A para-aramid paper and a method for preparing the same

Abstract

The present application relates to synthetic fiber paper manufacturing technology field, specifically relates to a kind of p-aramid paper and its preparation method, belong to synthetic fiber paper manufacturing technology field.The preparation method is: p-aramid short-cut fiber and potassium hydroxide are added to dimethyl sulfoxide, then water is added, and stirring dispersion obtains nanofiber dispersion liquid;P-aramid short-cut fiber is added to nanofiber dispersion liquid and is defibered, is uniformly mixed, and p-aramid short-cut fiber dispersion liquid is obtained;Metaparamid polymerization liquid, nanofiber dispersion liquid, continuous stable sedimentation agent is added to sedimentation equipment, and high-speed shearing obtains sedimentation fiber, then cooling forming in water washing pool, and multistage washing obtain metaparamid sedimentation fiber;P-aramid short-cut fiber dispersion liquid, metaparamid sedimentation fiber are obtained by wet papermaking p-aramid paper.The p-aramid paper has higher mechanical property, good evenness, and high density, reduces the risk of glue penetration in the process of p-aramid paper preparation honeycomb.

Description

Technical Field

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

[0002] Para-aramid paper, made from para-aramid fibers through a papermaking process, has advantages such as light weight, high strength, excellent dielectric properties, excellent solvent properties, and superior thermal dimensional stability. It can be used as a structural material, insulating material, wave-transparent material, and filter material, and is widely used in aerospace, military equipment, electronics and electrical appliances and other industries.

[0003] However, because the poly(p-phenylene terephthalamide) (PPTA) molecular chain that makes up para-aramid fibers has a rigid structure, and the fiber surface is hydrophobic, smooth, and highly inert, para-aramid fibers and their differentiated products (short fibers, pulp, and precipitated fibers) are prone to agglomeration in water, making uniform dispersion difficult. This reduces the uniformity of para-aramid paper, and some areas have high porosity, leading to glue permeation during honeycomb fabrication. Furthermore, the smooth and inert surface of para-aramid fibers results in weak inter-fiber bonding, preventing the utilization of para-aramid's excellent mechanical properties. Chinese patent application CN1884692A uses a dispersant to disperse the fibers, significantly improving paper uniformity and thus enhancing paper strength and other properties. Chinese patent application CN1710196A uses a dispersant to disperse chopped para-aramid fibers and pulp fibers to prepare a mixed pulp. This pulp is then wet-formed, pressed, and dried to obtain fiber paper. The resulting fiber paper is then uniformly impregnated with a para-aramid solution, subjected to hot or cold pressing, coagulated, and the solvent is washed away. Finally, it is dehydrated, pressed, and dried to obtain the final all-para-aramid paper. While this patent improves paper uniformity and mechanical properties, other mechanical properties such as tensile strength and tear resistance still require further improvement. Furthermore, the method of dispersing fibers with a dispersant is expensive, and the addition of a dispersant during preparation complicates wastewater treatment. Additionally, the presence of the dispersant affects the paper's temperature resistance and dielectric properties.

[0004] Therefore, developing a para-aramid paper with high uniformity and excellent mechanical properties is of great value. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a para-aramid paper and its preparation method. The para-aramid paper has higher mechanical properties, better uniformity, and higher density, reducing the risk of glue penetration during the preparation of honeycomb paper.

[0006] The technical solution of this invention to solve the above-mentioned technical problems is as follows: a method for preparing para-aramid paper, wherein the preparation method is as follows:

[0007] S1. Preparation of nanofiber dispersion:

[0008] Para-aramid short-cut fibers and potassium hydroxide were added to dimethyl sulfoxide, and then water was added and stirred to disperse, thus obtaining the nanofiber dispersion.

[0009] S2. Preparation of para-aramid short-cut fiber dispersion and meta-aramid precipitated fibers:

[0010] Para-aramid short-cut fibers were added to the nanofiber dispersion for dissolution and mixed evenly to obtain the para-aramid short-cut fiber dispersion.

[0011] Meta-aramid polymer solution, nanofiber dispersion and precipitant are continuously and stably added to the precipitation equipment, and high-speed shearing is used to obtain precipitated fibers. Then, the fibers are cooled and shaped in a water washing tank and washed in multiple stages to obtain meta-aramid precipitated fibers.

[0012] S3. Preparation of para-aramid paper:

[0013] Para-aramid short fiber dispersion and meta-aramid precipitated fiber are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain para-aramid paper.

[0014] Furthermore, in step S1, the stirring time is 4 to 24 hours, and the storage temperature of the nanofiber dispersion is 15-25°C.

[0015] Furthermore, in step S1, the weight ratio of para-aramid fiber, dimethyl sulfoxide, water and potassium hydroxide is (0.05-3): (80-100): (0.01-0.08): (0.15-4).

[0016] Furthermore, in step S2, when preparing the para-aramid short-cut fiber dispersion, the disintegration time is 5 to 15 minutes; the mass concentration of para-aramid short-cut fibers in the para-aramid short-cut fiber dispersion is 0.05% to 1%.

[0017] Furthermore, in step S2, when preparing the meta-aramid precipitated fiber, the temperature of the meta-aramid polymerization solution is 35-50°C, the solid content is 8%-15%, and the viscosity at 25°C is 100-450 Po.

[0018] When preparing the meta-aramid precipitated fiber, the weight ratio of the nanofiber dispersion, the precipitant and the meta-aramid polymer solution is (5-20):(5-12):(80-100).

[0019] Furthermore, in step S2, when preparing the meta-aramid precipitated fiber, the high-speed shearing speed is 3500-6000 rpm, and the high-speed shearing time is 40-90 s.

[0020] Furthermore, in step S2, when preparing the meta-aramid precipitated fiber, the precipitating agent is a mixture of the following substances in parts by weight: 5-18 parts chloride salt, 40-50 parts water, and 40-50 parts N,N-dimethylacetamide.

[0021] The chloride salt is at least one of lithium chloride, calcium chloride, and magnesium chloride.

[0022] Furthermore, in step S3, the weight ratio of the para-aramid short-cut fiber dispersion to the meta-aramid precipitated fiber is (8-2):(2-8), and the total weight of the para-aramid short-cut fiber dispersion and the meta-aramid precipitated fiber is 10 parts.

[0023] Furthermore, in step S3, the hot pressing conditions are: temperature 180~220℃, vehicle speed 5~20m / min, and pressure 100~300 N / mm.

[0024] The present invention also discloses a para-aramid paper, which is prepared according to the preparation method described in the present invention.

[0025] The beneficial effects of this invention are:

[0026] 1. The nanofiber dispersion is an anionic system, which is very stable and has a certain viscosity. This system can disperse and maintain a certain steady state of para-aramid chopped fibers, allowing for good dispersion of the fibers without the addition of a dispersant and preventing flocculation. This results in para-aramid paper having higher uniformity and better mechanical properties.

[0027] 2. During the precipitation of the nanofiber dispersion in water, para-aramid chopped fibers adhere to their surfaces, roughening the previously smooth surface. This enhances the interfacial bonding strength between para-aramid chopped fibers and between para-aramid chopped fibers and meta-aramid precipitated fibers, resulting in greater interfiber bonding and better stress transfer, thus improving the adhesion of the aramid paper. Furthermore, this roughness is not achieved by sacrificing the original properties of the para-aramid fibers. Simultaneously, this method can significantly reduce the porosity of the para-aramid paper, thereby improving its uniformity and yielding para-aramid paper with excellent mechanical properties. The meta-aramid precipitated surface prepared by this invention has more micro-wrinkles, resulting in stronger bonding with other fibers and further enhancing the adhesion of the aramid paper.

[0028] 3. Introducing para-aramid nanofiber dispersion into the preparation process of meta-aramid precipitate reduces the crystallinity of the meta-aramid fibers, making them easier to melt during hot pressing, resulting in stronger fiber bonding and a smoother surface. Simultaneously, it increases the density and reduces the porosity of the para-aramid paper, significantly reducing the risk of adhesive permeation during the preparation of honeycomb paper.

[0029] 4. Compared to conventional meta-aramid precipitation, the meta-aramid fibers precipitated in this invention are low-crystallinity meta-aramid precipitates, which can achieve good melting and bonding at relatively low hot-pressing temperatures. This significantly reduces production energy consumption while maintaining the good mechanical properties of aramid paper. The preparation process of this invention is simple, energy-efficient, and easy to control. Detailed Implementation

[0030] 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.

[0031] 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.

[0032] A method for preparing para-aramid paper, wherein the preparation method comprises:

[0033] S1. Preparation of nanofiber dispersion:

[0034] Para-aramid short fibers and potassium hydroxide were added to dimethyl sulfoxide, then water was added, and the mixture was mechanically stirred to obtain a stable nanofiber dispersion.

[0035] S2. Preparation of para-aramid short-cut fiber dispersion and meta-aramid precipitated fibers:

[0036] Para-aramid short-cut fibers were added to the nanofiber dispersion for dissolution. After dissolution for a certain period of time, the dispersion was stirred evenly to obtain the para-aramid short-cut fiber dispersion.

[0037] Meta-aramid polymerization liquid, nanofiber dispersion liquid, and precipitant are continuously and stably added to the precipitation equipment. The precipitation equipment shears the fibers at high speed and then discharges them into a water washing tank for further cooling and molding. The precipitated fiber mixture containing N,N-dimethylacetamide solvent is washed through multiple stages to remove the N,N-dimethylacetamide solvent, resulting in meta-aramid precipitated fibers with low crystallinity.

[0038] S3. Preparation of para-aramid paper:

[0039] Para-aramid short fiber dispersion and meta-aramid precipitated fiber are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain para-aramid paper.

[0040] Specifically, in step S1, the stirring time is 4 to 24 hours, and the storage temperature of the nanofiber dispersion is 15 to 25°C.

[0041] Specifically, in step S1, the weight ratio of para-aramid fiber, dimethyl sulfoxide, water and potassium hydroxide is (0.05-3): (80-100): (0.01-0.08): (0.15-4).

[0042] Specifically, in step S2, when preparing the para-aramid short-cut fiber dispersion, the disintegration time is 5 to 15 minutes; the mass concentration of para-aramid short-cut fibers in the para-aramid short-cut fiber dispersion is 0.05% to 1%.

[0043] Specifically, in step S2, when preparing the meta-aramid precipitated fiber, the temperature of the meta-aramid polymerization solution is 35-50°C, the solid content is 8%-15%, and the viscosity at 25°C is 100-450 Po.

[0044] When preparing the meta-aramid precipitated fiber, the weight ratio of the nanofiber dispersion, the precipitant and the meta-aramid polymer solution is (5-20):(5-12):(80-100).

[0045] Specifically, in step S2, when preparing the meta-aramid precipitated fiber, the high-speed shearing speed is 3500-6000 rpm, and the high-speed shearing time is 40-90 s.

[0046] Specifically, in step S2, when preparing the meta-aramid precipitated fiber, the precipitating agent is a mixture of the following substances in parts by weight: 5-18 parts chloride salt, 40-50 parts water, and 40-50 parts N,N-dimethylacetamide.

[0047] The chloride salt is at least one of lithium chloride, calcium chloride, and magnesium chloride.

[0048] Specifically, in step S3, the weight ratio of para-aramid chopped fibers to meta-aramid precipitated fibers in the para-aramid chopped fiber dispersion is (8-2):(2-8), and the total weight of the para-aramid chopped fiber dispersion and the meta-aramid precipitated fibers is 10 parts.

[0049] Specifically, in step S3, the hot pressing conditions are: temperature 180~220℃, vehicle speed 5~20m / min, and pressure 100~300 N / mm.

[0050] More specifically, the para-aramid chopped fibers used in the embodiments of the present invention are produced by Taihe New Materials Group Co., Ltd., with a length of 4-8 mm and a fineness of 1.5 dtex-2.0 dtex; the solvent in the meta-aramid polymerization solution used in the embodiments of the present invention is N,N-dimethylacetamide.

[0051] A para-aramid paper, wherein the para-aramid paper is prepared according to the preparation method described in this invention.

[0052] Example 1

[0053] Preparation of para-aramid paper:

[0054] S1. Preparation of nanofiber dispersion:

[0055] Para-aramid short-cut fibers (1.5 dtex, 5 mm) and potassium hydroxide were added to dimethyl sulfoxide, and then water was added. The mixture was mechanically stirred for 12 h to obtain a stable nanofiber dispersion. The weight ratio of para-aramid fibers, dimethyl sulfoxide, water and potassium hydroxide was 2:90:0.05:2. The nanofiber dispersion was stored at 20 °C.

[0056] S2. Preparation of para-aramid short-cut fiber dispersion and meta-aramid precipitated fibers:

[0057] (1) Preparation of para-aramid short fiber dispersion:

[0058] Para-aramid short-cut fibers were added to the nanofiber dispersion for dissolution. After dissolution for 10 minutes, the dispersion was stirred evenly to obtain the para-aramid short-cut fiber dispersion. The mass concentration of para-aramid short-cut fibers in the dispersion was 0.6%.

[0059] (2) Preparation of meta-aramid precipitated fibers:

[0060] Meta-aramid polymer solution, nanofiber dispersion and precipitant are continuously and stably added to the precipitation equipment. The precipitated fiber is obtained by high-speed shearing at 5000 rpm for 50 seconds. Then it is discharged into the washing tank for further cooling and molding. The precipitated fiber mixture containing N,N-dimethylacetamide solvent is washed through multiple stages to remove the N,N-dimethylacetamide solvent, and meta-aramid precipitated fiber with low crystallinity is obtained.

[0061] The weight ratio of nanofiber dispersion, precipitant, and meta-aramid polymer solution is 15:10:90.

[0062] The temperature of the meta-aramid polymerization solution is 35℃, the solid content is 12%, and the viscosity at 25℃ is 300Po.

[0063] The precipitant, by weight, consists of 10 parts calcium chloride, 45 parts water, and 45 parts N,N-dimethylacetamide.

[0064] S3. Preparation of para-aramid paper:

[0065] Para-aramid short fiber dispersion and meta-aramid precipitated fiber are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain para-aramid paper.

[0066] The weight ratio of para-aramid short-cut fibers to meta-aramid precipitated fibers in the para-aramid short-cut fiber dispersion is 5:5.

[0067] The hot pressing conditions are: temperature 200℃, vehicle speed 10m / min, and pressure 200 N / mm.

[0068] Example 2

[0069] Preparation of para-aramid paper:

[0070] S1. Preparation of nanofiber dispersion:

[0071] Para-aramid short-cut fibers (1.5 dtex, 5 mm) and potassium hydroxide were added to dimethyl sulfoxide, followed by water. The mixture was mechanically stirred for 24 h to obtain a stable nanofiber dispersion. The weight ratio of para-aramid fibers, dimethyl sulfoxide, water, and potassium hydroxide was 0.05:80:0.01:0.15. The nanofiber dispersion was stored at 15 °C.

[0072] S2. Preparation of para-aramid short-cut fiber dispersion and meta-aramid precipitated fibers:

[0073] (1) Preparation of para-aramid short fiber dispersion:

[0074] Para-aramid short-cut fibers were added to the nanofiber dispersion for dissolution. After dissolution for 5 minutes, the dispersion was stirred evenly to obtain the para-aramid short-cut fiber dispersion. The mass concentration of para-aramid short-cut fibers in the dispersion was 0.05%.

[0075] (2) Preparation of meta-aramid precipitated fibers:

[0076] Meta-aramid polymer solution, nanofiber dispersion and precipitant are continuously and stably added to the precipitation equipment. The precipitated fiber is obtained by high-speed shearing at 6000 rpm for 40 seconds. Then it is discharged into the washing tank for further cooling and molding. The precipitated fiber mixture containing N,N-dimethylacetamide solvent is washed through multiple stages to remove the N,N-dimethylacetamide solvent, and meta-aramid precipitated fiber with low crystallinity is obtained.

[0077] The weight ratio of nanofiber dispersion, precipitant, and meta-aramid polymer solution is 20:12:100.

[0078] The temperature of the meta-aramid polymerization solution is 40℃, the solid content is 8%, and the viscosity at 25℃ is 100Po.

[0079] The precipitant, by weight, consists of 5 parts lithium chloride, 45 parts water, and 50 parts N,N-dimethylacetamide.

[0080] S3. Preparation of para-aramid paper:

[0081] Para-aramid short fiber dispersion and meta-aramid precipitated fiber are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain para-aramid paper.

[0082] The weight ratio of para-aramid chopped fibers to meta-aramid precipitated fibers in the para-aramid chopped fiber dispersion is 2:8.

[0083] The hot pressing conditions are: temperature 180℃, vehicle speed 5m / min, and pressure 100 N / mm.

[0084] Example 3

[0085] Preparation of para-aramid paper:

[0086] S1. Preparation of nanofiber dispersion:

[0087] Para-aramid short-cut fibers (2.0 dtex, 6 mm) and potassium hydroxide were added to dimethyl sulfoxide, and then water was added. The mixture was mechanically stirred for 4 hours to obtain a stable nanofiber dispersion. The weight ratio of para-aramid fibers, dimethyl sulfoxide, water and potassium hydroxide was 3:100:0.08:4. The nanofiber dispersion was stored at 25°C.

[0088] S2. Preparation of para-aramid short-cut fiber dispersion and meta-aramid precipitated fibers:

[0089] (1) Preparation of para-aramid short fiber dispersion:

[0090] Para-aramid short-cut fibers were added to the nanofiber dispersion for dissolution. After dissolution for 15 minutes, the dispersion was stirred evenly to obtain the para-aramid short-cut fiber dispersion. The mass concentration of para-aramid short-cut fibers in the dispersion was 1%.

[0091] (2) Preparation of meta-aramid precipitated fibers:

[0092] Meta-aramid polymer solution, nanofiber dispersion and precipitant are continuously and stably added to the precipitation equipment. The precipitated fiber is obtained by high-speed shearing at 3500 rpm for 90 seconds. Then it is discharged into the washing tank for further cooling and molding. The precipitated fiber mixture containing N,N-dimethylacetamide solvent is washed through multiple stages to remove the N,N-dimethylacetamide solvent, and meta-aramid precipitated fiber with low crystallinity is obtained.

[0093] The weight ratio of the nanofiber dispersion, the precipitant, and the meta-aramid polymer solution is 5:5:80.

[0094] The temperature of the meta-aramid polymerization solution is 50℃, the solid content is 15%, and the viscosity at 25℃ is 450po.

[0095] The precipitant, by weight, consists of 18 parts magnesium chloride, 42 parts water, and 40 parts N,N-dimethylacetamide.

[0096] S3. Preparation of para-aramid paper:

[0097] Para-aramid short fiber dispersion and meta-aramid precipitated fiber are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain para-aramid paper.

[0098] The weight ratio of para-aramid chopped fibers to meta-aramid precipitated fibers in the para-aramid chopped fiber dispersion is 8:2.

[0099] The hot pressing conditions are: temperature 220℃, vehicle speed 20m / min, and pressure 300 N / mm.

[0100] Example 4

[0101] Preparation of para-aramid paper:

[0102] S1. Preparation of nanofiber dispersion:

[0103] Para-aramid short-cut fibers (1.7 dtex, 6 mm) and potassium hydroxide were added to dimethyl sulfoxide, and then water was added. The mixture was mechanically stirred for 16 h to obtain a stable nanofiber dispersion. The weight ratio of para-aramid fibers, dimethyl sulfoxide, water and potassium hydroxide was 1:85:0.03:1. The nanofiber dispersion was stored at 25 °C.

[0104] S2. Preparation of para-aramid short-cut fiber dispersion and meta-aramid precipitated fibers:

[0105] (1) Preparation of para-aramid short fiber dispersion:

[0106] Para-aramid chopped fibers were added to a nanofiber dispersion for dissolution. After dissolution for 12 minutes, the dispersion was stirred until homogeneous to obtain the para-aramid chopped fiber dispersion. The mass concentration of para-aramid chopped fibers in the dispersion was 0.2%.

[0107] (2) Preparation of meta-aramid precipitated fibers:

[0108] Meta-aramid polymer solution, nanofiber dispersion and precipitant are continuously and stably added to the precipitation equipment. The precipitated fiber is obtained by high-speed shearing at 5000 rpm for 50 seconds. Then it is discharged into the washing tank for further cooling and molding. The precipitated fiber mixture containing N,N-dimethylacetamide solvent is washed through multiple stages to remove the N,N-dimethylacetamide solvent, and meta-aramid precipitated fiber with low crystallinity is obtained.

[0109] The weight ratio of the nanofiber dispersion, the precipitant, and the meta-aramid polymer solution is 10:10:90.

[0110] The temperature of the meta-aramid polymerization solution is 35℃, the solid content is 12%, and the viscosity at 25℃ is 300Po.

[0111] The precipitant, by weight, consists of 15 parts calcium chloride, 45 parts water, and 40 parts N,N-dimethylacetamide.

[0112] S3. Preparation of para-aramid paper:

[0113] Para-aramid short fiber dispersion and meta-aramid precipitated fiber are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain para-aramid paper.

[0114] The weight ratio of para-aramid chopped fibers to meta-aramid precipitated fibers in the para-aramid chopped fiber dispersion is 6:4.

[0115] The hot pressing conditions are: temperature 200℃, vehicle speed 15m / min, and pressure 150 N / mm.

[0116] Comparative Example 1

[0117] Para-aramid paper was prepared using the same method as in Example 1, except that in step S1, the storage temperature of the nanofiber dispersion was increased. In this Comparative Example 1, the storage temperature of the nanofiber dispersion was 35°C.

[0118] Comparative Example 2

[0119] Para-aramid paper was prepared using the same method as in Example 1, except that in step S1, the storage temperature of the nanofiber dispersion was lowered. In Comparative Example 2, the storage temperature of the nanofiber dispersion was 5°C.

[0120] Comparative Example 3

[0121] Para-aramid paper was prepared using the same method as in Example 1, except that in step S2, when preparing meta-aramid precipitated fibers, the proportion of nanofiber dispersion was increased. In this Comparative Example 3, the weight ratio of nanofiber dispersion, precipitant, and meta-aramid polymer solution was 25:10:90.

[0122] Comparative Example 4

[0123] Para-aramid paper was prepared using the same method as in Example 1, except that in step S2, when preparing meta-aramid precipitated fibers, the proportion of nanofiber dispersion was reduced. In this Comparative Example 4, the weight ratio of nanofiber dispersion, precipitant, and meta-aramid polymer solution was 1:10:90.

[0124] Comparative Example 5

[0125] Para-aramid paper was prepared using the same method as in Example 1, except that in step S2, when preparing meta-aramid precipitated fibers, the shear rate was increased. In this Comparative Example 5, the shear rate in step S2 was 8000 rpm.

[0126] Comparative Example 6

[0127] Para-aramid paper was prepared using the same method as in Example 1, except that in step S2, when preparing meta-aramid precipitated fibers, the shear rate was reduced. In this Comparative Example 6, the shear rate in step S2 was 2000 rpm.

[0128] Comparative Example 7

[0129] Using a conventional method, the nanofiber dispersion was coated onto the surface of aramid paper. The specific preparation process is as follows:

[0130] S1. Preparation of nanofiber dispersion:

[0131] Nanofiber dispersions were prepared using the same method as in Example 1;

[0132] S2. Preparation of para-aramid paper:

[0133] Para-aramid chopped fibers and meta-aramid precipitated fibers are loosened, stirred, and then wet-formed, pressed, and dried to obtain para-aramid base paper; wherein the weight ratio of para-aramid chopped fibers to meta-aramid precipitated fibers is 5:5.

[0134] S3, Coating of nanofiber dispersion:

[0135] The nanofiber dispersion prepared in step S1 is uniformly coated on one side of the para-aramid paper prepared in step S2, and then washed and dried. The above operation steps are repeated on the other side of the para-aramid paper to control the total coating amount of nanofibers on the para-aramid paper to be 2 g / m². 2 Finally, the para-aramid paper coated with nanofibers on both sides is hot-pressed to obtain the final product. The hot-pressing conditions are: temperature 200℃, speed 10m / min, and pressure 200 N / mm.

[0136] Comparative Example 8

[0137] Para-aramid paper was prepared using the same method as in Example 1, except that conventional methods were used to prepare the para-aramid chopped fiber dispersion and the meta-aramid precipitated fibers. Specifically, in Comparative Example 8, no nanofiber dispersion was used when preparing the para-aramid chopped fiber dispersion, and no nanofiber solution was added during the preparation of the meta-aramid precipitated fibers.

[0138] The specific preparation process of the para-aramid short-cut fiber dispersion in Comparative Example 8 is as follows:

[0139] Para-aramid chopped fibers were added to an appropriate amount of water for dissolution. After dissolution for 10 minutes, the mixture was stirred evenly to obtain the para-aramid chopped fiber dispersion. The mass concentration of para-aramid chopped fibers in the dispersion was 0.6%.

[0140] The specific preparation process of the meta-aramid fiber dispersion in Comparative Example 8 is as follows:

[0141] The meta-aramid polymerization solution and precipitant are continuously and stably fed into the precipitation equipment. The precipitated fiber is obtained by high-speed shearing at 5000 rpm for 50 seconds. Then, it is discharged into the washing tank for further cooling and molding. The precipitated fiber mixture containing N,N-dimethylacetamide solvent is washed through multiple stages to remove the N,N-dimethylacetamide solvent, resulting in meta-aramid precipitated fiber with low crystallinity.

[0142] The weight ratio of the precipitant to the meta-aramid polymerization solution is 10:90.

[0143] The temperature of the meta-aramid polymerization solution is 35℃, the solid content is 12%, and the viscosity at 25℃ is 300Po.

[0144] The precipitant, by weight, consists of 10 parts calcium chloride, 45 parts water, and 45 parts N,N-dimethylacetamide.

[0145] Comparative Example 9

[0146] Para-aramid paper was prepared using the same method as in Example 1, except that a conventional method was used to prepare the para-aramid short-cut fiber dispersion. Specifically, no nanofiber dispersion was used in the preparation of the para-aramid short-cut fiber dispersion in Comparative Example 9. The specific preparation process for the para-aramid short-cut fiber dispersion in Comparative Example 9 is as follows:

[0147] Para-aramid chopped fibers were added to an appropriate amount of water for dissolution. After dissolution for 10 minutes, the mixture was stirred evenly to obtain the para-aramid chopped fiber dispersion. The mass concentration of para-aramid chopped fibers in the dispersion was 0.6%.

[0148] Comparative Example 10

[0149] Para-aramid paper was prepared using the same method as in Example 1, except that meta-aramid precipitated fibers were prepared using conventional methods. Specifically, no nanofiber dispersion was used when preparing the meta-aramid precipitated fibers in Comparative Example 10. The specific preparation process for the meta-aramid precipitated fibers in Comparative Example 10 is as follows:

[0150] The meta-aramid polymerization solution and precipitant are continuously and stably fed into the precipitation equipment. The precipitated fiber is obtained by high-speed shearing at 5000 rpm for 50 seconds. Then, it is discharged into the washing tank for further cooling and molding. The precipitated fiber mixture containing N,N-dimethylacetamide solvent is washed through multiple stages to remove the N,N-dimethylacetamide solvent, resulting in meta-aramid precipitated fiber with low crystallinity.

[0151] The weight ratio of the precipitant to the meta-aramid polymerization solution is 10:90.

[0152] The temperature of the meta-aramid polymerization solution is 35℃, the solid content is 12%, and the viscosity at 25℃ is 300Po.

[0153] The precipitant, by weight, consists of 10 parts calcium chloride, 45 parts water, and 45 parts N,N-dimethylacetamide.

[0154] The aramid paper prepared in the above embodiments and comparative examples was subjected to performance testing. The specific testing methods involved are as follows.

[0155] The quantitative testing method refers to standard GB / T 451.2;

[0156] The thickness test method refers to the standard GB / T 451.3;

[0157] The test methods for tensile strength and elongation are based on the standard GB / T 12914.

[0158] The tear resistance test method refers to the standard GB / T 455;

[0159] The uniformity index was measured by the Micro-Scanner testing instrument;

[0160] Porosity was measured by a mercury porosimeter.

[0161] The specific test results are shown in Tables 1 and 2 below.

[0162] Table 1 Test data of mechanical properties of para-aramid paper

[0163]

[0164] Table 2 Other performance test data of para-aramid paper

[0165]

[0166] As can be seen from the data in the table above, the para-aramid paper prepared by the method described in Examples 1-4 of this invention has excellent mechanical properties, good uniformity, low porosity, and no glue permeation, which can effectively avoid glue permeation during the honeycomb preparation process. In Examples 1-4 of this invention, the para-aramid chopped fibers are well dispersed in the nano-dispersion liquid, significantly improving the overall performance of the para-aramid paper. Simultaneously, the aramid nanofibers adhering to the surface of the para-aramid chopped fibers act as a binder, filling the pores of the aramid paper and strengthening the interaction with other fibers. Furthermore, the introduction of nanofiber dispersion liquid during the preparation of meta-aramid precipitated fibers moderately reduces their crystallinity, achieving a balance between energy saving and superior performance in the processing. Compared to conventional meta-aramid precipitated fibers, the meta-aramid precipitated fibers prepared in this invention have more micro-wrinkles on their surface, resulting in stronger bonding with other fibers. Simultaneously, strong hydrogen bonds can form between the nanofibers and the para-aramid chopped or meta-aramid precipitated fibers. Under multiple effects, the para-aramid paper in this invention has excellent overall performance.

[0167] A comparison of the data from Comparative Examples 1, 2, and 1 shows that increasing or decreasing the storage temperature of the nano-dispersion significantly reduces the mechanical properties of the para-aramid paper. This is because at a suitable temperature, the para-aramid chopped fibers disperse more uniformly, resulting in more uniform meta-aramid precipitated fiber sizes and maintaining appropriate crystallinity and microstructure (i.e., more micro-wrinkles on the surface). Therefore, the overall performance of the final para-aramid paper is significantly improved.

[0168] A comparison of the data from Comparative Examples 3 and 4 with Example 1 shows that increasing or decreasing the proportion of the nanofiber dispersion significantly reduces the overall performance of the para-aramid paper. This is because selecting an appropriate nanofiber ratio ensures that the prepared meta-aramid precipitated fibers have more uniform size and maintain suitable crystallinity and microstructure, resulting in superior mechanical properties of the prepared para-aramid paper. Furthermore, selecting an appropriate nanofiber ratio optimizes the dispersion of the chopped para-aramid fibers, contributing to the overall good performance of the para-aramid paper.

[0169] A comparison of the data from Comparative Examples 5, 6, and 1 shows that maintaining a suitable shear rate results in better overall performance of the para-aramid paper. When the shear rate is too high, the length of the meta-aramid precipitated fibers decreases, and the film characteristics of the meta-aramid precipitated fibers also diminish. This reduces the contact area between the meta-aramid precipitated fibers and the chopped para-aramid fibers, leading to a decrease in the paper's mechanical properties and compressive strength. When the shear rate is too low, the shear force on the aramid droplets is insufficient, and the dispersed aramid droplets in the precipitant are too large to fully extend into a film state, thus causing a decline in the overall performance of the aramid paper. Furthermore, maintaining a certain shear rate is crucial for the crystallinity of the meta-aramid precipitated fibers. When the shear rate is too high, the aramid droplets, under high-speed shearing, easily form a film state, destroying the crystalline structure and resulting in excessively low crystallinity. This reduces fiber strength and further degrades the mechanical properties of the aramid paper. Conversely, excessively low shear rates result in excessively high crystallinity of meta-aramid precipitated fibers, leading to excessive aggregation of polymer chain segments, reduced porosity, and decreased flexibility of the molecular chains, thereby reducing the mechanical properties of the paper. This invention, by controlling conditions, achieves a moderately lower crystallinity in the prepared meta-aramid precipitated fibers compared to traditional meta-aramid precipitated fibers. This not only saves energy consumption in the hot-pressing process but also significantly improves the overall performance of para-aramid paper.

[0170] A comparison of the data from Comparative Example 7 and Example 1 shows that, compared to coating nanofibers onto the surface of aramid paper, the para-aramid paper of this invention has better overall performance.

[0171] The data comparison between Comparative Example 8 and Example 1 shows that, compared with the conventional method for preparing para-aramid paper, the para-aramid paper prepared by the present invention has significantly improved overall performance.

[0172] A comparison of the data from Comparative Examples 9, 10 and 1 shows that aramid paper prepared using both meta-aramid precipitated fibers and para-aramid chopped fiber dispersions of the present invention has better overall performance.

[0173] 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.

[0174] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing para-aramid paper, characterized in that, The preparation method is as follows: S1. Preparation of nanofiber dispersion: Para-aramid short-cut fibers and potassium hydroxide were added to dimethyl sulfoxide, and then water was added and stirred to disperse, thus obtaining the nanofiber dispersion. S2. Preparation of para-aramid short-cut fiber dispersion and meta-aramid precipitated fibers: Para-aramid short-cut fibers were added to the nanofiber dispersion for dissolution and mixed evenly to obtain the para-aramid short-cut fiber dispersion. Meta-aramid polymer solution, nanofiber dispersion, and precipitant are continuously and stably added to a precipitation device, and high-speed shearing is used to obtain precipitated fibers. The fibers are then cooled and shaped in a water washing tank and subjected to multi-stage water washing to obtain meta-aramid precipitated fibers. The high-speed shearing speed is 3500-6000 rpm. S3. Preparation of para-aramid paper: Para-aramid short-cut fiber dispersion and meta-aramid precipitated fiber are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain para-aramid paper; the hot-pressing temperature is 180-220℃. In step S1, the weight ratio of para-aramid fiber, dimethyl sulfoxide, water, and potassium hydroxide is (0.05–3): (80–100): (0.01–0.08): (0.15–4). When preparing the meta-aramid precipitated fiber, the weight ratio of the nanofiber dispersion, the precipitant and the meta-aramid polymer solution is (5-20):(5-12):(80-100).

2. The method for preparing para-aramid paper according to claim 1, characterized in that, In step S1, the stirring time is 4 to 24 hours, and the storage temperature of the nanofiber dispersion is 15 to 25°C.

3. The method for preparing para-aramid paper according to claim 1, characterized in that, In step S2, when preparing the para-aramid short-cut fiber dispersion, the disintegration time is 5 to 15 minutes; the mass concentration of para-aramid short-cut fibers in the para-aramid short-cut fiber dispersion is 0.05% to 1%.

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

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

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

7. The method for preparing para-aramid paper according to claim 1, characterized in that, In step S3, the weight ratio of para-aramid short-cut fibers to meta-aramid precipitated fibers in the para-aramid short-cut fiber dispersion is (8-2):(2-8), and the total weight of para-aramid short-cut fibers and meta-aramid precipitated fibers in the para-aramid short-cut fiber dispersion is 10 parts.

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

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

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