Aramid microfiber and its preparation method and apparatus

Abstract

This invention discloses an aramid fine fiber and its preparation method and apparatus. The apparatus includes a liquid inlet unit, a collector, and a booster. The liquid inlet unit includes a liquid inlet plate and a liquid inlet conveying pipe. The liquid inlet plate includes a liquid distribution plate with several liquid inlet holes and a first mesh surface covered on the liquid distribution plate. The liquid inlet conveying pipe is connected to the liquid distribution plate. A docking panel covered with a second mesh surface is provided opposite the first mesh surface. The booster drives the first and second mesh surfaces to reciprocate between close contact and a distance of more than 5 cm. After contact and separation, the two mesh surfaces generate filaments. The collector collects the fine fibers. The preparation method of aramid fine fiber is as follows: (1) Prepare an aramid polymer solution; (2) Prepare ultrafine aramid fiber bundles using the above apparatus; (3) Obtain ultrafine aramid fibers with smaller diameter and larger specific surface area by stretching and heat setting. This invention can significantly improve the interfacial bonding strength of fibers in aramid paper and effectively improve the mechanical strength and dielectric properties of aramid paper.

Description

Technical Field

[0001] This invention belongs to the field of new materials, and specifically relates to an aramid microfiber and its preparation method and apparatus. Background Technology

[0002] Aramid fibers are synthetic fibers spun from linear polyamides containing aromatic rings. They are divided into fully aromatic polyamide fibers and aliphatic polyamide fibers containing aromatic rings. The main varieties include poly(m-phenylene isophthalamide) fiber (meta-aramid), poly(p-phenylene terephthalamide) fiber (para-aramid), and poly(p-phenylene terephthalamide) fiber. Meta-aramid is formed by the condensation polymerization of m-phenylene diamine and isophthaloyl chloride. The amide groups in the meta-aramid macromolecule are interconnected by meta-phenyl groups, and its covalent bonds do not have a conjugation effect. Its internal rotational energy is relatively lower than that of para-aramid fibers, and the macromolecular chain exhibits a flexible structure. Its strength and modulus are comparable to those of typical polyesters and nylons. Meta-aramid fiber is a high-tech specialty fiber with excellent mechanical properties, stable chemical properties, and excellent heat resistance.

[0003] The production technology of aramid microfiber has been a hot research topic in recent years. Aramid microfiber is a high-quality, high-tech fiber. It retains the excellent mechanical, acid and alkali resistance, high temperature resistance, and flame retardant properties of aramid. At the same time, due to its smaller diameter, it has a larger specific surface area and adhesion, resulting in characteristics such as soft hand feel, high strength, gentleness, and higher moisture absorption than ordinary aramid. Its fibers and fabrics possess numerous advantages, including a soft hand feel, lightweight and softness, breathability, good drape, and self-extinguishing properties, leading to the continuous expansion of the application of ultrafine aramid fiber in textiles, clothing, papermaking, and filtration. However, the lack of domestic technology for producing ultrafine aramid fiber means that existing aramid manufacturers cannot meet the domestic market demand.

[0004] Currently, there is no efficient technology in China for producing ultrafine meta-aramid fibers. For example, Chinese patent 202111349941.2 discloses an aramid fiber, its preparation method, and its application. This involves repeatedly stretching and washing the fiber to obtain an aramid single fiber with a linear density of 2.7 dtex and a strength of 3.7 cN / dtex. Chinese patent 202111491249.3 discloses a spinning method for meta-aramid fibers, achieving a fiber fineness of 1.5 dtex and a single fiber strength of up to 5.10–5.23 cN / dtex. Other reported aramid fine fiber production technologies include electrospinning, rotary jet spinning, jet spinning, and mechanical processing. However, electrospinning has low production efficiency and difficulty in size control; mechanical methods have high energy consumption and power requirements; and jet spinning produces aramid fibers with large diameters, uncontrollable lengths, and a wide size distribution. In summary, current domestic aramid fiber manufacturing technologies primarily focus on single-fiber strength, neglecting techniques for producing ultrafine fibers (fibers with an average diameter of less than 10 μm). Therefore, finding a rapid and effective technology for preparing aramid fine fibers is crucial for realizing their functionalization, high performance, and diversified applications in various fields such as aramid paper, textile materials, reinforcing materials, battery separators, electrically insulating nanopaper, flexible electronic devices, and adsorption filtration media. Summary of the Invention

[0005] The primary objective of this invention is to overcome the shortcomings and deficiencies of the prior art and provide a method for preparing ultrafine aramid fibers.

[0006] Another object of the present invention is to provide ultrafine aramid fibers prepared by the method described above.

[0007] Another object of the present invention is to provide a molding apparatus for preparing ultrafine aramid fibers by the method described above.

[0008] Another object of the present invention is to provide applications of the aforementioned ultrafine aramid fibers.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] An apparatus for preparing fine fibers includes a liquid inlet unit, a collector, and a booster. The liquid inlet unit includes a liquid inlet plate and a liquid inlet delivery pipe. The liquid inlet plate includes a liquid distribution plate with a plurality of liquid inlet holes and a first mesh surface covering the liquid distribution plate. The liquid inlet delivery pipe is connected to the liquid distribution plate. A docking panel covered with a second mesh surface is disposed opposite the first mesh surface. The booster drives the liquid inlet plate and / or the docking panel to move, causing the first mesh surface and the second mesh surface to reciprocate between close contact and a distance of more than 5 cm. After contact and separation, the two mesh surfaces generate fiber pulling. Each time the distance between the two mesh surfaces reaches or approaches its maximum, the collector passes through the space between the two mesh surfaces to collect the fine fibers.

[0011] Preferably, the first and second mesh surfaces are mesh blankets or mesh grids; the booster drives the docking panel to move.

[0012] Preferably, the collector consists of two or more collecting plates driven by a motor to rotate, with the collecting plates moving between a first mesh surface and a second mesh surface.

[0013] A method for preparing aramid microfibers includes the following steps:

[0014] (1) Preparation of aramid polymer solution;

[0015] (2) Using the above device to prepare ultrafine aramid fiber bundles: The aramid polymer dispersion obtained by diluting the aramid polymer solution in step (1) is introduced into the liquid feeding unit. The booster is turned on so that the first mesh surface and the second mesh surface are in close contact and then separated. Numerous fine filaments are generated between the two mesh surfaces. The collector collects the aramid filaments through the gap between the two mesh surfaces. When the collector leaves, the two mesh surfaces are in close contact again under the drive of the booster and then separated and drawn. The collector collects the aramid filaments through the gap between the two mesh surfaces again. This cycle is repeated to collect oriented ultrafine aramid fiber bundles.

[0016] (3) Ultrafine aramid fiber bundles are stretched and shaped to obtain ultrafine aramid fibers.

[0017] Preferably, the concentration of the aramid polymer dispersion in step (2) is 5-30% by mass; the maximum distance between the first and second mesh surfaces is 5-100 cm; the liquid feeding rate is 0.1-50 mL / min; and the temperature of the aramid polymer dispersion entering the liquid feeding unit is 25-80 °C.

[0018] Preferably, (1) the preparation of the aramid polymer solution is: a neutral aramid polymer solution is prepared by polymerizing m-phenylenediamine and isophthaloyl chloride in an organic solvent under low temperature and protective atmosphere conditions; the molar ratio of m-phenylenediamine to isophthaloyl chloride is 100:(85-120); isophthaloyl chloride is added in 2-5 batches.

[0019] Preferably, the concentration of the aramid polymer dispersion in step (2) is 10-25% by mass, the maximum spacing between the first and second mesh surfaces is 15-50 cm, the liquid feeding rate is 10-40 mL / min, and the aramid polymer dispersion is also subjected to vacuum defoaming pretreatment.

[0020] Preferably, the stretching and shaping of the ultrafine aramid fiber bundle in step (3) is as follows: the ultrafine aramid fiber bundle collected in step (2) is twisted into a thin thread, and then replaced and washed in the extraction solution and washing solution, then stretched and then heat-shaped to finally obtain ultrafine aramid fiber.

[0021] Preferably, in step (3), the stretching ratio is 0.1 to 5.0, the stretching temperature is 30 to 150°C, the heat setting temperature is 260 to 330°C, and the time is 1 to 30 minutes; the extraction solution is an aqueous solution or alcoholic solution of one or more of dimethylacetamide, dimethylformamide, dimethyl sulfoxide, ethylene glycol, glycerol, and acetone.

[0022] Preferably, the extract in step (3) is a curing solution (a single solvent, an aqueous solution of a solvent, an alcoholic solution of a solvent, or other solutions with curing effects); preferably, it is one or a mixture of dimethylacetamide, dimethylformamide, dimethyl sulfoxide, ethylene glycol, glycerol, and acetone; more preferably, the extract is N,N-dimethylacetamide or a mixed solution of N,N-dimethylacetamide with ethylene glycol and water.

[0023] Preferably, in step (1) the preparation of aramid polymer: under low temperature and nitrogen protection atmosphere, the cosolvent and m-phenylenediamine are dissolved in N,N-dimethylacetamide, and then isophthaloyl chloride is added to obtain a reaction solution; as the reaction proceeds, the temperature of the reaction solution gradually increases, and after heat preservation treatment, an alkaline agent is added for neutralization to prepare a neutral aramid polymer solution.

[0024] The co-solvent is one or more of lithium bromide, lithium chloride, calcium chloride, and calcium bromide; the heat preservation treatment is performed at 40-80°C for 0.5-12 hours; the alkaline agent is one or more of calcium oxide, calcium hydroxide, lithium hydroxide, magnesium hydroxide, sodium hydroxide, and organic amine.

[0025] The aramid fibers prepared by the above method have a diameter of less than 5 μm.

[0026] The aramid fibers described can be used to prepare aramid paper, textiles, diaphragms, electrical insulation materials, adsorption and filtration materials, flexible electronic device substrates, etc.

[0027] The method and apparatus for preparing aramid fine fibers described above are also applicable to the preparation of other fine fibers, such as para-aramid fibers, polyacrylonitrile fibers, viscose fibers, spandex fibers, and other synthetic fibers.

[0028] The present invention has the following advantages and effects compared with the prior art:

[0029] (1) This invention allows for the easy acquisition of aramid fibers of different diameters by changing the distance between the upper and lower plates and the liquid flow rate. The amide groups in the meta-aramid macromolecules are interconnected by meta-phenyl groups, and their covalent bonds do not exhibit conjugation. Their internal rotation energy is relatively lower than that of para-aramid fibers, resulting in a flexible macromolecular chain that can withstand certain external forces. The stretching of the polymer molecules increases the length and angle of the chemical bonds, promoting the straightening and alignment of the aramid polymer chains. Furthermore, the size of the aramid fibers can be controlled and adjusted by regulating the feed concentration, feed temperature, stretching distance, and the size and type of the mesh openings.

[0030] (2) The aramid fine fibers prepared by the present invention have a smaller diameter and a larger specific surface area, which can significantly improve the interfacial bonding strength of the fibers in aramid paper, effectively enhance the mechanical strength and dielectric properties of aramid paper, and can be widely used in the field of high-end insulating new materials.

[0031] (3) The preparation of aramid fine fibers by the present invention is not only simple and convenient, but also has higher production efficiency than conventional preparation methods. It is suitable for continuous industrial production and has wide applications in papermaking, filtration, textiles, rubber, flexible circuit boards and other fields.

[0032] (4) The aramid fine fiber preparation technology in this invention is simple to operate, convenient and easy to implement, and has higher production efficiency than the current conventional preparation methods. It is suitable for industrial continuous production and can significantly improve the dielectric properties and interfacial bonding properties of aramid paper.

[0033] (5) The efficient preparation technology of aramid fine fibers of the present invention can also increase its functionalization and performance by adding functional units (such as functional nanoparticles, conductive polymers, thermally conductive fillers, etc.) to aramid polymers. This is of great significance for the diversified application of aramid fine fibers in various fields such as reinforcing materials, textile materials, battery separators, electrically insulating nanopaper, flexible electronic devices, and adsorption filter media. Attached Figure Description

[0034] Figure 1 This is a flowchart illustrating the preparation process of the aramid microfibers of this invention.

[0035] Figure 2 This is a schematic diagram of the apparatus for preparing aramid fine fibers.

[0036] Figure 3 This is a microscope image of the aramid fine fibers prepared in Example 4.

[0037] Figure 4 This is a diameter distribution diagram of the aramid fine fibers prepared in Example 4.

[0038] Figure 5 This is a microscope image of the aramid fine fibers prepared in Example 5.

[0039] Figure 6 This is a diameter distribution diagram of the aramid fine fibers prepared in Example 5. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to embodiments, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field. Test methods in the following embodiments that do not specify specific experimental conditions are generally performed under conventional experimental conditions. Unless otherwise specified, the reagents and raw materials used in the present invention are all commercially available.

[0041] The starting materials used in the preparation method of this invention can be purchased from the market or prepared according to existing technical methods.

[0042] like Figure 2 As shown, the apparatus for preparing aramid fine fibers according to this embodiment includes: first to fourth collecting plates 1-4, an upper liquid inlet plate 5, a lower plate 6, a circulation booster 7, a liquid inlet conveying pipe 8, a distribution plate 9 in the upper liquid inlet plate 5, a mesh blanket 10 in the upper liquid inlet plate 5, a feed main pipe 11, and a motor 14. The upper liquid inlet plate is a square with a side length of 30mm, and its surface material is made of stainless steel, chrome-plated alloy, or plastic; the dimensions of the upper liquid inlet plate and the lower plate can also be adjusted according to actual production. The size of the collecting plate can be adjusted according to the distance between the upper and lower plates.

[0043] The performance testing reference standards for aramid fibers and aramid paper involved in the embodiments of this invention are as follows:

[0044] Average diameter (GB / T 10685-2007), tensile strength (GB / T 453.2-2002), tear strength (GB / T455-2002), electrical strength (GB / T 1408.1-2016), dielectric constant and dielectric loss factor (GB / T 1409-2006).

[0045] Blank group

[0046] Aramid short fibers and aramid pulp were mixed in a mass ratio of 5:5 to form paper with a basis weight of 40 g / m². 2 The aramid paper, after being hot-pressed at 200℃, has a thickness of 0.05mm.

[0047] Example 1

[0048] An aramid microfiber, the preparation method of which is as follows:

[0049] (1) Preparation of aramid polymer: Under a nitrogen atmosphere and at a low temperature of 5℃, m-phenylenediamine was dissolved in N,N-dimethylacetamide, and lithium chloride was added. Then, isophthaloyl chloride was added in one step, controlling the molar ratio of m-phenylenediamine to isophthaloyl chloride to be 100:85. The temperature was gradually increased as the reaction proceeded, and finally held at 40℃ for 0.5 h. After the holding period, calcium oxide was added for neutralization to prepare a neutral aramid polymer solution.

[0050] (2) Preparation of ultrafine aramid fibers: The aramid polymer dispersion obtained in step (1) is diluted to a certain concentration and then defoamed under vacuum. It is then transported to the liquid inlet delivery pipe 8. Figure 2 On the upper inlet plate 5 of the molding equipment, the circulation booster 7 is turned on, and the lower plate 6 is raised so that it comes into close contact with the upper inlet plate 5 and then separates. Due to the rough surfaces of the upper and lower plates, countless fine filaments are generated in the upper and lower plates. At this time, the first collecting plate 1 collects the aramid fibers on its surface through the gap between the upper and lower plates. After the first collecting plate 1 moves away from the upper and lower plates, the circulation booster 7 continues to work, raising the lower plate 6 so that it comes into close contact with the upper inlet plate 5 and then separates. At this time, the second collecting plate 2 collects the aramid fibers on its surface through the gap between the upper and lower plates. This process is repeated, and after a certain period of collection, oriented ultrafine aramid fiber bundles are obtained.

[0051] The concentration of the aramid polymer dispersion is 8% by mass; the upper inlet plate is a stainless steel / chrome-plated alloy / plastic square frame with a side length of 30mm; the distance between the upper and lower plates is 5cm; and the inlet speed is 10mL / min at a temperature of 25℃.

[0052] (3) Stretching and shaping of ultrafine aramid fiber: The ultrafine aramid fiber obtained from the net in step (2) is twisted into a thin thread, and then replaced and washed in the extraction liquid and washing liquid. Finally, it is stretched on a universal testing machine and then heat-shaped in a high-temperature oven to finally prepare ultrafine aramid fiber.

[0053] The extraction solution was an aqueous solution of dimethylacetamide, with a mass ratio of dimethylacetamide:ethylene glycol:water = 50:40:10. The extraction temperature was 20℃ for 1 min; the water washing temperature was 20℃ for 5 min; the stretching ratio was 0.8, and the stretching temperature was 30℃. The heat setting temperature was 260℃ for 1 min.

[0054] The aramid fibers prepared above were formed on a Kayser fiber former to a basis weight of 40 g / m². 2 The aramid paper, prepared by hot pressing at 200℃ with a mass ratio of aramid chopped fibers: aramid pulp: aramid fine fibers = 5:4.5:0.5, has a thickness of 0.05mm.

[0055] Example 2

[0056] An aramid microfiber, the preparation method of which is as follows:

[0057] (1) Preparation of aramid polymer: m-phenylenediamine was dissolved in N,N-dimethylacetamide at 8℃ under a nitrogen atmosphere, and lithium chloride was added. Then, isophthaloyl chloride was added twice, controlling the molar ratio of m-phenylenediamine to isophthaloyl chloride to be 100:100. The temperature was gradually increased as the reaction proceeded, and finally held at 60℃ for 2 hours. After the holding period, propylenediamine was added for neutralization to prepare a neutral aramid polymer solution.

[0058] (2) Preparation of ultrafine aramid fibers: Refer to Example 1. The concentration of the aramid polymer dispersion is 10% by mass; the upper inlet plate is a stainless steel / chrome-plated alloy / plastic square frame with a side length of 30 mm; the distance between the upper and lower plates is 15 cm; the inlet speed is 20 mL / min at a temperature of 35 °C.

[0059] (3) Stretching and shaping of ultrafine aramid fiber: The ultrafine aramid fiber obtained from the net in step (2) is twisted into a thin thread, and then replaced and washed in the extraction liquid and washing liquid. Finally, it is stretched on a universal testing machine and then heat-shaped in a high-temperature oven to finally prepare ultrafine aramid fiber.

[0060] The extraction solution was an aqueous solution of dimethylacetamide, with a mass ratio of dimethylacetamide:ethylene glycol:water = 40:40:20. The extraction temperature was 50℃ for 10 min; the water washing temperature was 55℃ for 10 min; the stretching ratio was 1.6, and the stretching temperature was 80℃. The heat setting temperature was 280℃ for 5 min.

[0061] The aramid fibers prepared above were formed on a Kayser fiber former to a basis weight of 40 g / m². 2 The aramid paper, prepared by hot pressing at 200℃ with a mass ratio of aramid chopped fiber: aramid pulp: aramid fine fiber = 4.5: 4.5: 1, has a thickness of 0.05 mm.

[0062] Example 3

[0063] An aramid microfiber, the preparation method of which is as follows:

[0064] (1) Preparation of aramid polymer: m-phenylenediamine was dissolved in N,N-dimethylacetamide at 10℃ under a nitrogen atmosphere, and lithium chloride was added. Then, isophthaloyl chloride was added in three separate additions, controlling the molar ratio of m-phenylenediamine to isophthaloyl chloride to be 100:110. The temperature was gradually increased as the reaction proceeded, eventually reaching 70℃ and being maintained for 4 hours. After this temperature treatment, calcium oxide was added for neutralization, yielding a neutral aramid polymer solution.

[0065] (2) Preparation of ultrafine aramid fibers: Refer to Example 1. The concentration of the aramid polymer dispersion is 18% by mass; the upper inlet plate is a stainless steel / chrome-plated alloy / plastic square frame with a side length of 30 mm; the distance between the upper and lower plates is 30 cm; the inlet speed is 30 mL / min at a temperature of 40 °C.

[0066] (3) Stretching and shaping of ultrafine aramid fiber: The ultrafine aramid fiber obtained from the net in step (2) is twisted into a thin thread, and then replaced and washed in the extraction liquid and washing liquid. Finally, it is stretched on a universal testing machine and then heat-shaped in a high-temperature oven to finally prepare ultrafine aramid fiber.

[0067] The extraction solution was an aqueous solution of dimethylacetamide, with a mass ratio of dimethylacetamide:ethylene glycol:water = 40:30:30. The extraction temperature was 60℃ for 30 min; the water washing temperature was 65℃ for 30 min; the stretching ratio was 2.4, and the stretching temperature was 100℃. The heat setting temperature was 300℃ for 10 min.

[0068] The aramid fibers prepared above were formed on a Kayser fiber former to a basis weight of 40 g / m². 2 The aramid paper, prepared by hot pressing at 200℃ with aramid short fiber: aramid pulp: aramid fine fiber in a mass ratio of 4:5:1, has a thickness of 0.05mm.

[0069] Example 4

[0070] An aramid microfiber, the preparation method of which is as follows:

[0071] (1) Preparation of aramid polymer: m-phenylenediamine was dissolved in N,N-dimethylacetamide at 15℃ under a nitrogen atmosphere, and lithium chloride was added. Then, isophthaloyl chloride was added in five separate additions, controlling the molar ratio of m-phenylenediamine to isophthaloyl chloride to be 100:120. The temperature was gradually increased as the reaction proceeded, eventually reaching 80℃ and being maintained for 5 hours. After this temperature treatment, calcium oxide was added for neutralization, yielding a neutral aramid polymer solution.

[0072] (2) Preparation of ultrafine aramid fibers: Refer to Example 1. The concentration of the aramid polymer dispersion is 28% by mass; the upper inlet plate is a stainless steel / chrome-plated alloy / plastic square frame with a side length of 30 mm; the distance between the upper and lower plates is 50 cm; the inlet speed is 40 mL / min at a temperature of 50 °C.

[0073] (3) Stretching and shaping of ultrafine aramid fiber: The ultrafine aramid fiber obtained from the net in step (2) is twisted into a thin thread, and then replaced and washed in the extraction liquid and washing liquid. Finally, it is stretched on a universal testing machine and then heat-shaped in a high-temperature oven to finally prepare ultrafine aramid fiber.

[0074] The extraction solution was a mixture of dimethylacetamide, ethylene glycol, and water in a mass ratio of dimethylacetamide:ethylene glycol:water = 30:40:30. The extraction temperature was 90℃ for 60 min; the water washing temperature was 90℃ for 30 min; the stretching ratio was 3.1, and the stretching temperature was 150℃. The heat setting temperature was 330℃ for 20 min.

[0075] The aramid fibers prepared above were formed on a Kayser fiber former to a basis weight of 40 g / m². 2 The aramid paper, prepared by hot pressing at 200℃ with a mass ratio of aramid chopped fibers: aramid pulp: aramid fine fibers = 3.5: 5: 1.5, has a thickness of 0.05 mm.

[0076] Example 5

[0077] An aramid microfiber, the preparation method of which is as follows:

[0078] (1) Preparation of aramid polymer: m-phenylenediamine was dissolved in N,N-dimethylacetamide at 10℃ under a nitrogen atmosphere, and lithium chloride was added. Then, isophthaloyl chloride was added in three separate additions, controlling the molar ratio of m-phenylenediamine to isophthaloyl chloride to be 100:103. The temperature was gradually increased as the reaction proceeded, and finally maintained at 80℃ for 3 hours. After the heat treatment, calcium oxide was added for neutralization to prepare a neutral aramid polymer solution.

[0079] (2) Preparation of ultrafine aramid fibers: Refer to Example 1. The concentration of the aramid polymer dispersion is 16% by mass; the upper inlet plate is a stainless steel / chrome-plated alloy / plastic square frame with a side length of 30 mm; the distance between the upper and lower plates is 50 cm; the inlet rate is 40 mL / min at a temperature of 40 °C.

[0080] (3) Stretching and shaping of ultrafine aramid fiber: The ultrafine aramid fiber obtained from the net in step (2) is twisted into a thin thread, and then replaced and washed in the extraction liquid and washing liquid. Finally, it is stretched on a universal testing machine and then heat-shaped in a high-temperature oven to finally prepare ultrafine aramid fiber.

[0081] The extraction solution was an aqueous solution of dimethylacetamide and ethylene glycol, with a mass ratio of dimethylacetamide:ethylene glycol:water = 35:35:30. The extraction temperature was 70℃ for 5 min; the water washing temperature was 50℃ for 10 min; the stretching ratio was 3.2, and the stretching temperature was 120℃. The heat setting temperature was 295℃ for 5 min.

[0082] The aramid fibers prepared above were formed on a Kayser fiber former to a basis weight of 40 g / m². 2 The aramid paper, prepared by hot pressing at 200℃ with a mass ratio of aramid chopped fibers: aramid pulp: aramid fine fibers = 4:4.5:1.5, has a thickness of 0.05mm.

[0083] Example 6

[0084] Compared with Example 3, the extract was an aqueous solution of dimethylacetamide in a mass ratio of dimethylacetamide:water = 40:60. Other conditions remained unchanged.

[0085] Example 7

[0086] Compared with Example 3, the extract was a mixed solution of dimethylacetamide, glycerol, and water in a mass ratio of dimethylacetamide:glycerol:water = 40:30:30. Other conditions remained unchanged.

[0087] Example 8

[0088] Compared with Example 3, the distance between the upper and lower plates was changed to 100cm, while other conditions remained unchanged. Due to the excessively large distance between the upper and lower plates, the aramid fibers were prone to breakage, resulting in a larger size distribution of the collected aramid fibers.

[0089] Example 9

[0090] Compared with Example 3, the temperature of the aramid polymer dispersion entering the upper inlet plate was 80°C, while other conditions remained unchanged.

[0091] Example 10

[0092] Compared with Example 3, the extract consisted of water, and other conditions remained unchanged.

[0093] Example 11

[0094] Compared with Example 3, the concentration of the aramid polymer dispersion was 2% by mass, while other conditions remained unchanged. Due to the excessively low polymer concentration, the fiber bundles could not be collected properly during the preparation process, making it difficult for the fibers to form and be collected on the collection plate.

[0095] Effect Example

[0096] The diameter of the prepared aramid fibers was characterized, and the performance of the prepared aramid paper was tested. The test results are shown in Table 1. The tensile strength, tear strength, electrical strength, dielectric constant, and dielectric loss factor of the paper involved in this embodiment of the invention were tested according to national standard testing methods and industry standards, specifically: tensile strength (GB / T453-2002), tear strength (GB-T 455-2002), electrical strength (GB / T 1408.1-2016), dielectric constant, and dielectric loss factor (GB / T 1409-2006).

[0097] Table 1. Summary of Test Results for Aramid Fine Fibers and Aramid Paper

[0098]

[0099] As can be seen from Table 1, the aramid fine fibers prepared by this invention have significant application effects and broad application prospects in the field of high-performance aramid paper.

[0100] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing aramid microfibers, characterized in that, Includes the following steps: (1) Preparation of aramid polymer solution: a neutral aramid polymer solution is prepared by polymerization reaction of m-phenylenediamine and isophthaloyl chloride in an organic solvent at low temperature and under a protective atmosphere; the molar ratio of m-phenylenediamine to isophthaloyl chloride is 100:(85-120); isophthaloyl chloride is added in 2-5 batches; (2) Using the apparatus for preparing fine fibers to prepare ultrafine aramid fiber bundles: The aramid polymer dispersion obtained by diluting the aramid polymer solution in step (1) is introduced into the liquid feeding unit. The booster is turned on so that the first mesh surface and the second mesh surface are in close contact and then separated. Numerous fine filaments are generated between the two mesh surfaces. The collector collects the aramid filaments through the gap between the two mesh surfaces. When the collector leaves, the two mesh surfaces are in close contact again under the drive of the booster and then separated and drawn. The collector collects the aramid filaments through the gap between the two mesh surfaces again. This cycle is repeated to collect oriented ultrafine aramid fiber bundles. (3) Ultrafine aramid fiber bundles are stretched and heat-set to obtain ultrafine aramid fibers; The concentration of the aramid polymer dispersion in step (2) is 5-30% by mass; the maximum distance between the first and second mesh surfaces is 5-100 cm; the liquid feeding rate is 0.1-50 mL / min; and the temperature of the aramid polymer dispersion entering the liquid feeding unit is 25-80℃. The apparatus for preparing fine fibers includes a liquid inlet unit, a collector, and a booster. The liquid inlet unit includes a liquid inlet plate and a liquid inlet delivery pipe. The liquid inlet plate includes a liquid distribution plate with several liquid inlet holes and a first mesh surface covering the liquid distribution plate. The liquid inlet delivery pipe is connected to the liquid distribution plate. A docking panel covered with a second mesh surface is provided opposite the first mesh surface. The booster drives the liquid inlet plate and / or the docking panel to move, causing the first mesh surface and the second mesh surface to reciprocate between close contact and a distance of more than 5 cm. After contact and separation, the two mesh surfaces generate filaments. The collector passes between the two mesh surfaces to collect the fine fibers.

2. The preparation method according to claim 1, characterized in that, The first and second mesh surfaces are either netting or mesh grids; the booster drives the docking panel to move.

3. The preparation method according to claim 2, characterized in that, The collector consists of two or more collecting plates driven by a motor to rotate, with the collecting plates moving between the first and second mesh surfaces.

4. The preparation method according to claim 1, 2, or 3, characterized in that, The concentration of the aramid polymer dispersion in step (2) is 10-25% by mass, the maximum distance between the first and second mesh surfaces is 15-50 cm, the liquid feeding rate is 10-40 mL / min, and the aramid polymer dispersion is also subjected to vacuum defoaming pretreatment.

5. The preparation method according to claim 1, 2, or 3, characterized in that, The stretching and shaping of the ultrafine aramid fiber bundle in step (3): The ultrafine aramid fiber bundle collected in step (2) is twisted into a thin thread, and then replaced and washed in the extract and water, then stretched and then heat-shaped to finally obtain ultrafine aramid fiber.

6. The method according to claim 5, characterized in that, The stretching ratio in step (3) is 0.1 to 5.0, and the stretching temperature is 30 to 150°C; the heat setting temperature is 260 to 330°C; the extraction solution is an aqueous solution or alcoholic solution of one or more of dimethylacetamide, dimethylformamide, dimethyl sulfoxide, ethylene glycol, glycerol, and acetone.

7. The method according to claim 6, characterized in that, The extract in step (3) is N,N-dimethylacetamide or a mixed solution of N,N-dimethylacetamide, ethylene glycol, and water; Step (1) Preparation of aramid polymer: Under low temperature and nitrogen protection atmosphere, the cosolvent and m-phenylenediamine are dissolved in N,N-dimethylacetamide, and then isophthaloyl chloride is added to obtain a reaction solution; as the reaction proceeds, the temperature of the reaction solution gradually increases. After heat preservation treatment, an alkaline agent is added for neutralization to prepare a neutral aramid polymer solution. The co-solvent is one or more of lithium bromide, lithium chloride, calcium chloride, and calcium bromide; the heat preservation treatment is performed at 40-80°C for 0.5-12 hours; the alkaline agent is one or more of calcium oxide, calcium hydroxide, lithium hydroxide, magnesium hydroxide, sodium hydroxide, and organic amine.

8. The ultrafine aramid fiber prepared by the method according to any one of claims 1-7, characterized in that, The diameter of the aramid microfiber is less than 5µm.

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