A coil insulating glue composition and a preparation method thereof

Abstract

The application discloses a coil insulating glue composition and a preparation method thereof, and the composition comprises the following components: bisphenol A type epoxy resin 40-55 parts; methyl tetrahydrophthalic anhydride 30-40 parts; 2-ethyl-4-methyl imidazole 0.5-1.5 parts; benzyl glycidyl ether 5-10 parts; aluminum oxide 15-25 parts; gamma-glycidyl ether oxygen propyl trimethoxysilane 0.5-1.0 parts; surface hydroxylated nano zirconium oxide 3-8 parts; hexagonal boron nitride nanosheet 4-10 parts; microcapsule 3-7 parts; and the components synergize with each other, and the composition has excellent high-temperature insulation, thermal conductivity and fracture toughness recovery rate, and effectively solves the pain points of easy fatigue cracking and electric breakdown of traditional coil insulating materials.

Description

Technical Field

[0001] This invention relates to the field of insulating adhesive technology, specifically to a coil insulating adhesive composition and its preparation method. Background Technology

[0002] With the rapid development of electric drive systems for new energy vehicles, drive motors are continuously evolving towards higher power density, higher speed, and higher efficiency. At the same time, the high-frequency PWM pulse voltage output by the inverter generates a severe voltage superposition effect at the motor winding ends. The insulation material is subjected to the severe test of multiple composite stresses of "electricity-heat-mechanical" over a long period of time, and its reliability has become the core bottleneck restricting the lifespan and safety of the motor.

[0003] Existing coil insulation adhesives typically use bisphenol A type epoxy resin as a base, cured with conventional curing agents. To cope with extreme operating conditions, numerous improvement studies have been conducted in the industry, but all face irreconcilable technical contradictions: Firstly, regarding corona resistance: current conventional improvement methods involve doping with inorganic fillers such as nano-silica and titanium dioxide to enhance resistance to electrolytic corrosion. However, nanoparticles have high surface energy, are prone to aggregation, and have poor compatibility with organic resin matrices. This not only leads to a sharp increase in the viscosity of the mixed adhesive and deteriorates the vacuum impregnation process, but also introduces a large number of microscopic gaps and defects at the two-phase interface. These defects are more likely to become sources of partial discharge under high-frequency electric fields, resulting in a bottleneck in improving corona resistance lifespan and making it difficult to meet the insulation requirements of next-generation silicon carbide high-frequency inverters.

[0004] Secondly, regarding thermal conductivity and heat dissipation: the thermal conductivity of pure organic polymer matrices is generally low, and the industry commonly uses high-filler-content micron-sized inorganic thermally conductive fillers (such as spherical alumina) to improve it. However, high filler content often severely damages the integrity of the resin crosslinking network, leading to a significant decrease in the mechanical toughness of the cured product; at the same time, single-scale spherical fillers are difficult to form continuous three-dimensional thermal conductive pathways at low addition levels, and the interfacial thermal resistance between particles remains high, making it difficult to balance thermal conductivity and processing rheology.

[0005] Thirdly, regarding resistance to microcracks and self-healing: Under the intense thermal cycling and high-frequency mechanical vibration of motors, the insulation layer is highly susceptible to the initiation and gradual propagation of microcracks. Traditional toughening methods involve introducing flexible phases such as carboxyl-terminated nitrile butadiene rubber (CTBN), but this physical phase separation often comes at the cost of severely sacrificing the material's glass transition temperature and high-temperature volume resistivity. More importantly, existing insulation systems are all "passive defenses," meaning that once microcracks form, they cannot heal themselves, ultimately leading to penetrating partial discharge and breakdown.

[0006] In summary, existing insulating adhesive modification technologies exhibit a bottleneck effect, with each aspect (corona resistance, high thermal conductivity, and crack resistance / self-healing) mutually constraining each other. Therefore, developing a novel coil insulating adhesive composition that addresses these three core properties through microscopic interfaces and network structures, achieving positive synergy, is of paramount engineering significance and holds broad application prospects. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a coil insulating adhesive composition and its preparation method. This invention breaks through the bottleneck of traditional insulating materials, and macroscopically possesses excellent high-frequency corona resistance, high-efficiency thermal conductivity, and intelligent self-healing ability. It can effectively resist the composite stress damage of "electric-thermal-mechanical" and significantly improve the operational reliability and service life of new energy motors under extreme operating conditions.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a coil insulating adhesive composition comprising, by weight, the following components: 40-55 parts of bisphenol A type epoxy resin; 30-40 parts of methyltetrahydrophthalic anhydride; 0.5-1.5 parts of 2-ethyl-4-methylimidazolium; 5-10 parts of benzyl glycidyl ether; 15-25 parts of alumina; 0.5-1.0 parts of γ-glycidyl etheroxypropyltrimethoxysilane; 3-8 parts of surface-hydroxylated nano-zirconia; 4-10 parts of hexagonal boron nitride nanosheets; 3-7 parts of microcapsules.

[0009] The alumina has a D50 of 3~8 μm.

[0010] Preferably, the surface-hydroxylated nano-zirconia is prepared by the following method: Dissolve ZrOCl2·8H2O in water, add ammonia to adjust the pH to alkaline, and obtain zirconium hydroxide precipitate. Transfer the precipitate and mother liquor into a hydrothermal reactor for hydrothermal treatment, wash, dry and calcine to obtain zirconium hydroxide precipitate.

[0011] More preferably, the mass-to-volume ratio of ZrOCl2·8H2O to water is 1g:8~12mL; the mass fraction of ammonia water is 25%~28%, and the pH is adjusted to 9.5~10.5; the hydrothermal treatment temperature is 160~200℃ and the time is 10~14h; the calcination temperature is 280~320℃ and the time is 1.5~2.5h.

[0012] The surface-hydroxylated zirconium oxide nanoparticles have an average particle size of 50-80 nm and a surface hydroxyl density ≥ 2.5 OH / nm. 2 ; This step aims to prepare nano-zirconia particles with a high surface hydroxyl density. By combining ammonia precipitation with a hydrothermal process, the crystal structure and particle size of the nano-zirconia can be effectively controlled, and its surface can be enriched with hydroxyl groups (-OH). The calcination temperature range is sufficient to remove physically adsorbed water from the particle surface, but lower than the temperature at which chemically adsorbed hydroxyl groups (Zr-OH) are largely removed (typically >350℃), thus ensuring that the resulting nanoparticles maintain a high density of active hydroxyl groups. This provides a material basis for subsequent grafting of silane coupling agents and hydrogen bonding at the epoxy resin interface.

[0013] Preferably, the hexagonal boron nitride nanosheets are prepared by the following method: Hexagonal boron nitride powder was dispersed in isopropanol, ultrasonically treated, and then centrifuged in two stages. After the first stage of centrifugation, the supernatant was collected and centrifuged in the second stage. After the second stage of centrifugation, the precipitate was collected, dried, and the product was obtained.

[0014] More preferably, the mass-to-volume ratio of hexagonal boron nitride powder to isopropanol is 1g:80~120mL; the ultrasonic power is 300~500W, and the ultrasonic time is 6~10h; the first centrifugation speed is 2000~4000rpm and the time is 15~25min; the second centrifugation speed is 6000~9000rpm and the time is 25~35min; the precipitate obtained after centrifugation is vacuum dried at 50~70℃.

[0015] The thickness of the hexagonal boron nitride nanosheets is 2~5nm, and the aspect ratio is ≥100.

[0016] This step employs a liquid-phase ultrasonic exfoliation method to prepare two-dimensional hexagonal boron nitride (h-BN) nanosheets. The surface tension of isopropanol is highly compatible with the surface energy of hexagonal boron nitride, significantly reducing the energy barrier during the exfoliation process. Under the high-power ultrasonic cavitation effect of 300–500 W, the van der Waals forces between h-BN layers are broken, achieving liquid-phase exfoliation. Subsequently, gradient centrifugation is used for fractionation: the first stage of low-speed centrifugation (2000–4000 rpm) is used to settle and remove non-exfoliated thick sheets and large particles; the second stage of high-speed centrifugation (6000–9000 rpm) is used to centrifuge and enrich nanosheets with uniform thickness (such as a oligolayer structure), ensuring that the filler has an extremely high aspect ratio, which is beneficial for forming an efficient thermal conductivity network in the resin.

[0017] Preferably, the microcapsules are prepared by the following method: (1) Mix melamine, formaldehyde and water, adjust the pH to alkaline, heat to react, and obtain MF prepolymer solution; (2) Add terminal epoxy polydimethylsiloxane and anionic emulsifier to water, stir and disperse to obtain an oil-in-water emulsion; (3) Add the MF prepolymer solution to the emulsion, adjust the pH to acidic, heat to react, heat to solidify, filter, wash and dry to obtain the product.

[0018] More preferably, In step (1), the molar ratio of melamine to formaldehyde is 1:2.5~3.5, the mass-volume ratio of melamine to water is 1g:8~15mL, the pH is adjusted to 8.5~9.0, the reaction temperature is 65~75℃, and the reaction time is 1~2h.

[0019] In step (2), the anionic emulsifier is sodium dodecyl sulfate (SDS), and the ratio of terminal epoxy polydimethylsiloxane, sodium dodecyl sulfate and water is 15~25g:0.3~0.8g:100mL, the dispersion speed is 1000~1500rpm, and the dispersion time is 20~40min; the epoxy equivalent of the terminal epoxy polydimethylsiloxane is 600~900g / eq.

[0020] In step (3), the mass ratio of MF prepolymer solution to oil-in-water emulsion is 1:4~7, the pH is adjusted to 4.0~4.5, the reaction temperature is 60~70℃, the reaction time is 2.5~3.5h, the temperature after heating is 75~85℃, the curing time is 1~2h, and after filtration and washing, it is vacuum dried at 45~55℃ for 20~28h.

[0021] This step uses in-situ polymerization to prepare core-shell structured microcapsules. Step (1) Under alkaline conditions, melamine and formaldehyde undergo a nucleophilic addition reaction to generate water-soluble hydroxymethyl melamine prepolymer (MF prepolymer). Step (2) Utilizing the surface-active effect of anionic emulsifier (SDS), hydrophobic terminal epoxy polydimethylsiloxane (core material) is dispersed in water under strong shear to form a stable oil-in-water (O / W) emulsion. The concentration of SDS used must be higher than its critical micelle concentration to ensure the stability of the emulsion. Step (3) The system is adjusted to acidity, and the water-soluble MF prepolymer undergoes a condensation reaction at the oil-water interface, crosslinking into a network of melamine-formaldehyde resin that coats the surface of the core material. Subsequently, the temperature is raised to promote complete curing of the shell layer, giving the microcapsules good mechanical strength and thermal stability, ensuring that they do not break in the subsequent mixing process.

[0022] A second aspect of the present invention provides a method for preparing the above-mentioned coil insulating adhesive composition, comprising the following steps: S1. Alumina, surface-hydroxylated nano-zirconia, hexagonal boron nitride nanosheets and γ-glycidyl etheroxypropyltrimethoxysilane are premixed and then added to bisphenol A type epoxy resin and benzyl glycidyl ether. The mixture is heated and dispersed to obtain component A. S2. After cooling component A, add the microcapsules and stir at low speed to obtain component A containing microcapsules. S3. Mix methyltetrahydrophthalic anhydride with 2-ethyl-4-methylimidazole to obtain component B; S4. Mix component A and component B, and degas under vacuum to obtain the final product.

[0023] More preferably, in step S1, the heating temperature is 70~90℃, the dispersion speed is 1500~2500rpm, and the dispersion time is 40~80min; in step S2, the temperature is lowered to 45~55℃, the stirring speed is 200~500rpm, and the stirring time is 10~20min; in step S4, the mass ratio of component A to component B is 95~105:33~39, the vacuum degassing degree is ≤-0.08MPa, and the degassing time is 15~25min.

[0024] This preparation method employs a two-component (A / B adhesive) formulation strategy to prevent premature gelation of the epoxy resin and curing agent. Step S1 involves high-speed dispersion at 70-90℃ to reduce resin viscosity, while a coupling agent is used to perform in-situ surface modification of the inorganic filler, ensuring uniform dispersion. In step S2, the temperature must be lowered to 45-55℃ and the stirring speed reduced to 200-500 rpm before adding the microcapsules. This is to prevent damage to the microcapsule shell structure from high temperature and strong shear force. Step S4 involves a rigorous vacuum degassing treatment (≤-0.08 MPa) after final mixing to effectively remove air bubbles introduced during stirring, preventing microporous defects in the cured insulation layer and ensuring the corona resistance and partial discharge performance of the motor coil.

[0025] A third aspect of the present invention provides the application of the coil insulating adhesive composition in the insulation of coils of drive motors or variable frequency motors in new energy vehicles. The application includes: impregnating the coil with the coil insulating adhesive composition under vacuum pressure, and then curing it sequentially at 80~90℃ for 1.5~2.5h, 110~130℃ for 2.5~3.5h, and 145~155℃ for 1.5~2.5h.

[0026] Vacuum pressure impregnation (VPI process) first involves evacuating the air from between coil turns and inside the windings, and then applying pressure to allow low-viscosity insulating adhesive to penetrate deeply and fill all gaps.

[0027] The stepped three-stage curing process designed in conjunction with this invention has a clear kinetic basis: Low-temperature initial curing stage at 80~90℃: The viscosity of the system decreases and cross-linking is initiated, gel formation occurs, resin loss is prevented, and internal defects caused by the rapid exothermic polymerization reaction are reduced; Main curing stage at 110~130℃: Epoxy groups and acid anhydrides undergo large-scale cross-linking network construction to form the main resin skeleton; High-temperature curing stage at 145~155℃: This stage further increases the crosslinking density, promotes the complete reaction of unreacted residual groups, and relaxes and releases the internal stress generated during curing, ultimately obtaining a dense, heat-resistant, and highly insulating cured product. Furthermore, the maximum temperature of this curing process does not exceed 155℃; under these conditions, the microcapsule shell remains stable and does not decompose or lose weight.

[0028] Compared with the prior art, the present invention has the following beneficial effects: The insulating adhesive composition of this invention constructs a stable and reliable insulating matrix through scientific formulation. Each basic component plays the following physicochemical roles in the system: Bisphenol A epoxy resin, as the polymer matrix, provides excellent mechanical strength, electrical insulation properties, and strong adhesion to motor coils after curing. Methyltetrahydrophthalic anhydride, as an anhydride curing agent, has moderate reactivity and volatility; after crosslinking, it significantly increases the crosslinking density of the system, giving the cured product excellent heat resistance and weather resistance. 2-Ethyl-4-methylimidazolium, as a curing accelerator, reduces the activation energy of the crosslinking reaction, allowing the system to crosslink smoothly within a set step temperature program, avoiding localized burst polymerization or residual thermal stress. Benzyl glycidyl ether, as a monofunctional reactive diluent, effectively reduces the initial viscosity to improve permeability; its epoxy groups participate in the crosslinking network, avoiding insulating micropores caused by conventional solvent evaporation. Alumina, as an insulating and thermally conductive filler, constructs a basic rigid thermally conductive framework within the resin, effectively improving the overall thermal conductivity and basic anti-corona properties of the insulating adhesive. γ-glycidoxypropyltrimethoxysilane, as a silane coupling agent, bridges the inorganic filler and resin matrix through chemical bonds, improving the wetting and dispersion state of the filler and reducing the risk of interfacial thermal resistance and local electric field distortion. Building upon this basic system, this invention further introduces three core modifying components: surface-hydroxylated nano-zirconia, hexagonal boron nitride nanosheets, and microcapsules, achieving a performance breakthrough in the insulation system under electro-thermal-mechanical composite stress.

[0029] Surface-hydroxylated nano-zirconia, with its high density of surface-active hydroxyl groups, can not only strengthen the interfacial adhesion between the filler and the organic matrix through hydrogen and chemical bonds, effectively inhibiting the initiation of interfacial microcracks; at the same time, the high specific surface area of ​​the nanoparticles can form high-density charge trapping sites in the polymer matrix, homogenizing the local micro electric field distribution, thereby significantly extending the corona resistance life of the insulation system under PWM high-frequency pulse impact conditions.

[0030] Hexagonal boron nitride nanosheets, with their large aspect ratio and excellent in-plane thermal conductivity anisotropy, can effectively bridge the contact thermal resistance gaps between spherical alumina particles at relatively low addition amounts. This component constructs a continuous three-dimensional heat transfer network within the system, enabling rapid heat dissipation of local hot spots generated during coil operation, preventing local thermal runaway, and achieving a significant leap in overall thermal conductivity without compromising the system's intrinsic high insulation resistance.

[0031] The introduction of epoxy-terminated polydimethylsiloxane (PDMS) microcapsules provides a mechanism for spontaneous repair of microscopic damage in the system. The melamine-formaldehyde (MF) resin shell endows the capsules with excellent heat resistance, and the residual hydroxymethyl groups on the shell surface can covalently bond with the epoxy matrix, preventing interfacial stress concentration. When mechanical vibration or thermal shock causes cracks that damage the shell, the released PDMS core material flows into the crack. Its epoxy groups co-cur with the residual acid anhydride and imidazole accelerator in the matrix in situ, forming a chemically bonded repair layer. The polysiloxane segments in this repair layer not only maintain extremely high insulating volume resistivity but also significantly reduce the stress at the crack tip and inhibit secondary cracking through low-modulus flexibility and toughening.

[0032] When the above three components coexist, the system exhibits a nonlinear combined gain that exceeds the superposition of a single component: The high interfacial bonding ability of nano-ZrO2-OH, the high thermal conductivity framework construction ability of h-BN nanosheets, and the crack repair ability of microcapsules act on different nodes in the three-stage failure chain of insulation failure: "interfacial debonding - thermal stress concentration - crack propagation". The three form an interconnected multi-level protection mechanism, rather than an independent superposition of functions.

[0033] The high density of hydroxyl groups on the surface of nano-ZrO2-OH helps improve its dispersion uniformity in the resin, thereby reducing the interference of its local enrichment on the orientation of h-BN nanosheets and enabling more effective construction of the thermally conductive network. At the same time, the microcapsules are uniformly distributed in the system in the form of discrete particles, without blocking the surface thermally conductive pathways formed by the h-BN nanosheets. The maintenance of thermal conductivity, in turn, reduces the risk of local heat accumulation in the system during operation, thereby slowing down the generation rate of thermal aging-induced cracks, reducing the frequency of passive consumption of microcapsules, and extending the effective lifespan of the self-healing function. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Of course, the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0035] Unless otherwise specified, all chemical reagents and materials in this invention are purchased from the market or synthesized from raw materials purchased from the market.

[0036] A method for preparing a coil insulating adhesive composition includes the following steps: (1) Dissolve ZrOCl2·8H2O in water (mass-volume ratio of 1g:8~12mL), add 25%~28% ammonia water to adjust the pH to 9.5~10.5 to obtain zirconium hydroxide precipitate; transfer the precipitate and mother liquor into a hydrothermal reactor and perform hydrothermal treatment at 160~200℃ for 10~14h; after treatment, wash and dry, and calcine at 280~320℃ for 1.5~2.5h to obtain surface hydroxylated nano-zirconia.

[0037] (2) Disperse hexagonal boron nitride powder in isopropanol (mass-volume ratio of 1g: 80~120mL) and sonicate at 300~500W for 6~10h; then perform two-stage centrifugation: the first stage centrifugation speed is 2000~4000rpm and the time is 15~25min, and the supernatant is taken for the second stage centrifugation; the second stage centrifugation speed is 6000~9000rpm and the time is 25~35min, the centrifuged precipitate is collected and vacuum dried at 50~70℃ to obtain hexagonal boron nitride nanosheets.

[0038] (3) Mix melamine and formaldehyde at a molar ratio of 1:2.5~3.5, add water (melamine to water mass-volume ratio of 1g:8~15mL), adjust the pH to 8.5~9.0, and heat at 65~75℃ for 1~2h to obtain MF prepolymer solution; mix terminal epoxy-terminated polydimethylsiloxane, sodium dodecyl sulfate (anionic emulsifier) ​​and water at a ratio of 15~25g:0.3~0.8g:100mL The mixture was stirred and dispersed at 1000-1500 rpm for 20-40 min to obtain an oil-in-water emulsion. The above MF prepolymer solution was mixed with the emulsion at a mass ratio of 1:4-7, the pH was adjusted to 4.0-4.5, and the mixture was reacted at 60-70℃ for 2.5-3.5 h. Then, the mixture was heated to 75-85℃ to solidify for 1-2 h. Finally, the mixture was filtered, washed, and vacuum dried at 45-55℃ for 20-28 h to obtain microcapsules.

[0039] (4) Weigh 15-25 parts of alumina, 3-8 parts of surface-hydroxylated nano-zirconia, 4-10 parts of hexagonal boron nitride nanosheets and 0.5-1.0 parts of γ-glycidyl etheroxypropyltrimethoxysilane according to the weight range of the claims and premix them; add the premix to a mixture of 40-55 parts of bisphenol A type epoxy resin and 5-10 parts of benzyl glycidyl ether, and heat and disperse at 70-90°C and 1500-2500 rpm for 40-80 min; after cooling to 45-55°C, add 3-7 parts of the above microcapsules and stir at low speed at 200-500 rpm for 10-20 min to obtain component A containing microcapsules.

[0040] (5) Weigh 30-40 parts of methyltetrahydrophthalic anhydride and 0.5-1.5 parts of 2-ethyl-4-methylimidazole, mix them evenly to obtain component B.

[0041] (6) Mix the above component A and component B at a mass ratio of 95~105:33~39, and perform vacuum degassing for 15~25 minutes under a vacuum degree ≤-0.08MPa to obtain the coil insulation adhesive composition.

[0042] (7) The coil insulation composition prepared above is applied to the coil insulation of the drive motor or frequency converter of new energy vehicle. After vacuum pressure impregnation treatment of the motor coil, it is cured at 80~90℃ for 1.5~2.5h, 110~130℃ for 2.5~3.5h, and 145~155℃ for 1.5~2.5h in sequence to complete the preparation of the coil insulation layer.

[0043] The present invention will be further described below through specific embodiments.

[0044] Example 1 A method for preparing a coil insulating adhesive composition includes the following steps: (1) Dissolve ZrOCl2·8H2O in water (mass-volume ratio of 1g:10mL), add 26.5% ammonia water to adjust the pH to 10.0, and obtain zirconium hydroxide precipitate; transfer the precipitate and mother liquor into a hydrothermal reactor and perform hydrothermal treatment at 180℃ for 12h; after treatment, wash and dry, and calcine at 300℃ for 2h to obtain surface hydroxylated nano-zirconia.

[0045] (2) Disperse hexagonal boron nitride powder in isopropanol (mass-volume ratio of 1g:100mL) and sonicate at 400W for 8h; then perform two-stage centrifugation: the first stage centrifugation speed is 3000rpm and the time is 20min, and the supernatant is taken for the second stage centrifugation; the second stage centrifugation speed is 7500rpm and the time is 30min, the centrifuged precipitate is collected and vacuum dried at 60℃ to obtain hexagonal boron nitride nanosheets.

[0046] (3) Melamine and formaldehyde were mixed at a molar ratio of 1:3.0, water was added (the mass-volume ratio of melamine to water was 1g:11.5mL), the pH was adjusted to 8.8, and the mixture was heated at 70℃ for 1.5h to obtain an MF prepolymer solution; terminal epoxy polydimethylsiloxane, sodium dodecyl sulfate and water were mixed at a ratio of 20g:0.55g:100mL, and the mixture was stirred and dispersed at 1250rpm for 30min to obtain an oil-in-water emulsion; the above MF prepolymer solution and emulsion were mixed at a mass ratio of 1:5.5, the pH was adjusted to 4.3, and the mixture was reacted at 65℃ for 3h, then heated to 80℃ for 1.5h to solidify, and finally filtered, washed and vacuum dried at 50℃ for 24h to obtain microcapsules.

[0047] (4) Weigh 20g of alumina, 5.5g of surface-hydroxylated nano-zirconia, 7g of hexagonal boron nitride nanosheets and 0.75g of γ-glycidyl etheroxypropyltrimethoxysilane and premix them; add the premix to a mixture of 47.5g of bisphenol A epoxy resin and 7.5g of benzyl glycidyl ether, heat and disperse at 80℃ and 2000rpm for 60min; after cooling to 50℃, add 5g of the above microcapsules, stir at 350rpm for 15min to obtain component A containing microcapsules.

[0048] (5) Weigh 35g of methyltetrahydrophthalic anhydride and 1.0g of 2-ethyl-4-methylimidazole, mix them evenly, and obtain component B.

[0049] (6) Mix the above component A and component B at a mass ratio of 100:36 (take 100g of component A and 36g of component B), and perform vacuum degassing for 20min under a vacuum degree of -0.09MPa to obtain the coil insulation adhesive composition.

[0050] (7) The coil insulation adhesive composition prepared above is applied to the coil insulation of the drive motor or frequency converter of new energy vehicle. After vacuum pressure impregnation treatment of the motor coil, it is cured at 85°C for 2 hours, 120°C for 3 hours and 150°C for 2 hours in sequence to complete the preparation of the coil insulation layer.

[0051] Example 2 A method for preparing a coil insulating adhesive composition includes the following steps: (1) Dissolve ZrOCl2·8H2O in water (mass-volume ratio of 1g:8mL), add 25% ammonia water to adjust pH to 9.5 to obtain zirconium hydroxide precipitate; transfer the precipitate and mother liquor into a hydrothermal reactor and perform hydrothermal treatment at 160℃ for 14h; after treatment, wash and dry, and calcine at 280℃ for 2.5h to obtain surface hydroxylated nano-zirconia.

[0052] (2) Disperse hexagonal boron nitride powder in isopropanol (mass-volume ratio of 1g:80mL) and sonicate at 300W for 10h; then perform two-stage centrifugation: the first stage centrifugation speed is 2000rpm and the time is 25min, and the supernatant is taken for the second stage centrifugation; the second stage centrifugation speed is 6000rpm and the time is 35min, the centrifuged precipitate is collected and vacuum dried at 50℃ to obtain hexagonal boron nitride nanosheets.

[0053] (3) Melamine and formaldehyde were mixed at a molar ratio of 1:2.5, water was added (the mass-volume ratio of melamine to water was 1g:8mL), the pH was adjusted to 8.5, and the mixture was heated at 65℃ for 2h to obtain an MF prepolymer solution; terminal epoxy polydimethylsiloxane, sodium dodecyl sulfate and water were mixed at a ratio of 15g:0.3g:100mL, and the mixture was stirred and dispersed at 1000rpm for 40min to obtain an oil-in-water emulsion; the above MF prepolymer solution and emulsion were mixed at a mass ratio of 1:4, the pH was adjusted to 4.0, and the mixture was reacted at 60℃ for 3.5h, then heated to 75℃ for 2h to solidify, and finally filtered, washed and vacuum dried at 45℃ for 28h to obtain microcapsules.

[0054] (4) Weigh 15g of alumina, 3g of surface-hydroxylated nano-zirconia, 4g of hexagonal boron nitride nanosheets and 0.5g of γ-glycidyl etheroxypropyltrimethoxysilane and premix them; add the premix to a mixture of 40g of bisphenol A epoxy resin and 5g of benzyl glycidyl ether, and heat and disperse at 70℃ and 1500rpm for 80min; after cooling to 45℃, add 3g of the above microcapsules and stir at 200rpm for 20min to obtain component A containing microcapsules.

[0055] (5) Weigh 30g of methyltetrahydrophthalic anhydride and 0.5g of 2-ethyl-4-methylimidazole, mix them evenly to obtain component B.

[0056] (6) Mix the above component A and component B at a mass ratio of 95:33 (take 95g of component A and 33g of component B), and perform vacuum degassing for 15min under a vacuum degree of -0.08MPa to obtain the coil insulation adhesive composition.

[0057] (7) The coil insulation adhesive composition prepared above is applied to the coil insulation of the drive motor or frequency converter of new energy vehicle. After vacuum pressure impregnation treatment of the motor coil, it is cured at 80℃ for 2.5h, 110℃ for 3.5h and 145℃ for 2.5h in sequence to complete the preparation of the coil insulation layer.

[0058] Example 3 A method for preparing a coil insulating adhesive composition includes the following steps: (1) Dissolve ZrOCl2·8H2O in water (mass-volume ratio of 1g:12mL), add 28% ammonia water to adjust the pH to 10.5 to obtain zirconium hydroxide precipitate; transfer the precipitate and mother liquor into a hydrothermal reactor and perform hydrothermal treatment at 200℃ for 10h; after treatment, wash and dry, and calcine at 320℃ for 1.5h to obtain surface hydroxylated nano-zirconia.

[0059] (2) Disperse hexagonal boron nitride powder in isopropanol (mass-volume ratio of 1g:120mL) and sonicate at 500W for 6h; then perform two-stage centrifugation: the first stage centrifugation speed is 4000rpm and the time is 15min, and the supernatant is taken for the second stage centrifugation; the second stage centrifugation speed is 9000rpm and the time is 25min, the centrifuged precipitate is collected and vacuum dried at 70℃ to obtain hexagonal boron nitride nanosheets.

[0060] (3) Melamine and formaldehyde were mixed at a molar ratio of 1:3.5, water was added (the mass-volume ratio of melamine to water was 1g:15mL), the pH was adjusted to 9.0, and the mixture was heated at 75℃ for 1h to obtain an MF prepolymer solution; terminal epoxy polydimethylsiloxane, sodium dodecyl sulfate and water were mixed at a ratio of 25g:0.8g:100mL, and the mixture was stirred and dispersed at 1500rpm for 20min to obtain an oil-in-water emulsion; the above MF prepolymer solution and emulsion were mixed at a mass ratio of 1:7, the pH was adjusted to 4.5, and the mixture was reacted at 70℃ for 2.5h, then heated to 85℃ to solidify for 1h, and finally filtered, washed and vacuum dried at 55℃ for 20h to obtain microcapsules.

[0061] (4) Weigh 25g of alumina, 8g of surface-hydroxylated nano-zirconia, 10g of hexagonal boron nitride nanosheets and 1.0g of γ-glycidyl etheroxypropyltrimethoxysilane and premix them; add the premix to a mixture of 55g of bisphenol A epoxy resin and 10g of benzyl glycidyl ether, and heat and disperse at 90℃ and 2500rpm for 40min; after cooling to 55℃, add 7g of the above microcapsules and stir at low speed at 500rpm for 10min to obtain component A containing microcapsules.

[0062] (5) Weigh 40g of methyltetrahydrophthalic anhydride and 1.5g of 2-ethyl-4-methylimidazole, mix them evenly, and obtain component B.

[0063] (6) Mix the above component A and component B at a mass ratio of 105:39 (take 105g of component A and 39g of component B), and perform vacuum degassing for 25min under a vacuum degree of -0.095MPa to obtain the coil insulation adhesive composition.

[0064] (7) The coil insulation composition prepared above is applied to the coil insulation of the drive motor or frequency converter of new energy vehicle. After vacuum pressure impregnation treatment of the motor coil, it is cured at 90℃ for 1.5h, 130℃ for 2.5h and 155℃ for 1.5h in sequence to complete the preparation of the coil insulation layer.

[0065] Comparative Example 1 This comparative example provides a coil insulating adhesive composition, which differs from Example 1 only in that: the self-made surface-hydroxylated nano-zirconia is not added; instead, it is replaced in equal amounts with commercially available ordinary nano-zirconia powder (which does not possess high-density surface hydroxyl groups). The specific preparation and application steps are as follows: (1) Preparation of hexagonal boron nitride nanosheets: Same as in Example 1.

[0066] (2) Preparation of microcapsules: Same as in Example 1.

[0067] (3) Weigh 20g of alumina, 5.5g of commercially available ordinary nano-zirconia powder, 7g of hexagonal boron nitride nanosheets and 0.75g of γ-glycidyl etheroxypropyltrimethoxysilane and premix them; add the premix to a mixture of 47.5g of bisphenol A type epoxy resin and 7.5g of benzyl glycidyl ether, heat and disperse at 80℃ and 2000rpm for 60min; after cooling to 50℃, add 5g of the above microcapsules and stir at low speed at 350rpm for 15min to obtain component A.

[0068] (4) Weigh 35g of methyltetrahydrophthalic anhydride and 1.0g of 2-ethyl-4-methylimidazole, mix them evenly, and obtain component B.

[0069] (5) Mix the above component A and component B at a mass ratio of 100:36 (take 100g of component A and 36g of component B), and perform vacuum degassing for 20min under a vacuum degree of -0.09MPa to obtain the coil insulation adhesive composition.

[0070] (6) The above composition is applied to the insulation of the motor coil. After vacuum pressure impregnation treatment of the motor coil, it is cured at 85°C for 2 hours, 120°C for 3 hours and 150°C for 2 hours in sequence to complete the preparation of the coil insulation layer.

[0071] Comparative Example 2 This comparative example provides a coil insulating adhesive composition, which differs from Example 1 only in that: instead of adding self-made high aspect ratio hexagonal boron nitride nanosheets, it is replaced in equal amounts with commercially available ordinary micron-sized h-BN raw powder (unexfoliated). The specific preparation and application steps are as follows: (1) Preparation of surface hydroxylated nano-zirconia: Same as in Example 1.

[0072] (2) Preparation of microcapsules: Same as in Example 1.

[0073] (3) Weigh 20g of alumina, 5.5g of surface-hydroxylated nano-zirconia, 7g of commercially available micron-sized hexagonal boron nitride powder and 0.75g of γ-glycidyl etheroxypropyltrimethoxysilane and premix them; add the premix to a mixture of 47.5g of bisphenol A epoxy resin and 7.5g of benzyl glycidyl ether, heat and disperse at 80℃ and 2000rpm for 60min; after cooling to 50℃, add 5g of the above microcapsules and stir at 350rpm for 15min to obtain component A.

[0074] (4) Weigh 35g of methyltetrahydrophthalic anhydride and 1.0g of 2-ethyl-4-methylimidazole, mix them evenly, and obtain component B.

[0075] (5) Mix the above component A and component B at a mass ratio of 100:36, and perform vacuum degassing for 20 minutes under a vacuum degree of -0.09MPa to obtain the coil insulation adhesive composition.

[0076] (6) After impregnation, the coil insulation layer is cured at 85℃ for 2 hours, 120℃ for 3 hours, and 150℃ for 2 hours in sequence to complete the preparation of the coil insulation layer.

[0077] Comparative Example 3 This comparative example provides a coil insulating adhesive composition, which differs from Example 1 only in that: instead of adding microcapsules encapsulated by MF resin, an equal amount of liquid terminal epoxy-terminated polydimethylsiloxane (i.e., the core material component of the microcapsules) is directly added. The specific preparation and application steps are as follows: (1) Preparation of surface hydroxylated nano-zirconia: Same as in Example 1.

[0078] (2) Preparation of hexagonal boron nitride nanosheets: Same as in Example 1.

[0079] (3) Weigh 20g of alumina, 5.5g of surface hydroxylated nano-zirconia, 7g of hexagonal boron nitride nanosheets and 0.75g of γ-glycidyl etheroxypropyltrimethoxysilane and premix them; add the premix to a mixture of 47.5g of bisphenol A type epoxy resin and 7.5g of benzyl glycidyl ether, heat and disperse at 80℃ and 2000rpm for 60min; after cooling to 50℃, add 5g of pure liquid terminal epoxy polydimethylsiloxane, stir at low speed at 350rpm for 15min to obtain component A.

[0080] (4) Weigh 35g of methyltetrahydrophthalic anhydride and 1.0g of 2-ethyl-4-methylimidazole, mix them evenly, and obtain component B.

[0081] (5) Mix the above component A and component B at a mass ratio of 100:36, and perform vacuum degassing for 20 minutes under a vacuum degree of -0.09MPa to obtain the coil insulation adhesive composition.

[0082] (6) After impregnation, the coil insulation layer is cured at 85℃ for 2 hours, 120℃ for 3 hours, and 150℃ for 2 hours in sequence to complete the preparation of the coil insulation layer.

[0083] I. Performance Testing Methods 1. Corona resistance life (high-frequency pulse life): Refer to IEC TS 60034-18-41 standard. Under a high temperature environment of 155℃, a bipolar high-frequency PWM square wave power supply (frequency f=20kHz, peak-to-peak voltage V=3.0kV, rise rate 100kV / μs) was used to conduct a corona resistance aging test on a 1.0mm thick cured sample, and the time to electrical breakdown of the sample was recorded (unit: h).

[0084] 2. Thermal conductivity: Referring to ISO 22007-2 standard, the thermal conductivity of the cured sample was tested at 25℃ using a transient plane heat source method (TPS) thermal conductivity meter (unit: W·m). -1 ·K -1 ).

[0085] 3. Self-healing rate (fracture toughness recovery rate): The single-sided notch bending (SENB) method was used. Standard specimens with pre-cut notches were prepared according to ASTM E1820 standard, and the initial fracture toughness K0 (unit: MPa·m) was tested. ^ (1 / 2)); Subsequently, a three-point bending load was applied to the specimen, causing the crack to propagate forward approximately 20% of the specimen thickness from the pre-made notch before unloading, thus maintaining the specimen's integrity (incomplete fracture); The damaged specimen was then placed in a 150°C oven and heated for 2 hours to simulate the hot spot conditions of a motor operation, triggering in-situ repair of the microcapsule; After cooling to room temperature, its fracture toughness K was tested again using the same method. h Calculate the repair rate η=K h / K0×100%.

[0086] 4. High-temperature volume resistivity: Referring to the IEC62631-3-1 standard, the three-electrode method is used. After applying a test voltage at 150℃ for 60s, the steady-state value is read. The volume resistivity of the sample (unit: Ω·cm) is measured using a high-resistivity meter to evaluate the insulation reliability of the material in high-temperature service and when it contains a flexible phase.

[0087] Table 1 Performance Test Results Comparative Example 1, using ordinary nano-zirconia, experienced a sharp drop in its corona resistance lifetime to 2150 hours, approximately 41% lower than Example 1 (3650 hours). This demonstrates that the high-density hydroxyl groups on the surface of the self-made ZrO2 are crucial: hydroxyl groups not only improve the dispersibility of nanoparticles in the resin, preventing electric field distortion caused by agglomeration, but also construct a high-density network of charge-trapping sites within the polymer matrix, significantly resisting corona erosion under high-frequency PWM pulses. Furthermore, the self-healing rate of Comparative Example 1 also decreased, indicating that the presence of the ZrO2-OH component has a synergistic contribution to the recovery of electrical function after crack repair.

[0088] Comparative Example 2 used unpeeled ordinary micron-sized h-BN raw powder, which has a thermal conductivity of only 0.85 W·m. -1 ·K -1 This is far lower than the 1.26 W·m⁻¹ in Example 1. -1 ·K -1 Data shows that high aspect ratio h-BN nanosheets must be used to effectively bridge the gaps between spherical alumina particles with low filler content, eliminate interfacial contact thermal resistance, form a three-dimensional continuous rapid heat conduction network, and prevent the accumulation of thermal stress in local hot spots inside the motor.

[0089] Comparative Example 3, which directly incorporates liquid terminal epoxy-based PDMS without an MF shell, showed a decrease in high-temperature volume resistivity and a sharp drop in self-healing rate to 22.3% compared to Example 1. This indicates that the unencapsulated liquid PDMS participates uniformly in crosslinking during the system's curing process, failing to form a high-concentration core material for directional flow and in-situ co-curing during crack propagation, resulting in near-complete loss of self-healing function. Simultaneously, the local plasticizing effect of liquid PDMS on the matrix crosslinking network also contributed to a certain degree of decrease in high-temperature volume resistivity. In contrast, the MF-shelled microcapsules not only maintain covalent bonding with the matrix during normal service without interfering with intrinsic insulation properties, but also rupture at the crack tip when stress concentration occurs, achieving an intelligent self-healing mechanism of "stress-triggered release → in-situ co-curing crosslinking," resulting in a crack healing strength recovery rate as high as 86.5%.

[0090] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A coil insulating adhesive composition, characterized in that, By weight, it comprises the following components: 40-55 parts of bisphenol A type epoxy resin; 30-40 parts of methyltetrahydrophthalic anhydride; 0.5-1.5 parts of 2-ethyl-4-methylimidazolium; 5-10 parts of benzyl glycidyl ether; 15-25 parts of alumina; 0.5-1.0 parts of γ-glycidyl etheroxypropyltrimethoxysilane; 3-8 parts of surface-hydroxylated nano-zirconia; 4-10 parts of hexagonal boron nitride nanosheets; and 3-7 parts of microcapsules.

2. The coil insulating adhesive composition according to claim 1, characterized in that, The surface-hydroxylated nano-zirconia is prepared by the following method: ZrOCl2·8H2O is dissolved in water, ammonia is added to adjust the pH to alkaline, and zirconium hydroxide precipitate is obtained. The precipitate and mother liquor are transferred to a hydrothermal reactor for hydrothermal treatment, washed, dried and calcined to obtain the final product.

3. The coil insulating adhesive composition according to claim 2, characterized in that, The mass-to-volume ratio of ZrOCl2·8H2O to water is 1g:8~12mL; the mass fraction of ammonia water is 25%~28%, and the pH is adjusted to 9.5~10.5; the hydrothermal treatment temperature is 160~200℃ and the time is 10~14h; the calcination temperature is 280~320℃ and the time is 1.5~2.5h.

4. The coil insulating adhesive composition according to claim 1, characterized in that, The hexagonal boron nitride nanosheets are prepared by the following method: hexagonal boron nitride powder is dispersed in isopropanol, ultrasonically treated, and then centrifuged in two stages. After the first stage of centrifugation, the supernatant is taken for the second stage of centrifugation. After the second stage of centrifugation, the precipitate is taken and dried to obtain the final product.

5. The coil insulating adhesive composition according to claim 4, characterized in that, The mass-to-volume ratio of hexagonal boron nitride powder to isopropanol was 1 g: 80~120 mL; the ultrasonic power was 300~500 W, and the ultrasonic time was 6~10 h; the first centrifugation speed was 2000~4000 rpm, and the time was 15~25 min; the second centrifugation speed was 6000~9000 rpm, and the time was 25~35 min; the precipitate obtained after centrifugation was vacuum dried at 50~70℃.

6. The coil insulating adhesive composition according to claim 1, characterized in that, The microcapsules are prepared by the following method: (1) Mix melamine, formaldehyde and water, adjust the pH to alkaline, heat to react, and obtain MF prepolymer solution; (2) Add terminal epoxy polydimethylsiloxane and anionic emulsifier to water, stir and disperse to obtain an oil-in-water emulsion; (3) Add the MF prepolymer solution to the emulsion, adjust the pH to acidic, heat to react, heat to solidify, filter, wash and dry to obtain the product.

7. The coil insulating adhesive composition according to claim 6, characterized in that, In step (1), the molar ratio of melamine to formaldehyde is 1:2.5~3.5, the mass-volume ratio of melamine to water is 1g:8~15mL, the pH is adjusted to 8.5~9.0, the reaction temperature is 65~75℃, and the reaction time is 1~2h. In step (2), the anionic emulsifier is sodium dodecyl sulfate, and the ratio of terminal epoxy polydimethylsiloxane, sodium dodecyl sulfate and water is 15~25g:0.3~0.8g:100mL, the dispersion speed is 1000~1500rpm, and the dispersion time is 20~40min; In step (3), the mass ratio of MF prepolymer solution to oil-in-water emulsion is 1:4~7, the pH is adjusted to 4.0~4.5, the reaction temperature is 60~70℃, the reaction time is 2.5~3.5h, the temperature after heating is 75~85℃, the curing time is 1~2h, and after filtration and washing, it is vacuum dried at 45~55℃ for 20~28h.

8. A method for preparing the coil insulating adhesive composition according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Alumina, surface-hydroxylated nano-zirconia, hexagonal boron nitride nanosheets and γ-glycidyl etheroxypropyltrimethoxysilane are premixed and then added to bisphenol A type epoxy resin and benzyl glycidyl ether. The mixture is heated and dispersed to obtain component A. S2. After cooling component A, add the microcapsules and stir at low speed to obtain component A containing microcapsules. S3. Mix methyltetrahydrophthalic anhydride with 2-ethyl-4-methylimidazole to obtain component B; S4. Mix component A and component B, and degas under vacuum to obtain the final product.

9. The preparation method according to claim 8, characterized in that, In step S1, the heating temperature is 70~90℃, the dispersion speed is 1500~2500rpm, and the dispersion time is 40~80min; in step S2, the temperature is lowered to 45~55℃, the stirring speed is 200~500rpm, and the stirring time is 10~20min; in step S4, the mass ratio of component A to component B is 95~105:33~39, the vacuum degassing degree is ≤-0.08MPa, and the degassing time is 15~25min.

10. The application of the coil insulating adhesive composition according to any one of claims 1 to 7 in the insulation of coils of drive motors or frequency converters in new energy vehicles, the application comprising: After the coil is impregnated with the coil insulation adhesive composition under vacuum pressure, it is cured sequentially at 80~90℃ for 1.5~2.5h, 110~130℃ for 2.5~3.5h, and 145~155℃ for 1.5~2.5h.

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