stain-resistant film on various substrates. [Solution] An aqueous inorganic coating agent comprising colloidal silica, at least one of a sodium phosphate compound and a potassium phosphate compound, boric acid, an inorganic thickener, and water.

Description

[Technical Field]

[0001] The present invention relates to an aqueous inorganic coating agent and a coating method. [Background technology]

[0002] Conventionally, coating agents aimed at preventing contamination of substrates are 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 film. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 4658093 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The purpose of this disclosure is to provide an aqueous inorganic coating agent that can form a highly antifouling film on various substrates. [Means for solving the problem]

[0005] This disclosure includes the following aspects: [1] Colloidal silica and At least one of a sodium phosphate compound and a potassium phosphate compound, Boric acid and, Inorganic thickeners and A water-based inorganic coating agent containing water. [2] The inorganic thickener comprises one or more smectites or sepiolites, as described in [1] above, in the aqueous inorganic coating agent. [3] Furthermore, an aqueous inorganic coating agent according to [1] or [2] above, comprising monoaluminum phosphate. [4] Furthermore, an aqueous inorganic coating agent according to any of the above [1] to [3], which includes an inorganic abrasive. [5] The aqueous inorganic coating agent according to [4] above, comprising one or more inorganic abrasives selected from the group consisting of aluminum oxide, cerium oxide, and mesoporous silica. [6] Furthermore, an aqueous inorganic coating agent according to any of the above [1] to [5], comprising an inorganic curing agent containing a metal element. [7] The inorganic curing agent is the aqueous inorganic coating agent according to [6] above, comprising a metal stainate salt. [8] The aqueous inorganic coating agent according to [6] or [7] 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. [9] An aqueous inorganic coating agent of any of the above [1] to [8], having a pH of 5.0 to 9.0.

[10] An aqueous inorganic coating agent according to any of the above [1] to [9], having a solid content concentration of 0.1 to 30.0% by mass.

[11] Apply one of the aqueous inorganic coating agents [1] to

[10] above to the surface of the substrate, and A coating method comprising subsequently rubbing the surface of the substrate in the presence of water to form a coating film.

[12] A coating method comprising applying one of the aqueous inorganic coating agents [1] to

[10] above to the surface of a substrate under pressure to form a film.

[13] The coating method according to

[11] or

[12] , wherein the substrate has a surface formed of an organic material.

[14] A coating method according to any of the above

[11] to

[13] , wherein the substrate has a surface formed of an inorganic material.

[15] Furthermore, after the formation of the coating film, heating the coating film at 80 to 250°C for 8 to 30 minutes, and the coating method according to any one of the above

[11] to

[14] .

Advantages of the Invention

[0006] According to the present disclosure, an aqueous inorganic coating agent capable of forming a coating film having high antifouling properties on various substrates, and a coating method using this aqueous inorganic coating agent are provided.

Brief Description of the Drawings

[0007] [Figure 1] It is a photograph of a part of the hood of an automobile coated with the aqueous inorganic coating agent of Example 1. [Figure 2A] It is a photograph of a part of a railway vehicle coated with the aqueous inorganic coating agent of Example 2. [Figure 2B] It is a photograph of a part of a railway vehicle coated with the aqueous inorganic coating agent of Example 2 [Figure 3] It is a photograph of a signboard on a highway coated with the aqueous inorganic coating agent of Example 2. [Figure 4] It is a photograph of a part of a ship hull coated with the aqueous inorganic coating agent of Example 3. [Figure 5] It is a photograph of a part of the painted section of a bridge iron plate coated with the aqueous inorganic coating agent of Example 2. [Figure 6] It is a photograph of the back door of an automobile coated with the aqueous inorganic coating agent of Example 1. [Figure 7A] It is a photograph of a post before construction. [Figure 7B] It is a photograph of a post coated with the aqueous inorganic coating agent of Example 2. [Figure 8] It is a photograph of a mirror-finished stainless steel door coated with the aqueous inorganic coating agent of Example 3.

Modes for Carrying Out the Invention

[0008] [Aqueous Inorganic Coating Agent] The aqueous inorganic coating agent of this disclosure comprises colloidal silica, at least one of a sodium phosphate compound and a potassium phosphate compound, boric acid, an inorganic thickener, and water. Such an aqueous inorganic coating agent is in gel form and can form a highly antifouling film on various substrates.

[0009] "Aqueous" means that the solvent is water. "Inorganic" means that it is not an organic substance. "Organic substance" means a compound containing carbon atoms (C). "Aqueous inorganic coating agent" means a coating agent in which the solvent is water and no organic substances are added. Because the aqueous inorganic coating agent of this disclosure does not contain organic substances, the resulting film is less prone to degradation (especially UV degradation). However, the inclusion of unavoidable organic substances in the aqueous inorganic coating agent is acceptable. The inclusion of organic substances below the detection limit is acceptable in the aqueous inorganic coating agent.

[0010] The aqueous inorganic coating agent of this disclosure includes an inorganic thickener. The inorganic thickener increases the viscosity of the aqueous inorganic coating agent and improves the adhesion between the substrate (especially an organic substrate) and the film formed by the aqueous inorganic coating agent (hereinafter sometimes referred to as an antifouling film).

[0011] Inorganic coating agents containing water as a solvent generally do not adhere well to organic substrates (substrates having a surface formed from at least organic materials). For example, the surface of a substrate with a coating, which is one type of organic substrate, may have irregularities due to the coating method. Inorganic coating agents that have become gel-like with an inorganic thickener can penetrate these depressions and further cover the protrusions. Therefore, their adhesion is improved.

[0012] Furthermore, the inorganic coating agent of this disclosure forms a uniform antifouling film regardless of the operator's skill level. In addition, the antifouling film does not alter the texture of the organic substrate.

[0013] The antifouling properties are achieved by the superhydrophilicity of the antifouling coating. Superhydrophilicity is obtained by sodium phosphate compounds or potassium phosphate compounds (hereinafter sometimes collectively referred to as "alkali metal phosphates"). Alkali metal phosphates are hygroscopic or water-retaining. When moisture from the atmosphere is attracted to the alkali metal phosphate, the hydrophilic groups (SiOH groups) of alkaline colloidal silica and hydroxide ions (OH) are attracted to it. - It combines with the aqueous inorganic coating agent and is retained as trace amounts of water on the film formed by the aqueous inorganic coating agent. As a result, the antifouling film exhibits superhydrophilicity. The water can be contained in the atmosphere. Even such trace amounts of water will exhibit superhydrophilicity. Furthermore, the retention of water gives the film an antistatic effect, making it difficult for dirt to adhere.

[0014] Due to its superhydrophilic properties, dirt adhering to the substrate is easily washed away with water. This removal of dirt by water is called a self-cleaning action. This self-cleaning action is exhibited, for example, by rainfall or washing with water.

[0015] "Superhydrophilicity" refers to a water contact angle of 15 degrees or less (especially 10 degrees or less). The water contact angle can be measured in accordance with JIS R 3257, Test method for wettability of substrate glass surfaces (static droplet method).

[0016] Conventionally, antifouling coatings have used organofluorine compounds (PFAS, PFOA, etc.), such as fluororesins. In recent years, the U.S. Environmental Protection Agency (EPA) has published a PFAS strategic roadmap, and the Food and Drug Administration (FDA) has announced that it will be verifying the amount of PFAS contained in food. As can be seen from these developments, there are concerns about the environmental and health impacts of organofluorine compounds. The coating agent disclosed herein does not require the use of organofluorine compounds and can achieve high antifouling properties. In addition, the coating agent disclosed herein exhibits an antistatic effect that cannot be obtained with organofluorine compounds, so the film formed by the coating agent disclosed herein has remarkable antifouling properties.

[0017] The aqueous inorganic coating agents in the embodiments of this disclosure will be described in detail below, but the present invention is not limited to these embodiments.

[0018] The solid content concentration of the aqueous inorganic coating agent is not particularly limited and is set appropriately according to the application and purpose. The solid content concentration of the aqueous inorganic coating agent may be 0.1 to 30.0% by mass. This can suppress variations in film thickness. The solid content concentration of the aqueous inorganic coating agent may be 5.0 to 25.0% by mass.

[0019] Solid content is also called non-volatile content. The solid content of aqueous inorganic coating agents is the residue after heating. The solid content concentration can be calculated from the residue after heating the aqueous inorganic coating agent at 200°C for 20 minutes, in accordance with JIS K 5601-1-2, the method for measuring residue after heating.

[0020] The content of each component is the ratio of the solid content concentration (heated residue) of that component to the total solid content concentration (heated residue) of the aqueous inorganic coating agent.

[0021] The pH of the aqueous inorganic coating agent is not particularly limited and may be in the neutral range. The pH of the aqueous inorganic coating agent may be, for example, 5.0 to 9.0 or 6.0 to 8.0. The pH of the aqueous inorganic coating agent containing an inorganic curing agent may be 5.9 to 9.0 or 6.9 to 9.0.

[0022] (Colloidal silica) Colloidal silica crosslinks to form a coating on the substrate.

[0023] Colloidal silica is also called silica sol. Colloidal silica is colloidal particles that mainly consist of silicic acid (SiO2) or hydrated silicic acid. Colloidal silica can be amorphous. The particle shape is not particularly limited and may be spherical or crushed.

[0024] The average particle size of colloidal silica is not particularly limited and can be appropriately selected depending on the application and purpose. For example, the average particle size of colloidal silica may be 3 to 100 nm or 3 to 50 nm. Multiple types of colloidal silica with different average particle sizes may be used in combination.

[0025] The average particle size of colloidal silica is the particle size (D50) at which the cumulative volume, measured by a laser diffraction particle size analyzer, reaches 50%.

[0026] Examples of colloidal silica include at least one of alkaline colloidal silica and neutral colloidal silica. Both alkaline and neutral colloidal silica may be included, or alkaline colloidal silica may be included alone.

[0027] In particular, alkaline colloidal silica and neutral colloidal silica may be used in combination. By using alkaline and neutral colloidal silica, the pH of the inorganic coating agent can be easily adjusted. For example, when applying an inorganic coating agent to glass, it is desirable that the pH be slightly alkaline, because glass is prone to so-called alkali burn. In addition, by using alkaline and neutral colloidal silica, the amount of moisture adsorbed by the resulting antifouling film can be more easily adjusted, thereby suppressing condensation or fogging of the substrate. This is because alkaline colloidal silica adsorbs moisture more easily than neutral colloidal silica.

[0028] The ratio of alkaline colloidal silica to neutral colloidal silica is set appropriately according to the application and purpose. For example, the alkaline colloidal silica content is 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.

[0029] Alkaline colloidal silica is negatively charged colloidal silica. Alkaline colloidal silica may be obtained, for example, by dispersing silica particles in water and stabilizing them with sodium dioxide or the like.

[0030] Neutral colloidal silica has a pH in the neutral range of approximately 7.3. Neutral colloidal silica is produced, for example, by the sol-gel method. pH adjustment can be performed, for example, by adding an acidic or alkaline substance.

[0031] In aqueous inorganic coating agents, the surface of alkaline colloidal silica contains SiOH groups and OH groups. - Numerous such particles exist. As a result, an electrical double layer is formed, suppressing aggregation between alkaline colloidal silica particles. Neutral colloidal silica has a stable surface charge, resulting in appropriate electrostatic repulsion between particles and suppressing aggregation. In aqueous inorganic coating agents, colloidal silica is stably dispersed.

[0032] Examples of commercially available colloidal silica include Nissan Chemical Industries' "Snowtex®" series, Fuso Chemical Industries' "Quattron®" PL series, JGC Catalysts & Chemicals' "Cataloid®" series, ADEKA's "Adelite" series, Remet's "Syton" series, Nalco Chem's "Nalcoag-1060" and "Nalcoag-ID21~64", and WRGrace's "Ludox®" series.

[0033] The colloidal silica content is set appropriately according to the application and purpose. The colloidal silica content may be, for example, 10.0 to 90.0% by mass based on 100% by mass of the solid content of the aqueous inorganic coating agent. The above colloidal silica content may be 85.0% by mass or less, or 75% by mass or less. The above colloidal silica content may be 10.0 to 85.0% by mass, or 10.0 to 75.0% by mass.

[0034] (Inorganic thickener) Inorganic thickeners do not contain carbon atoms. Examples of inorganic thickeners include fumed silica and clay minerals. Fumed silica may be hydrophobic or hydrophilic. Examples of clay minerals include at least one silicate selected from the group consisting of aluminum (Al), magnesium (Mg), iron (Fe), and titanium (Ti).

[0035] Examples of clay minerals include smectite, a swollen silicate with a layered structure, and sepiolite, a hydrated magnesium silicate with a chain structure, one or more of these. Smectite is a general term for swollen layered silicates. Examples of smectite include montmorillonite, bydelite, nontronite, saponite, and hectorite. Smectite and sepiolite may be synthetic compounds. Bentonite is a representative example of clay containing montmorillonite as its main component.

[0036] Examples of commercially available fumed silica products include "AEROSIL 200," "AEROSIL RY 200," "AEROSIL RX 200," "AEROSIL R 202," and "AEROSIL R 208" from Nippon Aerosil Co., Ltd., and "Carplex BS-306" and "Carplex #80" from DSL. Japan Co., Ltd.

[0037] Examples of commercially available smectite include the refined bentonite "Kunipia-F" and "Kunipia-G" manufactured by Kunimine Industries Co., Ltd., the synthetic saponites "Smecton-SA" and "Smecton-ST", the natural sukumetite "OPTIGEL-CD, CK, CK XR, CL, CL XR, LX, W724, WA, WH, WM, WX" manufactured by BYK, and the layered silicate "LAPONITE RD, RDS, s482, SL25".

[0038] The amount of inorganic thickener is set appropriately according to the application and purpose. For continuous processing in-house, such as in a factory, the aqueous inorganic coating agent may have low viscosity. For maintenance of indoor equipment, the aqueous inorganic coating agent may have medium viscosity. For maintenance of outdoor equipment, the aqueous inorganic coating agent may have high viscosity.

[0039] The amount of inorganic thickener may be, for example, 0.5 to 65.0% by mass based on 100% by mass of the solid content of the aqueous inorganic coating agent. The above amount of inorganic thickener may be 1.0% by mass or more, 5.0% by mass or more, or 10.0% by mass or more. The above amount of inorganic thickener may be 55.0% by mass or less, 50.0% by mass or less, or 40.0% by mass or less. The above amount of inorganic thickener may be 1.0 to 55.0% by mass, 5.0 to 50.0% by mass, or 10.0 to 40.0% by mass.

[0040] (Sodium phosphate compound) The sodium phosphate compound contributes to the expression of super hydrophilicity as described above. The sodium phosphate compound is used particularly when flexibility or viscoelasticity is required for the coating.

[0041] Examples of the sodium phosphate compound include disodium hydrogen phosphate anhydride (NaH2PO4), sodium dihydrogen phosphate crystal (NaH2PO4·2H2O), disodium hydrogen phosphate crystal (Na2HPO4·12H2O), trisodium phosphate anhydride (Na3PO4), trisodium phosphate crystal (Na3PO4·12H2O), sodium pyrophosphate crystal (Na4P2O7), sodium pyrophosphate crystal (Na4P2O7·10H2O), disodium dihydrogen pyrophosphate (Na2H2P2O7), sodium tripolyphosphate (Na5P3O 10 ), sodium tetrapolyphosphate (Na6P4O 13 ), sodium hexametaphosphate ((NaPO3) n ), acidic sodium hexametaphosphate ([Na x H y (PO3) x+y n ). These can be used alone or in combination of two or more.

[0042] (Potassium phosphate compound) The potassium phosphate compound contributes to the expression of super hydrophilicity as described above. Examples of the potassium phosphate compound include potassium dihydrogen phosphate (KH2PO4), dipotassium hydrogen phosphate (K2HPO4), and potassium metaphosphate. These can be used alone or in combination of two or more.

[0043] ​The total content of alkali metal phosphates is set appropriately according to 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 70.0% by mass per 100% by mass of the solid content of the aqueous inorganic coating agent. The above content of alkali metal phosphates may be 1.0% by mass or more, 5.0% by mass or more, or 10.0% by mass or more. The above content of alkali metal phosphates may be 65.0% by mass or less, or 60.0% by mass or less. The above content of alkali metal phosphates may be 1.0 to 65.0% by mass, 5.0 to 60.0% by mass, or 10.0 to 60.0% by mass.

[0044] At least one of sodium dihydrogen phosphate and dipotassium hydrogen phosphate may be used because they are easily soluble in water.

[0045] (Boric acid) Boric acid (H3BO3) improves the adhesion between colloidal silica and the substrate. Boric acid also functions as a pH adjuster.

[0046] The boric acid content is set appropriately according to the application and purpose. The boric acid content may be, for example, 0.5 to 35.0% by mass based on 100% by mass of the solid content of the aqueous inorganic coating agent. The boric acid content may be 1.0% by mass or more, 2.0% by mass or more, or 3.0% by mass or more. The boric acid content may be 30.0% by mass or less, 20.0% by mass or less, or 15.0% by mass or less. The boric acid content may be 1.0 to 30.0% by mass, 2.0 to 20.0% by mass, or 3.0 to 15.0% by mass.

[0047] (Aluminum monophosphate) Aqueous inorganic coating agents may contain monoaluminum phosphate. Monoaluminum phosphate densifies the film while suppressing shrinkage of the coating layer during curing. Monoaluminum phosphate is represented as Al2O3·3P2O5·6H2O. From the viewpoint of wear resistance or sliding properties, monoaluminum phosphate is preferably used together with potassium phosphate compounds.

[0048] Examples of commercially available monoaluminum phosphate include liquid monoaluminum phosphate products from Taki Chemical Co., Ltd., such as the product names "50L," "50LH," "100L," and "100P," and powdered monoaluminum phosphate products such as "Acidophos® 37," "Acidophos® 75," and "Acidophos® 120M."

[0049] The content of monoaluminum phosphate is set appropriately according to the application and the desired hardness. The content of monoaluminum phosphate may be, for example, 0.5 to 5.0% by mass based on 100% by mass of the solid content of the aqueous inorganic coating agent. The above content of monoaluminum phosphate may be 0.8% by mass or more, or 1.0% by mass or more. The above content of monoaluminum phosphate may be 4.5% by mass or less, or 4.0% by mass or less. The above content of monoaluminum phosphate may be 0.8 to 4.5% by mass, or 1.0 to 4.0% by mass.

[0050] (Inorganic abrasives) Inorganic abrasives also contribute to improving the adhesion between the antifouling coating and the substrate. Inorganic abrasives do not contain carbon atoms. When an aqueous inorganic coating agent containing an inorganic abrasive is applied and polished, the surface of the substrate is activated while avoiding contact with the atmosphere, and the OH groups generated by the activation can quickly chemically bond with colloidal silica. In addition, the abrasive removes dirt from the substrate surface. As a result, the adhesion between the coating agent and the substrate is further improved.

[0051] 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 individually or in combination of two or more. Aluminum oxide is suitable for stainless steel, fiber-reinforced plastics (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.

[0052] Mesoporous silica may be blended with other inorganic abrasives. Mesoporous silica absorbs pressure from polishers and other equipment, suppressing damage to the substrate, and also adsorbs dirt that has been removed from the substrate, thereby enhancing the cleaning effect.

[0053] The amount of inorganic abrasive is set appropriately according to the application and purpose. The amount of inorganic abrasive may be, for example, 2.0 to 30.0% by mass or 3.0 to 20.0% by mass, based on 100% by mass of the solid content of the aqueous inorganic coating agent.

[0054] The average particle size or particle size of the inorganic abrasive is not particularly limited and is selected appropriately depending on the type of substrate. The table below shows an example of the correspondence between the substrate and the average particle size or particle size of the inorganic abrasive.

[0055] [Table 1]

[0056] The average particle size of the inorganic abrasive is the particle size (D50) at which the cumulative volume, measured by a laser diffraction particle size distribution analyzer, reaches 50%. The particle size of the inorganic abrasive is a value in accordance with JIS R 6001-1 2017 and JIS R 6001-2 2017.

[0057] (Inorganic curing agent) Aqueous inorganic coating agents may contain an inorganic curing agent. The inorganic curing agent contains a metal element but does not contain carbon atoms. In aqueous inorganic coating agents, the inorganic curing agent ionizes to generate metal ions. These metal ions adsorb onto the surface of colloidal silica, promoting aggregation of colloidal silica particles. As a result, crosslinking (hardening) between colloidal silica particles becomes easier, improving the strength of the coating. The inorganic curing agent can particularly improve abrasion resistance and durability. It is desirable to incorporate the inorganic curing agent into aqueous inorganic coating agents, especially for inorganic substrates and high-hardness substrates.

[0058] 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 ionized metal in water. The inorganic curing agent may be water-soluble and colorless.

[0059] In terms of easily generating ionized metals, inorganic hardening agents may contain metal elements other than heavy metals, and may also contain alkali metals and alkaline earth metals. In terms of suppressing discoloration of the antifouling coating, inorganic hardening agents may be, for example, zinc hydroxide or indium tin oxide (ITO).

[0060] Examples of alkali metals include at least one selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). Examples of alkaline earth metals include at least one selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

[0061] The inorganic curing agent may contain a metal stinate salt. Examples of metal stinate salts include zinc stinate (Zn2SnO4), barium stinate (BaSnO3), sodium stinate (Na2SnO3), and potassium stinate (K2SnO3).

[0062] The inorganic curing agent may contain one or more selected from the group consisting of potassium stannate, sodium stannate, zinc stannate, zinc hydroxide, and indium tin oxide. These dissolve in water to form a colorless, transparent aqueous solution.

[0063] The amount of inorganic curing agent is set appropriately according to the application and purpose. The amount of inorganic curing agent may be 10 to 50% by mass or 15 to 40% by mass, relative to 100% by mass of the solid content of the aqueous inorganic coating agent, in order to suppress aggregation and precipitation.

[0064] (Alkali metal silicates) Aqueous inorganic coating agents may contain alkali metal silicates. Alkali metal silicates differ from inorganic thickeners in that they do not contain Al, Mg, Fe, and Ti. Alkali metal silicates are added depending on the substrate, purpose, and application. Alkali metal silicates particularly enhance the film strength after firing.

[0065] Examples of alkali metals include at least one selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).

[0066] Examples of alkali metal silicates include sodium silicate, potassium silicate, and lithium silicate. These can be used individually or in combination of two or more. Sodium silicate is particularly suitable.

[0067] Sodium silicate is also known as 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.

[0068] The alkali metal silicate content is set appropriately according to the application and purpose. The alkali metal silicate content may be 0.5 to 8.0% by mass, or 2.0 to 4.0% by mass, based on 100% by mass of the solid content of alkali metal silicate.

[0069] (solvent) Aqueous inorganic coating agents contain water as a solvent. Examples of water include purified water, deionized water, tap water, and deionized water. Because water does not easily evaporate during storage, it can suppress changes in the physical properties of the aqueous inorganic coating agent over time.

[0070] Specific examples of components contained in the aqueous inorganic coating agent of this disclosure are as follows. (1) Colloidal silica, sodium phosphate compound, boric acid, inorganic thickener, inorganic abrasive, and water (2) Colloidal silica, potassium phosphate compound, boric acid, inorganic thickener, monoaluminum phosphate and water (3) Colloidal silica, sodium phosphate compounds and / or potassium phosphate compounds, boric acid, inorganic thickeners, inorganic curing agents, inorganic abrasives, water (4) Colloidal silica, sodium phosphate compound, boric acid, inorganic thickener, inorganic curing agent, and water

[0071] (Preparation method) Aqueous inorganic coating agents are prepared, for example, as follows: First, boric acid and alkali metal phosphate are added to water. The mixture is heated and dissolved until clear to create an aqueous solution of the additives. The boric acid and alkali metal phosphate may be in powder form or aqueous solution form. Next, a predetermined amount of water, the above aqueous solution of additives, colloidal silica, and an inorganic thickener are added and thoroughly stirred. After that, a curing agent or the like is added as needed and the mixture is thoroughly stirred again.

[0072] [Coating Method] • First Embodiment A coating method according to the first embodiment of this disclosure comprises applying the aqueous inorganic coating agent of this disclosure to the surface of a substrate, and then rubbing the surface of the substrate in the presence of water to form a film. Specifically, the film is completed by rubbing the surface of the substrate in the presence of water and then drying it.

[0073] After applying the aqueous inorganic coating agent, rubbing the surface of the substrate in the presence of water before drying allows active ingredients such as colloidal silica to adhere to the substrate surface, resulting in a dense and highly durable coating.

[0074] "Rubbing" means moving another object while it is in contact with the surface of a substrate. You may rub the surface of the substrate while applying pressure. "In the presence of water" means with water interposed between the surface of the substrate and the object being rubbed. For example, you may rub the surface of the substrate while applying water to it, or you may rub the surface of the substrate after applying water to it.

[0075] Water-based inorganic coatings can be applied, for example, by rollers, mobile semi-automatic coating machines, indoor fixed fully automatic or semi-automatic coating machines, brushes, painting with cloth products (e.g., microfiber cloths), coaters (roll coaters, die coaters, etc.), screen printing, or electric sanders or electric polishers equipped with buffs.

[0076] Electric sanders are not particularly limited. Examples of electric sanders include orbital sanders and disc sanders. Examples of commercially available electric sanders include Makita's Random Orbit Sander (model number: BO06050), Cordless Random Orbital Sander (model number: BO1800), and KYOCERA (formerly Ryobi)'s Square Orbital Sander (model number: NS-3250M).

[0077] Electric polishers are not particularly limited. Examples of electric polishers include double-action, single-action, and gear-action polishers. A commercially available electric polisher is, for example, the electric sander polisher (model number: PE-2100) manufactured by KYOCERA (formerly RYOBI).

[0078] The material used to rub the surface of the substrate is not particularly limited and may be, for example, a cloth or a buff. The friction may be performed by an electric polisher or the like. The buff is not particularly limited and, for example, a short-pile wool buff or a sponge buff can be used.

[0079] The amount of aqueous inorganic coating agent applied and the amount of water are not particularly limited.

[0080] • Second embodiment A coating method according to a second embodiment of the present disclosure comprises applying the aqueous inorganic coating agent of the present disclosure to the surface of a substrate under pressure to form a film.

[0081] By applying the aqueous inorganic coating agent under pressure, active ingredients such as colloidal silica are fixed to the surface of the substrate, resulting in a dense and highly durable coating.

[0082] Methods of applying coating under pressure include, for example, rollers, mobile semi-automatic coating machines, indoor fixed fully automatic or semi-automatic coating machines, brushes, painting using cloth products (e.g., microfiber cloths), screen printing, and methods using coaters (roll coaters, die coaters, etc.). The applied pressure is not limited and is set appropriately depending on the substrate, etc.

[0083] The amount of aqueous inorganic coating agent applied is not particularly limited.

[0084] In the first and second embodiments, after applying the aqueous inorganic coating agent and before it dries, the coated surface may be rubbed with a soft sponge buff or the like moistened with water. This removes any excess aqueous inorganic coating agent and eliminates unevenness in the coating, resulting in a smooth film.

[0085] In the first and second embodiments, after film formation, the surface may be finished by dry wiping with a microfiber cloth or the like, or by wiping with water.

[0086] In the first and second embodiments, when using an aqueous inorganic coating agent containing an inorganic abrasive, it is desirable to remove the inorganic abrasive by applying water after application of the aqueous inorganic coating agent but before drying. Since the inorganic abrasive does not participate in the curing system, it can be easily removed with water. If necessary, the substrate surface may be rubbed or squeegeeed while applying water or after applying water.

[0087] In the first and second embodiments, the aqueous inorganic coating agent may be heated at 80-250°C for 8-30 minutes after application, before or after drying. Heating may 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 100-200°C. The heating time may be 10 minutes or more, or 12 minutes or more. The heating time may be 25 minutes or less, or 20 minutes or less. The heating time may be 10-25 minutes, or 12-20 minutes. Heat treatment is not necessarily required.

[0088] (Application) Water-based inorganic coatings can be used for a variety of applications. They can be used for surface coating of both organic and inorganic substrates. Water-based inorganic coatings are applicable to both outdoor and indoor facilities. The antifouling film formed by the water-based inorganic coating makes it difficult for dirt to adhere, and furthermore, it can be easily removed by rain or washing.

[0089] Water-based inorganic coatings can be used for the maintenance of existing buildings and their ancillary structures, or vehicles. They can also be used in heat-curing coating processes during the manufacturing of industrial products. Examples of applications include automobiles, railway vehicles, ship hulls, aircraft, containers, highway signs, tunnel walls, bridges, structures, glass or acrylic aquariums, musical instruments, furniture, eyeglasses, writing instruments, fishing gear, office equipment such as printers and copiers, wallpaper, and electronic devices such as smartphones and computers.

[0090] (base material) The substrate to be treated with the aqueous inorganic coating agent is not particularly limited. For convenience, a substrate having a surface formed of at least organic material will be referred to as an organic substrate, and a substrate having a surface formed of at least inorganic material will be referred to as an inorganic substrate. The aqueous inorganic coating agent can be applied to both organic and inorganic substrates. When heat curing is performed, an inorganic substrate is preferable.

[0091] Examples of inorganic materials include metals, stone, glass, mirrors, ceramics, and marble. Examples of metals include stainless steel, titanium, aluminum, and copper. The surface of metals may be formed by a plating layer. On the surface of an inorganic substrate, a layer of inorganic material may be formed by, for example, an ITO film, SiO2 deposition, or sputtering. The surface of an inorganic substrate may be subjected to treatments such as polishing or alkaline degreasing.

[0092] Examples of organic materials include various thermoplastic resins, thermosetting resins, FRPs, and rigid films. The organic substrate may be surface-treated. In particular, surface treatment to impart hydrophilic groups (OH groups) may be performed. Examples of surface treatments include corona treatment, plasma treatment, and SiO2 sputtering. The surface of a rigid organic substrate may be polished. [Examples]

[0093] The present invention will be further described by the following examples, but the present invention is not limited thereto. In the examples, "%" means mass percent. The blending ratio (solid content) of each component is shown in Table 1.

[0094] Details of the materials used in the examples are as follows: • Colloidal silica Nissan Chemical Corporation, product name "Snowtex 40", average particle size 10-20 nm, solid content concentration 40.5%, alkaline. Alkali metal phosphates Potassium dihydrogen phosphate, manufactured by Taihei Chemical Industry Co., Ltd., in powder form. Anhydrous sodium dishydrogen phosphate, manufactured by Taihei Chemical Industry Co., Ltd., in powder form. Boric acid Taiyo Chemical Industry Co., Ltd., purified boric acid, powder form • Inorganic thickener Manufactured by Kunimine Industries Co., Ltd., product name "Kunipia-F", refined bentonite. Manufactured by Kunimine Industries Co., Ltd., product name "Kunipia-G", refined bentonite • Inorganic curing agent Potassium stinate aqueous solution, solid content concentration approximately 33% by mass • Inorganic abrasives Mesoporous silica, average particle size 100 μm • Aluminum monophosphate Manufactured by Taki Chemical Co., Ltd., product name "100L", liquid, solid content concentration 50% by mass

[0095] [Example 1] 38.73 g of anhydrous sodium dihydrogen phosphate powder and 6.01 g of purified boric acid powder were placed in a stainless steel heating container, and approximately 91.92 g of water was added. The mixture was heated until it became colorless and transparent, dissolving each powder and yielding a total of 136.66 g of additive aqueous solution (1).

[0096] Separately, 43.8g of colloidal silica was added to 1880.34g of water and stirred well at room temperature. The entire 136.66g of the additive aqueous solution (1) was then added and stirred well to obtain 2060.8g of additive aqueous solution (2).

[0097] 26.4 g of inorganic thickener (purified bentonite, "Kunipia-F") was added to 880 g of additive aqueous solution (2), and the mixture was stirred well until there were no lumps. Subsequently, 155 g of inorganic hardening agent (potassium stanate aqueous solution, solid content concentration approximately 33% by mass) was added and the mixture was stirred well to obtain an aqueous inorganic coating agent (solid content concentration 12.18% by mass, pH 9.0).

[0098] [Example 2] 25.37 g of anhydrous potassium dihydrate powder and 19.09 g of purified boric acid powder were placed in a stainless steel heating container, and approximately 269.01 g of water was added. The mixture was heated until it became colorless and transparent, dissolving each powder and yielding a total of 313.47 g of additive aqueous solution (1).

[0099] Separately, 245 g of colloidal silica was added to 1447.49 g of water and stirred well at room temperature. To this, the entire 313.47 g of the additive aqueous solution (1) and 10 g of monoaluminum phosphate (solid content concentration 50% by mass) were added and stirred well to obtain 2015.96 g of additive aqueous solution (2).

[0100] 72 g of inorganic thickener (purified bentonite, "Kunipia-G") was added to 800 g of additive aqueous solution (2), and the mixture was stirred well until there were no lumps to obtain an aqueous inorganic coating agent (solid content concentration 23.50% by mass, pH 8.2).

[0101] [Example 3] 52.96 g of anhydrous sodium dihydrogen phosphate powder and 5.88 g of purified boric acid powder were placed in a stainless steel heating container, and approximately 205.97 g of water was added. The mixture was heated until it became colorless and transparent, dissolving each powder and yielding a total of 264.81 g of additive aqueous solution (1).

[0102] Separately, 88.2g of colloidal silica was added to 1706.99g of water and stirred well at room temperature to obtain 2060g of additive aqueous solution (2).

[0103] To 800g of additive aqueous solution (2), an additional 200g of colloidal silica and 50g of inorganic abrasive (mesoporous silica) were added sequentially, stirring well each time. Next, 30g of inorganic thickener (purified bentonite, "Kunipia-F") was added and stirred well until there were no lumps. Finally, 180g of inorganic hardening agent (potassium stanate aqueous solution, solid content concentration approximately 33% by mass) was added and stirred well to obtain an aqueous inorganic coating agent (solid content concentration 22.26% by mass, pH 8.9).

[0104] [Table 2]

[0105] [Example of application 1] Application to the hood (painted surface) of a car. The aqueous inorganic coating agent of Example 1 was applied to the painted surface (organic substrate) of a car hood, and then the coated surface was rubbed with a water-moistened sponge buff to remove any unevenness in the coating. After drying, it was wiped with water to form an anti-fouling film.

[0106] Figure 1 is a photograph of a portion of the hood of a car that has been treated with the aqueous inorganic coating agent of Example 1. The upper part of Figure 1 is untreated, while the lower part is treated. It was confirmed that there is no dirt adhering to the lower part.

[0107] [Example of application 2] Application to railway vehicles (painted surface and tape portion) The aqueous inorganic coating agent of Example 2 was applied to the painted surface (organic substrate) of a stainless steel railway vehicle and to tape (organic substrate) attached to the railway vehicle. Subsequently, the coated surface was rubbed with a water-moistened sponge buff to remove any unevenness in the coating. After drying, a damp cloth was used to finish and form an anti-fouling film.

[0108] Figure 2A is a photograph of a portion of the painted surface of a railway vehicle that was treated with the aqueous inorganic coating agent of Example 2. Figure 2B is a photograph of a portion of tape applied to the outer surface of a railway vehicle. An antifouling film was formed on the original surface that was exposed after the dirt was removed.

[0109] [Example of application 3] Application to highway signs (rigid film) The aqueous inorganic coating agent of Example 2 was applied to a highway sign covered with a rigid film, and then the coated surface was rubbed with a water-moistened sponge buff to remove any unevenness in the coating. Next, it was allowed to dry to form an anti-fouling film.

[0110] Figure 3 is a photograph of a highway sign that was coated with the aqueous inorganic coating agent of Example 2. The left half of the sign is uncoated, while the right half is coated. It was confirmed that the right half was free of dirt and had vivid colors.

[0111] [Example of Construction 4] Construction on a ship (made of FRP) The aqueous inorganic coating agent of Example 3 was applied to an FRP vessel, and then the coated surface was rubbed with a water-dampened sponge buff to remove any unevenness in the coating. After drying, it was wiped with water to form an antifouling film.

[0112] Figure 4 is a photograph of a portion of a ship that was coated with the aqueous inorganic coating agent of Example 3.

[0113] [Example of application 5] Application to bridge steel plates (painted surface) The aqueous inorganic coating agent of Example 2 was applied to the painted surface of the bridge steel plate, and then the coated surface was rubbed with a water-moistened sponge buff to remove any unevenness in the coating. Next, it was allowed to dry to form an antifouling film.

[0114] Figure 5 is a photograph of a portion of a bridge steel plate treated with the aqueous inorganic coating agent of Example 2. The bridge is located near the coast, and is expected to reduce salt buildup, prevent fouling, and provide a self-cleaning effect through rainfall.

[0115] [Example of installation 6] Installation on the back door of a car The aqueous inorganic coating agent of Example 1 was applied to the painted surface (organic substrate) of a car's tailgate. Subsequently, the coated surface was rubbed with a water-moistened sponge buff to remove any unevenness in the coating. After drying, it was wiped with water to form an anti-fouling film.

[0116] Figure 6 is a photograph of a car's tailgate that was treated with the aqueous inorganic coating agent of Example 1. The tailgate on the right is untreated, while the one on the left is treated. The tailgate's surface had chalked due to UV degradation. By rubbing it with the highly adhesive inorganic coating agent, the chalked areas were removed, exposing the original paint surface, and an anti-fouling film could be formed on top of it.

[0117] [Example of installation 7] Installation on a mailbox The aqueous inorganic coating agent of Example 2 was applied to the painted surface (organic substrate) of a mailbox, and then the coated surface was rubbed with a water-moistened sponge buff to remove any unevenness in the coating. Next, it was allowed to dry to form an anti-fouling film.

[0118] Figure 7A is a photograph of the post before application. Figure 7B is a photograph of the post after it has been treated with the water-based inorganic coating agent of Example 2. The post in Figure 7A had chalked white on its surface due to UV degradation. As can be seen in Figure 7B, by rubbing with the highly adhesive inorganic coating agent, the chalked portion was peeled off, exposing the original paint surface, and an antifouling film was formed on top of it.

[0119] [Example of installation 8] Installation on a door (mirror-finish stainless steel) The aqueous inorganic coating agent of Example 3 was applied to a mirror-finished stainless steel (inorganic substrate) door of a boutique shop. Subsequently, the coated surface was rubbed with a water-dampened sponge buff to remove any unevenness in the coating. After drying, it was wiped with water to form an anti-fouling film.

[0120] Figure 8 is a photograph of a mirror-finished stainless steel door coated with the aqueous inorganic coating agent of Example 3. Although the aqueous inorganic coating agent of Example 3 contains an inorganic abrasive, Figure 8 shows that an antifouling film was formed on the mirror-finished surface without scratching it.

[0121] [Example of work 9] Application to a monument (made of mirror-finished stainless steel) The aqueous inorganic coating agent of Example 3 was applied to a mirror-finished stainless steel mathematical model monument (inorganic substrate), and then the coated surface was rubbed with a water-moistened sponge buff to remove any unevenness in the coating. After drying, it was wiped with water to form an anti-fouling film.

[0122] The monument is located outdoors on the island of Yerba Buena in San Francisco, and is expected to require no maintenance for a long period of time due to its properties such as resistance to dirt accumulation, self-cleaning action through rainfall, and resistance to UV degradation. [Industrial applicability]

[0123] The aqueous inorganic coating agent of this disclosure can form a film with high antifouling properties on various substrates.

Claims

1. Colloidal silica and At least one of a sodium phosphate compound and a potassium phosphate compound, Boric acid and, Inorganic thickeners and Water and, A water-based inorganic coating agent containing monoaluminum phosphate.

2. Colloidal silica and At least one of a sodium phosphate compound and a potassium phosphate compound, Boric acid and, Inorganic thickeners and Water and, An aqueous inorganic coating agent comprising one or more inorganic abrasives selected from the group consisting of aluminum oxide, cerium oxide, and mesoporous silica.

3. Colloidal silica and At least one of a sodium phosphate compound and a potassium phosphate compound, Boric acid and, Inorganic thickeners and Water and, An aqueous inorganic coating agent comprising an inorganic curing agent containing a metal stainate salt.

4. Colloidal silica and At least one of a sodium phosphate compound and a potassium phosphate compound, Boric acid and, Inorganic thickeners and Water and, An aqueous inorganic coating agent comprising one or more inorganic curing agents selected from the group consisting of potassium stannate, sodium stannate, zinc stannate, zinc hydroxide, and indium tin oxide.

5. The aqueous inorganic coating agent according to any one of claims 1 to 4, wherein the inorganic thickener comprises one or more smectites or sepiolites.

6. Furthermore, the aqueous inorganic coating agent according to any one of claims 2 to 4, further comprising monoaluminum phosphate.

7. Furthermore, the aqueous inorganic coating agent according to claim 1, 3, or 4, further comprising an inorganic abrasive.

8. The aqueous inorganic coating agent according to claim 7, wherein the inorganic abrasive comprises one or more selected from the group consisting of aluminum oxide, cerium oxide, and mesoporous silica.

9. Furthermore, the aqueous inorganic coating agent according to claim 1, 2, or 4, further comprising an inorganic curing agent containing a metal element.

10. The aqueous inorganic coating agent according to claim 9, wherein the inorganic curing agent comprises a metal stainate salt.

11. The aqueous inorganic coating agent according to claim 9, 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.

12. An aqueous inorganic coating agent according to any one of claims 1 to 4, wherein the pH is 5.0 to 9.

0.

13. An aqueous inorganic coating agent according to any one of claims 1 to 4, wherein the solid content concentration is 0.1 to 30.0% by mass.

14. Applying the aqueous inorganic coating agent described in any one of claims 1 to 4 to the surface of the substrate, A coating method comprising subsequently rubbing the surface of the substrate in the presence of water to form a coating film.

15. A coating method comprising applying an aqueous inorganic coating agent according to any one of claims 1 to 4 to the surface of a substrate under pressure to form a film.

16. The coating method according to claim 14, wherein the substrate has a surface formed of an organic material.

17. The coating method according to claim 15, wherein the substrate has a surface formed of an organic material.

18. The coating method according to claim 14, wherein the substrate has a surface formed of an inorganic material.

19. The coating method according to claim 15, wherein the substrate has a surface formed of an inorganic material.

20. Furthermore, the coating method according to claim 14, comprising heating the coating at 80 to 250°C for 8 to 30 minutes after the formation of the coating.

21. The coating method according to claim 15, further comprising heating the coating at 80 to 250°C for 8 to 30 minutes after the formation of the coating.

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