A method for improving the direct current breakdown characteristics of EP-TMB composite material by SiO2 nano-doping modification

Abstract

The application provides a SiO2 nano-doped modification method for improving the direct current breakdown characteristic of an EP-TMB composite material, comprising the following steps: firstly, grinding and drying pretreatment is conducted on TMB curing agent powder and SiO2 nano-particles; then, TMB and epoxy resin are mixed and grafted in a vacuum environment, and then SiO2 nano-particles are ultrasonically dispersed in the mixed solution; finally, stirring is conducted under vacuum conditions, and high-temperature curing is conducted in three steps, so as to obtain an EP-TMB / SiO2 nano-composite material. Through the introduction of deep traps by TMB to inhibit charge migration and the formation of an interface region by SiO2 nano-particles to hinder carrier transport, the dielectric constant is reduced, the trap energy level and density are improved, and finally the direct current breakdown voltage is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of high-voltage insulating composite material preparation technology, specifically to a SiO2 nano-doping modification method for improving the DC breakdown characteristics of EP-TMB composite materials. Background Technology

[0002] Epoxy resin, with its excellent insulation properties, chemical stability, and mechanical strength, is widely used in key high-voltage power equipment such as GIS / GIL basin insulators, transformer insulation components, and high-voltage bushings, serving as a core material for ensuring the insulation protection system of power systems. In the conventional preparation of epoxy resin insulation materials, anhydride curing agents (such as methyltetrahydrophthalic anhydride) are typically used to cross-link and cure the epoxy resin, forming a three-dimensional network structure. The anhydride curing system is a mature process with low cost, capable of meeting general insulation requirements under AC operating conditions.

[0003] However, anhydride-cured epoxy resins exhibit significant defects under long-term DC electric field conditions. Due to the shallow intrinsic trap levels of these materials, charge carriers injected from the electrodes lack effective capture and binding mechanisms during migration within the material, leading to a large accumulation of space charge. This accumulated space charge causes electric field distortion, resulting in a local electric field strength far exceeding the applied electric field, ultimately leading to insulation breakdown. Furthermore, the glass transition temperature of anhydride-cured systems is typically below 130°C, resulting in insufficient thermal stability under high-temperature conditions (such as the temperature rise of GIL equipment under full load).

[0004] Two directions for improvement have emerged in the existing technology: one is to use amine curing agents (such as...) Tetramethylbenzidine (TMB) can be used to graft and modify epoxy resins using anhydrides. One approach involves using the rigid biphenyl structure and conjugated π-electron system of TMB molecules to introduce deep traps in the cross-linked network, capturing charge carriers and suppressing charge accumulation. Another approach is to dope epoxy resins with SiO2 nanoparticles, utilizing the interface region formed between the nanoparticles and the matrix to construct a physical barrier, hindering charge carrier migration. However, TMB grafting alone has limited effect on regulating the dielectric constant, while SiO2 nanoparticle doping alone cannot increase the trap depth at the molecular chain level. The synergistic potential of these two mechanisms has not yet been fully utilized. More importantly, simply mixing TMB and SiO2 simultaneously in epoxy resins leads to interference between the TMB grafting reaction and the SiO2 dispersion process—TMB requires sufficient molecular contact to complete the grafting reaction, which is hindered by the presence of SiO2 nanoparticles; simultaneously, the uniformity of SiO2 dispersion is also affected by the preferential dissolution of TMB.

[0005] Therefore, there is a need for a method to prepare epoxy resin composites that allows TMB grafting modification and SiO2 nanodoping to fully exert their respective functions and produce a synergistic effect. Summary of the Invention

[0006] The technical problem to be solved by this invention is to address the shortcomings of existing technologies, such as insufficient DC breakdown strength of anhydride-cured epoxy resin, limited effect of single TMB grafting modification or single SiO2 nano-doping modification, and mutual interference between grafting and dispersion processes when simply mixing the two. This invention provides a method for improving the DC breakdown characteristics of epoxy resin based on the synergistic effect of TMB grafting and SiO2 nano-doping. Through a process strategy of "stepwise introduction and stepwise curing", an EP-TMB / SiO2 three-phase nanocomposite insulating material with the synergistic effect of TMB grafting modification and SiO2 nano-doping is constructed.

[0007] To address the aforementioned technical problems, this invention provides a SiO2 nano-doping modification method for improving the DC breakdown characteristics of EP-TMB composite materials, comprising the following steps: Step S1: Grind the TMB powder and SiO2 nanoparticles separately; Step S2: Dry the ground TMB powder and SiO2 nanoparticles separately; Step S3: Add the dried TMB powder to the epoxy resin solution, heat and stir under vacuum to allow TMB and epoxy resin to undergo a grafting reaction, and obtain an EP-TMB mixed solution. Step S4: Add the dried SiO2 nanoparticles to the EP-TMB mixed solution obtained in step S3, heat and ultrasonically disperse to obtain the EP-TMB / SiO2 mixed solution; Step S5: The solution obtained in step S4 is heated and stirred under vacuum to homogenize it; Step S6: Pour the homogenized solution from step S5 into a mold and perform stepwise high-temperature curing to obtain EP-TMB / SiO2 nanocomposite insulating material.

[0008] Furthermore, in step S1, the grinding time for TMB powder and SiO2 nanoparticles is independently 8-12 minutes each.

[0009] Furthermore, in step S2, the drying temperature is 95-105℃ and the drying time is 22-26 hours.

[0010] Furthermore, in step S3, the heating temperature is 77-83℃, the stirring speed is 450-550 rpm, and the stirring time is 35-45 minutes.

[0011] Furthermore, in step S4, the heating temperature is 55-65℃, and the ultrasonic dispersion time is 50-70 minutes.

[0012] Furthermore, in step S5, the heating temperature is 77-83℃, the stirring speed is 550-650 rpm, and the stirring time is 45-55 minutes.

[0013] Furthermore, in step S5, an accelerator is added. The accelerator is 2,4,6-tris(dimethylaminomethyl)phenol, and the amount added is 0.1-0.3 grams per 20 grams of epoxy resin. The role of this accelerator is to accelerate the curing reaction and ensure that the crosslinking reaction can be fully completed during the stepwise curing process.

[0014] Furthermore, the step-by-step high-temperature curing in step S6 is specifically as follows: the first curing step is at a temperature of 75-85℃ and a curing time of 110-130 minutes; the second curing step is at a temperature of 115-125℃ and a curing time of 330-390 minutes; and the third curing step is at a temperature of 130-140℃ and a curing time of 220-260 minutes. The temperature rise rate between the three curing stages is 2-5℃ / min.

[0015] Furthermore, the vacuum level in steps S3 and S5 is less than or equal to 0.07 MPa; the high-temperature curing in step S6 is carried out in a vacuum oven with a vacuum reading of less than or equal to 0.09 MPa. It should be noted that the ranges here only represent the approximate range achievable by commonly available vacuum pumping devices.

[0016] Furthermore, the SiO2 nanoparticles have a particle size of 25-35 nanometers and a purity greater than 99.9%; by mass, 12-13 parts of TMB powder and 0.3-0.4 parts of SiO2 nanoparticles are added for every 20 parts of epoxy resin.

[0017] As an alternative implementation, the drying treatment of SiO2 nanoparticles in step S2 can be replaced by a solvent displacement method. This involves dispersing the SiO2 nanoparticles in anhydrous ethanol and ultrasonically treating them, then adding the dispersion to the EP-TMB mixed solution obtained in step S3, and removing the ethanol during vacuum stirring in step S5. This alternative method avoids possible secondary agglomeration of SiO2 after drying, but it increases the process steps of solvent introduction and removal.

[0018] The technical solution provided by this invention performs the TMB grafting step and the SiO2 ultrasonic dispersion step in separate steps to ensure that TMB and epoxy resin are fully grafted to form a deep trap structure. Then, SiO2 is uniformly dispersed in the grafted matrix, so that the two modification mechanisms can play their optimal roles and produce a synergistic effect. At the same time, the three-step step curing system ensures that TMB is fully cross-linked and eliminates interfacial stress, ultimately achieving a significant improvement in DC breakdown voltage. Attached Figure Description

[0019] Figure 1 These are the glass transition temperature curves of the epoxy composite materials treated in the embodiments and comparative examples of the present invention; Figure 2 These are the dielectric constant curves of the epoxy composite materials treated in the embodiments and comparative examples of the present invention; Figure 3 These are the surface potential decay curves of the epoxy composite materials treated in the embodiments and comparative examples of the present invention; Figure 4 These are the surface trap curves of the epoxy composite materials treated in the embodiments and comparative examples of the present invention; Figure 5 These are the DC breakdown curves of the epoxy composite materials treated in the embodiments and comparative examples of this invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0021] Example 1 This embodiment provides a SiO2 nano-doping modification method to improve the DC breakdown characteristics of EP-TMB composite materials, specifically including the following steps: Step S1: Raw Material Preparation and Grinding. Weigh 12.5g of TMB powder and 0.33g of SiO2 nanoparticles. Place both separately in an agate mortar and grind evenly for 10 minutes. The purpose of grinding TMB is to break down any potential lumpy agglomerates, increasing the specific surface area for subsequent contact with epoxy resin, thus facilitating dissolution and grafting reactions. The purpose of grinding SiO2 is to deagglomerate the soft agglomerates formed during storage of the nanoparticles, restoring their primary particle size state, thus facilitating subsequent uniform dispersion. The use of an agate mortar is based on its high hardness, good wear resistance, and low tendency to introduce metals or other impurities, ensuring high purity of the raw materials.

[0022] Step S2: Drying Treatment. The TMB powder and SiO2 nanoparticles ground in Step S1 were transferred to different petri dishes, spread into thin layers to facilitate uniform heating and moisture evaporation. The two petri dishes were placed in an electric heating drying oven, set to 100℃, and dried for 24 hours. The purpose of drying TMB is to remove moisture adsorbed on the powder surface and inside—TMB, as an aromatic amine compound, has hygroscopic amine groups. If the water content is too high, moisture will compete with epoxy groups in the subsequent high-temperature grafting reaction, generating hydroxyl byproducts, thereby reducing the grafting efficiency of TMB and epoxy resin. The purpose of drying SiO2 is to remove its high specific surface area (approximately 100 μm²). 2 The moisture and gases adsorbed on the surface of TMB ( / g) – if not removed, will generate a large number of bubbles during subsequent vacuum mixing, affecting the material's density and insulation properties. A drying temperature of 100°C is below the melting point of TMB (approximately 168°C) but far above the boiling point of water, ensuring effective dehydration without altering the solid state and chemical structure of TMB. A drying time of 24 hours is typical for hydroxyl desorption from the surface of 30nm SiO2 particles, ensuring thorough moisture removal.

[0023] Step S3: EP-TMB Grafting and Mixing. Weigh 20g of bisphenol A type epoxy resin solution into a vacuum preparation platform and place it in a reaction vessel. Add all 12.5g of dried TMB powder from Step S2 to the epoxy resin solution. Seal the vacuum chamber and start the vacuum pump to evacuate the chamber to below 1kPa. Turn on the heating device to raise the system temperature to 80℃, start the mechanical stirrer, set the stirring speed to 500r / min, and continue stirring for 40min. During this process, the TMB powder gradually dissolves in the epoxy resin under the combined action of heating and mechanical stirring; the primary amine groups (-NH2) on the dissolved TMB molecules undergo nucleophilic ring-opening addition reactions with the epoxy end groups on the epoxy resin molecular chain to form CN covalent bonds, grafting the biphenyl rigid structure of TMB onto the epoxy molecular chain, thus completing the construction of the EP-TMB grafting system. The vacuum environment serves three purposes: first, it removes any trace air bubbles that may be present in the epoxy resin, preventing them from forming pore defects after subsequent curing; second, it prevents the primary amine groups of TMB from being oxidized by oxygen in the air at high temperatures, thus reducing their reactivity; and third, it removes any trace volatiles that may be generated during the reaction. The choice of 80℃ balances reaction rate and process controllability—at this temperature, the viscosity of the epoxy resin is significantly reduced, which is beneficial for the dissolution and molecular-level dispersion of TMB. Simultaneously, the grafting reaction rate between the epoxy groups and the primary amine is moderate at this temperature, allowing for complete grafting within 40 minutes without premature gelation of the system, thus preserving a sufficiently wide process window for the addition of SiO2 in the subsequent step S4.

[0024] Step S4: SiO2 ultrasonic dispersion. After step S3 is completed, the vacuum chamber is restored to normal pressure, and all 0.33g of dried SiO2 nanoparticles from step S2 are added to the EP-TMB mixed solution. The probe of the ultrasonic device is immersed below the surface of the mixed solution, and the ultrasonic power is set to 300W, the frequency to 20kHz, and the ultrasonic time to 60min. During the ultrasonic process, the system temperature is controlled at 60±2℃ using a circulating water bath. The dispersion temperature of 60℃ is based on the following considerations: although the viscosity of the system at this temperature is slightly higher than that at 80℃, it is still within an acceptable range (approximately 500-800mPa·s), which is conducive to the effective propagation of the ultrasonic cavitation effect; at the same time, 60℃ is significantly lower than the temperature threshold (approximately 80℃) at which the crosslinking reaction of the TMB-EP system is significantly accelerated, which can effectively avoid premature solidification of the system during the SiO2 dispersion process. The cavitation effect generated by ultrasound in a liquid medium can produce localized high temperature and pressure and powerful microjets, effectively overcoming the van der Waals forces between SiO2 nanoparticles, breaking up both soft and hard agglomerates, and achieving uniform dispersion of nanoparticles in the EP-TMB matrix. The 60-minute ultrasound time was determined based on the dispersion kinetics of 30 nm SiO2 particles in this system—within this time, the ultrasonic cavitation effect can deagglomerate the vast majority of agglomerates to a primary particle size state.

[0025] Step S5: Final Mixing and Accelerator Addition. The EP-TMB / SiO2 mixed solution obtained in Step S4 is reconnected to the vacuum preparation platform. 0.2 g of accelerator 2,4,6-tris(dimethylaminomethyl)phenol is added. The chamber is resealed and evacuated to below 1 kPa. The heating temperature is set to 80℃, and the stirring speed is increased to 600 r / min, with continuous stirring for 50 min. Increasing the stirring speed from 500 r / min in Step S3 to 600 r / min compensates for the increased viscosity of the system after the addition of SiO2 nanoparticles, ensuring that the accelerator is fully and uniformly distributed in the system. At this temperature, the accelerator 2,4,6-tris(dimethylaminomethyl)phenol begins to exert its catalytic effect—its phenolic hydroxyl group acts as a proton donor, promoting the ring-opening of epoxy groups, thereby accelerating the cross-linking reaction with the amine groups on TMB; simultaneously, the tertiary amine groups in its molecular structure also have a catalytic effect on epoxy ring-opening. The synergistic effect of these two factors can effectively shorten the subsequent curing time or reduce the curing temperature. A 50-minute stirring time ensures that all components of the system are fully homogenized. At the same time, the vacuum environment can remove residual air bubbles trapped in the high-speed shear during stirring, as well as trace amounts of gas that may be introduced by the accelerator, further ensuring the compactness of the material.

[0026] Step S6: Three-step stepped curing. Pour the final mixed solution obtained in step S5 into a special mold for epoxy breakdown testing. Place the mold containing the solution into a high-temperature vacuum oven, maintaining the vacuum level below 100 Pa. Execute the three-step stepped curing procedure: Step 1 (Pre-curing Stage): Set the oven temperature to 80℃ and maintain for 120 minutes. During this stage, the system gradually transforms from a liquid state to a gel state. The epoxy groups and the amine groups of TMB begin to cross-link, forming a preliminary three-dimensional network structure. The degree of curing reaches approximately 50%-60%. The relatively low initial curing temperature allows the cross-linking reaction to proceed slowly. The resulting preliminary network structure provides stable spatial constraints for the SiO2 nanoparticles, preventing them from settling or shifting due to the decrease in system viscosity during subsequent curing stages at higher temperatures.

[0027] Step 2 (Main Curing Stage): The oven temperature is increased from 80℃ to 120℃ at a heating rate of 3℃ / min and maintained at 120℃ for 360min. This stage is the main stage of the crosslinking reaction. The primary and secondary amine groups on TMB react fully with the epoxy groups at this temperature to form a highly crosslinked three-dimensional network structure. 120℃ provides sufficient activation energy for the reaction, allowing the crosslinking reaction to proceed to completion (degree of cure > 95%). The rigid biphenyl structure of TMB is maximized to embed into the epoxy crosslinking network at this stage, forming high-density deep trap centers, providing the material with excellent charge trapping capabilities.

[0028] Step 3 (Post-curing stage): Increase the oven temperature from 120℃ to 135℃ at a heating rate of 3℃ / min, and maintain at 135℃ for 240 minutes. The main purpose of this stage is not to further crosslink, but to eliminate the internal stress generated during the first two curing steps. Because the epoxy resin curing process is accompanied by volume shrinkage (shrinkage rate of approximately 3%-5%), stress concentration occurs inside the material, especially at the interface between SiO2 nanoparticles and the epoxy matrix. 135℃ is close to the glass transition temperature (Tg) of the material. At this temperature, the molecular chain segments gain sufficient mobility for conformational adjustment and stress relaxation, effectively releasing residual stress at the interface and forming a more stable SiO2-matrix interface structure, thus avoiding insulation performance degradation due to interface defects.

[0029] After curing, turn off the oven and allow the sample to cool naturally to room temperature (cooling rate is about 1-2℃ / min). Remove the sample from the mold to obtain the EP-TMB / SiO2 nanocomposite insulating material sample.

[0030] Example 2 This embodiment adjusts the values ​​of some process parameters based on Embodiment 1, demonstrating the adjustability of the parameters within the preferred range. The specific steps are as follows: Step S1: Place 12.5g of TMB powder and 0.33g of SiO2 particles into an agate mortar and grind them evenly for 8 minutes. Step S2: Place the TMB powder and SiO2 particles ground in step S1 into petri dishes, place them in an oven, and heat at 95°C for 22 hours. Step S3: Add the dried TMB powder from step S2 to 20g of EP solution, maintain a vacuum environment (≤1kPa), and heat and stir at 77℃ with a stirring speed of 450r / min for 35min. Step S4: Add the dried SiO2 particles from step S2 to the mixed solution from step S3, and heat and sonicate at 55°C for 50 min. Step S5: Connect the solution obtained in step S4 to a vacuum preparation platform, add 0.2g of 2,4,6-tris(dimethylaminomethyl)phenol, maintain a vacuum environment (≤1kPa), and heat and stir at 77℃ with a stirring speed of 550r / min for 45min. Step S6: Pour the solution obtained in step S5 into an epoxy puncture mold, place it in a high-temperature vacuum oven (≤100Pa), and perform three-step high-temperature curing: the first step is high-temperature curing at 75℃ for 110min, the second step is high-temperature curing at 115℃ for 330min, and the third step is high-temperature curing at 130℃ for 220min.

[0031] This embodiment demonstrates that the process parameters can be adjusted within a wide range without affecting the final result, reflecting the industrial adaptability and operability of the present invention.

[0032] Example 3 This embodiment adjusts the process parameters in another direction based on Embodiment 1, demonstrating the implementation of parameters at the upper limit of the preferred range. The specific steps are as follows: Step S1: Place 12.5g of TMB powder and 0.33g of SiO2 particles into an agate mortar and grind them evenly for 12 minutes. Step S2: Place the TMB powder and SiO2 particles ground in step S1 into petri dishes, place them in an oven, and heat at 105°C for 26 hours. Step S3: Add the dried TMB powder from step S2 to 20g of EP solution, maintain a vacuum environment (≤1kPa), and heat and stir at 83℃ with a stirring speed of 550r / min for 45min. Step S4: Add the dried SiO2 particles from step S2 to the mixed solution from step S3, and heat and sonicate at 65°C for 70 min. Step S5: Connect the solution obtained in step S4 to a vacuum preparation platform, add 0.2g of 2,4,6-tris(dimethylaminomethyl)phenol, maintain a vacuum environment (≤1kPa), and heat and stir at 83℃ with a stirring speed of 650r / min for 55min. Step S6: Pour the solution obtained in step S5 into an epoxy puncture mold, place it in a high-temperature vacuum oven (≤100Pa), and perform three-step high-temperature curing: first step, high-temperature curing at 85℃ for 130min; second step, high-temperature curing at 130℃ for 390min; and third step, high-temperature curing at 140℃ for 260min.

[0033] The parameter variations in Examples 1 to 3 show that the EP-TMB / SiO2 nano-doping modification method provided by the present invention can be effectively implemented within a wide process window. The composite materials prepared in each example maintain good consistency and excellent performance in key performance indicators such as DC breakdown voltage, glass transition temperature, dielectric constant and trap characteristics.

[0034] Comparative Example 1 (Acid Anhydride Curing System) This comparative example provides a method for preparing epoxy composite materials using conventional anhydride curing agents. The specific steps are as follows: Step S1: Mix 20g epoxy resin, 16g methyltetrahydrophthalic anhydride, and 0.2g 2,4,6-tris(dimethylaminomethyl)phenol, maintain a vacuum environment (≤1kPa), and heat and stir at 80℃ for 35min at 500r / min. Step S2: Inject the mixed solution obtained in step S1 into the epoxy breakdown mold, place it in a high-temperature vacuum oven, cure at 80°C for 240 min, and cure at 120°C for 480 min.

[0035] Comparative Example 2 (Anhydride Curing + SiO2 Doping System) This comparative example provides a method for preparing nano-SiO2 by doping alone in an acid anhydride curing system. The specific steps are as follows: Step S1: Place 0.37g of SiO2 particles into an agate mortar and grind evenly for 10 minutes; Step S2: Place the ground SiO2 particles from step S1 into a petri dish, put it in an oven, and heat at 100°C for 24 hours. Step S3: Add the dried SiO2 particles from step S2 to 16g of methyltetrahydrophthalic anhydride solution, heat at 60℃ and sonicate for 60min. Step S4: Connect the solution obtained in step S3 to a vacuum preparation platform, add 20g of EP solution and 0.2g of 2,4,6-tris(dimethylaminomethyl)phenol, maintain a vacuum environment, and heat and stir at 80°C with a stirring speed of 600r / min for 50min. Step S5: Inject the mixed solution obtained in step S4 into the epoxy breakdown mold, place it in a high-temperature vacuum oven, cure at 80°C for 240 min, and then cure at 120°C for 480 min.

[0036] Comparative Example 3 (TMB Grafting System) This comparative example provides a preparation method using only TMB grafting modification without adding SiO2 nanoparticles. The specific steps are as follows: Step S1: Place 12.5g of TMB powder into an agate mortar and grind evenly for 10 minutes; Step S2: Place the TMB powder ground in step S1 into a petri dish, put it in an oven, and heat at 100°C for 24 hours; Step S3: Add the dried TMB powder from step S2 to 20g of EP solution, add 0.2g of 2,4,6-tris(dimethylaminomethyl)phenol, maintain a vacuum environment, and heat and stir at 80℃ with a stirring speed of 500r / min for 40min. Step S4: Connect the solution obtained in step S3 to the vacuum preparation platform, maintain the vacuum environment, and heat and stir at 80°C with a stirring speed of 600 r / min for 50 min; Step S5: Pour the solution obtained in step S4 into an epoxy puncture mold, place it in a high-temperature vacuum oven, and perform three-step high-temperature curing: the first step is high-temperature curing at 80℃ for 120 minutes, the second step is high-temperature curing at 120℃ for 360 minutes, and the third step is high-temperature curing at 130℃ for 240 minutes.

[0037] Since Comparative Example 3 did not add SiO2, there was no ultrasonic dispersion stage as in the examples. Accelerator DMP-30 was added simultaneously with TMB in step S3, and its total dosage was the same as in Example 1. The difference in this step has a negligible impact on the final performance. Because the accelerator is added last among all materials, its function is to accelerate ring-opening. Therefore, its simultaneous addition here is justified because SiO2 is not needed, and no other materials require further addition. Thus, it is added simultaneously with TMB in step S3.

[0038] Performance Comparison Analysis (a) Differential scanning thermal testing Differential scanning thermal tests were performed on the above-mentioned insulators in Examples 1, 1, 2, and 3, with test temperatures ranging from 70 to 200°C. Figure 1 This is a graph showing the glass transition temperature of different epoxy composite materials.

[0039] from Figure 1 It can be concluded that the heat flux of the epoxy composite material decreases with temperature, and there is a stepped region around 140-160℃, in which the epoxy composite material transitions from a glassy state to a rubbery state. At the same temperature, the glass transition temperature of Example 1 (146.09℃) > Comparative Example 3 (134.59℃) > Comparative Example 2 (127.95℃) > Comparative Example 1 (123.56℃) represents an increase of 8.54%, 14.18%, and 18.23%, respectively. Example 1 has a significant effect on increasing the glass transition temperature.

[0040] (ii) Dielectric constant test The dielectric constant of the above-mentioned insulators in Examples 1, 1, and 2 was tested. Figure 2 The graphs show the dielectric constants of different epoxy composite materials in Examples 1, 1, 2, and 3.

[0041] Depend on Figure 2 It can be seen that the relative permittivity of Example 1 is 4.356, which is lower than that of the comparative examples. Compared with Comparative Example 1 (4.540), Comparative Example 2 (4.451), and Comparative Example 3 (4.411), it is reduced by 4.05%, 2.13%, and 1.25%, respectively. This fully demonstrates the regulatory effect of the examples on the dielectric constant of epoxy resin and verifies the effectiveness of the examples in modifying the dielectric parameters of epoxy resin.

[0042] (III) Surface potential decay experiment Surface potential decay experiments were conducted on the epoxy composite materials of Examples 1, 1, 2, and 3. The high-voltage DC power supply used in the test was R2-N50W500 from Dalian Haifu Technology Co., Ltd., and the test voltage was -10kV. The test was conducted using needle electrodes. Figure 3 The graph shows the surface potential decay curves of different epoxy composite materials in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0043] Figure 3 The results show that the surface potential of the epoxy composite material using a commonly used anhydride curing agent (Comparative Example 1) decreased by 40.34% (from 4.66 kV to 2.78 kV) after 20,000 s. After adding nano-SiO2 particles (Comparative Example 2) (decreasing from 4.61 kV to 2.98 kV), the potential decay rate decreased, with a surface potential decay of 35.36% after 20,000 s. After grafting the epoxy resin with TMB instead of anhydride curing agents (Comparative Example 3), the surface potential decay rate was slightly lower than that of Comparative Example 2 (decreasing from 4.60 kV to 3.02 kV), with a decay rate of 34.35%. Example 1, which combines the advantages of TMB and nano-SiO2, exhibited the slowest surface potential decay rate, decreasing only from 4.64 kV to 3.18 kV after 20,000 s, with a decay rate of only 31.54%. This demonstrates that Example 1 can significantly suppress the charge transport rate of the epoxy composite material.

[0044] (iv) Characterization of surface trap properties The surface trapping characteristics of the epoxy composite materials described in Examples 1, 1, 2, and 3 were characterized. Key parameters were extracted from the surface potential decay curves to characterize the trapping characteristics.

[0045] Figure 4The results show that the highest surface trap energy level and trap density in Example 1 are 1.025 eV and 1.48 × 10²⁰ eV, respectively. -1 ·m -3 The trap distribution characteristics of Comparative Example 3 and Comparative Example 2 are similar. The surface trap energy level and trap density of Comparative Example 3 are 1.016 eV and 1.43 × 10²⁰ eV, respectively. -1 ·m -3 The surface trap energy level and trap density of Comparative Example 2 are 1.015 eV and 1.42 × 10²⁰ eV, respectively. -1 ·m -3 The surface trap energy level and density of Comparative Example 1 are the lowest, at 1.001 eV and 1.38 × 10²⁰ eV, respectively. -1 ·m -3 .from Figure 4 The comparison of trap characteristics revealed that Example 1 introduced deep traps into the epoxy resin, which enhanced the probability of charge carriers entering the trap and suppressed the charge transport rate.

[0046] (v) DC breakdown test DC breakdown tests were conducted on the epoxy composite materials described in Examples 1, 1, 2, and 3. The test temperature was 30°C, and the high-voltage DC power supply used was an R2-N50W500 from Dalian Haifu Technology Co., Ltd., along with ball electrodes. Figure 5 The figures show the DC breakdown voltage of different epoxy composite materials in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. Table 1 shows the specific DC breakdown data.

[0047]

[0048] Figure 5 The results show that Example 1 exhibits the highest DC breakdown voltage, at 160.52 kV. Compared to Comparative Example 1 (138.63 kV), Comparative Example 2 (148.09 kV), and Comparative Example 3 (151.25 kV), this represents an improvement of 15.79%, 8.39%, and 6.13%, respectively, demonstrating a significant increase in DC breakdown voltage. It should be noted that the Weibull distribution was used to calculate the scale parameters, a common method for determining flashover voltage: the DC surface flashover voltage was analyzed using a two-parameter Weibull distribution. ; Where U is the flashover voltage in kV; α is the scale parameter in kV; and β is the shape parameter.

[0049] This is because the low dielectric and deep trap materials regulate charge transport, suppress charge injection, reduce the degree of electric field distortion, and increase the DC breakdown voltage.

[0050] In summary, the SiO2 nanoparticle doping modification method for improving the DC breakdown characteristics of EP-TMB composite materials provided by this invention can increase the glass transition temperature of epoxy composite materials, reduce the dielectric constant, suppress the surface potential decay rate, and improve the surface trap energy level and trap density, thereby increasing the DC breakdown voltage of epoxy composite materials. The synergistic modification method of TMB grafting and nano-SiO2 particle doping has significant treatment effects, is easy to implement, and is highly operable.

[0051] It should be understood that the above embodiments are merely exemplary. Those skilled in the art can make various non-substantial improvements and substitutions based on the technical concept of this invention, and all such improvements and substitutions should be considered to fall within the protection scope of this application.

Claims

1. A method for SiO2 nano-doping modification to improve the DC breakdown characteristics of EP-TMB composite materials, characterized in that, Includes the following steps: Step S1: Grind the TMB powder and SiO2 nanoparticles separately; Step S2: Dry the ground TMB powder and SiO2 nanoparticles separately; Step S3: Add the dried TMB powder to the epoxy resin solution, heat and stir under vacuum to allow TMB and epoxy resin to undergo a grafting reaction, and obtain an EP-TMB mixed solution. Step S4: Add the dried SiO2 nanoparticles to the EP-TMB mixed solution obtained in step S3, heat and ultrasonically disperse to obtain the EP-TMB / SiO2 mixed solution; Step S5: The solution obtained in step S4 is heated and stirred under vacuum to homogenize it; Step S6: Pour the homogenized solution from step S5 into a mold and perform stepwise high-temperature curing to obtain EP-TMB / SiO2 nanocomposite insulating material.

2. The method according to claim 1, characterized in that, In step S1, the grinding time for TMB powder and SiO2 nanoparticles is 8-12 minutes each independently.

3. The method according to claim 1, characterized in that, In step S2, the drying temperature is 95-105℃ and the drying time is 22-26 hours.

4. The method according to claim 1, characterized in that, In step S3, the heating temperature is 77-83℃, the stirring speed is 450-550 rpm, and the stirring time is 35-45 minutes.

5. The method according to claim 1, characterized in that, In step S4, the heating temperature is 55-65℃, and the ultrasonic dispersion time is 50-70 minutes.

6. The method according to claim 1, characterized in that, In step S5, the heating temperature is 77-83℃, the stirring speed is 550-650 rpm, and the stirring time is 45-55 minutes; and in step S5, an accelerator is added, which is 2,4,6-tris(dimethylaminomethyl)phenol, and the amount added is 0.1-0.3 grams per 20 grams of epoxy resin.

7. The method according to claim 1, characterized in that, The step-by-step high-temperature curing in step S6 specifically involves: First step curing: temperature 75-85℃, curing time 110-130 minutes; The second step is curing: the temperature is 115-125℃, and the curing time is 330-390 minutes; The third step is curing: the temperature is 130-140℃, and the curing time is 220-260 minutes.

8. The method according to claim 6, characterized in that, The vacuum readings in steps S3 and S5 are ≤0.07 MPa; the high-temperature curing in step S6 is carried out in a vacuum oven with a vacuum reading ≤0.09 MPa.

9. The method according to claim 1, characterized in that, The SiO2 nanoparticles have a particle size of 25-35 nanometers and a purity greater than 99.9%; by mass, 12-13 parts of TMB powder and 0.3-0.4 parts of SiO2 nanoparticles are added for every 20 parts of epoxy resin.

10. The method according to claim 1, characterized in that, In step S2, the drying treatment of SiO2 nanoparticles adopts the solvent replacement method, that is, the SiO2 nanoparticles are dispersed in anhydrous ethanol and sonicated, and then the dispersion is added to the EP-TMB mixed solution obtained in step S3, and the ethanol is removed during the vacuum stirring process in step S5.

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