An aramid nanofiber / boron nitride nanosheet coating composite meta-aramid paper and a preparation method and application thereof

Abstract

This invention belongs to the field of insulating and thermally conductive materials technology, and discloses an aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper, its preparation method, and its application. The method includes: adding hexagonal boron nitride to a PVA / DMSO solution and magnetically stirring to achieve pre-wetting; ball milling, washing, and diluting the pre-wetting solution to obtain a BNNS / DMSO dispersion; mixing the BNNS / DMSO dispersion with an ANF / DMSO dispersion, then coating it onto meta-aramid base paper; immersing the BNNS / ANF composite slurry-coated meta-aramid base paper in water for displacement, and drying to obtain the displacement-treated paper; drying and hot-pressing the displacement-treated paper to obtain the aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper. This invention achieves uniform dispersion and in-plane orientation of boron nitride nanosheets in the aramid matrix, enabling the composite material to maintain excellent electrical insulation while significantly improving thermal conductivity.

Description

Technical Field

[0001] This invention belongs to the field of insulating and thermally conductive materials technology, and specifically relates to a meta-aramid paper with an aramid nanofiber / boron nitride nanosheet coating, its preparation method, and its application. Background Technology

[0002] Aramid paper, as a high-performance insulating material, is widely used in the field of electrical insulation due to its advantages of being lightweight, high-strength, having good insulation properties, and excellent thermal stability. However, due to the inherently low thermal conductivity of aramid fibers, traditional aramid paper has a low thermal conductivity, which can easily lead to problems such as local overheating, insulation aging, and performance degradation in electrical equipment during long-term operation, seriously restricting the reliable operation of high-power-density electrical equipment. Therefore, developing aramid paper-based materials that combine high insulation, high thermal conductivity, and excellent thermal stability has become a critical task that urgently needs to be addressed.

[0003] Currently, the main approach is to add thermally conductive fillers during the preparation of aramid paper, and to combine the fillers with aramid fibers through grafting modification and physical bonding to improve the thermal conductivity of traditional aramid paper. Commonly used inorganic thermally conductive fillers include three categories: metallic materials, carbon-based materials, and ceramic materials. Compared to metallic and carbon-based materials, ceramic materials have become a research hotspot in the field of thermally conductive fillers due to their high thermal conductivity, excellent electrical insulation, good thermal stability, relatively low cost, and simple processing technology. Among them, hexagonal boron nitride (h-BN) is a typical ceramic filler. As a ceramic material, aramid paper exhibits strong application competitiveness in the field of thermal management due to its unique crystal structure and excellent comprehensive performance. In addition, boron nitride nanosheets (BNNS), as a common nanostructure form of h-BN, improve its thermal conductivity by reducing interlayer phonon-phonon scattering, with a theoretical thermal conductivity that can even reach 2000 W / mK. Based on this, it is generally believed in the industry that selecting boron nitride or boron nitride nanosheets of appropriate size as fillers for composite modification of aramid paper is an effective technical path to further improve the electrical insulation performance of aramid paper and endow it with thermal conductivity.

[0004] However, in practical applications, hexagonal boron nitride and boron nitride nanosheets are difficult to achieve uniform dispersion in aramid fiber matrix, and are prone to agglomeration. This results in the inability to effectively form heat conduction channels, making it difficult to fully utilize their high thermal conductivity. Consequently, the thermal conductivity of aramid paper is not improved, and insulation aging is easily caused by local overheating, which fails to meet the stringent requirements of high power density electrical equipment for insulation materials. Summary of the Invention

[0005] To address the technical problems existing in the prior art, this invention provides an aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper, its preparation method, and its application, in order to solve the technical problem that the prior art is unable to fully utilize the high thermal conductivity of hexagonal boron nitride and boron nitride nanosheets, resulting in poor improvement of the thermal conductivity of aramid paper and easy insulation aging caused by local overheating.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a method for preparing aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper, comprising: Hexagonal boron nitride was added to a PVA / DMSO solution, and pre-wetting was achieved by magnetic stirring to obtain a pre-wetting solution. The pre-wetting solution was ball-milled, washed, and diluted to obtain a BNNS / DMSO dispersion. The BNNS / DMSO dispersion was mixed with the ANF / DMSO dispersion to obtain the BNNS / ANF composite slurry; BNNS / ANF composite slurry was coated onto meta-aramid base paper, and the meta-aramid base paper coated with BNNS / ANF composite slurry was immersed in water for displacement, dried, and the displacement paper was obtained. The replaced paper is dried and hot-pressed to obtain aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper.

[0007] Furthermore, the ratio of hexagonal boron nitride, PVA and DMSO in the pre-wetting solution is (1-4) g: (0.2-0.8) g: (20-80) mL.

[0008] Furthermore, the mass ratio of BNNS / DMSO dispersion to ANF / DMSO dispersion is (6-8):(2-4); wherein the concentration of BNNS / DMSO dispersion is 50-100 mg / mL and the concentration of ANF / DMSO dispersion is 10-20 mg / mL.

[0009] Furthermore, the preparation process of meta-aramid base paper is as follows: Meta-aramid short-cut fibers, meta-aramid precipitated fibers, and water are mixed and dispersed to obtain a slurry suspension; The pulp suspension is prepared into a meta-aramid wet paper web using a wet papermaking process; the meta-aramid wet paper web is then pressed and dried to obtain meta-aramid base paper.

[0010] Furthermore, during the process of coating the BNNS / ANF composite slurry onto the meta-aramid base paper, the coating thickness is 1-2 mm.

[0011] Furthermore, the meta-aramid base paper coated with BNNS / ANF composite pulp is immersed in water for displacement to obtain the displacement paper. The displacement time is 5-8 hours.

[0012] Furthermore, the replaced paper is dried and hot-pressed to obtain aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper. The drying temperature is 90-110℃, the drying pressure is 0.2-0.6Mpa, and the drying time is 15-20min.

[0013] Furthermore, the replaced paper is dried and hot-pressed to obtain aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper. The hot-pressing temperature is 130-180℃, the hot-pressing pressure is 8-10 MPa, and the hot-pressing time is 5-15 min.

[0014] This invention also provides an aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper, prepared using the aforementioned method; wherein the thermal conductivity of the aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper is 1.95-3.25 W·m. -1 ·K -1 .

[0015] The present invention also provides an application of aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper as a thermally conductive and insulating material in electrical equipment.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a method for preparing a meta-aramid paper with an aramid nanofiber / boron nitride nanosheet coating. This method employs polyvinyl alcohol-assisted ball milling of hexagonal boron nitride to control the size of the boron nitride nanosheets. Combined with the in-situ encapsulation and interfacial adhesion of aramid nanofibers, a dense layered thermally conductive paper is constructed in one step using a blade coating process. This achieves uniform dispersion and in-plane orientation of the boron nitride nanosheets in the aramid matrix, resulting in a composite material that significantly improves thermal conductivity while maintaining excellent electrical insulation. Specifically, hexagonal boron nitride is treated with a PVA-assisted ball milling process. The mechanical shear force during the milling process disrupts the van der Waals forces between the hexagonal boron nitride layers, effectively exfoliating and controlling the size of the boron nitride nanosheets. Simultaneously, the aramid nanofibers obtained through KOH / DMSO treatment possess extremely high specific surface area and abundant active sites, serving as a molecular adhesive for effective encapsulation of the boron nitride nanosheets. The two form a multimodal interface through hydrogen bonds, NB chemical bonds, and physical entanglement. The interaction ensures that boron nitride nanosheets remain uniformly dispersed in the ANF matrix even with high filler content, completely solving the problem of boron nitride nanosheet agglomeration and avoiding interruption of thermal conduction channels and increased interfacial thermal resistance. Secondly, through the processes of scraping, solvent replacement, and hot pressing, a biomimetic brick-and-mortar ordered structure with interlocking layers and networks is constructed. The in-plane oriented stacked BNNS forms a continuous low thermal resistance phonon transport channel, significantly improving the thermal conductivity of aramid paper. At the same time, the horizontal arrangement of BNNS and the ANF insulating network together extend the torsional electrical breakdown path, effectively suppressing insulation aging caused by local overheating. The tight integration of the ANF three-dimensional network with the paper-based fibers overcomes the problem of mutual constraints between thermal conductivity and mechanical properties in traditional high-filler composite materials, taking into account the material's heat resistance, self-extinguishing properties, and mechanical stability. Ultimately, the composite aramid paper possesses excellent high thermal conductivity, high insulation, and good thermal stability, meeting the requirements of high-power-density electrical equipment for insulation materials.

[0017] The aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper and its application provided by this invention possess all the advantages of the above-mentioned preparation method of aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 The image shows a SEM image of BNNS in the BNNS / DMSO dispersion in Example 1. Figure 2Cross-sectional SEM image of meta-aramid base paper and meta-aramid paper composite with aramid nanofiber / boron nitride nanosheet coating in Example 4; Figure 2 In the figures, (a1) is a cross-sectional SEM image of the meta-aramid base paper at a scale of 500µm; (b1) is a cross-sectional SEM image of the aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper in Example 4 at a scale of 200µm; (a2) is a cross-sectional SEM image of the meta-aramid base paper at a scale of 200µm; (b2) is a cross-sectional SEM image of the aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper in Example 4 at a scale of 100µm; (a3) ​​is a cross-sectional SEM image of the meta-aramid base paper at a scale of 100µm; and (b3) is a cross-sectional SEM image of the aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper in Example 4 at a scale of 10µm. Figure 3 The thermal conductivity diagrams are for the aramid nanofiber / boron nitride nanosheet coating composite meta-aramid paper in Examples 1-6. Detailed Implementation

[0020] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0021] This invention provides a method for preparing aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper, comprising the following steps: Step 1: Weigh 0.2-0.8g of polyvinyl alcohol (PVA); dissolve the weighed PVA in 20-80mL of dimethyl sulfoxide (DMSO) in an oil bath at 90℃, then transfer to room temperature and stir magnetically to obtain a PVA / DMSO solution.

[0022] Step 2: Weigh 1-4g of hexagonal boron nitride (h-BN) and add it to a PVA / DMSO solution. Stir magnetically for 48h to achieve pre-wetting and obtain a pre-wetting solution.

[0023] Step 3: Take 5-20 mL of the pre-wetting solution, ball mill for 12-24 h, wash 3-5 times with DMSO, and then dilute with DMSO to obtain a BNNS / DMSO dispersion with a concentration of 50-100 mg / mL.

[0024] Step 4: Weigh 5-10g of para-aramid fiber (PPTA) and 5-10g of potassium hydroxide (KOH), and disperse the weighed para-aramid fiber and potassium hydroxide in 250-500mL of DMSO to obtain an ANF / DMSO dispersion with a concentration of 10-20mg / mL.

[0025] Step 5: Mix the BNNS / DMSO dispersion and the ANF / DMSO dispersion at a mass ratio of (6-8):(2-4) to obtain the BNNS / ANF composite slurry.

[0026] Step 6: Weigh 1-2g of meta-aramid chopped fibers, 2-3g of meta-aramid precipitated fibers, and 1-3L of water, and add them to the stirring chamber of a standard fiber descrambler for slurry preparation. Then, descramble the fibers using the standard fiber descrambler for 10,000-30,000 rpm to obtain a slurry suspension.

[0027] Step 7: Homogenize the pulp suspension using a homogenizing roller 10-20 times for 8-15 seconds. Then, pass it through a forming wire with a diameter of 200 mm and a mesh size of 200 mesh, and dehydrate and form it under vacuum. After the pulp is filtered, vacuum it again for 5-10 seconds to obtain a meta-aramid wet paper web. Then, press it under a pressure of 0.2-0.6 MPa for 3-6 minutes. After that, dry it in a paper dryer at 90-110℃ and 0.2-0.6 MPa for 8-20 minutes to obtain meta-aramid base paper.

[0028] Step 8: Apply the BNNS / ANF composite slurry to the meta-aramid base paper using a doctor blade, controlling the coating thickness to be 1-2 mm. After coating, transfer the paper to deionized water and allow it to displace for 5-8 hours to obtain the displaced paper. Place the displaced paper in a paper dryer and dry it at a temperature of 90-110℃ and a pressure of 0.2-0.6 MPa for 15-20 minutes to obtain the dried paper.

[0029] Step 9: Use a flat vulcanizing machine to hot press the dried paper at a temperature of 130-180℃, a pressure of 8-10 MPa, and a time of 5-15 minutes to obtain aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper.

[0030] Preparation principle: The method for preparing meta-aramid paper with aramid nanofiber / boron nitride nanosheet coating provided by this invention, based on interfacial chemical regulation and multi-scale structural design strategies, completely solves the problem of boron nitride nanosheet aggregation, avoiding interruption of heat conduction channels and increase in interfacial thermal resistance. Specifically, firstly, PPTA is deprotonated using a KOH / DMSO system to disrupt its intermolecular hydrogen bond network, endowing aramid nanofibers (ANF) with extremely high specific surface area and abundant interfacial active sites, enabling them to effectively encapsulate boron nitride (BNNS) as a molecular adhesive. Simultaneously, hexagonal boron nitride is ball-milled with PVA-assisted milling, and the mechanical properties during the ball milling process... Shear force disrupts the van der Waals forces between h-BN layers to achieve effective exfoliation; the size of BNNS is controlled by adjusting the volume concentration of the BNNS dispersion in the ball mill jar, combined with the in-situ coating and interfacial adhesion of ANF, resulting in three types of multi-mode interfacial interactions: hydrogen bonds, NB chemical bonds, and physical entanglement. The synergistic effect of these multi-mode interfaces ensures that BNNS can be uniformly dispersed in the ANF matrix without agglomeration even at a filling content as high as 80 wt%. This fundamentally solves the background technical problem of BNNS being difficult to disperse uniformly and prone to agglomeration, avoiding the interruption of heat conduction channels and the increase of interfacial thermal resistance caused by agglomeration.

[0031] In this invention, a multi-scale structural design strategy of layer-network interlocking is adopted, enabling the in-plane oriented stacked boron nanofibers (BNNS) to form continuous low thermal resistance phonon transport channels, significantly improving the thermal conductivity of aramid paper. Specifically, firstly, by controlling the ball mill speed and slurry volume, hexagonal boron nitride is exfoliated into BNNS with a suitable aspect ratio and appropriate edge modification with hydroxyl functional groups. Subsequently, the obtained BNNS is composited with aramid nanofibers. Utilizing the amide group-rich characteristics of ANF, in-situ coating and stable dispersion of BNNS are achieved through multi-mode interactions of hydrogen bonding, physical entanglement, and interfacial chemical bonding. The composite slurry is then coated onto the surface of meta-aramid paper substrate using a doctor blade shearing process. The initial shearing action induces the orientation of BNNS along the coating direction. Solvent exchange then gels and fixes the orientation structure using ANF. Hot pressing further densifies the BNNS, causing them to stack tightly in the in-plane direction. Simultaneously, a three-dimensional ANF network permeates the BNNS layers, forming physical entanglement and interfacial bonds with the paper-based fibers. This ultimately results in a biomimetic "brick-and-mortar" ordered structure, with rigid BNNS as the "bricks" and the flexible ANF network as the "mortar." This biomimetic "brick-and-mortar" ordered structure enables the in-plane oriented BNNS to construct continuous, low-thermal-resistance phonon transport channels, achieving an in-plane thermal conductivity of 3.25 W·m⁻¹ at a high filler content of 80 wt%. -1 ·K -1Compared to pure PMIA, the breakdown strength is improved by 378%. On the other hand, the horizontal arrangement of BNNS and the ANF insulation network together extend and distort the electrical breakdown path, effectively suppressing the risk of insulation aging caused by local overheating. The breakdown strength reaches 25.9kV / mm, which is 245% higher than that of pure PMIA. In addition, ANF, as the main mechanical load-bearing phase, achieves efficient stress and heat transfer through strong interfacial coupling, overcoming the technical problem of mutual restriction between thermal conductivity and mechanical properties in traditional high-filler composite materials. At the same time, the physical barrier effect of BNNS endows the material with excellent heat resistance and self-extinguishing properties.

[0032] The following specific embodiments further explain the preparation method of the aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper provided by the present invention: Example 1 This embodiment 1 provides a method for preparing aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper, including the following steps: Step 1: Weigh 0.2g of polyvinyl alcohol (PVA); dissolve the weighed PVA in 20mL of dimethyl sulfoxide (DMSO) in an oil bath at 90℃, then transfer to room temperature and stir magnetically to obtain a PVA / DMSO solution.

[0033] Step 2: Weigh 1g of hexagonal boron nitride (h-BN) and add it to the PVA / DMSO solution. Stir magnetically for 48h to achieve pre-wetting and obtain the pre-wetting solution.

[0034] Step 3: Take 5 mL of the pre-wetting solution, ball mill for 24 h, wash 3 times with DMSO, and then dilute with DMSO to obtain a BNNS / DMSO dispersion with a concentration of 100 mg / mL.

[0035] Step 4: Weigh 10g of para-aramid fiber (PPTA) and 10g of potassium hydroxide (KOH), and disperse the weighed para-aramid fiber and potassium hydroxide in 500mL of DMSO to obtain an ANF / DMSO dispersion with a concentration of 20mg / mL.

[0036] Step 5: Mix the BNNS / DMSO dispersion and the ANF / DMSO dispersion at a mass ratio / volume ratio of 6:4 to obtain the BNNS / ANF composite slurry.

[0037] Step 6: Weigh 1.0g of meta-aramid chopped fiber, 2.0g of meta-aramid precipitated fiber and 2L of water, and add them to the stirring chamber of a standard fiber descrambler for slurry preparation. Then descramble the fiber using the standard fiber descrambler for 20,000 rpm to obtain a slurry suspension.

[0038] Step 7: Homogenize the pulp suspension using a homogenizing roller 10 times for 15 seconds. Then, pass it through a forming wire with a diameter of 200 mm and a mesh size of 200 mesh, and dehydrate and form it under vacuum. After the pulp is filtered, vacuum it again for 10 seconds to obtain a meta-aramid wet paper web. Then press it at a pressure of 0.6 MPa for 6 minutes. After that, dry it in a paper dryer at 95℃ and 0.4 MPa for 10 minutes to obtain meta-aramid base paper.

[0039] Step 8: Apply the BNNS / ANF composite slurry to the meta-aramid base paper using a doctor blade, controlling the coating thickness to 1 mm. After coating, transfer the paper to deionized water and allow it to displace for 8 hours to obtain the displaced paper. Place the displaced paper in a paper dryer and dry it at 95°C and 0.4 MPa for 15 minutes to obtain the dried paper.

[0040] Step 9: Use a flat vulcanizing machine to hot press the dried paper at a temperature of 130℃, a pressure of 8 MPa, and a time of 15 min to obtain aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper.

[0041] Example 2 This embodiment 2 provides a method for preparing aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper, including the following steps: Step 1: Weigh 0.4g of PVA; dissolve the weighed PVA in 40mL of DMSO in a 90℃ oil bath, then transfer to room temperature and stir magnetically to obtain a PVA / DMSO solution.

[0042] Step 2: Weigh 2g of h-BN and add it to the PVA / DMSO solution. Stir magnetically for 48h to achieve pre-wetting and obtain the pre-wetting solution.

[0043] Step 3: Take 20 mL of the pre-wetting solution, ball mill for 24 h, wash 5 times with DMSO, and then dilute with DMSO to obtain a BNNS / DMSO dispersion with a concentration of 100 mg / mL.

[0044] Step 4: Weigh 10g of PPTA and 10g of KOH, and disperse the weighed PPTA and KOH in 500mL of DMSO to obtain an ANF / DMSO dispersion with a concentration of 20mg / mL.

[0045] Step 5: Mix the BNNS / DMSO dispersion and the ANF / DMSO dispersion at a mass ratio / volume ratio of 6:4 to obtain the BNNS / ANF composite slurry.

[0046] Step 6: Weigh 1.5g of meta-aramid chopped fiber, 2.9g of meta-aramid precipitated fiber and 2L of water, and add them to the stirring chamber of a standard fiber descrambler for slurry preparation. Then descramble the fiber using the standard fiber descrambler for 10,000 rpm to obtain a slurry suspension.

[0047] Step 7: Homogenize the pulp suspension using a homogenizing roller 12 times for 12 seconds. Then, pass it through a forming wire with a diameter of 200 mm and a mesh size of 200 mesh, and dehydrate and form it under vacuum. After the pulp is filtered, vacuum it for another 8 seconds to obtain a meta-aramid wet paper web. Then press it at a pressure of 0.2 MPa for 3 minutes. After that, dry it in a paper dryer at 100℃ and 0.4 MPa for 10 minutes to obtain meta-aramid base paper.

[0048] Step 8: Apply the BNNS / ANF composite slurry to the meta-aramid base paper using a doctor blade, controlling the coating thickness to be 1.5 mm. After the coating is completed, transfer the paper to deionized water and allow it to displace for 8 hours to obtain the displaced paper. Place the displaced paper in a paper dryer and dry it at a temperature of 100℃ and a pressure of 0.4 MPa for 15 minutes to obtain the dried paper.

[0049] Step 9: Use a flat vulcanizing machine to hot press the dried paper at a temperature of 150℃, a pressure of 8 MPa, and a time of 10 min to obtain aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper.

[0050] Example 3 This embodiment 3 provides a method for preparing aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper, including the following steps: Step 1: Weigh 0.6g of PVA; dissolve the weighed PVA in 20mL of DMSO in a 90℃ oil bath, then transfer to room temperature and stir magnetically to obtain a PVA / DMSO solution.

[0051] Step 2: Weigh 3g of h-BN and add it to the PVA / DMSO solution. Stir magnetically for 48h to achieve pre-wetting and obtain the pre-wetting solution.

[0052] Step 3: Take 20 mL of the pre-wetting solution, ball mill for 24 h, wash 5 times with DMSO, and then dilute with DMSO to obtain a BNNS / DMSO dispersion with a concentration of 100 mg / mL.

[0053] Step 4: Weigh 5g of PPTA and 5g of KOH, and disperse the weighed PPTA and KOH in 250mL of DMSO to obtain an ANF / DMSO dispersion with a concentration of 20mg / mL.

[0054] Step 5: Mix the BNNS / DMSO dispersion and the ANF / DMSO dispersion at a mass ratio / volume ratio of 8:2 to obtain the BNNS / ANF composite slurry.

[0055] Step 6: Weigh 2.0g of meta-aramid chopped fibers, 3.0g of meta-aramid precipitated fibers and 1L of water, and add them to the stirring chamber of a standard fiber descrambler for slurry preparation. Then descramble the fibers for 15000r using the standard fiber descrambler to obtain a slurry suspension.

[0056] Step 7: Homogenize the pulp suspension using a homogenizing roller 15 times for 15 seconds; then, pass it through a forming wire with a diameter of 200 mm and a mesh count of 200 mesh, and dehydrate and form it under vacuum. After the pulp is filtered, vacuum it for another 8 seconds to obtain a meta-aramid wet paper web; then press it at a pressure of 0.5 MPa for 4 minutes; then dry it in a paper dryer at 110℃ and 0.4 MPa for 20 minutes to obtain meta-aramid base paper.

[0057] Step 8: Apply the BNNS / ANF composite slurry to the meta-aramid base paper using a doctor blade, controlling the coating thickness to 1 mm. After coating, transfer the paper to deionized water and allow it to displace for 8 hours to obtain the displaced paper. Place the displaced paper in a paper dryer and dry it at a temperature of 110℃ and a pressure of 0.4 MPa for 20 minutes to obtain the dried paper.

[0058] Step 9: Use a flat vulcanizing machine to hot press the dried paper at a temperature of 180℃, a pressure of 10 MPa, and a time of 10 min to obtain aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper.

[0059] Example 4 Example 4 provides a method for preparing aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper, including the following steps: Step 1: Weigh 0.8g of PVA; dissolve the weighed PVA in 80mL of DMSO in a 90℃ oil bath, then transfer to room temperature and stir magnetically to obtain a PVA / DMSO solution.

[0060] Step 2: Weigh 4g of h-BN and add it to the PVA / DMSO solution. Stir magnetically for 48h to achieve pre-wetting and obtain the pre-wetting solution.

[0061] Step 3: Take 5 mL of the pre-wetting solution, ball mill for 24 h, wash 4 times with DMSO, and then dilute with DMSO to obtain a BNNS / DMSO dispersion with a concentration of 100 mg / mL.

[0062] Step 4: Weigh 10g of PPTA and 10g of KOH, and disperse the weighed PPTA and KOH in 500mL of DMSO to obtain an ANF / DMSO dispersion with a concentration of 20mg / mL.

[0063] Step 5: Mix the BNNS / DMSO dispersion and the ANF / DMSO dispersion at a mass ratio / volume ratio of 8:2 to obtain the BNNS / ANF composite slurry.

[0064] Step 6: Weigh 1.5g of meta-aramid chopped fiber, 3.0g of meta-aramid precipitated fiber and 1L of water, and add them to the stirring chamber of a standard fiber descrambler for slurry preparation. Then descramble the fiber using the standard fiber descrambler for 20,000 rpm to obtain a slurry suspension.

[0065] Step 7: Homogenize the pulp suspension using a homogenizing roller 6 times for 15 seconds. Then, pass it through a forming wire with a diameter of 200 mm and a mesh count of 200 mesh, and dehydrate and form it under vacuum. After the pulp is filtered, vacuum it again for 6 seconds to obtain a meta-aramid wet paper web. Then press it at a pressure of 0.3 MPa for 5 minutes. After that, dry it in a paper dryer at 102℃ and 0.6 MPa for 20 minutes to obtain meta-aramid base paper.

[0066] Step 8: Apply the BNNS / ANF composite slurry to the meta-aramid base paper using a doctor blade, controlling the coating thickness to 1.5 mm. After coating, transfer the paper to deionized water and allow it to displace for 5 hours to obtain the displaced paper. Place the displaced paper in a paper dryer and dry it at a temperature of 103℃ and a pressure of 0.6 MPa for 20 minutes to obtain the dried paper.

[0067] Step 9: Use a flat vulcanizing machine to hot press the dried paper at a temperature of 180℃, a pressure of 10 MPa, and a time of 12 min to obtain aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper.

[0068] Example 5 Example 5 provides a method for preparing aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper, including the following steps: Step 1: Weigh 0.5g of PVA; dissolve the weighed PVA in 50mL of DMSO in a 90℃ oil bath, then transfer to room temperature and stir magnetically to obtain a PVA / DMSO solution.

[0069] Step 2: Weigh 2.5g of h-BN and add it to the PVA / DMSO solution. Stir magnetically for 48h to achieve pre-wetting and obtain the pre-wetting solution.

[0070] Step 3: Take 20 mL of the pre-wetting solution, ball mill it for 24 h, wash it twice with DMSO, and then dilute it with DMSO to obtain a BNNS / DMSO dispersion with a concentration of 100 mg / mL.

[0071] Step 4: Weigh 10g of PPTA and 10g of KOH, and disperse the weighed PPTA and KOH in 500mL of DMSO to obtain an ANF / DMSO dispersion with a concentration of 20mg / mL.

[0072] Step 5: Mix the BNNS / DMSO dispersion and the ANF / DMSO dispersion at a mass ratio / volume ratio of 7:3 to obtain the BNNS / ANF composite slurry.

[0073] Step 6: Weigh 1.7g of meta-aramid chopped fibers, 3.0g of meta-aramid precipitated fibers, and 1.5L of water, and add them to the stirring chamber of a standard fiber descrambler for slurry preparation. Then, descramble the fibers for 15,000 rpm using the standard fiber descrambler to obtain a slurry suspension.

[0074] Step 7: Homogenize the pulp suspension using a homogenizing roller 10 times for 12 seconds. Then, pass it through a forming wire with a diameter of 200 mm and a mesh size of 200 mesh, and dehydrate and form it under vacuum. After the pulp is filtered, vacuum it for another 6 seconds to obtain a meta-aramid wet paper web. Then press it under a pressure of 0.3 MPa for 5 minutes. After that, dry it in a paper dryer at 105℃ and 0.3 MPa for 16 minutes to obtain meta-aramid base paper.

[0075] Step 8: Apply the BNNS / ANF composite slurry to the meta-aramid base paper using a doctor blade, controlling the coating thickness to 1 mm. After coating, transfer the paper to deionized water and allow it to displace for 6 hours to obtain the displaced paper. Place the displaced paper in a paper dryer and dry it at a temperature of 105℃ and a pressure of 0.3 MPa for 16 minutes to obtain the dried paper.

[0076] Step 9: Use a flat vulcanizing machine to hot press the dried paper at a temperature of 160℃, a pressure of 8 MPa, and a time of 15 min to obtain aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper.

[0077] Example 6 This embodiment 6 provides a method for preparing aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper, including the following steps: Step 1: Weigh 0.8g of PVA; dissolve the weighed PVA in 80mL of DMSO in a 90℃ oil bath, then transfer to room temperature and stir magnetically to obtain a PVA / DMSO solution.

[0078] Step 2: Weigh 4g of h-BN and add it to the PVA / DMSO solution. Stir magnetically for 48h to achieve pre-wetting and obtain the pre-wetting solution.

[0079] Step 3: Take 5 mL of the pre-wetting solution, ball mill for 24 h, wash 4 times with DMSO, and then dilute with DMSO to obtain a BNNS / DMSO dispersion with a concentration of 100 mg / mL.

[0080] Step 4: Weigh 10g of PPTA and 10g of KOH, and disperse the weighed PPTA and KOH in 500mL of DMSO to obtain an ANF / DMSO dispersion with a concentration of 20mg / mL.

[0081] Step 5: Mix the BNNS / DMSO dispersion and the ANF / DMSO dispersion at a mass ratio / volume ratio of 7:3 to obtain the BNNS / ANF composite slurry.

[0082] Step 6: Weigh 1.5g of meta-aramid chopped fiber, 3.0g of meta-aramid precipitated fiber and 1L of water, and add them to the stirring chamber of a standard fiber descrambler for slurry preparation. Then descramble the fiber using the standard fiber descrambler for 20,000 rpm to obtain a slurry suspension.

[0083] Step 7: Homogenize the pulp suspension using a homogenizing roller 6 times for 15 seconds; then, pass it through a forming wire with a diameter of 200 mm and a mesh count of 200 mesh, and dehydrate and form it under vacuum. After the pulp is filtered, vacuum suction is applied for another 6 seconds to obtain a meta-aramid wet paper web; then press it at a pressure of 0.3 MPa for 6 minutes; finally, dry it in a paper dryer at 105℃ and 0.8 MPa for 15 minutes to obtain meta-aramid base paper.

[0084] Step 8: Apply the BNNS / ANF composite slurry to the meta-aramid base paper using a doctor blade, controlling the coating thickness to 1 mm. After coating, transfer the paper to deionized water and allow it to displace for 3 hours to obtain the displaced paper. Place the displaced paper in a paper dryer and dry it at a temperature of 106℃ and a pressure of 0.6 MPa for 10 minutes to obtain the dried paper.

[0085] Step 9: Use a flat vulcanizing machine to hot press the dried paper at a temperature of 200℃, a pressure of 10 MPa, and a time of 12 min to obtain aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper.

[0086] Performance test results explanation: The performance of the aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper prepared in Examples 1-6 was tested. Specifically, field emission scanning electron microscopy was used to test the cross-section of BNNS in the BNNS / DMSO dispersion in Example 4 and the prepared composite meta-aramid paper. The test conditions were secondary electron imaging mode and accelerating voltage of 10 kV. The in-plane thermal conductivity of the composite meta-aramid paper prepared in Examples 1-6 was tested using a Hot Disk (TPS 3500). The transverse size distribution of BNNS in the BNNS / DMSO dispersion in Examples 1-6 was tested using a laser particle size analyzer. The test conditions were room temperature and shading rate of 10%-15%.

[0087] Test results show that the thermal conductivity of the aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper prepared in Examples 1-6 is as follows: The thermal conductivity of the composite meta-aramid paper in Example 1 is 1.95 W·m. -1 ·K -1 The thermal conductivity of the composite meta-aramid paper in Example 2 is 1.75 W·m. -1 ·K -1 The thermal conductivity of the composite meta-aramid paper in Example 3 is 2.99 W·m. -1 ·K -1 The thermal conductivity of the composite meta-aramid paper in Example 4 is 3.25 W·m. -1 ·K -1 The thermal conductivity of the composite meta-aramid paper in Example 5 was 1.81 W·m. -1 ·K -1 The thermal conductivity of the composite meta-aramid paper in Example 6 is 2.61 W·m. -1 ·K -1 Secondly, the particle size of BNNS in Example 1 was 14.88µm; the particle size of BNNS in Example 2 was 22.35µm; the particle size of BNNS in Example 3 was 24.46µm; the particle size of BNNS in Example 4 was 13.82µm; the particle size of BNNS in Example 5 was 25.23µm; and the particle size of BNNS in Example 6 was 18.67µm.

[0088] As attached Figure 1 As shown, attached Figure 1 The attached image shows a SEM image of BNNS in the BNNS / DMSO dispersion in Example 4; from the attached image... Figure 1As can be seen, BNNS exhibits a typical lamellar morphology with uniform lateral size distribution, clear edges, and no obvious agglomeration. This indicates that the effective exfoliation and dispersion of hexagonal boron nitride in the DMSO system was successfully achieved by PVA-assisted liquid-phase ball milling. The resulting BNNS has a high aspect ratio and good dispersion stability. This microstructure characteristic lays the material foundation for the subsequent uniform dispersion, interfacial coating, and construction of the "lamella-network interlocking" structure of BNNS in the ANF matrix.

[0089] As attached Figure 2 As shown, attached Figure 2 The paper presents cross-sectional SEM images of meta-aramid base paper and the aramid nanofiber / boron nitride nanosheet coated meta-aramid paper in Example 4. As shown in Figures a1-a3, the cross-section of the meta-aramid base paper exhibits a loose, porous structure, with fibers overlapping to form a three-dimensional network. However, it contains numerous pores and voids, resulting in poor thermal conductivity and limited mechanical strength. In stark contrast, the cross-section of the composite meta-aramid paper after ANF@BNNS composite coating and hot pressing (Figures b1-b3) shows a dense, double-layer structure. The upper layer is the ANF@BNNS composite coating, with BNNS particles arranged in the in-plane direction within the coating. The tightly stacked and oriented layers form a continuous layered structure. The interface between the coating and the underlying meta-aramid paper base is tightly bonded without visible gaps or defects, indicating that a good interfacial fusion has been formed between the composite coating and the substrate. The microstructure of this cross section directly confirms the successful realization of the "layer-network interlocking" structure constructed in this invention in the composite paper. That is, BNNS acts as a rigid "brick" and is stacked in-plane in the coating, while ANF acts as a flexible "mortar" filling the spaces between the BNNS layers and penetrating and connecting to the paper base fibers to form an integrated and dense structure. This structure provides direct microstructural support for the composite material to achieve high in-plane thermal conductivity, high breakdown strength, and excellent mechanical properties.

[0090] As attached Figure 3 As shown, attached Figure 3 The accompanying diagrams show the thermal conductivity of the aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper prepared in Examples 1-6; from the appendix... Figure 3 As can be seen, the in-plane thermal conductivity of the composite paper continuously increases with the increase of boron nitride nanosheet filling from 60 wt% to 80 wt%; among them, the in-plane thermal conductivity reaches the highest value of 3.25 W·m when the filling amount is 80 wt%. - ¹·K - ¹, relatively pure meta-aramid base paper (0.68 W·m - ¹·K -¹) The thermal conductivity was increased by approximately 378%. This result indicates that with the increase of BNNS filling amount, the contact between BNNS inside the coating is more sufficient, forming a more continuous and dense in-plane orientation thermally conductive network, which effectively reduces the interfacial thermal resistance in the phonon transport process. It is worth noting that the size of the boron nitride nanosheets in Example 4 is 13.82µm. Its BNNS size has both a high aspect ratio and an appropriate amount of edge functional groups, which can achieve good in-plane orientation stacking in the coating and form a moderate interfacial interaction with the ANF matrix, thereby constructing a continuous, low-defect phonon transport channel and achieving a significant increase in thermal conductivity.

[0091] In this invention, boron nitride nanosheets with a high aspect ratio are introduced as thermally conductive fillers. Combined with the high strength, high flexibility, and excellent insulation properties of aramid fibers, a composite material system with an ordered structure and good interfacial bonding is constructed. This enables the prepared aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper thermally conductive material to not only possess high thermal conductivity but also maintain good electrical insulation, mechanical strength, and thermal stability. It can be widely used in high-power electronic devices, flexible electronic devices, and high-temperature insulation materials, meeting the needs of modern electronic devices for high-performance thermally conductive and insulating materials.

[0092] The above embodiments are merely one of the implementation methods for achieving the technical solution of the present invention. The scope of protection claimed by the present invention is not limited to this embodiment, but also includes any variations, substitutions and other implementation methods that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention.

Claims

1. A method for preparing a meta-aramid paper with an aramid nanofiber / boron nitride nanosheet coating, characterized in that, include: Hexagonal boron nitride was added to a PVA / DMSO solution, and pre-wetting was achieved by magnetic stirring to obtain a pre-wetting solution. The pre-wetting solution was ball-milled, washed, and diluted to obtain a BNNS / DMSO dispersion. The BNNS / DMSO dispersion was mixed with the ANF / DMSO dispersion to obtain the BNNS / ANF composite slurry; BNNS / ANF composite slurry was coated onto meta-aramid base paper, and the meta-aramid base paper coated with BNNS / ANF composite slurry was immersed in water for displacement, dried, and the displacement paper was obtained. The replaced paper is dried and hot-pressed to obtain aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper.

2. The method for preparing a meta-aramid paper with an aramid nanofiber / boron nitride nanosheet coating according to claim 1, characterized in that, The ratio of hexagonal boron nitride, PVA and DMSO in the pre-wetting solution is (1-4) g: (0.2-0.8) g: (20-80) mL.

3. The method for preparing a meta-aramid paper with an aramid nanofiber / boron nitride nanosheet coating according to claim 1, characterized in that, The mass ratio of BNNS / DMSO dispersion to ANF / DMSO dispersion is (6-8):(2-4); wherein the concentration of BNNS / DMSO dispersion is 50-100 mg / mL and the concentration of ANF / DMSO dispersion is 10-20 mg / mL.

4. The method for preparing a meta-aramid paper with an aramid nanofiber / boron nitride nanosheet coating according to claim 1, characterized in that, The preparation process of meta-aramid base paper is as follows: Meta-aramid short-cut fibers, meta-aramid precipitated fibers, and water are mixed and dispersed to obtain a slurry suspension; The pulp suspension is prepared into meta-aramid wet paper webs using a wet papermaking process. Meta-aramid wet paper webs are pressed and dried to obtain meta-aramid base paper.

5. The method for preparing a meta-aramid paper with an aramid nanofiber / boron nitride nanosheet coating according to claim 1, characterized in that, During the process of coating the BNNS / ANF composite slurry onto the meta-aramid base paper, the coating thickness is 1-2 mm.

6. The method for preparing a meta-aramid paper with an aramid nanofiber / boron nitride nanosheet coating according to claim 1, characterized in that, The meta-aramid base paper coated with BNNS / ANF composite slurry is immersed in water for displacement to obtain the displaced paper. The displacement time is 5-8 hours.

7. The method for preparing a meta-aramid paper with an aramid nanofiber / boron nitride nanosheet coating according to claim 1, characterized in that, In the process of drying and hot-pressing the replaced paper to obtain aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper, the drying temperature is 90-110℃, the drying pressure is 0.2-0.6Mpa, and the drying time is 15-20min.

8. The method for preparing a meta-aramid paper with an aramid nanofiber / boron nitride nanosheet coating according to claim 1, characterized in that, In the process of drying and hot-pressing the replaced paper to obtain aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper, the hot-pressing temperature is 130-180℃, the hot-pressing pressure is 8-10 MPa, and the hot-pressing time is 5-15 min.

9. A meta-aramid paper with an aramid nanofiber / boron nitride nanosheet coating, characterized in that, The composite meta-aramid paper, prepared by the method described in any one of claims 1-8, is an aramid nanofiber / boron nitride nanosheet coated composite paper with a thermal conductivity of 1.95-3.25 W·m. -1 ·K -1 .

10. The application of the aramid nanofiber / boron nitride nanosheet coated composite meta-aramid paper as described in claim 9, characterized in that, Used as a thermally conductive and insulating material in electrical equipment.

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