CN112458583B

CN112458583B - Para-aramid fiber, preparation method thereof and application of para-aramid fiber in preparation of molten metal splash protection clothing

Info

Publication number: CN112458583B
Application number: CN202011140303.5A
Authority: CN
Inventors: 马千里; 杨文华; 高殿飞; 张盼盼; 杜志林; 毕景中
Original assignee: YANTAI TAYHO ADVANCED MATERIALS CO Ltd
Current assignee: Taihe New Material Group Co ltd
Priority date: 2020-10-22
Filing date: 2020-10-22
Publication date: 2021-09-17
Anticipated expiration: 2040-10-22
Also published as: CN112458583A

Abstract

The invention discloses a para-aramid fiber, a preparation method thereof and application thereof in preparing molten metal splash protective clothing, and belongs to the field of aramid fibers and preparation methods thereof. The para-aramid short fiber suitable for the molten metal splash protection in industrial production is prepared by adopting the processes of high-pressure transmission and extrusion, a fine-hole spinneret plate and a low-temperature coagulating bath. The compactness of the fiber is improved by high-pressure conveying and extrusion of more than 10MP, the surface compactness and surface smoothness are increased by high-pressure spinneret orifices below 0.060mm, and the finer monofilament fineness reduces air holes generated by volatilization of sulfuric acid, so that the surface of the fiber is more perfect, and the fiber has better adsorption resistance of molten metal splashes. The molten metal splash protection fabric prepared based on the method has good high temperature resistance, surface compactness and flame retardance, can enable molten metal to quickly slip from the surface and not burn, and reduces casualties.

Description

Para-aramid fiber, preparation method thereof and application of para-aramid fiber in preparation of molten metal splash protection clothing

Technical Field

The invention belongs to the field of aramid fibers and preparation methods thereof, and relates to para-aramid fibers, a preparation method thereof and application thereof in preparing molten metal splash protective clothing.

Background

The smelting process is complex, and there are many dangerous sources in the whole production process, including smoke, noise, high-temperature radiation, splashing of metal solution and slag, blast furnace gas combustion explosion, coal dust explosion, etc. According to accident data statistics of the past years, the burning accidents are the most, and the burning accidents are specifically shown as the burns to human bodies caused by the overturning and falling of high-temperature metal liquid, the radiation heat of the high-temperature metal liquid, the splashing and leakage of molten metal and the like; the traditional individual protective articles are mainly made of wool, flame-retardant viscose, chinlon and other materials which are blended and processed into fabrics, and then the fabrics are made into protective clothing. The fabric is easy to wear and poor in tear resistance due to low strength of materials such as wool and flame-retardant viscose, and the nylon material is not flame-retardant, so that the flame-retardant and heat-insulating properties of the fabric can be improved only by increasing the proportion of the wool and the flame-retardant viscose and increasing the unit area mass of the fabric.

The molten metal splash protection fabric meets the requirement of the molten metal splash protection fabric in accordance with the aluminum water splash test of EN ISO 9185-2008, and the quality of the splash protection aluminum water is more than or equal to 100 g; the judgment criteria of EN ISO11612-2015 are shown in Table 1 by flame retardancy test using EN ISO 15025-2016A1+ A2.

TABLE 1 judgment standards for EN ISO11612-2015

The patent with the patent application number of CN201110133797.9 discloses a poly-p-phenylene terephthamide fiber and a preparation method thereof, the poly-p-phenylene terephthamide fiber is a medium-modulus poly-p-phenylene terephthamide fiber, the poly-p-phenylene terephthamide polymer with the logarithmic viscosity of 5.5-8.0 dL/g obtained by adopting a low-temperature solution polycondensation method is used as a raw material, and before the washing, neutralization and drying processes of a dry-jet wet spinning process, the poly-p-phenylene terephthamide fiber is prepared by stretching wet yarns which are not dried, the modulus of the poly-p-phenylene terephthamide fiber is 550-800 g/D, and the logarithmic viscosity is 5.0-7.5 dL/g, and a fiber product obtained by adopting the method has insufficient surface compactness and poor smoothness due to air holes and cannot meet the requirement of a merchant on a molten metal splashing material.

In summary, the para-aramid fiber has the characteristics of high monofilament strength, good flame retardance, excellent thermal stability and the like, and simultaneously has appropriate toughness for textile processing, so that the para-aramid fiber can be blended with wool, flame-retardant viscose and the like to prepare a fabric, the fabric can be used for preventing molten metal from splashing, the strength and the wear resistance of the fabric can be improved, and the weight of clothes is reduced.

Disclosure of Invention

The invention aims to overcome the defect that the para-aramid fiber is easy to be adhered when encountering high-temperature metal liquid due to poor smoothness in the prior art, and provides the para-aramid fiber, a preparation method thereof and application thereof in preparing molten metal splash protective clothing.

In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:

a preparation method of para-aramid fiber comprises the following steps:

step one, taking concentrated sulfuric acid as a solvent, and preparing a polymer mixed solution with the mass percent of 19-20% from a poly-p-phenylene terephthalamide raw material;

mixing the polymer mixed solution and concentrated sulfuric acid according to the ratio of 1: 4-1: 4.5, standing for dissolving for not less than 3 hours, and standing for 3-4 hours under a vacuum condition for defoaming to obtain a spinning solution;

and step three, extruding and pushing the spinning solution under the pressure of more than 10MP, filtering, passing through a spinneret plate with the aperture of 0.050-0.070 mm, and performing dry-jet wet spinning on the sprayed filaments to obtain the para-aramid fibers.

Preferably, the molecular weight of the poly-p-phenylene terephthalamide raw material in the first step is 40000-60000, and the viscosity is 6.5-7.5 dL/g; the poly-p-phenylene terephthamide raw material is prepared by a low-temperature solution polycondensation method.

Further preferably, the poly (p-phenylene terephthalamide) raw material is prepared by adding a raw material of poly (p-phenylene terephthalamide) to an N-methylpyrrolidone solvent in a molar ratio of 1: 1, and then carrying out low-temperature solution polycondensation to obtain the p-phthaloyl chloride and the p-phenylenediamine, wherein isocyanate is added in the preparation process;

more preferably, the adding amount of the isocyanate is 0.5 to 2 percent of the total mass of the p-phenylenediamine, the N-methylpyrrolidone and the terephthaloyl chloride;

further preferably, the isocyanate is one or more of L-lysine triisocyanate, toluene-2, 4, 6-triyl triisocyanate and triphenylmethane triisocyanate.

Preferably, the dry-jet wet-spinning process in the third step comprises the processes of solidification, extraction, spinning, washing, drying and shaping, oiling, winding and chopping.

Further preferably, the solidification process is specifically: the sprayed silk firstly passes through an air layer of 6-16 mm and then enters a dilute sulfuric acid solution with the temperature of 1-13 ℃ and the mass fraction of 1-5% for solidification.

Preferably, the washing comprises a primary washing process, an alkali washing neutralization process, a secondary alkali washing neutralization process and a secondary washing process; the drying and shaping are 4-12-grade hot drying and shaping at 110-240 ℃.

Preferably, the alkali washing neutralization process is to neutralize by using 0.1-2% of sodium hydroxide solution by mass fraction; and in the washing and drying and shaping processes, the winding speed is controlled to be 200-500 m/min.

The para-aramid fiber obtained by the preparation method has the linear density of 0.5-1.4D and the diameter of 5-12 microns.

The application of the para-aramid fiber in preparing the molten metal splash protective clothing comprises, by mass, 10-30% of para-aramid fiber, 40% of wool fiber and 30-50% of flame-retardant viscose fiber in the protective yarn for preparing the clothing.

Compared with the prior art, the invention has the following beneficial effects:

the invention discloses a preparation method of para-aramid fiber, which is used for preparing para-aramid short fiber suitable for molten metal splash protection in industrial production by adopting high-pressure transmission and extrusion, a fine-hole spinneret plate and a low-temperature coagulation bath process. The compactness of the fiber is improved by high-pressure conveying and extrusion of more than 10MP, the surface compactness and the surface smoothness are improved by a spinneret plate with high pressure and a pore diameter of 0.050-0.070 mm, the fine filament number reduces air holes generated by volatilization of sulfuric acid, the surface of the fiber is more perfect, the fiber has better adsorption resistance of molten metal splashes, the dissolving time in a dissolving machine is prolonged to be not less than 3 hours, the poly-p-phenylene terephthalamide is fully dissolved in concentrated sulfuric acid, and the dissolution and degradation are completed. The molten metal splash protection fabric prepared based on the method has good high temperature resistance, surface compactness and flame retardance, can enable molten metal to quickly slip from the surface and not burn, and reduces casualties. The dry-jet wet spinning process is adopted, and the fiber with high density and bright and smooth surface can be spun.

Furthermore, a certain amount of isocyanate is added, so that the isocyanate can participate in polymerization reaction and has the function of cross-linking and blocking, and the strength and the modulus of the prepared para-aramid short fiber are improved; the isocyanate is one or more of L-lysine triisocyanate, toluene-2, 4, 6-triyl triisocyanate and triphenylmethane triisocyanate.

Further, the poly-p-phenylene terephthalamide with the intrinsic viscosity of 6.5-7.5 dL/g can be obtained by adopting a low-temperature solution polycondensation method, and the low-temperature coagulating bath at the temperature of 1-13 ℃ can ensure that sulfuric acid is absorbed as soon as possible when meeting water and releasing heat, so that the fiber has a more perfect skin-core structure, the surface smoothness of the fiber is improved, and the fiber has a better anti-adsorption function.

Further, the dry-jet wet spinning process comprises the working procedures of solidification, extraction, spinning, washing, drying and shaping, oiling, winding and chopping, and the solidification process specifically comprises the following steps: the sprayed filaments firstly pass through an air layer of 6-16 mm and then enter a dilute sulfuric acid solution with the temperature of 1-13 ℃ and the mass fraction of 1-5% for solidification, so that the internal structure of the fiber is uniform, the crystallinity and the orientation degree are high, the strength is improved, and the surface of the fiber is smooth.

Further, the washing comprises the processes of primary washing, alkali washing neutralization, secondary alkali washing neutralization and secondary washing; the alkali washing neutralization process is to neutralize by using 0.1-2% of sodium hydroxide solution by mass fraction, and can remove residual solvent by cleaning.

Furthermore, the drying and shaping are multi-stage heat drying and shaping of 4-12 levels at 110-240 ℃, so that the fiber can reach a stable state on the premise of not damaging the performance.

The invention discloses a para-aramid fiber, which adopts a fine-hole spinneret plate to obtain a thinner fiber, and a molten metal splash protection fabric prepared based on the fine-hole spinneret plate has good high temperature resistance, surface compactness and flame retardance; the low-temperature coagulating bath is adopted, so that the crystallinity and the orientation degree of the para-aramid fiber are improved, the strength of the para-aramid fiber is improved, the surface of the para-aramid fiber is smooth, and the para-aramid fiber, the wool fiber and the flame-retardant viscose fiber can be used for preparing molten metal splash protective clothing together.

Drawings

FIG. 1 is an SEM image of para-aramid fibers at 1000 times magnification;

FIG. 2 is an SEM image of para-aramid fibers at 500 times magnification;

FIG. 3 is a weave pattern of fabrics of examples and comparative examples.

Detailed Description

In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It is to be understood that the terms in the description and in the claims, and in the drawings, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

The invention is described in further detail below with reference to the accompanying drawings:

example 1

A preparation method of para-aramid fiber comprises the following steps:

dissolving p-phenylenediamine into N-methylpyrrolidone by taking N-methylpyrrolidone as a solvent, and then adding paraphthaloyl chloride, wherein the molar ratio of the p-phenylenediamine to the paraphthaloyl chloride is 1: 1, dissolving and reacting for 50min to obtain a mixed solution, adding triphenylmethane triisocyanate into the mixed solution, wherein the addition amount of the triphenylmethane triisocyanate is 0.5% of the total mass of the mixed solution, and then carrying out polycondensation reaction at the low temperature of-10 ℃ for 5min to obtain the poly-p-dibenzoyl-p-phenylenediamine polymer raw material with the intrinsic viscosity of 6.5-7.5 dL/g.

(1) Adding poly-p-phenylene terephthalamide polymer raw materials with intrinsic viscosity of 6.5-7.5 dL/g into concentrated sulfuric acid with concentration of 99-101% to mix uniformly, and stirring to control the temperature to 80-90 ℃ to prepare a mixed solution with the mass percentage of the poly-p-phenylene terephthalamide being 19-20%; adding poly-p-phenylene terephthamide and concentrated sulfuric acid into a double-screw extruder according to a ratio, primarily mixing the poly-p-phenylene terephthamide and the concentrated sulfuric acid by the extruder, pushing the mixture into a dissolving machine to completely dissolve the poly-p-phenylene terephthamide in the concentrated sulfuric acid, wherein the dissolving time is not less than 3 hours, and performing vacuum defoaming on the poly-p-phenylene terephthamide for 3-4 hours to ensure that the dissolving performance and the degradation performance are consistent.

(2) The spinning solution which is fully mixed, well temperature-regulated and completely bubble-removed is delivered under high pressure, passes through a metering pump and is filtered, and then is sent into a fine-hole spinneret plate. And (3) spinning the spinning solution to form filaments after being sprayed out of a spinneret plate, passing through an air layer of 6-16 mm, entering low-temperature 1-5% dilute sulfuric acid coagulation bath liquid, and ensuring the compactness and smoothness of the fibers through high-pressure transmission and extrusion, a fine-hole spinneret plate and the low-temperature coagulation bath. The spun tows are subjected to primary washing, alkaline washing neutralization, secondary washing and drying processes, then are subjected to multi-stage heating, drying and shaping, are cooled, are oiled, are wound and formed, and are cut into short fibers, so that the para-aramid fibers with the fineness of 1.3D are obtained.

The morphology of the para-aramid fiber prepared in the embodiment is characterized, and the results are shown in fig. 1 and fig. 2, and the scanning electron microscope results show that the average linear density of the para-aramid fiber is 0.5-1.4D, and the diameter of the para-aramid fiber is 5-12 micrometers.

Example 2

The amount of triphenylmethane triisocyanate added was 1% by mass of the total of p-phenylenediamine, N-methylpyrrolidone, and terephthaloyl chloride, and the rest of the contents were the same as in example 1.

Example 3

The amount of triphenylmethane triisocyanate added was 1.5% by mass of the total of p-phenylenediamine, N-methylpyrrolidone and terephthaloyl chloride, and the rest was the same as in example 1.

Example 4

The amount of triphenylmethane triisocyanate added was 2% by mass of the total mass of p-phenylenediamine, N-methylpyrrolidone, and terephthaloyl chloride, and the rest of the contents were the same as in example 1.

Comparative example 1

The same procedure as in example 1 was repeated except that the amount of triphenylmethane triisocyanate added was 0.

Comparative example 2

The content of isocyanate in the existing 1.5D molten metal splash protection fiber on the market is 0.

The aramid fibers obtained in the above examples and comparative examples were subjected to performance tests, and the results are shown in table 2.

TABLE 2 Performance test results of aramid fibers of examples and comparative examples

As can be seen from examples 1 to 4 and comparative example 1 in table 2, as the content of the isocyanate increases, the breaking strength, elongation at break and modulus of the 1.3D para-aramid fiber are effectively improved, and the smoothness of the fiber is higher, so that the fabric manufactured based on the fiber is stiffer and smoother, is not easy to deform, has large impact resistance and has good surface compactness.

As can be seen from examples 1-4 and comparative example 2 in Table 2, the 1.3D para-aramid fiber prepared by the invention has better performance than the 1.5D para-aramid fiber on the market, and is a high-strength high-modulus fine denier filament.

Example 5

L-lysine triisocyanate was used in place of triphenylmethane triisocyanate in example 1, that is, L-lysine triisocyanate was added in an amount of 0.5% by mass based on the total mass of p-phenylenediamine, N-methylpyrrolidone and terephthaloyl chloride, and the remainder was the same as in example 1.

Wool, flame-retardant viscose and the 1.3D para-aramid fiber prepared in the embodiment are mixed according to a certain proportion range, and the mixture is spun to prepare a fabric, wherein the content of isocyanate in the 1.3D para-aramid fiber raw material is 0.5%, and the fabric texture diagram is shown in figure 3.

The mass percentages of the para-aramid fiber, the wool and the flame-retardant viscose are as follows: para-aramid: 10 percent; wool: 40 percent; and (3) flame-retardant adhesive: 50 percent.

Example 6

The amount of L-lysine triisocyanate added was 1% based on the total mass of p-phenylenediamine, N-methylpyrrolidone and terephthaloyl chloride, and the rest was the same as in example 5.

The mixture of wool, flame retardant viscose and the 1.3D para-aramid fiber prepared in this example was mixed in a certain ratio range, and the rest was the same as in example 5.

Example 7

The amount of L-lysine triisocyanate added was 1.5% by mass based on the total mass of p-phenylenediamine, N-methylpyrrolidone and terephthaloyl chloride, and the remainder was the same as in example 5.

Example 8

The amount of L-lysine triisocyanate added was 2.0% by mass of the total of p-phenylenediamine, N-methylpyrrolidone and terephthaloyl chloride, and the rest was the same as in example 5.

Example 9

Toluene-2, 4, 6-triyl triisocyanate was used in place of triphenylmethane triisocyanate in example 1, that is, toluene-2, 4, 6-triyl triisocyanate was added in an amount of 0.5% by mass based on the total mass of p-phenylenediamine, N-methylpyrrolidone and terephthaloyl chloride, and the rest was the same as in example 1.

The 1.3D para-aramid fiber prepared by the wool, the flame-retardant viscose and the embodiment is mixed according to a certain proportion range, wherein the mass percentages of the para-aramid fiber, the wool and the flame-retardant viscose are as follows: para-aramid: 20 percent; wool: 40 percent; and (3) flame-retardant adhesive: 40% and the rest is the same as in example 5.

Example 10

Toluene-2, 4, 6-triyl triisocyanate was added in an amount of 1.0% by mass based on the total mass of p-phenylenediamine, N-methylpyrrolidone and terephthaloyl chloride, and the remainder was the same as in example 9.

The same procedure as in example 9 was repeated except that the blend of wool, flame retardant adhesive and 1.3D para-aramid fiber prepared in this example was mixed in a certain ratio range.

Example 11

Toluene-2, 4, 6-triyl triisocyanate was added in an amount of 1.5% by mass based on the total mass of p-phenylenediamine, N-methylpyrrolidone and terephthaloyl chloride, and the remainder was the same as in example 9.

Example 12

Toluene-2, 4, 6-triyl triisocyanate was added in an amount of 2.0% by mass based on the total mass of p-phenylenediamine, N-methylpyrrolidone and terephthaloyl chloride, and the remainder was the same as in example 9.

Example 13

The 1.3D para-aramid fiber prepared in the embodiment 1 is mixed with wool, the flame-retardant viscose in a certain proportion range, wherein the mass percentages of the para-aramid fiber, the wool and the flame-retardant viscose are as follows: para-aramid: 30 percent; wool: 40 percent; and (3) flame-retardant adhesive: 30% and the rest is the same as in example 5.

Example 14

The same example 13 was repeated except that the blend of wool, flame retardant viscose and 1.3D para-aramid fiber obtained in example 2 above was mixed in a certain ratio range.

Example 15

The same example 13 was repeated except that the blend of wool, flame retardant viscose and 1.3D para-aramid fiber obtained in example 3 above was mixed in a certain ratio range.

Example 16

The same example 13 was repeated except that the blend of wool, flame retardant viscose and 1.3D para-aramid fiber obtained in example 4 above was mixed in a certain ratio range.

Comparative example 3

The 1.3D para-aramid fiber prepared by the wool, the flame-retardant viscose and the comparative example 1 is mixed according to a certain proportion range, wherein the mass percentages of the para-aramid fiber, the wool and the flame-retardant viscose are as follows: para-aramid: 10 percent; wool: 40 percent; and (3) flame-retardant adhesive: 50% and the rest is the same as in example 5.

Comparative example 4

The 1.3D para-aramid fiber prepared by the wool, the flame-retardant viscose and the comparative example 1 is mixed according to a certain proportion range, wherein the mass percentages of the para-aramid fiber, the wool and the flame-retardant viscose are as follows: para-aramid: 20 percent; wool: 40 percent; and (3) flame-retardant adhesive: 40% and the rest is the same as in example 5.

Comparative example 5

The 1.3D para-aramid fiber prepared by the wool, the flame-retardant viscose and the comparative example 1 is mixed according to a certain proportion range, wherein the mass percentages of the para-aramid fiber, the wool and the flame-retardant viscose are as follows: para-aramid: 30 percent; wool: 40 percent; and (3) flame-retardant adhesive: 30% and the rest is the same as in example 5.

Comparative example 6

The 1.5D para-aramid fiber prepared by the wool, the flame-retardant viscose and the comparative example 2 is mixed according to a certain proportion range, wherein the mass percentages of the para-aramid fiber, the wool and the flame-retardant viscose are as follows: para-aramid: 10 percent; wool: 40 percent; and (3) flame-retardant adhesive: 50% and the rest is the same as in example 5.

Comparative example 7

The 1.5D para-aramid fiber prepared by the wool, the flame-retardant viscose and the comparative example 2 is mixed according to a certain proportion range, wherein the mass percentages of the para-aramid fiber, the wool and the flame-retardant viscose are as follows: para-aramid: 20 percent; wool: 40 percent; and (3) flame-retardant adhesive: 40% and the rest is the same as in example 5.

Comparative example 8

The 1.5D para-aramid fiber prepared by the wool, the flame-retardant viscose and the comparative example 2 is mixed according to a certain proportion range, wherein the mass percentages of the para-aramid fiber, the wool and the flame-retardant viscose are as follows: para-aramid: 30 percent; wool: 40 percent; and (3) flame-retardant adhesive: 30% and the rest is the same as in example 5.

The weave patterns of the fabrics used in the examples and comparative examples are shown in FIG. 1. 2, the upper part and the lower part are twill, the black is warp yarn, and the white is weft yarn.

Molten metal splash prevention tests were performed on the fabrics prepared in the above examples and comparative examples, and the results are shown in table 3.

TABLE 3 molten metal splash protection test results for fabrics prepared in examples and comparative examples

From the data in table 3, the following conclusions can be drawn:

according to the change of the index data of the embodiment, on the basis of ensuring the elasticity and the flame retardance of the fabric, the more the para-aramid fiber content is, the better the surface compactness of the fabric is, and the better the splashing protection performance and the heat resistance performance of the molten metal are.

Comparing examples 5-8 with comparative example 3, it can be seen that the addition of isocyanates can effectively improve the heat resistance and strength of the fabric, and the optimal addition amount is 1-1.5% of the total mass of p-phenylenediamine, N-methylpyrrolidone and terephthaloyl chloride.

Comparing the examples and the comparative examples, it is understood that when the 1.3D para-aramid fiber of the same ratio is replaced with the 1.5D para-aramid fiber, the heat resistance, strength and other properties of the fabric are reduced.

The flame-lasting time and the smoldering time of the embodiment are both less than 2 seconds, so that the fabric is free from melting and dripping and is free from holes, and the requirement of international standard ISO11612-2015 is met. Therefore, the high-strength high-modulus molten metal splash protection short fiber has excellent molten metal splash protection performance and can meet the requirements of flame retardance and strength.

The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.

Claims

1. The preparation method of the para-aramid fiber is characterized by comprising the following steps:

mixing the polymer mixed solution with concentrated sulfuric acid according to the proportion of 1 (4-4.5), standing for dissolving for not less than 3 hours, and standing for 3-4 hours under a vacuum condition for defoaming to obtain a spinning solution;

extruding and pushing the spinning solution under the pressure of more than 10MP, filtering, passing through a spinneret plate with the aperture of 0.050-0.070 mm, and performing dry-jet wet spinning on the sprayed filaments to obtain para-aramid fibers;

the molecular weight of the poly-p-phenylene terephthamide raw material in the step one is 40000-60000, and the viscosity is 6.5-7.5 dL/g;

the poly-p-phenylene terephthalamide raw material is prepared by adding a raw material into an N-methyl pyrrolidone solvent according to a molar ratio of 1: 1, then carrying out low-temperature solution polycondensation to obtain the product, wherein isocyanate is added in the preparation process, and the adding amount of the isocyanate is 0.5-2% of the total mass of the p-phenylenediamine, the N-methylpyrrolidone and the p-phthaloyl chloride; the isocyanate is one or more of L-lysine triisocyanate, toluene-2, 4, 6-triyl triisocyanate and triphenylmethane triisocyanate.

2. The method for preparing the para-aramid fiber according to claim 1, wherein the dry-jet wet-spinning process of the third step comprises the processes of solidification, extraction, spinning, washing, drying and shaping, oiling, winding and chopping.

3. The preparation method of the para-aramid fiber according to claim 2, characterized in that the solidification process specifically comprises: the sprayed filaments firstly pass through an air layer of 6-16 mm and then enter a dilute sulfuric acid solution with the temperature of 1-13 ℃ and the mass fraction of 1-5% for solidification.

4. The preparation method of para-aramid fiber according to claim 2, wherein the washing includes primary washing, alkali washing neutralization, secondary alkali washing neutralization and secondary washing processes; the drying and shaping are 4-12-grade hot drying and shaping at 110-240 ℃.

5. The preparation method of the para-aramid fiber according to claim 4, characterized in that the alkali washing neutralization process is neutralization with 0.1-2% by mass of sodium hydroxide solution; and in the washing and drying and shaping processes, the winding speed is controlled to be 200-500 m/min.

6. The para-aramid fiber obtained by the preparation method according to any one of claims 1 to 5, wherein the para-aramid fiber has a linear density of 0.5 to 1.4D and a diameter of 5 to 12 μm.