Aqueous inorganic coating agent, coating film, and method for forming the coating film

Abstract

This invention provides an aqueous inorganic coating agent that has high stain resistance and can form a film with suppressed interference fringes, and a coating method using this aqueous inorganic coating agent. [Solution] An aqueous inorganic coating agent comprising a potassium silicate compound, colloidal silica, a sodium phosphate compound, boric acid, and water, wherein the content of the potassium phosphate compound is less than 0.10% by mass of the solid content of the aqueous inorganic coating agent.

Description

[Technical Field]

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

[0002] Conventionally, coating agents containing silicon dioxide, intended to prevent contamination of substrates, are known. For example, Patent Documents 1 to 3 disclose aqueous inorganic coating agents that are applied to the surface of organic or inorganic substrates to form a superhydrophilic transparent inorganic film. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Publication No. 7780832 [Patent Document 2] Publication No. 7803607 [Patent Document 3] Publication No. 7803608 [Overview of the project] [Problems that the invention aims to solve]

[0004] The coatings formed by the aqueous inorganic coating agents described in Patent Documents 1 to 3 are thought to be free of irregularities, have high surface reflectivity and surface refractive index, and are prone to interference fringes.

[0005] The present disclosure aims to provide an aqueous inorganic coating agent that has high antifouling properties and can form a film with suppressed interference fringes, and a method for forming a film using this aqueous inorganic coating agent. [Means for solving the problem]

[0006] This disclosure includes the following aspects: [1] A water-based inorganic coating agent, Potassium silicate compounds, Colloidal silica, Sodium phosphate compounds, Boric acid, and, Contains water, An aqueous inorganic coating agent in which the potassium phosphate compound content is less than 0.10% by mass of the solid content of the aqueous inorganic coating agent. [2] An aqueous inorganic coating agent according to [1] above, wherein the solid content concentration is 0.50 to 30.00% by mass. [3] The aqueous inorganic coating agent according to [1] or [2] above, wherein the boric acid content is 0.30 to 10.00% by mass of the solid content of the aqueous inorganic coating agent. [4] The aqueous inorganic coating agent further comprises a sodium silicate compound, any of the above [1] to [3] aqueous inorganic coating agents. [5] The colloidal silica content is 20.00 to 90.00% by mass of the solid content of the aqueous inorganic coating agent. An aqueous inorganic coating agent according to any of the above [1] to [4], wherein the content of the potassium silicate compound is 2.00 to 20.00% by mass of the solid content of the aqueous inorganic coating agent. [6] The sodium phosphate compound content is 0.10 to 5.00% by mass of the solid content of the aqueous inorganic coating agent. The aqueous inorganic coating agent according to [5], wherein the boric acid content is 1.00 to 10.00% by mass of the solid content of the aqueous inorganic coating agent. [7] The colloidal silica content is 5.00 to 35.00% by mass of the solid content of the aqueous inorganic coating agent. An aqueous inorganic coating agent according to any of the above [1] to [4], wherein the content of the potassium silicate compound is 5.00 to 40.00% by mass of the solid content of the aqueous inorganic coating agent. [8] The sodium phosphate compound content is 30.00 to 70.00% by mass of the solid content of the aqueous inorganic coating agent. The aqueous inorganic coating agent according to [7], wherein the boric acid content is 0.30 to 1.50% by mass of the solid content of the aqueous inorganic coating agent. [9] The content of the colloidal silica is 35.00 to 60.00% by mass of the solid content of the aqueous inorganic coating agent, The aqueous inorganic coating agent according to any one of [1] to [4] above, wherein the content of the potassium silicate compound is 1.00 to 20.00% by mass of the solid content of the aqueous inorganic coating agent.

[10] The content of the sodium phosphate compound is 0.02 to 2.00% by mass of the solid content of the aqueous inorganic coating agent, The aqueous inorganic coating agent according to [9] above, wherein the content of the boric acid is 0.30 to 1.50% by mass of the solid content of the aqueous inorganic coating agent.

[11] The aqueous inorganic coating agent according to any one of [1] to

[10] above, further comprising an inorganic abrasive.

[12] The aqueous inorganic coating agent according to any one of [1] to

[11] above, further comprising an inorganic thickener.

[13] The aqueous inorganic coating agent according to any one of [1] to

[12] above, further comprising an inorganic curing agent.

[14] The aqueous inorganic coating agent according to any one of [1] to

[13] above, further comprising primary aluminum phosphate.

[15] The aqueous inorganic coating agent according to any one of [1] to

[14] above, wherein the colloidal silica has an average particle diameter of 5 to 30 nm.

[16] A film formed by the aqueous inorganic coating agent according to any one of [1] to

[14] above.

[17] The film according to

[16] above, wherein the refractive index of light with a wavelength of 507 nm is 1.30 to 1.40.

[18] The film according to

[16] or

[17] above, wherein the transmittance of light with a wavelength of 370 to 870 nm incident at an angle of 90 degrees is 93.00% or more.

[19] A method for forming a coating, comprising applying one of the above-mentioned aqueous inorganic coating agents [1] to

[14] to the surface of a substrate under atmospheric pressure.

[20] A method for forming the coating according to

[19] , wherein the substrate has a surface formed of an organic material. [twenty one] A method for forming the coating according to

[19] or

[20] above, wherein the substrate has a surface formed of an inorganic material. [Effects of the Invention]

[0007] This disclosure provides an aqueous inorganic coating agent that has high antifouling properties and can form a film with suppressed interference fringes, and a method for forming a film using this aqueous inorganic coating agent. [Brief explanation of the drawing]

[0008] [Figure 1A] This is an atomic force microscope image (90 μm × 90 μm) of the coating surface obtained in Example 2. [Figure 1B] This is the surface structure profile obtained from data acquired by atomic force microscopy of the coating obtained in Example 2. [Figure 2A] This is an atomic force microscope image (90 μm × 90 μm) of the coating surface obtained in Comparative Example 1. [Figure 2B] This is the surface structure profile obtained from data acquired by atomic force microscopy of the coating obtained in Comparative Example 1. [Figure 3] This graph shows the light reflectance of the coating obtained in Example 2. [Figure 4A] This is a photograph of a portion of a railway vehicle (Malaysia Rail train) that was coated with the aqueous inorganic coating agent of Example 1. [Figure 4B] This is a photograph of a portion of a railway vehicle (Malaysia Rail train) that was coated with the aqueous inorganic coating agent of Example 1. [Figure 5] This is a photograph of a portion of a railway vehicle that has been coated with the aqueous inorganic coating agent of Example 3. [Figure 6]This is a photograph of a portion of a stainless steel elevator door that has been coated with the aqueous inorganic coating agent of Example 3. [Figure 7] This is a photograph of a mirror-finished stainless steel monument coated with the aqueous inorganic coating agent of Example 3. [Modes for carrying out the invention]

[0009] Interference fringes typically arise from the presence of multiple interfaces where reflection occurs. For example, interference between reflected light from the air / film and reflected light from the film / substrate creates fringes. One factor contributing to strong interference fringes is a large difference in refractive index between the air and the film. This is because a larger difference in refractive index results in greater reflection.

[0010] It has been discovered that by using colloidal silica and potassium silicate compounds in combination to increase the molar ratio (SiO2 / K2O), and by using sodium phosphate compounds and boric acid as acidic components, a coating can be formed that has a dense network of thin, high protrusions (hereinafter sometimes referred to as "pillars") mainly composed of SiO2.

[0011] High-density pillars form a mixed layer of silicon dioxide and air between the air and the coating. Due to this mixed layer, the refractive index of the coating is not intrinsic to the coating material, but rather the apparent refractive index when the region containing the mixed layer is viewed as an optically homogeneous medium. Since the apparent refractive index lies between the refractive index of air and the intrinsic refractive index of the coating, the refractive index difference between air and the coating (more precisely, the refractive index difference between air and the mixed layer) becomes small, resulting in a lower reflectivity of light. As a result, interference fringes are suppressed.

[0012] The aqueous inorganic coating agent of this disclosure comprises a potassium silicate compound, colloidal silica, a sodium phosphate compound, boric acid, and water.

[0013] Potassium silicate compounds are mixtures of silicon dioxide (SiO2), potassium oxide (K2O), and water (H2O), and are represented by the general formula: K2O·nSiO2·mH2O. In the formula, n represents the molar ratio of SiO2 / K2O, which is usually around 1.50 to 2.65. Colloidal silica mainly consists of silicon dioxide (SiO2) or silicon dioxide hydrate.

[0014] In this disclosure, potassium silicate compounds and colloidal silica are used in combination. Therefore, the molar ratio of total SiO2 to K2O in the aqueous inorganic coating agent (SiO2 / K2O) is greater than the molar ratio (n) of the potassium silicate compound. It is believed that the higher molar ratio (SiO2 / K2O) facilitates the formation of pillars.

[0015] In aqueous inorganic coating agents, the molar ratio (SiO2 / K2O) is preferably 3.00 or higher. The upper limit of the molar ratio (SiO2 / K2O) is set appropriately depending on the application and purpose, but 200.00 is preferred. The molar ratio (SiO2 / K2O) may be between 3.00 and 200.00. The molar ratio (SiO2 / K2O) may be 5.00 or higher, 10.00 or higher, or 12.00 or higher. The molar ratio (SiO2 / K2O) may be 190.00 or lower, 180.00 or lower, or 170.00 or lower. The molar ratio (SiO2 / K2O) may be between 5.00 and 190.00, 10.00 and 180.00, or 12.00 and 170.00.

[0016] The molar ratio (SiO2 / K2O) of total SiO2 to K2O in an aqueous inorganic coating agent can be calculated as follows: Determine the mass of SiO2 from the blending mass and composition of each component containing SiO2 (typically colloidal silica, potassium silicate compounds, and other alkali metal silicates (e.g., sodium silicate compounds)), and calculate the number of moles. Similarly, determine the mass of K2O from the blending mass and composition of the component containing K2O (typically potassium silicate compounds), and calculate the number of moles. The molar ratio (SiO2 / K2O) is obtained by dividing the number of moles of SiO2 by the number of moles of K2O. Potassium phosphate does not form K2O in aqueous inorganic coating agents, and therefore is not included in the components containing K2O.

[0017] In this disclosure, sodium phosphate compounds and boric acid are further used as acidic components. Potassium silicate compounds are generally very viscous liquids, but the neutralization effect of the acidic components reduces the viscosity of the aqueous inorganic coating agent. This reduction in viscosity allows the coating agent to be applied thinly and uniformly to the substrate surface. This is thought to result in the formation of high-density pillars.

[0018] Here, it is crucial that the product is substantially free of potassium phosphate compounds. The potassium phosphate compound content is less than 0.10% by mass of the solid content of the aqueous inorganic coating agent. The reason is not entirely clear, but it is thought that potassium phosphate compounds inhibit pillar formation. Furthermore, since potassium phosphate compounds can also act as a curing agent for silicic acid, the resulting coating tends to be hard and brittle.

[0019] Another method to suppress interference fringes is to make the coating thinner. Thin films can be formed, for example, by dry processes such as deposition using a vacuum apparatus, CVD, or sputtering. However, vacuum apparatuses are expensive. In addition, using a vacuum apparatus limits the location where the coating can be formed. Another method to suppress interference fringes is to apply an aqueous inorganic coating agent in a dot pattern on top of the formed coating using a spray gun or airless gun to cancel out the interference fringes. This method is simple because it can be carried out under atmospheric pressure. However, it inevitably results in a large film thickness, which limits its applications.

[0020] The aqueous inorganic coating agent of this disclosure allows for the formation of thin films (e.g., 80 nm or less in thickness) under atmospheric pressure using a wet process, without the need for expensive vacuum equipment. The thinness of the film further suppresses interference fringes.

[0021] In addition, the aqueous inorganic coating agent of this disclosure forms a film with high antifouling properties. The antifouling properties are exhibited by the superhydrophilicity of the film. Superhydrophilicity is obtained by a sodium phosphate compound. The sodium phosphate compound is hygroscopic or water-retentive. When moisture from the atmosphere is attracted to the sodium phosphate compound, the hydrophilic groups (SiOH groups) and / or hydroxide ions (OH) of colloidal silica are attracted to it. - It combines with the film and is retained as a trace amount of moisture on the film. As a result, the film exhibits superhydrophilicity. The moisture can be from the atmosphere. Even such a small amount of moisture will cause superhydrophilicity to occur. Furthermore, the retention of water gives the film an antistatic effect, making it difficult for dirt to adhere to it.

[0022] 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.

[0023] "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 3257:1999 Test method for wettability of substrate glass surfaces (static droplet method).

[0024] 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 aqueous inorganic coating agent disclosed herein does not require the use of organofluorine compounds and can achieve high antifouling performance. In addition, the aqueous inorganic coating agent disclosed herein provides an antistatic effect (for example, a surface resistivity of 10) that cannot be obtained with organofluorine compounds. 9 Because it exhibits a density of Ω or less, the film formed by the aqueous inorganic coating agent of this disclosure has remarkable antifouling properties.

[0025] Furthermore, the film formed from the aqueous inorganic coating agent of this disclosure has a low refractive index (e.g., 1.40 or less), high transparency, and excellent anti-fogging and abrasion resistance (e.g., pencil hardness of 3H or higher), as described above.

[0026] [Water-based inorganic coating agent] 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.

[0027] "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.

[0028] The solid content concentration of the aqueous inorganic coating agent is preferably 0.50 to 30.00% by mass, as this facilitates application in a wet process. The solid content concentration of the aqueous inorganic coating agent may be 0.80% by mass or more. The solid content concentration of the aqueous inorganic coating agent may be 20.00% by mass or less. The solid content concentration of the aqueous inorganic coating agent may be 0.80 to 20.00% by mass.

[0029] 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 5601-1-2:2008 Method for Measuring Residue After Heating.

[0030] 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.

[0031] (Potassium silicate compound) Potassium silicate compounds form a film on the substrate. As mentioned above, potassium silicate compounds are viscous liquids, and this viscosity is also thought to contribute to the formation of pillars.

[0032] Potassium silicate compounds are aqueous solutions consisting of silicate anions and potassium ions, and are represented by the general formula: K2O·nSiO2·mH2O (where n is approximately 1.50 to 2.65).

[0033] Potassium ions have a larger ionic radius and lower charge density than sodium ions found in typical water glass (sodium silicate compounds). Therefore, their interaction with the silicon and oxygen network (-Si-O-Si-) is considered to be relatively weak. Consequently, coatings formed using potassium silicate compounds are thought to be more glass-like and have a lower refractive index.

[0034] The content of the potassium silicate compound is set appropriately according to the molar ratio, application, and purpose. For example, the content of the potassium silicate compound may be 1.00 to 40.00% by mass of the solid content of the aqueous inorganic coating agent.

[0035] (Colloidal silica) Colloidal silica is thought to be incorporated into the (-Si-O-Si-) network, thereby relaxing the rigidity of the network. As a result, the resulting coating possesses both high toughness and excellent flexibility.

[0036] Colloidal silica is also called silica sol. Colloidal silica is colloidal particles mainly composed of silicon dioxide (SiO2) or silicon dioxide hydrate. Colloidal silica can be amorphous. The particle shape is not particularly limited and may be spherical or crushed.

[0037] 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, 3 to 50 nm, or 5 to 30 nm. In particular, when the average particle size of colloidal silica is 5 to 30 nm, the light transmittance of the coating can be further improved. The average particle size of colloidal silica may be 5 to 20 nm or 10 to 20 nm. Multiple types of colloidal silica with different average particle sizes may be used in combination.

[0038] 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%.

[0039] 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.

[0040] 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 oxide or the like.

[0041] 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.

[0042] The colloidal silica content is set appropriately depending on the application and purpose. For example, the colloidal silica content may be 5.00 to 90.00% by mass of the solid content of the aqueous inorganic coating agent.

[0043] (Sodium phosphate compound) Sodium phosphate compounds reduce the viscosity of aqueous inorganic coatings through neutralization. This allows for a thin, uniform application of the inorganic coating to the substrate surface. Sodium phosphate compounds also impart flexibility or viscoelasticity to the coating. In addition, as mentioned above, sodium phosphate compounds contribute to the development of superhydrophilicity.

[0044] Examples of sodium phosphate compounds include anhydrous sodium dihydrogen phosphate (NaH2PO4), sodium dihydrogen phosphate crystals (NaH2PO4·2H2O), disodium hydrogen phosphate crystals (Na2HPO4·12H2O), anhydrous trisodium phosphate (Na3PO4), trisodium phosphate crystals (Na3PO4·12H2O), tetrasodium pyrophosphate crystals (Na4P2O7), tetrasodium pyrophosphate crystals (Na4P2O7·10H2O), sodium dihydrogen pyrophosphate (Na2H2P2O7), and sodium tripolyphosphate compounds (Na5P3O 10) Sodium tetrapolyphosphate compound (Na6P4O 13 ) Sodium hexametaphosphate compound ((NaPO3) n ) Acidic sodium hexametaphosphate compound ([Na x H y (PO3) x+y n ) may be mentioned. These may be used alone or in combination of two or more kinds.

[0045] The content of the sodium phosphate compound is appropriately set according to the molar ratio, use and purpose. The content of the sodium phosphate compound may be, for example, 0.02 to 70.00% by mass of the solid content of the aqueous inorganic coating agent.

[0046] (Boric acid) Boric acid (H3BO3) has a neutralizing effect. Boron contained in boric acid is also presumed to be incorporated into the network formed by silicon and oxygen. Thereby, the flexibility of the film is further enhanced, and the adhesion between the film and the substrate is improved.

[0047] The content of boric acid is appropriately set according to the use and purpose. The content of boric acid is preferably 0.30 to 10.00% by mass of the solid content of the aqueous inorganic coating agent. When the above content of boric acid is 0.30% by mass or more, a thin film is likely to be formed. When the above content of boric acid is 10.00% by mass or less, the refractive index of the film can be further reduced. The above content of boric acid may be 0.60% by mass or more, and may be 0.70% by mass or more. The above content of boric acid may be 9.00% by mass or less, and may be 8.00% by mass or less. The above content of boric acid may be 0.60 to 9.00% by mass, and may be 0.70 to 8.00% by mass.

[0048] (Solvent) The aqueous inorganic coating agent contains water as a solvent. Examples of water include purified water, pure water, tap water, and ion-exchanged water. Since water is difficult to volatilize during storage, changes in the physical properties of the aqueous inorganic coating agent over time can be suppressed.

[0049] ​ (Potassium phosphate compounds) The aqueous inorganic coating agent is substantially free of potassium phosphate compounds. The potassium phosphate compound content is less than 0.10% by mass of the solid content of the aqueous inorganic coating agent. Examples of potassium phosphate compounds include potassium dihydrogen phosphate (KH2PO4), dipotassium hydrogen phosphate (K2HPO4), and potassium metaphosphate compounds.

[0050] (Borate compounds) The aqueous inorganic coating agent may contain boric acid compounds other than boric acid. The boric acid compounds can interact with sodium phosphate compounds to further enhance the flexibility of the coating film. The content of the boric acid compounds may be adjusted as appropriate according to the desired flexibility. The content of the boric acid compounds is preferably 0.50% by mass or more of the solid content of the aqueous inorganic coating agent. The above content of the boric acid compounds is preferably 15.00% by mass or less, and may be 10.00% by mass or less. The content of the boric acid compounds is preferably 0 to 15.00% by mass of the solid content of the aqueous inorganic coating agent, may be 0.50 to 15.00% by mass, and may be 0.50 to 10.00% by mass.

[0051] Examples of boric acid compounds include boric acid oxides, salts, and dehydration condensates. Specific examples include boron trioxide, borates, diborates, tetraborates, pentaborates, metaboric acid, and polyboric acid. Substances that form salts with boric acid include sodium, ammonia, zinc, manganese, cobalt, nickel, potassium, lithium, and calcium. These can be used individually or in combination of two or more.

[0052] (Alkali metal silicates) Aqueous inorganic coating agents may contain alkali metal silicates other than potassium silicate compounds. These other alkali metal silicates differ from the inorganic thickeners described later in that they do not contain Al, Mg, Fe, and Ti. These other alkali metal silicates are added depending on the substrate, purpose, and application. These other alkali metal silicates can further enhance the film strength.

[0053] Examples of alkali metals include at least one selected from the group consisting of lithium (Li), sodium (Na), rubidium (Rb), cesium (Cs), and francium (Fr).

[0054] Other alkali metal silicates include, for example, sodium silicate compounds and lithium silicate compounds. These can be used individually or in combination of two or more. Sodium silicate compounds are particularly suitable. Sodium silicate compounds further enhance the flexibility of the coating. By using potassium silicate compounds and sodium silicate compounds in combination, the coating can become harder, more flexible, and less prone to cracking.

[0055] Sodium silicate compounds are also called sodium silicate or water glass. Sodium silicate compounds are mixtures of silicon dioxide (SiO2), sodium oxide (Na2O), and water (H2O). The molar ratio m (SiO2 / Na2O) of SiO2 to Na2O is not particularly limited. Commercially available sodium silicate compounds can be used.

[0056] Other alkali metal silicates affect the molar ratio (SiO2 / K2O). The content of alkali metal silicates is set appropriately according to the application and purpose. Preferably, the content of other alkali metal silicates is 0.50 to 35.00% by mass of the solid content of the aqueous inorganic coating agent. The above content of other alkali metal silicates may be 0.55% by mass or more, or 0.60% by mass or more. The above content of other alkali metal silicates may be 30.00% by mass or less, 28.00% by mass or less, 20.00% by mass or less, or 17.00% by mass or less. The above content of other alkali metal silicates may be 0.55 to 30.00% by mass, 0.55 to 28.00% by mass, 0.60 to 20.00% by mass, or 0.60 to 17.00% by mass.

[0057] (Inorganic abrasives) Aqueous inorganic coating agents may contain inorganic abrasives. These inorganic abrasives contribute to improved adhesion between the coating and the substrate. Inorganic abrasives do not contain carbon atoms. When an aqueous inorganic coating agent containing inorganic abrasives is applied and polished, the substrate surface is activated while avoiding contact with the atmosphere, and the OH groups generated by this activation can quickly chemically bond with colloidal silica. In addition, the abrasive removes dirt from the substrate surface. These factors further improve the adhesion between the coating agent and the substrate.

[0058] 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.

[0059] 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.

[0060] 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 of the solid content of the aqueous inorganic coating agent.

[0061] 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.

[0062] [Table 1]

[0063] 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.

[0064] (Inorganic thickener) Aqueous inorganic coating agents may contain inorganic thickeners. 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).

[0065] 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.

[0066] 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.

[0067] 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".

[0068] 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.

[0069] The amount of inorganic thickener may be, for example, 0.50 to 65.00% by mass of the solid content of the aqueous inorganic coating agent. The above amount of inorganic thickener may be 1.00% by mass or more, 5.00% by mass or more, or 10.00% by mass or more. The above amount of inorganic thickener may be 55.00% by mass or less, 50.00% by mass or less, or 40.00% by mass or less. The above amount of inorganic thickener may be 1.00 to 55.00% by mass, 5.00 to 50.00% by mass, or 10.00 to 40.00% by mass.

[0070] (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.

[0071] 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.

[0072] 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 coating, inorganic hardening agents may be, for example, zinc hydroxide or indium tin oxide (ITO).

[0073] 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).

[0074] 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).

[0075] 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.

[0076] The amount of inorganic curing agent is set appropriately according to the application and purpose. The amount of inorganic curing agent may be 10.00 to 50.00% by mass, 15.00 to 45.00% by mass, or 15.00 to 42.00% by mass of the solid content of the aqueous inorganic coating agent, in that aggregation and precipitation are suppressed.

[0077] (Aluminum monophosphate) Aqueous inorganic coating agents may contain monoaluminum phosphate. Monoaluminum phosphate densifies the film while suppressing shrinkage of the coating layer during curing. In addition, monoaluminum phosphate may also contribute to pillar formation. Monoaluminum phosphate is represented as Al2O3·3P2O5·6H2O.

[0078] 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."

[0079] 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, 0.50 to 5.00% by mass of the solid content of the aqueous inorganic coating agent. The above content of monoaluminum phosphate may be 0.80% by mass or more, or 1.00% by mass or more. The above content of monoaluminum phosphate may be 4.50% by mass or less, or 4.00% by mass or less. The above content of monoaluminum phosphate may be 0.80 to 4.50% by mass, or 1.00 to 4.00% by mass.

[0080] (Preparation method) Aqueous inorganic coating agents are prepared by mixing their components. Powdered components (e.g., boric acid, potassium phosphate, sodium phosphate) are heated in water until transparent and dissolved.

[0081] (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.

[0082] 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.

[0083] 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.

[0084] Embodiment 1 The aqueous inorganic coating agent according to this embodiment is particularly suitable for organic substrates. The film formed from the aqueous inorganic coating agent according to this embodiment has high stain resistance, suppresses interference fringes, is flexible, and has excellent adhesion to organic substrates.

[0085] In the aqueous inorganic coating agent according to this embodiment, the content of potassium phosphate compound is less than 0.10% by mass of the solid content of the aqueous inorganic coating agent. The aqueous inorganic coating agent according to this embodiment may contain at least one selected from the group consisting of inorganic abrasives, inorganic thickeners, inorganic curing agents, and monoaluminum phosphate.

[0086] In this embodiment, the colloidal silica content is preferably 20.00 to 90.00% by mass of the solid content of the aqueous inorganic coating agent. When the colloidal silica content is 20.00% by mass or more, the coating can become dense. When the colloidal silica content is 90.00% by mass or less, a thin coating is more easily formed. The colloidal silica content may be 55.00% by mass or more, and may be 60.00% by mass or more. The colloidal silica content may be 87.00% by mass or less, and may be 85.00% by mass or less. The colloidal silica content may be 55.00 to 87.00% by mass, and may be 60.00 to 85.00% by mass.

[0087] The potassium silicate compound content is preferably 2.00 to 20.00% by mass of the solid content of the aqueous inorganic coating agent. If the potassium silicate compound content is 2.00% by mass or more, the coating may become denser. If the potassium silicate compound content is 20.00% by mass or less, a thinner coating is more easily formed. The potassium silicate compound content may be 2.50% by mass or more, and may be 3.00% by mass or more. The potassium silicate compound content may be 15.00% by mass or less, and may be 12.00% by mass or less. The potassium silicate compound content may be 2.50 to 15.00% by mass, and may be 3.00 to 12.00% by mass.

[0088] The sodium phosphate compound content is preferably 0.10 to 5.00% by mass of the solid content of the aqueous inorganic coating agent. When the sodium phosphate compound content is 0.10% by mass or more, the flexibility of the coating is further improved. When the sodium phosphate compound content is 5.00% by mass or less, the adhesion of the coating to the substrate is further improved. The sodium phosphate compound content may be 0.20% by mass or more, and may be 0.30% by mass or more. The sodium phosphate compound content may be 2.00% by mass or less, and may be 1.00% by mass or less. The sodium phosphate compound content may be 0.20 to 2.00% by mass, and may be 0.30 to 1.00% by mass.

[0089] The boric acid content is preferably 1.00 to 10.00% by mass of the solid content of the aqueous inorganic coating agent. If the boric acid content is 1.00% by mass or more, the flexibility of the coating is further improved. If the boric acid content is 10.00% by mass or less, a sufficient neutralization effect can be obtained. The boric acid content may be 4.00% by mass or more, or 5.00% by mass or more. The boric acid content may be 9.00% by mass or less, or 8.50% by mass or less. The boric acid content may be 4.00 to 9.00% by mass, or 5.00 to 8.50% by mass.

[0090] It is preferable that the material contains a sodium silicate compound. The sodium silicate compound content is preferably 3.00 to 20.00% by mass of the solid content of the aqueous inorganic coating agent. If the sodium silicate compound content is 3.00% by mass or more, cracking of the coating can be further suppressed. If the sodium silicate compound content is 20.00% by mass or less, the flexibility of the coating is improved. The sodium silicate compound content may be 3.50% by mass or more, and may be 4.00% by mass or more. The sodium silicate compound content may be 18.00% by mass or less, and may be 17.00% by mass or less. The sodium silicate compound content may be 3.50 to 18.00% by mass, and may be 4.00 to 17.00% by mass.

[0091] The pH of the aqueous inorganic coating agent according to this embodiment at room temperature (20-22°C) is preferably 5.00 to 10.00 from the viewpoint of the working environment. The above pH may be 6.00 or higher, or 7.00 or higher. The above pH may be 9.50 or lower, or 9.00 or lower. The above pH may be 6.00 to 9.50, or 7.00 to 9.00.

[0092] In this embodiment, the solid content concentration of the aqueous inorganic coating agent is preferably 1.00 to 10.00% by mass, in that the texture of the organic substrate is less likely to be impaired. The solid content concentration of the aqueous inorganic coating agent may be 1.50% by mass or more, and may be 2.00% by mass or more. The solid content concentration of the aqueous inorganic coating agent may be 8.00% by mass or less, and may be 5.00% by mass or less. The solid content concentration of the aqueous inorganic coating agent may be 1.50 to 8.00% by mass, and may be 2.00 to 5.00% by mass.

[0093] In the aqueous inorganic coating agent according to this embodiment, the molar ratio (SiO2 / K2O) is preferably 50.00 to 200.00. When the molar ratio (SiO2 / K2O) is 50.00 or higher, protrusions are more easily formed, and the interference fringe suppression effect is further improved. When the molar ratio (SiO2 / K2O) is 200.00 or lower, a mixed layer is more easily formed, and the interference fringe suppression effect is further improved. The above molar ratio may be 70.00 or higher, 80.00 or higher, or 90.00 or higher. The above molar ratio may be 180.00 or lower, 160.00 or lower, or 130.00 or lower. The above molar ratio may be 70.00 to 180.00, 80.00 to 160.00, or 90.00 to 160.00.

[0094] Embodiment 2 The aqueous inorganic coating agent according to this embodiment is particularly suitable for glass. The aqueous inorganic coating agent is especially suitable for lenses, optical glass, wafers, and sensors that require high optical properties. The film formed from the aqueous inorganic coating agent according to this embodiment has high antifouling properties and suppresses interference fringes.

[0095] In addition, the film formed from the aqueous inorganic coating agent according to this embodiment has a low refractive index and high light transmittance. For example, the refractive index of light with a wavelength of 507 nm is 1.30 to 1.40, and the transmittance of light with a wavelength of 370 to 870 nm incident at an angle of 90 degrees is 93.00% or more. The refractive index of the above light is preferably 1.38 or less, and may be 1.35 or less.

[0096] In the aqueous inorganic coating agent according to this embodiment, the content of potassium phosphate compound is less than 0.10% by mass of the solid content of the aqueous inorganic coating agent. The aqueous inorganic coating agent according to this embodiment may contain at least one selected from the group consisting of inorganic abrasives, inorganic thickeners, inorganic curing agents, and monoaluminum phosphate.

[0097] In this embodiment, the colloidal silica content is preferably 5.00 to 35.00% by mass of the solid content of the aqueous inorganic coating agent. If the colloidal silica content is 5.00% by mass or more, the refractive index may be further reduced. If the colloidal silica content is 35.00% by mass or less, a thin film is more easily formed. The colloidal silica content may be 8.00% by mass or more, or 10.00% by mass or more. The colloidal silica content may be 32.00% by mass or less, or 30.00% by mass or less. The colloidal silica content may be 8.00 to 32.00% by mass, or 10.00 to 30.00% by mass.

[0098] The content of the potassium silicate compound is preferably 5.00 to 40.00% by mass of the solid content of the aqueous inorganic coating agent. When the content of the potassium silicate compound is within the above range, pillars are more easily formed. The content of the potassium silicate compound may be 7.00% by mass or more, and may be 8.00% by mass or more. The content of the potassium silicate compound may be 35.00% by mass or less, 30.00% by mass or less, and may be 20.00% by mass or less. The content of the potassium silicate compound may be 7.00 to 35.00% by mass, 7.00 to 30.00% by mass, and may be 8.00 to 20.00% by mass.

[0099] The sodium phosphate compound content is preferably 30.00 to 70.00% by mass of the solid content of the aqueous inorganic coating agent. When the sodium phosphate compound content is within the above range, the flexibility of the coating is further improved. The sodium phosphate compound content may be 40.00% by mass or more, and may be 50.00% by mass or more. The sodium phosphate compound content may be 68.00% by mass or less, and may be 65.00% by mass or less. The sodium phosphate compound content may be 40.00 to 68.00% by mass, and may be 50.00 to 65.00% by mass.

[0100] The boric acid content is preferably 0.30 to 1.50% by mass of the solid content of the aqueous inorganic coating agent. When the boric acid content is within the above range, adhesion to substrates such as glass is further improved. The boric acid content may be 0.50% by mass or more, and may be 0.60% by mass or more. The boric acid content may be 1.20% by mass or less, and may be 1.00% by mass or less. The boric acid content may be 0.50 to 1.20% by mass, and may be 0.60 to 1.00% by mass.

[0101] It is preferable that the material contains a sodium silicate compound. The sodium silicate compound content is preferably 0.50 to 10.00% by mass of the solid content of the aqueous inorganic coating agent. When the sodium silicate compound content is within the above range, the curing rate of potassium silicate is controlled, and the occurrence of cracks and other damage to the coating is suppressed. The sodium silicate compound content may be 0.55% by mass or more, and may be 0.60% by mass or more. The sodium silicate compound content may be 8.00% by mass or less, and may be 3.00% by mass or less. The sodium silicate compound content may be 0.55 to 8.00% by mass, and may be 0.60 to 3.00% by mass.

[0102] The pH of the aqueous inorganic coating agent according to this embodiment at room temperature (20-22°C) is preferably 3.00 to 7.00. This improves workability. The above pH may be 4.00 or higher, or 4.50 or higher. The above pH may be 6.50 or lower, or 6.00 or lower. The above pH may be 4.00 to 6.50, or 4.50 to 6.00.

[0103] The solid content concentration of the aqueous inorganic coating agent according to this embodiment is preferably 0.50 to 8.00% by mass. This suppresses uneven coating and can further improve light transmittance. The solid content concentration of the aqueous inorganic coating agent may be 1.00% by mass or more, and may be 1.30% by mass or more. The solid content concentration of the aqueous inorganic coating agent may be 5.00% by mass or less, and may be 3.00% by mass or less. The solid content concentration of the aqueous inorganic coating agent may be 1.00 to 5.00% by mass, and may be 1.30 to 3.00% by mass.

[0104] In the aqueous inorganic coating agent according to this embodiment, the molar ratio (SiO2 / K2O) is preferably 5.00 to 30.00. When the molar ratio (SiO2 / K2O) is 5.00 or higher, pillars are more easily formed, and the interference fringe suppression effect is further improved. When the molar ratio (SiO2 / K2O) is 30.00 or lower, a mixed layer is more easily formed, and the interference fringe suppression effect is further improved. The above molar ratio may be 8.00 or higher, 10.00 or higher, or 12.00 or higher. The above molar ratio may be 25.00 or lower, 22.00 or lower, or 20.00 or lower. The above molar ratio may be 8.00 to 25.00, 10.00 to 22.00, or 12.00 to 20.00.

[0105] Embodiment 3 The aqueous inorganic coating agent according to this embodiment is particularly suitable for metal substrates (e.g., stainless steel, aluminum, titanium, copper, brass, tin). The film formed from the aqueous inorganic coating agent according to this embodiment has high antifouling properties and suppresses interference fringes. In addition, it has high hardness and excellent adhesion to metal substrates, so high durability can be expected.

[0106] In the aqueous inorganic coating agent according to this embodiment, the content of potassium phosphate compound is less than 0.10% by mass of the solid content of the aqueous inorganic coating agent. The aqueous inorganic coating agent according to this embodiment may contain at least one selected from the group consisting of inorganic abrasives, inorganic thickeners, inorganic curing agents, and monoaluminum phosphate. Preferably, the aqueous inorganic coating agent according to this embodiment contains at least one inorganic abrasive and an inorganic curing agent.

[0107] In this embodiment, the colloidal silica content is preferably 35.00 to 60.00% by mass of the solid content of the aqueous inorganic coating agent. When the colloidal silica content is 35.00% by mass or more, the strength and density of the coating are further improved. When the colloidal silica content is 60.00% by mass or less, coating unevenness is suppressed and light transmittance can be further improved. The colloidal silica content may be 40.00% by mass or more, 42.00% by mass or more, or 43.00% by mass or more. The colloidal silica content may be 59.00% by mass or less, or 58.00% by mass or less. The colloidal silica content may be 40.00 to 59.00% by mass, 42.00 to 59.00% by mass, or 43.00 to 58.00% by mass.

[0108] The potassium silicate compound content is preferably 1.00 to 20.00% by mass of the solid content of the aqueous inorganic coating agent. When the potassium silicate compound content is within the above range, the adhesion of the coating to the substrate is further improved. The potassium silicate compound content may be 1.20% by mass or more, 1.30% by mass or more, or 1.40% by mass or more. The potassium silicate compound content may be 18.00% by mass or less, or 15.00% by mass or less. The potassium silicate compound content may be 1.20 to 18.00% by mass, 1.30 to 18.00% by mass, 1.30 to 15.00% by mass, or 1.40 to 15.00% by mass.

[0109] The sodium phosphate compound content is preferably 0.02 to 2.00% by mass of the solid content of the aqueous inorganic coating agent. When the sodium phosphate compound content is within the above range, the flexibility of the coating is improved. The sodium phosphate compound content may be 0.03% by mass or more, 0.04% by mass or more, 0.05% by mass or more, or 0.06% by mass or more. The sodium phosphate compound content may be 1.50% by mass or less, or 1.00% by mass or less. The sodium phosphate compound content may be 0.03 to 1.50% by mass, 0.04 to 1.50% by mass, 0.05 to 1.00% by mass, or 0.06 to 1.00% by mass.

[0110] The boric acid content is preferably 0.30 to 1.50% by mass of the solid content of the aqueous inorganic coating agent. When the boric acid content is within the above range, adhesion to the metal substrate is further improved. The boric acid content may be 0.50% by mass or more, and may be 0.60% by mass or more. The boric acid content may be 1.20% by mass or less, and may be 1.00% by mass or less. The boric acid content may be 0.50 to 1.20% by mass, and may be 0.60 to 1.20% by mass, and may be 0.60 to 1.00% by mass.

[0111] The sodium silicate compound may or may not be included. The sodium silicate compound content is preferably 0 to 10.00% by mass of the solid content of the aqueous inorganic coating agent. When the sodium silicate compound content is within the above range, the curing rate of potassium silicate is controlled, and the occurrence of cracks and other damage to the coating is suppressed. The alkali metal silicate content may be 0.30% by mass or more, or 0.40% by mass or more. The alkali metal silicate content may be 3.00% by mass or less, or 2.00% by mass or less. The alkali metal silicate content may be 0 to 3.00% by mass, or 0.30 to 2.00% by mass, or 0.40 to 2.00% by mass.

[0112] The pH of the aqueous inorganic coating agent according to this embodiment at room temperature (20-22°C) is preferably 7.00 to 13.00. This improves the pot life and workability of the coating agent. The above pH may be 8.00 or higher, or 9.50 or higher. The above pH may be 12.50 or lower, or 12.00 or lower. The above pH may be 8.00 to 12.50, or 9.50 to 12.00.

[0113] The solid content concentration of the aqueous inorganic coating agent according to this embodiment is preferably 3.00 to 25.00% by mass. This improves the adhesion of the coating to the substrate. The solid content concentration of the aqueous inorganic coating agent may be 5.00% by mass or more, and may be 10.00% by mass or more. The solid content concentration of the aqueous inorganic coating agent may be 20.00% by mass or less, and may be 18.00% by mass or less. The solid content concentration of the aqueous inorganic coating agent may be 5.00 to 20.00% by mass, and may be 10.00 to 18.00% by mass.

[0114] In the aqueous inorganic coating agent according to this embodiment, the molar ratio (SiO2 / K2O) is preferably 50.00 to 250.00. When the molar ratio (SiO2 / K2O) is 50.00 or higher, protrusions are more easily formed, and the interference fringe suppression effect is further improved. When the molar ratio (SiO2 / K2O) is 250.00 or lower, a mixed layer is more easily formed, and the interference fringe suppression effect is further improved. The above molar ratio may be 80.00 or higher, 100.00 or higher, or 120.00 or higher. The above molar ratio may be 220.00 or lower, 200.00 or lower, or 180.00 or lower. The above molar ratio may be 80.00 to 220.00, 100.00 to 200.00, or 120.00 to 180.00.

[0115] [Coating] The aqueous inorganic coating agent of this disclosure forms a film with high stain resistance and suppressed interference fringes. The film of this disclosure has a dense network of fine, high protrusions mainly composed of silicon dioxide.

[0116] (Refractive index) The refractive index of the coating at a wavelength of 507 nm is preferably 1.30 to 1.40. Considering that the refractive index inherent to silicon dioxide is 1.45, the refractive index of the coating is sufficiently small. Having the refractive index of the coating in this range enhances the interference fringe suppression effect. The refractive index of the coating is preferably 1.35 or less. The refractive index of the coating is preferably 1.30 to 1.35.

[0117] The refractive index of a coating is not inherent to the coating material itself, but rather represents the apparent refractive index when the region containing the mixed layer is viewed as an optically homogeneous medium. The refractive index (apparent refractive index) of a coating can be measured using an ellipsometer (for example, JA Woollam Japan, product name "M-2000V-SUT").

[0118] (transmittance) The light reflectivity of the coating is reduced, which improves the light transmittance to the coating. The transmittance of light with a wavelength of 370-870 nm incident on the coating at a 90-degree angle can be 93.00% or higher. Therefore, the coating of this disclosure has excellent AR (Anti-Reflection) effect.

[0119] The transmittance of an article having a coating of the present disclosure on a transparent substrate (e.g., a glass substrate) may be greater than or equal to that of the substrate. The transmittance of the above light may be 100.00% or more. The transmittance of the coating can be measured with a spectrophotometer (e.g., Hitachi, Ltd., product name "U-4100"). Even when the angle of incidence is changed (e.g., 20 degrees and 36 degrees), the transmittance of light with a wavelength of 370 to 870 nm may be 100.00% or more.

[0120] (thickness) The thickness of the coating in this disclosure is, for example, 80 nm or less. Because the coating is thin, interference fringes can be further suppressed. The thickness of the coating may be 70 nm or less, 60 nm or less, 50 nm or less, or 40 nm or less. The thickness of the coating may be 5 nm or more, 10 nm or more, 15 nm or more, or 20 nm or more. The thickness of the coating may be 5 to 80 nm, 10 to 70 nm, 15 to 60 nm, 20 to 50 nm, or 20 to 40 nm.

[0121] The film thickness is obtained using an ellipsometer (for example, the "M-2000V-SUT" model manufactured by JA Woollam Japan). Using an ellipsometer, the film thickness is obtained as if the film were optically equivalent and uniform.

[0122] (Uneven structure) The surface irregularities of the coatings of this disclosure can be characterized, for example, by the arithmetic mean roughness Ra and the ten-point mean roughness Rz. The arithmetic mean roughness Ra indicates the average size of the irregularities on the coating surface; a larger arithmetic mean roughness Ra indicates larger average irregularities. The ten-point mean roughness Rz is an index that indicates the representative irregularity height within the evaluation length. The coatings of this disclosure may have large values ​​for both the arithmetic mean roughness Ra and the ten-point mean roughness Rz. That is, the coatings of this disclosure can be said to have large irregularities overall. These large irregularities are a hypothetical mixed layer of silicon dioxide and air, forming a mixed layer containing a large amount of air. This mixed layer reduces the refractive index of the coating and reduces the reflectivity of light by the coating.

[0123] In addition, since the proportion of air in the mixed layer changes continuously in the vertical direction, the refractive index is thought to change continuously within the mixed layer as well. This is expected to further suppress the generation of interference fringes.

[0124] (density) The surface of the coating of this disclosure has, for example, approximately 1000 particles / 10 μm. 2The above-mentioned protrusions are formed. It is thought that the refractive index decreases due to the high density of these protrusions. The density of the protrusions can be obtained using an atomic force microscope (AFM). The AFM can scan the surface irregularities and visualize them in three dimensions. An example of an AFM is the "AFM5500MII" manufactured by Hitachi High-Tech Corporation.

[0125] (Arithmetic mean roughness Ra) The arithmetic mean roughness Ra indicates the average size of the surface irregularities of the coating. A higher Ra value suggests that the surface has larger irregularities overall.

[0126] The Ra of the coating surface is preferably 2.00 to 10.00 nm. If the Ra is 2.00 nm or higher, the above mixed layer is more easily formed, and the above refractive index decreases. If the Ra is 10.00 nm or lower, the transmittance improves. The Ra may be 3.00 nm or higher. The Ra may be 8.00 nm or lower. The Ra may be 3.00 to 8.00 nm.

[0127] The arithmetic mean roughness Ra corresponds to the value calculated using data obtained by AFM in accordance with JIS B 0601:2013 4.2.1.

[0128] (Ten-point mean roughness Rz) The ten-point mean roughness Rz is an index that indicates the typical surface roughness height within the evaluation length. A larger Rz indicates a higher average peak. The coating in this disclosure has a large Ra and a large Rz, which means that large irregularities are formed across the entire surface of the coating. These uniform, large irregularities reduce the refractive index of the coating.

[0129] The Rz of the film surface is preferably 40.00 to 100.00 nm. When the Rz is within this range, a mixed layer is more easily formed, and the refractive index becomes smaller.

[0130] The ten-point mean roughness Rz corresponds to a value calculated using data obtained by AFM, in accordance with JIS B 0601:2013 Annex JA. The ten-point mean roughness Rz is also referred to as RzJIS.

[0131] The following numerical ranges for the ratio (Rz / Ra) and maximum cross-sectional height Rt are based on the assumption that Ra is between 2.00 and 10.00 nm, and Rz is between 40.00 and 100.00 nm.

[0132] (Rz / Ra) The ratio of the ten-point average roughness Rz to the arithmetic mean roughness Ra (Rz / Ra) is preferably between 10.00 and 25.00. A ratio (Rz / Ra) of 10.00 or higher indicates that the convex portions have a certain height. Therefore, the above-mentioned mixed layer is more easily formed, and the above-mentioned refractive index may become smaller. A ratio (Rz / Ra) of 25.00 or lower indicates that there are few large, protruding convex portions, and that the convex portions are generally uniform in the height direction. When the height of the convex portions is uniform, local changes in reflectance and refractive index are suppressed, and interference fringes may be further suppressed.

[0133] The ratio (Rz / Ra) may be 12.00 or greater, and may be 15.00 or greater. The ratio (Rz / Ra) may be 23.00 or less, and may be 20.00 or less. The ratio (Rz / Ra) may be between 12.00 and 23.00, and may be between 15.00 and 20.00.

[0134] (Maximum cross-sectional height Rt) The maximum cross-sectional height Rt is the sum of the maximum peak height Rp and the maximum valley depth Rv of the roughness curve over the evaluation length. A larger Rt indicates the presence of higher peaks.

[0135] The maximum cross-sectional height Rt of the coating surface is preferably 50.00 to 150.00 nm. If Rt is 50.00 nm or higher, the above mixed layer is more easily formed, and the above refractive index may become smaller. If Rt is 150.00 nm or lower, it can be seen that there are few extremely high protrusions and that the protrusions are generally uniform in the height direction.

[0136] The above Rt may be 70.00 nm or greater, or 90.00 nm or greater. The above Rt may be 140.00 nm or less, or 130.00 nm or less. The above Rt may be between 70.00 and 140.00 nm, or 90.00 and 130.00 nm.

[0137] The maximum cross-sectional height Rt corresponds to the value calculated in accordance with JIS B 0601:2013 4.1.5 using data obtained by AFM.

[0138] [Method for forming a coating] The coating according to this disclosure is formed by a method comprising applying an aqueous inorganic coating agent containing a potassium silicate compound, colloidal silica, a sodium phosphate compound, boric acid, and water to the surface of a substrate under atmospheric pressure. By using the above aqueous inorganic coating agent, a thin film (for example, a coating with a thickness of 80 nm or less) can be formed under atmospheric pressure in a wet process without using expensive vacuum equipment. The reason why a thin film can be formed under atmospheric pressure with this inorganic coating agent is unknown, but this method allows for the formation of a thin film even when the solid content concentration of the aqueous inorganic coating agent is high.

[0139] Wet processes under atmospheric pressure include, for example, spin coating, dipping, spray coating, 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, methods using coaters (roll coaters, die coaters, etc.), spray painting, and inkjet painting.

[0140] The amount of aqueous inorganic coating agent applied is not particularly limited. Regardless of the amount applied, the film thickness can be 80 nm or less.

[0141] After applying the water-based inorganic coating agent, before it dries, the coated surface may be rubbed with a soft sponge buff or similar material moistened with water. This removes any excess water-based inorganic coating agent and eliminates any unevenness in the coating.

[0142] After the coating is formed, the surface may be finished by wiping it dry or wet with a microfiber cloth or similar material.

[0143] When using an aqueous inorganic coating agent containing inorganic abrasives, it is desirable to remove the inorganic abrasives by applying water after applying the aqueous inorganic coating agent but before it dries. Since the inorganic abrasives do not participate in the curing system, they can be easily removed with water. If necessary, the substrate surface may be rubbed or squeegeeed while applying water or after applying water.

[0144] The method may also include heating at 80-250°C for 8-30 minutes after applying the aqueous inorganic coating agent, either before or after drying. Heating can improve abrasion resistance. The pencil hardness of the aqueous inorganic coating agent according to Embodiment 3 after curing at room temperature is about 5H, which is sufficiently practical, but heating at 200°C for 20 minutes can improve the pencil hardness to 9H. Pencil hardness is evaluated in accordance with JIS K5600-5-4:1999 scratch hardness (pencil method).

[0145] The heating temperature may be 100°C or higher. The heating temperature may be 200°C or lower. The heating temperature may be between 100°C and 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. Heat treatment is not necessarily required.

[0146] (Application) The aqueous inorganic coating agent disclosed herein can be used for a variety of applications. It can be applied to both outdoor and indoor facilities. It can be applied to both organic and inorganic substrates.

[0147] Water-based inorganic coatings can be used for the maintenance of existing buildings and their ancillary structures, as well as vehicles. For example, water-based inorganic coatings can be applied to automobiles, railway vehicles, ship hulls, aircraft, containers, highway signs, tunnel walls, bridges, structures, glass or acrylic aquariums, musical instruments, furniture, writing instruments, fishing gear, office equipment such as printers and copiers, wallpaper, and electronic devices such as computers. Water-based inorganic coatings are particularly suitable for coating glass used in smartphones, eyeglasses, VR goggles, surveillance cameras, and automobiles.

[0148] Aqueous inorganic coating agents are particularly suitable for forming AR coatings on camera lens surfaces, color image sensors, wafers, and other surfaces that require high optical properties (high transmittance, low reflectance). [Examples]

[0149] 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.

[0150] Details of the materials used in the examples are as follows: • Colloidal silica Product name: Snowtex 40, manufactured by Nissan Chemical Corporation, average particle size: 10-20 nm, solid content concentration: 40.5% by mass, alkaline. • Potassium silicate compounds Product name: "C Potassium Silicate", manufactured by Nippon Chemical Industrial Co., Ltd., potassium silicate aqueous solution, molar ratio (n) 2.65, solid content concentration 40.0% by mass, silicon dioxide particle size 1-3 nm • Sodium silicate compounds Product name: "Special No. 1 Sodium Silicate", manufactured by Toso Sangyo Co., Ltd., No. 2 Sodium Silicate J2, Solid content concentration: 47.08% by mass, Molar ratio (m): 2.50 Sodium phosphate compound Sodium dihydrogen phosphate, manufactured by Taihei Chemical Industry Co., Ltd., in powder form. • Potassium phosphate Potassium dihydrogen phosphate, manufactured by Taihei Chemical Industry Co., Ltd., in powder form. Boric acid Taiyo Chemical Industry Co., Ltd., purified boric acid, powder form

[0151] [Example 1] (1) Preparation of aqueous inorganic coating agent As shown in the table below, each component was mixed to obtain an aqueous inorganic coating agent with a solid content of 2.37% by mass. The obtained aqueous inorganic coating agent is particularly suitable for organic substrates.

[0152] (2) Formation of the coating A sponge buff (for automotive paint finishing) attached to a single polisher (manufactured by KYOCERA (formerly RYOBI)) was soaked with 10g of the above-mentioned water-based inorganic coating agent. After spraying water onto the surface of the painted substrate (organic substrate), the surface was painted using the single polisher. Then, the surface was rubbed with a microfiber cloth wrung out tightly with water to obtain a coating.

[0153] [Example 2] (1) Preparation of aqueous inorganic coating agent As shown in the table below, each component was mixed to obtain an aqueous inorganic coating agent with a solid content of 1.88% by mass. The obtained aqueous inorganic coating agent is particularly suitable for lenses, optical glass, wafers, and sensors that require high optical properties.

[0154] (2) Formation of the coating A glass substrate was coated with the above-mentioned aqueous inorganic coating agent using spin coating to obtain a film. The refractive index of the film, measured using an ellipsometer (manufactured by JA Woollam Japan, product name "M-2000V-SUT"), was 1.30.

[0155] [Example 3] (1) Preparation of aqueous inorganic coating agent As shown in the table below, each component was mixed to obtain an aqueous inorganic coating agent with a solid content of 12.03% by mass. The obtained aqueous inorganic coating agent is particularly suitable for coating metals.

[0156] (2) Formation of the coating A buffing pad (manufactured by Monotaro) attached to a single polisher (Kyocera (formerly Ryobi), electric sander polisher, model number: PE-2100) was soaked with 10g of the above-mentioned water-based inorganic coating agent. After spraying water onto the surface of a stainless steel metal substrate, the surface was painted using the single polisher. Then, water was poured over the surface to remove any excess and obtain a coating.

[0157] [Comparative Example 1] (1) Preparation of aqueous inorganic coating agent As shown in the table below, each component was mixed to obtain an aqueous inorganic coating agent with a solid content of 5.67% by mass. Since this aqueous inorganic coating agent does not contain any components containing K2O, the molar ratio (SiO2 / K2O) could not be calculated.

[0158] (2) Formation of the coating A glass substrate was coated with the above-mentioned aqueous inorganic coating agent using spin coating to obtain a film. The refractive index of the film, measured using an ellipsometer (manufactured by JA Woollam Japan, product name "M-2000V-SUT"), was 1.42.

[0159] [Table 2]

[0160] [Rating 1] The coatings obtained in Example 2 and Comparative Example 1 were evaluated using an AFM or ellipsometer. A Hitachi High-Technologies Corporation product, "AFM5500MII," was used as the AFM. A JA Woollam Japan product, "M-2000V-SUT," was used as the ellipsometer.

[0161] (thickness) Example 2: Thickness 30nm Comparative Example 1: Thickness 50nm

[0162] (exterior) Figure 1A is an AFM image (90 μm × 90 μm) of a portion of the coating obtained in Example 2. Figure 1B is a surface structure profile obtained from the AFM data of the coating obtained in Example 2. As can be seen from Figures 1A and 1B, the aqueous inorganic coating agent of this disclosure forms pillars at high density on the substrate.

[0163] Figure 2A is an AFM image (90 μm × 90 μm) of a portion of the coating obtained in Comparative Example 1. Figure 2B is the surface structure profile obtained from the AFM data of the coating obtained in Comparative Example 1. A comparison of Figures 2A and 2B with Figures 1A and 1B shows that the protrusions formed by the aqueous inorganic coating agent in Comparative Example 1 vary greatly in thickness and length.

[0164] (Surface roughness) Each value related to surface roughness was calculated using data obtained by AFM, in accordance with JIS B 0601:2013. Ten measurements were taken, and the average of the eight values ​​obtained by dividing the maximum and minimum values ​​was used as the measured value. The results are shown in the table below.

[0165] [Table 3]

[0166] [Rating 2] The aqueous inorganic coating agent or film obtained in Example 2 was evaluated as follows.

[0167] (transmittance) A polyethylene naprethane film (PEN substrate) was coated with the aqueous inorganic coating agent of Example 2 using a microfiber cloth to obtain a sample with a coating. Light with a wavelength of 370-870 nm was incident at angles of 90 degrees, 20 degrees, or 36 degrees, and the transmittance was measured using a spectrophotometer (Hitachi High-Tech Corporation, product name "U-4000"). The transmittance of the sample, with the transmittance of the PEN substrate set to 100%, is shown in the table below.

[0168] [Table 4]

[0169] (reflectance) The reflectance of the above sample at wavelengths of 300 to 2100 nm was measured using a spectrophotometer (Hitachi High-Tech Corporation, product name "UH4150"). Figure 3 shows the reflectance of the sample when the reflectance of the PEN substrate is set to 100%.

[0170] (brightness) The brightness of the transmitted image of the above sample when visible light (wavelength 380-780 nm) was incident at a 45-degree angle was measured using a measuring device manufactured by Kato Optical Research Co., Ltd. The maximum brightness was 130 cd / m². 2 For reference, when the brightness of a sample coated with fluororesin was similarly measured, the maximum brightness was 119 cd / m². 2 It was confirmed that the coating of this disclosure has a lower reflectivity and higher transmittance than the fluororesin coating.

[0171] [Rating 3] The coating obtained in Example 3 was evaluated as shown in the table below.

[0172] [Table 5]

[0173] [Example of application 1] Application to railway vehicles (organic paint coating) A thumb-sized amount of the water-based inorganic coating agent from Example 1 was applied to several spots on a buffing pad attached to a single polisher. The water-based inorganic coating agent was then applied to the organic paint coating surface (organic substrate) of a railway vehicle using the single polisher described above. Subsequently, the painted surface was polished with a water-moistened sponge buffing pad. After drying, a damp cloth was used to finish and form a protective film. Figures 4A and 4B are photographs of a portion of a railway vehicle coated with the aqueous inorganic coating agent of Example 1.

[0174] [Example of application 2] Application to railway vehicles (made of stainless steel) A thumb-sized amount of the water-based inorganic coating agent from Example 3 was applied to several spots on a buffing pad attached to a single polisher. The water-based inorganic coating agent was then applied to the stainless steel parts of the railway vehicle using the single polisher described above. Subsequently, the painted surface was polished with a water-moistened sponge buffing pad. After drying, a damp cloth was used to finish and form a protective film. Figure 5 is a photograph of a portion of a railway vehicle that was coated with the aqueous inorganic coating agent of Example 3.

[0175] [Example of installation 3] Installation on elevator doors (stainless steel) In the same manner as in Example 2, the water-based inorganic coating agent of Example 3 was applied to the stainless steel door of the elevator to form a protective film. Figure 6 is a photograph of a portion of a stainless steel elevator door that was coated with the aqueous inorganic coating agent of Example 3.

[0176] [Example of Construction 4] Construction on 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) installed outdoors on Hierba Buena Island in San Francisco. Subsequently, the coated surface was polished with a water-moistened sponge buff. After drying, the surface was wiped with water to form a protective film. Figure 7 is a photograph of a mirror-finished stainless steel monument coated with the aqueous inorganic coating agent of Example 3. [Industrial applicability]

[0177] The aqueous inorganic coating agent of this disclosure has high antifouling properties and can form a film with suppressed interference fringes on various substrates.

Claims

1. A water-based inorganic coating agent, Potassium silicate compounds, Colloidal silica, Sodium phosphate compounds, Boric acid, and, Contains water, An aqueous inorganic coating agent in which the potassium phosphate compound content is less than 0.10% by mass of the solid content of the aqueous inorganic coating agent.

2. The aqueous inorganic coating agent according to claim 1, wherein the solid content concentration is 0.50 to 30.00% by mass.

3. The aqueous inorganic coating agent according to claim 1, wherein the boric acid content is 0.30 to 10.00% by mass of the solid content of the aqueous inorganic coating agent.

4. The aqueous inorganic coating agent according to claim 1, wherein the aqueous inorganic coating agent further comprises a sodium silicate compound.

5. The colloidal silica content is 20.00 to 90.00% by mass of the solid content of the aqueous inorganic coating agent. The aqueous inorganic coating agent according to claim 1, wherein the content of the potassium silicate compound is 2.00 to 20.00% by mass of the solid content of the aqueous inorganic coating agent.

6. The content of the sodium phosphate compound is 0.10 to 5.00% by mass of the solid content of the aqueous inorganic coating agent. The aqueous inorganic coating agent according to claim 5, wherein the content of boric acid is 1.00 to 10.00% by mass of the solid content of the aqueous inorganic coating agent.

7. The colloidal silica content is 5.00 to 35.00% by mass of the solid content of the aqueous inorganic coating agent. The aqueous inorganic coating agent according to claim 1, wherein the content of the potassium silicate compound is 5.00 to 40.00% by mass of the solid content of the aqueous inorganic coating agent.

8. The sodium phosphate compound content is 30.00 to 70.00% by mass of the solid content of the aqueous inorganic coating agent. The aqueous inorganic coating agent according to claim 7, wherein the content of boric acid is 0.30 to 1.50% by mass of the solid content of the aqueous inorganic coating agent.

9. The colloidal silica content is 35.00 to 60.00% by mass of the solid content of the aqueous inorganic coating agent. The aqueous inorganic coating agent according to claim 1, wherein the content of the potassium silicate compound is 1.00 to 20.00% by mass of the solid content of the aqueous inorganic coating agent.

10. The content of the sodium phosphate compound is 0.02 to 2.00% by mass of the solid content of the aqueous inorganic coating agent. The aqueous inorganic coating agent according to claim 9, wherein the content of boric acid is 0.30 to 1.50% by mass of the solid content of the aqueous inorganic coating agent.

11. The aqueous inorganic coating agent according to claim 1, wherein the aqueous inorganic coating agent further comprises an inorganic abrasive.

12. The aqueous inorganic coating agent according to claim 1, wherein the aqueous inorganic coating agent further comprises an inorganic thickener.

13. The aqueous inorganic coating agent according to claim 1, wherein the aqueous inorganic coating agent further comprises an inorganic curing agent.

14. The aqueous inorganic coating agent according to claim 1, wherein the aqueous inorganic coating agent further comprises monoaluminum phosphate.

15. The aqueous inorganic coating agent according to claim 1, wherein the colloidal silica has an average particle size of 5 to 30 nm.

16. A coating formed by the aqueous inorganic coating agent described in claim 1.

17. The coating according to claim 16, wherein the refractive index of light with a wavelength of 507 nm is 1.30 to 1.

40.

18. The coating according to claim 16, wherein the transmittance of light with a wavelength of 370 to 870 nm incident at an angle of 90 degrees is 93.00% or more.

19. A method for forming a coating, comprising applying the aqueous inorganic coating agent described in claim 1 to the surface of a substrate under atmospheric pressure.

20. The method for forming a coating according to claim 19, wherein the substrate has a surface formed of an organic material.

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

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