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

Abstract

Provided are: a silica sol which contains an organic acid and is dispersed in a nitrogen-containing organic solvent; and an insulating resin composition which contains the silica sol and a nitrogen-containing polymer. A silica sol in which silica particles having an average primary particle diameter of 5-100 nm are dispersed in a nitrogen-containing organic solvent, the silica sol containing a carboxylic acid having 1-3 carbon atoms at a ratio of 80-1500 ppm. The nitrogen-containing organic solvent is a silica sol of an amide-based solvent. The nitrogen-containing organic solvent is silicon dioxide sol of dimethyl acetamide, dimethyl formamide or dimethyl propionamide. And a silica sol in which the carboxylic acid having 1-3 carbon atoms is formic acid, acetic acid, or propionic acid. An insulating resin composition includes a 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 them. Background Art

[0002] Silica sols in which surface-modified silica particles are dispersed in a solvent are known. For example, a method is disclosed in which hydroxyl groups on the surface of inorganic oxide particles such as silica react with an alcohol to introduce an alkoxy group and be organicized, thereby 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 a silica sol dispersed in a toluene solvent is disclosed.

[0003] In addition, a silica sol obtained by solvent-exchanging a methanol-dispersed silica sol with acetonitrile to obtain an acetonitrile-methanol mixed solvent-dispersed silica sol and then reacting phenyltrimethoxysilane is disclosed (see Patent Document 2).

[0004] In addition, a silica sol in which the surface of silica particles is modified with an aluminum compound is disclosed (see Patent Document 3).

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

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2005-200294

[0009] Patent Document 2: International Publication No. 2009 / 008509

[0010] Patent Document 3: Japanese Patent Application Laid-Open No. 2011-026183

[0011] Patent Document 4: International Publication No. 2022 / 097694 Summary of the Invention

[0012] Problems to be Solved by the Invention

[0013] An object of the present invention is to provide a silica sol obtained by dispersing silica particles in a nitrogen-containing organic solvent that is used for mixing well with a polar resin such as polyimide or polyamide. Another object is to provide a resin composition in which these silica sols are compounded with a resin, and an insulated coated wire that can maintain a high insulation life for a long time when made into an insulating resin composition.

[0014] Means for solving the problem

[0015] In a first aspect, the present invention is 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, and a carboxylic acid having 1 to 3 carbon atoms is contained in the silica sol in a proportion of 80 to 1500 ppm;

[0016] In a second aspect, it is the silica sol according to the first aspect, wherein the nitrogen-containing organic solvent is an amide-based solvent;

[0017] In a third aspect, it is the silica sol according to the first aspect or the second aspect, wherein the nitrogen-containing organic solvent is dimethylacetamide, dimethylformamide, or dimethylpropionamide;

[0018] In a fourth aspect, it is the silica sol according to any one of the first to third aspects, wherein the carboxylic acid having 1 to 3 carbon atoms is formic acid, acetic acid, or propionic acid;

[0019] In a fifth aspect, it is the silica sol according to any one of the first to fourth aspects, wherein the water content in the silica sol is 0.1 to 10.0% by mass;

[0020] In a sixth aspect, it is the silica sol according to any one of the first to fifth aspects, wherein when the SiO2 concentration is 30% by mass, the viscosity measured at 25 °C is 3 to 500 mPa·s;

[0021] In a seventh aspect, it is the silica sol according to any one of the first to sixth aspects, which contains alkali metal ions in a proportion of 300 ppm or less, wherein the alkali metal ions represent alkali metal ions including lithium, sodium, and potassium;

[0022] In an eighth aspect, it is the silica sol according to any one of the first to seventh aspects, wherein the silica particles are coated with at least one silane compound or its hydrolyzate selected from the formulas (1) to (3):

[0023]

Chemical 1

[0024] R 1 a Si(R 2 ) 4-a Formula (1)

[0025] 〔R 3 b Si(R 4 ) 3-b 〕2Yc Formula (2)

[0026] R 5 d Si(R 6 ) 4-d Formula (3)

[0027] In formula (1), each R 1 is independently an alkyl group, a haloalkyl group, an alkenyl group, an aryl group, or an organic group having (meth)acryloyl, mercapto, amino, ureido, carboxyl, acid anhydride, carboxylic ester, epoxy, hydroxyl, or cyano group, and is bonded to the silicon atom through an Si-C bond. Each R 2 independently represents an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group, and a represents an integer from 1 to 3.

[0028] In formula (2) and formula (3), each R 3 and each R 5 are independently an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms and are bonded to the silicon atom through an Si-C bond. Each R 4 and each R 6 independently 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 from 1 to 3, c is an integer of 0 or 1, and d is an integer from 1 to 3;

[0029] As the 9th aspect, an insulating resin composition comprising the silica sol and the nitrogen-containing polymer according to any one of the 1st to 8th aspects;

[0030] As the 10th aspect, the insulating resin composition according to the 9th aspect, wherein the mass part of the nitrogen-containing polymer is 1 to 100 relative to 1 mass part of the silica contained in the silica sol;

[0031] As the 11th aspect, the insulating resin composition according to the 9th or 10th aspect, wherein the nitrogen-containing polymer is polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, or polyesterimide;

[0032] As the 12th aspect, an insulating resin composition, wherein the viscosity (mPa·s) of the silica-containing polyamic acid prepared by mixing the silica sol according to any one of the 1st to 8th aspects and the polyamic acid formed from 4,4'-diaminodiphenyl ether (DDE) and pyromellitic dianhydride (PMDA) as a resin at a mass ratio of resin / SiO2 = 80 / 20 after storage at 50°C for 7 days is 1.20 times or less of the viscosity before storage;

[0033] As a 13th aspect, it is an insulating resin composition, wherein a silica-containing polyamic acid prepared by mixing the silica sol according to any one of the 1st to 8th aspects and a polyamic acid formed from 4,4'-diaminodiphenyl ether (DDE) and pyromellitic dianhydride (PMDA) as a resin in a mass ratio of resin / SiO2 = 80 / 20 is heated on a Cu plate at 290°C to obtain a Cu plate sintered with silica-containing polyimide (film thickness: 29 - 32 μm), and the dielectric breakdown life at a test temperature of 155°C (in air), an applied voltage of 3.0 kV, and a frequency of 50 Hz is 50 minutes or more;

[0034] As a 14th aspect, it is an insulated coated wire insulated and coated with the insulating resin composition according to any one of the 9th to 13th aspects;

[0035] As a 15th aspect, it is a method for manufacturing the silica sol according to any one of the 1st to 8th aspects, which includes the following steps (A) to (B):

[0036] (A) step: Prepare a silica sol in which silica particles having an average primary particle size of 5 - 100 nm are dispersed in an aqueous medium; and

[0037] (B) step: Adjust the silica sol obtained in step (A) to contain a carboxylic acid having 1 - 3 carbon atoms in a proportion of 80 - 1500 ppm and replace it with a nitrogen-containing organic solvent;

[0038] As a 16th aspect, it is a method for manufacturing the silica sol according to the 15th aspect, wherein a step (C) of additionally adding at least one silane compound of the formulas (1) to (3) according to claim 7 is added during or after step (B);

[0039] As a 17th aspect, it is a method for manufacturing the insulating resin composition according to any one of the 9th to 14th aspects, which includes a step (D) of mixing the silica sol obtained by the 15th or 16th aspect and a nitrogen-containing polymer;

[0040] As an 18th aspect, it is a method for manufacturing the insulating resin composition according to the 17th aspect, wherein a step (E) of further removing a part or all of the nitrogen-containing organic solvent from the insulating resin composition is added to step (D).

[0041] Effects of the Invention

[0042] Regarding an insulating resin formed by coating and curing an insulating resin composition, in order to improve the insulation resistance of a substrate, silica particles can be contained in the insulating resin composition. The silica particles can protect the substrate from insulation breakdown caused by discharge by tightly forming a firm coating layer with the insulating resin. Most of the insulating resins use nitrogen-containing polymers with high insulation properties. These nitrogen-containing polymers are, for example, polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, or polyesterimide, etc., which are synthesized from diamine and acid anhydride and have two-part structures including polar parts such as an imide skeleton, carboxyl group, amide bond, etc., and hydrophobic parts contained in the diamine molecule and the acid anhydride molecule.

[0043] A silica sol dispersed in a nitrogen-containing organic solvent with high compatibility with a nitrogen-containing polymer is mixed with the nitrogen-containing polymer to produce an insulating resin composition. When the insulating resin composition is used as an enameled wire coating material, in order to coat the enameled wire with a uniform film thickness, it is important to perform appropriate viscosity management on-site.

[0044] According to the present invention, at the stage of the silica sol dispersed in a nitrogen-containing organic solvent, by containing a specific amount of organic acid in the nitrogen-containing organic solvent, an increase in the viscosity of the silica sol can be suppressed. In addition, according to the present invention, when mixing the silica sol dispersed in a nitrogen-containing organic solvent with a nitrogen-containing polymer to form an insulating resin composition (varnish), by containing a specific amount of organic acid, an increase in the viscosity of the insulating resin composition can be reduced.

[0045] The present invention relates to a silica sol dispersed in a nitrogen-containing organic solvent and a method for manufacturing an insulating resin composition by adding these sols to a nitrogen-containing polymer, including cases where the organic acid is initially included in the nitrogen-containing organic solvent and the nitrogen-containing polymer, and cases where the organic acid is newly added. By measuring them to make the content within the set range of the present invention, stabilization of the viscosities of the silica sol and the insulating resin composition can be achieved. Detailed Embodiments

[0046] The preferred embodiments of the present invention are described below. However, the following embodiments are illustrative of the present invention, and the present invention is not limited by any of the following embodiments.

[0047] One embodiment of the present invention is 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, and a carboxylic acid having 1 to 3 carbon atoms is contained in the silica sol in a proportion of 80 to 1500 ppm.

[0048] In one embodiment of the present invention, the silica particles contained in the silica sol have an average primary particle size of 5 to 100 nm. As the average primary particle size of the silica particles, the particle size (nm) measured by the nitrogen adsorption method (BET method) can be used.

[0049] The nitrogen-containing organic solvent used in the present invention has at least a functional group containing a nitrogen atom. As the functional group having a nitrogen atom, an amino group, a nitro group, a cyano group, etc. can be cited. Among them, an amide-based solvent in which a nitrogen-containing functional group and a carbonyl group are present in one molecule of the solvent molecule is preferably used. As such a solvent, solvents having a chain structure and a cyclic structure can be cited. As the functional group containing a nitrogen atom, an amino group, a nitro group, a cyano group can be cited, and an amino group is preferably used. The amino group and the carbonyl group may be adjacent or may exist via a carbon atom, and can be used as an amide bond, for example, and an amide-based solvent is preferably used.

[0050] Specific examples of the nitrogen-containing organic solvent include, for example, dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, dimethylpropionamide, N-methylpyrrolidone, N-ethylpyrrolidone, tetramethylurea, hexamethylphosphoric triamide, dimethylacrylamide, acryloylmorpholine, hydroxyethylacrylamide, isopropylacrylamide, diethylacrylamide, dimethylaminopropylacrylamide, 3-methoxy-N,N-dimethylpropionamide, 3-butoxy-N,N-dimethylpropionamide, dimethylaminopropylacrylamide methyl chloride quaternary salt, dimethylaminoethyl acrylate benzyl chloride quaternary salt, etc.

[0051] Among them, as the nitrogen-containing organic solvent, dimethylacetamide, dimethylformamide, or dimethylpropionamide can be preferably used. It should be noted that other solvents can be contained in the nitrogen-containing organic solvent as long as the effects of the present invention are not impaired.

[0052] That is, in all the solvents, the nitrogen-containing organic solvent can be contained in a proportion of 50 to 100% by volume, 90 to 100% by volume, 98 to 100% by volume, or 99 to 100% by volume, and other solvents can also be contained in a proportion of 0 to less than 50% by volume, 0 to less than 10% by volume, 0 to less than 2% by volume, or 0 to less than 1% by volume.

[0053] As other solvents, 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, amine-based solvents can be cited.

[0054] Specific examples of such solvents include, for example, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, etc., ester solvents such as methyl acetate, ethyl acetate, butyl acetate, etc., alcohol solvents such as methanol, ethanol, isopropyl alcohol, benzyl alcohol, etc., glycol ether solvents such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monopropyl ether, diethylene glycol monobutyl ether, etc., hydrocarbon solvents such as benzene, toluene, xylene, n-hexane, cyclohexane, etc., halogen solvents such as dichloromethane, trichloroethylene, perchloroethylene, etc., ether solvents such as dioxane, diethyl ether, tetrahydrofuran, etc., glycol solvents such as ethylene glycol, diethylene glycol, propylene glycol, polyethylene glycol, etc., amine solvents such as monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, N-methylethanolamine, 2-amino-2-methyl-1-propanol, etc.

[0055] In one embodiment of the present invention, as the organic acid, a carboxylic acid having 1 to 3 carbon atoms is preferably used, and formic acid, acetic acid, or propionic acid is more preferably used. These organic acids are preferred because of their high compatibility with nitrogen-containing organic solvents and nitrogen-containing polymers.

[0056] In one embodiment of the present invention, the water content in the silica sol is preferably 0.1 to 10.0% by mass.

[0057] In addition, with respect to the viscosity of the above silica sol, when the SiO2 concentration is 30% by mass, the viscosity measured at 25°C is preferably 3 to 500 mPa·s.

[0058] The alkali metal ions (wherein the alkali metal ions represent alkali metal ions including lithium, sodium, and potassium) can be contained in a proportion of 300 ppm or less, or 30 to 300 ppm, or 30 to 200 ppm. For example, with respect to the alkali metal ions, by making the sodium ions within the above range, an increase in the viscosity of the silica sol dispersed in the nitrogen-containing organic solvent can be suppressed.

[0059] In one embodiment of the present invention, the silica sol can contain alkali metal ions (wherein the alkali metal refers to alkali metal ions including lithium, sodium, and potassium) in a proportion of 300 ppm or less, or 30 - 300 ppm, or 30 - 200 ppm, and can contain them in a proportion of 0.03 mass% or less, or 0.003 mass% - 0.03 mass%, or 0.003 mass% - 0.02 mass%. For example, relative to the mass of SiO2 contained in the silica sol with a silica concentration of 30 mass%, the alkali metal converted to M2O can be contained in an amount of 1000 ppm or less, or 100 ppm - 1000 ppm or less, or 100 ppm - 6.70 ppm or less. Further, when the silica sol dispersed in a nitrogen-containing organic solvent and a nitrogen-containing polymer are mixed to produce an insulating resin composition, in the insulating resin composition, relative to SiO2, it is preferably to contain the alkali metal converted to M2O in an amount of 1000 ppm or less, or 100 ppm - 1000 ppm or less, or 100 ppm - 670 ppm or less.

[0060] The silica particles in the silica sol of the present invention can be coated by adding at least one silane compound selected from Formula (1) to Formula (3).

[0061] In Formula (1), R 1 are each an alkyl group, a haloalkyl group, an alkenyl group, an aryl group, or an organic group having (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a carboxyl group, an acid anhydride group, a carboxylate group, an epoxy group, a hydroxyl group, or a cyano group, and are bonded to the silicon atom through an Si - C bond, and R 2 are each an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group, a represents an integer of 1 - 3.

[0062] In Formula (2) and Formula (3), R 3 and R 5 are each an alkyl group having 1 - 3 carbon atoms or an aryl group having 6 - 30 carbon atoms and are bonded to the silicon atom through an Si - C bond, R 4 and R 6 are each 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 - 3, c is an integer of 0 or 1, and d is an integer of 1 - 3.

[0063] The above-mentioned alkyl group is an alkyl group having 1 to 18 carbon atoms, and examples thereof include methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, 1-methylcyclopropyl, 2-methylcyclopropyl, n-pentyl, 1-methyl-n-butyl, 2-methyl-n-butyl, 3-methyl-n-butyl, 1,1-dimethyl-n-propyl, 1,2-dimethyl-n-propyl, 2,2-dimethyl-n-propyl, 1-ethyl-n-propyl, cyclopentyl, 1-methylcyclobutyl, 2-methylcyclobutyl, 3-methylcyclobutyl, 1,2-dimethylcyclopropyl, 2,3-dimethylcyclopropyl, 1-ethylcyclopropyl, 2-ethylcyclopropyl, n-hexyl, 1-methyl-n-pentyl, 2-methyl-n-pentyl, 3-methyl-n-pentyl, 4-methyl-n-pentyl, 1,1-dimethyl-n-butyl, 1,2-dimethyl-n-butyl, 1,3-dimethyl-n-butyl, 2,2-dimethyl-n-butyl, 2,3-dimethyl-n-butyl, 3,3-dimethyl-n-butyl, 1-ethyl-n-butyl, 2-ethyl-n-butyl, 1,1,2-trimethyl-n-propyl, 1,2,2-trimethyl-n-propyl, 1-ethyl-1-methyl-n-propyl, 1-ethyl-2-methyl-n-propyl, cyclohexyl, 1-methylcyclopentyl, 2-methylcyclopentyl, 3-methylcyclopentyl, 1-ethylcyclobutyl, 2-ethylcyclobutyl, 3-ethylcyclobutyl, 1,2-dimethylcyclobutyl, 1,3-dimethylcyclobutyl, 2,2-dimethylcyclobutyl, 2,3-dimethylcyclobutyl, 2,4-dimethylcyclobutyl, 3,3-dimethylcyclobutyl, 1-n-propylcyclopropyl, 2-n-propylcyclopropyl, 1-isopropylcyclopropyl, 2-isopropylcyclopropyl, 1,2,2-trimethylcyclopropyl, 1,2,3-trimethylcyclopropyl, 2,2,3-trimethylcyclopropyl, 1-ethyl-2-methylcyclopropyl, 2-ethyl-1-methylcyclopropyl, 2-ethyl-2-methylcyclopropyl, and 2-ethyl-3-methylcyclopropyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, etc., but are not limited thereto.

[0064] In addition, as the alkylene group, an alkylene group derived from the above-mentioned alkyl group can be cited.

[0065] The above-mentioned aryl group is an aryl group having 6 to 30 carbon atoms, and examples thereof include phenyl, naphthyl, anthryl, pyrenyl, etc.

[0066] As the alkenyl group, alkenyl groups having 2 to 10 carbon atoms can be cited. For example, vinyl, 1-propenyl, 2-propenyl, 1-methyl-1-ethenyl, 1-butenyl, 2-butenyl, 3-butenyl, 2-methyl-1-propenyl, 2-methyl-2-propenyl, 1-ethylvinyl, 1-methyl-1-propenyl, 1-methyl-2-propenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 1-n-propylethylene, 1-methyl-1-butenyl, 1-methyl-2-butenyl, 1-methyl-3-butenyl, 2-ethyl-2-propenyl, 2-methyl-1-butenyl, 2-methyl-2-butenyl, 2-methyl-3-butenyl, 3-methyl-1-butenyl, 3-methyl-2-butenyl, 3-methyl-3-butenyl, 1,1-dimethyl-2-propenyl, 1-isopropylethylene, 1,2-dimethyl-1-propenyl, 1,2-dimethyl-2-propenyl, 1-cyclopentenyl, 2-cyclopentenyl, 3-cyclopentenyl, 1-hexenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl, 5-hexenyl, 1-methyl-1-pentenyl, 1-methyl-2-pentenyl, 1-methyl-3-pentenyl, 1-methyl-4-pentenyl, 1-n-butylethylene, 2-methyl-1-pentenyl, 2-methyl-2-pentenyl, etc. can be cited, but are not limited thereto.

[0067] As the above alkoxy group, alkoxy groups having 1 to 10 carbon atoms can be cited. For example, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-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, n-hexyloxy, etc. can be cited, but are not limited thereto.

[0068] As the above acyloxy group, acyloxy groups having 2 to 10 carbon atoms can be cited. For example, methylcarbonyloxy, ethylcarbonyloxy, n-propylcarbonyloxy, isopropylcarbonyloxy, n-butylcarbonyloxy, isobutylcarbonyloxy, sec-butylcarbonyloxy, tert-butylcarbonyloxy, n-pentylcarbonyloxy, 1-methyl-n-butylcarbonyloxy, 2-methyl-n-butylcarbonyloxy, 3-methyl-n-butylcarbonyloxy, 1,1-dimethyl-n-propylcarbonyloxy, 1,2-dimethyl-n-propylcarbonyloxy, 2,2-dimethyl-n-propylcarbonyloxy, 1-ethyl-n-propylcarbonyloxy, n-hexylcarbonyloxy, 1-methyl-n-pentylcarbonyloxy, 2-methyl-n-pentylcarbonyloxy, etc. can be cited, but are not limited thereto.

[0069] As the above halogen group, fluorine, chlorine, bromine, iodine, etc. can be cited.

[0070] The above-mentioned (meth)acryloyl group refers to both acryloyl group and methacryloyl group. Examples of the organic group having a (meth)acryloyl group include 3-methacryloyloxypropyl, 3-acryloyloxypropyl, etc.

[0071] Examples of the organic group having a mercapto group include 3-mercaptopropyl.

[0072] Examples of the organic group having an amino group include 2-aminoethyl, 3-aminopropyl, N-2-(aminoethyl)-3-aminopropyl, N-(1,3-dimethylbutylene)aminopropyl, N-phenyl-3-aminopropyl, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyl, etc.

[0073] Examples of the organic group having a ureido group include 3-ureidopropyl.

[0074] Examples of the organic group having an epoxy group include glycidyl group, 3,4-epoxycyclohexyl. The form in which these epoxy groups are ring-opened to generate hydroxyl groups may be included.

[0075] Examples of the organic group having a cyano group include 3-cyanopropyl.

[0076] As the compounds of the above formula (2) and formula (3), compounds capable of forming trimethylsilyl groups on the surface of silica particles are preferred.

[0077] These compounds can be exemplified as follows.

[0078]

Chemical formula 2

[0079]

[0080] In the above formula, R 12 is an alkoxy group, and examples include methoxy group and ethoxy group. The above-mentioned silane compound can be a silane compound manufactured by Shin-Etsu Chemical Co., Ltd. On the surface of silica particles, hydroxyl groups, for example, silanol groups if they are silica particles, can react with the above-mentioned silane compound, and a process of coating the silica particles with the above-mentioned silane compound using a siloxane bond is carried out. Regarding the reaction temperature, it can be carried out at a temperature in the range from 20°C to the boiling point of its dispersion medium, for example, in the range of 20°C to 100°C. Regarding the reaction time, it can be carried out for about 0.1 to 6 hours.

[0081] Regarding the silane coupling agent, as the coating amount on the surface of silica particles, the number of silicon atoms in the silane compound can be 0.1 atoms / nm 2 to 5.0 atoms / nm 2A silane compound having an equivalent coating amount is added to the silica sol to coat the surface of the silica particles.

[0082] Water is required for the hydrolysis of the above silane compound, but if it is a sol of an aqueous solvent, these aqueous solvents are used. It is possible to use the moisture remaining in the solvent when the aqueous medium solvent is replaced with an organic solvent containing methanol and ethanol. For example, it is possible to use moisture present in an amount of 0.01 to 10.0% by mass, or 0.1 to 7.0% by mass. In addition, the hydrolysis can be carried out using a catalyst or without a catalyst.

[0083] In the case of carrying out without a catalyst, it is the case where acidic sites are present on the surface of the silica particles. In the case of using a catalyst, examples of the hydrolysis catalyst include metal chelates, organic acids, inorganic acids, organic bases, and inorganic bases. Examples of the metal chelate as the hydrolysis catalyst include triethoxy - mono(acetylacetone)titanium, triethoxy - mono(acetylacetone)zirconium, etc. Examples of the organic acid as the hydrolysis catalyst include acetic acid, oxalic acid, etc. Examples of the inorganic acid as the hydrolysis catalyst include hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, phosphoric acid, etc. Examples of the organic base as the hydrolysis catalyst include pyridine, pyrrole, piperazine, quaternary ammonium salts. Examples of the inorganic base as the hydrolysis catalyst include ammonia, sodium hydroxide, potassium hydroxide.

[0084] One embodiment of the present invention is an insulating resin composition containing the above silica sol and a nitrogen - containing polymer. The mass part of the nitrogen - containing polymer can be 1 to 100 with respect to 1 mass part of the silica contained in the silica sol.

[0085] In one embodiment of the present invention, a carboxylic acid having 1 to 3 carbon atoms is contained in the silica sol in a proportion of 80 to 1500 ppm. Thus, the viscosity of the silica sol measured using a B - type viscometer can be set in the range of 3 to 500 mPa·s. In the case of not containing the above carboxylic acid, the viscosity shows 500 mPa·s or more, for example, 790 mPa·s to 3600 mPa·s, and has a thickening tendency, so it is not preferred.

[0086] In one embodiment of the present invention, an organic acid having 1 to 3 carbon atoms may be contained in the silica sol in a proportion of 80 to 1500 ppm, and may be contained in the silica sol in a proportion of 0.008% by mass to 0.15% by mass. This is, for example, equivalent to 0.00027 g to 0.005 g relative to the mass of SiO2 contained in the silica sol having a silica concentration of 30% by mass, and 270 ppm to 5000 ppm of the above organic acid may be contained relative to the SiO2 contained in the silica sol. When the silica sol dispersed in a nitrogen-containing organic solvent is mixed with a nitrogen-containing polymer to produce an insulating resin composition, it is preferable that the above organic acid is also contained in the insulating resin composition in a proportion of 2.70 ppm to 5000 ppm relative to SiO2.

[0087] Examples of the nitrogen-containing polymer include polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, or polyesterimide.

[0088] Regarding the stability of the insulating resin composition, the viscosity (mPa·s) of the silica-containing polyamic acid prepared by mixing the silica sol and the polyamic acid formed from 4,4'-diaminodiphenyl ether (DDE) and pyromellitic dianhydride (PMDA) as the resin at a mass ratio of resin / SiO2 = 80 / 20 after being stored at 50°C for 7 days can be set to be 1.20 times or less of the viscosity before storage, 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.

[0089] Regarding the insulation property of the insulating resin composition, the silica-containing polyamic acid prepared by mixing the silica sol and the polyamic acid formed from 4,4'-diaminodiphenyl ether (DDE) and pyromellitic dianhydride (PMDA) as the resin at a mass ratio of resin / SiO2 = 80 / 20 is heated on a Cu plate at 290°C to obtain a Cu plate sintered with silica-containing polyimide (film thickness: 29 to 32 μm), and an insulating resin composition having an insulation breakdown life of 50 minutes or more, or in the range of 50 minutes to 1000 minutes, or in the range of 60 minutes to 500 minutes, or in the range of 60 minutes 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 is obtained.

[0090] By insulatingly coating these insulating resin compositions on enameled wires or the like, an insulated coated wire is obtained.

[0091] The silica sol of the present invention can be produced by a method including the following steps (A) to (B):

[0092] (A) Process: Prepare a silica sol in which silica particles having an average primary particle diameter of 5 to 100 nm are dispersed in an aqueous medium; and

[0093] (B) Process: Adjust the silica sol obtained in the (A) process to contain a carboxylic acid having 1 to 3 carbon atoms at a ratio of 80 to 1500 ppm, and simultaneously replace it with a nitrogen-containing organic solvent.

[0094] In the (B) process, the carboxylic acid can be added in the process of replacing the aqueous medium solvent with a nitrogen-containing organic solvent. Alternatively, the carboxylic acid can also be added before replacing the solvent with a nitrogen-containing organic solvent. However, since a part of the carboxylic acid may be removed during the solvent replacement, it can be added after the solvent replacement so as to fall within the specified range.

[0095] In the (B) process or after the (B) process is completed, a (C) process of additionally adding at least one silane compound of formulas (1) to (3) can be added. By adding the silane compound, the surface of the silica particles can be coated with the silane compound.

[0096] Combine the silica sol dispersed in the nitrogen-containing organic solvent of the present invention with a nitrogen-containing polymer to obtain an insulating resin composition (resin varnish).

[0097] Regarding the insulating resin composition (resin varnish), after the (A) process to the (B) process, or the (A) process to the (C) process is completed, a (D) process and an (E) process can be further added for manufacturing:

[0098] (D) Process: Mix the silica sol dispersed in the nitrogen-containing organic solvent and the nitrogen-containing polymer;

[0099] (E) Process: Remove a part or all of the nitrogen-containing organic solvent from the silica sol obtained in the (D) process.

[0100] Relative to 1 part by mass of the silica contained in the silica sol, the nitrogen-containing polymer can be blended at a ratio of 1 to 100 parts by mass.

[0101] Examples of the nitrogen-containing polymer include polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, or polyesterimide.

[0102] The insulating resin composition is heated and cured at the temperature at which the solvent evaporates by coating a conductor that requires insulation, so that an insulating film can be formed on the surface of the conductor. The heating temperature for removing the solvent is determined according to the temperature and pressure. If it is under normal pressure, it is about 150°C to 300°C, or for imidization of the resin, it is about 150°C to 400°C.

[0103] As the above-mentioned conductor, a metal wire, particularly a copper wire, is used. The copper wire is coated with an enamel film to form an electric wire, which is used in industrial and household motors, transformers, coils, etc.

[0104] Regarding the insulating resin composition of the present invention, an insulated coated wire can be manufactured by a method of coating an enamel-coated copper wire or by directly coating the insulating resin composition on the copper wire instead of the enamel.

[0105] Regarding the above-mentioned insulating resin composition, it is obtained by mixing in a ratio of 1 to 100, or 1 to 50, or 1 to 10 parts by mass of a nitrogen-containing polymer with respect to 1 part by mass of the silica contained in the silica sol.

[0106] The insulating resin composition is obtained by mixing and stirring the silica sol and the polymer using a mixer and a disperser. Additives can be added as needed in these preparations.

[0107] The conductor coated with the insulating resin composition of the present invention has insulation and flexibility.

[0108] The flexibility is measured according to JIS C 3216-3 item 5. For example, an insulated coated wire having an insulating coating layer with a thickness of 35 μm obtained from an insulating resin composition containing a nitrogen-containing polymer in a ratio of 4 parts by mass with respect to 1 part by mass of silica preferably has a flexibility of 1d to 2d. Among them, regarding the above-mentioned flexibility, the minimum winding diameter d at which no cracks are generated in the insulating coating film of the insulated coated wire with 20% elongation with respect to the insulated coated wire without elongation is obtained, and the minimum winding diameter without generating cracks is measured in the range from the self-diameter (1d) to n times the self-diameter (nd).

[0109] Examples

[0110] [Measurement of SiO2 Concentration]

[0111] The silica sol is placed in a crucible, dried at 150 °C, and then the obtained gel is calcined at 1000 °C, and the calcination residue is measured and calculated.

[0112] [Measurement of Average Primary Particle Size (Particle Size by Nitrogen Adsorption Method)]

[0113] The specific surface area of the powder obtained by drying the acidic silica sol at 300 °C is measured using a specific surface area measuring device Monosorb (registered trademark) MS-16 (manufactured by Yuasa Ionics Co., Ltd.).

[0114] [Measurement of Moisture]

[0115] It is obtained by the Karl Fischer titration method.

[0116] Measurement of Viscosity

[0117] The viscosity of the silica sol was measured using a B-type rotational viscometer (manufactured by Toki Sangyo Co., Ltd.).

[0118] Measurement of Cationic Components in the Organic Sol

[0119] Pure water was added to the sol to prepare a silica concentration of 3% by mass. To 8 g of the diluted sol, 200 μL of 1N nitric acid aqueous solution was added and left overnight. The resulting liquid was centrifuged (5000 rpm × 30 minutes) using Amicon Ultra-15 10k (molecular weight cut-off 10,000) manufactured by Merck & Co., Inc., and the obtained filtrate was diluted 10 times with pure water and measured by cation chromatography.

[0120] Measurement of Anionic Components in the Organic Sol

[0121] The following describes the pretreatment conditions of the silica sol.

[0122] 50 μL of the organosilica sol sample was dissolved in 950 μL of the electrophoresis solution (containing 40 mM of quinolinic acid, 90 mM of 2-amino-2-hydroxymethyl-1,3-propanediol (Tris), and 0.7 mM of cetyltrimethylammonium hydroxide (HDTMA), pH 7.4), and centrifugation was performed using a centrifuge (Model 6200, Kubota Corporation) (centrifugation conditions: 10000 rpm, 10 minutes, 15 °C). 475 μL of the obtained supernatant was taken into a vial for electrophoresis measurement. 25 μL of a solution obtained by dissolving 1 mg of sodium nitrate in 10 mL of the electrophoresis solution (sodium nitrate concentration 100 ppm) was added to the sample taken into the above vial for electrophoresis measurement to prepare a sample for capillary electrophoresis measurement.

[0123] The following describes the pretreatment conditions of the capillary column.

[0124] Before measurement, the electrophoresis solution was passed through the capillary at a pressure of 915 mbar for 20 minutes for pretreatment. Then, before and after each sample measurement, ethanol (manufactured by Junsei Chemical Co., Ltd., reagent special grade) was passed through the capillary at a pressure of 915 mbar for 180 seconds, 0.1M sodium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Corporation, for volumetric analysis) was passed through for 360 seconds, ultrapure water (trade name Milli-Q) was passed through for 300 seconds, and the electrophoresis solution was passed through for 300 seconds to clean the capillary.

[0125] The following describes the measurement conditions of capillary electrophoresis.

[0126] · Apparatus: A capillary electrophoresis system (trade name: Agilent 7100, manufactured by Agilent Technology, Inc.).

[0127] · Capillary: Model G1600 - 64311 manufactured by Agilent (inner diameter 75 μm, total length 112.5 cm, effective length 104 cm, fused silica capillary)

[0128] · Detector: PDA detector (Sig. = 400 nm ± 10 nm, Ref. = 265 nm ± 5 nm)

[0129] · Voltage: -25 kV

[0130] · Electrophoresis temperature: 25 °C

[0131] · 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

[0132] Sample injection: Pressure 50 mbar, injection time 6 seconds (pressure injection method)

[0133] For analysis, it is quantified by normalizing with the peak area of nitrate ions (the peak area of organic acid ions divided by the peak area of sodium nitrate).

[0134] [Solid content of polyamic acid]

[0135] After taking polyamic acid into an aluminum cup, it is calcined at 200 °C, and the calcination residue is measured and calculated.

[0136] (Example 1)

[0137] 412 g of a water-dispersed silica sol with the trade name PL-3 (average primary particle size: 35 nm, silica concentration: 20% by mass, manufactured by Fuso Chemical Industry Co., Ltd.) was placed in a 1-L eggplant-shaped flask. While evaporating and distilling off the solvent using a rotary evaporator under a reduced pressure of 150 to 70 Torr and a bath temperature of 80 to 90°C, DMAC (dimethylacetamide) was supplied to replace the dispersion medium of the sol with DMAC, thereby obtaining a 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 obtained sol was placed in a 500-mL eggplant-shaped flask. While stirring the sol with a magnetic stirrer, 0.058 g of acetic acid was added and kept at room temperature for 2 hours, thereby obtaining a DMAC-dispersed silica sol (1) (silica concentration: 30.0% by mass, water content: 6.7% by 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)).

[0138] (Example 2)

[0139] 169 g of the DMAC-dispersed silica sol (1) obtained in Example 1 was placed in a 500-mL eggplant-shaped flask. While stirring the sol with a magnetic stirrer, 0.1514 g of a 4N aqueous sodium hydroxide solution was added. Then, while evaporating and distilling off the solvent using a rotary evaporator under a reduced pressure of 70 Torr and a bath temperature of 90°C, DMAC was supplied to obtain a DMAC-dispersed silica sol (silica concentration: 30.0% by mass, water content: 3.4% by mass, viscosity: 23 mPa·s). Then, an additional DMAC replacement was carried out using a rotary evaporator under a reduced pressure of 70 Torr and a bath temperature of 90°C to obtain a DMAC-dispersed silica sol (2) (silica concentration: 30.0% by mass, water content: 3.4% by mass, viscosity: 23 mPa·s, Na ion content: 82 ppm in terms of alkali metal ions in the sol, acetic acid content in the sol: 370 ppm).

[0140] (Example 3)

[0141] 616 g of an aqueous dispersion silica sol with the trade name PL-2L (average primary particle diameter: 17 nm, silica concentration: 19% by mass, manufactured by Fuso Chemical Industry Co., Ltd.) was placed in a 2-L eggplant-shaped flask. While evaporating and distilling off the solvent under a reduced pressure of 150 to 70 Torr and a bath temperature of 80 to 90 °C using a rotary evaporator, DMAC (dimethylacetamide) was supplied to replace the dispersion medium of the sol with DMAC, thereby obtaining 557 g of a 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 using a magnetic stirrer, 3.1 g of phenyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM-103) was added, and then the liquid temperature was maintained at 90 °C for 2 hours. 282 g of the obtained sol was placed in a 1-L eggplant-shaped flask, 0.075 g of acetic acid was added, and then 0.26 g of a 4N aqueous sodium hydroxide solution was added, followed by continued stirring for 30 minutes. Then, while evaporating and distilling off the solvent under a reduced pressure of 100 to 70 Torr and a bath temperature of 110 °C using a rotary evaporator, DMAC was supplied to obtain a DMAC-dispersed silica sol (3) (silica concentration: 30.3% by mass, water content: 0.9% by mass, viscosity: 8 mPa·s, Na ion content: 120 ppm in terms of alkali metal ions in the sol, acetic acid content in the sol: 400 ppm).

[0142] (Example 4)

[0143] 351 g of a water-dispersed silica sol with the trade name SNOWTEX O-33 (average primary particle size: 12 nm, silica concentration: 33% by mass, manufactured by Nissan Chemical Industries, Ltd.) was placed in a 1-L eggplant-shaped flask. While stirring the sol with a magnetic stirrer, 0.25 g of a 4N NaOH aqueous solution was added, and stirring was continued for 30 minutes. Then, while evaporating and distilling off the solvent using a rotary evaporator under a reduced pressure of 150 to 110 Torr and a bath temperature of 90°C, DMAC was supplied to replace the dispersion medium of the sol with DMAC, thereby obtaining 352 g of a silica sol dispersed in a DMAC-water mixed solvent (silica concentration: 33.0% by mass, water content: 11.7% by mass). After adding 4.3 g of phenyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM-103), the liquid temperature was maintained at 90°C for 2 hours. Then, while evaporating and distilling off the solvent using a rotary evaporator under a reduced pressure of 100 to 70 Torr and a bath temperature of 110°C, DMAC was supplied, thereby obtaining a DMAC-dispersed silica sol (4) (silica concentration: 30.2% by mass, water content: 0.3% by mass, viscosity: 8 mPa·s; for the alkali metal ions in the sol, the Na ion content was 200 ppm, the acetic acid content in the sol was 111 ppm, and the formic acid content was 36 ppm). At this time, by controlling the amount of acetic acid generated by the hydrolysis of DMAC within a certain range, a DMAC-dispersed silica sol was obtained.

[0144] (Example 5)

[0145] 140 g of a methanol-dispersed silica sol with the 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 eggplant-shaped flask. After adding 3.3 g of phenyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM-103), the liquid temperature was maintained at 60°C for 5 hours. Then, after adding 6.8 g of dimethylpolysiloxane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KF-96L 0.65 cs), 14 g of DMAC was added, and the liquid temperature was maintained at 60°C for 3 hours. Then, while evaporating and distilling off the solvent using a rotary evaporator under a reduced pressure of 450 to 110 Torr and a bath temperature of 85 to 125°C, DMAC was supplied to replace the dispersion medium of the sol with DMAC, thereby obtaining a DMAC-dispersed silica sol (5) (silica concentration: 30.2% by mass, water content: 0.1% by mass, viscosity: 7 mPa·s; for the alkali metal ions in the sol, the Na ion content was 150 ppm, the acetic acid content in the sol was 65 ppm, and the formic acid content was 87 ppm). At this time, by controlling the amount of carboxylic acid generated by the hydrolysis of DMAC within a certain range, a DMAC-dispersed silica sol was obtained.

[0146] (Example 6)

[0147] 200 g of aqueous silica sol with the trade name SNOWTEX OXS (average primary particle size of 5 nm according to Sears, silica concentration of 10.5% by mass, pH 2.8, manufactured by Nissan Chemical Industries, Ltd.) was placed in a 1 L eggplant-shaped flask. While stirring the sol with a magnetic stirrer, 4.3 g of 3-glycidoxypropyltrimethoxysilane (trade name KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.) was added, and then the liquid temperature was maintained at 80 °C for 4 hours.

[0148] Then, while evaporating and distilling off the solvent at a pressure of 150 - 70 Torr and a bath temperature of 90 °C using a rotary evaporator, DMF (N,N-dimethylformamide) was supplied to replace the dispersion medium of the sol with DMF, thereby obtaining a DMF-dispersed silica sol (6) (silica concentration of 15.9% by mass, water content of 1.0% by mass, viscosity of 4 mPa·s. Regarding the alkali metal ions in the sol, the Na ion content was 100 ppm, and the formic acid content in the sol was 1375 ppm). At this time, by controlling the amount of carboxylic acid generated by the hydrolysis of DMF within a certain range, a DMF-dispersed silica sol was obtained.

[0149] (Comparative Example 1)

[0150] 412 g of an aqueous silica sol with the trade name PL-3 (average primary particle size of 35 nm, silica concentration of 20% by mass, manufactured by Fuso Chemical Industry Co., Ltd.) was placed in a 1 L eggplant-shaped flask. While evaporating and distilling off the solvent at a reduced pressure of 150 - 70 Torr and a bath temperature of 80 - 90 °C using a rotary evaporator, DMAC (dimethylacetamide) was supplied to replace the dispersion medium of the sol with DMAC, thereby obtaining a DMAC-dispersed silica sol (R1) (silica concentration of 30.0% by mass, water content of 6.7% by mass, viscosity of 790 mPa·s). 172.3 g of the obtained sol was placed in a 500 mL eggplant-shaped flask, and while stirring the sol with a magnetic stirrer, it was maintained at room temperature for 2 hours, thereby obtaining a DMAC-dispersed silica sol (R1) (silica concentration of 30.0% by mass, water content of 6.7% by mass, viscosity of 790 mPa·s, the alkali metal ions in the sol were below the detection limit (less than 10 ppm), and the acetic acid content in the sol was 30 ppm).

[0151] (Comparative Example 2)

[0152] 15.5 g of the DMAC-dispersed silica sol (R1) obtained in Comparative Example 1 was taken into a 20 ml glass bottle, and 0.039 g of an 8% sulfuric acid aqueous solution was added to the sol and shaken. As a result, the sol lost its fluidity and gelled.

[0153] (Comparative Example 3)

[0154] 616 g of a water-dispersed silica sol with the trade name PL-2L (average primary particle size: 17 nm, silica concentration: 19% by mass, manufactured by Fuso Chemical Industry Co., Ltd.) was placed in a 2-L eggplant-shaped flask. While evaporating and distilling off the solvent under a reduced pressure of 150 - 70 Torr and a bath temperature of 80 - 90°C using a rotary evaporator, DMAC (dimethylacetamide) was supplied to replace the dispersion medium of the sol with DMAC, thereby obtaining 557 g of a 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 using a magnetic stirrer, 3.1 g of phenyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM-103) was added, and then the liquid temperature was maintained at 90°C for 2 hours, thereby obtaining a highly viscous silica sol dispersed in DMAC (R3) (silica concentration: 27.6% by mass, water content: 5.2% by mass, viscosity: 3600 mPa·s, the alkali metal ions in the sol were below the detection limit (less than 10 ppm), and the acetic acid content in the sol was 31 ppm).

[0155] (Comparative Example 4)

[0156] 130 g of the silica sol dispersed in DMAC (4) obtained in Example 4 was placed in a 500-mL eggplant-shaped flask. While stirring using a magnetic stirrer, 0.26 g of acetic acid was added, and the mixture was maintained at room temperature for 2 hours, thereby obtaining a silica sol dispersed in DMAC (R4) (silica concentration: 30.2% by mass, water content: 0.3% by mass, viscosity: 16 mPa·s, the Na ion content in terms of the alkali metal ions in the sol was 200 ppm, the acetic acid content in the sol was 1926 ppm, and the formic acid content was 39 ppm).

[0157] (Synthesis Example 1) Preparation of polyamic acid

[0158] Using 4,4'-diaminodiphenyl ether (DDE), pyromellitic dianhydride (PMDA), NMP (N-methylpyrrolidone) as a solvent, and DMAC (dimethylacetamide), polymerization was carried out at a temperature of 50°C with stirring to obtain a polyamic acid corresponding to formula (4) (solid content: 17% by mass, viscosity at 25°C measured using an E-type viscometer: 13640 mPa·s). For the polymerization of the polyamic acid, the above DDE and PMDA were polymerized in an equimolar ratio of 1:1. The weight-average molecular weight of the obtained polyamic acid was 63000. n in formula (4) is the number of repeating units.

[0159] [Chemical Formula 3]

[0160]

[0161] (Thermal Stability Test of Insulating Resin Composition)

[0162] The DMAC-dispersed silica sol obtained in Example 4 and Comparative Example 4 and the polyamic acid obtained in Synthesis Example 1 were added and mixed in a glass bottle in such a way that the mass ratio of resin / SiO2 was 80 / 20, and degassed and stirred for 20 minutes using a vacuum degassing machine (manufactured by EME Co., Ltd., trade name V-mini 300) to obtain a silica-containing polyamic acid. The viscosities (mPa·s) at an initial temperature of 25°C and the viscosities (mPa·s) measured after storing at 50°C for 7 days and then cooling to 25°C are shown in the table below.

[0163]

Table 1

[0164] Table 1

[0165]

[0166] The silica-containing polyamic acid obtained in Example 4 and Comparative Example 4 was coated on a Cu plate (manufactured by AS ONE Co., Ltd., trade name HC0536, 300 mm × 300 mm, 0.5 mm thick) using an applicator (manufactured by BEVS Co., Ltd., trade name: Film Coater B / M150mm with film thickness adjustment function), and then solvent removal and thermal curing were carried out under the conditions of 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 sintered with silica-containing polyimide (film thickness: 29 - 32 μm). It was cut into squares with a side length of 5 cm to prepare specimens for insulation tests.

[0167] (Measurement of Dielectric Breakdown Life)

[0168] For plate-shaped samples with a size of 50 mm × 50 mm and a thickness of 0.5 mm, the dielectric breakdown life of the above-mentioned insulation test specimens was measured at a test temperature of 155°C (in air), an applied voltage of 3.0 kV, and a frequency of 50 Hz using a dielectric breakdown test device manufactured by YAMAYO Test Instruments Co., Ltd., model: YST-243WS. Regarding the electrode shape, a flat electrode (φ = 25 mm) was used at the bottom and a spherical electrode (φ = 20 mm) was used at the top, and the electrodes were both set in contact with the sample for the test. The measurement was carried out 3 to 4 times with an applied voltage of 3.0 kV, and the average value was recorded. It should be noted that as a blank test, only the polyimide resin without silica was used as the sample and measured in the same way.

[0169]

Table 2

[0170] Table 2

[0171]

[0172] The silica sol dispersed in a nitrogen-containing organic solvent containing a specified amount of an organic acid (such as acetic acid) does not have a high viscosity when compared with the DMAC-dispersed silica sol without an organic acid (such as acetic acid) in terms of viscosity with the same solid content. Therefore, when compounded with a nitrogen-containing polymer to form an insulating resin composition, the workability is good.

[0173] Regarding the insulating resin composition formed by compounding a silica sol dispersed in a nitrogen-containing organic solvent containing more than the specified amount of an organic acid (such as acetic acid) with a nitrogen-containing polymer, compared with the insulating resin composition formed by compounding a DMAC-dispersed silica sol containing a specified amount of an organic acid (such as acetic acid) with a nitrogen-containing polymer, in the thermal stability test after storage at 50 °C for 7 days, an increase in the viscosity of the insulating resin composition was found.

[0174] In addition, it is known that the silica sol dispersed in a nitrogen-containing organic solvent containing a specified amount of an organic acid (such as acetic acid) has a longer insulation life compared with a polyimide resin without silica.

[0175] In the present invention, the silica sol dispersed in a nitrogen-containing organic solvent containing a specified amount of an organic acid (such as acetic acid) has a low viscosity. Therefore, when compounded with a nitrogen-containing polymer to form an insulating resin composition and coated on a substrate, it can retain the solid content capable of maintaining the insulating properties, and a film capable of being coated on the substrate is obtained. Therefore, the obtained insulating substrate can have a long insulation life.

[0176] Industrial applicability

[0177] The silica sol dispersed in a nitrogen-containing organic solvent containing a specified amount of an organic acid (such as acetic acid) has a low viscosity. Therefore, when compounded with a nitrogen-containing polymer to form an insulating resin composition and coated on a substrate, it can retain the solid content capable of maintaining the insulating properties, and an insulating film capable of being coated on the substrate is obtained.

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 a carboxylic acid having 1 to 3 carbon atoms is contained in the silica sol in a proportion of 80 to 1500 ppm.

2. The silica sol according to claim 1, wherein, The nitrogen-containing organic solvent is an amide-based solvent.

3. The silica sol according to claim 1 or 2, wherein The nitrogen-containing organic solvent is dimethylacetamide, dimethylformamide, or dimethylpropionamide.

4. The silica sol according to claim 1 or 2, wherein The carboxylic acid having 1 to 3 carbon atoms is formic acid, acetic acid, or propionic acid.

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

6. The silica sol according to claim 1 or 2, wherein When the SiO2 concentration is 30% by mass, the viscosity measured at 25 °C is 3 to 500 mPa·s.

7. The silica sol according to claim 1 or 2 contains alkali metal ions in a proportion of 300 ppm or less, wherein Alkali metal ions mean alkali metal ions including lithium, sodium, and potassium.

8. The silica sol according to claim 1 or 2, wherein The silica particles are coated with at least one silane compound or its hydrolyzate selected from Formula (1) to Formula (3): [Chemical 1] R 1 a Si(R 2 ) 4-a Formula (1) [R 3 b Si(R 4 ) 3-b ₂Y c Formula (2) R 5 d Si(R 6 ) 4-d Formula (3) In formula (1), R 1 each is an alkyl group, a haloalkyl group, an alkenyl group, an aryl group, or an organic group having (meth)acryloyl, mercapto, amino, ureido, carboxyl, acid anhydride, carboxylic acid ester, epoxy, hydroxyl, or cyano group, and is bonded to a silicon atom through an 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 are bonded to the silicon atom through an Si-C bond, R 4 and R 6 each 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.

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

10. The insulating resin composition according to claim 9, wherein, With respect to 1 part by mass of the silica contained in the silica sol, the mass part of the nitrogen-containing polymer is 1 to 100.

11. The insulating resin composition according to claim 9, wherein, The nitrogen-containing polymer is polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, or polyesterimide.

12. Insulating resin composition, wherein, The viscosity (mPa·s) of the silica-containing polyamic acid prepared by mixing the silica sol according to Claim 1 and a polyamic acid formed from 4,4'-diaminodiphenyl ether (DDE) and pyromellitic dianhydride (PMDA) as a resin at a mass ratio of resin / SiO2 = 80 / 20 after storage at 50 °C for 7 days is 1.20 times or less of the viscosity before storage.

13. Insulating resin composition, wherein, The silica-containing polyamic acid prepared by mixing the silica sol according to Claim 1 and a polyamic acid formed from 4,4'-diaminodiphenyl ether (DDE) and pyromellitic dianhydride (PMDA) as a resin at a mass ratio of resin / SiO2 = 80 / 20 is heated on a Cu plate at 290 °C to obtain a Cu plate sintered with silica-containing polyimide (film thickness: 29 to 32 μm), and the dielectric breakdown life at a test temperature of 155 °C (in air), an applied voltage of 3.0 kV, and a frequency of 50 Hz is 50 minutes or more.

14. An insulated coated wire insulated and coated with the insulating resin composition according to any one of Claims 9 to 13.

15. A method for manufacturing the silica sol according to Claim 1 or 2, comprising the following steps (A) to (B): (A) Step: Prepare a silica sol in which silica particles having an average primary particle diameter of 5 to 100 nm are dispersed in an aqueous medium; and (B) Step: Adjust the silica sol obtained in step (A) to contain a carboxylic acid having 1 to 3 carbon atoms in a proportion of 80 to 1500 ppm and replace it with a nitrogen-containing organic solvent.

16. The method for manufacturing the silica sol according to claim 15, wherein, Add additionally in step (B) or after step (B) Step (C) of at least one silane compound of Formulas (1) to (3) according to Claim 7.

17. The method for producing an insulating resin composition according to any one of claims 9 to 13, which includes a step (D) of mixing the silica sol according to claim 1 and a nitrogen-containing polymer.

18. The method for manufacturing an insulating resin composition according to claim 17, wherein, A step (E) of further removing a part or all of the nitrogen-containing organic solvent from the insulating resin composition is added to step (D).

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