Aluminum silica sol and resin composition dispersed in a nitrogen-containing solvent

Abstract

This invention provides silica sol dispersed in a nitrogen-containing solvent, silica-blended resin compositions compounded with nitrogen-containing polymers, and particularly insulating resin compositions. The silica sol of this invention is formed by dispersing silica particles with an average primary particle size of 5-100 nm containing aluminum atoms in a nitrogen-containing solvent. The aluminum atoms are bonded to the surface of the silica particles at a ratio of 800-20000 ppm / SiO2 (Al2O3 equivalent) by leaching the silica particles in an aqueous solution selected from sulfuric acid, nitric acid, and hydrochloric acid. Furthermore, the aluminum atoms present in the entire silica particle as a ratio of 2700-30000 ppm / SiO2 (Al2O3 equivalent) are determined by dissolution with an aqueous hydrofluoric acid solution. Aluminosilicate sites are formed on the surface of the silica particles, and the nitrogen-containing solvent contains carbonyl and amino groups within its molecules.

Description

[0001] This invention is a divisional application of patent application filed on November 4, 2021, with application number 202180006735.3 and title "Aluminum-containing silica sol dispersed in a nitrogen-containing solvent and a resin composition". Technical Field

[0002] The present invention relates to aluminum-containing silica sol dispersed in a nitrogen-containing solvent, and resin compositions of the silica sol and nitrogen-containing polymers, particularly insulating resin compositions. Background Technology

[0003] A method has been disclosed for obtaining inorganic oxide sols dispersed in organic solvents such as toluene by reacting hydroxyl groups on the surface of inorganic oxide particles, such as silica, with alcohols to introduce alkoxysilanes and thus organically modify them. This method discloses the reaction of phenyltrimethoxysilanes in a methanol-dispersed silica sol to form a silica sol dispersed in toluene solvent (see Patent Document 1).

[0004] In addition, a silica sol dispersed by acetonitrile-methanol mixed solvent is disclosed by displacing methanol with acetonitrile solvent to obtain silica sol, and then reacting it with phenyltrimethoxysilane (see Patent Document 2).

[0005] In addition, a silica sol with aluminum compound modified on the surface of silica particles was disclosed (see Patent Document 3).

[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 Summary of the Invention

[0011] [The problem the invention aims to solve]

[0012] The object of this invention is to obtain a silica sol in which silica particles are dispersed in a nitrogen-containing solvent that allows for good compatibility with polar resins such as polyimide or polyamide. Furthermore, a resin composition formed by mixing these silica sols and resins is provided, which, when formulated as an insulating resin composition, provides an insulated coated conductor with a high insulation life.

[0013] [Methods for solving the problem]

[0014] The first point of this invention is a silica sol, which is formed by dispersing silica particles with an average primary particle size of 5 to 100 nm containing aluminum atoms in a nitrogen-containing solvent. The aluminum atoms are bonded to the surface of the silica particles at a ratio of 800 to 20000 ppm / SiO2 (calculated as Al2O3).

[0015] Viewpoint 2 is the silica sol described in Viewpoint 1, wherein at least one silane compound selected from the following general formulas (1) to (3) or its hydrolysate are bonded to the silica particles.

[0016] R 1 a Si(R 2 ) 4-a Equation (1)

[0017] [R] 3 b Si(R 4 ) 3-b 2Y c Equation (2)

[0018] R 5 d Si(R 6 ) 4-d Equation (3)

[0019] In equation (1), R 1 It is a phenyl or phenyl-containing organogroup, an amino or amino-containing organogroup, a (meth)acryloyl or (meth)acryloyl-containing organogroup, a vinyl or vinyl-containing organogroup, an alkyl group having 1 to 10 carbon atoms that may contain a halogen atom, or a combination thereof, R 2 This indicates an alkoxy, acyloxy, or halogen group, where 'a' represents an integer from 1 to 3.

[0020] In equations (2) and (3), R 3 and R 5 They are alkyl groups with 1 to 3 carbon atoms or aryl groups with 6 to 30 carbon atoms, and R 3 and R 5 R is bonded to silicon atoms via Si-C bonds. 4 and R 6 They represent alkoxy, acyloxy, or halogen groups respectively; Y represents 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.

[0021] Viewpoint 3 is the silica sol described in viewpoint 2, wherein the silane compound of general formula (1) binds 0.5 to 5.0 particles per unit area on the surface of silica particles. 2 .

[0022] Viewpoint 4 is the silica sol of any one of Viewpoints 1 to 3, wherein the aluminum atoms bound to the surface of the silica particles, as measured by leaching method by leaching the silica particles in an aqueous solution of at least one mineral acid selected from sulfuric acid, nitric acid and hydrochloric acid, are in the form of Al2O3 at a ratio of 800 to 20000 ppm / SiO2.

[0023] Viewpoint 5 is the silica sol described in any one of Viewpoints 1 to 3, wherein the aluminum atoms bound to the surface of the silica particles, as measured by leaching in an aqueous solution of at least one mineral acid selected from sulfuric acid, nitric acid, and hydrochloric acid, are in a ratio of 800 to 20,000 ppm / SiO2 (calculated as Al2O3); and the aluminum atoms present in the entire silica particles, as measured by dissolution in an aqueous solution of hydrofluoric acid, are in a ratio of 2,700 to 30,000 ppm / SiO2 (calculated as Al2O3).

[0024] Viewpoint 6 is the silica sol described in any one of views 1 to 5, wherein the amount of negative charge on the surface of the silica particles is 0.25 to 0.45 μeq / m. 2 .

[0025] Viewpoint 7 is the silica sol described in any one of Viewpoints 1 to 6, and the nitrogen-containing solvent is an amide solvent.

[0026] Viewpoint 8 is the silica sol of any one of Viewpoints 1 to 6, wherein the nitrogen-containing solvent is dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or N-ethylpyrrolidone.

[0027] Viewpoint 9 is a composition comprising any one of Viewpoints 1 to 8, a silica sol, and a nitrogen-containing polymer.

[0028] Viewpoint 10 is a composition comprising an insulating resin comprising any one of Viewpoints 1 to 8, a silica sol and a nitrogen-containing polymer.

[0029] Viewpoint 11 is the composition described in viewpoint 9 or 10, wherein the mass part of the nitrogen-containing polymer is 1 to 100 relative to 1 part by mass of silica particles contained in the silica sol.

[0030] Viewpoint 12 is the composition of any one of Viewpoints 9 to 11, wherein the nitrogen-containing polymer is any one of polyimide, polyamide, polyamic acid, polyamide-imide, polyether-imide, or polyester-imide.

[0031] Viewpoint 13 is the composition of any one of Viewpoints 9 to 12, wherein the viscosity of the composition after storage at 50°C for 2 weeks is 0.80 to 1.05 times that of the initial viscosity measured at 25°C.

[0032] Viewpoint 14 is an insulated wire, which is made by insulating the wire with a composition of insulating resin as described in Viewpoint 10.

[0033] Viewpoint 15 describes an insulated wire with a thickness of 23 μm, insulated with a composition of insulating resin as described in Viewpoint 10, and the flexibility of the insulating coating layer is 1d to 2d.

[0034] The concentration of silica particles in the nitrogen-containing solvent of the composition is adjusted to 15% by mass.

[0035] Viewpoint 16 describes an insulated conductor with a 23μm thick insulating coating of a composition of insulating resin described in Viewpoint 10. Its insulation life, measured under conditions of a pulsed voltage of 1.5kVp, bipolar polarity, and a 10kHz rectangular wave, ranges from 0.2 to 20 hours.

[0036] The concentration of silica particles in the nitrogen-containing solvent of the composition is adjusted to 15% by mass.

[0037] Viewpoint 17 is a method for manufacturing silica sol according to any one of Viewpoints 1 to 8, comprising the following steps (A) and (B).

[0038] (A) Process: A process for obtaining an aqueous silica sol with an average primary particle size of 5-100 nm, in which aluminum atoms (calculated as Al2O3) are bonded to the surface of silica particles at a ratio of 800-20000 ppm / SiO2.

[0039] (B) Process: The process of replacing the solvent of the silica sol obtained in process (A) with a nitrogen-containing solvent.

[0040] Viewpoint 18 is the method for manufacturing silica sol described in viewpoint 17. The aqueous silica sol in step (A) is obtained by contacting an aqueous solution of alkali metal silicate containing aluminum atoms, or an aqueous solution of alkali metal silicate containing aluminum atoms in the form of aluminate, with a cation exchange resin to perform cation exchange, and heating the obtained active silica at 80 to 300°C.

[0041] Viewpoint 19 is the method for manufacturing silica sol described in viewpoint 17. The aqueous silica sol in step (A) is obtained by adding aluminum atoms in the form of aluminate to the aqueous silica sol and heating the aqueous silica sol at 80 to 300°C.

[0042] Viewpoint 20 is a method for manufacturing silica sol according to any one of Viewpoints 17 to 19, wherein after step (A), there is a step (A-1) in which the silica sol obtained from step (A) is reacted with the silane compound of formula (1).

[0043] Viewpoint 21 is a method for manufacturing silica sol according to any one of Viewpoints 17 to 20, wherein after step (A) or step (A-1), the water in the aqueous silica sol obtained from step (A) or step (A-1) is replaced with methanol.

[0044] Invention Effects

[0045] The aluminum-containing silica particles have aluminum atoms at the aluminosilicate sites on their surface that are 4-coordinated and negatively charged. Therefore, the silica sol containing these silica particles exhibits a negative zeta potential across the entire pH range, with a large absolute value. Furthermore, the nitrogen-containing solvent used in this invention is a solvent with carbonyl and amino groups within its molecule, exhibiting high polarity through its polarized structure and the lone pair electrons of the nitrogen atom.

[0046] The silica sol of the present invention, with its polar structure of nitrogen-containing solvent and aluminosilicate sites formed by aluminum, causes the surface of silica particles to carry a negative charge, thereby enabling the formation of a dispersion in which silica particles in nitrogen-containing solvent have high dispersibility.

[0047] To form these aluminosilicate sites, one method uses silica particles that are: aluminate is added to an aqueous solution of alkali metal silicates before the silica particles are formed, followed by cation exchange, and then heated to form aluminosilicate sites from active silicic acid containing aluminate ions throughout the silica particles. Alternatively, aluminate can be added after the formation of a silica sol, followed by heat treatment to form aluminosilicate sites on the surface of the silica particles. While any method capable of forming aluminosilicate sites can be used in this invention, what is needed when dispersing in a nitrogen-containing solvent with a polar structure is the presence of aluminosilicate sites on the surface of the silica particles; any method is acceptable as long as aluminosilicate sites can be formed on the surface of the silica particles.

[0048] Wiring materials and substrate materials require not only electrical insulation but also improved impact resistance and abrasion resistance. As resins with high electrical insulation properties, polymers containing carbonyl and nitrogen atoms, such as polyimide, polyamide, polyamide-imide, and polyesterimide, are often used.

[0049] When introducing nanoscale silica particles with good compatibility into these polymers, it is preferable to use an organic solvent that disperses the silica particles in a dispersion medium to disperse the silica sol. The dispersion medium for organic solvent-dispersed silica sol has a high degree of common structure with the polymer structure, allowing for good compatibility mixing into the polymer and the formation of a varnish. By using a nitrogen-containing solvent as such a dispersion medium, it is possible to mix well with the aforementioned resin, resulting in a clear varnish of the silica-dispersed coating composition that is not cloudy after mixing.

[0050] When a varnish containing a silica dispersion composition is applied to an insulating resin composition for wires requiring insulation coating, the presence of a negatively charged surface on the silica particles is initially considered disadvantageous for insulation. However, it has been unexpectedly found to possess very high insulation performance. In conventional varnishes with insufficiently dispersed silica particles, silica agglomerates in the coated resin, creating vulnerable areas between these locally distributed aggregates. Upon discharge, these areas experience insulation breakdown, resulting in loss of insulation. Conversely, in this invention, because sufficiently dispersed silica particles are present in the varnish, the silica is highly dispersed in the coated resin. The absence of locally distributed (i.e., uniformly distributed) silica particles allows for the formation of a uniform silica layer within the resin. Therefore, upon discharge, the silica particles effectively shield against discharge, resulting in high insulation performance.

[0051] The silica sol dispersed in a nitrogen-containing solvent of the present invention has high compatibility with nitrogen-containing polymers and can form a resin composition in which silica particles are fully dispersed. When this varnish is used as an insulating resin composition, it can be coated onto a conductor requiring insulation (e.g., copper wire or enameled copper wire) to obtain an insulated wire. Attached Figure Description

[0052] Figure 1 These are photographs showing the evaluation test results of the transparency of the silica-blended resin varnish of Example 4.

[0053] Figure 2 These are photographs showing the evaluation test results of the transparency of the silica-blended resin varnish of Example 8.

[0054] Figure 3 These are photographs showing the evaluation test results of the transparency of the silica-blended resin varnish of Comparative Example 1.

[0055] Figure 4 These are photographs showing the evaluation test results of the transparency of the silica-blended resin varnish of Comparative Example 4.

[0056] Figure 5 These are photographs showing evaluation tests of the transparency of resin varnishes without added silica, used as a reference.

[0057] Figure 6 These are photographs showing the evaluation test of the transparency of the cured silica-blended resin varnish of Example 4.

[0058] Figure 7 These are photographs showing the evaluation test of the transparency of the cured silica-blended resin varnish of Example 8.

[0059] Figure 8These are photographs showing the evaluation test results of the transparency of the cured silica-blended resin varnish of Comparative Example 1.

[0060] Figure 9 These are photographs showing the evaluation test results of the transparency of the cured silica-blended resin varnish of Comparative Example 4.

[0061] Figure 10 These are photographs showing evaluation tests of the transparency of cured resin varnishes without added silica, used as a reference. Detailed Implementation

[0062] The present invention is a silica sol formed by dispersing silica particles with an average primary particle size of 5-100 nm containing aluminum atoms in a nitrogen-containing solvent. The aluminum atoms are bonded to the surface of the silica particles at a ratio of 800-20000 ppm / SiO2 (calculated as Al2O3).

[0063] The average primary particle size of the silica particles of the present invention can be measured using the particle size (nm) by nitrogen adsorption method (BET method).

[0064] In addition, the silica sol of the present invention has good dispersibility in nitrogen-containing solvents, and the particle size measured by dynamic light scattering (DLS) in nitrogen-containing solvents is in the range of 5-100 nm or 10-70 nm.

[0065] The ratio of dynamic light scattering (DLS) to nitrogen adsorption (BET) is 1.10–4.50 or 1.20–4.00.

[0066] In this invention, aluminum atoms can be expressed as Al2O3 by leaching aluminum onto the surface of silica particles using an aqueous solution of at least one mineral acid selected from sulfuric acid, nitric acid, and hydrochloric acid. Specifically, aluminum atoms on the silica particle surface are converted to Al2O3 at a ratio of 800–20000, 800–10000, or 800–500 ppm / SiO2. The presence of aluminosilicate sites on the silica surface is important for dispersion in highly polar nitrogen-containing solvents. The aluminum present as aluminosilicate on the silica particle surface can be leached (dissolved) from the silica particles using an aqueous solution of at least one mineral acid selected from sulfuric acid, nitric acid, and hydrochloric acid, causing the aluminum to form a structure close to aluminum salts, aluminum oxides, or aluminum hydroxide. The aluminum in the solution is then measured using an ICP emission spectrometer and expressed as Al2O3. The leaching (dissolving) method using an aqueous solution of nitric acid is particularly important. The nitric acid aqueous solution used for leaching can have a pH range of 0.5–4.0, 0.5–3.0, 0.5–2.0, or 1.0–1.5, typically a nitric acid aqueous solution with a pH of 1.0 can be used. For example, 100 mL of the above-mentioned nitric acid aqueous solution can be added to 1 g of silica and maintained at a temperature of 20–70°C or 40–60°C for 10–24 hours to leach aluminum compounds from the surface of the silica particles, which can then be used as an analytical sample.

[0067] In this invention, the silica particle surface is defined as the region capable of dissolving aluminum compounds through the aforementioned leaching process. The solvent is evaporated from the silica sol and then dried at 250°C. The resulting silica is crushed into silica powder. 20 mL of a pH 1.0 nitric acid aqueous solution is added to 0.2 g of this silica powder and shaken thoroughly. After maintaining the solution in a constant temperature bath at 50°C for 17 hours, it is centrifuged and filtered. The aluminum content in the resulting liquid is measured using an ICP emission spectrometer. The aluminum content, converted to Al2O3, is divided by the mass of the silica powder to obtain the amount of aluminum bound to the silica particle surface (Al2O3 / SiO2) (ppm).

[0068] Furthermore, even when aluminosilicates are formed on the surface of silica particles, depending on the manufacturing method, some methods do not selectively form them only on the surface; aluminosilicates can also form inside the silica particles. The aluminum present throughout the silica particles, including both the surface and the interior, is converted to Al2O3 and combines with the silica particles at a ratio of 2700–30000 ppm / SiO2.

[0069] The aluminum present in all silica particles can be determined by dissolving the silica particles in an aqueous hydrofluoric acid solution, and then converted to Al2O3. In other words, the aluminum present as aluminosilicate in the silica particles can be dissolved in an aqueous hydrofluoric acid solution, and the solution can be measured using an ICP emission spectrometer, converted to Al2O3, and expressed as the aluminum present in the entire silica particle composition.

[0070] By forming aluminosilicate sites on the surface of silica particles in this way, the amount of negative charge present on the silica particle surface was measured to be 0.25–0.45 μeq / m. 2 .

[0071] The nitrogen-containing 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 include chain and cyclic structures. Examples of functional groups containing a nitrogen atom include amino, nitro, and cyano groups, but amino groups are preferred. Although amino and carbonyl groups can be adjacent or separated by a carbon atom, they can be used, for example, in the form of an amide group, and amide solvents are preferred.

[0072] Specific examples of nitrogen-containing solvents include dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, tetramethylurea, hexamethylphosphoric triamine, dimethylacrylamide, acrylmorpholine, hydroxyethylacrylamide, isopropylacrylamide, diethylacrylamide, dimethylaminopropylacrylamide, 3-methoxy-N,N-dimethylpropaneamide, 3-butoxy-N,N-dimethylpropaneamide, dimethylaminopropylacrylamide methyl quaternary salt chloride, and dimethylaminoethyl acrylate benzyl quaternary salt chloride.

[0073] Examples of nitrogen-containing solvents include dimethylacetamide, dimethylformamide, N-methylpyrrolidone, and N-ethylpyrrolidone.

[0074] In this invention, other solvents may be included in the nitrogen-containing solvent, as long as the effect is not compromised.

[0075] That is, the total solvent may contain nitrogen-containing solvents in proportions of 50-100 vol%, 90-100 vol%, 98-100 vol%, or 99-100 vol%, and other solvents may be contained in amounts of 0 or more but less than 50 vol%, 0 or more but less than 10 vol%, 0 or more but less than 2 vol%, or 0 or more but less than 1 vol%.

[0076] Other solvents that can be listed include water, ketones, esters, alcohols, glycols and ethers, hydrocarbons, halogens, ethers, glycols, and amines.

[0077] Examples of solvents that can be listed include ketones such as acetone, butanone, methyl isobutyl ketone, diisobutyl ketone, and cyclohexanone; esters such as methyl acetate, ethyl acetate, and butyl acetate; alcohols such as methanol, ethanol, isopropanol, and benzyl alcohol; glycol ethers 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; hydrocarbons such as benzene, toluene, xylene, n-hexane, and cyclohexane; halogens such as dichloromethane, trichloroethylene, and perchloroethylene; ethers such as dioxane, diethyl ether, and tetrahydrofuran; glycols such as ethylene glycol, diethylene glycol, propylene glycol, and polyethylene glycol; and amines such as monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, N-methylethanolamine, and 2-amino-2-methyl-1-propanol.

[0078] In this invention, the surface of silica particles may be coated with at least one silane compound selected from general formulas (1) to (3) or its hydrolysate.

[0079] In equation (1), R 1 It is a phenyl or phenyl-containing organogroup, an amino or amino-containing organogroup, a (meth)acryloyl or (meth)acryloyl-containing organogroup, a vinyl or vinyl-containing organogroup, an alkyl group having 1 to 10 carbon atoms that may contain a halogen atom, or a combination thereof, R 2 It represents an alkoxy, acyloxy, or halogen group, and a represents an integer from 1 to 3.

[0080] In equations (2) and (3), R 3 and R 5 They are alkyl groups with 1 to 3 carbon atoms or aryl groups with 6 to 30 carbon atoms, and R 3 and R 5 R is bonded to silicon atoms via Si-C bonds. 4 and R 6 They represent alkoxy, acyloxy, or halogen groups respectively; Y represents 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.

[0081] In particular, silane compounds in general formula (1) in which a = 1 or 2 can be used, with a = 1 being especially preferred.

[0082] As vinyl or vinyl-containing organic groups, functional groups 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, 1-hexenyl, 1-octenyl, etc.

[0083] Examples of alkoxy groups include straight-chain, branched, or cyclic alkyl groups having 1 to 10 carbon atoms, such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, and tert-butoxy.

[0084] In addition, examples of acyloxy groups with 2 to 10 carbon atoms include methyl carbonyloxy, ethyl carbonyloxy, n-propyl carbonyloxy, and isopropyl carbonyloxy.

[0085] In addition, halogen groups can be listed as fluorine, chlorine, bromine, iodine, etc., with fluorine atoms being preferred.

[0086] The following can be cited as a specific example of a silane compound of formula (1).

[0087] Examples of phenyl-containing silanes include phenyltrimethoxysilane, phenyltriethoxysilane, dimethoxydiphenylsilane, phenylmethyldimethoxysilane, (2,2-diphenylethyl)trimethoxysilane, and fluorene-based silane coupling agents (e.g., Osaka Gaskemical Co., Ltd.'s Ogusol SC-001 and SC-003).

[0088] Examples of silanes containing a phenyl organic group include p-styryltrimethoxysilane and N-phenyl-3-aminopropyltrimethoxysilane.

[0089] Specific examples of amino-containing silane compounds include aminopropyltrimethoxysilane, aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, and 3-ureapropyltrialkoxysilane.

[0090] Examples of silanes having or containing a (meth)acryloyl group include 3-methacryloyloxypropyltrimethoxysilane, 3-methacryloyloxypropyltriethoxysilane, 3-methacryloyloxypropylmethyldimethoxysilane, 3-methacryloyloxypropylmethyldiethoxysilane, 3-acryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltriethoxysilane, 4-methacryloyloxybutyltrimethoxysilane, 5-methacryloyloxypentyltrimethoxysilane, 6-methacryloyloxyhexyltrimethoxysilane, 7-methacryloyloxyheptyltrimethoxysilane, and 8-methacryloyloxyoctyltrimethoxysilane.

[0091] Examples of silanes having or containing vinyl or vinyl-containing organic groups include vinyltrimethoxysilane, vinyltriethoxysilane, 1-butenyltrimethoxysilane, 1-butenyltriethoxysilane, 1-octenyltrimethoxysilane, and 1-octenyltriethoxysilane.

[0092] Examples of silanes having alkyl groups containing 1 to 10 carbon atoms that may contain halogen atoms include methyltrimethoxysilane, methyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, and 3,3,3-trifluoropropyltriethoxysilane.

[0093] Examples of functional group combinations include N-phenyl-3-aminopropyltrimethoxysilane and N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane.

[0094] Formulas (2) and (3) are preferably compounds that can form trimethylsilyl groups on the surface of silica particles.

[0095] Examples of these compounds include:

[0096]

[0097] In the above formula, R 12 It is an alkoxy group; examples include methoxy and ethoxy groups.

[0098] These silanes can use silane coupling agents manufactured by Shin-Etsu Chemical Co., Ltd.

[0099] In this invention, when coating the surface of silica particles with at least one silane compound selected from formulas (1) to (3), the silane compound of formula (1) to (3) is added to an aqueous silica sol or a methanol silica sol, and stirred for 1 to 10 hours at a temperature of 10 to 60°C, usually at room temperature (20°C). The hydrolysis of at least one silane compound selected from formulas (1) to (3) requires water. In the case of an aqueous silica sol, the aqueous medium becomes the water for hydrolysis. In the case of a methanol silica sol, the water present when the aqueous medium is replaced with methanol can be used as the water for hydrolysis.

[0100] It is possible to obtain at least one silane compound selected from the above general formulas (1) to (3) at a density of 0.5 to 5.0 particles / nm per unit area of ​​the silica particle surface. 2 0.5–4.0 per nm 2 0.5–3.0 per nm 2 or 0.5–2.0 per nm 2 The amount of silica particles combined with it.

[0101] The silica sol of the present invention can be manufactured by the following steps (A) to (B).

[0102] (A) Process: A process for obtaining an aqueous silica sol with an average primary particle size of 5-100 nm, in which aluminum atoms (calculated as Al2O3) are bonded to the surface of silica particles at a ratio of 800-20000 ppm / SiO2.

[0103] (B) Process: The process of replacing the solvent of the silica sol obtained in process (A) with a nitrogen-containing solvent.

[0104] The aqueous silica sol in step (A) can be obtained by cation exchange of an aqueous solution of an alkali metal silicate containing aluminum atoms or an aqueous solution of an alkali metal silicate containing aluminum atoms in the form of aluminates, followed by heating the resulting active silicic acid at 80–300°C. Examples of the aluminates mentioned above include sodium aluminate and potassium aluminate, and examples of the aqueous solutions of alkali metal silicates include sodium silicate and potassium silicate. The aluminate can be added as a 0.1–30% by mass aqueous solution to the aqueous solution of the alkali metal silicate at a temperature of 20–100°C and stirred for 0.1–24 hours. Cation exchange is carried out by contacting a H-type strong acid cation exchange resin. After cation exchange, contact with an anion exchange resin may be performed if necessary. The active silicic acid containing the aluminate ions thus produced is heated at 80–300°C for 0.1–24 hours, thereby creating the silica sol in step (A) where aluminosilicate sites are formed on the surface and inside the silica particles.

[0105] Furthermore, the aqueous silica sol in step (A) can be used as an aqueous silica sol obtained by adding aluminum atoms in the form of aluminates and heating the aqueous silica sol at 80–300°C. Examples of aluminates include sodium aluminate and potassium aluminate. The aluminates can be added as a 0.1–30% by mass aqueous solution to the silica sol and stirred for 0.1–24 hours at a temperature of 20–100°C. By heating the silica sol containing aluminate ions at 80–300°C for 0.1–24 hours, the silica sol of step (A) with aluminosilicate sites formed on the surface and inside the silica particles is produced.

[0106] (A) The silica sol obtained in the process can be subjected to cation exchange or anion exchange as needed. In addition, the pH can be adjusted to 2-5, 2-4 or 2-3.

[0107] Furthermore, an evaporator or ultrafiltration device can be used to adjust the silica concentration to 5–50% by mass or 10–30% by mass.

[0108] (A) In the process of coating the surface of silica particles with silane compound, the silane compound is added after the process of (A) is completed.

[0109] (A) Before replacing the solvent of the nitrogen-containing solvent obtained in the process with a nitrogen-containing solvent in the process (B), the water in the aqueous silica sol in the process (A) can be replaced with methanol.

[0110] (B) In the process, the solvent of the silica sol obtained in process (A) can be replaced with a nitrogen-containing solvent. Solvent replacement is carried out by evaporation and ultrafiltration using an evaporator.

[0111] Evaporation via an evaporator is carried out at a temperature of 30–200°C and a pressure of 50–600 Torr.

[0112] (B) A base may be added in the process. As a base, amines, alcoholic sodium hydroxide, and potassium hydroxide can be used. Examples of amines include triethylamine, isopropylamine, diisopropylamine, n-propylamine, di-n-propylamine, isobutylamine, diisobutylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, tri-n-octylamine, N-ethyldiisopropylamine, cyclohexylamine, dicyclohexylamine, N,N-n-diisopropylethylamine, tri-n-pentylamine, etc., alkylamines, aralkylamines such as benzylamine, piperidine, n-methylpiperidine, quinine, etc., alicyclic amines, quaternary ammonium such as tetramethylammonium hydroxide, imidazole, imidazole derivatives, 1,8-diaza-bicyclo(5,4,0)undec-7-ene, 1,5-diaza-bicyclo(4,3,0)non-5-ene, 1,4-diaza-bicyclo(2,2,2)octane, etc.

[0113] The nitrogen-containing solvent-dispersed silica sol obtained through process (B) can be mixed with pure water, methanol, and nitrogen-containing solvent-dispersed sol in a mass ratio of 1:1:1 to adjust the pH to 4.0–10.0, 4.0–9.5, or 4.0–9.0.

[0114] In step (B), nitrogen-containing solvents may be present in proportions of 50–100 vol%, 90–100 vol%, 98–100 vol%, or 99–100 vol% of all solvents, while other solvents may be present in amounts of 0 or more but less than 50 vol%, 0 or more but less than 10 vol%, 0 or more but less than 2 vol%, or 0 or more but less than 1 vol%. As for other solvents, water and methanol contained in the silica sol of step (A) are permissible as long as they are within the above ranges and do not impair the effect.

[0115] A coating composition (resin varnish) can be obtained by combining the silica sol dispersed in a nitrogen-containing solvent of the present invention with a nitrogen-containing polymer.

[0116] In addition, the silica sol dispersed in a nitrogen-containing solvent of the present invention can be combined with a nitrogen-containing polymer to obtain an insulating resin composition (resin varnish).

[0117] Examples of combinations of nitrogen-containing polymers and silane compounds coated on silica particles include the following. For example, a preferred combination with a polyamide-imide resin can be a combination of the polyamide-imide resin with a silane containing phenyl silane, trifluoroalkyl silane, alkyl silane, amino silane, or a combination thereof. More specifically, examples can be given of coating compositions or insulating resin compositions formed by combining a polyamide-imide resin with a sol formed by dispersing silica particles coated with phenyltrimethoxysilane, silica particles coated with 3,3,3-trifluoropropyltrimethoxysilane, or silica particles coated with methyltrimethoxysilane in a DMAC (N,N-dimethylacetamide) solvent.

[0118] In addition, a preferred combination with a polyimide resin may be a combination of a polyimide resin with a silane containing a phenyl group, a silane containing an amino group, or a silane containing a combination of the above.

[0119] More specifically, examples of coating compositions or insulating resin compositions containing the following combinations can be listed:

[0120] A combination of polyimide resin and silica particles coated with N-phenyl-3-aminopropyltrimethoxysilane dispersed in DMAC (N,N-dimethylacetamide) solvent to form a sol.

[0121] Resin varnishes, such as coating compositions and insulating resin compositions, can be obtained with 1 to 100 parts by mass of silica contained in the silica sol and the nitrogen-containing polymer. The nitrogen-containing polymer includes polyimide, polyamide, polyamic acid, polyamide-imide, polyether-imide, and polyesterimide.

[0122] The viscosity of the above-mentioned coating composition, insulating resin composition, and other resin varnishes after storage at 50°C for 2 weeks is 0.80 to 1.05 times that of the initial viscosity measured at 25°C, indicating high storage stability. The viscosity measurement after storage at 50°C for 2 weeks was performed by immediately cooling the varnish to 25°C after removing it from the 50°C constant temperature storage chamber, and then measuring the viscosity at 25°C.

[0123] An insulating resin composition is coated onto a conductor requiring insulation, and then heated to cure at a temperature at which the solvent evaporates, thereby forming an insulating coating layer on the conductor surface. The heating temperature for removing the solvent is determined by the pressure; if at atmospheric pressure, it is approximately 150°C to 220°C.

[0124] The conductors mentioned above are metallic wires, particularly copper wires. Copper wires are coated with enamel film to become electrical wires, which are used in industrial applications, household motors, transformers, coils, etc.

[0125] The insulating resin composition of the present invention can be used to manufacture insulated wires by coating enameled copper wires or by directly coating the copper wires with the insulating resin composition instead of coating them with enamel.

[0126] The above-mentioned insulating resin composition is obtained by mixing 1 to 100 parts by mass of a nitrogen-containing polymer relative to 1 part by mass of silica contained in the silica sol.

[0127] The insulating resin composition is obtained by mixing or stirring silica sol and polymer using a stirrer or disperser. Additives may be added as needed during these formulations.

[0128] The nitrogen-containing polymers mentioned above are preferably polyimides, polyamides, polyamic acids, polyamide-imides, polyether-imides, and polyester-imides.

[0129] The conductor coated with the insulating resin composition of the present invention has both insulating and flexible properties.

[0130] The flexibility, measured according to JIS C 3216-3, item 5, refers to the flexibility of an insulated conductor with a 23 μm thickness, formed by insulating with an insulating resin composition having a silica concentration adjusted to 15% by mass, and the insulation coating having a flexibility of 1d to 2d. This flexibility is the minimum winding diameter d at which no cracks are visible on the insulation film, calculated by stretching the insulated conductor by 20% relative to the unstretched insulated conductor. The minimum winding diameter without cracks is measured based on the conductor's own diameter (1d), which is within the range of n times (nd) of its own diameter.

[0131] Furthermore, insulation performance was measured according to JIS C 3216-5, section 4. The insulated conductor, made by coating a 23 μm thick insulating resin composition with a silica concentration adjusted to 15% by mass, was tested with an insulation life of 0.2 to 20 hours or 0.1 to 10 hours, measured using a pulsed voltage of 1.5 kVp (bipolar, 10 kHz rectangular wave). The insulation life was defined as the time taken to reach the point where an insulation breakdown current of 5 mA was detected after applying a step-up voltage of 500 V / s between the two wires of the insulated conductor at a temperature of 155°C while maintaining a 50 mm distance between them.

[0132] Example

[0133] (Analysis Methods)

[0134] [Measurement of SiO2 concentration]

[0135] The silica sol was placed in a crucible and heated to dry it at a temperature 10°C higher than the boiling point of the dispersion medium to remove the dispersion medium. The resulting silica gel was then calcined at 1000°C, and the calcination allowance was calculated.

[0136] [Measurement of average primary particle size (nitrogen adsorption method (BET method) particle size)]

[0137] The specific surface area of ​​acidic silica sol dried at 300°C was determined using a specific surface area measuring device (Monosobe MS-16, manufactured by Yuasa Ionicus Co., Ltd.). The average primary particle size was calculated using the following formula: Average primary particle size (nm) = 2720 / Specific surface area (m²) 2 / g)

[0138] [Moisture content determination]

[0139] Obtained by Karl Fischer titration.

[0140] [Measurement of the viscosity of silica sol]

[0141] The measurements were taken at 20°C using an Ostwald viscometer.

[0142] [Viscosity measurement of resin varnish]

[0143] Measurements were taken at 25°C using a Type B viscometer (Toki Sangyo, Type B BMII viscometer).

[0144] [pH Measurement]

[0145] The pH was measured at 20°C using a pH meter (manufactured by East Asia Dykeke Co., Ltd.).

[0146] For silica sol dispersed in organic solvents, the solution prepared by mixing pure water, methanol and organic solvent in a mass ratio of 1:1:1 with silica sol is measured.

[0147] [Measurement of particle size using dynamic light scattering method]

[0148] The particle size was measured using a dynamic light scattering particle size analyzer (Zeta Saizanono manufactured by Spectoris).

[0149] [Measurement of the amount of aluminum present on all silicon dioxide particles]

[0150] The silica gel obtained by drying silica sol was decomposed with hydrofluoric acid solution and then dissolved with nitric acid aqueous solution. The aluminum content in the resulting aqueous solution was measured using an ICP emission spectrometer and divided by the mass of silica to obtain the total aluminum content (Al2O3 / SiO2) (ppm) present in the silica particles.

[0151] [Measurement of the amount of aluminum bonded to the silica surface]

[0152] Take 5g of silica sol and place it in a crucible. Heat it on a hot plate at a temperature 10°C above the solvent's boiling point to evaporate the solvent. Then, dry it in a desiccator at 250°C for 2 hours. The resulting silica gel is then crushed into powder using a mortar and pestle. Add 0.2g of the obtained silica powder to a 20mL polypropylene container (polypropylene plastic bottle), add 20mL of nitric acid aqueous solution adjusted to pH 1.0, and vibrate vigorously by hand for 10 minutes. Next, place the sample in an ultrasonic cleaner (Aswan, AS486) for 10 minutes to fully mix the silica powder and nitric acid aqueous solution. Keep it in a constant temperature bath at 50°C for 17 hours. Afterward, place the contents into a centrifugal ultrafiltration filter (product name: Amicon Ultra-15, molecular weight fraction 10,000), and determine the aluminum content in the filtrate obtained after centrifugation using an ICP emission spectrometer. The amount of aluminum bonded to the silica surface (Al2O3 / SiO2) (ppm) is determined by dividing the obtained aluminum content by the mass of silica powder.

[0153] [Measurement of the negative charge on the surface of silica particles]

[0154] Prepare 100g of acidic silica sol with a silica concentration adjusted to 0.5% by mass. Add ammonia solution and adjust the pH to 5.0 at 20℃ to prepare an aqueous solution for determination. Take 20g of the prepared aqueous solution and use a flow potential measuring device (MicrotracBEL, Stabino PMX400) with N / 400 DADMAC solution (Wako Pure Chemical Industries, Ltd.) as the cation standard titrant. The flow potential titration value obtained by measuring the cation flow potential is taken as the amount of surface negative charge. The value obtained by the above measurement is the average surface negative charge per 1g of silica particles (μeq / g). Divide this value by the specific surface area of ​​the silica particles (m²). 2 / g), and the obtained value is taken as the amount of negative charge per unit specific surface area on the surface of silicon dioxide particles.

[0155] [Synthesis Example 1 / Synthesis of Acidic Silica Sol (1)]

[0156] A water-dispersed silica sol (1) was prepared. (Average primary particle size 11 nm, pH 9, silica concentration 20% by mass, Al2O3 concentration 0.17% by weight, manufactured by Nissan Chemical Co., Ltd.)

[0157] 2500g of an aqueous dispersion of silica sol (1) prepared from an aqueous solution of an alkali metal silicate containing aluminum atoms was placed in a 3L SUS autoclave reactor and subjected to hydrothermal treatment at 150°C for 5.0 hours. 2000g of the resulting sol was then passed through a column at approximately 25°C filled with 200mL of hydrogen-form strong acidic cation exchange resin Amber Light IR-120B at a space velocity of 5 per hour, yielding 2000g of acidic silica sol (1) (pH 2.5, SiO2 concentration 20% by mass, aluminum content (Al2O3 / SiO2) bound to the surface of silica particles 4500ppm, aluminum content (Al2O3 / SiO2) present on the entire silica particles 5915ppm, average primary particle size 11nm, negative charge 0.43μeq / m). 2 ).

[0158] [Synthesis Example 2 / Synthesis of Acidic Silica Sol (2)]

[0159] 2500g of an aqueous dispersion of silica sol (1) made from an aqueous solution of an alkali metal silicate containing aluminum atoms was placed in a 3L SUS autoclave reactor and subjected to hydrothermal treatment at 245°C for 2.5 hours. 2000g of the resulting sol was passed through a column at approximately 25°C filled with 200mL of hydrogen-form strong acidic cation exchange resin Amber Light IR-120B at a space velocity of 5 per hour, yielding 2000g of acidic silica sol (2) (pH 2.9, SiO2 concentration 20% by mass, aluminum content (Al2O3 / SiO2) bound to the surface of silica particles 3200ppm, aluminum content (Al2O3 / SiO2) present on the entire silica particles 7534ppm, average primary particle size 21nm, negative charge 0.40μeq / m). 2 ).

[0160] [Synthesis Example 3 / Synthesis of Acidic Silica Sol (3)]

[0161] Except that the heating temperature of the autoclave in Synthesis Example 1 was changed from 150°C to 110°C, the same procedure as in Synthesis Example 1 was followed to obtain acidic silica sol (3) (pH 2.6, SiO2 concentration 20% by mass, aluminum content (Al2O3 / SiO2) bound to the surface of silica particles 4000ppm, aluminum content (Al2O3 / SiO2) present in all silica particles 5400ppm, average primary particle size 11nm, negative charge 0.39μeq / m 2 ).

[0162] [Synthesis Example 4 / Synthesis of Acidic Silica Sol (4)]

[0163] A water-dispersed silica sol (2) was prepared (average primary particle size 9.5 nm, pH 3, silica concentration 18% by mass, Al2O3 concentration 0.5% by weight, manufactured by Nissan Chemical Co., Ltd.).

[0164] 2500g of an aqueous dispersion of silica sol (2) made from an aqueous solution of an alkali metal silicate containing aluminum atoms was placed in a 3L SUS autoclave reactor and subjected to hydrothermal treatment at 130°C for 5.0 hours. 2000g of the resulting sol was passed through a column filled with 200mL of hydrogen-form strong acidic cation exchange resin Amber Light IR-120B at approximately 25°C at a space velocity of 5 ppm to obtain 2000g of acidic silica sol (4) (pH 2.6, SiO2 concentration 18% by mass, aluminum content (Al2O3 / SiO2) bound to the surface of silica particles 4000ppm, aluminum content (Al2O3 / SiO2) present on the entire silica particles 5454ppm, average primary particle size 9.5nm, negative charge 0.41μeq / m 2 ).

[0165] [Synthesis Example 5 / Synthesis of Acidic Silica Sol (5)]

[0166] A water-dispersed silica sol (3) (average primary particle size 4 nm, pH 10, silica concentration 15% by mass, Al2O3 concentration 0.43% by weight, manufactured by Nissan Chemical Co., Ltd.) was prepared.

[0167] 2500 g of an aqueous dispersion of silica sol (3) prepared from an aqueous solution of an alkali metal silicate containing aluminum atoms was placed in a 3 L SUS autoclave reactor and subjected to hydrothermal treatment at 120 °C for 5.0 hours. 2000 g of the resulting sol was passed through a column filled with hydrogen-form strong acidic cation exchange resin Amber Light IR-120B at approximately 25 °C at a space velocity of 5 per hour to obtain 2000 g of acidic silica sol (5) (pH 2.7, SiO2 concentration 14% by mass, aluminum content (Al2O3 / SiO2) bound to the surface of silica particles 17000 ppm, aluminum content (Al2O3 / SiO2) present on the entire silica particles 22857 ppm, average primary particle size 5 nm, negative charge 0.29 μeq / m 2 ).

[0168] [Comparative Synthesis Example 1 / Preparation of Acidic Silica Sol (6)]

[0169] Acidic silica sol (6) was prepared (pH 2.6, SiO2 concentration 20% by mass, aluminum content (Al2O3 / SiO2) bound to the surface of silica particles 760ppm, aluminum content (Al2O3 / SiO2) present on the entire silica particles 2300ppm, average primary particle size 11nm, negative charge 0.30μeq / m). 2 (Made by Nissan Chemical Co., Ltd.). This silica sol is a silica sol manufactured using an aqueous solution of an alkali metal silicate containing aluminum atoms as a raw material.

[0170] [Comparative Synthesis Example 2 / Preparation of Acidic Silica Sol (7)]

[0171] Acidic silica sol (7) was prepared (pH 3, SiO2 concentration 20% by mass, aluminum content (Al2O3 / SiO2) bound to the surface of silica particles 450 ppm, aluminum content (Al2O3 / SiO2) present on the entire silica particles 2570 ppm, average primary particle size 21 nm, negative charge 0.35 μeq / m 2 (Made by Nissan Chemical Co., Ltd.). This silica sol is a silica sol manufactured using an aqueous solution of an alkali metal silicate containing aluminum atoms as a raw material.

[0172] [Comparative Synthesis Example 3 / Preparation of Acidic Silica Sol (8)]

[0173] Acidic silica sol (8) was prepared (pH 3, SiO2 concentration 20% by mass, aluminum content (Al2O3 / SiO2) bound to the surface of silica particles 460 ppm, aluminum content (Al2O3 / SiO2) present on the entire silica particles 2500 ppm, average primary particle size 45 nm, negative charge 0.31 μeq / m). 2 (Made by Nissan Chemical Co., Ltd.). This silica sol is a silica sol manufactured using an aqueous solution of an alkali metal silicate containing aluminum atoms as a raw material.

[0174] [Comparative Synthesis Example 4 / Preparation of Acidic Silica Sol (9)]

[0175] A water-dispersed silica sol (4) was prepared. (Average primary particle size 4 nm, pH 12, silica concentration 7% by mass, Al2O3 concentration 0.7% by weight, manufactured by Nissan Chemical Co., Ltd.)

[0176] 2500g of water-dispersed silica sol (4) made from an aqueous solution of alkali metal silicates containing aluminum atoms was placed in a 3L SUS autoclave reactor. After hydrothermal treatment at 110°C for 5.0 hours, it gelled and could not be used to make acidic sol.

[0177] (Example 1)

[0178] 1000g of acidic silica sol (1) was placed in a 2L bowl-shaped flask. While stirring the sol with a magnetic stirrer, 1.6g of N,N-diisopropylethylamine and 400g of N,N-dimethylacetamide (hereinafter referred to as DMAC) were added and mixed for 15 minutes. Using a rotary evaporator, under reduced pressure (pressure 170 Torr, bath temperature 105°C), 200g of DMAC was added while water was distilled off, thereby obtaining 1000g of DMAC·water mixed solvent dispersed silica sol (silica concentration 20% by weight, water 20% by mass). While stirring the obtained silica sol with a magnetic stirrer, 16.3g of phenyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM-103) was added, and the liquid temperature was maintained at 60°C for 1 hour. Then, 0.8g of N,N-diisopropylethylamine was added and the mixture was maintained at 60°C for 1 hour. Subsequently, using a rotary evaporator, under reduced pressure (pressure 170–90 Torr, bath temperature 105–125 °C), DMAC (400 g) was added while water was distilled off, thus obtaining a DMAC-dispersed silica sol (silica concentration 30.5% by mass, pH 4.7, viscosity (20 °C) 4.8 mPa·s, water 0.1% by mass, dynamic light scattering particle size 24 nm, average primary particle size 11 nm, and silane compound binding per unit area of ​​silica particle surface 1.0 particles / nm). 2The amount of aluminum bonded to the surface of the silica particles (Al2O3 / SiO2) is 2915 ppm, and the amount of aluminum present on the entire silica particles (Al2O3 / SiO2) is 5797 ppm.

[0179] The DMAC dispersed silica sol obtained in Example 1 was mixed with a polyamide-imide insulating resin varnish (manufactured by Showa Denko Materias Co., Ltd., trade name HPC-5012-32, resin solids content 32% by mass, NMP (N-methyl-2-pyrrolidone) solvent) in a glass bottle with a resin / SiO2 ratio of 85 / 15. The mixture was shaken vigorously by hand approximately 10 times, and then mixed at 23°C for 12 hours using a mixing stirrer (Mixlocker, manufactured by Assone Co., Ltd., trade name MR-5) to obtain a silica-mixed polyamide-imide resin varnish (resin / SiO2 = 85 / 15).

[0180] Regarding the appearance of the obtained varnish, after being stored at 50°C for 4 weeks, it was as transparent as the original polyamide-imide resin varnish. The initial viscosity was 2600 cps, the viscosity of the varnish after being stored at 50°C for 2 weeks was 2620 cps, and the viscosity after being stored at 50°C for 4 weeks was 2630 cps.

[0181] (Example 2)

[0182] By adding 8.4 g of 2% NaOH methanol solution (containing 18% by mass water) to 670 g of DMAC dispersed silica sol obtained by the method described in Example 1, a DMAC dispersed silica sol was obtained with the following properties: silica concentration 30.1% by mass, pH 8.5, viscosity (20°C) 5.6 mPa·s, water content 0.3% by mass, dynamic light scattering particle size 28 nm, average primary particle size 11 nm, and silane compound binding density per unit area of ​​silica particle surface 1.0 particles / nm. 2 The amount of aluminum bonded to the surface of the silica particles (Al2O3 / SiO2) is 2915 ppm, and the amount of aluminum present on the entire silica particles (Al2O3 / SiO2) is 5797 ppm.

[0183] Using the obtained silica sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. Regarding the appearance of the obtained varnish, it was as transparent as the original polyamide-imide resin varnish after being stored at 50°C for 4 weeks. The initial viscosity was 2640 cps, which decreased to 2400 cps after 2 weeks of storage at 50°C and to 2200 cps after 4 weeks of storage at 50°C.

[0184] (Example 3)

[0185] By adding 1.2 g of tri-n-pentylamine to 667 g of the DMAC dispersed silica sol obtained by the method of Example 1, a DMAC dispersed silica sol was obtained with the following properties: silica concentration 30.5% by mass, pH 8.5, viscosity (20°C) 5.5 mPa·s, moisture 0.1% by mass, dynamic light scattering particle size 27 nm, average primary particle size 11 nm, and silane compound binding per unit area of ​​silica particle surface 1.0 particles / nm. 2 The amount of aluminum bonded to the surface of the silica particles (Al2O3 / SiO2) is 2915 ppm, and the amount of aluminum present on the entire silica particles (Al2O3 / SiO2) is 5797 ppm.

[0186] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. Regarding the appearance of the resulting varnish, it was as transparent as the original polyamide-imide resin varnish after being stored at 50°C for 2 weeks. The initial viscosity was 2700 cps, which decreased to 2500 cps after 2 weeks of storage at 50°C and to 2400 cps after 4 weeks of storage at 50°C.

[0187] (Example 4)

[0188] 1000g of the acidic silica sol (1) obtained in Example 1 was placed in a 2L glass reactor equipped with a stirrer, condenser, thermometer, and two inlets. While the sol in the reactor was kept boiling, methanol vapor generated in another vaporizer was continuously introduced into the silica sol in the reactor. As the liquid level gradually rose, the water was replaced with methanol. The replacement was stopped when the distillate volume was 9L, yielding 1100g of methanol-dispersed silica sol (SiO2 concentration 20.5% by mass, water 1.6% by mass, viscosity 2mPa·s).

[0189] 1000g of the obtained methanol sol was placed in a 2L round-bottom flask. While stirring the sol with a magnetic stirrer, 21.2g of phenyltrimethoxysilane was added, and the solution was maintained at 60°C for 1 hour. Next, 1.6g of N,N-diisopropylethylamine was added, and the solution was maintained at 60°C for 1 hour. Afterward, 19.6g of phenyltrimethoxysilane and 150g of butanone were added, and the solution was maintained at 60°C for 5 hours. Subsequently, the solvent was removed by evaporation in a rotary evaporator at a reduced pressure of 450–110 Torr and a bath temperature of 85–125 °C while DMAC was supplied, thus replacing the dispersion medium of the sol with DMAC. This yielded a DMAC-dispersed silica sol (silica concentration 30.5% by mass, pH 4.6, viscosity (20 °C) 5 mPa·s, water content 0.1% by mass, dynamic light scattering particle size 18 nm, average primary particle size 11 nm, and silane compound binding density per unit area of ​​silica particle surface 2.5 particles / nm). 2 The amount of aluminum bonded to the surface of the silica particles (Al2O3 / SiO2) is 2330 ppm, and the amount of aluminum present on the entire silica particles (Al2O3 / SiO2) is 5619 ppm.

[0190] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. Regarding the appearance of the resulting varnish, it was as transparent as the original polyamide-imide resin varnish after being stored at 50°C for 4 weeks. The initial viscosity was 2400 cps, which decreased to 2420 cps after 2 weeks of storage at 50°C, and to 2400 cps after 4 weeks of storage at 50°C.

[0191] (Example 5)

[0192] Except that 17.9 g of 3,3,3-trifluoropropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM-7703) was added in place of 16.3 g of phenyltrimethoxysilane in Example 1, the DMAC dispersed silica sol was obtained in the same manner as in Example 1 (silica concentration 30.5% by mass, pH 4.6, viscosity (20°C) 6.6 mPa·s, water content 0.1% by mass, dynamic light scattering particle size 28 nm, average primary particle size 11 nm, and silane compound binding amount per unit area of ​​silica particle surface 1.0 particles / nm). 2 The amount of aluminum bonded to the surface of the silica particles (Al2O3 / SiO2) is 3050 ppm, and the amount of aluminum present on the entire silica particles (Al2O3 / SiO2) is 5797 ppm.

[0193] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. Regarding the appearance of the resulting varnish, it was as transparent as the original polyamide-imide resin varnish after being stored at 50°C for 4 weeks. The initial viscosity was 2260 cps; the viscosity decreased to 2000 cps after being stored at 50°C for 2 weeks, and to 1860 cps after being stored at 50°C for 4 weeks.

[0194] (Example 6)

[0195] Except that in Example 1, 11.2 g of methyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM-13) was added to replace 16.3 g of phenyltrimethoxysilane, DMAC dispersed silica sol was obtained in the same manner as in Example 1 (silica concentration 30.5% by mass, pH 4.8, viscosity (20°C) 4.8 mPa·s, moisture 0.1% by mass, dynamic light scattering particle size 28 nm, average primary particle size 11 nm, and silane compound binding amount per unit area of ​​silica particle surface 1.0 particles / nm). 2 The amount of aluminum bonded to the surface of silica particles (Al2O3 / SiO2) is 3240 ppm, and the amount of aluminum present on the entire silica particles (Al2O3 / SiO2) is 5797 ppm.

[0196] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. Regarding the appearance of the resulting varnish, it was as transparent as the original polyamide-imide resin varnish after being stored at 50°C for 4 weeks. The initial viscosity was 2570 cps, which decreased to 2520 cps after 2 weeks of storage at 50°C, and to 2480 cps after 4 weeks of storage at 50°C.

[0197] (Example 7)

[0198] Except that phenyltrimethoxysilane was not added in Example 1, the process was carried out in the same manner as in Example 1, and DMAC dispersed silica sol (silica concentration 20.5% by mass, pH 4.5, moisture 0.1% by mass, dynamic light scattering particle size 40 nm, average primary particle size 11 nm, aluminum content (Al2O3 / SiO2) bound on the surface of silica particles 4490 ppm, aluminum content (Al2O3 / SiO2) present on all silica particles 5915 ppm).

[0199] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. Regarding the appearance of the resulting varnish, it was as transparent as the original polyamide-imide resin varnish after being stored at 50°C for 4 weeks. The initial viscosity was 1600 cps; the viscosity decreased to 1560 cps after being stored at 50°C for 2 weeks, and to 1480 cps after being stored at 50°C for 4 weeks.

[0200] (Example 8)

[0201] 1000g of acidic silica sol (2) was placed in a 2L glass reactor equipped with a stirrer, condenser, thermometer, and two inlets. While the sol in the reactor was kept boiling, methanol vapor generated in another vaporizer was continuously passed into the silica sol in the reactor. As the liquid level gradually rose, water was replaced with methanol. The replacement was stopped when the volume of the distillate was 9L, yielding 1100g of methanol-dispersed silica sol. The obtained methanol-dispersed silica sol had the following characteristics: SiO2 concentration 20% by mass, water content 1.0% by mass, and viscosity 2 mPa·s.

[0202] 1000g of the obtained methanol sol was placed in a 2L round-bottom flask. While stirring the sol with a magnetic stirrer, 11.7g of phenyltrimethoxysilane was added, and the solution was kept at 60°C for 1 hour. Next, 1.6g of N,N-diisopropylethylamine was added, and the solution was kept at 60°C for 1 hour. After that, 10.8g of phenyltrimethoxysilane and 150g of butanone were added, and the solution was kept at 60°C for 5 hours. Subsequently, the solvent was removed by evaporation in a rotary evaporator at a reduced pressure of 450–110 Torr and a bath temperature of 85–125 °C, while DMAC was supplied to replace the dispersion medium of the sol with DMAC, thus obtaining a DMAC-dispersed silica sol (silica concentration 30.5% by mass, pH 4.9, viscosity (20 °C) 7.4 mPa·s, water 0.1% by mass, dynamic light scattering particle size 39 nm, average primary particle size 21 nm, and silane compound binding per unit area of ​​silica particle surface 2.5 particles / nm). 2 The amount of aluminum bonded to the surface of the silica particles (Al2O3 / SiO2) is 3054 ppm, and the amount of aluminum present on the entire silica particles (Al2O3 / SiO2) is 7308 ppm.

[0203] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. Regarding the appearance of the resulting varnish, it was as transparent as the original polyamide-imide resin varnish after being stored at 50°C for 4 weeks. The initial viscosity was 2400 cps; the viscosity decreased to 2220 cps after being stored at 50°C for 2 weeks, and to 2300 cps after being stored at 50°C for 4 weeks.

[0204] (Example 9)

[0205] 1000g of acidic silica sol (2) was placed in a 2L bowl-shaped flask. While stirring the sol with a magnetic stirrer, 1.6g of N,N-diisopropylethylamine and 400g of DMAC were added and mixed for 15 minutes. Using a rotary evaporator, 200g of DMAC was added under reduced pressure (pressure 170 Torr, bath temperature 105°C) while water was distilled off, thereby obtaining 1000g of silica sol dispersed in a DMAC-water mixed solvent (20% by weight of silica and 20% by weight of water). While stirring the obtained sol with a magnetic stirrer, 9.0g of phenyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM-103) was added, and the liquid temperature was maintained at 60°C for 1 hour. Then, 0.8g of N,N-diisopropylethylamine was added and the mixture was maintained at 60°C for 1 hour. Subsequently, DMAC was supplied to the evaporator under reduced pressure (pressure 170–90 Torr, bath temperature 105–125 °C) while water was removed by distillation, thereby obtaining DMAC dispersed silica sol (silica concentration 30.5% by mass, viscosity (20 °C) 13.4 mPa·s, water 0.2% by mass). By adding 1.0 g of tri-n-pentylamine to 670 g of the obtained DMAC dispersed silica sol, a new DMAC dispersed silica sol was obtained (silica concentration 30.5% by mass, pH 8.6, viscosity (20 °C) 13.4 mPa·s, water 0.2% by mass, dynamic light scattering particle size 42 nm, average primary particle size 21 nm, and silane compound binding density per unit area of ​​silica particle surface 1.0 particles / nm). 2 The amount of aluminum bound to the surface of the silica particles (Al2O3 / SiO2) is 2444 ppm, and the amount of aluminum present on the entire silica particles (Al2O3 / SiO2) is 7383 ppm.

[0206] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. Regarding the appearance of the resulting varnish, it was as transparent as the original polyamide-imide resin varnish after being stored at 50°C for 4 weeks. The initial viscosity was 2600 cps, which decreased to 2360 cps after 2 weeks at 50°C and to 2160 cps after 4 weeks at 50°C.

[0207] (Example 10)

[0208] Except that phenyltrimethoxysilane was not added in Example 9, DMAC dispersed silica sol (silica concentration 20.5% by mass, pH 4.5, moisture 0.1% by mass, dynamic light scattering particle size 43.0 nm, average primary particle size 21 nm, aluminum content (Al2O3 / SiO2) bound on the surface of silica particles 3130 ppm, aluminum content (Al2O3 / SiO2) present on all silica particles 7534 ppm) was obtained by proceeding in the same manner as in Example 9.

[0209] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. Regarding the appearance of the resulting varnish, it was as transparent as the original polyamide-imide resin varnish after being stored at 50°C for 4 weeks. The initial viscosity was 1440 cps; the viscosity decreased to 1380 cps after being stored at 50°C for 2 weeks, and to 1440 cps after being stored at 50°C for 4 weeks.

[0210] (Example 11)

[0211] By using acidic silica sol (3), and reacting and solvent displacement were carried out in the same manner as in Example 1, a DMAC dispersed silica sol (silica concentration 30.5% by mass, pH 4.4, viscosity (20°C) 4.8 mPa·s, moisture 0.1% by mass, dynamic light scattering particle size 24 nm, average primary particle size 11 nm, and silane compound binding per unit area on silica particle surface 1.0 particles / nm) was obtained. 2 The amount of aluminum bound to the surface of the silica particles (Al2O3 / SiO2) is 2663 ppm, and the amount of aluminum present on the entire silica particles (Al2O3 / SiO2) is 5297 ppm.

[0212] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. Regarding the appearance of the resulting varnish, it was as transparent as the original polyamide-imide resin varnish after being stored at 50°C for 4 weeks. The initial viscosity was 2600 cps, which decreased to 2550 cps after 2 weeks of storage at 50°C and to 2500 cps after 4 weeks of storage at 50°C.

[0213] (Example 12)

[0214] Except for replacing 19.6 g of phenyltrimethoxysilane with 25.2 g of N-phenyl-3-aminopropyltrimethoxysilane in Example 4, the reaction and solvent substitution were carried out in the same manner as in Example 4 to obtain DMAC dispersed silica sol (silica concentration 30.5% by mass, pH 4.7, viscosity (20°C) 5 mPa·s, water content 0.1% by mass, dynamic light scattering particle size 20 nm, average primary particle size 11 nm, and silane compound binding amount per unit area of ​​silica particle surface 2.5 particles / nm). 2 The amount of aluminum bonded to the surface of silica particles (Al2O3 / SiO2) is 2780 ppm, and the amount of aluminum present on the entire silica particles (Al2O3 / SiO2) is 5560 ppm.

[0215] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. Regarding the appearance of the resulting varnish, it was as transparent as the original polyamide-imide resin varnish after being stored at 50°C for 4 weeks. The initial viscosity was 2450 cps, which decreased to 2470 cps after 2 weeks of storage at 50°C and to 2490 cps after 4 weeks of storage at 50°C.

[0216] (Example 13)

[0217] 1000g of acidic silica sol (4) was placed in a 2L glass reactor equipped with a stirrer, condenser, thermometer, and two inlets. While the sol in the reactor was kept boiling, methanol vapor generated in another vaporizer was continuously passed into the silica sol in the reactor. As the liquid level gradually rose, water was replaced with methanol. The replacement was stopped when the volume of the distillate was 9L, yielding 1100g of methanol-dispersed silica sol. The obtained methanol-dispersed silica sol had the following characteristics: SiO2 concentration 20% by mass, water content 1.0% by mass, and viscosity 2 mPa·s.

[0218] 1000g of the obtained methanol sol was placed in a 2L round-bottom flask. While stirring the sol with a magnetic stirrer, 24.6g of phenyltrimethoxysilane was added, and the solution was kept at 60°C for 1 hour. Next, 1.8g of N,N-diisopropylethylamine was added, and the solution was kept at 60°C for 1 hour. Then, 22.7g of phenyltrimethoxysilane and 150g of butanone were added, and the solution was kept at 60°C for 5 hours. Subsequently, the solvent was removed by evaporation using a rotary evaporator at a reduced pressure of 450–110 Torr and a bath temperature of 85–125 °C, while DMAC was supplied simultaneously, thereby replacing the dispersion medium of the sol with DMAC. This yielded a DMAC-dispersed silica sol (silica concentration 30.7 wt%, pH 4.4, viscosity (20 °C) 7.8 mPa·s, water content 0.1 wt%, dynamic light scattering particle size 20 nm, average primary particle size 9.5 nm, and silane compound binding density per unit area of ​​silica particle surface 2.5 particles / nm). 2 The amount of aluminum bonded to the surface of the silica particles (Al2O3 / SiO2) is 2230 ppm, and the amount of aluminum present on the entire silica particles (Al2O3 / SiO2) is 5072 ppm.

[0219] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. Regarding the appearance of the resulting varnish, it was as transparent as the original polyamide-imide resin varnish after being stored at 50°C for 4 weeks. The initial viscosity was 2200 cps, which decreased to 2400 cps after 2 weeks of storage at 50°C, and to 2200 cps after 4 weeks of storage at 50°C.

[0220] (Example 14)

[0221] 500g of acidic silica sol (5) and 500g of pure water were placed in a 2L glass reactor equipped with a stirrer, condenser, thermometer, and two inlets. While keeping the sol in the reactor boiling, methanol vapor generated in another vaporizer was continuously introduced into the silica sol in the reactor. As the liquid level gradually rose, the water was replaced with methanol. The replacement was stopped when the volume of the distillate reached 9L, yielding 1100g of methanol-dispersed silica sol. The obtained methanol-dispersed silica sol had the following composition: SiO2 concentration 12% by mass, water 1.0% by mass.

[0222] 1000g of the obtained methanol sol was placed in a 2L round-bottom flask. While stirring the sol with a magnetic stirrer, 23.1g of phenyltrimethoxysilane was added, and the solution was kept at 60°C for 1 hour. Next, 1.8g of N,N-diisopropylethylamine was added, and the solution was kept at 60°C for 1 hour. Then, 21.0g of phenyltrimethoxysilane and 150g of butanone were added, and the solution was kept at 60°C for 5 hours. Subsequently, while using a rotary evaporator to evaporate and remove the solvent at a reduced pressure of 450–110 Torr and a bath temperature of 85–125 °C, DMAC was supplied simultaneously to replace the dispersion medium of the sol, thus obtaining a DMAC-dispersed silica sol (silica concentration 20.8% by mass, pH 3.6, viscosity (20 °C) 46 mPa·s, water content 0.1% by mass, dynamic light scattering particle size 60 nm, average primary particle size 5.3 nm, and silane compound binding per unit area of ​​silica particle surface 2.5 particles / nm). 2 The amount of aluminum bonded to the surface of the silica particles (Al2O3 / SiO2) is 7286 ppm, and the amount of aluminum present on the entire silica particles (Al2O3 / SiO2) is 21028 ppm.

[0223] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. Regarding the appearance of the resulting varnish, it was as transparent as the original polyamide-imide resin varnish after being stored at 50°C for 4 weeks. The initial viscosity was 2180 cps, which remained at 2180 cps after 2 weeks of storage at 50°C, and 2200 cps after 4 weeks of storage at 50°C.

[0224] (Example 15)

[0225] 1000g of the methanol-dispersed silica sol (SiO2 concentration 20.5% by mass, water content 1.6% by mass, viscosity 2 mPa·s) described in Example 4 was placed in a 2L round-bottom flask. While stirring the sol with a magnetic stirrer, 19.6g of hexamethyldisiloxane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KF-96L) was added, and the liquid temperature was maintained at 60°C for 3 hours. Then, while evaporating the solvent using a rotary evaporator at a reduced pressure of 450–110 Torr and a bath temperature of 85–125°C, DMAC was supplied to replace the dispersion medium of the sol, thereby obtaining a DMAC-dispersed silica sol (silica concentration 30.3% by mass, pH 3.8, viscosity (20°C) 4.0 mPa·s, water content 0.1% by mass, dynamic light scattering particle size 27 nm, average primary particle size 11 nm, and silane compound binding amount per unit area of ​​silica particle surface 2.0 particles / nm). 2The aluminum content (Al2O3 / SiO2) present on all silicon dioxide particles is 5619 ppm.

[0226] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. Regarding the appearance of the resulting varnish, it was as transparent as the original polyamide-imide resin varnish after being stored at 50°C for 4 weeks. The initial viscosity was 2300 cps, which decreased to 2160 cps after 2 weeks and 4 weeks at 50°C.

[0227] (Example 16)

[0228] Except that the sol dispersion medium in Example 4 was changed from DMAC to NMP (N-methyl-2-pyrrolidone), the reaction and solvent replacement were carried out in the same manner as in Example 4 to obtain an NMP-dispersed silica sol (silica concentration 30.0% by mass, pH 4.8, viscosity (20°C) 10 mPa·s, water content 0.1% by mass, average primary particle size 11 nm, and silane compound binding per unit area of ​​silica particle surface 2.5 particles / nm). 2 The aluminum content (Al2O3 / SiO2) present on all silicon dioxide particles is 5797 ppm.

[0229] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. Regarding the appearance of the resulting varnish, it was as transparent as the original polyamide-imide resin varnish after being stored at 50°C for 4 weeks. The initial viscosity was 2800 cps, which decreased to 2720 cps after 2 weeks of storage at 50°C and to 2660 cps after 4 weeks of storage at 50°C.

[0230] (Comparative Example 1)

[0231] Except that acidic silica sol (4) was used instead of acidic silica sol (1) in Example 7, the same procedure was carried out as in Example 7 to obtain DMAC dispersed silica sol (silica concentration 20.5% by mass, pH 4.5, viscosity (20°C) 3 mPa·s, moisture 0.9% by mass, dynamic light scattering particle size 18 nm, average primary particle size 11 nm, aluminum content (Al2O3 / SiO2) bound on the surface of silica particles 760 ppm, aluminum content (Al2O3 / SiO2) present on all silica particles 2300 ppm).

[0232] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. The resulting varnish was cloudy from the outset, indicating silica agglomeration. The initial viscosity was 2000 cps, and after being stored at 50°C for 2 weeks, the viscosity was 2400 cps, and the varnish remained cloudy.

[0233] (Comparative Example 2)

[0234] Except that acidic silica sol (4) was used instead of acidic silica sol (1) in Example 4, the process was the same as in Example 4, and DMAC dispersed silica sol (silica concentration 30.5% by mass, pH 4.2, viscosity (20°C) 4.3 mPa·s, moisture 0.1% by mass, dynamic light scattering particle size 16 nm, average primary particle size 11 nm, and silane compound binding per unit area of ​​silica particle surface 2.5 particles / nm) was obtained. 2 The amount of aluminum (Al2O3 / SiO2) bonded to the surface of the silica particles is 380 ppm, and the amount of aluminum (Al2O3 / SiO2) present on the entire silica particles is 2300 ppm.

[0235] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. The resulting varnish was initially transparent, but became cloudy after being placed at 50°C for 2 weeks.

[0236] The initial viscosity was 2240 cps. After being stored at 50°C for 2 weeks, the viscosity of the varnish decreased to 3340 cps, and the appearance became cloudy. After being stored at 50°C for 4 weeks, the viscosity decreased to 3620 cps, and the appearance remained cloudy.

[0237] (Comparative Example 3)

[0238] Except that acidic silica sol (7) was used instead of acidic silica sol (2) in Example 10, the same procedure was performed as in Example 10 to obtain DMAC dispersed silica sol (silica concentration 20.5% by mass, pH 4.0, viscosity (20°C) 3.8 mPa·s, moisture 0.4% by mass, dynamic light scattering particle size 14 nm, average primary particle size 21 nm, aluminum content (Al2O3 / SiO2) bound on the surface of silica particles 450 ppm, aluminum content (Al2O3 / SiO2) present on all silica particles 2570 ppm).

[0239] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. The resulting varnish was cloudy from the outset, indicating silica agglomeration. The initial viscosity was 1800 cps, and after being stored at 50°C for 2 weeks, the viscosity was 2100 cps, and the varnish remained cloudy.

[0240] (Comparative Example 4)

[0241] Except that acidic silica sol (7) was used instead of acidic silica sol (2) in Example 9, the process was the same as in Example 9, and DMAC dispersed silica sol (silica concentration 30.5% by mass, pH 8.6, viscosity (20°C) 9.8 mPa·s, moisture 0.3% by mass, dynamic light scattering particle size 20 nm, average primary particle size 21 nm, and silane compound binding per unit area on silica particle surface 1.0 particles / nm) was obtained. 2 The amount of aluminum (Al2O3 / SiO2) bonded to the surface of the silica particles is 300 ppm, and the amount of aluminum (Al2O3 / SiO2) present on the entire silica particles is 2495 ppm.

[0242] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. The resulting varnish was cloudy from the outset, indicating silica agglomeration. The initial viscosity was 2700 cps, and after being stored at 50°C for 2 weeks, the viscosity was 3200 cps, and the varnish remained cloudy.

[0243] (Comparative Example 5)

[0244] Except that acidic silica sol (8) was used instead of acidic silica sol (2) in Example 10, the same procedure was performed as in Example 10 to obtain DMAC dispersed silica sol (silica concentration 20.5% by mass, pH 4.3, viscosity (20°C) 2 mPa·s, moisture 0.1% by mass, dynamic light scattering particle size 90 nm, average primary particle size 45 nm, aluminum content (Al2O3 / SiO2) bound on the surface of silica particles 460 ppm, aluminum content (Al2O3 / SiO2) present on all silica particles 2500 ppm).

[0245] Using the obtained sol, a silica-blended polyamide-imide resin varnish (resin / SiO2 = 85 / 15) was obtained in the same manner as in Example 1. The resulting varnish was initially transparent, but became cloudy after being placed at 50°C for 2 weeks.

[0246] The initial viscosity was 1500 cps. After being stored at 50°C for 2 weeks, the viscosity of the varnish decreased to 2240 cps, and the appearance became cloudy. After being stored at 50°C for 4 weeks, the viscosity decreased to 2640 cps, and the appearance remained cloudy.

[0247] (Transparency test of silica-blended polyamide-imide resin varnish)

[0248] A glass shallow dish was filled with a mixture of silica and polyamide-imide varnish to achieve a height of 3 mm. Two 10 mm high spacers were placed separately on a printed sheet of paper, and the shallow dish containing the varnish was placed on top of the spacers. The transparency was evaluated based on whether the text in the drawing was legible when viewed from above.

[0249] If the silica-polyamide-imide resin varnish has high transparency, text can be read. The silica-polyamide-imide resin varnishes of Examples 4 and 8 can read text as clearly as the reference polyamide-imide resin varnish. On the other hand, the silica-polyamide-imide resin varnishes of Comparative Examples 1 and 4 are cloudy and the text cannot be read. Figures 1-5 The image shows these results. Figure 1 These are photographs showing the evaluation test results for the transparency of the silica-blended resin varnish of Example 4. Figure 2 These are photographs showing the evaluation test results for the transparency of the silica-blended resin varnish of Example 8. Figure 3 These are photographs showing the evaluation test results for the transparency of the silica-blended resin varnish of Comparative Example 1. Figure 4 These are photographs showing the evaluation test results for the transparency of the silica-blended resin varnish in Comparative Example 4. Figure 5 These are photographs used as a reference to evaluate the transparency of resin varnishes without added silica.

[0250] (Transparency test of silica-polymerized polyamide resin cured film)

[0251] A coating of silica-polyamide-imide resin varnish was prepared on a glass substrate using an applicator. The coating was then dried in a dryer at 250°C for 45 minutes to obtain a cured film of the silica-polyamide-imide resin (cured film thickness 35 μm). Two 10 mm high spacers were placed separately on a printed sheet of paper, and the glass substrate with the cured film was placed on top of these spacers. The transparency was evaluated based on whether the text in the image was legible when viewed from above.

[0252] If the cured film of silica-polyamide resin has high transparency, the text can be read. The cured films obtained from silica-polyamide resin varnishes of Examples 4 and 8 can read the text as clearly as the cured film obtained from polyamide resin varnish used in the reference. On the other hand, the cured films obtained from silica-polyamide resin varnishes of Comparative Examples 1 and 4 are cloudy and the text cannot be read. Figure 6 These are photographs showing the evaluation test results of the transparency of the cured silica-blended resin varnish of Example 4. Figure 7 These are photographs showing the evaluation test results of the transparency of the cured silica-blended resin varnish of Example 8. Figure 9 These are photographs showing the evaluation test results for the transparency of the cured silica-blended resin varnish of Comparative Example 4. Figure 10 These are photographs showing evaluation tests of the transparency of cured resin varnishes without added silica, used as a reference.

[0253] (Preparation of the insulating resin composition)

[0254] (Example E1)

[0255] 1.0 kg of the DMAC dispersed silica sol obtained in Example 3 was placed in a 10 L plastic container, and 6.5 kg of polyamide-imide insulating resin varnish (manufactured by Showa Denko Materias Co., Ltd., trade name HPC-5012-32, resin solids content 32% by mass, NMP solvent) was added while stirring with a mechanical mixer. The mixture was stirred at room temperature for 2 hours to obtain silica sol mixed polyamide-imide resin varnish (resin / SiO2 = 85 / 15).

[0256] (Example E2)

[0257] 1.0 kg of the DMAC dispersed silica sol obtained in Example 8 was placed in a 10 L plastic container and stirred with a mechanical mixer. At the same time, 6.5 kg of polyamide-imide insulating resin varnish (manufactured by Showa Denko Materias Co., Ltd., trade name HPC-5012-32, resin solids content 32% by mass, NMP solvent) was added and stirred at room temperature for 2 hours to obtain silica sol mixed polyamide-imide resin varnish (resin / SiO2 = 85 / 15).

[0258] (Example E3)

[0259] 0.5 kg of DMAC dispersed silica sol and 0.4 kg of DMAC obtained in Example 3 were placed in a 10 L plastic container. While stirring with a mechanical mixer, 6.1 kg of polyamide-imide insulating resin varnish was added. The mixture was stirred at room temperature for 2 hours to obtain silica sol mixed with polyamide-imide resin varnish (resin / SiO2 = 93 / 7).

[0260] (Example E4)

[0261] 1.0 kg of the DMAC dispersed silica sol obtained in Example 14 was placed in a 10 L plastic container, and 6.0 kg of polyamide-imide insulating resin varnish was added while stirring with a mechanical mixer. The mixture was stirred at room temperature for 2 hours to obtain silica sol mixed with polyamide-imide resin varnish (resin / SiO2 = 90 / 10).

[0262] (Fabrication and evaluation of insulated wires)

[0263] Polyamide-imide resin varnish (manufactured by Showa Denko Materias Co., Ltd., trade name HPC-5012-32) was coated onto a copper conductor (0.4 mm in diameter) and baked to cure, thereby forming an insulating layer with a thickness of 4 μm. Then, the silica sol mixed polyamide-imide resin varnish obtained in Examples E1 to E4 above was coated, baked and cured, and finally an insulated wire with an insulating coating layer with a thickness of 23 μm was prepared.

[0264] In addition, as a reference example, an insulated wire with a 23μm thick insulating coating was produced by coating a copper conductor (0.4mm in diameter) with a polyamide-imide insulating resin varnish (manufactured by Showa Denko Materias Co., Ltd., trade name HPC-5012-32) and baking it.

[0265] The flexibility, insulation breakdown voltage, and insulation life (Vt test) of the insulated conductors obtained above were evaluated. The evaluation methods and conditions are shown below.

[0266] (Flexible)

[0267] In accordance with JIS C 3216-3 5, the qualified winding diameter that does not produce cracks on the film was investigated (using enameled wire with no stretching and after stretching by 20%).

[0268] In the flexibility test (without stretching), the unstretched insulated wire is wound onto a winding rod with a diameter of 1 to 10 times the diameter of the insulated wire conductor. The minimum winding diameter that does not show any cracks in the insulating film when measured using an optical microscope is measured.

[0269] In the flexibility test (20% elongation), the insulated wire was stretched by 20%. The same test as described above (without elongation) was then performed.

[0270] The flexibility test results show that the minimum winding diameter without cracking is the winding diameter itself (1d), the minimum winding diameter without cracking is twice the winding diameter itself (2d), and the minimum winding diameter without cracking is three times the winding diameter itself (3d). It can be said that the smaller the minimum winding diameter d, the better the flexibility.

[0271] (Insulation breakdown voltage)

[0272] According to JIS C 3216-5, section 4, a 50Hz AC voltage is applied between the two wires of the test piece, maintaining a 50mm distance, and the voltage at which insulation breaks down is measured. The boost voltage is 500V / s, and the insulation breakdown detection current is 5mA.

[0273] (Vt test)

[0274] In accordance with JIS C 3216-54, two test pieces were prepared and placed in an environment with a temperature of 155°C. The following voltage was applied between two lines that were kept 50 mm apart, and the time until breakdown was measured.

[0275] • Frequency: 10kHz rectangular wave

[0276] • Pulse width: 5μs

[0277] Bipolarity

[0278] • Pulse start-rise time: 80ns

[0279] Table 1

[0280]

[0281] Table 2

[0282]

[0283] The reference example consists only of polyamide-imide insulating resin varnish.

[0284] The insulated wire obtained in Example 1 significantly increases insulation life while maintaining mechanical properties compared to wires coated with polyamide-imide without mixed silica.

[0285] Industry availability

[0286] This invention provides silica sols in which silica particles are dispersed in a nitrogen-containing solvent (for good mixing with polyimide or polyamide-based polar resins). Resin compositions of these silica sols and resins, when used as insulating resin compositions, can provide insulated coated wires with high insulation resistance.

Claims

1. A composition comprising an insulating resin, said insulating resin comprising silica sol and a nitrogen-containing polymer, The silica sol is formed by dispersing silica particles with an average primary particle size of 5-100 nm containing aluminum atoms in a solvent. The total solvent content of the silica sol contains 98-100% by volume of a nitrogen-containing solvent and 0% to less than 2% by volume of other solvents. These other solvents are selected from water, ketone solvents, ester solvents, alcohol solvents, glycol ether solvents, hydrocarbon solvents, halogen solvents, ether solvents, glycol solvents, and amine solvents. The aluminum atoms, converted to Al2O3, were found to be bonded to the surface of the silica particles at a ratio of 800 to 20,000 ppm / SiO2, determined by leaching the silica particles in an aqueous solution of at least one mineral acid selected from sulfuric acid, nitric acid, and hydrochloric acid. Furthermore, the proportion of aluminum atoms present in the entire silica particles, converted to Al2O3 and determined by the dissolution method using hydrofluoric acid aqueous solution, was 2700-30000 ppm / SiO2. Aluminosilicate sites are formed on the surface of the silica particles. The nitrogen-containing solvent has carbonyl and amino groups within its molecules.

2. The composition of claim 1, wherein the silica particles are bonded with at least one silane compound selected from the following general formulas (1) to (3) or a hydrolysate thereof. In equation (1), R 1 It is a phenyl or phenyl-containing organogroup, an amino or amino-containing organogroup, a (meth)acryloyl or (meth)acryloyl-containing organogroup, a vinyl or vinyl-containing organogroup, an alkyl group optionally containing a halogen atom and having 1 to 10 carbon atoms, or a combination thereof, R 2 This indicates an alkoxy, acyl, or halogen group, where 'a' represents an integer from 1 to 3. In equations (2) and (3), R 3 and R 5 They are alkyl groups with 1 to 3 carbon atoms or aryl groups with 6 to 30 carbon atoms, and R 3 and R 5 R is bonded to silicon atoms via Si-C bonds. 4 and R 6 They represent alkoxy, acyloxy, or halogen groups respectively; Y represents 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.

3. The composition of claim 2, wherein the silane compound of general formula (1) binds 0.5 to 5.0 particles per unit area on the surface of the silica particles. 2 .

4. The composition according to any one of claims 1 to 3, wherein the amount of negative charge present on the surface of the silica particles is 0.25 to 0.45 μeq / m. 2 .

5. The composition according to any one of claims 1 to 3, wherein the nitrogen-containing solvent is an amide solvent.

6. The composition according to any one of claims 1 to 3, wherein the nitrogen-containing solvent is dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or N-ethylpyrrolidone.

7. The composition according to any one of claims 1 to 3, wherein the mass parts of the nitrogen-containing polymer are 1 to 100 relative to 1 part by mass of silica particles contained in the silica sol.

8. The composition according to any one of claims 1 to 3, wherein the nitrogen-containing polymer is any one of polyimide, polyamide, polyamic acid, polyamide-imide, polyether-imide, and polyester-imide.

9. The composition according to any one of claims 1 to 3, wherein the viscosity of the composition after storage at 50°C for 2 weeks is 0.80 to 1.05 times that of the initial viscosity measured at 25°C.

10. An insulated wire, formed by insulating the wire with a composition of insulating resin as described in any one of claims 1 to 6.

11. An insulated wire, comprising an insulated wire having a thickness of 23µm covered with a composition of insulating resin as described in any one of claims 1 to 6, wherein the flexibility of the insulating covering layer is 1d to 2d. The concentration of silica particles in the solvent of the composition is adjusted to 15% by mass.

12. An insulated wire, comprising an insulated wire having a thickness of 23µm insulated with a composition of insulating resin as described in any one of claims 1 to 6, wherein the insulation life measured under conditions of a pulsed voltage of 1.5kVp, bipolar, and a 10kHz rectangular wave is 0.2 to 20 hours. The concentration of silica particles in the solvent of the composition is adjusted to 15% by mass.

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