Preparation method of high-thermal-conductivity epoxy resin composite material induced by alternating-current electric field

Abstract

The invention discloses a preparation method of a high-thermal-conductivity epoxy resin composite material. Belongs to the technical field of epoxy resin composite material preparation. The invention aims to solve the technical problem that the heat-conducting property of the epoxy resin composite material is not obviously improved under the condition of low filling amount. Before the epoxy resin is cured, hexagonal boron nitride in the epoxy resin is oriented along the direction of an electric field by adopting a method of alternating-current electric field induction and multi-dimensional filler compounding, and spherical aluminum oxide exists among hexagonal boron nitride sheets to promote the lap joint of the filler, so that the formation of a heat conduction channel in the epoxy resin is promoted; and the preparation of the high-thermal-conductivity epoxy composite material is realized under a relatively low filling amount. Compared with a common doped composite material, the prepared epoxy resin composite material has the advantages that under the same filling amount, the heat conductivity is obviously improved, and the electrical insulation property is well maintained; the material can be applied to equipment such as a dry-type transformer, and has important significance for realizing high-voltage, large-capacity and high-power operation of the equipment.

Description

Technical Field

[0001] This invention belongs to the field of epoxy resin composite material preparation technology, specifically relating to a method for preparing a high thermal conductivity epoxy resin composite material induced by an alternating electric field. Background Technology

[0002] Epoxy resin possesses excellent electrical insulation, thermal stability, and corrosion resistance, making it a commonly used casting insulation material for dry-type transformers. However, epoxy resin itself has low thermal conductivity, which prevents the heat generated during equipment operation from dissipating in a timely manner. This internal temperature rise poses a significant threat to the safe and stable operation of the equipment, limiting its application in high-voltage, high-capacity, and high-power dry-type transformers. Currently, the most common method to improve the thermal conductivity of epoxy resin is to dope it with highly thermally conductive inorganic fillers to create complete thermal conductivity pathways within the epoxy resin matrix. However, this method often requires a large amount of thermally conductive filler to achieve a significant improvement in thermal conductivity. This is because the thermally conductive filler is randomly distributed within the epoxy resin, and at low filler concentrations, the probability of overlap between fillers is small, resulting in incomplete thermal conductivity pathways. Furthermore, excessive thermally conductive filler can compromise the material's electrical insulation properties. Therefore, researching how to significantly improve the thermal conductivity of epoxy resin while maintaining good electrical insulation performance at low filler concentrations is crucial for the safe and stable operation of future high-level dry-type transformers. Summary of the Invention

[0003] The purpose of this invention is to address the problem of limited improvement in the thermal conductivity of epoxy resin composites with low filler content, and to provide a method for preparing high thermal conductivity epoxy resin composites induced by an alternating current electric field. The epoxy resin composite material prepared by this invention, at the same filler content, exhibits significantly improved thermal conductivity compared to ordinary doped composites, while maintaining good electrical insulation properties. This material can be applied to equipment such as dry-type transformers, and is of great significance for achieving high-voltage, high-capacity, and high-power operation of such equipment.

[0004] To address the aforementioned technical problems, the present invention adopts the following technical solution: Before the epoxy resin is cured, this invention uses an alternating electric field induction and multidimensional filler compounding method to orient the hexagonal boron nitride in the epoxy resin along the direction of the electric field. The spherical alumina present between the hexagonal boron nitride sheets promotes the overlap of the fillers and promotes the formation of thermally conductive pathways inside the epoxy resin. This enables the preparation of high thermal conductivity epoxy composite materials with a low filler content.

[0005] The purpose of this invention is to provide a method for preparing a high thermal conductivity epoxy resin composite material induced by an alternating electric field, which is carried out according to the following steps: Step 1: After preheating E51 epoxy resin, mix it thoroughly with methyl hexahydrophthalic anhydride (MHHPA), then add appropriate amounts of hexagonal boron nitride (h-BN) and spherical alumina (Al2O3) in sequence, stir thoroughly, and then sonicate for a period of time to remove air bubbles from the suspension; then add a small amount of 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), and continue stirring for a period of time to obtain epoxy resin precasting material.

[0006] Step 2: Pour the epoxy resin precast refractory into the mold, then place the mold in an oven and apply AC voltage to both sides of the mold; Step 3: Gradient temperature increase curing to obtain the epoxy resin composite material.

[0007] Further specifying that in step 1, E51 needs to be preheated at 60°C for 30 minutes before use, and the preheating is carried out in an oven.

[0008] Further specifying, in step 1, the amount of E51 epoxy resin is 20 g, the amount of methyl hexahydrophthalic anhydride (MHHPA) is 17 g, and the mass ratio of E51 epoxy resin to MHHPA is 100:85; the amount of h-BN is 3.288 g, the amount of Al2O3 is 0.822 g, and the mass ratio of h-BN to Al2O3 is 4:1; the amount of DMP-30 is 0.06 g, and the mass ratio of E51 to DMP-30 is 100:0.03.

[0009] Further, in step 1, the thickness d of the h-BN used is ≤100 nm and the inner diameter of the wafer is 1 μm-3 μm.

[0010] To further specify, in step 1, the diameter of the Al2O3 used is 3-4 μm.

[0011] Further specifying, in step 1, the stirring temperature is 75°C and the stirring speed is 300 r / min.

[0012] Further specifying, in step 1, at 75℃ and 0.675 W / cm² 2 Ultrasonic oscillation can be achieved using an ultrasonic cleaner.

[0013] Further specifying, in step 2, the thickness of the mold is 2.5 mm.

[0014] To further specify, in step 2, the oven temperature is set to 80°C.

[0015] Further specifying, in step 2, the AC voltage waveform is output by an arbitrary waveform generator (AFG3200C) and applied to both sides of the mold via a high-voltage amplifier (Model30 / 20A).

[0016] Further specifying, in step 2, the AC voltage frequency is 5 Hz, 50 Hz, 500 Hz, or 5000 Hz.

[0017] Further specifying, in step 2, the AC voltage is applied for 20 min or 40 min.

[0018] Further specifying, in step 2, after applying an AC voltage, the electric field strength amplitude in the epoxy resin composite material is 200 V / mm.

[0019] Further specifying, in step 2, the curing process is to cure at 100℃ for 2 hours and at 120℃ for 4 hours.

[0020] The present invention has the following beneficial effects: This invention discloses a method for preparing high thermal conductivity epoxy resin composites induced by an alternating current electric field. Using E51 epoxy resin as a matrix, multidimensional high thermal conductivity fillers (h-BN and Al2O3) are added. The synergistic effect of h-BN and Al2O3 promotes the formation of thermally conductive pathways. An alternating current electric field induces h-BN to orient along the electric field direction (out-of-plane thermal conductivity direction) within the epoxy resin, enhancing out-of-plane thermal efficiency and forming more complete thermally conductive pathways within the epoxy resin. After curing the epoxy resin, this structure is preserved, resulting in the corresponding epoxy resin composite. Compared to the indiscriminate construction of thermally conductive pathways through direct doping of fillers, this invention utilizes the inductive effect of an alternating current electric field to orient h-BN in a specific direction, increasing the probability of filler overlap along the electric field direction. The presence of Al2O3 between h-BN flakes further increases the probability of filler overlap perpendicular to the electric field direction, thus promoting the construction of thermally conductive pathways and solving the problem of insignificant improvement in thermal conductivity of epoxy resin composites with low filler content.

[0021] The epoxy resin composite material prepared using this invention exhibits significantly improved thermal conductivity and excellent electrical insulation properties compared to directly doped composite materials with the same filler content. By utilizing the compounding of multidimensional fillers and the inductive effect of an alternating electric field, the thermal conductivity of the epoxy resin composite material is significantly improved even with low filler content. This provides a new approach for developing epoxy resin composite materials that integrate thermal conductivity and insulation properties, and is of great significance for achieving high voltage, large capacity, and high power in dry-type transformers.

[0022] For a deeper understanding of the features and technical content of this invention, please refer to the accompanying detailed description and drawings. It should be noted that the drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0023] Figure 1 The results are the thermal conductivity test results for epoxy resin composite materials; Figure 2 The results are from scanning electron microscopy characterization of the cross-section of the uninduced epoxy resin composite material. Figure 3 The results of scanning electron microscopy characterization of the cross-section of epoxy resin composite material induced by a 5 Hz AC electric field for 40 min are shown. Figure 4 The results of AC breakdown strength tests of epoxy resin and its composites at power frequency with an induction time of 20 min are shown. Figure 5 The results are the AC breakdown strength test results of epoxy resin and its composites at power frequency when the induction time is 40 min. Detailed Implementation

[0024] The present invention will be described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but should not be considered as limiting the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0025] Example 1: The preparation method of the high thermal conductivity epoxy resin composite material induced by AC electric field in this example is carried out according to the following steps: Step 1: Preheat 20 g of E51 epoxy resin in an oven at 60℃ for 30 min. Then add 17 g of MHHPA and stir the mixture with a magnetic stirrer at 75℃ and 300 r / min for 20 min. Next, add 3.288 g of h-BN and 0.822 g of Al2O3 to the mixture sequentially, and continue stirring at 75℃ for 12 h to obtain a suspension. The mass ratio of h-BN to Al2O3 in the suspension is 4:1, and the two together account for 10 wt% of the suspension.

[0026] The stirred suspension was placed in an ultrasonic cleaner and ultrasonically vibrated for 2 hours in a 75°C water bath environment, with an ultrasonic power density of 0.675 W / cm³. 2 Remove air bubbles from the suspension.

[0027] Add 0.06 g of DMP-30 to the suspension and continue stirring at 75℃ and 300 r / min for 5 min to obtain epoxy resin precasting material.

[0028] Step 2: Pour the epoxy resin precast material into a mold with a thickness of 2.5 mm, and place the mold in an 80°C oven. Use an arbitrary waveform generator (AFG3200C) to output an AC voltage with a amplitude of 500 V through a high voltage amplifier (Model30 / 20A) to make the electric field strength inside the composite material 200 V / mm, the voltage frequency 5 Hz, and the application time 20 min.

[0029] Step 3: Disconnect the AC voltage and use a gradient temperature increase in the oven to cure the epoxy resin. The curing conditions are 100℃ for 2 hours and 120℃ for 4 hours. Perform thermal conductivity and AC breakdown strength tests on the cured samples.

[0030] Example 2 The difference between this embodiment and Embodiment 1 is that the AC voltage frequency is 50 Hz, while the other steps and parameters are the same as in Embodiment 1.

[0031] Example 3 The difference between this embodiment and Embodiment 1 is that the AC voltage frequency is 500 Hz, while the other steps and parameters are the same as in Embodiment 1.

[0032] Example 4 The difference between this embodiment and Embodiment 1 is that the AC voltage frequency is 5000 Hz, while the other steps and parameters are the same as in Embodiment 1.

[0033] Example 5 The difference between this embodiment and Embodiment 1 is that the AC voltage is applied for 40 minutes, while the other steps and parameters are the same as in Embodiment 1.

[0034] Example 6 The difference between this embodiment and Embodiment 1 is that the AC voltage frequency is 50 Hz and the application time is 40 min, while the other steps and parameters are the same as in Embodiment 1.

[0035] Example 7 The difference between this embodiment and Embodiment 1 is that the AC voltage frequency is 500 Hz and the application time is 40 min, while the other steps and parameters are the same as in Embodiment 1.

[0036] Example 8 The difference between this embodiment and Embodiment 1 is that the AC voltage frequency is 5000 Hz and the application time is 40 min, while the other steps and parameters are the same as in Embodiment 1.

[0037] Comparative Example 1 (1) 20 g of E51 epoxy resin was placed in an oven at 60°C and preheated for 30 min. Then, 17 g of MHHPA was added to the mixture, and the mixture was stirred at 75°C for 20 min using a magnetic stirrer. Then, 3.288 g of h-BN and 0.822 g of Al2O3 were added to the mixture in sequence, and the mixture was stirred at 75°C for 12 h to obtain a suspension. The mass ratio of h-BN to Al2O3 in the suspension was 4:1, and the two accounted for 10 wt% of the suspension.

[0038] (2) Place the stirred suspension in an ultrasonic cleaner and ultrasonically vibrate it in a 75°C water bath for 2 hours to remove air bubbles from the suspension.

[0039] (3) Add 0.06 g DMP-30 to the suspension and continue stirring at 75°C for 5 min to obtain epoxy resin precasting material.

[0040] (4) The epoxy resin precast material was poured into a mold with a thickness of 2.5 mm, and the mold was placed in an oven. The epoxy resin was cured by gradient heating in the oven. The curing conditions were 100℃ for 2 h and 120℃ for 4 h. The thermal conductivity and AC breakdown strength of the cured sample (uninduced epoxy resin composite material) were tested. The thermal conductivity of the uninduced epoxy resin composite material was 0.356 W / m·K.

[0041] Comparative Example 2 (1) Place 20 g of E51 epoxy resin in an oven at 60°C and preheat for 30 min. Then add 17 g of MHHPA and stir the mixture at 75°C for 12 h using a magnetic stirrer.

[0042] (2) Place the stirred mixture in an ultrasonic cleaner and ultrasonically vibrate it in a 75°C water bath for 2 hours to remove air bubbles from the suspension.

[0043] (3) Add 0.06 g DMP-30 to the mixture and continue stirring at 75°C for 5 min to obtain epoxy resin precasting material.

[0044] (4) The epoxy resin precast material was poured into a mold with a thickness of 2.5 mm, and the mold was placed in an oven. The epoxy resin was cured by gradient heating in the oven. The curing conditions were 100℃ for 2 h and 120℃ for 4 h. The thermal conductivity and AC breakdown strength of the cured sample (pure E51 epoxy resin) were tested. The thermal conductivity of pure E51 epoxy resin was 0.18 W / m·K.

[0045] The thermal conductivity test results of epoxy resin composites are as follows: Figure 1As shown. Compared with pure E51 epoxy resin, the thermal conductivity of the uninduced epoxy resin composite increased from 0.18 W / m·K to 0.356 W / m·K. This is the result of the interaction and synergy between h-BN and Al2O3 within the epoxy resin, promoting the formation of thermal conductivity pathways. Figure 2 As shown in the red dashed box, compared to uninduced epoxy resin composites with the same filler content, the thermal conductivity of all composites induced by AC electric field is improved to varying degrees. This is because, under the action of the electric field, h-BN is deflected along the direction of the electric field (out-of-plane thermal conduction direction), enhancing the thermal conductivity efficiency in the out-of-plane thermal conduction direction, such as... Figure 2 and Figure 3 As shown by the yellow dashed line, after being induced by the electric field, h-BN exhibits a clear orientation behavior (the left-to-right direction is the out-of-plane thermal conduction direction). Figure 1 It is known that, under the same electric field application time, the higher the frequency of the alternating current electric field, the lower the thermal conductivity of the epoxy resin composite material. This is because the higher the frequency of the alternating current electric field, the faster the direction of the electric field changes. Each time the electric field direction changes, the direction of the electric field deflection force on h-BN changes. Therefore, at high frequencies, h-BN often does not have enough time to achieve sufficient orientation along the electric field direction, resulting in insufficient thermal conductivity pathways. Furthermore, at the same frequency and time, the longer the induction time, the more obvious the h-BN orientation and the higher the thermal conductivity. After 40 minutes of induction with an alternating current electric field of 200 V / m and a frequency of 5 Hz, the thermal conductivity of the epoxy resin composite material reached 0.496, which is 39.33% higher than the thermal conductivity of the uninduced epoxy resin composite material with the same filler content, and 175.56% higher than the thermal conductivity of pure E51 epoxy resin. The test results of the power frequency AC breakdown strength of epoxy resin and its composites under different induction times are as follows: Figure 4 and Figure 5 As shown in the figure, the addition of h-BN and Al2O3 resulted in varying degrees of decrease in the AC breakdown field strength of all composite materials. This is because the addition of inorganic fillers inevitably introduces various defects (agglomeration electric field distortion points, bubbles, etc.) into the epoxy resin, leading to a decrease in the breakdown field strength. After electric field induction, the breakdown field strength improved, possibly because the oriented h-BN optimized the originally severely distorted electric field. After 20 minutes of AC electric field induction with an amplitude of 200 V / m and a frequency of 5 Hz, the AC breakdown field strength of the epoxy resin composite material was 64.81 kV / mm, maintaining a relatively high level and meeting the application requirements of equipment such as dry-type transformers.

[0046] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the scope of the present invention.

Claims

1. A method for preparing a high thermal conductivity epoxy resin composite material induced by an alternating electric field, characterized in that, Includes the following steps: Step 1: After preheating E51 epoxy resin, mix it thoroughly with methyl hexahydrophthalic anhydride (MHHPA), then add hexagonal boron nitride (h-BN) and spherical alumina (Al2O3) in sequence, stir thoroughly, and ultrasonically vibrate; add 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), stir until uniform, and obtain the precast refractory; Step 2: Pour the precast refractory into the mold, then place it in an oven and apply AC voltage to both sides of the mold; Step 3: Gradient temperature increase curing to obtain the epoxy resin composite material.

2. The method according to claim 1, characterized in that, In step 1, preheat at 60 ℃ for 30 min.

3. The method according to claim 1, characterized in that, The mass ratio of E51 epoxy resin, MHHPA, h-BN and Al2O3 is 20:17:3.288:0.

822.

4. The method according to claim 1, characterized in that, In step 1, the thickness of the h-BN used is d≤100 nm and the inner diameter of the wafer is 1 μm-3 μm; the diameter of the Al2O3 used is 3 μm-4 μm.

5. The method for preparing a high thermal conductivity epoxy resin composite material induced by an alternating electric field according to claim 1, characterized in that, In step 1, the mixture is stirred at 300 r / min and 75℃.

6. The method according to claim 1, characterized in that, At 75℃, 0.675 W / cm 2 Ultrasonic oscillation.

7. The method according to claim 1, characterized in that, The mass ratio of E51 to DMP-30 is 100:0.

03.

8. The method according to claim 1, characterized in that, In step 2, the mold thickness is 2.5 mm, the oven temperature is set to 80℃, the AC voltage frequency is 5 Hz, 50 Hz, 500 Hz or 5000 Hz, the time is 20 min or 40 min, and the electric field strength amplitude is 200 V / mm.

9. The method according to claim 1, characterized in that, The curing process involves curing at 100 ℃ for 2 hours and at 120 ℃ for 4 hours.

10. An epoxy resin composite material prepared by the method according to any one of claims 1-9.

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