Composite heat-conducting paper as well as preparation method and application thereof

Abstract

The embodiment of the invention provides composite heat-conducting paper as well as a preparation method and application thereof. The preparation method comprises the following steps: adding the first aramid fiber into an acid solution to obtain a first reaction solution; the acid liquor comprises chlorosulfonic acid and trifluoromethanesulfonic acid; adding boron nitride nanosheets into the first reaction solution to obtain a second reaction solution; adding a pH regulator into the second reaction liquid to obtain a first composite product; modifying the first composite product with a silane coupling agent to obtain a second composite product; adding the second composite product into an aqueous solution of polyoxyethylene ether to obtain a third reaction solution; preparing second aramid fiber, fibrid and sodium polyacrylate into fiber dispersion liquid, and mixing the fiber dispersion liquid with the third reaction liquid to obtain composite slurry; and carrying out wet papermaking to obtain the composite heat-conducting paper. The aramid fibers are efficiently dissociated and the boron nitride nanosheets are uniformly dispersed through a super-acid system under a mild condition, so that the purpose of improving the heat-conducting property of the aramid composite paper without obviously sacrificing the mechanical property is achieved.

Description

Technical Field

[0001] This application relates to the field of special functional paper preparation technology, specifically to a composite thermally conductive paper, its preparation method and application. Background Technology

[0002] With the rapid development of cutting-edge technologies such as information technology, new energy, and aerospace, the demand for high-performance materials is becoming increasingly urgent, especially for composite materials with excellent thermal conductivity and good electrical insulation. Traditional materials, such as polymers, metals, and their alloys, while performing well in certain fields, often fall short when dealing with high power density, high-frequency transmission, and extreme environmental conditions. Among these, aramid fibers, with their excellent mechanical strength, high-temperature resistance, and low dielectric constant, are widely used as matrix materials for high-performance composite materials; however, their inherently low thermal conductivity limits their potential for expansion in high heat flux density applications.

[0003] However, traditional aramid composite materials, especially aramid paper, have poor intrinsic thermal conductivity (<0.2 W·m). -1 ·K -1 The existing thermal conductivity of aramid-based composites is insufficient to meet the requirements of high-power devices for coordinated insulation and heat dissipation management. To improve the thermal conductivity of aramid-based composites, researchers have experimented with adding various thermally conductive fillers, such as alumina, graphene, carbon nanotubes, and boron nitride nanosheets. Among these, alumina and graphene have been extensively studied due to their respective advantages. However, alumina has limited thermal conductivity, and while graphene exhibits excellent thermal conductivity, its high electrical conductivity compromises the insulation properties of aramid fibers. Furthermore, both fillers exhibit poor dispersion within the aramid matrix, leading to filler agglomeration, increased interfacial thermal resistance, and severely limiting the improvement in the thermal conductivity of the composite. In addition, the addition of traditional fillers often results in a decrease in the mechanical properties of the composite and an increase in processing difficulty, undoubtedly increasing the complexity of material applications.

[0004] Meanwhile, in traditional preparation methods, the lack of effective chemical bonds between the filler and aramid fibers results in high interfacial thermal resistance, severely limiting the thermal conductivity of the composite material. Furthermore, the introduction of fillers may disrupt the integrity of the original aramid fiber network structure, leading to a decrease in the dielectric properties and mechanical strength of the composite material, making it difficult to meet the stringent requirements of high-power electronic devices for high-performance composite materials. In addition, conventional acid hydrolysis processes (such as concentrated sulfuric acid) severely damage aramid fibers, resulting in low nanofiber yields and numerous defects.

[0005] In other words, the thermally conductive fillers in the existing aramid-based composite thermally conductive paper have poor dispersion, high interfacial thermal resistance, and poor mechanical properties. Therefore, the corresponding composite thermally conductive paper cannot simultaneously meet the requirements of high thermal conductivity, high strength and toughness, low defects, high insulation, and lightweight.

[0006] There is currently no good solution to the above problems. Summary of the Invention

[0007] This application provides a composite thermally conductive paper, its preparation method, and its application, in order to at least solve the technical problem that existing composite thermally conductive papers cannot simultaneously meet the requirements of high thermal conductivity, high strength and toughness, low defects, high insulation, and lightweight.

[0008] According to one aspect of the embodiments of this application, a method for preparing composite thermally conductive paper is provided, comprising: step S1, dispersing a first aramid fiber with an acid solution and subjecting it to a first reaction to obtain a first reaction solution; the acid solution includes chlorosulfonic acid and trifluoromethanesulfonic acid; step S2, dispersing boron nitride nanosheets with the first reaction solution to obtain a second reaction solution; mixing a pH adjuster with the second reaction solution to obtain a first composite product; step S3, modifying the first composite product with a silane coupling agent to obtain a second composite product; step S4, dispersing the second composite product with polyoxyethylene ether to obtain a third reaction solution; step S5, preparing a fiber dispersion by dispersing the second aramid fiber, precipitated fiber, and sodium polyacrylate, and mixing the fiber dispersion with the third reaction solution to obtain a composite slurry; and step S6, preparing the composite thermally conductive paper from the composite slurry.

[0009] Further, in step S1, the volume ratio of chlorosulfonic acid to trifluoromethanesulfonic acid in the acid solution is (1-10):(10-1); and / or, the solid content of the first aramid fiber in the acid solution is 0.01 g / mL to 0.2 g / mL; and / or, the first dispersion is carried out by stirring, and the stirring is carried out at -5℃ to 0℃; and / or, the reaction temperature of the first reaction is 25±2℃, and the heating rate to reach the reaction temperature is 2±0.02℃ / min.

[0010] Further, in step S2, the weight ratio of boron nitride nanosheets to first aramid fibers in the second reaction solution is (1-5):(5-1); and / or, step S2 further includes: adding a pH adjuster to the second reaction solution at -5℃ to 0℃ until the pH value of the second reaction solution is 7±0.2, and obtaining the first composite product by solid-liquid separation.

[0011] Furthermore, step S3 also includes: preparing a modified solution by mixing the silane coupling agent with ethanol, adding the first composite product to the modified solution, and stirring at 60±5℃ to obtain the second composite product.

[0012] Further, in step S4, the polyoxyethylene ether is added in the form of a polyoxyethylene ether solution, and the mass concentration of the polyoxyethylene ether in the polyoxyethylene ether solution is 0.5 ± 0.01%; and / or, in the third reaction solution, the solid content of the second composite product is 0.1% to 20%; preferably, the polyoxyethylene ether solution is selected from one or more of the following: an aqueous solution of polyoxyethylene ether, an isopropanol solution of polyoxyethylene ether, a toluene solution of polyoxyethylene ether, a xylene solution of polyoxyethylene ether, and an ethanol solution of polyoxyethylene ether.

[0013] Further, in step S5, the weight ratio of the second aramid fiber to the precipitated fiber is (1-5):1; and / or, the mass concentration of sodium polyacrylate in the fiber dispersion is 0.8±0.1%; and / or, the volume ratio of the fiber dispersion to the third reaction solution is 1:(1-10); and / or, the pH value of the composite slurry is 9.0-9.5.

[0014] Further, step S6 includes: step S6-1, preparing the composite pulp into fiber paper by wet papermaking; wet papermaking includes: forming fiber wet paper on a polyester wire mesh, and the fiber wet paper is subjected to a first dewatering treatment and a second dewatering treatment in sequence to obtain fiber paper; step S6-2, the fiber paper is subjected to a drying treatment and a hot pressing treatment in sequence to obtain composite thermally conductive paper.

[0015] Furthermore, in step S6-2, the drying process includes a first drying, a second drying, and a third drying performed sequentially; and / or, the hot pressing process is performed at a temperature of 150℃ to 300℃, a pressure of 1MPa to 20MPa, and a time of 1min to 30min.

[0016] According to another aspect of the embodiments of this application, a composite thermal conductive paper is also provided, which is prepared by the above-described method for preparing composite thermal conductive paper; the composite thermal conductive paper includes boron nitride nanosheets, and the content of boron nitride nanosheets is 1wt% to 50wt% based on the total weight of the composite thermal conductive paper as 100%.

[0017] According to another aspect of the embodiments of this application, the above-mentioned composite thermally conductive paper is also provided as an insulating and heat-insulating material in the fields of industrial equipment, aerospace, electronic devices and new energy.

[0018] In this embodiment, an acid-coordinated exfoliation method is adopted. The aramid fibers are efficiently dissociated and boron nitride nanosheets are uniformly dispersed under mild conditions through a superacid system of chlorosulfonic acid and trifluoromethanesulfonic acid. This achieves the goal of improving the thermal conductivity of aramid composite paper without significantly sacrificing mechanical properties, thereby realizing the technical effect of preparing high thermal conductivity, high toughness, high insulation, and lightweight composite materials. This solves the technical problems of poor thermal conductivity, high interfacial thermal resistance, and difficulty in synergistic mechanical and insulation properties of traditional aramid paper. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0020] As described in the background art, existing composite thermal conductive papers suffer from poor dispersion and interfacial compatibility of thermal conductive fillers, making it difficult for them to simultaneously meet the requirements of high thermal conductivity, high strength and toughness, low defects, high insulation, and lightweight. To address the aforementioned technical problems, according to embodiments of this application, a method for preparing composite thermally conductive paper is provided, comprising: step S1, dispersing a first aramid fiber with an acid solution and subjecting it to a first reaction to obtain a first reaction solution; the acid solution includes chlorosulfonic acid and trifluoromethanesulfonic acid; step S2, dispersing boron nitride nanosheets with the first reaction solution to obtain a second reaction solution; mixing a pH adjuster with the second reaction solution to obtain a first composite product; step S3, modifying the first composite product with a silane coupling agent to obtain a second composite product; step S4, dispersing the second composite product with polyoxyethylene ether to obtain a third reaction solution; step S5, preparing a fiber dispersion by combining the second aramid fiber, precipitated fiber, and sodium polyacrylate; mixing the fiber dispersion with the third reaction solution to obtain a composite slurry; and step S6, preparing the composite thermally conductive paper from the composite slurry.

[0021] This application employs a superacid synergistic exfoliation method, utilizing a chlorosulfonic acid and trifluoromethanesulfonic acid superacid system to efficiently dissociate aramid fibers and uniformly disperse boron nitride nanosheets under mild conditions. This achieves the goal of improving the thermal conductivity of aramid composite paper without significantly sacrificing mechanical properties. Specifically, in step S1, the first aramid fiber is dispersed in a mixture of chlorosulfonic acid and trifluoromethanesulfonic acid, thereby efficiently dissociating the aramid fiber under mild conditions to form nanoscale fiber bundles without excessively damaging the fiber structure. This maximizes the preservation of the microstructural integrity of the aramid fiber, thus improving its mechanical properties as a matrix material. Subsequently, in step S2, boron nitride nanosheets are added and uniformly distributed in the first reaction solution through a second dispersion process, forming a second reaction solution. This process not only promotes the uniform dispersion of boron nitride nanosheets among the aramid nanofibers but, more importantly, ensures that the pH value of the solution is neutral through the addition of a pH adjuster, creating an ideal environment for subsequent solid-liquid separation and composite material preparation. The first composite product obtained through solid-liquid separation is a preliminary combination of boron nitride nanosheets and aramid nanofibers. At this point, strong chemical bonds have not yet formed between the two materials, but they have already shown a good physical mixing state.

[0022] Furthermore, in steps S3 and S4, the first composite product undergoes modification with a silane coupling agent and a third dispersion in a polyoxyethylene ether aqueous solution to form the second composite product, which ultimately becomes the third reaction solution. During this process, the silane coupling agent introduces amino groups onto the surface of the boron nitride nanosheets, and these amino groups form covalent bonds with the hydroxyl groups of the aramid fibers, significantly enhancing the interfacial bonding strength and reducing the interfacial thermal resistance. Additionally, the polyoxyethylene ether further improves the solid-liquid wettability of the reaction system, forming a highly dispersible slurry system, thereby further optimizing the chemical modification and the formation of chemical bonds.

[0023] Finally, steps S5 and S6 promote a tighter arrangement of aramid fibers and reduce porosity; at the same time, they also promote further interface optimization between boron nitride nanosheets and aramid fibers, ultimately resulting in a composite thermally conductive paper that possesses comprehensive properties such as lightweight, high thermal conductivity, high insulation and good flexibility.

[0024] In particular, in the preparation method provided in this application, a mixed acid formed by chlorosulfonic acid and trifluoromethanesulfonic acid is used to dissociate aramid fibers. This not only efficiently exfoliates the aramid fibers but also activates boron nitride nanosheets under mild conditions. This may be because both chlorosulfonic acid (HSO3Cl) and trifluoromethanesulfonic acid (CF3SO3H) are superacids, and their Hammett strength functions are much lower than those of conventional strong acids, thus providing higher proton and H+ ions. + The density allows for the breaking of chemical bonds on the material surface, initiating new chemical reactions without damaging the material's basic structure. From the perspective of aramid fibers, chlorosulfonic acid and trifluoromethanesulfonic acid can alter the surface properties of aramid fibers, introducing new chemical groups, such as sulfonyl groups (-SO3H), thereby enhancing the physical adsorption and chemical reaction between the fibers and boron nitride nanosheets. From the perspective of boron nitride nanosheets, the superacid system formed by chlorosulfonic acid and trifluoromethanesulfonic acid can more significantly activate the surface of boron nitride nanosheets, creating more active sites, thereby forming stronger chemical bonds with aramid fibers, improving the interfacial bonding between the two, reducing interfacial thermal resistance, and ultimately significantly improving the overall thermal conductivity of the resulting composite thermally conductive paper.

[0025] To avoid ambiguity, the precipitated fiber used in this invention is essentially an aramid fiber, a special type of synthetic fiber material formed by the precipitation of aramid polymers (such as meta-aramid 1313 or para-aramid 1414) through a specific process. The diameter of the precipitated fiber is shorter than that of the first and second aramid fibers, and it also has a specific specific surface area.

[0026] Specifically, the preparation methods of precipitated fibers include:

[0027] Synthesis: A low-temperature solution polymerization method is employed. Under nitrogen protection, aromatic diamines (such as m-phenylenediamine and p-phenylenediamine) are dissolved in a polar solvent (such as N,N-dimethylacetamide / DMAC). Aromatic dicarboxylic acid chlorides (such as isophthaloyl chloride) are added at low temperature (0–20°C) to initiate a polycondensation reaction, generating an aramid polymer solution. Alkaline reagents are used to ensure the solution is neutral. Low-melting-point water-soluble modifiers (such as polyethylene glycol and polyvinylpyrrolidone) are added to the polymer solution to improve the dispersibility and specific surface area of ​​the precipitated fibers.

[0028] Formation: A high-speed shear precipitation method is used. The precipitating solution and precipitant (a mixture of water / DMAC / calcium chloride) are fed into a precipitator. Under the shearing action of a high-speed rotating cutter head (2000–8000 rpm), sheet-like or fibrous nascent fibers are formed. Further high-speed shearing at 4000–10000 rpm dissociates the fibers into bundles, which are then sieved through a vibrating screen (0.1–5 mm aperture). The precipitant is typically a salt solution (such as a 10–40% aqueous solution of calcium chloride and DMAC), which promotes coagulation and formation through non-solvent diffusion, thus obtaining the precipitated fibers.

[0029] To promote more effective dissociation of aramid fibers and reduce potential fiber structure damage under strong acid conditions, thereby more effectively preserving the original high strength and low dielectric constant properties of aramid fibers, the volume ratio of chlorosulfonic acid to trifluoromethanesulfonic acid in the acid solution in step S1 is preferably (1-10):(10-1). Furthermore, to promote stronger bonding between aramid fibers and boron nitride nanosheets in subsequent processes, thereby improving the dispersibility of boron nitride as a thermally conductive filler in the final composite thermally conductive paper and significantly enhancing the planar thermal conductivity of the composite thermally conductive paper, the volume ratio of chlorosulfonic acid to trifluoromethanesulfonic acid in the acid solution is preferably 1:(0.9-1.1).

[0030] Furthermore, the solid content of the first aramid fiber in the acid solution is 0.01 g / mL to 0.2 g / mL, preferably 0.02 g / mL to 0.03 g / mL. Excessive solid content may lead to fiber agglomeration, affecting the uniformity of the dispersion and thus the thermal conductivity of the composite material; while excessively low solid content reduces reaction efficiency and increases production costs. Therefore, the aforementioned preferred and more preferred solid content of the first aramid fiber in the acid solution promotes better contact between the aramid fiber and the acid solution, thereby more effectively balancing fiber dissociation efficiency and dispersion stability, ultimately producing a composite thermally conductive paper with balanced thermal conductivity and mechanical strength.

[0031] In several embodiments, to provide a more stable environment for more uniform dispersion and initial bonding between boron nitride nanosheets and aramid fibers, thereby further improving the manufacturing efficiency and performance consistency of the composite thermal conductive paper, the first dispersion is preferably carried out by stirring at -5°C to 0°C; and / or, the reaction temperature of the first reaction is 25±2°C, and the heating rate to reach the reaction temperature is 2±0.02°C / min. Furthermore, step S1 preferably further includes: swelling the aramid fiber raw material in N-methylpyrrolidone to obtain the first aramid fiber, thereby pre-softening the molecular chains of the aramid fiber, making it easier to disperse in the subsequent acidic environment. Based on this, to further reduce structural damage and improve the mechanical properties of the subsequently formed composite thermal conductive paper, the swelling treatment temperature is more preferably 80±5°C, and the time is 2±0.5h.

[0032] Furthermore, in order to better balance the dispersion uniformity of the boron nitride nanosheets as a thermally conductive filler and the structural integrity of the aramid fiber matrix, in the second reaction solution of step S2, the weight ratio of boron nitride nanosheets to the first aramid fiber is preferably (1-5):(5-1); more preferably 1:(0.9-1.1), so as to comprehensively improve the mechanical properties and thermal insulation properties of the final composite thermally conductive paper.

[0033] For step S2, it preferably further includes: adding a pH adjuster to the second reaction solution at -5℃ to 0℃ until the pH value of the second reaction solution is 7±0.2, and then performing solid-liquid separation to obtain the first composite product. In this preferred embodiment, the neutral pH environment can better maintain the charge state of the surfaces of each component, promote the electrostatic interaction between the boron nitride nanosheet filler and the fiber, and also help maintain the structural integrity of the fiber web, so as to obtain a composite thermally conductive paper with better quality and stronger toughness.

[0034] As mentioned earlier, boron nitride nanosheets, acting as thermally conductive fillers, achieve uniform dispersion in the composite thermally conductive paper by forming stable chemical bonds with aramid fibers. Therefore, a thickness of 10 nm to 20 nm and a sheet diameter of 500 nm to 2000 nm are preferred to significantly enhance contact with the fiber matrix, optimize heat transfer efficiency, and result in a composite thermally conductive paper with higher planar thermal conductivity.

[0035] In several embodiments, the pH adjuster is selected from one or more of sodium carbonate, sodium bicarbonate, ammonia, calcium hydroxide, potassium hydroxide, and sodium hydroxide, and the pH adjuster is added in the form of an aqueous solution with a mass fraction of 10 ± 2%.

[0036] To further enhance the interfacial compatibility between boron nitride nanosheets and aramid fibers, reduce interfacial thermal resistance, and improve the mechanical and dielectric properties of the resulting composite thermally conductive paper, step S3 preferably further includes: preparing a modified solution by mixing a silane coupling agent with ethanol, adding the first composite product to the modified solution, and stirring at 60±5°C to obtain a second composite product. Further, the weight ratio of the silane coupling agent to the first composite product is preferably 1:(5-100), more preferably 1:(10-25), and even more preferably 1:(14-16); and / or, preferably, the mass fraction of the silane coupling agent in the modified solution is 0.8%-1.2%, so that the silane coupling agent molecules can more fully cover the surface of the boron nitride nanosheets, thereby more effectively introducing functional groups (such as amino groups) that form covalent bonds with the aramid fibers, and thus more effectively improving the various properties of the resulting composite thermally conductive paper.

[0037] In several specific embodiments, the preferred silane coupling agent is selected from one or more of KH550, KH570, KH580, A-174, A-1160, A-1310, A-1630 and F8261.

[0038] In step S4, polyoxyethylene ether is added in the form of a polyoxyethylene ether solution. To improve the dispersibility of the second composite product in this solution and further reduce agglomeration, thereby improving the uniformity of the composite slurry in the subsequent wet papermaking process and obtaining a more dense, structurally stable, and mechanically stronger composite thermal conductive paper, the preferred mass concentration of polyoxyethylene ether is 0.5 ± 0.01%. And / or, in the third reaction solution, the solid content of the second composite product is 0.1% to 20%, preferably 5% to 15%, more preferably 13 ± 0.5%. Specifically, the polyoxyethylene ether solution is selected from one or more of the following: an aqueous solution of polyoxyethylene ether, an isopropanol solution of polyoxyethylene ether, a toluene solution of polyoxyethylene ether, a xylene solution of polyoxyethylene ether, and an ethanol solution of polyoxyethylene ether.

[0039] Further, in step S5, the weight ratio of the second aramid fiber to the precipitated fiber is preferably (1-5):1; and / or, the mass concentration of sodium polyacrylate in the fiber dispersion is preferably 0.8 ± 0.1%, so as to better balance the tensile strength, durability, and planar thermal conductivity of the final composite thermally conductive paper. Also, to promote higher uniformity and structural stability of the thermally conductive composite network formed by the boron nitride nanosheets and the aramid fiber matrix, the volume ratio of the fiber dispersion to the third reaction liquid is preferably 1:(1-10), more preferably 1:(0.9-1.1), thereby controlling the boron nitride nanosheets in the resulting composite slurry within a more suitable content range, and more significantly achieving a comprehensive improvement in the insulation and thermal conductivity, as well as high strength and high toughness of the composite thermally conductive paper. Preferably, the pH value of the resulting composite slurry is 9.0-9.5, which can further optimize the stability of the composite slurry, reduce the flocculation of boron nitride nanosheets and aramid fibers during the pulping process, and thus improve the uniformity and high flatness of the final composite thermally conductive paper.

[0040] In several embodiments, to form a composite thermally conductive paper with a more stable structure, stronger tensile strength, and more uniform dispersion of boron nitride nanosheets, it is preferable that the lengths of the first aramid fiber and the second aramid fiber are each independently 1 μm to 5 μm; and / or, the length of the precipitated fiber is 0.1 μm to 0.5 μm, and the specific surface area is 5 m². 2 / g~50m 2 / g.

[0041] In step S6, in order to further improve the density and flatness of the composite thermally conductive paper, the step preferably includes: step S6-1, preparing the composite slurry into fiber paper by wet papermaking; wet papermaking includes: forming fiber wet paper on a polyester wire mesh, and the fiber wet paper is subjected to a first dehydration treatment and a second dehydration treatment in sequence to obtain fiber paper; step S6-2, the fiber paper is subjected to a drying treatment and a hot pressing treatment in sequence to obtain composite thermally conductive paper.

[0042] In several embodiments, the first dehydration treatment is carried out at -0.04 MPa to -0.02 MPa to achieve a dryness of 10% to 15% in the wet fiber paper; and / or, the second dehydration treatment is carried out at -0.08 MPa to -0.06 MPa to achieve a dryness of 20% to 25% in the wet fiber paper, thereby obtaining the fiber paper. In this preferred embodiment, the first dehydration treatment is carried out under a low vacuum pressure of -0.04 MPa to -0.02 MPa. This pressure range can gently promote the initial removal of moisture from the wet fiber paper, achieving a dryness of 10% to 15%, which helps to better reduce damage to the fiber structure and initially stabilize the thermally conductive paper structure. The second dehydration treatment is carried out under a high vacuum pressure of -0.08 MPa to -0.06 MPa, further increasing the dryness of the wet fiber paper to 20% to 25%, thereby further increasing the degree of dehydration, improving the density of the fiber paper, and thus optimizing its heat conduction path, achieving a more significant improvement in thermal conductivity. Compared to a one-step dehydration process, the preferred two-stage dehydration process described above reduces fiber structure damage, thereby more effectively preserving the integrity of the aramid fibers and the good dispersion of the boron nitride nanosheets, the thermally conductive filler. This ultimately helps to further improve the mechanical properties and thermal conductivity of the composite thermally conductive paper. More specifically, a polyester mesh size of 60±10 mesh is preferred, allowing for more precise control of the flow of the composite slurry and the arrangement of the fibers, thereby further improving the density and uniformity of the resulting composite thermally conductive paper and optimizing its thermal conductivity and mechanical properties.

[0043] In the drying process of step S6-2, it is preferable to include a first drying, a second drying, and a third drying performed sequentially. A gradient, step-by-step drying process can more effectively achieve a balanced improvement in thermal conductivity, structural stability, and insulation. Based on this, in several embodiments: the first drying is carried out at a temperature of 60±5℃ and a humidity of 60±5%RH to achieve a dryness of 40%–45% in the fiber paper, thereby more effectively maintaining the integrity and stability of the microstructure in the composite paper at this point. During the second drying process, a large amount of moisture is removed from the fiber paper; therefore, this process is preferably carried out at a temperature of 100±5℃ and a humidity of 30±5%RH to achieve a dryness of 85%–90% in the fiber paper, thereby more effectively reducing uneven shrinkage of the wet fiber paper due to moisture evaporation, maintaining the stability of the fiber network, and ultimately improving the density and flatness of the composite thermally conductive paper, optimizing its thermal conductivity and mechanical properties. Finally, in order to more thoroughly remove the residual water from the fiber paper and ultimately give it a higher density, thereby promoting a higher thermal conductivity between the boron nitride nanosheets and aramid fibers, the third drying is preferably carried out at a temperature of 140±10℃ and a humidity of 15±2%RH, so that the dryness of the fiber paper reaches 95% to 99%.

[0044] In the hot pressing process of step S6-2, in order to more significantly densify the fiber network and improve the contact tightness between boron nitride nanosheets and aramid fibers, thereby further optimizing the thermal conductivity of the resulting composite thermally conductive paper, the preferred process temperature is 150℃~300℃, the pressure is 1MPa~20MPa, and the time is 1min~30min; more preferably, the temperature is 220±10℃, the pressure is 10±0.5MPa, and the time is 1min~3min.

[0045] Embodiments of this application also provide a composite thermally conductive paper, which is prepared by the above-described method for preparing composite thermally conductive paper. The composite thermally conductive paper includes boron nitride nanosheets, and the content of boron nitride nanosheets is 1 wt% to 50 wt% based on 100% of the total weight of the composite thermally conductive paper. In the composite thermally conductive paper obtained by the above preparation method, the boron nitride nanosheets exhibit higher dispersibility and interfacial compatibility, and stronger bonding with the aramid fiber matrix. Therefore, it is possible to achieve a significant improvement in thermal conductivity and insulation performance while maintaining lightweight and flexibility. Furthermore, to further balance the thermal conductivity and toughness of the composite thermally conductive paper, the content of boron nitride nanosheets is preferably 2 wt% to 8 wt%.

[0046] Embodiments of this application also provide an application of the aforementioned composite thermally conductive paper as an insulating and heat-insulating material in the fields of industrial equipment, aerospace, electronic devices, and new energy. Because the composite thermally conductive paper provided in this application possesses unique properties such as high thermal conductivity, high insulation, lightweight, and good flexibility, it is particularly suitable for high-end applications requiring simultaneous optimization of heat dissipation and insulation performance. Especially in the fields of high-frequency and high-power 5G communication equipment and high-performance computers, the low dielectric constant and high thermal conductivity of the aforementioned composite thermally conductive paper can significantly reduce energy loss during signal transmission, improve the heat dissipation efficiency of the equipment, and extend the service life of the equipment. In new energy vehicle batteries and large-scale energy storage systems, the aforementioned composite thermally conductive paper can effectively manage the heat within the battery module, preventing battery performance degradation or safety hazards caused by overheating. Simultaneously, its excellent insulation properties can also improve the overall safety of the battery system, reduce energy loss, and extend the driving range.

[0047] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0048] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0049] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0050] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0051] Example 1

[0052] A method for preparing composite thermally conductive paper:

[0053] (1-1) Weigh 5g of PPTA aramid short-cut fiber (5μm in length, model Kevlar-29), immerse it in 500mL of acetone for ultrasonic cleaning, and vacuum dry it at 60℃ for 12h; immerse the dried fiber in 500mL of N-methylpyrrolidone (NMP), stir at 80℃ for 2h to swell, and vacuum filter to obtain fiber filter cake.

[0054] (1-2) Under nitrogen protection, chlorosulfonic acid and trifluoromethanesulfonic acid were mixed at a volume ratio of 1:1 and stirred in an ice bath (-5℃~0℃) for 30 min to prepare 200 mL of superacid solution; 5 g of fiber filter cake was added to the superacid solution (i.e., the solid content of aramid fiber in the acid solution was 0.025 g / mL), stirred at low temperature (-5~0℃) for 1 h, and then heated to 25℃ at a rate of 2℃ / min to react for 24 h.

[0055] (2-1) Add 5g of boron nitride nanosheet powder (thickness 15nm, sheet diameter 2000nm) to the above reaction solution and mix evenly; subject the mixture to probe sonication (power 800W, pulse mode on / off = 3s / 1s, time 2h) and high-speed stirring under ice bath conditions to obtain boron nitride nanosheet / aramid nanofiber dispersion, i.e., the second reaction solution, wherein the weight ratio of boron nitride nanosheet to aramid fiber is 1:1.

[0056] (2-2) Pour the obtained second reaction solution into an ice-water mixture (-5 to 0℃), and add 15% Na2CO3 solution as a pH adjuster to neutralize it to pH=7. Centrifuge and wash 5 times, and freeze dry to obtain composite powder, which is the first composite product.

[0057] (3) Weigh 1g of KH550 silane coupling agent, dissolve it in 400mL of ethanol to prepare a KH550 ethanol solution with a mass concentration of 1%, add 15g of the obtained first composite product (i.e., the weight ratio of silane coupling agent to the first composite product is 1:15), and stir at 60℃ for 2h to achieve silane coupling agent modification and obtain the second composite product.

[0058] (4) Add 100g of a 0.5% polyoxyethylene ether (PEO) aqueous solution to the obtained second composite product, and use probe ultrasonic treatment (power 500W, pulse mode on / off = 3s / 1s, time 1h) to obtain a homogeneous suspension, namely the third reaction solution, wherein the solid content of the second composite product is 13%.

[0059] (5) Weigh 65g of aramid short-cut fiber (3μm in length, Kevlar-29) and 25g of precipitated fiber (Kevlar fiber, Kevlar-49, 0.4μm in length, with a specific surface area of ​​30m²). 2 The fiber dispersion was prepared by dispersing the second aramid fiber (g) in 9500 mL of a deionized aqueous solution containing 0.8% sodium polyacrylate (i.e., the weight ratio of the second aramid fiber to the precipitated fiber was 2.6:1) to obtain a fiber dispersion. Then, 9500 mL of a third reaction solution (i.e., the volume ratio of the fiber dispersion to the third reaction solution was 1:1) was added to the obtained fiber dispersion, and the pH was adjusted to 9.0–9.5 to obtain a composite slurry.

[0060] (6-1) A single-layer polyester wire mesh (60 mesh) is provided, tilted at 10°, and the composite pulp is evenly sprayed onto the wire surface through a headbox to form a wet fiber paper. Preliminary dewatering under low vacuum (-0.04MPa to -0.02MPa) achieves a wet paper sheet dryness of 10% to 15%, while deep dewatering under high vacuum (-0.08MPa to -0.06MPa) achieves a wet paper sheet dryness of 20% to 25%, thus obtaining the fiber paper.

[0061] (6-2) Drying treatment: The fiber paper is pre-dried (i.e., first drying) at 60℃ and 60% RH to achieve a dryness of 40%–45%; the main drying (i.e., second drying) at 100℃ and 30% RH to achieve a dryness of 85%–90%; and the final drying (i.e., third drying) at 140℃ and 15% RH to achieve a dryness of 95%–99%. Hot pressing treatment: The dried fiber paper is hot-pressed at 220℃ and 10MPa for 3 minutes to obtain an aramid composite thermally conductive paper with a boron nitride nanosheet filling of approximately 5wt%.

[0062] Example 2

[0063] A method for preparing composite thermally conductive paper:

[0064] The only difference between this embodiment and Embodiment 1 is that the volume ratio of chlorosulfonic acid to trifluoromethanesulfonic acid in steps (1-2) is changed to 1:10.

[0065] Example 3

[0066] A method for preparing composite thermally conductive paper:

[0067] The only difference between this embodiment and Embodiment 1 is that the volume ratio of chlorosulfonic acid to trifluoromethanesulfonic acid in steps (1-2) is changed to 10:1.

[0068] Example 4

[0069] A method for preparing composite thermally conductive paper:

[0070] The only difference between this embodiment and Embodiment 1 is that the weight of the fiber filter cake in step (1-2) is changed to 2g, that is, the solid content of aramid fiber in acid solution is changed to 0.01g / mL.

[0071] Example 5

[0072] A method for preparing composite thermally conductive paper:

[0073] The only difference between this embodiment and Embodiment 1 is that the weight of the fiber filter cake in step (1-2) is changed to 40g, that is, the solid content of aramid fiber in the acid solution is changed to 0.2g / mL.

[0074] Example 6

[0075] A method for preparing composite thermally conductive paper:

[0076] The only difference between this embodiment and Embodiment 1 is that the weight of boron nitride nanosheets in step (2-1) is changed to 25g, that is, the weight ratio of boron nitride nanosheets to aramid fibers in the second reaction solution is changed to 1:5.

[0077] Example 7

[0078] A method for preparing composite thermally conductive paper:

[0079] The only difference between this embodiment and Embodiment 1 is that the weight of boron nitride nanosheets in step (2-1) is changed to 1g, that is, the weight ratio of boron nitride nanosheets to aramid fibers in the second reaction solution is changed to 5:1.

[0080] Example 8

[0081] A method for preparing composite thermally conductive paper:

[0082] The only difference between this embodiment and Embodiment 1 is that the weight ratio of the silane coupling agent to the first composite product in step (3) is changed to 1:5.

[0083] Example 9

[0084] A method for preparing composite thermally conductive paper:

[0085] The only difference between this embodiment and Embodiment 1 is that the weight ratio of the silane coupling agent to the first composite product in step (3) is changed to 1:100.

[0086] Example 10

[0087] A method for preparing composite thermally conductive paper:

[0088] The only difference between this embodiment and Example 1 is that the mass concentration of the PEO aqueous solution in step (4) is changed to 0.1%, and the amount of PEO aqueous solution added is changed so that the solid content of the second composite product in the third reaction solution is changed to 20%.

[0089] Example 11

[0090] A method for preparing composite thermally conductive paper:

[0091] The only difference between this embodiment and Example 1 is that the mass concentration of the PEO aqueous solution in step (4) is changed to 1.0%, and the amount of PEO aqueous solution added is changed so that the solid content of the second composite product in the third reaction solution is changed to 0.1%.

[0092] Example 12

[0093] A method for preparing composite thermally conductive paper:

[0094] The only difference between this embodiment and Example 1 is that the mass concentration of the deionized aqueous solution of sodium polyacrylate in step (5) is changed to 0.5%, and the amount of the third reaction liquid is changed so that the volume ratio of the fiber dispersion to the third reaction liquid is changed to 1:0.8.

[0095] Example 13

[0096] A method for preparing composite thermally conductive paper:

[0097] The only difference between this embodiment and Example 1 is that the mass concentration of the deionized aqueous solution of sodium polyacrylate in step (5) is changed to 1.2%, and the amount of the third reaction liquid is changed so that the volume ratio of the fiber dispersion to the third reaction liquid is changed to 1:1.2.

[0098] Example 14

[0099] A method for preparing composite thermally conductive paper:

[0100] The only difference between this embodiment and Embodiment 1 is that in step (6-1), dehydration is carried out only once at -0.08MPa to -0.06MPa, and the dryness of the wet paper sheet reaches 20% to 25%, thus obtaining fiber paper.

[0101] Example 15

[0102] A method for preparing composite thermally conductive paper:

[0103] The only difference between this embodiment and Embodiment 1 is that in step (6-2), no pre-drying is performed. Instead, the main drying (i.e., the second drying) is carried out directly at 100°C and 30% RH to achieve a dryness of 85% to 90% for the fiber paper. Then, the final drying (i.e., the third drying) is carried out at 140°C and 15% RH to achieve a dryness of 95% to 99% for the fiber paper.

[0104] Example 16

[0105] A method for preparing composite thermally conductive paper:

[0106] The only difference between this embodiment and Embodiment 1 is that in step (6-2), the final drying is carried out only at a temperature of 140°C and a humidity of 15%, and the dryness of the fiber paper reaches 95% to 99%.

[0107] Example 17

[0108] A method for preparing composite thermally conductive paper:

[0109] The only difference between this embodiment and Embodiment 1 is that in step (6-2), the temperature of the hot pressing process is changed to 100°C, the pressure is changed to 20MPa, and the time is changed to 30min.

[0110] Example 18

[0111] A method for preparing composite thermally conductive paper:

[0112] The only difference between this embodiment and Embodiment 1 is that in step (6-2), the temperature of the hot pressing process is changed to 300°C, the pressure is changed to 1 MPa, and the time is changed to 1 min.

[0113] Comparative Example 1

[0114] A method for preparing thermally conductive paper:

[0115] The only difference between this comparative example and Example 1 is that steps (1) to (4) were not performed. Instead, the fiber dispersion obtained in step (5) was used directly as a composite slurry, and thermally conductive paper without boron nitride nanosheets was prepared through step (6).

[0116] Comparative Example 2

[0117] A method for preparing thermally conductive paper:

[0118] The only difference between this comparative example and Example 1 is that steps (1) to (4) were not performed. Instead, the fiber dispersion obtained in step (5) was used directly as the composite slurry, and 5 wt% (based on the total weight of the composite slurry being 100%) of boron nitride nanosheets were added to it. Then, through step (6), thermally conductive paper was prepared.

[0119] Comparative Example 3

[0120] A method for preparing thermally conductive paper:

[0121] The only difference between this comparative example and Example 1 is that steps (1) to (3) were not performed. Instead, 5g of PPTA aramid short-cut fibers, 5g of boron nitride nanosheet powder, and 1g of KH550 silane coupling agent were directly added to 100g of polyoxyethylene ether (PEO) aqueous solution with a mass concentration of 0.5%, and a homogeneous suspension was prepared by probe ultrasonic treatment (power 500W, pulse mode on / off = 3s / 1s, time 1h). This suspension was used as the third reaction liquid and prepared as thermal conductive paper through steps (5) to (6).

[0122] Comparative Example 4

[0123] A method for preparing thermally conductive paper:

[0124] The only difference between this comparative example and Example 1 is that, in step (4), an equal weight of deionized water is used instead of the polyoxyethylene ether (PEO) aqueous solution.

[0125] Comparative Example 5

[0126] A method for preparing thermally conductive paper:

[0127] The only difference between this comparative example and Example 1 is that, in steps (1-2), an equal weight of concentrated sulfuric acid (98% by mass) is used instead of the superacid solution formed by chlorosulfonic acid and trifluoromethanesulfonic acid.

[0128] Test methods

[0129] Density (ρ): Calculated using conventional methods.

[0130] Specific heat capacity (C) p ): Measured using the sapphire method with a Netzsch DSC3500.

[0131] Thermal conductivity (parallel to the paper plane): First, the thermal diffusivity α of each thermally conductive paper sample was measured using a flash thermal diffusivity meter (LFA-467). Then, the thermal diffusivity α was calculated using λ=α·ρ·C. p The corresponding planar thermal conductivity is calculated.

[0132] Tensile strength: Tested using a universal testing machine according to GB / T 528-2009.

[0133] Dielectric constant: The dielectric constant of 5 to 12 GHz was obtained by using an E4900A vector network analyzer according to GB / T 12636-2008.

[0134] The thermal conductive paper samples obtained from each embodiment and comparative example were subjected to the above tests, and the results are shown in Table 1.

[0135] Table 1

[0136]

[0137]

[0138] As can be seen from the above description, compared with the comparative examples, the embodiments of the present invention have achieved the preparation of composite thermally conductive paper with superior comprehensive performance. In the obtained composite thermally conductive paper, the boron nitride nanosheets have higher dispersibility and interfacial compatibility, and the bonding with the aramid fiber matrix is ​​also stronger. Therefore, it is possible to achieve a significant improvement in thermal conductivity and insulation performance while maintaining lightweight and flexibility and without excessively reducing mechanical strength.

[0139] In particular, Example 1 demonstrates significant performance advantages in its boron nitride nanosheet / aramid composite thermal conductive paper: planar thermal conductivity >3.5 W / (m·K), more than 10 times higher than that of traditional aramid paper (0.3 W / (m·K)), solving the heat dissipation bottleneck of high-power devices. Although its density increases slightly, its tensile strength only decreases by 12.5%, mainly due to the optimized interfacial bonding between boron nitride nanosheets and aramid fibers, achieving an efficient balance between lightweight and mechanical properties. Furthermore, the composite thermal conductive paper obtained in Example 1 has a dielectric constant of 2.8 at frequencies of 5–12 GHz, slightly higher than that of traditional aramid paper, but still within the low dielectric range (conventional polymer materials >3.0). Combined with the insulating properties of boron nitride (breakdown voltage ≥35 kV / mm), it can well meet the requirements of low dielectric loss and high heat dissipation for 5G high-frequency circuits, making it suitable for chip packaging, power battery separators, and aerospace heat dissipation components, achieving a breakthrough synergy in thermal conductivity, insulation, and high-frequency adaptability.

[0140] More specifically, in the various embodiments:

[0141] Comparing Examples 2 and 3 with Example 1, it can be seen that in step S1, the preferred volume ratio of chlorosulfonic acid to trifluoromethanesulfonic acid can promote the formation of a stronger bonding force between aramid fibers and boron nitride nanosheets, thereby improving the dispersibility of boron nitride as a thermally conductive filler in the final composite thermally conductive paper, and thus significantly enhancing the planar thermal conductivity of the composite thermally conductive paper.

[0142] Comparing Examples 4 and 5 with Example 1, it can be seen that in step S1, the preferred solid content of aramid fiber in the acid solution can promote better contact between aramid fiber and acid solution, thereby more effectively balancing fiber dissociation efficiency and dispersion stability, and finally preparing a composite thermally conductive paper with balanced thermal conductivity and mechanical strength.

[0143] Comparing Examples 6 and 7 with Example 1, it can be seen that in step S2, the preferred weight ratio of boron nitride nanosheets to aramid fibers in the second reaction solution can better balance the dispersion uniformity of the boron nitride nanosheets as a thermally conductive filler and the structural integrity of the aramid fiber matrix network, thereby comprehensively improving the mechanical properties and thermal insulation of the final composite thermally conductive paper.

[0144] Comparing Examples 8 and 9 with Example 1, it can be seen that in step S3, the preferred weight ratio of silane coupling agent to the first composite product can enable the silane coupling agent, a modifier molecule, to more fully cover the surface of the boron nitride nanosheets, thereby more effectively introducing functional groups (such as amino groups) that form covalent bonds with aramid fibers, and thus more effectively improving the various properties of the obtained composite thermal conductive paper.

[0145] Comparing Examples 10 and 11 with Example 1, it can be seen that in step S4, the preferred mass concentration of the PEO aqueous solution and the solid content of the second composite product in the third reaction solution can improve the dispersibility of the second composite product in the solution, further reduce agglomeration, thereby improving the uniformity of the composite slurry in the subsequent wet papermaking process, and obtaining a more dense, structurally stable, and mechanically stronger composite thermal conductive paper.

[0146] Comparing Examples 12 and 13 with Example 1, it can be seen that in step S5, the preferred mass concentration of the deionized aqueous solution of sodium polyacrylate and the preferred volume ratio of the fiber dispersion to the third reaction liquid can better balance the tensile strength, durability, and planar thermal conductivity of the final composite thermal conductive paper, and more significantly achieve a comprehensive improvement in the insulation and thermal conductivity, as well as the high strength and high toughness of the composite thermal conductive paper.

[0147] Comparing Example 14 with Example 1, it can be seen that in step S6, the dehydration process is preferably two-stage compared to one-stage dehydration, which can reduce fiber structure damage and thus more effectively preserve the integrity of aramid fibers and the good dispersion state of boron nitride nanosheets as thermally conductive fillers. Ultimately, this is beneficial to further improve the mechanical properties and thermal conductivity of the composite thermally conductive paper.

[0148] Comparing Examples 15 and 16 with Example 1, it can be seen that in step S6, the drying process is preferably divided into three stages, which can more effectively achieve a balanced improvement in thermal conductivity, structural stability and insulation.

[0149] Comparing Examples 17 and 18 with Example 1, it can be seen that in step S6, the preferred hot-pressing conditions can more significantly densify the fiber network, improve the contact tightness between boron nitride nanosheets and aramid fibers, and thus further optimize the thermal conductivity of the resulting composite thermally conductive paper.

[0150] In the above embodiments of this application, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0151] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for preparing a composite thermally conductive paper, characterized in that, include: Step S1: The first aramid fiber is first dispersed with acid solution and then subjected to a first reaction to obtain a first reaction solution; the acid solution includes chlorosulfonic acid and trifluoromethanesulfonic acid. Step S2: The boron nitride nanosheets are dispersed in the first reaction solution to obtain a second reaction solution; the pH adjuster is mixed with the second reaction solution to obtain the first composite product. Step S3: The first composite product is modified with a silane coupling agent to obtain the second composite product; Step S4: The second composite product is dispersed with polyoxyethylene ether in a third dispersion to obtain a third reaction solution; Step S5: The second aramid fiber, the precipitated fiber and sodium polyacrylate are prepared into a fiber dispersion. The fiber dispersion is mixed with the third reaction liquid to obtain a composite slurry. Step S6: Prepare the composite thermally conductive paper from the composite slurry.

2. The method for preparing the composite thermally conductive paper according to claim 1, characterized in that, In step S1 The volume ratio of chlorosulfonic acid to trifluoromethanesulfonic acid in the acid solution is (1-10):(10-1); and / or, The first aramid fiber has a solid content of 0.01 g / mL to 0.2 g / mL in the acid solution; and / or, The first dispersion is carried out by stirring, and the stirring is carried out at -5°C to 0°C; and / or, The reaction temperature of the first reaction is 25±2℃, and the heating rate to reach the reaction temperature is 2±0.02℃ / min.

3. The method for preparing the composite thermally conductive paper according to claim 1, characterized in that, In step S2 In the second reaction solution, the weight ratio of the boron nitride nanosheets to the first aramid fiber is (1-5):(5-1); and / or, Step S2 further includes: adding the pH adjuster to the second reaction solution at -5℃ to 0℃ until the pH value of the second reaction solution is 7±0.2, and obtaining the first composite product through solid-liquid separation.

4. The method for preparing composite thermally conductive paper according to any one of claims 1 to 3, characterized in that, Step S3 further includes: preparing a modified solution by mixing the silane coupling agent with ethanol, adding the first composite product to the modified solution, and stirring at 60±5℃ to obtain the second composite product.

5. The method for preparing composite thermally conductive paper according to any one of claims 1 to 3, characterized in that, In step S4 The polyoxyethylene ether is added in the form of a polyoxyethylene ether solution, and the mass concentration of the polyoxyethylene ether in the polyoxyethylene ether solution is 0.5 ± 0.01%; and / or, In the third reaction solution, the solid content of the second composite product is 0.1% to 20%; Preferably, the polyoxyethylene ether solution is selected from one or more of the following: an aqueous solution of polyoxyethylene ether, an isopropanol solution of polyoxyethylene ether, a toluene solution of polyoxyethylene ether, a xylene solution of polyoxyethylene ether, and an ethanol solution of polyoxyethylene ether.

6. The method for preparing composite thermally conductive paper according to any one of claims 1 to 3, characterized in that, In step S5 The weight ratio of the second aramid fiber to the precipitated fiber is (1-5):1; and / or, In the fiber dispersion, the mass concentration of sodium polyacrylate is 0.8 ± 0.1%; and / or, The volume ratio of the fiber dispersion to the third reaction solution is 1:(1-10); and / or, The pH value of the composite slurry is 9.0 to 9.

5.

7. The method for preparing composite thermally conductive paper according to any one of claims 1 to 3, characterized in that, Step S6 includes: Step S6-1: The composite pulp is prepared into fiber paper using a wet papermaking process; the wet papermaking process includes: forming a wet fiber paper on a polyester wire mesh, and the wet fiber paper is subjected to a first dewatering treatment and a second dewatering treatment in sequence to obtain the fiber paper; In step S6-2, the fiber paper is successively subjected to drying and hot pressing treatments to obtain the composite thermally conductive paper.

8. The method for preparing the composite thermally conductive paper according to claim 7, characterized in that, In step S6-2, The drying process includes a first drying, a second drying, and a third drying performed sequentially; and / or, The hot pressing treatment is performed at a temperature of 150℃ to 300℃, a pressure of 1MPa to 20MPa, and a time of 1min to 30min.

9. A composite thermally conductive paper, characterized in that, The composite thermal conductive paper is prepared by the method of any one of claims 1 to 8; the composite thermal conductive paper includes boron nitride nanosheets, and the content of boron nitride nanosheets is 1 wt% to 50 wt% based on the total weight of the composite thermal conductive paper as 100%.

10. The application of the composite thermally conductive paper according to claim 9 as an insulating and heat-insulating material in the fields of industrial equipment, aerospace, electronic devices and new energy.

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