High-voltage-resistant insulating epoxy resin composite material, preparation method and application

Abstract

The invention belongs to the technical field of electrical insulation composite materials, and provides a high-voltage-resistant insulation epoxy resin composite material, a preparation method and application. The high-voltage-resistant insulation epoxy resin composite material is prepared by taking a bisphenol A epoxy resin and novolac epoxy resin synergistic system as a matrix, surface modified nano aluminum oxide as a functional filler and an E-glass fiber three-dimensional woven preform as a reinforcing phase; a temperature control gradient VARTM process is adopted for forming, nanometer aluminum oxide is subjected to double-layer silane gradient coating treatment, a deep trap energy level is formed to restrain space charge accumulation, the power frequency breakdown strength of the material is larger than or equal to 35 kV / mm, the volume resistivity is larger than or equal to 1015 omega.cm, the bending strength is larger than or equal to 350 MPa, and the material is suitable for high-voltage electrical equipment such as insulating operation rods and all-insulating racks.

Description

Technical Field

[0001] This invention belongs to the field of electrical insulation composite material preparation technology, specifically involving high-voltage resistant insulating epoxy resin composite materials, preparation methods and applications, and is particularly suitable for insulation protection of high-voltage electrical equipment such as power system insulating operating rods and fully insulated platforms. Background Technology

[0002] As power systems develop towards higher voltage and larger capacity, higher requirements are placed on the electrical and mechanical properties of insulating materials. Insulated operating rods and fully insulated platforms, as important safety protection tools in power systems, need to operate reliably for extended periods in complex outdoor environments, withstanding multiple stresses such as high electric field strength, temperature fluctuations, ultraviolet radiation, and damp heat aging.

[0003] Traditional insulating materials mainly include ceramics, glass, and silicone rubber. While ceramics and glass materials possess excellent insulation properties and chemical stability, they suffer from drawbacks such as high mass, brittleness, and difficulty in processing, making it difficult to meet the demands for lightweight and complex shape fabrication. Silicone rubber materials have good hydrophobic properties, but their mechanical strength is low and their surface hardness is insufficient, making them susceptible to damage from external forces during practical use.

[0004] Epoxy resin-based composites are widely used in the field of power equipment insulation due to their excellent electrical insulation properties, high mechanical strength, and good processability. However, conventional epoxy resin composites are prone to partial discharge and electrical dendrite formation under high-voltage electric fields, leading to deterioration of insulation performance. In high-temperature and high-humidity environments, the volume resistivity of the material decreases significantly, and the breakdown strength is reduced. At the same time, traditional molding processes are difficult to guarantee the molding quality and performance uniformity of large-sized complex structural parts.

[0005] Chinese patent CN111363315A, entitled "An Epoxy Resin Insulating Material and Its Preparation Method and Application," discloses an epoxy resin insulating material using organosilicon-modified alicyclic epoxy resin combined with active microsilica filler, formed via the APG process. It is primarily used for outdoor insulator sheath materials. This technical solution improves the material's hydrophobic properties by introducing Si-CH3 bonds; however, the material lacks fiber reinforcement, resulting in limited mechanical strength, and the APG process is difficult to apply to the fabrication of large, complex structural components.

[0006] In recent years, nanotechnology has made significant progress in the field of insulating materials. Studies have shown that nano-Al2O3 fillers can form deep trap energy levels in epoxy resin matrices, effectively suppressing space charge accumulation and charge migration, and improving the breakdown strength and resistance to electrical aging of materials. However, the high specific surface energy of nanoparticles makes them prone to aggregation in the matrix, affecting dispersion uniformity and interfacial bonding strength. How to achieve effective dispersion and interface optimization of nanofillers remains a key issue restricting their engineering applications.

[0007] Vacuum-assisted resin transfer molding (VARTM) is an advanced composite material molding technology with advantages such as low cost, ability to fabricate large and complex structural parts, and controllable fiber volume fraction. However, conventional VARTM processes suffer from problems such as uneven resin flow, high porosity, and large curing shrinkage stress, which affect the insulation reliability of composite materials.

[0008] Therefore, developing a high-voltage insulating epoxy resin composite material with excellent electrical insulation properties, high mechanical strength, and good environmental adaptability, and establishing a corresponding preparation process, is of great significance for improving the safety protection level of power systems. Summary of the Invention

[0009] The purpose of this invention is to overcome the technical defects of existing epoxy resin insulating materials, such as insufficient mechanical strength, difficulty in dispersing nanofillers, and poor adaptability to molding processes, and to provide high-voltage resistant insulating epoxy resin composite materials and their preparation methods.

[0010] To achieve the above objectives, the present invention adopts the following technical solution.

[0011] This invention provides a high-voltage resistant insulating epoxy resin composite material, which, by weight, comprises: 100 parts epoxy resin matrix, 0.5-5 parts surface-modified nano alumina, 80-150 parts glass fiber preform, 80-120 parts acid anhydride curing agent, 0.3-1.0 parts accelerator, and 1-4 parts silane coupling agent.

[0012] The epoxy resin matrix is ​​composed of bisphenol A type epoxy resin and phenolic epoxy resin mixed in a mass ratio of (70-90):(10-30);

[0013] The surface-modified nano-alumina consists of nano-alumina particles coated with a double-layer silane gradient, with a particle size of 20-80 nm and a specific surface area of ​​80-200 m². 2 / g.

[0014] Furthermore, the bisphenol A type epoxy resin has an epoxy equivalent of 180-195 g / eq and a viscosity of 11000-14000 mPa·s at 25°C.

[0015] The phenolic epoxy resin has an epoxy equivalent of 170-190 g / eq and an epoxy functionality of 2.5-3.5.

[0016] Furthermore, the glass fiber preform is an E-glass fiber three-dimensional braided preform or an E-glass fiber multiaxial warp-woven fabric;

[0017] The E-glass fiber has a single filament diameter of 9-17 μm and a volume resistivity ≥10. 14 Ω·cm;

[0018] The areal density of the glass fiber preform is 300-800 g / m³. 2 The number of layers ranges from 4 to 16.

[0019] Furthermore, the surface-modified nano-alumina bilayer silane gradient coating structure comprises:

[0020] The inner layer is a γ-aminopropyltriethoxysilane (KH550) coating layer, with a coating amount of 1-3% of the mass of nano-alumina;

[0021] The outer layer is a γ-glycidyl etheroxypropyltrimethoxysilane (KH560) coating layer, with a coating amount of 2-5% of the mass of nano-alumina.

[0022] Furthermore, the anhydride curing agent is at least one of methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, and methylnadic anhydride;

[0023] The accelerator is at least one of 2-ethyl-4-methylimidazole, 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), and benzyldimethylamine.

[0024] Further, the silane coupling agent is at least one selected from γ-glycidoxypropyltrimethoxysilane (KH560), γ-aminopropyltriethoxysilane (KH550), and vinyltrimethoxysilane.

[0025] The present invention also provides a method for preparing the above-mentioned high-voltage resistant insulating epoxy resin composite material, comprising the following steps:

[0026] Step S1, Preparation of surface-modified nano-alumina:

[0027] S1.1, Dry the nano-alumina powder at 80-120℃ for 2-4 hours to remove surface adsorbed water;

[0028] S1.2, the dried nano-alumina is dispersed in anhydrous ethanol and ultrasonically dispersed for 20-40 min to obtain a nano-alumina suspension, wherein the mass concentration of nano-alumina is 5-15%;

[0029] S1.3, add γ-aminopropyltriethoxysilane (KH550) dropwise to the suspension, the amount of which is 1-3% of the mass of nano-alumina, and stir the reaction at 50-70℃ for 1-2 hours to complete the inner layer coating;

[0030] S1.4, continue to add γ-glycidyl etheroxypropyltrimethoxysilane (KH560) dropwise to the reaction system of step S1.3, the amount added is 2-5% of the mass of nano alumina, stir the reaction at 60-80℃ for 2-4 hours to complete the outer coating;

[0031] S1.5, the reaction product is centrifuged, washed 2-3 times with anhydrous ethanol, and vacuum dried at 60-80℃ for 8-12h to obtain surface-modified nano-alumina.

[0032] Step S2, Preparation of modified epoxy resin mixture:

[0033] S2.1, Bisphenol A type epoxy resin and phenolic epoxy resin are mixed at a mass ratio of (70-90):(10-30) and stirred at 50-70℃ for 30-60 min to obtain epoxy resin matrix;

[0034] S2.2, add surface-modified nano-alumina into the epoxy resin matrix and disperse it at high speed for 30-60 min under vacuum degree ≤500Pa and temperature 50-70℃, with a rotation speed of 2000-4000 rpm.

[0035] S2.3, add silane coupling agent, continue stirring for 20-40 minutes to obtain modified epoxy resin mixture.

[0036] Step S3, Preparation of curing agent premix:

[0037] The anhydride curing agent and accelerator are mixed evenly at 40-60℃ and degassed under vacuum for 20-40 minutes to obtain the curing agent premix.

[0038] Step S4, Surface treatment of the glass fiber preform:

[0039] Dry the glass fiber preform at 120-150℃ for 1-2 hours to remove surface moisture and sizing agent residue, and then cool it to room temperature for later use.

[0040] Step S5, Temperature-Controlled Gradient VARTM Molding:

[0041] S5.1, the surface-treated glass fiber preform is laid in the mold according to the designed layering sequence, and the release cloth, flow guide net and vacuum bag are laid to seal the perimeter of the mold;

[0042] S5.2, Evacuate the mold to a vacuum level ≤100Pa, maintain for 10-20 minutes, and check the vacuum seal.

[0043] S5.3, the modified epoxy resin mixture and the curing agent premix are mixed at a mass ratio of 100:(80-120), and degassed under a vacuum of ≤500Pa for 10-20 minutes to obtain the impregnation resin.

[0044] S5.4, Open the resin inlet valve and inject the impregnation resin into the mold under vacuum negative pressure. Control the mold temperature to 40-60℃ and the resin injection rate to 50-200g / min.

[0045] S5.5 After the resin filling is completed, close the inlet valve and continue to maintain the vacuum for 5-15 minutes to allow the resin to fully impregnate the fiber;

[0046] S5.6 employs a gradient temperature curing procedure: In the first stage, the temperature is increased from room temperature to 80-100℃ at a rate of 1-3℃ / min, and held for 1-2 hours; in the second stage, the temperature is increased to 120-140℃ at a rate of 1-2℃ / min, and held for 2-4 hours; in the third stage, the temperature is increased to 150-170℃ at a rate of 0.5-1℃ / min, and held for 1-3 hours.

[0047] S5.7 After curing, cool to below 60°C at a rate of 1-2°C / min, and demold to obtain a high-voltage resistant insulating epoxy resin composite material.

[0048] Furthermore, the high-speed dispersion in step S2.2 employs a planetary mixer or a high-shear disperser;

[0049] The planetary mixer has a common rotational speed of 20-40 rpm and a free rotational speed of 2000-4000 rpm.

[0050] Furthermore, the resin injection in step S5.4 adopts either center-point injection or linear injection method;

[0051] When preparing rod-shaped products with a length exceeding 500 mm, a linear injection method is adopted, with the injection ports evenly distributed along the length direction of the product.

[0052] Furthermore, in the gradient temperature curing procedure in step S5.6:

[0053] The preferred insulation temperature for the first stage is 90℃, and the preferred insulation time is 1.5h.

[0054] The preferred temperature for the second stage of heat preservation is 130℃, and the preferred heat preservation time is 3 hours.

[0055] The preferred temperature for the third stage of heat preservation is 160℃, and the preferred heat preservation time is 2 hours.

[0056] The present invention also provides the application of the above-mentioned high-voltage resistant insulating epoxy resin composite material or the high-voltage resistant insulating epoxy resin composite material prepared by the above preparation method in high-voltage electrical equipment, especially in the application of insulating operating rods, fully insulating platforms, insulating supports and insulating crossarms.

[0057] The technical solution of the present invention has the following advantages:

[0058] First, the high-voltage resistant insulating epoxy resin composite material provided by this invention uses a synergistic system of bisphenol A type epoxy resin and phenolic epoxy resin as the matrix. Bisphenol A type epoxy resin provides excellent mechanical toughness and processing performance, while the multifunctional structure of phenolic epoxy resin increases the crosslinking density. The synergistic effect of the two forms a highly crosslinked three-dimensional network structure, significantly improving the material's glass transition temperature, thermal stability, and resistance to electrical tracking. Compared with a single alicyclic epoxy system, this synergistic system, while ensuring good electrical insulation performance, exhibits higher mechanical strength and better heat resistance.

[0059] Secondly, this invention employs surface-modified nano-alumina as a functional filler. Through a bilayer silane gradient coating technology, the amino groups of the inner KH550 react with the hydroxyl groups on the surface of the nano-alumina to form stable chemical bonds, while the epoxy groups of the outer KH560 react chemically with the epoxy resin matrix, achieving covalent bonding between the nano-filler and the matrix. This bilayer coating structure effectively prevents nanoparticle aggregation and improves dispersion uniformity; simultaneously, it forms deep trap energy levels (trap depth approximately 1.2-1.8 eV) at the nanoparticle-matrix interface, effectively suppressing space charge injection and accumulation, and improving the material's breakdown strength and partial discharge resistance. The amount of nano-alumina added is controlled within the range of 0.5-5 parts; within this range, uniform dispersion of the nano-filler can be achieved, avoiding aggregation and defects caused by excessive addition.

[0060] Third, this invention introduces an E-glass fiber three-dimensional braided preform as a reinforcing phase. The high volume resistivity of glass fiber (≥...) The Ω·cm (0.5 Ω·cm) ensures the overall insulation performance of the composite material; the three-dimensional braided structure provides excellent interlaminar shear strength and anti-delamination ability, avoiding the problem of delamination failure that is prone to occur under bending load in traditional two-dimensional fabric laminate structures. Glass fiber reinforcement enables the composite material to achieve a bending strength of 350-500MPa and a bending modulus of 18-28GPa, meeting the high mechanical performance requirements of the insulating operating rod.

[0061] Fourth, this invention employs a temperature-controlled gradient VARTM molding process. By precisely controlling the resin injection temperature and the gradient curing procedure, it achieves full resin impregnation of the fibers and effective release of curing shrinkage stress. The first stage of low-temperature insulation gels the resin and establishes a preliminary cross-linking network; the second stage of medium-temperature insulation promotes deep resin curing and completes the main cross-linking reaction; the third stage of high-temperature post-curing further increases the degree of cross-linking and eliminates residual stress. This gradient curing procedure controls the porosity of the composite material to below 0.5% and achieves a fiber volume fraction of 55-65%, significantly improving the insulation reliability of the material.

[0062] Fifth, the high-voltage resistant insulating epoxy resin composite material prepared by this invention has excellent comprehensive properties: power frequency breakdown strength ≥35kV / mm, volume resistivity ≥ Ω·cm, surface resistivity ≥ The material exhibits a resistance to tracking up to 1A4.5; flexural strength ≥350MPa, flexural modulus ≥18GPa, interlaminar shear strength ≥40MPa; glass transition temperature ≥140℃, and thermal decomposition temperature (5% weight loss) ≥350℃. This material is particularly suitable for insulation protection of high-voltage electrical equipment such as insulated operating rods and fully insulated platforms with voltage levels ranging from 10-500kV. Attached Figure Description

[0063] Figure 1 This is a comparison chart of thermogravimetric analysis curves.

[0064] Figure 2 This is a differential scanning calorimetry curve.

[0065] Figure 3 For dynamic thermomechanical analysis of dual Y-axis curves.

[0066] Figure 4 This is a scanning electron microscope image showing the dispersion of surface-modified nano-alumina in an epoxy resin matrix. Detailed Implementation

[0067] The following embodiments are provided to better understand the present invention and are not intended to limit the scope of the preferred embodiments, nor do they constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0068] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0069] The technical solution of this invention is based on the following principles and mechanisms:

[0070] This invention selects bisphenol A type epoxy resin (DGEBA) and phenolic epoxy resin (Novolac Epoxy) as synergistic components of the matrix resin, based on the following design principles:

[0071] From a molecular structure perspective, bisphenol A epoxy resins contain flexible isopropyl (-C(CH3)2-) linking groups and rigid benzene ring structures in their molecular chains, endowing the cured products with good toughness and processing properties. Their epoxy equivalent is 180-195 g / eq, with a moderate molecular weight distribution and viscosity suitable for liquid molding processes. Phenolic epoxy resins possess multiple epoxy groups (epoxy functionality 2.5-3.5), and the phenolic structure on the molecular chain provides a rich rigid benzene ring backbone, which can significantly improve crosslinking density and thermal stability.

[0072] From the perspective of cross-linking network formation, the bifunctional structure of bisphenol A epoxy resin forms linear chain extensions, while the multifunctional structure of phenolic epoxy resin provides network nodes. The two work synergistically to form a highly cross-linked three-dimensional network. When the mass ratio of bisphenol A epoxy resin to phenolic epoxy resin is (70-90):(10-30), the cross-linking density of the cured product can reach a certain level while ensuring good processing performance. - mol / cm 3 .

[0073] From the perspective of electrical insulation performance, high crosslinking density restricts the migration path of charge carriers, thereby increasing volume resistivity and breakdown strength. The abundant benzene rings in the phenolic structure provide excellent arc resistance and resistance to tracking, and the π-electron cloud of the benzene rings can effectively absorb discharge energy, delaying the electrical erosion of the material.

[0074] Nano-alumina (α-Al₂O₃ or γ-Al₂O₃) is an important insulating filler. Its high bandgap (approximately 9 eV) and high thermal conductivity (approximately 30 W / (m·K)) make it valuable for applications in high-voltage insulating materials. However, the high specific surface energy (80-200 m² / g) of nanoparticles... 2 / g) makes it very easy for it to agglomerate, affecting the uniformity of dispersion and interfacial properties.

[0075] This invention uses a double-layer silane gradient coating technology to solve the above problems:

[0076] The first coating layer uses γ-aminopropyltriethoxysilane (KH550), and its chemical reaction mechanism is as follows:

[0077] The ethoxy group (-OC2H5) in the KH550 molecule hydrolyzes to generate silanol (-Si-OH). The silanol then undergoes a dehydration condensation reaction with the active hydroxyl groups on the surface of nano-alumina, forming Al-O-Si covalent bonds. Maintaining the reaction temperature between 50-70℃ is beneficial for controlling the equilibrium of the hydrolysis-condensation reaction and preventing the self-condensation of silane molecules. The amino group (-NH2) at the terminal of the KH550 molecule extends outward, providing active sites for the second coating layer.

[0078] The second coating layer uses γ-glycidoxypropyltrimethoxysilane (KH560). After hydrolysis of its methoxy groups, it partially crosslinks with the first coating layer (KH550), while the epoxy groups remain active. The reaction temperature is increased to 60-80℃ to promote the ring-opening addition reaction between the epoxy groups and amino groups, establishing a chemical bond between the two silane layers. The terminal epoxy groups of the KH560 molecule can react with the epoxy groups of the epoxy resin matrix or the curing agent, achieving covalent bonding between the nanofiller and the matrix.

[0079] The interfacial effect of this double-layer coating structure is manifested in the following aspects:

[0080] From the perspective of interface layer structure, the bilayer silane coating forms an organic-inorganic hybrid interface layer with a thickness of approximately 2-5 nm. The modulus of this interface layer is between that of the inorganic nanoparticles (approximately 300 GPa) and the organic matrix (approximately 3 GPa), which can effectively transfer stress and avoid debonding failure caused by interfacial stress concentration.

[0081] From the perspective of charge trapping, the Si-O-Al covalent bonds and the polar groups in the organosilane molecules form deep trap energy levels in the interfacial region. According to density functional theory (DFT) calculations, the depth of this interfacial trap is approximately 1.2-1.8 eV, falling within the category of deep traps. Deep traps can effectively capture injected charges, reduce space charge density, and decrease the degree of electric field distortion, thereby improving the breakdown strength of the material.

[0082] From the perspective of thermal conductivity, the addition of nano-alumina and good interfacial bonding improve the thermal conductivity of the composite material (from 0.2 W / (m·K) of pure epoxy to 0.4-0.6 W / (m·K)), which is beneficial for dissipating the heat generated by partial discharge and delaying the occurrence of thermal breakdown.

[0083] E-glass fiber, used as a reinforcing fiber for electrical insulation, mainly consists of SiO2 (52-56%), Al2O3 (12-16%), CaO (16-25%), and B2O3 (5-10%), exhibiting excellent electrical insulation properties (volume resistivity ≥ 10%). It has good mechanical properties (tensile strength of about 3400 MPa and elastic modulus of about 73 GPa).

[0084] This invention selects a three-dimensional woven preform or a multi-axial warp-knitted fabric as the reinforcing phase:

[0085] The structural features of three-dimensional braided prefabricated structures are as follows: yarns interweave in three mutually perpendicular directions to form an integral structure. Axial yarns provide longitudinal load-bearing capacity, while the braided yarns form an interlocking structure in the thickness direction, effectively improving interlaminar shear strength and impact resistance. For rod-shaped products such as insulating operating rods, the Z-axis fibers of the three-dimensional braided structure can effectively resist delamination under bending loads.

[0086] The structural characteristics of multiaxial warp-knitted fabrics are: multiple layers of oriented fibers are bound and fixed by warp-knitting yarns, allowing for various layup combinations such as ±45° / 0° / 90°. Compared with traditional woven fabrics, the fibers in multiaxial fabrics are straightened, without buckling, resulting in higher utilization of mechanical properties. The warp-knitting structure provides a certain degree of fiber connection between layers, and the interlayer shear strength is superior to that of simple laminated structures.

[0087] Surface treatment of the glass fiber preform is crucial for ensuring interfacial performance. Commercially available glass fibers are typically coated with organosilane sizing agents, but the formulation of these agents may not be perfectly compatible with the resin system of this invention. Drying at 120-150°C removes the organic components of the original sizing agent, exposing the silanol groups (-Si-OH) on the fiber surface, facilitating subsequent chemical bonding with the silane coupling agent in the resin system.

[0088] Fiber volume fraction ( (VARTM) is a key parameter affecting the mechanical properties of composite materials. This invention optimizes the VARTM process parameters to... It should be controlled within the range of 55-65%. According to the mixing law of composite materials mechanics:

[0089] .

[0090] in For the modulus of composite materials, This is the fiber modulus (approximately 73 GPa). This represents the matrix modulus (approximately 3.5 GPa). When When the fiber orientation is 60%, the theoretical flexural modulus is approximately 45 GPa. Considering the influence of factors such as fiber orientation and interfacial efficiency, the actual flexural modulus is approximately 50-70% of the theoretical value, i.e., 18-28 GPa.

[0091] The basic principle of Vacuum Assisted Resin Transfer Molding (VARTM) is to use vacuum negative pressure to drive resin flow and impregnate the fiber preform. The resin flow in the porous fiber medium follows Darcy's Law:

[0092] ,

[0093] in The resin flow rate is... The permeability of the prefabricated structure, For resin viscosity, This represents the pressure gradient. Therefore, reducing resin viscosity and increasing the pressure gradient are effective methods to accelerate resin flow and shorten mold filling time.

[0094] This invention employs a temperature control strategy to optimize resin flow behavior:

[0095] During the injection stage, the temperature is controlled at 40-60℃ to reduce the resin viscosity to the range of 300-800 mPa·s, significantly improving fluidity. Excessively high temperatures accelerate resin gelation and shorten the workable time; excessively low temperatures result in excessively high viscosity, making it difficult for the resin to fully wet the fibers.

[0096] The resin injection rate should be controlled between 50-200 g / min to avoid air bubble entrainment due to excessively fast injection and premature resin gelation due to excessively slow injection. For large-sized products, a multi-point injection method should be used, with the injection ports evenly distributed along the length of the product to ensure uniform advancement of the resin flow front.

[0097] This invention employs a three-stage gradient temperature curing process, the design of which is based on the following:

[0098] The first stage (room temperature → 80-100℃, holding for 1-2 hours): The resin begins to gel, the molecular weight increases rapidly, and the system viscosity rises to the gel point. This stage mainly involves the esterification reaction of epoxy groups with acid anhydrides and the etherification reaction of epoxy-hydroxyl groups, establishing preliminary linear segments and branched structures. The holding temperature is controlled near the gel temperature to avoid internal stress and bubble problems caused by excessively intense exothermic peaks.

[0099] Second stage (80-100℃→120-140℃, heat preservation for 2-4 hours): Entering the deep curing stage, the network structure is rapidly established, and the glass transition temperature (… The curing reaction reaches 80-95% at this stage, and the material acquires its main mechanical properties. The heating rate should be controlled at 1-2℃ / min to avoid internal stress caused by excessive temperature gradient.

[0100] The third stage (120-140℃→150-170℃, holding for 1-3 hours): the post-curing stage, further increasing the degree of crosslinking and completing the reaction of residual epoxy groups. This stage brings the degree of curing close to 100%. Increase to the final value. The post-curing temperature should be 20-30°C higher than the service temperature to eliminate the impact of thermal history on performance.

[0101] During the cooling phase, the material is cooled slowly at a rate of 1-2℃ / min to avoid microcracks and debonding caused by excessive thermal stress. Demolding is performed when the temperature drops below 60℃, at which point the material has sufficient strength and rigidity.

[0102] The high electrical insulation performance of the composite material of this invention stems from the following synergistic effect:

[0103] From the perspective of the matrix resin, epoxy networks with high crosslinking density have a high band gap (approximately 8 eV) and a high threshold energy for carrier generation. The benzene ring π-electron cloud in the phenolic structure can absorb high-energy electrons, reduce the secondary electron emission coefficient, and suppress the initiation and growth of electrical trees.

[0104] From the perspective of nanofillers, surface-modified nano-alumina forms numerous interfacial regions within the matrix. The deep trapping energy levels (1.2-1.8 eV) of these interfacial regions effectively trap injected charges, reducing the space charge density. The high bandgap (approximately 9 eV) and high thermal conductivity of the nanoparticles enhance the breakdown threshold and thermal stability of the localized regions.

[0105] From the perspective of fiber reinforcement, the high resistivity of E-glass fiber (≥ The fiber strength (Ω·cm) ensures overall insulation performance. The fiber-matrix interface blocks the propagation path of electrical trees, extending electrical treeing lifetime. The improved mechanical properties from fiber reinforcement resist mechanical deformation under electrical stress, maintaining the integrity of the insulation structure.

[0106] From a process quality perspective, the low porosity (<0.5%) of the VARTM process reduces internal air gap defects and prevents partial discharge. The high fiber volume fraction (55-65%) improves the density and uniformity of the material.

[0107] Example 1

[0108] This embodiment provides a high-voltage resistant insulating epoxy resin composite material, comprising:

[0109] 100g bisphenol A type epoxy resin (E-51, epoxy equivalent 186g / eq), 20g phenolic epoxy resin (F-51, epoxy equivalent 178g / eq, epoxy functionality 3.0), 2g surface-modified nano-alumina (particle size 40nm, specific surface area 150m²). 2 / g), 100g methyltetrahydrophthalic anhydride, 0.5g 2-ethyl-4-methylimidazolium, 2g KH560 and glass fiber preform (E-glass fiber multiaxial warp-woven fabric, areal density 600g / m²). 2 (8 floors in total).

[0110] The preparation methods of the above materials include:

[0111] Step 1: Preparation of surface-modified nano-alumina

[0112] 100g of nano-alumina powder was dried at 100℃ for 3h to remove surface adsorbed water. The dried nano-alumina was dispersed in 1000g of anhydrous ethanol and ultrasonically dispersed for 30min to obtain a nano-alumina suspension with a mass concentration of 10%.

[0113] Add 2g of KH550 (2% of the mass of nano-alumina) dropwise to the suspension and stir at 60℃ for 1.5h to complete the inner coating. Continue to add 3.5g of KH560 (3.5% of the mass of nano-alumina) dropwise and stir at 70℃ for 3h to complete the outer coating.

[0114] The reaction product was centrifuged (8000 rpm, 10 min), washed three times with anhydrous ethanol, and vacuum dried at 70 °C for 10 h to obtain surface-modified nano-alumina.

[0115] Step 2: Preparation of modified epoxy resin mixture

[0116] 100g of bisphenol A epoxy resin and 20g of phenolic epoxy resin were stirred at 60℃ for 45min to obtain an epoxy resin matrix. 2g of surface-modified nano-alumina was added to the epoxy resin matrix, and the mixture was dispersed at high speed using a planetary mixer for 45min (30rpm revolution, 3000rpm rotation) under vacuum of 300Pa and temperature of 60℃. 2g of KH560 was added, and stirring continued for 30min to obtain a modified epoxy resin mixture.

[0117] Step 3: Preparation of Curing Agent Premix

[0118] 100g of methyltetrahydrophthalic anhydride and 0.5g of 2-ethyl-4-methylimidazole were mixed evenly at 50℃ and degassed under vacuum for 30min to obtain a curing agent premix.

[0119] Step 4: Surface treatment of the fiberglass preform

[0120] Cut the E-glass fiber multiaxial warp-knitted fabric to the design size (300mm×50mm×8 layers), dry it at 130℃ for 1.5h, and cool it to room temperature for later use.

[0121] Step 5: Temperature-controlled gradient VARTM molding

[0122] The surface-treated fiberglass preform is placed in a rod-shaped mold (internal cavity dimensions 300mm × 50mm × 30mm), and a release cloth, a flow guide net, and a vacuum bag are laid on top. The mold perimeter is then sealed with sealing tape. The mold is evacuated to a vacuum level of 50Pa and maintained for 15 minutes to confirm that there are no leaks.

[0123] The modified epoxy resin mixture and the curing agent premix were mixed at a mass ratio of 100:83 and degassed under a vacuum of 300 Pa for 15 min to obtain the impregnation resin. The resin inlet valve was opened, and the impregnation resin was injected into the mold under vacuum, controlling the mold temperature at 50℃ and the resin injection rate at approximately 100 g / min. After the resin filling was complete, the inlet valve was closed, and the vacuum was maintained for another 10 min.

[0124] A gradient temperature curing procedure was adopted: the temperature was increased from room temperature to 90℃ at a rate of 2℃ / min and held for 1.5 hours; the temperature was increased to 130℃ at a rate of 1.5℃ / min and held for 3 hours; the temperature was increased to 160℃ at a rate of 0.8℃ / min and held for 2 hours. After curing, the temperature was cooled to 50℃ at a rate of 1.5℃ / min, and the product was demolded to obtain a high-voltage resistant insulating epoxy resin composite material.

[0125] Example 2

[0126] This embodiment provides a high-voltage resistant insulating epoxy resin composite material, comprising:

[0127] 90g bisphenol A type epoxy resin (E-51), 30g phenolic epoxy resin (F-51), 3g surface-modified nano-alumina (particle size 60nm, specific surface area 120m²) 2 / g), 115g methylhexahydrophthalic anhydride, 0.8g DMP-30, 3g KH560 and glass fiber preform (E-glass fiber three-dimensional braided preform, areal density 500g / m³), 115g methylhexahydrophthalic anhydride, 0.8g DMP-30, 3g KH560 and glass fiber preform (E-glass fiber three-dimensional braided preform, areal density 2 (Total of 10 floors).

[0128] The preparation methods of the above materials include:

[0129] Step 1: Preparation of surface-modified nano-alumina

[0130] Nano-alumina powder was dried at 110℃ for 2.5 h. The dried nano-alumina was dispersed in anhydrous ethanol (12% by mass) and ultrasonically dispersed for 35 min. KH550 (2.5% by mass of nano-alumina) was added dropwise, and the mixture was stirred at 65℃ for 1.5 h; KH560 (4% by mass of nano-alumina) was then added dropwise, and the mixture was stirred at 75℃ for 3.5 h. The mixture was centrifuged, washed, and vacuum dried at 75℃ for 10 h to obtain surface-modified nano-alumina.

[0131] Step 2: Preparation of modified epoxy resin mixture

[0132] 90g of bisphenol A epoxy resin and 30g of phenolic epoxy resin were stirred at 65℃ for 50min to obtain an epoxy resin matrix. 3g of surface-modified nano-alumina was added to the epoxy resin matrix and dispersed at high speed for 50min under a vacuum of 400Pa and a temperature of 65℃. 3g of KH560 was added, and stirring continued for 35min to obtain a modified epoxy resin mixture.

[0133] Step 3: Preparation of Curing Agent Premix

[0134] 115g of methylhexahydrophthalic anhydride and 0.8g of DMP-30 were mixed evenly at 55℃ and degassed under vacuum for 35min to obtain a curing agent premix.

[0135] Step 4: Surface treatment of the fiberglass preform

[0136] The E-glass fiber three-dimensional braided preform was dried at 140℃ for 1.5h and then cooled to room temperature for later use.

[0137] Step 5: Temperature-controlled gradient VARTM molding

[0138] The fiberglass preform is placed in the mold, and auxiliary materials are laid and sealed. A vacuum of 80 Pa is applied and maintained for 15 minutes. The modified epoxy resin mixture and the curing agent premix are mixed at a mass ratio of 100:87, degassed, and then injected into the mold at a temperature of 55°C and an injection rate of approximately 120 g / min.

[0139] Gradient temperature curing procedure: Increment to 95℃ at 2.5℃ / min, hold for 1.5h; increment to 135℃ at 1.5℃ / min, hold for 3h; increment to 165℃ at 0.8℃ / min, hold for 2h. Cool and demold to obtain a high-voltage resistant insulating epoxy resin composite material.

[0140] Example 3

[0141] This embodiment provides a high-voltage resistant insulating epoxy resin composite material, comprising:

[0142] 80g bisphenol A type epoxy resin (E-51), 20g phenolic epoxy resin (F-51), 1g surface-modified nano alumina (particle size 30nm, specific surface area 180m²) 2 / g), 90g methyltetrahydrophthalic anhydride, 0.4g 2-ethyl-4-methylimidazolium, 1.5g KH560 and glass fiber preform (E-glass fiber multiaxial warp-woven fabric, areal density 400g / m²). 2 (6 floors in total).

[0143] The preparation method of the above materials is similar to that of Example 1, with the main difference being:

[0144] In step one, the KH550 coating amount is 1.5%, and the KH560 coating amount is 3%.

[0145] In step two, the epoxy resin matrix is ​​prepared at a temperature of 55°C and the stirring time is 40 min; the nanofiller is dispersed at a temperature of 55°C for 40 min.

[0146] In step five, the mold temperature is 45℃, and the resin injection rate is approximately 80g / min. The gradient heating program is as follows: increase to 85℃ at 1.8℃ / min and hold for 1.5h; increase to 125℃ at 1.2℃ / min and hold for 2.5h; increase to 155℃ at 0.6℃ / min and hold for 2h.

[0147] Example 4

[0148] This embodiment provides a high-voltage resistant insulating epoxy resin composite material, comprising:

[0149] 85g bisphenol A type epoxy resin (E-51), 25g phenolic epoxy resin (F-51), 4g surface-modified nano alumina (particle size 50nm, specific surface area 130m²) 2 / g), 105g methylnadic anhydride, 0.6g benzyl dimethylamine, 2.5g KH550 and glass fiber preform (E-glass fiber three-dimensional braided preform, areal density 700g / m³). 2 (It has 12 floors in total).

[0150] The preparation method of the above materials is similar to that of Example 2, with the main difference being:

[0151] In step one, KH550 was used as the inner coating agent (coating amount 2.5%) and KH560 was used as the outer coating agent (coating amount 4.5%).

[0152] In step two, 2.5g of KH550 is added as a silane coupling agent.

[0153] In step three, methyl nadic anhydride is used as a curing agent, which has better heat resistance than methyl tetrahydrophthalic anhydride.

[0154] The gradient heating program in step five is as follows: increase to 95℃ at 2℃ / min and hold for 2 hours; increase to 140℃ at 1.5℃ / min and hold for 3.5 hours; increase to 170℃ at 1℃ / min and hold for 2.5 hours.

[0155] Example 5

[0156] This embodiment provides a high-voltage resistant insulating epoxy resin composite material, comprising:

[0157] 95g bisphenol A type epoxy resin (E-51), 15g phenolic epoxy resin (F-51), 0.5g surface-modified nano-alumina (particle size 25nm, specific surface area 190m²) 2 / g), 95g methyltetrahydrophthalic anhydride, 0.3g 2-ethyl-4-methylimidazolium, 1g KH560 and glass fiber preform (E-glass fiber multiaxial warp-woven fabric, areal density 350g / m²). 2 (5 floors in total).

[0158] The preparation method of the above materials is similar to that of Example 1. The main difference is that the amount of nanofiller added is reduced to 0.5g, which is suitable for occasions where transparency is required; the number of glass fiber layers is reduced to 5, which is suitable for thin-walled structural parts.

[0159] Example 6

[0160] This embodiment provides a high-voltage resistant insulating epoxy resin composite material, comprising:

[0161] 75g bisphenol A type epoxy resin (E-51), 35g phenolic epoxy resin (F-51), 5g surface-modified nano alumina (particle size 70nm, specific surface area 100m²) 2 / g), 120g methylhexahydrophthalic anhydride, 1.0g DMP-30, 4g mixed silane coupling agent (KH560:KH550=2:1 mass ratio) and glass fiber preform (E-glass fiber three-dimensional braided preform, areal density 800g / m²). 2 (It has 14 floors in total).

[0162] The preparation method of the above materials is similar to that of Example 2. The main difference is that the proportion of phenolic epoxy resin is increased to 35% to further improve the heat resistance; the amount of nanofiller added is increased to 5g to enhance the resistance to electrical aging; and the number of glass fiber layers is increased to 14 to improve mechanical strength and make it suitable for heavy load conditions.

[0163] Comparative Example 1

[0164] This comparative example provides an epoxy resin composite material, which differs from Example 1 in that it does not contain surface-modified nano-alumina, while other components and process parameters are the same as in Example 1.

[0165] Comparative Example 2

[0166] This comparative example provides an epoxy resin composite material, which differs from Example 1 in that it uses unmodified nano-alumina (addition amount 2g), while other components and process parameters are the same as in Example 1.

[0167] Comparative Example 3

[0168] This comparative example provides an epoxy resin composite material, which differs from Example 1 in that only bisphenol A type epoxy resin (120g) is used, and no phenolic epoxy resin is added. Other components and process parameters are the same as in Example 1.

[0169] Comparative Example 4

[0170] This comparative example provides an epoxy resin composite material, which differs from Example 1 in that it uses a conventional curing procedure (directly heating to 150°C and holding for 4 hours) instead of a gradient heating procedure. Other components and process parameters are the same as in Example 1.

[0171] The epoxy resin composites prepared in Examples 1-6 and Comparative Examples 1-4 were subjected to performance tests. The test methods and results are as follows:

[0172] 1. Electrical performance testing

[0173] Test method for power frequency breakdown strength: Refer to GB / T 1408.1-2016, use cylindrical electrodes (diameter 25mm), and conduct the test in transformer oil at a voltage increase rate of 1kV / s.

[0174] Test method for volume resistivity: Refer to GB / T 31838.2-2019, with a sample size of 100mm×100mm×3mm, and test at 23℃ and 50% relative humidity.

[0175] Test method for surface resistivity: Refer to GB / T 31838.3-2019, and the test conditions are the same as above.

[0176] Test method for resistance to tracking: Refer to GB / T 6553-2014, inclined plane method test.

[0177] 2. Mechanical property testing

[0178] Test methods for flexural strength and flexural modulus: refer to GB / T 2567-2021, specimen size 80mm×15mm×4mm, span 64mm, loading rate 2mm / min.

[0179] Test method for interlaminar shear strength: Refer to GB / T 3357-2014, short beam method, sample size 40mm×10mm×5mm, span 25mm.

[0180] 3. Thermal performance testing

[0181] Test method for glass transition temperature: Refer to GB / T 19466.2-2004, use differential scanning calorimetry (DSC), and the heating rate is 10℃ / min.

[0182] Test method for thermal decomposition temperature (5% weight loss): Refer to GB / T 27761-2011, use thermogravimetric analysis (TGA), nitrogen atmosphere, heating rate 10℃ / min.

[0183] 4. Physical performance testing

[0184] Porosity test method: Refer to GB / T 3365-2008, density method for calculation.

[0185] Test method for fiber volume fraction: Refer to GB / T 3366-1996, determination by burning method.

[0186] Performance indicators Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Power frequency breakdown strength (kV / mm) 42 45 38 48 36 46 32 35 34 30 Volume resistivity / (Ω·cm) Surface resistivity / Ω Tracking resistance rating 1A4.5 1A4.5 1A4.0 1A4.5 1A4.0 1A4.5 1A3.5 1A4.0 1A3.5 1A3.5 Bending strength / MPa 420 480 380 520 360 550 400 390 380 350 Flexural modulus / GPa 22 25 19 28 18 30 21 20 20 18 Interlaminar shear strength / MPa 52 58 45 62 42 65 48 44 46 38 Glass transition temperature / °C 148 155 142 162 140 158 145 144 132 138 Thermal decomposition temperature (5% weight loss) / ℃ 365 375 358 382 355 378 360 358 348 352 Porosity / % 0.35 0.30 0.42 0.28 0.45 0.32 0.38 0.52 0.40 1.2 Fiber volume fraction / % 58 62 55 64 52 65 57 56 57 55

[0187] As can be seen from the above test results, the high-voltage insulating epoxy resin composite materials prepared in Examples 1-6 all possess excellent electrical insulation and mechanical properties: power frequency breakdown strength of 36-48 kV / mm and volume resistivity of - Ω·cm, tracking resistance rating reaches 1A4.0-1A4.5; flexural strength is 360-550MPa, flexural modulus is 18-30GPa, interlaminar shear strength is 42-65MPa; glass transition temperature is 140-162℃.

[0188] Comparative Example 1, without the addition of nano-alumina, had a power frequency breakdown strength of 32 kV / mm, which was 24% lower than that of Example 1, indicating that the deep trapping effect of nano-alumina plays an important role in improving the breakdown strength.

[0189] Comparative Example 2 used unmodified nano-alumina, which had an interlaminar shear strength of 44 MPa, a decrease of 15% compared to Example 1, and a porosity of 0.52%, an increase of 49% compared to Example 1, indicating that surface modification is crucial for improving the dispersibility and interfacial bonding strength of nanofillers.

[0190] Comparative Example 3, without the addition of phenolic epoxy resin, had a glass transition temperature of 132°C, which was 11% lower than that of Example 1, and its tracking resistance level dropped to 1A3.5. This indicates that the multifunctional structure of phenolic epoxy resin has a significant contribution to improving heat resistance and tracking resistance.

[0191] Comparative Example 4, which did not employ a gradient temperature curing process, had a porosity of 1.2%, which was 243% higher than that of Example 1. The power frequency breakdown strength decreased to 30 kV / mm, and the interlaminar shear strength decreased to 38 MPa. This indicates that the gradient temperature curing process plays a crucial role in controlling porosity and improving the quality of composite materials.

[0192] Based on the above analysis, this invention achieves comprehensive performance optimization of high-voltage insulating epoxy resin composite materials through the synergistic effect of epoxy resin synergistic system, surface-modified nano-alumina, glass fiber reinforcement, and temperature-controlled gradient VARTM process, thus meeting the technical requirements for insulation protection of high-voltage electrical equipment.

[0193] like Figure 1 As shown, the mass loss of unmodified nano-alumina at 800℃ is 0.8%, mainly due to the removal of surface adsorbed water; the mass loss of surface-modified nano-alumina at 800℃ is 5.2%, of which the mass loss in the temperature range of 250-450℃ is 4.1%, corresponding to the thermal decomposition of the organosilane coating layer, confirming that the bilayer silane has been effectively grafted onto the surface of nano-alumina.

[0194] like Figure 2 As shown, the peak curing temperature of the synergistic system in Example 1 was 142°C, and the enthalpy of the reaction was 385 J / g; the peak curing temperature of the single bisphenol A epoxy resin system in Comparative Example 3 was 148°C, and the enthalpy of the reaction was 325 J / g. The enthalpy of the synergistic system was 18.5% higher than that of the single system, indicating that the multifunctional structure of the phenolic epoxy resin participated in the curing reaction, increasing the crosslinking density.

[0195] like Figure 3 As shown, the storage modulus of the cured product in Example 1 was 3.2 GPa (tested at 25°C), and the glass transition temperature was 155°C (the temperature corresponding to the peak of the loss factor); the storage modulus of the cured product in Comparative Example 3 was 2.8 GPa (tested at 25°C), and the glass transition temperature was 138°C. The glass transition temperature of the synergistic system was increased by 17°C compared to the single system, and the storage modulus was increased by 14.3%, further confirming that phenolic epoxy resin improved the crosslinking density and rigidity of the cured product.

[0196] like Figure 4 As shown, the surface-modified nano-alumina exhibits good dispersion in the epoxy resin matrix. The nanoparticles have a particle size of 30-50 nm, and there is no obvious agglomeration between the particles. The particles are tightly bonded to the matrix interface, indicating that the bilayer silane gradient coating effectively improves the dispersibility and interfacial compatibility of the nano-alumina.

[0197] The superior overall performance of the technical solution of this invention stems from the synergistic effect mechanism of its various technical features:

[0198] From a materials system design perspective, the synergistic system of bisphenol A epoxy resin and phenolic epoxy resin balances both processing and performance characteristics. The linear segments of bisphenol A epoxy resin provide toughness and flowability, while the multifunctional structure of phenolic epoxy resin provides high crosslinking density and heat resistance. The three-dimensional network structure formed by their synergy significantly improves the glass transition temperature and electrical tracking resistance while ensuring mechanical toughness.

[0199] From an interface design perspective, the bilayer silane gradient coating of surface-modified nano-alumina achieves triple interface optimization: the covalent bonding between nanoparticles and the inner silane layer improves coating stability; the crosslinking between the inner and outer silane layers enhances the integrity of the interface layer; and the covalent connection between the outer epoxy groups and the resin matrix achieves chemical bridging of the inorganic-organic phases. This interface structure achieves the dual functions of stress transfer and charge trapping at the molecular level.

[0200] From the perspective of reinforcement system design, the E-glass fiber three-dimensional braided structure overcomes the shortcomings of low interlaminar strength in traditional laminated structures. The presence of Z-direction fibers effectively resists the delamination tendency under bending loads. The exposed silanol groups on the fiber surface react with silane coupling agents to establish a chemical bond between the fiber and the matrix, significantly improving the interfacial bonding strength.

[0201] From a process design perspective, the temperature-controlled gradient VARTM process achieves precise control over resin flow and curing behavior. Temperature optimization during the injection stage ensures sufficient resin wetting of the fibers; the three-stage gradient curing procedure effectively releases curing shrinkage stress by controlling reaction exothermics and temperature gradients, keeping porosity at an extremely low level.

[0202] Compared with existing technologies, the differentiating mechanism of this invention is reflected in the following aspects: the organosilicon-modified alicyclic epoxy / microsilica powder system of CN111363315A; the multifunctional phenolic epoxy blend system of this invention to improve crosslinking density; the deep trap effect of nano-alumina interface to improve breakdown strength; the three-dimensional reinforcement of glass fiber to improve mechanical strength; and the VARTM process to adapt to the preparation of large and complex structural parts. It achieves technical isolation and performance improvement in four dimensions: material system, reinforcement method, filler type, and molding process.

[0203] The above description is merely a preferred embodiment of the present invention and does not limit the scope of the patent. Any equivalent structural or procedural transformations made using the content of this specification, or direct or indirect applications in other related technical fields, should be included within the scope of the claims of the present invention.

Claims

1. A high-voltage resistant insulating epoxy resin composite material, characterized in that, By weight, its raw materials include: 100 parts epoxy resin matrix, 0.5-5 parts surface-modified nano alumina, 80-150 parts glass fiber preform, 80-120 parts acid anhydride curing agent, 0.3-1.0 parts accelerator and 1-4 parts silane coupling agent; The epoxy resin matrix is ​​composed of bisphenol A type epoxy resin and phenolic epoxy resin mixed in a mass ratio of (70-90):(10-30); The surface-modified nano-alumina consists of nano-alumina particles coated with a double-layer silane gradient, with a particle size of 20-80 nm and a specific surface area of ​​80-200 m². 2 / g.

2. The high-voltage resistant insulating epoxy resin composite material according to claim 1, characterized in that, The bisphenol A type epoxy resin has an epoxy equivalent of 180-195 g / eq and a viscosity of 11000-14000 mPa·s at 25°C. The phenolic epoxy resin has an epoxy equivalent of 170-190 g / eq and an epoxy functionality of 2.5-3.

5.

3. The high-voltage resistant insulating epoxy resin composite material according to claim 1 or 2, characterized in that, The glass fiber preform is an E-glass fiber three-dimensional braided preform or an E-glass fiber multiaxial warp braid; The E-glass fiber has a single filament diameter of 9-17 μm and a volume resistivity ≥10. 14 Ω·cm; The areal density of the glass fiber preform is 300-800 g / m³. 2 The number of layers ranges from 4 to 16.

4. The high-voltage resistant insulating epoxy resin composite material according to any one of claims 1-3, characterized in that, The surface-modified nano-alumina bilayer silane gradient coating structure includes: The inner layer is a γ-aminopropyltriethoxysilane coating layer, with a coating amount of 1-3% of the mass of nano-alumina; The outer layer is a γ-glycidyl etheroxypropyltrimethoxysilane coating layer, with a coating amount of 2-5% of the mass of nano-alumina.

5. The high-voltage resistant insulating epoxy resin composite material according to claim 1, characterized in that, The anhydride curing agent is at least one of methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride and methylnadic anhydride; The accelerator is at least one selected from 2-ethyl-4-methylimidazole, 2,4,6-tris(dimethylaminomethyl)phenol and benzyldimethylamine.

6. A method for preparing the high-voltage resistant insulating epoxy resin composite material according to any one of claims 1-5, characterized in that, Includes the following steps: Step S1, Preparation of surface-modified nano-alumina: Nano-alumina is dispersed in anhydrous ethanol, γ-aminopropyltriethoxysilane is added first for inner layer coating, then γ-glycidoxypropyltrimethoxysilane is added for outer layer coating, and after drying, surface-modified nano-alumina is obtained. Step S2, Preparation of modified epoxy resin mixture: Bisphenol A type epoxy resin and phenolic epoxy resin are mixed, surface modified nano alumina and silane coupling agent are added, and the mixture is dispersed under vacuum at high speed to obtain modified epoxy resin mixture. Step S3, Preparation of curing agent premix: Mix the acid anhydride curing agent and accelerator evenly, and then degas under vacuum to obtain the curing agent premix; Step S4, Surface treatment of the glass fiber preform: Dry the glass fiber preform at 120-150℃; Step S5, Temperature-Controlled Gradient VARTM Molding: The glass fiber preform is laid in the mold, and after vacuuming, a mixture of modified epoxy resin mixture and curing agent premix is ​​injected. The mixture is cured using a gradient temperature curing program. After cooling and demolding, a high-voltage resistant insulating epoxy resin composite material is obtained.

7. The method for using the high-voltage resistant insulating epoxy resin composite material according to claim 6, characterized in that, In step S1: The reaction temperature for the inner coating is 50-70℃, and the reaction time is 1-2 hours. The reaction temperature for the outer coating is 60-80℃, and the reaction time is 2-4h.

8. The method for using a high-voltage resistant insulating epoxy resin composite material according to claim 6 or 7, characterized in that, The gradient temperature curing process in step S5 includes: In the first stage, the temperature is raised from room temperature to 80-100℃ at a rate of 1-3℃ / min and held for 1-2 hours. In the second stage, the temperature is increased to 120-140℃ at a rate of 1-2℃ / min and held for 2-4 hours. In the third stage, the temperature is increased to 150-170℃ at a rate of 0.5-1℃ / min and held for 1-3 hours.

9. The preparation method according to any one of claims 6-8, characterized in that, In step S5: The mold is evacuated to a vacuum level ≤100Pa; The resin injection temperature is 40-60℃, and the injection rate is 50-200g / min.

10. The application of the high-voltage resistant insulating epoxy resin composite material prepared by the method of any one of claims 1-5 or any one of claims 6-9 in high-voltage electrical equipment.

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