A composition of silica sol and insulating resin dispersed in a nitrogen-containing organic solvent containing organic acids.

Abstract

Provided are silica sols containing organic acids dispersed in nitrogen-containing organic solvents, and insulating resin compositions comprising the silica sol and nitrogen-containing polymers. The silica sol is a silica sol in which silica particles having an average primary particle size of 5-100 nm are dispersed in a nitrogen-containing organic solvent, and the silica sol contains a carboxylic acid with 1-3 carbon atoms in a proportion of 80-1500 ppm. The nitrogen-containing organic solvent is an amide-based silica sol. The nitrogen-containing organic solvent is a silica sol containing dimethylacetamide, dimethylformamide, or dimethylpropionamide. The carboxylic acid with 1-3 carbon atoms is a silica sol containing formic acid, acetic acid, or propionic acid. The insulating resin composition comprises a silica sol and a nitrogen-containing polymer.

Description

Technical Field

[0001] This invention relates to silica sol dispersed in a nitrogen-containing organic solvent containing organic acids such as acetic acid, insulating resin compositions using the sol, and methods for manufacturing the same. Background Technology

[0002] Silica sols, which are formed by dispersing surface-modified silica particles in solvents, 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 an alcohol to introduce alkoxy groups and thus organicate them, resulting in an inorganic oxide sol dispersed in an organic solvent such as toluene (see Patent Document 1). In this method, a silica sol dispersed in toluene is reacted with phenyltrimethoxysilane to produce a silica sol dispersed in toluene.

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

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

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

[0006] Existing technical documents

[0007] Patent documents

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

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

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

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

[0012] The problem that the invention aims to solve

[0013] The object of this invention is to provide a silica sol obtained by dispersing silica particles in a nitrogen-containing organic solvent that is well compatible with polar resins of polyimide and polyamide. Furthermore, the object is to provide an insulating coated conductor that, when used to formulate an insulating resin composition in combination with these silica sols, can maintain a high insulation life for a long period.

[0014] Methods for solving problems

[0015] The present invention, as a first point of view, is a silica sol, which is a silica sol in which silica particles with an average primary particle size of 5 to 100 nm are dispersed in a nitrogen-containing organic solvent, and the silica sol contains a carboxylic acid with 1 to 3 carbon atoms in a proportion of 80 to 1500 ppm.

[0016] As a second point of view, the silica sol described in the first point of view is wherein the nitrogen-containing organic solvent is an amide solvent;

[0017] As a third point of view, the silica sol described in the first or second point of view is wherein the nitrogen-containing organic solvent is dimethylacetamide, dimethylformamide, or dimethylpropionamide;

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

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

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

[0021] As a seventh point of view, the silica sol according to any one of the first to sixth points of view contains alkali metal ions in a proportion of less than 300 ppm, wherein the alkali metal ions are alkali metal ions including lithium, sodium and potassium.

[0022] As the eighth point of view, for a silica sol according to any one of the first to seventh points of view, wherein the silica particles are coated with at least one silane compound selected from formula (1) to formula (3) or its hydrolysate:

[0023]

Chemistry 1

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

[0025] [R] 3 b Si(R 4 ) 3-b 2Yc Equation (2)

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

[0027] In equation (1), R 1 Each of the following groups is an alkyl, haloalkyl, alkenyl, aryl, or has an organic group having (meth)acryloyl, mercapto, amino, urea, carboxyl, anhydride, carboxyl ester, epoxy, hydroxyl, or cyano group, and is bonded to a silicon atom via a Si-C bond. 2 Each represents an alkoxy, acyloxy, hydroxyl, or halogen group, and 'a' represents an integer from 1 to 3.

[0028] In equations (2) and (3), R 3 and R 5 Each is an alkyl group having 1 to 3 carbon atoms, or an aryl group having 6 to 30 carbon atoms, and is bonded to silicon atoms via Si-C bonds. 4 and R 6 Each represents an alkoxy, acyloxy, hydroxyl, or halogen group; Y represents an alkylene, NH group, or oxygen atom; b is an integer from 1 to 3; c is an integer from 0 to 1; and d is an integer from 1 to 3.

[0029] As a ninth point of view, it is an insulating resin composition comprising silica sol and a nitrogen-containing polymer according to any one of the first to eighth points of view;

[0030] As a tenth point of view, the insulating resin composition according to the ninth point of view is wherein the mass part of the nitrogen-containing polymer is 1 to 100 relative to 1 part by mass of silica contained in the silica sol.

[0031] As the 11th point of view, it is an insulating resin composition according to the 9th or 10th point of view, wherein the nitrogen-containing polymer is a polyimide, polyamide, polyamic acid, polyamide-imide, polyether-imide, or polyester-imide;

[0032] As a 12th point of view, an insulating resin composition is provided, wherein the silica-coated polyamic acid prepared by the silica sol according to any one of the first to eighth points of view, and the polyamic acid formed by 4,4'-diaminodiphenyl ether (DDE) and pyromellitic anhydride (PMDA) as resin at a mass ratio of resin / SiO2 = 80 / 20, has a viscosity (mPa·s) of less than 1.20 times that before storage after being stored at 50°C for 7 days;

[0033] As the 13th point of view, an insulating resin composition is provided, wherein a silica-coated polyamic acid prepared according to any one of the first to eighth points of view, and a polyamic acid formed from 4,4'-diaminodiphenyl ether (DDE) and pyromellitic anhydride (PMDA) as resin, at a mass ratio of resin / SiO2 = 80 / 20, is heated on a Cu plate at 290°C to obtain a Cu plate with sintered silica-coated polyimide (coating thickness: 29-32 μm), and the insulation 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 the 14th point of view, the insulated coated conductor is insulated with an insulating resin composition according to any one of the 9th to 13th points of view;

[0035] As the 15th point of view, a method for manufacturing silica sol according to any one of the 1st to 8th points of view includes the following steps (A) to (B):

[0036] (A) Process: Prepare silica sol with an average primary particle size of 5–100 nm dispersed in an aqueous medium; and

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

[0038] As the 16th point of view, a method for manufacturing silica sol according to the 15th point of view includes a (C) step in which at least one silane compound of formula (1) to formula (3) according to the 8th point of view is added during or after step (B).

[0039] As the 17th point of view, a method for manufacturing an insulating resin composition according to any one of the 9th to 14th points of view includes a (D) step of mixing silica sol obtained by the 15th or 16th point of view with a nitrogen-containing polymer.

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

[0041] The effects of the invention

[0042] In the case of insulating resins formed by coating and curing insulating resin compositions, silica particles can be included in the insulating resin composition to improve the insulation resistance of the substrate. The silica particles, by forming a strong coating layer tightly with the insulating resin, can protect the substrate from insulation damage caused by discharge. Most insulating resins use nitrogen-containing polymers with high insulation properties. These nitrogen-containing polymers are, for example, polyimides, polyamides, polyamic acids, polyamide-imides, polyether-imides, or polyester-imides, synthesized using diamines and acid anhydrides. They have a two-part structure: an imide backbone, polar parts such as carboxyl groups and amide bonds, and hydrophobic parts contained in the diamine molecule and the acid anhydride molecule.

[0043] An insulating resin composition is prepared by mixing silica sol dispersed in a nitrogen-containing organic solvent with a nitrogen-containing polymer. When using this insulating resin composition as a coating material for enameled wires, proper viscosity management in the field is crucial to ensure uniform film thickness coating of the enameled wires.

[0044] According to the present invention, in the stage of dispersing silica sol in a nitrogen-containing organic solvent, by containing a specific amount of organic acid in the nitrogen-containing organic solvent, the increase in viscosity of the silica sol can be suppressed. Furthermore, according to the present invention, when mixing 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, the increase in viscosity of the insulating resin composition can be reduced.

[0045] This invention relates to silica sol dispersed in a nitrogen-containing organic solvent, and to methods of adding these sols to nitrogen-containing polymers to manufacture insulating resin compositions, including cases where organic acids are initially contained in the nitrogen-containing organic solvent and the nitrogen-containing polymer, and cases where organic acids are newly added. By measuring their content to within the range specified in this invention, the viscosity of the silica sol and the insulating resin composition can be stabilized. Detailed Implementation

[0046] The preferred embodiments of the present invention will be described below. However, the following embodiments are illustrative of the present invention and are not intended to limit the present invention in any way.

[0047] One embodiment of the present invention is a silica sol, which 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 the silica sol contains a carboxylic acid with 1 to 3 carbon atoms at a ratio 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. The average primary particle size of the silica particles can be measured using the nitrogen adsorption method (BET method) in nm.

[0049] The nitrogen-containing organic solvent used in this invention has at least a functional group containing a nitrogen atom. Examples of functional groups containing a nitrogen atom include amino, nitro, and cyano groups. Preferably, amide solvents contain both a nitrogen-containing functional group and a carbonyl group in one molecule of the solvent molecule. Examples of such solvents include solvents with chain or cyclic structures. Examples of functional groups containing a nitrogen atom include amino, nitro, and cyano groups; amino groups are preferred. The amino and carbonyl groups can be adjacent or separated by a carbon atom, for example, they can be used as an amide bond; amide solvents are preferred.

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

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

[0052] That is, the total solvent may contain nitrogen-containing organic solvents in proportions of 50-100 vol%, 90-100 vol%, 98-100 vol%, or 99-100 vol%, and may also contain other solvents in proportions of 0-less than 50 vol%, 0-less than 10 vol%, 0-less than 2 vol%, or 0-less than 1 vol%.

[0053] Other solvents that can be listed include water, ketone solvents, ester solvents, alcohol solvents, glycol ether solvents, hydrocarbon solvents, halogen solvents, ether solvents, glycol solvents, and amine solvents.

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

[0055] In one embodiment of the invention, carboxylic acids having 1 to 3 carbon atoms are preferably used as organic acids, and for example, formic acid, acetic acid, or propionic acid are more preferred. These organic acids are preferred because they have 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] Furthermore, regarding the viscosity of the aforementioned silica sol, when the SiO2 concentration is set to 30% by mass, a viscosity of 3 to 500 mPa·s measured at 25°C is preferred.

[0058] It can contain alkali metal ions (wherein alkali metal ions refer to alkali metal ions including lithium, sodium, and potassium) at a ratio of less than 300 ppm, or 30 to 300 ppm, or 30 to 200 ppm. For example, with regard to alkali metal ions, by making sodium ions within the above range, it is possible to suppress the increase in viscosity of silica sol dispersed in nitrogen-containing organic solvents.

[0059] In one embodiment of the present invention, the silica sol may contain alkali metal ions (wherein alkali metal refers to alkali metal ions including lithium, sodium, and potassium) at a ratio of 300 ppm or less, or 30 to 300 ppm, or 30 to 200 ppm, and may contain alkali metal ions at a ratio of 0.03% by mass or less, or 0.003% by mass to 0.03% by mass, or 0.003% by mass to 0.02% by mass. For example, relative to the mass of SiO2 contained in a silica sol with a silica concentration of 30% by mass, it may contain alkali metal ions converted to M2O at a ratio of 1000 ppm or less, or 100 ppm to 1000 ppm or less, or 100 ppm to 6.70 ppm or less. In addition, when mixing silica sol dispersed in a nitrogen-containing organic solvent with a nitrogen-containing polymer to manufacture an insulating resin composition, the insulating resin composition preferably contains 1000 ppm or less, or 100 ppm to 1000 ppm or less, or 100 ppm to 670 ppm or less of an alkali metal equivalent to M2O, relative to SiO2.

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

[0061] In equation (1), R 1 Each of the following groups is an alkyl, haloalkyl, alkenyl, aryl, or has an organic group having (meth)acryloyl, mercapto, amino, urea, carboxyl, anhydride, carboxyl ester, epoxy, hydroxyl, or cyano group, and is bonded to a silicon atom via a Si-C bond. 2 Each represents an alkoxy, acyloxy, hydroxyl, or halogen group, and 'a' represents an integer from 1 to 3.

[0062] In equations (2) and (3), R 3 and R 5 Each is an alkyl group having 1 to 3 carbon atoms, or an aryl group having 6 to 30 carbon atoms, and is bonded to silicon atoms via Si-C bonds. 4 and R 6 Each represents an alkoxy, acyloxy, hydroxyl, or halogen group; Y represents an alkylene, NH group, or oxygen atom; b is an integer from 1 to 3; c is an integer from 0 to 1; and d is an integer from 1 to 3.

[0063] The alkyl groups mentioned above are alkyl groups having 1 to 18 carbon atoms, and examples 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, and 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, heptadecanyl, octadecyl, etc., but not limited to these.

[0064] In addition, as alkylene compounds, examples of alkylene compounds derived from the aforementioned alkyl groups can be listed.

[0065] The aryl groups mentioned above are aryl groups with 6 to 30 carbon atoms, such as phenyl, naphthyl, anthracene, pyrene, etc.

[0066] Alkenes with 2 to 10 carbon atoms can be listed, such as vinyl, 1-propenyl, 2-propenyl, 1-methyl-1-vinyl, 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-propylvinyl, 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-isopropylvinyl, 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-butylvinyl, 2-methyl-1-pentenyl, 2-methyl-2-pentenyl, etc., but not limited to these.

[0067] Examples of alkoxy groups with 1 to 10 carbon atoms include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, n-pentoxy, 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, but these are not limited to these.

[0068] Examples of acyloxy groups with 2 to 10 carbon atoms include methyl carbonyloxy, ethyl carbonyloxy, n-propyl carbonyloxy, isopropyl carbonyloxy, n-butyl carbonyloxy, isobutyl carbonyloxy, sec-butyl carbonyloxy, tert-butyl carbonyloxy, n-pentyl carbonyloxy, 1-methyl n-butyl carbonyloxy, 2-methyl n-butyl carbonyloxy, 3-methyl n-butyl carbonyloxy, 1,1-dimethyl n-propyl carbonyloxy, 1,2-dimethyl n-propyl carbonyloxy, 2,2-dimethyl n-propyl carbonyloxy, 1-ethyl n-propyl carbonyloxy, n-hexyl carbonyloxy, 1-methyl n-pentyl carbonyloxy, 2-methyl n-pentyl carbonyloxy, etc., but are not limited to these.

[0069] Examples of halogen groups include fluorine, chlorine, bromine, and iodine.

[0070] The term "(meth)acryloyl" refers to both acryloyl and methacryloyl groups. Examples of organic groups containing a (meth)acryloyl group include 3-methacryloyloxypropyl and 3-acryloyloxypropyl.

[0071] Examples of organic groups containing a thiol group include 3-mercaptopropyl.

[0072] Examples of organic groups containing amino groups include 2-aminoethyl, 3-aminopropyl, N-2-(aminoethyl)-3-aminopropyl, N-(1,3-dimethylbutylene)aminopropyl, N-phenyl-3-aminopropyl, and N-(vinylbenzyl)-2-aminoethyl-3-aminopropyl.

[0073] Examples of organic groups containing a urea group include 3-ureopropyl.

[0074] Examples of organic groups containing epoxy groups include glycidyl and 3,4-epoxycyclohexyl. These epoxy groups can be incorporated into forms that involve ring-opening to generate hydroxyl groups.

[0075] Examples of organic groups containing a cyano group include 3-cyanopropyl.

[0076] As compounds of formulas (2) and (3) above, compounds that can form trimethylsilyl groups on the surface of silica particles are preferred.

[0077] Examples of these compounds are as follows.

[0078]

Chemistry 2

[0079]

[0080] In the above formula, R 12 The alkoxy group can be, for example, methoxy or ethoxy. The silane compound described above can be a silane compound manufactured by Shin-Etsu Chemical Co., Ltd. On the surface of silica particles, hydroxyl groups, or silanol groups (if silica particles) can react with the silane compound to perform a process of coating the silica particles with the silane compound using siloxane bonds. Regarding the reaction temperature, it can be carried out at a temperature ranging from 20°C to the boiling point of the dispersion medium, for example, from 20°C to 100°C. Regarding the reaction time, it can be carried out for approximately 0.1 to 6 hours.

[0081] Regarding silane coupling agents, as a coating amount on the surface of silica particles, the number of silicon atoms in the silane compound is 0.1 atoms / nm. 2 ~5.0 units / nm 2A silane compound of equivalent coating amount is added to the silica sol to coat the surface of the silica particles.

[0082] Water is required in the hydrolysis of the aforementioned silane compounds, but if the sol is in an aqueous solvent, then these aqueous solvents are used. Water remaining in the solvent when the aqueous medium solvent is replaced with an organic solvent containing methanol or ethanol can be used. For example, water present in amounts of 0.01–10.0% by mass or 0.1–7.0% by mass can be used. Furthermore, hydrolysis can be carried out using a catalyst or without a catalyst.

[0083] In the absence of a catalyst, where the silica particles have acidic sites on their surface, when a catalyst is used, the hydrolysis catalyst can be categorized as a metal chelate, organic acid, inorganic acid, organic base, or inorganic base. Examples of metal chelates that can be used as hydrolysis catalysts include triethoxy-mono(acetylacetone)titanium and triethoxy-mono(acetylacetone)zirconium. Examples of organic acids that can be used as hydrolysis catalysts include acetic acid and oxalic acid. Examples of inorganic acids that can be used as hydrolysis catalysts include hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and phosphoric acid. Examples of organic bases that can be used as hydrolysis catalysts include pyridine, pyrrole, piperazine, and quaternary ammonium salts. Examples of inorganic bases that can be used as hydrolysis catalysts include ammonia, sodium hydroxide, and potassium hydroxide.

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

[0085] In one embodiment of the present invention, the silica sol contains a carboxylic acid with 1 to 3 carbon atoms at a ratio of 80 to 1500 ppm, thereby allowing the viscosity of the silica sol using a type B viscometer to be set in the range of 3 to 500 mPa·s. Without the aforementioned carboxylic acid, the viscosity exhibits 500 mPa·s or higher, for example, from 790 mPa·s to 3600 mPa·s, showing a tendency to thicken, and is therefore 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 at a ratio of 80 to 1500 ppm, and may be contained in the silica sol at a ratio of 0.008% to 0.15% by mass. For example, this corresponds to 0.00027 g to 0.005 g of the aforementioned organic acid relative to the mass of SiO2 contained in a silica sol with a silica concentration of 30% by mass, and may contain 270 ppm to 5000 ppm of the aforementioned organic acid 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 manufacture an insulating resin composition, it is preferable that the aforementioned organic acid is also contained in the insulating resin composition at a ratio of 2.70 ppm to 5000 ppm relative to SiO2.

[0087] Examples of nitrogen-containing polymers include polyimide, polyamide, polyamic acid, polyamide-imide, polyether-imide, or polyester-imide.

[0088] As for the stability of the insulating resin composition, the viscosity (mPa·s) of the silica-integrated polyamic acid prepared by storing it at 50°C for 7 days, consisting of silica sol and polyamic acid formed from 4,4'-diaminodiphenyl ether (DDE) and pyromellitic anhydride (PMDA) as resin at a mass ratio of resin / SiO2 = 80 / 20, can be set to be less than 1.20 times, or 0.80 to 1.20 times, or 1.00 to 1.20 times, or 1.05 to 1.20 times the viscosity before storage.

[0089] Regarding the insulation properties of the insulating resin composition, a silica-coated polyamic acid was prepared by heating a Cu plate at 290°C with silica sol and polyamic acid formed from 4,4'-diaminodiphenyl ether (DDE) and pyromellitic anhydride (PMDA) as resin at a resin / SiO2 mass ratio of 80 / 20, to obtain a Cu plate with sintered silica-coated polyimide (coating thickness: 29-32 μm). The resulting insulating resin composition had an insulation breakdown life of 50 minutes or more, or 50 minutes to 1000 minutes, or 60 minutes to 500 minutes, or 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.

[0090] By coating these insulating resin compositions with insulation materials such as enameled wire, an insulated conductor is obtained.

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

[0092] (A) Process: Prepare silica sol with an average primary particle size of 5–100 nm dispersed in an aqueous medium; and

[0093] (B) Step: Adjust the silica sol obtained in step (A) to contain 1 to 3 carboxylic acids with a carbon atom ratio of 80 to 1500 ppm, and replace it with a nitrogen-containing organic solvent.

[0094] In step (B), carboxylic acid can be added during the process of replacing the aqueous medium solvent with a nitrogen-containing organic solvent. Alternatively, carboxylic acid can be added before the solvent replacement with a nitrogen-containing organic solvent, but sometimes some carboxylic acid is removed during the solvent replacement process, so it can be added after the solvent replacement in a manner that falls within a specified range.

[0095] In or after step (B), a step (C) can be performed by adding at least one silane compound of formula (1) to (3). By adding the silane compound, the surface of the silica particles can be coated with the silane compound.

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

[0097] Regarding the insulating resin composition (resin varnish), after the completion of steps (A) to (B) or steps (A) to (C), steps (D) and (E) can be added to further manufacture it:

[0098] (D) Process: Mixing silica sol dispersed in a nitrogen-containing organic solvent with a nitrogen-containing polymer;

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

[0100] The nitrogen-containing polymer can be combined in a ratio of 1 to 100 parts by mass relative to 1 part by mass of silica contained in the silica sol.

[0101] Examples of nitrogen-containing polymers include polyimide, polyamide, polyamic acid, polyamide-imide, polyether-imide, or polyester-imide.

[0102] An insulating resin composition is applied to a conductor requiring insulation and then cured by heating at a temperature at which the solvent evaporates, thereby forming an insulating film on the conductor surface. The heating temperature for removing the solvent is determined based on temperature and pressure; under normal pressure, it is approximately 150°C to 300°C, or for imidization of the resin, it is approximately 150°C to 400°C.

[0103] The conductors used are metal wires, particularly copper wires. Copper wires are coated with an enamel coating to create electrical wires, which are used in industrial and household motors, transformers, coils, and the like.

[0104] With regard to the insulating resin composition of the present invention, insulating coated conductors can be manufactured by a method of coating copper wire with enamel coating or by directly coating copper wire with insulating resin composition instead of enamel coating.

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

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

[0107] Conductors coated with the insulating resin composition of the present invention have both insulating and flexible properties.

[0108] The flexibility is determined according to item 5 of JIS C 3216-3. For example, an insulated conductor with an insulating coating layer of 35 μm thickness obtained by using an insulating resin composition containing a nitrogen-containing polymer in a ratio of 4 parts by mass relative to 1 part by mass of silica preferably has a flexibility of 1d to 2d. Regarding the aforementioned flexibility, the minimum winding diameter d at which no cracking is found in the insulating film when the insulated conductor with 20% elongation is compared to the insulated conductor without elongation is determined. The minimum winding diameter at which no cracking occurs is measured in the range from the diameter (1d) to n times the diameter (nd).

[0109] Example

[0110] [Determination of SiO2 concentration]

[0111] The silica sol was placed in a crucible and dried at 150°C. The resulting gel was then calcined at 1000°C, and the calcination residue was measured to calculate the result.

[0112] [Determination of average primary particle size (nitrogen adsorption method particle size)]

[0113] The specific surface area of ​​powder dried at 300°C using a Monosorb MS-16 (manufactured by YuasaIonics Co., Ltd.) specific surface area measuring device was determined.

[0114] [Moisture content determination]

[0115] The result was obtained using Karl Fischer titration.

[0116] [Viscosity Measurement]

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

[0118] [Determination of cationic components in organosols]

[0119] Add pure water to the sol to prepare a silica concentration of 3% by mass. Add 200 μL of 1N nitric acid aqueous solution to 8 g of diluted sol and let stand overnight. Centrifuge the resulting liquid using Merck's Ammicon Ultra-15 10k (molecular weight cutoff 10,000) at 5000 rpm for 30 minutes. Dilute the filtrate 10 times with pure water and determine its composition by cation exchange chromatography.

[0120] [Determination of Anionic Components in Organosols]

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

[0122] Dissolve 50 μL of the organosilica sol sample 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). Centrifuge using a Model 6200 (Kubota Corporation) (centrifugation conditions: 10000 rpm, 10 min, 15°C). Transfer 475 μL of the resulting supernatant to a vial for electrophoresis analysis. Add 25 μL of a solution (100 ppm sodium nitrate) obtained by dissolving 1 mg sodium nitrate in 10 mL of electrophoresis buffer to the sample collected in the vial to prepare a sample for capillary electrophoresis analysis.

[0123] The following describes the pretreatment conditions for capillary columns.

[0124] Before the assay, the electrophoresis buffer was pretreated by passing it through a capillary at a pressure of 915 mbar for 20 minutes. Then, before and after each sample assay, the capillary was cleaned by sequentially passing ethanol (manufactured by Junsei Chemical Co., Ltd., premium reagent grade) through the capillary at a pressure of 915 mbar for 180 seconds, 0.1 M sodium hydroxide aqueous solution (manufactured by Fujifilm and Koden Pharmaceutical Co., Ltd., for volumetric analysis) through the capillary for 360 seconds, ultrapure water (trade name Milli-Q) through the capillary for 300 seconds, and the electrophoresis buffer through the capillary for 300 seconds.

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

[0126] • Apparatus: Capillary electrophoresis system (trade name: Agilent 7100, manufactured by Agilent Technology Co., Ltd.).

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

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

[0129] Voltage: -25kV

[0130] Electrophoresis temperature: 25℃

[0131] Electrophoresis buffer: Contains 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] Regarding the analysis, the peak area of ​​nitrate ions is normalized (the peak area of ​​organic acid ions divided by the peak area of ​​sodium nitrate) for quantification.

[0134] [Solid components of polyamic acid]

[0135] After the polyamic acid was placed into an aluminum cup, it was fired at 200°C. The firing residue was measured and calculated.

[0136] (Example 1)

[0137] 412 g of water-dispersed silica sol (commercial 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 round-bottom flask. The solvent was evaporated and distilled off using a rotary evaporator at a reduced pressure of 150–70 Torr and a bath temperature of 80–90 °C. At the same time, DMAC (dimethylacetamide) was supplied to replace the dispersion medium of the sol with DMAC, thereby obtaining DMAC-dispersed silica sol (R1) (silica concentration 30.0% by mass, water 6.7% by mass, viscosity 790 mPa·s). 172.3 g of the obtained sol was placed into a 500 mL round-bottom flask. While stirring the sol with a magnetic stirrer, 0.058 g of acetic acid was added. The mixture was kept at room temperature for 2 hours to obtain DMAC dispersed silica sol (1) (silica concentration 30.0% by mass, water 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 round-bottom flask. While stirring the sol with a magnetic stirrer, 0.1514 g of 4 N sodium hydroxide aqueous solution was added. Then, while evaporating and distilling off the solvent using a rotary evaporator at 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 wt%, water content 3.4 wt%, viscosity 23 mPa·s). Then, additional DMAC was added and replaced using a rotary evaporator at 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 wt%, water content 3.4 wt%, viscosity 23 mPa·s, Na ion content 82 ppm, acetic acid content 370 ppm).

[0140] (Example 3)

[0141] 616g of water-dispersed silica sol (trade name PL-2L, average primary particle size 17nm, silica concentration 19% by mass, manufactured by Fuso Chemical Industry Co., Ltd.) was placed in a 2L round-bottom flask. While evaporating and distilling off the solvent using a rotary evaporator at a reduced pressure of 150–70 Torr and a bath temperature of 80–90°C, DMAC (dimethylacetamide) was added to replace the dispersion medium of the sol, resulting in 557g of DMAC-water mixed solvent-dispersed silica sol (silica concentration 21.0% by mass, water 17.3% by mass). While stirring the sol with a magnetic stirrer, 3.1g of phenyltrimethoxysilane (manufactured by Shin-Etsu Chemical Industry Co., Ltd., trade name KBM-103) was added, and the liquid temperature was maintained at 90°C for 2 hours. 282g of the obtained sol was placed into a 1L round-bottom flask, 0.075g of acetic acid was added, and then 0.26g of 4N sodium hydroxide aqueous solution was added. The mixture was stirred for 30 minutes. Then, the solvent was evaporated and distilled off using a rotary evaporator at a reduced pressure of 100-70 Torr and a bath temperature of 110°C while being supplied to DMAC, thereby obtaining DMAC dispersed silica sol (3) (silica concentration 30.3% by mass, water 0.9% by mass, viscosity 8 mPa·s, Na ion content of 120 ppm and acetic acid content of 400 ppm in the sol).

[0142] (Example 4)

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

[0144] (Example 5)

[0145] 140g of methanol-dispersed silica sol (commercial name: methanol silica sol, average primary particle size: 12nm, silica concentration: 30% by mass, manufactured by Nissan Chemical Co., Ltd.) was placed in a 0.5L round-bottom flask. 3.3g of phenyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., commercial name: KBM-103) was added, and the solution was kept at 60°C for 5 hours. Then, 6.8g of dimethylpolysiloxane (manufactured by Shin-Etsu Chemical Co., Ltd., commercial name: KF-96L 0.65cs) was added, followed by 14g of DMAC. The solution was kept at 60°C for 3 hours. Then, while evaporating and distilling off the solvent using a rotary evaporator at a reduced pressure of 450–110 Torr and a bath temperature of 85–125 °C, DMAC is supplied to replace the dispersion medium of the sol, thereby obtaining DMAC-dispersed silica sol (5) (silica concentration 30.2% by mass, water 0.1% by mass, viscosity 7 mPa·s, Na ion content 150 ppm, acetic acid content 65 ppm, and formic acid content 87 ppm in the sol). At this time, by controlling the amount of carboxylic acid generated by the hydrolysis of DMAC within a certain range, DMAC-dispersed silica sol is obtained.

[0146] (Example 6)

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

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

[0149] (Comparative Example 1)

[0150] 412 g of water-dispersed silica sol (commercial 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 round-bottom flask. While evaporating and distilling off the solvent using a rotary evaporator at a reduced pressure of 150–70 Torr and a bath temperature of 80–90 °C, DMAC (dimethylacetamide) was supplied to replace the dispersion medium of the sol with DMAC, thereby obtaining DMAC-dispersed silica sol (R1) (silica concentration 30.0% by mass, water 6.7% by mass, viscosity 790 mPa·s). 172.3 g of the obtained sol was placed into a 500 mL round-bottom flask and stirred with a magnetic stirrer while being kept at room temperature for 2 hours to obtain DMAC dispersed silica sol (R1) (silica concentration 30.0% by mass, water 6.7% by mass, viscosity 790 mPa·s, alkali metal ions in the sol below the detection limit (less than 10 ppm), acetic acid content in the sol 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 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] 616g of water-dispersed silica sol (trade name PL-2L, average primary particle size 17nm, silica concentration 19% by mass, manufactured by Fuso Chemical Industry Co., Ltd.) was placed in a 2L round-bottom flask. The solvent was evaporated and distilled off using a rotary evaporator at a reduced pressure of 150-70 Torr and a bath temperature of 80-90°C. At the same time, DMAC (dimethylacetamide) was supplied to replace the dispersion medium of the sol with DMAC, thereby obtaining 557g of DMAC-water mixed solvent dispersed silica sol (silica concentration 21.0% by mass, water 17.3% by mass). While stirring the sol with a magnetic stirrer, 3.1 g of phenyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade 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% by mass, water 5.2% by 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).

[0155] (Comparative Example 4)

[0156] 130g of the DMAC dispersed silica sol (4) obtained in Example 4 was placed into a 500mL round-bottom flask. While stirring with a magnetic stirrer, 0.26g of acetic acid was added and kept at room temperature for 2 hours to obtain DMAC dispersed silica sol (R4) (silica concentration 30.2% by mass, water 0.3% by mass, viscosity 16mPa·s, Na ion content 200ppm, acetic acid content 1926ppm, formic acid content 39ppm).

[0157] (Synthetic Example 1) Preparation of Polyamic Acid

[0158] Polymerization was carried out using 4,4'-diaminodiphenyl ether (DDE), pyromellitic dianhydride (PMDA), NMP (N-methylpyrrolidone), and DMAC (dimethylacetamide) as solvents at 50°C with stirring to obtain polyamic acid equivalent to formula (4) (solids content 17% by mass, viscosity at 25°C 13640 mPa·s using an E-type viscometer). For the polymerization of polyamic acid, an equimolar ratio of DDE to PMDA of 1:1 was used. The resulting polyamic acid had a weight-average molecular weight of 63000. In formula (4), n represents the number of repeating units.

[0159]

Transformation 3

[0160]

[0161] (Thermal stability test of insulating resin composition)

[0162] The DMAC-dispersed silica sol obtained in Example 4 and Comparative Example 4 was mixed with the polyamic acid obtained in Synthesis Example 1 at a mass ratio of resin / SiO2 = 80 / 20 in a glass bottle. The mixture was then degassed and stirred for 20 minutes using a vacuum degassing machine (EME Corporation, trade name V-mini 300) to obtain silica-integrated polyamic acid. The initial viscosity (mPa·s) at 25°C and the viscosity (mPa·s) measured after storage at 50°C for 7 days and cooling to 25°C are shown in the table below.

[0163] Table 1

[0164] Table 1

[0165]

[0166] The silica-integrated polyamic acid obtained in Example 4 and Comparative Example 4 was coated onto a Cu plate (manufactured by AS ONE, trade name HC0536, 300mm × 300mm, 0.5mm thick) using a coating applicator (manufactured by BEVS, trade name: film coating applicator B / M150mm with film thickness adjustment function). Solvent removal and thermosetting were then performed 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 with sintered silica-integrated polyimide (film thickness: 29–32 μm). These were then cut into 5cm squares to prepare insulation test specimens.

[0167] (Determination of insulation failure life)

[0168] For plate-shaped samples measuring 50mm × 50mm and 0.5mm thick, the insulation failure life of the aforementioned insulation test specimens was determined using an insulation failure test apparatus (model YST-243WS) manufactured by YAMAYO Testing Instruments Co., Ltd., at a test temperature of 155℃ (in air), an applied voltage of 3.0kV, and a frequency of 50Hz. Regarding the electrode shape, a flat electrode (φ = 25mm) was used at the bottom, and a spherical electrode (φ = 20mm) was used at the top. Both electrodes were positioned in contact with the sample during the test. Three to four measurements were performed using an applied voltage of 3.0kV, and the average value was recorded. It should be noted that, as a blank test, only polyimide resin without silica was used as the sample, and the same measurement was performed.

[0169] Table 2

[0170] Table 2

[0171]

[0172] Compared to DMAC dispersed silica sol containing a specified amount of organic acid (such as acetic acid) in a nitrogen-containing organic solvent, the silica sol containing no organic acid (such as acetic acid) does not have a high viscosity when comparing the viscosity of the same solid components. Therefore, it has good workability when combined with nitrogen-containing polymers to form insulating resin compositions.

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

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

[0175] In this invention, the silica sol dispersed in a nitrogen-containing organic solvent containing a specified amount of organic acid (such as acetic acid) has a low viscosity. Therefore, when it is formulated with a nitrogen-containing polymer to form an insulating resin composition and then coated onto a substrate, solid components capable of maintaining insulating properties are retained, resulting in a film that can be coated onto the substrate. Consequently, the obtained insulating substrate can have a long insulation life.

[0176] Industrial availability

[0177] The silica sol containing a specified amount of organic acid (such as acetic acid) dispersed in a nitrogen-containing organic solvent has a low viscosity. Therefore, when it is formulated with a nitrogen-containing polymer to form an insulating resin composition and coated onto a substrate, it can retain the solid components that can be used to maintain the insulating properties, thus obtaining an insulating film that can be coated onto the substrate.

Claims

1. A silica sol which is a dispersion of silica particles having an average primary particle diameter of 5 to 100 nm in a nitrogen-containing organic solvent, and which contains a carboxylic acid having 1 to 3 carbon atoms at a proportion of 80 to 1500 ppm in the silica sol. The viscosity at 25°C is 3 to 500 mPa-s when the Si02 concentration is 30 mass%, The nitrogen-containing organic solvent is dimethylacetamide, dimethylformamide, or dimethylpropionamide.

2. The silica sol of 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 carboxylic acid having 1 to 3 carbon atoms is formic acid, acetic acid, or propionic acid.

4. The silica sol according to claim 1 or 2, wherein, The amount of water in the silica sol is 0.1 to 10.0 mass%.

5. The silica sol according to claim 1 or 2, which contains alkali metal ions at a proportion of 300 ppm or less, wherein, The alkali metal ion represents an alkali metal ion including lithium, sodium, and potassium.

6. The silica sol according to claim 1 or 2, wherein, The silica particles are coated with at least one silane compound selected from the group consisting of Formula (1) to Formula (3) or a hydrolyzate thereof: [Chemical 1] In formula (1), R 1 each is an alkyl group, a haloalkyl 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 anhydride group, a carboxylate group, an epoxy group, a hydroxyl group, or a cyano group, and is bonded to the silicon atom through 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 each is an alkyl group having 1 to 3 carbon atoms, or an aryl group having 6 to 30 carbon atoms and is bonded to the silicon atom through a Si-C bond, 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.

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

8. The insulating resin composition according to claim 7, wherein The mass parts of the nitrogen-containing polymer relative to 1 mass part of silica contained in the silica sol is 1 to 100.

9. The insulating resin composition according to claim 7, wherein The nitrogen-containing polymer is a polyimide, a polyamide, a polyamide acid, a polyamide-imide, a polyether-imide, or a polyester-imide.

10. An insulating resin composition, wherein, The viscosity (mPa-s) of the silica-complexed polyamide acid prepared by mixing the silica sol according to claim 1 and a polyamide acid formed from 4,4'-diamino diphenyl ether (DDE) and pyromellitic anhydride (PMDA) as a resin in a mass ratio of resin / Si02 = 80 / 20 after the silica-complexed polyamide acid is stored at 50°C for 7 days is 1.20 times or less the viscosity before storage.

11. An insulating resin composition, wherein, The Cu plate sintered with the silica-complexed polyamide-imide is coated with a film having a thickness of 29 to 32 μm, and the insulation breakdown life at a test temperature of 155°C, an applied voltage of 3.0 kV, and a frequency of 50 Hz in air is 50 minutes or more.

12. An insulating coated wire insulated with the insulating resin composition according to any one of claims 7 to 11.

13. A method for producing the silica sol according to claim 1 or 2, comprising the following (A) step to (B) step: (A) Step: 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; and (B) Step: adjusting the silica sol obtained in the (A) step to contain a carboxylic acid having 1 to 3 carbon atoms at a proportion of 80 to 1500 ppm, and replacing with a nitrogen-containing organic solvent.

14. The method for producing a silica sol according to claim 13, wherein (C) Step of additionally adding at least one silane compound of Formula (1) to Formula (3) according to claim 6 in the (B) step or after the end of the (B) step.

15. The production method of the insulating resin composition according to any one of claims 7 to 11, comprising a (D) step of mixing the silica sol according to claim 1 and the nitrogen-containing polymer.

16. The method of producing an insulating resin composition according to claim 15, wherein The (D) step is further added a (E) step of removing a part or all of the nitrogen-containing organic solvent from the insulating resin composition.

Images