Water-based inorganic coating agent and coating method

Abstract

Provided is an aqueous inorganic coating agent capable of forming a coating film having high antifogging properties. [Solution] The aqueous inorganic coating agent comprises small-particle colloidal silica having an average particle diameter of 3 nm or more and 10 nm or less, large-particle colloidal silica having an average particle diameter of more than 10 nm and 100 nm or less, at least one of a sodium phosphate compound and a potassium phosphate compound, boric acid, 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] In recent years, with the development of technology related to virtual reality, there has been a demand for anti-fogging properties, particularly for the glasses of VR goggles, to prevent their optical properties from being impaired over the long term.

[0005] An object of the present disclosure is to provide an aqueous inorganic coating agent capable of forming a coating film having high anti-fogging properties. [Means for solving the problem]

[0006] The present disclosure includes the following aspects. [1] Small particle size colloidal silica with an average particle size of 3 nm to 10 nm, Large particle size colloidal silica with an average particle size of more than 10 nm and less than 100 nm, At least one of a sodium phosphate compound and a potassium phosphate compound; Boric acid, and water. [2] The aqueous inorganic coating agent according to [1] above, which has a pH of 5.0 to 8.0. [3] The small particle size colloidal silica is alkaline, The aqueous inorganic coating agent according to the above [1] or [2], wherein the large particle size colloidal silica is neutral. [4] The aqueous inorganic coating agent according to any one of the above [1] to [3], which has a solid content concentration of 0.1 to 25.0 mass %. [5] The aqueous inorganic coating agent according to any one of the above [1] to [4] further contains an alkali metal silicate. [6] Applying any one of the aqueous inorganic coating agents [1] to [5] 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. [7] A coating method comprising applying any one of the aqueous inorganic coating agents [1] to [5] above to the surface of a substrate while applying pressure to form a coating. [8] The coating method according to [6] or [7] 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]

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

[0008] [Figure 1] In Application Example 1, a container filled with boiling water was covered with a glass plate treated with the aqueous inorganic coating agent of Example 1, and after 5 minutes, a photograph of the inside of the container was taken through the glass plate. [Figure 2]In Application Example 2, a container filled with boiling water was covered with a glass plate treated with the aqueous inorganic coating agent of Example 2, and after 5 minutes, a photograph of the inside of the container was taken through the glass plate. [Figure 3] In Comparative Application Example 1, a container filled with boiling water was covered with a glass plate treated with the aqueous inorganic coating agent of Comparative Example 1, and after 5 minutes, a photograph of the inside of the container was taken through the glass plate. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Water-based inorganic coating agent] The aqueous inorganic coating agent of the present disclosure contains small-particle colloidal silica having an average particle size of 3 nm to 10 nm, large-particle colloidal silica having an average particle size of more than 10 nm and not more than 100 nm, at least one of a sodium phosphate compound and a potassium phosphate compound, boric acid, and water. Such an aqueous inorganic coating agent forms a coating film with high anti-fogging properties.

[0010] In this disclosure, "high anti-fogging properties" refers to the ability to have excellent anti-fogging properties and maintain this effect for a long period of time. "Fogging" refers to the refraction or scattering of light caused by water droplets adhering to a surface. Large water droplets in particular can act like lenses and distort images. "Anti-fogging properties" refer to the ability to reduce the adhesion of water droplets that cause image distortion and to suppress the refraction or scattering of light.

[0011] "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.

[0012] The coating formed by the aqueous inorganic coating agent of the present disclosure (hereinafter, sometimes referred to as an anti-fog coating) has high adhesion to the substrate. Furthermore, the anti-fog coating has superhydrophilic properties, so it can quickly turn water droplets into a film. Additionally, the anti-fog coating can prevent excessive water adsorption and suppress the adhesion of large water droplets. These actions result in high anti-fog properties.

[0013] High adhesion and suppression of excessive water adsorption are achieved by using at least two types of colloidal silica with different average particle sizes. Large-particle colloidal silica adheres firmly to the substrate, improving the durability of the coating. Meanwhile, large-particle colloidal silica creates irregularities on the coating surface. Water tends to accumulate in these irregularities, resulting in large droplets adhering to the coating surface. The lens effect of these droplets causes image distortion. Small-particle colloidal silica penetrates into the gaps between the large-particle colloidal silica particles, smoothing the coating surface. This suppresses excessive water adsorption to the coating and reduces the formation of large droplets. In particular, the combined use of small-particle colloidal silica with an average particle size of 3 nm to 10 nm and large-particle colloidal silica with an average particle size of more than 10 nm to 100 nm results in a smoother coating surface, further reducing the formation of droplets.

[0014] The presence of two or more types of colloidal silica with different average particle sizes can be confirmed using an electron microscope. The average particle size is the primary particle size. The average particle size may be the catalog value for the colloidal silica.

[0015] There are two or more types of colloidal silica with different average particle sizes, and these average particle sizes can also be obtained using, for example, the Nicomp (registered trademark) DLS system manufactured by Nihon Entegris, LLC, which utilizes dynamic scattering. The average particle size is the peak value obtained with this device.

[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 anti-fog coating exhibit superhydrophilicity. The moisture may be that contained in the atmosphere. Even with such a trace amount of moisture, superhydrophilicity is exhibited.

[0017] 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.

[0018] "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).

[0019] That is, the aqueous inorganic coating agent of the present disclosure can provide a coating film that not only has high antifogging properties but also has antifouling properties due to its self-cleaning action, and the antifouling properties are also maintained for a long period of time.

[0020] 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 exhibit high anti-fouling and anti-fogging properties without the need for organic fluorine compounds or surfactants.

[0021] 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.

[0022] 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 %.

[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 limited and is appropriately set depending on the application. The pH of the aqueous inorganic coating agent may be in the neutral range. The pH of the aqueous inorganic coating agent may be, for example, 5.0 to 8.0, or 6.0 to 8.0.

[0026] (colloidal silica) The colloidal silica crosslinks to form a coating on the substrate. In the present disclosure, at least two types of colloidal silica, small particle size colloidal silica and large particle size colloidal silica, are used in combination.

[0027] 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.

[0028] The average particle size of the small particle size colloidal silica is 3.0 nm or more and 10.0 nm or less. The average particle size of the small particle size colloidal silica may be 4.0 nm or more. The average particle size of the small particle size colloidal silica may be 9.0 nm or less, 8.0 nm or less, or 7.0 nm or less. The average particle size of the small particle size colloidal silica may be 3.0 to 9.0 nm, 4.0 to 9.0 nm, 4.0 to 8.0 nm, or 4.0 to 7.0 nm.

[0029] The average particle size of the large-particle-size colloidal silica is greater than 10.0 nm and not greater than 100.0 nm. The average particle size of the large-particle-size colloidal silica may be 12.0 nm or greater, or 14.0 nm or greater. The average particle size of the large-particle-size colloidal silica may be 50.0 nm or less, 30.0 nm or less, or 20.0 nm or less. The average particle size of the large-particle-size colloidal silica may be 12.0 to 50.0 nm, 12.0 to 30.0 nm, 12.0 to 20.0 nm, or 14.0 to 20.0 nm.

[0030] The content of the small particle size colloidal silica is appropriately set depending on the application and purpose. The content of the small particle size colloidal silica may be 20.0 mass% or more, 30.0 mass% or more, or 35.0 mass% or more, relative to 100 mass% of the solid content of the aqueous inorganic coating agent. The content of the small particle size colloidal silica may be 80.0 mass% or less, 70.0 mass% or less, or 60.0 mass% or less. The content of the small particle size colloidal silica may be 20.0 to 80.0 mass%, 30.0 to 70.0 mass%, or 35.0 to 60.0 mass%.

[0031] The content of the large-particle size colloidal silica is appropriately set depending on the application and purpose. The content of the large-particle size colloidal silica may be 5.0% by mass or more, 10.0% by mass or more, or 20.0% by mass or more, relative to 100% by mass of the solid content of the aqueous inorganic coating agent. The content of the large-particle size colloidal silica may be 60.0% by mass or less, or 50.0% by mass or less. The content of the large-particle size colloidal silica may be 5.0 to 60.0% by mass, 10.0 to 60.0% by mass, or 20.0 to 50.0% by mass.

[0032] The ratio of the content of small-particle-size colloidal silica to the content of large-particle-size colloidal silica is appropriately set depending on the application and purpose. The content of small-particle-size colloidal silica may be greater than the content of large-particle-size colloidal silica. Since small-particle-size colloidal silica has a larger surface area, it has higher water adsorption properties and easily forms a water film. The content of small-particle-size colloidal silica may be 1.0 times or more, or 1.2 times or more, the content of large-particle-size colloidal silica. From the viewpoint of suppressing excessive water adsorption, the content of small-particle-size colloidal silica may be 2.5 times or less, or 2.2 times or less, the content of large-particle-size colloidal silica. The content of small-particle-size colloidal silica may be 1.0 to 2.5 times, or 1.2 to 2.2 times the content of large-particle-size colloidal silica.

[0033] 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 alone may be included. Alkaline colloidal silica is negatively charged colloidal silica. The pH of alkaline colloidal silica sol is said to be about 9 to 10.5. The pH of neutral colloidal silica sol is said to be about 7.3.

[0034] 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. In addition, the use of alkaline and neutral colloidal silica allows for easier adjustment of the moisture adsorption amount of the resulting anti-fogging coating. This is because alkaline colloidal silica adsorbs moisture more easily than neutral colloidal silica.

[0035] In particular, alkaline small particle size colloidal silica and neutral large particle size colloidal silica may be used in combination, which provides a good balance of adhesion of the anti-fogging coating, water film formation, and prevention of water droplet adhesion.

[0036] 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.

[0037] The alkaline colloidal silica may be, for example, silica particles dispersed in water and stabilized with sodium dioxide or the like.

[0038] Neutral colloidal silica is produced, for example, by a sol-gel method. The pH can be adjusted, for example, by adding an acidic or alkaline substance.

[0039] 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.

[0040] (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.

[0041] (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.

[0042] 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 8.0 mass% or more. The content of alkali metal phosphates may be 40.0 mass% or less, 20.0 mass% or less, or 15.0 mass% or less. The content of alkali metal phosphates may be 1.0 to 40.0 mass%, 5.0 to 20.0 mass%, or 8.0 to 15.0 mass%.

[0043] At least one of sodium dihydrogen phosphate and dipotassium hydrogen phosphate may be used, as they are easily soluble in water.

[0044] (boric acid) Boric acid (H3BO3) improves adhesion between colloidal silica and the substrate. Boric acid also acts as a pH adjuster.

[0045] 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.

[0046] (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.

[0047] 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).

[0048] 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.

[0049] 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.

[0050] 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.

[0051] (aluminum monophosphate) Aqueous inorganic coating agents may contain monoaluminum phosphate. Monoaluminum phosphate is added depending on the substrate, purpose, application, etc. For example, when the anti-fog coating is formed by heat curing, monoaluminum phosphate can increase the hardness of the anti-fog coating. Monoaluminum phosphate is expressed as Al2O3·3P2O5·6H2O.

[0052] 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."

[0053] 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.

[0054] (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.

[0055] Specific examples of components contained in the aqueous inorganic coating agent of the present disclosure are as follows. (1) Alkaline small particle size colloidal silica, neutral large particle size colloidal silica, sodium phosphate compound, boric acid, and water (2) Alkaline small particle size colloidal silica, neutral large particle size colloidal silica, potassium phosphate compound, boric acid, and water (3) Alkaline small particle size colloidal silica, neutral large particle size colloidal silica, sodium phosphate compound, potassium phosphate compound, boric acid, and water (4) The above component (1), (2), or (3), and an alkali metal silicate (5) The above component (1), (2), or (3), and monoaluminum phosphate (6) The above component (1), (2), or (3), alkali metal silicate, and monoaluminum phosphate

[0056] (Preparation method) The aqueous inorganic coating agent is prepared, for example, as follows: First, boric acid, an alkali metal phosphate, and, if necessary, an alkali metal silicate and / or aluminum monophosphate are added to water. The mixture is heated and dissolved until transparent, creating 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, and small-particle and large-particle colloidal silica are mixed and stirred.

[0057] (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 anti-fog coating film formed by the aqueous inorganic coating agent is dense and does not easily impair the properties of the optical glass.

[0058] 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.

[0059] (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.

[0060] Examples of inorganic materials include glass and mirrors, and examples of organic materials include various thermoplastic resins and various thermosetting resins.

[0061] The organic substrate may be transparent. Specifically, "transparent" means that the total light transmittance is 80% or more. The total light transmittance can be measured by a method conforming to JIS K 7361-1. The organic substrate may be colorless or colored. Examples of the organic substrate include transparent films made of polycarbonate and acrylic resin. The organic substrate may be surface-treated. In particular, the surface may be treated to impart hydrophilic groups (OH groups). Examples of surface treatments include corona treatment, plasma treatment, and SiO2 sputtering.

[0062] [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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] The amount of the aqueous inorganic coating agent to be applied and the amount of water are not particularly limited.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] The amount of the aqueous inorganic coating agent to be applied is not particularly limited.

[0071] In the first and second embodiments, the method may further comprise heating at 80 to 250°C for 8 to 30 minutes after forming the coating. By heating, a coating having high hardness is formed. 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 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 to 25 minutes, or 12 to 20 minutes.

[0072] By using the aqueous inorganic coating agent of the present disclosure, a coating having high hardness can be formed even when cured at room temperature (20 to 25°C). For example, an anti-fog 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 anti-fog 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 anti-fog 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]

[0073] 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.

[0074] Details of the materials used in the examples are as follows: Small particle size colloidal silica Alkaline, manufactured by Nissan Chemical Industries, product name "Snowtex XS", average particle size (Sears method, catalog value) 5 nm, solid content concentration 20 mass%, stabilized with sodium dioxide Large particle size colloidal silica A Alkaline, manufactured by Nissan Chemical Industries, product name "Snowtex 40", average particle size (catalog value) 10-15 nm, solid content concentration 40 mass% Large particle size colloidal silica B Neutral, manufactured by Fuso Chemical Co., Ltd., Quattron (registered trademark) PL series, product name "PL-1", pH 7.3, average particle size (catalog value) 15 nm, solid content concentration 12 mass% 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

[0075] [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.

[0076] Separately, 262 g of small particle size colloidal silica (alkaline), 157 g of large particle size colloidal silica B (neutral), 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 2160 g of an aqueous inorganic coating agent (solids concentration 4.86 mass%, pH 7.6).

[0077] [Example 2] In the same manner as above, a total of 208 g of an aqueous additive solution was obtained. Separately, 157 g of small particle size colloidal silica (alkaline) and 79 g of large particle size colloidal silica A (alkaline) were added to 1530 g of water and stirred thoroughly at room temperature. The entire 208 g of the additive aqueous solution was then added and stirred thoroughly to obtain 1974 g of an aqueous inorganic coating agent (solid content concentration 4.03 mass %, pH 7.8).

[0078] [Comparative Example 1] An aqueous coating agent (solid content concentration 2.69 mass %, pH 7.75) was prepared in the same manner as in Example 2, except that large particle size colloidal silica was not added.

[0079] [Table 1]

[0080] [Application example 1] Application to glass The aqueous inorganic coating agent of Example 1 was applied to one surface of a glass plate, 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 an anti-fogging coating.

[0081] Boiling water was poured into a stainless steel container and the container was covered with the treated glass plate, with the surface on which the anti-fogging coating was formed facing downwards (towards the container) to prevent steam from escaping.

[0082] Figure 1 shows a photograph of the inside of a container filled with boiling water, taken five minutes after the glass plate treated with the aqueous inorganic coating agent of Example 1 was placed over the container. The surface of the glass plate facing the container was clear and the bottom of the container was visible through the glass plate. In Figures 1 and 2, the water droplets adhering to the inner surface of the container appear donut-shaped.

[0083] Although very fine water droplets were uniformly attached to the container-side surface of the glass plate, they did not cause fogging. Since such fine water droplets are unlikely to impair optical properties, it was confirmed that the inorganic coating agent of the present disclosure is suitable for optical glass such as VR goggles.

[0084] [Application example 2] Application to glass The aqueous inorganic coating agent of Example 2 was applied to one surface of a glass plate, 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 an anti-fogging coating.

[0085] The glass plate was observed in the same manner as in Application Example 1. Figure 2 is a photograph of the inside of a container filled with boiling water, taken through the glass plate treated with the aqueous inorganic coating agent of Example 2, after 5 minutes had elapsed.

[0086] Although large water droplets were observed on the container-facing surface of the glass plate, the bottom of the container was clearly visible through the glass plate, and the large water droplets did not run off.

[0087] [Comparative application example 1] Application to glass The aqueous inorganic coating agent of Comparative Example 1 was applied to one surface of a glass plate, 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 an anti-fogging coating.

[0088] The glass plate was observed in the same manner as in Application Example 1. Fig. 3 is a photograph of the inside of a container filled with boiling water, taken through the glass plate treated with the aqueous inorganic coating agent of Comparative Example 1, after 5 minutes had elapsed.

[0089] Although the photograph itself is unclear, it is possible to confirm that several large droplets of water were attached to the surface of the glass plate facing the container. The amount of water droplets increased over time, and the enlarged droplets sometimes fell off due to their own weight. It was not possible to clearly see the bottom of the container through the glass plate. [Industrial Applicability]

[0090] The aqueous inorganic coating agent of the present disclosure can impart high anti-fogging properties to various substrates.

Claims

1. alkaline small particle colloidal silica having an average particle size of 3 nm or more and 10 nm or less; neutral large-particle colloidal silica having an average particle size of more than 10 nm and not more than 100 nm; At least one of a sodium phosphate compound and a potassium phosphate compound; Boric acid, 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 the coating is formed.

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