Alumina-based composite sol composition, method for producing the same, and method for producing alumina-based composite thin film

Abstract

The present invention addresses the issue of providing a coating composition that can produce an alumina-based composite thin film having good insulation properties and high hardness, by using a thermal treatment at a comparatively low temperature in a sol-gel process. The present invention provides an alumina-based composite sol composition that includes: an alumina sol (A) including an alumina hydrate; an alkoxysilane compound (B); a polyvalent organic acid (C); and a solvent (D). The alumina hydrate content in the alumina sol (A) is 3%–11% by mass.

Description

Technical Field

[0001] The present invention relates to an alumina-based composite sol composition for forming an alumina-based composite thin film, a method for producing the same, and a method for producing such an alumina-based composite thin film. The present invention also relates to an alumina sol and a method for producing the same.

Background Art

[0002] Alumina sol is produced by a wet method such as the sol-gel method, and its production methods are diverse. Alumina sol is used in various applications. For example, as a thickener, a suspending agent, a catalyst, a polymer Reinforcement agent and a binder, as a surface modifier for metals, inorganic powders, porous carriers, etc., as a porous self-supporting film, as a film formed on a substrate, and as an adsorbent for water treatment. The alumina hydrate particles contained in the alumina sol include particles of various shapes such as plate-like, columnar, needle-like, particulate, and fibrous. The physical properties of the alumina sol vary depending on the shape of the alumina hydrate particles, and the applications also differ depending on the physical properties.

[0003] It is known to form an insulating film on the surface of a substrate to impart insulation to the substrate such as metal or graphite. It is also known to form a transparent film having a hard coat function on the surface of a substrate such as glass, a plastic sheet, or a plastic lens to improve the scratch resistance of a display device or the like.

[0004] As methods for producing thin films of metal oxides, there are vapor phase processes such as PVD and CVD, and liquid phase processes such as sol-gel and electrophoresis.

[0005] Patent Document 1 discloses a coating composition capable of forming an alumina thin film excellent in film-forming property, denseness, gas barrier property, thermal stability, electrical insulation property, antifouling property, antistatic property, etc. by a sol-gel method. The composition is an alumina sol obtained by hydrolysis of aluminum alkoxide and contains fibrous or acicular alumina hydrate particles or alumina particles defined by a minor axis of 1 to 10 nm, a major axis of 100 to 10,000 nm, and an aspect ratio (major axis / minor axis) of 30 to 5,000, and 5 to 2,000 parts by mass of an alkoxysilane compound with respect to 100 parts by mass of the alumina hydrate particles or alumina particles.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] To obtain a film with high insulation as an insulating coating or a film with high hardness as a hard coating, it is necessary to have a dense structure with sufficiently small pores in the coating film and no generation of cracks. Conventional alumina sols have often had poor adhesion between particles because the shapes of the particles in the sol are rhombic, spherical like chestnuts, distorted spherical, columnar, etc. In such sols, the particles are not tightly connected to each other, and it has been difficult to uniformly cover the surface of the substrate.

[0008] On the one hand, the sol-gel method, which is one of the methods for manufacturing thin films of metal oxides, can perform all its processes at normal pressure and has few process steps. Therefore, it is a cheaper and simpler method compared to vapor phase methods (PVD, CVD, etc.) and electrophoresis methods. However, there is a problem that cracks are likely to occur in the film due to the shrinkage of the metal oxide during the process of the solvent of the coating composition volatilizing. In addition, in the sol-gel method, in order to manufacture a dense film without pores, it is necessary to perform heat treatment at a temperature of 500 °C or higher after applying the coating composition to the substrate, so there are limitations on the materials of the substrate to be applied.

[0009] The coating composition described in Patent Document 1 performs heat treatment at a wide range of temperatures, for example, 50 °C to 1500 °C, depending on the substrate to be applied and the purpose when manufacturing an alumina thin film. However, in order to impart insulation, heat treatment at a temperature of at least 300 °C or higher is required.

[0010] Therefore, an object of the present invention is to provide a coating composition capable of manufacturing an alumina-based thin film having high insulation and hardness by heat treatment at a relatively low temperature by the sol-gel method.

Means for Solving the Problems

[0011] The specific means for solving the above problems are as follows. The first embodiment of the present invention is the following alumina-based composite sol composition. (1) An alumina-based composite sol composition containing (A) an alumina sol containing an alumina hydrate, (B) an alkoxysilane compound, (C) a polyvalent organic acid, and (D) a solvent, wherein the amount of the alumina hydrate in the (A) alumina sol is 3% by mass to 11% by mass. (2) An alumina-based composite sol composition containing (A) an alumina sol containing an alumina hydrate, (B) an alkoxysilane compound, (C) a polyvalent organic acid, and (D) a solvent, wherein the amount of the alumina hydrate in the alumina-based composite sol composition is 1.6% by mass to 6.8% by mass. (3)(C) The polyvalent organic acid is selected from at least one of itaconic acid, citric acid, glutaric acid, succinic acid, citraconic acid, maleic acid, malonic acid, or malic acid, and the alumina-based composite sol composition according to (1) or (2) above. (4)(A) The alumina sol containing an alumina hydrate is an alumina sol obtained by hydrolysis of an aluminum alkoxide, and the alumina-based composite sol composition according to any one of (1) to (3) above. (5) The alumina hydrate is flaky alumina hydrate particles defined by a short diameter of 5 to 15 nm and a long diameter of 10 to 50 nm, and the alumina-based composite sol composition according to any one of (1) to (4) above. (6) The alumina hydrate has at least one crystal form selected from the group consisting of amorphous, boehmite, and pseudoboehmite, and the alumina-based composite sol composition according to any one of (1) to (5) above. (7)(B) The alkoxysilane compound is represented by the following general formula (1): R 1 n (R 3 ) m Si(OR 2 ) 4-m-n (1) (In the formula, R 1 represents an epoxy-containing group or a (meth)acrylic group, R 2 and R 3 represent an alkyl group having 1 to 4 carbon atoms, n is in the range of 0 to 2, m is in the range of 0 to 3, and n + m is in the range of 0 to 3.) and the alumina-based composite sol composition according to any one of (1) to (6) above. (8)(D) The solvent is water, alcohol, or a combination of water and alcohol, and the alumina-based composite sol composition according to any one of (1) to (7) above. (9)(B) The amount of the alkoxysilane compound is 105 to 460 parts by mass with respect to 100 parts by mass of the alumina hydrate, and the alumina-based composite sol composition according to any one of (1) to (8) above. (10) The amount of the polyvalent organic acid is 1 to 20 parts by mass with respect to 100 parts by mass of the solid content in the alumina-based composite sol composition, and the alumina-based composite sol composition according to any one of (1) to (9) above. (11) The alumina-based composite sol composition according to any one of (1) to (10) above, which is a coating composition. (12) The alumina-based composite sol composition according to any one of (1) to (11) above, which is an insulating coating agent or a hard coating agent.

[0012] The second embodiment of the present invention is a method for producing the following alumina-based composite sol composition. (13) A method for producing an alumina-based composite sol composition, which includes mixing (A) an alumina sol containing an alumina hydrate, (B) an alkoxysilane compound, (C) a polyvalent organic acid, and (D) a solvent, wherein the amount of the alumina hydrate in the alumina sol (A) is 3% by mass to 11% by mass. (14) A method for producing an alumina-based composite sol composition, which includes mixing (A) an alumina sol containing an alumina hydrate, (B) an alkoxysilane compound, (C) a polyvalent organic acid, and (D) a solvent, wherein the amount of the alumina hydrate in the alumina-based composite sol composition is 1.6% by mass to 6.8% by mass. (15) The method for producing an alumina-based composite sol composition according to (13) or (14) above, wherein the polyvalent organic acid (C) is selected from at least one of itaconic acid, citric acid, glutaric acid, succinic acid, citraconic acid, maleic acid, malonic acid, or malic acid. (16) The method for producing an alumina-based composite sol composition according to any one of (13) to (15) above, wherein the alumina sol (A) containing an alumina hydrate is an alumina sol obtained by hydrolysis of an aluminum alkoxide. (17) The method for producing an alumina-based composite sol composition according to any one of (13) to (16) above, wherein the alumina hydrate is plate-like alumina hydrate particles defined by a short diameter of 5 to 15 nm and a long diameter of 10 to 50 nm. The method for producing the alumina-based composite sol composition according to any one of (13) to (17) above, wherein the alumina hydrate has at least one crystal form selected from the group consisting of amorphous, boehmite, and pseudoboehmite. (19) (B) The alkoxysilane compound is represented by the following general formula (1): R 1 n (R 3 ) m Si(OR 2 ) 4-m-n (1) (In the above formula, R 1 represents an epoxy-containing group or a (meth)acrylic group, R 2 and R 3 represent an alkyl group having 1 to 4 carbon atoms, n is in the range of 0 to 2, m is in the range of 0 to 3, and n + m is in the range of 0 to 3.) The method for producing the alumina-based composite sol composition according to any one of (13) to (18) above, which is represented by (20) (D) The method for producing the alumina-based composite sol composition according to any one of (13) to (19) above, wherein the solvent is water, alcohol, or a combination of water and alcohol. (21) (B) The method for producing the alumina-based composite sol composition according to any one of (13) to (20) above, wherein the amount of the alkoxysilane compound is 105 to 460 parts by mass with respect to 100 parts by mass of the alumina hydrate. (22) (C) The method for producing the alumina-based composite sol composition according to any one of (13) to (21) above, wherein the amount of the polyvalent organic acid is 1 to 20 parts by mass with respect to 100 parts by mass of the total amount of the alumina hydrate in the (A) alumina sol and the (B) alkoxysilane compound.

[0013] The third embodiment of the present invention is a method for producing an alumina-based composite thin film, which includes applying the alumina-based composite sol composition according to any one of (1) to (12) above to the surface of a substrate and curing it. The fourth embodiment of the present invention is an alumina sol containing flaky alumina hydrate particles defined by a short diameter of 5 to 15 nm and a long diameter of 10 to 50 nm. The fifth embodiment of the present invention includes: (1) a step of stirring an aluminum alkoxide in water at a temperature of 70°C to 100°C in the absence of an acid; (2) a step of adding an acid to the reaction solution obtained in the step (1) and stirring. This is a method for producing an alumina sol according to the fourth embodiment of the present invention.

Advantages of the Invention

[0014] According to the first embodiment of the present invention, an alumina-based composite sol composition can be obtained, which can produce an alumina-based composite thin film having high insulation and hardness, excellent adhesion to a substrate, and applicability to various substrates by a sol-gel method with heat treatment at a relatively low temperature. Further, according to the second embodiment of the present invention, an alumina-based composite sol composition can be produced, which can produce an alumina-based composite thin film having high insulation and hardness, excellent adhesion to a substrate, and applicability to various substrates by a sol-gel method with heat treatment at a relatively low temperature. Moreover, according to the third embodiment of the present invention, an alumina-based composite thin film having high insulation and hardness, excellent adhesion to a substrate, and applicability to various substrates can be produced by a sol-gel method with heat treatment at a relatively low temperature. Also, according to the fourth embodiment of the present invention, an alumina sol suitable for the production of an alumina-based composite sol composition can be obtained, which can produce an alumina-based composite thin film having high insulation and hardness, excellent adhesion to a substrate, and applicability to various substrates by a sol-gel method with heat treatment at a relatively low temperature. Furthermore, according to the fifth embodiment of the present invention, an alumina sol suitable for the production of an alumina-based composite sol composition can be produced, which can produce an alumina-based composite thin film having high insulation and hardness, excellent adhesion to a substrate, and applicability to various substrates by a sol-gel method with heat treatment at a relatively low temperature.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Embodiment for Carrying Out the Invention

[0016] [Alumina-based Composite Sol Composition and Method for Producing the Same] The alumina-based composite sol composition according to the first embodiment of the present invention contains (A) an alumina sol containing an alumina hydrate, (B) an alkoxysilane compound, (C) a polyvalent organic acid, and (D) a solvent. Here, the amount of the alumina hydrate in the (A) alumina sol is 3% by mass to 11% by mass. Alternatively, here, the amount of the alumina hydrate in the alumina-based composite sol composition is 1.6% by mass to 6.8% by mass. According to the present embodiment, an alumina-based composite sol composition can be obtained which can produce an alumina-based composite thin film having high insulation and hardness, excellent adhesion to a substrate, and applicable to various substrates by a sol-gel method with heat treatment at a relatively low temperature.

[0017] (A) Alumina Sol The alumina-based composite sol composition contains (A) an alumina sol containing an alumina hydrate. The alumina sol is a colloidal solution in which fine particles of the alumina hydrate are dispersed in a dispersion medium such as water or alcohol. When the dispersion medium is water, the composition of the colloid is formally represented by Al2O3·nH2O. There are various production methods for the alumina sol, and the form and crystallinity of the fine particles of the alumina hydrate vary depending on each production method and production conditions. Note that "alumina" is synonymous with "aluminum oxide" whose compositional formula is represented by Al2O3.

[0018] In this embodiment, the amount of alumina hydrate in the alumina sol is 3% to 11% by mass, preferably 3% to 9% by mass, and more preferably 3% to 5% by mass. By setting the amount of alumina hydrate in the alumina sol to 3% by mass or more, the viscosity of the alumina-based composite sol composition can be moderately increased, the coatability of the alumina-based composite sol composition can be improved, and the insulating property can be enhanced. By setting the amount of alumina hydrate in the alumina sol to 11% by mass or less, it is possible to prevent the viscosity of the alumina-based composite sol composition from being too high, improve the coatability of the coating composition, and improve the dielectric breakdown strength. Here, the amount of alumina hydrate in this alumina sol corresponds to the charged amount when producing the composition.

[0019] Alternatively, in this embodiment, the amount of alumina hydrate in the alumina-based composite sol composition is 1.6% to 6.8% by mass, preferably 1.6% to 5.5% by mass, and more preferably 1.8% to 4.5% by mass. By setting the amount of alumina hydrate in the alumina-based composite sol composition to 1.6% by mass or more, the viscosity of the alumina-based composite sol composition can be moderately increased, the coatability of the alumina-based composite sol composition can be improved, and the insulating property can be enhanced. By setting the amount of alumina hydrate in the alumina-based composite sol composition to 6.8% by mass or less, it is possible to prevent the viscosity of the alumina-based composite sol composition from being too high, improve the coatability of the coating composition, and improve the dielectric breakdown strength. Here, the amount of alumina hydrate in this alumina-based composite sol composition corresponds to the charged amount when producing the composition.

[0020] Aluminum sol is produced by a wet method such as the sol-gel method, and there are a variety of manufacturing methods. The sol-gel method is a method in which metal organic compounds such as metal alkoxides, metal acetylacetonates, and metal carboxylates, and metal inorganic compounds such as nitrates, chlorides, and sulfates are hydrolyzed and dehydrated polycondensed in a solution to obtain a sol in which metal oxides or metal hydroxides are dispersed, and then the reaction is further advanced to cause gelation (solidification) to create an oxide solid. Such methods include, for example, a method of hydrolyzing aluminum alkoxide (B.E. Yoldas, Amer. Ceram. Soc. Bull. 54, 289 (1975), etc.), a method of hydrothermally treating an alumina gel obtained by neutralizing a water-soluble basic aluminum salt with an alkali in the presence of an organic acid (Japanese Patent Laid-Open No. Sho 53-112299, Japanese Patent Laid-Open No. Sho 54-116398), a method of hydrothermally treating an alumina gel obtained by a liquid-phase neutralization reaction between an acidic aluminum compound and an alkaline substance in the presence of a monovalent inorganic acid (Japanese Patent Laid-Open No. Sho 55-27824), a method of reacting an aqueous solution of an alkali metal aluminate and an aqueous solution of an organic hydroxyl acid by a neutralization reaction (Japanese Patent Laid-Open No. Sho 59-223223), and various other methods. In the present embodiment, from the viewpoint of obtaining amorphous, boehmite or pseudo-boehmite type alumina, the aluminum sol is preferably an aluminum sol obtained by hydrolysis of aluminum alkoxide.

[0021] The alumina hydrate particles contained in the aluminum sol include particles of various shapes such as plate-like, columnar, needle-like, particulate, and fibrous. The physical properties of the aluminum sol vary depending on the shape of the alumina hydrate particles, and the uses also vary depending on the physical properties. In the present embodiment, from the viewpoint of manufacturing a dense thin film with high insulation and hardness, (A) the alumina hydrate in the aluminum sol is preferably flaky alumina hydrate particles defined by a short diameter of 5 to 15 nm and a long diameter of 10 to 50 nm. The aluminum sol containing flaky alumina hydrate particles defined by a short diameter of 5 to 15 nm and a long diameter of 10 to 50 nm is the fourth embodiment of the present invention. In this specification, the particle diameter of the alumina hydrate particles is taken as the value obtained by a transmission electron microscope (TEM).

[0022] Many crystalline forms of alumina are known, such as amorphous, boehmite, pseudo-boehmite, γ-alumina, θ-alumina, and α-alumina. In the present embodiment, from the viewpoint of the insulating properties of the alumina-based composite thin film, (A) the alumina hydrate in the alumina sol preferably has at least one crystal form selected from the group consisting of amorphous, boehmite, and pseudo-boehmite. The crystal form of the alumina hydrate in the alumina sol can be prepared, for example, by adjusting the type of aluminum alkoxide, its hydrolysis conditions, or peptization conditions described later. Here, the crystal form of the alumina hydrate in the alumina sol can be confirmed using an X-ray diffractometer (for example, trade name "Ultima IV", manufactured by Rigaku Corporation) under the following conditions. In the present embodiment, amorphous or low-crystalline boehmite or pseudo-boehmite is preferred, and in that case, the X-ray diffraction shows a broad spectrum. <Condition> Tube target: Cu, tube voltage: 40 kV, tube current: 40 mA, sampling width: 0.020°, scanning speed: 20° / min, divergence slit: 2 / 3°, divergence vertical limit slit: 10 mm, scattering slit: 13 mm, receiving slit: 13 mm

[0023] An alumina sol containing flaky alumina hydrate particles defined by a minor axis of 5 to 15 nm and a major axis of 10 to 50 nm can be prepared, for example, by (1) a step of stirring an aluminum alkoxide in water at a temperature of 70°C to 100°C in the absence of an acid, (2) a step of adding an acid to the reaction solution obtained in the step (1) and stirring by a method including the above steps. This method for producing the alumina sol is the fifth embodiment of the present invention.

[0024] In the above step (1), the aluminum alkoxide in water is stirred at a temperature of 70°C to 100°C in the absence of an acid. By stirring at a temperature of 70°C to 100°C, through the hydrolysis reaction and polycondensation reaction of the aluminum alkoxide in water, a sol in which aluminum hydrate is dispersed in the solution is obtained. The stirring can be carried out in either an air atmosphere or an inert gas atmosphere such as nitrogen or argon, but it is preferably carried out in an inert gas atmosphere such as nitrogen or argon. The stirring in step (1) is carried out at a temperature of 70°C to 100°C, preferably at a temperature of 80°C to 90°C. The stirring time in step (1) can vary depending on conditions such as the stirring temperature, but is, for example, 1 minute to 1 hour.

[0025] Specific examples of the aluminum alkoxide include aluminum ethoxide, aluminum n-butoxide, aluminum sec-butoxide, aluminum tert-butoxide, aluminum isopropoxide, and the like. In this specification, the aluminum alkoxide also includes an aluminum chelate. Specific examples of such an aluminum chelate include cyclic aluminum oligomers, diisopropoxy(ethylacetoacetato)aluminum, tris(ethylacetoacetato)aluminum, and the like. Among these compounds, those having an alkoxyl group with 2 to 5 carbon atoms are preferred because they have appropriate hydrolyzability and it is easy to remove by-products.

[0026] In the above step (1), the solid content concentration of the aluminum alkoxide in water is preferably 9 to 18% by mass, more preferably 9 to 12% by mass. When the solid content concentration is 9% by mass or more, the obtained aluminum hydrate particles can be made to have an appropriate size. On the other hand, when the solid content concentration is 18% by mass or less, the stirrability of the reaction solution can be maintained well.

[0027] Next, an acid is added to the reaction solution obtained in the above step (1) and stirred (step (2)). In this step (2), the coagulated solid is dispersed again in the solution by the action of the acid to form a colloid (peptization effect). Thereby, a sol in which the alumina hydrate is dispersed in the solution can be formed. In step (2), the hydrolysis reaction and polycondensation reaction of the unreacted aluminum alkoxide may also occur simultaneously.

[0028] The sol formation process is due to the competitive reaction between the hydrolysis reaction of the alkoxide group and the polycondensation reaction by the Al-OH group. Therefore, the reaction rate ratio between the hydrolysis reaction and the polycondensation reaction becomes an important factor. In the conventional method for producing alumina sol by hydrolyzing aluminum alkoxide, the stirring of aluminum alkoxide in water has been carried out from the beginning in the presence of an acid for hydrolysis. In the present embodiment, step (1) is carried out in the absence of an acid, and by adding an acid in step (2), the reaction rates of the hydrolysis reaction and the polycondensation reaction are controlled, and the structure of the sol is controlled.

[0029] The acid used in the above step (2) is preferably a monovalent acid, and examples thereof include inorganic acids such as nitric acid and hydrochloric acid, and organic acids such as formic acid, acetic acid, propionic acid, and butyric acid. Organic acids are preferred because they hardly affect the performance of the obtained film and are easy to handle. As the organic acid, acetic acid is preferred in terms of operability and economy. The amount of the acid used is preferably 0.05 to 0.2 molar times, more preferably 0.1 to 0.16 molar times, based on the aluminum alkoxide.

[0030] The stirring in step (2) is carried out, for example, at a temperature of 70°C to 100°C, preferably at a temperature of 80°C to 90°C. The stirring in step (2) may vary depending on the stirring conditions, but is carried out, for example, for 50 hours to 150 hours, preferably for 70 hours to 120 hours.

[0031] In steps (1) and (2), alcohol is produced as a by-product by the hydrolysis reaction of the aluminum alkoxide. This alcohol may be distilled off from the reaction system, or may not be distilled off particularly.

[0032] After step (2), if necessary, the reaction solution is cooled to room temperature, and the supernatant of the reaction solution is collected by centrifugation or the like to obtain an alumina sol.

[0033] (B) alkoxysilane compound The alumina-based composite sol composition contains (B) an alkoxysilane compound. In the present specification, (B) the alkoxysilane compound refers to a compound having one or more alkoxy groups on silicon. In the present embodiment, (B) the alkoxysilane compound is preferably represented by the following general formula (1): R 1 n (R 3 ) m Si(OR 2 ) 4-m-n (1) (In the above formula, R 1 represents an epoxy-containing group or a (meth)acrylic group, R 2 and R 3 represent an alkyl group having 1 to 4 carbon atoms, n is in the range of 0 to 2, m is in the range of 0 to 3, and n + m is in the range of 0 to 3.) It is a compound represented by.

[0034] In the finally obtained sol composition, by containing (B) an alkoxysilane compound, although its specific structure is not clear, the alumina hydrate in (A) the alumina sol binds to the silanol groups formed by hydrolysis of a part of (B) the alkoxysilane compound, and an alumina hydrate-alkoxysilane compound complex (also referred to as an alumina-based complex in this specification) is generated, and it is considered that a sol in which it is dispersed in the solution is formed. That is, the alumina-based composite sol composition is a colloidal solution in which fine particles of the alumina-based complex are dispersed in the dispersion medium. However, a part of (B) the alkoxysilane compound remains in the solution without being hydrolyzed, and the alumina hydrate particles in (A) the alumina sol that are not bound to the silanol groups also exist in the solution. Therefore, the alumina-based composite sol composition contains, as a solid content, an alumina-based complex, an alumina hydrate, and an alkoxysilane compound.

[0035] (B) The amount of the alkoxysilane compound is preferably mixed in an amount of 105 to 460 parts by mass, more preferably 150 to 450 parts by mass, and even more preferably 250 to 400 parts by mass with respect to 100 parts by mass of the alumina hydrate in (A) the alumina sol. Here, the amount of this (B) alkoxysilane compound corresponds to the charged amount when mixed with (A) the alumina sol.

[0036] Specific examples of the alkoxysilane compound include so-called silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-acryloxypropyltrimethoxysilane, etc., and tetraethoxysilane (TEOS). Other specific examples of the alkoxysilane compound include vinyltrimethoxysilane, vinyltriethoxysilane, p-styryltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-ureidopropyltrialkoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, 3-trimethoxysilylpropylsuccinic anhydride and other silane coupling agents. The alkoxysilane compound is appropriately selected according to the type of the substrate to be coated. These can be used alone or in combination of two or more.

[0037] (C) Polyvalent organic acid The alumina-based composite sol composition contains (C) a polyvalent organic acid. In the present specification, the polyvalent organic acid refers to a compound having two or more carboxy groups or sulfo groups in one molecule, preferably a compound having two or more carboxy groups in one molecule, and more preferably a compound having two carboxy groups in one molecule. By containing (C) the polyvalent organic acid, crosslinking occurs within and / or between the particles of the alumina-based composite sol, stabilizing the alumina-based composite sol particles. Further, by containing (C) the polyvalent organic acid, a composite in which alumina hydrate, an alkoxysilane compound, and the polyvalent organic acid are crosslinked is formed in the resulting alumina-based composite thin film, and an alumina-based composite thin film having a dense structure, high insulation properties, and high hardness can be formed.

[0038] Examples of the polyvalent organic acid include oxalic acid, itaconic acid, citric acid, glutaric acid, succinic acid, citraconic acid, maleic acid, malonic acid, malic acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, trimesic acid, aconitic acid, oxaloacetic acid, etc. Preferably, it is itaconic acid, citric acid, glutaric acid, succinic acid, citraconic acid, maleic acid, malonic acid, or malic acid. These can be used alone or in combination of two or more.

[0039] The polyvalent organic acid may be in the form of a salt. Examples of the salt of the polyvalent organic acid include alkali metal salts, alkaline earth metal salts, ammonium salts, and amine salts. Among these, from the viewpoint of enhancing the solubility of the polyvalent organic acid in water, an alkali metal salt or an ammonium salt is preferable, and a sodium salt, a potassium salt, or an ammonium salt is more preferable.

[0040] (C) The amount of the polyvalent organic acid is preferably 1 to 20 parts by mass, more preferably 2 to 15 parts by mass, based on 100 parts by mass in total of the amount of the alumina hydrate in the alumina sol and the amount of the alkoxysilane compound. Alternatively, the amount of the polyvalent organic acid is preferably 1 to 20 parts by mass, more preferably 2 to 15 parts by mass, based on 100 parts by mass of the solid content in the alumina-based composite sol composition. The amount of the polyvalent organic acid (C) corresponds to the charged amount during the production of the composition.

[0041] (D) Solvent The alumina-based composite sol composition contains (D) a solvent. As the solvent, water, alcohols such as methanol, ethanol, and propanol, or a combination of water and alcohol can be used, and preferably water, ethanol, or a combination of water and ethanol.

[0042] Additives such as a curing agent, a viscosity modifier, a pH adjuster, and a pigment component may be blended in the alumina-based composite sol composition as long as they do not adversely affect its performance.

[0043] In one embodiment, the solid content in the alumina-based composite sol composition is preferably in the range of 6.5 to 15% by mass. When the solid content is 6.5% by mass or more, the film thickness per coating becomes sufficient. On the other hand, when the total solid content is 15% by mass or less, the operability during film formation and the stability of the coating liquid can be obtained. The solid content in the alumina-based composite sol composition includes the alumina-based composite, alumina hydrate, and alkoxysilane compound present in the alumina-based composite sol composition. The amount of the solvent (D) is preferably adjusted so that the amount of the alumina hydrate in the alumina-based composite sol composition is 1.6% to 6.8% by mass. Also, the amount of the solvent (D) is preferably adjusted so that the solid content in the alumina-based composite sol composition is in the range of 6.5 to 15% by mass.

[0044] In one embodiment, the viscosity of the alumina-based composite sol composition is preferably 14 to 22 mPa·s. When the viscosity is within this range, the film thickness per coating becomes sufficient, and the operability during film formation and the stability of the coating liquid can be obtained.

[0045] The alumina-based composite sol composition can be produced by mixing (A) an alumina sol containing an alumina hydrate, (B) an alkoxysilane compound, (C) a polyvalent organic acid, and (D) a solvent. Here, the amount of the alumina hydrate in the (A) alumina sol is 3% by mass to 11% by mass. Alternatively, here, the amount of the alumina hydrate in the alumina-based composite sol composition is 1.6% by mass to 6.8% by mass. This method for producing the alumina-based composite sol composition is the second embodiment of the present invention. As a method of mixing, these components may be mixed at once, or for example, while mixing (A) the alumina sol and (D) the solvent to obtain a first mixed solution, (B) the alkoxysilane compound, (C) the polyvalent organic acid, and (D) the solvent are mixed to obtain a second mixed solution, and then these first and second mixed solutions may be mixed.

[0046] The mixing of these components can be carried out, for example, at a temperature of 10°C to 100°C, preferably at room temperature. The mixing time of these components can vary depending on the mixing temperature, but is, for example, 1 to 200 hours, preferably 50 to 120 hours.

[0047] The alumina-based composite sol composition can be used as a coating composition. In particular, since an alumina-based composite thin film having high insulation and hardness, excellent adhesion to a substrate, and applicable to various substrates can be produced at a relatively low temperature by the sol-gel method, it can be used as an insulating coating agent or a hard coating agent. When used as an insulating coating agent, for example, metal-based substrates such as iron, copper, aluminum, titanium, steel, stainless steel (SUS), brass, etc.; ceramic-based substrates such as Al2O3, SiO2, ZrO, TiO2, glass, tile, pottery, etc.; organic matter-based substrates such as plastics such as carbon, graphite, paper, wood chips, polyvinyl alcohol, polypropylene, polycarbonate, polyimide, polyethylene terephthalate, acrylic resin, polyurethane, etc.; and substrates such as magnetic materials. When used as a hard coating agent, for example, metal-based substrates such as iron, copper, aluminum, titanium, steel, stainless steel (SUS), brass, etc.; ceramic-based substrates such as Al2O3, SiO2, ZrO, TiO2, glass, tile, pottery, etc.; organic matter-based substrates such as plastics such as carbon, graphite, paper, wood chips, polyvinyl alcohol, polypropylene, polycarbonate, polyimide, polyethylene terephthalate, acrylic resin, polyurethane, etc.; and substrates such as magnetic materials. More specifically, it can be used for insulating coating or hard coating of the inner surface of the device (such as aluminum, SUS, etc.), insulating coating or hard coating of the winding coil (such as Cu, etc.), insulating coating or hard coating of the flexible substrate (such as polyimide, polyethylene terephthalate, etc.), insulating coating or hard coating on the magnetic body, insulating coating of metal powder or carbon powder, insulating coating or hard coating of electronic components, and insulating coating or hard coating on ceramics such as glass and silica.

[0048] In addition, the alumina-based composite sol composition can be used as a sealing agent. For example, it can be used for sealing thermal spray coatings (metals and ceramics) and porous materials.

[0049] [Method for Producing Alumina-Based Composite Thin Film] The method for manufacturing the alumina-based composite thin film in this embodiment includes applying the alumina-based composite sol composition according to the first embodiment to the surface of a substrate and curing it.

[0050] The substrate to which the alumina-based composite sol composition is applied is not limited in type or shape, and includes metal-based substrates such as iron, copper, aluminum, titanium, steel, stainless steel (SUS), brass, etc.; ceramic-based substrates such as Al2O3, SiO2, ZrO, TiO2, glass, tile, pottery, etc.; organic-based substrates such as plastics such as carbon, graphite, paper, wood chips, polyvinyl alcohol, polypropylene, polycarbonate, polyimide, polyethylene terephthalate, acrylic resin, polyurethane, etc.; substrates such as magnetic materials.

[0051] As a method for applying the alumina-based composite sol composition, it can be appropriately selected according to the type of the substrate, such as dip method, spin method, spray method, jet dispensing method, screen printing, laminar flow method, electrophoresis method, etc.

[0052] After applying the alumina-based composite sol composition to the surface of the substrate, it is cured by heat treatment to form an alumina-based composite thin film. The heat treatment temperature is, for example, 80°C to 230°C, preferably 110°C to 200°C. The heat treatment time can vary depending on the heat treatment temperature, but is, for example, 5 minutes to 60 minutes. Since the alumina-based composite sol composition of the first embodiment does not need to be heat-treated at a temperature of 500°C or higher required for sintering of metal oxides, it can be applied to various substrates. In addition, the alumina-based composite sol composition of the first embodiment can form an alumina-based composite thin film having a dense structure, high insulation, and high hardness even by heat treatment at a relatively low temperature.

[0053] Although the specific structure of the alumina-based composite thin film is not clear, it is considered to form a complex in which an alumina hydrate, an alkoxysilane compound, and a polyvalent organic acid are crosslinked, and has a dense and strong structure. As a result, the alumina-based composite thin film exhibits high insulation and hardness.

[0054] The thickness of the alumina-based composite thin film can be appropriately selected according to the application. For example, it is 0.01 μm to 30 μm, preferably 0.1 μm to 10 μm, and more preferably 1 μm to 5 μm. When the film thickness is within the above range, desired insulation and hardness can be obtained, and the generation of cracks during heat treatment can be avoided.

Examples

[0055] Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0056] [Production of aluminum sol] Preparation Example 1 Production of alumina sol A Into a 50 l reaction vessel, 43880 g of pure water and 4570 g of aluminum isopropoxide were put, the liquid temperature was raised to 85 °C while stirring, and stirred for 10 minutes. 1550 g of acetic acid aqueous solution (210 g of acetic acid) was added to the reaction solution, and the reaction was carried out at 85 °C for 72 to 120 hours. The reaction solution was cooled to room temperature to terminate the reaction. The reaction solution was centrifuged while confirming the particle size with a laser diffraction / scattering type particle size distribution measuring device (LA-960, manufactured by Horiba, Ltd.), and the supernatant was collected to obtain alumina sol A. As a result of observing the obtained alumina sol A with a transmission electron microscope (TEM) (HT7700, manufactured by Hitachi High-Tech Corporation (100 kV)), as shown in Fig. 2, it was a sol in which flaky alumina hydrate particles defined by a short diameter of 5 to 15 nm and a long diameter of 10 to 50 nm were dispersed. The alumina hydrate concentration in the alumina sol was 3% by mass.

[0057] Preparation Example 2 Production of alumina sol B Except that 43380 g of pure water and 5070 g of aluminum isopropoxide were used, the procedure of Preparation Example 1 was repeated to obtain alumina sol B in which flaky alumina hydrate particles defined by a short diameter of 5 to 15 nm and a long diameter of 10 to 50 nm were dispersed. The alumina hydrate concentration in the alumina sol was 4% by mass.

[0058] Preparation Example 3 Production of alumina sol C Except that 39,880 g of pure water and 8,570 g of aluminum isopropoxide were used, the procedure of Preparation Example 1 was repeated to obtain an alumina sol C in which flaky alumina hydrate particles defined by a minor axis of 5 to 15 nm and a major axis of 10 to 50 nm were dispersed. The alumina hydrate concentration in the alumina sol was 11% by mass.

[0059] Preparation Example 4 Production of Alumina Sol D Except that 44,130 g of pure water and 4,320 g of aluminum isopropoxide were used, the procedure of Preparation Example 1 was repeated to obtain an alumina sol D in which flaky alumina hydrate particles defined by a minor axis of 5 to 15 nm and a major axis of 10 to 50 nm were dispersed. The alumina hydrate concentration in the alumina sol was 2.5% by mass.

[0060] Preparation Example 5 Production of Alumina Sol E Except that 39,630 g of pure water and 8,820 g of aluminum isopropoxide were used, the procedure of Preparation Example 1 was repeated to obtain an alumina sol E in which flaky alumina hydrate particles defined by a minor axis of 5 to 15 nm and a major axis of 10 to 50 nm were dispersed. The alumina hydrate concentration in the alumina sol was 11.5% by mass.

[0061] [Production of Alumina-Based Composite Sol Composition] (Examples 1 to 14 and Comparative Examples 1 to 3) The raw materials and charged amounts (parts by mass) listed in Table 1 were used. Alumina sol and pure water were placed in a 50 l reaction vessel and stirred at room temperature for 60 minutes to obtain a reaction solution A. On the other hand, an alkoxysilane compound and an organic acid solution containing a polyvalent organic acid and water were mixed and stirred at room temperature for 1 hour to obtain a reaction solution B. The reaction solution B was added to the reaction solution A, and the mixture was stirred at room temperature for 96 hours to obtain the alumina-based composite sol compositions of Examples 1 to 14 and Comparative Examples 1 to 2. In Comparative Example 3, the alumina-based composite sol composition of Comparative Example 3 was obtained in the same manner as in the procedure of Example 1, except that the polyvalent organic acid was not included.

[0062] In the table, the (B) alkoxysilane compounds used are as follows. (B) Alkoxysilane compound A: 3-glycidoxypropyltrimethoxysilane [Chemical formula] (B) Alkoxysilane compound B: 3-glycidoxypropyltriethoxysilane [Chemical formula]

[0063] [Viscosity measurement] The viscosities of the alumina-based composite sol compositions of the examples and comparative examples were measured using a Brookfield viscometer DV2TCP (cone: CPA-52Z, rotation speed: 200 rpm).

[0064] [Manufacture of alumina-based composite thin film] The alumina-based composite sol compositions of the examples and comparative examples were coated on an aluminum substrate (base material) by the dipping method and heat-treated at 150 °C for 1 hour to obtain an alumina-based composite thin film on the aluminum substrate. As shown in Figure 1, the alumina-based composite thin film was a thin film having transparency. The film thickness of the alumina-based composite thin film was measured using an electromagnetic / vortex current type small film thickness measuring instrument Dualscope FMP40 (manufactured by Fischer Instruments Co., Ltd.). The results are shown in Table 1.

[0065] [Dielectric breakdown strength] The alumina-based composite sol compositions of the examples and comparative examples were coated on an aluminum substrate (base material) by the dipping method and heat-treated at 150 °C for 1 hour to obtain an alumina-based composite thin film on the aluminum substrate. Using this alumina-based composite thin film on the aluminum substrate, the dielectric breakdown voltage was measured using a withstand voltage tester DAC-6041 (manufactured by Soken Electric Co., Ltd.), and the dielectric breakdown strength was calculated. The results are shown in Table 1. When the dielectric breakdown strength is 200 V / μm or more, the dielectric breakdown strength is high and it is considered good.

[0066] [Adhesion 1] The alumina-based composite sol compositions of the examples and comparative examples were coated on an aluminum substrate (base material) by the dipping method, heat-treated at 150 °C for 1 hour, and an alumina-based composite thin film on the aluminum substrate was obtained. For the alumina-based composite thin film on this aluminum substrate, the adhesion was evaluated by the method specified in JIS K 5600-5-6. The results are shown in Table 1. When the adhesion evaluation is 1 or less, the adhesion is high and it is considered good.

[0067] [Hardness (pencil hardness)] The alumina-based composite sol compositions of the examples and comparative examples were coated on an aluminum substrate (base material) by the dipping method, heat-treated at 150 °C for 1 hour, and an alumina-based composite thin film on the aluminum substrate was obtained. For the alumina-based composite thin film on this aluminum substrate, the hardness of the coating film was tested by the pencil hardness test specified in JIS K 5600-5-4. The results are shown in Table 1. When the pencil hardness is 6H or higher, the hardness is high and it is considered good.

[0068] [Insulation resistance] The alumina-based composite sol compositions of the examples and comparative examples were coated on an aluminum substrate (base material) by the dipping method, heat-treated at 150 °C for 1 hour, and an alumina-based composite thin film on the aluminum substrate was obtained. Electrodes were arranged on the alumina-based composite thin film portion, and the insulation resistance value when a voltage of 100 V was applied was measured with an ultra-high insulation meter SM-8220 (manufactured by Hioki E.E. Corporation). The results are shown in Table 1. When the insulation resistance value is 1.0E+11 Ω or more, the insulation property is high and it is considered good.

[0069]

Table 1-1

[0070]

Table 1-2

[0071]

Table 1-3

[0072] As can be seen from the results shown in Table 1, by using the alumina-based composite sol compositions of Examples 1 to 14, alumina-based composite thin films with high insulation, dielectric breakdown strength, adhesion, and hardness could be produced. On the other hand, the alumina-based composite thin film produced using the alumina-based composite sol composition of Comparative Example 1 did not obtain sufficient insulation. The alumina-based composite thin film produced using the alumina-based composite sol composition of Comparative Example 2 did not obtain sufficient dielectric breakdown strength. In the alumina-based composite sol composition of Comparative Example 3, a thin film with a sufficient film thickness could not be produced, and the measurement of insulation, dielectric breakdown strength, adhesion, and hardness itself was impossible.

[0073] [Adhesion 2] The alumina-based composite sol composition of Example 2 was coated on an aluminum substrate, an alumina substrate, a glass substrate, and a polyimide substrate by the dipping method, and heat-treated at 150 °C for 1 hour to obtain alumina-based composite thin films on various substrates. The adhesion of the alumina-based composite thin films on these various substrates was evaluated by the method specified in JIS K 5600-5-6. The results are shown in Table 2. When the adhesion evaluation is 1 or less, the adhesion is high and is considered good. As can be seen from the results shown in Table 2, the adhesion was good on all substrates.

[0074]

Table 2

[0075] The disclosure of Japanese Patent Application No. 2020-203873 (filing date: December 9, 2020) is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated to be incorporated by reference.

Explanation of Reference Signs

[0076] 1 Coating part 2 Uncoated part (aluminum substrate)

Claims

1. An alumina-based composite sol composition comprising (A) an alumina sol containing an alumina hydrate, (B) an alkoxysilane compound, (C) a polyvalent organic acid, and (D) a solvent, wherein the amount of the alumina hydrate in the (A) alumina sol is 3% by mass to 11% by mass.

2. An alumina-based composite sol composition comprising (A) an alumina sol containing an alumina hydrate, (B) an alkoxysilane compound, (C) a polyvalent organic acid, and (D) a solvent, wherein the amount of the alumina hydrate in the alumina-based composite sol composition is 1.6% by mass to 6.8% by mass.

3. The alumina-based composite sol composition according to claim 1 or 2, wherein the (C) polyvalent organic acid is selected from at least one of itaconic acid, citric acid, glutaric acid, succinic acid, citraconic acid, maleic acid, malonic acid, or malic acid.

4. The alumina-based composite sol composition according to any one of claims 1 to 3, wherein the (A) alumina sol containing an alumina hydrate is an alumina sol obtained by hydrolysis of an aluminum alkoxide.

5. The alumina-based composite sol composition according to any one of claims 1 to 4, wherein the alumina hydrate is plate-like alumina hydrate particles defined by a short diameter of 5 to 15 nm and a long diameter of 10 to 50 nm.

6. The alumina-based composite sol composition according to any one of claims 1 to 5, wherein the alumina hydrate has at least one crystal form selected from the group consisting of amorphous, boehmite, and pseudoboehmite.

7. The (B) alkoxysilane compound of the alumina-based composite sol composition according to any one of claims 1 to 6 is represented by the following general formula (1): R １ ｎ (R ３ ) ｍ Si(OR ２ ) ４－ｍ－ｎ (1) (In the formula, R １ represents an epoxy-containing group or a (meth)acrylic group, R ２ and R ３ represent an alkyl group having 1 to 4 carbon atoms, n is in the range of 0 to 2, m is in the range of 0 to 3, and n + m is in the range of 0 to 3.) The alumina-based composite sol composition according to any one of claims 1 to 6.

8. The alumina-based composite sol composition according to any one of claims 1 to 7, wherein the (D) solvent is water, alcohol, or a combination of water and alcohol.

9. The alumina-based composite sol composition according to any one of claims 1 to 8, wherein the amount of the (B) alkoxysilane compound is 105 to 460 parts by mass with respect to 100 parts by mass of the alumina hydrate.

10. The alumina-based composite sol composition according to any one of claims 1 to 9, wherein the amount of the (C) polyvalent organic acid is 1 to 20 parts by mass with respect to 100 parts by mass of the solid content in the alumina-based composite sol composition.

11. The alumina-based composite sol composition according to any one of claims 1 to 10, which is a coating composition.

12. The alumina-based composite sol composition according to any one of claims 1 to 11, which is an insulating coating agent or a hard coating agent.

13. A method for producing an alumina-based composite thin film, comprising applying the alumina-based composite sol composition according to any one of claims 1 to 12 to a substrate surface and curing it.

14. A method for producing an alumina-based composite sol composition, comprising mixing (A) an alumina sol containing an alumina hydrate, (B) an alkoxysilane compound, (C) a polyvalent organic acid, and (D) a solvent, wherein the amount of the alumina hydrate in the (A) alumina sol is 3% by mass to 11% by mass.

15. (1) A step of stirring aluminum alkoxide in water at a temperature of 70°C to 100°C in the absence of an acid, (2) A step of adding an acid to the reaction solution obtained in the step (1) and stirring. A method for producing an alumina sol containing plate-like alumina hydrate particles defined by a minor axis of 5 to 15 nm and a major axis of 10 to 50 nm, comprising the steps.

Images