A meta-aramid paper and a method of making the same

Abstract

The present application relates to synthetic fiber paper manufacturing technology field, specifically to a kind of meta-aramid paper and preparation method thereof, the preparation method is: the short-cut fiber of para-aramid is added to dimethyl sulfoxide with potassium hydroxide, then water is added, stirring dispersion, obtain nanofiber dispersion liquid;The short-cut fiber of meta-aramid is added to nanofiber dispersion liquid and is defibrated, uniformly mixed, obtain the short-cut fiber dispersion liquid of meta-aramid;Meta-aramid polymerization liquid, nanofiber dispersion liquid, continuous stable addition of sedimentation agent in sedimentation equipment, high-speed shearing obtains sedimentation fiber, again cooling forming in water washing pool, multistage washing obtains meta-aramid sedimentation fiber;The short-cut fiber dispersion liquid of meta-aramid, meta-aramid sedimentation fiber is defibrated, stirred, again after wet forming, pressing, drying, hot pressing, obtain meta-aramid paper.The meta-aramid paper has higher tensile strength, evenness, tightness and insulation performance, and better internal binding force and surface strength.

Description

TECHNICAL FIELD

[0001] The present application relates to a meta-aramid paper and a preparation method thereof, and belongs to the technical field of synthetic fiber paper manufacturing. BACKGROUND

[0002] The meta-aramid paper is prepared by using meta-aramid short fibers and meta-aramid fibrids as raw materials, forming by wet papermaking, and then performing hot pressing. In the meta-aramid paper, the short fibers are uniformly dispersed in the paper as a skeleton material, which determines the physical strength and mechanical properties of the paper; the meta-aramid fibrids are used as filling and bonding materials, which soften under heat in the hot pressing process, and form the overall mechanical structure of the paper through the bonding of the short fibers and the self-bonding, thereby endowing the paper with overall strength and performance. The meta-aramid paper has excellent mechanical properties, dielectric properties, chemical stability, and flexible processability, and is widely used in high-temperature-resistant insulating materials. After impregnation, the meta-aramid paper can be made into high-strength lightweight honeycomb structural materials, which are widely used in the fields of aerospace, national defense, electronic communication, etc.

[0003] However, the surface of the short fibers in the meta-aramid paper will be rough and the fibers will fall off when the meta-aramid paper is subjected to friction during use. The thick paper is prone to delamination or blistering when subjected to alternating loads, and the surface strength and interlayer bonding strength are low, which limits the application of the meta-aramid paper in high-end fields such as aerospace, rail transportation, and national defense. At the same time, when the meta-aramid paper is used to prepare honeycomb materials, occasional glue penetration occurs, which increases the cost of downstream customers.

[0004] In addition, the meta-aramid short fibers are prone to flocculation during dispersion, which greatly affects the uniformity of the meta-aramid during the papermaking process, and further affects the mechanical properties and insulating properties of the meta-aramid paper.

[0005] In order to improve the bonding strength of aramid fibers, Chinese patent application CN110886145A uses one-step high-temperature hot pressing to improve the bonding force between fibers. However, the aramid fibers are severely plasticized at high temperatures, resulting in a decrease in the tearing performance of the aramid paper and poor bonding of the thick paper, which is prone to delamination. Chinese patent application CN113969427A prepares a network structure aramid micro-nano fiber for preparing aramid paper to improve the internal bonding strength of the aramid paper. Although the tensile strength and dielectric strength of the aramid paper are improved, the internal bonding strength of the aramid paper is not high, and the overall performance still needs to be further improved. Chinese patent application CN106531374A prepares a flame-retardant insulating composite material by laminating aramid paper and polyimide film, which can improve the high-temperature resistance and flame retardance of the composite material, and is applied to transformers of various frequencies. However, these methods introduce powders or film materials of different materials into the aramid paper, and the interface bonding force between the two materials is weak due to the interface effect of different materials, which is prone to delamination and blistering during long-term use.

[0006] To improve the uniformity of meta-aramid paper, existing technologies typically employ the addition of dispersants to enhance the dispersibility of aramid chopped fibers. While this method offers some improvement, it is expensive, and the addition of dispersants during the manufacturing process complicates wastewater treatment. Furthermore, the presence of dispersants affects the paper's temperature resistance and insulation properties.

[0007] Therefore, developing a meta-aramid paper with high bonding strength and high uniformity is of great value. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a meta-aramid paper and its preparation method. The meta-aramid paper exhibits higher uniformity, bonding strength, and insulation properties, reducing the risk of delamination and shedding during use. Simultaneously, it increases the density and reduces the porosity of the meta-aramid paper, significantly minimizing the risk of adhesive permeation during the preparation of honeycomb cells.

[0009] The technical solution of this invention to solve the above-mentioned technical problems is as follows: a method for preparing meta-aramid paper, wherein the preparation method is as follows:

[0010] S1. Preparation of nanofiber dispersion:

[0011] 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.

[0012] S2, Preparation of meta-aramid short-cut fiber dispersion and meta-aramid precipitated fibers:

[0013] Meta-aramid short-cut fibers were added to the nanofiber dispersion for dissolution and mixed evenly to obtain the meta-aramid short-cut fiber dispersion.

[0014] 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 meta-aramid 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.

[0015] S3, Preparation of meta-aramid paper:

[0016] Meta-aramid short-cut fiber dispersion and meta-aramid precipitated fibers are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain meta-aramid paper.

[0017] Furthermore, in step S1, the stirring time is 4 to 24 hours, and the storage temperature of the nanofiber dispersion is 15 to 25°C.

[0018] 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).

[0019] Furthermore, in step S2, when preparing the meta-aramid short-cut fiber dispersion, the disintegration time is 5 to 15 minutes; the mass concentration of the meta-aramid short-cut fiber in the dispersion is 0.05% to 1%.

[0020] 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.

[0021] 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).

[0022] 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.

[0023] 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.

[0024] The chloride salt is at least one of lithium chloride, calcium chloride, and magnesium chloride.

[0025] Furthermore, the weight ratio of the intermediate aramid chopped fiber to the meta-aramid precipitated fiber in the meta-aramid chopped fiber dispersion is (8-2):(2-8), and the total weight of the intermediate aramid chopped fiber and the meta-aramid precipitated fiber in the meta-aramid chopped fiber dispersion is 10 parts.

[0026] Furthermore, in step S3, the hot pressing conditions are: temperature 180~210℃, vehicle speed 5~18m / min, and pressure 100~280 N / mm.

[0027] The present invention also discloses a meta-aramid paper, wherein the meta-aramid paper is prepared according to the preparation method described in the present invention.

[0028] The beneficial effects of this invention are:

[0029] 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 meta-aramid chopped fibers, allowing for good dispersion of the meta-aramid chopped fibers without the addition of a dispersant, and preventing flocculation. This results in meta-aramid paper having higher uniformity, better mechanical properties, and better insulation properties.

[0030] 2. During the precipitation of the nanofiber dispersion in water, para-aramid nanofibers adhere to the surface of the meta-aramid chopped fibers, roughening the smooth surface of the meta-aramid chopped fibers. This enhances the interfacial bonding strength between meta-aramid chopped fibers and between meta-aramid chopped fibers and meta-aramid precipitated fibers, resulting in greater inter-fiber bonding and better stress transfer, thus improving the adhesion of the aramid paper. Moreover, this roughness is not achieved by sacrificing the original properties of the meta-aramid fibers. Simultaneously, this method can significantly reduce the porosity of the meta-aramid paper, thereby improving its insulation properties and yielding meta-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 improving the adhesion of the aramid paper.

[0031] 3. Introducing para-aramid nanofibers during the preparation of meta-aramid precipitated paper reduces the crystallinity of the meta-aramid fibers, making them easier to melt during hot pressing and resulting in stronger bonding between the fibers. This reduces the risk of delamination, fuzzing, and shedding of the meta-aramid paper during use. Simultaneously, it increases the density and reduces the porosity of the meta-aramid paper, significantly reducing the risk of adhesive permeation during the preparation of honeycomb structures.

[0032] 4. Compared to conventional meta-aramid precipitated fibers, the low-crystallinity meta-aramid precipitated fibers in this invention can achieve excellent melting and bonding at relatively low hot-pressing temperatures, significantly reducing 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

[0033] 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.

[0034] 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.

[0035] A method for preparing meta-aramid paper, wherein the preparation method comprises:

[0036] S1. Preparation of nanofiber dispersion:

[0037] 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.

[0038] S2, Preparation of meta-aramid short-cut fiber dispersion and meta-aramid precipitated fibers:

[0039] Meta-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 meta-aramid short-cut fiber dispersion.

[0040] Meta-aramid polymerization liquid, nanofiber dispersion liquid, and precipitating agent are continuously and stably added to the precipitation equipment. The precipitated fibers are obtained by high-speed shearing and then discharged into the 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.

[0041] S3, Preparation of meta-aramid paper:

[0042] Meta-aramid short-cut fiber dispersion and meta-aramid precipitated fibers are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain meta-aramid paper.

[0043] 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.

[0044] 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).

[0045] Specifically, in step S2, when preparing the meta-aramid short-cut fiber dispersion, the disintegration time is 5 to 15 minutes; the mass concentration of the meta-aramid short-cut fiber in the dispersion is 0.05% to 1%.

[0046] 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.

[0047] 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).

[0048] 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.

[0049] 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.

[0050] The chloride salt is at least one of lithium chloride, calcium chloride, and magnesium chloride.

[0051] More specifically, the storage temperature of the precipitant is 4–20°C.

[0052] Specifically, in step S3, the weight ratio of the meta-aramid chopped fiber to the meta-aramid precipitated fiber in the meta-aramid chopped fiber dispersion is (8-2):(2-8), and the total weight of the meta-aramid chopped fiber to the meta-aramid precipitated fiber in the meta-aramid chopped fiber dispersion is 10 parts.

[0053] Specifically, in step S3, the hot pressing conditions are: temperature 180~210℃, vehicle speed 5~18m / min, and pressure 100~280 N / mm.

[0054] More specifically, the para-aramid chopped fibers and meta-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.

[0055] A meta-aramid paper, wherein the meta-aramid paper is prepared according to the preparation method described in this invention.

[0056] Example 1

[0057] Preparation of a meta-aramid paper:

[0058] S1. Preparation of nanofiber dispersion:

[0059] 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 12 h to obtain a stable nanofiber dispersion. The weight ratio of para-aramid fibers, dimethyl sulfoxide, water, and potassium hydroxide was 1.5:95:0.06:2.5. The nanofiber dispersion was stored at 20 °C.

[0060] S2, Preparation of meta-aramid short-cut fiber dispersion and meta-aramid precipitated fibers:

[0061] (1) Preparation of meta-aramid short-cut fiber dispersion:

[0062] Meta-aramid short-cut fibers were added to a nanofiber dispersion for dissolution. After dissolution for 12 minutes, the dispersion was stirred evenly to obtain the meta-aramid short-cut fiber dispersion. The mass concentration of meta-aramid short-cut fibers in the dispersion was 0.8%.

[0063] (2) Preparation of meta-aramid precipitated fibers:

[0064] 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.

[0065] The weight ratio of nanofiber dispersion, precipitant, and meta-aramid polymer solution is 15:10:90.

[0066] The temperature of the meta-aramid polymerization solution is 35℃, the solid content is 12%, and the viscosity at 25℃ is 300Po.

[0067] The precipitant, by weight, consists of 10 parts calcium chloride, 45 parts water, and 45 parts N,N-dimethylacetamide.

[0068] S3, Preparation of meta-aramid paper:

[0069] Meta-aramid short-cut fiber dispersion and meta-aramid precipitated fiber are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain meta-aramid paper.

[0070] The weight ratio of meta-aramid chopped fiber to meta-aramid precipitated fiber in the dispersion is 4:6.

[0071] The hot pressing conditions are: temperature 190℃, vehicle speed 15m / min, and pressure 180 N / mm.

[0072] Example 2

[0073] Preparation of a meta-aramid paper:

[0074] S1. Preparation of nanofiber dispersion:

[0075] Para-aramid short-cut fibers (2 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 0.05:85:0.02:0.15. The nanofiber dispersion was stored at 15 °C.

[0076] S2, Preparation of meta-aramid short-cut fiber dispersion and meta-aramid precipitated fibers:

[0077] (1) Preparation of meta-aramid short-cut fiber dispersion:

[0078] Meta-aramid short-cut fibers (2 dtex, 5 mm) were added to the nanofiber dispersion for dissolution. After dissolution for 15 min, the dispersion was stirred evenly to obtain the meta-aramid short-cut fiber dispersion. The mass concentration of meta-aramid short-cut fibers in the dispersion was 1%.

[0079] (2) Preparation of meta-aramid precipitated fibers:

[0080] 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.

[0081] The weight ratio of nanofiber dispersion, precipitant, and meta-aramid polymer solution is 20:12:100.

[0082] The temperature of the meta-aramid polymerization solution is 40℃, the solid content is 8%, and the viscosity at 25℃ is 100Po.

[0083] The precipitant, by weight, consists of 5 parts lithium chloride, 45 parts water, and 50 parts N,N-dimethylacetamide.

[0084] S3, Preparation of meta-aramid paper:

[0085] Meta-aramid short-cut fiber dispersion and meta-aramid precipitated fiber are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain meta-aramid paper.

[0086] The weight ratio of meta-aramid chopped fiber to meta-aramid precipitated fiber in the dispersion is 2:8.

[0087] The hot pressing conditions are: temperature 180℃, vehicle speed 5m / min, and pressure 100 N / mm.

[0088] Example 3

[0089] Preparation of a meta-aramid paper:

[0090] S1. Preparation of nanofiber dispersion:

[0091] Para-aramid short-cut fibers (1.7 dtex, 6 mm) and potassium hydroxide were added to dimethyl sulfoxide, followed by water. The mixture was mechanically stirred for 4 hours to obtain a stable nanofiber dispersion. The weight ratio of para-aramid short-cut fibers, dimethyl sulfoxide, water, and potassium hydroxide was 3:100:0.08:4. The nanofiber dispersion was stored at 25°C.

[0092] S2, Preparation of meta-aramid short-cut fiber dispersion and meta-aramid precipitated fibers:

[0093] (1) Preparation of meta-aramid short-cut fiber dispersion:

[0094] Meta-aramid short-cut fibers (1.5 dtex, 6 mm) were added to the nanofiber dispersion for dissolution. After dissolution for 5 min, the dispersion was stirred evenly to obtain the meta-aramid short-cut fiber dispersion. The mass concentration of meta-aramid short-cut fibers in the dispersion was 0.05%.

[0095] (2) Preparation of meta-aramid precipitated fibers:

[0096] 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.

[0097] The weight ratio of the nanofiber dispersion, the precipitant, and the meta-aramid polymer solution is 5:5:80.

[0098] The temperature of the meta-aramid polymerization solution is 50℃, the solid content is 15%, and the viscosity at 25℃ is 450po.

[0099] The precipitant, by weight, consists of 18 parts magnesium chloride, 42 parts water, and 40 parts N,N-dimethylacetamide.

[0100] S3, Preparation of meta-aramid paper:

[0101] Meta-aramid short-cut fiber dispersion and meta-aramid precipitated fiber are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain meta-aramid paper.

[0102] The weight ratio of meta-aramid chopped fiber to meta-aramid precipitated fiber in the dispersion is 8:2.

[0103] The hot pressing conditions are: temperature 210℃, vehicle speed 18m / min, and pressure 280 N / mm.

[0104] Example 4

[0105] Preparation of a meta-aramid paper:

[0106] S1. Preparation of nanofiber dispersion:

[0107] Para-aramid short-cut fibers (2 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 1:80:0.01:1. The nanofiber dispersion was stored at 25 °C.

[0108] S2, Preparation of meta-aramid short-cut fiber dispersion and meta-aramid precipitated fibers:

[0109] (1) Preparation of meta-aramid short-cut fiber dispersion:

[0110] Meta-aramid short-cut fibers (1.5 dtex, 5 mm) were added to the nanofiber dispersion for dissolution. After dissolution for 8 minutes, the dispersion was stirred evenly to obtain the meta-aramid short-cut fiber dispersion. The mass concentration of meta-aramid short-cut fibers in the dispersion was 0.15%.

[0111] (2) Preparation of meta-aramid precipitated fibers:

[0112] 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.

[0113] The weight ratio of the nanofiber dispersion, the precipitant, and the meta-aramid polymer solution is 10:10:90.

[0114] The temperature of the meta-aramid polymerization solution is 35℃, the solid content is 12%, and the viscosity at 25℃ is 300Po.

[0115] The precipitant, by weight, consists of 15 parts calcium chloride, 45 parts water, and 40 parts N,N-dimethylacetamide.

[0116] S3, Preparation of meta-aramid paper:

[0117] Meta-aramid short-cut fiber dispersion and meta-aramid precipitated fiber are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain meta-aramid paper.

[0118] The weight ratio of meta-aramid chopped fiber to meta-aramid precipitated fiber in the dispersion is 6:4.

[0119] The hot pressing conditions are: temperature 200℃, vehicle speed 18m / min, and pressure 160 N / mm.

[0120] Comparative Example 1

[0121] Meta-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 Comparative Example 1, the storage temperature of the nanofiber dispersion was 35°C.

[0122] Comparative Example 2

[0123] Meta-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.

[0124] Comparative Example 3

[0125] Meta-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.

[0126] Comparative Example 4

[0127] Meta-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.

[0128] Comparative Example 5

[0129] Meta-aramid paper was prepared using the same method as in Example 1, except that in step S2, the shear rate was increased when preparing meta-aramid precipitated fibers. In Comparative Example 5, the shear rate in step S2 was 8000 rpm.

[0130] Comparative Example 6

[0131] Meta-aramid paper was prepared using the same method as in Example 1, except that in step S2, the shear rate was reduced when preparing meta-aramid precipitated fibers. In Comparative Example 6, the shear rate in step S2 was 2000 rpm.

[0132] Comparative Example 7

[0133] Using a conventional method, the nanofiber dispersion was coated onto the surface of aramid paper. The specific preparation process is as follows:

[0134] S1. Preparation of nanofiber dispersion:

[0135] Nanofiber dispersions were prepared using the same method as in Example 1;

[0136] S2, Preparation of meta-aramid paper:

[0137] Meta-aramid chopped fibers and meta-aramid precipitated fibers are loosened, stirred, and then wet-formed, pressed, and dried to obtain meta-aramid base paper; wherein the weight ratio of meta-aramid chopped fibers to meta-aramid precipitated fibers is 4:6.

[0138] S3, Coating of nanofiber dispersion:

[0139] The nanofiber dispersion prepared in step S1 is uniformly coated on one side of the meta-aramid paper prepared in step S2, then washed with water and dried. The above steps are then repeated on the other side of the meta-aramid paper to control the total coating amount of nanofibers on the meta-aramid paper to be 2 g / m².2 Finally, the meta-aramid paper coated with nanofibers on both sides is hot-pressed to obtain the final product. The hot-pressing conditions are: temperature 190℃, speed 15m / min, and pressure 180 N / mm.

[0140] Comparative Example 8

[0141] Meta-aramid paper was prepared using the same method as in Example 1, except that conventional methods were used to prepare the meta-aramid chopped fiber dispersion and the meta-aramid precipitated fibers. Specifically, in Comparative Example 8, no nanofiber dispersion was used when preparing the meta-aramid chopped fiber dispersion, and no nanofiber solution was added during the preparation of the meta-aramid precipitated fibers.

[0142] The specific preparation process of the meta-aramid short-cut fiber dispersion in Comparative Example 8 is as follows:

[0143] Meta-aramid chopped fibers were added to an appropriate amount of water for dissolution. After dissolution for 12 minutes, the mixture was stirred evenly to obtain the meta-aramid chopped fiber dispersion. The mass concentration of meta-aramid chopped fibers in the meta-aramid chopped fiber dispersion was 0.8%.

[0144] The specific preparation process of the meta-aramid fiber dispersion in Comparative Example 8 is as follows:

[0145] 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.

[0146] The weight ratio of the precipitant to the meta-aramid polymerization solution is 10:90.

[0147] The temperature of the meta-aramid polymerization solution is 35℃, the solid content is 12%, and the viscosity at 25℃ is 300Po.

[0148] The precipitant, by weight, consists of 10 parts calcium chloride, 45 parts water, and 45 parts N,N-dimethylacetamide.

[0149] Then, using the same method as in Example 1, the meta-aramid short-cut fiber dispersion and meta-aramid precipitated fiber prepared in Comparative Example 8 were loosened, stirred, and then subjected to wet forming, pressing, drying, and hot pressing to obtain meta-aramid paper.

[0150] Comparative Example 9

[0151] Meta-aramid paper was prepared using the same method as in Example 1, except that a conventional method was used to prepare the meta-aramid short-cut fiber dispersion. Specifically, no nanofiber dispersion was used in the preparation of the meta-aramid short-cut fiber dispersion in Comparative Example 9. The specific preparation process for the meta-aramid short-cut fiber dispersion in Comparative Example 9 is as follows:

[0152] Meta-aramid chopped fibers were added to an appropriate amount of water for dissolution. After dissolution for 12 minutes, the mixture was stirred evenly to obtain the meta-aramid chopped fiber dispersion. The mass concentration of meta-aramid chopped fibers in the meta-aramid chopped fiber dispersion was 0.8%.

[0153] Comparative Example 10

[0154] Meta-aramid paper was prepared using the same method as in Example 1, except that conventional methods were used to prepare the meta-aramid precipitated fibers. 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:

[0155] 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.

[0156] The weight ratio of the precipitant to the meta-aramid polymerization solution is 10:90.

[0157] The temperature of the meta-aramid polymerization solution is 35℃, the solid content is 12%, and the viscosity at 25℃ is 300Po.

[0158] The precipitant, by weight, consists of 10 parts calcium chloride, 45 parts water, and 45 parts N,N-dimethylacetamide.

[0159] The aramid paper prepared in the above embodiments and comparative examples was subjected to performance testing. The specific testing methods involved are as follows.

[0160] The quantitative testing method refers to standard GB / T 451.2;

[0161] The thickness test method refers to the standard GB / T 451.3;

[0162] The test methods for tensile strength and elongation are based on the standard GB / T 12914.

[0163] The tear resistance test method refers to the standard GB / T 455;

[0164] The dielectric strength test method refers to the standard GB / T 1408.1;

[0165] The surface strength test method refers to standard GB / T 22837;

[0166] The test method for internal bond strength shall refer to standard GB / T 26203;

[0167] The uniformity index was measured by the Micro-Scanner testing instrument;

[0168] Porosity was measured by a mercury porosimeter.

[0169] The specific test results are shown in Tables 1 and 2 below.

[0170] Table 1 Test data of mechanical properties of meta-aramid paper

[0171]

[0172] Table 2 Other performance test data of meta-aramid paper

[0173]

[0174] As can be seen from the data in the table above, the meta-aramid paper prepared by the method described in this invention in Examples 1-4 has good uniformity, low porosity, and excellent mechanical and insulating properties. Furthermore, the meta-aramid paper prepared by the method described in this invention in Examples 1-4 has high surface strength and internal bonding strength, which can largely avoid delamination and fuzzing, improving user satisfaction. At the same time, the reduced porosity also reduces the risk of adhesive permeation during the honeycomb preparation process of the meta-aramid paper. In Examples 1-4 of this invention, the meta-aramid short-cut fibers are well dispersed in the nano-dispersion liquid, significantly improving the overall performance of the meta-aramid paper. Simultaneously, the aramid nanofibers adhering to the surface of the meta-aramid short-cut fibers act as a binder, filling the pores of the meta-aramid paper and strengthening the interaction with other fibers. In addition, 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 excellent performance in the processing. Compared to conventional meta-aramid precipitated fibers, the meta-aramid precipitated surface prepared by this invention has more micro-wrinkles, resulting in stronger bonding with other fibers. Simultaneously, strong hydrogen bonds can form between the aramid nanofibers and the short-cut or precipitated meta-aramid fibers. Under these multiple effects, the meta-aramid paper of this invention exhibits excellent overall properties.

[0175] 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, compressive strength, surface strength, internal bonding strength, and uniformity of the meta-aramid paper. This is because at a suitable temperature, the aramid chopped fibers disperse more uniformly, resulting in more uniform sizes of the prepared meta-aramid precipitated fibers, while maintaining appropriate crystallinity and microstructure (i.e., more micro-wrinkles on the surface). Therefore, the overall performance of the final aramid paper is significantly improved.

[0176] A comparison of the data from Comparative Examples 3 and 4 with Example 1 shows that increasing or decreasing the proportion of nanofibers significantly reduces the overall performance of the meta-aramid paper. This is because selecting an appropriate nanofiber ratio ensures that the prepared meta-aramid precipitated fibers are more uniform in size and maintain suitable crystallinity and microstructure, resulting in superior mechanical properties and higher compressive strength in the prepared meta-aramid paper. Furthermore, selecting an appropriate nanofiber ratio allows for a more optimal dispersion of the aramid chopped fibers, contributing to the overall good performance of the aramid paper.

[0177] 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 meta-aramid paper. When the shear rate is too high, the length of the meta-aramid precipitated fibers decreases, and the film characteristics of these fibers diminish, leading to a reduced contact area between the meta-aramid precipitated fibers and the chopped aramid fibers. This results in 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, further degrading the overall performance of the meta-aramid paper. Furthermore, maintaining a certain shear rate is crucial for the crystallinity of the meta-aramid precipitated fibers. Excessive shear rate causes the aramid droplets to easily form a film state under high-speed shearing, disrupting the crystalline structure and resulting in 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 to moderately reduce the crystallinity of the prepared meta-aramid precipitated fibers compared to traditional meta-aramid precipitated fibers, not only saves energy consumption in the hot-pressing process but also significantly improves the overall performance of meta-aramid paper.

[0178] 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 meta-aramid paper of this invention has better overall performance.

[0179] The data comparison between Comparative Example 8 and Example 1 shows that, compared with the conventional method for preparing meta-aramid paper, the meta-aramid paper prepared by the present invention has significantly improved mechanical properties, compressive strength, and internal and surface strength of the paper, avoiding phenomena such as fuzzing and delamination during paper use.

[0180] Comparison of data from Comparative Examples 9, 10 and 1 shows that aramid paper prepared using both meta-aramid precipitated fibers and meta-aramid chopped fiber dispersions of the present invention has better overall performance.

[0181] In summary, the meta-aramid paper of this invention has higher tensile strength, uniformity, density and insulation properties, while also having better internal bonding and surface strength, avoiding delamination, fuzzing and glue seepage during use.

[0182] 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.

[0183] 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 meta-aramid paper, characterized in that, The preparation method is as follows: S1. Preparation of nanofiber dispersion: Para-aramid chopped fibers and potassium hydroxide were added to dimethyl sulfoxide, and then water was added and stirred to disperse the nanofibers to obtain the nanofiber dispersion. The weight ratio of para-aramid fibers, dimethyl sulfoxide, water and potassium hydroxide was (0.05-3):(80-100):(0.01-0.08):(0.15-4). The nanofiber dispersion was stored at a temperature of 15-25°C. S2, Preparation of meta-aramid short-cut fiber dispersion and meta-aramid precipitated fibers: Meta-aramid short-cut fibers were added to the nanofiber dispersion for dissolution and mixed evenly to obtain the meta-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 meta-aramid precipitated fibers. Then, the fibers are 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. When preparing the meta-aramid precipitated fibers, the weight ratio of the nanofiber dispersion, the precipitant, and the meta-aramid polymerization liquid is (5-20):(5-12):(80-100). S3, Preparation of meta-aramid paper: Meta-aramid short-cut fiber dispersion and meta-aramid precipitated fibers are loosened, stirred, and then wet-formed, pressed, dried and hot-pressed to obtain meta-aramid paper.

2. The method for preparing meta-aramid paper according to claim 1, characterized in that, In step S1, the stirring time is 4 to 24 hours.

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

4. The method for preparing meta-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 meta-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 meta-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 meta-aramid paper according to claim 1, characterized in that, The weight ratio of intermediate aramid chopped fibers to meta-aramid precipitated fibers in the meta-aramid chopped fiber dispersion is (8-2):(2-8), and the total weight of intermediate aramid chopped fibers and meta-aramid precipitated fibers in the meta-aramid chopped fiber dispersion is 10 parts.

8. The method for preparing meta-aramid paper according to claim 1, characterized in that, In step S3, the hot pressing conditions are: temperature 180~210℃, vehicle speed 5~18m / min, and pressure 100~280 N / mm.

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

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