Flame-retardant electrical insulation paste and application thereof

Abstract

The invention relates to the technical field of insulating materials, and discloses a flame-retardant electrical insulating paste and application thereof, the insulating paste is formed by independently packaging a component A and a component B; the component A comprises bisphenol A epoxy resin, polycaprolactone diol, aluminum diethylphosphinate, zinc borate, an epoxy group functionalized silane oligomer and the like; the component B comprises methylhexahydrophthalic anhydride and zinc acetylacetonate; a component A is prepared through a melt coating and thermal dilution process, and filler dispersion and interface modification are assisted by using molten polycaprolactone; according to the insulating glue, the process viscosity is effectively reduced by utilizing the phase change characteristic of polycaprolactone, a cured product is endowed with cold and heat impact toughness, a damp and heat aging resistant interface is constructed through the silane oligomer, and a high flame retardant grade is realized by combining a halogen-free flame retardant system. The product provided by the invention has excellent potting manufacturability, cracking resistance and aging-resistant insulativity, and is suitable for potting protection of a driving motor and a high-voltage transformer of a new energy automobile.

Description

Technical Field

[0001] This invention relates to the field of insulating materials technology, specifically to a flame-retardant electrical insulating adhesive and its applications. Background Technology

[0002] Epoxy resin potting compounds are widely used in the insulation protection of drive motors for new energy vehicles, high-voltage transformers, and power electronic modules due to their excellent electrical insulation, mechanical strength, and adhesive properties. As electrical equipment develops towards higher voltage and higher power density, higher requirements are placed on the flame retardancy rating of potting materials, typically requiring a UL94 V-0 rating. To achieve this goal, existing technologies improve flame retardancy by adding large amounts of inorganic flame retardants.

[0003] However, high filler content of inorganic flame retardants increases the viscosity of the adhesive, leading to poor flowability and difficulty in penetrating the complex gaps and deep coils within the device. This can easily result in cavitation or unfilled areas within the potting compound. Although adding reactive diluents can temporarily reduce viscosity, the low-viscosity system cannot provide sufficient yield stress support during storage, causing the high-density flame retardant particles to settle and stratify, affecting product consistency. Furthermore, high filler content disrupts the continuity of the resin matrix, causing the cured product to become brittle and increasing internal stress. When faced with thermal shocks caused by motor start-up and shutdown or drastic changes in ambient temperature, the potting layer is prone to cracking or peeling off from metal components, thus losing its protective function.

[0004] On the other hand, to improve the interfacial bonding between inorganic fillers and organic resin matrices, silane coupling agents are often introduced for surface treatment in industry. Currently, most commonly used silane coupling agents are small-molecule monomers with low boiling points. In the preparation and potting processes of high-performance insulating adhesives, high-temperature and high-vacuum degassing processes are required. This causes small-molecule silanes to easily volatilize and escape before the reaction, failing to form an effective coating layer on the filler surface. The resulting interfacial defects become channels for water molecule penetration under high-temperature and high-humidity environments, initiating interfacial hydrolysis. Consequently, the insulation resistance and breakdown voltage of the material decrease after aging, failing to meet the reliability requirements for long-term operation.

[0005] Furthermore, traditional preparation processes often employ direct mixing methods, where the high-viscosity resin matrix struggles to adequately wet the dried powder filler, easily trapping microbubbles at microscopic interfaces and creating a potential for partial discharge. Simultaneously, improper control of the curing reaction rate and excessively concentrated exothermic reactions can exacerbate curing shrinkage stress, further impacting the dimensional stability and structural integrity of large or thick-walled devices. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a flame-retardant electrical insulating adhesive and its application, solving the problems of existing high flame-retardant potting materials struggling to balance low process viscosity and high thermal shock resistance at high filler contents, as well as the decreased insulation reliability and interfacial bonding failure of traditional small molecule silane coupling agents due to high-temperature vacuum volatilization under humid and hot aging conditions.

[0007] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a flame-retardant electrical insulating adhesive, which adopts the following technical solution: A flame-retardant electrical insulating adhesive, consisting of independently encapsulated components A and B; Component A is made from the following raw materials in parts by weight: 90-110 parts of bisphenol A type epoxy resin, 12-25 parts of polycaprolactone diol, 30-50 parts of aluminum diethylphosphinate, 3-10 parts of zinc borate, 0.5-3.0 parts of epoxy-functionalized silane oligomer, and 0.1-0.5 parts of defoamer. Component B is made from the following raw materials in parts by weight: 80-100 parts of methylhexahydrophthalic anhydride and 0.5-2.0 parts of zinc acetylacetonate; The mixing weight ratio of component A to component B is 100:54-55.

[0008] By adopting the above technical solution, the present invention achieves a balance between processability and physical properties through the synergistic effect of each component. The specific mechanism is as follows: Phase change toughening and viscosity reduction mechanism of polycaprolactone diol: Polycaprolactone diol is a semi-crystalline solid at room temperature. When dispersed in the system, it acts as a physical thixotropic support, preventing the high-density aluminum diethylphosphinate and zinc borate fillers from settling during storage. When heated to operating temperatures above 60°C, polycaprolactone diol melts into a low-viscosity fluid, reducing the mixed viscosity of the high-filler system and endowing the adhesive with the ability to wet micro-crevices. During the curing reaction, the terminal hydroxyl groups of polycaprolactone diol undergo ring-opening esterification with the anhydride curing agent, chemically bonding flexible polyester segments into the epoxy resin crosslinking network. This flexible segment microscopically increases the molecular weight between crosslinking points, dissipating internal stress caused by temperature changes, thereby improving the cured product's resistance to thermal shock cracking.

[0009] Interfacial strengthening mechanism of epoxy-functionalized silane oligomers: Unlike monomeric silanes, the oligomers used in this invention have higher molecular weight and boiling point, and do not volatilize during vacuum degassing and heat curing, ensuring that the effective components remain on the filler surface. Their molecular structure contains multiple silanol groups (or their precursor methoxy groups) and epoxy groups. During curing, the silanol groups undergo a condensation reaction with the hydroxyl groups on the surfaces of aluminum diethylphosphinate and zinc borate, forming strong inorganic filler-Si-O chemical bonds; the epoxy groups at the other end participate in the cross-linking reaction of the resin matrix. This multi-site anchoring effect constructs a dense interfacial layer between the inorganic filler and the organic resin, blocking the diffusion channels of water molecules along the interface and improving the compatibility between the filler and the resin.

[0010] Third, the latent catalytic mechanism of zinc acetylacetonate: Zinc acetylacetonate acts as a Lewis acid catalyst, forming a complex with acid anhydrides. This complex is stable at low temperatures, resulting in a long pot life for the mixed adhesive. At high temperatures, the complex dissociates, releasing zinc ions that catalyze the ring-opening esterification reaction between the epoxy groups and the acid anhydrides. This thermal latency ensures that the reaction proceeds uniformly within the curing temperature range, avoiding internal stress caused by localized burst polymerization.

[0011] Preferably, component A is made from raw materials comprising the following parts by weight: 95-105 parts of bisphenol A type epoxy resin, 15-20 parts of polycaprolactone diol, 35-45 parts of aluminum diethylphosphinate, 5-8 parts of zinc borate, 1.0-2.0 parts of epoxy-functionalized silane oligomer, and 0.2-0.4 parts of defoamer; Component B is made from the following raw materials in parts by weight: 85-95 parts of methylhexahydrophthalic anhydride and 0.8-1.2 parts of zinc acetylacetonate.

[0012] By adopting the above technical solution, the ratio of filler content to resin matrix was further optimized, ensuring that the flame retardancy rating reaches V-0 while maintaining suitable fluidity of the adhesive and mechanical strength of the cured product.

[0013] Preferably, the epoxy-functionalized silane oligomer has an average degree of polymerization of 3-10, and the defoamer is selected from polyether-modified polysiloxane defoamers; The preparation method of the epoxy-functionalized silane oligomer includes: mixing γ-glycidoxypropyltrimethoxysilane with methanol, adding dropwise an aqueous solution containing formic acid, and after the addition is completed at below 50°C, heating to 65°C and refluxing for 4-8 hours, and removing byproducts by rotary evaporation under reduced pressure at 85-95°C to obtain the epoxy-functionalized silane oligomer. Wherein, the molar ratio of γ-glycidoxypropyltrimethoxysilane to methanol is 1.0:1.5-2.5; the molar ratio of γ-glycidoxypropyltrimethoxysilane to water is 1.0:0.8-1.2; and the molar ratio of γ-glycidoxypropyltrimethoxysilane to formic acid is 1.0:0.002-0.006.

[0014] By adopting the above technical solution, the hydrolysis and condensation reaction process of silane was precisely controlled. The reaction principle is as follows: Partial hydrolysis reaction: Under acidic (formic acid) conditions, the methoxy group (-OCH3) in γ-glycidoxypropyltrimethoxysilane undergoes a substitution reaction with water to generate an active silanol group (-Si-OH) and the byproduct methanol. Methanol, as a solvent, increases the miscibility of water and silane, ensuring the reaction proceeds in a homogeneous system.

[0015] Controlled condensation reaction: The generated silanol groups are unstable. Under heating and reflux conditions, the silanol groups between different silane molecules undergo dehydration condensation to form a siloxane skeleton (-Si-O-Si-).

[0016] Molecular weight control: By controlling the molar ratio of water to 0.8-1.2 (close to the stoichiometry but slightly deficient or slightly excess) and the amount of acid catalyst (0.002-0.006), the indefinite extension of the condensation reaction is limited, preventing the formation of high-polymerization gels or solids, ultimately yielding oligomers with an average degree of polymerization of 3-10. Oligomers in this degree of polymerization range exhibit both low volatility and retain liquid flowability and sufficient epoxy functional group density.

[0017] Preferably, component A is prepared by a melt coating and hot dilution process, including the following steps: The polycaprolactone diol, aluminum diethylphosphinate, zinc borate, and epoxy-functionalized silane oligomer are mixed and heated to 80-90°C. The aluminum diethylphosphinate and zinc borate are then surface-wetted and coated with the molten polycaprolactone diol to obtain a filler pre-dispersion. Maintaining the temperature at 80-90℃, the bisphenol A type epoxy resin preheated to 60-70℃ is added to the filler pre-dispersion, and hot dilution and dispersion are carried out to obtain a resin mixture. The resin mixture is defoamed under vacuum conditions, cooled to below 50°C, and the defoamer is added and mixed evenly to obtain component A.

[0018] By adopting the above technical solution and utilizing specific process steps, the microstructure of the material was improved: Melt carrier coating mechanism: Before adding high-viscosity epoxy resin, the extremely low viscosity of molten polycaprolactone diol at 80-90℃ is utilized as a carrier. At this temperature, the system viscosity is extremely low, allowing polycaprolactone to rapidly penetrate into the filler aggregates, facilitating full contact between the epoxy-functionalized silane oligomers and the surfaces of aluminum diethylphosphines and zinc borate. Under high temperature and high-speed shearing, the silane oligomers undergo in-situ chemical grafting on the filler surface. Compared to direct mixing, this step eliminates the gas film on the filler surface, achieving pre-wetting of the filler.

[0019] Hot dilution and phase inversion: After the filler surface is coated with an oleophilic polycaprolactone / silane layer, epoxy resin is added for dilution. Due to the modified surface properties of the filler, the interfacial compatibility with the epoxy resin is greatly improved, thereby achieving uniform dispersion in the resin matrix, reducing bubble entrainment, and increasing the breakdown voltage of the insulation system.

[0020] Preferably, the flame-retardant electrical insulating adhesive is prepared by heating component A to 60-70°C to melt it into a fluid, mixing it evenly with component B in a certain proportion and degassing it under vacuum to obtain a mixed adhesive solution, injecting the mixed adhesive solution into a mold or device, and curing it by heating to obtain the flame-retardant electrical insulating adhesive; the heating curing process includes: maintaining a constant temperature of 70-90°C for 1-3 hours, maintaining a constant temperature of 110-130°C for 1-3 hours, and maintaining a constant temperature of 140-160°C for 1-4 hours.

[0021] By adopting the above technical solution, phased curing is implemented to manage internal stress: The first stage (70-90℃) is the pre-gelation stage, during which the viscosity of the system decreases, which is conducive to the escape of residual microbubbles. At the same time, the reaction rate is slow, which prevents explosive polymerization. The second stage (110-130℃) is the cross-linking network formation stage, in which polycaprolactone segments are chemically fixed in the network; The third stage (140-160℃) is the post-curing stage, which eliminates reaction byproducts and residual stress, and increases the crosslinking density to achieve the final heat-resistant mechanical properties.

[0022] Secondly, the present invention provides an application of the above-mentioned flame-retardant electrical insulating adhesive in the potting protection of drive motors, high-voltage transformers, or power electronic modules of new energy vehicles, using the following technical solution: The application of a flame-retardant electrical insulating adhesive in the potting protection of drive motors, high-voltage transformers, or power electronic modules of new energy vehicles, wherein the flame-retardant electrical insulating adhesive is used as a potting material to fill the internal gaps of the device, coil windings, or around electronic components, and is cured by heating to form an insulating protective layer.

[0023] By adopting the above technical solution, this invention utilizes the low viscosity of polycaprolactone diol after heating to improve the wetting and filling properties of the adhesive to the windings and micro-gaps, reducing the risk of partial discharge. The introduced flexible segments buffer thermal stress to prevent the device from cracking under frequent thermal shocks. At the same time, the hydrophobic interfacial layer constructed by epoxy-functionalized silane oligomers effectively blocks water molecule penetration, maintains electrical insulation performance under humid and hot conditions, and, combined with the synergistic charring and flame-retardant effect of aluminum diethylphosphines and zinc borate, ensures the safety of the device under overheating or arcing faults, thereby meeting the long-term protection requirements of new energy vehicle drive motors, high-voltage transformers, and power electronic modules under complex operating conditions.

[0024] This invention provides a flame-retardant electrical insulating adhesive and its application. It has the following beneficial effects: 1. This invention solves the contradiction between high flame retardant filler, process viscosity, and material toughness by introducing polycaprolactone diol in combination with aluminum diethylphosphinate and zinc borate. Polycaprolactone diol is crystalline at room temperature, providing physical thixotropic support to prevent the high-density flame retardant from settling; after heating and melting, it transforms into a low-viscosity fluid, reducing the viscosity of the adhesive mixture and ensuring penetration and potting of complex device gaps; after curing, the flexible polyester segments introduced into the crosslinking network can effectively dissipate internal stress, giving the cured material excellent resistance to thermal shock and preventing cracking.

[0025] 2. This invention uses self-made epoxy-functionalized silane oligomers to modify the surface of inorganic fillers, improving the insulation reliability of the material in humid and hot environments. Compared with conventional monomeric silanes, this oligomer has a higher molecular weight, avoiding volatilization loss in the high-temperature vacuum degassing process. Its multi-site anchoring structure constructs a dense hydrophobic interface layer between the resin matrix and the inorganic filler, inhibiting the interface hydrolysis reaction caused by water vapor penetration, and improving the volume resistivity retention and bonding strength of the insulating adhesive after aging.

[0026] 3. This invention utilizes molten polycaprolactone as a carrier to drive silane to in-situ wet and coat the filler, which improves the filler dispersion and reduces air gap defects caused by poor wetting; combined with zinc acetylacetone latent catalyst and staged curing process, the reaction rate and heat release are effectively controlled, ensuring the dense molding and dimensional stability of the potting layer for thick-walled or large devices. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the preparation examples, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0029] Polycaprolactone diol, CAS number 36890-68-3, has a number-average molecular weight Mn of approximately 2000; Polyethylene glycol, abbreviated as PEG 2000, has CAS number 25322-68-3 and an average molecular weight of approximately 2000.

[0030] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a method for preparing epoxy-functionalized silane oligomers, including the following steps: In a dry four-necked flask equipped with a mechanical stirrer, reflux condenser, thermometer, and constant-pressure dropping funnel, 236.3 g (1.0 mol) of γ-glycidyl etheroxypropyltrimethoxysilane and 60 g of methanol were added, and the system was stirred until homogeneous. 14.4 g (0.8 mol) of deionized water and 0.2 g of formic acid were pre-mixed and slowly added dropwise to the flask over 30 minutes through the constant-pressure dropping funnel, while controlling the temperature of the reaction solution to not exceed 50°C during the addition. After the addition was complete, the reaction system was heated to 65°C and kept under reflux for 4 hours. After the reaction was completed, the apparatus was changed to a vacuum distillation apparatus, and methanol and byproducts were removed by rotary evaporation under oil bath temperature of 85°C and vacuum of -0.098 MPa until no distillate flowed out, yielding a colorless, transparent, low-viscosity liquid, which is epoxy-functionalized silane oligomer A, with an average degree of polymerization of approximately 3-4.

[0031] Preparation Example 2: This preparation example provides a method for preparing epoxy-functionalized silane oligomers, including the following steps: In a dry four-necked flask equipped with a mechanical stirrer, reflux condenser, thermometer, and constant-pressure dropping funnel, 236.3 g (1.0 mol) of γ-glycidyl etheroxypropyltrimethoxysilane and 60 g of methanol were added, and the system was stirred until homogeneous. 18.0 g (1.0 mol) of deionized water and 0.2 g of formic acid were pre-mixed and slowly added dropwise to the flask over 30 minutes through the constant-pressure dropping funnel, while controlling the temperature of the reaction solution to not exceed 50°C during the addition. After the addition was complete, the reaction system was heated to 65°C and kept under reflux for 6 hours. After the reaction was completed, the apparatus was changed to a vacuum distillation apparatus, and methanol and byproducts were removed by rotary evaporation under oil bath temperature of 90°C and vacuum degree of -0.098 MPa until no fraction flowed out, yielding a pale yellow viscous liquid, which is epoxy-functionalized silane oligomer B, with an average degree of polymerization of approximately 5-7.

[0032] Preparation Example 3: This preparation example provides a method for preparing epoxy-functionalized silane oligomers with a high degree of polymerization, including the following steps: In a dry four-necked flask equipped with a mechanical stirrer, reflux condenser, thermometer, and constant-pressure dropping funnel, 236.3 g (1.0 mol) of γ-glycidyl etheroxypropyltrimethoxysilane and 60 g of methanol were added, and the system was stirred until homogeneous. 21.6 g (1.2 mol) of deionized water and 0.2 g of formic acid were pre-mixed and slowly added dropwise to the flask over 30 minutes through the constant-pressure dropping funnel, while controlling the temperature of the reaction solution to not exceed 50°C during the addition. After the addition was complete, the reaction system was heated to 65°C and kept under reflux for 8 hours. After the reaction was completed, the apparatus was changed to a vacuum distillation apparatus, and methanol and byproducts were removed by rotary evaporation under oil bath temperature of 95°C and vacuum of -0.098 MPa until no distillate flowed out, yielding a yellow, high-viscosity liquid, which is epoxy-functionalized silane oligomer C, with an average degree of polymerization of approximately 8-10.

[0033] Examples 1-3: Example 1: This embodiment provides a method for preparing a flame-retardant electrical insulating adhesive, specifically including the following steps: (1) Preparation of component A: In a planetary stirred tank with a heating jacket and a high-speed dispersion plate, first add 15 parts of polycaprolactone diol, 35 parts of aluminum diethylphosphinate, 5 parts of zinc borate and 1.0 part of epoxy-functionalized silane oligomer A obtained in Preparation Example 1. At this time, epoxy resin is strictly prohibited from being added. Turn on the heating to raise the temperature of the reactor to 80°C. After the polycaprolactone is completely melted, turn on the high-speed dispersion and set the linear velocity to 15 m / s. Maintain the temperature at 80°C and stir for 30 minutes. Use the molten polycaprolactone as a carrier to carry the silane oligomer to complete the coating of the filler surface. Then, while maintaining the temperature inside the reactor at 80°C, 100 parts of bisphenol A epoxy resin preheated to 60°C were slowly added into the reactor. After the addition was completed, the resin was dispersed at a linear velocity of 15 m / s for 20 minutes for hot dilution and phase inversion. Next, maintain the temperature at 80℃, turn on the vacuum pump to achieve a vacuum of -0.098MPa, and degas for 15 minutes; Finally, cooling water is introduced to lower the temperature. When the temperature drops to 50°C, 0.3 parts of polyether-modified polysiloxane defoamer are added. Stirring is continued and the mixture is cooled to 40°C before being discharged to obtain a paste-like component A.

[0034] (2) Preparation of component B: 85 parts of methylhexahydrophthalic anhydride were heated to 45°C, 0.8 parts of zinc acetylacetone were added, and the mixture was stirred for 30 minutes until it was completely dissolved and clear. After cooling and filtration, component B was obtained.

[0035] (3) Mixing and curing: When using, heat component A to 60°C to melt it into a low-viscosity fluid, mix it evenly with component B in a weight ratio of 100:55 and degas it under vacuum; Inject the mixed adhesive into the mold or electronic device and cure it according to the following procedure: 80℃ for 2 hours, 120℃ for 2 hours, and 150℃ for 2 hours. After curing, allow it to cool naturally to room temperature to obtain a cured flame-retardant electrical insulating adhesive material.

[0036] Example 2: This embodiment provides a method for preparing a flame-retardant electrical insulating adhesive, specifically including the following steps: (1) Preparation of component A: In a planetary stirred tank with a heating jacket and a high-speed dispersion plate, first add 18 parts of polycaprolactone diol, 40 parts of aluminum diethylphosphinate, 6.5 parts of zinc borate and 1.5 parts of epoxy-functionalized silane oligomer B obtained in Preparation Example 2. At this time, epoxy resin is strictly prohibited from being added. Turn on the heating to raise the temperature of the reactor to 85°C. After the polycaprolactone is completely melted, turn on the high-speed dispersion and set the linear velocity to 18 m / s. Maintain the temperature at 85°C and stir for 35 minutes. Use the molten polycaprolactone as a carrier to drive the silane oligomer to complete the coating of the filler surface. Then, while maintaining the temperature inside the reactor at 85°C, 100 parts of bisphenol A epoxy resin preheated to 65°C were slowly added into the reactor. After the addition was completed, the resin was dispersed at a linear velocity of 18 m / s for 25 minutes for hot dilution and phase inversion. Next, maintain the temperature at 85℃, turn on the vacuum pump to achieve a vacuum of -0.098MPa, and degas for 20 minutes. Finally, cooling water is introduced to lower the temperature. When the temperature drops to 50°C, 0.3 parts of polyether-modified polysiloxane defoamer are added. Stirring is continued and the mixture is cooled to 40°C before being discharged to obtain a paste-like component A.

[0037] (2) Preparation of component B: 90 parts of methylhexahydrophthalic anhydride were heated to 50°C, 1.0 part of zinc acetylacetone was added, and the mixture was stirred for 45 minutes until it was completely dissolved and clear. After cooling and filtration, component B was obtained.

[0038] (3) Mixing and curing: When using, heat component A to 65°C to melt it into a low-viscosity fluid, mix it evenly with component B in a weight ratio of 100:54, and then degas it under vacuum. Inject the mixed adhesive into the mold or electronic device and cure it according to the following procedure: 80℃ for 2 hours, 120℃ for 2 hours, and 150℃ for 2 hours. After curing, allow it to cool naturally to room temperature to obtain a cured flame-retardant electrical insulating adhesive material.

[0039] Example 3: This embodiment provides a method for preparing a flame-retardant electrical insulating adhesive, specifically including the following steps: (1) Preparation of component A: In a planetary stirred tank with a heating jacket and a high-speed dispersion plate, first add 20 parts of polycaprolactone diol, 45 parts of aluminum diethylphosphinate, 8 parts of zinc borate and 2.0 parts of epoxy-functionalized silane oligomer C obtained in Preparation Example 3. At this time, epoxy resin is strictly prohibited from being added. Turn on the heating to raise the temperature of the reactor to 90°C. After the polycaprolactone is completely melted, turn on the high-speed dispersion and set the linear velocity to 20 m / s. Maintain the temperature at 90°C and stir for 45 minutes. Use the molten polycaprolactone as a carrier to carry the silane oligomer to complete the coating of the filler surface. Then, while maintaining the temperature inside the reactor at 90°C, 100 parts of bisphenol A epoxy resin preheated to 70°C were slowly added into the reactor. After the addition was completed, the resin was dispersed at a linear velocity of 20 m / s for 30 minutes for hot dilution and phase inversion. Next, maintain the temperature at 90℃, turn on the vacuum pump to achieve a vacuum of -0.098MPa, and degas for 20 minutes; Finally, cooling water is introduced to lower the temperature. When the temperature drops to 50°C, 0.3 parts of polyether-modified polysiloxane defoamer are added. Stirring is continued and the mixture is cooled to 40°C before being discharged to obtain a paste-like component A.

[0040] (2) Preparation of component B: 95 parts of methylhexahydrophthalic anhydride were heated to 55°C, 1.2 parts of zinc acetylacetone were added, and the mixture was stirred for 60 minutes until it was completely dissolved and clear. After cooling and filtration, component B was obtained.

[0041] (3) Mixing and curing: When using, heat component A to 70°C to melt it into a low-viscosity fluid, mix it evenly with component B in a weight ratio of 100:55 and degas it under vacuum; Inject the mixed adhesive into the mold or electronic device and cure it according to the following procedure: 80℃ for 2 hours, 120℃ for 2 hours, and 150℃ for 2 hours. After curing, allow it to cool naturally to room temperature to obtain a cured flame-retardant electrical insulating adhesive material.

[0042] Comparative Examples 1-6: Comparative Example 1: The difference compared to Example 2 lies in the preparation process of component A. This comparative example did not employ the high-temperature melt pre-wetting and hot dilution process. Specifically, the following steps were taken: polycaprolactone diol, aluminum diethylphosphinate, zinc borate (which are solid powders at room temperature), liquid epoxy-functionalized silane oligomer B, and bisphenol A epoxy resin were directly added into a stirred tank and mechanically mixed uniformly at room temperature. Subsequently, the mixture was heated to 50°C for vacuum degassing. The remaining steps and raw material amounts were the same as in Example 2.

[0043] Comparative Example 2: The difference between this example and Example 2 lies in the raw materials of component A. In this comparative example, an equal part by weight of monomer γ-glycidoxypropyltrimethoxysilane (KH-560) was used to replace the self-made epoxy-functionalized silane oligomer B. The amounts of other raw materials and the preparation process were the same as in Example 2.

[0044] Comparative Example 3: The difference between this example and Example 2 lies in the raw materials of component A. Epoxy-functionalized silane oligomer B was not added in this comparative example; the amounts of other raw materials and the preparation process are the same as in Example 2.

[0045] Comparative Example 4: The difference between this example and Example 2 lies in the raw materials of component A. In this comparative example, polyethylene glycol (PEG 2000) was used in place of polycaprolactone diol in equal parts by weight; the amounts of other raw materials and the preparation process were the same as in Example 2.

[0046] Comparative Example 5: Compared with Example 2, the difference lies in the preparation process of component A. In step (1) of this comparative example, after the polycaprolactone melts and drives the silane oligomer to complete the coating and dispersion of the filler, cooling water is first passed through to cool the material in the reactor to room temperature (25°C), and then bisphenol A type epoxy resin is added for mixing and dispersion. The remaining steps and raw material amounts are the same as in Example 2.

[0047] Comparative Example 6: The difference between this example and Example 2 lies in the raw materials of component B. In this comparative example, an equal part by weight of the conventional imidazole catalyst 2-ethyl-4-methylimidazolium (2E4MZ) was used to replace zinc acetylacetonate, while the amounts of the remaining raw materials and the preparation process were the same as in Example 2.

[0048] Test Examples 1-4: Test Example 1: Temperature-Sensitive Rheological Properties and Storage Stability Test This test case aims to verify the rheological behavior of component A under different temperatures and shear fields, thereby evaluating the inhibitory effect of polycaprolactone (PCL) crystallization phase change on filler sedimentation and the viscosity reduction effect after high-temperature melting.

[0049] Experimental steps: Sample preparation: Fresh A-component adhesive solutions prepared in Example 2, Comparative Example 1 (cold mixing process) and Comparative Example 4 (PEG replacing PCL) were selected as test samples.

[0050] Thixotropy and static yield tests: A rotational rheometer was used with a 25mm flat rotor and a spacing of 1mm. Under constant temperature of 25℃, the samples were measured at low shear rates (0.1s⁻¹). -1 ) and high shear rate (10s) -1The apparent viscosity at the given conditions is 1 / 3. The thixotropic index (TI value) is calculated as the ratio of the low-shear viscosity to the high-shear viscosity.

[0051] Temperature-dependent viscosity scanning: The rheometer was set to oscillation mode with a frequency of 1 Hz and a strain of 1%. The temperature of the sample was scanned at a heating rate of 5 °C / min. The complex viscosity change curves were recorded from 25 °C to 90 °C. The viscosity data at 60 °C (near the melting point of PCL) and 80 °C (pouring temperature) were recorded in particular.

[0052] Simulated high-temperature sedimentation test: Take 50 mL of each of the above samples and inject them into stoppered graduated cylinders. After sealing, place them in a 60℃ oven and let them stand for 48 hours to simulate transportation or long-term preheating. After removing them and allowing them to cool naturally to room temperature, measure the height of the hard precipitate layer at the bottom and the total liquid level, and calculate the sedimentation rate.

[0053] The test results are shown in Table 1: Table 1. Summary of Rheological Properties and Settlement Stability Test Data Test Item / Sample Number Example 2 Comparative Example 1 Comparative Example 4 Low shear viscosity at 25℃ (Pa·s, @0.1s⁻¹) 145.3 42.8 35.6 High shear viscosity at 25℃ (Pa·s, @10s⁻¹) 18.6 19.5 16.2 Thixotropic index (TI value) 7.81 2.19 2.20 Dynamic viscosity at 60℃ (Pa·s) 4.2 11.5 3.8 Dynamic viscosity at 80℃ (Pa·s) 1.1 7.6 0.9 Settlement rate (%) at 60℃ / 48h 0.5 18.3 8.4 Note: @0.1s -1 This indicates that under a shear rate of 0.1 sec, @10s -1 Under the condition of a shear rate of 10 per second.

[0054] Results Analysis and Conclusions: Based on the data analysis in Table 1, Example 2 exhibits obvious solid-liquid phase transition characteristics in its rheological properties, verifying the technical mechanism of the present invention based on PCL crystallization network control.

[0055] First, at room temperature (25°C), the low-shear viscosity of Example 2 reached 145.3 Pa·s, and the thixotropic index reached 7.81, significantly higher than that of Comparative Example 1 and Comparative Example 4. This indicates that through melt dispersion and cooling crystallization processes, the PCL molecular chains successfully formed a microcrystalline network structure in the epoxy resin matrix. This physically cross-linked network can effectively support high-density flame retardant particles (such as aluminum diethylphosphinate and zinc borate) under static conditions, preventing them from sinking due to gravity; however, once subjected to high shear forces (such as stirring or pumping), the microcrystalline network structure is temporarily disrupted, and the viscosity rapidly decreases to 18.6 Pa·s, ensuring operational feasibility. In contrast, Comparative Example 1 used a cold mixing process, where PCL existed independently in powder form, failing to form a continuous support network, resulting in poor thixotropy of the system; although the PEG used in Comparative Example 4 is also a semi-crystalline polymer, its compatibility with epoxy resin is too good and its hardness is low, making it difficult to construct a high-strength yield stress layer, thus resulting in a lower low-shear viscosity.

[0056] Secondly, during the heating process, the viscosity of Example 2 abruptly decreased to 4.2 Pa·s near 60°C (the melting point of PCL), and further decreased to 1.1 Pa·s at 80°C. This indicates that as the temperature rises, the PCL crystals melt, releasing the bound liquid phase components. Simultaneously, the molten PCL fluid itself becomes a low-viscosity lubricant, reducing internal friction between the fillers. This data demonstrates the effectiveness of the hot dilution effect. In contrast, in Comparative Example 1, because the filler surface was not fully coated with silane oligomers in a high-temperature molten state, the interfacial wettability between the filler and the resin was poor, resulting in a viscosity that remained at a relatively high level of 7.6 Pa·s at high temperatures, leading to high flow resistance.

[0057] Finally, the sedimentation test data directly reflects the stability of the system. Comparative Example 1 showed a sedimentation rate as high as 18.3% at 60℃, indicating severe separation between the unmodified filler and the resin. Comparative Example 4 showed a sedimentation rate of 8.4%, indicating insufficient thermal stability of the PEG system. In contrast, Example 2 showed a sedimentation rate of only 0.5%, demonstrating that even after PCL melting, the long-chain chemical bonds (grafting) formed on the filler surface by the silane oligomers during the preparation process increased the filler's hydrodynamic radius and steric hindrance in the resin, allowing the system to maintain good suspension stability under high temperature and low viscosity conditions.

[0058] Test Example 2: Application Process Performance and Reliability Testing for Damp Heat Aging This test case aims to comprehensively evaluate the process operation window, flame retardancy rating after curing, and insulation reliability of insulating adhesive in practical applications, with a focus on the impact of different modification methods on the material interface stability.

[0059] Experimental steps: Sample preparation: Take component A prepared in Examples 1-3 and Comparative Examples 1-6 respectively, heat to 60℃ to melt, mix with component B according to their respective formulation ratios, and degas under a vacuum of -0.098MPa for 5 minutes. Pour the mixed adhesive into a preheated aluminum mold and cure according to the programs of 80℃ / 2h, 120℃ / 2h and 150℃ / 2h. After demolding, cut into strips that meet the standard requirements.

[0060] Process performance test: The initial viscosity of the mixed adhesive was measured at a constant temperature of 60°C using a rotational viscometer; then, the temperature was kept constant at 60°C, and the time required for the viscosity to increase to twice the initial value was recorded as the pot life.

[0061] Thermomechanical properties and flame retardancy testing: The glass transition temperature (Tg) of the cured material was tested using a dynamic thermomechanical analyzer in single cantilever mode at a heating rate of 3℃ / min and a frequency of 1Hz. A vertical burning test was performed on a 1.6mm thick sample according to the UL-94 standard, and the presence or absence of dripping and the total afterflame time were recorded.

[0062] PCT High-Pressure Accelerated Aging Test: The initial volume resistivity and weight of the cured sheet (100 mm in diameter, 2 mm in thickness) were measured. The sample was placed in a high-pressure accelerated aging chamber, and the conditions were set at 121°C, 100% relative humidity, and 2.0 atm pressure for 48 hours. After removal, the surface moisture was wiped dry, and the water absorption rate and the volume resistivity after aging were immediately tested. The volume resistivity retention rate was calculated.

[0063] The test results are shown in Table 2: Table 2. Summary of test data for process performance, flame retardancy and damp heat aging resistance Test Project Mixed viscosity (mPa·s, 60℃) Pot life (min, 60℃) Tg (°C) UL-94 rating (1.6mm) PCT water absorption rate (%) PCT resistivity retention (%) Example 1 820 255 132.4 V-0 0.28 91.5 Example 2 760 248 135.1 V-0 0.25 94.2 Example 3 890 260 138.6 V-0 0.31 90.8 Comparative Example 1 2450 230 124.5 V-1 0.68 65.3 Comparative Example 2 780 240 129.2 V-0 0.55 42.1 Comparative Example 3 1240 235 126.8 V-1 0.82 18.6 Comparative Example 5 1560 245 128.5 V-0 0.44 78.9 Comparative Example 6 810 45 131.0 V-0 0.27 92.1 Note: According to the UL-94 vertical burning test standard, V-0 indicates that after two 10-second flame tests, the afterflame time of each test does not exceed 10 seconds, the total afterflame time does not exceed 50 seconds, and there are no burning droplets igniting the degreased cotton below; V-1 indicates that after two 10-second flame tests, the afterflame time of each test does not exceed 30 seconds, the total afterflame time does not exceed 250 seconds, and there are no burning droplets igniting the degreased cotton below.

[0064] Results Analysis and Conclusions: Based on the data in Table 2, the contribution of each technical feature of the present invention to the final performance can be clearly analyzed through data comparison in different dimensions.

[0065] Regarding process performance, the mixed viscosity of Examples 1-3 was controlled below 900 mPa·s, significantly lower than the 2450 mPa·s of Comparative Example 1. This confirms the necessity of the melt interface grafting process: in the examples, the molten polycaprolactone-assisted silane oligomer fully wetted and coated the inorganic filler, reducing the frictional resistance between the fillers; while Comparative Example 1 used cold mixing, resulting in severe filler agglomeration and a surge in viscosity. Furthermore, the pot life of Comparative Example 6 was only 45 minutes, far lower than the approximately 250 minutes of the examples, indicating that zinc acetylacetonate, as a latent curing agent, effectively solved the problem of insufficient operating time in high-temperature infusion processes.

[0066] Regarding flame retardant performance, dispersion quality directly affects flame retardant efficiency. All examples achieved V-0 rating, while Comparative Examples 1 and 3, due to uneven filler dispersion or weak interfacial bonding, were prone to local defects or microcracks during combustion, leading to dripping or flame spread, and only achieved V-1 rating.

[0067] In the crucial PCT (Potentially Transformed Tolerant Heat) aging test, the differences in data directly reflect the integrity of the interface structure. Example 2 exhibited a resistivity retention rate as high as 94.2% and a water absorption rate of only 0.25%, indicating the formation of a dense hydrophobic barrier within it.

[0068] Comparing Example 2 and Comparative Example 2 (monomer silane), although their initial viscosities are similar, the resistivity retention rate of Comparative Example 2 after aging is only 42.1%. This is because the monomer silane (KH-560) has a low boiling point and volatilizes significantly during high-temperature melting and vacuum degassing, resulting in a low actual grafting rate, interface defects, and easy water vapor intrusion along the interface. In contrast, the silane oligomer used in this invention has a large molecular weight and a high boiling point, enabling it to withstand high-temperature processes without volatilization, thus preserving a complete interface layer.

[0069] Compared with Comparative Example 2, Comparative Example 3 (without silane) showed that the resistivity retention rate of Comparative Example 3 dropped to 18.6%, indicating that the physical interface without chemical bonding is prone to hydrolysis and peeling under high temperature and high humidity, leading to insulation failure.

[0070] Comparing Example 2 with Comparative Example 5 (process difference), Comparative Example 5 involved cooling the resin before adding it, which may have caused the silane oligomers to be rejected or embedded during PCL crystallization, failing to react effectively with the resin on the outermost layer. Therefore, its aging resistance (78.9%) was lower than that of Example 2. This further confirms the importance of the hot dilution process for maintaining interfacial activity.

[0071] Test Example 3: Thermal Shock Resistance and Dielectric Breakdown Strength Test This test case aims to examine the material's crack resistance (toughness) under extreme temperature alternating environment and its insulation tolerance under high electric field, with a focus on verifying the synergistic effect of the flexible segments introduced by polycaprolactone and the interface layer constructed by silane oligomers against internal stress.

[0072] Experimental steps: Sample preparation: Take the adhesive prepared in Examples 1-3 and the comparative example, respectively, and pour it into a cylindrical aluminum mold with a 10mm diameter hexagonal nut in the center (to create stress concentration as a metal insert) and a circular mold with a thickness of 1.0mm. Curing is carried out according to the aforementioned procedure. 10 insert samples and 5 circular samples are prepared for each formulation.

[0073] Thermal shock test: Place the insert sample in a two-chamber thermal shock test chamber. Set the low temperature to -40℃ and the high temperature to 130℃, with a dwell time of 30 minutes for each temperature and a transition time of less than 10 seconds. After every 10 cycles, remove the sample and observe the surface and interior for microcracks using a magnifying glass. Record the number of cycles when the first crack appears. If no crack appears after 150 cycles, stop the test.

[0074] Dielectric strength test: According to IEC 60243-1 standard, the circular sample is placed in an insulating oil bath. Using a voltage breakdown tester, a ball electrode with a diameter of 25mm is selected. An AC voltage is applied at a step-up rate of 2kV / s until the sample is broken down. The breakdown voltage value is recorded and the dielectric strength (kV / mm) is calculated.

[0075] The test results are shown in Table 3: Table 3. Summary of thermal shock resistance and dielectric strength test data Test Item / Sample Number Number of thermal shock cycles for cracking (times) Dielectric breakdown strength (kV / mm) Example 1 120 (No cracks) 22.4 Example 2 150 (no cracks) 23.8 Example 3 135 23.1 Comparative Example 1 30 18.2 Comparative Example 2 80 20.5 Comparative Example 3 10 16.7 Comparative Example 4 50 17.9 Results Analysis and Conclusions: According to the data in Table 3, there are significant differences in thermal shock resistance between the examples and the comparative examples, which directly confirms the mechanism of the synergistic effect of the polycaprolactone flexible segments and the silane oligomers reinforcing the interface.

[0076] Example 2 exhibited optimal crack resistance without cracking after undergoing 150 rigorous thermal shock cycles. This is because polycaprolactone (PCL) in component A, as a macromolecular diol, participated in the curing reaction of the epoxy resin, introducing flexible polyester segments into the crosslinking network and effectively reducing the internal stress of the cured product. Simultaneously, the silane oligomer formed a high-strength chemical bond layer between the filler and the resin. When the metal insert experienced significant interfacial stress due to thermal expansion and contraction, the flexible PCL segments provided deformation allowance, while the dense interfacial layer prevented delamination between the filler and the resin. Together, these factors effectively dissipated stress energy and inhibited crack initiation and propagation.

[0077] In contrast, Comparative Example 3 (silane-free) cracked after only 10 cycles. This is because the inorganic filler (such as aluminum diethylphosphonate) has a large difference in thermal expansion coefficients with the organic resin matrix. The interface, lacking chemical bonding, rapidly peels off under thermal shock, becoming a stress concentration point and crack initiation site.

[0078] Comparative Example 1 (cold mixing process), although with the same formulation, only lasted for 30 cycles. This indicates that if the filler is not pre-melted and coated with PCL and silane oligomers, the agglomerated particles not only fail to transfer stress but also become defect points in the system, significantly reducing the material's impact resistance.

[0079] Comparative Example 4 (PEG substitution) exhibited 50 cracking cycles and a dielectric strength of only 17.9 kV / mm, significantly lower than the examples. This indicates that while PEG can provide some flexibility, its high hygroscopicity and poor compatibility with epoxy anhydride systems compared to PCL (polycaprolactone) demonstrate its superior performance. PCL's ester structure is a better match for anhydride curing systems and offers better hydrophobicity, thus ensuring toughness without sacrificing electrical insulation properties. Example 2's high dielectric strength of 23.8 kV / mm further proves that the dense interface layer effectively reduces the formation of internal air gaps and conductive channels.

[0080] Test Example 4: Bond Strength and Damp Heat Aging Durability Test This test case aims to evaluate the adhesion of insulating adhesive to metal substrates and examine the stability of interfacial adhesion strength under long-term high temperature and high humidity conditions, thereby verifying the wetting advantages brought by the melt low viscosity process and the interfacial anchoring effect of silane oligomers.

[0081] Experimental steps: Substrate treatment and sample preparation: An aluminum alloy sheet with dimensions of 100mm × 25mm × 2mm was selected as the substrate to be bonded. The overlapping area was sanded with 240-grit sandpaper, followed by ultrasonic cleaning with acetone for 5 minutes and drying. The adhesive prepared in Examples 1-3 and the comparative example were applied to the overlapping surfaces of the two aluminum sheets, respectively, with the overlap length controlled at 12.5mm and the adhesive layer thickness controlled at 0.2mm, and fixed with clamps.

[0082] Curing and initial testing: The clamped specimens were placed in an oven and cured according to the following procedures: 80℃ for 2 hours, 120℃ for 2 hours, and 150℃ for 2 hours. After curing, the specimens were cooled to room temperature and left to stand for 24 hours. Tensile shear strength tests were performed using a universal testing machine at a tensile rate of 5 mm / min. Five parallel specimens were tested in each group, and the maximum load was recorded and the shear strength (MPa) was calculated.

[0083] Damp heat aging durability test: Take another set of prepared cured samples from each group and place them in a constant temperature and humidity test chamber. Set the conditions as follows: temperature 85℃, relative humidity 85%. After 500 hours of continuous aging, remove the samples and allow them to recover for 2 hours under standard conditions. Then, perform tensile shear strength tests under the above conditions and calculate the strength retention rate after aging.

[0084] The test results are shown in Table 4: Table 4. Summary of test data on tensile shear strength and aging retention of aluminum. Test Item / Sample Number Initial shear strength (MPa) Shear strength (MPa) after 500 hours at 85℃ / 85%RH Strength retention rate (%) Example 1 18.4 16.1 87.5 Example 2 19.8 17.6 88.9 Example 3 20.3 17.4 85.7 Comparative Example 1 12.5 7.2 57.6 Comparative Example 2 17.9 9.4 52.5 Comparative Example 3 16.2 4.5 27.8 Comparative Example 4 14.8 8.3 56.1 Comparative Example 6 19.1 16.5 86.4 Results Analysis and Conclusions: According to the data in Table 4, the embodiments of the present invention show significant advantages in terms of adhesive strength and durability, which is closely related to the improved interfacial wettability brought about by the preparation process.

[0085] The initial shear strength of Example 2 reached 19.8 MPa, higher than that of Comparative Example 1 (12.5 MPa). This difference is due to the different process paths. Example 2 employed a high-temperature melting process, utilizing molten polycaprolactone (PCL) as a carrier. Its extremely low melt viscosity allowed the adhesive to rapidly fill the micro-pits and textures on the aluminum alloy surface, forming a good mechanical interlock. Simultaneously, silane oligomers migrated to the interface during this process, undergoing a condensation reaction with the hydroxyl groups on the metal surface. In contrast, Comparative Example 1 used a cold mixing process, resulting in a high system viscosity and poor wetting and spreading ability on the substrate surface. This led to a reduced actual contact area and numerous micro-voids at the interface, resulting in a lower initial strength.

[0086] After 500 hours of humid heat aging at 85°C, the strength retention rate of Example 2 remained at 88.9%, while that of Comparative Example 2 (monomer silane) plummeted to 52.5%, and that of Comparative Example 3 (silane-free) dropped even further to 27.8%. This result profoundly reveals the structural advantages of silane oligomers over monomeric silanes. The monomeric silane used in Comparative Example 2, due to its small molecular weight, is prone to volatilization and loss during high-temperature mixing and high-vacuum degassing processes, resulting in a severely insufficient effective grafting rate at the interface. Furthermore, the remaining portion, due to its short molecular chain and low cross-linking density, is prone to reverse hydrolysis of the siloxane bonds formed under humid heat, leading to interface failure. In contrast, the epoxy-functionalized silane oligomer synthesized in this invention has a larger molecular weight, is heat-resistant and non-volatile, and forms a multi-site anchored network hydrophobic layer on the metal surface, effectively blocking the penetration of water molecules into the adhesive-aluminum interface and inhibiting interfacial hydrolysis, thereby ensuring the bonding reliability under long-term harsh environments.

[0087] Furthermore, the aging retention rate of Comparative Example 4 (PEG replacement) was only 56.1%, which once again confirms that the strong hydrophilicity of PEG leads to a large amount of water being absorbed into the adhesive layer, causing colloidal swelling and a decrease in interfacial bonding, while the good hydrophobicity of PCL helps to maintain structural stability in humid and hot environments.

Claims

1. A flame-retardant electrical insulating adhesive, characterized in that, It consists of two independently packaged components, A and B. Component A is made from raw materials comprising the following parts by weight: 90-110 parts of bisphenol A type epoxy resin, 12-25 parts of polycaprolactone diol, 30-50 parts of aluminum diethylphosphinic acid, 3-10 parts of zinc borate, 0.5-3.0 parts of epoxy-functionalized silane oligomer, and 0.1-0.5 parts of defoamer. Component B is made from raw materials comprising the following parts by weight: 80-100 parts of methylhexahydrophthalic anhydride, 0.5-2.0 parts of zinc acetylacetonate; The mixing weight ratio of component A to component B is 100:54-55.

2. The flame-retardant electrical insulating adhesive according to claim 1, characterized in that, Component A is made from raw materials comprising the following parts by weight: 95-105 parts of bisphenol A type epoxy resin, 15-20 parts of polycaprolactone diol, 35-45 parts of aluminum diethylphosphinic acid, 5-8 parts of zinc borate, 1.0-2.0 parts of epoxy-functionalized silane oligomer, and 0.2-0.4 parts of defoamer. Component B is made from raw materials comprising the following parts by weight: 85-95 parts of methylhexahydrophthalic anhydride, 0.8-1.2 parts of zinc acetylacetonate.

3. The flame-retardant electrical insulating adhesive according to claim 1, characterized in that, The epoxy-functionalized silane oligomer has an average degree of polymerization of 3-10, and the defoamer is selected from polyether-modified polysiloxane defoamers.

4. The flame-retardant electrical insulating adhesive according to claim 3, characterized in that, The method for preparing the epoxy-functionalized silane oligomer includes: γ-glycidoxypropyltrimethoxysilane was mixed with methanol, and an aqueous solution containing formic acid was added dropwise. After the addition was completed at below 50°C, the mixture was heated to 65°C and refluxed for 4-8 hours. Byproducts were removed by rotary evaporation under reduced pressure at 85-95°C to obtain the epoxy-functionalized silane oligomer. Wherein, the molar ratio of γ-glycidoxypropyltrimethoxysilane to methanol is 1.0:1.5-2.5; the molar ratio of γ-glycidoxypropyltrimethoxysilane to water is 1.0:0.8-1.2; and the molar ratio of γ-glycidoxypropyltrimethoxysilane to formic acid is 1.0:0.002-0.

006.

5. The flame-retardant electrical insulating adhesive according to claim 1, characterized in that, Component A is prepared through a melt coating and hot dilution process, including the following steps: The polycaprolactone diol, aluminum diethylphosphinate, zinc borate, and epoxy-functionalized silane oligomer are mixed and heated to 80-90°C. The aluminum diethylphosphinate and zinc borate are then surface-wetted and coated with the molten polycaprolactone diol to obtain a filler pre-dispersion. Maintaining the temperature at 80-90℃, the bisphenol A type epoxy resin preheated to 60-70℃ is added to the filler pre-dispersion, and hot dilution and dispersion are carried out to obtain a resin mixture. The resin mixture is defoamed under vacuum conditions, cooled to below 50°C, and the defoamer is added and mixed evenly to obtain component A.

6. The flame-retardant electrical insulating adhesive according to claim 5, characterized in that, The stirring linear velocity during the melt coating process is 15-20 m / s, and the stirring time is 30-45 minutes; the stirring linear velocity during the hot dilution process is 15-20 m / s, and the stirring time is 20-30 minutes.

7. The flame-retardant electrical insulating adhesive according to claim 1, characterized in that, The preparation method of component B includes the following steps: The methylhexahydrophthalic anhydride was heated to 45-55°C, and the zinc acetylacetone was added. The mixture was stirred until it was clear and transparent, cooled, and filtered to obtain component B.

8. The flame-retardant electrical insulating adhesive according to claim 1, characterized in that, The flame-retardant electrical insulating adhesive is prepared by the following method: Component A is heated to 60-70℃ and melted into a fluid. It is then mixed with component B in a specific ratio and degassed under vacuum to obtain a mixed adhesive. The mixed adhesive is injected into a mold or device and cured by heating to obtain the flame-retardant electrical insulating adhesive.

9. The flame-retardant electrical insulating adhesive according to claim 8, characterized in that, The heat curing process includes: Maintain a constant temperature of 70-90℃ for 1-3 hours, 110-130℃ for 1-3 hours, and 140-160℃ for 1-4 hours.

10. The application of the flame-retardant electrical insulating adhesive according to any one of claims 1 to 9 in the potting protection of drive motors, high-voltage transformers or power electronic modules of new energy vehicles.