Corona-resistant insulating paint for enameled wire and method for preparing the same

Abstract

This invention discloses a corona-resistant insulating varnish for enameled wire and its preparation method, belonging to the technical field of insulating coatings. The raw materials for preparing the corona-resistant insulating varnish for enameled wire include aromatic tricarboxylic anhydride, aromatic diisocyanate, and hydroxyl-modified composite nanoparticles; the hydroxyl-modified composite nanoparticles comprise silica nanoparticles and layered double hydroxides. This invention significantly increases the hydroxyl modification density by introducing layered double hydroxides and silica composites, enabling the composite particles to be covalently anchored to the prepolymer backbone through esterification, resulting in uniform release after curing. This achieves a balance between storage stability and curing uniformity, making it suitable for enameled wire applications in high-voltage motors.

Description

Technical Field

[0001] This invention relates to the field of insulating materials technology, and in particular to a corona-resistant insulating varnish for enameled wire and its preparation method. Background Technology

[0002] With the rapid development of new energy vehicles, high-voltage motors, and variable frequency drive technologies, the performance requirements of motor systems on enameled wires are becoming increasingly stringent. In particular, the widespread application of 800V high-voltage platforms demands that enameled wires not only possess excellent heat resistance but also superior corona resistance. Corona discharge is a major cause of coil insulation failure due to partial discharge. Its principle involves charged particles generated by partial discharge colliding with the insulating material, leading to polymer chain breakage and thermal decomposition. Simultaneously, ozone triggers chemical corrosion, ultimately causing insulation breakdown. Therefore, improving the corona resistance of enameled wires has become a key technical challenge in the development of high-voltage motor insulation materials.

[0003] Currently, a common method to improve the corona resistance of enameled wires is to add inorganic nanoparticles (such as silica, alumina, and titanium dioxide) to the insulating varnish and disperse them in insulating resins such as polyamide-imide through physical blending. The high dielectric constant and thermal stability of the inorganic particles create an organic-inorganic interface within the varnish film, blocking corona erosion. However, this physical blending method suffers from poor storage stability and uneven dispersion after curing. Existing technologies attempt to introduce nanoparticles into the polymer backbone through chemical bonding. Through a chemical bonding-thermal release mechanism, nanoparticles are chemically anchored to the prepolymer backbone before curing, avoiding physical agglomeration. After curing, the ester bonds break, releasing the particles in situ and uniformly dispersing them in the coating film, effectively solving the storage stability and dispersion uniformity problems of traditional physical blending methods. However, the following shortcomings remain: the hydroxyl group density on the silica surface is limited, and some particles cannot be fully modified, remaining in physical form and affecting the overall corona resistance. Summary of the Invention

[0004] This application provides a corona-resistant insulating varnish for enameled wire and its preparation method, thereby solving the problems in the prior art.

[0005] This application provides a corona-resistant insulating varnish for enameled wires, wherein the raw materials for preparing the corona-resistant insulating varnish for enameled wires include aromatic tricarboxylic anhydride, aromatic diisocyanate and alcohol hydroxyl-modified composite nanoparticles; The hydroxyl-modified composite nanoparticles comprise silica nanoparticles and layered double hydroxides. The alcohol-hydroxyl-modified composite nanoparticles were obtained by modification with an epoxy silane coupling agent and a secondary amine.

[0006] Furthermore, the alcohol-hydroxyl-modified composite nanoparticles also contain a calcium-based compound, which is selected from at least one of calcium hydroxide or calcium oxide.

[0007] Furthermore, the layered double hydroxide comprises high aspect ratio sheets and low aspect ratio particles; The aspect ratio of the high aspect ratio sheet is 20-50; The aspect ratio of the low aspect ratio particles is 2-5; The mass ratio of the high aspect ratio sheet to the low aspect ratio particle is 0.5:1-2:1.

[0008] Furthermore, based on a solid content of 100% for the corona-resistant insulating varnish used in the enameled wire, the mass of the alcohol-hydroxyl-modified composite nanoparticles is 1%-40%. The D50 particle size of the silica nanoparticles is 10nm-80nm; The D50 particle size of the layered double hydroxide is 30nm-80nm.

[0009] Furthermore, the aromatic tricarboxylic anhydride includes trimellitic anhydride; The aromatic diisocyanate includes at least one of 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, naphthalene diisocyanate, phenyl dimethylene diisocyanate, biphenyl diisocyanate, diphenyl sulfone diisocyanate, or diphenyl ether diisocyanate.

[0010] The method for preparing the above-mentioned corona-resistant insulating varnish for enameled wire is characterized by comprising the following steps: S1. Part of the aromatic tricarboxylic acid anhydride is subjected to an esterification reaction with the alcohol hydroxyl-modified composite nanoparticles to obtain an intermediate product; S2. The intermediate product obtained in step S1, the remaining aromatic tricarboxylic anhydride and aromatic diisocyanate are subjected to a polycondensation reaction to obtain the corona-resistant insulating varnish for enameled wire.

[0011] Furthermore, the esterification reaction in step S1 is carried out at a temperature of 60℃-80℃ for 2h-4h. The polycondensation reaction described in step S2 adopts a staged heating method: heating to 60℃-80℃ for 2h-4h, and then heating to 120℃-150℃ for 6h-12h.

[0012] Furthermore, the preparation method of the alcohol hydroxyl-modified composite nanoparticles includes: (A1) Reaction of epoxy silane coupling agent with silica nanoparticles and layered double hydroxides yields epoxy silane-modified composite particles. (A2) The epoxy silane-modified composite particles obtained in step (A1) are subjected to a ring-opening reaction with a secondary amine to obtain the alcohol hydroxyl-modified composite nanoparticles. Based on a total mass of 100% for silica nanoparticles and layered double hydroxides, the mass of the epoxy silane coupling agent is 5%-15%. The secondary amine comprises 20%-40% of the total mass of the epoxy silane-modified composite particles, which is 100% of the total mass.

[0013] Furthermore, in step (A1), the reaction is carried out in a mixed solvent of ethanol and water at a temperature of 40°C-60°C for 8-16 hours. In step (A2), the ring-opening reaction is carried out in xylene solvent at a reaction temperature of 70℃-90℃ for 4h-8h.

[0014] An enameled wire includes a conductor and an insulating layer covering the conductor, the insulating layer being formed by curing the aforementioned corona-resistant insulating varnish for enameled wire.

[0015] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages: By compositing layered double hydroxides with silica nanoparticles, the high density of aluminum hydroxyl groups on the surface of the layered double hydroxides compensates for the lack of silanol hydroxyl groups on the silica surface, increasing the alcohol hydroxyl modification density by 30%-50%. Esterification covalently anchors the composite particles to the polyamide-imide prepolymer backbone. After curing, the ester bonds break, releasing the particles, effectively avoiding the agglomeration and sedimentation problems of nanoparticles in physical blending methods. No sedimentation was observed after 6 months of storage at room temperature; the particles were uniformly dispersed after curing, demonstrating significantly improved storage stability and curing uniformity.

[0016] By introducing calcium-based compounds to form an in-situ core-shell structure with layered double hydroxides, the calcium-based compounds react with carbonate ions released between the layers of the layered double hydroxides to form insoluble calcium carbonate precipitate, which is deposited on the surface of the layered double hydroxides to form a core-shell structure. The amount of carbonate ion released is reduced from 0.48 mg / g to 0.05 mg / g, with an inhibition rate of 89.6%, completely solving the ion migration problem caused by the introduction of layered double hydroxides, and significantly improving the pass rate of the pressure resistance test.

[0017] By designing layered double hydroxides as a gradient combination of high aspect ratio sheets and low aspect ratio particles, the high aspect ratio sheets are oriented and aligned in the coating film to form a flow-conducting framework, while the low aspect ratio particles can be controllably debonded under electro-thermal-mechanical coupling to form nanoscale air gap traps of 80nm-120nm. The initial corona resistance time reached 223h. After aging for 1000h under high-frequency pulse conditions of 180℃, 10kHz, and 1500Vp, the corona resistance time remained at 186h, with a retention rate of 83.4%, an improvement of 13 percentage points compared to the system without the gradient combination. The charge decay half-life was shortened from 65s to 45s, and the surface charge was rapidly neutralized, effectively suppressing partial discharge triggering.

[0018] By optimizing the composition ratio and particle size matching of inorganic particles, the elongation of the coating film is maintained at 44%-45%, which meets the requirements of enameled wire winding (≥40%).

[0019] Through optimized design of parameters in each step, the preparation method exhibits minimal batch-to-batch performance fluctuations when scaled up to a 100L reactor, with viscosity controlled between 1850cp and 1920cp and solid content consistently between 24.8% and 25.1%, making it suitable for industrial production.

[0020] By employing a three-tiered progressive technology approach of chemical bonding anchoring, ion locking conversion, and path-guided protection, this technology effectively solves the technical problems of poor storage stability, uneven dispersion after curing, potential electrical performance hazards caused by ion migration, and insufficient service reliability due to interface fatigue damage under high-frequency pulse conditions. This results in a high-performance corona-resistant insulating varnish for enameled wires that integrates stable storage, uniform curing, and reliable service. Detailed Implementation

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] Example 1: This example provides a corona-resistant insulating varnish for enameled wires, the preparation method of which includes the following steps: S1. Preparation of SiO2 / LDH composite nanoparticles modified with alcohol hydroxyl groups, the raw materials include: Silica nanoparticles: hydrophilic, D 50 =30nm, specific surface area 150m² 2 / g.

[0023] Layered double hydroxides (LDHs): Magnesium aluminum hydrotalcite (Mg6Al2(OH)) 16CO3·4H2O), D 50 =50nm, aspect ratio 3-5.

[0024] Epoxysilane coupling agent: γ-glycidoxypropyltrimethoxysilane (GPTMS), purity ≥98%.

[0025] Secondary amine: Dioctadecylamine, purity ≥95%.

[0026] Solvents: ethanol / water mixture (volume ratio 1:1) and xylene.

[0027] The preparation method is as follows: 80g of silica nanoparticles and 20g of LDH were added to an ethanol / water mixture (1L), ultrasonically dispersed for 30min to form a uniform suspension, the pH was adjusted to 7.5, 10g of GPTMS was added, stirred for 15min, heated to 50℃, and reacted for 12h under nitrogen protection. After the reaction was completed, the mixture was centrifuged, washed twice with ethanol, and vacuum dried at 60℃ for 12h to obtain epoxysilane-modified SiO2 / LDH composite particles (mass ratio 8:2). The epoxy silane-modified composite particles (90g) were dispersed in xylene (360g), with a solid content of 20%. Dioctadecylamine (27g, accounting for 30% of the composite particle mass) was added, the temperature was raised to 80℃, and the reaction was stirred for 5h. After the reaction was completed, a dispersion of SiO2 / LDH composite nanoparticles modified with alcohol hydroxyl groups (solid content 20%) was obtained, which was denoted as component A.

[0028] Synthesis of S2, polyamide-imide insulating varnish: A mixed solvent of N-methylpyrrolidone (NMP, 1.0 kg) and xylene (0.25 kg) was added to a 10 L reactor. Component A (0.79 kg, containing 158 g of composite particles, including 126.4 g of SiO2 and 1.6 g of LDH) was added, along with trimellitic anhydride (TMA, 110 g). The mixture was stirred and heated to 75 °C and reacted for 3 h to obtain the intermediate product.

[0029] NMP (2.42 kg), trimellitic anhydride (790 g), and diphenylmethane diisocyanate (MDI, 692 g) were added to the reactor. The molar ratio of acidic groups (anhydride + carboxyl groups) to isocyanate groups was controlled at 1:1. The temperature was increased in stages: first, the temperature was raised to 70 °C and reacted for 3 h; then, the temperature was raised to 140 °C and reacted for 8 h. After the reaction was completed, a polyamide-imide insulating varnish with a viscosity of 1851 cp (25 °C) and a solid content of 25% was obtained, denoted as varnish A.

[0030] S3. Preparation of enameled wire: The above-mentioned paint A was used as the topcoat and coated on the surface of a copper conductor (0.25 mm in diameter) using a high-speed enameling machine. The primer was a commercially available polyamide-imide insulating varnish (comprising 30% polyamide-imide resin, 69% mixed solvent, and 1% additives by mass ratio; the mixed solvent included 70% N-methylpyrrolidone, 15% xylene, 10% S-100, and 5% γ-butyrolactone). The number of coating passes was 1 (primer) + 16 (topcoat). The oven temperature was 330℃ at the inlet, 370℃ in the middle, and 400℃ at the outlet, with a machine speed of 90 m / min, to produce an enameled wire (topcoat thickness 75 μm).

[0031] The corona resistance performance was tested according to GB / T21707-2018 (155℃, 50Hz, 1500Vp), and the corona resistance time was 105h. The elongation was tested according to GB / T4074.3-2008, and the result was 44%. The number of pinholes in the salt water test was 0 according to GB / T4074.5-2008. The softening breakdown test (220℃, 1min) was performed according to GB / T4074.21-2018, and the result was qualified. Compared with the control system without LDH (SiO2 only, corona resistance time 46h), the corona resistance performance of this embodiment was improved by 128%, and the storage stability was good (no sedimentation after 6 months of storage at room temperature).

[0032] With the total amount of silica and layered double hydroxide (LDH) remaining constant (100g), reducing the amount of LDH by 10g (10g) results in a decrease in corona resistance time of at least 20h and an increase in elongation of less than 2%, while increasing the amount of LDH by 10g (30g) results in an increase in corona resistance time of at least 10h and a decrease in elongation of at least 3%. Example 2: After introducing layered double hydroxide (LDH), the carbonate ions (CO3) between the LDH layers... 2- The technical problem of releasing and migrating into the paint film during high-temperature curing, resulting in decreased insulation resistance and unacceptable withstand voltage performance, has been further improved.

[0033] The only difference from Example 1 is that the hydroxyl-modified composite nanoparticles adopt a ternary system of silica, layered double hydroxide (LDH) and calcium-based compound (Ca(OH)2), and an LDH@CaCO3 core-shell structure is generated in situ during the preparation process. All other steps and parameters are the same as in Example 1.

[0034] Specifically, the silica nanoparticles (D) used in this embodiment are: 50 =30nm), LDH (magnesium aluminum hydrotalcite, D 50 =50nm, interlayer anion CO3 2-The epoxy silane coupling agent (GPTMS), secondary amine (bis(octadecylamine)), and solvent are the same as in Example 1. The difference is that Ca(OH)₂ nanoparticles (D) are additionally introduced in this example. 50 =15nm, purity ≥99%), and the composition ratio of inorganic particles is adjusted to SiO2:LDH:Ca(OH)2=75:15:10 (mass ratio).

[0035] 120 g of silica nanoparticles, 24 g of LDH, and 16 g of Ca(OH)₂ were added to an ethanol / water mixture (1.5 L) and ultrasonically dispersed for 40 min to form a homogeneous suspension. The pH was adjusted to 8.5 (Ca(OH)₂ made the system weakly alkaline), and 16 g of GPTMS (10% of the total inorganic particles) was added and stirred for 15 min. The mixture was heated to 50 °C and reacted under nitrogen protection for 12 h. After the reaction was completed, the mixture was centrifuged, washed twice with ethanol, and vacuum dried at 60 °C for 12 h to obtain epoxysilane-modified SiO₂ / LDH / Ca(OH)₂ ternary composite particles.

[0036] The epoxy silane-modified ternary composite particles (120 g) were dispersed in xylene (480 g), with a solid content of 20%. Dioctadecylamine (36 g, accounting for 30% of the composite particle mass) was added, and the mixture was heated to 80 °C and stirred for 5 h. During the reaction, Ca(OH)₂ reacted with trace amounts of CO₂ and CO₃²⁻ released from the LDH interlayer. 2- The reaction resulted in the in-situ formation of a CaCO3 thin layer on the LDH surface, forming an LDH@CaCO3 core-shell structure. After the reaction, a ternary composite nanoparticle dispersion (20% solid content) modified with alcohol hydroxyl groups was obtained, denoted as component B.

[0037] The synthesis method of polyamide-imide insulating varnish is exactly the same as that of Example 1, except that component A in Example 1 is replaced with component B in this example.

[0038] The preparation and application of enameled wires employ the same coating process as in Example 1.

[0039] Compared to Example 1, Example 2 has a longer corona resistance time of 142 hours, and the elongation is the same as that of Example 1 (45%). CO3 2- Release amount: 0.05 mg / g (Example 1: 0.48 mg / g).

[0040] Example 3: Under the coupled conditions of high-frequency pulse, temperature cycling and electrostrictive stress, the technical problems of interface fatigue damage, shell peeling and insufficient long-term service reliability caused by the difference in thermal expansion coefficients of LDH and CaCO3 are further improved.

[0041] The difference from Example 2 is that in Example 3, the LDH in the alcohol hydroxyl-modified composite nanoparticles is a gradient combination of high aspect ratio sheets and low aspect ratio particles mixed at a mass ratio of 1:1, and the composition ratio of inorganic particles is adjusted to SiO2:LDH total:Ca(OH)2=80:12:8. The remaining steps and parameters are the same as in Example 2.

[0042] Specifically, the silica nanoparticles (D) used in this embodiment are: 50 =40nm), Ca(OH)2 nanoparticles (D 50 =15nm), epoxy silane coupling agent (GPTMS), secondary amine (bis(octadecylamine)), and solvent are the same as in Example 2. The difference is that LDH uses two different morphologies of magnesium aluminum hydrotalcite: High aspect ratio LDH sheets: prepared by hydrothermal method, with a chemical composition of Mg6Al2(OH). 16 CO3·4H2O has a transverse dimension of approximately 180 nm, a thickness of approximately 8 nm, and an aspect ratio of approximately 35.

[0043] Low aspect ratio LDH particles: Commercial magnesium aluminum hydrotalcite is ball-milled and screened, D 50 =50nm, aspect ratio approximately 3.5.

[0044] The composition ratio of inorganic particles was adjusted to SiO2:LDH total:Ca(OH)2 = 80:12:8 (mass ratio), in which the mass ratio of high aspect ratio lamellae to low aspect ratio particles in LDH total was 1:1.

[0045] High aspect ratio LDH sheets (9.6 g) and low aspect ratio LDH particles (9.6 g) were mixed and added to an ethanol / water mixture (1 L), and ultrasonically dispersed for 30 min. Silica nanoparticles (128 g) and Ca(OH)₂ (12.8 g) were added, and ultrasonic dispersion was continued for 20 min to form a homogeneous suspension (total inorganic particles 160 g). The pH was adjusted to 8.5, and GPTMS (16 g, accounting for 10% of the total inorganic particles) was added, and the mixture was stirred for 15 min. The temperature was raised to 50 °C, and the reaction was carried out under nitrogen protection for 12 h. After the reaction, the mixture was centrifuged, washed twice with ethanol, and vacuum dried at 60 °C for 12 h to obtain epoxysilane-modified gradient LDH composite particles.

[0046] The epoxy silane-modified composite particles (120 g) were dispersed in xylene (480 g), with a solid content of 20%. Dioctadecylamine (36 g, accounting for 30% of the composite particle mass) was added, and the mixture was heated to 80 °C and stirred for 5 h. During the reaction, Ca(OH)₂ reacted with trace amounts of CO₂ and CO₃²⁻ released from the LDH interlayer. 2-The reaction resulted in the in-situ formation of a CaCO3 thin layer on the LDH surface, forming an LDH@CaCO3 core-shell structure. After the reaction, a gradient LDH composite nanoparticle dispersion (20% solid content) modified with alcohol hydroxyl groups was obtained, denoted as component C.

[0047] The synthesis method of polyamide-imide insulating varnish is exactly the same as that of Example 2, except that component B in Example 2 is replaced with component C in this example.

[0048] The preparation and application of enameled wires employ the same coating process as in Example 2.

[0049] Performance tests were conducted according to the same testing standards as in Example 1, with the addition of a high-frequency pulse aging test (180°C, 10kHz, 1500Vp) to verify long-term service stability. The experimental results are shown in Table 1; Table 1 Comparison of experimental results between Example 3 and Example 2 Example 1 utilizes the high density of hydroxyl groups in LDH to compensate for the insufficient active sites on the silica surface, thereby increasing the hydroxyl modification density by 30-50%. The esterification reaction covalently anchors the composite particles to the prepolymer backbone. After curing, the ester bonds break, releasing the particles and achieving a balance between storage stability and uniform curing.

[0050] Example 2: CO3 released via Ca(OH)2 and LDH 2- The in-situ reaction generates CaCO3, which releases harmful ions and transforms them into beneficial inorganic interfaces. At the same time, the CaCO3 shell protects LDH from acid degradation.

[0051] Example 3 uses high aspect ratio LDH sheets to form a flow-guiding framework and low aspect ratio LDH particles to controllably debond and form nanoscale air gap traps, guiding corona energy from attacking the polymer backbone to a preset region for dissipation.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A corona-resistant insulating varnish for enameled wire, characterized in that, The raw materials for preparing the corona-resistant insulating varnish for enameled wires include aromatic tricarboxylic acid anhydride, aromatic diisocyanate, and alcohol hydroxyl-modified composite nanoparticles. The hydroxyl-modified composite nanoparticles comprise silica nanoparticles and layered double hydroxides. The alcohol-hydroxyl-modified composite nanoparticles were obtained by modification with an epoxy silane coupling agent and a secondary amine.

2. The corona-resistant insulating varnish for enameled wire according to claim 1, characterized in that, The hydroxyl-modified composite nanoparticles also contain calcium-based compounds, which are selected from at least one of calcium hydroxide or calcium oxide.

3. The corona-resistant insulating varnish for enameled wire according to claim 1 or 2, characterized in that, The layered double hydroxide comprises high aspect ratio sheets and low aspect ratio particles; The aspect ratio of the high aspect ratio sheet is 20-50; The aspect ratio of the low aspect ratio particles is 2-5; The mass ratio of the high aspect ratio sheet to the low aspect ratio particle is 0.5:1-2:

1.

4. The corona-resistant insulating varnish for enameled wire according to claim 1, characterized in that, Based on a solid content of 100% for the corona-resistant insulating varnish used in enameled wires, the mass of the alcohol-hydroxyl-modified composite nanoparticles is 1%-40%. The D50 particle size of the silica nanoparticles is 10nm-80nm; The D50 particle size of the layered double hydroxide is 30nm-80nm.

5. The corona-resistant insulating varnish for enameled wire according to claim 1, characterized in that, The aromatic tricarboxylic anhydride includes trimellitic anhydride; The aromatic diisocyanate includes at least one of 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, naphthalene diisocyanate, phenyl dimethylene diisocyanate, biphenyl diisocyanate, diphenyl sulfone diisocyanate, or diphenyl ether diisocyanate.

6. A method for preparing a corona-resistant insulating varnish for enameled wire as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Part of the aromatic tricarboxylic acid anhydride is subjected to an esterification reaction with the alcohol hydroxyl-modified composite nanoparticles to obtain an intermediate product; S2. The intermediate product obtained in step S1, the remaining aromatic tricarboxylic anhydride and aromatic diisocyanate are subjected to a polycondensation reaction to obtain the corona-resistant insulating varnish for enameled wire.

7. The preparation method according to claim 6, characterized in that, The esterification reaction in step S1 is carried out at a temperature of 60℃-80℃ for 2h-4h. The polycondensation reaction described in step S2 adopts a staged heating method: heating to 60℃-80℃ for 2h-4h, and then heating to 120℃-150℃ for 6h-12h.

8. The preparation method according to claim 6, characterized in that, The preparation method of the alcohol hydroxyl-modified composite nanoparticles includes: (A1) Reaction of epoxy silane coupling agent with silica nanoparticles and layered double hydroxides yields epoxy silane-modified composite particles. (A2) The epoxy silane-modified composite particles obtained in step (A1) are subjected to a ring-opening reaction with a secondary amine to obtain the alcohol hydroxyl-modified composite nanoparticles. Based on a total mass of 100% for silica nanoparticles and layered double hydroxides, the mass of the epoxy silane coupling agent is 5%-15%. The secondary amine comprises 20%-40% of the total mass of the epoxy silane-modified composite particles, which is 100% of the total mass.

9. The preparation method according to claim 8, characterized in that, In step (A1), the reaction is carried out in a mixed solvent of ethanol and water at a temperature of 40°C-60°C for 8-16 hours. In step (A2), the ring-opening reaction is carried out in xylene solvent at a reaction temperature of 70℃-90℃ for 4h-8h.

10. An enameled wire, characterized in that, It includes a conductor and an insulating layer covering the conductor, the insulating layer being formed by curing the corona-resistant insulating varnish for enameled wire as described in any one of claims 1-5.

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