Aramid-based heat-generating paper and a method for preparing the same

Abstract

The present application relates to synthetic fiber paper manufacturing technology field, specifically relates to a kind of aramid-based heating paper and its preparation method, the preparation method is: the para-aramid short-cut fiber and potassium hydroxide are added to dimethyl sulfoxide, then add water, stirring dispersion obtains nanofiber dispersion liquid;Carbon fiber, aramid short-cut fiber are added to nanofiber dispersion liquid and are defibered, are uniformly mixed to obtain short-cut fiber dispersion liquid;M-aramid polymerization liquid, nanofiber dispersion liquid, sedimentation agent are added to sedimentation equipment, high-speed shearing obtains sedimentation fiber, again cooling forming in water washing pool, multistage washing obtains m-aramid sedimentation fiber;Short-cut fiber dispersion liquid, m-aramid sedimentation fiber are uniformly mixed, then pass through wet papermaking, press drying, hot-pressing treatment obtains aramid-based heating paper.The preparation method in the carbon fiber, aramid short-cut fiber can be well dispersed, and the aramid-based heating paper prepared has higher evenness, better mechanical properties and heating performance.

Description

Technical Field

[0001] This invention relates to an aramid-based heating paper and its preparation method, belonging to the field of synthetic fiber paper manufacturing technology. Background Technology

[0002] Carbon fiber is an inert fiber material with high tensile strength, light weight, high temperature resistance, good electrical conductivity, and corrosion resistance. Its carbon content exceeds 95%, and the tightly packed, orderly arranged graphite layers on its surface result in a smooth surface free of functional groups. Currently, the production and processing of carbon paper mainly relies on wet forming, that is, dispersing carbon fibers in an aqueous dispersant, followed by chemical compounding and high-temperature treatment to obtain carbon paper. During the dispersion process, the carbon fibers are prone to aggregation and clumping, leading to uneven dispersion. Consequently, the prepared carbon fiber heating paper exhibits uneven temperature distribution, and localized overheating can pose significant safety hazards.

[0003] Currently, carbon fiber dispersion methods are divided into physical modification and chemical modification. Physical modification includes ultrasonic dispersion and the addition of dispersants (e.g., the methods disclosed in Chinese patent applications CN117661374A and CN113293640A); chemical modification includes polydopamine modification and adipic acid modification. However, these methods are generally cumbersome, have high chemical synthesis costs, and the chemical treatment can damage the carbon fiber to some extent, affecting its performance.

[0004] In addition, the fibers used in existing technologies generally have low temperature resistance and are mostly used in low-temperature heating fields. Their operating temperature is generally below 80°C, which cannot meet the needs of high-temperature heating fields.

[0005] Therefore, developing a heating paper with uniform heating, high heating efficiency, and applicable to high-temperature heating fields, and its preparation method, is of great value. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing an aramid-based heating paper and its preparation method. In this method, carbon fibers can be well dispersed, resulting in an aramid-based heating paper with higher uniformity, better mechanical properties, and superior heating performance. Furthermore, the aramid-based heating paper exhibits excellent temperature resistance, making it suitable for high-temperature heating applications.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a method for preparing aramid-based heating paper, wherein the preparation method is as follows:

[0008] S1. Preparation of nanofiber dispersion:

[0009] Para-aramid short-cut fibers and potassium hydroxide were added to dimethyl sulfoxide, and then water was added and stirred to disperse, thus obtaining the nanofiber dispersion.

[0010] S2, Preparation of short-cut fiber dispersion and meta-aramid precipitated fibers:

[0011] Carbon fiber and aramid short-cut fibers are added to the nanofiber dispersion for dissolution and mixed evenly to obtain the short-cut fiber dispersion.

[0012] Meta-aramid polymer solution, nanofiber dispersion and precipitant are continuously and stably added to the precipitation equipment, and high-speed shearing is used to obtain precipitated fibers. Then, the fibers are cooled and shaped in a water washing tank and washed in multiple stages to obtain meta-aramid precipitated fibers.

[0013] S3. Preparation of aramid-based heating paper:

[0014] Aramid-based heating paper is obtained by dissolving and stirring the short fiber dispersion and meta-aramid precipitated fibers, followed by wet molding, pressing, drying, and hot pressing.

[0015] Furthermore, in step S1, the stirring time is 4 to 24 hours, and the storage temperature of the nanofiber dispersion is 15 to 25°C.

[0016] Furthermore, the weight ratio of para-aramid fiber, dimethyl sulfoxide, water and potassium hydroxide is (0.05-3):(80-100):(0.01-0.08):(0.15-4).

[0017] Furthermore, in step S2, when preparing the chopped fiber dispersion, the aramid chopped fiber is para-aramid chopped fiber or meta-aramid chopped fiber, and the disintegration time is 5-10 min;

[0018] The mass concentration of the aramid chopped fibers in the chopped fiber dispersion is 0.05% to 1%, and the mass concentration of the carbon fibers in the chopped fiber dispersion is 0.01% to 0.5%.

[0019] Furthermore, in step S2, when preparing the meta-aramid precipitated fiber, the temperature of the meta-aramid polymerization solution is 35-50°C, the solid content is 8%-15%, and the viscosity at 25°C is 100-450 Po.

[0020] When preparing the meta-aramid precipitated fiber, the weight ratio of the nanofiber dispersion, the precipitant and the meta-aramid polymer solution is (5-20):(5-12):(80-100).

[0021] Furthermore, in step S2, when preparing the meta-aramid precipitated fiber, the high-speed shearing speed is 3500-6000 rpm, and the high-speed shearing time is 40-90 s.

[0022] Furthermore, in step S2, when preparing the meta-aramid precipitated fiber, the precipitating agent is a mixture of the following substances in parts by weight: 5-18 parts chloride salt, 40-50 parts water, and 40-50 parts N,N-dimethylacetamide.

[0023] The chloride salt is at least one of lithium chloride, calcium chloride, and magnesium chloride.

[0024] Furthermore, in step S3, the weight ratio of short-cut fibers to meta-aramid precipitated fibers in the short-cut fiber dispersion is 5:5, and the carbon fiber in the short-cut fiber dispersion accounts for 10% to 30% of the total weight of the short-cut fibers.

[0025] Furthermore, in step S3, the hot pressing conditions are: temperature 180~220℃, vehicle speed 5~20m / min, and pressure 100~300 N / mm.

[0026] An aramid-based heating paper is provided, wherein the aramid-based heating paper is prepared according to the preparation method described in this invention, and the aramid-based heating paper can be applied in the field of high-temperature heating.

[0027] The beneficial effects of this invention are:

[0028] 1. The nanofiber dispersion is an anionic system, which is very stable and has a certain viscosity. This system can disperse aramid chopped fibers and carbon fibers and maintain a certain steady state. Even without the addition of a dispersant, the aramid chopped fibers and carbon fibers can be well dispersed and are less prone to flocculation. The resulting aramid-based heating paper has higher uniformity and better mechanical properties. The more uniform dispersion of carbon fibers in the aramid-based heating paper also makes the conductive network more uniform, resulting in higher heating efficiency and more uniform heating.

[0029] 2. Aramid fiber is a high-performance fiber material with high strength, high modulus, lightweight, folding resistance, high temperature resistance, flame retardancy, and corrosion resistance. However, it suffers from poor thermal conductivity, easy flocculation, and difficulty in dispersion. Carbon fiber has high strength, high modulus, corrosion resistance, and good thermal stability, but it has shortcomings such as low elongation at break, poor inter-fiber bonding force during composite formation, and susceptibility to brittle fracture. In this invention, during the precipitation of the nanofiber dispersion in water, para-aramid nanofibers adhere to the surfaces of aramid chopped fibers and carbon fibers, making the smooth surfaces of the aramid chopped fibers and carbon fibers rough. Therefore, the interfacial bonding strength between fibers is enhanced, the inter-fiber bonding force is greater, and stress is better transferred, improving the bonding force of the aramid-based heating paper and avoiding the problems of low tensile strength and high brittleness of aramid-based heating paper. At the same time, this invention does not sacrifice the original mechanical properties of aramid chopped fibers and carbon fibers, and better utilizes the properties of both. In addition, this method can significantly reduce the porosity of aramid-based heating paper, improve the bonding density, and thus improve the overall performance of aramid-based heating paper.

[0030] 3. Introducing para-aramid nanofibers during the preparation of meta-aramid precipitation reduces the crystallinity of the meta-aramid fibers, making them easier to melt during hot pressing, resulting in stronger inter-fiber bonding and a smoother surface. Simultaneously, it increases the density and reduces the porosity of the aramid-based heating paper, forming a more complete conductive path, lowering resistance, and increasing heating power.

[0031] 4. Compared to conventional meta-aramid precipitated fibers, the low-crystallinity meta-aramid precipitated fibers in this invention can achieve excellent melting and bonding at relatively low hot-pressing temperatures, significantly reducing production energy consumption while maintaining the good mechanical properties of aramid-based heating paper. The preparation process of this invention is simple, energy-efficient, and easy to control. Detailed Implementation

[0032] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0034] A method for preparing aramid-based heating paper, wherein the preparation method comprises:

[0035] S1. Preparation of nanofiber dispersion:

[0036] Para-aramid short-cut fibers and potassium hydroxide were added to dimethyl sulfoxide, then water was added, and the mixture was mechanically stirred to obtain the nanofiber dispersion.

[0037] S2, Preparation of short-cut fiber dispersion and meta-aramid precipitated fibers:

[0038] Carbon fiber and aramid short-cut fibers are added to the nanofiber dispersion for dissolution and mixed evenly to obtain the short-cut fiber dispersion.

[0039] Meta-aramid polymerization solution, nanofiber dispersion, and precipitant are continuously and stably added to a precipitation device. The precipitant is then sheared at high speed by the precipitation device into precipitated fibers, which are then discharged into a washing tank for further cooling and shaping. The cooled and shaped precipitated fiber mixture containing N,N-dimethylacetamide solvent is then subjected to multi-stage washing to remove the N,N-dimethylacetamide solvent, resulting in meta-aramid precipitated fibers with low crystallinity.

[0040] S3. Preparation of aramid-based heating paper:

[0041] Aramid-based heating paper is obtained by dissolving and stirring the short fiber dispersion and meta-aramid precipitated fibers, followed by wet molding, pressing, drying, and hot pressing.

[0042] Specifically, in step S1, the stirring time is 4 to 24 hours, and the storage temperature of the nanofiber dispersion is 15 to 25°C.

[0043] Specifically, the weight ratio of para-aramid fiber, dimethyl sulfoxide, water and potassium hydroxide is (0.05-3): (80-100): (0.01-0.08): (0.15-4).

[0044] Specifically, in step S2, when preparing the chopped fiber dispersion, the aramid chopped fiber is para-aramid chopped fiber or meta-aramid chopped fiber, and the disintegration time is 5-10 min;

[0045] The mass concentration of the aramid chopped fibers in the chopped fiber dispersion is 0.05% to 1%, and the mass concentration of the carbon fibers in the chopped fiber dispersion is 0.01% to 0.5%.

[0046] Specifically, in step S2, when preparing the meta-aramid precipitated fiber, the temperature of the meta-aramid polymerization solution is 35-50°C, the solid content is 8%-15%, and the viscosity at 25°C is 100-450 Po.

[0047] When preparing the meta-aramid precipitated fiber, the weight ratio of the nanofiber dispersion, the precipitant and the meta-aramid polymer solution is (5-20):(5-12):(80-100).

[0048] Specifically, in step S2, when preparing the meta-aramid precipitated fiber, the high-speed shearing speed is 3500-6000 rpm, and the high-speed shearing time is 40-90 s.

[0049] Specifically, in step S2, when preparing the meta-aramid precipitated fiber, the precipitating agent is a mixture of the following substances in parts by weight: 5-18 parts chloride salt, 40-50 parts water, and 40-50 parts N,N-dimethylacetamide.

[0050] The chloride salt is at least one of lithium chloride, calcium chloride, and magnesium chloride.

[0051] More specifically, the precipitant is stored at a temperature of 4–20°C.

[0052] Specifically, in step S3, the weight ratio of short-cut fibers to meta-aramid precipitated fibers in the short-cut fiber dispersion is 5:5, and the carbon fiber in the short-cut fiber dispersion accounts for 10% to 30% of the total weight of the short-cut fibers.

[0053] Specifically, in step S3, the hot pressing conditions are: temperature 180~220℃, vehicle speed 5~20m / min, and pressure 100~300 N / mm.

[0054] More specifically, the para-aramid chopped fibers and meta-aramid chopped fibers used in the embodiments of the present invention are produced by Taihe New Materials Group Co., Ltd., with a length of 4-8 mm and a fineness of 1.5 dtex-2.0 dtex; the carbon fibers used in the embodiments of the present invention have a length of 3 mm-6 mm and a diameter of 5-7 μm. The solvent in the meta-aramid polymerization solution used in the embodiments of the present invention is N,N-dimethylacetamide.

[0055] An aramid-based heating paper, wherein the aramid-based heating paper is prepared according to the preparation method described in this invention.

[0056] Example 1

[0057] Preparation of an aramid-based heating paper

[0058] S1, Preparation of Nanofiber Dispersion

[0059] Para-aramid chopped fibers and potassium hydroxide were added to dimethyl sulfoxide, and then water was added. The mixture was mechanically stirred for 10 hours to obtain a stable nanofiber dispersion. The weight ratio of para-aramid fibers, dimethyl sulfoxide, water and potassium hydroxide was 2:85:0.04:3. The nanofiber dispersion was stored at 20°C.

[0060] Preparation of S2, aramid short-cut fiber dispersion and meta-aramid precipitated fibers

[0061] (1) Preparation of short fiber dispersion

[0062] Carbon fiber and para-aramid chopped fibers were added to a nanofiber dispersion for dissolution. After dissolution for 8 minutes, the dispersion was stirred until homogeneous to obtain the chopped fiber dispersion. The mass concentration of para-aramid chopped fibers in the chopped fiber dispersion was 0.5%, and the mass concentration of carbon fiber in the chopped fiber dispersion was 0.2%.

[0063] (2) Preparation of meta-aramid precipitated fibers

[0064] Meta-aramid polymer solution, nanofiber dispersion and precipitant are continuously and stably added to the precipitation equipment. The precipitated fiber is obtained by high-speed shearing at 5000 rpm for 50 seconds. Then it is discharged into the washing tank for further cooling and molding. The precipitated fiber mixture containing N,N-dimethylacetamide solvent is washed through multiple stages to remove the N,N-dimethylacetamide solvent, and meta-aramid precipitated fiber with low crystallinity is obtained.

[0065] The weight ratio of the nanofiber dispersion, the precipitant, and the meta-aramid polymer solution is 10:15:90.

[0066] The temperature of the meta-aramid polymerization solution is 35℃, the solid content is 10%, and the viscosity at 25℃ is 195Po.

[0067] The precipitant, by weight, consists of 10 parts calcium chloride, 45 parts water, and 45 parts N,N-dimethylacetamide.

[0068] S3. Preparation of aramid-based heating paper

[0069] Short fiber dispersion and meta-aramid precipitated fibers are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain aramid-based heating paper.

[0070] The weight ratio of short-cut fibers to meta-aramid precipitated fibers in the short-cut fiber dispersion is 5:5, and the carbon fiber in the short-cut fiber dispersion accounts for 10% of the total weight of the short-cut fibers.

[0071] The hot pressing conditions are: temperature 200℃, vehicle speed 10m / min, and pressure 150 N / mm.

[0072] Example 2

[0073] Preparation of an aramid-based heating paper

[0074] S1, Preparation of Nanofiber Dispersion

[0075] Para-aramid chopped fibers and potassium hydroxide were added to dimethyl sulfoxide, and then water was added. The mixture was mechanically stirred for 24 hours to obtain a stable nanofiber dispersion. The weight ratio of para-aramid fibers, dimethyl sulfoxide, water and potassium hydroxide was 0.15:80:0.01:0.15. The nanofiber dispersion was stored at 15°C.

[0076] S2. Preparation of aramid short-cut fiber dispersion and meta-aramid precipitated fibers:

[0077] (1) Preparation of short fiber dispersion

[0078] Carbon fiber and para-aramid chopped fiber were added to a nanofiber dispersion for dissolution. After dissolution for 5 minutes, the dispersion was stirred evenly to obtain the chopped fiber dispersion. The mass concentration of para-aramid chopped fiber in the dispersion was 0.05%, and the mass concentration of carbon fiber in the dispersion was 0.01%.

[0079] (2) Preparation of meta-aramid precipitated fibers

[0080] Meta-aramid polymer solution, nanofiber dispersion and precipitant are continuously and stably added to the precipitation equipment. The precipitated fiber is obtained by high-speed shearing at 6000 rpm for 40 seconds. Then it is discharged into the washing tank for further cooling and molding. The precipitated fiber mixture containing N,N-dimethylacetamide solvent is washed through multiple stages to remove the N,N-dimethylacetamide solvent, and meta-aramid precipitated fiber with low crystallinity is obtained.

[0081] The weight ratio of nanofiber dispersion, precipitant, and meta-aramid polymer solution is 20:12:100.

[0082] The temperature of the meta-aramid polymerization solution is 40℃, the solid content is 8%, and the viscosity at 25℃ is 100Po.

[0083] The precipitant, by weight, consists of 5 parts lithium chloride, 45 parts water, and 50 parts N,N-dimethylacetamide.

[0084] S3. Preparation of aramid-based heating paper

[0085] Short fiber dispersion and meta-aramid precipitated fibers are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain aramid-based heating paper.

[0086] The weight ratio of short-cut fibers to meta-aramid precipitated fibers in the short-cut fiber dispersion is 5:5, and the carbon fiber in the short-cut fiber dispersion accounts for 15% of the total weight of the short-cut fibers.

[0087] The hot pressing conditions are: temperature 180℃, vehicle speed 5m / min, and pressure 100 N / mm.

[0088] Example 3

[0089] Preparation of an aramid-based heating paper:

[0090] S1, Preparation of Nanofiber Dispersion

[0091] Para-aramid chopped fibers and potassium hydroxide were added to dimethyl sulfoxide, and then water was added. The mixture was mechanically stirred for 4 hours to obtain a stable nanofiber dispersion. The weight ratio of para-aramid fibers, dimethyl sulfoxide, water and potassium hydroxide was 3:100:0.07:4. The nanofiber dispersion was stored at 25°C.

[0092] Preparation of S2, aramid short-cut fiber dispersion and meta-aramid precipitated fibers

[0093] (1) Preparation of short fiber dispersion

[0094] Carbon fibers and meta-aramid chopped fibers are added to a nanofiber dispersion for dissolution. After dissolution for 10 minutes, the dispersion is stirred evenly to obtain the chopped fiber dispersion. The mass concentration of the meta-aramid chopped fibers in the chopped fiber dispersion is 1%, and the mass concentration of the carbon fibers in the chopped fiber dispersion is 0.5%.

[0095] (2) Preparation of meta-aramid precipitated fibers

[0096] Meta-aramid polymer solution, nanofiber dispersion and precipitant are continuously and stably added to the precipitation equipment. The precipitated fiber is obtained by high-speed shearing at 3500 rpm for 90 seconds. Then it is discharged into the washing tank for further cooling and molding. The precipitated fiber mixture containing N,N-dimethylacetamide solvent is washed through multiple stages to remove the N,N-dimethylacetamide solvent, and meta-aramid precipitated fiber with low crystallinity is obtained.

[0097] The weight ratio of the nanofiber dispersion, the precipitant, and the meta-aramid polymer solution is 5:5:90.

[0098] The temperature of the meta-aramid polymerization solution is 50℃, the solid content is 15%, and the viscosity at 25℃ is 450po.

[0099] The precipitant, by weight, consists of 18 parts magnesium chloride, 40 parts water, and 42 parts N,N-dimethylacetamide.

[0100] S3. Preparation of aramid-based heating paper

[0101] Short fiber dispersion and meta-aramid precipitated fibers are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain aramid-based heating paper.

[0102] The weight ratio of short-cut fibers to meta-aramid precipitated fibers in the short-cut fiber dispersion is 5:5, and carbon fibers account for 25% of the total weight of the short-cut fibers in the short-cut fiber dispersion.

[0103] The hot pressing conditions are: temperature 220℃, vehicle speed 20m / min, and pressure 300 N / mm.

[0104] Example 4

[0105] Preparation of an aramid-based heating paper

[0106] S1, Preparation of Nanofiber Dispersion

[0107] Para-aramid chopped fibers and potassium hydroxide were added to dimethyl sulfoxide, and then water was added. The mixture was mechanically stirred for 16 hours to obtain a stable nanofiber dispersion. The weight ratio of para-aramid fibers, dimethyl sulfoxide, water and potassium hydroxide was 0.05:85:0.08:2. The nanofiber dispersion was stored at 25°C.

[0108] Preparation of S2, short-cut fiber dispersion and meta-aramid precipitated fibers

[0109] (1) Preparation of short fiber dispersion

[0110] Carbon fibers and meta-aramid chopped fibers were added to a nanofiber dispersion for dissolution. After dissolution for 6 minutes, the dispersion was stirred until homogeneous to obtain the chopped fiber dispersion. The mass concentration of the meta-aramid chopped fibers in the chopped fiber dispersion was 0.6%, and the mass concentration of the carbon fibers in the chopped fiber dispersion was 0.3%.

[0111] (2) Preparation of meta-aramid precipitated fibers

[0112] Meta-aramid polymer solution, nanofiber dispersion and precipitant are continuously and stably added to the precipitation equipment. The precipitated fiber is obtained by high-speed shearing at 5000 rpm for 50 seconds. Then it is discharged into the washing tank for further cooling and molding. The precipitated fiber mixture containing N,N-dimethylacetamide solvent is washed through multiple stages to remove the N,N-dimethylacetamide solvent, and meta-aramid precipitated fiber with low crystallinity is obtained.

[0113] The weight ratio of the nanofiber dispersion, the precipitant, and the meta-aramid polymer solution is 10:10:80.

[0114] The temperature of the meta-aramid polymerization solution is 35℃, the solid content is 12%, and the viscosity at 25℃ is 300Po.

[0115] The precipitant, by weight, consists of 15 parts calcium chloride, 43 parts water, and 42 parts N,N-dimethylacetamide.

[0116] S3. Preparation of aramid-based heating paper

[0117] Short fiber dispersion and meta-aramid precipitated fibers are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain aramid-based heating paper.

[0118] In the chopped fiber dispersion, the weight ratio of chopped fibers to meta-aramid precipitated fibers is 5:5, and the carbon fibers in the chopped fiber dispersion account for 30% of the total weight of the chopped fibers.

[0119] The hot pressing conditions are: temperature 190℃, vehicle speed 10m / min, and pressure 180 N / mm.

[0120] Comparative Example 1

[0121] Aramid-based heating paper was prepared using the same method as in Example 1, except that in step S1, the storage temperature of the nanofiber dispersion was increased. In Comparative Example 1, the storage temperature of the nanofiber dispersion was 35°C.

[0122] Comparative Example 2

[0123] Aramid-based heating paper was prepared using the same method as in Example 1, except that in step S1, the storage temperature of the nanofiber dispersion was lowered. In Comparative Example 2, the storage temperature of the nanofiber dispersion was 5°C.

[0124] Comparative Example 3

[0125] Aramid-based heating paper was prepared using the same method as in Example 1, except that in step S2, when preparing meta-aramid precipitated fibers, the proportion of nanofiber dispersion was increased. In this comparative example 3, the weight ratio of nanofiber dispersion, precipitant, and meta-aramid polymer solution was 25:10:90.

[0126] Comparative Example 4

[0127] Aramid-based heating paper was prepared using the same method as in Example 1, except that in step S2, when preparing meta-aramid precipitated fibers, the proportion of nanofiber dispersion was reduced. In this Comparative Example 4, the weight ratio of nanofiber dispersion, precipitant, and meta-aramid polymer solution was 1:10:90.

[0128] Comparative Example 5

[0129] Aramid-based heating paper was prepared using the same method as in Example 1, except that in step S2, when preparing meta-aramid precipitated fibers, the shear rate was increased. In Comparative Example 5, the shear rate in step S2 was 8000 rpm.

[0130] Comparative Example 6

[0131] Aramid-based heating paper was prepared using the same method as in Example 1, except that in step S2, when preparing meta-aramid precipitated fibers, the shear rate was reduced. In Comparative Example 6, the shear rate in step S2 was 2000 rpm.

[0132] Comparative Example 7

[0133] Using a conventional method, a nanofiber dispersion was coated onto the surface of aramid-based heating paper. The specific preparation process is as follows:

[0134] S1. Preparation of nanofiber dispersion:

[0135] Nanofiber dispersions were prepared using the same method as in Example 1;

[0136] Preparation of S2, short-cut fiber dispersion and meta-aramid precipitated fibers

[0137] (1) Preparation of short fiber dispersion

[0138] The steps are the same as in Example 1, except that no nanofiber dispersion was used in the preparation of the chopped fiber dispersion.

[0139] Carbon fiber and para-aramid chopped fiber are added to an appropriate amount of water for dissolution. After dissolution for 8 minutes, the mixture is stirred evenly to obtain the chopped fiber dispersion. The mass concentration of para-aramid chopped fiber in the chopped fiber dispersion is 0.5%, and the mass concentration of carbon fiber in the chopped fiber dispersion is 0.2%.

[0140] (2) Preparation of meta-aramid precipitated fibers

[0141] The preparation steps are the same as in Example 1, except that no nanofiber solution was added during the preparation of meta-aramid precipitated fibers. The specific steps are as follows:

[0142] The meta-aramid polymerization solution and precipitant are continuously and stably fed into the precipitation equipment. The precipitated fiber is obtained by high-speed shearing at 5000 rpm for 50 seconds. Then, it is discharged into the washing tank for further cooling and molding. The precipitated fiber mixture containing N,N-dimethylacetamide solvent is washed through multiple stages to remove the N,N-dimethylacetamide solvent, thus obtaining meta-aramid precipitated fiber.

[0143] The weight ratio of the precipitant to the meta-aramid polymerization solution is 15:90.

[0144] The temperature of the meta-aramid polymerization solution is 35℃, the solid content is 10%, and the viscosity at 25℃ is 195Po.

[0145] The precipitant, by weight, consists of 10 parts calcium chloride, 45 parts water, and 45 parts N,N-dimethylacetamide.

[0146] S3. Preparation of aramid-based heating paper

[0147] Aramid-based heating paper is obtained by dissolving and stirring aramid short-cut fiber dispersion and meta-aramid precipitated fiber, followed by wet molding, pressing and drying.

[0148] The weight ratio of short-cut fibers to meta-aramid precipitated fibers in the short-cut fiber dispersion is 5:5, and the carbon fiber in the short-cut fiber dispersion accounts for 8% of the total weight of the short-cut fibers.

[0149] S4, Coating of Nanofiber Dispersion

[0150] The nanofiber dispersion prepared in step S1 is uniformly coated on one side of the aramid-based heating paper prepared in step S3, and then washed and dried. The above operation steps are repeated on the other side of the aramid-based heating paper to control the total coating amount of nanofibers on the aramid-based heating paper to be 2 g / m². 2 Finally, the aramid-based heating paper coated with nanofibers on both sides is hot-pressed to obtain the final product. The hot-pressing conditions are: temperature 200℃, speed 10m / min, and pressure 150 N / mm.

[0151] Comparative Example 8

[0152] Aramid-based heating paper was prepared using the same method as in Example 1, except that the chopped fiber dispersion and meta-aramid precipitated fibers were prepared using conventional methods. Specifically, in Comparative Example 8, no nanofiber dispersion was used when preparing the chopped fiber dispersion, and no nanofiber solution was added during the preparation of the meta-aramid precipitated fibers.

[0153] The preparation processes of the short-cut fiber dispersion and meta-aramid precipitated fibers in this comparative example are as follows:

[0154] (1) Preparation of short fiber dispersion

[0155] Carbon fiber and para-aramid chopped fiber are added to an appropriate amount of water for dissolution. After dissolution for 8 minutes, the mixture is stirred evenly to obtain the chopped fiber dispersion. The mass concentration of para-aramid chopped fiber in the chopped fiber dispersion is 0.5%, and the mass concentration of carbon fiber in the chopped fiber dispersion is 0.2%.

[0156] (2) Preparation of meta-aramid precipitated fibers

[0157] The meta-aramid polymerization solution and precipitant are continuously and stably fed into the precipitation equipment. The precipitated fiber is obtained by high-speed shearing at 5000 rpm for 50 seconds. Then, it is discharged into the washing tank for further cooling and molding. The precipitated fiber mixture containing N,N-dimethylacetamide solvent is washed through multiple stages to remove the N,N-dimethylacetamide solvent, thus obtaining meta-aramid precipitated fiber.

[0158] The weight ratio of the precipitant to the meta-aramid polymerization solution is 15:90.

[0159] The temperature of the meta-aramid polymerization solution is 35℃, the solid content is 10%, and the viscosity at 25℃ is 195Po.

[0160] The precipitant, by weight, consists of 10 parts calcium chloride, 45 parts water, and 45 parts N,N-dimethylacetamide.

[0161] Comparative Example 9

[0162] Aramid-based heating paper was prepared using the same method as in Example 1, except that a conventional method was used to prepare the chopped fiber dispersion. Specifically, no nanofiber dispersion was used in the preparation of the chopped fiber dispersion in Comparative Example 9. The specific preparation process for the chopped fiber dispersion in Comparative Example 9 is as follows:

[0163] Carbon fiber and para-aramid chopped fiber are added to an appropriate amount of water for dissolution. After dissolution for 8 minutes, the mixture is stirred evenly to obtain the chopped fiber dispersion. The mass concentration of para-aramid chopped fiber in the chopped fiber dispersion is 0.5%, and the mass concentration of carbon fiber in the chopped fiber dispersion is 0.2%.

[0164] Comparative Example 10

[0165] Aramid-based heating paper was prepared using the same method as in Example 1, except that: meta-aramid precipitated fibers were prepared using conventional methods, that is, no nanofiber dispersion was used when preparing meta-aramid precipitated fibers in Comparative Example 10. The preparation process of meta-aramid precipitated fibers in Comparative Example 10 was the same as that of meta-aramid precipitated fibers in Comparative Example 8.

[0166] The aramid-based heating paper prepared in the above embodiments and comparative examples was subjected to performance testing. The specific testing methods involved are as follows.

[0167] The quantitative testing method refers to standard GB / T 451.2;

[0168] The thickness test method refers to the standard GB / T 451.3;

[0169] The test methods for tensile strength and elongation are based on the standard GB / T 12914.

[0170] The tear resistance test method refers to the standard GB / T 455;

[0171] The heating technology indicators refer to the standard GB / T4564; the electro-thermal radiation conversion rate of the radiating surface refers to the proportion of electrical energy consumed by carbon fiber paper when it is energized and converted into thermal radiation energy. The higher the proportion, the higher the heating efficiency of the product.

[0172] The specific test results are shown in Table 1 below.

[0173] Table 1 Performance test data of aramid-based heating paper

[0174]

[0175] As can be seen from the data in the table above, the aramid-based heating paper prepared by the method described in this invention in Examples 1-4 has good uniformity and excellent mechanical and heating properties. Furthermore, the aramid-based heating paper prepared by the method described in this invention in Examples 1-4 has extremely high electrothermal emissivity conversion rate and very uniform radiant surface temperature.

[0176] In Examples 1-4 of this invention, carbon fiber and aramid chopped fibers are well dispersed in the nano-dispersion liquid, significantly improving the overall performance of the aramid-based heating paper. Simultaneously, the aramid nanofibers adhering to the surfaces of the carbon fiber and aramid chopped fibers act as a binder, filling the pores of the aramid-based heating paper and strengthening the interaction with other fibers, effectively avoiding the problems of low mechanical properties and brittleness caused by poor bonding between aramid and carbon fibers. Furthermore, the introduction of the nanofiber dispersion liquid during the preparation of meta-aramid precipitated fibers moderately reduces their crystallinity, achieving a balance between energy saving and superior performance in the processing. Compared to conventional meta-aramid precipitated fibers, the meta-aramid precipitated fibers prepared in this invention have more micro-wrinkles on their surface, resulting in stronger bonding with other fibers. Simultaneously, strong hydrogen bonds can form between the nanofibers and carbon fiber, aramid chopped fibers, or meta-aramid precipitated fibers. Under these multiple effects, the aramid-based heating paper of this invention exhibits excellent overall performance.

[0177] A comparison of the data from Comparative Examples 1, 2, and 1 shows that increasing or decreasing the storage temperature of the nano-dispersion significantly reduces the mechanical properties, uniformity, and electrothermal radiation conversion efficiency of the aramid-based heating paper. This is because at suitable temperatures, the carbon fibers and chopped aramid fibers disperse more uniformly, resulting in more uniform size of the prepared meta-aramid precipitated fibers, while maintaining appropriate crystallinity and microstructure (i.e., more micro-wrinkles on the surface). Therefore, the overall performance of the final aramid-based heating paper is significantly improved.

[0178] A comparison of the data from Comparative Examples 3 and 4 with Example 1 shows that increasing or decreasing the proportion of nanofibers significantly reduces the overall performance of the aramid-based heating paper. This is because selecting an appropriate nanofiber ratio ensures more uniform size of the prepared meta-aramid precipitated fibers, maintaining suitable crystallinity and microstructure, resulting in better uniformity and superior mechanical and heating properties in the prepared aramid-based heating paper. Furthermore, selecting an appropriate nanofiber ratio optimizes the dispersion of carbon fibers and chopped aramid fibers, thus endowing the aramid-based heating paper with excellent mechanical properties, uniformity, and heating performance.

[0179] A comparison of the data from Comparative Examples 5, 6, and 1 shows that maintaining a suitable shear rate results in better overall performance of the aramid-based heating paper. When the shear rate is too high, the length of the meta-aramid precipitated fibers decreases, and the film characteristics of these fibers also diminish. This reduces the contact area between the meta-aramid precipitated fibers and carbon fibers or chopped aramid fibers, leading to a decrease in the paper's mechanical and heating properties. When the shear rate is too low, the shear force on the aramid droplets is insufficient, and the dispersed aramid droplets in the precipitant are too large to fully extend into a film state, thus causing a decline in the overall performance of the aramid-based heating paper. Furthermore, maintaining a certain shear rate is crucial for the crystallinity of the meta-aramid precipitated fibers. When the shear rate is too high, the aramid droplets, under high-speed shearing, easily form a film state, destroying the crystalline structure and resulting in excessively low crystallinity. This reduces fiber strength and further degrades the mechanical properties of the aramid-based heating paper. Conversely, excessively low shear rates result in excessively high crystallinity of meta-aramid precipitated fibers, leading to excessive aggregation of polymer chain segments, reduced porosity, and decreased flexibility of the molecular chains, thereby reducing the mechanical properties of the paper. This invention, by controlling conditions to moderately reduce the crystallinity of the prepared meta-aramid precipitated fibers compared to traditional meta-aramid precipitated fibers, can both save energy consumption in the hot-pressing process and significantly improve the overall performance of aramid-based heating paper.

[0180] The data comparison between Comparative Example 7 and Example 1 shows that, compared with the method of coating nanofibers on the surface of aramid-based heating paper, the aramid-based heating paper of the present invention has better overall performance.

[0181] The data comparison between Comparative Example 8 and Example 1 shows that, compared with the conventional preparation method of aramid-based heating paper, the aramid-based heating paper prepared by the present invention has significant improvements in mechanical properties, uniformity, and heating performance.

[0182] Comparison of data from Comparative Examples 9, 10 and 1 shows that the aramid-based heating paper prepared by using both the meta-aramid precipitated fiber and the meta-aramid short-cut fiber dispersion of the present invention has better overall performance.

[0183] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0184] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing aramid-based heating paper, characterized in that, The preparation method is as follows: S1. Preparation of nanofiber dispersion: Para-aramid short-cut fibers and potassium hydroxide were added to dimethyl sulfoxide, and then water was added and stirred to disperse, thus obtaining the nanofiber dispersion. In step S1, the weight ratio of para-aramid short-cut fibers, dimethyl sulfoxide, water and potassium hydroxide is (0.05-3):(80-100):(0.01-0.08):(0.15-4); The storage temperature for the nanofiber dispersion is 15-25℃; S2, Preparation of short-cut fiber dispersion and meta-aramid precipitated fibers: Carbon fiber and aramid short-cut fibers are added to the nanofiber dispersion for dissolution and mixed evenly to obtain the short-cut fiber dispersion. Meta-aramid polymer solution, nanofiber dispersion and precipitant are continuously and stably added to the precipitation equipment, and high-speed shearing is used to obtain precipitated fibers. Then, the fibers are cooled and shaped in a water washing tank and washed in multiple stages to obtain meta-aramid precipitated fibers. When preparing the meta-aramid precipitated fibers, the weight ratio of the nanofiber dispersion, the precipitant, and the meta-aramid polymerization liquid is (5-20):(5-12):(80-100); the high-speed shearing speed is 3500-6000 rpm. S3. Preparation of aramid-based heating paper: Aramid-based heating paper is obtained by dissolving and stirring the short fiber dispersion and meta-aramid precipitated fibers, followed by wet molding, pressing, drying, and hot pressing.

2. The method for preparing an aramid-based heating paper according to claim 1, characterized in that, In step S1, the stirring time is 4 to 24 hours.

3. The method for preparing an aramid-based heating paper according to claim 1, characterized in that, In step S2, when preparing the chopped fiber dispersion, the aramid chopped fiber is para-aramid chopped fiber or meta-aramid chopped fiber, and the disintegration time is 5-10 min; The aramid chopped fibers have a mass concentration of 0.05% to 1% in the chopped fiber dispersion, and the carbon fibers have a mass concentration of 0.01% to 0.5% in the chopped fiber dispersion.

4. The method for preparing an aramid-based heating paper according to claim 1, characterized in that, In step S2, when preparing the meta-aramid precipitated fiber, the temperature of the meta-aramid polymerization solution is 35-50°C, the solid content is 8%-15%, and the viscosity at 25°C is 100-450 Po.

5. The method for preparing an aramid-based heating paper according to claim 1, characterized in that, In step S2, when preparing the meta-aramid precipitated fiber, the high-speed shearing time is 40-90 seconds.

6. The method for preparing an aramid-based heating paper according to claim 1, characterized in that, In step S2, when preparing the meta-aramid precipitated fiber, the precipitating agent is a mixture of the following substances in parts by weight: 5-18 parts chloride salt, 40-50 parts water, and 40-50 parts N,N-dimethylacetamide. The chloride salt is at least one of lithium chloride, calcium chloride, and magnesium chloride.

7. The method for preparing an aramid-based heating paper according to claim 1, characterized in that, In step S3, the weight ratio of short-cut fibers to meta-aramid precipitated fibers in the short-cut fiber dispersion is 5:5, and the carbon fiber accounts for 10% to 30% of the total weight of the short-cut fibers in the short-cut fiber dispersion.

8. The method for preparing an aramid-based heating paper according to claim 1, characterized in that, In step S3, the hot pressing conditions are: temperature 180~220℃, vehicle speed 5~20m / min, and pressure 100~300N / mm.

9. An aramid-based heating paper, characterized in that, The aramid-based heating paper is prepared according to the preparation method described in any one of claims 1-8.

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