A core-shell dual thermally conductive aramid fiber, thermally conductive insulating paper, its preparation method and application

Abstract

This invention discloses a core-shell dual thermally conductive aramid fiber, a thermally conductive insulating paper, and their preparation methods and applications. The preparation method of the core-shell dual thermally conductive aramid fiber includes: mixing a meta-aramid polymer solution with a hydroxylated boron nitride nanosheet dispersion to obtain a composite spinning solution, and using a wet spinning process to prepare a core-type meta-aramid thermally conductive fiber; separately, diluting the meta-aramid polymer solution and adding KOH solution dropwise to obtain an aramid anion coating solution; finally, sequentially impregnating the core-type meta-aramid thermally conductive fiber in the aramid anion coating solution and the hydroxylated boron nitride nanosheet aqueous dispersion to obtain the core-shell dual thermally conductive aramid fiber. The core-shell dual thermally conductive aramid fiber prepared by this invention has excellent mechanical and thermal conductivity properties. The thermally conductive aramid insulating paper-based material prepared from this fiber has broad application prospects in high-power motors, new energy vehicle battery pack insulation, and lightweight heat dissipation components for aerospace.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of papermaking industry and polymer materials, and specifically relates to a core-shell dual thermally conductive aramid fiber, thermally conductive insulating paper, its preparation method and application. Background Technology

[0002] In recent years, with the rapid iteration and development of high-power-density electronic and electrical equipment, thermal management issues have become increasingly prominent. Besides continuously driving the development of heat dissipation technologies towards more efficient solutions such as phase-change cooling and liquid cooling, the thermal resistance bottleneck caused by insulating materials in the heat dissipation path is also becoming increasingly serious, restricting the improvement of the overall heat dissipation efficiency of the equipment. Against this backdrop, developing new insulating materials that combine excellent insulation properties with good thermal conductivity has become a key aspect of designing and manufacturing next-generation high-performance electronic and electrical equipment.

[0003] Aramid paper, with its excellent mechanical, thermal, and electrical properties, as well as its lightweight and flexibility, has become an indispensable insulating component in equipment such as electric motors, transformers, and generators. However, the intrinsic thermal conductivity of commercially available aramid paper is often very low (0.1 to 0.2 W·m). -1 ·K -1 This severely hinders the dissipation of heat inside the equipment, seriously affecting the long-term stability and service life of the equipment under extreme working environments.

[0004] Aramid paper is typically made by blending chopped aramid fibers and precipitated aramid fibers in a specific ratio. The chopped fibers, formed from cut aramid filaments, are stiff and usually serve as the paper's structural framework. The precipitated fibers, formed by the high-speed shearing of aramid polymer solutions in water, are amorphous and primarily function as binders and fillers in the paper. In the wet-process forming process, the chopped and precipitated fibers are separately dispersed in water, then uniformly mixed, and finally vacuum filtered, dried, and hot-pressed to obtain aramid paper. To improve the thermal conductivity of aramid paper, current technologies often employ the direct addition of thermally conductive fillers (such as boron nitride or aluminum nitride) during the wet-process papermaking. However, this method has significant drawbacks: poor interfacial compatibility between the filler and the aramid substrate leads to uneven filler dispersion, low retention, and often disordered and inefficient thermal conductivity pathways.

[0005] To address the aforementioned shortcomings, Chinese patent application CN 119553547 A discloses a method for constructing a highly efficient thermally conductive network within paper using thermally conductive chopped fibers. This method involves pre-encapsulating modified boron nitride nanosheets within aramid thermally conductive fibers using wet spinning technology, and then blending the aramid thermally conductive fibers with commercially available precipitated fibers to form a thermally conductive paper. This method achieves 100% filler retention and, thanks to its efficient thermal conductivity pathways, significantly improves thermal conductivity with a relatively low filler content (5 wt%). However, this strategy still faces new challenges in practical applications: the thermally conductive network within the paper is composed of randomly dispersed and overlapping chopped fibers, while the thermally conductive filler is completely encapsulated within the fibers. This results in a lack of effective thermally conductive media at the contact interface between adjacent thermally conductive fibers, leading to high interfacial thermal resistance. This structural defect limits further improvements in the overall thermal conductivity of the composite paper. Summary of the Invention

[0006] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing core-shell dual thermally conductive aramid fibers.

[0007] Another object of the present invention is to provide core-shell dual thermally conductive aramid fibers prepared by the above method.

[0008] Another object of the present invention is to provide a thermally conductive insulating paper and a method for preparing the same.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A method for preparing a core-shell dual thermally conductive aramid fiber includes the following steps:

[0011] (1) Preparation of nucleo-type meta-aramid thermal conductive fiber: Hydroxylated boron nitride nanosheets were dispersed in an organic solvent to prepare a hydroxylated boron nitride nanosheet dispersion, and a meta-aramid polymer solution was prepared; the meta-aramid polymer solution and the hydroxylated boron nitride nanosheet dispersion were thoroughly mixed to obtain a BNNs-OH / PMIA composite spinning solution; the BNNs-OH / PMIA composite spinning solution was used to prepare nucleo-type meta-aramid thermal conductive fiber by wet spinning process;

[0012] (2) Preparation of core-shell dual thermally conductive aramid fiber: First, take another portion of the meta-aramid polymer solution prepared in step (1) and dilute it with an organic solvent to obtain PMIA diluent; then add KOH solution to PMIA diluent and stir thoroughly to obtain deprotonated aramid anion coating solution (APA coating solution); immerse the core-type meta-aramid thermally conductive fiber obtained in step (1) in the APA coating solution and the aqueous dispersion of hydroxylated boron nitride nanosheets in sequence to obtain the core-shell dual thermally conductive aramid fiber.

[0013] Further, the meta-aramid polymer solution in step (1) is prepared by dissolving meta-aramid in an organic solvent (e.g., N,N-dimethylacetamide), or by the following steps:

[0014] Under a protective atmosphere, m-phenylenediamine was dissolved in an organic solvent to prepare a m-phenylenediamine solution. Then, under low temperature and continuous stirring, isophthaloyl chloride was slowly added to the m-phenylenediamine solution in multiple batches. After the addition was completed, the stirring speed was increased, and the temperature of the reaction system was controlled within the range of 30°C to 60°C to carry out the polycondensation reaction. The total reaction time was 2 to 48 hours. Finally, an acid-binding agent was added to adjust the pH to obtain a meta-aramid (PMIA) polymer solution.

[0015] More preferably, the purity of both monomers, m-phenylenediamine and isophthaloyl chloride, is greater than 99.9%; the organic solvent is N,N-dimethylacetamide with a purity greater than 99.99% and a water content of less than 500 ppm; and the protective gas is nitrogen.

[0016] More preferably, the molar ratio of m-phenylenediamine to isophthaloyl chloride is (1-10):(1-10); more preferably 1:(1.005-1.01); and more preferably 1:1.005.

[0017] More preferably, the concentration of the m-phenylenediamine solution is 0.5–2 mol / L; more preferably 0.8–1.2 mol / L; and even more preferably 1.1 mol / L.

[0018] More preferably, the stirring speed when adding isophthaloyl chloride is 100-600 rpm; more preferably 500-600 rpm.

[0019] More preferably, after the addition of materials is completed, the stirring speed is increased to 1000-2000 rpm; more preferably, the stirring speed is increased to 1000 rpm; the low temperature is -20℃ to 0℃ (preferably -2℃ to -6℃; more preferably -5℃).

[0020] More preferably, the polycondensation reaction is specifically carried out by controlling the temperature of the reaction system within the range of 30°C to 60°C, and continuing the reaction for 1 to 10 hours (preferably 4 hours) after the reaction system exhibits the phenomenon of "climbing rod".

[0021] More preferably, the acid-binding agent is Ca(OH)2; the pH adjustment is to adjust the pH to 7.0-7.4.

[0022] Further, the concentration of the hydroxylated boron nitride nanosheet dispersion in step (1) is 1 to 30 mg / g, preferably 15 mg / g; the organic solvent is N,N-dimethylacetamide.

[0023] Further, in the BNNs-OH / PMIA composite spinning solution in step (1), the mass ratio of meta-aramid (PMIA) and hydroxylated boron nitride nanosheets (BNNs-OH) is (100-50):(0-50), preferably 90:10.

[0024] Further, in step (1), the solid content of the BNNs-OH / PMIA composite spinning solution is 1% to 50%, preferably 10% to 20%.

[0025] Further, the wet spinning conditions in step (1) are as follows: the nozzle extrusion speed is 10-100 cm / min, the residence time in the coagulation bath is 1-500 s, the coagulation bath temperature is 20-60℃, the stretching ratio is 1.1-50 times, and the heat setting temperature is 50-600℃. The coagulation bath is a mixed solution of N,N-dimethylacetamide and water. Preferred conditions are: the nozzle extrusion speed is 50 cm / min, the residence time in the coagulation bath is 30-80 s, the coagulation bath temperature is 25-45℃, the stretching ratio is 2.4-5.0 times, the heat setting temperature is 320℃, and the volume ratio of N,N-dimethylacetamide to water in the coagulation bath is 58:42.

[0026] Further, the concentration of the PMIA diluent in step (2) is 1-50 mg / g, preferably 10 mg / g; the concentration of the KOH solution is 0.1-3 mol / L, preferably 1.25 mol / L; the PMIA diluent and KOH solution are mixed at a mass ratio of (10-100):(1-10), preferably 25:1;

[0027] Further, the organic solvent in step (2) is N,N-dimethylacetamide; the concentration of the aqueous dispersion of the hydroxylated boron nitride nanosheets is 1-10 mg / g, preferably 4 mg / g.

[0028] Further, the immersion time of the core-type thermal conductive fiber in the APA coating solution and the BNNs-OH dispersion in step (2) is 1-20 min and 1-10 min, respectively, preferably 3 min and 2 min.

[0029] Further, the hydroxylated boron nitride nanosheets described in steps (1) and (2) are prepared by the following steps: hexagonal boron nitride powder, water, and sodium hydroxide are mixed and ball-milled, acid-washed, water-washed, and filtered to obtain boron nitride paste; then, the paste is dispersed in an isopropanol aqueous solution, further exfoliated by ultrasonic cell disruption, large-sized unexfoliated boron nitride is removed by centrifugation, and the supernatant is taken to obtain BNNs-OH dispersion. The dispersion is freeze-dried to obtain hydroxylated boron nitride nanosheets; the mass ratio of hexagonal boron nitride, water, and sodium hydroxide is (1-10):(10-100):(1-20) (preferably 1:50:4).

[0030] The ball milling conditions are: rotation speed 100-3000 rpm, ball milling time 2-96 h; more preferred conditions are: rotation speed 1500-2000 rpm, ball milling time 24-36 h;

[0031] The grinding balls used in the ball mill are 5mm diameter agate balls and 2mm diameter agate balls, with a mass ratio of 3:2 and a ball-to-material mass ratio of 3:2.

[0032] The pickling process uses hydrochloric acid with a concentration of 1-2 mol / L. The pickling is repeated multiple times until the product becomes neutral.

[0033] The conditions for centrifugation to remove large-sized, unpeeled boron nitride are: rotation speed of 1000–4000 rpm and centrifugation time of 20–40 min (preferably 30 min).

[0034] The aforementioned cell wall breaking ultrasound uses a pulse mode, with 3 seconds of ultrasound followed by a 3-second pause, an amplitude of 30%, and a total ultrasound duration of 30 minutes.

[0035] The ball milling process used is a planetary ball mill.

[0036] The present invention also provides the application of the core-shell dual thermally conductive aramid fiber in the preparation of insulating materials.

[0037] A method for preparing thermally conductive insulating paper includes the following steps: cutting the core-shell dual thermally conductive aramid fiber described in this invention into short fibers, adding a dispersant and water to prepare a short fiber suspension; separately taking meta-aramid precipitated fibers and preparing a precipitated fiber suspension through a disintegration treatment; mixing the above-mentioned short fiber suspension and precipitated fiber suspension evenly in proportion, and then performing wet papermaking, pressing and dehydration, and hot pressing to obtain thermally conductive insulating paper.

[0038] Furthermore, the length of the chopped fibers is 1 to 100 mm; preferably 3 to 6 mm.

[0039] Furthermore, the dispersant is preferably polyethylene oxide with a viscosity-average molecular weight of approximately 100,000.

[0040] Further, the amount of dispersant added is 0.1 to 0.5% of the mass of the chopped fiber; preferably 0.3% of the mass of the chopped fiber; the mass ratio of the chopped fiber to the meta-aramid precipitated fiber is (1 to 10): (1 to 10); preferably (3 to 5): (5 to 7).

[0041] Furthermore, the mass concentration of the chopped fiber suspension is 0.01-10%, preferably 0.1%; the mass concentration of the precipitated fiber suspension is 0.01-10%, preferably 0.1%.

[0042] Furthermore, the chopped fiber suspension can be obtained by processing with a high-speed blender, with the processing conditions being: 10,000 rpm for 3 to 5 minutes (preferably 3 minutes).

[0043] Furthermore, the rotation speed of the de-icing process is 800-1200 rpm; preferably 1000 rpm.

[0044] The pressing and dehydration conditions are as follows: pressing and dehydration at 25℃ and 0.2 MPa pressure for 5 min;

[0045] The hot pressing conditions are: hot pressing temperature 50-600℃, hot pressing pressure 0.01-20 MPa, and hot pressing time 0.1-48 h; preferably: hot pressing temperature 200℃, hot pressing pressure 0.5 MPa, and hot pressing time 30 min.

[0046] Furthermore, the basis weight of the thermally conductive insulating paper is 1–100 g / m². 2 Preferably, it is 50–70 g / m³. 2 .

[0047] The thermally conductive insulating paper described in this invention has applications in multiple fields such as electrical equipment, electronic information, aerospace, and automotive industries.

[0048] The present invention has the following advantages and effects compared with the prior art:

[0049] 1. This invention utilizes a physical blending process of hydroxylated boron nitride nanosheets and meta-aramid polymer solution to prepare a spinning solution. The hydroxyl groups of the filler and the amide bonds of the polymer form abundant hydrogen bonds, ensuring good interfacial compatibility between the filler and the substrate, and guaranteeing the stability of the spinning solution. The stretching process promotes the coordinated alignment of BNNs-OH with PMIA molecules, enhancing the filler orientation, directionally regulating the composite fiber structure, and ensuring excellent mechanical and thermal conductivity properties of the fiber.

[0050] 2. This invention differs from core-type thermally conductive fibers by utilizing an aramid anionic solution with the same chemical composition as the substrate to coat the fiber surface with a layer of BNNs-OH, forming a "core-shell dual thermally conductive" structure. This design, while preserving the directional thermal conduction pathways within the fiber, extends and constructs a second thermal conduction pathway on the fiber surface, effectively filling the interfacial thermal resistance gaps at the overlapping nodes of adjacent fibers. This achieves efficient heat transfer within and between fibers, significantly improving the overall thermal conductivity of the paper.

[0051] 3. The physical blending and surface coating processes used in this invention are highly compatible with existing wet papermaking processes for aramid paper, requiring no large-scale modifications to production equipment. The prepared thermally conductive aramid insulating paper-based material has broad application prospects in high-power motors, new energy vehicle battery pack insulation, and lightweight heat dissipation components for aerospace applications. Attached Figure Description

[0052] Figure 1 This is a schematic diagram illustrating the preparation process of the core-shell dual thermally conductive aramid fiber and its thermally conductive insulating paper in Embodiment 1 of the present invention.

[0053] Figure 2 The image shows an atomic force microscope (AFM) image of BNNs-OH prepared in Example 1 of this invention. In the image, A is the AFM image of BNNs-OH; B is the height variation curve along the straight line in Figure A.

[0054] Figure 3 The image shows an SEM image of the thermally conductive fiber in Example 1 of this invention. In this image, A is the core-type meta-aramid thermally conductive fiber obtained in step (3); and B is the core-shell dual thermally conductive meta-aramid fiber obtained in step (4).

[0055] Figure 4 This is a physical image of the thermally conductive insulating paper prepared in Example 4 of the present invention. Detailed Implementation

[0056] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field. Test methods in the following embodiments that do not specify specific experimental conditions are generally performed according to conventional experimental conditions or the experimental conditions recommended by the manufacturer. Unless otherwise specified, the starting materials in the preparation methods of the present invention can be purchased from the market or prepared according to existing technical methods.

[0057] The preparation process of the thermally conductive aramid insulating paper-based material of this invention is as follows: Figure 1 As shown.

[0058] The precipitation fibers involved in the embodiments and comparative examples of this invention are meta-aramid precipitation fibers, purchased from Ganzhou Longbang Materials Technology Co., Ltd., with a fineness of 2 denier.

[0059] The polyethylene oxide used in the embodiments and comparative examples of this invention was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with a viscosity-average molecular weight of approximately 100,000.

[0060] In the embodiments and comparative examples of this invention, the tensile strength index was tested in accordance with GB / T12914-2008; the thermal conductivity of the composite paper was tested using a thermal constant analyzer (Hot Disk TPS2200), with each sample tested 5 times and the average value taken as the thermal conductivity.

[0061] Example 1

[0062] A method for preparing a core-shell dual thermally conductive fiber and its thermally conductive paper includes the following steps:

[0063] (1) Preparation of BNNs-OH: h-BN powder (2g), water (100g), sodium hydroxide (8g) and 100g agate beads (the weight ratio of 5 mm and 2 mm beads was 3:2) were mixed evenly and added to an agate jar for ball milling at 2000 rpm for 24 h. After ball milling, the ball milling product was first washed with 2 mol / L hydrochloric acid, and then repeatedly washed with a large amount of water until pH=7. After filtration, h-BN paste was obtained. Subsequently, the paste was dispersed in isopropanol solution (isopropanol solution concentration was 0.5 mg / mL), and further exfoliated using a cell-wall breaking ultrasonic machine for 30 min. The resulting dispersion was centrifuged at 2000 rpm for 30 min to remove large-sized unexfoliated h-BN, and the supernatant was taken to obtain BNNs-OH dispersion. After freeze-drying the dispersion, BNNs-OH was obtained.

[0064] (2) Preparation of BNNs-OH / PMIA composite spinning solution: m-phenylenediamine and isophthalic acid chloride with a purity of 99.9% or higher, and N,N-dimethylacetamide solution with a purity of 99.99% or higher and a water content of less than 500 ppm were used; the molar ratio of m-phenylenediamine and isophthalic acid chloride participating in the reaction was 1:1.008; the specific steps were as follows: under nitrogen atmosphere, m-phenylenediamine was first dissolved in N,N-dimethylacetamide to prepare a 1.2 mol / L solution, and placed at a low temperature of -5℃. Isophthalic acid chloride was slowly added multiple times at a stirring speed of 600 rpm. After the isophthalic acid chloride was completely added, the stirring speed was increased to 1000 rpm, and the reaction temperature was controlled between 30℃ and 60℃. After the rod climbing phenomenon occurred, the reaction was continued for 4 hours. Then, the acid-binding agent Ca(OH)2 was added to adjust the pH to 7.0 to obtain the PMIA polymer solution. The BNNs-OH from step (1) was dispersed in DMAc at a concentration of 15 mg / g. Then the dispersion was thoroughly mixed with a portion of the PMIA polymer solution to obtain the BNNs-OH / PMIA composite spinning solution. The mass ratio of PMIA to BNNs-OH was 90:10.

[0065] (3) Preparation of nucleo-meta-aramid thermally conductive fiber: The solid content of the composite spinning solution in step (2) was adjusted to 15%, the spinning nozzle speed was set to 50 cm / min, and after extrusion, the fiber was immersed in a coagulation bath (DMAc: H2O = 58: 42, volume ratio) for 80 seconds. The coagulation bath temperature was 25℃, and the fiber was initially formed into a nascent fiber. The nascent fiber was stretched to a predetermined ratio of 4.33 times by a quadriaxial stretching machine, thoroughly washed with water, dried and heat-set at 320℃ to obtain nucleo-meta-aramid thermally conductive fiber;

[0066] (4) Preparation of core-shell dual thermally conductive aramid fiber: First, take a portion of the PMIA polymer solution obtained in step (2) and dilute it with DMAc. After vigorous stirring, a PMIA / DMAc solution of 10 mg / g is obtained. Then, 10 g of 1.25 mol / L KOH solution is added dropwise to the diluted 200 g PMIA / DMAc solution and stirred thoroughly to obtain a deprotonated aramid anion (APA) coating solution. The core-shell dual thermally conductive meta aramid fiber obtained in step (3) is immersed in the APA coating solution and the BNNs-OH dispersion (4 mg / g) obtained in step (1) in sequence for 2 min and 3 min, respectively, to obtain the core-shell dual thermally conductive meta aramid fiber.

[0067] (5) Preparation of thermally conductive insulating paper: The core-shell dual thermally conductive aramid fibers obtained in step (4) were cut into 6mm short fibers. With the help of dispersant (polyethylene oxide, amount of which is 0.3% of the mass of the short fibers) and water, a 0.1 wt% suspension was prepared by blending at 10000 rpm for 3 min (based on the mass of the short fibers). The precipitated fibers were weighed according to a mass ratio of 50:50 between the short fibers and the precipitated fibers. After the precipitated fibers were disintegrated by a fiber disintegrator at 1000 rpm, a 0.1 wt% suspension was prepared. The short fibers and the precipitated fiber suspension were mixed and stirred evenly. After wet papermaking, the wet paper web was pressed and dehydrated at 25℃ and 0.2MPa pressure for 5 min. Then it was directly thermoformed (i.e., aramid wet paper was obtained by wet papermaking and then dried and formed). The temperature was 200℃, the pressure was 0.5MPa, the time was 30 min, and the paper basis weight was 60.6 g / m². 2 This yields thermally conductive insulating paper.

[0068] The thermally conductive insulating paper was tested for performance, and its tensile strength index and thermal conductivity were 121.34 N·m / g and 1.341 W / (m·K), respectively.

[0069] Example 2

[0070] A method for preparing a core-shell dual thermally conductive fiber and its thermally conductive paper includes the following steps:

[0071] (1) Preparation of BNNs-OH: h-BN powder (2g), water (100g), sodium hydroxide (8g) and 100g agate beads (the weight ratio of 5 mm and 2 mm beads was 3:2) were mixed evenly and added to an agate jar for ball milling at 1000 rpm for 30 h. After ball milling, the ball milling product was first washed with 2 mol / L hydrochloric acid, and then repeatedly washed with a large amount of water until pH=7. After filtration, h-BN paste was obtained. Subsequently, the paste was dispersed in 0.5 mg / mL isopropanol solution and further exfoliated using a cell-wall breaking ultrasonic machine for 30 min. The resulting dispersion was centrifuged at 3000 rpm for 40 min to remove large-sized unexfoliated h-BN. The supernatant was taken to obtain BNNs-OH dispersion. After freeze-drying the dispersion, BNNs-OH was obtained.

[0072] (2) Preparation of BNNs-OH / PMIA composite spinning solution: m-phenylenediamine and isophthalic acid chloride with a purity of 99.9% or higher, and N,N-dimethylacetamide solution with a purity of 99.99% or higher and a water content of 500ppm or less are used; the molar ratio of m-phenylenediamine and isophthalic acid chloride participating in the reaction is 1:1.001; the specific steps are as follows: under nitrogen atmosphere, m-phenylenediamine is first dissolved in N,N-dimethylacetamide to prepare a 1.0mol / L solution, and placed at a low temperature of -6℃. Isophthalic acid chloride is slowly added multiple times, and the stirring speed is 600rpm. After the isophthalic acid chloride is completely added, the stirring speed is increased to 1000rpm. The reaction temperature is controlled between 30℃ and 60℃. After the rod climbing phenomenon occurs, the reaction continues for 4h. Then, the acid-binding agent Ca(OH)2 is added to adjust the pH to 7.0 to obtain the PMIA polymer solution. The BNNs-OH from step (1) was dispersed in DMAc at a concentration of 20 mg / g. Then the dispersion was thoroughly mixed with a portion of the PMIA polymer solution to obtain the BNNs-OH / PMIA composite spinning solution. The mass ratio of PMIA to BNNs-OH was 95:5.

[0073] (3) Preparation of nucleo-meta-aramid thermally conductive fiber: The solid content of the composite spinning solution in step (2) was adjusted to 17%, the spinning nozzle speed was set to 30 cm / min, and after the spinneret was extruded, it was immersed in a coagulation bath (DMAc: H2O=58: 42, volume ratio) for 50 s. The coagulation bath temperature was 25℃, and the fiber was initially formed into a nascent fiber. The nascent fiber was stretched to a predetermined ratio of 4.17 times by a quadriaxial stretching machine, thoroughly washed with water, dried and heat-set at 320℃ to obtain nucleo-meta-aramid thermally conductive fiber;

[0074] (4) Preparation of core-shell dual thermally conductive aramid fiber: First, take a portion of the PMIA polymer solution obtained in step (2) and dilute it with DMAc. After vigorous stirring, a PMIA / DMAc solution of 20 mg / g is obtained. Then, 8 g of 1.25 mol / L KOH solution is added dropwise to the diluted 200 g PMIA / DMAc solution and stirred thoroughly to obtain a deprotonated aramid anion (APA) coating solution. The core-type meta-aramid thermally conductive fiber obtained in step (3) is immersed in the APA coating solution and the BNNs-OH dispersion (3 mg / g) obtained in step (1) in sequence for 3 min and 4 min, respectively, to obtain the core-shell dual thermally conductive aramid fiber.

[0075] (5) Preparation of thermally conductive insulating paper: The core-shell dual thermally conductive aramid fibers obtained in step (4) were cut into 5mm short fibers. With the help of dispersant (polyethylene oxide, amount of which is 0.3% of the mass of the short fibers) and water, a 0.1 wt% suspension was prepared by blending at 10000 rpm for 3 min (based on the mass of the short fibers). The precipitated fibers were weighed according to a mass ratio of 50:50 between the short fibers and the precipitated fibers. After the precipitated fibers were disintegrated by a fiber disintegrator at 1000 rpm, a 0.1 wt% suspension was prepared. The short fibers and the precipitated fiber suspension were mixed and stirred evenly. After wet papermaking, the wet paper web was pressed and dehydrated at 25℃ and 0.2MPa pressure for 5 min. Then it was directly thermoformed (i.e., aramid wet paper was obtained by wet papermaking and then dried and formed). The temperature was 200℃, the pressure was 0.5MPa, the time was 30 min, and the paper basis weight was 56.6 g / m². 2 This yields thermally conductive insulating paper.

[0076] The thermally conductive insulating paper was tested for performance, and its tensile strength index and thermal conductivity were 173.12 N·m / g and 1.103 W / (m·K), respectively.

[0077] Example 3

[0078] A method for preparing a core-shell dual thermally conductive fiber and its thermally conductive paper includes the following steps:

[0079] (1) Preparation of BNNs-OH: h-BN powder (2g), water (100g), sodium hydroxide (8g) and 100g agate beads (the weight ratio of 5 mm and 2 mm beads was 3:2) were mixed evenly and added to an agate jar for ball milling at 2000 rpm for 24 h. After ball milling, the ball milling product was first washed with 2 mol / L hydrochloric acid, and then repeatedly washed with a large amount of water until pH=7. After filtration, h-BN paste was obtained. Subsequently, the paste was dispersed in 0.5 mg / mL isopropanol solution and further exfoliated using a cell-wall breaking ultrasonic machine for 30 min. The resulting dispersion was centrifuged at 3000 rpm for 40 min to remove large-sized unexfoliated h-BN. The supernatant was taken to obtain BNNs-OH dispersion. After freeze-drying the dispersion, BNNs-OH was obtained.

[0080] (2) Preparation of BNNs-OH / PMIA composite spinning solution: m-phenylenediamine and isophthalic acid chloride with a purity of 99.9% or higher, and N,N-dimethylacetamide solution with a purity of 99.99% or higher and a water content of less than 500 ppm were used; the molar ratio of m-phenylenediamine and isophthalic acid chloride participating in the reaction was 1:1.001; the specific steps were as follows: under nitrogen atmosphere, m-phenylenediamine was first dissolved in N,N-dimethylacetamide to prepare a 1.1 mol / L solution, and placed at a low temperature of -5℃. Isophthalic acid chloride was slowly added multiple times at a stirring speed of 600 rpm. After the isophthalic acid chloride was completely added, the stirring speed was increased to 1000 rpm. The reaction temperature was controlled between 30℃ and 60℃. After the rod climbing phenomenon occurred, the reaction was continued for 4 hours. Then, the acid-binding agent Ca(OH)2 was added to adjust the pH to 7.0 to obtain the PMIA polymer solution. The BNNs-OH from step (1) was dispersed in DMAc at a concentration of 40 mg / g. Then, the dispersion and a portion of the PMIA polymer solution were thoroughly mixed to obtain the BNNs-OH / PMIA composite spinning solution. The mass ratio of PMIA to BNNs-OH was 92.5:7.5.

[0081] (3) Preparation of nucleo-meta-aramid thermally conductive fiber: The solid content of the composite spinning solution in step (2) was adjusted to 19%, the spinning nozzle speed was set to 50 cm / min, and after extrusion, the fiber was immersed in a coagulation bath (DMAc: H2O=58: 42, volume ratio) for 80 s. The coagulation bath temperature was 25℃, and the fiber was initially formed into a nascent fiber. The nascent fiber was stretched to a predetermined ratio of 4.33 times by a quadriaxial stretching machine, thoroughly washed with water, dried and heat-set at 320℃ to obtain nucleo-meta-aramid thermally conductive fiber;

[0082] (4) Preparation of core-shell dual thermally conductive aramid fiber: First, take a portion of the PMIA polymer solution obtained in step (2) and dilute it with DMAc. After vigorous stirring, a PMIA / DMAc solution of 10 mg / g is obtained. Then, 8 g of 1.25 mol / L KOH solution is added dropwise to the diluted 200 g PMIA / DMAc solution and stirred thoroughly to obtain a deprotonated aramid anion (APA) coating solution. The core-shell dual thermally conductive meta-aramid fiber obtained in step (3) is immersed in the APA coating solution and BNNs-OH dispersion (5 mg / g) in sequence for 1 min and 1 min, respectively, to obtain the core-shell dual thermally conductive meta-aramid fiber.

[0083] (5) Preparation of thermally conductive insulating paper: The core-shell dual thermally conductive aramid fibers obtained in step (4) are cut into 5mm short fibers. With the help of dispersant (polyethylene oxide, the amount is 0.3% of the mass of the short fibers) and water, a 0.1 wt% suspension is prepared by blending at 10000 rpm for 3 min (based on the mass of the short fibers). The precipitated fibers are weighed according to a mass ratio of 50:50 between the short fibers and the precipitated fibers. The precipitated fibers are then disintegrated by a fiber disintegrator at 1000 rpm and prepared into a 0.1 wt% suspension. The short fibers and the precipitated fiber suspension are mixed and stirred evenly. After wet papermaking, the wet paper web is pressed and dehydrated at 25℃ and 0.2MPa pressure for 5 min. Then it is directly thermoformed (i.e., aramid wet paper is obtained by wet papermaking and then dried and formed). The temperature is 200℃, the pressure is 0.5MPa, the time is 30 min, and the paper basis weight is 60.0 g / m². 2 This yields thermally conductive insulating paper.

[0084] The thermally conductive insulating paper was tested for performance, and its tensile strength index and thermal conductivity were 84.11 N·m / g and 1.223 W / (m·K), respectively.

[0085] Example 4

[0086] A method for preparing a core-shell dual thermally conductive fiber and its thermally conductive paper includes the following steps:

[0087] (1) Preparation of BNNs-OH: h-BN powder (2g), water (100g), sodium hydroxide (8g) and 100g agate beads (the weight ratio of 5 mm and 2 mm beads was 3:2) were mixed evenly and added to an agate jar for ball milling at 3000 rpm for 36 h. After ball milling, the ball milling product was first washed with 2 mol / L hydrochloric acid, and then repeatedly washed with a large amount of water until pH=7. After filtration, h-BN paste was obtained. Subsequently, the paste was dispersed in 0.5 mg / mL isopropanol solution and further exfoliated using a cell-wall breaking ultrasonic machine for 30 min. The resulting dispersion was centrifuged at 2000 rpm for 30 min to remove large-sized unexfoliated h-BN. The supernatant was taken to obtain BNNs-OH dispersion. After freeze-drying the dispersion, BNNs-OH was obtained.

[0088] (2) Preparation of BNNs-OH / PMIA composite spinning solution: m-phenylenediamine and isophthalic acid chloride with a purity of 99.9% or higher, and N,N-dimethylacetamide solution with a purity of 99.99% or higher and a water content of less than 500 ppm were used; the molar ratio of m-phenylenediamine and isophthalic acid chloride participating in the reaction was 1:1.002; the specific steps were as follows: under nitrogen atmosphere, m-phenylenediamine was first dissolved in N,N-dimethylacetamide to prepare a 0.9 mol / L solution, and placed at a low temperature of -9℃. Isophthalic acid chloride was slowly added multiple times at a stirring speed of 600 rpm. After the isophthalic acid chloride was completely added, the stirring speed was increased to 1000 rpm, and the reaction temperature was controlled between 30℃ and 60℃. After the rod climbing phenomenon occurred, the reaction was continued for 4 hours. Then, the acid-binding agent Ca(OH)2 was added to adjust the pH to 7.0 to obtain the PMIA polymer solution. The BNNs-OH from step (1) was dispersed in DMAc at a concentration of 15 mg / g. Then, the dispersion was thoroughly mixed with a portion of the PMIA polymer solution to obtain the BNNs-OH / PMIA composite spinning solution. The mass ratio of PMIA to BNNs-OH was 90:10.

[0089] (3) Preparation of nucleo-meta-aramid thermally conductive fiber: The solid content of the composite spinning solution in step (2) was adjusted to 15%, the spinning nozzle speed was set to 50 cm / min, and after extrusion, the fiber was immersed in a coagulation bath (DMAc: H2O=58: 42, volume ratio) for 80 s. The coagulation bath temperature was 25℃, and the fiber was initially formed into a nascent fiber. The nascent fiber was stretched to a predetermined ratio of 4.33 times by a quadriaxial stretching machine, thoroughly washed with water, dried and heat-set at 320℃ to obtain nucleo-meta-aramid thermally conductive fiber;

[0090] (4) Preparation of core-shell dual thermally conductive aramid fiber: First, take a portion of the PMIA polymer solution obtained in step (2) and dilute it with DMAc. After vigorous stirring, a PMIA / DMAc solution of 20 mg / g is obtained. Then, 10 g of 1.25 mol / L KOH solution is added dropwise to the diluted 200 g PMIA / DMAc solution and stirred thoroughly to obtain a deprotonated aramid anion (APA) coating solution. The core-shell type meta-aramid thermally conductive fiber obtained in step (3) is immersed in the APA coating solution and BNNs-OH dispersion (4 mg / g) in sequence for 4 min and 2 min, respectively, to obtain the core-shell type dual meta-aramid thermally conductive fiber.

[0091] (5) Preparation of thermally conductive insulating paper: The core-shell dual thermally conductive aramid fibers obtained in step (4) were cut into 6mm short fibers. With the help of dispersant (polyethylene oxide, the amount of which is 0.3% of the mass of the short fibers) and water, a 0.1 wt% suspension was prepared by blending at 10000 rpm for 3 min (based on the mass of the short fibers). The precipitated fibers were weighed according to a mass ratio of 55:45 between the short fibers and the precipitated fibers. The precipitated fibers were then dispersed by a fiber disintegrator at 1000 rpm and prepared into a 0.1 wt% suspension. The short fibers and the precipitated fiber suspension were mixed and stirred evenly. After wet papermaking, the wet paper web was pressed and dehydrated at 25℃ and 0.2MPa for 5 min. Then, it was directly thermoformed (i.e., aramid wet paper was obtained by wet papermaking and then dried and formed). The temperature was 200℃, the pressure was 0.5MPa, the time was 30 min, and the paper basis weight was 60.6 g / m². 2 This yields thermally conductive insulating paper.

[0092] The thermally conductive insulating paper was tested for performance, and its tensile strength index and thermal conductivity were 133.52 N·m / g and 1.437 W / (m·K), respectively.

[0093] Compare with Example 1

[0094] A thermally conductive aramid insulating paper-based material, the preparation method of which is as follows:

[0095] (1) Preparation of BNNs-OH: h-BN powder (2g), water (100g), sodium hydroxide (8g) and 100g agate beads (the weight ratio of 5 mm and 2 mm beads was 3:2) were mixed evenly and added to an agate jar for ball milling at 2000 rpm for 24 h. After ball milling, the ball milling product was first washed with 2 mol / L hydrochloric acid, and then repeatedly washed with a large amount of water until pH=7. After filtration, h-BN paste was obtained. Subsequently, the paste was dispersed in 0.5 mg / mL isopropanol solution and further exfoliated using a cell-wall breaking ultrasonic machine for 30 min. The resulting dispersion was centrifuged at 2000 rpm for 30 min to remove large-sized unexfoliated h-BN. The supernatant was taken to obtain BNNs-OH dispersion. After freeze-drying the dispersion, BNNs-OH was obtained.

[0096] (2) Preparation of BNNs-OH / PMIA composite spinning solution: m-phenylenediamine and isophthalic acid chloride with a purity of 99.9% or higher, and N,N-dimethylacetamide solution with a purity of 99.99% or higher and a water content of less than 500 ppm were used; the molar ratio of m-phenylenediamine and isophthalic acid chloride participating in the reaction was 1:1.008; the specific steps were as follows: under nitrogen atmosphere, m-phenylenediamine was first dissolved in N,N-dimethylacetamide to prepare a 1.2 mol / L solution, and placed at a low temperature of -5℃. Isophthalic acid chloride was slowly added multiple times at a stirring speed of 600 rpm. After the isophthalic acid chloride was completely added, the stirring speed was increased to 1000 rpm, and the reaction temperature was controlled between 30℃ and 60℃. After the rod climbing phenomenon occurred, the reaction was continued for 4 hours. Then, the acid-binding agent Ca(OH)2 was added to adjust the pH to 7.0 to obtain the PMIA polymer solution. The BNNs-OH from step (1) was dispersed in DMAc at a concentration of 15 mg / g. Then the dispersion and the PMIA polymer solution were thoroughly mixed to obtain the BNNs-OH / PMIA composite spinning solution. The mass ratio of PMIA to BNNs-OH was 90:10.

[0097] (3) Preparation of nucleo-meta-aramid thermally conductive fiber: The solid content of the composite spinning solution in step (2) was adjusted to 15%, the spinning nozzle speed was set to 50 cm / min, and after extrusion, the fiber was immersed in a coagulation bath (DMAc: H2O=58: 42, volume ratio) for 80 s. The coagulation bath temperature was 25℃, and the fiber was initially formed into a nascent fiber. The nascent fiber was stretched to a predetermined ratio of 4.33 times by a quadriaxial stretching machine, thoroughly washed with water, dried and heat-set at 320℃ to obtain nucleo-meta-aramid thermally conductive fiber;

[0098] (4) Preparation of thermally conductive insulating paper: The nucleotype meta-aramid thermally conductive fibers obtained in step (3) are cut into 6mm short fibers. With the help of dispersant (polyethylene oxide, the amount is 0.3% of the mass of the short fibers) and water, a 0.1 wt% suspension is prepared by blending at 10000 rpm for 3 minutes (based on the mass of the short fibers). The precipitated fibers are weighed according to a mass ratio of 50:50 between the short fibers and the precipitated fibers. The precipitated fibers are then dispersed by a fiber disintegrator at 1000 rpm and prepared into a 0.1 wt% suspension. The short fibers and the precipitated fiber suspension are mixed and stirred evenly. After wet papermaking, the wet paper web is pressed and dehydrated at 25℃ and 0.2MPa pressure for 5 minutes. Then it is directly thermoformed (i.e., aramid wet paper is obtained by wet papermaking and then dried and formed). The temperature is 200℃, the pressure is 0.5MPa, the time is 30 minutes, and the paper basis weight is 60.6 g / m². 2 This yields thermally conductive insulating paper.

[0099] The thermally conductive insulating paper was tested for performance, and its tensile strength index and thermal conductivity were 113.41 N·m / g and 0.741 W / (m·K), respectively.

[0100] Compare with Example 2

[0101] A thermally conductive aramid insulating paper-based material, the preparation method of which is as follows:

[0102] (1) Preparation of BNNs-OH: h-BN powder (2g), water (100g), sodium hydroxide (8g) and 100g agate beads (the weight ratio of 5 mm and 2 mm beads was 3:2) were mixed evenly and added to an agate jar for ball milling at 1000 rpm for 30 h. After ball milling, the ball milling product was first washed with 2 mol / L hydrochloric acid, and then repeatedly washed with a large amount of water until pH=7. After filtration, h-BN paste was obtained. Subsequently, the paste was dispersed in 0.5 mg / mL isopropanol solution and further exfoliated using a cell-wall breaking ultrasonic machine for 30 min. The resulting dispersion was centrifuged at 3000 rpm for 40 min to remove large-sized unexfoliated h-BN. The supernatant was taken to obtain BNNs-OH dispersion. After freeze-drying the dispersion, BNNs-OH was obtained.

[0103] (2) Preparation of PMIA spinning solution: m-phenylenediamine and isophthalic acid chloride with a purity of 99.9% or higher, and N,N-dimethylacetamide solution with a purity of 99.99% or higher and a water content of less than 500 ppm are used; the molar ratio of m-phenylenediamine and isophthalic acid chloride participating in the reaction is 1:1.001; the specific steps are as follows: under nitrogen atmosphere, m-phenylenediamine is first dissolved in N,N-dimethylacetamide to prepare a 1.0 mol / L solution, and placed at a low temperature of -6℃. Isophthalic acid chloride is slowly added multiple times, and the stirring speed is 600 rpm. After the isophthalic acid chloride is completely added, the stirring speed is increased to 1000 rpm, and the reaction temperature is controlled between 30℃ and 60℃. After the rod climbing phenomenon occurs, the reaction continues for 4 hours. Then, the acid-binding agent Ca(OH)2 is added to adjust the pH to 7.0 to obtain PMIA polymer solution.

[0104] (3) Preparation of meta-aramid fiber: Adjust the solid content of the spinning solution in step (2) to 17%, set the spinning nozzle speed to 30 cm / min, and after the spinneret is extruded, immerse it in a coagulation bath (DMAc: H2O=58: 42, volume ratio) for 50 s. The coagulation bath temperature is 25℃, and the fiber is initially formed into a nascent fiber. The nascent fiber is stretched to a predetermined ratio of 4.17 times by a quadriaxial stretching machine, thoroughly washed with water, dried and heat-set at 320℃ to obtain nucleated meta-aramid thermally conductive fiber;

[0105] (4) Preparation of shell-shaped thermally conductive aramid fiber: First, dilute the PMIA polymer solution obtained in step (2) with DMAc and stir vigorously to obtain a PMIA / DMAc solution of 20 mg / g. Then, add 8 g of 1.25 mol / L KOH solution to the diluted 200 g PMIA / DMAc solution and stir thoroughly to obtain a deprotonated aramid anion (APA) coating solution; immerse the meta-aramid fiber obtained in step (3) in the APA coating solution and BNNs-OH dispersion (3 mg / g) in sequence for 1 min and 10 min, respectively, to obtain shell-shaped meta-aramid thermally conductive fiber;

[0106] (5) Preparation of thermally conductive insulating paper: The shell-shaped meta-aramid thermally conductive fibers obtained in step (4) are cut into 5mm short fibers. With the help of dispersant (polyethylene oxide, the amount is 0.3% of the mass of the short fibers) and water, a 0.1 wt% suspension is prepared by blending at 10000 rpm for 3 minutes (based on the mass of the short fibers). The precipitated fibers are weighed according to a mass ratio of 50:50 between the short fibers and the precipitated fibers. The precipitated fibers are then dispersed by a fiber disintegrator at 1000 rpm and prepared into a 0.1 wt% suspension. The short fibers and the precipitated fiber suspension are mixed and stirred evenly. After wet papermaking, the wet paper web is pressed and dehydrated at 25℃ and 0.2MPa pressure for 5 minutes. Then it is directly thermoformed (i.e., aramid wet paper is obtained by wet papermaking and then dried and formed). The temperature is 200℃, the pressure is 0.5MPa, the time is 30 minutes, and the paper basis weight is 56.6g / m 2 This yields thermally conductive insulating paper.

[0107] The thermally conductive insulating paper was tested for performance, and its tensile strength index and thermal conductivity were 193.42 N·m / g and 0.315 W / (m·K), respectively.

[0108] Compare with Example 3

[0109] A thermally conductive aramid insulating paper-based material, the preparation method of which is as follows:

[0110] (1) Preparation of BNNs-OH: h-BN powder (2g), water (100g), sodium hydroxide (8g) and 100g agate beads (the weight ratio of 5 mm and 2 mm beads was 3:2) were mixed evenly and added to an agate jar for ball milling at 2000 rpm for 24 h. After ball milling, the ball milling product was first washed with 2 mol / L hydrochloric acid, and then repeatedly washed with a large amount of water until pH=7. After filtration, h-BN paste was obtained. Subsequently, the paste was dispersed in 0.5 mg / mL isopropanol solution and further exfoliated using a cell-wall breaking ultrasonic machine for 30 min. The resulting dispersion was centrifuged at 3000 rpm for 40 min to remove large-sized unexfoliated h-BN. The supernatant was taken to obtain BNNs-OH dispersion. After freeze-drying the dispersion, BNNs-OH was obtained.

[0111] (2) Preparation of PMIA spinning solution: m-phenylenediamine and isophthalic acid chloride with a purity of 99.9% or higher, and N,N-dimethylacetamide solution with a purity of 99.99% or higher and a water content of less than 500 ppm are used; the molar ratio of m-phenylenediamine and isophthalic acid chloride participating in the reaction is 1:1.001; the specific steps are as follows: under nitrogen atmosphere, m-phenylenediamine is first dissolved in N,N-dimethylacetamide to prepare a 1.1 mol / L solution, and placed at a low temperature of -5℃. Isophthalic acid chloride is slowly added multiple times, and the stirring speed is 600 rpm. After the isophthalic acid chloride is completely added, the stirring speed is increased to 1000 rpm, and the reaction temperature is controlled between 30℃ and 60℃. After the rod climbing phenomenon occurs, the reaction continues for 4 hours. Then, the acid-binding agent Ca(OH)2 is added to adjust the pH to 7.0 to obtain the polymer solution.

[0112] (3) Preparation of meta-aramid fibers: The solid content of the polymer solution in step (2) was adjusted to 19%, the spinning nozzle speed was set to 50 cm / min, and after extrusion, the fibers were immersed in a coagulation bath (DMAc: H2O = 58: 42, volume ratio) for 80 seconds. The coagulation bath temperature was 25℃, and the fibers were initially formed into nascent fibers. The nascent fibers were stretched to a predetermined ratio of 4.33 times by a quadriaxial stretching machine, thoroughly washed with water, dried, and heat-set at 320℃ to obtain meta-aramid fibers.

[0113] (4) Preparation of thermally conductive insulating paper: The aramid fibers obtained in step (3) are cut into short fibers of 5 mm. With the help of dispersant (polyethylene oxide, the amount is 0.3% of the mass of the short fibers) and water, the mixture is prepared into a suspension of 0.1 wt% (based on the mass of the short fibers) by blending at 10000 rpm for 3 min. The precipitated fibers were weighed according to a mass ratio of 50:50, and after being disintegrated by a fiber disintegrator at 1000 rpm, a suspension of 0.1 wt% was prepared. The chopped fibers, precipitated fibers, and the boron nitride nanosheet suspension prepared in step (1) were mixed, with the amount of boron nitride nanosheets added being equivalent to 20% of the mass of the chopped fibers. After stirring evenly, the paper was wet-processed, and then the wet paper web was pressed and dehydrated at 25°C and 0.2 MPa for 5 min. Then it was directly thermoformed (i.e., aramid wet paper was obtained through wet papermaking and then dried and formed), with a temperature of 200°C, a pressure of 0.5 MPa, a time of 30 min, and a paper basis weight of 60.0 g / m². 2 This yields thermally conductive insulating paper.

[0114] The thermally conductive insulating paper was tested for performance, and its tensile strength index and thermal conductivity were 54.70 N·m / g and 0.348 W / (m·K), respectively.

[0115] Compare with Example 4

[0116] A thermally conductive aramid insulating paper-based material, the preparation method of which is as follows:

[0117] (1) Preparation of h-BN / PMIA composite spinning solution: m-phenylenediamine and isophthalic acid chloride with a purity of 99.9% or higher, and N,N-dimethylacetamide solution with a purity of 99.99% or higher and a water content of 500ppm or less are used; the molar ratio of m-phenylenediamine and isophthalic acid chloride participating in the reaction is 1:1.002; the specific steps are as follows: under nitrogen atmosphere, m-phenylenediamine is first dissolved in N,N-dimethylacetamide to prepare a 0.9 mol / L solution, and placed at a low temperature of -9℃. Isophthalic acid chloride is slowly added multiple times at a stirring rate of 600rpm. After the isophthalic acid chloride is completely added, the stirring speed is increased to 1000rpm. The reaction temperature is controlled between 30℃ and 60℃. After the rod climbing phenomenon occurs, the reaction continues for 4h. Then, the acid-binding agent Ca(OH)2 is added to adjust the pH to 7.0 to obtain PMIA polymer solution. h-BN was dispersed in DMAc at a concentration of 15 mg / g. The dispersion was then thoroughly mixed with a portion of the PMIA polymer solution to obtain an h-BN / PMIA composite spinning solution with a mass ratio of PMIA to h-BN of 90:10.

[0118] (2) Preparation of nucleo-meta-aramid thermally conductive fiber: The solid content of the composite spinning solution in step (2) was adjusted to 15%, and the spinning nozzle speed was set to 50 cm / min. After extrusion, the fiber was immersed in a coagulation bath (DMAc: H2O = 58: 42, volume ratio) for 80 seconds. The coagulation bath temperature was 25℃, and the fiber was initially formed into nascent fiber. The nascent fiber was stretched to a predetermined ratio of 4.33 times by a quadriaxial stretching machine, thoroughly washed with water, dried, and heat-set at 320℃ to obtain nucleo-meta-aramid thermally conductive fiber.

[0119] (3) Preparation of core-shell dual thermally conductive aramid fiber: First, take a portion of the PMIA polymer solution obtained in step (1), stir vigorously to obtain a PMIA / DMAc solution of 20 mg / g. Then, add 10 g of 1.25 mol / L KOH solution to the diluted 200 g PMIA / DMAc solution and stir thoroughly to obtain a deprotonated aramid anion (APA) coating solution; immerse the core-type meta-aramid thermally conductive fiber obtained in step (2) in the APA coating solution and h-BN aqueous dispersion (4 mg / g) in sequence for 2 min and 5 min respectively to obtain the core-shell dual thermally conductive aramid fiber;

[0120] (4) Preparation of thermally conductive insulating paper: The core-shell dual thermally conductive aramid fibers obtained in step (3) were cut into 6mm short fibers. With the help of dispersant (polyethylene oxide, the amount of which is 0.3% of the mass of the short fibers) and water, a 0.1 wt% suspension was prepared by blending at 10000 rpm for 3 min (based on the mass of the short fibers). The precipitated fibers were weighed according to a mass ratio of 55:45 between the short fibers and the precipitated fibers. The precipitated fibers were then disintegrated by a fiber disintegrator at 1000 rpm and prepared into a 0.1 wt% suspension. The short fibers and the precipitated fiber suspension were mixed and stirred evenly. After wet papermaking, the wet paper web was pressed and dehydrated at 25℃ and 0.2MPa for 5 min. Then, it was directly thermoformed (i.e., aramid wet paper was obtained by wet papermaking and then dried and formed). The temperature was 200℃, the pressure was 0.5MPa, the time was 30 min, and the paper basis weight was 60.6 g / m². 2 This yields thermally conductive insulating paper.

[0121] The thermally conductive insulating paper was tested for performance, and its tensile strength index and thermal conductivity were 81.44 N·m / g and 0.632 W / (m·K), respectively.

[0122] Table 1 Data Summary

[0123]

[0124] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing core-shell dual thermally conductive aramid fiber, characterized in that, Includes the following steps: (1) Hydroxylated boron nitride nanosheets were dispersed in an organic solvent to prepare a hydroxylated boron nitride nanosheet dispersion, and a meta-aramid polymer solution was prepared. The meta-aramid polymer solution and the hydroxylated boron nitride nanosheet dispersion were thoroughly mixed to obtain a BNNs-OH / PMIA composite spinning solution. The BNNs-OH / PMIA composite spinning solution was then used to prepare a nucleated meta-aramid thermally conductive fiber using a wet spinning process. (2) Take another portion of the meta-aramid polymer solution prepared in step (1) and dilute it with an organic solvent to obtain a PMIA diluent; then add KOH solution to the PMIA diluent to obtain an aramid anion coating solution; immerse the core-type meta-aramid thermally conductive fiber obtained in step (1) in the aramid anion coating solution and the aqueous dispersion of hydroxylated boron nitride nanosheets in sequence to obtain the core-shell dual thermally conductive aramid fiber.

2. The preparation method according to claim 1, characterized in that, The meta-aramid polymer solution in step (1) is prepared by dissolving meta-aramid in an organic solvent, or by the following steps: Under a protective atmosphere, m-phenylenediamine is dissolved in an organic solvent to prepare a m-phenylenediamine solution; then, under low temperature and continuous stirring conditions, isophthaloyl chloride is added to the m-phenylenediamine solution. After the addition is complete, the stirring speed is increased, and the temperature of the reaction system is controlled within the range of 30℃ to 60℃ to carry out the polycondensation reaction. The total reaction time is 2 to 48 hours. Finally, an acid-binding agent is added to adjust the pH to obtain a meta-aramid polymer solution; the molar ratio of m-phenylenediamine to isophthaloyl chloride is (1 to 10): (1 to 10).

3. The preparation method according to claim 2, characterized in that, The stirring speed when adding isophthaloyl chloride is 100-600 rpm; after the addition is complete, the stirring speed is increased to 1000-2000 rpm. The aforementioned low temperature ranges from -20℃ to 0℃. The acid-binding agent is Ca(OH)2, and the pH adjustment is to adjust the pH to 7.0-7.

4.

4. The preparation method according to claim 1, characterized in that, The concentration of the hydroxylated boron nitride nanosheet dispersion in step (1) is 1–30 mg / g, and the organic solvent is N,N-dimethylacetamide; In step (1), the mass ratio of meta-aramid to hydroxylated boron nitride nanosheets in the BNNs-OH / PMIA composite spinning solution is (100-50):(0-50). The solid content of the BNNs-OH / PMIA composite spinning solution in step (1) is 1% to 50%.

5. The preparation method according to claim 1, characterized in that, The conditions for wet spinning in step (1) are as follows: the nozzle extrusion speed is 10-100 cm / min, the residence time in the coagulation bath is 1-500 s, the coagulation bath temperature is 20-60℃, the stretching ratio is 1.1-50 times, the heat setting temperature is 50-600℃, and the coagulation bath is a mixed solution of N,N-dimethylacetamide and water.

6. The preparation method according to claim 1, characterized in that, In step (2), the concentration of the PMIA diluent is 1–50 mg / g, the concentration of the KOH solution is 0.1–3 mol / L, and the PMIA diluent and KOH solution are mixed at a mass ratio of (10–100):(1–10). The organic solvent in step (2) is N,N-dimethylacetamide, and the concentration of the aqueous dispersion of the hydroxylated boron nitride nanosheets is 1-10 mg / g; In step (2), the immersion time of the nucleus-type thermal conductive fiber in the APA coating solution and the BNNs-OH dispersion solution is 1-20 min and 1-10 min, respectively.

7. A core-shell dual thermally conductive aramid fiber, characterized in that, It is prepared by the method described in any one of claims 1-6.

8. A thermally conductive insulating paper, characterized in that, It is prepared by the following steps: the core-shell dual thermally conductive aramid fiber as described in claim 7 is cut into short fibers, a dispersant and water are added to prepare a short fiber suspension; meta-aramid precipitating fibers are separately prepared into a precipitating fiber suspension after decomposition treatment; The chopped fiber suspension and the precipitated fiber suspension are mixed evenly in a certain proportion, and then wet papermaking, pressing and dehydration, and hot pressing are performed to obtain thermally conductive insulating paper.

9. The thermally conductive insulating paper according to claim 8, characterized in that, The length of the chopped fibers is 1–100 mm; the dispersant is polyethylene oxide; The amount of the dispersant added is 0.1% to 0.5% of the mass of the chopped fibers; The mass ratio of the chopped fibers to the meta-aramid precipitated fibers is (1-10):(1-10). The rotation speed for the de-icing process is 800–1200 rpm; The pressing and dehydration conditions are as follows: pressing and dehydration at 25℃ and 0.2MPa pressure for 5 min; The hot pressing conditions are as follows: hot pressing temperature 50-600℃, hot pressing pressure 0.01-20 MPa, and hot pressing time 0.1-48 h.

10. The application of the thermally conductive insulating paper according to claim 8 or 9 in the fields of electrical equipment, electronic information, aerospace or automotive industries.

Images