A high-toughness, high DC breakdown strength and high glass transition temperature all-organic epoxy composite material and a preparation method thereof

Abstract

This invention belongs to the field of functional composite materials technology and discloses an all-organic epoxy composite material with high toughness, high DC breakdown strength, and high glass transition temperature, as well as its preparation method. The components include epoxy resin, carboxyl-terminated liquid nitrile rubber, curing agent, accelerator, and polyvinylcarbazole. The carboxyl-terminated liquid nitrile rubber content is 8 wt%~12 wt% of the epoxy resin mass, the curing agent content is 78 wt%~82 wt% of the epoxy resin mass, the accelerator content is 0.8 wt%~1.2 wt% of the epoxy resin mass, and the polyvinylcarbazole content is 0.6 wt%~1.0 wt% of the epoxy resin mass. The all-organic epoxy composite material obtained by this invention exhibits improved tensile strength, flexural strength, and DC breakdown strength compared to pure EP, while maintaining a high glass transition temperature. This invention provides theoretical and experimental support for developing all-organic epoxy composite materials that balance toughness, thermal stability, and insulation properties.

Description

Technical Field

[0001] This invention belongs to the field of functional composite materials technology, and particularly relates to an all-organic epoxy composite material with high toughness, high DC breakdown strength and high glass transition temperature and its preparation method. Background Technology

[0002] High-voltage, high-power electronic equipment supports the localization of new power systems and high-end equipment, with broad prospects, such as flexible DC transmission technology, IGBTs, dry-type reactors, and wide-bandgap devices. In power equipment such as solid-state transformers and dry-type reactors, epoxy resin is widely used as a casting insulation material due to its excellent mechanical properties, adhesion, dimensional stability, electrical insulation, and heat resistance. To maintain a stable lifespan in high-temperature and high-pressure environments, the material requires high mechanical strength and a high glass transition temperature (T0). g ) and high DC breakdown strength (E b () is indispensable.

[0003] Although epoxy resin, with its highly cross-linked three-dimensional structure, exhibits high breakdown strength, this structure can also lead to insufficient fracture toughness, making the material prone to defects such as microcracks or microvoids during use or curing. It is well known that even minute defects in insulating materials can cause local electric field distortion under high-field conditions, inducing partial discharge and thus reducing insulation reliability.

[0004] To overcome the inherent brittleness of epoxy resins, various toughening strategies have been developed, which can be broadly categorized into homogeneous toughening and heterogeneous toughening. Heterogeneous toughening has become the most commonly used method for epoxy resins due to its mature technology, wide applicability, and significant toughening efficiency. Liquid rubber with polar groups and flexible segments (CTBN) is one of the most representative epoxy resin liquid rubber toughening agents. Its introduction significantly improves the toughness of epoxy resins, but it is usually accompanied by a significant decrease in glass transition temperature and a deterioration in insulation properties. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides an all-organic epoxy composite material with high toughness, high DC breakdown strength, and high glass transition temperature, as well as a method for its preparation. This invention can improve the toughness of epoxy resin composite materials while maintaining the material's breakdown strength and glass transition temperature.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A high-toughness, high DC breakdown strength, and high glass transition temperature all-organic epoxy composite material comprises epoxy resin, carboxyl-terminated liquid nitrile rubber, curing agent, accelerator, and polyvinylcarbazole. The carboxyl-terminated liquid nitrile rubber comprises 8 wt% to 12 wt% of the epoxy resin mass, the curing agent comprises 78 wt% to 82 wt% of the epoxy resin mass, the accelerator comprises 0.8 wt% to 1.2 wt% of the epoxy resin mass, and the polyvinylcarbazole comprises 0.6 wt% to 1.0 wt% of the epoxy resin mass.

[0007] Preferably, the epoxy resin is a bisphenol A type epoxy resin.

[0008] Preferably, the curing agent is 4-methylhexahydrophthalic anhydride.

[0009] Preferably, the accelerator is 2,4,6-tris(dimethylaminomethyl)phenol.

[0010] This invention also provides a method for preparing the all-organic epoxy composite material with high toughness, high DC breakdown strength and high glass transition temperature as described above, comprising the following steps: Epoxy resin is added to a polyvinylcarbazole solution, mixed evenly, and the solvent in the polyvinylcarbazole solution is evaporated to obtain a mixture of epoxy resin and polyvinylcarbazole. Add carboxyl-terminated liquid nitrile rubber to the mixture of epoxy resin and polyvinylcarbazole, mix the carboxyl-terminated liquid nitrile rubber evenly and pre-react it with epoxy resin to obtain a mixture system. A curing agent and an accelerator are added to the mixture, and the mixture is mixed evenly, degassed, and cured to obtain the all-organic epoxy composite material with high toughness, high DC breakdown strength, and high glass transition temperature.

[0011] Preferably, the solvent in the polyvinylcarbazole solution is tetrahydrofuran.

[0012] Preferably, after adding epoxy resin to the polyvinylcarbazole solution, the mixture is stirred in a vacuum environment at 65~75℃ and 290~310 r / min for 7.5~8.5 h to allow the solvent in the polyvinylcarbazole solution to evaporate, thereby obtaining a mixture of epoxy resin and polyvinylcarbazole.

[0013] Preferably, after adding carboxyl-terminated liquid nitrile rubber to the mixture of epoxy resin and polyvinylcarbazole, the mixture is stirred at 55-65°C and 290-310 r / min for 115-125 min to ensure uniform mixing of the carboxyl-terminated liquid nitrile rubber and pre-reaction with the epoxy resin, thereby obtaining a mixture system.

[0014] Preferably, after adding the curing agent and accelerator to the mixture, it is stirred at a speed of 1950~2050 r / min for 14~16 min, followed by degassing and curing.

[0015] Preferably, during degassing, after mixing evenly, static degassing is performed for 14-16 minutes, followed by vacuum degassing for 25-35 minutes to achieve degassing; During curing, the degassed mixed solution is poured into a mold, first cured at 75~85℃ for 115~125min, then heated to 100~110℃ for 115~125min, then heated to 115~125℃ for 235~245min, and after cooling, the high toughness, high DC breakdown strength and high glass transition temperature of the all-organic epoxy composite material is obtained.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention provides a high-toughness, high DC breakdown strength, and high glass transition temperature all-organic epoxy composite material. The composite material uses epoxy resin as the matrix and is compounded with carboxyl-terminated liquid nitrile rubber, curing agent, accelerator, and polyvinylcarbazole in the specified proportions of this application. The components work synergistically to overcome the defects in the prior art where the toughness of epoxy resin is improved but the glass transition temperature decreases and the insulation performance deteriorates when carboxyl-terminated liquid nitrile rubber is used to toughen the epoxy resin. Specifically, this invention controls the amount of carboxyl-terminated liquid nitrile rubber to be 8 wt%~12 wt% of the epoxy resin mass. The carboxyl-terminated liquid nitrile rubber contains polar groups and flexible segments, which can form a heterogeneous rubber toughening phase within the epoxy matrix. When the material is subjected to external force, this rubber phase can induce crazes, passivate crack tips, improve the inherent brittleness of epoxy resin, reduce the generation of microcracks and microvoids during curing and service, and reduce the risk of local electric field distortion and partial discharge caused by the aforementioned defects. This, in turn, improves the toughness and mechanical reliability of the composite material. Compared to the tensile strength of pure epoxy resin (41.9 MPa) and flexural strength (90.5 MPa), after modification with carboxyl-terminated liquid nitrile rubber, the tensile strength of the sample increased to 53.5 MPa and the flexural strength increased to 91.7 MPa. MPa, the mechanical properties are significantly improved. If the amount of end-carboxyl liquid nitrile rubber added is too high, the rubber phase is prone to agglomeration, which will cause a decrease in heat resistance and insulation performance. If the amount added is too low, effective toughening cannot be achieved. The dosage range defined by this invention can give full play to its toughening effect, while avoiding the performance degradation problem caused by excessive addition.This invention further limits the amount of polyvinylcarbazole to 0.6wt%~1.0wt% of the epoxy resin mass. The carbazole group in the polyvinylcarbazole molecule has strong polarization and charge trapping capabilities, which can introduce deep traps in the composite system, inhibiting carrier migration and space charge accumulation, thereby improving the DC breakdown strength. Compared with the DC breakdown strength of pure epoxy resin (354.27 kV / mm) and the DC breakdown strength of only adding carboxyl-terminated liquid nitrile rubber (369.18 kV / mm), the DC breakdown strength of the all-organic epoxy composite material of this invention, which has high toughness, high DC breakdown strength, and high glass transition temperature, reaches 397.08 kV / mm, an improvement of 15.4% compared with pure epoxy resin. At the same time, polyvinylcarbazole can improve the interfacial compatibility between the epoxy resin and the carboxyl-terminated liquid nitrile rubber phases. It promotes more uniform dispersion of the rubber phase in the matrix, reduces the phase separation scale, and forms a denser and more stable cured crosslinked network. This effect is also reflected in the mechanical properties. After compounding with polyvinylcarbazole, the tensile strength of the composite material further reaches about 53.9 MPa, and the flexural strength reaches about 91.3 MPa. Polyvinylcarbazole itself has an aromatic rigid structure, which can also compensate for the heat loss caused by the flexible segments of the end-carboxyl liquid nitrile rubber. The glass transition temperature of pure epoxy resin is 129.8℃. When only end-carboxyl liquid nitrile rubber is added, the glass transition temperature drops to 122.23℃. After compounding with polyvinylcarbazole, the glass transition temperature rises back to 123.37℃, which effectively alleviates the problem of reduced glass transition temperature caused by the modification of end-carboxyl liquid nitrile rubber and ensures the heat resistance and dimensional stability of the material under high-temperature conditions. This invention limits the curing agent and accelerator to 78wt%~82wt% and 0.8wt%~1.2wt% of the epoxy resin mass, respectively. This ratio allows for full cross-linking of the epoxy resin, constructing a complete three-dimensional cross-linked network, providing fundamental mechanical and insulating properties for the composite material. Simultaneously, it is compatible with the modified system of carboxyl-terminated liquid nitrile rubber and polyvinylcarbazole, avoiding incomplete or excessive cross-linking caused by an imbalance in the curing agent and accelerator ratios. This prevents curing defects, matrix brittleness, and insufficient interfacial bonding, ensuring the toughening effect of the carboxyl-terminated liquid nitrile rubber and fully utilizing the charge regulation, interface optimization, and glass transition temperature compensation functions of polyvinylcarbazole. In summary, this invention achieves toughening through the synergistic ratio of its components, relying on carboxyl-terminated liquid nitrile rubber, while simultaneously improving insulation performance and compensating for the glass transition temperature with the help of polyvinylcarbazole. Ultimately, it enhances the toughness of the epoxy composite material while achieving higher DC breakdown strength and a higher glass transition temperature.

[0017] The method for preparing a fully organic epoxy composite material with high toughness, high DC breakdown strength, and high glass transition temperature in this invention involves first mixing epoxy resin with a polyvinyl carbazole solution until homogeneous, then evaporating and removing the solvent, followed by adding carboxyl-terminated liquid nitrile rubber, mixing and pre-reacting, and finally adding a curing agent and an accelerator. The process involves mixing, degassing, and curing to obtain the composite material. By relying on a specific order of feeding and process settings, the function of each modified component is fully utilized, overcoming the problem of uneven component dispersion that is easily caused by simple direct blending. The specific principle is as follows: First, adding epoxy resin to a polyvinylcarbazole solution and then removing the solvent allows the polyvinylcarbazole to fully dissolve using the solvent system, achieving uniform dispersion of polyvinylcarbazole in the epoxy resin matrix. This avoids local agglomeration of polyvinylcarbazole caused by direct powder feeding, providing a foundation for polyvinylcarbazole to exert its charge-trapping ability and improve the interfacial compatibility between epoxy resin and terminal carboxyl-terminated liquid nitrile rubber. If the polyvinylcarbazole is not uniformly dispersed, it is difficult to effectively introduce deep traps into the system to suppress carrier migration and space charge accumulation, and it is also impossible to effectively improve the interfacial state, weakening its effect on improving DC breakdown strength and compensating for glass transition temperature. Secondly, in epoxy resin... Adding carboxyl-terminated liquid nitrile rubber to a polyvinylcarbazole mixture for mixing and pre-reaction allows the carboxyl-terminated liquid nitrile rubber to react with the epoxy resin beforehand. This facilitates the formation of a rubber toughening phase of suitable size in the matrix, fully leveraging the toughening effect of the polar groups and flexible segments of the carboxyl-terminated liquid nitrile rubber. The rubber phase induces crazes and blunts crack tips, improving the inherent brittleness of the epoxy resin and reducing the generation of microcracks and microvoids within the cured material. This lowers the risk of defect-induced local electric field distortion and partial discharge. However, if the feeding order is reversed, and the carboxyl-terminated liquid nitrile rubber and epoxy resin are mixed first before introducing polyvinylcarbazole, the polyvinylcarbazole is difficult to distribute sufficiently at the interface between the two phases, resulting in poorer interface modification and easier agglomeration of the rubber phase, which adversely affects the material's heat resistance and insulation properties. Subsequently, a curing agent and an accelerator are added to the mixture system. After thorough mixing, degassing, and curing, the mixing process ensures full contact between the curing agent, accelerator, and modified matrix. The degassing operation removes air bubbles from the system, preventing them from remaining inside the material and forming voids and defects. The curing process causes the epoxy resin to crosslink and form a complete three-dimensional crosslinked network. This preparation method has mild overall process conditions. Through the combination of stepwise blending, pre-reaction, degassing, and curing processes, it not only ensures the toughening effect of the carboxyl-terminated liquid nitrile rubber but also fully realizes the charge regulation, interface optimization, and glass transition temperature compensation functions of polyvinylcarbazole. This method can stably prepare all-organic epoxy composite materials with high toughness, high DC breakdown strength, and high glass transition temperature. Attached Figure Description

[0018] Figure 1(a) is a diagram of the preparation process of the all-organic epoxy composite material with high toughness, high DC breakdown strength and high glass transition temperature of the present invention (hereinafter referred to as EP / CTBN / PVK all-organic epoxy composite material or EP / CTBN / PVK). Figure 1(b) is a schematic diagram of the reaction principle of the preparation process of the all-organic epoxy composite material with high toughness, high DC breakdown strength and high glass transition temperature of the present invention. Figure 2(a) shows the tensile strength results of the materials obtained in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 of the present invention; Figure 2(b) shows the bending strength results of the materials obtained in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 of the present invention. Figure 3 The graph shows the DC breakdown strength results of the materials obtained in Embodiment 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 of the present invention. Figure 4 The graph shows the glass transition temperature results of the materials obtained in Examples 1, 1, 2, 3 and 4 of this invention. Detailed Implementation

[0019] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.

[0020] The present invention provides a high-toughness, high DC breakdown strength, and high glass transition temperature all-organic epoxy composite material, the components of which include epoxy resin (EP), carboxyl-terminated liquid nitrile rubber (CTBN), curing agent, accelerator, and polyvinylcarbazole (PVK); wherein the content of the carboxyl-terminated liquid nitrile rubber is 8 wt% to 12 wt% of the epoxy resin mass, the content of the curing agent is 78 wt% to 82 wt% of the epoxy resin mass, the content of the accelerator is 0.8 wt% to 1.2 wt% of the epoxy resin mass, and the content of the polyvinylcarbazole is 0.6 wt% to 1.0 wt% of the epoxy resin mass.

[0021] In the above-described embodiments of the present invention, the epoxy resin may be a bisphenol A type epoxy resin, more preferably an E51 epoxy resin, the curing agent may be 4-methylhexahydrophthalic anhydride (i.e., methylhexahydrophthalic anhydride (MHHPA)), and the accelerator may be 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30).

[0022] As shown in Figures 1(a) and 1(b), the method for preparing the above-mentioned all-organic epoxy composite material with high toughness, high DC breakdown strength and high glass transition temperature according to the present invention includes the following steps: S1. A mixture system is prepared by combining tetrahydrofuran (THF), epoxy resin (EP), and carboxyl-terminated liquid nitrile butadiene rubber (CTBN). Specifically, the detailed steps of this process include: S11. Add tetrahydrofuran (THF) to a beaker, heat the beaker in an oil bath at 55±5℃, then add solid PVK to the beaker and stir until the solid PVK dissolves, obtaining mixture I (i.e., polyvinylcarbazole solution). Tetrahydrofuran serves as the solvent for polyvinylcarbazole and needs to be removed subsequently; the amount added should only be sufficient to dissolve all the subsequently added solid PVK.

[0023] S12. Place the beaker from S11 and mixture I together in a vacuum environment, and add the epoxy resin matrix to mixture I. Heat the beaker to 70±5℃ and stir at 300±10r / min for 7.5~8.5h. At this time, tetrahydrofuran (THF) has completely evaporated and the material has been stirred evenly to obtain mixture II.

[0024] S13. Transfer the mixture II obtained in S12 to a mixing container, add CTBN to the mixing container and stir evenly, and stir at 300±10 r / min for 115~125 min at 60±5℃ to carry out blending prepolymerization to obtain the mixture III composite system.

[0025] S2. Add curing agent and accelerator to the mixture system obtained in S13 (i.e., the mixture III composite system), and stir at a speed of 2000±50 r / min for 14~16 min to make the material uniformly mixed; then first statically degas for 14~16 min, and then vacuum degas for 25~35 min to achieve degassing; then pour the degassed mixture into a mold, first cure at 80±5℃ for 115~125 min, then raise the temperature to 105±5℃ for 115~125 min, and then raise the temperature to 120±5℃ for 235~245 min to obtain the all-organic epoxy composite material of the present invention with high toughness, high DC breakdown strength and high glass transition temperature.

[0026] In the above-described scheme of this invention, polyvinylcarbazole (PVK) is added to the composite system. The technical route and mechanism are as follows: using epoxy resin as the matrix, polyvinylcarbazole (PVK) is introduced for solution blending modification to obtain an EP / CTBN / PVK blend system with high toughness and good heat resistance. In this invention, PVK plays a dual role in the EP / CTBN composite system, primarily regulating electrical properties and optimizing the interface. On one hand, the carbazole groups in PVK have strong polarization and charge trapping capabilities, which can increase the dielectric constant of the system and introduce deep traps, inhibiting carrier migration and space charge accumulation, thereby improving insulation stability and DC breakdown strength. On the other hand, PVK can improve the interfacial compatibility between the EP and CTBN phases, promoting more uniform dispersion of the CTBN rubber phase, reducing phase separation scale, and making the cured network more dense and stable. Simultaneously, the aromatic rigid structure of PVK can also improve the thermal stability and glass transition temperature of the material to a certain extent, offsetting the negative impact of the introduction of CTBN. Therefore, in this composite system, CTBN is mainly responsible for toughening, while PVK is mainly responsible for enhancing dielectric and insulating properties, further increasing the DC specificity of pure EP by 15.4%. The two work synergistically to achieve comprehensive optimization of the material's mechanical and electrical properties. This invention features mild conditions, a short process flow, low energy consumption, and suitability for large-scale production, providing theoretical and experimental support for developing all-organic epoxy composite materials that balance toughness, thermal stability, and insulating properties.

[0027] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified.

[0028] The epoxy resin used in this embodiment of the invention is preferably a bisphenol A type epoxy resin, and more preferably E51, which is purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0029] The curing agent methylhexahydrophthalic anhydride (MHHPA) and the catalyst (i.e. the accelerator) 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30) used in the embodiments of the present invention were both purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0030] The toughening agent described in this embodiment of the invention is CTBN liquid rubber (viscosity: 30000, molecular weight: 2000~3000), purchased from UTB Technology (Suzhou) Co., Ltd. PVK organic semiconductor was purchased from Aladdin Reagent Co., Ltd.

[0031] Example 1 The method for producing a fully organic epoxy composite material with high toughness, high DC breakdown strength, and high glass transition temperature in this embodiment includes the following processes: Add 10 ml of tetrahydrofuran (THF) to a beaker, weigh 0.4 g of PVK solid, and add the PVK solid to the beaker. Stir the beaker containing the tetrahydrofuran (THF) and PVK solid mixture thoroughly in an oil bath at 60 ± 5 °C until the PVK solid is completely dissolved to obtain a polyvinylcarbazole solution.

[0032] Then, 50g of E51 epoxy resin matrix was added to the polyvinylcarbazole solution. Then, under vacuum, the beaker containing the mixture of epoxy resin matrix and polyvinylcarbazole solution was stirred for 8h at 70±5℃ and 300±10r / min to remove THF and promote the uniform dispersion of PVK in the epoxy resin. Then, the mixture in the beaker was transferred to a mixer.

[0033] Add 5g of CTBN to the mixing container. Prepolymerize the system in the mixing container at 60±5℃ and 300±10r / min for 2 h to ensure thorough mixing and pre-reaction of CTBN and epoxy groups. Then, add 40g of curing agent MHHPA and 0.5g of accelerator DMP-30 to the mixing container. Stir at 2000±50 r / min for 15 min, then statically degas for 15 min. Finally, perform vacuum degassing for 30 min to further remove residual bubbles, thereby obtaining a CTBN-modified epoxy resin casting solution with PVK (EP / CTBN / PVK). The CTBN-modified epoxy resin casting liquid was poured into a mold and cured in an oven. During curing, a step-by-step curing process was adopted, which involved curing at 80±5℃ for 2 h, 105±5℃ for 2 h, and 120±5℃ for 4 h. After curing, the mixture was naturally cooled to room temperature to obtain the all-organic epoxy composite material with high toughness, high DC breakdown strength, and high glass transition temperature of this embodiment.

[0034] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the amount of CTBN added is 10g, while the remaining steps are the same as in Example 1, as follows: 50g of epoxy resin matrix and 10g of CTBN were added to a mixing container. The system in the mixing container was prepolymerized at 60±5℃ and 300±10r / min for 2 h to ensure sufficient mixing and pre-reaction of CTBN and epoxy groups. Then, 40g of curing agent MHHPA and 0.5g of accelerator DMP-30 were added to the mixing container. The mixture was stirred at 2000±50 r / min for 15 min, followed by static degassing for 15 min. Vacuum degassing was then performed for 30 min to further remove residual bubbles, yielding an epoxy resin casting solution. This epoxy resin casting solution was poured into a mold and cured in an oven using a stepwise curing process: 80±5℃ for 2 h, 105±5℃ for 2 h, and 120±5℃ for 4 h, to obtain the epoxy composite material of this comparative example.

[0035] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that PVK is not introduced for modification; the remaining steps are the same as in Example 1, as follows: Add 5g of CTBN to the mixing container. Prepolymerize the system in the mixing container at 60±5℃ and 300±10r / min for 2 h to ensure sufficient mixing and pre-reaction of CTBN and epoxy groups. Then, add 40g of curing agent MHHPA and 0.5g of accelerator DMP-30 to the mixing container. Stir at 2000±50 r / min for 15 min, then statically degas for 15 min. Perform vacuum degassing for 30 min to further remove residual bubbles, thereby obtaining a CTBN-modified epoxy resin casting liquid with (EP / CTBN). Pour the CTBN-modified epoxy resin casting liquid into a mold and cure it in an oven. During curing, a stepwise curing process is used: 80±5℃ for 2 h, 105±5℃ for 2 h, and 120±5℃ for 4 h. After natural cooling to room temperature, the high-toughness, high DC breakdown strength, and high glass transition temperature all-organic epoxy composite material of this embodiment is obtained.

[0036] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that PVK is not introduced for modification, and the amount of CTBN added is 10g. The remaining steps are the same as in Example 1, as follows: 50g of epoxy resin matrix and 10g of CTBN were added to a mixing container. The system in the mixing container was prepolymerized at 60±5℃ and 300±10r / min for 2 h to ensure sufficient mixing and pre-reaction of CTBN and epoxy groups. Then, 40g of curing agent MHHPA and 0.5g of accelerator DMP-30 were added to the mixing container. The mixture was stirred at 2000±50 r / min for 15 min, followed by static degassing for 15 min. Vacuum degassing was then performed for 30 min to further remove residual bubbles, yielding an epoxy resin casting solution. This epoxy resin casting solution was poured into a mold and cured in an oven using a stepwise curing process: 80±5℃ for 2 h, 105±5℃ for 2 h, and 120±5℃ for 4 h, to obtain the epoxy composite material of this comparative example.

[0037] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that PVK and CTBN are not introduced for modification; the curing is performed directly. The remaining steps are the same as in Example 1, as follows: Add 50g of epoxy resin matrix, 40g of curing agent MHHPA, and 0.5g of accelerator DMP-30 to a mixing container. Stir the system in the mixing container at 2000±50 r / min for 15 min at room temperature, then degas statically for 15 min. Next, perform vacuum degassing for 30 min to further remove residual air bubbles, obtaining an epoxy resin casting liquid. Pour the epoxy resin casting liquid into a mold and cure it in an oven. During curing, a step-by-step curing process is used: 80±5℃ for 2 h, 105±5℃ for 2 h, and 120±5℃ for 4 h, to obtain the epoxy composite material of this comparative example.

[0038] The materials obtained in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 were tested for mechanical strength, DC breakdown strength, and glass transition temperature. Tensile and flexural mechanical properties were determined according to GB / T2567. The performance of the resin casting was tested according to the 2021 test method, and the experimental results are shown in Figure 2(a) and Figure 2(b); the DC breakdown strength was tested according to GB / T1408.2. Tests were conducted in 2016, and the experimental results are as follows: Figure 3 As shown; the glass transition temperature Tg was determined using differential scanning calorimetry (DSC), referring to GB / T19466.2. The test was conducted according to the 2004 standard, and the experimental results are as follows: Figure 4 As shown.

[0039] As shown in Figure 2(a), the tensile strengths of the materials obtained in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 are 53.9 MPa, 42.3 MPa, 53.5 MPa, 42.4 MPa, and 41.8 MPa, respectively. The material obtained in Comparative Example 4 is an unmodified pure epoxy resin matrix with a tensile strength of 41.8 MPa. Compared to the material obtained in Comparative Example 4, the material obtained in Comparative Example 2, after being modified with CTBN, showed an increase in tensile strength to 53.5 MPa, an increase of 28.0%, indicating that the addition of CTBN liquid rubber can effectively improve the tensile mechanical properties of the epoxy resin matrix. However, when the amount of CTBN added was further increased, as shown in Comparative Example 3, the tensile strength decreased to 42.4 MPa. Further introduction of PVK into the CTBN-modified system yielded the material obtained in Example 1, whose tensile strength was further increased to 53.9 MPa. The reason for this is that PVK can improve the interfacial compatibility between the epoxy resin and CTBN rubber phases, promoting a more uniform dispersion of the CTBN rubber phase within the epoxy matrix, resulting in a denser and more stable cross-linked network after curing, thereby further improving the tensile strength of the composite material. In the figure, the error bars represent the standard deviation of test results from multiple sets of parallel samples. The error bars of the material obtained in Comparative Example 2 are longer, indicating a greater dispersion in the test data of the pure epoxy resin sample. After modification with CTBN and PVK, the error bars of the samples are narrowed, and the repeatability of the mechanical property tests of the modified composite material is improved.

[0040] As shown in Figure 2(b), the flexural strengths of the materials obtained in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 are 91.3 MPa, 81.4 MPa, 91.7 MPa, 81.3 MPa, and 90.5 MPa, respectively. The addition of CTBN slightly increased the flexural strength, and the introduction of PVK maintained this strength, but the overall improvement was limited. However, as the CTBN content increased to 20%, as shown in Comparative Example 4, the flexural strength decreased. This indicates that a 10% CTBN addition has a better effect on improving the flexural strength performance of the materials. The error bars for the flexural strength of the five groups of samples are all relatively short, indicating that the parallel sample tests for flexural performance have small dispersion and good repeatability.

[0041] from Figure 3As can be seen, the DC breakdown strengths of the materials obtained in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 are 397.08 kV / mm, 326.87 kV / mm, 369.18 kV / mm, 301.23 kV / mm, and 354.27 kV / mm, respectively. Compared with the material obtained in Comparative Example 4, the DC breakdown strength of the material obtained in Comparative Example 2 is improved after the introduction of CTBN. However, as the CTBN addition increases to 20%, as shown in Comparative Examples 1 and 3, the breakdown strength decreases. It can be seen that 10% CTBN addition has a better effect on improving the breakdown strength performance of the material. After the material obtained in Example 1 is compounded with PVK, the DC breakdown strength is further improved. The carbazole group in PVK has charge trapping ability, which can introduce deep traps, inhibit carrier migration and space charge accumulation, thereby further improving the DC breakdown strength of the composite material.

[0042] from Figure 4 As can be seen, the glass transition temperatures of the materials obtained in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 are 123.37℃, 108.62℃, 122.23℃, 106.16℃, and 129.8℃, respectively. Compared with the material obtained in Comparative Example 4, the glass transition temperature of the material obtained in Comparative Example 2, which only added CTBN, decreased. As the CTBN addition increased to 20%, as shown in Comparative Example 4, the glass transition temperature further decreased. This is a typical negative impact of introducing flexible CTBN rubber segments. After introducing PVK, the glass transition temperature of the material obtained in Example 1 rebounded, and as the CTBN addition increased to 20%, as shown in Comparative Example 3, the glass transition temperature continued to rise. The aromatic rigid structure of PVK partially offset the deteriorating effect of CTBN on heat resistance, balancing the material's toughness and thermal stability.

[0043] The test results of the above embodiments and comparative examples show that, compared with pure EP, the introduction of CTBN can significantly improve tensile strength, flexural strength and DC breakdown strength, but at the same time it will reduce the glass transition temperature. On this basis, the further introduction of PVK not only further enhances the mechanical properties and DC breakdown strength, but also effectively raises the glass transition temperature, thereby offsetting the adverse effects of CTBN on the heat resistance of the material.

[0044] As can be seen from the above-described scheme of this invention, the all-organic epoxy composite material system (denoted as the EP / CTBN / PVK system) with high toughness, high DC breakdown strength, and high glass transition temperature of this invention improves the toughness and insulation properties of the material by introducing carboxyl-terminated liquid nitrile rubber (CTBN). Simultaneously, the introduction of polyvinyl carbazole (PVK) not only further enhances the DC breakdown strength of the material but also effectively mitigates the effect of the reduced glass transition temperature caused by CTBN. Phase-field simulations verified the intrinsic mechanism and scientific validity of CTBN and PVK in controlling the breakdown process. This system has significant practical value in the fields of DC, AC, and high-frequency power equipment.

[0045] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A fully organic epoxy composite material with high toughness, high DC breakdown strength, and high glass transition temperature, characterized in that, Its components include epoxy resin, carboxyl-terminated liquid nitrile rubber, curing agent, accelerator, and polyvinylcarbazole, wherein the content of the carboxyl-terminated liquid nitrile rubber is 8 wt% to 12 wt% of the epoxy resin mass, the content of the curing agent is 78 wt% to 82 wt% of the epoxy resin mass, the content of the accelerator is 0.8 wt% to 1.2 wt% of the epoxy resin mass, and the content of polyvinylcarbazole is 0.6 wt% to 1.0 wt% of the epoxy resin mass.

2. The all-organic epoxy composite material with high toughness, high DC breakdown strength, and high glass transition temperature according to claim 1, characterized in that, The epoxy resin used is bisphenol A type epoxy resin.

3. The all-organic epoxy composite material with high toughness, high DC breakdown strength, and high glass transition temperature according to claim 1, characterized in that, The curing agent is 4-methylhexahydrophthalic anhydride.

4. The all-organic epoxy composite material with high toughness, high DC breakdown strength, and high glass transition temperature according to claim 1, characterized in that, The accelerator is 2,4,6-tris(dimethylaminomethyl)phenol.

5. A method for preparing a fully organic epoxy composite material with high toughness, high DC breakdown strength, and high glass transition temperature as described in any one of claims 1-4, characterized in that, The process includes the following: Epoxy resin is added to a polyvinylcarbazole solution, mixed evenly, and the solvent in the polyvinylcarbazole solution is evaporated to obtain a mixture of epoxy resin and polyvinylcarbazole. Add carboxyl-terminated liquid nitrile rubber to the mixture of epoxy resin and polyvinylcarbazole, mix the carboxyl-terminated liquid nitrile rubber evenly and pre-react it with epoxy resin to obtain a mixture system. A curing agent and an accelerator are added to the mixture, which is then mixed evenly, degassed, and cured to obtain the all-organic epoxy composite material with high toughness, high DC breakdown strength, and high glass transition temperature.

6. The method for preparing a high-toughness, high DC breakdown strength and high glass transition temperature all-organic epoxy composite material according to claim 5, characterized in that, The solvent used in the polyvinylcarbazole solution is tetrahydrofuran.

7. The method for preparing a high-toughness, high DC breakdown strength and high glass transition temperature all-organic epoxy composite material according to claim 6, characterized in that, After adding epoxy resin to a polyvinylcarbazole solution, the mixture is stirred in a vacuum environment at 65-75°C and 290-310 r / min for 7.5-8.5 h to allow the solvent in the polyvinylcarbazole solution to evaporate, thus obtaining a mixture of epoxy resin and polyvinylcarbazole.

8. The method for preparing a high-toughness, high DC breakdown strength and high glass transition temperature all-organic epoxy composite material according to claim 5, characterized in that, After adding carboxyl-terminated liquid nitrile rubber to the mixture of epoxy resin and polyvinylcarbazole, the mixture is stirred at 55-65°C and 290-310 r / min for 115-125 min to ensure uniform mixing of the carboxyl-terminated liquid nitrile rubber and pre-reaction with the epoxy resin, thereby obtaining a mixture system.

9. The method for preparing a high-toughness, high DC breakdown strength and high glass transition temperature all-organic epoxy composite material according to claim 5, characterized in that, After adding curing agent and accelerator to the mixture, stir at 1950~2050 r / min for 14~16 min, and then degas and cure.

10. The method for preparing a high-toughness, high DC breakdown strength and high glass transition temperature all-organic epoxy composite material according to claim 5, characterized in that, During degassing, after mixing evenly, first perform static degassing for 14-16 minutes, and then perform vacuum degassing for 25-35 minutes to achieve degassing; During curing, the degassed mixed solution is poured into a mold, first cured at 75~85℃ for 115~125min, then heated to 100~110℃ for 115~125min, then heated to 115~125℃ for 235~245min, and after cooling, the high toughness, high DC breakdown strength and high glass transition temperature of the all-organic epoxy composite material is obtained.

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