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

Abstract

The present application relates to the technical field of high-performance fiber, in particular to a meta-aramid fiber and a preparation method and application thereof, the preparation method is as follows: a crosslinking agent is added into a meta-aramid stock solution and mixed uniformly to form a spinning solution; the crosslinking agent is an aromatic compound containing at least three acyl chloride groups; the spinning solution is preheated, dry spinning is adopted to form a primary filament, the primary filament enters a drawing bath for drawing, and then is washed with water, dried, and heat treated to obtain a meta-aramid fiber. The meta-aramid fiber is applied to the preparation of meta-aramid paper. Compared with the meta-aramid prepared by traditional dry spinning, the present application solves the technical problems in the prior art, such as the difficulty in balancing the strength and elongation of the meta-aramid fiber, and the need for a high-concentration salt / solvent conditioning solution for continuous production. Moreover, the cross section of the meta-aramid fiber is kidney-shaped, and the aramid paper prepared therefrom has stronger overall performance.

Description

Technical Field

[0001] This invention relates to a meta-aromatic polyamide fiber, its preparation method, and its application, belonging to the field of high-performance fiber preparation technology. Background Technology

[0002] Meta-aramid fibers (commonly known as meta-aramid) are widely used in fire-resistant clothing, high-temperature filter materials, electrical insulating paper, and honeycomb structure materials due to their excellent high-temperature resistance, flame retardancy, and insulation properties. Currently, the main methods for preparing meta-aramid include wet spinning and dry spinning. Wet spinning typically has a spinning speed of only 15-30 m / min, resulting in low production efficiency. Furthermore, the resulting fibers are mostly cylindrical in cross-section with a small specific surface area, limiting their bonding force with precipitated fibers and restricting further applications in high-performance materials such as aramid paper. Dry spinning, on the other hand, offers significant advantages such as high spinning speed (up to 400 m / min or more), kidney-shaped fiber cross-section (large specific surface area), low internal porosity, and superior mechanical properties. Therefore, it has become an important development direction for improving the production efficiency and product quality of meta-aramid.

[0003] To address the challenge of continuous dry spinning production, existing technologies, such as CN102534839A, disclose a method for preparing meta-aramid fibers via continuous dry spinning. This method involves polymerizing m-phenylenediamine and isophthaloyl chloride at low temperature, followed by neutralization and filtration to obtain a spinning solution. The spinning solution is then heated and passed through a spinneret into a hot tunnel to remove the solvent, causing the fibers to solidify and form nascent fibers. These nascent fibers are subsequently soaked in a mixture of water and organic solvent for a certain period, followed by washing, stretching, drying, and heat treatment to obtain the finished fibers. This process enables continuous dry spinning of meta-aramid fibers, improving production efficiency.

[0004] However, the aforementioned existing technologies still have significant shortcomings in continuous dry spinning processes. On the one hand, to ensure that the nascent fibers maintain sufficient plasticity during stretching and avoid fiber breakage, this method must use a mixture containing high concentrations of salt and organic solvents (e.g., 1-3 wt% calcium chloride and 5-10 wt% DMAc) as the stretching bath. The nascent fibers need to be immersed in this mixture and stretched. This not only increases the consumption of solvents and salts but also leads to high wastewater treatment costs and significant environmental pressure. On the other hand, the elongation at break of meta-aramid fibers prepared using this method typically only reaches about 15%, and further increasing the elongation often leads to a decrease in tensile strength, creating a technical contradiction where strength and elongation are difficult to balance. Furthermore, in existing dry spinning processes, the fibers form a dense cortex structure within the spinning channel, with the core and cortex having the same composition. Subsequent stretching relies mainly on external force for forced orientation, which easily generates internal defects, limiting further improvement in the overall mechanical properties of the fibers.

[0005] Therefore, how to achieve efficient continuous dry spinning of meta-aramid fibers without relying on a high-concentration salt / solvent stretching bath, while simultaneously obtaining high tensile strength and high elongation at break, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a meta-aromatic polyamide fiber, its preparation method, and its applications. Compared to meta-aramid fibers prepared by traditional dry spinning, this invention solves the technical problems of existing technologies, such as the difficulty in achieving both strength and elongation of meta-aramid fibers and the need for high-concentration salt / solvent conditioning solutions for continuous production.

[0007] The technical solution of this invention to solve the above-mentioned technical problems is as follows: a method for preparing meta-aromatic polyamide fibers, wherein the preparation method is as follows: S1. A crosslinking agent is added to the meta-aromatic polyamide stock solution and mixed evenly to form a spinning solution; the crosslinking agent is an aromatic compound containing at least three acyl chloride groups; S2. After the spinning solution is preheated, it is dry-spun to form nascent filaments. The nascent filaments are then stretched in a stretching bath, and then washed, dried, and heat-treated to obtain the meta-aromatic polyamide fiber.

[0008] Further, in step S1, the crosslinking agent is selected from at least one of pyromellitic pyromellitic chloride and 1,2,4,5-benzenetetra(formyl chloride); The amount of crosslinking agent added is 0.05%-0.5% of the mass of the meta-aromatic polyamide in the meta-aromatic polyamide stock solution.

[0009] Furthermore, in step S2, the preheating temperature of the spinning solution is 100-150℃.

[0010] Furthermore, in the dry spinning process of step S2, the spinning solution, after being filtered and degassed, is preheated and then extruded through a spinneret and stretched through a tunnel to obtain the nascent filament. The temperature inside the tunnel is 170-250℃, the time the nascent filament spends in the tunnel is 13-27s, and the stretching ratio of the nascent filament in the tunnel is 10-20 times.

[0011] Furthermore, the stretching bath is pure water or a dilute solution, the dilute solution is an aqueous solution containing calcium chloride and DMAc, the mass content of calcium chloride in the dilute solution is 1-3 wt%, and the mass content of DMAc in the dilute solution is 5-10 wt%.

[0012] Furthermore, the stretching bath temperature is 30-60℃, and the nascent filament is stretched 3-5 times in the stretching bath.

[0013] Further, in step S2, the fiber is sprayed and washed with deionized water at 60-90℃. After washing, the fiber is dried on a drying roller at 150-200℃ and then heat-treated in a hot tunnel at 300-350℃ for 20-60 seconds. The stretching ratio is 1-1.2 times, and finally meta-aromatic polyamide fiber is obtained.

[0014] Furthermore, the meta-aromatic polyamide stock solution has a viscosity of 5000-10000 Po at 25°C and a solid content of 18-22 wt%.

[0015] The present invention also discloses a meta-aromatic polyamide fiber, wherein the meta-aromatic polyamide fiber is prepared according to the preparation method described in the present invention.

[0016] The present invention also discloses an application of meta-aromatic polyamide fiber, which is used in the preparation of meta-aramid paper.

[0017] The beneficial effects of this invention are: This invention provides a method for preparing meta-aromatic polyamide fibers and their applications. The method involves adding a trifunctional crosslinking agent to the polymerization solution and synergistically controlling process conditions such as the spinning solution temperature, dry spinning tunnel temperature and partitioning, stretching bath composition, and heat treatment time to obtain fibers with a "micro-crosslinked surface, uncrosslinked core" gradient structure and a kidney-shaped cross-section. These fibers exhibit a breaking strength of 4-6 cN / dtex and a breaking elongation of 39-45%, and can be stretched 3-5 times in pure water, reducing environmental costs. The mechanical properties of the resulting aramid paper are significantly superior to those of wet-spun products.

[0018] After the crosslinking agent is added to the spinning solution, the spinning solution is preheated to a suitable temperature before being extruded through the spinneret into the channel. If the preheating temperature is too low, the viscosity of the spinning solution increases, the fluidity decreases, the extrusion pressure of the spinneret increases, resulting in poor spinning or filament breakage, and it is also not conducive to the appropriate crosslinking reaction in the channel. If the preheating temperature is too high, the crosslinking agent undergoes pre-crosslinking during the transport process, leading to gelation of the original solution or a sharp increase in the filtration pressure difference, making continuous spinning impossible. The preheating temperature of this invention maintains the thermal stability and rheological uniformity of the spinning solution during the transport and spinning stages, while preserving the reactivity required for the crosslinking agent to undergo surface crosslinking in the subsequent channel.

[0019] The spinning solution after extrusion through the spinneret enters the dry spinning tunnel. The temperature and time the fibers spend within the tunnel are controlled. The crosslinking agent reacts with the amine groups on the polymer molecular chains. Because heat is transferred from the surface inwards, the surface layer preferentially reaches the reaction temperature and undergoes crosslinking, while the core layer remains uncrosslinked due to its lower temperature and insufficient reaction time. This facilitates subsequent stretching operations and yields meta-aromatic polyamide fibers with high breaking strength and high elongation at break.

[0020] The presence of the crosslinking agent provides reaction sites, the preheating temperature of the spinning solution provides an activity retention window for the crosslinking agent from the transport section to the reaction section, the channel temperature and transit time limit the spatial range and extent of the crosslinking reaction, and the heat treatment time ensures that the crosslinking reaction is fully completed on the surface and does not spread to the core. These four factors work synergistically to form a gradient structure of "micro-crosslinked surface and uncrosslinked core." This structure gives the fiber surface rigidity to provide high strength (4-6 cN / dtex), while the core maintains the plasticity of linear molecules to provide high elongation at break (39-45%), solving the problem of achieving both strength and elongation in existing dry-spun meta-aramid fibers.

[0021] Because the fiber has a gradient structure of "micro-crosslinked surface and uncrosslinked core," the core maintains sufficient plasticity and molecular chain slippage ability in aqueous media, allowing it to withstand 3-5 times the stretch in pure water without breaking. The micro-crosslinked surface network acts as a mechanical barrier, preventing excessive plasticization of the core from causing tensile instability.

[0022] In dry spinning, the solvent evaporates from the fiber surface, and the core shrinks, naturally forming a kidney-shaped cross-section. The addition of a cross-linking agent improves the mechanical strength of the sheath through surface cross-linking, ensuring the kidney-shaped cross-section remains regular during subsequent washing, stretching, and hot pressing, preventing collapse due to core shrinkage or external forces. Uncross-linked fiber sheaths are physically solidified layers with weak resistance to deformation, making the kidney-shaped cross-section prone to irregular deformation during subsequent processing. In this invention, the cross-linking agent and the kidney-shaped cross-section form a synergistic relationship: cross-linking provides morphological stability, while the kidney shape provides a high specific surface area (significantly larger than that of cylindrical fibers spun in wet spinning). Together, they provide a structural advantage for tight bonding with the precipitated fibers. The larger specific surface area and regular cross-sectional profile of the kidney-shaped meta-aramid fibers significantly increase the number of contact points, contact area, and mechanical locking force between the fiber and the precipitated fibers, forming a denser and more uniform three-dimensional network structure. This greatly improves the internal bonding strength and surface strength of the applied aramid paper, resulting in high-quality aramid paper. Attached Figure Description

[0023] Figure 1 Thermogravimetric images of meta-aromatic polyamide fibers prepared in Example 1; Figure 2 This is a SEM image of the meta-aromatic polyamide fiber obtained in Example 1; Figure 3 This is a SEM image of the cross-section of the meta-aromatic polyamide fiber obtained in Example 1. Detailed Implementation

[0024] 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.

[0025] 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.

[0026] A method for preparing meta-aromatic polyamide fibers, wherein the preparation method comprises: S1. A crosslinking agent is added to the meta-aromatic polyamide stock solution and mixed evenly to form a spinning solution; the crosslinking agent is an aromatic compound containing at least three acyl chloride groups; S2. After the spinning solution is preheated, it is dry-spun to form nascent filaments. The nascent filaments are then stretched in a stretching bath, and then washed, dried, and heat-treated to obtain the meta-aromatic polyamide fiber.

[0027] Specifically, in step S1, the crosslinking agent is selected from at least one of trimesoyl chloride (TMC) and 1,2,4,5-benzenetetra(formyl chloride); The amount of crosslinking agent added is 0.05%-0.5% of the mass of the meta-aromatic polyamide in the meta-aromatic polyamide stock solution.

[0028] Preferably, the crosslinking agent is selected from trimesoyl chloride.

[0029] Specifically, in step S2, the preheating temperature of the spinning solution is 100-150℃.

[0030] Specifically, in the dry spinning process of step S2, the spinning solution after filtration and degassing is extruded through a spinneret and stretched through a tunnel to obtain the nascent filament. The temperature inside the tunnel is 170-250℃, the time the nascent filament spends in the tunnel is 13-27s, and the stretching ratio of the nascent filament in the tunnel is 10-20 times.

[0031] More preferably, the channel is divided into a shaping zone, a reaction zone, and a conditioning zone along the fiber travel direction.

[0032] The temperature in the setting zone is 170-180℃, the dwell time is 2-5 seconds, and the stretching ratio is 2-4 times. This allows the fiber surface to be initially set, the solvent to partially evaporate, and the crosslinking agent to not react significantly. The fiber maintains good plasticity and can be pre-stretched 2-4 times without damaging the surface.

[0033] The reaction zone temperature is 200-250℃, the residence time is 10-15 s, and the stretching ratio is 4-8 times. The crosslinking agent and amine groups undergo the main crosslinking reaction in this zone to form a surface micro-crosslinked structure, while the core completes high-ratio orientation under protection.

[0034] The conditioning zone temperature is 170-190℃, the residence time is 2-7 seconds, and the stretch ratio is 0.9-2.5 times, which makes the internal and external temperatures of the fiber more uniform and eliminates internal stress. Active guide rollers are installed at the tunnel exit and the connection of each zone. The stretch ratio of each zone is independently controlled by the difference in linear speed of each group of guide rollers, and the total stretch ratio is controlled at 10-20 times.

[0035] The addition of an aromatic compound (crosslinking agent) containing at least three acyl chloride groups endows the fiber with "crosslinkable" properties, and the three-zone design provides better conditions for the precise utilization of this property. The temperature of the setting zone is relatively lower than the significant reaction temperature of the crosslinking agent. Pre-stretching 2-4 times within this window allows for preliminary setting of the fiber surface and initial orientation of the core before the crosslinking reaction occurs, without consuming the activity of the crosslinking agent. Compared to single-zone or two-zone channels, this design avoids the stretching difficulties caused by insufficient stretching in the low-temperature zone or pre-crosslinking in the high-temperature zone. The reaction zone precisely matches the high-efficiency reaction temperature of the crosslinking agent and amine groups. Performing 4-8 times main stretching in this zone allows the core to achieve high-ratio orientation under the protection of the forming crosslinked surface layer, forming a synergistic structure of micro-crosslinking on the surface and high orientation in the core. Compared to schemes without zones or with mismatched reaction zone temperatures, this design significantly improves crosslinking efficiency and orientation uniformity, thus achieving a more stable balance between high strength and high elongation. The conditioning zone slows down the crosslinking agent reaction, and the 0.9-2.5 times micro-stretching or relaxation effectively eliminates internal stress and prevents the fiber from drying out and becoming brittle due to excessive solvent evaporation, making subsequent stretching processes impossible. In summary, the three-zone design, combined with the crosslinking agent, allows the crosslinking agent to play a better role, improving process robustness and overall product performance.

[0036] Specifically, the stretching bath is pure water or a dilute solution, the dilute solution is an aqueous solution containing calcium chloride and DMAc, the mass content of calcium chloride in the dilute solution is 1-3 wt%, and the mass content of DMAc in the dilute solution is 5-10 wt%.

[0037] Preferably, the stretching bath is pure water.

[0038] Specifically, the stretching bath temperature is 30-60℃, and the nascent filaments are stretched 3-5 times in the stretching bath.

[0039] Specifically, in step S2, after the spinning solution is filtered through a 300-mesh candle filter, it is vacuum degassed for 5-10 hours at 80-100℃ and a vacuum degree of 50-100Pa. The degassed spinning solution is preheated and then extruded at a speed of 13-20 m / min after passing through a metering pump, a filter screen, and a spinneret. The spinneret has 100, 200, 400, or 600 holes with a diameter of 0.1-0.3 mm, a circular shape, and an aspect ratio of 1:3. The winding speed is 150-300 m / min. The spinning speed is m / min to obtain nascent yarn. The nascent yarn is stretched 10-20 times in the dry spinning tunnel. The nascent yarn is in a semi-transparent and moist state and is then placed in a stretching bath at a temperature of 30-60℃. The stretching bath can be pure water or a dilute solution. The nascent yarn is stretched 3-5 times in the stretching bath and then sprayed with deionized water at 60-90℃. This process usually requires a washing time of more than 10 minutes. During this time, the DMAc content in the fiber should be less than 300 ppm. After washing, the fiber is dried on a drying roller at 150-200℃ and then heat-treated in a hot tunnel at 300-350℃ for 20-60 seconds with a stretch ratio of 1-1.2 times, finally obtaining meta-aromatic polyamide fiber.

[0040] More specifically, the preparation method of the meta-aromatic polyamide stock solution is as follows: under a nitrogen atmosphere, m-phenylenediamine is dissolved in N,N-dimethylacetamide (DMAc). After stirring and dissolving at -10 to 0°C and 100 to 300 rpm, a DMAc solution of m-phenylenediamine is obtained. Then, the stirring speed is adjusted to 300 rpm, and isophthaloyl chloride is slowly and uniformly added. This process generally takes 30 to 60 minutes. After the addition is complete, the reaction is allowed to proceed for 2 to 4 hours. After the reaction reaches equilibrium, a certain mass fraction of calcium hydroxide or calcium oxide is added to neutralize the hydrogen chloride generated in the reaction until the pH of the stock solution is 6 to 8, thus obtaining a meta-aromatic polyamide stock solution with a polymer solid content of 18 to 22 wt%.

[0041] More specifically, in the preparation process of the meta-aromatic polyamide stock solution, the molar ratio of m-phenylenediamine to isophthaloyl chloride is 1:(0.9-1.1), and in the embodiments of the present invention, the molar ratio of m-phenylenediamine to isophthaloyl chloride is 1:1.

[0042] Specifically, the meta-aromatic polyamide stock solution has a viscosity of 5000-10000 Po at 25°C, a specific logarithmic viscosity of 1.6-2 dL / g (solvent is DMAc, test temperature 30°C), and a solid content of 18-22 wt%. The meta-aromatic polyamide stock solution has a weight-average molecular weight of 450,000-500,000 and a molecular weight distribution of 1.8-2.4. The stock solution is mixed uniformly with a crosslinking agent to form a spinning solution. During spinning, the crosslinking agent reacts with the amine groups on the polymer molecular chain, forming a slightly crosslinked structure on the fiber surface. The resulting nascent fiber core is not crosslinked and retains good plasticity, allowing for high-ratio stretching even in pure water or low-concentration solutions.

[0043] A meta-aramid polyamide fiber, wherein the meta-aramid polyamide fiber is prepared according to the preparation method described in this invention. The meta-aramid polyamide fiber has a breaking strength of 4-6 cN / dtex, a breaking elongation of 39-45%, and a tensile modulus of 78-100 cN / dtex.

[0044] The present invention also discloses an application of meta-aromatic polyamide fiber, which is used in the preparation of meta-aramid paper.

[0045] More specifically, the preparation method of meta-aramid paper is as follows: the meta-aramid polyamide fiber is prepared into short fibers and then added to dimethyl sulfoxide with potassium hydroxide, followed by the addition of water and stirring to disperse, thereby obtaining the meta-aramid short fiber dispersion; the storage temperature of the fiber dispersion is 15-25℃; the meta-aramid polymerization liquid and precipitating agent are continuously and stably added to a precipitation device, and the meta-aramid precipitated fibers are obtained by high-speed shearing, followed by cooling and molding in a water washing tank and multi-stage water washing to obtain the meta-aramid precipitated fibers; the high-speed shearing speed is 3000-6000 rpm and the shearing time is 60-90 s; the meta-aramid short fiber dispersion and the meta-aramid precipitated fibers are loosened, stirred, and then wet-formed and hot-pressed to obtain meta-aramid paper.

[0046] More specifically, in the preparation process of meta-aramid paper, the weight ratio of meta-aramid chopped fiber dispersion, intermediate aromatic polyamide fiber, dimethyl sulfoxide, water, and potassium hydroxide is (0.1-2):(60-99):(0.01-0.1):(0.1-5). The meta-aramid chopped fiber monofilaments are 1-3 dtex and 3-6 mm in length.

[0047] When preparing meta-aramid precipitated fibers, the weight ratio of the precipitant to the meta-aramid polymerization solution is (10-15):(60-120). The meta-aramid polymerization solution has a solid content of 15%-19 wt% and a viscosity of 600-800 Po at 25°C.

[0048] The precipitant comprises calcium chloride, water and N,N-dimethylacetamide, wherein the weight ratio of calcium chloride, water and N,N-dimethylacetamide is (10-20):(30-60):(30-60).

[0049] The dissolution time of the meta-aramid short-cut fiber dispersion and the meta-aramid precipitated fiber is 10-20 min; the mass ratio of the meta-aramid short-cut fiber dispersion to the meta-aramid precipitated fiber is (20-40):(60-80).

[0050] The wet molding hot pressing conditions are: temperature 160-230℃, speed 8-20 m / min, and pressure 200-300 N / mm.

[0051] Example 1: Preparation of meta-aromatic polyamide fibers.

[0052] The preparation method of a meta-aromatic polyamide fiber is as follows: S1. Under a nitrogen atmosphere, m-phenylenediamine was dissolved in 1874 parts by mass of N,N-dimethylacetamide (DMAc, water content ≤100 ppm). After stirring and dissolving at 0℃ and 200 rpm, a DMAc solution of m-phenylenediamine was obtained. Then, the stirring speed was adjusted to 300 rpm, and 461.13 parts by mass of isophthaloyl chloride were added uniformly over 30 min. After the addition was complete, the temperature was controlled at -5~0℃ and the reaction was carried out for 2 h. After the reaction reached equilibrium, calcium hydroxide was added to neutralize the hydrogen chloride generated in the reaction until the pH of the original solution was 7, thus obtaining a meta-aromatic polyamide stock solution with a polymer solid content of 20 wt%.

[0053] Trimethylbenzene chloride (TMC) is added to the stock solution at an amount of 0.1% of the polymer weight, and the mixture is stirred evenly to form a spinning solution.

[0054] S2. The spinning solution is filtered through a 300-mesh candle filter and then vacuum degassed for 5 hours at 80°C and a vacuum degree of 50 Pa. The degassed spinning solution is preheated to 120°C and extruded at a speed of 14.73 m / min after passing through a metering pump, a filter screen, and a 400-hole spinneret. The spinneret has an orifice diameter of 0.2 mm and an aspect ratio of 1:3. The winding speed is 150 m / min to obtain nascent filament. The temperature inside the tunnel is 200°C, the nascent filament passes through the tunnel for 18 s, and the stretch ratio of the nascent filament inside the tunnel is 10.2 times.

[0055] The nascent filaments are then stretched in a stretching bath at 50°C using pure water. The nascent filaments are stretched 3.3 times in the stretching bath, followed by spraying with deionized water at 80°C for 20 minutes. After washing, the fibers are dried on a drying roller at 200°C and then heat-treated in a hot tunnel at 350°C for 50 seconds with a stretch ratio of 1, ultimately yielding meta-aromatic polyamide fibers.

[0056] Example 2: Preparation of meta-aromatic polyamide fibers.

[0057] The preparation method of a meta-aromatic polyamide fiber is as follows: S1. Under a nitrogen atmosphere, 246.24 parts by mass of m-phenylenediamine were dissolved in 1874 parts by mass of N,N-dimethylacetamide (DMAc, water content ≤100 ppm). After stirring and dissolving at 0℃ and 200 rpm, a DMAc solution of m-phenylenediamine was obtained. Then, the stirring speed was adjusted to 300 rpm, and 461.13 parts by mass of isophthaloyl chloride were added uniformly over 30 min. After the addition was complete, the temperature was controlled at -3~0℃ and the reaction was carried out for 2 h. After the reaction reached equilibrium, a certain amount of calcium oxide was added to neutralize the hydrogen chloride generated in the reaction until the pH of the original solution was 7, thus obtaining a meta-aromatic polyamide stock solution with a polymer solid content of 20 wt%.

[0058] Trimethylbenzene chloride (TMC) is added to the stock solution at an amount of 0.1% of the polymer weight, and the mixture is stirred evenly to form a spinning solution.

[0059] S2. The spinning solution is filtered through a 300-mesh candle filter and then vacuum degassed for 5 hours at 80°C and a vacuum degree of 50 Pa. The degassed spinning solution is preheated to 100°C and extruded at a speed of 19.11 m / min after passing through a metering pump, a filter screen, and a 400-hole spinneret. The spinneret has an orifice diameter of 0.2 mm and an aspect ratio of 1:3. The winding speed is 200 m / min to obtain nascent filament. The temperature inside the tunnel is 230°C, the nascent filament passes through the tunnel for 15 seconds, and the stretch ratio of the nascent filament inside the tunnel is 10.5 times.

[0060] The nascent filament was then stretched in a stretching bath at 50°C using pure water. The nascent filament was stretched 3.5 times in the stretching bath, followed by spraying with deionized water at 80°C for 20 minutes. After washing, the fiber was dried on a drying roller at 200°C, and then heat-treated in a hot tunnel at 350°C for 50 seconds with a stretch ratio of 1, ultimately yielding meta-aromatic polyamide fiber.

[0061] Example 3: Preparation of meta-aromatic polyamide fibers.

[0062] The preparation method of a meta-aromatic polyamide fiber is as follows: S1. Under a nitrogen atmosphere, 246.24 parts by mass of m-phenylenediamine were dissolved in 1874 parts by mass of N,N-dimethylacetamide (DMAc, water content ≤100 ppm). After stirring and dissolving at 0℃ and 200 rpm, a DMAc solution of m-phenylenediamine was obtained. Then, the stirring speed was adjusted to 300 rpm, and 461.13 parts by mass of isophthaloyl chloride were added uniformly over 30 min. After the addition was complete, the temperature was controlled at -8~-2℃ and the reaction was carried out for 2 h. After the reaction reached equilibrium, a certain amount of calcium hydroxide was added to neutralize the hydrogen chloride generated in the reaction until the pH of the original solution was 7.5, thus obtaining a meta-aromatic polyamide stock solution with a polymer solid content of 20 wt%.

[0063] Trimethylbenzene chloride (TMC) is added to the stock solution at an amount of 0.1% of the polymer weight, and the mixture is stirred evenly to form a spinning solution.

[0064] S2. The spinning solution is filtered through a 300-mesh candle filter and then vacuum degassed for 5 hours at 80°C and a vacuum degree of 50 Pa. The degassed spinning solution is preheated to 150°C and extruded at a speed of 19.11 m / min after passing through a metering pump, a filter screen, and a 400-hole spinneret. The spinneret has an orifice diameter of 0.2 mm and an aspect ratio of 1:3. The winding speed is 250 m / min to obtain nascent filament. The temperature inside the tunnel is 250°C, the nascent filament passes through the tunnel for 13 s, and the stretch ratio of the nascent filament inside the tunnel is 13.1 times.

[0065] The nascent filament is then stretched in a stretching bath at 50°C using pure water. The nascent filament is stretched three times in the stretching bath, followed by spraying with deionized water at 80°C for 20 minutes. After washing, the fiber is dried on a drying roller at 200°C and then heat-treated in a hot tunnel at 350°C for 50 seconds with a stretch ratio of 1, ultimately yielding meta-aromatic polyamide fiber.

[0066] Example 4: Preparation of meta-aromatic polyamide fibers.

[0067] The preparation method of a meta-aromatic polyamide fiber is as follows: S1. Under a nitrogen atmosphere, 246.24 parts by mass of m-phenylenediamine were dissolved in 1874 parts by mass of N,N-dimethylacetamide (DMAc, water content ≤100 ppm). After stirring and dissolving at 0℃ and 200 rpm, a DMAc solution of m-phenylenediamine was obtained. Then, the stirring speed was adjusted to 300 rpm, and 461.13 parts by mass of isophthaloyl chloride were added uniformly over 30 min. After the addition was complete, the temperature was controlled at -10~-5℃ and the reaction was carried out for 2 h. After the reaction reached equilibrium, a certain amount of calcium hydroxide was added to neutralize the hydrogen chloride generated in the reaction until the pH of the original solution was 7, thus obtaining a meta-aromatic polyamide stock solution with a polymer solid content of 20 wt%.

[0068] Trimethylbenzene chloride (TMC) is added to the stock solution at an amount of 0.1% of the polymer weight, and the mixture is stirred evenly to form a spinning solution.

[0069] S2. The spinning solution is filtered through a 300-mesh candle filter and then vacuum degassed for 5 hours at 80°C and a vacuum degree of 50 Pa. The degassed spinning solution is preheated to 130°C and extruded at a speed of 14.73 m / min after passing through a metering pump, a filter screen, and a 600-hole spinneret. The spinneret has an orifice diameter of 0.2 mm and an aspect ratio of 1:3. The winding speed is 200 m / min to obtain nascent filament. The temperature inside the tunnel is 220°C, the nascent filament passes through the tunnel for 16 s, and the stretch ratio of the nascent filament inside the tunnel is 13.6 times.

[0070] The nascent filament is then stretched in a stretching bath at 50°C using pure water. The nascent filament is stretched three times in the stretching bath, followed by spraying with deionized water at 80°C for 20 minutes. After washing, the fiber is dried on a drying roller at 200°C and then heat-treated in a hot tunnel at 350°C for 50 seconds with a stretch ratio of 1, ultimately yielding meta-aromatic polyamide fiber.

[0071] Example 5: Preparation of meta-aromatic polyamide fibers.

[0072] The preparation method of a meta-aromatic polyamide fiber is as follows: S1. Under a nitrogen atmosphere, 212.16 parts by mass of m-phenylenediamine were dissolved in 1874 parts by mass of N,N-dimethylacetamide (DMAc, water content ≤100 ppm). After stirring and dissolving at 0℃ and 200 rpm, a DMAc solution of m-phenylenediamine was obtained. Then, the stirring speed was adjusted to 300 rpm, and 397.32 parts by mass of isophthaloyl chloride were added uniformly over 30 min. After the addition was complete, the temperature was controlled at -5~0℃ and the reaction was carried out for 2 h. After the reaction reached equilibrium, a certain amount of calcium hydroxide was added to neutralize the hydrogen chloride generated in the reaction until the pH of the original solution was 7, thus obtaining a meta-aromatic polyamide stock solution with a polymer solid content of 18 wt%.

[0073] Add trimesoyl chloride (TMC) to the stock solution at a concentration of 0.5% of the polymer weight, and mix thoroughly to form a spinning solution.

[0074] S2. The spinning solution is filtered through a 300-mesh candle filter and then vacuum degassed for 5 hours at 80°C and a vacuum degree of 50 Pa. The degassed spinning solution is preheated to 130°C and extruded at a speed of 14.73 m / min after passing through a metering pump, a filter screen, and a 600-hole spinneret. The spinneret has an orifice diameter of 0.2 mm and an aspect ratio of 1:3. The winding speed is 150 m / min to obtain nascent filament. The temperature inside the channel is 230°C, the nascent filament passes through the channel for 18 s, and the stretch ratio of the nascent filament inside the channel is 10.2 times.

[0075] The nascent filament was then stretched in a stretching bath at 60°C using pure water. The nascent filament was stretched 3.3 times in the stretching bath, and then sprayed with deionized water at 90°C for 20 minutes. After washing, the fiber was dried on a drying roller at 200°C, and then heat-treated in a hot tunnel at 300°C for 60 seconds with a stretch ratio of 1, finally yielding meta-aromatic polyamide fiber.

[0076] Example 6: Preparation of meta-aromatic polyamide fibers.

[0077] The preparation method of a meta-aromatic polyamide fiber is as follows: S1. Under a nitrogen atmosphere, 283.49 parts by mass of m-phenylenediamine were dissolved in 1730 parts by mass of N,N-dimethylacetamide (DMAc, water content ≤100 ppm). After stirring and dissolving at 0℃ and 200 rpm, a DMAc solution of m-phenylenediamine was obtained. Then, the stirring speed was adjusted to 300 rpm, and 530.90 parts by mass of isophthaloyl chloride were added uniformly over 30 min. After the addition was complete, the temperature was controlled at -5~0℃ and the reaction was carried out for 2 h. After the reaction reached equilibrium, a certain amount of calcium hydroxide was added to neutralize the hydrogen chloride generated in the reaction until the pH of the original solution was 7, thus obtaining a meta-aromatic polyamide stock solution with a polymer solid content of 22 wt%.

[0078] 1,2,4,5-Benzenetetra(formyl chloride) was added to the stock solution at an amount of 0.1% of the polymer weight, and the mixture was stirred evenly to form a spinning solution.

[0079] S2. The spinning solution is filtered through a 300-mesh candle filter and then vacuum degassed for 5 hours at 80°C and a vacuum degree of 50 Pa. The degassed spinning solution is preheated to 140°C and extruded at a speed of 14.73 m / min after passing through a metering pump, a filter screen, and a 600-hole spinneret. The spinneret has an orifice diameter of 0.2 mm and an aspect ratio of 1:3. The winding speed is 150 m / min to obtain nascent filament. The temperature inside the tunnel is 240°C, the nascent filament passes through the tunnel for 20 seconds, and the stretch ratio of the nascent filament inside the tunnel is 10.2 times.

[0080] The nascent filament was then stretched in a stretching bath at 30°C using pure water. The nascent filament was stretched 3.3 times in the stretching bath. Subsequently, it was sprayed with deionized water at 60°C for 20 minutes. After washing, the fiber was dried on a drying roller at 150°C and then heat-treated in a hot tunnel at 350°C for 20 seconds with a stretch ratio of 1, ultimately yielding meta-aromatic polyamide fiber.

[0081] Example 7: Preparation of meta-aromatic polyamide fibers.

[0082] The preparation method of a meta-aromatic polyamide fiber is as follows: S1, Same as Example 1 S2. The spinning solution is filtered through a 300-mesh candle filter and then vacuum degassed for 5 hours at 80°C and a vacuum degree of 50Pa. The degassed spinning solution is preheated to 120°C and then extruded at a speed of 14.73 m / min after passing through a metering pump, a filter screen, and a 400-hole spinneret. The spinneret has a hole diameter of 0.2 mm and a length-to-diameter ratio of 1:3. The extruded filaments are obtained by passing through a channel to obtain nascent filaments.

[0083] The channel is divided into a setting zone, a reaction zone, and a conditioning zone along the fiber travel direction. The setting zone has a temperature of 170℃, a residence time of 3 seconds, and a stretch ratio of 3 times; the reaction zone has a temperature of 250℃, a residence time of 10 seconds, and a stretch ratio of 4 times; and the conditioning zone has a temperature of 190℃, a residence time of 5 seconds, and a stretch ratio of 1.02 times.

[0084] The nascent filaments are then stretched in a stretching bath at 50°C using pure water. The nascent filaments are stretched three times in the stretching bath, followed by spraying with deionized water at 80°C for 20 minutes. After washing, the fibers are dried on a drying roller at 200°C and then heat-treated in a hot tunnel at 350°C for 50 seconds with a stretch ratio of 1, ultimately yielding meta-aromatic polyamide fibers.

[0085] Example 8: Preparation of meta-aromatic polyamide fibers.

[0086] The preparation method of a meta-aromatic polyamide fiber is as follows: S1, Same as Example 1 S2. The spinning solution is filtered through a 300-mesh candle filter and then vacuum degassed for 5 h at 80°C and a vacuum degree of 50 Pa. The degassed spinning solution is preheated to 120°C and then extruded at a speed of 19.11 m / min after passing through a metering pump, a filter screen, and a 400-hole spinneret. The spinneret has a hole diameter of 0.2 mm and an aspect ratio of 1:3. The extruded filaments are obtained by passing through a channel to obtain nascent filaments.

[0087] The channel is divided into a setting zone, a reaction zone, and a conditioning zone along the fiber travel direction. The setting zone has a temperature of 180℃, a residence time of 3 seconds, and a stretch ratio of 2; the reaction zone has a temperature of 200℃, a residence time of 15 seconds, and a stretch ratio of 5; and the conditioning zone has a temperature of 170℃, a residence time of 2 seconds, and a stretch ratio of 1.02.

[0088] The nascent filaments are then stretched in a stretching bath at 50°C using pure water. The nascent filaments are stretched three times in the stretching bath, followed by spraying with deionized water at 80°C for 20 minutes. After washing, the fibers are dried on a drying roller at 200°C and then heat-treated in a hot tunnel at 350°C for 50 seconds with a stretch ratio of 1, ultimately yielding meta-aromatic polyamide fibers.

[0089] Comparative Example 1: Preparation of meta-aromatic polyamide fibers.

[0090] Meta-aromatic polyamide fibers were prepared using the same method as in Example 1, except that no crosslinking agent was added in step S1 of Comparative Example 1, and the meta-aromatic polyamide dope was directly used for dry spinning. Other process conditions were the same as in Example 1.

[0091] Comparative Example 2: Preparation of meta-aromatic polyamide fibers.

[0092] Meta-aromatic polyamide fibers were prepared using the same method as in Example 1, except that the amount of TMC added in step S1 of Comparative Example 2 was increased to 1.0% of the polymer weight, and other process conditions were the same as in Example 1.

[0093] Comparative Example 3: Preparation of meta-aromatic polyamide fibers.

[0094] Meta-aromatic polyamide fibers were prepared using the same method as in Example 1, except that the preheating temperature of the spinning solution was reduced to 80°C in step S2 of Comparative Example 3, while other process conditions were the same as in Example 1.

[0095] Comparative Example 4: Preparation of meta-aromatic polyamide fibers.

[0096] Meta-aromatic polyamide fibers were prepared using the same method as in Example 1, except that in step S2 of Comparative Example 4, the preheating temperature of the spinning solution was increased to 200°C, and other process conditions were the same as in Example 1.

[0097] Comparative Example 5: Preparation of meta-aromatic polyamide fibers.

[0098] Meta-aromatic polyamide fibers were prepared using the same method as in Example 1, except that the time for the nascent filament to pass through the channel in step S2 of Comparative Example 5 was 10 s (less than the time specified in this invention), and other process conditions were the same as in Example 1.

[0099] Comparative Example 6: Preparation of meta-aromatic polyamide fibers.

[0100] Meta-aromatic polyamide fibers were prepared using the same method as in Example 1, except that the time for the nascent filament to pass through the channel in step S2 of Comparative Example 6 was 35 s (longer than the time limit specified in this invention), and other process conditions were the same as in Example 1.

[0101] The meta-aromatic polyamide fibers prepared in the above examples and comparative examples were subjected to performance tests. In the table, Taimeda is a wet-spun product of Taihe New Materials Co., Ltd. The specific test results are shown in Table 1 below. The test methods involved are GB / T 14335 and GB / T 14337.

[0102] Table 1. Performance data of meta-aromatic polyamide fibers

[0103] Note: Although some examples / comparative examples use the same method to prepare meta-aromatic polyamide stock solutions, the viscosity and molecular weight of the stock solutions obtained by polymerization of different batches using the same process can only be similar, and will not be completely consistent between different batches.

[0104] The data in the table above shows that the meta-aromatic polyamide fibers prepared by the method described in this invention in Examples 1-8 have excellent breaking strength, elongation at break, and tensile modulus. The entire preparation process uses dry spinning, which allows for direct stretching in pure water, reducing environmental impact and facilitating industrial application. Furthermore, a comparison of the experimental results of Examples 7-8 with those of Examples 1-6 shows that a well-planned design of the shaping zone, reaction zone, and conditioning zone within the preparation channel is more conducive to obtaining fiber products with superior overall performance.

[0105] Figure 1 Thermogravimetric images of the meta-aromatic polyamide fibers prepared in Example 1 are shown below. Figure 1 It can be seen that the meta-aromatic polyamide fiber prepared by this invention begins to decompose at 425℃, and the decomposition rate reaches its maximum at 453.4℃, proving that the fiber has good heat resistance. Figure 2 The image shows a SEM image of the meta-aromatic polyamide fiber prepared in Example 1. Figure 2 It can be seen that the fibers prepared by this invention have a smooth surface, uniform thickness, and a single filament diameter of 18-20 μm; Figure 3 This is a cross-sectional image of the meta-aromatic polyamide fiber prepared in Example 1. Figure 3 It can be seen that the cross-section of the meta-aromatic polyamide fiber is a regular kidney shape. In dry spinning, the solvent evaporates from the fiber surface, and the core shrinks, naturally forming a kidney-shaped cross-section. After the addition of the crosslinking agent, the surface crosslinking reaction improves the mechanical strength of the cortex, ensuring the kidney-shaped cross-section remains regular during subsequent washing, stretching, and hot pressing, preventing cross-section collapse due to core shrinkage or external force. The uncrosslinked fiber cortex is a physically solidified layer with weak resistance to deformation, and the kidney-shaped cross-section is prone to irregular deformation during subsequent processing. In this invention, the crosslinking agent and the kidney-shaped cross-section work synergistically: crosslinking provides morphological stability, and the kidney shape provides a high specific surface area (significantly larger than that of wet-spun cylindrical fibers). Together, they provide a structural advantage for close bonding with the precipitated fibers.

[0106] A comparison of the results of Comparative Example 1 and Example 1 shows that the nascent filament of Comparative Example 1 without the addition of a crosslinking agent broke in the stretching bath and could not be stretched. The addition of the crosslinking agent can improve the plasticity and spinnability of the fiber, forming a gradient structure of "micro-crosslinked surface and uncrosslinked core" during dry spinning. This allows the nascent filament to maintain sufficient toughness and tensile stability, avoiding the problem of filament breakage caused by excessive brittleness of the sheath or excessive shrinkage of the core in uncrosslinked fibers.

[0107] A comparison of the results from Comparative Example 2 and Example 1 shows that increasing the amount of crosslinking agent resulted in a spooling phenomenon, poor spinnability, and inability to be wound. This is because excessive small-molecule crosslinking agent alters the rheological behavior of the spinning solution, leading to decreased fiber stability during spinneret extrusion. Simultaneously, excessively high crosslinking agent concentrations result in violent and uneven reactions in the subsequent high-temperature zone of the spinneret, making it difficult to form an ideal gradient structure. This, in turn, causes the fiber to become brittle overall or contaminates the spinneret. The amount of crosslinking agent added in this invention ensures adequate crosslinking to form a gradient structure without affecting the extrusion stability and spinnability of the spinning solution. This is more conducive to obtaining fibers with excellent overall performance.

[0108] The comparison between the results of Comparative Example 3 and Example 1 shows that when the preheating temperature is too low, the viscosity of the spinning solution is too high, the fluidity decreases, the extrusion pressure of the spinneret increases, and the crosslinking agent has insufficient reactivity, which prevents the formation of surface micro-crosslinking structures in the channel in time, resulting in poor fiber formation.

[0109] A comparison of the results from Comparative Example 4 and Example 1 shows that excessively high preheating temperatures cause the crosslinking agent to undergo pre-crosslinking in the conveying section, resulting in partial gelation of the spinning solution. After the fiber enters the channel, the crosslinking reaction becomes excessive and uneven, and the core is also crosslinked, losing its plasticity. Therefore, it cannot produce sufficient deformation and breaks when stretched in pure water. This invention avoids pre-crosslinking by controlling the preheating temperature, thus preserving the stretchability of the core.

[0110] The comparison between the results of Comparative Example 5 and Example 1 shows that the fiber filaments have too short a passage time in the channel, the cross-linking reaction has not occurred sufficiently, the surface cross-linking density is insufficient, the fiber strength is low, and the core orientation is insufficient, which makes it easy to generate fuzz during subsequent stretching and washing.

[0111] A comparison of the results from Comparative Example 6 and Example 1 shows that when the fiber filaments pass through the channel for too long, heat is fully transferred to the core, causing the core to also become cross-linked. This makes the fiber brittle and loses its plasticity, thus preventing it from withstanding deformation and breaking when stretched in pure water. This invention precisely controls the passage time, ensuring that the cross-linking reaction is confined to the surface layer, while the core remains in an uncross-linked, plastic state.

[0112] A comparison of the performance test results of the wet-spun Temeda finished yarn and those of Examples 1-8 shows that the mechanical properties of the meta-aromatic polyamide fiber prepared by dry spinning in this invention are significantly better than those of the fiber prepared by conventional wet spinning.

[0113] To verify the application effect of the fibers prepared in the above embodiments on meta-aramid paper, the following methods were used to prepare meta-aramid paper, except that different meta-aromatic polyamide fibers were used. The specific preparation methods are as follows: Meta-aramid fibers were prepared into short fibers and then mixed with potassium hydroxide, water, and dimethyl sulfoxide in a mass ratio of 0.5:0.2:0.05:80. The mixture was stirred and dispersed to obtain a meta-aramid short fiber dispersion. The storage temperature of the meta-aramid short fiber dispersion was 15-25℃.

[0114] The meta-aramid chopped fiber monofilaments are 2-2.5 dtex and 5 mm long.

[0115] Meta-aramid polymerization solution and precipitating agent were continuously and stably added to a precipitation device at a mass ratio of 85:15. High-speed shearing was used to obtain a meta-aramid precipitated fiber precipitate, which was then cooled and shaped in a water washing tank and subjected to multi-stage washing to obtain meta-aramid precipitated fibers. The high-speed shearing speed was 4000 rpm, and the shearing time was 60 s. The solid content of the meta-aramid polymerization solution was 19 wt% (mass content), and the viscosity at 25°C was 680 Po. The precipitating agent comprised calcium chloride, water, and N,N-dimethylacetamide, wherein the weight ratio of calcium chloride, water, and N,N-dimethylacetamide was 10:40:50.

[0116] Meta-aramid short-cut fiber dispersion and meta-aramid precipitated fiber were dispersed for 15 min, stirred, and then subjected to wet molding and hot pressing to obtain dry spinning to prepare meta-aramid paper.

[0117] The mass ratio of the meta-aramid short-cut fiber dispersion to the meta-aramid precipitated fiber is 30:70.

[0118] The specific process conditions for wet hot pressing are: temperature 200℃, speed 15 m / min, and pressure 200 N / mm.

[0119] The performance of meta-aramid paper was tested, and the specific test results are shown in Table 2 below. The test methods involved are as follows: basis weight test method refers to standard GB / T 451.2; thickness test method refers to standard GB / T 451.3; tensile strength and elongation test method refers to standard GB / T 12914; tear strength test method refers to standard GB / T 455; surface strength test method refers to standard GB / T 22837; and internal bond strength test method refers to standard GB / T 26203.

[0120] Table 2 Performance data of meta-aramid paper

[0121] According to the test results in Table 2, the aramid paper made from the meta-aromatic polyamide fibers prepared in Examples 1-8 of this invention (Application Examples 1-8) exhibits significantly better mechanical properties than the comparative application examples made from conventional wet-spun fibers under the same basis weight and thickness conditions. Specifically, the longitudinal tensile strength, transverse tensile strength, longitudinal elongation, transverse elongation, internal bond strength, longitudinal tear strength, transverse tear strength, and surface strength of Application Examples 1-8 are all significantly higher than those of the comparative application examples. This is because the present invention, by adding a crosslinking agent and controlling the dry spinning process, forms a gradient structure of "micro-crosslinked surface and uncrosslinked core." The fiber cross-section is kidney-shaped, with a large specific surface area and a regular surface. The number of contact points and mechanical locking force between the fiber and the precipitated fiber are significantly increased, thereby forming a denser and more uniform three-dimensional network structure during wet forming and hot pressing. This endows the aramid paper with higher tensile strength, tear strength, and internal bond strength, while also improving elongation and surface resistance to fuzzing and delamination.

[0122] Further comparison of Application Examples 1-6 and 7-8 shows that the aramid paper of Application Examples 7-8 outperforms the aramid paper of Application Examples 1-6 in all aspects. This is because the fibers of Application Examples 7-8 employ a three-zone channel design (setting zone, reaction zone, and conditioning zone). This design allows for precise spatial and temporal matching between the crosslinking reaction and the stretching orientation: the setting zone performs low-temperature pre-stretching for initial orientation without consuming the activity of the crosslinking agent; the reaction zone performs high-temperature main stretching and crosslinking simultaneously, with the core achieving high-ratio orientation under the protection of the crosslinked surface layer; and the conditioning zone eliminates internal stress and terminates excessive crosslinking. The three-zone design optimizes the utilization efficiency of the crosslinking agent, resulting in a more complete gradient structure, further improving the fiber's breaking strength and elongation, and thus significantly enhancing the mechanical properties of the aramid paper. Therefore, the preferred three-zone channel design of this invention can further improve the overall performance of aramid paper and has higher industrial application value.

[0123] 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.

[0124] 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 process for producing a meta- aramid fiber, characterized by, The preparation method is as follows: S1. A crosslinking agent is added to the meta-aromatic polyamide stock solution and mixed evenly to form a spinning solution; the crosslinking agent is selected from at least one of pyromellitic tricarboxylic acid chloride and 1,2,4,5-benzenetetra(carboxylic acid chloride); The amount of crosslinking agent added is 0.05%-0.5% of the mass of the meta-aromatic polyamide in the meta-aromatic polyamide stock solution; S2. After the spinning solution is preheated, it is dry-spun to form nascent filaments. The nascent filaments are then stretched in a stretching bath and then washed, dried and heat-treated to obtain the meta-aromatic polyamide fiber. In the dry spinning process of step S2, the spinning solution, after being filtered and defoamed, is preheated and then extruded through a spinneret and stretched through a tunnel to obtain the nascent filament. The temperature inside the tunnel is 170-250℃, and the nascent filament stays in the tunnel for 13-27 seconds. The preheating temperature of the spinning solution is 100-150℃.

2. The method for preparing meta-aromatic polyamide fibers according to claim 1, characterized in that, In the dry spinning process of step S2, the stretch ratio of the nascent filament in the channel is 10-20 times.

3. The method for preparing meta-aromatic polyamide fiber according to claim 1, characterized in that, The stretching bath is pure water or a dilute solution, wherein the dilute solution is an aqueous solution containing calcium chloride and DMAc, wherein the mass content of calcium chloride in the dilute solution is 1-3 wt%, and the mass content of DMAc in the dilute solution is 5-10 wt%.

4. The method for preparing meta-aromatic polyamide fibers according to claim 1, characterized in that, The stretching bath temperature is 30-60℃, and the nascent filaments are stretched 3-5 times in the stretching bath.

5. The method for preparing meta-aromatic polyamide fibers according to claim 1, characterized in that, In step S2, the fiber is sprayed and washed with deionized water at 60-90℃. After washing, the fiber is dried on a drying roller at 150-200℃ and then heat-treated in a hot tunnel at 300-350℃ for 20-60 seconds. The stretching ratio is 1-1.2 times, and finally meta-aromatic polyamide fiber is obtained.

6. The method for preparing meta-aromatic polyamide fiber according to claim 1, characterized in that, The meta-aromatic polyamide stock solution has a viscosity of 5000-10000 Po at 25°C and a solid content of 18-22 wt%.

7. A meta-aromatic polyamide fiber, characterized in that, The meta-aromatic polyamide fiber is prepared according to the preparation method described in any one of claims 1-6.

8. An application of the meta-aromatic polyamide fiber according to claim 7, characterized in that, The meta-aromatic polyamide fiber is used in the preparation of meta-aramid paper.

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