High-thermal-conductivity aramid insulation paper based on surface coating technology and preparation method thereof

Abstract

The application discloses high-thermal-conductivity aramid insulation paper based on a surface coating technology and a preparation method thereof, and belongs to the field of aramid insulation paper-based functional materials. The method is characterized in that: amino-modified BN-NH2 is prepared by one-step covalent grafting, modified aramid nanofiber ANF is prepared by ultraviolet ozone radiation, an amino-epoxy group, a hydroxyl-epoxy group and an amino-hydroxyl triple chemical bond synergistic ternary anchoring interface structure is constructed by compounding epoxy resin, and the composite coating is coated on the surface of aramid base paper and hot-pressed into shape. The application solves the problems of poor dispersion of boron nitride, weak interface combination and discontinuous thermal conduction path, realizes a substantial improvement in thermal conductivity while retaining excellent insulation and mechanical properties of aramid paper, is controllable and easy to mass-produce in process, and is suitable for high-end equipment insulation and thermal management scenes.

Description

Technical Field

[0001] This invention belongs to the technical field of aramid insulating paper-based functional materials, specifically relating to a high thermal conductivity aramid insulating paper based on surface coating technology and its preparation method. Background Technology

[0002] With the rapid iteration of high-end fields such as 5G / 6G communications, national defense and military industry, aerospace, rail transportation, and new energy equipment, electronic and electrical systems are developing towards high integration, high power, lightweight, high temperature resistance, and long lifespan. The heat flux density of core components under high frequency, high load, and closed operating conditions is rising sharply, and thermal management failure has become a core bottleneck restricting the reliability, stability, and service life of equipment. As a key support and protection component of electrical systems, insulating materials not only need to possess excellent electrical insulation, mechanical strength, and thermal stability, but also must achieve efficient heat conduction to quickly dissipate the working heat of the devices, avoiding performance degradation, insulation breakdown, structural failure, and even system paralysis caused by local overheating. This places stringent requirements on insulating materials, including high thermal conductivity, high insulation, high mechanical strength, temperature and weather resistance, and lightweight flexibility.

[0003] Aramid paper-based materials, made from chopped aramid fibers and precipitated aramid fibers through wet papermaking and hot pressing, have become core insulation and structural materials for dry-type transformers, traction motors, radar modules, aerospace power supplies, and special protective equipment due to their comprehensive advantages such as low density, ultra-high specific strength, and excellent dielectric properties. They are irreplaceable in high-end equipment insulation, honeycomb structure support, and integrated electromagnetic wave transmission. However, traditional aramid paper, limited by its intrinsic molecular structure, has extremely low thermal conductivity, making it difficult for heat to transfer and diffuse quickly, easily leading to localized heat accumulation. Furthermore, its high surface chemical inertness, weak interfacial bonding, limited functionality, and insufficient resistance to corona discharge and damp heat make it unsuitable for extreme operating conditions, failing to meet the thermal management and insulation protection requirements of next-generation high-power, high-density electronic equipment.

[0004] To overcome the thermal conductivity bottleneck of aramid paper, the industry generally adopts inorganic thermally conductive filler composite modification technology. Among them, hexagonal boron nitride has become the preferred filler for thermal conductivity modification of aramid paper due to its high thermal conductivity, high insulation, low density, and chemical stability. However, existing technologies have many insurmountable drawbacks: First, boron nitride has a smooth surface and strong chemical inertness, resulting in poor dispersibility and easy agglomeration in water-based papermaking systems. High filler content can easily lead to defects, resulting in a significant decrease in insulation performance and mechanical strength. Second, unmodified boron nitride has weak interfacial bonding and high interfacial thermal resistance with the aramid fiber matrix, making it difficult to construct a continuous and efficient thermal conductivity pathway, thus limiting the thermal conductivity improvement effect. Third, conventional filler blending modification easily damages the original paper structure, making it difficult to synergistically improve mechanical properties, insulation properties, and thermal conductivity properties, and even causing problems such as dielectric constant mismatch and electric field distortion. Fourth, existing modification processes often involve strong acid and alkali pretreatment, which can easily damage the crystal structure and aramid fiber properties. The processes are complex, have poor controllability, and are costly, making them difficult to adapt to industrial mass production.

[0005] Therefore, there is an urgent need to develop a new modification technology that can significantly improve thermal conductivity, achieve strong interfacial bonding, and make the process green and controllable while maintaining the excellent intrinsic properties of aramid paper, so as to meet the urgent needs of high-end equipment for multifunctional synergy of insulating materials. Summary of the Invention

[0006] The purpose of this invention is to overcome the technical defects of existing technologies, such as poor dispersion of hexagonal boron nitride, weak interfacial bonding, discontinuous thermal conductivity pathways, and complex and uncontrollable modification processes. This invention provides a high thermal conductivity aramid insulating paper based on surface coating technology and its preparation method. This method involves a one-step direct covalent grafting of hexagonal boron nitride for amylation modification, combined with ultraviolet ozone radiation to activate aramid nanofibers through hydroxylation, and the construction of a triple chemical bond synergistically enhancing the interfacial structure using epoxy resin adhesive. Utilizing the covalent and hydrogen bonding between amino and hydroxyl groups and epoxy groups, the modified thermally conductive filler and reinforcing fibers are composited and loaded onto the surface of the aramid base paper via surface coating. During hot pressing, a dense and continuous thermally conductive network is formed, achieving a synergistic improvement in the thermal conductivity, mechanical properties, and insulation properties of the aramid insulating paper.

[0007] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: A method for preparing high thermal conductivity aramid insulating paper based on surface coating technology includes the following steps: (1) Mix aramid short-cut fibers, aramid precipitated fibers and water, transfer to a fiber dissociator for dissolution, and obtain a mixed slurry after thorough and uniform mixing. (2) The mixed pulp is placed in a rapid paper forming machine and wet paper forming technology is used to obtain aramid wet paper web. After drying, aramid base paper is obtained. (3) Amination modification of hexagonal boron nitride h-BN was carried out by a one-step direct covalent grafting method, and amino groups were introduced on its surface to obtain modified hexagonal boron nitride BN-NH2. (4) The surface of aramid nanofibers was irradiated with ultraviolet light to introduce a large number of oxygen-containing functional groups, thereby obtaining modified aramid nanofibers ANF. (5) The obtained BN-NH2 and modified aramid nanofibers ANF are mixed with water, and an adhesive is added and mixed evenly to obtain a composite coating. (6) The composite coating is applied to the surface of the aramid base paper, and after drying, it is hot-pressed using a high-temperature roller hot press to obtain high thermal conductivity aramid insulating paper.

[0008] Key invention points: Step (3) achieves surface amination of h-BN through one-step direct covalent grafting; Step (4) achieves surface hydroxylation of aramid nanofibers through ultraviolet radiation; and the epoxy resin adhesive is used to construct a triple chemical bond to synergistically enhance the interface structure. First bonding: The amino groups introduced on the surface of h-BN undergo a ring-opening reaction with the epoxy groups in the epoxy resin adhesive to form stable covalent bonds; The second bonding: The hydroxyl groups introduced on the surface of aramid nanofibers undergo a ring-opening reaction with the epoxy groups in the epoxy resin adhesive to form stable covalent bonds; The third bonding: The amino groups on the surface of h-BN interact with the hydroxyl groups on the surface of aramid nanofibers under hot-pressing conditions, and can further dehydrate and condense to form covalent bonds.

[0009] Through the synergistic construction of the aforementioned triple chemical bonds, a stable fully covalent cross-linked network was established among aramid nanofibers, boron nitride, and the adhesive, realizing a ternary anchored interface structure of filler-fiber-matrix. This design not only significantly enhances the interfacial bonding force and overall structural stability of the composite system, but also simultaneously improves thermal conductivity and mechanical properties, producing a synergistic enhancement effect of "1+1+1>3".

[0010] Preferably, based on oven-dry weight, the mass ratio of aramid chopped fibers to aramid precipitated fibers in step (1) is (50-80):(20-50).

[0011] Preferably, the total mass concentration of fibers in the mixed slurry in step (1) is 0.02-0.5%.

[0012] The preferred one-step direct covalent grafting method is as follows: (1) Preparation of diazonium salt solution: under ice bath conditions, aromatic amine compounds are dissolved in hydrochloric acid aqueous solution, and sodium nitrite is added to carry out diazotization reaction to obtain diazonium salt solution; (2) Grafting reaction: Hexagonal boron nitride h-BN is dispersed in hydrochloric acid aqueous solution and mixed with the diazonium salt solution prepared in step (1). The reaction is carried out under an inert atmosphere and heated. After the reaction is completed, the solid product is separated, washed with organic solvent and deionized water in sequence, and dried to obtain BN-NH2.

[0013] More preferably, the aromatic amine compound in step (1) is at least one of p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, p-aminophenol, and 2-methyl-4-aminophenol; the concentration of the hydrochloric acid aqueous solution is 1.0-2.0 mol / L; the molar ratio of the aromatic amine compound to sodium nitrite is 1:1; the temperature of the diazotization reaction is 0-5℃, and the reaction time is 1-2 hours.

[0014] More preferably, the average particle size of the hexagonal boron nitride in step (2) is 1-5 μm; the concentration of the hydrochloric acid aqueous solution is 1.0-2.0 mol / L; the reaction temperature is 50-70℃ and the reaction time is 2-6 hours; the reaction is carried out under an inert atmosphere; the organic solvent is selected from at least one of N,N-dimethylformamide, N-methylpyrrolidone, and anhydrous ethanol; the drying is vacuum drying at a temperature of 50-70℃ for 12-24 hours.

[0015] Preferably, the ultraviolet radiation treatment is carried out in an ozone (O3) atmosphere, with the aramid nanofibers placed in an ultraviolet ozone cleaner, under ultraviolet light at a wavelength of 254 nm and an ozone concentration of 50 g / m³. 3 Under these conditions, the modified aramid nanofibers (ANF) were obtained by treating them for 10-30 minutes.

[0016] Preferably, in step (5), the mass ratio of BN-NH2 to modified aramid nanofiber ANF is 5-9:1-5; the adhesive accounts for 5-25% of the solid dry mass in the composite coating; the total mass concentration of BN-NH2 and modified aramid nanofiber ANF in the composite coating is 0.5-3%; and the adhesive is epoxy resin.

[0017] Preferably, the coating is a double-sided coating, and the coating method is roller coating or spray coating, with a coating amount of 1-9 g / m² for the composite coating. 2 The hot pressing temperature is 200-280℃ and the pressure is 4-8MPa.

[0018] This invention also provides a high thermal conductivity aramid insulating paper, prepared using the above-described method. The resulting insulating paper is used in aerospace, special protective equipment, and rail transportation fields.

[0019] The beneficial effects of this invention are: (1) By adopting a one-step direct covalent grafting method to introduce amino groups on the surface of hexagonal boron nitride, there is no need for pre-hydroxylation treatment, which avoids the damage to the boron nitride crystal structure caused by strong acid and strong base pretreatment. The grafting process is mild and controllable. The modified boron nitride has significantly improved dispersion stability in aqueous systems, which solves the technical problem of easy agglomeration and difficult dispersion of unmodified boron nitride. (2) High-density oxygen-containing polar functional groups such as hydroxyl groups were introduced on the surface of aramid nanofibers by ultraviolet ozone synergistic treatment, which significantly enhanced the surface chemical activity of the fibers and effectively improved their interfacial bonding performance with the matrix material. (3) A triple chemical bond synergistic enhancement interface structure was constructed, namely, the amino group on the surface of hexagonal boron nitride forms a covalent bond with the epoxy group in the adhesive, the hydroxyl group on the surface of aramid nanofiber forms a covalent bond with the epoxy group in the adhesive, and the amino group on the surface of hexagonal boron nitride forms a hydrogen bond with the hydroxyl group on the surface of aramid nanofiber under hot pressing conditions and can be further dehydrated and condensed to form a covalent bond, thus realizing the ternary anchoring interface structure of filler-fiber-matrix and producing a synergistic enhancement effect of "1+1+1>3"; (4) In summary, this invention uses surface coating technology to load the modified functional coating onto the surface of aramid base paper, forming a dense and continuous thermally conductive network during hot pressing. This not only preserves the excellent mechanical and insulation properties of the aramid base paper but also significantly improves its thermal conductivity, avoiding the damage to the internal structure of the paper caused by traditional blending modification. The process is simple and controllable, and easy to industrialize. The high thermal conductivity aramid insulating paper prepared has high thermal conductivity, excellent electrical insulation, good mechanical strength, and temperature and weather resistance. It can be widely used in insulation and thermal management scenarios in high-end fields such as 5G / 6G communication equipment, aerospace power systems, rail transit traction motors, and new energy equipment, meeting the stringent requirements of high-power, high-density electronic equipment for the multi-functional synergy of insulating materials. Attached Figure Description

[0020] Figure 1 A scanning electron microscope (SEM) cross-sectional image of a high thermal conductivity aramid insulating paper based on surface coating technology prepared in Example 7 of the present invention; Figure 2 This is a scanning electron microscope (SEM) planar image of a high thermal conductivity aramid insulating paper based on surface coating technology prepared in Example 7 of the present invention. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to specific embodiments, but it is not limited thereto.

[0022] Example 1 A method for preparing high thermal conductivity aramid insulating paper based on surface coating technology includes the following steps: (1) Aramid short-cut fibers (3-5 mm in length and 10-30 μm in diameter) and aramid precipitated fibers (1-3 mm in length and 20-50 μm in diameter) are mixed with water, and the mass ratio of the aramid short-cut fibers to the aramid precipitated fibers is 60:40 based on oven-dry weight. The mixture is transferred to a fiber dissociator and decomposed for 5 min. After thorough mixing, a mixed slurry is obtained, wherein the total mass concentration of the fibers is 0.05%. (2) The mixed pulp obtained in step (1) is placed in a rapid paper forming machine and wet paper forming technology is used to obtain aramid wet paper web. After pressing at 0.5MPa and drying at 100℃, aramid base paper is obtained. (3) Under ice-water bath conditions, 2.16 g (20 mmol) of p-phenylenediamine was dissolved in 30 mL of 1.5 mol / L hydrochloric acid solution and magnetically stirred until completely dissolved. 1.38 g (20 mmol) of sodium nitrite was dissolved in 10 mL of deionized water and slowly added dropwise to the above p-phenylenediamine hydrochloric acid solution under vigorous stirring, controlling the dropping rate to maintain the reaction temperature at 0-5℃. After the addition was complete, the reaction was continued to be stirred in an ice bath for 1 hour to obtain a p-aminophenyl diazonium salt solution (prepared immediately before use).

[0023] Weigh 2.0 g of hexagonal boron nitride (h-BN, average particle size 3 μm) and disperse it in 50 mL of 1.5 mol / L hydrochloric acid solution. Sonicate the dispersion for 30 minutes. Slowly add the diazonium salt solution prepared in step (1) to the above BN dispersion. After mixing evenly, heat to 60 °C and stir magnetically for 4 hours under nitrogen protection.

[0024] After the reaction was complete, the mixture was allowed to cool naturally to room temperature and then centrifuged (8000 rpm, 10 minutes) to collect the solid product.

[0025] The product was washed three times each with N,N-dimethylformamide, anhydrous ethanol, and deionized water, and centrifuged after each wash. The washed product was placed in a vacuum drying oven and dried at 60°C for 24 hours to obtain modified boron nitride with surface-grafted aminophenyl groups, denoted as BN-NH2.

[0026] (4) Place the aramid nanofibers in an ultraviolet ozone cleaner and treat them for 30 minutes under ultraviolet light with a wavelength of 254nm and an ozone concentration of 50g / m³ to obtain modified aramid nanofibers ANF rich in various oxygen-containing groups.

[0027] (5) The BN-NH2 and modified aramid nanofiber ANF obtained in steps (3) and (4) are mixed with water at an oven-dry mass ratio of 8:2. Waterborne epoxy resin adhesive (the solid content of waterborne epoxy resin is 65%±2%) is added at 10% of the oven-dry mass of the coating solids and then mixed evenly to obtain a composite coating. The mass concentration of the coating is 1.5% (the total mass concentration of BN-NH2 and modified aramid nanofiber ANF in the composite coating). (6) Apply the composite coating obtained in step (5) to one side of the aramid base paper using a roller coating process, and dry for 5 minutes. Then repeat the above operation to apply the coating to the other side of the aramid base paper using a roller coating process, and dry for 5 minutes. The coating amount of the composite coating is 3 g / m². 2 The coating speed is 4m / min, and finally, the paper is hot-pressed at 240℃ and 6MPa using a roller hot press at a speed of 3m / min to obtain high thermal conductivity aramid insulating paper.

[0028] Example 2 A method for preparing high thermal conductivity aramid insulating paper based on surface coating technology includes the following steps: (1) Aramid short-cut fibers (3-5 mm in length and 10-30 μm in diameter) and aramid precipitated fibers (1-3 mm in length and 20-50 μm in diameter) are mixed with water, and the mass ratio of the aramid short-cut fibers to the aramid precipitated fibers is 50:20 based on oven-dry weight. The mixture is transferred to a fiber disintegrator and decomposed for 5 min. After thorough mixing, a mixed slurry is obtained, wherein the total mass concentration of the fibers is 0.02%. (2) The mixed pulp obtained in step (1) is placed in a rapid paper forming machine and wet paper forming technology is used to obtain aramid wet paper web. After pressing at 0.5MPa and drying at 100℃, aramid base paper is obtained. (3) Under ice-water bath conditions, 2.16 g (20 mmol) of p-phenylenediamine was dissolved in 30 mL of 1.5 mol / L hydrochloric acid solution and magnetically stirred until completely dissolved. 1.38 g (20 mmol) of sodium nitrite was dissolved in 10 mL of deionized water and slowly added dropwise to the above p-phenylenediamine hydrochloric acid solution under vigorous stirring, controlling the dropping rate to maintain the reaction temperature at 0-5℃. After the addition was complete, the reaction was continued to be stirred in an ice bath for 1 hour to obtain a p-aminophenyl diazonium salt solution (prepared immediately before use).

[0029] Weigh 2.0 g of hexagonal boron nitride (h-BN, average particle size 1 μm) and disperse it in 50 mL of 1.0 mol / L hydrochloric acid solution, and sonicate for 30 minutes. Slowly add the diazonium salt solution prepared in step (1) to the above BN dispersion, mix well, and then heat to 50 °C. Stir magnetically for 6 hours under nitrogen protection.

[0030] After the reaction was complete, the mixture was allowed to cool naturally to room temperature and then centrifuged (8000 rpm, 10 minutes) to collect the solid product.

[0031] The product was washed three times each with N,N-dimethylformamide and deionized water, and centrifuged after each wash. The washed product was placed in a vacuum drying oven and dried at 50°C for 24 hours to obtain modified boron nitride with surface grafted aminophenyl, denoted as BN-NH2.

[0032] (4) Place the aramid nanofibers in an ultraviolet ozone cleaner and treat them for 30 minutes under ultraviolet light with a wavelength of 254nm and an ozone concentration of 50g / m³ to obtain modified aramid nanofibers ANF rich in various oxygen-containing groups.

[0033] (5) The BN-NH2 and modified aramid nanofiber ANF obtained in steps (3) and (4) are mixed with water at an oven-dry mass ratio of 5:1. Waterborne epoxy resin adhesive (the solid content of waterborne epoxy resin is 65%±2%) is added at 5% of the oven-dry mass of the coating solids and then mixed evenly to obtain a composite coating. The mass concentration of the coating is 0.5% (the total mass concentration of BN-NH2 and modified aramid nanofiber ANF in the composite coating). (6) Apply the composite coating obtained in step (5) to one side of the aramid base paper using a roller coating process, and dry for 5 minutes. Then repeat the above operation to apply the coating to the other side of the aramid base paper using a roller coating process, and dry for 5 minutes. The coating amount of the composite coating is 1 g / m². 2 The roller coating speed is 4m / min, and finally, the paper is hot-pressed at 200℃ and 8MPa using a roller hot press at a roller speed of 3m / min to obtain high thermal conductivity aramid insulating paper.

[0034] Example 3 A method for preparing high thermal conductivity aramid insulating paper based on surface coating technology includes the following steps: (1) Aramid short-cut fibers (3-5 mm in length and 10-30 μm in diameter) and aramid precipitated fibers (1-3 mm in length and 20-50 μm in diameter) are mixed with water, and the mass ratio of the aramid short-cut fibers to the aramid precipitated fibers is 80:50 based on oven-dry weight. The mixture is transferred to a fiber dissociator and decomposed for 5 min. After thorough mixing, a mixed slurry is obtained, wherein the total mass concentration of fibers is 0.5%. (2) The mixed pulp obtained in step (1) is placed in a rapid paper forming machine and wet paper forming technology is used to obtain aramid wet paper web. After pressing at 0.5MPa and drying at 100℃, aramid base paper is obtained. (3) Under ice-water bath conditions, 2.16 g (20 mmol) of p-phenylenediamine was dissolved in 30 mL of 1.5 mol / L hydrochloric acid solution and magnetically stirred until completely dissolved. 1.38 g (20 mmol) of sodium nitrite was dissolved in 10 mL of deionized water and slowly added dropwise to the above p-phenylenediamine hydrochloric acid solution under vigorous stirring, controlling the dropping rate to maintain the reaction temperature at 0-5℃. After the addition was complete, the reaction was continued to be stirred in an ice bath for 1 hour to obtain a p-aminophenyl diazonium salt solution (prepared immediately before use).

[0035] Weigh 2.0 g of hexagonal boron nitride (h-BN, average particle size 5 μm) and disperse it in 50 mL of 2.0 mol / L hydrochloric acid solution. Sonicate the dispersion for 30 minutes. Slowly add the diazonium salt solution prepared in step (1) to the above BN dispersion. After mixing evenly, heat to 70 °C and stir magnetically for 2 hours under nitrogen protection.

[0036] After the reaction was complete, the mixture was allowed to cool naturally to room temperature and then centrifuged (8000 rpm, 10 minutes) to collect the solid product.

[0037] The product was washed three times each with anhydrous ethanol and deionized water, and centrifuged after each wash. The washed product was placed in a vacuum drying oven and dried at 70°C for 12 hours to obtain modified boron nitride with surface-grafted aminophenyl, denoted as BN-NH2.

[0038] (4) Place the aramid nanofibers in an ultraviolet ozone cleaner and treat them for 30 minutes under ultraviolet light with a wavelength of 254nm and an ozone concentration of 50g / m³ to obtain modified aramid nanofibers ANF rich in various oxygen-containing groups.

[0039] (5) The BN-NH2 and modified aramid nanofiber ANF obtained in steps (3) and (4) are mixed with water at an oven-dry mass ratio of 9:5. Waterborne epoxy resin adhesive (the solid content of waterborne epoxy resin is 65%±2%) is added at 25% of the oven-dry mass of the coating solids and then mixed evenly to obtain a composite coating. The mass concentration of the coating is 3% (the total mass concentration of BN-NH2 and modified aramid nanofiber ANF in the composite coating). (6) Apply the composite coating obtained in step (5) to one side of the aramid base paper using a roller coating process, and dry for 5 minutes. Then repeat the above operation to apply the coating to the other side of the aramid base paper using a roller coating process, and dry for 5 minutes. The coating amount of the composite coating is 9 g / m². 2 The coating speed is 4 m / min, and finally, the paper is hot-pressed at 280℃ and 4 MPa using a roller hot press at a speed of 3 m / min to obtain high thermal conductivity aramid insulating paper.

[0040] Example 4 In step (5) of Example 1, BN-NH2 and modified aramid nanofiber ANF were replaced with an oven-dry mass ratio of 7:3, and all other parameters were the same as in Example 1.

[0041] Example 5 In step (5) of Example 1, BN-NH2 and modified aramid nanofiber ANF were replaced with an oven-dry mass ratio of 9:1, and all other parameters were the same as in Example 1.

[0042] Example 6 The coating amount in step (6) of Example 1 was changed to 6 g / m 2 All other parameters are the same as in Example 1.

[0043] Example 7 The coating amount in step (6) of Example 1 was changed to 9 g / m 2 All other parameters are the same as in Example 1.

[0044] Comparative Example 1 (1) Aramid short-cut fibers (3-5 mm in length and 10-30 μm in diameter) and aramid precipitated fibers (1-3 mm in length and 20-50 μm in diameter) are mixed with water, and the mass ratio of the aramid short-cut fibers to the aramid precipitated fibers is 60:40 based on oven-dry weight. The mixture is transferred to a fiber dissociator and decomposed for 5 min. After thorough mixing, a mixed slurry is obtained, wherein the total mass concentration of the fibers is 0.05%. (2) The mixed pulp obtained in step (1) is placed in a rapid paper forming machine and wet paper forming technology is used to obtain aramid wet paper web. After pressing at 0.5MPa and drying at 100℃, thermally conductive aramid base paper is obtained. (3) The aramid base paper obtained in step (2) is hot-pressed at 240℃ and 6MPa using a roller hot press with a roller speed of 3m / min to obtain aramid insulating paper.

[0045] This comparative example was prepared without BN-NH2, without modified aramid nanofibers (ANF), without composite coating or epoxy resin addition; it was simply hot-pressed from pure aramid base paper without any thermal conductivity modification treatment.

[0046] Comparative Example 2 In this comparative example, compared with Example 1, the steps are completely the same except that the preparation and addition of modified aramid nanofibers (ANF) are not carried out. That is, only BN-NH2 is introduced as a single thermally conductive filler and epoxy resin is used as an adhesive (the modified aramid nanofibers (ANF) are missing, only BN-NH2 + epoxy resin is used).

[0047] A method for preparing aramid insulating paper includes the following steps: (1) Aramid short-cut fibers (3-5 mm in length and 10-30 μm in diameter) and aramid precipitated fibers (1-3 mm in length and 20-50 μm in diameter) are mixed with water. The mass ratio of the aramid short-cut fibers to the aramid precipitated fibers is 60:40 based on the oven-dry weight. The mixture is transferred to a fiber disintegrator and decomposed for 5 min. After thorough mixing, a mixed slurry is obtained, wherein the total mass concentration of the fibers is 0.05%. (2) The mixed pulp obtained in step (1) is placed in a rapid paper forming machine and wet paper forming technology is used to obtain aramid wet paper web. After pressing at 0.5MPa and drying at 100℃, aramid base paper is obtained. (3) Under ice-water bath conditions, 2.16 g (20 mmol) of p-phenylenediamine was dissolved in 30 mL of 1.5 mol / L hydrochloric acid solution and magnetically stirred until completely dissolved. 1.38 g (20 mmol) of sodium nitrite was dissolved in 10 mL of deionized water and slowly added dropwise to the above p-phenylenediamine hydrochloric acid solution under vigorous stirring, controlling the dropping rate to maintain the reaction temperature at 0-5℃. After the addition was complete, the reaction was stirred in an ice bath for 1 hour to obtain a p-aminophenyl diazonium salt solution (prepared immediately before use); 2.0 g of hexagonal boron nitride (h-BN, average particle size 3 μm) was weighed and dispersed in 50 mL of 1.5 mol / L hydrochloric acid solution and ultrasonically dispersed for 30 minutes. The prepared diazonium salt solution was slowly added to the BN dispersion. After mixing thoroughly, the mixture was heated to 60°C and magnetically stirred for 4 hours under nitrogen protection. After the reaction, the mixture was allowed to cool naturally to room temperature and centrifuged (8000 rpm, 10 minutes) to collect the solid product. The product was washed three times each with N,N-dimethylformamide, anhydrous ethanol, and deionized water, centrifuged after each wash. The washed product was placed in a vacuum drying oven and dried under vacuum at 60°C for 24 hours to obtain modified boron nitride with surface grafted aminophenyl, denoted as BN-NH2. (4) Mix the BN-NH2 obtained in step (3) with water, add 10% of the dry weight of the coating solids of waterborne epoxy resin adhesive (the solid content of waterborne epoxy resin is 65%±2%) and mix evenly to obtain a composite coating. The mass concentration of the coating is 1.5% (the mass concentration of BN-NH2 in the composite coating). (5) Apply the composite coating obtained in step (4) to one side of the aramid base paper using a roller coating process, and dry for 5 minutes. Then repeat the above operation to apply the coating to the other side of the aramid base paper using a roller coating process, and dry for 5 minutes. The coating amount of the composite coating is 3 g / m². 2 The coating speed is 4m / min, and finally, the paper is hot-pressed at 240℃ and 6MPa using a roller hot press at a speed of 3m / min to obtain aramid insulating paper.

[0048] Key differences: The aramid nanofiber modification step is eliminated, and no modified aramid nanofiber ANF is added. The composite coating is prepared and applied using only BN-NH2 and epoxy resin.

[0049] Comparative Example 3 Compared with Example 1, this comparative example is completely identical except that the preparation and addition of BN-NH2 aramid nanofibers are not carried out. That is, only the modified aramid nanofibers ANF are introduced and epoxy resin is used as an adhesive (BN-NH2 is missing, only the modified aramid nanofibers ANF + epoxy resin are used).

[0050] A method for preparing aramid insulating paper includes the following steps: (1) Aramid short-cut fibers (3-5 mm in length and 10-30 μm in diameter) and aramid precipitated fibers (1-3 mm in length and 20-50 μm in diameter) are mixed with water, and the mass ratio of the aramid short-cut fibers to the aramid precipitated fibers is 60:40 based on oven-dry weight. The mixture is transferred to a fiber dissociator and decomposed for 5 min. After thorough mixing, a mixed slurry is obtained, wherein the total mass concentration of the fibers is 0.05%. (2) The mixed pulp obtained in step (1) is placed in a rapid paper forming machine and wet paper forming technology is used to obtain aramid wet paper web. After pressing at 0.5MPa and drying at 100℃, aramid base paper is obtained. (3) Place the aramid nanofibers in an ultraviolet ozone cleaner, and expose them to ultraviolet light at a wavelength of 254nm and an ozone concentration of 50g / m². 3 Under the conditions of 30 min, modified aramid nanofibers ANF rich in various oxygen-containing groups were obtained; (4) The modified aramid nanofibers ANF obtained in step (3) are mixed with water, and 10% of the dry weight of the coating solids of waterborne epoxy resin adhesive (the solid content of waterborne epoxy resin is 65%±2%) is added and mixed evenly to obtain a composite coating. The mass concentration of the coating is 1.5% (mass concentration of modified aramid nanofibers ANF in the composite coating). (5) Apply the composite coating obtained in step (4) to one side of the aramid base paper using a roller coating process, and dry for 5 minutes. Then repeat the above operation to apply the coating to the other side of the aramid base paper using a roller coating process, and dry for 5 minutes. The coating amount of the composite coating is 3 g / m². 2 The coating speed is 4m / min, and finally, the paper is hot-pressed at 240℃ and 6MPa using a roller hot press at a speed of 3m / min to obtain aramid insulating paper.

[0051] Key differences: The hexagonal boron nitride amination modification step is eliminated, and no BN-NH2 is added. The composite coating is prepared solely using modified aramid nanofibers (ANF) and epoxy resin.

[0052] Comparative Example 4 Compared with Example 1, this comparative example only replaces epoxy resin with PVA; all other steps and processes are the same as in Example 1. A method for preparing aramid insulating paper includes the following steps: (1) Aramid short-cut fibers (3-5 mm in length and 10-30 μm in diameter) and aramid precipitated fibers (1-3 mm in length and 20-50 μm in diameter) are mixed with water, and the mass ratio of the aramid short-cut fibers to the aramid precipitated fibers is 60:40 based on oven-dry weight. The mixture is transferred to a fiber disintegrator and decomposed for 5 min. After thorough mixing, a mixed slurry is obtained, wherein the total mass concentration of the fibers is 0.05%. (2) The mixed pulp obtained in step (1) is placed in a rapid paper forming machine and wet paper forming technology is used to obtain aramid wet paper web. After pressing at 0.5MPa and drying at 100℃, aramid base paper is obtained. (3) Under ice-water bath conditions, 2.16 g (20 mmol) of p-phenylenediamine was dissolved in 30 mL of 1.5 mol / L hydrochloric acid solution and magnetically stirred until completely dissolved. 1.38 g (20 mmol) of sodium nitrite was dissolved in 10 mL of deionized water and slowly added dropwise to the above p-phenylenediamine hydrochloric acid solution under vigorous stirring, controlling the dropping rate to maintain the reaction temperature at 0-5℃. After the addition was complete, the reaction was stirred in an ice bath for 1 hour to obtain a p-aminophenyl diazonium salt solution (prepared immediately before use); 2.0 g of hexagonal boron nitride (h-BN, average particle size 3 μm) was weighed and dispersed in 50 mL of 1.5 mol / L hydrochloric acid solution and ultrasonically dispersed for 30 minutes. The prepared diazonium salt solution was slowly added to the BN dispersion. After mixing thoroughly, the mixture was heated to 60°C and magnetically stirred for 4 hours under nitrogen protection. After the reaction, the mixture was allowed to cool naturally to room temperature and centrifuged (8000 rpm, 10 minutes) to collect the solid product. The product was washed three times each with N,N-dimethylformamide, anhydrous ethanol, and deionized water, centrifuged after each wash. The washed product was placed in a vacuum drying oven and dried under vacuum at 60°C for 24 hours to obtain modified boron nitride with surface-grafted aminophenyl groups, denoted as BN-NH2. (4) Place the aramid nanofibers in an ultraviolet ozone cleaner, and apply ultraviolet light at a wavelength of 254 nm and an ozone concentration of 50 g / m². 3 Under the conditions of 30 min, modified aramid nanofibers ANF rich in various epoxy groups were obtained; (5) The BN-NH2 and modified aramid nanofiber ANF obtained in steps (3) and (4) are mixed with water at an oven-dry mass ratio of 8:2. After adding 10% of the oven-dry mass of PVA adhesive, the mixture is mixed evenly to obtain a composite coating. The mass concentration of the coating is 1.5% (the total mass concentration of BN-NH2 and modified aramid nanofiber ANF in the composite coating). (6) The composite coating obtained in step (5) is applied to one side of the aramid base paper by roller coating and dried for 5 minutes. Then the above operation is repeated to apply the coating to the other side of the aramid base paper by roller coating and dried for 5 minutes. The coating amount of the composite coating is 3 g / m² and the roller coating speed is 4 m / min. Finally, the paper is hot-pressed at 240℃ and 6 MPa using a roller hot press with a roller speed of 3 m / min to obtain aramid insulating paper.

[0053] Key differences: The preparation and formulation of BN-NH2 and modified aramid nanofibers (ANF) are retained, but the adhesive is replaced with conventional water-based PVA adhesive instead of epoxy resin, with no epoxy groups involved in interfacial bonding.

[0054] Comparative Example 5 In this comparative example, compared to Example 1, except that unmodified hexagonal boron nitride (i.e., raw h-BN without diazonium salt grafting) was used instead of BN-NH2, and the UV ozone treatment of modified aramid nanofibers (ANF) was not performed, all other steps and parameters were completely consistent with Example 1, namely: A method for preparing aramid insulating paper includes the following steps: (1) Aramid short-cut fibers (3-5 mm in length and 10-30 μm in diameter) and aramid precipitated fibers (1-3 mm in length and 20-50 μm in diameter) are mixed with water, and the mass ratio of the aramid short-cut fibers to the aramid precipitated fibers is 60:40 based on oven-dry weight. The mixture is transferred to a fiber disintegrator and decomposed for 5 min. After thorough mixing, a mixed slurry is obtained, wherein the total mass concentration of the fibers is 0.05%. (2) The mixed pulp obtained in step (1) is placed in a rapid paper forming machine and wet paper forming technology is used to obtain aramid wet paper web. After pressing at 0.5MPa and drying at 100℃, aramid base paper is obtained. (3) Weigh 2.0 g of unmodified hexagonal boron nitride (h-BN, average particle size 3 μm) and set aside for use; (4) Weigh out the unmodified aramid nanofibers and set aside for use; (5) Mix unmodified h-BN and unmodified ANF with water at an oven-dry mass ratio of 8:2, add 10% of the oven-dry mass of the coating solids of waterborne epoxy resin adhesive (the solid content of waterborne epoxy resin is 65%±2%), and mix evenly to obtain a composite coating. The mass concentration of the coating is 1.5% (the total mass concentration of h-BN and ANF in the composite coating). (6) The composite coating obtained in step (4) is applied to one side of the aramid base paper by roller coating and dried for 5 minutes. Then the above operation is repeated to apply the coating to the other side of the aramid base paper by roller coating and dried for 5 minutes. The coating amount of the composite coating is 3 g / m² and the roller coating speed is 4 m / min. Finally, the paper is hot-pressed at 240℃ and 6 MPa using a roller hot press with a roller speed of 3 m / min to obtain aramid insulating paper.

[0055] Key difference: The h-BN amination modification and ANF modification steps are eliminated, and composite coatings are prepared directly using unmodified h-BN and unmodified ANF with epoxy resin.

[0056] Performance testing Samples were prepared according to the methods of the examples and comparative examples, and their thermal conductivity and mechanical strength were tested. Five samples were repeated for each experiment, and the average of all results was taken. The test methods are as follows: Microscopic morphological characterization: The surface of the experimental sample was observed using a scanning electron microscope (SEM). The sample was sputter-coated with gold. The scanning voltage was 10 kV and the scanning speed was 60 mm / min. Mechanical property testing: The experimental samples were placed in a constant temperature and humidity environment of (23±0.5)℃ and (50±5)% for 12 hours to equilibrate. Mechanical properties were tested according to the following national standards: tensile strength (GB / T 12914-2018) and tear strength (GB / T455-2002(9)).

[0057] Electrical insulation performance test: The experimental sample was cut into circular pieces with a diameter of 10 cm, and the paper breakdown voltage and breakdown strength were tested at room temperature. The insulation performance of the sample was tested according to the following national standard: breakdown strength (GB / T 1408.1-2016).

[0058] Thermal conductivity test: Calculate the thermal conductivity of the sample using the following formula.

[0059] λ = α × Cp × ρ Where: α is the thermal diffusion rate coefficient of aramid paper, m² / s, measured at 25℃ using a Netzsch LFA 467 laser flash tester; Cp is the specific heat capacity of aramid paper, J / (kg·K), measured by the sapphire method using a PerkinElmer DSC8000 differential scanning calorimeter; ρ is the density of aramid paper, kg / m³, calculated from mass (m) and volume (v) using ρ = m / v.

[0060] Table 1 Performance Test Results

[0061] Data shows that after the surface coating modification of pure aramid base paper (Comparative Example 1) according to the present invention, the in-plane thermal conductivity of Example 1 increased to 9.82 W / (m·K), and the overall thermal conductivity increased from 0.1872 W / (m·K) to 0.2238 W / (m·K). This directly proves that the technical design of the present invention, which uses BN-NH2 as the core thermally conductive phase and constructs a continuous thermally conductive network through surface coating, effectively breaks through the technical bottleneck of poor intrinsic thermal conductivity of traditional aramid paper and achieves a significant enhancement of thermal conductivity.

[0062] Comparative Example 2, lacking modified aramid nanofibers (ANF), was coated only with BN-NH2 + epoxy resin. Its in-plane thermal conductivity decreased to 8.21 W / (m·K), a 16.40% decrease compared to Example 1. Tensile strength and tear strength also decreased significantly. This is because without the bridging and reinforcing effect of modified aramid nanofibers (ANF), the dispersion of BN-NH2 in the coating decreased, resulting in a discontinuous thermally conductive network and weakened interfacial bonding. Comparative Example 3, also lacking BN-NH2, was coated only with modified aramid nanofibers (ANF) + epoxy resin. Its in-plane thermal conductivity was only 7.49 W / (m·K), only 76.27% of that of Example 1. This demonstrates that modified aramid nanofibers (ANF) lack a core thermally conductive function. BN-NH2 is the core filler for improving the thermal conductivity of aramid paper, while modified aramid nanofibers (ANF), as a reinforcing and bonding phase, form a synergistic complex with BN-NH2, ensuring the continuity of the thermally conductive network and the stability of the coating structure.

[0063] Comparative Example 4, in which epoxy resin was replaced with PVA, retained the compound system of BN-NH2 and modified aramid nanofibers (ANF), but the in-plane thermal conductivity decreased to 9.07 W / (m·K), the tensile strength was only 2.67 kN / m, and the tear strength was 684 mN, all of which were significantly inferior to those of Example 1. This is because PVA lacks epoxy groups and cannot undergo ring-opening reactions with the amino groups of BN-NH2 and the hydroxyl groups of the modified aramid nanofibers (ANF) to form covalent bonds. It relies solely on physical bonding to achieve interfacial adhesion, resulting in high interfacial thermal resistance and weak bonding. It cannot construct an interfacial structure with synergistic enhancement of amino-epoxy, hydroxyl-epoxy, and amino-hydroxyl triple chemical bonds. This directly verifies the uniqueness of epoxy resin as a bridging adhesive and the core role of the triple chemical bond interfacial design of this invention in synergistic performance improvement.

[0064] Example 7 exhibits the best thermal conductivity among all examples, with an in-plane thermal conductivity of 11.85 W / (m·K) and an overall thermal conductivity of 0.2786 W / (m·K), while also possessing excellent insulation and mechanical properties. Figure 1 and Figure 2 The images show cross-sectional and planar views obtained using scanning electron microscopy. The images reveal that the paper surface is uniformly and completely covered by a BN-nanofiber coating. Compared to the internal structure of aramid paper, the coating on both the upper and lower surfaces is dense and continuous, which is beneficial for constructing efficient in-plane thermal conductivity pathways. These results confirm that a stable, fully covalently cross-linked network is formed between the aramid nanofibers, boron nitride, and the adhesive, achieving a ternary anchored interface structure of filler-fiber-matrix. This design not only significantly enhances the interfacial bonding and overall structural stability of the composite system but also achieves simultaneous improvement in thermal conductivity and mechanical properties, resulting in a significant synergistic enhancement effect.

[0065] The performance of each embodiment showed a regular change with the adjustment of process parameters: as the proportion of BN-NH2 increased (Examples 1, 4, 5, 8:2→7:3→9:1), the thermal conductivity gradually increased, as the high proportion of BN-NH2 further optimized the thermal conductivity network; as the coating amount increased (Examples 1, 6, 7, 3→6→9g / m²), the overall thermal conductivity continued to improve, and the breakdown strength of all embodiments remained above 13.533kV / mm, tensile strength ≥3.12kN / m, and tear strength ≥812mN, proving that the present invention effectively retains the excellent insulation and mechanical properties of aramid base paper while improving thermal conductivity, solving the industry pain point of the contradiction between thermal conductivity improvement and insulation and mechanical properties in traditional modification technology.

[0066] Comparative Example 5, using unmodified h-BN and unmodified ANF, showed an in-plane thermal conductivity of only 8.53 W / (m·K), and a significant decrease in insulation and mechanical properties. This is because the unmodified filler surface is chemically inert, resulting in weak interfacial bonding with epoxy resin and aramid paper, easily leading to interfacial defects and filler agglomeration, causing thermal network breakage and decreased structural stability. Comparative Example 1 shows that the one-step aminated BN-NH2 and UV ozone-modified aramid nanofibers (ANF) of this invention, by introducing active functional groups on the filler surface, significantly improve the dispersibility and interfacial bonding of the filler, laying the foundation for the construction of triple chemical bonds.

[0067] In summary, the scientific and advanced nature of the BN-NH2+ modified aramid nanofiber ANF + epoxy resin ternary synergistic system and triple chemical bond interface structure design of this invention is remarkable. This technology achieves a leapfrog improvement in the thermal conductivity of aramid insulating paper while also taking into account its excellent insulation and mechanical properties. Moreover, the process is simple, controllable, green, and environmentally friendly. Compared with traditional modification technologies, it has significant technical advantages and can meet the stringent requirements of high-end equipment for multifunctional synergy of insulating materials.

[0068] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

Claims

1. A method for preparing high thermal conductivity aramid insulating paper based on surface coating technology, characterized in that, Includes the following steps: (1) Mix aramid short-cut fibers, aramid precipitated fibers and water, transfer to a fiber dissociator for dissolution, and obtain a mixed slurry after thorough and uniform mixing. (2) The mixed pulp is placed in a rapid paper forming machine and wet paper forming technology is used to obtain aramid wet paper web. After drying, aramid base paper is obtained. (3) Amination modification of hexagonal boron nitride h-BN was carried out by a one-step direct covalent grafting method, and amino groups were introduced on its surface to obtain modified hexagonal boron nitride BN-NH2. (4) The surface of aramid nanofibers was irradiated with ultraviolet light to introduce a large number of oxygen-containing functional groups, thereby obtaining modified aramid nanofibers ANF. (5) The obtained BN-NH2 and modified aramid nanofibers ANF are mixed with water, and an adhesive is added and mixed evenly to obtain a composite coating. (6) The composite coating is applied to the surface of the aramid base paper, and after drying, it is hot-pressed using a high-temperature roller hot press to obtain high thermal conductivity aramid insulating paper.

2. The method for preparing high thermal conductivity aramid insulating paper based on surface coating technology according to claim 1, characterized in that, Based on oven-dry weight, the mass ratio of aramid chopped fibers to aramid precipitated fibers in step (1) is (50-80):(20-50).

3. The method for preparing high thermal conductivity aramid insulating paper based on surface coating technology according to claim 1, characterized in that, Step (1) The total mass concentration of fibers in the mixed slurry is 0.02-0.5%.

4. The method for preparing high thermal conductivity aramid insulating paper based on surface coating technology according to claim 1, characterized in that, The one-step direct covalent grafting method is as follows: (1) Preparation of diazonium salt solution: under ice bath conditions, aromatic amine compounds are dissolved in hydrochloric acid aqueous solution, and sodium nitrite is added to carry out diazotization reaction to obtain diazonium salt solution; (2) Grafting reaction: Hexagonal boron nitride h-BN is dispersed in hydrochloric acid aqueous solution and mixed with the diazonium salt solution prepared in step (1). The reaction is carried out under an inert atmosphere and heated. After the reaction is completed, the solid product is separated, washed with organic solvent and deionized water in sequence, and dried to obtain BN-NH2.

5. The method for preparing high thermal conductivity aramid insulating paper based on surface coating technology according to claim 4, characterized in that, In step (1), the aromatic amine compound is at least one of p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, p-aminophenol, and 2-methyl-4-aminophenol; the concentration of the hydrochloric acid aqueous solution is 1.0-2.0 mol / L; the molar ratio of the aromatic amine compound to sodium nitrite is 1:1; the temperature of the diazotization reaction is 0-5℃, and the reaction time is 1-2 hours.

6. The method for preparing high thermal conductivity aramid insulating paper based on surface coating technology according to claim 4, characterized in that, The average particle size of the hexagonal boron nitride in step (2) is 1-5 μm; the concentration of the hydrochloric acid aqueous solution is 1.0-2.0 mol / L; the reaction temperature is 50-70℃ and the reaction time is 2-6 hours; the reaction is carried out under an inert atmosphere; the organic solvent is selected from at least one of N,N-dimethylformamide, N-methylpyrrolidone, and anhydrous ethanol; the drying is vacuum drying at a temperature of 50-70℃ for 12-24 hours.

7. The method for preparing high thermal conductivity aramid insulating paper based on surface coating technology according to claim 1, characterized in that, The ultraviolet radiation treatment was carried out in an ozone (O3) atmosphere, with the aramid nanofibers placed in an ultraviolet ozone cleaner, exposed to 254nm ultraviolet light and an ozone concentration of 50g / m³. 3 Under these conditions, the modified aramid nanofibers (ANF) were obtained by treating them for 10-30 minutes.

8. The method for preparing high thermal conductivity aramid insulating paper based on surface coating technology according to claim 1, characterized in that, In step (5), the mass ratio of BN-NH2 to modified aramid nanofiber ANF is 1-5:5-9; the adhesive accounts for 5-25% of the solid dry mass in the composite coating; the total mass concentration of BN-NH2 and modified aramid nanofiber ANF in the composite coating is 0.5-3%; and the adhesive is epoxy resin.

9. The method for preparing high thermal conductivity aramid insulating paper based on surface coating technology according to claim 1, characterized in that, The coating is a double-sided coating, applied by roller coating or spraying, with a coating weight of 1-9 g / m². 2 The hot pressing temperature is 200-280℃ and the pressure is 4-8MPa.

10. A high thermal conductivity aramid insulating paper, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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