Hydrophobic silica sol, coating composition, and method for producing same

Abstract

The present invention addresses the problem of providing: a silica sol in which silica particles are dispersed in a nitrogen-containing solvent for mixing with a polyimide-based or polyamide-based polar resin with good compatibility; an insulating resin composition obtained by mixing these silica sol and a resin; and an insulating coated conductive wire which has a long insulation life for a long period of time. [Solution] A silica sol in which silica particles having an average primary particle diameter of 5-100 nm are dispersed in a nitrogen-containing solvent, said silica particles containing groups (a), (b), and (c) on at least some of the particle surfaces thereof, the groups (a), (b), and (c) are bonded to the surface of the silica particles in such a manner that the total of the groups (a) and (b) is 1.0-8.0 / nm2 per surface area of the silica particles per 1 square nm, the group (c) is 0.3-2.0 / nm2 per surface area of the silica particles per 1 square nm, and (the total of the groups (a) and (b)) / (group (c)) is 2-20 in terms of molar ratio. The group (a) is an aromatic ring or an organic group (a) containing an aromatic ring, the group (b) is an alkyl group (b) having 1-3 carbon atoms, and the group (c) is an alkoxy group (c) having 1-3 carbon atoms. An insulating resin composition containing a silica sol and a nitrogen-containing polymer. The insulating coated wire is obtained by insulating and coating a wire with an insulating coating layer formed from an insulating resin composition.

Description

Technical Field

[0001] The present invention relates to a hydrophobic silica sol dispersed in a nitrogen-containing solvent, a coating composition using the hydrophobic silica sol, and methods for producing the same. Background Art

[0002] A method is disclosed for reacting hydroxyl groups on the surfaces of inorganic oxide particles, such as silica, with alcohols to introduce alkoxysilyl groups for organicization, thereby obtaining an inorganic oxide sol dispersed in an organic solvent such as toluene. This method discloses reacting phenyltrimethoxysilane with a methanol-dispersed silica sol to produce a silica sol dispersed in a toluene solvent (see Patent Document 1).

[0003] Furthermore, there is disclosed a silica sol in which a methanol-dispersed silica sol is subjected to solvent replacement with acetonitrile to obtain an acetonitrile / methanol mixed solvent-dispersed silica sol, and then phenyltrimethoxysilane is reacted therewith (see Patent Document 2).

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

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

[0006] Prior art literature

[0007] Patent Literature

[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] The present invention provides a silica sol in which silica particles are dispersed in a nitrogen-containing solvent that is compatible with polyimide and polyamide-based polar resins. Furthermore, the present invention provides a resin composition obtained by mixing this silica sol with a resin, and an insulating resin composition that, when prepared as an insulating resin composition, provides an insulated coated wire capable of maintaining a long, high insulation life.

[0014] Means for solving problems

[0015] In the present invention, as a first aspect, a silica sol is provided, wherein silica particles having an average primary particle size of 5 to 100 nm are dispersed in a nitrogen-containing solvent, wherein the silica particles contain (a) groups, (b) groups, and (c) groups on at least a portion of the particle surface, and the number of (a) groups, (b) groups, and (c) groups, such that the total number of (a) groups and (b) groups is 1.0 to 8.0 groups / nm per square nm of the surface area of ​​the silica particles. 2 The number of the group (c) above is 0.3 to 2.0 per square nm of the surface area of ​​the silica particles. 2 , (the total of (a) groups and (b) groups) / ((c) groups) are bonded to the surface of the silica particles at a molar ratio of 2 to 20, the (a) group is an aromatic ring or an organic group containing an aromatic ring (a), the (b) group is an alkyl group having 1 to 3 carbon atoms (b), and the (c) group is an alkoxy group having 1 to 3 carbon atoms (c), According to a second aspect, the silica sol according to the first aspect is a silica particle having at least a portion of its particle surface coated with a hydrolyzate of a silane compound represented by formula (1) in the form of an aromatic ring or an organic group (a) containing an aromatic ring.

[0016] (In formula (1), R 1 is an aromatic ring or an organic group containing an aromatic ring, and represents a group bonded to a silicon atom via a Si-C bond, R 2 represents an alkoxy group, and a is an integer of 1 to 3. )

[0017] According to a third aspect, the silica sol according to the first or second aspect is a silica particle having at least a portion of its particle surface coated with a hydrolyzate of a silane compound represented by formula (2) or (3) in the form of an alkyl group (b) having 1 to 3 carbon atoms.

[0018] (In formula (2) and formula (3), R 3 and R 5 Each is an alkyl group having 1 to 3 carbon atoms and represents a group bonded to a silicon atom via a Si-C bond, R 4 and R 6 Each represents an alkoxy 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.

[0019] According to a fourth aspect, in the silica sol according to any one of the first to third aspects, the silica particles are silica particles containing aluminum atoms. According to a fifth aspect, in the silica sol according to the fourth aspect, the aluminum atoms are present in the silica particles as a whole at a ratio of 10 to 10,000 ppm / SiO2 in terms of Al2O3. As a sixth aspect, in the silica sol according to any one of the first to fifth aspects, the silica particles are subjected to saturated adsorption in an environment where the humidity is continuously changed from 10% to 90% at 23° C., and the water vapor adsorption amount (mg) of the silica particles is per 100 m 2 The surface of the silica particles becomes 70 mg or less of silica particles, According to a seventh aspect, in the silica sol according to any one of the first to sixth aspects, the nitrogen-containing solvent is an amide solvent. According to an eighth aspect, in the silica sol according to any one of the first to sixth aspects, the nitrogen-containing solvent is dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or N-ethylpyrrolidone. According to a ninth aspect, a coating composition is provided, comprising the silica sol according to any one of the first to eighth aspects and a nitrogen-containing polymer. According to a tenth aspect, in the coating composition according to the ninth aspect, the nitrogen-containing polymer is present in an amount of 1 to 100 parts by mass per part by mass of the silica particles contained in the silica sol. According to an eleventh aspect, in the coating composition according to the ninth aspect or the tenth aspect, the nitrogen-containing polymer is any one of polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, and polyesterimide. According to a twelfth aspect, an insulating resin composition comprises the silica sol according to any one of the first to eighth aspects and a nitrogen-containing polymer. According to a 13th aspect, in the composition according to the 12th aspect, the amount of the nitrogen-containing polymer is 1 to 100 parts by mass per 1 part by mass of silica contained in the silica sol. According to a fourteenth aspect, in the composition according to the twelfth aspect or the thirteenth aspect, the nitrogen-containing polymer is any one of polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, and polyesterimide. According to a fifteenth aspect, an insulating coated conductive wire is provided, wherein the conductive wire is insulatingly coated with an insulating coating layer formed from the insulating resin composition according to any one of the tenth to twelfth aspects. According to a sixteenth aspect, the insulated coated wire according to the fifteenth aspect is provided, wherein the insulating coating has a thickness of 35 μm, a silica particle content of 20% by mass, and a flexibility of 1d to 2d. The flexibility is determined by determining the minimum winding diameter d at which no cracking is observed in the insulating coating of the insulating coated wire after 20% elongation and the insulating coated wire after no elongation, wherein the minimum winding diameter at which no cracking occurs is measured within a range from the insulating coating's diameter (1d) to n times the insulating coating's diameter (nd). According to a seventeenth aspect, the insulated coated wire according to the fifteenth or sixteenth aspect is provided, wherein the thickness of the insulating coating is 35 μm, the amount of silica particles mixed is 20% by mass, and the insulation life measured under conditions of a pulsed applied voltage of 1.5 kVp (bipolar, 10 kHz rectangular wave) is 80 hours or longer. The insulation life is defined as the time until an insulation breakdown detection current of 5 mA is detected when a voltage is applied between two wires of the insulated coated wire at a boosted voltage of 500 V / s, maintained at a distance of 50 mm between the two wires and at a temperature of 40°C. As an eighteenth aspect, a method for producing a silica sol according to any one of the first to eighth aspects comprises the following steps (A) to (C): Step (A): preparing a silica sol in which silica particles having an average primary particle size of 5 to 100 nm are dispersed in an alcohol solvent having 1 to 3 carbon atoms; Step (B): adding the silane compound represented by the above formula (1) and the silane compound represented by the above formula (2) or the above formula (3) to the silica sol obtained in step (A); and Step (C): a step of replacing the dispersion medium of the silica sol obtained in step (B) from an alcohol solvent having 1 to 3 carbon atoms with a nitrogen-containing solvent. According to a nineteenth aspect, in the method for producing a silica sol according to the eighteenth aspect, the silica sol used in the step (A) is a silica sol obtained by replacing the aqueous medium solvent of the aqueous silica sol with an alcohol having 1 to 3 carbon atoms. According to a 20th aspect, there is provided the method for producing a silica sol according to the 18th aspect, wherein the silica sol used in the step (A) is a silica sol obtained by replacing the aqueous medium solvent of each of the aqueous silica sol (a-1) and the aqueous silica sol (a-2) with an alcohol having 1 to 3 carbon atoms, wherein the aqueous silica sol (a-1) is obtained by adding an alkali metal aluminate to an aqueous active silicic acid solution and heating the mixture, and wherein the aqueous silica sol (a-2) is obtained by adding an alkali metal aluminate to an aqueous silica sol and heating the mixture. According to a 21st aspect, there is provided the method for producing a silica sol according to any one of the 18th to 20th aspects, wherein the silica sol used in the step (A) is a silica sol obtained by replacing the aqueous medium solvent of an aqueous silica sol subjected to a hydrothermal treatment at 180 to 240° C. for 0.1 to 10 hours with an alcohol having 1 to 3 carbon atoms; According to a 22nd aspect, a method for producing an insulating resin composition according to any one of the 12th to 14th aspects is provided, comprising steps (A) to (E). Step (A): preparing a silica sol in which silica particles having an average primary particle size of 5 to 100 nm are dispersed in an alcohol solvent having 1 to 3 carbon atoms; Step (B): adding the silane compound represented by the above formula (1) and the silane compound represented by the above formula (2) or the above formula (3) to the silica sol obtained in step (A); (C) step: a step of replacing the dispersion medium of the silica sol obtained in the (B) step from an alcohol solvent having 1 to 3 carbon atoms to a nitrogen-containing solvent; Step (D): a step of mixing the silica sol in which the silica particles obtained in step (C) are dispersed in a nitrogen-containing solvent with a nitrogen-containing polymer; and Step (E): A step of removing part or all of the nitrogen-containing solvent from the silica sol obtained in step (D).

[0020] Effects of the Invention

[0021] In order to maintain the insulating properties of insulating resin compositions and cured products thereof for a long period of time, the insulating resin compositions and cured products thereof themselves must have low hygroscopicity. In order to suppress dielectric breakdown in insulating resin compositions and cured products thereof, the insulating resin compositions are often incorporating inorganic oxide particles, such as silica particles. Therefore, in order to ensure that insulating resin compositions and cured products thereof have low hygroscopicity, the inorganic oxide particles (silica particles) contained in the insulating resin compositions themselves must also have low hygroscopicity.

[0022] In order to reduce the hygroscopicity of silica particles, it is effective to coat the surface of the silica particles with an aromatic ring group or an organic group containing an aromatic ring group and a hydrophobic alkyl group.

[0023] On the other hand, in order to mix the silica particles with the nitrogen-containing polymer in a highly dispersible state and obtain silica particles highly dispersed in the nitrogen-containing polymer, it is preferable to mix the silica particles with the nitrogen-containing polymer in the form of a silica sol. When mixing a highly polar nitrogen-containing polymer with the silica sol, the dispersion medium of the silica sol is preferably also a highly polar organic solvent. For example, amide-based nitrogen-containing solvents such as dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or N-ethylpyrrolidone can be used. It has been found that when a nitrogen-containing solvent is used as the dispersion medium, the hydrophobic silica particles have a hydrophobic aromatic ring or an organic group containing an aromatic ring (a), an alkyl group having 1 to 3 carbon atoms (b), and an alkoxy group having 1 to 3 carbon atoms (c) that enhances compatibility with the nitrogen-containing solvent, thereby forming a silica sol that can be stably dispersed in the nitrogen-containing solvent.

[0024] The present invention is a silica sol in which silica particles are dispersed in a nitrogen-containing solvent. The silica particles contain (a) groups, (b) groups, and (c) groups, and the total number of (a) groups, (b) groups, and (c) groups relative to the surface area of ​​the silica particles is 1.0 to 8.0 groups / nm. 2 The number of the group (c) above is 0.3 to 2.0 per square nm of the surface area of ​​the silica particles. 2 The (a) group and the (b) group are combined in a molar ratio of 2 to 20, 2 to 15, 2 to 10, or 2 to 7, wherein the (a) group is an aromatic ring or an organic group containing an aromatic ring (a), the (b) group is an alkyl group (b) having 1 to 3 carbon atoms, and the (c) group is an alkoxy group (c) having 1 to 3 carbon atoms. Thus, the silica sol using a nitrogen-containing solvent as a dispersion medium can be mixed with the nitrogen-containing polymer with good compatibility, enabling the production of a stable insulating resin composition. When an insulating coated wire is produced using the insulating resin composition, the components are uniformly distributed throughout the insulating resin film, thereby suppressing the occurrence of high-voltage breakdown of the insulating coating layer due to component inhomogeneity, and achieving a long and long insulation life for the insulating coated wire. DETAILED DESCRIPTION

[0025] The present invention provides a silica sol in which silica particles are dispersed in a nitrogen-containing solvent. The silica sol 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 solvent. The silica particles contain (a) groups, (b) groups, and (c) groups on at least a portion of the particle surface. The total number of the (a) groups, (b) groups, and (c) groups relative to 1 square nm of the surface area of ​​the silica particles is 1.0 to 8.0 groups / nm. 2 1.0~6.0 / nm2 1.0~4.0 / nm 2 2.0~6.0 / nm 2 2.0~4.0 / nm 2 or 2.5~4.0 / nm 2 The number of the group (c) above is 0.3 to 2.0 per square nm of the surface area of ​​the silica particles. 2 , 0.3~1.8 / nm 2 , 0.3~1.5 / nm 2 , 0.5~1.5 / nm 2 or 0.4~1.0 / nm 2 , (the total of (a) groups and (b) groups) / ((c) groups) are bonded to the surface of the silica particles at a molar ratio of 2 to 20, 2 to 15, 2 to 10, 2 to 6.5, or 2 to 7, the (a) group is an aromatic ring or an organic group (a) containing an aromatic ring, the (b) group is an alkyl group (b) having 1 to 3 carbon atoms, and the (c) group is an alkoxy group (c) having 1 to 3 carbon atoms. By containing an aromatic ring or an organic group (a) containing an aromatic ring on at least a part of the surface of the silica particles, the dispersibility in a nitrogen-containing solvent for mixing with a polar resin (nitrogen-containing polymer) of a polyimide or polyamide system with good compatibility is improved. By the total of the (a) group and the (b) group being 1.0 to 8.0 groups / nm per 1 square nm of the surface area of ​​the silica particles. 2 The number of the group (c) above is 0.3 to 2.0 per square nm of the surface area of ​​the silica particles. 2 The silica particles are bonded to the surface of the silica particles at a molar ratio of (total of (a) groups and (b) groups) / ((c) groups) of 2 to 20, thereby making the silica particles low in hygroscopicity and improving the moisture resistance of the insulating resin composition containing the silica particles.

[0026] Furthermore, the number of the groups (a) bonded to the surface of the silica particles may be 0.2 / nm. 2 Above or 0.2~2.0 / nm 2 or 0.2~1.5 / nm 2 or 0.2~1.0 / nm 2 The range of (b) groups can be 1.0 to 6.0 per nm. 2 or 1.0~5.0 / nm 2 or 1.0~4.0 / nm 2 range.

[0027] The average primary particle size of the silica particles of the present invention can be determined by using the specific surface area (S) measured by a nitrogen adsorption method (BET method).N2 ) The specific surface area diameter thus calculated is used as the particle diameter (nm). For example, the specific surface area diameter (average primary particle diameter: D (nm)) is the specific surface area S measured by the nitrogen adsorption method (BET method). N2 (m 2 / g), and the primary particle diameter calculated by the formula D (nm) = 2720 / S N2 refers to the particle diameter of spherical silica particles after conversion.

[0028] In addition, the silica particles contained in the silica sol of the present invention have good dispersibility in a nitrogen-containing solvent, and the particle diameter measured by the dynamic light scattering method (DLS method) in the nitrogen-containing solvent shows a range of 5 to 100 nm or 10 to 70 nm.

[0029] The nitrogen-containing solvent used in the present invention has at least a functional group containing a nitrogen atom. Examples of the functional group having a nitrogen atom include an amino group, a nitro group, a cyano group, etc. 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 suitable, and a chain structure and a cyclic structure can be cited. Examples of the nitrogen-containing functional group include an amino group, a nitro group, a cyano group, but an amino group is preferably used. The amino group and the carbonyl group may be adjacent or may be present via a carbon atom, and can be used as an amide bond, for example, and an amide-based solvent is preferably used.

[0030] Specific examples of the nitrogen-containing solvent include, for example, dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, tetramethylurea, hexamethylphosphoric triamide, dimethylacrylamide, acrylylmorpholine, 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.

[0031] Furthermore, preferred examples of the nitrogen-containing solvent include dimethylacetamide, dimethylformamide, N-methylpyrrolidone, and N-ethylpyrrolidone.

[0032] As long as the effects of the present invention are not impaired, other solvents can be contained in the nitrogen-containing solvent.

[0033] That is, the nitrogen-containing solvent can be contained in the total solvent 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 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.

[0034] Examples of other solvents include water, ketone solvents, ester solvents, alcohol solvents, glycol ether solvents, hydrocarbon solvents, halogen solvents, ether solvents, glycol solvents, and amine solvents.

[0035] Examples thereof 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, isopropyl alcohol, 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; hydrocarbon solvents such as benzene, toluene, xylene, n-hexane, and cyclohexane; halogen solvents such as dichloromethane, trichloroethylene, and perchloroethylene; Ether solvents such as alkane, 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.

[0036] In the present invention, silica particles can be coated with the silane compound represented by formula (1) or a hydrolyzate thereof in the form of an aromatic ring or an organic group (a) containing an aromatic ring.

[0037] In formula (1), R 1 is an aromatic ring or an organic group containing an aromatic ring, and represents a group bonded to a silicon atom via a Si-C bond, R 2 represents an alkoxy group, and a is an integer of 1 to 3. Examples of the aromatic ring include phenyl, naphthyl, anthracenyl, and pyrenyl. The hydrogen atoms of these aromatic ring groups may be substituted with hydrophobic groups such as alkyl, aryl, and alkenyl groups. 2 represents an alkoxy group, and a is an integer of 1 to 3.

[0038] In the present invention, silica particles can be coated with a silane compound represented by formula (2) or formula (3) or a hydrolyzate thereof in the form of an alkyl group (b) having 1 to 3 carbon atoms.

[0039] In formula (2) and formula (3), R 3 and R 5 Each is an alkyl group having 1 to 3 carbon atoms and represents a group bonded to a silicon atom via a Si-C bond, R 4 and R 6 Each represents an alkoxy 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.

[0040] Examples of the alkoxy group include alkoxy groups having a linear, branched, or cyclic alkyl moiety having 1 to 10 carbon atoms, such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, and tert-butoxy.

[0041] Specific examples of the silane compound represented by formula (1) include phenyltrimethoxysilane, phenyltriethoxysilane, and phenylmethyldimethoxysilane.

[0042] The silane compounds represented by the above formula (2) and formula (3) are preferably compounds that can form trimethylsilyl groups on the surfaces of silica particles.

[0043] Examples of these compounds include the following.

[0044]

[0045] In the above formula, R 12 The alkoxy group includes, for example, a methoxy group and an ethoxy group.

[0046] As these silane compounds, silane coupling agents manufactured by Shin-Etsu Chemical Co., Ltd. can be used.

[0047] In the present invention, when the surface of silica particles is coated with at least one silane compound selected from formulas (1) to (3) or a hydrolyzed condensate thereof, the coating is achieved by adding the silane compound represented by formulas (1) to (3) to an aqueous silica sol or a silica sol dispersed in an alcohol having 1 to 3 carbon atoms, and stirring the mixture at a temperature of 10 to 60° C., typically for 1 to 10 hours. Water is required for the hydrolysis of the at least one silane compound selected from formulas (1) to (3). In the case of an aqueous silica sol, the aqueous medium serves as the water of hydrolysis. In the case of a silica sol dispersed in an alcohol having 1 to 3 carbon atoms, the water present when the aqueous medium solvent is replaced with the alcohol having 1 to 3 carbon atoms can serve as the water of hydrolysis.

[0048] The silica particles can be obtained as follows, wherein at least a portion of the surface of the particles comprises (a) groups, (b) groups, and (c) groups, and the total number of the (a) groups, (b) groups, and (c) groups is 1.0 to 8.0 groups / nm per square nm of the surface area of ​​the silica particles. 2 The number of the group (c) above is 0.3 to 2.0 per square nm of the surface area of ​​the silica particles. 2The silica particles are bonded to the surface of the silica particles in a molar ratio of (total of (a) groups and (b) groups) / ((c) groups) of 2 to 20, 2 to 15, 2 to 10, or 2 to 7, wherein the (a) groups are the aromatic ring or the organic group containing an aromatic ring (a), the (b) groups are alkyl groups having 1 to 3 carbon atoms (b), and the (c) groups are alkoxy groups having 1 to 3 carbon atoms (c). The silica particles may be coated with the (a) groups and (b) groups in a molar ratio of (a) groups:(b) groups of 1:2 to 10.

[0049] In the present invention, silica particles containing aluminum atoms can be used as the silica particles. Silica particles containing aluminum atoms at a ratio of 10 to 10,000 ppm / SiO2, calculated as Al2O3, as measured by measuring the aluminum present throughout the silica particles. The presence of aluminum atoms on the silica surface forms aluminosilicate sites, allowing the silica particles to be dispersed in highly polar nitrogen-containing solvents.

[0050] The aluminum present in the entire silica particles can be measured by a dissolution method using a hydrofluoric acid aqueous solution and expressed as Al2O3. Specifically, the aluminum present in the entire silica particles as aluminosilicate can be expressed as Al2O3 by dissolving the silica particles in a hydrofluoric acid aqueous solution and measuring the resulting solution using an ICP emission spectrometer.

[0051] The silica particles contained in the silica sol of the present invention have low hygroscopicity when the silica particles in the sol are separated and the moisture absorption is measured. The moisture absorption is the amount of moisture per 100 m2 of silica particles when saturated adsorption is performed under an environment with humidity continuously changing from 10% to 90% at 23°C. 2 The amount of water vapor adsorbed on the surface of the silica particles (mg) is preferably 0.1mg / 100m 2 The amount of water vapor adsorption on the surface of the silica particles is less than 70 mg. For example, the water vapor adsorption amount (mg) can be set to 100 m 2 The range of the silica particle surface is 1.0 to 70 mg or 5.0 to 70 mg or 5.0 to 50 mg or 5.0 to 40 mg or 5.0 to 30 mg. The time until the saturated adsorption amount is reached varies depending on the adsorption amount. In the case of measuring a sample with a large adsorption amount, a long time is required. The time until the saturated adsorption amount is reached can be measured, for example, in the range of 0.1 hours to 24 hours. The confirmation of reaching the saturated adsorption amount is considered to be the range in which the increase in the adsorption amount disappears relative to the time axis. By making the above-mentioned water vapor adsorption amount (mg) per 100m 2The silica particles have a surface area of ​​1.0 to 70 mg, so that the silica particles have low hygroscopicity and can suppress dielectric breakdown of the insulating resin composition and its cured product.

[0052] The silica sol of the present invention is obtained by a production method comprising the following steps (A) to (C). Step (A): preparing a silica sol in which silica particles having an average primary particle size of 5 to 100 nm are dispersed in an alcohol solvent having 1 to 3 carbon atoms. Step (B): adding the silane compound represented by formula (1) and the silane compound represented by formula (2) or formula (3) to the silica sol obtained in step (A). Step (C): This step is to replace the dispersion medium of the silica sol obtained in step (B) from an alcohol solvent having 1 to 3 carbon atoms with a nitrogen-containing solvent.

[0053] The silica sol used in the step (A) can be a silica sol obtained by replacing the aqueous medium solvent of the aqueous silica sol with an alcohol having 1 to 3 carbon atoms.

[0054] Examples of the alcohol having 1 to 3 carbon atoms include methanol, ethanol, n-propanol, and isopropanol.

[0055] Furthermore, the silica sol used in step (A) may be a silica sol obtained by replacing the aqueous medium solvent of each of the aqueous silica sols (a-1) and (a-2) with an alcohol having 1 to 3 carbon atoms. The aqueous silica sol (a-1) is obtained by adding an alkali metal aluminate to an aqueous solution of active silicic acid and heating the mixture, and the aqueous silica sol (a-2) is obtained by adding an alkali metal aluminate to an aqueous silica sol and heating the mixture.

[0056] Examples of the aluminate include sodium aluminate and potassium aluminate. A 0.1-30% by mass aqueous solution of the aluminate can be added to the silica sol at a temperature of 20-100°C and stirred for 0.1-24 hours. By heating the silica sol containing aluminate ions at 80-300°C for 0.1-24 hours, aluminosilicate sites can be formed on the surface of the silica particles, as well as on the surface and within the silica particles.

[0057] Furthermore, the silica sol used in step (A) may be obtained by replacing the aqueous medium solvent of an aqueous silica sol hydrothermally treated at 180 to 240° C. for 0.1 to 10 hours with an alcohol having 1 to 3 carbon atoms, regardless of whether or not it contains a predetermined amount of aluminate ions.

[0058] The silica sol obtained in step (A) may be subjected to cation exchange or anion exchange as needed.

[0059] Step (B) is a step of adding a silane compound represented by formula (1) (tentatively referred to as silane compound A) and a silane compound represented by formula (2) or formula (3) (tentatively referred to as silane compound B) to the silica sol obtained in step (A). The order of adding the silane compound A and the silane compound B can be any order. For example, the silane compound represented by formula (1) (silane compound A) or its hydrolysis-condensation product can be added after the silica particles are coated with the silane compound represented by formula (1) (silane compound A) or its hydrolysis-condensation product.

[0060] In step (C), the dispersion medium of the silica sol obtained in step (B) can be replaced from the alcohol solvent having 1 to 3 carbon atoms to a nitrogen-containing solvent. This solvent replacement can be performed using an evaporator or UF concentration. After the solvent replacement, the silica concentration in the silica sol can be adjusted to 5 to 50% by mass or 10 to 30% by mass.

[0061] In step (C), the nitrogen-containing solvent may be contained in a ratio of 50 to 100 volume%, 90 to 100 volume%, 98 to 100 volume%, or 99 to 100 volume% of the total solvent, and other solvents may be contained in a ratio of 0 to less than 50 volume%, 0 to less than 10 volume%, 0 to less than 2 volume%, or 0 to less than 1 volume%. As other solvents, water and alcohols having 1 to 3 carbon atoms dispersed in the silica sol in step (A) may be contained within the above ranges, as long as the effect is not impaired.

[0062] The nitrogen-containing solvent is an amide-based solvent. Examples of the nitrogen-containing solvent include dimethylacetamide, dimethylformamide, N-methylpyrrolidone, and N-ethylpyrrolidone.

[0063] The silica sol containing the nitrogen-containing solvent of the present invention as a dispersion medium is combined with a nitrogen-containing polymer to obtain a coating composition (resin varnish).

[0064] Furthermore, the silica sol containing the nitrogen-containing solvent of the present invention as a dispersion medium is combined with a nitrogen-containing polymer to obtain an insulating resin composition (resin varnish).

[0065] The insulating resin composition (resin varnish) may further include steps (D) and (E) in addition to the above-mentioned steps (A) to (C). Step (D): a step of mixing the silica sol in which the silica particles obtained in step (C) are dispersed in a nitrogen-containing solvent with a nitrogen-containing polymer. Step (E): A step of removing part or all of the nitrogen-containing solvent from the silica sol obtained in step (D).

[0066] Examples of combinations of nitrogen-containing polymers and silane compounds for coating silica particles include the following: A coating composition can be prepared by dispersing silica particles coated with phenyl groups derived from phenyltrimethoxysilane as a silane compound and trimethylsilyl groups derived from hexamethyldisiloxane as a silane compound in dimethylacetamide (DMAC), a nitrogen-containing solvent, in a silica sol, and further combining the nitrogen-containing polymer.

[0067] The coating composition can be used as an insulating resin composition.

[0068] The coating composition, insulating resin composition, or other resin varnish can be obtained, wherein the nitrogen-containing polymer is present in an amount of 1 to 100, 1 to 50, or 1 to 10 parts by mass per 1 part by mass of the silica particles contained in the silica sol. Examples of the nitrogen-containing polymer include polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, and polyesterimide.

[0069] The insulating resin composition can be applied to a conductor requiring insulation and then cured by heating at a temperature at which the solvent evaporates, thereby forming an insulating film (insulating coating) on ​​the conductor surface. The heating temperature for removing the solvent is determined by the temperature and pressure; at normal pressure, the heating temperature is approximately 150°C to 300°C, and for imidization of the resin, the heating temperature is approximately 150°C to 400°C.

[0070] Examples of the conductor include metal wires, and copper wires are particularly useful. Copper wires are coated with enamel to form electric wires, which are used in industrial and household motors, transformers, coils, and the like.

[0071] The insulated coated conductive wire can be produced by coating a varnish-coated copper wire with an insulating coating formed from the insulating resin composition of the present invention or by directly coating a copper wire with an insulating coating formed from the insulating resin composition instead of the varnish.

[0072] The insulating resin composition is obtained by mixing a nitrogen-containing polymer at a ratio of 1 to 100, 1 to 50, or 1 to 10 parts by mass with respect to 1 part by mass of silica particles contained in the silica sol.

[0073] The insulating resin composition is obtained by mixing and stirring the silica sol and the polymer using a mixer or a disperser. Additives may be added during the preparation as needed.

[0074] The insulating coating layer formed from the insulating resin composition of the present invention has insulating properties and flexibility.

[0075] Flexibility is measured according to JIS C 3216-3, Item 5. An insulated coated wire having an insulating coating layer adjusted to a thickness of 35 μm and containing 20% ​​silica particles using an insulating resin composition has a flexibility of 1d to 2d. The flexibility is determined by determining the minimum winding diameter (d) at which no cracks are observed in the insulation coating of the insulated coated wire after 20% elongation and for the insulated coated wire without elongation. The minimum winding diameter at which no cracks occur is measured within a range from the original diameter (1d) to n times the original diameter (nd).

[0076] The dielectric breakdown voltage (BDV) is measured in accordance with JIS C 3216-5, Section 4. The BDV (absolute dry) of an insulated wire having an insulating coating layer adjusted to a thickness of 35 μm and containing 20% ​​by mass of silica particles, when subjected to a 50 Hz AC voltage, is 42% or higher, or 42% to 90%, 42% to 70%, 42% to 60%, or 43% to 60%. The dielectric breakdown voltage is the voltage at which a dielectric breakdown detection current of 5 mA is detected after applying a boost voltage of 500 V / s with a distance of 50 mm between the two wires of the insulated wire. The BDV (absolute dry) is the value measured after drying the insulated wire at 120°C for 30 minutes. The BDV (absolute dry) is the value measured after storing the insulated wire at 40°C and 95% relative humidity for 72 hours.

[0077] Insulation properties were measured in accordance with JIS C 3216-5, Section 4. The insulation life of an insulated coated wire having an insulating coating layer adjusted to a thickness of 35 μm and containing 20% ​​silica particles using an insulating resin composition, measured under conditions of a pulsed voltage of 1.5 kVp (bipolar, 10 kHz rectangular wave), was 80 hours or longer, typically 80 to 1000 hours or 100 to 600 hours. The insulation life is defined as the time it takes for a voltage of 500 V / s to be applied between the two wires of the insulated coated wire, maintained at a distance of 50 mm and at a temperature of 40°C, to detect a dielectric breakdown current of 5 mA.

[0078] Example

[0079] (Analysis Method)

[0080] 〔Determination of SiO2 concentration〕

[0081] The silica sol was placed in a crucible and dried at 150° C., and the obtained gel was calcined at 1000° C. for 30 minutes, and the calcined residue was measured and calculated.

[0082] [Measurement of average primary particle size (nitrogen adsorption method particle size)]

[0083] The silica sol was dried at 300°C and pulverized in a mortar. The sample was then heated at 250°C for 2 hours to prepare a measurement sample. The specific surface area of ​​the sample was measured using a Monosob MS-16 (manufactured by Yuasa Ionics Co., Ltd.). The average primary particle size was calculated using the following formula.

[0084] Average primary particle size (nm) = 2720 / specific surface area (m 2 / g)

[0085] 〔Determination of moisture〕

[0086] It was obtained by Karl Fischer titration.

[0087] pH measurement

[0088] The pH was measured using a pH meter (manufactured by Toa DiKeKe Co., Ltd.).

[0089] [Determination of viscosity]

[0090] The viscosity of the silica sol was measured using a B-type rotational viscometer (manufactured by Toki Sangyo Co., Ltd.).

[0091] [Determination of particle size by dynamic light scattering (DLS)]

[0092] The particle size was measured using a dynamic light scattering particle size analyzer (manufactured by Marubank, trade name: Zeta Sizerano).

[0093] 〔Determination of total aluminum content〕

[0094] Metal element analysis was performed using an ICP emission spectrometer (manufactured by Rigaku Corporation, trade name CIROS120 EOP). The silica gel obtained by drying the silica sol was decomposed with a hydrofluoric acid solution and then dissolved with an aqueous nitric acid solution. The aluminum content in the resulting aqueous solution was measured using an ICP emission spectrometer and divided by the mass of the silica to determine the amount of aluminum present in the entire silica particles (Al2O3 / SiO2) (ppm).

[0095] [Determination of carbon content and alkoxy group bonding amount]

[0096] (1) 3 mL of silica sol dispersed in an organic solvent was added to a 30 cc centrifuge tube, and 20 mL of toluene was added.

[0097] (2) After centrifugation (10,000 rpm x 30 minutes), the supernatant was removed.

[0098] (3) After adding 4 mL of acetone to redissolve the gel, 10 mL of toluene and 4 mL of hexane were added, and centrifugation was performed (10,000 rpm×30 minutes).

[0099] (4) After further performing (2) to (3) again, the supernatant was removed.

[0100] (5) The obtained gel was vacuum-dried at 60° C., and the obtained powder was pulverized in a mortar and dried at 150° C. for 2 hours to obtain silica powder.

[0101] The carbon content of the powder obtained above was measured using an elemental analyzer (manufactured by Parkin Elmer, trade name: 2400 II CHNS / O).

[0102] 0.2 g of the powder was mixed and dissolved in 10 mL of a 0.05 N sodium hydroxide aqueous solution, and the mixture was subjected to gas chromatography to measure the amount of alkoxy groups bonded to the surface.

[0103] [Determination of phenyl and alkyl groups]

[0104] The silica powder used in the elemental analysis was subjected to NMR analysis using a nuclear magnetic resonance spectrometer (Bruker, trade name: AVANCE III500, measurement conditions: 29Si CP / MAS method). The amount of phenyl groups and alkyl groups bonded to the surface were calculated from the area ratio of the resulting NMR spectrum, the carbon content, and the amount of alkoxy groups described above.

[0105] 〔Measurement of water vapor adsorption amount〕

[0106] The silica powder used in the measurement of the amount of alkoxy groups bonded was measured using a water vapor adsorption and desorption measuring apparatus (Tiy エイ インスツルメント The water vapor saturation adsorption capacity was measured using a Japan product (trade name: Q5000 SA) (under an environment where the relative humidity varied from 10% to 90%, and the measurement temperature was 23°C).

[0107] The value obtained by the above measurement is per 100m 2 Water vapor adsorption on the surface of silica particles (mg оfwater / 100m 2 of sample).

[0108] [Solid content of polyamic acid]

[0109] The polyamic acid was placed in an aluminum cup and calcined at 200°C, and the calcination residue was measured and calculated. In this specification, the solid content refers to the content after removing the solvent component from the total components of the composition or silica sol.

[0110] (Synthesis Example 1) Preparation of polyamic acid

[0111] 4,4'-diaminodiphenyl ether (DDE), pyromellitic dianhydride (PMDA), NMP (N-methylpyrrolidone) and DMAC (dimethylacetamide) as solvents were used to carry out polymerization at 50°C under stirring to obtain a polyamic acid (solid content 17%, viscosity at 25°C measured by an E-type viscometer of 13640 mPa) corresponding to formula (3). s). Polyamic acid was polymerized using an equimolar ratio of DDE and PMDA of 1:1. The weight-average molecular weight of the resulting polyamic acid was 63,000. In formula (4), n is the number of repeating units.

[0112]

[0113] (Example 1)

[0114] Step (A): 2.0 kg of a water-dispersed silica sol (average primary particle size 12 nm, pH 9, silica concentration 20 mass %, Al2O3 concentration 0.17 mass %, manufactured by Nissan Chemical Co., Ltd.) was passed through a column at approximately 25°C filled with a hydrogen-type strongly acidic cation exchange resin, Anvarite IR-120B, at a space velocity of 5 t / h to obtain an acidic silica sol (silica concentration 20.0 mass %, pH 2.6).

[0115] 1130 g of the acidic silica sol was placed in a 2-liter glass reactor equipped with a stirrer, condenser, thermometer, and two inlets. While the sol in the reactor was boiling, methanol vapor generated in a separate boiler was continuously blown into the silica sol, slowly raising the liquid level while replacing the water with methanol. The replacement was completed when the volume of the distillate reached 9 L, yielding 1100 g of methanol-dispersed silica sol. The resulting methanol-dispersed silica sol had a silica concentration of 20.6% by mass, a water content of 1.6% by mass, and a viscosity of 2 mPa. s.

[0116] Step (B): 1000 g of the methanol sol was placed in a 2 L eggplant flask. While stirring the sol with an electromagnetic stirrer, 22.8 g of phenyltrimethoxysilane was added, and the liquid temperature was maintained at 60°C for 5 hours. Next, 46.6 g of hexamethyldisiloxane and 150 g of DMAC (dimethylacetamide) were added, and the liquid temperature was maintained at 60°C for 3 hours.

[0117] Step (C): Subsequently, DMAC was added while the solvent was evaporated and distilled off using a rotary evaporator at a reduced pressure of 450 to 110 Torr and a bath temperature of 85 to 125° C., and the dispersion medium of the sol was replaced with DMAC to obtain a DMAC-dispersed silica sol (silicon dioxide concentration 30.6% by mass, pH 4.1, viscosity (20° C.) 4 mPa sq.). s, water 0.1 mass%, methanol 0.1 mass%, dynamic light scattering particle size 26 nm, (c) group of silica particles: methoxyl group binding amount 0.6 / nm 2 , (a) group: phenyl binding amount 0.7 / nm 2 , (b) group: alkyl binding amount 2.7 / nm 2 The molar ratio of (total of a group and b group) / (c group) = 6.2, the water vapor adsorption capacity is 21.6 (mg оf water / 100m 2 of sample. The time until the saturated adsorption amount was reached was 605 minutes. ).

[0118] (Example 2)

[0119] Step (D): 2500 g of a water-dispersed silica sol (average primary particle size 12 nm, pH 3, silica concentration 33% by mass, manufactured by Nissan Chemical Industries, Ltd.) was placed in a 3 L glass reactor. While the sol was stirred with a stirrer, 65.7 g of a 10% aqueous sodium hydroxide solution was added and maintained for 3 hours.

[0120] Step (E): 2500 g of the water-dispersed silica sol was placed in a 3-liter SUS autoclave reactor and hydrothermally synthesized at 210° C. for 2.5 hours to obtain a hydrothermally treated silica sol (average primary particle size 22 nm, pH 10, silica concentration 33% by mass).

[0121] Step (F): The obtained sol was used to perform ion exchange in the same manner as in the step (A) of Example 1 to obtain an acidic silica sol (pH 3, silica concentration 30% by mass).

[0122] Step (G): The obtained acidic silica sol was subjected to solvent replacement in the same manner as in step (A) of Example 1 to obtain a methanol-dispersed silica sol. The obtained methanol-dispersed silica sol had a silica concentration of 30.5% by mass, a pH of 3.8, a water content of 1.5% by mass, and a viscosity of 4 mPa. s.

[0123] 1000 g of the methanol sol was placed in a 2 L eggplant flask. While stirring the sol with an electromagnetic stirrer, 12.4 g of phenyltrimethoxysilane was added, and the liquid temperature was maintained at 60°C for 5 hours. Next, 25.4 g of hexamethyldisiloxane and 150 g of DMAC (dimethylacetamide) were added, and the liquid temperature was maintained at 60°C for 3 hours.

[0124] Then, solvent replacement was carried out in the same manner as in step (C) of Example 1 to obtain a DMAC-dispersed silica sol (silica concentration 30.6% by mass, pH 4.7, viscosity (20° C.) 9 mPa s). s, water 0.1 mass%, methanol 0.1 mass%, dynamic light scattering particle size 27 nm, (c) group of silica particles: methoxy group binding amount 0.6 / nm 2 , (a) group: phenyl binding amount 0.4 / nm 2 , (b) group: alkyl binding amount 3.2 / nm 2 The molar ratio of (total of a group and b group) / (c group) = 5.6, and the water vapor adsorption capacity is 11.3 (mg оf water / 100m 2 of sample. The time until the saturated adsorption amount was reached was 345 minutes. ).

[0125] (Example 3)

[0126] 1000 g of the methanol-dispersed silica sol obtained in step (G) of Example 2 was placed in a 2 L eggplant flask. While stirring the sol with an electromagnetic stirrer, 31.1 g of phenyltrimethoxysilane was added, and the liquid temperature was maintained at 60°C for 5 hours. Next, 25.3 g of hexamethyldisilazane and 150 g of DMAC (dimethylacetamide) were added, and the liquid temperature was maintained at 60°C for 3 hours.

[0127] Then, solvent replacement was carried out in the same manner as in step (C) of Example 1 to obtain a DMAC-dispersed silica sol (silica concentration 30.9 mass %, pH 5.3, viscosity (20° C.) 15 mPa sq. s, water 0.1 mass%, methanol 0.1 mass%, dynamic light scattering particle size 24 nm, (c) group of silica particles: methoxyl group binding amount 0.9 / nm 2, (a) group: phenyl binding amount 1.0 / nm 2 , (b) group: alkyl binding amount 1.8 / nm 2 The molar ratio of (total of group a and group b) / (group c) = 3.0, and the water vapor adsorption capacity is 7.3 (mg оf water / 100m 2 of sample. The time until the saturated adsorption amount was reached was 255 min. ).

[0128] (Example 4)

[0129] 1000 g of methanol-dispersed silica sol (average primary particle size 45 nm, silica concentration 40% by mass, manufactured by Nissan Chemical Co., Ltd.) was placed in a 2 L eggplant-shaped flask. While stirring the sol with an electromagnetic stirrer, 20.2 g of phenyltrimethoxysilane was added, and the liquid temperature was maintained at 60°C for 5 hours. Next, 16.4 g of hexamethyldisilazane and 150 g of DMAC (dimethylacetamide) were added, and the liquid temperature was maintained at 60°C for 3 hours.

[0130] Then, solvent replacement was carried out in the same manner as in step (C) of Example 1 to obtain a DMAC-dispersed silica sol (silica concentration 30.8% by mass, pH 4.7, viscosity (20° C.) 4 mPa sq. s, water 0.1 mass%, methanol 0.1 mass%, dynamic light scattering particle size 88 nm, (c) group of silica particles: methoxy group binding amount 0.8 / nm 2 , (a) group: phenyl binding amount 1.1 / nm 2 , (b) group: alkyl binding amount 1.9 / nm 2 The molar ratio of (total of group a and group b) / (group c) = 3.8, and the water vapor adsorption capacity is 8.3 (mg оf water / 100m 2 of sample. The time until the saturated adsorption amount was reached was 210 minutes. ).

[0131] (Comparative Example 1)

[0132] 1000 g of the methanol-dispersed sol obtained in step (A) of Example 1 was placed in a 2 L eggplant-shaped flask. While stirring the sol with an electromagnetic stirrer, 15.3 g of phenyltrimethoxysilane was added, and the liquid temperature was maintained at 60°C for 1 hour. Next, 1.6 g of N,N-diisopropylethylamine was added, followed by 150 g of methyl ethyl ketone, and the liquid temperature was maintained at 60°C for 5 hours.

[0133] Then, solvent replacement was carried out in the same manner as in step (C) of Example 1 to obtain a DMAC-dispersed silica sol (silica concentration 30.6% by mass, pH 4.7, viscosity (20° C.) 6 mPa sq. s, water 0.1 mass%, methanol 0.1 mass%, dynamic light scattering particle size 21 nm, (c) group of silica particles: methoxyl group binding amount 1.0 / nm 2 , (a) group: phenyl binding amount 0.8 / nm 2 , (b) base: 0 / nm 2 The molar ratio of (total of group a and group b) / (group c) = 0.8, the water vapor adsorption capacity is 101.3 (mg оf water / 100m 2 of sample. The time until the saturated adsorption amount was reached was 855 minutes. ).

[0134] (Comparative Example 2)

[0135] 1000 g of the methanol-dispersed sol obtained in step (A) of Example 1 was placed in a 2 L eggplant-shaped flask. While stirring the sol with an electromagnetic stirrer, 38.3 g of phenyltrimethoxysilane was added, and the liquid temperature was maintained at 60°C for 1 hour. Next, 1.6 g of N,N-diisopropylethylamine was added, followed by 150 g of methyl ethyl ketone, and the liquid temperature was maintained at 60°C for 5 hours.

[0136] Then, solvent replacement was carried out in the same manner as in step (C) of Example 1 to obtain a DMAC-dispersed silica sol (silica concentration 30.3 mass %, pH 4.5, viscosity (20° C.) 5 mPa sq. s, water 0.1 mass%, methanol 0.4 mass%, dynamic light scattering particle size 27 nm, (c) group of silica particles: methoxy group binding amount 1.2 / nm 2 , (a) group: phenyl binding amount 1.2 / nm 2 , (b) base: 0 / nm 2 The molar ratio of (total of a group and b group) / (c group) = 1.0, the water vapor adsorption capacity is 81.5 (mg оf water / 100m 2 of sample. The time until the saturated adsorption amount was reached was 795 minutes.).

[0137] (Comparative Example 3)

[0138] 1000 g of water-dispersed silica sol (average primary particle size 12 nm, pH 3, silica concentration 33% by mass, manufactured by Nissan Chemical Industries, Ltd.) was subjected to solvent replacement in the same manner as in step (A) of Example 1 to obtain 1100 g of methanol-dispersed silica sol. The resulting methanol-dispersed silica sol had a silica concentration of 30.5% by mass, a pH of 4.2, a water content of 1.5% by mass, and a viscosity of 2 mPa. s.

[0139] 1000 g of the methanol-dispersed sol was placed in a 2 L eggplant-shaped flask. While stirring the sol with an electromagnetic stirrer, 56.9 g of phenyltrimethoxysilane was added, and the liquid temperature was maintained at 60°C for 1 hour. Next, 2.4 g of N,N-diisopropylethylamine was added, followed by 150 g of methyl ethyl ketone, and the liquid temperature was maintained at 60°C for 5 hours.

[0140] Then, solvent replacement was carried out in the same manner as in step (C) of Example 1 to obtain a DMAC-dispersed silica sol (silica concentration 30.5% by mass, pH 5.3, viscosity (20° C.) 5 mPa sq. s, water 0.1 mass%, methanol 0.2 mass%, dynamic light scattering particle size 15 nm, (c) group of silica particles: methoxyl group binding amount 1.0 / nm 2 , (a) group: phenyl binding amount 0.9 / nm 2 , (b) base: 0 / nm 2 The molar ratio of (total of group a and group b) / (group c) = 0.9, and the water vapor adsorption capacity is 98.2 (mg оf water / 100m 2 of sample. The time until saturated adsorption was reached was 925 minutes.). Although the silica particles contain the group (a), they do not contain the group (b), and therefore have a high water vapor adsorption capacity.

[0141] (Comparative Example 4)

[0142] 1000 g of the methanol-dispersed sol obtained in step (A) of Comparative Example 3 was placed in a 2 L eggplant flask. While stirring the sol with an electromagnetic stirrer, 46.6 g of hexamethyldisiloxane was added, and the liquid temperature was maintained at 60° C. for 3 hours.

[0143] Then, solvent replacement was carried out in the same manner as in step (C) of Example 1 to obtain a DMAC-dispersed silica sol (silica concentration 30.2% by mass, pH 4.2, viscosity (20° C.) 3 mPa sq. s, water 0.2 mass%, methanol 0.3 mass%, dynamic light scattering particle size 13 nm, (c) group of silica particles: methoxy group binding amount 0.5 / nm2 , (a) base: 0 / nm 2 , (b) group: alkyl binding amount 3.3 / nm 2 The molar ratio of (total of a group and b group) / (c group) = 6.6, and the water vapor adsorption capacity is 13.7 (mg оf water / 100m 2 The time until the saturated adsorption amount was reached was 505 minutes. The obtained DMAC-dispersed silica sol had insufficient dispersibility of the silica particles in the DMAC solvent and poor coating properties.

[0144] (Production and Evaluation of Enameled Wire)

[0145] 13 kg of the polyamic acid obtained in Synthesis Example 1 was added to a 20 L plastic container and stirred with a mechanical stirrer. 1.8 kg of an organic solvent-dispersed silica sol obtained by the same method as for the organic solvent-dispersed silica sol described in Examples 1 and 2 and 4.4 kg of DMAC were added, and stirred at room temperature for 1 hour to obtain a silica-blended polyamic acid (insulating resin composition, resin / SiO2 = 80 / 20, solid content 15%).

[0146] The silica-blended polyamic acid was applied and sintered on a copper conductor (1.0 mm in diameter) to produce an insulated wire having an insulating layer with a thickness of 35 μm.

[0147] For comparison, a copper conductor (1.0 mm diameter) was coated with a silica-blended polyamic acid mixed with the organic solvent-dispersed silica sol described in Comparative Examples 1 to 3 and sintered to produce an insulated wire having an insulation layer 32 to 35 μm thick. However, in Comparative Example 4, due to poor dispersion of the silica sol (silica particles) in the polyamic acid, no enameled wire could be produced.

[0148] The flexibility and insulation life (Vt test) of the insulated wire obtained above were evaluated. The evaluation method and conditions are shown below.

[0149] (Flexibility test)

[0150] The acceptable winding diameter without film cracking was investigated according to JIS C 3216-3 Item 5 (using enameled wire without elongation and after 20% elongation).

[0151] The flexibility test (without extension) involves winding an unstretched insulated wire around a winding rod having a diameter 1 to 10 times the conductor diameter of the insulated wire, and measuring the minimum winding diameter at which no cracks are observed in the insulating film using an optical microscope.

[0152] The flexibility test (20% elongation) was conducted by elongating the insulated wire by 20%, and then performing the same test as above (no elongation).

[0153] The results of the flexibility test are that the minimum winding diameter without cracking is its own diameter (1d), the minimum winding diameter without cracking is twice its own diameter (2d), and the minimum winding diameter without cracking is three times its own diameter (3d). The smaller the minimum winding diameter d is, the better the flexibility is.

[0154] (Dielectric breakdown voltage)

[0155] According to JIS C 3216-5, Section 4, a 50 Hz AC voltage was applied between two wires of two test pieces held 50 mm apart, and the voltage at which insulation breakdown occurred was measured. The boost voltage was 500 V / s, and the insulation breakdown test current was 5 mA.

[0156] BDV (absolute dry voltage) is a method of measuring the dielectric breakdown voltage of an insulated wire after drying it at 120° C. for 30 minutes.

[0157] BDV (hygroscopic absorption voltage) is measured after storing the insulated wire at 40°C and 95% relative humidity for 72 hours. A higher BDV (hygroscopic absorption / absolutely dry) indicates greater moisture resistance.

[0158] (Vt insulation life test)

[0159] According to JIS C 3216-5, item 4, two test pieces were prepared and placed in an environment with a temperature of 40°C. The following voltage was applied between the two lines, and the time until breakdown was measured.

[0160] Voltage: 1.5kV Frequency: 10kHz rectangular wave Pulse width: 5μs Bipolarity Pulse rise time: 80ns [Table 1]

[0161] [Table 2]

[0162] [Table 3]

[0163] The insulated wires obtained in Examples 1 and 2 had significantly longer insulation life while maintaining mechanical properties compared to the wires coated in Comparative Examples 1 to 3. Furthermore, the insulated wires obtained in Examples 1 to 4 had improved moisture resistance compared to the wire coated in Comparative Example 1.

[0164] Industrial availability

[0165] The present invention provides a silica sol in which silica particles are dispersed in a nitrogen-containing solvent that is compatible with polyimide and polyamide-based polar resins. Furthermore, the present invention provides a resin composition obtained by mixing this silica sol with a resin, and an insulating resin composition that, when prepared as an insulating resin composition, provides an insulated coated wire capable of maintaining a long, high insulation life.

Claims

1. A silica sol comprising silica particles having an average primary particle size of 5 to 100 nm dispersed in a nitrogen-containing solvent. The silica particles contain a group, b group, and c group on at least a portion of the particle surface, and the total number of a group, b group, and c group is 1.0 to 8.0 groups / nm per square nm of the surface area of ​​the silica particles. 2 The number of C groups per square nm of the surface area of ​​the silica particles is 0.3 to 2.0 / nm. 2 , (the total of group a and group b) / (group c) is bonded to the surface of the silica particles in a molar ratio of 2 to 20, the group a is an aromatic ring or an organic group a containing an aromatic ring, the group b is an alkyl group b having 1 to 3 carbon atoms, and the group c is an alkoxy group c having 1 to 3 carbon atoms.

2. The silica sol according to claim 1, wherein the silica particles are silica particles having at least a portion of their particle surfaces coated with a hydrolyzate of a silane compound represented by formula (1) in the form of an aromatic ring or an organic group containing an aromatic ring. In formula (1), R 1 is an aromatic ring or an organic group containing an aromatic ring, and represents a group bonded to a silicon atom via a Si-C bond, R 2 represents an alkoxy group, and a is an integer of 1 to 3.

3. The silica sol according to claim 1 or 2, wherein the silica particles are silica particles having at least a portion of their surface coated with a hydrolyzate of a silane compound represented by formula (2) or formula (3) in the form of an alkyl group b having 1 to 3 carbon atoms, In formula (2) and formula (3), R 3 and R 5 Each is an alkyl group having 1 to 3 carbon atoms and represents a group bonded to a silicon atom via a Si-C bond, R 4 and R 6 Each represents an alkoxy 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. 4 . The silica sol according to claim 1 , wherein the silica particles are silica particles containing aluminum atoms. 5 . The silica sol according to claim 4 , wherein the aluminum atoms are present in the entire silica particles at a ratio of 10 to 10,000 ppm / SiO 2 in terms of Al 2 O 3 .

6. The silica sol according to any one of claims 1 to 5, wherein the silica particles are subjected to saturated adsorption in an environment with humidity continuously varying from 10% to 90% at 23°C, and the amount of water vapor adsorbed by the silica particles is 2 The silica particles have a surface area of ​​70 mg or less, and the unit of the water vapor adsorption amount is mg. 7 . The silica sol according to claim 1 , wherein the nitrogen-containing solvent is an amide solvent. 8 . The silica sol according to claim 1 , wherein the nitrogen-containing solvent is dimethylacetamide, dimethylformamide, N-methylpyrrolidone or N-ethylpyrrolidone. 9 . A coating composition comprising the silica sol according to claim 1 and a nitrogen-containing polymer. 10 . The coating composition according to claim 9 , wherein the amount of the nitrogen-containing polymer is 1 to 100 parts by mass relative to 1 part by mass of the silica particles contained in the silica sol. 11 . The coating composition according to claim 9 , wherein the nitrogen-containing polymer is any one of polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide and polyesterimide. 12 . An insulating resin composition comprising the silica sol according to claim 1 and a nitrogen-containing polymer. 13 . The insulating resin composition according to claim 12 , wherein the amount of the nitrogen-containing polymer is 1 to 100 parts by mass relative to 1 part by mass of the silica particles contained in the silica sol. 14 . The insulating resin composition according to claim 12 , wherein the nitrogen-containing polymer is any one of polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, and polyesterimide. 15 . An insulated coated conductive wire, comprising a conductive wire coated with an insulating coating layer formed from the insulating resin composition according to claim 12 . 16 . The insulated coated wire according to claim 15 , wherein the insulating coating layer has a thickness of 35 μm, a blending amount of silica particles of 20% by mass, and has a flexibility of 1d to 2d, wherein: The flexibility is determined by determining the minimum winding diameter d at which no cracking is observed in the insulation film of an insulated coated wire that has been stretched 20% and an insulated coated wire that has not been stretched. The minimum winding diameter at which no cracking occurs is measured from the original diameter, i.e., 1d, to n times the original diameter, i.e., nd.

17. The insulated coated wire according to claim 15 or 16, wherein the insulating coating layer has a thickness of 35 μm and a silica particle content of 20 mass %, and the insulation life measured under the conditions of a pulsed voltage of 1.5 kVp, bipolarity, and a 10 kHz rectangular wave is 80 hours or longer. The insulation life is the time until an insulation breakdown detection current of 5 mA is detected when a voltage is applied between the two insulating coated conductors at a boost voltage of 500 V / s with the distance between the two conductors maintained at 50 mm and at a temperature of 40° C.

18. The method for producing a silica sol according to any one of claims 1 to 8, comprising the following steps A to C: Step A: preparing a silica sol in which silica particles having an average primary particle size of 5 to 100 nm are dispersed in an alcohol solvent having 1 to 3 carbon atoms; Step B: a step of adding a silane compound represented by the following formula (1) and a silane compound represented by the following formula (2) or the following formula (3) to the silica sol obtained in step A; and Step C: A step in which the dispersion medium of the silica sol obtained in step B is replaced from an alcohol solvent having 1 to 3 carbon atoms to a nitrogen-containing solvent. Silane compound represented by formula (1): In formula (1), R 1 is an aromatic ring or an organic group containing an aromatic ring, and represents a group bonded to a silicon atom via a Si-C bond, R 2 represents an alkoxy group, a is an integer from 1 to 3; Silane compound represented by formula (2) or formula (3): In formula (2) and formula (3), R 3 and R 5 Each is an alkyl group having 1 to 3 carbon atoms and represents a group bonded to a silicon atom via a Si-C bond, R 4 and R 6 Each represents an alkoxy 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. 19 . The method for producing a silica sol according to claim 18 , wherein the silica sol used in the step A is a silica sol obtained by replacing the aqueous medium solvent of the aqueous silica sol with an alcohol having 1 to 3 carbon atoms.

20. The method for producing a silica sol according to claim 18, wherein the silica sol used in step A is a silica sol obtained by replacing the aqueous medium solvent of each of aqueous silica sol a-1 or aqueous silica sol a-2 with an alcohol having 1 to 3 carbon atoms, wherein the aqueous silica sol a-1 is obtained by adding an alkali metal aluminate to an aqueous active silicic acid solution and heating the mixture, and wherein the aqueous silica sol a-2 is obtained by adding an alkali metal aluminate to an aqueous silica sol and heating the mixture.

21. The method for producing a silica sol according to any one of claims 18 to 20, wherein the silica sol used in the step A is a silica sol obtained by replacing the aqueous medium solvent of an aqueous silica sol hydrothermally treated at 180 to 240°C for 0.1 to 10 hours with an alcohol having 1 to 3 carbon atoms.

22. The method for producing an insulating resin composition according to any one of claims 12 to 14, comprising steps A to E. Step A: preparing a silica sol in which silica particles having an average primary particle size of 5 to 100 nm are dispersed in an alcohol solvent having 1 to 3 carbon atoms; Step B: a step of adding a silane compound represented by the following formula (1) and a silane compound represented by the following formula (2) or the following formula (3) to the silica sol obtained in step A; Step C: a step of replacing the dispersion medium of the silica sol obtained in step B from an alcohol solvent having 1 to 3 carbon atoms with a nitrogen-containing solvent; Step D: a step of mixing the silica sol in which the silica particles obtained in step C are dispersed in a nitrogen-containing solvent with a nitrogen-containing polymer; and Step E: A step of removing part or all of the nitrogen-containing solvent from the silica sol obtained in step D. Silane compound represented by formula (1): In formula (1), R 1 is an aromatic ring or an organic group containing an aromatic ring, and represents a group bonded to a silicon atom via a Si-C bond, R 2 represents an alkoxy group, a is an integer from 1 to 3; Silane compound represented by formula (2) or formula (3): In formula (2) and formula (3), R 3 and R 5 Each is an alkyl group having 1 to 3 carbon atoms and represents a group bonded to a silicon atom via a Si-C bond, R 4 and R 6 Each represents an alkoxy 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.

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