A meta-aramid fiber and a preparation method and application thereof

Abstract

The application discloses a meta-aramid fiber and a preparation method and application thereof, and relates to the technical field of aramid fibers, and specifically discloses a preparation method of the meta-aramid fiber, which comprises the following steps: dissolving m-phenylenediamine in a first solvent, adding isophthaloyl chloride, adding lye after reaction, and filtering to obtain a primary filtrate; adding isophthaloyl chloride in the primary filtrate, adding lye after reaction, and filtering to obtain a secondary filtrate; adding isophthaloyl chloride in the secondary filtrate, adding lye and ethylenediamine after reaction, and filtering to obtain a final filtrate; performing jet spinning forming treatment, and then sequentially performing two-stage coagulation forming treatment to obtain meta-aramid fiber filaments; wherein the two-stage coagulation forming treatments are both completed in a coagulation bath of a second solvent, calcium chloride and water; the second solvent is N,N-dimethylacetamide or N-methylpyrrolidone; performing water bath stretching and quenching to obtain the meta-aramid fiber; and the meta-aramid fiber is prepared by adopting a step-by-step prepolymerization method and a segmented coagulation bath process, and has good linear density, tensile strength, elongation at break, modulus and thermal stability.

Description

Technical Field

[0001] This invention belongs to the field of aramid fiber technology, and specifically relates to a meta-aramid fiber, its preparation method, and its application. Background Technology

[0002] As the speed of high-speed trains gradually increases, higher requirements are placed on the power of the high-speed motors that supply power. Meta-aramid insulating paper, as the winding insulation layer of high-speed motors, provides them with the necessary insulation performance; therefore, it is widely used in high-speed motors.

[0003] Meta-aramid fiber, as an important component of aramid insulating paper, has the advantages of high insulation, high mechanical strength, high temperature resistance and low shrinkage. The performance of meta-aramid fiber is mainly affected by the fiber spinning process. At present, wet spinning is commonly used to prepare meta-aramid fiber. However, the synergistic effect of the degree of polymerization of aramid molecules and coagulation bath conditions during the spinning process has not been studied in depth. This can easily lead to the synthesized meta-aramid fiber not meeting the requirements of high-speed motors in terms of crystallinity, mechanical properties and thermal stability. Summary of the Invention

[0004] To address the technical problems existing in the prior art, this invention provides a meta-aramid fiber, its preparation method, and its application, in order to solve the technical problem that when preparing meta-aramid fibers using wet spinning, the crystallinity, mechanical properties, and thermal stability of the synthesized meta-aramid fibers easily fail to meet the requirements of high-speed motors.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] This invention provides a method for preparing meta-aramid fibers, comprising the following steps:

[0007] Step 1: After dissolving m-phenylenediamine in the first solvent, add isophthaloyl chloride to carry out a prepolymerization reaction. After the reaction, add alkali solution to neutralize HCl molecules, filter, and obtain a first filtrate.

[0008] Step 2: Add isophthaloyl chloride to the primary filtrate to carry out a prepolymerization reaction. After the reaction, add alkaline solution to neutralize HCl molecules, filter, and obtain a secondary filtrate.

[0009] Step 3: Add isophthaloyl chloride to the secondary filtrate to carry out a prepolymerization reaction. After the reaction, add alkaline solution to neutralize HCl molecules, and then add ethylenediamine to neutralize the remaining isophthaloyl chloride after the prepolymerization reaction. Filter to obtain the final filtrate.

[0010] Step 4: The final filtrate is spun into fibers to obtain filaments; the filaments are then subjected to two-stage coagulation to obtain meta-aramid fiber filaments; wherein, both stages of coagulation are completed in a coagulation bath of a second solvent, calcium chloride and water; wherein, the second solvent is N,N-dimethylacetamide or N-methylpyrrolidone.

[0011] Step 5: The meta-aramid fiber filament is subjected to water bath stretching and quenching to obtain the meta-aramid fiber.

[0012] Furthermore, in step 1, the first solvent is N,N-dimethylacetamide or N-methylpyrrolidone.

[0013] Furthermore, in step 1, the prepolymerization reaction is carried out at a temperature of -15 to -5°C.

[0014] Furthermore, in step 2, the prepolymerization reaction is carried out at a temperature of -15 to -5°C.

[0015] Furthermore, in step 3, the prepolymerization reaction is carried out at a temperature of 0–6°C.

[0016] Furthermore, in step 4, during the first stage of solidification, the solidification temperature is 6–10°C; the mass concentration of calcium chloride in the solidification bath is 8–10%, and the mass percentage of water is 10%–15%.

[0017] Furthermore, in step 4, during the second-stage solidification and molding, the solidification and molding temperature is 10-15℃; the mass concentration of calcium chloride in the solidification bath is 5-7%, and the mass percentage of water is 15%-20%.

[0018] Furthermore, in step 5, during water bath stretching, the water bath temperature is 15–20°C, the stretching length is 2–2.5 times the original length, and the quenching temperature is 400–410°C.

[0019] The present invention also provides a meta-aramid fiber, which is prepared by the method described above for preparing a meta-aramid fiber; wherein the meta-aramid fiber has a fineness of 1.4 to 2.0 dtex, a breaking strength of 4.2 to 6.5 cN / dtex, a breaking elongation of 1.3% to 3.0%, an elastic modulus of 210 to 465 cN / dtex, and a thermal weight loss of 1.2% to 2.4% at 400℃.

[0020] The present invention also provides an application of meta-aramid fibers, which are used as a matrix material for aramid insulating paper.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] This invention provides a meta-aramid fiber, its preparation method, and its applications. Using m-phenylenediamine and isophthaloyl chloride as monomers, a multi-step prepolymerization method is employed to reduce the occurrence of byproducts during the reaction. This stepwise method addresses the negative impacts of HCl on the synthesis of meta-aramid, such as reduced molecular weight and decreased crystallinity. Specifically, after each prepolymerization reaction, an alkaline solution is used to absorb the HCl molecules generated during the reaction, and finally, ethylenediamine is used to neutralize excess isophthaloyl chloride. A two-stage coagulation process is utilized, employing a gradient-stage coagulation bath to enhance the molding completeness of the meta-aramid, allowing the meta-aramid to gradually transform from the solution into fiber, thus improving the quality of the fiber. Meta-aramid fibers exhibit good crystallinity, mechanical properties, and thermal stability. This invention utilizes a stepwise prepolymerization method and a segmented coagulation bath process to prepare meta-aramid fibers, resulting in fibers with excellent linear density, tensile strength, elongation at break, modulus, and thermal stability. The meta-aramid fibers have a fineness of 1.4–2.0 dtex, a breaking strength of 4.2–6.5 cN / dtex, an elongation at break of 1.3%–3.0%, an elastic modulus of 210–465 cN / dtex, and a thermal weight loss of 1.2–2.4% at 400℃. These meta-aramid fibers can be used as the matrix material for high-performance aramid insulating paper. Detailed Implementation

[0023] To make the technical problems solved by the present invention, the technical solutions, and the beneficial effects clearer, the following specific embodiments provide a further detailed description of the present invention. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of the invention.

[0024] This invention provides a method for preparing meta-aramid fibers, comprising the following steps:

[0025] Step 1: Dissolve 1-1.1 kg of m-phenylenediamine in 10-12 kg of a first solvent, add 0.35-0.4 kg of isophthaloyl chloride under a stirring rate of 300-500 r / min, and carry out a prepolymerization reaction at a temperature of -15 to -5℃ to obtain the initial prepolymerization product; wherein, the first solvent is N,N-dimethylacetamide or N-methylpyrrolidone.

[0026] Step 2: Add Ca(OH)2 to the product of the initial prepolymerization reaction to neutralize the HCl molecules generated in the prepolymerization reaction in Step 1. Then, filter the product CaCl2 using a multi-layer filter cloth to remove the byproduct and obtain a pale yellow transparent liquid, which is the first filtrate.

[0027] Step 3: Add 0.35-0.4 kg of isophthaloyl chloride to the primary filtrate and carry out a prepolymerization reaction at a temperature of -15 to -5℃ to obtain the secondary prepolymerization product.

[0028] Step 4: Add Ca(OH)2 to the product of the secondary prepolymerization reaction to neutralize the HCl molecules generated in the prepolymerization reaction in step 3, and filter to obtain the secondary filtrate.

[0029] Step 5: Add 0.35-0.4 kg of isophthaloyl chloride to the secondary filtrate and carry out a prepolymerization reaction at a temperature of 0-6°C to obtain the tertiary prepolymerization product.

[0030] Step 6: Add Ca(OH)2 to the product of the three prepolymerization reactions to neutralize the HCl molecules generated in the prepolymerization reaction in step 5. Then add ethylenediamine to neutralize the remaining isophthaloyl chloride after the prepolymerization reaction. Finally, filter the solution with a filter cloth to obtain a yellow transparent polymer solution, which is the final filtrate.

[0031] Step 7: The final filtrate is fed into a spinning device after passing through a metering pump. The spinning device is used to spin the final filtrate into fiber filaments. The spinneret in the spinning device has circular or square holes with a diameter of 0.02-0.3 mm and a number of holes of 200-1200.

[0032] Step 8: The fiber filaments are subjected to a two-stage coagulation molding process to obtain meta-aramid fiber filaments. Both stages of coagulation molding are performed in a coagulation bath containing a second solvent, calcium chloride, and water. The second solvent is N,N-dimethylacetamide or N-methylpyrrolidone. During the first stage of coagulation molding, the coagulation temperature is 6–10°C; the mass concentration of calcium chloride in the coagulation bath is 8–10%, and the mass percentage of water is 10%–15%. During the second stage of coagulation molding, the coagulation temperature is 10–15°C; the mass concentration of calcium chloride in the coagulation bath is 5–7%, and the mass percentage of water is 15%–20%.

[0033] Step 9: The meta-aramid fiber filament is subjected to water bath stretching and quenching to obtain the meta-aramid fiber; wherein, during water bath stretching, the water bath temperature is 15-20℃, the stretching length is 2-2.5 times, and the quenching temperature is 400-410℃.

[0034] Preparation principle:

[0035] In the preparation of meta-aramid fibers according to this invention, a portion of isophthaloyl chloride and m-phenylenediamine are first mixed. The isophthaloyl chloride and m-phenylenediamine undergo a condensation reaction to form poly(m-phenylenediamine isophthaloyl chloride) oligomers, generating the byproduct HCl. Since the byproduct HCl can affect the degree of polymerization, an alkaline solution, such as Ca(OH)2, is added to neutralize the byproduct HCl, and water and CaCl2 are removed by filtration, thereby increasing the degree of reaction. Because when poly(m-phenylenediamine isophthaloyl chloride) polymers are directly prepared using a one-step molding method, the byproduct HCl affects the polymerization of the product. The degree of polymerization and crystallinity; In this invention, a poly(m-phenylene isophthalamide) polymer is formed by sequentially performing secondary and tertiary prepolymerization. The stepwise reaction reduces the adverse effects of the byproduct HCl on the product and improves the mechanical strength and thermal stability of the polymer. Secondly, the prepared poly(m-phenylene isophthalamide) solution is solidified into poly(m-phenylene isophthalamide) fiber in a coagulation bath through a spinneret. The mass concentration of calcium chloride in the two-step coagulation bath gradually decreases, which is beneficial to improving the forming of the fiber material and improving the mechanical strength and thermal stability of the meta-aramid fiber, i.e., the poly(m-phenylene isophthalamide) fiber.

[0036] Example 1

[0037] This embodiment 1 provides a method for preparing meta-aramid fibers, including the following steps:

[0038] Step 1: Dissolve 1 kg of m-phenylenediamine in 12 kg of a first solvent, add 0.35 kg of isophthaloyl chloride under a stirring rate of 500 r / min, and carry out a prepolymerization reaction at a temperature of -15℃ to obtain the initial prepolymerization product; wherein, the first solvent is N,N-dimethylacetamide.

[0039] Step 2: Add Ca(OH)2 to the product of the initial prepolymerization reaction to neutralize the HCl molecules generated in the prepolymerization reaction in Step 1. Then, filter the product CaCl2 using a multi-layer filter cloth to remove the byproduct and obtain a pale yellow transparent liquid, which is the first filtrate.

[0040] Step 3: Add 0.35 kg of isophthaloyl chloride to the primary filtrate and carry out a prepolymerization reaction at a temperature of -15°C to obtain the secondary prepolymerization product.

[0041] Step 4: Add Ca(OH)2 to the product of the secondary prepolymerization reaction to neutralize the HCl molecules generated in the prepolymerization reaction in step 3, and filter to obtain the secondary filtrate.

[0042] Step 5: Add 0.35 kg of isophthaloyl chloride to the secondary filtrate and carry out a prepolymerization reaction at a temperature of 6°C to obtain the tertiary prepolymerization product.

[0043] Step 6: Add Ca(OH)2 to the product of the three prepolymerization reactions to neutralize the HCl molecules generated in the prepolymerization reaction in step 5. Then add ethylenediamine to neutralize the remaining isophthaloyl chloride after the prepolymerization reaction. Finally, filter the solution with a filter cloth to obtain a yellow transparent polymer solution, which is the final filtrate.

[0044] Step 7: The final filtrate is fed into a spinning device after passing through a metering pump. The spinning device is used to spin the final filtrate into fiber filaments. The spinning device has 1000 holes on the spinneret plate with a circular distribution and a diameter of 0.05 mm.

[0045] Step 8: The fiber filaments are subjected to a two-stage coagulation molding process to obtain meta-aramid fiber filaments. Both stages of coagulation molding are performed in a coagulation bath containing a second solvent, calcium chloride, and water. The second solvent is N,N-dimethylacetamide or N-methylpyrrolidone. During the first stage of coagulation molding, the coagulation temperature is 6°C, and the mass concentration of calcium chloride in the coagulation bath is 8% and the mass percentage of water is 10%. During the second stage of coagulation molding, the coagulation temperature is 10°C, and the mass concentration of calcium chloride in the coagulation bath is 5% and the mass percentage of water is 15%.

[0046] Step 9: The meta-aramid fiber filament is subjected to water bath stretching and quenching to obtain the meta-aramid fiber; wherein, during water bath stretching, the water bath temperature is 15℃, the stretching length is 2 times, and the quenching temperature is 400℃.

[0047] Performance testing:

[0048] The meta-aramid fiber prepared in Example 1 was subjected to performance testing. The test results showed that the fineness of the meta-aramid fiber was 1.6 dtex, the breaking strength was 6.0 cN / dtex, the breaking elongation was 1.6%, the elastic modulus was 380 cN / dtex, and the thermal weight loss at 400℃ was 1.5%.

[0049] Example 2

[0050] This embodiment 1 provides a method for preparing meta-aramid fibers, including the following steps:

[0051] Step 1: Dissolve 1.1 kg of m-phenylenediamine in 10 kg of a first solvent, add 0.4 kg of isophthaloyl chloride under a stirring rate of 300 r / min, and carry out a prepolymerization reaction at a temperature of -5℃ to obtain the initial prepolymerization product; wherein, the first solvent is N-methylpyrrolidone.

[0052] Step 2: Add Ca(OH)2 to the product of the initial prepolymerization reaction to neutralize the HCl molecules generated in the prepolymerization reaction in Step 1. Then, filter the product CaCl2 using a multi-layer filter cloth to remove the byproduct and obtain a pale yellow transparent liquid, which is the first filtrate.

[0053] Step 3: Add 0.4 kg of isophthaloyl chloride to the primary filtrate and carry out a prepolymerization reaction at a temperature of -5°C to obtain the secondary prepolymerization product.

[0054] Step 4: Add Ca(OH)2 to the product of the secondary prepolymerization reaction to neutralize the HCl molecules generated in the prepolymerization reaction in step 3, and filter to obtain the secondary filtrate.

[0055] Step 5: Add 0.4 kg of isophthaloyl chloride to the secondary filtrate and carry out a prepolymerization reaction at 0°C to obtain the tertiary prepolymerization product.

[0056] Step 6: Add Ca(OH)2 to the product of the three prepolymerization reactions to neutralize the HCl molecules generated in the prepolymerization reaction in step 5. Then add ethylenediamine to neutralize the remaining isophthaloyl chloride after the prepolymerization reaction. Finally, filter the solution with a filter cloth to obtain a yellow transparent polymer solution, which is the final filtrate.

[0057] Step 7: The final filtrate is fed into a spinneret after passing through a metering pump. The spinneret is used to spin the final filtrate into filaments. The spinneret has 1200 holes in a circular pattern on the spinneret plate with a diameter of 0.02 mm.

[0058] Step 8: The fiber filaments are subjected to a two-stage coagulation molding process to obtain meta-aramid fiber filaments. Both stages of coagulation molding are performed in a coagulation bath containing a second solvent, calcium chloride, and water. The second solvent is N,N-dimethylacetamide or N-methylpyrrolidone. During the first stage of coagulation molding, the coagulation temperature is 10°C, and the mass concentration of calcium chloride in the coagulation bath is 10% and the mass percentage of water is 15%. During the second stage of coagulation molding, the coagulation temperature is 15°C, and the mass concentration of calcium chloride in the coagulation bath is 7% and the mass percentage of water is 20%.

[0059] Step 9: The meta-aramid fiber filament is subjected to water bath stretching and quenching to obtain the meta-aramid fiber; wherein, during water bath stretching, the water bath temperature is 20℃, the stretching length is 2.5 times, and the quenching temperature is 410℃.

[0060] Performance testing:

[0061] The meta-aramid fiber prepared in Example 2 was subjected to performance testing. The test results showed that the fineness of the meta-aramid fiber was 1.4 dtex, the breaking strength was 6.5 cN / dtex, the breaking elongation was 1.3%, the elastic modulus was 465 cN / dtex, and the thermal weight loss at 400℃ was 1.2%.

[0062] Example 3

[0063] This embodiment 1 provides a method for preparing meta-aramid fibers, including the following steps:

[0064] Step 1: Dissolve 1.05 kg of m-phenylenediamine in 11 kg of a first solvent, add 0.38 kg of isophthaloyl chloride under a stirring rate of 400 r / min, and carry out a prepolymerization reaction at a temperature of -12 °C to obtain the initial prepolymerization product; wherein, the first solvent is N,N-dimethylacetamide.

[0065] Step 2: Add Ca(OH)2 to the product of the initial prepolymerization reaction to neutralize the HCl molecules generated in the prepolymerization reaction in Step 1. Then, filter the product CaCl2 using a multi-layer filter cloth to remove the byproduct and obtain a pale yellow transparent liquid, which is the first filtrate.

[0066] Step 3: Add 0.39 kg of isophthaloyl chloride to the primary filtrate and carry out a prepolymerization reaction at a temperature of -10°C to obtain the secondary prepolymerization product.

[0067] Step 4: Add Ca(OH)2 to the product of the secondary prepolymerization reaction to neutralize the HCl molecules generated in the prepolymerization reaction in step 3, and filter to obtain the secondary filtrate.

[0068] Step 5: Add 0.39 kg of isophthaloyl chloride to the secondary filtrate and carry out a prepolymerization reaction at a temperature of 3°C to obtain the tertiary prepolymerization product.

[0069] Step 6: Add Ca(OH)2 to the product of the three prepolymerization reactions to neutralize the HCl molecules generated in the prepolymerization reaction in step 5. Then add ethylenediamine to neutralize the remaining isophthaloyl chloride after the prepolymerization reaction. Finally, filter the solution with a filter cloth to obtain a yellow transparent polymer solution, which is the final filtrate.

[0070] Step 7: The final filtrate is fed into a spinneret after passing through a metering pump. The spinneret is used to spin the final filtrate into filaments. The spinneret has 800 holes on the spinneret plate with a square distribution and a diameter of 0.1 mm.

[0071] Step 8: The fiber filaments are subjected to a two-stage coagulation process to obtain meta-aramid fiber filaments. Both stages of coagulation are performed in a coagulation bath containing a second solvent, calcium chloride, and water. The second solvent is N,N-dimethylacetamide or N-methylpyrrolidone. During the first stage of coagulation, the coagulation temperature is 8°C, and the mass concentration of calcium chloride in the coagulation bath is 9% and the mass percentage of water is 13%. During the second stage of coagulation, the coagulation temperature is 13°C, and the mass concentration of calcium chloride in the coagulation bath is 6% and the mass percentage of water is 18%.

[0072] Step 9: The meta-aramid fiber filament is subjected to water bath stretching and quenching to obtain the meta-aramid fiber; wherein, during water bath stretching, the water bath temperature is 18℃, the stretching length is 2.3 times, and the quenching temperature is 405℃.

[0073] Performance testing:

[0074] The meta-aramid fiber prepared in Example 3 was subjected to performance testing. The test results showed that the fineness of the meta-aramid fiber was 1.8 dtex, the breaking strength was 4.2 cN / dtex, the breaking elongation was 3.0%, the elastic modulus was 210 cN / dtex, and the thermal weight loss at 400℃ was 2.4%.

[0075] Example 4

[0076] This embodiment 1 provides a method for preparing meta-aramid fibers, including the following steps:

[0077] Step 1: Dissolve 1 kg of m-phenylenediamine in 1.08 kg of a first solvent, add 0.36 kg of isophthaloyl chloride under a stirring rate of 350 r / min, and carry out a prepolymerization reaction at a temperature of -13℃ to obtain the initial prepolymerization product; wherein, the first solvent is N-methylpyrrolidone.

[0078] Step 2: Add Ca(OH)2 to the product of the initial prepolymerization reaction to neutralize the HCl molecules generated in the prepolymerization reaction in Step 1. Then, filter the product CaCl2 using a multi-layer filter cloth to remove the byproduct and obtain a pale yellow transparent liquid, which is the first filtrate.

[0079] Step 3: Add 0.38 kg of isophthaloyl chloride to the primary filtrate and carry out a prepolymerization reaction at a temperature of -12°C to obtain the secondary prepolymerization product.

[0080] Step 4: Add Ca(OH)2 to the product of the secondary prepolymerization reaction to neutralize the HCl molecules generated in the prepolymerization reaction in step 3, and filter to obtain the secondary filtrate.

[0081] Step 5: Add 0.38 kg of isophthaloyl chloride to the secondary filtrate and carry out a prepolymerization reaction at a temperature of 4°C to obtain the tertiary prepolymerization product.

[0082] Step 6: Add Ca(OH)2 to the product of the three prepolymerization reactions to neutralize the HCl molecules generated in the prepolymerization reaction in step 5. Then add ethylenediamine to neutralize the remaining isophthaloyl chloride after the prepolymerization reaction. Finally, filter the solution with a filter cloth to obtain a yellow transparent polymer solution, which is the final filtrate.

[0083] Step 7: The final filtrate is fed into a spinneret after passing through a metering pump. The spinneret is used to spin the final filtrate into filaments. The spinneret has 200 holes on the spinneret plate with a square distribution and a diameter of 0.3 mm.

[0084] Step 8: The fiber filaments are subjected to a two-stage coagulation molding process to obtain meta-aramid fiber filaments. Both stages of coagulation molding are performed in a coagulation bath containing a second solvent, calcium chloride, and water. The second solvent is N,N-dimethylacetamide or N-methylpyrrolidone. During the first stage of coagulation molding, the coagulation temperature is 9°C; the mass concentration of calcium chloride in the coagulation bath is 8.5%, and the mass percentage of water is 12%. During the second stage of coagulation molding, the coagulation temperature is 12°C; the mass concentration of calcium chloride in the coagulation bath is 5.5%, and the mass percentage of water is 17%.

[0085] Step 9: The meta-aramid fiber filament is subjected to water bath stretching and quenching to obtain the meta-aramid fiber; wherein, during water bath stretching, the water bath temperature is 17℃, the stretching length is 2.2 times, and the quenching temperature is 407℃.

[0086] Performance testing:

[0087] The meta-aramid fiber prepared in Example 1 was subjected to performance testing. The test results showed that the fineness of the meta-aramid fiber was 2.0 dtex, the breaking strength was 5.5 cN / dtex, the breaking elongation was 2.0%, the elastic modulus was 408 cN / dtex, and the thermal weight loss at 400℃ was 2.0%.

[0088] The meta-aramid fiber described in this invention, along with its preparation and application, utilizes a stepwise prepolymerization method and a segmented coagulation bath process to produce meta-aramid fibers with excellent linear density, tensile strength, elongation at break, modulus, and thermal stability. The meta-aramid fiber fineness is 1.4–2.0 dtex, its breaking strength is 4.2–6.5 cN / dtex, its elongation at break is 1.3%–3.0%, its elastic modulus is 210–465 cN / dtex, and its thermal weight loss at 400℃ is 1.2–2.4%. It can be used as a matrix material for high-performance insulating paper.

[0089] The above embodiments are merely one of the implementation methods for achieving the technical solution of the present invention. The scope of protection claimed by the present invention is not limited to this embodiment, but also includes any variations, substitutions and other implementation methods that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention.

Claims

1. A method for preparing meta-aramid fibers, characterized in that, Includes the following steps: Step 1: After dissolving m-phenylenediamine in the first solvent, add isophthaloyl chloride to carry out a prepolymerization reaction. After the reaction, add alkali solution to neutralize HCl molecules, filter, and obtain a primary filtrate. In Step 1, the prepolymerization reaction is carried out at a temperature of -15~-5℃. Step 2: Add isophthaloyl chloride to the primary filtrate to carry out a prepolymerization reaction. After the reaction, add alkali solution to neutralize HCl molecules, filter, and obtain a secondary filtrate. In Step 2, the prepolymerization reaction is carried out at a temperature of -15~-5℃. Step 3: Add isophthaloyl chloride to the secondary filtrate to carry out a prepolymerization reaction. After the reaction, add alkali solution to neutralize HCl molecules, and then add ethylenediamine to neutralize the remaining isophthaloyl chloride after the prepolymerization reaction. Filter to obtain the final filtrate. In step 3, the prepolymerization reaction is carried out at a temperature of 0~6℃. Step 4: The final filtrate is spun into fibers to obtain filaments; the filaments are then subjected to two-stage coagulation to obtain meta-aramid fiber filaments; wherein, both stages of coagulation are completed in a coagulation bath of a second solvent, calcium chloride and water; wherein, the second solvent is N,N-dimethylacetamide or N-methylpyrrolidone. Step 5: The meta-aramid fiber filament is subjected to water bath stretching and quenching to obtain the meta-aramid fiber; in Step 5, the water bath temperature is 15~20℃, the stretching length is 2~2.5 times, and the quenching temperature is 400~410℃. In step 4, during the first stage of solidification, the solidification temperature is 6~10℃; the mass concentration of calcium chloride in the solidification bath is 8~10%, and the mass percentage of water is 10%~15%. In step 4, during the second stage of solidification, the solidification temperature is 10~15℃; the mass concentration of calcium chloride in the solidification bath is 5~7%, and the mass percentage of water is 15%~20%.

2. The method for preparing meta-aramid fiber according to claim 1, characterized in that, In step 1, the first solvent is N,N-dimethylacetamide or N-methylpyrrolidone.

3. A meta-aramid fiber, characterized in that, The meta-aramid fiber is prepared by the method for preparing meta-aramid fiber as described in any one of claims 1-2; wherein the meta-aramid fiber has a fineness of 1.4~2.0 dtex, a breaking strength of 4.2~6.5 cN / dtex, a breaking elongation of 1.3%~3.0%, an elastic modulus of 210~465 cN / dtex, and a thermal weight loss of 1.2~2.4% at 400℃.

4. The application of a meta-aramid fiber as described in claim 3, characterized in that, The meta-aramid fibers are used as the matrix material for aramid insulating paper.