Insulating and heat-conducting aramid paper and preparation method thereof

Abstract

The application belongs to the technical field of high-performance aramid paper-based insulation and heat-conducting materials, and particularly discloses an insulation and heat-conducting aramid paper and a preparation method thereof. The method comprises the following steps: performing cold calendering treatment on meta-aramid base paper to obtain pre-calendered paper; mixing aramid resin liquid and hydroxylated boron nitride nanosheets to obtain aramid resin / hydroxylated boron nitride nanosheet dispersion liquid; placing the pre-calendered paper into the aramid resin / hydroxylated boron nitride nanosheet dispersion liquid for impregnation treatment to obtain impregnated paper; performing extrusion on the impregnated paper, then placing the impregnated paper in a proton donor solution for soaking, drying treatment, and obtaining dried paper; performing cold calendering treatment on the dried paper, then placing the dried paper in a natural environment for internal stress release, then performing cold calendering treatment again, drying, and obtaining the insulation and heat-conducting aramid paper. The application realizes triple improvement of insulation performance, mechanical performance and heat-conducting performance of aramid paper.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-performance aramid paper-based insulation and heat-conducting materials, and particularly relates to an insulation and heat-conducting aramid paper and a preparation method thereof. BACKGROUND

[0002] The meta-aramid base paper is formed by using meta-aramid short fibers and meta-aramid fibrids as raw materials and through wet papermaking; due to the chemical inertness of aramid fibers, the small amount of surface active groups and the smooth surface of the short fibers, only a small number of hydrogen bonds exist between the fibers in the meta-aramid base paper, the interfacial bonding force is weak, and the meta-aramid base paper has the disadvantages of loose structure, low strength and poor insulation.

[0003] In order to solve the above problems, the meta-aramid base paper is often treated by a hot pressing process in production; during the hot pressing process, the fibrids absorb heat and reach the glass transition temperature to partially melt, fill in the pores of the base paper under pressure and produce a bonding effect, so that the aramid fibers are tightly combined with each other, and finally the aramid paper with high mechanical strength and excellent insulation is obtained, which has a wide application in the fields of aerospace, rail transportation and electronic appliances.

[0004] However, in the traditional hot pressing process, the paper tightness is too high due to the high hot pressing temperature and pressure, the process is difficult to accurately control, and the paper may appear as a sheepskin in some local areas; secondly, the strength of the short fibers is also greatly damaged; therefore, the traditional hot pressing process has limited improvement on the mechanical strength and structural density of the paper; moreover, the structural characteristics of aramid fibers determine their low thermal conductivity, and under the long-term working conditions of high frequency and high voltage, a large amount of heat accumulates in the aramid paper, the temperature is too high, the breakdown risk of the aramid paper under high-frequency voltage is significantly increased, and the service life of the paper is also reduced under high-temperature conditions; therefore, the development of a new aramid paper preparation process has great significance for the development of high-performance aramid paper-based insulation and heat-conducting materials. SUMMARY

[0005] In view of the technical problems existing in the prior art, the application provides an insulation and heat-conducting aramid paper and a preparation method thereof, so as to solve the technical problems that the traditional hot pressing process has limited improvement on the mechanical strength and structural density of the paper, and the thermal conductivity is low.

[0006] To achieve the above-mentioned purposes, the technical scheme adopted by the application is as follows:

[0007] The application provides a preparation method of an insulation and heat-conducting aramid paper, which comprises the following steps:

[0008] The meta-aramid base paper is subjected to cold calendering treatment to obtain a pre-calendered paper;

[0009] mixing aramid resin liquid with hydroxylated boron nitride nanosheet to obtain aramid resin / hydroxylated boron nitride nanosheet dispersion liquid;

[0010] putting the pre-calendered paper into the aramid resin / hydroxylated boron nitride nanosheet dispersion liquid for impregnation treatment to obtain impregnated paper;

[0011] squeezing the impregnated paper, then soaking it in a proton donor solution, drying to obtain dried paper;

[0012] cold calendering the dried paper, then placing it in a natural environment for internal stress release, then cold calendering again, drying to obtain the insulating and heat-conducting aramid paper.

[0013] Further, the process of cold calendering the meta-aramid base paper to obtain the pre-calendered paper is as follows:

[0014] using a double-zone soft roll cold calendering device to cold calender the meta-aramid base paper at different pressure gradients to obtain the pre-calendered paper; wherein in the double-zone soft roll cold calendering device, the first pressure zone pre-calendering speed is 0.2-2.0 m / min, the first pressure zone pre-calendering pressure is 0.5-5 MPa, the second pressure zone pre-calendering speed is 0.2-2.0 m / min, and the second pressure zone pre-calendering pressure is 5-12 MPa.

[0015] Further, in the aramid resin / hydroxylated boron nitride nanosheet dispersion liquid, the addition amount of the hydroxylated boron nitride nanosheet is 5-30 wt%, and the rest is the aramid resin liquid; wherein the aramid resin liquid is prepared by using meta-aramid fibrid, LiCl and DMAc, and the solid content of the aramid resin liquid is 2-10 wt%.

[0016] Further, the process of squeezing the impregnated paper is as follows:

[0017] using a squeezing roll to squeeze the impregnated paper to squeeze out excess aramid resin / hydroxylated boron nitride nanosheet dispersion liquid; wherein the squeezing roll speed is 0.5-3.0 m / min, and the pressure is 0.1-0.8 MPa.

[0018] Further, the proton donor solution is prepared by mixing a proton donor with deionized water at a volume ratio of 1:(1-8); wherein the proton donor is one of formic acid, methanol and anhydrous ethanol.

[0019] Further, the impregnated paper is extruded, then soaked in a quality donor solution, dried to obtain the dried paper, wherein the drying temperature is 60-100 DEG C, and the drying time is 1-5 min.

[0020] Further, the dried paper is treated by soft roll cold calendering equipment, wherein the speed of the soft roll cold calendering is 3.0-8.0 m / min, and the pressure is 15-21 MPa.

[0021] Further, when the soft roll cold calendering equipment is used for the second time, the speed of the cold calendering is 1.0-4.0 m / min, and the pressure is 8-15 MPa.

[0022] Further, the dried paper is treated by cold calendering, then placed in a natural environment for internal stress release, then treated by cold calendering again, dried to obtain the insulating and heat-conducting aramid paper, wherein the drying temperature is 100-120 DEG C, and the time is 4-10 min.

[0023] The application further provides an insulating and heat-conducting aramid paper prepared by the preparation method.

[0024] Compared with the prior art, the application has the following beneficial effects:

[0025] The application provides an insulating and heat-conducting aramid paper and a preparation method thereof. A large number of hydrogen bonds are generated after aramid resin liquid is mixed with hydroxylated boron nitride nanosheets, so that the aramid resin liquid uniformly and tightly coats the well-dispersed hydroxylated boron nitride nanosheets and forms a bridge between inorganic particles. Then, the aramid resin in the aramid resin / hydroxylated boron nitride nanosheet dispersion liquid is fully penetrated and reduced in situ on the surface and inside of the pre-pressed and polished paper by the impregnation method, and physical entanglement and hydrogen bond action are formed between the aramid fibers, thereby forming a dense structure. Meanwhile, since the hydroxylated boron nitride nanosheets are coated in the aramid resin, the hydroxylated boron nitride nanosheets will also fully penetrate into the surface structure of the paper along with the flow of the aramid resin, and tightly combine with the fibers on the surface and inside of the paper, thereby forming a good heat-conducting network in the surface and inside structure of the paper. The soft roll cold calendering technology is further used to realize the compaction of the paper in the longitudinal direction, so that more heat-conducting paths are formed between the hydroxylated boron nitride nanosheet particles, the aramid resin acts as an adhesive to increase the interfacial combination of the hydroxylated boron nitride nanosheet and the aramid fiber, and after protonation reduction and secondary soft roll cold pressing, more hydrogen bond combinations are generated between the hydroxylated boron nitride nanosheet and the fiber, thereby forming a dense'reinforced concrete' structure, and realizing the triple improvement of the insulating performance, mechanical performance and heat-conducting performance of the aramid paper. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a surface scanning electron micrograph of meta-aramid base paper;

[0027] Figure 2 It is a surface scanning electron micrograph of the insulating and heat-conducting aramid paper prepared in Example 2;

[0028] Figure 3 It is a comparison diagram of tensile strengths of the insulating and heat-conducting aramid paper prepared in Example 2 and the meta-aramid base paper;

[0029] Figure 4 It is a comparison diagram of breakdown strengths of the insulating and heat-conducting aramid paper prepared in Example 2 and the meta-aramid base paper;

[0030] Figure 5 It is a comparison diagram of heat-conducting coefficients of the insulating and heat-conducting aramid paper prepared in Example 2 and the meta-aramid base paper. DETAILED DESCRIPTION

[0031] In order to make the technical problems solved by the application, the technical solutions and beneficial effects clearer, the following specific embodiments are used to further illustrate the application. It should be understood that the specific embodiments described herein are only used to explain the application, and are not used to limit the application.

[0032] The application provides a preparation method of an insulating and heat-conducting aramid paper, which comprises the following steps:

[0033] Step 1, the meta-aramid fibrid and the meta-aramid short-cut fiber are placed in a fiber defibrator, and a polyethylene oxide solution with a mass concentration of 0.03-0.06% is added as a dispersant, and then defibrated at 10000-20000r to obtain a pulp dispersion; the pulp dispersion is poured into a paper sheet former to filter and form, dried to obtain a meta-aramid base paper; wherein the dry mass ratio of the meta-aramid fibrid to the meta-aramid short-cut fiber is (1-4):1, and the addition amount of the polyethylene oxide solution is 0.1-0.5% of the dry mass of the meta-aramid short-cut fiber; the drying temperature is 100-120°C, and the time is 5-10min; the basis weight of the meta-aramid base paper is 40-90g / m 2 .

[0034] Step 2, the meta-aramid base paper is treated by double-pressure zone soft roll cold pressing with different pressure gradients using a double-zone soft roll cold pressing device to obtain a pre-calendered paper; wherein in the double-zone soft roll cold pressing device, the first pressure zone pre-calendering speed is 0.2-2.0m / min, the first pressure zone pre-calendering pressure is 0.5-5MPa, the second pressure zone pre-calendering speed is 0.2-2.0m / min, and the second pressure zone pre-calendering pressure is 5-12MPa.

[0035] Step 3, LiCl is added to DMAc, stirred for 10-30min, then meta-aramid fibrid is added, and magnetic stirring is carried out for 2-8h, the magnetic stirring speed is 500-800r / min, finally the aramid resin solution with a solid content of 2-10wt% is obtained; boron nitride nanosheet (BNNS) is mixed with H2O2 solution with a mass concentration of 30%-50% according to a solid-liquid ratio of 0.1-0.5g / ml, then placed in a reaction kettle for mechanical stirring for 20-24h to obtain a pre-reaction mixture; wherein the mechanical stirring speed is 700-900r / min; then the pre-reaction mixture is subjected to a heating reaction, the heating reaction temperature is 100-130°C, the heating reaction time is 24-28h, after the reaction kettle is cooled to room temperature, centrifugal washing with deionized water is carried out, and vacuum drying is carried out to obtain hydroxylated boron nitride nanosheet.

[0036] Step 4, the aramid resin solution and the hydroxylated boron nitride nanosheet are mixed to obtain an aramid resin / hydroxylated boron nitride nanosheet dispersion liquid for impregnation treatment of the pre-calendered paper; wherein in the aramid resin / hydroxylated boron nitride nanosheet dispersion liquid, the addition amount of the hydroxylated boron nitride nanosheet is 5-30wt%, and the rest is the aramid resin solution.

[0037] Step 5, the pre-pressed paper is put into the aramid resin / hydroxylated boron nitride nanosheet dispersion solution for impregnation treatment to obtain impregnated paper; then, the impregnated paper is extruded by an extrusion roller to extrude the excess aramid resin / hydroxylated boron nitride nanosheet dispersion solution, and the dispersion solution is further uniformly distributed in the paper by the extrusion effect to obtain extruded paper; wherein the extrusion roller speed is 0.5-3.0 m / min, and the pressure is 0.1-0.8 MPa.

[0038] Step 6, the proton donor is mixed with deionized water in a volume ratio of 1:(1-8) to obtain a proton donor solution; then, the extruded paper is soaked in the proton donor solution, dried to obtain dried paper; wherein the proton donor is one of formic acid, methanol and anhydrous ethanol; the drying temperature is 60-100℃, and the drying time is 1-5 min.

[0039] Step 7, the dried paper is cold calendered by a soft roller cold calendering equipment to obtain once cold calendered aramid paper; wherein the soft roller cold calendering speed is 3.0-8.0 m / min, and the pressure is 15-21 MPa; then, the once cold calendered aramid paper is placed in a natural environment for internal stress release for 6-18 min, and then cold calendered again, dried to obtain the insulating and heat-conducting aramid paper; wherein the cold calendering speed is 1.0-4.0 m / min, and the pressure is 8-15 MPa during the second cold calendering; the drying temperature is 100-120℃, and the time is 4-10 min.

[0040] Preparation principle:

[0041] The preparation method of the insulating and heat-conducting aramid paper provided by the application utilizes aramid resin liquid and hydroxylated BNNS to obtain aramid resin / hydroxylated boron nitride nanosheet dispersion liquid, a large number of hydrogen bonds are generated between the aramid resin liquid and the hydroxylated BNNS in the aramid resin / hydroxylated boron nitride nanosheet dispersion liquid, the aramid resin liquid uniformly and closely coats the well-dispersed hydroxylated BNNS, and a bridge is formed between inorganic particles; then, the aramid resin in the aramid resin / hydroxylated boron nitride nanosheet dispersion liquid is fully penetrated and reduced in situ on the surface and inside of the pre-pressed and calendered paper by the impregnation method, physical entanglement and hydrogen bond action are formed between the aramid resin and the aramid fibers in the pre-pressed and calendered paper, and a dense structure is formed; at the same time, the hydroxylated BNNS is coated in the aramid resin and fully penetrates into the surface structure of the paper along with the flow of the aramid resin, tightly combines with the fibers on the surface and inside of the paper, and forms a good heat-conducting network in the surface and inside structure of the paper, and the soft roll cold calendering technology is further used to realize the compaction of the paper in the longitudinal direction, so that more heat-conducting paths are formed between the BNNS particles; in the application, the aramid resin liquid with the same homology as the aramid fibers is used to impregnate the aramid base paper, the aramid fibers are chemically swelled or partially dissolved by the polar solvent in the aramid resin liquid, the interaction between the aramid resins is weakened, the molecular chain movement is more flexible, and the aramid fibers are more easily tightly combined under the action of subsequent high pressure; at the same time, the aramid resin and the hydroxylated BNNS in the dispersion liquid also penetrate into the inside of the paper along with the solvent molecules during the impregnation process, the hydroxylated BNNS forms a heat-conducting path in the paper, the aramid resin acts as an adhesive to increase the interfacial bonding between the hydroxylated BNNS and the aramid fibers, and after protonation reduction and secondary soft roll cold pressing, the hydroxylated BNNS is tightly wrapped with the fibers to generate more hydrogen bond combinations, forming a dense “reinforced concrete” structure, and realizing the triple improvement of the insulation performance, mechanical performance and heat-conducting performance of the aramid paper; wherein the tensile strength of the insulating and heat-conducting aramid paper is 25.34-36.32 MPa, the breakdown strength is 11.02-18.07 kV / mm, and the heat-conducting coefficient is 0.08-0.14 W / (m·K), which provides a new idea for the preparation of high-performance aramid paper.

[0042] Example 1

[0043] The example 1 provides a preparation method of insulating and heat-conducting aramid paper, which comprises the following steps:

[0044] Step 1, meta-aramid fibrid and meta-aramid short-cut fiber are added into a fiber defibrator in a ratio of 2:1 by dry mass, and a polyethylene oxide solution with a mass concentration of 0.04% is added as a dispersant, and then defibrated at 12000r to obtain a pulp dispersion; the pulp dispersion is poured into a paper sheet former, uniformly pulped, dewatered, formed, pressed, and vacuum dried at 103°C for 6min to obtain a meta-aramid base paper; wherein the addition amount of the polyethylene oxide solution is 0.4% of the dry mass of the meta-aramid short-cut fiber; the basis weight of the meta-aramid base paper is 60g / m 2 .

[0045] Step 2, a double-zone soft roll cold pressing device is used to perform double-pressing-zone soft roll cold calendering treatment on the meta-aramid base paper at different pressure gradients to obtain a pre-calendered paper; wherein in the double-zone soft roll cold pressing device, the pre-calendering speed of the first pressing zone at room temperature is 1.5m / min, and the pre-calendering pressure of the first pressing zone is 0.5MPa; the pre-calendering speed of the second pressing zone at room temperature is 1.5m / min, and the pre-calendering pressure of the second pressing zone is 6MPa.

[0046] Step 3, 0.68g of LiCl is added to 200g of DMAc, stirred for 12min, and then 4.09g of meta-aramid fibrid by dry mass is added, and magnetically stirred for 3h at a stirring speed of 700r / min, to finally obtain an aramid resin solution with a solid content of 3wt%; boron nitride nanosheets (BNNS) are mixed with a H2O2 solution with a mass concentration of 40% at a solid-liquid ratio of 0.12g / ml, and then placed in a reaction kettle for mechanical stirring for 21h to obtain a pre-reaction mixture; wherein the mechanical stirring speed is 720r / min; then, the pre-reaction mixture is subjected to a heating reaction at a heating reaction temperature of 108°C for a heating reaction time of 25h, and after the reaction kettle is cooled to room temperature, centrifugal washing is performed with deionized water, and vacuum drying is performed to obtain hydroxylated boron nitride nanosheets.

[0047] Step 4, the aramid resin solution and the hydroxylated boron nitride nanosheets are mixed to obtain an aramid resin / hydroxylated boron nitride nanosheet dispersion solution for impregnation treatment of the pre-calendered paper; wherein in the aramid resin / hydroxylated boron nitride nanosheet dispersion solution, the addition amount of the hydroxylated boron nitride nanosheets is 5wt%, and the rest is the aramid resin solution.

[0048] Step 5, the pre-pressed paper is put into the aramid resin / hydroxylated boron nitride nanosheet dispersion solution for impregnation treatment to obtain an impregnated paper; then, the impregnated paper is extruded by an extrusion roller to extrude the excess aramid resin / hydroxylated boron nitride nanosheet dispersion solution, and the dispersion solution is further uniformly distributed in the paper by the extrusion effect, to obtain an extruded paper; wherein the extrusion roller speed is 3.0 m / min, and the pressure is 0.3 MPa.

[0049] Step 6, formic acid and deionized water are mixed in a volume ratio of 1:8 to obtain a proton donor solution; then, the extruded paper is soaked in the proton donor solution to realize solvent exchange and protonation reduction, to obtain a soaked paper; the soaked paper is placed in a sheet former and dried at 60℃ for 3 min, to obtain a dried paper.

[0050] Step 7, the dried paper is cold calendered by a soft roller cold calendering device to obtain an aramid paper after first cold calendering; wherein the soft roller cold calendering speed is 8.0 m / min, and the pressure is 20 MPa; then, the aramid paper after first cold calendering is placed in a natural environment for internal stress release for 10 min, and then cold calendered again; then, the aramid paper is dried in a sheet former at 120℃ for 5 min, to obtain the insulating and heat-conducting aramid paper; wherein the cold calendering speed is 2.2 m / min, and the pressure is 8 MPa during the second cold calendering.

[0051] Performance detection results:

[0052] The mechanical properties, insulation properties and heat conduction properties of the insulating and heat-conducting aramid paper prepared in this embodiment 1 are detected, and the detection results show that the tensile strength of the insulating and heat-conducting aramid paper is 25.34 MPa, the breakdown strength is 11.02 kV / mm, and the thermal conductivity is 0.08 W / (m·K).

[0053] Embodiment 2

[0054] This embodiment 2 provides a preparation method of an insulating and heat-conducting aramid paper, comprising the following steps:

[0055] Step 1, meta-aramid fibrid and meta-aramid short-cut fiber are added into a fiber defibrator in a ratio of 1.5:1 by dry mass, and a polyethylene oxide solution with a mass concentration of 0.05% is added as a dispersant, and then defibrated at 15000r to obtain a pulp dispersion; the pulp dispersion is poured into a paper sheet former, and after uniform pulp, dehydration, shaping, pressing, and vacuum drying at 106°C for 7min, a meta-aramid base paper is obtained; wherein the addition amount of the polyethylene oxide solution is 0.2% of the dry mass of the meta-aramid short-cut fiber; the basis weight of the meta-aramid base paper is 70g / m 2 .

[0056] Step 2, a double-zone soft roll cold pressing device is used to perform double-pressure zone soft roll cold calendering treatment on the meta-aramid base paper at different pressure gradients to obtain a pre-calendered paper; wherein in the double-zone soft roll cold pressing device, the first pressure zone pre-calendering speed at room temperature is 0.2m / min, and the first pressure zone pre-calendering pressure is 0.5MPa; the second pressure zone pre-calendering speed at room temperature is 0.2m / min, and the second pressure zone pre-calendering pressure is 12MPa.

[0057] Step 3, 1.76g of LiCl is added to 200g of DMAc, stirred for 20min, and then 8.84g of meta-aramid fibrid by dry mass is added, and magnetic stirring is performed for 3.5h at a stirring speed of 600r / min, to finally obtain an aramid resin solution with a solid content of 5wt%; boron nitride nanosheets (BNNS) are mixed with a H2O2 solution with a mass concentration of 48% in a solid-liquid ratio of 0.12g / ml, and then placed in a reaction kettle for mechanical stirring for 23h to obtain a pre-reaction mixture; wherein the mechanical stirring speed is 780r / min; then, the pre-reaction mixture is subjected to a heating reaction at a heating reaction temperature of 116°C for a heating reaction time of 27h, and after the reaction kettle is cooled to room temperature, centrifugal washing is performed with deionized water, and vacuum drying is performed to obtain hydroxylated boron nitride nanosheets.

[0058] Step 4, the aramid resin solution and the hydroxylated boron nitride nanosheets are mixed to obtain an aramid resin / hydroxylated boron nitride nanosheet dispersion solution for impregnation treatment of the pre-calendered paper; wherein in the aramid resin / hydroxylated boron nitride nanosheet dispersion solution, the addition amount of the hydroxylated boron nitride nanosheets is 25wt%, and the rest is the aramid resin solution.

[0059] Step 5, the pre-pressed paper is put into the aramid resin / hydroxylated boron nitride nanosheet dispersion solution for impregnation treatment to obtain an impregnated paper; then, the impregnated paper is extruded by an extrusion roller to extrude the excess aramid resin / hydroxylated boron nitride nanosheet dispersion solution, and the dispersion solution is further uniformly distributed in the paper by the extrusion effect, to obtain an extruded paper; wherein the extrusion roller speed is 2.8 m / min, and the pressure is 0.8 MPa.

[0060] Step 6, methanol and deionized water are mixed in a volume ratio of 1:1 to obtain a proton donor solution; then, the extruded paper is soaked in the proton donor solution to realize solvent exchange and protonation reduction, to obtain a soaked paper; the soaked paper is placed in a sheet former and dried at 80℃ for 1 min to obtain a dried paper.

[0061] Step 7, the dried paper is cold calendered by a soft roller cold calendering device to obtain an aramid paper after first cold calendering; wherein the soft roller cold calendering speed is 3.0 m / min, and the pressure is 21 MPa; then, the aramid paper after first cold calendering is placed in a natural environment for internal stress release for 13 min, and then cold calendered again, and then dried in a sheet former at 110℃ for 4 min to obtain the insulating and heat-conducting aramid paper; wherein the cold calendering speed is 1.0 m / min, and the pressure is 15 MPa during the second cold calendering.

[0062] Performance detection results:

[0063] The mechanical properties, insulation properties and heat conduction properties of the insulating and heat-conducting aramid paper prepared in this embodiment 2 are detected, and the detection results show that the tensile strength of the insulating and heat-conducting aramid paper is 36.32 MPa, the breakdown strength is 18.07 kV / mm, and the thermal conductivity is 0.14 W / (m·K).

[0064] Embodiment 3

[0065] This embodiment 3 provides a preparation method of an insulating and heat-conducting aramid paper, comprising the following steps:

[0066] Step 1, para-aramid fibrid fibers and para-aramid short-cut fibers are added into a fiber defibrator in a ratio of 1:1 by absolute dry mass, and a polyethylene oxide solution with a mass concentration of 0.06% is added as a dispersant, and then defibrated at 18000r to obtain a pulp dispersion; pour the pulp dispersion into a paper sheet former, uniformly pulp, dewater, form, press, and vacuum dry at 105°C for 6min to obtain para-aramid base paper; wherein the addition amount of the polyethylene oxide solution is 0.4% of the absolute dry mass of the para-aramid short-cut fibers; the basis weight of the para-aramid base paper is 55g / m 2 .

[0067] Step 2, a double-zone soft roll cold pressing device is used to perform double-pressure-zone soft roll cold calendering treatment on the para-aramid base paper at different pressure gradients to obtain pre-calendered paper; wherein in the double-zone soft roll cold pressing device, the pre-calendering speed of the first pressure zone at room temperature is 2.0m / min, and the pre-calendering pressure of the first pressure zone is 1.2MPa; the pre-calendering speed of the second pressure zone at room temperature is 2.0m / min, and the pre-calendering pressure of the second pressure zone is 5MPa.

[0068] Step 3, 3.77g of LiCl is added to 200g of DMAc, stirred for 25min, and then 22.64g of para-aramid fibrid fibers by absolute dry mass are added, and magnetic stirring is performed at a stirring speed of 600r / min for 3.5h to obtain an aramid resin solution with a solid content of 10wt%; boron nitride nanosheets (BNNS) are mixed with a H2O2 solution with a mass concentration of 32% in a solid-liquid ratio of 0.17g / ml, and then placed in a reaction kettle for mechanical stirring for 24h to obtain a pre-reaction mixture; wherein the mechanical stirring speed is 840r / min; then, the pre-reaction mixture is subjected to a heating reaction, the heating reaction temperature is 112°C, the heating reaction time is 26h, after the reaction kettle is cooled to room temperature, centrifugal washing is performed with deionized water, and vacuum drying is performed to obtain hydroxylated boron nitride nanosheets.

[0069] Step 4, the aramid resin solution and the hydroxylated boron nitride nanosheets are mixed to obtain an aramid resin / hydroxylated boron nitride nanosheet dispersion solution for impregnation treatment of the pre-calendered paper; wherein in the aramid resin / hydroxylated boron nitride nanosheet dispersion solution, the addition amount of the hydroxylated boron nitride nanosheets is 30wt%, and the rest is the aramid resin solution.

[0070] Step 5: The pre-calendered paper is immersed in the aramid resin / hydroxylated boron nitride nanosheet dispersion for impregnation treatment to obtain impregnated paper; then, the impregnated paper is squeezed by a squeeze roller to squeeze out excess aramid resin / hydroxylated boron nitride nanosheet dispersion, and the dispersion is further evenly distributed in the paper by the squeezing action to obtain squeezed paper; wherein, the speed of the squeeze roller is 0.7m / min and the pressure is 0.1MPa.

[0071] Step 6: Mix anhydrous ethanol and deionized water at a volume ratio of 1:6 to obtain a proton donor solution; then, immerse the squeezed paper in the proton donor solution to achieve solvent exchange and protonation reduction, and obtain the soaked paper; place the soaked paper in a paper machine and dry it at 100°C for 5 minutes to obtain the dried paper.

[0072] Step 7: Using a soft roller cold calendering device, the dried paper is subjected to cold calendering treatment to obtain aramid paper after one cold calendering treatment; wherein, the soft roller cold calendering speed is 7.3m / min and the pressure is 15MPa; then, the aramid paper after the first cold calendering treatment is placed in a natural environment to release internal stress for 7min, and then subjected to cold calendering treatment again, and then dried in a sheeter at 100℃ for 10min to obtain the insulating and thermally conductive aramid paper; wherein, during the second cold calendering treatment, the cold calendering speed is 4.0m / min and the pressure is 9MPa.

[0073] Performance test results:

[0074] The mechanical properties, insulation properties, and thermal conductivity of the insulating and thermally conductive aramid paper prepared in Example 3 were tested. The test results showed that the tensile strength of the insulating and thermally conductive aramid paper was 30.56 MPa, the breakdown strength was 15.86 kV / mm, and the thermal conductivity was 0.10 W / (m·K).

[0075] As attached Figures 1-2 As shown, attached Figure 1 The image shows a scanning electron microscope (SEM) image of the surface of the meta-aramid base paper, with attached... Figure 2 The attached image shows a scanning electron microscope (SEM) image of the surface of the insulating and thermally conductive aramid paper prepared in Example 2; from the attached image... Figures 1-2It can be seen that the meta-aramid base paper structure is relatively loose, and has obvious pore structure; after impregnation and cold pressing light treatment of aramid resin / hydroxylated BNNS dispersion liquid, the pores are filled with aramid polymer and BNNS particles, the fibers are tightly combined, and the paper structure is obviously densified, and obvious convex structure can be observed on the surface of the paper, which indicates that BNNS and aramid fibers form good combination and no powder falling phenomenon occurs; therefore, impregnation of dispersion liquid combined with cold pressing light treatment can improve the problems of loose and porous aramid base paper, poor bonding force between inorganic particles and fibers, improve the densification of the paper, and finally improve the mechanical properties, insulation performance and thermal conductivity of the aramid base paper.

[0076] As shown in FIG. 1, the tensile strength of the meta-aramid base paper is 2.48 MPa, and the tensile strength of the aramid paper prepared in Example 2 is 36.32 MPa, which is 14.7 times that of the meta-aramid base paper. Figures 3-5 As shown in FIG. 2, the breakdown strength of the meta-aramid base paper is 8.07 kV / mm, and the breakdown strength of the aramid paper prepared in Example 2 is 18.07 kV / mm, which is 2.2 times that of the meta-aramid base paper. Figure 3 As shown in FIG. 3, the thermal conductivity of the meta-aramid base paper is 0.04 W / (m·K), and the thermal conductivity of the aramid paper prepared in Example 2 is 0.14 W / (m·K), which is 3.5 times that of the meta-aramid base paper. Figure 4 As shown in FIG. 4, the tensile strength of the meta-aramid base paper is 2.48 MPa, and the tensile strength of the aramid paper prepared in Example 2 is 36.32 MPa, which is 14.7 times that of the meta-aramid base paper. Figure 5 As shown in FIG. 5, the breakdown strength of the meta-aramid base paper is 8.07 kV / mm, and the breakdown strength of the aramid paper prepared in Example 2 is 18.07 kV / mm, which is 2.2 times that of the meta-aramid base paper. Figures 3-5 As shown in FIG. 6, the thermal conductivity of the meta-aramid base paper is 0.04 W / (m·K), and the thermal conductivity of the aramid paper prepared in Example 2 is 0.14 W / (m·K), which is 3.5 times that of the meta-aramid base paper.

[0077] The insulating and heat-conducting aramid paper and the preparation method thereof, aramid resin liquid of the same origin as aramid fiber is used to impregnate hydroxylated BNNS on the aramid paper, the polar solvent in the resin liquid causes chemical swelling or partial dissolution of the aramid fiber, the interaction between the aramid polymers is weakened, the molecular chain movement is more flexible, and the aramid fibers are more easily combined under the subsequent high pressure; at the same time, the polymers and BNNS in the dispersion liquid also penetrate into the paper with the solvent molecules during the impregnation process, the BNNS forms a heat-conducting path in the paper, and the aramid polymer acts as an adhesive to increase the interfacial bonding between the BNNS and the aramid fiber. After protonation reduction and secondary soft roll cold pressing, the BNNS is tightly wrapped with the fiber to produce more hydrogen bond combinations, forming a dense'reinforced concrete' structure, realizing the triple improvement of the insulation performance, mechanical property and heat-conducting property of the aramid paper, and providing a new idea for the preparation of the aramid paper.

[0078] The above examples are only one of the implementation manners of the technical scheme of the present application, and the scope of protection claimed by the present application is not limited to the above examples, but also includes any changes, substitutions and other implementation manners easily thought of by those skilled in the art within the technical scope disclosed by the present application.

Claims

1. A method for preparing an insulating and thermally conductive aramid paper, characterized in that, include: Meta-aramid base paper is subjected to cold calendering to obtain pre-calendered paper; Aramid resin solution was mixed with hydroxylated boron nitride nanosheets to obtain an aramid resin / hydroxylated boron nitride nanosheet dispersion. The pre-calendered paper is immersed in the aramid resin / hydroxylated boron nitride nanosheet dispersion for impregnation treatment to obtain impregnated paper. The impregnated paper is squeezed, then immersed in a proton donor solution and dried to obtain dried paper. The dried paper is subjected to cold calendering, then placed in a natural environment to release internal stress, followed by cold calendering again and drying to obtain the insulating and thermally conductive aramid paper. Boron nitride nanosheets (BNNS) were mixed with a 30%-50% H2O2 solution at a solid-liquid ratio of 0.1-0.5 g / ml, and then placed in a reaction vessel and mechanically stirred for 20-24 h to obtain a pre-reaction mixture; wherein the mechanical stirring speed was 700-900 r / min; then, the pre-reaction mixture was heated to a temperature of 100-130℃ for 24-28 h. After the reaction vessel cooled to room temperature, the mixture was washed with deionized water by centrifugation and vacuum dried to obtain hydroxylated boron nitride nanosheets; The process of cold-calendering meta-aramid base paper to obtain pre-calendered paper is as follows: A dual-zone soft roll cold pressing device is used to perform dual-zone soft roll cold pressing calendering treatment with different pressure gradients on meta-aramid base paper to obtain pre-calendered paper; wherein, in the dual-zone soft roll cold pressing device, the pre-calendering speed of the first zone is 0.2-2.0 m / min, the pre-calendering pressure of the first zone is 0.5-5 MPa, the pre-calendering speed of the second zone is 0.2-2.0 m / min, and the pre-calendering pressure of the second zone is 5-12 MPa.

2. The method for preparing an insulating and thermally conductive aramid paper according to claim 1, characterized in that, In the aramid resin / hydroxylated boron nitride nanosheet dispersion, the amount of hydroxylated boron nitride nanosheets added is 5-30 wt%, and the remainder is the aramid resin liquid; wherein, the aramid resin liquid is prepared by meta-aramid precipitated fibers, LiCl and DMAc, and the solid content of the aramid resin liquid is 2-10 wt%.

3. The method for preparing an insulating and thermally conductive aramid paper according to claim 1, characterized in that, The process of squeezing the impregnated paper is as follows: The impregnated paper is squeezed using a squeeze roller to squeeze out excess aramid resin / hydroxylated boron nitride nanosheet dispersion; wherein the squeeze roller speed is 0.5-3.0 m / min and the pressure is 0.1-0.8 MPa.

4. The method for preparing an insulating and thermally conductive aramid paper according to claim 1, characterized in that, The proton donor solution is prepared by mixing a proton donor with deionized water in a volume ratio of 1:(1-8); wherein the proton donor is one of formic acid, methanol and anhydrous ethanol.

5. The method for preparing an insulating and thermally conductive aramid paper according to claim 1, characterized in that, The impregnated paper is squeezed, then immersed in a proton donor solution, and dried to obtain the dried paper. During the process, the drying temperature is 60-100℃ and the drying time is 1-5 minutes.

6. The method for preparing an insulating and thermally conductive aramid paper according to claim 1, characterized in that, The dried paper is subjected to cold calendering using a soft roller calendering device; the cold calendering speed is 3.0-8.0 m / min and the pressure is 15-21 MPa.

7. The method for preparing an insulating and thermally conductive aramid paper according to claim 1, characterized in that, When using a soft roller cold calendering machine for a second cold calendering process, the cold calendering speed is 1.0-4.0 m / min and the pressure is 8-15 MPa.

8. The method for preparing an insulating and thermally conductive aramid paper according to claim 1, characterized in that, The dried paper is subjected to cold calendering, then placed in a natural environment to release internal stress, followed by cold calendering again and drying. In the process of obtaining the insulating and thermally conductive aramid paper, the drying temperature is 100-120℃ and the time is 4-10min.

9. An insulating and thermally conductive aramid paper, characterized in that, The insulating and thermally conductive aramid paper is prepared using the preparation method described in any one of claims 1-8; wherein the insulating and thermally conductive aramid paper has a tensile strength of 25.34-36.32 MPa, a breakdown strength of 11.02-18.07 kV / mm, and a thermal conductivity of 0.08-0.14 W / (m·K).

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