High-thermal-conductivity epoxy composite material efficiently induced and oriented by high-frequency high-voltage bipolar square wave electric field and preparation method of high-thermal-conductivity epoxy composite material

Abstract

The invention discloses a high-thermal-conductivity epoxy composite material efficiently induced and oriented by a high-frequency high-voltage bipolar square wave electric field and a preparation method of the high-thermal-conductivity epoxy composite material. An epoxy resin mixed solution doped with hexagonal boron nitride is subjected to defoaming, pouring and curing. During curing, high-frequency square-wave voltage is applied for electric field orientation induction, and then the curing procedure is continued, so that the epoxy resin composite material is completely cured. The waveform distortion problem caused by the dielectric constant of liquid epoxy under low frequency is fully considered, the spatial orientation of hexagonal boron nitride (h-BN) is accurately regulated and controlled by adopting the dynamic polarization effect of the high-frequency and high-voltage bipolar square wave electric field, a through continuous heat conduction network is formed, the transfer path of heat in the specific direction is optimized, and the heat conduction efficiency is improved. The scattering of phonons at an interface is effectively reduced, so that the heat-conducting property of the epoxy composite material is greatly improved. By optimizing the synergism of the high-frequency high-voltage bipolar square wave electric field intensity and the boron nitride doping amount, the balance of heat conduction, insulation and mechanical properties is realized under the condition of low filling amount.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of epoxy resin composite materials, and specifically relates to a high-frequency, high-voltage, bipolar square wave electric field-efficiently induced orientation high-thermal conductivity epoxy composite material and a preparation method thereof. Background Art

[0002] Epoxy resins are widely used in electronic packaging and other fields due to their excellent insulation and mechanical properties. To ensure safe and reliable operation of equipment, insulating materials must possess excellent thermal conductivity. However, the intrinsic thermal conductivity of pure epoxy resin is very low, typically only around 0.18-0.21 W / (m·K), which cannot meet the high-temperature resistance and heat dissipation requirements of electrical equipment, seriously affecting its stable operation. Current research on improving the thermal conductivity of epoxy resin composite insulation materials primarily utilizes two strategies: filling-based and intrinsic-based. Intrinsic-based modification aims to increase crystallinity by manipulating the order of polymer molecular chains, reducing phonon scattering, thereby extending the phonon free path and increasing phonon transmission rate. However, these approaches are limited by complex synthesis processes and high production costs, and the actual improvement in thermal conductivity is limited, making them unable to meet the stringent heat dissipation requirements of high-power applications. In contrast, filling-based solutions have become the mainstream technology due to their ease of implementation and manageable costs. By introducing highly thermally conductive fillers (such as boron nitride and aluminum oxide) to create heat conduction channels, they can effectively improve thermal conductivity. However, high filling content can easily cause filler agglomeration, a sharp increase in matrix viscosity and deterioration of mechanical properties, while randomly dispersed fillers at low filling content are difficult to form an effective heat conduction path, and the improvement in thermal conductivity is limited.

[0003] In recent years, researchers have attempted to optimize filler orientation through electric field-induced techniques. For example, direct current (DC), alternating current (AC), or pulsed electric fields are used to align boron nitride nanosheets to create efficient thermally conductive networks. However, existing electric field methods face significant bottlenecks: high-voltage electric fields (e.g., greater than 10 kV) can easily cause breakdown of the epoxy matrix, making them suitable only for ultrathin samples; DC fields struggle to balance the degree of orientation with the orientation time and field magnitude; low-frequency AC fields (e.g., 50 Hz) have low orientation efficiency and are difficult to adapt to highly filled systems; while microsecond pulsed electric fields can be applied to bulk materials, their frequency effects and electrothermal synergy mechanisms remain unclear; and while low-frequency square waves can enhance thermal conductivity, the effect is not significant. Furthermore, current research on electric field-induced orientation techniques rarely addresses the impact of liquid epoxy capacitance on the voltage waveform during pressurization. When applying a high-frequency electric field, the large capacitance of uncured epoxy resin can severely distort the voltage waveform and reduce its amplitude, causing the actual applied electric field to deviate significantly from the expected value. For example, a sine wave can be distorted into a triangle wave, while a square wave can be distorted into a microsecond pulse wave, weakening the effectiveness of the electric field-induced orientation. Therefore, there is an urgent need for an electric field orientation method that can effectively improve thermal conductivity at a lower doping level while ensuring that the voltage waveform is applied correctly. Summary of the Invention

[0004] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a high-thermal conductivity epoxy composite material and a preparation method thereof that can efficiently induce orientation by a high-frequency, high-voltage, bipolar square wave electric field. The present invention can solve the problems of the lack of obvious improvement in the thermal conductivity of epoxy composite materials and the unclear process of the existing electric field induced orientation method.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: A method for preparing a high-thermal-conductivity epoxy composite material induced by a high-frequency, high-voltage, bipolar square-wave electric field, comprising the following steps: The epoxy resin mixed solution doped with hexagonal boron nitride is degassed and poured, and then cured. During the curing process, a high-frequency, high-voltage, bipolar square wave voltage is applied to the poured sample to induce electric field orientation. After the high-frequency, high-voltage, bipolar square wave voltage is applied, the curing procedure is continued to completely cure the epoxy resin composite material to obtain a high thermal conductivity epoxy composite material.

[0006] Preferably, the raw materials of the epoxy resin mixed solution include epoxy resin, 4-methylhexahydrophthalic anhydride, 2, 4, 6-tris(dimethylaminomethyl)phenol and hexagonal boron nitride, wherein the mass ratio of epoxy resin, 4-methylhexahydrophthalic anhydride and 2, 4, 6-tris(dimethylaminomethyl)phenol is (98-102):(78-82):1, and the mass of hexagonal boron nitride is 10%-25% of the total mass of epoxy resin, 4-methylhexahydrophthalic anhydride and 2, 4, 6-tris(dimethylaminomethyl)phenol.

[0007] Preferably, the diameter of the hexagonal boron nitride is 5-15 μm.

[0008] Preferably, the mold for casting the epoxy resin mixed solution doped with hexagonal boron nitride includes an insulating clip, flat electrodes are provided on both sides of the insulating clip, the insulating clip is provided with a through hole along its thickness direction, the insulating clip and the flat electrodes on both sides form a casting molding cavity at the through holes, the insulating clip is provided with a gate connected to the casting molding cavity, and an insulating plate is provided on the side of each flat electrode away from the insulating clip.

[0009] Preferably, before applying a high-frequency square wave voltage to the cast sample for electric field orientation induction, several molds are connected to a high-frequency square wave voltage application circuit in a series-parallel circuit structure, and a protection capacitor is connected in series to the high-voltage end of the high-frequency square wave voltage application circuit; thereafter, a high-frequency square wave voltage is applied to the cast sample for electric field orientation induction; The total capacitance in the high-frequency square wave voltage application circuit is no greater than the capacitance when a single mold is filled with a liquid epoxy resin mixed solution doped with hexagonal boron nitride.

[0010] Preferably, the high-frequency square wave voltage application circuit includes a high-frequency square wave power supply, and several molds are connected to the high-frequency square wave power supply in a series-parallel circuit structure. The high-frequency square wave power supply is also connected to an oscilloscope. The oscilloscope is used to observe the voltage waveform output by the high-frequency square wave power supply. During the process of applying a high-frequency square wave voltage to the cast sample to induce electric field orientation, the output voltage of the high-frequency square wave power supply is adjusted by observing the voltage waveform displayed on the oscilloscope to maintain the output voltage amplitude of the high-frequency square wave power supply constant.

[0011] Preferably, the thickness of the insulating clip is 0.2-1 mm, and the flat electrodes on both sides of the insulating clip are in contact with the side surfaces of the insulating clip.

[0012] Preferably, the epoxy resin mixed solution doped with hexagonal boron nitride is cured in an oven. During the curing process, when a high-frequency square wave voltage is applied to the cast sample for electric field orientation induction, the oven temperature is the initial temperature of the curing procedure of the epoxy resin mixed solution doped with hexagonal boron nitride.

[0013] Preferably, during the curing process, when a high-frequency square wave voltage is applied to the cast sample for electric field orientation induction, the frequency of the high-frequency square wave voltage is above 10 kHz, the electric field strength is 0.5-2 kV / mm, and the orientation induction time is 40-60 min.

[0014] The present invention also provides a high thermal conductivity epoxy composite material, which is prepared by the preparation method of the high thermal conductivity epoxy composite material with high frequency and high voltage bipolar square wave electric field efficient induced orientation as described above.

[0015] The present invention has the following beneficial effects: In the present invention's method for preparing a high-thermal-conductivity epoxy composite material with efficient orientation induced by a high-frequency, high-voltage, bipolar square-wave electric field, a high-frequency, high-voltage, bipolar square-wave voltage is applied to the cast sample during the curing process to induce electric field orientation. During this process, the dynamic polarization effect of the high-frequency, high-voltage, bipolar square-wave electric field precisely regulates the spatial orientation of the hexagonal boron nitride (h-BN), forming a continuous thermal conductive network that runs through it. This optimizes the heat transfer path along a specific direction and effectively reduces phonon scattering at the interface, thereby improving the thermal conductivity of the epoxy composite material. By optimizing the synergy between the high-frequency, high-voltage, bipolar square-wave electric field intensity and the boron nitride doping level, the present invention achieves a balance of thermal conductivity, insulation, and mechanical properties at a low filler level. Compared to traditional AC and DC electric field induction technologies, the steep rising edge characteristics of high-frequency, high-voltage bipolar square waves significantly enhance the driving force of the electric field on h-BN. Compared to low-frequency, low-voltage pulsed square waves, the high-frequency bipolar square waves used in the present invention can generate electric field forces in opposite directions on the boron nitride particles, generating efficient dielectrophoretic force drive, improving their in-situ steering efficiency, preventing the particles from moving in one direction, thereby preventing particle agglomeration and forming a continuous thermal conductive network. It matches the appropriate electric field strength for large-diameter boron nitride particles and improves the efficiency of thermal path construction. The present invention provides a new material solution with high thermal conductivity and strong insulation for lightweight and high-density packaging in the fields of high-voltage power equipment, high-power integrated circuits, etc.

[0016] Furthermore, the present invention utilizes an oscilloscope to detect the voltage waveform of the electric field induction process throughout the entire process, thereby improving the impact of voltage waveform changes on the degree of orientation during the orientation process. The polyimide protection capacitor design effectively suppresses electrolytic bubble defects, ensures the insulation reliability of the material, and provides a new solution for the preparation of thinner samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1(a) shows the first model of the mold for preparing a high-thermal-conductivity epoxy-based composite material for induction of high-frequency, high-voltage, bipolar, square-wave electric fields according to the present invention. Figure 1(b) shows the second model of the mold for preparing a high-thermal-conductivity epoxy-based composite material for induction of high-frequency, high-voltage, bipolar, square-wave electric fields according to the present invention (one side of the flat electrode and insulating plate are not shown).

[0018] Figure 2 This is a circuit model diagram of the high-frequency, high-voltage, bipolar square wave electric field used in the embodiments of the present invention to induce the orientation of boron nitride in epoxy resin.

[0019] Figure 3 This is a preparation model diagram of a high thermal conductivity epoxy-based composite material induced by a high-frequency, high-voltage, bipolar square wave electric field in an embodiment of the present invention.

[0020] Figure 4 Schematic diagram of the connection of multiple mold circuits during high-frequency and high-voltage bipolar square wave electric field induction in an embodiment of the present invention.

[0021] Figure 5 The dielectric constant of liquid epoxy resin changes with frequency and temperature.

[0022] Figure 6 This is a diagram showing the waveform changes during high-frequency and high-voltage bipolar square wave electric field induction in an embodiment of the present invention.

[0023] In the figure, 1- flat electrode, 2- gate, 3- insulating clip, 3-1- casting molding cavity, 4- insulating plate, 6- oscilloscope, 7- high voltage probe, 8- high frequency square wave power supply, 9- oven. DETAILED DESCRIPTION

[0024] The present invention will be described clearly and completely below with reference to the accompanying drawings and embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention, not all embodiments.

[0025] See Figure 1(a)- Figure 3 The method for preparing a high-thermal-conductivity epoxy composite material with high-frequency, high-voltage, bipolar square-wave electric field efficient induced orientation of the present invention specifically comprises the following steps: S1: Prepare a mixed solution of epoxy resin doped with h-BN (i.e., hexagonal boron nitride) and stir it evenly. After vacuum degassing, pour it into a mold as shown in Figures 1 (a) and 1 (b). The mold includes an insulating clip 3, and flat electrodes 1 are provided on both sides of the insulating clip 3. The insulating clip 3 is provided with through holes along its thickness direction. The insulating clip 3 and the flat electrodes 1 on both sides form a casting molding cavity 3-1 at the through holes. The insulating clip 3 is provided with a gate 2 connected to the casting molding cavity 3-1, and each flat electrode 1 is provided with an insulating plate 4 on the side away from the insulating clip 3. The insulating clip 3 has a thickness of 0.2-1 mm. The flat electrodes on either side of the insulating clip 3 are bonded to the sides of the insulating clip 3. Each flat electrode 1 is bonded to the adjacent insulating plate 4. The flat electrode 1 can be made of copper or brass, which has good conductivity. The insulating clip 3 and insulating plate can be made of polytetrafluoroethylene (PTFE) with excellent heat resistance and insulation properties. The through holes defined along the thickness of the insulating clip 3 are circular. The resulting high-thermal-conductivity epoxy composite material is a circular sample. When pouring the h-BN-doped epoxy resin mixed solution, pour it through the gate 2 and fill the entire casting cavity 3-1.

[0026] The raw materials of the epoxy resin mixed solution include epoxy resin, 4-methylhexahydrophthalic anhydride, 2, 4, 6-tris(dimethylaminomethyl)phenol and hexagonal boron nitride, wherein the mass ratio of epoxy resin, 4-methylhexahydrophthalic anhydride and 2, 4, 6-tris(dimethylaminomethyl)phenol is (100±2):(80±2):1, wherein the aforementioned "±2" is the allowable error in the amount of epoxy resin and 4-methylhexahydrophthalic anhydride added. Within this error range, the technical solution of the present invention is feasible, and the mass of hexagonal boron nitride is 10%-25% of the total mass of the epoxy resin, 4-methylhexahydrophthalic anhydride and 2, 4, 6-tris(dimethylaminomethyl)phenol. In the specific operation, epoxy resin, 4-methylhexahydrophthalic anhydride, and 2, 4, 6-tris(dimethylaminomethyl)phenol are added to a beaker according to the calculated reaction amount by weight. Then, 10% to 25% by mass of h-BN is added. The h-BN used in the present invention has a diameter of 5 to 15 μm. Mechanical stirring is then performed in a water bath for at least 30 minutes to uniformly disperse the h-BN in the epoxy resin mixed solution, thereby obtaining an epoxy resin mixed solution doped with hexagonal boron nitride. The stirring speed is 2000 to 2300 rpm, and vacuum degassing is performed for at least 10 minutes.

[0027] During vacuum degassing, the oven should be preheated at a temperature lower than the epoxy curing temperature to reduce the viscosity of the epoxy resin and facilitate the degassing process.

[0028] S2: Place the mold into the oven and connect it in series and parallel structure (such as Figure 4 As an example, the structure is not limited to Figure 4 example) is connected to the high-frequency square wave voltage application circuit (see Figure 2 ), a piece of polyimide film is used as a protective capacitor and connected in series to the high voltage end of the high frequency square wave voltage application circuit. Figure 2The high-frequency, high-voltage, bipolar square-wave voltage application circuit includes a high-frequency square-wave power supply 8. Several molds are connected to the high-frequency square-wave power supply 8 in a series-parallel circuit configuration. The high-frequency square-wave power supply 8 is also connected to an oscilloscope 6 for observing the voltage waveform output by the high-frequency square-wave power supply 8. In the present invention, the polyimide film used for the protective capacitor should be at least 0.1 mm thick to reduce the total capacitance of the high-frequency square-wave voltage application circuit, thereby reducing the current in the high-frequency square-wave voltage application circuit and preventing excessive current from electrolyzing the epoxy resin and generating bubbles. Furthermore, it prevents excessive voltage from causing breakdown of the protective capacitor. In the present invention, the series-parallel configuration of multiple molds should consider the following factors: 1) the total capacitance of the circuit cannot exceed the capacitance of the power supply under rated load (i.e., the total capacitance cannot exceed the capacitance of a single mold when filled with a liquid epoxy resin mixed solution doped with hexagonal boron nitride); 2) the voltage across each mold must be maintained at the required voltage; and 3) the total applied voltage should not be too high to prevent breakdown of the polyimide film in the protective capacitor. The mold series-parallel structure is determined according to the rated load of the power supply and the number of samples prepared in a single time, ensuring that the total capacitance of the circuit is not greater than the capacitance when a single mold is filled with liquid epoxy resin. Those skilled in the art can flexibly design it according to the actual situation and the above requirements. This invention is only given as an example. Figure 4 The circuit shown is not specifically limited.

[0029] S3: During the curing process, a high-frequency square wave voltage is applied through the high-frequency high-voltage bipolar square wave power supply 8. The output voltage of the high-frequency square wave power supply 8 is continuously adjusted by observing the waveform on the oscilloscope to maintain a constant output voltage amplitude of the high-frequency square wave power supply 8. Figure 5 It shows that the relative dielectric constant of uncured liquid epoxy resin is too large at low frequencies, resulting in excessively large circuit capacitance values, requiring a larger capacity power supply to ensure the accuracy of the output square wave waveform. At high frequencies (greater than 1kHz), the relative dielectric constant of liquid epoxy resin decreases, the capacitance value decreases, and the burden on the power supply is reduced, thereby significantly reducing the degree and duration of voltage waveform distortion. During the curing process, when a high-frequency square wave voltage is applied to the cast sample for electric field orientation induction, the oven temperature is the initial temperature of the curing procedure of the epoxy resin mixed solution doped with hexagonal boron nitride, the frequency of the high-frequency square wave voltage is above 10kHz, the electric field strength is 0.5~2kV / mm, and the orientation induction time is 40~60min. In the present invention, the oscilloscope should observe the voltage waveform applied to the high-voltage side of the epoxy resin. See Figure 6 Experimental observations show that from 0 to 30 minutes of pressurization, the voltage waveform gradually changes from a pulse wave to a square wave as the liquid epoxy capacitance changes, with the amplitude first decreasing, then increasing, and then decreasing again. From 30 to 60 minutes, the voltage waveform becomes a square wave with a stable amplitude. Therefore, during the orientation induction process, the oscilloscope should be closely monitored and the voltage output should be continuously adjusted to maintain a constant voltage amplitude.

[0030] S4: After the high-frequency, high-voltage, bipolar square wave voltage is applied, the curing process is continued to fully cure the epoxy resin composite. The curing process should continue after 40-60 minutes of electric field-induced orientation. The curing process is determined by the curing kinetics and empirical values.

[0031] In this approach, a high-frequency square wave voltage is applied for a specific time at the initial curing temperature. A polyimide film is connected in series with the high-voltage terminal to reduce loop current. The voltage amplitude is gradually adjusted to stabilize using an oscilloscope, thereby inducing the h-BN to align with the electric field. This approach addresses the issue of high capacitance in liquid epoxy resin during electric field orientation, establishing a new method for inducing high-frequency square wave voltage to simultaneously enhance the thermal conductivity and insulation properties of h-BN / epoxy resin composites.

[0032] Example 1 The method for preparing the high-thermal-conductivity epoxy composite material with high-efficiency induced orientation by a high-frequency, high-voltage, bipolar square-wave electric field in this embodiment specifically comprises the following steps: S1: Prepare an h-BN-doped epoxy resin solution in a beaker by combining E51 epoxy resin, 4-methylhexahydrophthalic anhydride, and 2,4,6-tris(dimethylaminomethyl)phenol in a mass ratio of 100:80:1. The beaker was then placed in a 60°C water bath and stirred uniformly with a mechanical stirrer at 2000 rpm. The mixture was vacuum-degassed in a preheated 60°C oven for 10 minutes before being poured into a mold. In this example, the distance between the copper plates (i.e., the spacing between the flat electrodes, which is also equal to the thickness of the insulating clip 3) was 1 mm.

[0033] The mass fraction of the doped h-BN is 25% (ie, the mass of h-BN is 25% of the total mass of E51 epoxy resin, 4-methylhexahydrophthalic anhydride and 2, 4, 6-tris(dimethylaminomethyl)phenol).

[0034] S2: Connect the mold to the circuit in a series-parallel structure, clamp a polyimide film with a side length of 60mm and a thickness of 0.1mm in the mold, and connect it in series at the high-voltage end as a protective capacitor.

[0035] The series-parallel structure is as follows Figure 4 As shown, C 0 is the polyimide protection capacitor, C 1- C 4 is the epoxy resin mixed solution doped with hexagonal boron nitride in the casting molding cavity 3-1.

[0036] S3: Apply a high-frequency, high-voltage, bipolar square wave voltage at 80°C. Observe the waveform on the oscilloscope and continuously adjust the voltage to maintain a constant voltage amplitude.

[0037] The frequency of the high-frequency square wave voltage is 10 kHz, and the electric field strength of the epoxy resin is 2 kV / mm.

[0038] The oscilloscope waveform changes as follows Figure 5 As shown in the figure, from 0 to 30 minutes of pressurization, the voltage waveform gradually changes from a pulse wave to a square wave as the liquid epoxy capacitance changes, and the amplitude decreases, then increases, and then decreases again. From 30 to 60 minutes, the voltage waveform becomes a square wave with a stable amplitude. During the orientation induction process, the oscilloscope is closely monitored and the voltage output is continuously adjusted to maintain a constant voltage amplitude of 2kV.

[0039] S4: After the voltage application is completed, the curing process is continued to completely cure the epoxy resin composite material.

[0040] The subsequent curing procedure includes: curing at 80° C. for 1 hour, heating to 105° C., curing at 105° C. for 2 hours, and finally heating to 120° C., and curing at 120° C. for 4 hours.

[0041] Example 2: The specific steps of the preparation method of this embodiment are different from those of Example 1 in that the frequency of the high-frequency square wave voltage in step S3 is adjusted to 10 kHz and the electric field strength of the epoxy resin is adjusted to 1.5 kV / mm. The other steps are the same as those of Example 1.

[0042] Example 3: The specific steps of the preparation method of this embodiment are different from those of Example 1 in that the frequency of the high-frequency square wave voltage in step S3 is adjusted to 10 kHz and the electric field strength of the epoxy resin is adjusted to 1 kV / mm. The other steps are the same as those of Example 1.

[0043] Example 4: The specific steps of the preparation method of this embodiment are different from those of Example 1 in that the h-BN doping mass fraction in step S1 is adjusted to 20%. The other steps are the same as those of Example 1.

[0044] Example 5: The specific steps of the preparation method of this embodiment differ from those of Example 1 in that the h-BN doping mass fraction in step S1 is adjusted to 20%; and in step S3, the high-frequency square wave voltage frequency is adjusted to 10 kHz, and the epoxy resin electric field strength is adjusted to 1.5 kV / mm. The other steps are the same as those of Example 1.

[0045] Example 6: The specific steps of the preparation method of this embodiment differ from those of Example 1 in that the h-BN doping mass fraction in step S1 is adjusted to 20%; and in step S3, the high-frequency square wave voltage frequency is adjusted to 10 kHz, and the epoxy resin electric field strength is adjusted to 1 kV / mm. The other steps are the same as those of Example 1.

[0046] Example 7: The specific steps of the preparation method of this embodiment differ from those of Example 1 in that the h-BN doping mass fraction in step S1 is adjusted to 10%; the high-frequency square wave voltage frequency in step S3 is adjusted to 10 kHz, and the epoxy resin electric field strength is adjusted to 1 kV / mm. The other steps are the same as those of Example 1.

[0047] Example 8: The specific steps of the preparation method of this embodiment differ from those of Example 1 in that the h-BN doping mass fraction in step S1 is adjusted to 10%; and the high-frequency square wave voltage frequency and the epoxy resin electric field strength in step S3 are adjusted to 10 kHz and 0.5 kV / mm, respectively. The other steps are the same as those of Example 1.

[0048] Comparative Example 1: The preparation method of this comparative example comprises the following steps: S1: Prepare an h-BN-doped epoxy resin solution in a beaker by combining E51 epoxy resin, 4-methylhexahydrophthalic anhydride, and 2, 4, 6-tris(dimethylaminomethyl)phenol at a mass ratio of 100:80:1. The h-BN doping concentration is 25% (i.e., the mass of h-BN is 25% of the total mass of E51 epoxy resin, 4-methylhexahydrophthalic anhydride, and 2, 4, 6-tris(dimethylaminomethyl)phenol). Place the beaker in a 60°C water bath and stir uniformly using a mechanical stirrer at 2000 rpm.

[0049] S2: After vacuum degassing in a preheated oven at 60° C. for 10 minutes, pour the mixture into a mold of the insulating clip 3 with a thickness of 1 mm.

[0050] S3: Place the mold in an oven and set the curing program as follows: first, heat to 80°C and cure at 80°C for 2 hours; then heat to 105°C and cure at 105°C for 2 hours; and finally heat to 120°C and cure at 120°C for 4 hours. This yields a randomly oriented h-BN / EP composite material.

[0051] Comparative Example 2: The specific steps of the preparation method of this comparative example are different from those of comparative example 1 in that the mass fraction of doped h-BN in step S1 is adjusted to 20%. The other steps are the same as those of comparative example 1.

[0052] Comparative Example 3: The specific steps of the preparation method of this comparative example are different from those of comparative example 1 in that the mass fraction of doped h-BN in step S1 is adjusted to 10%. The other steps are the same as those of comparative example 1.

[0053] Comparative Example 4: The specific steps of the preparation method of this comparative example are different from those of comparative example 1 in that h-BN is not doped in the adjustment step S1. The other steps are the same as those of comparative example 1.

[0054] Thermal conductivity testing: The above-described examples and comparative examples were tested using an LFA447 laser thermal conductivity analyzer. The samples were cut into 10mm squares with a thickness of 1mm. The samples were coated with graphite spray using a matching graphite spray can before measurement. The instrument directly measures the thermal diffusivity of the samples, which is then calculated using a formula to determine thermal conductivity.

[0055] The thermal conductivity of the above examples and comparative examples is shown in Table 1.

[0056] Table 1

[0057] The above experimental results show that the present invention uses a high-frequency, high-voltage square wave electric field to efficiently induce orientation to improve the thermal conductivity of epoxy composite materials with significant regularity. Under the same filling amount, as the electric field intensity increases, the thermal conductivity improvement rate increases significantly, with the highest improvement rate reaching 69.53%, which is significantly improved compared to the low-frequency, low-voltage pulse electric field, verifying the advantages of high-frequency, high-voltage square waves. Under the same electric field intensity, the thermal conductivity improvement rate increases with the decrease of doping content, indicating that the electric field is more sensitive to the regulation of orientation efficiency at low filling amounts. The full detection of the power output waveform during the application process proves the effectiveness of high-frequency, high-voltage square waves in electric field-induced orientation.

[0058] In addition, a synergistic effect exists between the filler content and the electric field strength. At a filler content of 20 wt%, when the electric field strength increases from 0.5 kV / mm to 2 kV / mm, the thermal conductivity increase jumps from 9.34% to 60.50%, revealing the existence of a critical electric field threshold. Below this threshold, the orientation efficiency is low, while above this value, the thermal conductivity increase of each system is significantly improved. This characteristic provides a key basis for parameter optimization in engineering applications, that is, by balancing the electric field strength and filler content, the orientation effect and economy can be ensured. It is worth noting that the experimental system can achieve significant performance improvements at an electric field strength of ≤2 kV / mm, and its voltage requirements are fully compatible with the safety standards of conventional engineering equipment. At the same time, even at low filler content, the thermal conductivity increase of more than 50% can still be maintained through the construction of the orientation network, fully demonstrating the potential of this technology to optimize filler utilization efficiency.

[0059] In summary, high-frequency, high-voltage bipolar square wave electric field can regulate the spatial distribution of fillers by inducing filler orientation, significantly improving thermal conductivity at low filler content, and its low voltage requirement meets engineering safety standards, providing a reliable technical path for the development of epoxy composite materials with high thermal conductivity, low filler loading and insulation reliability.

[0060] Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a high-thermal-conductivity epoxy composite material with high-efficiency induced orientation by a high-frequency, high-voltage, bipolar square wave electric field, characterized in that: The process includes the following: The epoxy resin mixed solution doped with hexagonal boron nitride is degassed and poured, and then cured. During the curing process, a high-frequency, high-voltage, bipolar square wave voltage is applied to the poured sample to induce electric field orientation. After the high-frequency, high-voltage, bipolar square wave voltage is applied, the curing procedure is continued to completely cure the epoxy resin composite material to obtain a high thermal conductivity epoxy composite material.

2. The method for preparing a high-thermal-conductivity epoxy composite material with high-frequency, high-voltage, bipolar square wave electric field efficient induced orientation according to claim 1, characterized in that: The raw materials of the epoxy resin mixed solution include epoxy resin, 4-methylhexahydrophthalic anhydride, 2, 4, 6-tris(dimethylaminomethyl)phenol and hexagonal boron nitride, wherein the mass ratio of the epoxy resin, 4-methylhexahydrophthalic anhydride and 2, 4, 6-tris(dimethylaminomethyl)phenol is (98-102):(78-82):1, and the mass of the hexagonal boron nitride is 10%-25% of the total mass of the epoxy resin, 4-methylhexahydrophthalic anhydride and 2, 4, 6-tris(dimethylaminomethyl)phenol.

3. The method for preparing a high-thermal-conductivity epoxy composite material with high-frequency, high-voltage, bipolar square-wave electric field efficient induced orientation according to claim 1 or 2, characterized in that: The diameter of the hexagonal boron nitride is 5-15 μm.

4. The method for preparing a high-thermal-conductivity epoxy composite material with high-frequency, high-voltage, bipolar square-wave electric field efficient induced orientation according to claim 1, characterized in that: A mold for casting a mixed solution of epoxy resin doped with hexagonal boron nitride comprises an insulating clip (3), flat electrodes (1) are provided on both sides of the insulating clip (3), the insulating clip (3) is provided with a through hole along its thickness direction, the insulating clip (3) and the flat electrodes (1) on both sides form a casting molding cavity (3-1) at the through hole, a gate (2) connected to the casting molding cavity (3-1) is provided on the insulating clip (3), and an insulating plate (4) is provided on the side of each flat electrode (1) away from the insulating clip (3).

5. The method for preparing a high-thermal-conductivity epoxy composite material with high-frequency, high-voltage, bipolar square-wave electric field efficient induced orientation according to claim 4, characterized in that: Before applying a high-frequency square wave voltage to the cast sample for electric field orientation induction, several molds are connected to the high-frequency square wave voltage application circuit in a series-parallel circuit structure, and a protection capacitor is connected in series to the high-voltage end of the high-frequency square wave voltage application circuit; then, the high-frequency square wave voltage is applied to the cast sample for electric field orientation induction; The total capacitance in the high-frequency square wave voltage application circuit is no greater than the capacitance when a single mold is filled with a liquid epoxy resin mixed solution doped with hexagonal boron nitride.

6. The method for preparing a high-thermal-conductivity epoxy composite material with high-frequency, high-voltage, bipolar square-wave electric field efficient induced orientation according to claim 5, characterized in that: The high-frequency square wave voltage application circuit includes a high-frequency square wave power supply (8), a plurality of molds are connected to the high-frequency square wave power supply (8) in a series-parallel circuit structure, and the high-frequency square wave power supply (8) is also connected to an oscilloscope (6). The oscilloscope (6) is used to observe the voltage waveform output by the high-frequency square wave power supply (8). During the process of applying the high-frequency square wave voltage to the cast sample to induce the electric field orientation, the output voltage of the high-frequency square wave power supply (8) is adjusted by observing the voltage waveform displayed by the oscilloscope (6), so as to maintain the output voltage amplitude of the high-frequency square wave power supply (8) constant.

7. The method for preparing a high-thermal-conductivity epoxy composite material with high-frequency, high-voltage, bipolar square-wave electric field efficient induced orientation according to claim 4, characterized in that: The thickness of the insulating clip (3) is 0.2-1 mm, and the flat electrodes on both sides of the insulating clip (3) are fitted to the side surfaces of the insulating clip (3).

8. The method for preparing a high-thermal-conductivity epoxy composite material with high-frequency, high-voltage, bipolar square-wave electric field efficient induced orientation according to claim 1, characterized in that: The curing of the epoxy resin mixed solution doped with hexagonal boron nitride is carried out in an oven. During the curing process, a high-frequency square wave voltage is applied to the cast sample to induce electric field orientation. The oven temperature is the initial temperature of the curing procedure of the epoxy resin mixed solution doped with hexagonal boron nitride.

9. The method for preparing a high-thermal-conductivity epoxy composite material with high-frequency, high-voltage, bipolar square-wave electric field efficient orientation induction according to claim 1, characterized in that: During the curing process, when a high-frequency square wave voltage is applied to the cast sample for electric field orientation induction, the frequency of the high-frequency square wave voltage is above 10 kHz, the electric field strength is 0.5~2 kV / mm, and the orientation induction time is 40~60 minutes.

10. A high thermal conductivity epoxy composite material, characterized in that: The high thermal conductivity epoxy composite material is prepared by the preparation method of the high thermal conductivity epoxy composite material with high-frequency, high-voltage, bipolar square wave electric field and high efficiency induced orientation according to any one of claims 1 to 9.

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