Silica sol dispersed in nitrogen-containing organic solvent containing organic acid and insulating resin composition

Abstract

Provided are: a silica sol dispersed in a nitrogen-containing organic solvent that contains an organic acid; and an insulating resin composition containing the silica sol and a nitrogen-containing polymer.　This silica sol is obtained by dispersing silica particles having an average primary particle size of 5-100 nm in a nitrogen-containing organic solvent. In the silica sol, a carboxylic acid having 1-3 carbon atoms is contained at a proportion of 80-1500 ppm. In the silica sol, the nitrogen-containing organic solvent is an amide-based solvent. In the silica sol, the nitrogen-containing organic solvent is dimethylacetamide, dimethylformamide, or dimethylpropionamide. In the silica sol, the carboxylic acid having 1-3 carbon atoms is formic acid, acetic acid, or propionic acid. This insulating resin composition contains the silica sol and a nitrogen-containing polymer.

Description

[Technical Field]

[0001] The present invention relates to a silica sol dispersed in a nitrogen-containing organic solvent containing an organic acid such as acetic acid, an insulating resin composition using the same, and methods for producing the same. [Background technology]

[0002] Silica sols in which surface-modified silica particles are dispersed in a solvent are known. For example, a method has been disclosed in which hydroxyl groups on the surface of inorganic oxide particles such as silica react with alcohol to introduce alkoxyl groups, thereby organifying the particles and obtaining an inorganic oxide sol dispersed in an organic solvent such as toluene (see Patent Document 1). In this method, phenyltrimethoxysilane is reacted with a methanol-dispersed silica sol, and the resulting silica sol is dispersed in a toluene solvent.

[0003] In addition, a silica sol dispersed in methanol is solvent-substituted with acetonitrile to obtain a silica sol dispersed in an acetonitrile-methanol mixed solvent, and then the silica sol is reacted with phenyltrimethoxysilane (see Patent Document 2).

[0004] Furthermore, a silica sol in which the surfaces of silica particles are modified with an aluminum compound has been disclosed (see Patent Document 3).

[0005] Also disclosed is an aluminum-containing silica sol dispersed in a nitrogen-containing solvent, and an insulating resin composition using the same (see Patent Document 4). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-200294 [Patent Document 2] International Publication No. 2009 / 008509 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-026183 [Patent Document 4] International Publication No. 2022 / 097694 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to provide a silica sol in which silica particles are dispersed in a nitrogen-containing organic solvent that allows for good compatibility with polar resins such as polyimide and polyamide resins, and also to provide a resin composition containing the silica sol and a resin, which, when used as an insulating resin composition, can provide an insulating coated conductor that can maintain a long insulation life. [Means for solving the problem]

[0008] In a first aspect, the present invention provides a silica sol in which silica particles having an average primary particle size of 5 to 100 nm are dispersed in a nitrogen-containing organic solvent, the silica sol containing a carboxylic acid having 1 to 3 carbon atoms in an amount of 80 to 1500 ppm. As a second aspect, the silica sol according to the first aspect, wherein the nitrogen-containing organic solvent is an amide solvent. As a third aspect, the silica sol according to the first aspect or the second aspect, in which the nitrogen-containing organic solvent is dimethylacetamide, dimethylformamide, or dimethylpropionamide. As a fourth aspect, the silica sol according to any one of the first to third aspects, in which the carboxylic acid having 1 to 3 carbon atoms is formic acid, acetic acid, or propionic acid. As a fifth aspect, the silica sol according to any one of the first to fourth aspects, in which the water content in the silica sol is 0.1 to 10.0 mass %. According to a sixth aspect, the silica sol according to any one of the first to fifth aspects has a viscosity of 3 to 500 mPa s when measured at 25°C in an SiO2 concentration of 30% by mass. As a seventh aspect, the silica sol according to any one of the first to sixth aspects, which contains alkali metal ions (wherein the alkali metal ions refer to alkali metal ions consisting of lithium, sodium, and potassium) at a ratio of 300 ppm or less; As an eighth aspect, the present invention provides a method for producing silica particles represented by formula (1) to formula (3):

[0009] [ka]

[0010] (In formula (1), R 1 are each an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a carboxyl group, an acid anhydride group, a carboxylic acid ester group, an epoxy group, a hydroxyl group, or a cyano group, and are bonded to a silicon atom by a Si-C bond; R 2 each represents an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group, and a represents an integer of 1 to 3; In formula (2) and formula (3), R 3 and R 5 are each an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms and bonded to a silicon atom by a Si-C bond, and R 4 and R 6 each represents an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group; Y represents an alkylene group, an NH group, or an oxygen atom; b is an integer of 1 to 3; c is an integer of 0 or 1; and d is an integer of 1 to 3. The silica sol according to any one of the first to seventh aspects, which is coated with at least one silane compound or a hydrolyzate thereof selected from the group consisting of: According to a ninth aspect, there is provided an insulating resin composition comprising the silica sol according to any one of the first to eighth aspects and a nitrogen-containing polymer. According to a tenth aspect, the insulating resin composition according to the ninth aspect, wherein the ratio of the parts by mass of the nitrogen-containing polymer to 1 part by mass of silica contained in the silica sol is 1 to 100. According to an eleventh aspect, the insulating resin composition according to the ninth or tenth aspect, wherein the nitrogen-containing polymer is polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, or polyesterimide; According to a twelfth aspect, there is provided an insulating resin composition comprising the silica sol according to any one of the first to eighth aspects, and a polyamic acid composed of 4,4'-diaminodiphenyl ether (DDE) and pyromellitic anhydride (PMDA) as a resin, the polyamic acid being adjusted to a mass ratio of resin / SiO2=80 / 20, and the composition being stored at 50°C for 7 days, the viscosity (mPa s) of which is 1.20 times or less of the viscosity before storage; According to a thirteenth aspect, there is provided an insulating resin composition comprising the silica sol according to any one of the first to eighth aspects, and a polyamic acid composed of 4,4'-diaminodiphenyl ether (DDE) and pyromellitic anhydride (PMDA) as a resin, the polyamic acid being adjusted to a mass ratio of resin / SiO2=80 / 20, and the silica-blended polyamic acid is heated at 290°C on a Cu plate to obtain a Cu plate (coating thickness: 29 to 32 µm) on which a silica-blended polyimide is baked, the insulating resin composition having a dielectric breakdown life of 50 minutes or longer at a test temperature of 155°C (in air), an applied voltage of 3.0 kV, and a frequency of 50 Hz; According to a fourteenth aspect, there is provided an insulating coated conductor that is insulatingly coated with the insulating resin composition according to any one of the ninth to thirteenth aspects. As a fifteenth aspect, the method comprises the following steps (A) and (B): Step (A): preparing a silica sol in which silica particles having an average primary particle diameter of 5 to 100 nm are dispersed in an aqueous medium; a step (B) of substituting the silica sol obtained in the step (A) with a nitrogen-containing organic solvent while adjusting the content of the carboxylic acid having 1 to 3 carbon atoms in the silica sol to 80 to 1500 ppm; As a 16th aspect, (B) during the process or (B) after the process is completed Eighth Viewpoint a step (C) of adding at least one silane compound represented by any one of formulas (1) to (3) according to the fifteenth aspect of the present invention; According to a seventeenth aspect, there is provided a method for producing an insulating resin composition according to any one of the ninth to fourteenth aspects, the method including a step (D) of mixing the silica sol obtained according to the fifteenth or sixteenth aspect with a nitrogen-containing polymer; and According to an eighteenth aspect, there is provided a method for producing an insulating resin composition according to the seventeenth aspect, further comprising the step (D) further comprising the step (E) of removing part or all of the nitrogen-containing organic solvent from the insulating resin composition. [Effects of the Invention]

[0011] The insulating resin obtained by coating and curing an insulating resin composition can contain silica particles in the insulating resin composition to improve the insulation resistance of the substrate. The silica particles form a tight, strong coating layer with the insulating resin, thereby protecting the substrate from dielectric breakdown due to discharge. Nitrogen-containing polymers with high insulating properties are often used as insulating resins. These nitrogen-containing polymers include, for example, polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, and polyesterimide. These nitrogen-containing polymers are synthesized from diamines and acid anhydrides, and have both polar moieties, such as an imide skeleton, a carboxyl group, or an amide bond, and hydrophobic moieties contained in the diamine molecule or the acid anhydride molecule.

[0012] The insulating resin composition is produced by mixing a silica sol dispersed in a nitrogen-containing organic solvent that is highly compatible with the nitrogen-containing polymer with the nitrogen-containing polymer. When the insulating resin composition is used as an enameled wire coating material, proper viscosity control is important in the field to coat the enameled wire with a uniform film thickness.

[0013] According to the present invention, at the stage of silica sol dispersed in a nitrogen-containing organic solvent, it is possible to suppress an increase in viscosity of the silica sol by adding a specific amount of organic acid to the nitrogen-containing organic solvent.Furthermore, according to the present invention, when the silica sol dispersed in the nitrogen-containing organic solvent is mixed with a nitrogen-containing polymer to form an insulating resin composition (varnish), it is possible to suppress an increase in viscosity of the insulating resin composition by adding a specific amount of organic acid.

[0014] The present invention also relates to a silica sol dispersed in a nitrogen-containing organic solvent and a method for producing an insulating resin composition by adding the sol to a nitrogen-containing polymer, and includes cases where an organic acid is originally contained in the nitrogen-containing organic solvent or the nitrogen-containing polymer, and cases where an organic acid is newly added. By measuring these and adjusting the content within the range set by the present invention, it is possible to achieve stabilization of the viscosity of the silica sol or the insulating resin composition. DETAILED DESCRIPTION OF THE INVENTION

[0015] Preferred embodiments of the present invention will be described below. However, the following embodiments are merely examples for explaining the present invention, and the present invention is not limited to the following embodiments. One embodiment of the present invention is a silica sol in which silica particles having an average primary particle diameter of 5 to 100 nm are dispersed in a nitrogen-containing organic solvent, and the silica sol contains a carboxylic acid having 1 to 3 carbon atoms in an amount of 80 to 1500 ppm.

[0016] In one embodiment of the present invention, the silica particles contained in the silica sol have an average primary particle diameter of 5 to 100 nm. The average primary particle diameter of the silica particles can be measured by a nitrogen gas adsorption method (BET method) in terms of particle diameter (nm).

[0017] The nitrogen-containing organic solvent used in the present invention has a functional group containing at least a nitrogen atom. Examples of functional groups containing a nitrogen atom include an amino group, a nitro group, and a cyano group. Among these, amide-based solvents in which a nitrogen-containing functional group and a carbonyl group exist in one solvent molecule are preferred, and examples of such solvents include those having a chain structure or a cyclic structure. Examples of functional groups containing a nitrogen atom include an amino group, a nitro group, and a cyano group, with the amino group being preferred. The amino group and the carbonyl group can be adjacent to each other or can exist via a carbon atom, but can be used, for example, as an amide bond, and amide-based solvents are preferred.

[0018] Specific examples of nitrogen-containing organic solvents include dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, dimethylpropionamide, N-methylpyrrolidone, N-ethylpyrrolidone, tetramethylurea, hexamethylphosphoric triamide, dimethylacrylamide, acryloylmorpholine, hydroxyethylacrylamide, isopropylacrylamide, diethylacrylamide, dimethylaminopropylacrylamide, 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, dimethylaminopropylacrylamide methyl chloride quaternary salt, and dimethylaminoethyl acrylate benzyl chloride quaternary salt.

[0019] Among these, dimethylacetamide, dimethylformamide, or dimethylpropionamide can be preferably used as the nitrogen-containing organic solvent. The nitrogen-containing organic solvent may contain other solvents as long as the effects of the present invention are not impaired.

[0020] That is, the nitrogen-containing organic solvent may be contained in an amount of 50 to 100 volume %, 90 to 100 volume %, 98 to 100 volume %, or 99 to 100 volume % of the total solvent, and other solvents may be contained in an amount of 0 to less than 50 volume %, 0 to less than 10 volume %, 0 to less than 2 volume %, or 0 to less than 1 volume %. Other solvents include water, ketone-based solvents, ester-based solvents, alcohol-based solvents, glycol ether-based solvents, hydrocarbon-based solvents, halogen-based solvents, ether-based solvents, glycol-based solvents, and amine-based solvents.

[0021] Specific examples of such solvents include ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, and cyclohexanone; ester-based solvents such as methyl acetate, ethyl acetate, and butyl acetate; alcohol-based solvents such as methanol, ethanol, isopropanol, and benzyl alcohol; glycol ether-based solvents such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monopropyl ether, and diethylene glycol monobutyl ether; hydrocarbon-based solvents such as benzene, toluene, xylene, n-hexane, and cyclohexane; halogen-based solvents such as dichloromethane, trichloroethylene, and perchloroethylene; ether-based solvents such as dioxane, diethyl ether, and tetrahydrofuran; glycol-based solvents such as ethylene glycol, diethylene glycol, propylene glycol, and polyethylene glycol; and amine-based solvents such as monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, N-methylethanolamine, and 2-amino-2-methyl-1-propanol.

[0022] In one embodiment of the present invention, the organic acid is preferably a carboxylic acid having 1 to 3 carbon atoms, and more preferably formic acid, acetic acid, or propionic acid, because these organic acids are highly compatible with nitrogen-containing organic solvents and nitrogen-containing polymers.

[0023] In one embodiment of the present invention, the water content in the silica sol is preferably 0.1 to 10.0% by mass. Furthermore, the viscosity of the silica sol is preferably 3 to 500 mPa·s when measured at 25° C. when the SiO2 concentration is 30 mass %.

[0024] The alkali metal ions (here, alkali metal ions refer to alkali metal ions consisting of lithium, sodium, and potassium) can be contained in a proportion of 300 ppm or less, 30 to 300 ppm, or 30 to 200 ppm. For example, by controlling the sodium ions content within the above range, it is possible to suppress an increase in viscosity of silica sol dispersed in a nitrogen-containing organic solvent.

[0025] In one embodiment of the present invention, the silica sol may contain alkali metal ions (here, alkali metals refer to alkali metal ions of lithium, sodium, and potassium) at a concentration of 300 ppm or less, or 30 to 300 ppm, or 30 to 200 ppm, and may contain 0.03 mass% or less, or 0.003 mass% to 0.03 mass%, or 0.003 mass% to 0.02 mass% in the silica sol. For example, a silica sol with a silica concentration of 30 mass% may contain 1000 ppm or less, or 100 ppm to 1000 ppm, or 100 ppm to 6.70 ppm of alkali metals converted to MO relative to the mass of SiO contained in the silica sol. Furthermore, when an insulating resin composition is produced by mixing a nitrogen-containing polymer with silica sol dispersed in a nitrogen-containing organic solvent, the insulating resin composition also preferably contains an alkali metal, calculated as MO, in an amount of 1000 ppm or less, or 100 ppm to 1000 ppm or less, or 100 ppm to 670 ppm or less relative to SiO.

[0026] The silica particles in the silica sol of the present invention can be coated by adding at least one silane compound selected from the group consisting of formulas (1) to (3). In formula (1), R 1 are each an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a carboxyl group, an acid anhydride group, a carboxylic acid ester group, an epoxy group, a hydroxyl group, or a cyano group, and are bonded to a silicon atom by a Si-C bond; R 2each represents an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group, and a represents an integer of 1 to 3; In formula (2) and formula (3), R 3 and R 5 are each an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms and bonded to a silicon atom by a Si-C bond, and R 4 and R 6 respectively represent an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group; Y represents an alkylene group, an NH group, or an oxygen atom; b is an integer of 1 to 3; c is an integer of 0 or 1; and d is an integer of 1 to 3.

[0027] The alkyl group is an alkyl group having 1 to 18 carbon atoms, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, a cyclopropyl group, an n-butyl group, an i-butyl group, an s-butyl group, a t-butyl group, a cyclobutyl group, a 1-methyl-cyclopropyl group, a 2-methyl-cyclopropyl group, an n-pentyl group, a 1-methyl-n-butyl group, a 2-methyl-n-butyl group, a 3-methyl-n-butyl group, a 1,1-dimethyl-n-propyl group, a 1,2-dimethyl-n-propyl group, a 2,2-dimethyl-n-propyl group, a 1-ethyl -n-Propyl, cyclopentyl, 1-methylcyclobutyl, 2-methylcyclobutyl, 3-methylcyclobutyl, 1,2-dimethylcyclopropyl, 2,3-dimethylcyclopropyl, 1-ethylcyclopropyl, 2-ethylcyclopropyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl group, 2,2-dimethyl-n-butyl group, 2,3-dimethyl-n-butyl group, 3,3-dimethyl-n-butyl group, 1-ethyl-n-butyl group, 2-ethyl-n-butyl group, 1,1,2-trimethyl-n-propyl group, 1,2,2-trimethyl-n-propyl group, 1-ethyl-1-methyl-n-propyl group, 1-ethyl-2-methyl-n-propyl group, cyclohexyl group, 1-methyl-cyclopentyl group, 2-methyl-cyclopentyl group, 3-methyl-cyclopentyl group, 1-ethyl-cyclobutyl group, 2-ethyl-cyclobutyl group group, 3-ethyl-cyclobutyl group, 1,2-dimethyl-cyclobutyl group, 1,3-dimethyl-cyclobutyl group, 2,2-dimethyl-cyclobutyl group, 2,3-dimethyl-cyclobutyl group, 2,4-dimethyl-cyclobutyl group, 3,3-dimethyl-cyclobutyl group, 1-n-propyl-cyclopropyl group, 2-n-propyl-cyclopropyl group, 1-i-propyl-cyclopropyl group, 2-i-propyl-cyclopropyl group, 1,2,2-trimethyl-cyclopropyl group, 1,2,3-trimethyl-cyclopropyl group, 2,2,Examples include, but are not limited to, 3-trimethyl-cyclopropyl group, 1-ethyl-2-methyl-cyclopropyl group, 2-ethyl-1-methyl-cyclopropyl group, 2-ethyl-2-methyl-cyclopropyl group, 2-ethyl-3-methyl-cyclopropyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, and octadecyl group. Examples of the alkylene group include alkylene groups derived from the above-mentioned alkyl groups.

[0028] The aryl group is an aryl group having 6 to 30 carbon atoms, and examples thereof include a phenyl group, a naphthyl group, an anthracene group, and a pyrene group. Examples of the alkenyl group include alkenyl groups having 2 to 10 carbon atoms, such as ethenyl, 1-propenyl, 2-propenyl, 1-methyl-1-ethenyl, 1-butenyl, 2-butenyl, 3-butenyl, 2-methyl-1-propenyl, 2-methyl-2-propenyl, 1-ethylethenyl, 1-methyl-1-propenyl, 1-methyl-2-propenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 1-n-propylethenyl, 1-methyl-1-butenyl, 1-methyl-2-butenyl, 1-methyl-3-butenyl, 2-ethyl-2-propenyl, 2-methyl-1-butenyl, 2-methyl-2-butenyl, and 2-methyl-3-butenyl. Examples of the alkyl group include, but are not limited to, a 3-methyl-1-butenyl group, a 3-methyl-2-butenyl group, a 3-methyl-3-butenyl group, a 1,1-dimethyl-2-propenyl group, a 1-i-propylethenyl group, a 1,2-dimethyl-1-propenyl group, a 1,2-dimethyl-2-propenyl group, a 1-cyclopentenyl group, a 2-cyclopentenyl group, a 3-cyclopentenyl group, a 1-hexenyl group, a 2-hexenyl group, a 3-hexenyl group, a 4-hexenyl group, a 5-hexenyl group, a 1-methyl-1-pentenyl group, a 1-methyl-2-pentenyl group, a 1-methyl-3-pentenyl group, a 1-methyl-4-pentenyl group, a 1-n-butylethenyl group, a 2-methyl-1-pentenyl group, and a 2-methyl-2-pentenyl group.

[0029] Examples of the alkoxy group include alkoxy groups having 1 to 10 carbon atoms, such as methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, t-butoxy, n-pentyloxy, 1-methyl-n-butoxy, 2-methyl-n-butoxy, 3-methyl-n-butoxy, 1,1-dimethyl-n-propoxy, 1,2-dimethyl-n-propoxy, 2,2-dimethyl-n-propoxy, 1-ethyl-n-propoxy, and n-hexyloxy groups, but are not limited to these.

[0030] Examples of the acyloxy group include acyloxy groups having 2 to 10 carbon atoms, such as a methylcarbonyloxy group, an ethylcarbonyloxy group, an n-propylcarbonyloxy group, an i-propylcarbonyloxy group, an n-butylcarbonyloxy group, an i-butylcarbonyloxy group, an s-butylcarbonyloxy group, a t-butylcarbonyloxy group, an n-pentylcarbonyloxy group, a 1-methyl-n-butylcarbonyloxy group, a 2-methyl-n-butylcarbonyloxy group, a 3-methyl-n-butylcarbonyloxy group, a 1,1-dimethyl-n-propylcarbonyloxy group, a 1,2-dimethyl-n-propylcarbonyloxy group, a 2,2-dimethyl-n-propylcarbonyloxy group, a 1-ethyl-n-propylcarbonyloxy group, an n-hexylcarbonyloxy group, a 1-methyl-n-pentylcarbonyloxy group, and a 2-methyl-n-pentylcarbonyloxy group. Examples of the halogen group include fluorine, chlorine, bromine, and iodine.

[0031] The (meth)acryloyl group refers to both an acryloyl group and a methacryloyl group. Examples of organic groups having a (meth)acryloyl group include a 3-methacryloxypropyl group and a 3-acryloxypropyl group. An example of the organic group having a mercapto group is a 3-mercaptopropyl group. Examples of organic groups having an amino group include a 2-aminoethyl group, a 3-aminopropyl group, an N-2-(aminoethyl)-3-aminopropyl group, an N-(1,3-dimethyl-butylidene)aminopropyl group, an N-phenyl-3-aminopropyl group, and an N-(vinylbenzyl)-2-aminoethyl-3-aminopropyl group.

[0032] An example of the organic group having a ureido group is a 3-ureidopropyl group. Examples of organic groups having an epoxy group include a glycidyl group and a 3,4-epoxycyclohexyl group. These epoxy groups may be ring-opened to generate hydroxyl groups. An example of an organic group having a cyano group is a 3-cyanopropyl group. The compounds of the above formulas (2) and (3) are preferably compounds that can form trimethylsilyl groups on the surface of silica particles. Examples of such compounds include the following.

[0033] [ka]

[0034] In the above formula, R 12 is an alkoxy group, for example, a methoxy group or an ethoxy group. As the silane compound, a silane compound manufactured by Shin-Etsu Chemical Co., Ltd. can be used. A process can be carried out in which the silane compound reacts with hydroxyl groups on the surface of silica particles (e.g., silanol groups in the case of silica particles) to coat the surface of the silica particles with the silane compound through siloxane bonds. The reaction temperature can be from 20°C to the boiling point of the dispersion medium, for example, in the range of 20°C to 100°C. The reaction time can be about 0.1 to 6 hours.

[0035] The silane coupling agent is used to coat the silica particle surface with a silicon atom count of 0.1 / nm. 2 ~5.0 pieces / nm 2 The surface of the silica particles can be coated by adding a silane compound corresponding to the coating amount to the silica sol. Water is required for the hydrolysis of the silane compound, and if the sol is an aqueous solvent, that aqueous solvent can be used. When the aqueous medium is replaced with an organic solvent such as methanol or ethanol, the water remaining in the solvent can be used. For example, water present in an amount of 0.01 to 10.0 mass % or 0.1 to 7.0 mass % can be used. Furthermore, the hydrolysis can be carried out with or without a catalyst.

[0036] When the hydrolysis is performed without a catalyst, the silica particle surface is acidic. When a catalyst is used, examples of hydrolysis catalysts include metal chelate compounds, organic acids, inorganic acids, organic bases, and inorganic bases. Examples of metal chelate compounds used as hydrolysis catalysts include triethoxy mono(acetylacetonato)titanium and triethoxy mono(acetylacetonato)zirconium. Examples of organic acids used as hydrolysis catalysts include acetic acid and oxalic acid. Examples of inorganic acids used as hydrolysis catalysts include hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and phosphoric acid. Examples of organic bases used as hydrolysis catalysts include pyridine, pyrrole, piperazine, and quaternary ammonium salts. Examples of inorganic bases used as hydrolysis catalysts include ammonia, sodium hydroxide, and potassium hydroxide.

[0037] One embodiment of the present invention is an insulating resin composition containing the above silica sol and a nitrogen-containing polymer, wherein the nitrogen-containing polymer may be contained in an amount of 1 to 100 parts by mass per part by mass of silica contained in the silica sol.

[0038] In one embodiment of the present invention, the silica sol contains 80 to 1500 ppm of a carboxylic acid having 1 to 3 carbon atoms, which allows the viscosity of the silica sol measured with a Brookfield viscometer to be set in the range of 3 to 500 mPa s. If the carboxylic acid is not contained, the viscosity will be 500 mPa s or higher, for example, 790 to 3600 mPa s, which is undesirable because it tends to thicken the silica sol.

[0039] In one embodiment of the present invention, the silica sol may contain an organic acid having 1 to 3 carbon atoms at a ratio of 80 to 1500 ppm, or at a ratio of 0.008% by mass to 0.15% by mass. This corresponds to 0.00027 g to 0.005 g of SiO2 contained in a silica sol having a silica concentration of 30% by mass, for example, and the organic acid may be contained at a ratio of 270 ppm to 5000 ppm relative to the SiO2 contained in the silica sol. When an insulating resin composition is produced by mixing the silica sol dispersed in a nitrogen-containing organic solvent with a nitrogen-containing polymer, the insulating resin composition preferably also contains the organic acid at a ratio of 2.70 ppm to 5000 ppm relative to the SiO2.

[0040] The nitrogen-containing polymer may be polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, or polyesterimide. The stability of the insulating resin composition can be determined by adjusting the mass ratio of silica-blended polyamic acid, which is made of silica sol, 4,4'-diaminodiphenyl ether (DDE), and pyromellitic anhydride (PMDA) as the resin, to a resin / SiO2 mass ratio of 80 / 20, so that the viscosity (mPa·s) after storage at 50°C for 7 days is 1.20 times or less, or in the range of 0.80 to 1.20 times, or in the range of 1.00 to 1.20 times, or in the range of 1.05 to 1.20 times, compared to the viscosity before storage.

[0041] The insulating properties of the insulating resin composition are determined by heating the silica-blended polyamic acid, which is made of silica sol, 4,4'-diaminodiphenyl ether (DDE), and polyamic acid composed of pyromellitic anhydride (PMDA) as the resin, at a mass ratio of resin / SiO2 of 80 / 20, onto a Cu plate at 290°C to obtain a Cu plate (coating thickness: 29 to 32 μm) on which the silica-blended polyimide is baked.The insulating resin composition obtained has a dielectric breakdown life of 50 minutes or more, or 50 to 1000 minutes, or 60 to 500 minutes, or 60 to 200 minutes, at a test temperature of 155°C (in air), an applied voltage of 3.0 kV, and a frequency of 50 Hz. These insulating resin compositions can be used to form insulating coatings on enameled wires or the like to obtain insulating coated conductors.

[0042] The silica sol of the present invention can be produced by the following steps (A) and (B): Step (A): preparing a silica sol in which silica particles having an average primary particle diameter of 5 to 100 nm are dispersed in an aqueous medium; Step (B): The silica sol obtained in Step (A) is substituted with a nitrogen-containing organic solvent while adjusting the content of a carboxylic acid having 1 to 3 carbon atoms to 80 to 1500 ppm. In step (B), the carboxylic acid can be added during the solvent substitution process from the aqueous medium to the nitrogen-containing organic solvent. Alternatively, the carboxylic acid can be added before the solvent substitution with the nitrogen-containing organic solvent. However, since a portion of the carboxylic acid may be removed during the solvent substitution process, the carboxylic acid can be added after the solvent substitution so as to fall within a predetermined range.

[0043] During or after the step (B), a step (C) of adding at least one silane compound represented by any one of formulas (1) to (3) can be added. The addition of the silane compound allows the surface of the silica particles to be coated with the silane compound. The silica sol dispersed in the nitrogen-containing organic solvent of the present invention can be combined with a nitrogen-containing polymer to obtain an insulating resin composition (resin varnish).

[0044] The insulating resin composition (resin varnish) may be further subjected to steps (D) and (E) after steps (A) and (B) or steps (A) and (C): Step (D): Step (D) of mixing the silica sol dispersed in the nitrogen-containing organic solvent with the nitrogen-containing polymer; Step (E): The silica sol can be produced by adding a step (E) of removing a part or all of the nitrogen-containing organic solvent from the silica sol obtained in step (D).

[0045] The nitrogen-containing polymer can be mixed in a ratio of 1 to 100 parts by mass per part by mass of silica contained in the silica sol. The nitrogen-containing polymer may be polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, or polyesterimide.

[0046] The insulating resin composition can be applied to a conductor that requires insulation and then heated and cured at a temperature at which the solvent evaporates, forming an insulating coating on the surface of the conductor. The heating temperature for removing the solvent is determined by the temperature and pressure, but is about 150°C to 300°C at normal pressure, or about 150°C to 400°C for imidization of the resin.

[0047] The conductor is a metal wire, particularly a copper wire, which is coated with enamel to form an electric wire and is used in industrial and domestic motors, transformers, coils, etc. The insulating resin composition of the present invention can be used to produce an insulating coated conductor by coating an enamel coated copper wire or by directly coating a copper wire with the insulating resin composition instead of enamel.

[0048] The insulating resin composition is obtained by mixing 1 part by mass of silica contained in silica sol with 1 to 100, 1 to 50, or 1 to 10 parts by mass of nitrogen-containing polymer.

[0049] The insulating resin composition can be obtained by mixing and stirring the silica sol and the polymer with a mixer or disperser. Additives can be added to the mixture as desired. A conductor coated with the insulating resin composition of the present invention has insulating properties and flexibility.

[0050] Flexibility is measured in accordance with JIS C 3216-3, Section 5. For example, an insulating coated conductor having a 35 μm-thick insulating coating layer obtained from an insulating resin composition containing 1 part by mass of silica and 4 parts by mass of a nitrogen-containing polymer preferably has a flexibility of 1d to 2d. Note that this flexibility is measured by determining the minimum winding diameter d at which cracks do not occur in the insulating coating of an insulating coated conductor stretched 20% compared to an insulating coated conductor at no stretch, and is measured within the range from the original diameter (1d) to n times the original diameter (nd). [Example]

[0051] [Measurement of SiO2 concentration] The silica sol was placed in a crucible and dried at 150°C, and the resulting gel was then fired at 1000°C, and the firing residue was weighed and calculated.

[0052] [Measurement of average primary particle size (particle size by nitrogen adsorption method)] The acidic silica sol was dried at 300° C., and the specific surface area of ​​the powder was measured using a specific surface area measuring device, Monosorb (registered trademark) MS-16 (manufactured by Yuasa Ionics Co., Ltd.).

[0053] [Moisture measurement] It was determined by Karl Fischer titration.

[0054] [Measurement of Viscosity] The viscosity of the silica sol was measured using a B-type rotational viscometer (manufactured by Toki Sangyo Co., Ltd.).

[0055] [Measurement of cationic components in organosol] Pure water was added to the sol to adjust the silica concentration to 3% by mass. 200 μL of 1N nitric acid aqueous solution was added to 8 g of the diluted sol and left overnight. The resulting solution was centrifuged (5,000 rpm x 30 minutes) using a Merck Amicon Ultra-15 10k (molecular weight cutoff: 10,000). The resulting filtrate was diluted 10 times with pure water and analyzed by cation chromatography.

[0056] [Measurement of anionic components in organosol] The conditions for pre-treating the silica sol are described below. 50 μL of the organosilica sol sample was dissolved in 950 μL of electrophoresis buffer (containing 40 mM quinolinic acid, 90 mM 2-amino-2-hydroxymethyl-1,3-propanediol (Tris), and 0.7 mM hexadecyltrimethylammonium hydroxide (HDTMA), pH 7.4), and the solution was centrifuged using a centrifuge (Model 6200, Kubota Shoji Co., Ltd.) (centrifugation conditions: 10,000 rpm, 10 minutes, 15°C). 475 μL of the resulting supernatant was transferred to an electrophoresis vial. 25 μL of a solution (sodium nitrate concentration: 100 ppm) prepared by dissolving 1 mg of sodium nitrate in 10 mL of electrophoresis buffer was added to the sample collected in the electrophoresis vial, and this was used as the sample for capillary electrophoresis.

[0057] The pretreatment conditions for the capillary column are described below. Before each measurement, the electrophoresis buffer was passed through the capillary at a pressure of 915 mbar for 20 minutes to perform preconditioning. Then, before and after each sample measurement, the capillary was washed by passing ethanol (Junsei Chemical Co., Ltd., special-grade reagent) for 180 seconds, 0.1 M sodium hydroxide solution (Fujifilm Wako Pure Chemical Co., Ltd., volumetric analysis grade) for 360 seconds, ultrapure water (Milli-Q) for 300 seconds, and the electrophoresis buffer for 300 seconds, all at a pressure of 915 mbar.

[0058] The conditions for capillary electrophoresis measurements are described below. Apparatus: A capillary electrophoresis system (trade name: Agilent 7100, manufactured by Agilent Technologies, Inc.) was used. Capillary: Agilent Model G1600-64311 (inner diameter 75 μm, total length 112.5 cm, effective length 104 cm, fused silica capillary) Detector: PDA detector (Sig.=400nm±10nm, Ref.=265nm±5nm) Voltage: -25kV Electrophoresis temperature: 25℃ Electrophoresis buffer: 40 mM quinolinic acid, 90 mM 2-amino-2-hydroxymethyl-1,3-propanediol (Tris), and 0.7 mM hexadecyltrimethylammonium hydroxide (HDTMA), pH 7.4 Sample injection: Pressure 50 mbar, injection time 6 seconds (pressure injection method) For analysis, the peak area of ​​the organic acid ions was normalized by the peak area of ​​the nitrate ions (the peak area of ​​the organic acid ions was divided by the peak area of ​​sodium nitrate) and quantified.

[0059] [Solid content of polyamic acid] The polyamic acid was placed in an aluminum cup and baked at 200°C, and the baking residue was weighed and calculated.

[0060] Example 1 412 g of water-dispersed silica sol (trade name PL-3) (average primary particle size 35 nm, silica concentration 20 mass%, manufactured by Fuso Chemical Co., Ltd.) was placed in a 1-L recovery flask, and the solvent was evaporated and distilled off using a rotary evaporator at a reduced pressure of 150 to 70 Torr and a bath temperature of 80 to 90°C while DMAC (dimethylacetamide) was added. The dispersant of the sol was replaced with DMAC, yielding DMAC-dispersed silica sol (R1) (silica concentration 30.0 mass%, water content 6.7 mass%, viscosity 790 mPa·s). 172.3 g of the obtained sol was placed in a 500 mL recovery flask, and 0.058 g of acetic acid was added while stirring the sol with a magnetic stirrer. The mixture was then kept at room temperature for 2 hours to obtain DMAC-dispersed silica sol (1) (silica concentration 30.0 mass%, water content 6.7 mass%, viscosity 257 mPa s, acetic acid content in the sol 370 ppm, alkali metal ions in the sol below the detection limit (less than 10 ppm)).

[0061] Example 2 169 g of the DMAC-dispersed silica sol (1) obtained in Example 1 was placed in a 500 mL eggplant flask, and 0.1514 g of 4N aqueous sodium hydroxide solution was added while stirring the sol with a magnetic stirrer. Then, by adding DMAC while evaporating the solvent at a reduced pressure of 70 Torr and a bath temperature of 90 ° C. in a rotary evaporator, a DMAC-dispersed silica sol was obtained (silica concentration 30.0 mass%, water 3.4 mass%, viscosity 23 mPa s). Then, additional DMAC replacement was performed at a reduced pressure of 70 Torr and a bath temperature of 90 ° C. in a rotary evaporator to obtain DMAC-dispersed silica sol (2) (silica concentration 30.0 mass%, water 3.4 mass%, viscosity 23 mPa s, alkali metal ion in the sol Na ion content 82 ppm, acetic acid content in the sol 370 ppm).

[0062] Example 3 616 g of water-dispersed silica sol (product name: PL-2L, average primary particle size: 17 nm, silica concentration: 19% by mass, manufactured by Fuso Chemical Co., Ltd.) was placed in a 2 L recovery flask. The solvent was evaporated using a rotary evaporator at a reduced pressure of 150-70 Torr and a bath temperature of 80-90°C while DMAC (dimethylacetamide) was added. The sol's dispersion medium was replaced with DMAC, yielding 557 g of silica sol dispersed in a DMAC-water mixed solvent (silica concentration: 21.0% by mass, water content: 17.3% by mass). While stirring the sol with a magnetic stirrer, 3.1 g of phenyltrimethoxysilane (product name: KBM-103, manufactured by Shin-Etsu Chemical Co., Ltd.) was added, and the liquid temperature was maintained at 90°C for 2 hours. 282 g of the resulting sol was placed in a 1 L recovery flask, and 0.075 g of acetic acid was added, followed by 0.26 g of 4N aqueous sodium hydroxide solution. The mixture was stirred for 30 minutes. Thereafter, the solvent was evaporated and distilled off in a rotary evaporator at a reduced pressure of 100 to 70 Torr and a bath temperature of 110°C while DMAC was added to obtain DMAC-dispersed silica sol (3) (silica concentration 30.3 mass%, water content 0.9 mass%, viscosity 8 mPa·s, alkali metal ion content in the sol was 120 ppm Na ion, and acetic acid content in the sol was 400 ppm).

[0063] Example 4 351 g of water-dispersed silica sol (trade name: Snowtex O-33, average primary particle size: 12 nm, silica concentration: 33% by mass, manufactured by Nissan Chemical Co., Ltd.) was placed in a 1-L recovery flask. While stirring the sol with a magnetic stirrer, 0.25 g of 4N NaOH aqueous solution was added and the mixture was stirred for 30 minutes. Subsequently, the solvent was evaporated in a rotary evaporator at a reduced pressure of 150-110 Torr and a bath temperature of 90°C while DMAC was added. The sol's dispersion medium was replaced with DMAC, yielding 352 g of silica sol dispersed in a DMAC-water mixed solvent (silica concentration: 33.0% by mass, water content: 11.7% by mass). 4.3 g of phenyltrimethoxysilane (trade name: KBM-103, manufactured by Shin-Etsu Chemical Co., Ltd.) was added, and the liquid temperature was maintained at 90°C for 2 hours. Then, by adding DMAC while evaporating the solvent in a rotary evaporator at a reduced pressure of 100-70 Torr and a bath temperature of 110°C, a DMAC-dispersed silica sol (4) was obtained (silica concentration 30.2% by mass, water 0.3% by mass, viscosity 8 mPa·s, alkali metal ion content in the sol: Na ion content 200 ppm, acetic acid content in the sol 111 ppm, formic acid content 36 ppm). During this process, the amount of acetic acid generated by hydrolysis of DMAC was controlled within the range, and a DMAC-dispersed silica sol was obtained.

[0064] Example 5 140 g of methanol-dispersed silica sol (trade name: methanol silica sol, average primary particle size 12 nm, silica concentration 30% by mass, manufactured by Nissan Chemical Industries, Ltd.) was placed in a 0.5 L recovery flask, and 3.3 g of phenyltrimethoxysilane (trade name: KBM-103, manufactured by Shin-Etsu Chemical Co., Ltd.) was added, followed by maintaining the liquid temperature at 60° C. for 5 hours. 6.8 g of dimethylpolysiloxane (trade name: KF-96L 0.65cs, manufactured by Shin-Etsu Chemical Co., Ltd.) was then added, followed by adding 14 g of DMAC, and maintaining the liquid temperature at 60° C. for 3 hours. Then, using a rotary evaporator, the solvent was evaporated at a reduced pressure of 450-110 Torr and a bath temperature of 85-125°C while DMAC was added, replacing the sol's dispersion medium with DMAC to obtain DMAC-dispersed silica sol (5) (silica concentration 30.2% by mass, water 0.1% by mass, viscosity 7 mPa·s, alkali metal ion content in the sol: Na ion content 150 ppm, acetic acid content 65 ppm, formic acid content 87 ppm). During this process, the amount of carboxylic acid generated by hydrolysis of DMAC was controlled within the range to obtain a DMAC-dispersed silica sol.

[0065] Example 6 200 g of a water-dispersed silica sol, trade name Snowtex OXS (average primary particle size according to Sears: 5 nm, silica concentration: 10.5 mass%, pH: 2.8, manufactured by Nissan Chemical Industries, Ltd.), was placed in a 1-L recovery flask, and while the sol was stirred with a magnetic stirrer, 4.3 g of 3-glycidoxypropyltrimethoxysilane (trade name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.) was added, and the liquid temperature was then maintained at 80°C for 4 hours. Subsequently, the solvent was evaporated in a rotary evaporator at a pressure of 150-70 Torr and a bath temperature of 90°C while DMF (N,N-dimethylformamide) was added, and the sol's dispersion medium was replaced with DMF to obtain DMF-dispersed silica sol (6) (silica concentration 15.9 mass%, water 1.0 mass%, viscosity 4 mPa·s, alkali metal ion content in the sol: Na ion content 100 ppm, formic acid content in the sol: 1375 ppm). During this process, the amount of carboxylic acid generated by hydrolysis of DMF was controlled within the range to obtain a DMF-dispersed silica sol.

[0066] (Comparative Example 1) 412 g of PL-3 water-dispersed silica sol (mean primary particle size 35 nm, silica concentration 20% by mass, manufactured by Fuso Chemical Co., Ltd.) was placed in a 1-L recovery flask and evaporated on a rotary evaporator at a reduced pressure of 150–70 Torr and a bath temperature of 80–90°C. While evaporating the solvent, DMAC (dimethylacetamide) was added to the sol to replace the dispersant. This yielded DMAC-dispersed silica sol (R1) (silica concentration 30.0% by mass, water content 6.7% by mass, viscosity 790 mPa s). 172.3 g of the resulting sol was placed in a 500-mL recovery flask and stirred with a magnetic stirrer at room temperature for 2 hours to obtain DMAC-dispersed silica sol (R1) (silica concentration 30.0% by mass, water content 6.7% by mass, viscosity 790 mPa s, alkali metal ion content below the detection limit (<10 ppm) in the sol, and acetic acid content 30 ppm in the sol).

[0067] (Comparative Example 2) 15.5 g of the DMAC-dispersed silica sol (R1) obtained in Comparative Example 1 was placed in a 20 ml glass bottle, and 0.039 g of an 8% aqueous sulfuric acid solution was added to the sol and shaken, causing the sol to lose fluidity and gel.

[0068] (Comparative Example 3) 616 g of water-dispersed silica sol (trade name PL-2L, average primary particle size 17 nm, silica concentration 19 mass%, manufactured by Fuso Chemical Co., Ltd.) was placed in a 2 L recovery flask, and the solvent was evaporated and distilled off using a rotary evaporator at a reduced pressure of 150 to 70 Torr and a bath temperature of 80 to 90°C while DMAC (dimethylacetamide) was added. The dispersant of the sol was replaced with DMAC, yielding 557 g of silica sol dispersed in a DMAC-water mixed solvent (silica concentration 21.0 mass%, water content 17.3 mass%). While stirring the sol with a magnetic stirrer, 3.1 g of phenyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name KBM-103) was added, and the liquid temperature was maintained at 90°C for 2 hours to obtain a high-viscosity DMAC-dispersed silica sol (R3) (silica concentration 27.6 mass%, water 5.2 mass%, viscosity 3600 mPa·s, alkali metal ions in the sol below the detection limit (less than 10 ppm), acetic acid content in the sol 31 ppm).

[0069] Comparative Example 4 130 g of the DMAC-dispersed silica sol (4) obtained in Example 4 was placed in a 500 mL recovery flask, and 0.26 g of acetic acid was added while stirring with a magnetic stirrer. The mixture was then kept at room temperature for 2 hours to obtain DMAC-dispersed silica sol (R4) (silica concentration 30.2 mass%, water 0.3 mass%, viscosity 16 mPa s, alkali metal ion content in the sol: Na ion content 200 ppm, acetic acid content in the sol 1926 ppm, formic acid content 39 ppm).

[0070] (Synthesis Example 1) Preparation of polyamic acid 4,4'-Diaminodiphenyl ether (DDE) and pyromellitic dianhydride (PMDA) were polymerized at 50°C with stirring using NMP (N-methylpyrrolidone) and DMAC (dimethylacetamide) as solvents to obtain polyamic acid (solid content 17% by mass, viscosity at 25°C measured with an E-type viscometer: 13,640 mPa·s) corresponding to formula (4). The polyamic acid was polymerized using an equimolar ratio of 1:1 DDE and PMDA. The weight-average molecular weight of the resulting polyamic acid was 63,000. n in formula (4) is the number of repeating units.

[0071] [ka]

[0072] (Thermal Stability Test of Insulating Resin Composition) The DMAC-dispersed silica sols obtained in Example 4 and Comparative Example 4 were added to and mixed with the polyamic acid obtained in Synthesis Example 1 in a glass bottle at a mass ratio of resin / SiO2 = 80 / 20, and the mixture was degassed and stirred for 20 minutes using a vacuum degasser (EME, trade name V-mini300) to obtain a silica-blended polyamic acid. The initial viscosity (mPa·s) at 25°C and the viscosity (mPa·s) measured after storing at 50°C for 7 days and then cooling to 25°C are shown in the table below.

[0073] [Table 1]

[0074] The silica-blended polyamic acid obtained in Example 4 and Comparative Example 4 was applied to a Cu plate (manufactured by AS ONE Corporation, product name HC0536, 300 mm × 300 mm, 0.5 mm thick) using an applicator (manufactured by BEVS, product name: Film applicator with film thickness adjustment function B / M150 mm). The solvent was then removed and the plate was thermally cured at 70°C for 30 minutes, 100°C for 30 minutes, 150°C for 30 minutes, and 290°C for 60 minutes to obtain a Cu plate (coating thickness: 29-32 μm) with a baked silica-blended polyimide. This was then cut into 5 cm squares to serve as insulation test samples.

[0075] (Measurement of dielectric breakdown life) Plate samples measuring 50 mm x 50 mm and 0.5 mm thick were used in a Yamayo Tester Co., Ltd. dielectric breakdown tester, model YST-243WS, to measure the dielectric breakdown life of the above-mentioned insulation test specimens at a test temperature of 155°C (in air), an applied voltage of 3.0 kV, and a frequency of 50 Hz. The electrodes used were a flat electrode (φ = 25 mm) at the bottom and a spherical electrode (φ = 20 mm) at the top, with both electrodes positioned so that they were in contact with the sample. Three to four measurements were performed at an applied voltage of 3.0 kV, and the average value was recorded. A sample of polyimide resin containing no silica was used as a blank, and similar measurements were taken.

[0076] [Table 2]

[0077] Silica sol dispersed in a nitrogen-containing organic solvent containing a predetermined amount of organic acid (acetic acid, etc.) does not have a higher viscosity than DMAC-dispersed silica sol that does not contain organic acid (acetic acid, etc.) when compared at the same solid content, and therefore has good workability even when blended with a nitrogen-containing polymer to form an insulating resin composition.

[0078] An insulating resin composition prepared by blending a silica sol dispersed in a nitrogen-containing organic solvent containing an organic acid (such as acetic acid) in excess of a specified amount with a nitrogen-containing polymer showed an increase in viscosity in a thermal stability test after storage at 50°C for 7 days, compared to an insulating resin composition prepared by blending a DMAC-dispersed silica sol containing a specified amount of organic acid (such as acetic acid) with a nitrogen-containing polymer.

[0079] It was also found that silica sol dispersed in a nitrogen-containing organic solvent containing a predetermined amount of organic acid (such as acetic acid) has a longer insulation life than polyimide resin that does not contain silica.

[0080] In the present invention, the silica sol dispersed in a nitrogen-containing organic solvent containing a predetermined amount of organic acid (such as acetic acid) has low viscosity, so when the silica sol is mixed with a nitrogen-containing polymer to form an insulating resin composition and applied to a substrate, a coating film that can coat the substrate while maintaining the solid content required to maintain insulating properties can be obtained, and the resulting insulating substrate has a long insulating life. [Industrial Applicability]

[0081] Silica sol dispersed in a nitrogen-containing organic solvent containing a predetermined amount of organic acid (such as acetic acid) has low viscosity, so when it is mixed with a nitrogen-containing polymer to form an insulating resin composition and coated onto a substrate, an insulating coating can be obtained that retains the solid content necessary to maintain the insulating properties and can be applied to the substrate.

Claims

1. A silica sol in which silica particles having an average primary particle diameter of 5 to 100 nm are dispersed in a nitrogen-containing organic solvent, and the silica sol contains a carboxylic acid in a proportion of 80 to 1500 ppm; the nitrogen-containing organic solvent is dimethylacetamide or dimethylformamide; The carboxylic acid is formic acid and / or acetic acid. Silica sol.

2. The silica sol according to claim 1, wherein the water content in the silica sol is 0.1 to 10.0 mass%.

3. SiO ２ 3. The silica sol according to claim 1, wherein the viscosity measured at 25° C. is 3 to 500 mPa·s when the concentration is 30% by mass.

4. 3. The silica sol according to claim 1, which contains alkali metal ions (wherein the alkali metal ions are alkali metal ions consisting of lithium, sodium, and potassium) in a proportion of 300 ppm or less.

5. The silica particles are represented by formulas (1) to (3): 【Chemistry 1】 (In formula (1), R １ are each an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a carboxyl group, an acid anhydride group, a carboxylic acid ester group, an epoxy group, a hydroxyl group, or a cyano group, and are bonded to a silicon atom by a Si—C bond, and R ２ each represents an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group, a represents an integer of 1 to 3, In formula (2) and formula (3), R ３ and R ５ are each an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms and bonded to a silicon atom by a Si—C bond, and R ４ and R ６ each represents an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group; Y represents an alkylene group, an NH group, or an oxygen atom; b is an integer of 1 to 3; c is an integer of 0 or 1; and d is an integer of 1 to 3.

2. The silica sol according to claim 1, which is coated with at least one silane compound selected from the group consisting of:

6. An insulating resin composition comprising the silica sol according to claim 1 and a nitrogen-containing polymer.

7. 7. The insulating resin composition according to claim 6, wherein the nitrogen-containing polymer is present in an amount of 1 to 100 parts by mass per part by mass of silica contained in the silica sol.

8. 7. The insulating resin composition according to claim 6, wherein the nitrogen-containing polymer is a polyimide, a polyamide, a polyamic acid, a polyamideimide, a polyetherimide, or a polyesterimide.

9. The silica sol according to claim 1, 4,4'-diaminodiphenyl ether (DDE), and polyamic acid composed of pyromellitic anhydride (PMDA) are used as a resin, and a resin / SiO ２ An insulating resin composition in which a silica-blended polyamic acid adjusted to a mass ratio of 80 / 20 is stored at 50°C for 7 days and the viscosity (mPa·s) thereof is 1.20 times or less of the viscosity before storage.

10. The silica sol according to claim 1, 4,4'-diaminodiphenyl ether (DDE), and polyamic acid composed of pyromellitic anhydride (PMDA) are used as a resin, and a resin / SiO ２ A silica-blended polyamic acid adjusted to a mass ratio of 80 / 20 is heated at 290°C on a Cu plate to bake a silica-blended polyimide onto the Cu plate (coating thickness: 29 to 32 μm), and the insulating resin composition has a dielectric breakdown life of 50 minutes or more when tested at a temperature of 155°C (in air), an applied voltage of 3.0 kV, and a frequency of 50 Hz.

11. An insulating coated conductor coated with the insulating resin composition according to any one of claims 6 to 10.

12. The following steps (A) and (B): Step (A): preparing a silica sol in which silica particles having an average primary particle diameter of 5 to 100 nm are dispersed in an aqueous medium; 2. The method for producing a silica sol according to claim 1, comprising: step (B): substituting the silica sol obtained in step (A) with a nitrogen-containing organic solvent, such as dimethylacetamide or dimethylformamide, while adjusting the silica sol to contain carboxylic acids, such as formic acid and / or acetic acid, in a proportion of 80 to 1500 ppm.

13. The method for producing a silica sol according to claim 12, further comprising the step (C) of adding at least one silane compound represented by any one of formulas (1) to (3) according to claim 5 during or after the step (B).

14. A method for producing the insulating resin composition according to any one of claims 6 to 10, comprising a step (D) of mixing the silica sol according to claim 1 with a nitrogen-containing polymer.

15. 15. The method for producing an insulating resin composition according to claim 14, further comprising the step (E) of removing a part or all of the nitrogen-containing organic solvent, dimethylacetamide or dimethylformamide, from the insulating resin composition, in addition to the step (D).

Images