Epoxy impregnated paper composite insulation material, preparation method and application thereof

Abstract

The application belongs to the technical field of polymer insulating materials, and discloses an epoxy impregnated paper composite insulating material and a preparation method and application thereof.The preparation method of the epoxy impregnated paper composite insulating material comprises the following steps: S1, mixing hexamethylene diisocyanate trimer and bisphenol AF, reacting to obtain a modified hyperbranched polymer; S2, mixing the modified hyperbranched polymer, an epoxy resin and an acid anhydride curing agent, adding a promoter after degassing and stirring, continuing to degas and stir to obtain a pouring mixture; and S3, impregnating insulating paper in the pouring mixture, and performing stage curing to obtain the epoxy impregnated paper composite insulating material.The modified hyperbranched polymer is introduced at the interface between the epoxy resin and the insulating paper, the interface polarization loss and charge accumulation under a high-frequency electric field are inhibited, the rigidity and thermal stability of the crosslinked network are improved, and the material exhibits excellent breakdown strength and insulating reliability in a wide frequency and wide temperature range.

Description

Technical Field

[0001] This invention relates to the field of polymer insulating materials technology, specifically to an epoxy resin impregnated paper composite insulating material, its preparation method, and its application. Background Technology

[0002] With the rapid development of flexible DC transmission projects, power electronic equipment generates complex broadband harmonic components during operation, especially on both the AC and DC sides, where high-frequency harmonics of 10kHz and above can be detected, and their amplitudes often exceed conventional design expectations. Under the influence of high-frequency harmonics, insulating materials are more prone to problems such as increased dielectric loss, increased local temperature rise, and accelerated insulation aging, thus adversely affecting the safe and stable operation of power equipment. Therefore, how to improve the service stability of insulating materials under high-frequency harmonic conditions has become an urgent technical problem to be solved in the field of flexible DC insulation.

[0003] Epoxy-impregnated paper composite insulation materials are widely used in high-voltage insulation components due to their good mechanical and electrical insulation properties. These materials are formed by combining an epoxy resin matrix and cellulose insulating paper, belonging to a typical multiphase composite insulation system. Compared with single-resin materials, they not only contain the resin matrix structure but also numerous heterogeneous interfaces between the resin and the insulating paper, making their performance evolution under high-frequency electric fields more complex.

[0004] To address the performance degradation of epoxy insulating materials under high-frequency conditions, existing technologies primarily focus on modifying the epoxy resin itself. For example, introducing inorganic fillers, fluorinated components, rigid segments, or adjusting the curing system can reduce dielectric loss, improve heat resistance, and enhance breakdown strength. These methods can improve the electrothermal properties of the resin to some extent and are currently common improvement techniques. However, these approaches mainly focus on the performance control of the epoxy resin itself, with little attention paid to the synergistic design of the structure and performance of the interface region between the epoxy resin and the insulating paper.

[0005] In fact, during the preparation of epoxy-impregnated paper composite insulation materials, the surface of the cellulose insulating paper has a certain limiting effect on the diffusion and cross-linking reaction of resin molecules, easily leading to the formation of a non-uniform structure near the interface that differs from the bulk phase region. The epoxy network near the fiber surface has a relatively low degree of cross-linking, potentially retaining more free segments, suspended segments, and polar groups. Simultaneously, cellulose itself contains a large number of hydroxyl groups. Therefore, the aforementioned interface region is more prone to polarization loss and localized heating under high-frequency electric fields, thus exacerbating the thermal-electric coupling degradation of the material and becoming a significant weak point in the performance decline of the composite insulation material.

[0006] In summary, there is an urgent need to propose a design method for composite insulation materials oriented towards epoxy-insulating paper heterogeneous interfaces. By synergistically regulating the charge migration behavior and cross-linked network structure of the interface region, the structural uniformity of the interface region can be improved, and the interface polarization loss and charge accumulation can be reduced. This would fundamentally enhance the withstand voltage, heat resistance, and long-term operational reliability of traditional epoxy-impregnated paper composite insulation materials under complex high-frequency electric field environments, providing solid technical support for the safe and stable operation of flexible DC transmission systems. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide an epoxy-impregnated paper composite insulating material, its preparation method, and its application.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing an epoxy-impregnated paper composite insulating material, comprising the following steps: S1. Hexamethylene diisocyanate trimer and bisphenol AF are mixed and reacted to obtain a modified hyperbranched polymer; the mass ratio of the hexamethylene diisocyanate trimer to the bisphenol AF is (3.75-5.4):1; S2. The modified hyperbranched polymer, epoxy resin, and anhydride curing agent are mixed, and after degassing and stirring, an accelerator is added. Degassing and stirring are continued to obtain a casting mixture; the mass ratio of the modified hyperbranched polymer to the epoxy resin is (0.05-0.25):1. S3. The insulating paper is impregnated in the casting mixture and cured in stages to obtain the epoxy resin impregnated paper composite insulating material.

[0009] This invention introduces a modified hyperbranched polymer formed by the reaction of hexamethylene diisocyanate trimer and bisphenol AF between an epoxy resin matrix and cellulose insulating paper. This constructs a multi-synergistic mechanism of "interfacial chemical bonding, charge transport regulation, network rigidity enhancement, and internal stress homogenization," systematically solving the performance degradation problem of epoxy-impregnated paper composite insulation materials under high-frequency complex electric fields. Specifically, the modified hyperbranched polymer synthesized in this invention carries active -NCO groups at its ends. These groups can chemically graft with the abundant hydroxyl groups on the surface of the cellulose insulating paper, forming a strong covalent bond at the resin-paper interface. This design fundamentally eliminates the weak interfacial layer formed by traditional physical bonding (such as hydrogen bonds or van der Waals forces), significantly improving the bonding between the resin matrix and the insulating paper, enhancing the continuity and uniformity of the interfacial microstructure, and reducing interfacial defects that act as sources of polarization loss and charge injection.

[0010] Secondly, the bisphenol AF structural units introduced into the modified hyperbranched polymer molecular chain synthesized in this invention contain highly electronegative fluorine-containing groups (-CF3). The introduction of fluorine reduces the overall dielectric constant of the material and creates deep trap energy levels within the material, effectively capturing migrating charge carriers and suppressing the accumulation and migration of space charge. This mechanism weakens the additional dielectric losses caused by orientation polarization and interface polarization under high-frequency electric fields and alleviates the resulting local heating and electric field distortion, thereby significantly improving the breakdown field strength and insulation stability of the material.

[0011] Furthermore, the rigid cyclic backbone (isocyanurate ring) provided by the hexamethylene diisocyanate trimer of the present invention can participate in the construction of the curing crosslinking network of epoxy resin. The introduction of this rigid structure improves the overall rigidity and glass transition temperature of the crosslinking system, suppresses the excessive thermal motion of molecular chain segments under the action of high temperature and high frequency alternating electric field, reduces the dielectric loss caused by chain segment relaxation, and enhances the structural retention ability of the material under combined thermal and electrical stress.

[0012] Furthermore, the polymer synthesized in this invention has a hyperbranched topology, with inherent vacancies and numerous branching sites within its molecules. This special structure, in conjunction with a multi-stage curing process, can provide the necessary structural relaxation space during the formation of the epoxy network, promote the uniform growth of the crosslinked network, effectively alleviate the internal stress concentration caused by curing shrinkage and thermal shrinkage, reduce microcracks and defects within the material, and further improve the long-term service reliability of the material.

[0013] In a preferred embodiment of the preparation method of the epoxy-impregnated paper composite insulating material of the present invention, in step S1, the modified hyperbranched polymer has the structural formula shown in formula (I): Formula (I).

[0014] In a preferred embodiment of the preparation method of the epoxy-impregnated paper composite insulating material of the present invention, in step S1, the mass ratio of the hexamethylene diisocyanate trimer to the bisphenol AF is (3.75-5):1.

[0015] In the preparation method of the epoxy-impregnated paper composite insulation material of the present invention, controlling the mass ratio of hexamethylene diisocyanate trimer and bisphenol AF within the above-mentioned range can better achieve the optimal balance between rigidity enhancement, charge trap density, and interfacial reactivity. If the ratio is too low, the rigid segments and fluorine content in the polymer will be too high, which will lead to increased brittleness of the system, uneven cross-linking, stress concentration at the interface, and a significant decrease in high-frequency breakdown strength. If the ratio is too high, the proportion of flexible segments will be too large, the cross-linking density will be insufficient, the thermal motion of the molecular chains will be intensified, and the heat resistance and high-temperature breakdown strength of the material will deteriorate.

[0016] Preferably, in step S1, the mass ratio of the hexamethylene diisocyanate trimer to the bisphenol AF is 5:1.

[0017] In a preferred embodiment of the preparation method of the epoxy resin impregnated paper composite insulating material of the present invention, in step S1, the reaction conditions are as follows: under a protective atmosphere, the temperature is first raised to 40℃-60℃, and then raised to 70℃-90℃ for 3h-6h.

[0018] Preferably, in step S1, the reaction conditions are as follows: under a nitrogen atmosphere, the temperature is first raised to 50°C, and then raised to 80°C for 4 hours.

[0019] In a preferred embodiment of the preparation method of the epoxy-impregnated paper composite insulating material of the present invention, in step S2, the mass ratio of the modified hyperbranched polymer to the epoxy resin is (0.1-0.15):1.

[0020] In the preparation method of the epoxy resin impregnated paper composite insulation material of the present invention, the mass ratio of modified hyperbranched polymer and epoxy resin is controlled within the above-mentioned range, which can more effectively enrich the modified hyperbranched polymer at the interface and participate in network construction, while not destroying the excellent insulation performance of the epoxy resin matrix.

[0021] Preferably, in step S2, the mass ratio of the modified hyperbranched polymer to the epoxy resin is 0.15:1.

[0022] In a preferred embodiment of the preparation method of the epoxy resin impregnated paper composite insulating material of the present invention, in step S2, the mass ratio of the epoxy resin to the anhydride curing agent and accelerator is 100:(70-90):(0.3-0.6).

[0023] Preferably, in step S2, the mass ratio of the epoxy resin to the anhydride curing agent and accelerator is 100:90:0.5.

[0024] In a preferred embodiment of the preparation method of the epoxy-impregnated paper composite insulating material of the present invention, in step S2, the epoxy resin includes bisphenol A type epoxy resin.

[0025] In a preferred embodiment of the preparation method of the epoxy resin impregnated paper composite insulating material of the present invention, in step S2, the anhydride curing agent includes at least one of tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, and methylnadic anhydride.

[0026] Preferably, in step S2, the anhydride curing agent includes methyltetrahydrophthalic anhydride.

[0027] In a preferred embodiment of the preparation method of the epoxy-impregnated paper composite insulating material of the present invention, in step S2, the accelerator includes N,N-dimethylbenzylamine and / or 2,4,6-tris(dimethylaminomethyl)phenol.

[0028] Preferably, in step S2, the promoter includes N,N-dimethylbenzylamine.

[0029] In a preferred embodiment of the preparation method of the epoxy resin impregnated paper composite insulating material of the present invention, in step S2, the temperature of the degassing and stirring is 100℃-140℃ and the time is 2h-5h; the time for continuing the degassing and stirring is 5min-20min.

[0030] Preferably, in step S2, the temperature of the degassing and stirring is 120°C and the time is 3 hours; the time for continuing the degassing and stirring is 10 minutes.

[0031] In a preferred embodiment of the preparation method of the epoxy-impregnated paper composite insulating material of the present invention, in step S3, the staged curing includes a first stage curing, a second stage curing, and a third stage curing; the temperature of the first stage curing is 70℃-100℃, and the time is 4h-6h; the temperature of the second stage curing is 120℃-150℃, and the time is 6h-10h; the temperature of the third stage curing is 160℃-180℃, and the time is 1h-3h.

[0032] In the preparation method of the epoxy resin impregnated paper composite insulation material of the present invention, the above-mentioned three-stage curing process can enable the insulation material to gradually form a uniform, dense and low internal stress cross-linked network inside the insulation paper, effectively avoiding micro-cracks and interface debonding caused by excessive curing, significantly enhancing the interfacial bonding strength of resin-fiber, reducing internal defects and stress concentration points, and comprehensively improving the long-term reliability of the material.

[0033] Preferably, in step S3, the curing temperature of the first stage is 80°C and the curing time is 5 hours; the curing temperature of the second stage is 130°C and the curing time is 8 hours; and the curing temperature of the third stage is 170°C and the curing time is 2 hours.

[0034] Secondly, the present invention provides an epoxy-impregnated paper composite insulating material prepared by the aforementioned preparation method.

[0035] Thirdly, the present invention provides the application of the epoxy-impregnated paper composite insulating material in high-voltage power bushings.

[0036] Compared with existing technologies, the beneficial effects of this invention are as follows: The epoxy-impregnated paper composite insulation material prepared by this invention, through the synergistic design of molecular structure and interface engineering, can maintain high AC breakdown strength under extreme high-frequency and high-temperature conditions, and exhibits comprehensive effectiveness in suppressing interface polarization, regulating charge transport, enhancing network thermal stability, and releasing internal stress. This provides a material solution for high-voltage insulation components used in flexible DC transmission that combines excellent high-frequency withstand voltage performance and long-term operational reliability. Firstly, by introducing a modified hyperbranched polymer with a suitable ratio of flexible to rigid segments, this invention optimizes the interfacial chemical bonding and dielectric matching characteristics between the resin matrix and the insulating paper fibers, significantly weakening the interface polarization effect and space charge accumulation under high-frequency electric fields, thereby delaying the breakdown process of the insulation material and improving high-frequency withstand voltage stability. Secondly, the cross-linked network constructed by this invention has a reasonable trap energy level distribution and charge carrier migration suppression capability, which can effectively capture and dissipate injected charges, suppress local electric field distortion, and reduce the probability of electrical tree initiation, thereby enhancing the withstand voltage lifetime and insulation reliability of the material under high electric field and high-frequency conditions. Furthermore, this invention utilizes a modified hyperbranched structure constructed from fluorinated monomers and isocyanate trimers, which increases the glass transition temperature and thermal decomposition initiation temperature of the resin matrix. Simultaneously, the introduction of moderately rigid segments into the crosslinking network suppresses the thermal motion and relaxation behavior of molecular chains at high temperatures, ensuring stable insulation performance across a wide temperature range. In addition, this invention employs a stepped temperature curing process, allowing the resin to gradually form a uniform, dense, and low-stress crosslinking network within the insulating paper. This effectively avoids microcracks and interfacial debonding caused by excessively rapid curing, significantly enhancing the resin-fiber interfacial bonding strength, reducing internal defects and stress concentration points, and comprehensively improving the long-term reliability of the material. Detailed Implementation

[0037] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0038] The following description, in conjunction with specific embodiments, illustrates the practical effects of the present invention.

[0039] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials, reagents, equipment, etc. used are all commercially available unless otherwise specified.

[0040] The raw materials used in the following embodiments and comparative examples are described below, but are not limited to these materials: Hexamethylene diisocyanate trimer was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Bisphenol AF was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Bisphenol A was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. E51 epoxy resin was purchased from Shanghai Xiongrun Resin Co., Ltd. CT5531 epoxy resin was purchased from Huntsman Corporation, USA. The insulating paper was purchased from Mingke Paper Co., Ltd.

[0041] Example 1: This embodiment provides a high-performance epoxy resin impregnated paper composite insulating material for bushings, the preparation method of which includes the following steps: S1. Synthesis of modified hyperbranched polymers 150g of hexamethylene diisocyanate trimer and 30g of bisphenol AF were added to a reaction vessel, nitrogen gas was introduced and the temperature was raised to 50°C and mixed thoroughly. Then the temperature was raised to 80°C and the reaction was carried out for 4 hours to obtain the modified hyperbranched polymer. The mass ratio of hexamethylene diisocyanate trimer to bisphenol AF is 5:1. The specific chemical formula for step S1 is shown in formula (II): Equation (II).

[0042] S2. Preparation of Casting Mixture Take 15g of the modified hyperbranched polymer obtained in step S1, 100g of E51 type epoxy resin and 90g of methyltetrahydrophthalic anhydride (acid anhydride curing agent) and mix them. Degas and stir at 120℃ for 3h. Then add 0.5g of N,N-dimethylbenzylamine (accelerator) and continue to degas and stir for 10min to obtain the casting mixture. The mass ratio of the modified hyperbranched polymer, E51 type epoxy resin, acid anhydride curing agent and accelerator is 15:100:90:0.5.

[0043] S3, Impregnation and Curing The insulating paper is impregnated into the casting mixture prepared in step S2, and then cured using a three-stage curing process: the first stage curing temperature is 80℃ and the curing time is 5h; the second stage curing temperature is 130℃ and the curing time is 8h; the third stage curing temperature is 170℃ and the curing time is 2h. Upon completion, a high-performance epoxy resin impregnated paper composite insulating material for bushings is obtained.

[0044] Example 2: This embodiment provides a high-performance epoxy resin impregnated paper composite insulating material for bushings, the preparation method of which includes the following steps: S1. Synthesis of modified hyperbranched polymers 150g of hexamethylene diisocyanate trimer and 40g of bisphenol AF were added to a reaction vessel, nitrogen gas was introduced and the temperature was raised to 60℃ and mixed thoroughly. Then the temperature was raised to 90℃ and reacted for 5h to obtain the modified hyperbranched polymer. The mass ratio of hexamethylene diisocyanate trimer to bisphenol AF is 3.75:1.

[0045] S2. Preparation of Casting Mixture Take 5g of the modified hyperbranched polymer obtained in step S1, 100g of E51 type epoxy resin and 80g of methyltetrahydrophthalic anhydride (acid anhydride curing agent) and mix them. Degas and stir at 140℃ for 5h. Then add 0.4g of N,N-dimethylbenzylamine (accelerator) and continue to degas and stir for 20min to obtain the casting mixture. The mass ratio of the modified hyperbranched polymer, E51 type epoxy resin, acid anhydride curing agent and accelerator is 5:100:80:0.4.

[0046] S3, Impregnation and Curing The insulating paper is impregnated into the casting mixture prepared in step S2, and then cured using a three-stage curing process: the first stage curing temperature is 80℃ and the curing time is 5h; the second stage curing temperature is 130℃ and the curing time is 8h; the third stage curing temperature is 170℃ and the curing time is 2h. Upon completion, a high-performance epoxy resin impregnated paper composite insulating material for bushings is obtained.

[0047] Example 3: This embodiment provides a high-performance epoxy resin impregnated paper composite insulating material for bushings, the preparation method of which includes the following steps: S1. Synthesis of modified hyperbranched polymers 150g of hexamethylene diisocyanate trimer and 30g of bisphenol AF were added to a reaction vessel, nitrogen gas was introduced and the temperature was raised to 50°C and mixed thoroughly. Then the temperature was raised to 80°C and the reaction was carried out for 4 hours to obtain the modified hyperbranched polymer. The mass ratio of hexamethylene diisocyanate trimer to bisphenol AF is 5:1.

[0048] S2. Preparation of Casting Mixture Take 15g of the modified hyperbranched polymer obtained in step S1, 100g of E51 type epoxy resin and 90g of methyl nadic anhydride (anhydride curing agent) and mix them. Degas and stir at 120℃ for 3h. Then add 0.5g of 2,4,6-tris(dimethylaminomethyl)phenol (accelerator) and continue to degas and stir for 10min to obtain the casting mixture. The mass ratio of the modified hyperbranched polymer, E51 type epoxy resin, acid anhydride curing agent and accelerator is 15:100:90:0.5.

[0049] S3, Impregnation and Curing The insulating paper is impregnated into the casting mixture prepared in step S2, and then cured using a three-stage curing process: the first stage curing temperature is 80℃ and the curing time is 5h; the second stage curing temperature is 130℃ and the curing time is 8h; the third stage curing temperature is 170℃ and the curing time is 2h. Upon completion, a high-performance epoxy resin impregnated paper composite insulating material for bushings is obtained.

[0050] Example 4: This embodiment provides a high-performance epoxy resin impregnated paper composite insulating material for bushings, the preparation method of which includes the following steps: S1. Synthesis of modified hyperbranched polymers 150g of hexamethylene diisocyanate trimer and 30g of bisphenol AF were added to a reaction vessel, nitrogen gas was introduced and the temperature was raised to 50°C and mixed thoroughly. Then the temperature was raised to 80°C and the reaction was carried out for 4 hours to obtain the modified hyperbranched polymer. The mass ratio of hexamethylene diisocyanate trimer to bisphenol AF is 5:1.

[0051] S2. Preparation of Casting Mixture Take 15g of the modified hyperbranched polymer obtained in step S1, 100g of E51 type epoxy resin and 90g of methyltetrahydrophthalic anhydride (acid anhydride curing agent) and mix them. Degas and stir at 120℃ for 3h. Then add 0.5g of N,N-dimethylbenzylamine (accelerator) and continue to degas and stir for 10min to obtain the casting mixture. The mass ratio of the modified hyperbranched polymer, E51 type epoxy resin, acid anhydride curing agent and accelerator is 15:100:90:0.5.

[0052] S3, Impregnation and Curing The insulating paper is impregnated into the casting mixture prepared in step S2, and then cured using a three-stage curing process: the first stage curing temperature is 100℃ and the curing time is 4 hours; the second stage curing temperature is 150℃ and the curing time is 10 hours; the third stage curing temperature is 180℃ and the curing time is 1 hour. Upon completion, a high-performance epoxy resin impregnated paper composite insulating material for bushings is obtained.

[0053] Example 5: This embodiment provides a high-performance epoxy resin impregnated paper composite insulating material for bushings, the only difference between its preparation method and that of Embodiment 1 is: In step S1, the mass of hexamethylene diisocyanate trimer is 162g, that is, the mass ratio of hexamethylene diisocyanate trimer to bisphenol AF is 5.4:1; The remaining steps are exactly the same as in Example 1.

[0054] Example 6: This embodiment provides a high-performance epoxy resin impregnated paper composite insulating material for bushings, the only difference between its preparation method and that of Embodiment 1 is: In step S2, 10g of the modified hyperbranched polymer obtained in step S1 is taken, that is, the mass ratio of the modified hyperbranched polymer, E51 type epoxy resin, acid anhydride curing agent, and accelerator is 10:100:90:0.5. The remaining steps are exactly the same as in Example 1.

[0055] Example 7: This embodiment provides a high-performance epoxy resin impregnated paper composite insulating material for bushings, the only difference between its preparation method and that of Embodiment 1 is: In step S2, 25g of the modified hyperbranched polymer obtained in step S1 is taken, that is, the mass ratio of the modified hyperbranched polymer, E51 type epoxy resin, acid anhydride curing agent, and accelerator is 25:100:90:0.5. The remaining steps are exactly the same as in Example 1.

[0056] Comparative Example 1: This comparative example provides a high-performance epoxy resin-impregnated paper composite insulating material for bushings, the preparation method of which includes the following steps: S1. Synthesis of modified hyperbranched polymers 150g of hexamethylene diisocyanate trimer and 150g of bisphenol AF were added to a reaction vessel, nitrogen gas was introduced and the temperature was raised to 50°C and mixed thoroughly. Then the temperature was raised to 80°C and the reaction was carried out for 4 hours to obtain the modified hyperbranched polymer. The mass ratio of hexamethylene diisocyanate trimer to bisphenol AF is 1:1.

[0057] S2. Preparation of Casting Mixture Take 15g of the modified hyperbranched polymer obtained in step S1, 100g of E51 type epoxy resin and 90g of methyltetrahydrophthalic anhydride (acid anhydride curing agent) and mix them. Degas and stir at 120℃ for 3h. Then add 0.5g of N,N-dimethylbenzylamine (accelerator) and continue to degas and stir for 10min to obtain the casting mixture. The mass ratio of the modified hyperbranched polymer, E51 type epoxy resin, acid anhydride curing agent and accelerator is 15:100:90:0.5.

[0058] S3, Impregnation and Curing The insulating paper is impregnated into the casting mixture prepared in step S2, and then cured using a three-stage curing process: the first stage curing temperature is 80℃ and the curing time is 5h; the second stage curing temperature is 130℃ and the curing time is 8h; the third stage curing temperature is 170℃ and the curing time is 2h. Upon completion, a high-performance epoxy resin impregnated paper composite insulating material for bushings is obtained.

[0059] Comparative Example 2: This comparative example provides a high-performance epoxy resin-impregnated paper composite insulating material for bushings, the preparation method of which includes the following steps: S1. Synthesis of modified hyperbranched polymers 150g of hexamethylene diisocyanate trimer and 18.75g of bisphenol AF were added to a reaction vessel, nitrogen gas was introduced and the temperature was raised to 50°C and mixed thoroughly. Then the temperature was raised to 80°C and reacted for 4 hours to obtain the modified hyperbranched polymer. The mass ratio of hexamethylene diisocyanate trimer to bisphenol AF is 8:1.

[0060] S2. Preparation of Casting Mixture Take 15g of the modified hyperbranched polymer obtained in step S1, 100g of E51 type epoxy resin and 90g of methyltetrahydrophthalic anhydride (acid anhydride curing agent) and mix them. Degas and stir at 120℃ for 3h. Then add 0.5g of N,N-dimethylbenzylamine (accelerator) and continue to degas and stir for 10min to obtain the casting mixture. The mass ratio of the modified hyperbranched polymer, E51 type epoxy resin, acid anhydride curing agent and accelerator is 15:100:90:0.5.

[0061] S3, Impregnation and Curing The insulating paper is impregnated into the casting mixture prepared in step S2, and then cured using a three-stage curing process: the first stage curing temperature is 80℃ and the curing time is 5h; the second stage curing temperature is 130℃ and the curing time is 8h; the third stage curing temperature is 170℃ and the curing time is 2h. Upon completion, a high-performance epoxy resin impregnated paper composite insulating material for bushings is obtained.

[0062] Comparative Example 3: This comparative example provides a high-performance epoxy resin-impregnated paper composite insulating material for bushings, the preparation method of which includes the following steps: S1. Synthesis of modified hyperbranched polymers 150g of hexamethylene diisocyanate trimer and 30g of bisphenol A were added to a reaction vessel, nitrogen gas was introduced and the temperature was raised to 50°C and mixed thoroughly. Then the temperature was raised to 80°C and reacted for 4 hours to obtain the modified hyperbranched polymer. The mass ratio of hexamethylene diisocyanate trimer to bisphenol A is 5:1.

[0063] S2. Preparation of Casting Mixture Take 15g of the modified hyperbranched polymer obtained in step S1, 100g of E51 type epoxy resin and 90g of methyltetrahydrophthalic anhydride (acid anhydride curing agent) and mix them. Degas and stir at 120℃ for 3h. Then add 0.5g of N,N-dimethylbenzylamine (accelerator) and continue to degas and stir for 10min to obtain the casting mixture. The mass ratio of the modified hyperbranched polymer, E51 type epoxy resin, acid anhydride curing agent and accelerator is 15:100:90:0.5.

[0064] S3, Impregnation and Curing The insulating paper is impregnated into the casting mixture prepared in step S2, and then cured using a three-stage curing process: the first stage curing temperature is 80℃ and the curing time is 5h; the second stage curing temperature is 130℃ and the curing time is 8h; the third stage curing temperature is 170℃ and the curing time is 2h. Upon completion, a high-performance epoxy resin impregnated paper composite insulating material for bushings is obtained.

[0065] Comparative Example 4: This comparative example provides a high-performance epoxy resin-impregnated paper composite insulating material for bushings, the preparation method of which includes the following steps: S1. Synthesis of modified hyperbranched polymers 150g of hexamethylene diisocyanate trimer and 30g of bisphenol AF were added to a reaction vessel, nitrogen gas was introduced and the temperature was raised to 50°C and mixed thoroughly. Then the temperature was raised to 80°C and the reaction was carried out for 4 hours to obtain the modified hyperbranched polymer. The mass ratio of hexamethylene diisocyanate trimer to bisphenol AF is 5:1.

[0066] S2. Preparation of Casting Mixture Take 40g of the modified hyperbranched polymer obtained in step S1, 100g of E51 type epoxy resin and 90g of methyltetrahydrophthalic anhydride (acid anhydride curing agent) and mix them. Degas and stir at 120℃ for 3h. Then add 0.5g of N,N-dimethylbenzylamine (accelerator) and continue to degas and stir for 10min to obtain the casting mixture. The mass ratio of the modified hyperbranched polymer, E51 type epoxy resin, acid anhydride curing agent and accelerator is 40:100:90:0.5.

[0067] S3, Impregnation and Curing The insulating paper is impregnated into the casting mixture prepared in step S2, and then cured using a three-stage curing process: the first stage curing temperature is 80℃ and the curing time is 5h; the second stage curing temperature is 130℃ and the curing time is 8h; the third stage curing temperature is 170℃ and the curing time is 2h. Upon completion, a high-performance epoxy resin impregnated paper composite insulating material for bushings is obtained.

[0068] Comparative Example 5: This comparative example provides a high-performance epoxy resin-impregnated paper composite insulating material for bushings, the preparation method of which includes the following steps: S1. Synthesis of modified hyperbranched polymers 150g of hexamethylene diisocyanate trimer and 30g of bisphenol AF were added to a reaction vessel, nitrogen gas was introduced and the temperature was raised to 50°C and mixed thoroughly. Then the temperature was raised to 80°C and the reaction was carried out for 4 hours to obtain the modified hyperbranched polymer. The mass ratio of hexamethylene diisocyanate trimer to bisphenol AF is 5:1.

[0069] S2. Preparation of Casting Mixture Take 2g of the modified hyperbranched polymer obtained in step S1, 100g of E51 type epoxy resin and 90g of methyltetrahydrophthalic anhydride (acid anhydride curing agent) and mix them. Degas and stir at 120℃ for 3h. Then add 0.5g of N,N-dimethylbenzylamine (accelerator) and continue to degas and stir for 10min to obtain the casting mixture. The mass ratio of the modified hyperbranched polymer, E51 type epoxy resin, acid anhydride curing agent and accelerator is 2:100:90:0.5.

[0070] S3, Impregnation and Curing The insulating paper is impregnated into the casting mixture prepared in step S2, and then cured using a three-stage curing process: the first stage curing temperature is 80℃ and the curing time is 5h; the second stage curing temperature is 130℃ and the curing time is 8h; the third stage curing temperature is 170℃ and the curing time is 2h. Upon completion, a high-performance epoxy resin impregnated paper composite insulating material for bushings is obtained.

[0071] Comparative Example 6: This comparative example provides a high-performance epoxy resin-impregnated paper composite insulating material for bushings, the preparation method of which includes the following steps: S1. Preparation of casting mixture Take 15g of CT5531 epoxy resin, 100g of E51 epoxy resin and 90g of methyltetrahydrophthalic anhydride (anhydride curing agent) and mix them. Degas and stir at 120℃ for 3h. Then add 0.5g of N,N-dimethylbenzylamine (accelerator) and continue to degas and stir for 10min to obtain the casting mixture. The mass ratio of CT5531 epoxy resin, E51 epoxy resin, acid anhydride curing agent and accelerator is 15:100:90:0.5.

[0072] S2, Impregnation and Curing The insulating paper is impregnated into the casting mixture prepared in step S1, and then cured using a three-stage curing process: the first stage curing temperature is 80℃ and the curing time is 5h; the second stage curing temperature is 130℃ and the curing time is 8h; the third stage curing temperature is 170℃ and the curing time is 2h. Upon completion, a high-performance epoxy resin impregnated paper composite insulating material for bushings is obtained.

[0073] Comparative Example 7: This comparative example provides a high-performance epoxy resin-impregnated paper composite insulating material for bushings, the preparation method of which includes the following steps: S1. Preparation of casting mixture Take 100g of E51 type epoxy resin and 90g of methyltetrahydrophthalic anhydride (acid anhydride curing agent), mix them, degas and stir at 120℃ for 3h, then add 0.5g of N,N-dimethylbenzylamine (accelerator), continue to degas and stir for 10min to obtain the casting mixture; The mass ratio of E51 type epoxy resin, acid anhydride curing agent and accelerator is 100:90:0.5.

[0074] S2, Impregnation and Curing The insulating paper is impregnated into the casting mixture prepared in step S1, and then cured using a three-stage curing process: the first stage curing temperature is 80℃ and the curing time is 5h; the second stage curing temperature is 130℃ and the curing time is 8h; the third stage curing temperature is 170℃ and the curing time is 2h. Upon completion, a high-performance epoxy resin impregnated paper composite insulating material for bushings is obtained.

[0075] Comparative Example 8: This comparative example provides a high-performance epoxy resin-impregnated paper composite insulating material for bushings, the preparation method of which includes the following steps: S1. Synthesis of modified hyperbranched polymers 150g of hexamethylene diisocyanate trimer and 30g of bisphenol AF were added to a reaction vessel, nitrogen gas was introduced for protection, the temperature was raised to 50℃ and mixed thoroughly, and then the temperature was raised to 80℃ and reacted for 4 hours to obtain the modified hyperbranched polymer. The mass ratio of hexamethylene diisocyanate trimer to bisphenol AF is 5:1.

[0076] S2. Preparation of casting mixture Take 15g of the modified hyperbranched polymer obtained in step S1, 100g of E51 type epoxy resin and 90g of methyltetrahydrophthalic anhydride (acid anhydride curing agent) and mix them. Degas and stir at 120℃ for 3h. Then add 0.5g of N,N-dimethylbenzylamine (accelerator) and continue to degas and stir for 10min to obtain the casting mixture. The mass ratio of the modified hyperbranched polymer, E51 type epoxy resin, acid anhydride curing agent and accelerator is 15:100:90:0.5.

[0077] S3, Impregnation and Curing The insulating paper is impregnated into the casting mixture prepared in step S2, and then directly cured at 150°C for 16 hours. Upon completion, a high-performance epoxy resin impregnated paper composite insulating material for bushings is obtained.

[0078] Test example: This test example demonstrates the AC breakdown strength test of the high-performance epoxy-impregnated paper composite insulation material for bushings in the above embodiments and comparative examples.

[0079] Test standard: The test is conducted in accordance with the national standard GB / T 1408.1-2016 "Test methods for electrical strength of insulating materials - Part 1: Test at power frequency".

[0080] Test method: The AC breakdown strength of the samples was tested at different frequencies (50 Hz, 10 kHz, 20 kHz, 30 kHz, test temperature 25 ℃) and at different temperatures (25 ℃, 60 ℃, 100 ℃, 120 ℃, test frequency 50 Hz). The specific test results are shown in Table 1 and Table 2.

[0081] Table 1. Test results of AC breakdown strength of high-performance epoxy-impregnated paper composite insulation materials for bushings in the examples and comparative examples at different frequencies. Table 2. AC breakdown strength test results of high-performance epoxy-impregnated paper composite insulation materials for bushings in the examples and comparative examples at different temperatures. As can be seen from Tables 1 and 2, the epoxy-impregnated paper composite insulating materials prepared in each embodiment of the present invention exhibit significantly better AC breakdown strength than the comparative examples under wide frequency range (50Hz-30kHz) and wide temperature range (25℃-120℃). Especially under extreme conditions of high frequency (30kHz) and high temperature (120℃), the breakdown strength attenuation of the materials in the embodiments is much smaller than that in the comparative examples. This fully demonstrates that the present invention, through molecular structure design and process optimization, successfully suppresses the degradation of the insulation performance of the material under high-frequency electric fields and high-temperature environments.

[0082] In contrast, the performance of each comparative example deteriorated to varying degrees due to deviations in raw material ratios, monomer selection, or process regimes. Specifically, Comparative Example 1, due to excessive bisphenol AF, had too many rigid segments in the modified hyperbranched polymer, resulting in increased system brittleness and uneven crosslinking. This led to severe interfacial polarization at high frequencies and temperatures, with a breakdown strength of only 18 kV / mm at 30 kHz, dropping to 32 kV / mm at 120 °C. Comparative Example 2, due to insufficient bisphenol AF, had an excessively high proportion of flexible segments in the modified hyperbranched polymer, resulting in insufficient crosslinking density and intensified molecular chain thermal motion at high temperatures, leading to a significantly lower breakdown strength than the example. Comparative Example 3, due to the improved hydrophobicity and heat resistance resulting from the lack of fluorine atoms, weakened the interfacial bonding between the resin matrix and the insulating paper, increased dielectric loss, and significantly deteriorated high-frequency and high-temperature performance. Comparative Example 4, with excessively high addition of modified hyperbranched polymer, had excessively high system viscosity, uneven impregnation, and numerous internal defects. Simultaneously, the excessive flexible segments disrupted the rigidity of the overall crosslinking network, leading to a comprehensive decrease in breakdown strength. Comparative Example 5, due to the modification... The insufficient content of hyperbranched polymer resulted in weak toughening and modification effects on epoxy resin, high system brittleness, and insufficient interfacial bonding with insulating paper, leading to limited improvement in high-frequency and high-temperature performance. Comparative Example 6, due to the significant difference in molecular structure between CT5531 and the modified hyperbranched polymer designed in this invention, struggled to form an ideal chemical bond and interfacial transition layer between the resin and insulating paper, resulting in a significantly lower breakdown strength at high frequencies compared to the examples. Comparative Example 7, a pure epoxy-anhydride system, lacked the stress buffering and interfacial compatibilization effects of flexible segments, resulting in high material brittleness, concentrated internal stress, and poor compatibility with insulating paper, leading to low breakdown strength at both high frequencies and high temperatures. Comparative Example 8 failed to form a staged optimized cross-linking network, resulting in excessively rapid resin curing, residual stress and unreacted groups, and microscopic voids at the impregnation interface between the insulating paper and resin, causing its breakdown strength to be lower than that of the examples under all test conditions.

[0083] In summary, this invention synthesizes a modified hyperbranched polymer with a suitable ratio of flexible to rigid segments by precisely controlling the molar ratio of hexamethylene diisocyanate trimer to bisphenol AF. Furthermore, by optimizing the mass ratio of this polymer to epoxy resin, an optimal balance is achieved between the resin system's viscosity, reactivity, and crosslinking density. Simultaneously, this invention employs a three-stage curing process—"first-stage curing-second-stage curing-third-stage curing"—to promote the gradual formation of a uniform, dense, and low-stress crosslinking network within the insulating paper. This effectively enhances the resin-fiber interfacial bonding, suppresses polarization losses under high-frequency electric fields and molecular chain thermal motion under high-temperature conditions, thereby enabling the material to exhibit higher AC breakdown strength and excellent insulation stability over a wide frequency (50Hz-30kHz) and temperature (25℃-120℃) range. This meets the long-term reliable operation requirements of high-voltage bushings and other power equipment under complex operating conditions.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an epoxy-impregnated paper composite insulating material, characterized in that, Includes the following steps: S1. Hexamethylene diisocyanate trimer and bisphenol AF are mixed and reacted to obtain a modified hyperbranched polymer; the mass ratio of the hexamethylene diisocyanate trimer to the bisphenol AF is (3.75-5.4):1; S2. The modified hyperbranched polymer, epoxy resin, and anhydride curing agent are mixed, and after degassing and stirring, an accelerator is added. Degassing and stirring are continued to obtain a casting mixture; the mass ratio of the modified hyperbranched polymer to the epoxy resin is (0.05-0.25):

1. S3. The insulating paper is impregnated in the casting mixture and cured in stages to obtain the epoxy resin impregnated paper composite insulating material.

2. The preparation method of the epoxy resin impregnated paper composite insulating material as described in claim 1, characterized in that, In step S1, the reaction conditions are as follows: under a protective atmosphere, the temperature is first raised to 40℃-60℃, and then raised to 70℃-90℃ for 3h-6h.

3. The method for preparing the epoxy-impregnated paper composite insulating material as described in claim 1, characterized in that, In step S2, the mass ratio of the epoxy resin to the anhydride curing agent and accelerator is 100:(70-90):(0.3-0.6).

4. The method for preparing the epoxy-impregnated paper composite insulating material as described in claim 1, characterized in that, In step S2, the epoxy resin includes bisphenol A type epoxy resin.

5. The method for preparing the epoxy-impregnated paper composite insulating material as described in claim 1, characterized in that, In step S2, the anhydride curing agent includes at least one of tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, and methylnadic anhydride.

6. The method for preparing the epoxy-impregnated paper composite insulating material as described in claim 1, characterized in that, In step S2, the promoter includes N,N-dimethylbenzylamine and / or 2,4,6-tris(dimethylaminomethyl)phenol.

7. The method for preparing the epoxy-impregnated paper composite insulating material as described in claim 1, characterized in that, In step S2, the temperature of the degassing and stirring is 100℃-140℃, and the time is 2h-5h; the time for continuing the degassing and stirring is 5min-20min.

8. The method for preparing the epoxy-impregnated paper composite insulating material as described in claim 1, characterized in that, In step S3, the staged curing includes a first stage of curing, a second stage of curing, and a third stage of curing; the temperature of the first stage of curing is 70℃-100℃, and the time is 4h-6h; the temperature of the second stage of curing is 120℃-150℃, and the time is 6h-10h; the temperature of the third stage of curing is 160℃-180℃, and the time is 1h-3h.

9. The epoxy-impregnated paper composite insulating material prepared by any one of the preparation methods described in claims 1-8.

10. The application of the epoxy-impregnated paper composite insulating material according to claim 9 in high-voltage power bushings.

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