Free silanol group-containing surface-treated silica sol dispersed in nitrogen-containing solvent, and insulating resin composition

Abstract

Provided is a silica sol in which silica particles are dispersed in a nitrogen-containing solvent for mixing with polyimide-based and polyamide-based polar resins in a state of good compatibility, said silica sol being capable of being subjected to additional silane treatment according to the use or the like, having excellent storage stability at a high concentration, and having both customizability and reliability. The silica sol contains silica particles having an average particle diameter of 5-100 nm obtained by a dynamic light scattering method and having an organic group containing an unsaturated bond between carbon atoms bonded to the surface, and a nitrogen-containing solvent, the amount of organic groups that are bound to the surfaces of the silica particles and that contain unsaturated bonds between carbon atoms is 0.1-2.0 per unit area of the surfaces of the silica particles, the concentration of the silica particles is 25-70 mass%, and free silanol groups are present on the surfaces of the silica particles. The amount of free silanol groups present per unit area on the surface of the silica particles is 0.4-1.2 per nm2.

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 comprising the silica sol and a nitrogen-containing polymer. Background Technology

[0002] It is known to obtain inorganic oxide sols dispersed in organic solvents such as toluene by reacting an alcohol with the hydroxyl groups on the surface of inorganic oxide particles such as silica to introduce alkoxysilyl groups and performing an organic surface treatment. For example, Patent Document 1 discloses a silica sol dispersed in toluene by reacting a silica sol dispersed in methanol with phenyltrimethoxysilane.

[0003] Patent document 2 discloses a silica sol obtained by performing a surface treatment with phenyltrimethoxysilane after obtaining an acetonitrile-methanol mixed solvent dispersed silica sol by solvent replacement with acetonitrile.

[0004] Patent document 3 discloses a silica-based microparticle aqueous dispersion sol containing silica microparticles whose surfaces are modified with aluminum.

[0005] Patent document 4 discloses a silica sol in which aluminum atoms are bonded to the surface of silica particles in a specified ratio and an insulating resin composition using the same, wherein the silica sol is an aluminum-containing silica sol in which silica particles containing aluminum atoms are dispersed in a nitrogen-containing solvent.

[0006] Existing technical documents

[0007] Patent documents

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

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

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

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

[0012] The problem that the invention aims to solve

[0013] The inventors conducted further research and found that when the above-mentioned surface-treated or surface-modified silica sol is effectively utilized, it is industrially useful to provide silica sol that can be subsequently subjected to additional silane treatment depending on the application (customizability). Furthermore, it is desirable to provide silica sol with high concentrations that also exhibit excellent stability before the aforementioned additional silane treatment (reliability). It was determined that there is room for further improvement in the viewpoint of combining such customizability and reliability.

[0014] The purpose of this invention is to provide a silica sol in which silica particles are dispersed in a nitrogen-containing solvent for mixing with polyimide-based and polyamide-based polar resins in a compatible state. This silica sol can be further treated with silanes according to the application, etc., and has excellent storage stability at high concentrations, combining customizability and reliability.

[0015] Methods for solving problems

[0016] In order to solve the above-mentioned problems, the inventors conducted repeated experiments and in-depth research, resulting in the completion of this invention. The main points of this invention are as follows.

[0017] [1] Silica sol is a silica sol containing silica particles with an average particle size of 5-100 nm obtained by dynamic light scattering, which are formed by organic groups containing unsaturated bonds between carbon atoms bonded to the surface, and a nitrogen-containing solvent.

[0018] The amount of organic groups containing unsaturated bonds between carbon atoms bonded to the surface of silica particles is 0.1 to 2.0 groups per unit area of ​​the silica particle surface. 2 ,

[0019] The concentration of silica particles is 25%–70% by mass.

[0020] Free silanol groups exist on the surface of silica particles, with an amount of 0.4–1.2 free silanol groups per unit area on the surface of the silica particles. 2 .

[0021] [2] According to the silica sol described in [1], the amount of alkoxy groups bonded to the surface of the silica particles is 0.001 to 0.03 per unit area of ​​the silica particle surface. 2 .

[0022] [3] According to the silica sol of [1], wherein the organic group containing the unsaturated bond between carbon atoms is an organic group containing a phenyl group or an organic group containing a (meth)acryloyl group.

[0023] [4] According to the silica sol of [1], wherein the organic group containing the unsaturated bond between carbon atoms is phenyl, phenylaminoalkyl, (meth)acryloyl, or (meth)acryloylalkyl.

[0024] [5] The silica sol according to [1], wherein the nitrogen-containing solvent is an amide solvent.

[0025] [6] The silica sol according to [1], wherein the nitrogen-containing solvent is dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or N-ethylpyrrolidone.

[0026] [7] An insulating resin composition comprising a silica sol and a nitrogen-containing polymer according to any one of [1] to [6].

[0027] [8] According to the insulating resin composition of [7], the mass parts of the nitrogen-containing polymer are 1 to 100 relative to 1 part by mass of silicon dioxide contained in the silica sol.

[0028] [9] The insulating resin composition according to [7], wherein the nitrogen-containing polymer is a polyimide, polyamide, polyamic acid, polyamide-imide, polyether-imide, or polyester-imide.

[0029] The effects of the invention

[0030] 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 polyimide-based and polyamide-based polar resins in a state of good compatibility, and to provide a silica sol that can be further treated with silane according to the application and has excellent storage stability at high concentrations, thus providing both customizability and reliability.

[0031] Furthermore, the silica sol dispersed in a nitrogen-containing solvent of the present invention has good compatibility with nitrogen-containing polymers such as polyimide and polyamide. By combining the silica sol with the nitrogen-containing polymer to form a composition, an insulating resin composition (resin varnish) with sufficiently dispersed silica particles can be obtained.

[0032] 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 conductors such as copper wires and enameled copper wires, thereby obtaining an insulating coated wire that can maintain a high insulation life for a long period of time. Detailed Implementation

[0033] The preferred embodiments of the present invention will be described below. However, the following embodiments are illustrative of the present invention and are not intended to limit the present invention in any way.

[0034] In this specification, the numerical range indicated by "~" refers to the range of values ​​described before and after "~" as lower and upper limits. It should be noted that, in this specification, the above-mentioned multiple numerical ranges, which are expressed as preferred ranges for a particular stage, can also be understood independently as preferred upper or lower limits, focusing only on their respective upper or lower limits.

[0035] [Silica sol and its manufacturing method]

[0036] The silica sol of the present invention comprises silica particles with an average particle size of 5-100 nm obtained by dynamic light scattering, which are formed by bonding organic groups containing unsaturated bonds between carbon atoms to the surface, and a nitrogen-containing solvent. The amount of organic groups containing unsaturated bonds between carbon atoms bonded to the surface of the silica particles is 0.1-2.0 per unit area of ​​the silica particle surface. 2 The concentration of silica particles is 25–70% by mass, and free silanol groups exist on the surface of the silica particles, with an amount of 0.4–1.2 free silanol groups per unit area on the surface of the silica particles. 2 .

[0037] Regarding the average primary particle size of silica particles, the specific surface area (Ssize) determined by the nitrogen adsorption method (BET method) can be used. N2 The specific surface area diameter is calculated as the particle size (nm). For example, the specific surface area diameter (average primary particle size: D (nm)) is the specific surface area S determined using the nitrogen adsorption method (BET method). N2 (m) 2 / g) and density ρ (g / cm³) 3 Using D (nm) = 6000 / ρ×S N2 The formula for calculating the first-order particle size refers to the particle diameter converted to spherical silica particles.

[0038] Furthermore, the particle size of the silica particles contained in the silica sol can be determined using the average particle size measured by dynamic light scattering (DLS). The silica sol of the present invention exhibits good dispersibility in nitrogen-containing solvents, and the average particle size obtained by dynamic light scattering in nitrogen-containing solvents is preferably 5 to 100 nm, more preferably 10 to 70 nm.

[0039] The silica particles of the present invention have organic groups containing unsaturated bonds between carbon atoms bonded to their surface.

[0040] In one embodiment of the present invention, as an organic group containing an unsaturated bond between carbon atoms, examples include organic groups containing phenyl groups or organic groups containing (meth)acryloyl groups. Specific examples include phenyl, phenylaminoalkyl, (meth)acryloyl, or (meth)acryloylalkyl. In the present invention, from the viewpoint of compatibility with nitrogen-containing polymers, phenyl or phenylaminoalkyl groups are preferred, and phenyl is more preferred.

[0041] Regarding the amount of organic groups containing unsaturated bonds between carbon atoms bonded to the surface of silica particles, considering the effects of the present invention, it is preferably 0.1 to 2.0 particles / nm per unit area of ​​silica particle surface. 2 More preferably, it is 0.1 to 1.5 per nm. 2 More preferably, the number is 0.2–1.0 per nm. 2 By increasing the amount of organic groups containing unsaturated bonds above the lower limit, excellent storage stability of silica sol is expected; conversely, by decreasing the amount of organic groups containing unsaturated bonds below the upper limit, excellent customizability (the ability to further bind organic groups to the surface of silica particles as needed) is expected.

[0042] In one embodiment of the present invention, alkoxy groups may be bonded to the surface of the silica particles. Examples of alkoxy groups include straight-chain, branched, or cyclic alkyl groups having 1 to 10 carbon atoms; specifically, examples include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, or tert-butoxy. In the present invention, from the viewpoint of compatibility and customizability with nitrogen-containing polymers, methoxy, ethoxy, and n-propoxy are preferred, and methoxy is more preferred.

[0043] Regarding the amount of alkoxy groups bonded to the surface of silica particles, considering the effects of this invention, it is preferably 0.001 to 0.03 particles / nm per unit area of ​​silica particle surface. 2 More preferably, it is 0.002 to 0.03 per nm. 2 More preferably, the number is 0.004–0.03 per nm. 2 A higher alkoxy group binding amount than the lower limit is expected to result in excellent compatibility with nitrogen-containing polymers, while a lower alkoxy group binding amount than the upper limit is expected to result in excellent customizability.

[0044] Regarding the silica sol of the present invention, even at a relatively high concentration of silica particles, excellent dispersibility and storage stability are observed. The concentration of silica particles contained in the silica sol of the present invention is preferably 25-70% by mass, more preferably 30-60% by mass, and even more preferably 40-50% by mass. A higher silica particle concentration than the lower limit is expected to increase the amount of silica particles incorporated into the resin while suppressing the thinning of the resin caused by the dispersing solvent introduced by the silica sol; a lower silica particle concentration than the upper limit is expected to result in excellent storage stability of the silica sol.

[0045] The silica sol of the present invention is a sol (dispersion) in which silica particles with organic groups containing unsaturated bonds between carbon atoms are dispersed in a nitrogen-containing solvent.

[0046] Nitrogen-containing solvents have at least a functional group containing a nitrogen atom. Examples of functional groups containing a nitrogen atom include amino, nitro, and cyano groups, with amino groups being preferred. Amide solvents are also preferred as nitrogen-containing solvents. Specific examples of nitrogen-containing solvents include dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, tetramethylurea, hexamethylphosphotriamide, dimethylacrylamide, acryloylmorpholine, hydroxyethylacrylamide, isopropylacrylamide, diethylacrylamide, dimethylaminopropylacrylamide, 3-methoxy-N,N-dimethylpropionamide, 3-butoxy-N,N-dimethylpropionamide, dimethylaminopropylacrylamide methyl quaternary salt, and dimethylaminoethyl acrylate benzyl chloride quaternary salt. Dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or N-ethylpyrrolidone are preferred among these.

[0047] Other solvents may be contained in the nitrogen-containing solvent, provided that the effects of the present invention are not impaired. As an example, the nitrogen-containing solvent may be contained in the total solvent at a ratio of 50-100% by volume, 90-100% by volume, 98-100% by volume, or 99-100% by volume, and other solvents may be contained at a ratio of 0-less than 50% by volume, 0-less than 10% by volume, 0-less than 2% by volume, or 0-less than 1% by volume.

[0048] It has the following characteristic: a specific range of free silanol groups are present on the surface of the silica particles of the present invention. Regarding the method for determining the free silanol groups, the method described in the section on [Determination of the Amount of Free Silanol Groups] described later can be used.

[0049] Regarding the amount of free silanol present on the surface of silica particles, considering the effects of the present invention, it is preferably 0.4 to 1.2 particles / nm per unit area of ​​silica particle surface. 2More preferably, it is 0.6–1.2 per nm. 2 More preferably, it is 0.8–1.1 per nm. 2 By increasing the amount of free silanol groups above the lower limit, excellent customizability is expected; conversely, by decreasing the amount of free silanol groups below the upper limit, excellent storage stability of the silica sol is expected.

[0050] Regarding the amount of free silanol groups present on the surface of silica particles, as described later, it is effective to adjust the amount of specific silane compounds, such as phenyltrimethoxysilane, represented by formula (1). By optimizing the reaction conditions when coating the surface of silica particles with specific silane compounds, etc., it is possible to appropriately adjust the amount of free silanols present on the surface of silica particles within a specified range after solvent replacement with a nitrogen-containing solvent, thereby providing silica sols that balance customizability and reliability.

[0051] The silica sol of the present invention can be manufactured by coating a silica surface with a silica sol through surface treatment or surface modification. An example of a method for manufacturing the silica sol of the present invention will be described below.

[0052] In this invention, silica particles can be coated with a silane compound or its hydrolysate represented by formula (1).

[0053]

Chemistry 1

[0054]

[0055] (In equation (1), R) 1 R represents an organic group containing unsaturated bonds between carbon atoms, and specifically a group bonded to silicon atoms via Si-C bonds. 2 The alkoxy group represents an alkoxy group, where a is an integer from 1 to 3. Examples of organic groups containing unsaturated bonds between carbon atoms include organic groups containing phenyl groups or organic groups containing (meth)acryloyl groups. Specific examples of silane compounds represented by formula (1) include phenyltrimethoxysilane, phenyltriethoxysilane, phenylmethyldimethoxysilane, phenylaminopropyltrimethoxysilane, phenylaminopropyltriethoxysilane, and methacryloyloxypropyltrimethoxysilane, acryloyloxypropyltrimethoxysilane, etc.

[0056] In this invention, for the surface modification of silica particles, hydrolyzable silane compounds of formula (2) and / or formula (3) can also be used with silane coupling agents of formula (1).

[0057]

Chemistry 2

[0058]

[0059] (In equations (2) and (3), R) 3 and R 5 Each is an alkyl group having 1 to 3 carbon atoms, and indicates a group bonded to silicon atoms by a Si-C bond, R 4 and R 6 Each represents an alkoxy group, Y represents an alkylene group, an NH group, or an oxygen atom, b is an integer from 1 to 3, c is an integer from 0 to 1, and d is an integer from 1 to 3.

[0060] Examples of alkoxy groups include those having a straight-chain, branched, or cyclic alkyl moiety with 1 to 10 carbon atoms, such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, and tert-butoxy.

[0061] The silane compounds represented by the above formulas (2) and (3) are preferably compounds that can form trimethylsilyl groups on the surface of silica particles.

[0062] The following structures can be exemplified as structures possessed by these compounds.

[0063]

Transformation 3

[0064]

[0065] In the above equation (2-3), R 12 It represents an alkoxy group, such as methoxy and ethoxy.

[0066] These silane compounds can be made using silane coupling agents manufactured by Shin-Etsu Chemical Industry Co., Ltd., Dow Toray Co., Ltd., and JNC Co., Ltd.

[0067] In this invention, the method for manufacturing silica sol can include the water glass method using water glass as a raw material, the alkoxide method using metal alkoxides as raw materials, and the gas-phase method using silicon chloride compounds as raw materials. Silica sol obtained by any of these methods can be used, but the water glass method is preferred.

[0068] As an example, the silica sol of the present invention can be obtained by a manufacturing method including the following steps (A), (B), (C), (D), and (E):

[0069] (A) Process: Prepare silica sol with an average primary particle size of 5-100 nm dispersed in an aqueous medium;

[0070] (B) Step: Add a nitrogen-containing solvent and an alkaline catalyst to the silica sol obtained in step (A);

[0071] (C) Step: Replace the silica sol solvent obtained in step (B) with a nitrogen-containing solvent;

[0072] (D) Step: Add a silane compound represented by formula (1) or any silane compound represented by formula (2) or formula (3);

[0073] (E) Step: Replace the dispersion medium solvent of the silica sol obtained in step (D) with a nitrogen-containing solvent.

[0074] The silica sol used in process (A) can be a silica sol dispersed in an aqueous medium (aqueous silica sol) with an average particle size in the range of 5–100 nm or 10–70 nm. The aqueous silica sol can be manufactured by heating a silica solution with a pH of 1–6 obtained by cation exchange treatment of an aqueous solution of alkali metal silicate with a solid component concentration of 1–10% by mass at 50–110 °C in the presence of an alkali. The cation exchange treatment can be carried out by passing the aqueous solution of alkali metal silicate into a column filled with a strongly acidic cation exchange resin.

[0075] As alkali metal silicates, sodium silicate, potassium silicate, lithium silicate, etc., can be used, and commercially available sodium silicate under names such as No. 1 sodium silicate, No. 2 sodium silicate, and No. 3 sodium silicate can also be used. Alternatively, alkali metal silicates can be obtained by adding sodium hydroxide, potassium hydroxide, lithium hydroxide, or quaternary ammonium hydroxide to a silicic acid solution obtained by hydrolyzing alkoxysilanes such as tetraethoxysilane and tetramethoxysilane.

[0076] Instead of the aqueous silica sol used in process (A), a silica sol in which the aqueous medium solvent is replaced by an alcohol with 1 to 3 carbon atoms can be used, such as by vacuum distillation or ultrafiltration.

[0077] As the silica sol used in process (A), an aqueous silica sol that has undergone hydrothermal treatment for 0.1 to 10 hours can be used.

[0078] (A) The silica sol obtained in the process can be subjected to cation exchange and anion exchange as needed.

[0079] Step (B) involves adding a nitrogen-containing solvent and an alkaline catalyst to the silica sol obtained in step (A). To suppress thickening during solvent displacement in step (C), it is preferable to add a nitrogen-containing solvent and an alkaline catalyst to the aqueous silica sol. The nitrogen-containing solvent is preferably an amide-based solvent, such as dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or N-ethylpyrrolidone. Alkaline catalysts include alkali metals such as sodium hydroxide and potassium hydroxide, and amines such as ethylenediamine and diethylenetriamine.

[0080] Step (C) is a step in which the dispersion medium solvent of the silica sol obtained in step (B) is replaced with a nitrogen-containing solvent. Solvent replacement can be performed using an evaporator or UF concentration. In the solvent replacement with the nitrogen-containing solvent, the water content can be adjusted to a range of 3.0 to 15.0% by weight or 5.0 to 10.0% by weight of the total solvent.

[0081] Step (D) involves adding a silane compound represented by formula (1) (referred to as silane compound A) and any selected silane compound represented by formula (2) or formula (3) (referred to as silane compound B) to the silica sol obtained in step (C). The order in which silane compound A and silane compound B are added can be any order, but it is preferable to add silane compound B (referred to as silane compound B) after coating silica particles with the silane compound represented by formula (1) (silane compound A) or its hydrolysate.

[0082] Step (E) is a step in which the dispersion medium solvent of the silica sol obtained in step (D) is replaced with a nitrogen-containing solvent. The silica concentration in the silica sol can be adjusted to 5–75% by mass, 20–70% by mass, or 25–70% by mass during or after the solvent replacement step.

[0083] In step (E), a nitrogen-containing solvent may be included in the total solvent at a proportion of 50–100 vol%, 90–100 vol%, 98–100 vol%, or 99–100 vol%, and other solvents may be included at a proportion of 0–less than 50 vol%, 0–less than 10 vol%, 0–less than 2 vol%, or 0–less than 1 vol%. Furthermore, various nitrogen-containing solvents may be included. As other solvents, it is permissible to include water or alcohols with 1–3 carbon atoms as contained in the silica sol of step (A) within the above-mentioned range, as long as the effect is not impaired.

[0084] Specific examples of nitrogen-containing solvents used for solvent replacement in process (C) are as described above.

[0085] [Insulating Resin Composition and Method for Manufacturing the Same]

[0086] The silica sol, which uses a nitrogen-containing solvent as a dispersion medium, and a nitrogen-containing polymer of the present invention can be combined to obtain an insulating resin composition (resin varnish).

[0087] The insulating resin composition (resin varnish) can be obtained by a method that includes steps (F) and (G) in addition to steps (A) to (E) described above.

[0088] (F) Step: The step of mixing the silica sol obtained in step (E) which is dispersed in a nitrogen-containing solvent with a nitrogen-containing polymer.

[0089] (G) Process: The process of removing part or all of the nitrogen-containing solvent from the silica sol obtained from (F) process.

[0090] Using the above method, as an example, silica particles coated with phenyl groups generated from phenyltrimethoxysilane (a silane compound) and trimethylsilyl groups generated from hexamethyldisiloxane (a silane compound) are dispersed in dimethylacetamide (DMAC), a nitrogen-containing solvent, to obtain a silica sol. By combining the nitrogen-containing polymer, an insulating resin composition can be manufactured.

[0091] Resin varnishes, such as insulating resin compositions, can be obtained where the mass fraction of the nitrogen-containing polymer is 1 to 100, 1 to 50, or 1 to 10 parts by mass relative to 1 part by mass of silica particles contained in the silica sol. Examples of nitrogen-containing polymers include polyimide, polyamide, polyamic acid, polyamide-imide, polyether-imide, and polyester-imide.

[0092] An insulating film (insulating coating) can be formed on the conductor surface by coating an insulating resin composition onto the conductor requiring insulation and then heating and curing it at a solvent evaporation temperature. The heating temperature for removing the solvent is determined according to temperature and pressure; if at atmospheric pressure, it is approximately 150°C to 300°C, or for imidization of the resin, it is approximately 150°C to 400°C.

[0093] As conductors, examples include metal wires such as copper wire and aluminum wire, with copper wire being particularly useful. Copper wire, as an electrical wire coated with enamel, is used in industrial and household applications such as motors, transformers, and coils.

[0094] By using the insulating resin composition of the present invention as an insulating coating layer, an insulating coating layer is applied to copper wire, thereby enabling the manufacture of an insulated conductor.

[0095] The above-mentioned insulating resin composition is obtained by mixing a nitrogen-containing polymer in a ratio of 1 to 100, 1 to 50, or 1 to 10 parts by mass relative to 1 part by mass of silica particles contained in the silica sol.

[0096] The insulating resin composition is obtained by mixing and stirring silica sol and polymer using a mixer or disperser. Additives can be added as needed during the mixing process.

[0097] Example

[0098] The following examples and comparative examples illustrate the present invention in more detail, but the present invention is not limited to the following examples.

[0099] (Analysis Methods)

[0100] [Determination of SiO2 concentration]

[0101] The silica sol was placed in a crucible and dried at 150°C. The resulting gel was then calcined at 1000°C for 30 minutes under atmospheric conditions. The remaining amount after calcination was measured and calculated.

[0102] [Determination of average primary particle size (nitrogen adsorption method particle size)]

[0103] The specific surface area (S) of silica particles in water-dispersed silica sol was determined by nitrogen adsorption. N2 In this case, after removing the water-soluble cations in the water-dispersed silica sol using an H-type cation exchange resin (manufactured by Dow Chemical, trade name: Amberlite IR-120B), the silica sol was dried at 290°C to prepare a test sample. The sample was then measured using a nitrogen adsorption method with a Monosorb instrument (manufactured by Quantachrome Instruments Japan), using a mixed gas of 30% N2 (nitrogen) and 70% He (helium) as the carrier gas, and the BET1 point method was employed.

[0104] The specific surface area (S) of silica particles dispersed in organic solvents by nitrogen adsorption method. N2 For the sample obtained in the later section (determination of carbon content) (a substance obtained by heating silica particles (powder) at 150°C), the BET1 point method was used for determination. The specific surface area value S obtained was... N2 (m) 2 / g) and density ρ (g / cm³) 3 The average primary particle size (nm) is calculated as 6000 / ρ×S. N2 Calculated. In this invention, the density ρ (g / cm³) of silicon dioxide particles is... 3 The value is calculated to be 2.2 (g / cm³). 3 ).

[0105] [Moisture content determination]

[0106] The moisture content was determined using a Karl Fischer moisture meter (manufactured by Kyoto Electronics Co., Ltd., trade name: MKA-610) and by Karl Fischer titration.

[0107] [pH Measurement]

[0108] The pH of the water-dispersed silica sol was measured at 20°C using a pH meter (manufactured by Toa DKK Co., Ltd., product name: MM-43X).

[0109] Regarding the pH of silica sol dispersed in organic solvents, when the organic solvent used as the dispersion medium is methanol (MeOH), a liquid in which silica sol and pure water are mixed at a mass ratio of 1:1 is used. When the organic solvent is a nitrogen-containing solvent, such as dimethylacetamide (DMAC), a liquid in which silica sol, MeOH, and pure water are mixed at a mass ratio of 1:1:1 is used, and the pH is measured at 20°C.

[0110] [Viscosity Measurement]

[0111] The viscosity of the silica sol was measured using an Ostwald viscometer at 20°C.

[0112] [Determination of average particle size using dynamic light scattering (DLS) method]

[0113] The average particle size obtained by DLS (average secondary particle size obtained by dynamic light scattering: also known as Z-average particle size or DLS average particle size) was measured using a dynamic light scattering particle size analyzer (manufactured by Malvern Panalytical, trade name: Zetasizer Nano). 0.1 g of the target silica sol was taken into a glass cell with a 10 mm optical path length, and then a solvent as the main component was added to the dispersion medium of the silica sol to obtain a silica sol with a count rate modulated to 200–400 kcps at an attenuator of 7. For example, MeOH was added to a methanol-based silica sol, and DMAC was added to a DMAC-based silica sol to obtain a silica sol with a count rate modulated to 200–400 kcps at an attenuator of 7. The prepared silica sol was adjusted so that the height from the bottom of the pool to the liquid surface was about 1 cm, and the average particle size of the silica sol was measured using attenuator 7.

[0114] [Determination of carbon content]

[0115] (1) Place 3 mL of silica sol dispersed in organic solvent in a 30 cc centrifuge tube and add 20 mL of toluene.

[0116] (2) After applying the centrifuge (centrifugal force 11000G×30 minutes), remove the supernatant.

[0117] (3) Add 4 mL of acetone to redissolve the gel, then add 4 mL of toluene and 10 mL of hexane. After centrifugation (11000 G × 30 minutes), remove the supernatant.

[0118] (4) Then proceed to (3) again.

[0119] (5) After the gel is vacuum dried at 60°C, the powder is pulverized in a mortar and dried at 150°C for 2 hours to obtain silica powder.

[0120] The carbon content (mass%) of the powder obtained above was determined using an elemental analysis apparatus (manufactured by PerkinElmer, trade name 2400IICHNS / O).

[0121] [Determination of the amount of alkoxy groups bound]

[0122] 0.2 g of the powder obtained in [Determination of Carbon Content] was mixed and dissolved with 10 mL of 0.05 N sodium hydroxide aqueous solution, and then analyzed by gas chromatography (manufactured by Shimadzu Corporation, product name: GC-2014s, column: PorapakQ, heating rate: 5℃ / min, temperature range: 20~250℃). The results of the gas chromatography determination and the specific surface area value S... N2 (m) 2 / g) to determine the amount of alkoxy groups bound to the surface (number / nm) 2 ).

[0123] [Determination of the amount of organic groups containing unsaturated bonds]

[0124] The amount of bound organic groups containing unsaturated bonds (number / nm) is determined by subtracting from the carbon content of the powder obtained from the [determination of carbon content] the amount of alcohol from which alkoxy groups in the silica particles are released, as determined by gas chromatography from the [determination of the amount of alkoxy groups bound], and the carbon content of the solvent (e.g., DMAC, dimethylacetamide, etc.) adsorbed onto the silica particles. 2 Quantitative.

[0125] The amount of organic groups containing unsaturated bonds bonded together (number / nm) 2 ) = [(C м -C A -C S ) / M P ×A b ] / (S N2 ×10 18 ×100)···Formula (I)

[0126] C м Carbon content of the powder (mass %)

[0127] C A Carbon content (mass%) equivalent to the amount of alcohol removed from the alkoxy group.

[0128] C S Carbon content (mass%) equivalent to the solvent adsorbed onto the silica particles.

[0129] M P The amount of carbon per mole in an organic group containing an unsaturated bond (72 g / mol in the case of phenyltrimethoxysilane).

[0130] A b Avogadro's constant is 6.02 × 10⁻⁶. 23 (units / mol)

[0131] S N2 Specific surface area (m²) 2 / g)

[0132] [Determination of Free Silanol Groups]

[0133] For silica sol, perform additional silane treatment according to the following steps to calculate the amount of free silanol groups.

[0134] (1) Place 100g of silica sol in a 250mL round-bottom flask, and while stirring the sol with a magnetic stirrer, add 2g of pure water. Then, add hexamethyldisilazane (manufactured by Shin-Etsu Chemical Industry Co., Ltd., trade name SZ-31) in a 3nm ratio. 2 After adding the amount (e.g., 7.4 g when the average primary particle size of silica particles is 12 nm and the silica concentration is 30% by mass), the liquid temperature is maintained at 90°C for 3 hours.

[0135] (2) While using a rotary evaporator to evaporate and distill the solvent at a depressurization of 450 to 110 Torr and a bath temperature of 85 to 125°C, the main component of the dispersion medium, such as DMAC in Example 1 described later, is supplied to obtain a silica sol that has been additionally treated with silane by hydrolyzing trimethylsilane generated from hexamethyldisilazane.

[0136] (3) Calculate the carbon content of the silica sol before and after the additional silane treatment in (2) according to [determination of carbon content].

[0137] (4) The carbon content containing unsaturated bonds and the carbon content from the additional silane treatment are calculated by subtracting from the carbon content in (3) the carbon content equivalent to the amount of alcohol removed from the alkoxy groups in the silica particles obtained from the gas chromatography determination of [the amount of alkoxy binding] and the carbon content equivalent to the solvent (e.g., DMAC, dimethylacetamide, etc.) adsorbed on the silica particles.

[0138] (5) The amount of free silanol groups per unit area on the silica surface (number / nm) is calculated using formula (II) based on the change in carbon content (mass%) of the silica sol before and after the addition of silane. 2 ).

[0139] The number of free silanol groups per unit area on the surface of silica (number / nm) 2 ) = [{C b -C a} / M c ×A b ] / (S N2 ×10 18 ×100)] ···Equation (II)

[0140] C b Carbon content (mass%) of silica sol after silane treatment.

[0141] C a Carbon content (mass%) of silica sol before silane treatment.

[0142] M c The amount of carbon in 1 mole of trimethylsilane (36 g / mol)

[0143] A b Avogadro's constant is 6.02 × 10⁻⁶. 23 (units / mol)

[0144] S N2 Specific surface area (m²) 2 / g)

[0145] [Storage stability of silica sol]

[0146] The silica sol was heated under reduced pressure using a rotary evaporator to obtain a 40% (w / w) concentrate. 50g of this concentrate was sealed in a 100ml glass bottle and stored at 50°C for one month. The viscosity of the silica sol before and after storage at 50°C was then used as an indicator of the change over one month at 50°C. The viscosity ratio was calculated using the following formula (III) to evaluate the storage stability of the silica sol. However, in the following formula (N), (X0) represents the viscosity before the storage stability test (immediately after sol preparation), (X... 1m The value indicates the viscosity after a storage stability test (after being kept at 50°C for 1 month).

[0147] Viscosity ratio: (X) 1m ) / (X0) ···(Equation (III))

[0148] It should be noted that preservation stability was evaluated using four levels, A to D, as shown below. The results are presented in Table 1.

[0149] <Evaluation Standard for Thermal Stability Test>

[0150] A: Viscosity ratio above 0.80 and below 1.06

[0151] B: Viscosity ratio greater than 1.06 and less than 1.11

[0152] C: Viscosity ratio greater than 1.11 but less than 2.01

[0153] D: Viscosity ratio is 2.01 or higher, or less than 0.80, or the silica sol produces turbidity, phase separation, sediment, or floating matter, or the silica concentration cannot be concentrated to 40% by mass.

[0154] (Determination of insulation life)

[0155] For the insulation test specimens prepared in the embodiments and comparative examples described later, an insulation failure test apparatus (model YST-243WS) manufactured by Sanyo Testing Instruments Co., Ltd. was used to determine 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. Regarding the electrode shape, a flat electrode was used at the bottom. =25mm), with a spherical electrode at the top ( =20mm), all electrodes were set to be in contact with the sample for testing. Four measurements were performed under an applied voltage of 2.0kV, and the average value was recorded.

[0156] It should be noted that insulation life is evaluated using four levels, A through D, as described below. The results are shown in Table 1.

[0157] (Insulation life evaluation standard)

[0158] A: Insulation life is over 700 minutes.

[0159] B: Insulation life is over 400 minutes but less than 700 minutes.

[0160] C: Insulation life is over 100 minutes but less than 400 minutes.

[0161] D: Insulation life is less than 100 minutes.

[0162] [Example 1]

[0163] (A) Process: Prepare water-dispersible silica sol ST-O-33 (average primary particle size 12nm, pH 3, silica concentration 33% by mass, density 2.2g / cm³). 3 (Manufactured by Nissan Chemical Co., Ltd.)

[0164] (B) Step: Place 1000g of the water-dispersible silica sol prepared in step (A) into a 2L round-bottom flask. While stirring the sol with a magnetic stirrer, add 200g of DMAC (dimethylacetamide, manufactured by Fujifilm and Koden Chemical, with a purity of 99.99% by mass). Then, add 0.8g of N,N-diisopropylethylamine (manufactured by Fujifilm and Koden Chemical, with a purity of 99.9% by mass) and keep at 25°C for 30 minutes.

[0165] (C) Process: The solvent of the sol obtained in (B) is evaporated and distilled off using a rotary evaporator at a reduced pressure of 300-120 Torr and a bath temperature of 108°C. At the same time, DMAC is supplied to replace the dispersion medium of the sol with DMAC, thereby obtaining DMAC dispersed silica sol (silica concentration 31.9% by mass, moisture 4.0% by mass).

[0166] (D) Step: Next, while stirring the DMAC dispersed silica sol obtained in step (C) with a magnetic stirrer, add 7.5g of phenyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM-103), and maintain the liquid temperature at 90°C for 1 hour. Next, add 1.8g of N,N-diisopropylethylamine, and maintain the liquid temperature at 90°C for 1 hour.

[0167] (E) Step: Solvent replacement is performed on the sol obtained in step (D) using the same method as in step (C) to obtain surface-treated DMAC dispersed silica sol (silica concentration 40.7% by mass, pH 4.7, viscosity 9 mPa·s, moisture 0.9% by mass). The average particle size obtained by dynamic light scattering method is 13 nm, and the specific surface area is 234 m². 2 / g, average primary particle size 12nm, carbon content 2.2% by mass, phenyl binding amount with silica particles 0.3 ions / nm 2 The amount of methoxy groups bound to silica particles is 0.005 per nm. 2 It can be seen that the viscosity of the surface-treated DMAC dispersed silica sol after storage at 50°C for one month changed by less than 10% from the initial viscosity, indicating excellent storage stability.

[0168] [Example 2]

[0169] Except for changing the amount of phenyltrimethoxysilane added to 10.8 g in step (D) of Example 1, the operation was carried out in the same manner as in Example 1 to obtain a surface-treated DMAC dispersed silica sol (silica concentration 40.6% by mass, pH 4.8, viscosity 8 mPa·s, moisture 0.8% by mass, average particle size of 13 nm and specific surface area of ​​234 m² obtained by dynamic light scattering method). 2 / g, average primary particle size 12nm, carbon content 2.5% by mass, phenyl binding amount with silica particles 0.4 ions / nm 2 The amount of methoxy groups bound to silica particles is 0.005 per nm. 2 It can be seen that the viscosity of the surface-treated DMAC dispersed silica sol after storage at 50°C for one month changed by less than 10% from the initial viscosity, indicating excellent storage stability.

[0170] [Example 3]

[0171] Except for changing the amount of phenyltrimethoxysilane added to 17.5 g in step (D) of Example 1, the operation was carried out in the same manner as in Example 1 to obtain a surface-treated DMAC dispersed silica sol (silica concentration 40.7% by mass, pH 4.7, viscosity 8 mPa·s, moisture 0.8% by mass, average particle size of 12 nm and specific surface area of ​​234 m² obtained by dynamic light scattering method). 2 / g, average primary particle size 12nm, carbon content 3.0% by mass, phenyl binding amount with silica particles 0.6 phenyl groups / nm 2 The amount of methoxy groups bound to silica particles is 0.02 per nm. 2 It can be seen that the viscosity of the surface-treated DMAC dispersed silica sol after storage at 50°C for one month changed by less than 10% from the initial viscosity, indicating excellent storage stability.

[0172] [Comparative Example 1]

[0173] Except for changing the amount of phenyltrimethoxysilane added to 2.5 g in step (D) of Example 1, the operation was carried out in the same manner as in Example 1 to obtain a surface-treated DMAC dispersed silica sol (silica concentration 34.8% by mass, pH 5.5, viscosity 14 mPa·s, moisture 0.9% by mass), with an average particle size of 22 nm and a specific surface area of ​​234 m² obtained by dynamic light scattering. 2 / g, average primary particle size 12nm, carbon content 1.7% by mass, phenyl group binding amount with silica particles 0.1 ions / nm 2 The amount of methoxy groups bound to silica particles is 0.0002 per nm. 2 It can be seen that the viscosity of the surface-treated DMAC dispersed silica sol after being stored at 50°C for one month changed by more than 20% from the initial viscosity, indicating poor storage stability.

[0174] (Synthetic Example 1) Preparation of Polyamic Acid

[0175] Using 496 g of 4,4'-diaminodiphenyl ether (DDE), 534 g of pyromellitic dianhydride (PMDA), and NMP (N-methylpyrrolidone) and DMAC (dimethylacetamide) as solvents, the polyamic acid was polymerized at 50°C for 13 hours with stirring to obtain a polyamic acid equivalent to formula (4) (solids content 17% by mass, viscosity at 25°C 13640 mPa·s using an E-type viscometer). For the polymerization of the polyamic acid, the above-mentioned DDE and PMDA were polymerized in an equimolar ratio of 1:1. The resulting polyamic acid had a weight-average molecular weight of 63000. In formula (4), n represents the number of repeating units.

[0176]

Chemistry 4

[0177]

[0178] After storing the DMAC dispersed silica sol obtained in Examples 1-3 and Comparative Example 1 at 50°C for 1 month, it was added to a glass bottle and mixed with the polyamic acid obtained in Synthesis Example 1 at a mass ratio of resin (as polyimide) / SiO2 = 80 / 20. The mixture was degassed and stirred for 20 minutes using a vacuum degassing machine (manufactured by EME Corporation, trade name V-mini300) to obtain silica-integrated polyamic acid.

[0179] Secondly, the obtained silica-polyamic acid composite was coated on alkali-free glass (manufactured by AsOne, trade name EAGLEXG, 200mm×200mm, 0.7mm thick) using a coating applicator (manufactured by BEVS, trade name: film coating applicator with film thickness adjustment function B / M150mm, coating film thickness (wet film thickness) 400μm, coating width 100mm). Solvent removal and thermal curing were then carried out under atmospheric conditions at 70°C for 30 minutes, followed by 100°C for 30 minutes, and finally 150°C for 30 minutes, thereby obtaining a silica-polyimide composite film on the alkali-free glass.

[0180] Next, the silica-polyimide film is peeled off from the alkali-free glass by making a cut with a knife. After being fixed in a metal frame (made by SUS), it is thermosetting at 400°C for 1 hour in an atmospheric atmosphere to obtain a silica-polyimide self-supporting film (film thickness 30-35 μm). It is then cut into 5 cm squares to make test specimens for insulation testing.

[0181] Table 1

[0182]

[0183] As shown in Table 1, the silica sols of Examples 1-3, which possess the technical features of the present invention, differ from the silica sol of Comparative Example 1. They are silica sols with a high concentration of free silanol groups capable of additional silane treatment, and also exhibit excellent storage stability. Therefore, it is demonstrated that by using the silica sol of the present invention, both customizability and reliability can be achieved.

[0184] In addition, compared with the silica sol obtained in Comparative Example 1, the silica sol obtained in Examples 1 to 3 can improve the insulation life of the silica-polyimide self-supporting film prepared after storage at 50°C for 1 month.

[0185] Industrial availability

[0186] The silica sol of the present invention is a high-concentration silica sol that can be further treated with silane, and also has excellent storage stability, thus providing a high-quality silica sol. When the silica sol is combined with a nitrogen-containing polymer and used as an insulating resin composition, it can provide an insulating coated conductor that can maintain a high insulation life for a long period of time.

Claims

1. Silica sol is a silica sol containing silica particles with an average particle size of 5–100 nm, obtained by dynamic light scattering, and an organic group with unsaturated bonds between carbon atoms bonded to the surface, along with a nitrogen-containing solvent. The amount of organic groups containing unsaturated bonds between carbon atoms bonded to the surface of silica particles is 0.1 to 2.0 groups per unit area of ​​the silica particle surface. 2 , The concentration of silica particles is 25%–70% by mass. Free silanol groups exist on the surface of silica particles, with an amount of 0.4–1.2 free silanol groups per unit area on the surface of the silica particles. 2 .

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

3. The silica sol according to claim 1, wherein, The organic group containing unsaturated bonds 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 claim 1, wherein, The organic group containing unsaturated bonds between carbon atoms is phenyl, phenylaminoalkyl, (meth)acryloyl, or (meth)acryloylalkyl.

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

6. 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 a silica sol and a nitrogen-containing polymer according to any one of claims 1 to 6.

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

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

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