High-strength high-thermal-conductivity aramid composite insulating paper and preparation method thereof

Abstract

The application relates to the technical field of insulating materials, and discloses a high-strength high-thermal-conductivity composite aramid fiber insulating paper and a preparation method. The composite aramid fiber insulating paper has a double-layer structure, the bottom layer is composed of pre-stretched aramid long fibers, and the surface layer is composed of aramid short-cut fibers, aramid deposited fibers and PDA-coated BNNS intercalation composite, wherein the BNNS is vertically arranged along the Z axis. The BNNS in the surface layer of the composite aramid fiber insulating paper is arranged in a direction, the thermal conductivity and the insulation performance can be optimized, the long fibers in the bottom layer are pre-stretched and treated by plasma to cooperatively improve the fiber orientation degree, and the composite aramid fiber insulating paper with cooperatively improved thermal conductivity, insulation and mechanical strength is obtained through gradient heat pressing; the composite aramid fiber insulating paper is suitable for power equipment, new energy motors and aerospace insulation fields in high-temperature environments.

Description

Technical Field

[0001] This invention relates to the field of insulating materials technology, specifically to a high-strength, high-thermal-conductivity composite aramid insulating paper and its preparation method. Background Technology

[0002] Aramid insulating paper, a functional material made from aramid fibers, has become a core material in strategic fields such as power equipment, aerospace, and new energy due to its excellent high-temperature resistance, high strength, superior insulation properties, and lightweight characteristics. However, as applications expand to extreme conditions, such as ultra-high-voltage power transmission and transformation, deep space exploration, and hydrogen fuel cell vehicle motors, traditional aramid paper faces multiple technical bottlenecks in performance and processing, urgently requiring breakthrough innovation.

[0003] Traditional aramid insulating paper is prone to molecular chain breakage and interfacial degradation under prolonged high temperatures, leading to a significant decrease in mechanical strength. For example, the tensile strength retention rate is typically below 60% at high temperatures, and the interlayer bonding force is insufficient, making it difficult to meet the structural stability requirements under high-load conditions. In addition, the material is prone to microcracks due to the mismatch in thermal expansion coefficients during thermal cycling, further accelerating performance degradation.

[0004] Modern industry has placed multifunctional demands on aramid insulating paper, requiring both high in-plane thermal conductivity for rapid heat dissipation and high volume resistivity to maintain insulation performance. Existing technologies struggle to balance these two properties; the introduction of fillers often leads to insulation degradation, while coatings that enhance insulation can hinder heat transfer. Furthermore, flame-retardant modification processes may reduce the material's mechanical strength, creating a trade-off between performance gains and losses.

[0005] The interlayer bonding strength of multilayer composite aramid insulating paper is insufficient, and delamination defects are easily generated due to thermal stress concentration during high-temperature pressing. Furthermore, fiber orientation control technologies, such as the synergistic effect of random distribution of short fibers and oriented arrangement of long fibers, are not yet mature, leading to unstable anisotropic properties of the material. While the introduction of nanofillers such as graphene and boron nitride can improve thermal conductivity or mechanical properties, their dispersion uniformity, interlayer bonding strength, and long-term stability still face challenges. The disordered stacking of nanosheets in the fiber matrix may block thermal conduction pathways, while high filler content can easily induce stress concentration, thus reducing the material's toughness. Summary of the Invention

[0006] This invention addresses the problems existing in the prior art by providing a high-strength, high-thermal-conductivity composite aramid insulating paper and its preparation method.

[0007] The technical solution adopted in this invention is: a method for preparing high-strength, high-thermal-conductivity composite aramid insulating paper, comprising the following steps: Step 1: Mix boron nitride nanosheets (BNNS) and polydopamine (PDA) solution, and allow them to react fully to obtain PDA-coated BNNS; Step 2: Alkali treatment is performed on meta-aramid short-cut fibers to obtain alkali-treated short-cut fibers; aramid precipitated fibers, alkali-treated short-cut fibers and PDA-coated BNNS are mixed in a solvent and mixed evenly to obtain a surface slurry; Step 3: During the filtration and film formation process of the surface slurry, ultrasonic waves are applied simultaneously along the Z-axis to pre-cur the surface film. Step 4: Stretch the fiber layer composed of aramid long fibers, maintain the stretched state, and then pre-press after activation treatment to obtain the bottom film; Step 5: Stack the bottom film and the top film, and then hot press them to obtain composite aramid insulating paper.

[0008] Furthermore, in step 2, the intermediate aramid short-cut fibers are treated with an alkali solution of 3 wt.% NaOH; after alkali treatment, they are washed and then subjected to plasma treatment in an oxygen atmosphere at a power of 150 W and a temperature of 80 °C.

[0009] Furthermore, the mass ratio of the aramid precipitated fiber and the alkali-treated short-cut fiber PDA-coated BNNS is 7:2:1; the solvent is an aqueous solution containing 0.2 wt.% polyethylene oxide.

[0010] Furthermore, the ultrasound conditions in step 3 are as follows: An ultrasonic probe with a power of 40 kHz was placed directly above the surface slurry; the ultrasonic power was 60 W, and the pulsed ultrasound was performed for 20 minutes; the pulse working mode was 2 seconds followed by a 1-second interval. The vacuum level during the filtration process is -0.08 MPa; The pre-curing temperature is 80 ℃, the pressure is 1 MPa, and the pre-curing time is 10 min.

[0011] Furthermore, the stretching conditions for the aramid long fibers in step 4 are as follows: The stretch ratio is 1.2:1, and the stretching speed is 10 mm / min.

[0012] Furthermore, the activation process in step 4 is as follows: Plasma treatment for 2 min, processing power of 200 W, argon flow rate of 10 L / min; The preloading conditions are as follows: The temperature was 80 ℃, the pressure was 2 MPa, and the pre-compression time was 3 min.

[0013] Furthermore, the hot pressing in step 5 is a gradient hot pressing; the hot pressing regime is as follows: In the first stage, the temperature was increased to 80 ℃ at a rate of 3 ℃ / min, and the pressure was simultaneously increased to 5 MPa at a gradient of 0.5 MPa / min, and the temperature and pressure were maintained for 15 min. In the second stage, the temperature was increased to 150 ℃ at a rate of 2 ℃ / min, and the pressure was increased to 10 MPa simultaneously, and the temperature and pressure were kept constant for 35 min. In the third stage, the temperature was reduced to 60 ℃ at a rate of 1 ℃ / min, and the pressure was simultaneously reduced to 5 MPa at a rate of 0.3 MPa / min, and the temperature and pressure were maintained at a constant level for 100 min.

[0014] A high-strength, high-thermal-conductivity composite aramid insulating paper, wherein the composite aramid insulating paper has a double-layer composite structure; The bottom layer is composed of pre-stretched aramid long fibers; the surface layer is composed of aramid short-cut fibers and aramid precipitated fibers, and PDA-coated BNNS intercalation composite, wherein the BNNS are arranged vertically along the Z-axis.

[0015] Furthermore, the aramid long fibers have a length of 5 mm and a diameter of 10–15 μm; the aramid short chopped fibers have a length of 3 mm and a diameter of 10–15 μm; and the aramid precipitated fibers have a length of 1–2 mm and a diameter of 5–10 μm.

[0016] Furthermore, the PDA is coated with BNNS with an orientation density of ≥100 sheets / μm, and the bottom and top layers have the same thickness.

[0017] The beneficial effects of this invention are: This invention constructs a two-layer structure of "intercalated thermal conductivity - super-orientation enhancement". The surface layer uses ultrasonic vibration to induce the vertical alignment of BNNS (Bipolar Non-Mechanical Synthetic Components), and with the synergy of vacuum filtration, the BNNS are oriented along the Z-axis, creating a cross-dimensional functional characteristic of "high in-plane thermal conductivity + out-of-plane super insulation". The bottom layer is strengthened by plasma treatment and mechanical pre-stretching, which enhances the mechanical strength of the material. This structural design significantly improves the reliability of the material in alternating temperature scenarios such as ultra-high voltage transformer windings.

[0018] This invention organically combines ultrasonic orientation, plasma activation, and gradient hot pressing to form a preparation process that reduces costs, improves the structural density of materials, and significantly enhances the mechanical and electrical properties of materials. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the double-layer insulating paper obtained by the present invention. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0021] A method for preparing a high-strength, high-thermal-conductivity composite aramid insulating paper includes the following steps: Step 1: Mix boron nitride nanosheets (BNNS) and polydopamine (PDA) solution, and allow them to react fully to obtain PDA-coated BNNS; Step 2: Alkali treatment is performed on meta-aramid chopped fibers to obtain alkali-treated chopped fibers; aramid precipitated fibers, alkali-treated chopped fibers, and PDA-coated BNNS are mixed in a solvent and mixed evenly to obtain a surface slurry; meta-aramid chopped fibers are alkali-treated with a 3 wt.% NaOH solution; after alkali treatment, the fibers are washed and then subjected to plasma treatment at a power of 150 W, a temperature of 80 ℃, and an oxygen atmosphere.

[0022] The mass ratio of aramid precipitated fibers and alkali-treated short-cut PDA-coated BNNS is 7:2:1; the solvent is an aqueous solution containing 0.2 wt.% polyethylene oxide.

[0023] Step 3: During the filtration and film formation process of the surface slurry, ultrasonic waves are applied simultaneously along the Z-axis to pre-cur the surface film. The ultrasound conditions are as follows: An ultrasonic probe with a power of 40 kHz was placed directly above the surface slurry; the ultrasonic power was 60 W, and the pulsed ultrasound was performed for 20 minutes; the pulse working mode was 2 seconds followed by a 1-second interval. The vacuum level during the filtration process is -0.08 MPa; The pre-curing temperature is 80 ℃, the pressure is 1 MPa, and the pre-curing time is 10 min.

[0024] Step 4: Stretch the fiber layer composed of aramid long fibers, maintain the stretched state, and then perform activation treatment followed by pre-compression to obtain the bottom film; the stretching conditions for the aramid long fibers are as follows: The stretch ratio is 1.2:1, and the stretching speed is 10 mm / min.

[0025] The activation process is as follows: Plasma treatment for 2 min, processing power of 200 W, argon flow rate of 10 L / min; The preloading conditions are as follows: The temperature was 80 ℃, the pressure was 2 MPa, and the pre-compression time was 3 min.

[0026] Step 5: Stack the bottom film and the top film, and then hot press them to obtain composite aramid insulating paper.

[0027] The hot pressing is a gradient hot pressing; the hot pressing process is as follows: In the first stage, the temperature was increased to 80 ℃ at a rate of 3 ℃ / min, and the pressure was simultaneously increased to 5 MPa at a gradient of 0.5 MPa / min, and the temperature and pressure were maintained for 15 min. In the second stage, the temperature was increased to 150 ℃ at a rate of 2 ℃ / min, and the pressure was increased to 10 MPa simultaneously, and the temperature and pressure were kept constant for 35 min. In the third stage, the temperature was reduced to 60 ℃ at a rate of 1 ℃ / min, and the pressure was simultaneously reduced to 5 MPa at a rate of 0.3 MPa / min, and the temperature and pressure were maintained at a constant level for 100 min.

[0028] Composite aramid insulating paper has a double-layer composite structure; such as Figure 1 As shown.

[0029] The bottom layer consists of pre-stretched aramid long fibers; the top layer is composed of aramid chopped fibers, aramid precipitated fibers, and PDA-coated BNNS intercalation, with the BNNS arranged vertically along the Z-axis. The aramid long fibers are 5 mm long and 10–15 μm in diameter; the aramid chopped fibers are 3 mm long and 10–15 μm in diameter; the aramid precipitated fibers are 1–2 mm long and 5–10 μm in diameter. The PDA-coated BNNS orientation density is ≥100 sheets / μm, and the bottom and top layers have the same thickness. The resulting composite aramid insulating paper has an in-plane thermal conductivity of 8.5 W / (m·K) and a volume resistivity >10¹. 6 Ω·cm, tensile strength ≥215 MPa.

[0030] Example A method for preparing a high-strength, high-thermal-conductivity composite aramid insulating paper includes the following steps: Step 1: Mix boron nitride nanosheets (BNNS) and polydopamine (PDA) solution, and allow them to react fully to obtain PDA-coated BNNS; First, dopamine hydrochloride was dissolved in Tris-HCl buffer solution at pH 8.5 and allowed to react completely to obtain polydopamine PDA solution.

[0031] BNNS and PDA were mixed at a mass ratio of 1:1 and added to a 2 mg / mL PDA solution. The mixture was then sonicated to ensure thorough dispersion of BNNS and reaction with PDA. The sonicated mixture was allowed to stand at room temperature for 12 hours to allow PDA to self-polymerize on the BNNS surface, forming a coating layer. After centrifugation at 8000 rpm for 10 min, washing three times with deionized water, and vacuum drying at 60 °C for 6 hours, PDA-coated BNNS (PDA@BNNS) was obtained with a coating rate ≥90%. The diameter of the BNNS was <50 nm.

[0032] Step 2: Alkali treatment is performed on meta-aramid short-cut fibers to obtain alkali-treated short-cut fibers; aramid precipitated fibers, alkali-treated short-cut fibers and PDA-coated BNNS are mixed in a solvent and mixed evenly to obtain a surface slurry; The alkali treatment process is as follows: Meta-aramid chopped fibers were alkali-treated with a 3 wt.% NaOH solution, stirred at 50 °C for 30 min, washed with water until neutral, pre-dried at 60 °C, and then plasma-treated for 1 min at 150 W and 80 °C under an oxygen atmosphere to enhance surface polarity. The aramid chopped fibers had a length of 3 mm and a diameter of 10–15 μm.

[0033] Aramid precipitated fibers, alkali-treated chopped fibers, and PDA@BNNS were added to an aqueous solution of polyethylene oxide (PEO) in a mass ratio of 7:2:1. The PEO concentration in the aqueous solution was 0.2 wt.%. The mixture was first stirred at low speed and then ultrasonically treated to obtain a surface slurry. The mixing speed and ultrasonic treatment conditions were set according to actual conditions. The aramid precipitated fibers had a length of 1–2 mm and a diameter of 5–10 μm; in this example, the length was 2 mm and the diameter was 8 μm.

[0034] Step 3: During the filtration and film formation process of the surface slurry, ultrasonic waves are applied simultaneously along the Z-axis to pre-cur the surface film. Ultrasonic waves perpendicular to the Z-axis are applied to the surface slurry to induce BNNS to align perpendicular to the Z-axis. Short chopped fibers are randomly distributed in the precipitated fiber network. After filtration to form a film, the film is pre-cured by hot pressing at 80 °C for 5 min under a pressure of 1 MPa to fix the orientation structure of BNNS.

[0035] The process by which ultrasonic vibration induces the vertical orientation alignment of BNNS is as follows: The mixed slurry was injected into a vacuum filtration device with a pore size of 0.22 μm. A 40 kHz ultrasonic probe was installed directly above the slurry surface, and the device was set to a power of 60 W, operating in pulse mode for 2 seconds followed by a 1-second interval for 20 minutes. Simultaneously, the vacuum pump was started to evacuate the vacuum in the filtration device to -0.08 MPa, driving the BNNS to align along the Z-axis perpendicular to the filter membrane. The wet membrane was then transferred to an 80 ℃ hot press and pre-cured under 1 MPa pressure for 10 minutes. The orientation of the BNNS was monitored using a microscope or X-ray diffraction to ensure an orientation density ≥100 sheets / μm.

[0036] Step 4: Stretch the fiber layer composed of aramid long fibers, keep it in a stretched state, and then pre-press it after activation treatment to obtain the bottom film; wherein the length of the aramid long fibers is 5 mm and the diameter is 12 μm.

[0037] The stretching conditions are as follows: The draw ratio is 1.2:1, meaning the length after stretching is 1.2 times the original length (based on the overall length of the fiber layer), and the Herman factor is ≥0.85. The stretching speed is 10 mm / min; ensure uniform fiber stretching and perform stretching at room temperature to avoid high temperatures affecting fiber properties. After stretching, use clamps to fix the fibers and maintain the stretched state until subsequent processing.

[0038] The stretched fiber layer was treated for 2 min at a power of 200 W and an argon flow rate of 10 L / min to introduce -COOH groups onto the surface. Finally, the activated fiber layer was pre-compressed at 80 ℃ and 2 MPa for 3 min. Plasma treatment activates the -OH and -COOH groups on the fiber surface, enhancing the interfacial bonding between the fiber and the resin.

[0039] Step 5: Stack the bottom film and the top film, spray a lignin epoxy resin transition layer between the layers, and then hot press to obtain composite aramid insulating paper.

[0040] The multi-layered composite structure with the sprayed transition layer is placed in a multi-stage temperature-controlled flatbed hot press, protected by an argon atmosphere to prevent oxidation. After the equipment is preheated, it enters the pre-pressing and dehydration stage, which is the first stage. The temperature is increased from room temperature to 80 ℃ at a rate of 3 ℃ / min, and the pressure is simultaneously increased to 5 MPa at a gradient of 0.5 MPa / min. The temperature and pressure are maintained at constant level for 15 min. The moisture content is reduced to below 15% by monitoring with the built-in humidity sensor, thus completing the initial densification.

[0041] Then, the main curing stage, or the second stage, begins: the temperature is increased to 150 °C at a rate of 2 °C / min, and the pressure is simultaneously increased to 10 MPa, and maintained at the same temperature and pressure for 35 min. During this period, the resin viscosity drops below 100 Pa·s to achieve complete cross-linking, while the ultrasonically oriented boron nitride nanosheets complete intercalation and anchoring through the movement of aramid molecular chains.

[0042] Finally, the stress release stage, or the third stage, begins, where the temperature is reduced to 60°C at a rate of 1°C / min, while the pressure is simultaneously reduced to 5 MPa at a rate of 0.3 MPa / min, and maintained at this constant temperature and pressure for 100 min. This process promotes the matching of the expansion coefficients of each layer.

[0043] The composite aramid insulating paper has a double-layer composite structure with a thickness of 0.4 mm; The bottom layer is composed of pre-stretched aramid long fibers; the top layer is composed of aramid short-cut fibers and aramid precipitated fibers intercalated with PDA-coated BNNS, wherein the BNNS are vertically oriented along the Z-axis. The orientation density of PDA-coated BNNS is ≥100 sheets / μm, the coating rate is ≥90%, and the coating layer thickness is less than 3 nm.

[0044] Performance tests showed that the tensile strength reached 218 MPa, the interlaminar peel strength was 9.5 N / cm, the in-plane thermal conductivity was 8.5 W / (m·K), and the volume resistivity remained at 1.8 × 10¹ at 300 ℃. 5 The resistivity of Ω·cm decreased by only 7.3% after 1000 hours of damp heat aging at 85 ℃ / 85 %RH, and no cracks appeared after 100 impacts with liquid nitrogen at -196 ℃.

[0045] To illustrate the effects of the present invention, a comparative example is provided. Comparative Example 1 Traditional single-layer aramid insulating paper, namely aramid precipitated fiber, is produced by conventional wet papermaking followed by isothermal hot pressing at 150℃ / 10 MPa for 30 min, resulting in an insulating paper with a thickness of 0.4 mm.

[0046] The tensile strength of the comparative sample was tested to be 155 MPa, the interlaminar peel strength was 4.8 N / cm, the in-plane thermal conductivity was 1.2 W / (m·K), the resistivity dropped sharply to 6.3×10¹³ Ω·cm at 300 ℃, the resistivity decreased by 61% after damp heat aging, and microcracks were generated after 10 liquid nitrogen impacts.

[0047] Comparative Example 2 For comparison purposes, all other steps in this comparative example are the same as in Example 1, except that the ultrasonic process in step 3 is not included.

[0048] Because the surface BNNS layer is not oriented, its in-plane thermal conductivity is only 3.1 W / (m·K), and its resistivity at 300 ℃ is 2.1×10¹. 4 Ω·cm, resistivity decreased by 28% under damp heat aging, interlayer peel strength was 6.2 N / cm, and local debonding occurred after 50 liquid nitrogen impacts.

[0049] By comparing Example 1 with Comparative Examples 1 and 2, it can be seen that the composite aramid insulating paper prepared by the method of the present invention has 608% better thermal conductivity and nearly 100% stronger interlayer bonding compared with traditional aramid insulating paper. At the same time, its damp heat stability and low temperature resistance are significantly better than the comparative schemes. Specific data comparisons are shown in Table 1.

[0050] Table 1. Performance test results of Example 1 and Comparative Example

[0051] This invention employs a double-layer gradient structure. The surface layer is composed of aramid fibers intercalated with PDA@BNNS, with the BNNS fibers vertically oriented along the Z-axis. The bottom layer is prepared from pre-stretched aramid long fibers through plasma treatment, fully leveraging the structural and functional advantages of the layered structure. The resulting composite aramid insulating paper exhibits an in-plane thermal conductivity of 8.5 W / (m·K) and a volume resistivity >10¹.6 Ω·cm, tensile strength ≥215 MPa.

[0052] This invention solves the problems of thermal conductivity-insulation contradiction, easy delamination between layers, and insufficient thermal stability faced by traditional aramid insulating paper under extreme conditions by constructing a "intercalated thermal conductivity-super-orientation enhancement" double-layer structure. The surface layer uses ultrasonic vibration to induce the vertical alignment of BNNS. Under the synergistic effect of 40 kHz ultrasound and -0.08 MPa vacuum filtration, the BNNS orientation density along the Z-axis reaches 150 sheets / μm, constructing a structure with "high in-plane thermal conductivity (8.5 / (m·K)) + out-of-plane super insulation (>10¹)". 6 The material exhibits a cross-dimensional functional characteristic of "Ω·cm", a performance index that is nearly 5 times higher than the in-plane thermal conductivity (1.5 W / (m·K)) of the randomly distributed BNNS composite system. Simultaneously, the breakdown voltage remains above 58 kV / mm, overcoming the bottleneck of insulation performance degradation caused by traditional filler modification. The bottom layer undergoes dual reinforcement through plasma treatment and mechanical pre-stretching, achieving an aramid long fiber orientation degree (Hermann factor) of 0.88 and a tensile strength exceeding 215 MPa. Combined with the main curing stage in the gradient hot pressing process, the interlayer peel strength is increased to 9.2 N / cm, an 84% increase compared to the conventional hot pressing process (5 N / cm). No interfacial delamination was observed during -196 ℃ liquid hydrogen immersion and 250 ℃ high-temperature cycling tests, significantly improving the material's reliability in alternating temperature scenarios such as ultra-high voltage transformer windings.

[0053] This invention achieves vertical alignment of BNNS in just 20 minutes through ultrasonic vibration, followed by plasma treatment in an argon atmosphere, increasing the resin-fiber chemical bonding ratio from 35% to 62%. A gradient hot-pressing process reduces the material porosity to 5.8% and controls the thermal shrinkage rate to below 0.3%, significantly improving structural density compared to the 12% porosity and 1.2% thermal shrinkage rate of traditional isothermal pressing.

[0054] In this invention, the components and interlayers exhibit a synergistic reinforcing effect. Through the interface formed by polydopamine coating of BNNS, the interlayer shear strength reaches 28 MPa, an 87% increase compared to the uncoated system. Simultaneously, the oxygen index is increased to 38, achieving a UL94 V-0 flame retardant rating, thus realizing an integrated system of "high strength, flame retardancy, and arc resistance." Furthermore, the lignin epoxy resin maintains long-term temperature resistance at 180℃ while allowing for controlled degradation in 1 mol / L NaOH solution, with a fiber recovery rate exceeding 89% and a strength retention rate of 85%.

Claims

1. A method for preparing a high-strength, high-thermal-conductivity composite aramid insulating paper, characterized in that, Includes the following steps: Step 1: Mix boron nitride nanosheets (BNNS) and polydopamine (PDA) solution, and allow them to react fully to obtain PDA-coated BNNS; Step 2: Alkali treatment is performed on meta-aramid short-cut fibers to obtain alkali-treated short-cut fibers; aramid precipitated fibers, alkali-treated short-cut fibers and PDA-coated BNNS are mixed in a solvent and mixed evenly to obtain a surface slurry; Step 3: During the filtration and film formation process of the surface slurry, ultrasonic waves are applied simultaneously along the Z-axis to pre-cur the surface film. Step 4: Stretch the fiber layer composed of aramid long fibers, maintain the stretched state, and then pre-press after activation treatment to obtain the bottom film; Step 5: Stack the bottom film and the top film, and then hot press them to obtain composite aramid insulating paper.

2. The method for preparing a high-strength, high-thermal-conductivity composite aramid insulating paper according to claim 1, characterized in that, In step 2, the intermediate aramid short-cut fibers are treated with an alkali solution of 3 wt.% NaOH; after alkali treatment, they are washed and then subjected to plasma treatment in an oxygen atmosphere at a power of 150 W and a temperature of 80 °C.

3. The method for preparing a high-strength, high-thermal-conductivity composite aramid insulating paper according to claim 1, characterized in that, The mass ratio of the aramid precipitated fiber and the alkali-treated short-cut fiber PDA-coated BNNS is 7:2:1; the solvent is an aqueous solution containing 0.2 wt.% polyethylene oxide.

4. The method for preparing a high-strength, high-thermal-conductivity composite aramid insulating paper according to claim 1, characterized in that, The ultrasound conditions in step 3 are as follows: An ultrasonic probe with a power of 40 kHz was placed directly above the surface slurry; the ultrasonic power was 60 W, and the pulsed ultrasound was performed for 20 min; the pulse working mode was 2 s followed by a 1 s interval. The vacuum level during the filtration process is -0.08 MPa; The pre-curing temperature is 80 ℃, the pressure is 1 MPa, and the pre-curing time is 10 min.

5. The high-strength, high-thermal-conductivity composite aramid insulating paper according to claim 1, characterized in that, The stretching conditions for the aramid long fibers in step 4 are as follows: The stretch ratio is 1.2:1, and the stretching speed is 10 mm / min.

6. The high-strength, high-thermal-conductivity composite aramid insulating paper according to claim 5, characterized in that, The activation process in step 4 is as follows: Plasma treatment for 2 min, processing power of 200 W, argon flow rate of 10 L / min; The preloading conditions are as follows: The temperature was 80 ℃, the pressure was 2 MPa, and the pre-compression time was 3 min.

7. The high-strength, high-thermal-conductivity composite aramid insulating paper according to claim 1, characterized in that, In step 5, the hot pressing is a gradient hot pressing; the hot pressing regime is as follows: In the first stage, the temperature was increased to 80 ℃ at a rate of 3 ℃ / min, and the pressure was simultaneously increased to 5 MPa at a gradient of 0.5 MPa / min, and the temperature and pressure were maintained for 15 min. In the second stage, the temperature was increased to 150 ℃ at a rate of 2 ℃ / min, and the pressure was increased to 10 MPa simultaneously, and the temperature and pressure were kept constant for 35 min. In the third stage, the temperature was reduced to 60 ℃ at a rate of 1 ℃ / min, and the pressure was simultaneously reduced to 5 MPa at a rate of 0.3 MPa / min, and the temperature and pressure were maintained at a constant level for 100 min.

8. A high-strength, high-thermal-conductivity composite aramid insulating paper obtained by any one of the preparation methods described in claims 1 to 7, characterized in that, The composite aramid insulating paper has a double-layer composite structure; The bottom layer is composed of pre-stretched aramid long fibers; the surface layer is composed of aramid short-cut fibers and aramid precipitated fibers, and PDA-coated BNNS intercalation composite, wherein the BNNS are arranged vertically along the Z-axis.

9. The high-strength, high-thermal-conductivity composite aramid insulating paper according to claim 8, characterized in that, The aramid long fibers have a length of 5 mm and a diameter of 10–15 μm; the aramid short chopped fibers have a length of 3 mm and a diameter of 10–15 μm; and the aramid precipitated fibers have a length of 1–2 mm and a diameter of 5–10 μm.

10. The high-strength, high-thermal-conductivity composite aramid insulating paper according to claim 8, characterized in that, The PDA is coated with BNNS with an orientation density of ≥100 sheets / μm, and the bottom and top layers have the same thickness.

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