Surface-treated silica sol containing free silanol groups dispersed in nitrogen-containing solvent and insulating resin composition

Abstract

The present invention provides a silica sol in which silica particles are dispersed in a nitrogen-containing solvent for mixing with a polyimide-based or polyamide-based polar resin in a state of good compatibility, which can be subjected to additional silane treatment depending on the application, etc., and which is highly customizable and reliable, with high concentration and excellent storage stability. A silica sol containing silica particles having an average particle size of 5 to 100 nm as determined by a dynamic light scattering method, the particles having organic groups containing unsaturated bonds between carbon atoms bonded to the surface thereof, and a nitrogen-containing solvent, wherein the number of organic groups containing unsaturated bonds between carbon atoms bonded to the surface of the silica particles is 0.1 to 2.0 per unit area of ​​the surface of the silica particles. 2 The silica particle concentration is 25 to 70 mass %, free silanol groups are present on the silica particle surface, and the number of free silanol groups present per unit area on the silica particle surface is 0.4 to 1.2 / nm 2 That is, silica sol.

Description

[Technical Field]

[0001] The present invention relates to a surface-treated silica sol having free silanol groups dispersed in a nitrogen-containing solvent, and an insulating resin composition containing the silica sol and a nitrogen-containing polymer. [Background technology]

[0002] A method is known in which an inorganic oxide sol dispersed in an organic solvent such as toluene is obtained by subjecting a surface treatment to organification by reacting an alcohol with hydroxyl groups on the surface of inorganic oxide particles such as silica to introduce alkoxysilyl groups. For example, Patent Document 1 discloses a silica sol obtained by reacting a methanol-dispersed silica sol with phenyltrimethoxysilane and dispersing the resulting silica sol in a toluene solvent.

[0003] Patent Document 2 discloses a silica sol obtained by subjecting a methanol-dispersed silica sol to solvent substitution with acetonitrile to obtain a silica sol dispersed in an acetonitrile-methanol mixed solvent, and then performing a surface treatment with phenyltrimethoxysilane.

[0004] Patent Document 3 discloses a silica-based fine particle water dispersion sol containing silica fine particles whose surfaces are modified with aluminum.

[0005] Patent Document 4 discloses an aluminum-containing silica sol in which silica particles containing aluminum atoms are dispersed in a nitrogen-containing solvent, in which the aluminum atoms are bonded to the surface of the silica particles at a predetermined ratio, and an insulating resin composition using the same. [Prior art documents] [Patent documents]

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

[0007] Further investigation by the present inventors has revealed that when utilizing silica sol that has been subjected to the above-mentioned surface treatment or surface modification, it would be industrially useful to provide a silica sol that can be subsequently subjected to additional silane treatment depending on the application, etc. (customizability), and that it is also desirable to provide a high-concentration silica sol that also has excellent storage stability even before the above-mentioned additional silane treatment is performed (reliability), and that there is room for further improvement in terms of achieving both such customizability and reliability.

[0008] The present invention aims to provide a silica sol in which silica particles are dispersed in a nitrogen-containing solvent for mixing with a polyimide-based or polyamide-based polar resin in a state of good compatibility, which can be subjected to additional silane treatment depending on the application, etc., and which is highly customizable and reliable, with high concentration and excellent storage stability. [Means for solving the problem]

[0009] The present inventors have conducted extensive experiments and intensive research aimed at solving the above problems, and as a result have completed the present invention. That is, the gist of the present invention is as follows. [1] A silica sol containing silica particles having an average particle size of 5 to 100 nm as measured by a dynamic light scattering method, the particles having an organic group containing an unsaturated bond between carbon atoms bonded to the surface, and a nitrogen-containing solvent, The number of organic groups containing unsaturated bonds between carbon atoms bonded to the surface of the silica particles is 0.1 to 2.0 per unit area of ​​the surface of the silica particles. 2 and The concentration of silica particles is 25 to 70 mass %, Free silanol groups are present on the surface of the silica particles, and the number of free silanol groups present per unit area on the surface of the silica particles is 0.4 to 1.2 / nm 2 That is, Silica sol. [2] The number of alkoxy groups bonded to the surface of the silica particles is 0.001 to 0.03 per unit area of ​​the surface of the silica particles. 2 The silica sol according to [1], [3] The silica sol according to [1], wherein the organic group containing an unsaturated bond between carbon atoms is an organic group containing a phenyl group or an organic group containing a (meth)acryloyl group. [4] The silica sol according to [1], wherein the organic group containing an unsaturated bond between carbon atoms is a phenyl group, a phenylaminoalkyl group, a (meth)acryloyl group, or a (meth)acryloylalkyl group. [5] The silica sol according to [1], wherein the nitrogen-containing solvent is an amide solvent. [6] The silica sol according to [1], wherein the nitrogen-containing solvent is dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or N-ethylpyrrolidone. [7] An insulating resin composition comprising the silica sol according to any one of [1] to [6] and a nitrogen-containing polymer. [8] The insulating resin composition according to [7], wherein the ratio of the nitrogen-containing polymer to 1 part by mass of silica contained in the silica sol is 1 to 100. [9] The insulating resin composition according to [7], wherein the nitrogen-containing polymer is polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, or polyesterimide. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a silica sol in which silica particles are dispersed in a nitrogen-containing solvent for mixing with a polyimide-based or polyamide-based polar resin in a state of good compatibility, and it is possible to provide a silica sol that can be subjected to additional silane treatment depending on the application, etc., and that is highly customizable and reliable, with a high concentration and excellent storage stability. Furthermore, the silica sol dispersed in the nitrogen-containing solvent of the present invention has good compatibility with nitrogen-containing polymers such as polyimides and polyamides, and by combining the silica sol with the nitrogen-containing polymer to form a composition, an insulating resin composition (resin varnish) in which silica particles are sufficiently dispersed can be obtained. The insulating resin composition of the present invention can be used as a coating material for conductors that require insulation. For example, by coating the surface of a conductor such as a copper wire or an enamel-coated copper wire, an insulating coated conductor wire that can maintain a long insulation life can be obtained. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present invention will be described below. However, the following embodiments are merely examples for explaining the present invention, and the present invention is not limited to the following embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. Note that in this specification, the above-mentioned multiple numerical ranges shown as stepwise preferable ranges can also be understood as independently preferable upper or lower limits, focusing only on each upper or lower limit.

[0012] [Silica sol and its manufacturing method] The silica sol of the present invention is a silica sol containing silica particles having an average particle size of 5 to 100 nm as determined by a dynamic light scattering method, and having organic groups containing unsaturated bonds between carbon atoms bonded to the surface thereof, and a nitrogen-containing solvent, wherein the number of organic groups containing unsaturated bonds between carbon atoms bonded to the surface of the silica particles is 0.1 to 2.0 per unit area of ​​the surface of the silica particles. 2 The silica particle concentration is 25 to 70 mass %, free silanol groups are present on the silica particle surface, and the number of free silanol groups present per unit area on the silica particle surface is 0.4 to 1.2 / nm 2 is.

[0013] The average primary particle size of silica particles is determined by the specific surface area (S N2 ) can be used as the particle diameter (nm). For example, the specific surface area diameter (average primary particle diameter: D (nm)) can be calculated by multiplying the specific surface area S measured by the nitrogen adsorption method (BET method). N2 (m 2 / g) and density ρ (g / cm 3 ) D(nm)=6000 / ρ×S N2 The primary particle diameter is calculated by the formula below, and means the particle diameter converted into that of spherical silica particles. The particle size of the silica particles contained in the silica sol can be measured by an average particle size measured by a dynamic light scattering method (DLS method). The silica sol of the present invention has good dispersibility in a nitrogen-containing solvent, and the average particle size measured by a dynamic light scattering method in a nitrogen-containing solvent is preferably 5 to 100 nm, more preferably 10 to 70 nm.

[0014] The silica particles of the present invention have organic groups containing unsaturated bonds between carbon atoms bonded to their surfaces. In one embodiment of the present invention, the organic group containing an unsaturated bond between carbon atoms may be an organic group containing a phenyl group or an organic group containing a (meth)acryloyl group, and specific examples thereof may include a phenyl group, a phenylaminoalkyl group, a (meth)acryloyl group, or a (meth)acryloylalkyl group. In the present invention, among these, from the viewpoint of compatibility with the nitrogen-containing polymer, a phenyl group or a phenylaminoalkyl group is preferred, and a phenyl group is more preferred.

[0015] Considering the effects of the present invention, the number of organic groups containing unsaturated bonds between carbon atoms bonded to the surface of the silica particles is 0.1 to 2.0 per unit area of ​​the surface of the silica particles. 2 It is preferable that the number of particles is 0.1 to 1.5 particles / nm 2 More preferably, the density is 0.2 to 1.0 particles / nm 2When the amount of unsaturated bond-containing organic groups bonded is greater than the lower limit, the effect of excellent storage stability of the silica sol is expected, and when the amount of unsaturated bond-containing organic groups bonded is less than the upper limit, the effect of excellent customizability (the property of being able to bond further organic groups to the surface of the silica particles as needed) is expected.

[0016] In one embodiment of the present invention, an alkoxy group may be bonded to the surface of the silica particles. Examples of the alkoxy group include alkoxy groups having a linear, branched, or cyclic alkyl moiety having 1 to 10 carbon atoms, and specific examples include methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, and t-butoxy groups. In the present invention, from the viewpoints of compatibility with nitrogen-containing polymers and customizability, methoxy, ethoxy, and n-propoxy groups are preferred, and methoxy is more preferred.

[0017] Considering the effects of the present invention, the number of alkoxy groups bonded to the surface of the silica particles is 0.001 to 0.03 / nm per unit area of ​​the surface of the silica particles. 2 It is preferable that the number of particles is 0.002 to 0.03 particles / nm 2 More preferably, the density is 0.004 to 0.03 particles / nm 2 When the amount of alkoxy groups bonded is greater than the lower limit, the effect of excellent compatibility with the nitrogen-containing polymer is expected, and when the amount of alkoxy groups bonded is less than the upper limit, the effect of excellent customizability is expected.

[0018] The silica sol of the present invention has excellent dispersibility and storage stability even when the silica particle concentration is relatively high. The concentration of silica particles contained in the silica sol of the present invention is preferably 25 to 70 mass %, more preferably 30 to 60 mass %, and even more preferably 40 to 50 mass %. A silica particle concentration higher than the lower limit is expected to have the effect of increasing the amount of silica particles blended into the resin while suppressing dilution of the resin due to the dispersion solvent brought in by the silica sol. A silica particle concentration lower than the upper limit is expected to have the effect of excellent storage stability of the silica sol.

[0019] The silica sol of the present invention is a sol (dispersion liquid) in which silica particles having organic groups containing unsaturated bonds between carbon atoms bonded to the surface thereof are dispersed in a nitrogen-containing solvent.

[0020] The nitrogen-containing solvent has a functional group containing at least a nitrogen atom, and examples of the functional group containing a nitrogen atom include an amino group, a nitro group, and a cyano group. Among these, an amino group is preferred. An amide solvent can be preferably used as the nitrogen-containing solvent. Specific examples of the nitrogen-containing solvent include dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, tetramethylurea, hexamethylphosphoric triamide, dimethylacrylamide, acryloylmorpholine, hydroxyethylacrylamide, isopropylacrylamide, diethylacrylamide, dimethylaminopropylacrylamide, 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, dimethylaminopropylacrylamide methyl chloride quaternary salt, and dimethylaminoethyl acrylate benzyl chloride quaternary salt. Among these, dimethylacetamide, dimethylformamide, N-methylpyrrolidone, and N-ethylpyrrolidone can be preferably used.

[0021] The nitrogen-containing solvent may contain other solvents as long as the effects of the present invention are not impaired. For example, the nitrogen-containing solvent may be contained in an amount of 50 to 100 volume %, 90 to 100 volume %, 98 to 100 volume %, or 99 to 100 volume % of the total solvent, and the other solvents may be contained in an amount of 0 to less than 50 volume %, 0 to less than 10 volume %, 0 to less than 2 volume %, or 0 to less than 1 volume %.

[0022] The silica particles of the present invention are characterized in that the surface thereof contains a specific range of free silanol groups. The free silanol groups can be measured using the method described in the section "Measurement of the amount of free silanol groups" below. Considering the effects of the present invention, the amount of free silanols present on the surface of silica particles is 0.4 to 1.2 / nm per unit area of ​​the surface of silica particles. 2 It is preferable that the number of particles is 0.6 to 1.2 particles / nm 2 More preferably, the density is 0.8 to 1.1 particles / nm 2 When the amount of free silanol groups present is greater than the lower limit, the effect of excellent customizability is expected, and when the amount of free silanol groups present is less than the upper limit, the effect of excellent storage stability of the silica sol is expected.

[0023] As described below, it is effective to adjust the amount of a specific silane compound, such as phenyltrimethoxysilane, added, which is represented by formula (1), to determine the amount of free silanol groups present on the surface of silica particles. By optimizing the reaction conditions for coating the surface of silica particles with a specific silane compound, the amount of free silanol groups present on the surface of silica particles after solvent substitution with a nitrogen-containing solvent can be appropriately adjusted to fall within a predetermined range, thereby providing a silica sol that is both customizable and reliable.

[0024] The silica sol of the present invention can be produced by coating the silica surface by surface-treating or surface-modifying the silica sol. An example of the method for producing the silica sol of the present invention will be described below.

[0025] In the present invention, silica particles are prepared by the method of the present invention, comprising: [ka] (In formula (1), R 1 represents an organic group containing an unsaturated bond between carbon atoms and bonded to a silicon atom via a Si-C bond, and R 2 represents an alkoxy group, and a is an integer of 1 to 3. Examples of the organic group containing an unsaturated bond between carbon atoms include an organic group containing a phenyl group and an organic group containing a (meth)acryloyl group. Specific examples of the silane compound represented by formula (1) include phenyltrimethoxysilane, phenyltriethoxysilane, phenylmethyldimethoxysilane, phenylaminopropyltrimethoxysilane, phenylaminopropyltriethoxysilane, methacryloyloxypropyltrimethoxysilane, and acryloyloxypropyltrimethoxysilane.

[0026] In the present invention, the surface modification of silica particles can also be carried out using a hydrolyzable silane compound of formula (2) and / or formula (3) together with the silane coupling agent of formula (1). [ka] (In formula (2) and formula (3), R 3 and R 5 are alkyl groups having 1 to 3 carbon atoms and bonded to a silicon atom via a Si-C bond, and R 4 and R 6 each represents an alkoxy group, Y represents an alkylene group, an NH group, or an oxygen atom, b is an integer of 1 to 3, c is an integer of 0 or 1, and d is an integer of 1 to 3.) or a hydrolyzate thereof.

[0027] The alkoxy group includes an alkoxy group having a linear, branched, or cyclic alkyl moiety having 1 to 10 carbon atoms, such as a methoxy group, an ethoxy group, an n-propoxy group, an i-propoxy group, an n-butoxy group, an i-butoxy group, an s-butoxy group, and a t-butoxy group.

[0028] The silane compounds represented by the above formulas (2) and (3) are preferably compounds capable of forming trimethylsilyl groups on the surfaces of silica particles. Examples of the structures of these compounds include the following structures. [ka] In the above formula (2-3), R 12 represents an alkoxy group, such as a methoxy group or an ethoxy group.

[0029] As these silane compounds, silane coupling agents manufactured by Shin-Etsu Chemical Co., Ltd., Dow Toray Co., Ltd., and JNC Corporation can be used.

[0030] In the present invention, silica sol can be produced by a water glass method using water glass as a raw material, an alkoxide method using metal alkoxide as a raw material, a gas phase method using silicon chloride compound as a raw material, etc. Silica sol obtained by any of the methods may be used, but the water glass method is preferable.

[0031] The silica sol of the present invention can be prepared, for example, by the following steps (A), (B), (C), (D), and (E): Step (A): preparing a silica sol in which silica particles having an average primary particle diameter of 5 to 100 nm are dispersed in an aqueous medium; Step (B): adding a nitrogen-containing solvent and an alkali catalyst to the silica sol obtained in step (A); Step (C): A step (C) of solvent-substituting the silica sol obtained in step (B) with a nitrogen-containing solvent; Step (D): Step (D) of adding a silane compound represented by formula (1) and, optionally, a silane compound represented by formula (2) or formula (3); Step (E): A step (E) of replacing the dispersion medium of the silica sol obtained in step (D) with a nitrogen-containing solvent; The method can be carried out by the following steps.

[0032] The silica sol used in step (A) can be a silica sol (aqueous silica sol) dispersed in an aqueous medium with an average particle size ranging from 5 to 100 nm or 10 to 70 nm. The aqueous silica sol can be produced by cation-exchanging an aqueous alkali silicate solution with a solids concentration of 1 to 10% by mass, to obtain a silicic acid solution with a pH of 1 to 6, and heating the resulting solution at 50 to 110°C in the presence of an alkali. The cation-exchange treatment can be carried out by passing the aqueous alkali silicate solution through a strongly acidic cation-exchange resin packed in a column.

[0033] As the alkali silicate, sodium silicate, potassium silicate, lithium silicate, etc. can be used, and sodium silicate commercially available under the names No. 1 sodium water glass, No. 2 sodium water glass, No. 3 sodium water glass, etc. can be used.Also usable are alkali silicates obtained by adding sodium hydroxide, potassium hydroxide, lithium hydroxide, or quaternary ammonium hydroxide to a silicic acid solution obtained by hydrolyzing an alkoxysilane such as tetraethoxysilane or tetramethoxysilane.

[0034] Instead of the aqueous silica sol used in step (A), a silica sol in which the aqueous medium has been solvent-substituted with an alcohol having 1 to 3 carbon atoms by vacuum distillation, ultrafiltration, or the like can be used.

[0035] The silica sol used in step (A) can be an aqueous silica sol that has been subjected to a hydrothermal treatment for 0.1 to 10 hours.

[0036] The silica sol obtained in step (A) can be subjected to cation exchange or anion exchange, if necessary.

[0037] In step (B), a nitrogen-containing solvent and an alkali catalyst are added to the silica sol obtained in step (A). To prevent thickening during solvent substitution in step (C), it is preferable to add a nitrogen-containing solvent and an alkali catalyst to the aqueous silica sol. The nitrogen-containing solvent is preferably an amide solvent, such as dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or N-ethylpyrrolidone. Examples of alkali catalysts include alkali metals such as sodium hydroxide and potassium hydroxide, and amines such as ethylenediamine and diethylenetriamine.

[0038] Step (C) is a step of replacing the dispersion medium of the silica sol obtained in step (B) with a nitrogen-containing solvent. Solvent replacement can be performed using an evaporator or UF concentration. In the solvent replacement with a nitrogen-containing solvent, the water content can be adjusted to a range of 3.0 to 15.0 wt. % or 5.0 to 10.0 wt. % of the total solvent.

[0039] Step (D) is a step of adding a silane compound represented by formula (1) (tentatively referred to as silane compound A) and, optionally, a silane compound represented by formula (2) or formula (3) (tentatively referred to as silane compound B) to the silica sol obtained in step (C). The order of addition of silane compound A and silane compound B may be any order, but it is preferable to coat silica particles with the silane compound represented by formula (1) (silane compound A) or its hydrolysis condensate, and then add the silane compound represented by formula (2) or formula (3) (silane compound B).

[0040] In step (E), the dispersion medium of the silica sol obtained in step (D) is replaced with a nitrogen-containing solvent. During or after the solvent replacement step, the silica concentration in the silica sol can be adjusted to 5 to 75 mass%, 20 to 70 mass%, or 25 to 70 mass%.

[0041] In step (E), the nitrogen-containing solvent may be contained in an amount of 50 to 100 volume %, 90 to 100 volume %, 98 to 100 volume %, or 99 to 100 volume % of the total solvent, and other solvents may be contained in an amount of 0 to less than 50 volume %, 0 to less than 10 volume %, 0 to less than 2 volume %, or 0 to less than 1 volume %. Multiple types of nitrogen-containing solvents may also be contained. Water and alcohol dispersions containing 1 to 3 carbon atoms contained in the silica sol in step (A) may be contained in the above-mentioned ranges as other solvents, as long as the effect is not impaired.

[0042] Specific examples of the nitrogen-containing solvent used for solvent substitution in step (C) are as described above.

[0043] [Insulating resin composition and its manufacturing method] An insulating resin composition (resin varnish) can be obtained by combining a silica sol in which the nitrogen-containing solvent of the present invention is used as a dispersion medium with a nitrogen-containing polymer.

[0044] The insulating resin composition (resin varnish) can be prepared by the above steps (A) to (E), and further steps (F) and (G): Step (F): Step (E) of mixing the silica sol obtained in step (E), in which the silica particles are dispersed in a nitrogen-containing solvent, with a nitrogen-containing polymer; Step (G): A step of removing a part or all of the nitrogen-containing solvent from the silica sol obtained in step (F); It can be obtained by a method comprising:

[0045] As an example, the above method can provide a silica sol in which silica particles coated with phenyl groups from phenyltrimethoxysilane as a silane compound and trimethylsilyl groups from hexamethyldisiloxane as a silane compound are dispersed in dimethylacetamide (DMAC) as a nitrogen-containing solvent, and can further be combined with a nitrogen-containing polymer to produce an insulating resin composition.

[0046] It is possible to obtain a resin varnish such as an insulating resin composition in which the parts by mass of the nitrogen-containing polymer per part by mass of silica particles contained in the silica sol is 1 to 100, or 1 to 50, or 1 to 10. Examples of the nitrogen-containing polymer include polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, and polyesterimide.

[0047] The insulating resin composition can be applied to a conductor that requires insulation and then heated and cured at a temperature at which the solvent evaporates, forming an insulating coating (insulating coating layer) on the surface of the conductor. The heating temperature for removing the solvent is determined by the temperature and pressure, but is about 150°C to 300°C at normal pressure, or about 150°C to 400°C for imidization of the resin.

[0048] Conductors include metal conductors such as copper wire and aluminum wire, with copper wire being particularly preferred. Copper wire is used as an enamel-coated electric wire in industrial and household motors, transformers, coils, etc.

[0049] An insulating coated conductor can be produced by coating a copper wire with an insulating coating layer using the insulating resin composition of the present invention as the insulating coating layer.

[0050] The insulating resin composition is obtained by mixing 1 to 100, 1 to 50, or 1 to 10 parts by mass of a nitrogen-containing polymer with 1 part by mass of silica particles contained in silica sol. The insulating resin composition can be obtained by mixing and stirring the silica sol and the polymer with a mixer or disperser. Additives can be added as desired during the blending process. [Example]

[0051] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0052] (Analysis method) [Measurement of SiO2 concentration] The silica sol was placed in a crucible and dried at 150°C, and the resulting gel was then fired at 1000°C for 30 minutes in the atmosphere, and the firing residue was weighed and calculated.

[0053] [Measurement of average primary particle size (particle size by nitrogen adsorption method)] The specific surface area (S) of silica particles in water-dispersed silica sol was measured by nitrogen adsorption. N2 ) was measured by removing water-soluble cations in the water-dispersed silica sol with an H-type cation exchange resin (Dow Chemical Company, trade name: Amberlite IR-120B), and then drying the silica sol at 290°C to prepare a measurement sample. This was then measured by the BET single-point method using a nitrogen adsorption specific surface area measuring device (trade name: Monosorb, manufactured by Quantachrome Instruments Japan LLC) with a mixed gas of 30% N2 (nitrogen) and 70% He (helium) as the carrier gas. The specific surface area (S) of silica particles in organic solvent-dispersed silica sols was measured by nitrogen adsorption. N2 The specific surface area S was measured by the BET single-point method using the measurement sample (silica particles (powder) heated at 150°C) obtained in the (Measurement of Carbon Content) section described later. N2 (m 2 / g) and density ρ (g / cm 3 ) Average primary particle size (nm) = 6000 / ρ × S N2 In the present invention, the density of the silica particles ρ (g / cm 3 ) is 2.2(g / cm 3 ) was calculated as

[0054] [Moisture measurement] The moisture content was determined by Karl Fischer titration using a Karl Fischer moisture meter (manufactured by Kyoto Electronics Manufacturing Co., Ltd., trade name: MKA-610).

[0055] [pH measurement] The pH of the water-dispersed silica sol was measured at 20°C using a pH meter (manufactured by DKK Toa Corporation, product name: MM-43X). The pH of the organic solvent-dispersed silica sol was measured at 20°C using a liquid obtained by mixing silica sol and pure water in a mass ratio of 1:1 when the organic solvent serving as the dispersion medium was methanol (MeOH), or a liquid obtained by mixing silica sol, MeOH, and pure water in a mass ratio of 1:1:1 when the organic solvent was a nitrogen-containing solvent, such as dimethylacetamide (DMAC).

[0056] [Measurement of Viscosity] The viscosity of the silica sol was measured at 20°C using an Ostwald viscometer.

[0057] [Measuring average particle size by dynamic light scattering (DLS) method] The average particle size measured by the DLS method (average secondary particle size measured by dynamic light scattering: Z-average particle size, also referred to as DLS average particle size) was measured using a dynamic light scattering particle size analyzer (Malvern Panalytical, product name: Zetasizer Nano). 0.1 g of the target silica sol was dispensed into a glass cell with a 10 mm optical path length, and the solvent that was the main component of the silica sol's dispersion medium was added to obtain a silica sol with a silica particle concentration adjusted to a count rate of 200 to 400 kcps when the attenuator was set to 7. For example, MeOH was added to a silica sol whose main component was methanol, and DMAC was added to a silica sol whose main component was DMAC, to obtain a silica sol with a silica particle concentration adjusted to a count rate of 200 to 400 kcps when the attenuator was set to 7. The prepared silica sol was placed in the cell so that the liquid level was approximately 1 cm above the bottom of the cell, and the DLS average particle size of the silica sol was measured using the attenuator.

[0058] [Measurement of carbon content] (1) Place 3 mL of organic solvent-dispersed silica sol in a 30 cc centrifuge tube and add 20 mL of toluene. (2) After centrifuging (centrifugal force 11,000 G x 30 minutes), the supernatant is removed. (3) 4 mL of acetone is added to redissolve the gel, and then 4 mL of toluene and 10 mL of hexane are added. The mixture is centrifuged (centrifugal force 11,000 G x 30 minutes), and the supernatant is removed. (4) Then repeat (3). (5) The obtained gel was vacuum dried at 60°C, and the obtained powder was then crushed in a mortar and dried at 150°C for 2 hours to obtain silica powder. The carbon content (mass %) of the powder obtained above was measured using an elemental analyzer (manufactured by PerkinElmer, trade name 2400II CHNS / O).

[0059] [Measurement of the amount of alkoxy groups bonded] 0.2 g of the powder obtained in [Measurement of carbon content] was mixed and dissolved in 10 mL of 0.05 N sodium hydroxide solution, and subjected to gas chromatography measurement (Shimadzu Corporation, product name: GC-2014s, column: PorapakQ, heating rate: 5 °C / min, temperature range: 20 to 250 °C). The gas chromatography measurement results and the specific surface area value S N2 (m 2 / g) to calculate the amount of alkoxy groups bound to the surface (number / nm 2 ) was measured.

[0060] [Measurement of the amount of unsaturated bond-containing organic groups] The carbon content corresponding to the amount of alcohol released from the alkoxy groups contained in the silica particles, obtained from the gas chromatography measurement in [Measurement of the amount of bonded alkoxy groups], and the carbon content corresponding to the solvent (e.g., DMAC, etc.: dimethylacetamide, etc.) adsorbed to the silica particles, are subtracted from the carbon content of the powder obtained in [Measurement of carbon content] to obtain the amount of bonded unsaturated bond group-containing organic groups (number / nm 2 ) was quantified. The number of unsaturated bond-containing organic groups bound (units / nm 2 )=[(C м -C A -C S ) / M P ×A b ] / (S N2 x10 18×100) Formula (I) C м : Carbon content of powder (mass%) C A : Carbon content (mass%) equivalent to the amount of alcohol eliminated from the alkoxy group C S : Carbon content (mass%) equivalent to the solvent adsorbed on silica particles M P : Amount of carbon per 1 mol contained in the organic group containing the unsaturated bond group (72 g / mol in the case of phenyltrimethoxysilane) A b : Avogadro's constant 6.02 x 10 23 (pieces / mol) S N2 : specific surface area (m 2 / g)

[0061] [Measurement of the amount of free silanol groups] The silica sol was subjected to additional silane treatment according to the following procedure, and the amount of free silanol groups was calculated. (1) 100 g of silica sol was placed in a 250 mL recovery flask, and 2 g of pure water was added while stirring the sol with a magnetic stirrer. Then, hexamethyldisilazane (Shin-Etsu Chemical Co., Ltd., product name SZ-31) was added at a concentration of 3 particles / nm. 2 (for example, 7.4 g when the average primary particle diameter of silica particles is 12 nm and the silica concentration is 30 mass %) is added, and then the liquid temperature is maintained at 90° C. for 3 hours. (2) The solvent is evaporated and distilled off in a rotary evaporator at a reduced pressure of 450 to 110 Torr and a bath temperature of 85 to 125°C while the main component of the dispersion medium, for example, DMAC in Example 1 described below, is supplied, and trimethylsilane, which is produced by hydrolysis of hexamethyldisilazane, is used to obtain an additional silane-treated silica sol. (3) The carbon content of the silica sol before and after the additional silane treatment in (2) is calculated according to [Measurement of carbon content]. (4) [Measurement of the amount of alkoxy group bond] The carbon content corresponding to the amount of alcohol released from the alkoxy groups contained in the silica particles obtained from the gas chromatography measurement and the carbon content corresponding to the solvent adsorbed on the silica particles (e.g., DMAC, etc.: dimethylacetamide, etc.) are subtracted from the carbon content in (3) to calculate the carbon content derived from the unsaturated bond-containing group and the additional silane treatment. (5) From the change in the carbon content (mass%) of the silica sol before and after the additional silane treatment, the amount of free silanol groups per unit area of ​​the silica surface (number / nm) was calculated using formula (II). 2 ) was calculated. The number of free silanol groups per unit area of ​​the silica surface (number / nm 2 )=[{C b -C a} / M c ×A b ] / (S N2 x10 18 ×100)] Formula (II) C b : Carbon content (mass%) of silica sol after additional silane treatment C a : Carbon content (mass%) of silica sol before additional silane treatment M c : Amount of carbon per mole of trimethylsilane (36g / mol) A b : Avogadro's constant 6.02 x 10 23 (pieces / mol) S N2 : specific surface area (m 2 / g)

[0062] [Storage stability of silica sol] Silica sol was heated under reduced pressure in a rotary evaporator to a concentration of 40% by mass, and 50 g of the concentrate was sealed in a 100 ml glass bottle and stored at 50°C for one month. From the viscosity of the silica sol before and after storage at 50°C, the viscosity ratio was calculated using the following formula (III) as an index of change over one month at 50°C, and the storage stability of the silica sol was evaluated. Note that (X0) in the following formula (N) indicates the viscosity before the storage stability test (immediately after the sol was prepared), and (X 1m) indicates the viscosity after a storage stability test (after being kept at 50°C for one month). Viscosity ratio:(X 1m ) / (X0)...(Formula (III)) The storage stability was evaluated using the following four levels of A to D. The results are shown in Table 1. <Thermal stability test evaluation criteria> A: Viscosity ratio is 0.80 or more and less than 1.06 B: Viscosity ratio is 1.06 or more and less than 1.11 C: Viscosity ratio is 1.11 or more and less than 2.01 D: Viscosity ratio is 2.01 or more or less than 0.80, or the silica sol becomes cloudy, phase separation occurs, sediment or floating matter occurs, or the silica concentration cannot be concentrated to 40% by mass.

[0063] (Measurement of insulation life) The insulation test samples prepared in the examples and comparative examples described below were used to measure the insulation life at a test temperature of 155°C (in air), an applied voltage of 2.0 kV, and a frequency of 50 Hz using a dielectric breakdown tester manufactured by Yamayo Testing Instruments Co., Ltd., model YST-243WS. The electrodes used were a flat electrode (φ=25 mm) at the bottom and a spherical electrode (φ=20 mm) at the top, with both electrodes positioned so as to be in contact with the sample. Four measurements were performed at an applied voltage of 2.0 kV, and the average value was recorded. The insulation life was evaluated using the following four levels of A to D. The results are shown in Table 1.

[0064] (Insulation life evaluation criteria) A: Insulation life is 700 minutes or more B: Insulation life is between 400 minutes and 700 minutes C: Insulation life is between 100 minutes and 400 minutes D: Insulation life is less than 100 minutes

[0065] [Example 1] Step (A): Water-dispersed silica sol ST-O-33 (average primary particle size 12 nm, pH 3, silica concentration 33% by mass, density 2.2 g / cm 3 (manufactured by Nissan Chemical Co., Ltd.) was prepared. Step (B): 1000 g of the water-dispersed silica sol prepared in Step (A) was placed in a 2-L recovery flask, and while stirring the sol with a magnetic stirrer, 200 g of DMAC (dimethylacetamide, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.99% by mass) was added, followed by the addition of 0.8 g of N,N-diisopropylethylamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.9% by mass), and the mixture was then maintained at 25°C for 30 minutes. Step (C): The sol obtained in step (B) was evaporated and distilled off in a rotary evaporator at a reduced pressure of 300 to 120 Torr and a bath temperature of 108°C while DMAC was added. The dispersion medium of the sol was replaced with DMAC, thereby obtaining a DMAC-dispersed silica sol (silica concentration 31.9% by mass, water content 4.0% by mass). Step (D): Next, while stirring the DMAC-dispersed silica sol obtained in step (C) with a magnetic stirrer, 7.5 g of phenyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name KBM-103) was added, and the liquid temperature was maintained at 90°C for 1 hour. Next, 1.8 g of N,N-diisopropylethylamine was added, and the liquid temperature was maintained at 90°C for 1 hour. Step (E): The sol obtained in step (D) was subjected to solvent substitution in the same manner as in step (C) to obtain a surface-treated DMAC-dispersed silica sol (silica concentration 40.7% by mass, pH 4.7, viscosity 9 mPa s, water content 0.9% by mass, average particle size measured by dynamic light scattering of 13 nm, specific surface area 234 m). 2 / g, average primary particle size 12 nm, carbon content 2.2 mass%, phenyl group bonded to silica particles 0.3 / nm 2 , the number of methoxy groups bonded to silica particles is 0.005 / nm 2 The viscosity of the obtained surface-treated DMAC-dispersed silica sol changed by less than 10% from the initial value after storage at 50°C for 1 month, demonstrating excellent storage stability.

[0066] [Example 2] The same procedure as in Example 1 was carried out, except that the amount of phenyltrimethoxysilane added in step (D) of Example 1 was changed to 10.8 g, to obtain a surface-treated DMAC-dispersed silica sol (silica concentration 40.6 mass%, pH 4.8, viscosity 8 mPa s, water content 0.8 mass%, average particle size measured by dynamic light scattering method 13 nm, specific surface area 234 m). 2 / g, average primary particle size 12 nm, carbon content 2.5 mass%, phenyl group bonded to silica particles 0.4 / nm 2 , the number of methoxy groups bonded to silica particles is 0.005 / nm 2 The viscosity of the obtained surface-treated DMAC-dispersed silica sol changed by less than 10% from the initial value after storage at 50°C for 1 month, demonstrating excellent storage stability.

[0067] [Example 3] The same procedure as in Example 1 was carried out, except that the amount of phenyltrimethoxysilane added in step (D) of Example 1 was changed to 17.5 g, to obtain a surface-treated DMAC-dispersed silica sol (silica concentration 40.7 mass%, pH 4.7, viscosity 8 mPa s, water content 0.8 mass%, average particle size measured by dynamic light scattering method 12 nm, specific surface area 234 m). 2 / g, average primary particle size 12 nm, carbon content 3.0 mass%, phenyl group bonded to silica particles 0.6 / nm 2 , the number of methoxy groups bonded to silica particles is 0.02 / nm 2 The viscosity of the obtained surface-treated DMAC-dispersed silica sol changed by less than 10% from the initial value after storage at 50°C for 1 month, demonstrating excellent storage stability.

[0068] [Comparative Example 1] The same procedure as in Example 1 was carried out, except that the amount of phenyltrimethoxysilane added in step (D) of Example 1 was changed to 2.5 g, to obtain a surface-treated DMAC-dispersed silica sol (silica concentration 34.8 mass%, pH 5.5, viscosity 14 mPa s, water content 0.9 mass%, average particle size by dynamic light scattering method 22 nm, specific surface area 234 m). 2 / g, average primary particle size 12 nm, carbon content 1.7 mass%, phenyl group bonded to silica particles 0.1 / nm 2, the number of methoxy groups bonded to silica particles is 0.0002 / nm 2 The viscosity of the obtained surface-treated DMAC-dispersed silica sol changed by 20% or more from the initial value after storage at 50°C for 1 month, indicating poor storage stability.

[0069] (Synthesis Example 1) Preparation of polyamic acid 496 g of 4,4'-diaminodiphenyl ether (DDE) and 534 g of pyromellitic dianhydride (PMDA) were polymerized with stirring at 50°C for 13 hours using NMP (N-methylpyrrolidone) and DMAC (dimethylacetamide) as solvents to obtain polyamic acid (solids content 17% by mass, viscosity at 25°C measured with an E-type viscometer: 13,640 mPa·s) corresponding to formula (4). The polyamic acid was polymerized using equimolar ratios of 1:1 DDE and PMDA. The weight-average molecular weight of the resulting polyamic acid was 63,000. n in formula (4) is the number of repeating units. [ka]

[0070] The DMAC-dispersed silica sols obtained in Examples 1 to 3 and Comparative Example 1 were stored at 50°C for 1 month, and then added to and mixed with the polyamic acid obtained in Synthesis Example 1 in a glass bottle at a mass ratio of resin (as polyimide) / SiO2 = 80 / 20. The mixture was degassed and stirred for 20 minutes using a vacuum degasser (manufactured by EME, trade name V-mini300), yielding a silica-blended polyamic acid.

[0071] Next, the obtained silica-blended polyamic acid was applied to alkali-free glass (manufactured by AS ONE Corporation, trade name EAGLEXG, 200 mm × 200 mm, 0.7 mm thick) using an applicator (manufactured by BEVS, trade name: Film applicator with film thickness adjustment function B / M 150 mm, applied film thickness (wet film thickness) 400 μm, application width 100 mm), and then the solvent was removed and the film was thermally cured in an atmospheric atmosphere at 70°C for 30 minutes, then at 100°C for 30 minutes, and finally at 150°C for 30 minutes, thereby obtaining a silica-blended polyimide film on the alkali-free glass.

[0072] Next, the silica-blended polyimide film was peeled off from the alkali-free glass by making cuts in the film with a cutter, and then fixed to a metal frame (made of stainless steel) and thermally cured at 400°C for 1 hour in an air atmosphere to obtain a silica-blended polyimide freestanding film (film thickness 30-35µm). This was cut into 5cm squares to prepare samples for insulation tests.

[0073] [Table 1]

[0074] As shown in the evaluation results in Table 1, the silica sols of Examples 1 to 3 having the technical features of the present invention are high-concentration silica sols containing free silanol groups that can be subjected to additional silane treatment, and are also excellent in storage stability, unlike the silica sol of Comparative Example 1. Therefore, it has been demonstrated that the use of the silica sol of the present invention can achieve both customizability and reliability. Furthermore, compared to the silica sol obtained in Comparative Example 1, the silica sols obtained in Examples 1 to 3 were able to improve the insulation life of the silica-blended polyimide freestanding films produced after storage at 50°C for one month. [Industrial Applicability]

[0075] The silica sol of the present invention is a high-concentration silica sol that can be subjected to additional silane treatment and also has excellent storage stability, making it possible to provide a high-quality silica sol.When the silica sol is blended with a nitrogen-containing polymer and used as an insulating resin composition, it is possible to provide an insulated conductor that can maintain a high insulation life for a long period of time.

Claims

1. A silica sol comprising silica particles having an average particle size of 5 to 100 nm as measured by a dynamic light scattering method, the particles having organic groups containing unsaturated bonds between carbon atoms bonded to the surface thereof, and a nitrogen-containing solvent, The number of organic groups containing unsaturated bonds between carbon atoms bonded to the surface of the silica particles is 0.1 to 2.0 per unit area of ​​the surface of the silica particles. ２ and The concentration of silica particles is 25 to 70% by mass, Free silanol groups are present on the surface of the silica particles, and the number of free silanol groups present per unit area on the surface of the silica particles is 0.4 to 1.2 / nm ２ That is, Silica sol.

2. The number of alkoxy groups bonded to the surface of the silica particles is 0.001 to 0.03 / nm per unit area of ​​the surface of the silica particles. ２ The silica sol according to claim 1, wherein

3. 2. The silica sol according to claim 1, wherein the organic group containing an unsaturated bond between carbon atoms is an organic group containing a phenyl group or an organic group containing a (meth)acryloyl group.

4. 2. The silica sol according to claim 1, wherein the organic group containing an unsaturated bond between carbon atoms is a phenyl group, a phenylaminoalkyl group, a (meth)acryloyl group, or a (meth)acryloylalkyl group.

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

6. 2. The silica sol according to claim 1, wherein the nitrogen-containing solvent is dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or N-ethylpyrrolidone.

7. An insulating resin composition comprising the silica sol according to any one of claims 1 to 6 and a nitrogen-containing polymer.

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

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

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