Continuous high-heat-resistant and environmentally friendly para-aramid diaphragm and preparation method thereof

Abstract

The present invention discloses a continuous, highly heat-resistant, and environmentally friendly para-aramid diaphragm and a preparation method thereof. The continuous, highly heat-resistant, and environmentally friendly para-aramid diaphragm is coated with a continuous, highly heat-resistant, and environmentally friendly para-aramid coating slurry. The continuous, highly heat-resistant, and environmentally friendly para-aramid coating slurry is prepared using a twin-screw extruder through a first slurry, a second slurry, and a third slurry. The first slurry includes: para-phenylenediamine; the second slurry is a molten liquid of terephthaloyl chloride; and the third slurry includes: fumed silica and boehmite. The twin-screw extrusion method is used to achieve a high-efficiency continuous synthesis step during the synthesis of the continuous, highly heat-resistant, and environmentally friendly para-aramid coating slurry. The fumed silica and boehmite are mixed so that the para-aramid fibers adsorb the fumed silica, increasing the gaps between the fibers and reducing the aggregation of the fibers due to hydrogen bonds. During the coating process, a high-humidity environment and ultrasonic spraying are used to pre-cure the diaphragm surface and reduce the extraction concentration.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a continuous, highly heat-resistant and environmentally friendly para-aramid diaphragm and a preparation method thereof. Background Art

[0002] Due to the unique nanofiber structure of para-aramid, hydrogen bonds between fibers easily cause them to agglomerate, resulting in the slurry forming a gel state, solidifying and deteriorating, resulting in a short shelf life. The time between synthesis and coating is tight, leaving little room for adjustment. Each synthesis of para-aramid takes more than 2 hours, resulting in low synthesis efficiency.

[0003] In the coating section, because the fiber solid content in the para-aramid slurry is low (a solid content exceeding 4% will cause the slurry to gel), the coating thickness is difficult to control. For example, if the thickness of the coating slurry is 5μm, only 1.5μm will remain after extraction and drying; traditional anilox rollers cannot increase the thickness of the para-aramid coating.

[0004] In the extraction section, if a low-concentration extractant is used for extraction, the para-aramid fibers will precipitate rapidly, causing the para-aramid structure to collapse and become pore-free, resulting in an excessively high air permeability value of the diaphragm. When a high-concentration extractant is used for extraction, the para-aramid fibers can be slowly precipitated, allowing the aramid fibers to be completely dispersed on the surface of the diaphragm. However, NMP extraction must be performed with a concentration of 90% or above, which results in excessively high costs and difficulty in handling the extractant. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for preparing a continuous, highly heat-resistant and environmentally friendly para-aramid coating slurry.

[0006] Another object of the present invention is to provide a continuous, highly heat-resistant, and environmentally friendly para-aramid diaphragm.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned continuous high-heat-resistant and environmentally friendly para-aramid diaphragm.

[0008] The purpose of the present invention is achieved through the following technical solutions.

[0009] A method for preparing a continuous high-heat-resistant and environmentally friendly para-aramid coating slurry comprises the following steps:

[0010] Step 1, prepare a twin-screw extruder, the twin-screw extruder is composed of a polymerization zone, a polymerization mixing zone and a heating zone from left to right, the left end of the polymerization zone is provided with a first feed port and a second feed port, the polymerization mixing zone is provided with a third feed port, and the right end of the heating zone is provided with a discharge port, the temperature of the polymerization zone is 0-5°C, the temperature of the polymerization mixing zone is 15-20°C, and the temperature of the heating zone is 20-30°C;

[0011] In step 1, the first feed port is located to the left of the second feed port, and the material between the third feed port and the second feed port is used to synthesize poly(p-phenylene terephthalamide) (PPTA). (The first and second slurries are used to synthesize poly(p-phenylene terephthalamide), while the third slurry is used to add ceramics. The functions of the third slurry are: 1. Mainly to allow the ceramics to be added in the middle of the polymerization process so that the fibers and ceramics are adsorbed together. 2. Adding ceramics and NMP in the middle of the process can slow down the polymerization of molecules, preventing the molecular weight from being too high during discharge, which would cause the slurry viscosity to be too high (a viscosity exceeding 20,000 mPa.s would be unusable), making it impossible to coat the diaphragm).

[0012] Step 2: first input the first slurry into the first feed port of the twin-screw extruder to fill the twin-screw extruder with the first slurry, and then input the second slurry into the second feed port in a spraying state. When the viscosity of the slurry at the discharge port of the twin-screw extruder reaches between 400 and 5000 mPa.s, input the third slurry into the third feed port until the viscosity of the slurry at the discharge port of the twin-screw extruder reaches more than 1000 cp. A continuous high-heat-resistant and environmentally friendly para-aramid coating slurry is obtained from the discharge port, wherein the speed ratio of the first slurry, the second slurry and the third slurry is (2 to 4):

[0013] (0.06-0.09): (0.6-0.8), the first slurry includes: p-phenylenediamine; the second slurry is a molten liquid of terephthaloyl chloride; the third slurry includes: fumed silica and boehmite;

[0014] In the step 2, the slurry in the twin-screw extruder runs from the first feed port to the second feed port for 0.2 to 1 second, the slurry in the twin-screw extruder runs from the second feed port to the polymerization mixing zone for 5 to 10 seconds, the slurry in the twin-screw extruder runs from the leftmost end of the polymerization mixing zone to the third feed port for 4 to 8 seconds, the slurry in the twin-screw extruder runs from the third feed port to the heating zone for 4 to 8 seconds, and the slurry in the twin-screw extruder runs from the leftmost end of the heating zone to the discharge port for 4 to 8 seconds.

[0015] The method for preparing the first slurry comprises: mixing calcium chloride and a first NMP solution, stirring until the calcium chloride is dissolved in the first NMP solution to obtain a first solution, cooling the first solution to 5 to 20° C. and then mixing with p-phenylenediamine, stirring until the p-phenylenediamine is uniformly dispersed in the first solution to obtain a first slurry, wherein, by weight, the ratio of the first NMP solution, calcium chloride, and p-phenylenediamine is (90 to 96.4): (2 to 8): (1.6 to 2);

[0016] In the above technical solution, the calcium chloride is dehydrated before being mixed with the first NMP solution. The dehydration method is calcining at 400-450° C. for 3-5 hours.

[0017] In the above technical solution, the water content of the first NMP solution is ≤0.2 wt%.

[0018] In the above technical solution, calcium chloride is dissolved in the first NMP solution by stirring at 75-85° C. for 4-6 hours.

[0019] In the above technical solution, p-phenylenediamine is uniformly dispersed in the first solution by stirring at 0-20° C. for 3-5 hours.

[0020] In the above technical solution, solid terephthaloyl chloride is heated at 80-95° C. until terephthaloyl chloride is formed into a molten liquid.

[0021] The method for preparing the third slurry includes: mixing fumed silica, boehmite and a second NMP solution, stirring, and sand grinding to obtain a third slurry, wherein, by mass, the ratio of the second NMP solution, fumed silica and boehmite is (78-87): (3-7): (10-15).

[0022] In the method for preparing the third slurry, the stirring time is 40 to 80 minutes.

[0023] In the above technical solution, the sanding time is 20 to 30 minutes, and the sanding speed is 1000 to 1500 r / min.

[0024] In the above technical solution, the water content of the second NMP solution is ≤0.2 wt%.

[0025] In the above technical solution, the rotation speed of the conveying rod in the twin-screw extruder is 20 to 30 r / min, and the rotation speed of the mixing rod is 20 to 30 r / min.

[0026] A method for preparing a continuous, highly heat-resistant, and environmentally friendly para-aramid diaphragm comprises the following steps:

[0027] S1, extruding a continuous high-heat-resistant and environmentally friendly para-aramid coating slurry through a die head and coating it on one or both sides of a base film, and pre-curing it in a humidity space for at least 0.5 minutes to obtain a semi-finished continuous high-heat-resistant and environmentally friendly para-aramid separator, wherein the humidity of the humidity space is 60-80% RH and the temperature of the humidity space is 25-35° C.;

[0028] In S1, the pre-curing treatment time in the humidity space is 0.5 to 2 minutes.

[0029] In S1, the humidity space includes: an air inlet, an air outlet and an ultrasonic spray head. The air inlet frequency is 5-7 Hz, the air outlet frequency is 5-7 Hz, and the ultrasonic spray head is used to spray atomized water into the humidity space. The ultrasonic spray frequency is 3-8 MHz.

[0030] In S1, the base film is a PE film.

[0031] In S1, the flow rate of the continuous high-heat-resistant and environmentally friendly para-aramid coating slurry extruded by the die head is 0.4-0.7 L / min, the coating speed is 15-30 m / min, and the thickness of the single-sided coating is 10-15 μm.

[0032] S2, extracting, drying, and shaping the semi-finished continuous high-heat-resistant and environmentally friendly para-aramid diaphragm to obtain the continuous high-heat-resistant and environmentally friendly para-aramid diaphragm.

[0033] In S2, the extraction is performed using a plurality of extractants in sequence, wherein the concentration of NMP in the plurality of extractants used in sequence decreases, and the concentration of NMP in the extractants is less than or equal to 60 wt%.

[0034] In the above technical solution, the extraction is carried out sequentially using a first extractant, a second extractant and a third extractant, wherein the first extractant and the second extractant are each a mixture of NMP and water, the concentration of NMP in the first extractant is 40-60 wt%, the concentration of NMP in the second extractant is 10-30 wt%, and the third extractant is water.

[0035] In S2, each of the extractants is placed in an extraction tank, and an extrusion roller is provided outside the extraction tank to extrude the semi-finished continuous high-heat-resistant and environmentally friendly para-aramid diaphragm removed from the extraction tank.

[0036] In S2, the drying temperature is 50-80°C; preferably, a first hot roller with a temperature of 50-80°C is used, and the diameter of the first hot roller is 400-600 mm.

[0037] In S2, the shaping temperature is 70-90°C; preferably, a second hot roller with a temperature of 70-90°C is used, and the diameter of the second hot roller is 200-300 mm.

[0038] In the above technical solution, the speed of passing through the first hot roller is 30-50 m / min, and the speed of passing through the second hot roller is 30-50 m / min.

[0039] In S2, the drying is located in an oven, and the shaping is located in a shaping oven. The oven is provided with a ventilation system, wherein the air intake frequency of the ventilation system is 15 to 50 Hz, and the air exhaust frequency of the ventilation system is 18 to 22 Hz; the film line length of the semi-finished continuous high-heat-resistant and environmentally friendly para-aramid diaphragm in the oven is 2 to 4 m, and the film line length of the semi-finished continuous high-heat-resistant and environmentally friendly para-aramid diaphragm in the shaping oven is 30 to 50 m.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] 1. The continuous high-heat-resistant and environmentally friendly para-aramid coating slurry of the present invention is synthesized by a twin-screw extrusion method, so that the synthesis process presents a high-efficiency continuous synthesis step;

[0042] 2. Mixing fumed silica and boehmite allows the para-aramid fiber to absorb fumed silica to increase the gaps between fibers and reduce the aggregation of fibers due to hydrogen bonds;

[0043] 3. Due to the low solid content of the continuous high heat-resistant and environmentally friendly para-aramid coating slurry, it is difficult to apply the coating thickness. The coating process adopts die extrusion coating, and the coating thickness is 15μm. After final extraction and drying, the thickness is maintained between 4 and 6μm.

[0044] 4. Use high humidity environment and ultrasonic spray during coating process to pre-cure the diaphragm surface and reduce the extraction concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a scanning electron microscope image of the continuous high-heat-resistant and environmentally friendly para-aramid diaphragm prepared in Example 1 of the present invention;

[0046] Figure 2 This is a cross-sectional electron microscope image of the continuous high-heat-resistant and environmentally friendly para-aramid diaphragm prepared in Example 1 of the present invention;

[0047] Figure 3 This is a scanning electron microscope image of the para-aramid diaphragm prepared in Comparative Example 1 of the present invention;

[0048] Figure 4 This is a scanning electron microscope image of the para-aramid diaphragm prepared in Comparative Example 2 of the present invention;

[0049] Figure 5 This is a scanning electron microscope image of the para-aramid diaphragm prepared in Comparative Example 3 of the present invention;

[0050] Figure 6 Schematic diagram of the present invention's twin-screw extruder for synthesizing continuous high-heat-resistant and environmentally friendly para-aramid coating slurry;

[0051] Figure 7Schematic diagram of the continuous high-heat-resistant and environmentally friendly para-aramid coating slurry coating base film, pre-curing treatment and extraction of the present invention;

[0052] Figure 8 This is a schematic diagram of the drying and shaping of the semi-finished continuous high-heat-resistant and environmentally friendly para-aramid diaphragm of the present invention. DETAILED DESCRIPTION

[0053] The technical solution of the present invention is further described below with reference to specific embodiments.

[0054] The basic information of the raw materials and equipment involved in the following examples is as follows:

[0055] The first NMP solution and the second NMP solution were both directly purchased N-methylpyrrolidone with a water content of ≤0.2wt% and a purity of 99.5%, purchased from Tianjin Hengxing Chemical Reagent Manufacturing Co., Ltd.

[0056] Calcium chloride, purity 99.5%, Tianjin Hengxing Chemical Reagent Manufacturing Co., Ltd.;

[0057] p-Phenylenediamine, purity 99.5%, Nanjing Lanbai Chemical Co., Ltd.;

[0058] Terephthaloyl chloride, purity 99.5%, Nanjing Lanbai Chemical Co., Ltd.;

[0059] Fumed silica, purity 99.5%, Hefei AVIC Nanotechnology Development Co., Ltd.;

[0060] Boehmite, purity 99.5%, Luoyang Zhongchao New Materials Co., Ltd.;

[0061] Pin-type horizontal sand mill, Paile, model PHE3000;

[0062] Twin-screw extruder, Nanjing Keerke Extrusion Equipment Co., Ltd., model KTE-75.

[0063] In the following examples and comparative examples, the base film is a PE film with a thickness of 12 μm.

[0064] The twin-screw extruder of the present invention pushes the slurry forward by rotating, realizing polymerization and transmission at the same time. A jacket is provided on the outside of the screw, and chilled water or hot water can be passed into the jacket to realize temperature control of the polymerization zone, polymerization mixing zone and heating zone. The twin screws in the twin-screw extruder are a conveying rod and a mixing rod. The conveying rod in the twin-screw extruder is mainly used to convey the slurry, and the mixing rod is mainly used to mix and stir the slurry.

[0065] In this scheme, the purpose of the pre-curing treatment is to make the para-aramid fibers on the continuous, high-heat-resistant, environmentally friendly para-aramid diaphragm more three-dimensional, fluffy, and porous under the clamping of ultrasonic spray. When the spray is sprayed onto the diaphragm, the para-aramid slowly precipitates, allowing the para-aramid fibers to be completely dispersed on the surface of the diaphragm to shape the surface. In order to make the spray more uniform and prevent water droplets from dripping onto the surface of the membrane, an air inlet is provided above the humidity space and an air outlet is provided below.

[0066] In this solution, the function of the squeezing roller in the extraction tank is to squeeze out the excess extractant, so as to clean it more thoroughly.

[0067] In this solution, a first heated roller performs drying, followed by a second heated roller for shaping, resulting in a smooth, continuous, highly heat-resistant, and environmentally friendly para-aramid separator. The primary challenge during the drying phase is the internal stress in the para-aramid. If left untreated, the resulting separator will exhibit severe warping, rendering it unusable. Shaping can address this internal stress.

[0068] In the technical solution of the present invention, multiple extractants are used in sequence for extraction, and the concentration of NMP in the multiple extractants used in sequence decreases. Finally, excess solvent on the surface is washed with water.

[0069] The test method for membrane rupture temperature is as follows: the membrane is cut into a sample with a length of 8 mm and a width of 2 mm, and the sample is placed in a dynamic thermomechanical analyzer (TMA instrument). The two sides of the sample are clamped with clips, and a tension of 0.03 N is applied. The temperature is raised from room temperature until the membrane breaks, and the temperature at the time of rupture is recorded as the membrane rupture temperature.

[0070] Liquid absorption rate test method: Cut the diaphragm into 30mm wide and 100mm long, weigh it and record it as the mass before immersion, soak it in lithium hexafluorophosphate electrolyte for 30 minutes, take it out and weigh it and record it as the mass after immersion, and calculate the liquid absorption rate (liquid absorption rate = (mass after immersion - mass before immersion) / mass before immersion).

[0071] Liquid retention rate test method: cut the diaphragm into 30 mm wide and 100 mm long, weigh it and record it as the mass before immersion, soak the diaphragm in lithium hexafluorophosphate electrolyte for 30 minutes, take it out and hang it for 30 minutes, use non-woven cloth to gently absorb the excess lithium hexafluorophosphate electrolyte on the surface and weigh it and record it as the mass of the liquid-retaining diaphragm, and calculate the liquid retention rate (liquid retention rate = (mass of liquid-retaining diaphragm - mass before immersion) / mass before immersion).

[0072] Example 1

[0073] A method for preparing a continuous high-heat-resistant and environmentally friendly para-aramid coating slurry comprises the following steps:

[0074] Step 1: prepare a twin-screw extruder (with an inner diameter of 100 mm), as Figure 6 As shown, the twin-screw extruder comprises a polymerization zone, a polymerization mixing zone and a heating zone from left to right. A first feed port and a second feed port are provided at the left end of the polymerization zone, the first feed port is located on the left side of the second feed port, a third feed port is provided on the polymerization mixing zone, the third feed port is located at 1 / 2 of the polymerization mixing zone, and the material between the third feed port and the second feed port is used to synthesize poly(p-phenylene terephthalamide) (PPTA). A discharge port is provided at the right end of the heating zone. The temperature of the polymerization zone is 0°C, the temperature of the polymerization mixing zone is 15°C, and the temperature of the heating zone is 20°C.

[0075] Step 2: first input the first slurry into the first feed port of the twin-screw extruder to fill the twin-screw extruder with the first slurry, and then input the second slurry into the second feed port in a spraying state. When the viscosity of the slurry at the discharge port of the twin-screw extruder reaches 400mPa.s (because the molten liquid of terephthaloyl chloride as the second slurry is a high-temperature molten state and is solid at low temperatures, if the second slurry is not sprayed well or is in a fluid state, the molten liquid of terephthaloyl chloride and the low-temperature solution in the twin-screw extruder will be in a liquid-like state). Fusion will directly form large blocks instead of fine particles, which will seriously affect the subsequent polymerization. ), the third slurry is input into the third feed port until the viscosity of the slurry at the discharge port of the twin-screw extruder reaches more than 1000cp, and a continuous high-heat-resistant and environmentally friendly para-aramid coating slurry is obtained from the discharge port. Among them, the speed ratio of the first slurry, the second slurry and the third slurry is 2:0.06:0.6, the flow rate of the first slurry is 2L / min, and the slurry in the twin-screw extruder is fed from the first feed port ( Figure 6 "Step 1 Slurry") runs right for 1s to reach the second feed port ( Figure 6 In the "step 2 slurry"), the slurry in the twin-screw extruder runs from the second feed port to the polymerization mixing zone for 10s, and the slurry in the twin-screw extruder runs from the leftmost end of the polymerization mixing zone to the third feed port for 8s. The slurry in the twin-screw extruder runs from the third feed port ( Figure 6 The slurry in the twin-screw extruder runs for 8 seconds from the left end of the heating zone to the discharge port. The speed of the conveying rod in the twin-screw extruder is 20 r / min, and the speed of the mixing rod stirring is 20 r / min.

[0076] The method for preparing a first slurry includes: mixing calcium chloride and a first NMP solution (with a water content of 0.1 wt%), stirring at 80° C. for 6 h until the calcium chloride is dissolved in the first NMP solution to obtain a first solution, cooling the first solution to 5° C. and then mixing with p-phenylenediamine, stirring at 0° C. for 3 h until the p-phenylenediamine is uniformly dispersed in the first solution to obtain a first slurry, wherein the ratio of the first NMP solution, calcium chloride, and p-phenylenediamine is 96.4:2:1.6 by mass, and the calcium chloride is dehydrated before being mixed with the first NMP solution by calcining in a muffle furnace at 420° C. for 4 h;

[0077] The second slurry is a molten liquid of terephthaloyl chloride, which is obtained by heating the solid terephthaloyl chloride in a tank at 80°C until the molten liquid of terephthaloyl chloride is formed;

[0078] The method for preparing the third slurry includes: mixing fumed silica, boehmite and a second NMP solution (water content of 0.1 wt%), stirring for 40 minutes, and sand milling at a speed of 1000 r / min for 20 minutes in a sand mill to obtain a third slurry, wherein, by mass, the ratio of the second NMP solution, fumed silica and boehmite is 87:3:10.

[0079] A method for preparing a continuous, highly heat-resistant, and environmentally friendly para-aramid diaphragm comprises the following steps:

[0080] S1, such as Figure 7 As shown, the continuous high heat-resistant and environmentally friendly para-aramid coating slurry is extruded through a die head and coated on a single side on a base film, and pre-cured in a humidity space for 0.5 min to obtain a semi-finished continuous high heat-resistant and environmentally friendly para-aramid diaphragm, wherein the humidity space includes: an air inlet, an air outlet and an ultrasonic spray head, the air inlet frequency is 5 Hz, the air outlet frequency is 5 Hz, the ultrasonic spray head is used to spray atomized water into the humidity space (the ultrasonic spray head breaks the water into tiny particles through high-frequency vibration, throws it off the water surface, and sprays it into the humidity space), the frequency of the ultrasonic spray is 3 MHz, the humidity of the humidity space is 60% RH, the temperature of the humidity space is 25 ° C, the flow rate of the continuous high heat-resistant and environmentally friendly para-aramid coating slurry extruded from the die head is 0.4 L / min, the coating speed is 15 m / min, and the thickness of the single-sided coating is 10 μm;

[0081] S2, extracting the semi-finished continuous high heat-resistant and environmentally friendly para-aramid membrane, drying it in an oven at 50°C, and shaping it in four shaping ovens at 70°C to obtain a continuous high heat-resistant and environmentally friendly para-aramid membrane, wherein the extraction is carried out in sequence with a first extractant, a second extractant, and a third extractant, the first extractant and the second extractant are each a mixture of NMP and water, the concentration of NMP in the first extractant is 40wt%, the concentration of NMP in the second extractant is 10wt%, and the third extractant is pure water, and the extractants are distributed in three extraction tanks, and an extrusion roller is provided outside each extraction tank to extrude the semi-finished continuous high heat-resistant and environmentally friendly para-aramid membrane removed from the extraction tank, and the function of the extrusion roller is to squeeze out excess extractant on the semi-finished continuous high heat-resistant and environmentally friendly para-aramid membrane, so that the solvent on the semi-finished continuous high heat-resistant and environmentally friendly para-aramid membrane is cleaned more cleanly; Figure 8 As shown, the drying oven is equipped with 4 first hot rollers, the diameter of the first hot roller is 400mm, the temperature of the first hot roller is 50℃, and the drying oven is equipped with an air exchange system to discharge moisture in time. The air intake frequency is 18HZ and the exhaust frequency is 20HZ; the shaping oven has four sub-ovens (the sub-ovens are heated by hot rollers and have no exhaust and heating system), and each sub-oven is equipped with 4 second hot rollers arranged in a vertical direction, the diameter of the second hot roller is 200mm, the temperature of the second hot roller is 70℃, the film line length of the semi-finished continuous high heat-resistant and environmentally friendly para-aramid diaphragm in the oven is 2m, the film line length of the semi-finished continuous high heat-resistant and environmentally friendly para-aramid diaphragm in the shaping oven is 30m, the speed passing through the first hot roller is 30m / min, and the speed passing through the second hot roller is 30m / min.

[0082] Example 2

[0083] A method for preparing a continuous high-heat-resistant and environmentally friendly para-aramid coating slurry comprises the following steps:

[0084] Step 1, prepare a twin-screw extruder (inner diameter of 120mm), the twin-screw extruder is composed of a polymerization zone, a polymerization mixing zone and a heating zone from left to right, the left end of the polymerization zone is provided with a first feed port and a second feed port, the first feed port is located on the left side of the second feed port, the polymerization mixing zone is provided with a third feed port, the third feed port is located at 1 / 2 of the polymerization mixing zone, and the third feed port and the second feed port are used to synthesize poly(p-phenylene terephthalamide) (PPTA), the right end of the heating zone is provided with a discharge port, the temperature of the polymerization zone is 3°C, the temperature of the polymerization mixing zone is 18°C, and the temperature of the heating zone is 25°C;

[0085] Step 2: first input the first slurry into the first feed port of the twin-screw extruder to fill the twin-screw extruder with the first slurry, then input the second slurry into the second feed port in a spraying state, and when the viscosity of the slurry at the discharge port of the twin-screw extruder reaches 2000mPa.s, finally input the third slurry into the third feed port until the viscosity of the slurry at the discharge port of the twin-screw extruder reaches more than 1000cp, and a continuous high-heat-resistant and environmentally friendly para-aramid coating slurry is obtained from the discharge port, wherein the speed ratio of the first slurry, the second slurry and the third slurry is 3:0.08:0.7, and the speed ratio of the first slurry, the second slurry and the third slurry is 3:0.08:0.7. The flow rate of the first slurry into the twin-screw extruder is 3L / min. The slurry in the twin-screw extruder runs from the first feed port to the right for 0.6s to the second feed port. The slurry in the twin-screw extruder runs from the second feed port to the polymerization mixing zone for 7s. The slurry in the twin-screw extruder runs from the leftmost end of the polymerization mixing zone to the third feed port for 5s. The slurry in the twin-screw extruder runs from the third feed port to the heating zone for 6s. The slurry in the twin-screw extruder runs from the leftmost end of the heating zone to the discharge port for 6s. The speed of the conveying rod in the twin-screw extruder is 25r / min, and the speed of the mixing rod stirring is 25r / min.

[0086] The method for preparing a first slurry includes: mixing calcium chloride and a first NMP solution (water content is 0.15wt%), stirring at 80°C for 6h until the calcium chloride is dissolved in the first NMP solution to obtain a first solution, cooling the first solution to 13°C and then mixing with p-phenylenediamine, stirring at 10°C for 3h until the p-phenylenediamine is uniformly dispersed in the first solution to obtain a first slurry, wherein the ratio of the first NMP solution, calcium chloride and p-phenylenediamine is 92.5:6:1.8 by mass, and the calcium chloride is dehydrated before being mixed with the first NMP solution by calcining in a muffle furnace at 420°C for 4h;

[0087] The second slurry is a molten liquid of terephthaloyl chloride, which is obtained by heating the solid terephthaloyl chloride in a tank at 90°C until a molten liquid of terephthaloyl chloride is formed;

[0088] The method for preparing the third slurry includes: mixing fumed silica, boehmite and a second NMP solution (water content of 0.15 wt%), stirring for 60 minutes, and sand milling at a speed of 1300 r / min for 25 minutes in a sand mill to obtain a third slurry, wherein, by mass, the ratio of the second NMP solution, fumed silica and boehmite is 82:5:13.

[0089] A method for preparing a continuous, highly heat-resistant, and environmentally friendly para-aramid diaphragm comprises the following steps:

[0090] S1, extruding a continuous high-heat-resistant and environmentally friendly para-aramid coating slurry through a die head and coating it on one side of a base film, and pre-curing it in a humidity space for 1.2 minutes to obtain a semi-finished continuous high-heat-resistant and environmentally friendly para-aramid diaphragm, wherein the humidity space includes: an air inlet, an air outlet, and an ultrasonic spray head, the air inlet frequency is 6 Hz, the air outlet frequency is 6 Hz, the ultrasonic spray head is used to spray atomized water into the humidity space, the ultrasonic spray frequency is 5 MHz, the humidity of the humidity space is 70% RH, the temperature of the humidity space is 30°C, the flow rate of the continuous high-heat-resistant and environmentally friendly para-aramid coating slurry extruded from the die head is 0.5 L / min, the coating speed is 22 m / min, and the thickness of the single-sided coating is 13 μm;

[0091] S2, extracting the semi-finished continuous high heat-resistant and environmentally friendly para-aramid membrane, drying it in an oven at 50°C, and shaping it in four shaping ovens at 70°C to obtain a continuous high heat-resistant and environmentally friendly para-aramid membrane, wherein the extraction is carried out in sequence with the first extractant, the second extractant and the third extractant, the first extractant and the second extractant are respectively a mixture of NMP and water, the concentration of NMP in the first extractant is 50wt%, the concentration of NMP in the second extractant is 18wt%, and the third extractant is pure water. The extractants are distributed in three extraction tanks, and an extrusion roller is provided outside each extraction tank to extrude the semi-finished continuous high heat-resistant and environmentally friendly para-aramid membrane removed from the extraction tank. The function of the extrusion roller is to squeeze out excess extractant on the semi-finished continuous high heat-resistant and environmentally friendly para-aramid membrane, so that the semi-finished continuous high heat-resistant and environmentally friendly para-aramid membrane is The solvent on the para-aramid diaphragm is cleaned more cleanly; the drying oven is equipped with 4 first hot rollers, the diameter of the first hot roller is 500mm, and the temperature of the first hot roller is 65℃. There is an air exchange system inside the drying oven to discharge moisture in time. The air intake frequency is 18HZ and the exhaust frequency is 20HZ; the shaping oven has four sub-ovens (the sub-oven is heated by hot rollers and has no exhaust and heating system), and each sub-oven is equipped with 4 second hot rollers arranged in a vertical direction, the diameter of the second hot roller is 250mm, and the temperature of the second hot roller is 80℃. The film line length of the semi-finished continuous high-heat-resistant and environmentally friendly para-aramid diaphragm in the oven is 3m, and the film line length of the semi-finished continuous high-heat-resistant and environmentally friendly para-aramid diaphragm in the shaping oven is 40m. The speed passing through the first hot roller is 40m / min, and the speed passing through the second hot roller is 40m / min.

[0092] Example 3

[0093] A method for preparing a continuous high-heat-resistant and environmentally friendly para-aramid coating slurry comprises the following steps:

[0094] Step 1, prepare a twin-screw extruder (inner diameter of 150mm), the twin-screw extruder is composed of a polymerization zone, a polymerization mixing zone and a heating zone from left to right, the left end of the polymerization zone is provided with a first feed port and a second feed port, the first feed port is located on the left side of the second feed port, the polymerization mixing zone is provided with a third feed port, the third feed port is located at 1 / 2 of the polymerization mixing zone, and the third feed port and the second feed port are used to synthesize poly(p-phenylene terephthalamide) (PPTA), the right end of the heating zone is provided with a discharge port, the temperature of the polymerization zone is 5°C, the temperature of the polymerization mixing zone is 20°C, and the temperature of the heating zone is 30°C;

[0095] Step 2: first input the first slurry into the first feed port of the twin-screw extruder to fill the twin-screw extruder with the first slurry, then input the second slurry into the second feed port in a spraying state, and when the viscosity of the slurry at the discharge port of the twin-screw extruder reaches 5000mPa.s, finally input the third slurry into the third feed port until the viscosity of the slurry at the discharge port of the twin-screw extruder reaches more than 1000cp, and a continuous high-heat-resistant and environmentally friendly para-aramid coating slurry is obtained from the discharge port, wherein the speed ratio of the first slurry, the second slurry and the third slurry is 4:0.09:0.8, and the speed ratio of the first slurry, the second slurry and the third slurry is 4:0.09:0.8. The flow rate of the first slurry into the twin-screw extruder is 4L / min. The slurry in the twin-screw extruder runs from the first feed port to the right for 0.2s to the second feed port. The slurry in the twin-screw extruder runs from the second feed port to the polymerization mixing zone for 5s. The slurry in the twin-screw extruder runs from the leftmost end of the polymerization mixing zone to the third feed port for 4s. The slurry in the twin-screw extruder runs from the third feed port to the heating zone for 4s. The slurry in the twin-screw extruder runs from the leftmost end of the heating zone to the discharge port for 4s. The speed of the conveying rod in the twin-screw extruder is 30r / min, and the speed of the mixing rod stirring is 30r / min.

[0096] The method for preparing a first slurry includes: mixing calcium chloride and a first NMP solution (water content is 0.18wt%), stirring at 80°C for 6h until the calcium chloride is dissolved in the first NMP solution to obtain a first solution, cooling the first solution to 20°C and then mixing with p-phenylenediamine, stirring at 20°C for 3h until the p-phenylenediamine is uniformly dispersed in the first solution to obtain a first slurry, wherein the ratio of the first NMP solution, calcium chloride and p-phenylenediamine is 90:8:2.0 by mass, and the calcium chloride is dehydrated before being mixed with the first NMP solution, and the dehydration method is calcined in a muffle furnace at 420°C for 4h;

[0097] The second slurry is a molten liquid of terephthaloyl chloride, which is obtained by heating the solid terephthaloyl chloride in a tank at 95°C until a molten liquid of terephthaloyl chloride is formed;

[0098] The method for preparing the third slurry includes: mixing fumed silica, boehmite and a second NMP solution (water content of 0.18 wt%), stirring for 80 minutes, and sand milling at a speed of 1500 r / min for 30 minutes in a sand mill to obtain a third slurry, wherein, by mass, the ratio of the second NMP solution, fumed silica and boehmite is 78:7:15.

[0099] A method for preparing a continuous, highly heat-resistant, and environmentally friendly para-aramid diaphragm comprises the following steps:

[0100] S1, extruding a continuous high-heat-resistant and environmentally friendly para-aramid coating slurry through a die head and coating it on one side of a base film, pre-curing it in a humidity space for 2 minutes to obtain a semi-finished continuous high-heat-resistant and environmentally friendly para-aramid diaphragm, wherein the humidity space includes: an air inlet, an air outlet, and an ultrasonic spray head, the air inlet frequency is 7 Hz, the air outlet frequency is 7 Hz, the ultrasonic spray head is used to spray atomized water into the humidity space, the ultrasonic spray frequency is 8 MHz, the humidity of the humidity space is 80% RH, the temperature of the humidity space is 35°C, the flow rate of the continuous high-heat-resistant and environmentally friendly para-aramid coating slurry extruded from the die head is 0.7 L / min, the coating speed is 30 m / min, and the thickness of the single-sided coating is 15 μm;

[0101] S2, extracting the semi-finished continuous high heat-resistant and environmentally friendly para-aramid membrane, drying it in an oven at 50°C, and shaping it in four shaping ovens at 70°C to obtain a continuous high heat-resistant and environmentally friendly para-aramid membrane, wherein the extraction is carried out in sequence with the first extractant, the second extractant and the third extractant, the first extractant and the second extractant are respectively a mixture of NMP and water, the concentration of NMP in the first extractant is 60wt%, the concentration of NMP in the second extractant is 30wt%, and the third extractant is pure water. The extractants are distributed in three extraction tanks, and an extrusion roller is provided outside each extraction tank to extrude the semi-finished continuous high heat-resistant and environmentally friendly para-aramid membrane removed from the extraction tank. The function of the extrusion roller is to squeeze out excess extractant on the semi-finished continuous high heat-resistant and environmentally friendly para-aramid membrane, so that the semi-finished continuous high heat-resistant and environmentally friendly para-aramid membrane is not oxidized. The solvent on the continuous high-heat-resistant and environmentally friendly para-aramid diaphragm is cleaned more cleanly; the drying oven used is equipped with 4 first hot rollers, the diameter of the first hot roller is 600mm, and the temperature of the first hot roller is 80℃. There is an air exchange system inside the drying oven to discharge moisture in time. The air intake frequency is 18HZ and the exhaust frequency is 20HZ; the shaping oven has four sub-ovens, each sub-ovens is equipped with 4 second hot rollers arranged in a vertical direction, the diameter of the second hot roller is 300mm, and the temperature of the second hot roller is 90℃. The film line length of the semi-finished continuous high-heat-resistant and environmentally friendly para-aramid diaphragm in the oven is 4m, and the film line length of the semi-finished continuous high-heat-resistant and environmentally friendly para-aramid diaphragm in the shaping oven is 50m. The speed passing through the first hot roller is 50m / min, and the speed passing through the second hot roller is 50m / min.

[0102] Comparative Example 1

[0103] A method for preparing a para-aramid diaphragm comprises the following steps:

[0104] Step 1: Mix the first solution and the second solution and stir for 30 minutes to obtain a para-aramid coating slurry, wherein the ratio of the first solution to the second solution is 70:30 by mass.

[0105] The first solution was prepared as follows: in a nitrogen atmosphere, calcium chloride and a first NMP solution (the same as the first NMP solution in Example 1) were mixed in a reactor, stirred at 60° C. for 1 hour to completely dissolve the calcium chloride, cooled to 10° C., p-phenylenediamine was added, and stirred for 15 minutes to completely dissolve the p-phenylenediamine, cooled to −2° C., terephthaloyl chloride was added, stirred for 10 minutes, returned to room temperature of 20 to 25° C., and stirred for 15 minutes to obtain a first solution, wherein, by mass, the ratio of the first NMP solution, calcium chloride, and the “total amount of p-phenylenediamine and terephthaloyl chloride” was 90:5:5, and by mass, the ratio of p-phenylenediamine to terephthaloyl chloride was 1:1.

[0106] The second solution was prepared as follows: fumed alumina, alumina particles, and a second NMP solution (the same as the second NMP solution in Example 1) were mixed, stirred for 40 minutes, and sand-milled in a sand mill at a speed of 1000 rpm for 20 minutes, wherein the ratio of the second NMP solution, fumed alumina, and alumina particles was 87:3:10 by mass.

[0107] Step 2: The para-aramid coating slurry is coated on the base film by an anilox roller method to form a coating with a thickness of 4 μm on the base film to obtain a semi-finished para-aramid diaphragm. The flow rate of the para-aramid coating slurry is 0.7 L / min; the coating speed is 30 m / min;

[0108] Step 3: The semi-finished para-aramid membrane is extracted with the first to tenth extractants in sequence, dried in an oven at 80°C after extraction, and rolled to obtain a para-aramid membrane, wherein the first to tenth extractants are placed in the first to tenth extraction tanks with a tank depth of 1m, respectively, the first to fourth extractants are each a mixture of NMP and water to form a coagulation bath, the concentration of NMP in the first extractant is 90wt%, the concentration of NMP in the second extractant is 70wt%, the concentration of NMP in the third extractant is 50%, the concentration of NMP in the fourth extractant is 30wt%, and the fifth to tenth extractants are deionized water; there are four hot rollers with a diameter of 400mm in the oven, the temperature of the hot rollers is 80°C, the air inlet frequency in the oven is 15HZ, and the exhaust frequency is 15HZ.

[0109] Comparative Example 2

[0110] A method for preparing a para-aramid diaphragm comprises the following steps:

[0111] The method for preparing a continuous high-heat-resistant and environmentally friendly para-aramid diaphragm in this comparative example is basically the same as that in Example 1, with the only difference being that this comparative example does not have a pre-curing treatment.

[0112] Comparative Example 3

[0113] A method for preparing a para-aramid diaphragm comprises the following steps:

[0114] The method for preparing a continuous high-heat-resistant and environmentally friendly para-aramid diaphragm in this comparative example is basically the same as that in Example 1, with the only difference being that the extruder used is replaced by a "single screw" instead of a "twin screw".

[0115] Figure 1 This is a surface scanning electron microscope image of the continuous high heat-resistant and environmentally friendly para-aramid diaphragm prepared in Example 1. Figure 1 It can be seen that the dispersion effect between para-aramid fibers is better and the boehmite is more evenly dispersed. Figure 2This is a cross-sectional electron microscope image of the continuous high heat-resistant and environmentally friendly para-aramid diaphragm prepared in Example 1. Figure 2 It can be seen that the fumed silica is completely adsorbed onto the para-aramid fiber, and the internal porosity is relatively high, which is beneficial to improving the liquid absorption rate of the continuous high-heat-resistant and environmentally friendly para-aramid diaphragm.

[0116] Figure 3 This is a scanning electron microscope image of the para-aramid diaphragm prepared in Comparative Example 1. As can be seen from the image, the para-aramid diaphragm synthesized using a blender has a relatively serious adhesion phenomenon between the para-aramid fibers, resulting in coarse para-aramid fibers. This is manifested macroscopically in that the viscosity of the para-aramid coating slurry is too high, making the process of use more difficult.

[0117] Figure 4 This is a scanning electron microscope image of the para-aramid membrane prepared in Comparative Example 2. Because the para-aramid membrane obtained in this comparative example was not pre-cured, the porosity on the surface of the para-aramid membrane was very low, and almost no obvious holes were visible;

[0118] Figure 5 This is a scanning electron microscope image of the para-aramid diaphragm prepared in Comparative Example 3. The use of a single screw will result in insufficient stirring of the para-aramid slurry during the synthesis process. In many cases, the material is discharged before the synthesis is complete, resulting in a very low molecular weight and a small amount of fiber.

[0119] Comparison of basic data of the continuous high heat-resistant and environmentally friendly para-aramid diaphragms prepared in Examples 1 to 3 and the para-aramid diaphragms prepared in Comparative Examples 1 to 3:

[0120] Table 1

[0121]

[0122] Comparative Example 1 is a para-aramid membrane prepared by a blender. It can be clearly seen from the data in Table 1 that the aramid fibers in Comparative Example 1 are seriously entangled with each other, the fibers become thicker, and are coated on the para-aramid membrane, resulting in the para-aramid membrane having a lower temperature resistance than the continuous high heat-resistant and environmentally friendly para-aramid membranes prepared by twin-screw extruders in Examples 1 to 3; the para-aramid membrane prepared by Comparative Example 2 has not undergone pre-curing treatment, resulting in a porosity of less than 30% and an air permeability of more than 300s / 100mL; Comparative Example 3 is a para-aramid membrane prepared by a single screw extruder. The single-screw synthesis cannot fully polymerize the para-aramid, resulting in a lower molecular weight and poor temperature resistance of the para-aramid membrane.

[0123] Comparison of the film rupture temperature data of the continuous high heat-resistant and environmentally friendly para-aramid diaphragms prepared in Examples 1 to 3 and the para-aramid diaphragms prepared in Comparative Examples 1 to 3:

[0124] Table 2

[0125]

[0126]

[0127] From the analysis of the film rupture temperature data in Table 2, it can be seen that the continuously produced para-aramid has less contact with moisture and oxygen in the middle, and the by-products are correspondingly less, which makes the diaphragm have higher temperature resistance.

[0128] Liquid absorption rate test of the continuous high heat-resistant and environmentally friendly para-aramid diaphragms prepared in Examples 1 to 3 and the para-aramid diaphragms prepared in Comparative Examples 1 to 3:

[0129] Table 3

[0130] Examples and Comparative Examples Liquid absorption rate Fluid retention rate Example 1 90.1％ 85.3％ Example 2 91.5％ 86.3％ Example 3 88.5％ 82.6％ Comparative Example 1 78.5％ 69.3％ Comparative Example 2 41.3％ 35.3％ Comparative Example 3 79.5％ 68.3％

[0131] According to the data analysis in Table 3, the continuous high heat-resistant and environmentally friendly para-aramid coating slurries prepared in Examples 1 to 3 contain fumed silica. Since the particle size of fumed silica is nanometer-scale and is not much different from the particle size of the para-aramid fiber, when synthesizing the continuous high heat-resistant and environmentally friendly para-aramid coating, the fumed silica will be quickly adsorbed onto the para-aramid fiber. When the continuous high heat-resistant and environmentally friendly para-aramid coating slurry prepared therefrom is coated on the base membrane, the para-aramid fiber is supported on the continuous high heat-resistant and environmentally friendly para-aramid diaphragm due to the adsorption of fumed silica, thereby greatly increasing the porosity. Such a structure can improve the liquid absorption rate of the continuous high heat-resistant and environmentally friendly para-aramid diaphragm.

[0132] The para-aramid fibers of the para-aramid diaphragm prepared in Comparative Example 1 were relatively coarse, so that the (nano-ceramic particles) were insufficient to support the para-aramid fibers, resulting in poor wettability of the para-aramid diaphragm.

[0133] The para-aramid diaphragm prepared in Comparative Example 2 was not pre-cured, had a porosity of about 20%, and had very poor wettability.

[0134] The molecular weight of the para-aramid fiber of the para-aramid diaphragm prepared by a single screw extruder in Comparative Example 3 is relatively small. Although it has little effect on the wettability, it is easy to cause the coating to fall off.

[0135] Ionic conductivity (temperature 25° C.) of the continuous high-heat-resistant and environmentally friendly para-aramid membranes prepared in Examples 1 to 3 and the para-aramid membranes prepared in Comparative Examples 1 to 3:

[0136] Table 4

[0137]

[0138] Ionic conductivity mainly tests the rate at which ions shuttle in the diaphragm. The detection of ionic conductivity can test the efficiency of the diaphragm in shuttling lithium ions in the battery. It can be seen from the data in Table 4 that the continuous high-heat-resistant and environmentally friendly para-aramid coating slurry prepared in Examples 1 to 3 is obtained by twin-screw polymerization, and the continuous high-heat-resistant and environmentally friendly para-aramid diaphragm obtained by coating it on the base membrane and pre-curing treatment has a more three-dimensional para-aramid fiber. This structure is more conducive to the shuttling of ions, thereby improving the ionic conductivity of the diaphragm.

[0139] The above is an exemplary description of the present invention. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other skilled in the art without expending creative labor falls within the scope of protection of the present invention.

Claims

1. A method for preparing a continuous high-heat-resistant and environmentally friendly para-aramid diaphragm, characterized in that: The following steps are involved: S1, extruding a continuous high-heat-resistant and environmentally friendly para-aramid coating slurry through a die head and coating it on one or both sides of a base film, and pre-curing it in a humidity space for at least 0.5 minutes to obtain a semi-finished continuous high-heat-resistant and environmentally friendly para-aramid separator, wherein the humidity of the humidity space is 60-80% RH and the temperature of the humidity space is 25-35° C.; S2, extracting, drying, and shaping the semi-finished continuous high-heat-resistant and environmentally friendly para-aramid diaphragm to obtain a continuous high-heat-resistant and environmentally friendly para-aramid diaphragm; The method for preparing the continuous high-heat-resistant and environmentally friendly para-aramid coating slurry comprises the following steps: Step 1, prepare a twin-screw extruder, the twin-screw extruder is composed of a polymerization zone, a polymerization mixing zone and a heating zone from left to right, the left end of the polymerization zone is provided with a first feed port and a second feed port, the polymerization mixing zone is provided with a third feed port, and the right end of the heating zone is provided with a discharge port, the temperature of the polymerization zone is 0-5°C, the temperature of the polymerization mixing zone is 15-20°C, and the temperature of the heating zone is 20-30°C; Step 2: first input the first slurry into the first feed port of the twin-screw extruder to fill the twin-screw extruder with the first slurry, and then input the second slurry into the second feed port in a spraying state. When the viscosity of the slurry at the discharge port of the twin-screw extruder reaches between 400 and 5000 mPa.s, input the third slurry into the third feed port until the viscosity of the slurry at the discharge port of the twin-screw extruder reaches more than 1000 cp, and a continuous high-heat-resistant and environmentally friendly para-aramid coating slurry is obtained from the discharge port, wherein the speed ratio of the first slurry, the second slurry and the third slurry is (2-4): (0.06-0.09): (0.6-0.8); The first slurry includes: p-phenylenediamine; The second slurry is a molten liquid of terephthaloyl chloride; The third slurry includes: fumed silica and boehmite.

2. The method according to claim 1, characterized in that In step 1, the first feed port is located on the left side of the second feed port, and the area between the third feed port and the second feed port is used to synthesize poly(p-phenylene terephthalamide).

3. The method according to claim 2, characterized in that The speed of the conveying rod in the twin-screw extruder is 20 to 30 r / min, and the speed of the mixing rod is 20 to 30 r / min. In the step 2, the slurry in the twin-screw extruder runs from the first feed port to the second feed port for 0.2 to 1 second, the slurry in the twin-screw extruder runs from the second feed port to the polymerization mixing zone for 5 to 10 seconds, the slurry in the twin-screw extruder runs from the leftmost end of the polymerization mixing zone to the third feed port for 4 to 8 seconds, the slurry in the twin-screw extruder runs from the third feed port to the heating zone for 4 to 8 seconds, and the slurry in the twin-screw extruder runs from the leftmost end of the heating zone to the discharge port for 4 to 8 seconds.

4. The method according to claim 3, characterized in that The method for preparing the first slurry includes: mixing calcium chloride and a first NMP solution, stirring until the calcium chloride is dissolved in the first NMP solution to obtain a first solution, cooling the first solution to 5-20°C and then mixing with p-phenylenediamine, stirring until the p-phenylenediamine is uniformly dispersed in the first solution to obtain a first slurry, wherein, by mass, the ratio of the first NMP solution, calcium chloride and p-phenylenediamine is (90-96.4): (2-8): (1.6-2).

5. The method according to claim 4, characterized in that The method for preparing the third slurry includes: mixing fumed silica, boehmite and a second NMP solution, stirring, and sand grinding to obtain a third slurry, wherein, by mass, the ratio of the second NMP solution, fumed silica and boehmite is (78-87): (3-7): (10-15).

6. The method according to claim 5, characterized in that The calcium chloride is dehydrated before being mixed with the first NMP solution by calcining at 400-450° C. for 3-5 hours.

7. The method according to claim 6, characterized in that The water content of the first NMP solution is ≤0.2 wt %, and the water content of the second NMP solution is ≤0.2 wt %.

8. The method according to claim 7, characterized in that The calcium chloride was dissolved in the first NMP solution by stirring at 75-85° C. for 4-6 h.

9. The method according to claim 8, characterized in that The p-phenylenediamine is uniformly dispersed in the first solution by stirring at 0-20° C. for 3-5 hours.

10. The method according to claim 9, characterized in that The solid terephthaloyl chloride is heated at 80-95° C. until a molten liquid of the terephthaloyl chloride is formed.

11. The method according to claim 10, characterized in that In the method for preparing the third slurry, the stirring time is 40 to 80 minutes.

12. The method according to claim 11, characterized in that The sand milling time is 20 to 30 minutes, and the sand milling speed is 1000 to 1500 r / min.

13. The method according to claim 12, characterized in that In S1, the pre-curing treatment time in the humidity space is 0.5 to 2 minutes.

14. The method according to claim 13, characterized in that In S1, the humidity space includes: an air inlet, an air outlet and an ultrasonic spray head. The air inlet frequency is 5-7 Hz, the air outlet frequency is 5-7 Hz, and the ultrasonic spray head is used to spray atomized water into the humidity space. The ultrasonic spray frequency is 3-8 MHz.

15. The method according to claim 14, characterized in that In S1, the flow rate of the continuous high-heat-resistant and environmentally friendly para-aramid coating slurry extruded by the die head is 0.4-0.7 L / min, the coating speed is 15-30 m / min, and the thickness of the single-sided coating is 10-15 μm.

16. The method according to claim 15, characterized in that The base film is a PE film.

17. The method according to claim 16, characterized in that In S2, the extraction is performed using a plurality of extractants in sequence, wherein the concentration of NMP in the plurality of extractants used in sequence decreases, and the concentration of NMP in the extractants is less than or equal to 60 wt%.

18. The method according to claim 17, characterized in that In S2, the drying temperature is 50-80°C, and the setting temperature is 70-90°C.

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