A compressed air filter element for battery raw material production

Abstract

The application discloses a compressed air filter element for battery raw material production, which comprises a PVDF framework and a filter medium, wherein the filter medium comprises a PTFE filter film and a high-molecular fiber fabric layer, and the pore size of the PTFE filter film is 1nm-100nm. The filter element has good impact resistance, is suitable for filtering metal particles in the compressed air for production, and reduces the metal introduction risk in the production process.

Description

Technical Field

[0001] This application relates to the field of filter materials, and in particular to a compressed air filter element for battery raw material production. Background Technology

[0002] In the precision manufacturing process of lithium batteries, compressed air is an indispensable auxiliary resource, widely used in several core stages such as raw material mixing, coating, drying, and assembly. The purity of compressed air directly affects the cleanliness of the production environment and the quality of the finished battery, which in turn affects the battery's performance, safety, reliability, and lifespan.

[0003] Especially in the production of lithium batteries, reactive metals such as copper and zinc play important roles in electrode materials, current collectors, and production equipment due to their excellent conductivity and cost-effectiveness. However, the frequent use of these metals, coupled with equipment wear and tear and material handling during production, results in a significant amount of copper, zinc, and other reactive metal particles suspended in the production environment. Without effective control measures, these metal particles can easily enter the production area through airborne transmission or the use of compressed air, and subsequently penetrate into battery raw materials, electrolytes, and even the internal structure of the battery.

[0004] The introduction of metallic foreign matter, especially copper and zinc, has had a significant negative impact on the performance and safety of lithium batteries. On one hand, metals such as copper and zinc can chemically react with lithium salts in the electrolyte to form insoluble compounds. This not only consumes valuable lithium resources but can also degrade electrolyte performance, increase battery internal resistance, and reduce energy density and cycle life. On the other hand, the presence of metal particles can trigger micro-short circuits within the battery, increasing self-discharge rate and, in severe cases, even triggering thermal runaway, threatening the safe and stable operation of the battery system. Summary of the Invention

[0005] To reduce the negative impact of metal particles in compressed air on lithium battery production, this application provides a compressed air filter element for battery raw material production.

[0006] This application provides a compressed air filter element for battery raw material production, comprising a PVDF skeleton and a filter medium, wherein the filter medium comprises a PTFE filter membrane and a polymer fiber fabric layer, and the PTFE filter membrane has a pore size of 1nm to 100nm.

[0007] Preferably, the polymer fiber fabric layer is a needle-punched nonwoven fabric, and its fiber raw material is selected from one or more of polyester fiber, polypropylene fiber and polyethylene fiber.

[0008] Preferably, the fiber is an ultrafine fiber with an average length of 0.2 to 1 micrometer.

[0009] Preferably, the thickness of the PTFE filter membrane is 3 to 10 micrometers.

[0010] Preferably, the basis weight of the polymer fiber fabric layer is 30-80 g / m². 2 .

[0011] Preferably, the PTFE filter membrane and the polymer fiber fabric layer are composited using a hot-press coating process.

[0012] In this application, the PVDF skeleton serves as the supporting structure, possessing excellent mechanical strength and temperature resistance. It can withstand the pressure and high temperature of compressed air. The PTFE filter membrane plays the primary filtration role; its tiny pore structure effectively filters out metal particles from the air. The polymer fiber fabric layer serves as a buffer, reducing the impact on the PTFE filter membrane, especially the impact of metal particles, and lowering the probability of breakage.

[0013] Preferably, the raw materials of the PTFE filter membrane include: 100 parts of PTFE dispersion resin, 20-30 parts of extrusion aid, 5-15 parts of modified filler, and 10-20 parts of olefin monomer-maleic anhydride copolymer, wherein the modified filler has hydroxyl groups grafted onto its surface.

[0014] Incorporating olefin monomer-maleic anhydride copolymer into the raw materials of PTFE filter membranes can introduce carboxyl groups into the filter membrane. These carboxyl groups react with the hydroxyl groups on the surface of the modified filler to crosslink and improve the mechanical strength and impact resistance of the filter membrane, thereby reducing the probability of the filter membrane rupturing under the impact of high-pressure gas or metal particles.

[0015] Preferably, the extrusion aid is selected from industrial white oil, lubricating oil, naphthenic oil, or aviation kerosene.

[0016] Preferably, the olefin-containing monomer is selected from at least one of phenyl isobutylene, butadiene, ethylene, propylene, and ethylene.

[0017] Preferably, the PTFE filter membrane is prepared as follows: Take PTFE dispersion resin, extrusion aid, modified filler and olefin monomer-maleic anhydride copolymer, mix them evenly, and gelatinize to obtain gelatinized mixture; The gelatinized mixture is pressed into a cylindrical blank on a blank press, extruded through a pusher, and then pressed into a strip-shaped base material through a calender. The strip-shaped substrate was subjected to longitudinal and transverse stretching. The stretched filter membrane was then placed in a high-temperature sintering furnace for heat setting to obtain a PTFE microporous membrane. The PTFE microporous membrane was frozen at -80 to -100°C for 30 minutes, then removed and placed at room temperature. The temperature was then raised to room temperature to obtain a frozen filter membrane. The frozen filter membrane is calendered again with a pressure of 1-2 MPa to obtain a PTFE filter membrane.

[0018] Preferably, the transverse stretch ratio is 4 to 6, and the longitudinal stretch ratio is 2 to 4.

[0019] Preferably, the raw materials for the modified filler include filler, PTFE emulsion, and hydroxyl-containing comonomer in a mass ratio of 1:6 to 10:2 to 3, wherein the PTFE emulsion contains 5 to 10% PTFE micropowder. Preferably, the hydroxyl-containing comonomer is selected from one or more of N-hydroxymethylacrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate.

[0020] Preferably, the filler is selected from one or more of calcium carbonate, silicon dioxide, silica powder, and alumina.

[0021] Preferably, the D50 particle size of the filler is 1 to 10 micrometers, more preferably 3 to 5 micrometers.

[0022] Preferably, the raw material for the modified filler further includes alkyl methacrylate, and the mass ratio of the filler to alkyl methacrylate is 1:0.4 to 0.6.

[0023] Preferably, the alkyl methacrylate is selected from one or more of butyl methacrylate, isooctyl methacrylate, decyl methacrylate, dodecyl methacrylate, tetradecyl methacrylate, or octadecyl methacrylate.

[0024] Preferably, the modified filler is prepared by the following method: PTFE micro powder was added to an emulsifier solution and stirred evenly to obtain a PTFE emulsion. Then, filler was added and stirred to disperse the emulsion. Hydroxyl comonomer and alkyl methacrylate were added and stirred evenly. After adding an initiator, the mixture was heated to carry out a copolymerization reaction. After the reaction was completed, the mixture was cooled and separated, filtered, washed, and dried to obtain the modified filler. Preferably, the temperature of the copolymerization reaction is 63–78°C.

[0025] Preferably, the amount of the initiator is 1.5 to 2.5% of the mass of the reactant monomer.

[0026] Preferably, the initiator is a peroxide initiator, more preferably potassium persulfate, ammonium persulfate or benzoyl peroxide.

[0027] The modified filler of this application exhibits good compatibility with PTFE, is easily dispersed, and can improve the mechanical strength of the resulting PTFE filter membrane. Specifically, the filler is pre-mixed uniformly with PTFE emulsion to form composite particles; then, monomers are polymerized in situ on the surface of the composite particles through a free radical copolymerization reaction to obtain a modified filler with hydroxyl-containing copolymers grafted onto its surface. Because this modified filler has a composite structure of PTFE and filler, it exhibits good compatibility with PTFE dispersion resin, dispersing well in the resin, which is beneficial for improving the mechanical strength of the resulting filter membrane. Furthermore, its abundant hydroxyl groups can react and crosslink with the maleic anhydride groups introduced into the PTFE resin, which is beneficial for improving the strength and impact resistance of the resulting filter membrane.

[0028] Furthermore, using alkyl methacrylates can introduce alkyl groups into the copolymer products on the surface of the modified filler, which can moderately reduce the hydroxyl distribution density and prevent excessive local crosslinking density, which would lead to excessively high filter membrane rigidity and reduced impact resistance. It should be noted that the aforementioned reduction in hydroxyl density does not mean a reduction in hydroxyl content.

[0029] In summary, this application has the following beneficial effects: 1. This application achieves effective filtration of metal particles in compressed air by combining a PTFE membrane with a polymer fiber fabric layer, reducing the probability of introducing metal foreign matter during lithium battery production. Furthermore, this application improves the mechanical strength of the resulting PTFE filter membrane through a crosslinking reaction by incorporating modified fillers containing olefin monomer-maleic anhydride copolymers and surface-grafted hydroxyl groups into the PTFE membrane.

[0030] 2. This application significantly improves the compatibility between the modified filler and PTFE resin by premixing the PTFE emulsion with the filler before in-situ polymerization, promoting their uniform dispersion. This allows the filler to effectively reinforce and toughen the PTFE filter membrane, enhancing its mechanical strength and impact resistance.

[0031] 3. By introducing alkyl groups on the surface of the modified filler, this application can prevent the membrane from becoming too rigid due to excessive local crosslinking density, which could lead to membrane brittleness and breakage, thus ensuring its filtration effect. Detailed Implementation

[0032] Preparation Example

[0033] Preparation Example 1 The modified filler is prepared by the following steps: 25g of fatty alcohol polyoxyethylene ether was added to 800g of water and stirred for 15min to obtain an emulsifier solution. 60g of PTFE micro powder (D50 of 2-3 microns) was added to the solution and stirred for 10min to obtain a PTFE emulsion. 100g of calcium carbonate (D50 of 3-5 microns) was then added and stirred for 20min. 230g of hydroxyethyl acrylate and 50g of dodecyl methacrylate were added and stirred for 10min. 4g of potassium peroxide was then added, and the mixture was heated to 75℃ for copolymerization. The reaction was carried out for 4h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed three times with deionized water, and dried in an oven to obtain the modified filler.

[0034] Preparation Example 2 The modified filler is prepared by the following steps: 20g of fatty alcohol polyoxyethylene ether was added to 700g of water and stirred for 10min to obtain an emulsifier solution. 50g of PTFE micro powder (D50 of 2-3 microns) was added to the solution and stirred for 10min to obtain a PTFE emulsion. 100g of alumina (D50 of 3-5 microns) was then added and stirred for 20min. 200g of hydroxyethyl methacrylate and 40g of dodecyl methacrylate were added and stirred for 10min. 3.5g of potassium peroxide was then added, and the mixture was heated to 73℃ for copolymerization. The reaction was carried out for 4h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed three times with deionized water, and dried in an oven to obtain the modified filler.

[0035] Preparation Example 3 The modified filler is prepared by the following steps: Add 30g of fatty alcohol polyoxyethylene ether to 900g of water and stir for 10min to obtain an emulsifier solution; add 50g of PTFE micro powder (D50 of 2-3 microns) to the solution and stir for 10min to obtain a PTFE emulsion; then add 100g of calcium carbonate (D50 of 3-5 microns) and stir for 20min; add 280g of hydroxyethyl acrylate and 60g of decyl methacrylate and stir for 10min; then add 6g of potassium peroxide and heat to 70℃ for copolymerization reaction for 5h. After the reaction is completed, cool to room temperature, centrifuge, wash three times with deionized water, and dry in an oven to obtain the modified filler.

[0036] Preparation Example 4 The modified filler was prepared without the addition of PTFE micro powder. The specific steps are as follows: Add 30g of fatty alcohol polyoxyethylene ether to 900g of water and stir for 10min to obtain an emulsifier solution; add 100g of calcium carbonate (D50 of 3-5 microns) to the solution and stir for 20min; add 280g of hydroxyethyl acrylate and 60g of decyl methacrylate and stir for 10min; then add 6g of potassium peroxide and heat to 70℃ for copolymerization reaction for 5h. After the reaction is completed, cool to room temperature, centrifuge, wash three times with deionized water, and dry in an oven to obtain the modified filler.

[0037] Preparation Example 5 The modified filler differs from Preparation Example 1 in that an equal amount of hydroxyethyl acrylate is used to replace 50g of dodecyl methacrylate in the raw materials.

[0038] Preparation Example 6 The modified filler differs from Preparation Example 1 in that an equal amount of dodecyl methacrylate is used instead of hydroxyethyl acrylate in the raw materials. Example

[0039] Example 1: A compressed air filter element for battery raw material production, the preparation steps are as follows: (1) Preparation of PTFE filter membrane Take 1000g of PTFE dispersion resin (650XTX), 220g of extrusion aid (15# white oil), 100g of the modified filler obtained in Preparation Example 1, and 160g of isobutylene-maleic anhydride copolymer (ISOBAM600) and mix them evenly. Then, gelatinize the mixture at 80°C for 16h to obtain the gelatinized mixture.

[0040] The gelatinized mixture is pressed into a cylindrical blank on a blank press, extruded through a pusher, and then pressed into a strip-shaped base material through a calender.

[0041] Following a process setting of a longitudinal stretching ratio of 4 and a longitudinal stretching temperature of 210℃, and a transverse stretching ratio of 6 and a transverse stretching temperature of 150℃, the strip-shaped substrate was subjected to longitudinal and transverse stretching sequentially. The stretched filter membrane was then placed in a high-temperature sintering furnace and heat-set at 400℃ to obtain a PTFE microporous membrane.

[0042] The PTFE microporous membrane was frozen at -100℃ for 30 minutes, then removed and placed at room temperature. The temperature was then raised to room temperature to obtain a frozen filter membrane.

[0043] The cryogenic filter membrane was calendered at 160°C at a speed of 5 m / min and a roller pressure of 1 MPa to obtain a PTFE filter membrane. Its average pore size was 60 nm, its thickness was 6 μm, and its porosity was 86%.

[0044] (2) Filter element preparation Take a weight of 50g / m 2The spunlace nonwoven fabric (made from PET microfibers with an average length of 0.5–1 micrometer) is used. The PTFE filter membrane prepared above is then heat-pressed with the spunlace nonwoven fabric to form a composite filter medium. The filter medium is then fixed to the PVDF frame using fasteners to obtain the filter element.

[0045] Example 2: A compressed air filter element for battery raw material production, the preparation steps are as follows: (1) Preparation of PTFE filter membrane Take 1000g of PTFE dispersion resin (650XTX), 200g of extrusion aid (15# white oil), 50g of the modified filler obtained in Preparation Example 2, and mix them evenly with 120g of styrene-maleic anhydride copolymer (SMA-20H). Gelatinize the mixture at 75°C for 20h to obtain the gelatinized mixture.

[0046] The gelatinized mixture is pressed into a cylindrical blank on a blank press, extruded through a pusher, and then pressed into a strip-shaped base material through a calender.

[0047] Following a process setting of a longitudinal stretching ratio of 3 and a longitudinal stretching temperature of 200℃, and a transverse stretching ratio of 5 and a transverse stretching temperature of 130℃, the strip-shaped substrate was subjected to longitudinal and transverse stretching sequentially. The stretched filter membrane was then placed in a high-temperature sintering furnace and heat-set at 430℃ to obtain a PTFE microporous membrane.

[0048] The PTFE microporous membrane was frozen at -100℃ for 30 minutes, then removed and placed at room temperature. The temperature was then raised to room temperature to obtain a frozen filter membrane.

[0049] The cryogenic filter membrane was calendered at 160°C at a speed of 5 m / min and a roller pressure of 1 MPa to obtain a PTFE filter membrane. Its average pore size was 80 nm, its thickness was 8 μm, and its porosity was 89%.

[0050] (2) Filter element preparation Take a weight of 50g / m 2 The spunlace nonwoven fabric (made from PET microfibers with an average length of 0.5–1 micrometer) is used. The PTFE filter membrane prepared above is then heat-pressed with the spunlace nonwoven fabric to form a composite filter medium. The filter medium is then fixed to the PVDF frame using fasteners to obtain the filter element.

[0051] Example 3: A compressed air filter element for battery raw material production, the preparation steps are as follows: (1) Preparation of PTFE filter membrane Take 1000g of PTFE dispersion resin (650XTX), 300g of extrusion aid (15# white oil), 150g of the modified filler obtained in Preparation Example 3, and mix them evenly with 200g of isobutylene-maleic anhydride copolymer (ISOBAM600). Gelatinize the mixture at 80℃ for 20h to obtain the gelatinized mixture.

[0052] The gelatinized mixture is pressed into a cylindrical blank on a blank press, extruded through a pusher, and then pressed into a strip-shaped base material through a calender.

[0053] Following a process setting of a longitudinal stretching ratio of 4 and a longitudinal stretching temperature of 200℃, and a transverse stretching ratio of 6 and a transverse stretching temperature of 120℃, the strip-shaped substrate was subjected to longitudinal and transverse stretching sequentially. The stretched filter membrane was then placed in a high-temperature sintering furnace and heat-set at 450℃ to obtain a PTFE microporous membrane.

[0054] The PTFE microporous membrane was frozen at -100℃ for 30 minutes, then removed and placed at room temperature. The temperature was then raised to room temperature to obtain a frozen filter membrane.

[0055] The cryogenic filter membrane was calendered at 160°C at a speed of 5 m / min and a roller pressure of 1 MPa to obtain a PTFE filter membrane. Its average pore size was 50 nm, its thickness was 5 μm, and its porosity was 84%.

[0056] (2) Filter element preparation Take a weight of 60g / m 2 The spunlace nonwoven fabric (made from PET microfibers with an average length of 0.5–1 micrometer) is used. The PTFE filter membrane prepared above is then heat-pressed with the spunlace nonwoven fabric to form a composite filter medium. The filter medium is then fixed to the PVDF frame using fasteners to obtain the filter element.

[0057] Example 4 is a compressed air filter element for battery raw material production. The difference from Example 1 is that, in the PTFE filter membrane preparation step, an equal amount of the modified filler obtained in Example 4 is used to replace the modified filler obtained in Example 1. The resulting PTFE filter membrane has an average pore size of 90 nm, a thickness of 8 micrometers, and a porosity of 90%.

[0058] Example 5 is a compressed air filter element for battery raw material production. The difference from Example 1 is that, in the PTFE filter membrane preparation step, an equal amount of the modified filler obtained in Example 5 is used to replace the modified filler obtained in Example 1. The resulting PTFE filter membrane has an average pore size of 70 nm, a thickness of 6 micrometers, and a porosity of 84%.

[0059] Example 6 is a compressed air filter element for battery raw material production. The difference from Example 1 is that, in the PTFE filter membrane preparation step, an equal amount of the modified filler obtained in Example 6 is used to replace the modified filler obtained in Example 1. The resulting PTFE filter membrane has an average pore size of 80 nm, a thickness of 5 micrometers, and a porosity of 89%.

[0060] Example 7: A compressed air filter element for battery raw material production. The difference from Example 1 is that, in the PTFE filter membrane preparation step, an equal amount of PTFE dispersion resin is used to replace the isobutylene-maleic anhydride copolymer (ISOBAM600). The resulting PTFE filter membrane has an average pore size of 90 nm, a thickness of 5 micrometers, and a porosity of 84%.

[0061] Example 8 is a compressed air filter element for battery raw material production. The difference from Example 6 is that, in the PTFE filter membrane preparation step, an equal amount of PTFE dispersion resin is used to replace the isobutylene-maleic anhydride copolymer (ISOBAM600). The resulting PTFE filter membrane has an average pore size of 100 nm, a thickness of 6 micrometers, and a porosity of 83%. Comparative Example

[0062] Comparative Example 1, a compressed air filter element for battery raw material production, differs from Example 8 in that a polymer fiber fabric layer replaces the PTFE filter membrane in the filter element preparation step. The specific operation is as follows: Take 2 tablets with a weight of 50g / m 2 The spunlace nonwoven fabric (made from PET microfiber with an average length of 0.5–1 micrometer) is hot-pressed and laminated to form a filter medium. The filter medium is then fixed to the PVDF frame with fasteners to produce the filter element.

[0063] Comparative Example 2, a compressed air filter element for battery raw material production, differs from Example 8 in that, in the filter element preparation step, a PTFE filter membrane replaces the polymer fiber fabric layer. The specific operation is as follows: Two PTFE filter membranes prepared in Example 8 were subjected to hot-press coating to create a composite filter medium. The filter medium was then fixed onto a PVDF frame using fasteners to obtain a filter element.

[0064] Performance testing

[0065] Experiment 1: Strength performance of PTFE filter membrane In accordance with the provisions of GB / T 1040.3-2006 "Determination of Tensile Properties of Plastics", the tensile strength (maximum tensile stress at fracture) and elongation (percentage increase in length compared to the original length at fracture) of the PTFE filter membranes obtained in each example were tested. The test sample width was 30 mm, the length was 100 mm, the clamping distance was 50 mm, the tensile speed was 50 mm / min, and each group of samples was tested 5 times, and the average value was taken.

[0066] Experiment 2: Impact Performance Test of PTFE Filter Membrane The impact performance of plastic simply supported beams was determined according to GB / T 1043.2-2018 "Determination of impact performance of plastic simply supported beams - Part 2: Instrumented impact test". Each group of samples was tested 5 times and the average value was taken.

[0067] Experiment 3: Filtration performance of metal particles The content (mass concentration) of metal elements in compressed air after filtration by the filter cartridge was determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). For specific operation instructions, please refer to the article "Determination of Metal Elements in Atmospheric Particulate Matter by ICP-AES" included in "Spectroscopy Laboratory".

[0068] Table 1. Performance Test Results

[0069] Note: The filter element of Comparative Example 2 cracked during the filtration process, and the test results of the metal element content in the filtered air are not representative.

[0070] The test results of Comparative Examples 1 and 2 show that the PTFE filter membrane plays the main role in filtering metal particles, while the polymer fiber fabric layer has a buffering and protective effect on the PTFE filter membrane, which can effectively alleviate the impact of metal particles and high-pressure gas on the filter membrane.

[0071] As demonstrated in Example 4, adding PTFE emulsion to the modified filler can effectively improve the mechanical properties of the PTFE membrane, such as tensile strength and elongation. This is because the composite particles formed by the PTFE emulsion and the filler exhibit good compatibility with the PTFE dispersion resin matrix after modification, which facilitates the dispersion of the modified filler, forms uniform cross-linking nodes, and improves mechanical properties. Simultaneously, uniform cross-linking nodes promote the formation of smaller and more uniform pore structures, but also reduce porosity.

[0072] As demonstrated in Examples 5-8, the hydroxyl groups on the surface of the modified filler and the maleic anhydride groups introduced into the base resin are key to improving the mechanical properties of the PTFE filter membrane. The cross-linking nodes formed by these two components on the filter membrane can effectively improve the membrane's strength and toughness (characterized by elongation). However, it is important to note that moderate cross-linking is a prerequisite for ensuring the membrane's toughness; excessive cross-linking will reduce the membrane's toughness. The alkyl methacrylate used in this application can reduce the excessive cross-linking phenomenon of the filter membrane.

[0073] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A compressed air filter element for battery raw material production, characterized in that, The device includes a PVDF skeleton and a filter medium, wherein the filter medium comprises a PTFE filter membrane and a polymer fiber fabric layer, and the PTFE filter membrane has a pore size of 1 nm to 100 nm. By weight, the raw materials of the PTFE filter membrane include: 100 parts PTFE dispersion resin, 20 to 30 parts extrusion aid, 5 to 15 parts modified filler, and 10 to 20 parts olefin monomer-maleic anhydride copolymer. The modified filler has hydroxyl groups grafted onto its surface. The raw materials of the modified filler include filler in a mass ratio of 1:6 to 10:2 to 3, PTFE emulsion, and hydroxyl-containing comonomer. The PTFE emulsion contains 5 to 10% PTFE micropowder.

2. The filter element according to claim 1, characterized in that, The fibers of the polymer fiber fabric layer are selected from one or more of polyester fibers, polypropylene fibers, and polyethylene fibers.

3. The filter element according to claim 1, characterized in that, The olefin-containing monomer is selected from at least one of isobutylene, butadiene, styrene, propylene, and ethylene.

4. The filter element according to claim 1, characterized in that, The hydroxyl-containing comonomer is selected from one or more of N-hydroxymethylacrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate.

5. The filter element according to claim 1, characterized in that, The filler is selected from one or more of calcium carbonate, silicon dioxide, silica powder, and alumina.

6. The filter element according to claim 1, characterized in that, The modified filler also includes alkyl methacrylate as a raw material, and the mass ratio of the filler to alkyl methacrylate is 1:0.4 to 0.

6.

7. The filter element according to claim 6, characterized in that, The alkyl methacrylate is selected from one or more of butyl methacrylate, isooctyl methacrylate, decyl methacrylate, dodecyl methacrylate, tetradecyl methacrylate, or octadecyl methacrylate.

8. The filter element according to claim 6, characterized in that, The modified filler is prepared as follows: PTFE micro powder was added to an emulsifier solution and stirred until homogeneous to obtain a PTFE emulsion. Then, filler was added and stirred to disperse the emulsion. Hydroxyl-containing comonomers and alkyl methacrylates were added and stirred until homogeneous. Initiator was added and the temperature was raised to 63-78℃ to carry out a copolymerization reaction. After the reaction was completed, the temperature was cooled down and the emulsion was separated, filtered, washed, and dried to obtain the modified filler.

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