Polytetrafluoroethylene microporous membrane and preparation method thereof

Abstract

The invention discloses a polytetrafluoroethylene microporous membrane and a preparation method thereof, nano silicon dioxide and hydrogenated petroleum resin powder are doped in polytetrafluoroethylene resin powder, and at the same time, auxiliary oil is added to assist blending; and then extruding into a blank, calendering, curing to remove auxiliary oil, and further carrying out two-way stretching and sintering to preliminarily obtain the polytetrafluoroethylene microporous membrane. Immersing the sintered polytetrafluoroethylene microporous membrane into a mixed solution of dioxane containing aldehyde monomers and deionized water, fixing nano silicon dioxide in the polytetrafluoroethylene microporous membrane by utilizing Schiff base reaction, and washing and drying to obtain the polytetrafluoroethylene microporous membrane with high temperature resistance, high strength and excellent long-term infiltration resistance.

Description

Technical Field

[0001] The invention specifically relates to a polytetrafluoroethylene microporous membrane and a preparation method thereof, belonging to the technical field of polymer materials. Background Art

[0002] The polytetrafluoroethylene microporous membrane is made of polytetrafluoroethylene as the main raw material, with the addition of corresponding additives, and is prepared through calendering, turning, stretching and other technologies to obtain a film with a microporous structure. In the (CF2-CF2) molecular chain of polytetrafluoroethylene, the C chain is tightly surrounded by the F atom, and the bond energy of the CF bond is very high, which makes polytetrafluoroethylene have excellent chemical stability. Therefore, the polytetrafluoroethylene microporous membrane has excellent chemical resistance, low friction coefficient and wide temperature range, and is widely used in filtration, separation, medical equipment and waterproof breathable materials.

[0003] Existing PTFE microporous membranes are mainly prepared by processes such as resin powder calendering, stretching and sintering, so that the membrane has a microporous structure and a certain mechanical strength, but there are still defects in long-term high-temperature environments, as well as in waterproof and oil-proof properties, long-term anti-infiltration properties, etc., especially in high-temperature environments, traditional PTFE microporous membranes are prone to performance degradation, resulting in reduced filtration efficiency and even membrane damage, which seriously affects its service life and reliability. In recent years, the introduction of nanomaterials has provided new ideas for improving the performance of PTFE microporous membranes, especially the introduction of nano-silicon dioxide to enhance the mechanical properties and thermal stability of polymer composites. Doping nano-silicon dioxide into PTFE resin can effectively improve the strength and thermal properties of membrane materials.

[0004] The Chinese patent "A silica-modified polytetrafluoroethylene based membrane material and its preparation method and application" with publication number CN117797655A discloses that porous silica microspheres are loaded on the surface of polytetrafluoroethylene microporous membranes, and heavy metal adsorption is achieved through the synergistic adsorption effect of the porous silica microspheres and the electrostatic interaction between the amino group and the carboxyl group of the binder.

[0005] The Chinese patent "A polytetrafluoroethylene microporous membrane and its preparation method" with publication number CN116272396A discloses that nano-silicon dioxide particles are wrapped inside the film. The obtained polytetrafluoroethylene microporous membrane has a three-layer structure, including upper and lower layers of tetrafluoroethylene resin and a middle layer of evenly dispersed nano-silicon dioxide.

[0006] In summary, the prior art usually modifies the performance of microporous membranes by adding nano-silicon dioxide into PTFE by physical doping, but the physical doping method is difficult to solve the problems of uniform dispersion and interface bonding of nano-materials in the matrix. Therefore, how to tightly combine nano-silicon dioxide with the PTFE matrix by chemical methods becomes the key to improving its comprehensive performance. Summary of the invention

[0007] In order to solve the problems existing in the prior art, the present invention provides a polytetrafluoroethylene microporous membrane and a preparation method thereof, wherein nano-silicon dioxide and hydrogenated petroleum resin powder are doped into PTFE resin powder, auxiliary oil is used to assist in blending, and a series of process treatments and chemical reactions are performed to obtain a PTFE microporous membrane with excellent high temperature resistance, high strength and long-term anti-infiltration performance.

[0008] In order to achieve the above-mentioned invention object, the present invention provides the following technical solutions:

[0009] The present invention provides a method for preparing a polytetrafluoroethylene microporous membrane, comprising the following steps:

[0010] (1) By weight, 100 to 120 parts of polytetrafluoroethylene resin powder, 1 to 12 parts of silicon dioxide, and 5 to 15 parts of hydrogenated petroleum resin powder are mixed uniformly;

[0011] (2) adding 20 to 30 parts of auxiliary oil to the uniformly mixed material to obtain a mixed material, pre-pressing the mixed material into a cylindrical billet, and then rolling the cylindrical billet through a calender to obtain a polytetrafluoroethylene casting sheet, which is then aged;

[0012] (3) the matured polytetrafluoroethylene casting sheet is subjected to asynchronous biaxial stretching and high-temperature sintering to obtain a heat-set polytetrafluoroethylene microporous membrane;

[0013] (4) immersing the heat-set polytetrafluoroethylene microporous membrane in a mixed solution of dioxane containing an aldehyde monomer and deionized water and oscillating the mixture at multiple frequencies for 70 to 80 hours;

[0014] (5) The polytetrafluoroethylene microporous membrane was taken out, and the polytetrafluoroethylene microporous membrane was washed with dioxane, deionized water and anhydrous ethanol respectively, dried and rolled up to obtain the polytetrafluoroethylene microporous membrane.

[0015] Preferably, in step (1), the silicon dioxide is pretreated with a silane coupling agent so that its surface contains amino groups; the silicon dioxide is non-porous, mesoporous or hollow.

[0016] Preferably, the hydrogenated petroleum resin powder in step (1) is obtained by dissolving hydrogenated petroleum resin pellets in N'N-dimethylformamide solution, then adding excess deionized water, and flocculating the solution; the hydrogenated petroleum resin is one or more of hydrogenated C5 petroleum resin, hydrogenated C9 petroleum resin, hydrogenated C5 / C9 petroleum resin or aromatic hydrogenated petroleum resin.

[0017] Preferably, the auxiliary oil in step (2) is a uniform single isoparaffin auxiliary or a mixture of multiple isoparaffin auxiliary.

[0018] Preferably, when the auxiliary oil is a mixture of multiple isoparaffin auxiliary agents, different isoparaffin auxiliary agents are frozen into ice cubes in liquid nitrogen before being blended for use.

[0019] Preferably, in step (2), the aging temperature is 50-110° C. and the aging time is 6-12 hours.

[0020] Preferably, in step (3), the high temperature sintering temperature is 320-370° C., and the high temperature sintering time is 5-20 min.

[0021] Preferably, the aldehyde monomer in step (4) is an aromatic compound having a difunctional group or a trifunctional group, and the molar concentration of the aldehyde monomer solution is 0.05 to 0.075 mol / L.

[0022] Preferably, the temperature of the mixed solution in step (4) is 100-130° C., and the volume ratio of dioxane to deionized water in the mixed solution is 10:2-10:5.

[0023] The invention also provides a polytetrafluoroethylene microporous membrane prepared according to the preparation method of the polytetrafluoroethylene microporous membrane.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention dopes nano silicon dioxide and hydrogenated petroleum resin powder into PTFE resin powder, uses auxiliary oil to assist blending, and finally prepares a high-performance PTFE microporous membrane with high temperature resistance, high strength and excellent long-term anti-infiltration performance through a series of process treatments such as extrusion into a blank, calendering, aging, biaxial stretching, sintering and chemical reaction. The auxiliary oil can infiltrate the PTFE powder, so that it can be fully agglomerated under pressure, and at the same time, the PTFE powder and silicon dioxide are evenly dispersed. Isoparaffin auxiliary agent is used as an oil auxiliary agent. Compared with straight-chain alkane auxiliary agent, isoparaffin auxiliary agent has a higher distillation range, better solubility and chemical stability, and can make the PTFE crystals of the mixture relax during the aging process, and the spiral structure of the chain is easier to open and become a tight and irregular winding state, thereby enhancing the interaction force between PTFE molecules, better film formation during the biaxial stretching process, and maintaining stability during the high-temperature sintering process.

[0026] 2. In the method provided by the present invention, after the matured polytetrafluoroethylene casting sheet is sintered at high temperature and then heat-set, the sintered polytetrafluoroethylene microporous membrane is immersed in a mixed solution of dioxane containing aldehyde monomers and deionized water. The silicon dioxide surface in the polytetrafluoroethylene microporous membrane carries amino groups, which react with the aldehyde-containing monomers to form a Schiff base through dehydration condensation. The Schiff base reaction requires equal amounts of aldehydes and amines to react. According to the content of amino groups in the polytetrafluoroethylene microporous membrane in the present invention, the molar concentration of the aldehyde monomer solution needs to be controlled within the concentration range of 0.05 to 0.075 mol / L. Therefore, it cannot be directly immersed in a solvent containing aldehyde monomers. The use of a mixed solution of dioxane and deionized water can effectively dissolve the aldehyde monomers, which is conducive to the Schiff base reaction. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with preferred embodiments. The endpoints of the ranges disclosed in the present invention and any values ​​are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be deemed to be specifically disclosed herein.

[0028] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0029] Example 1

[0030] A method for preparing a polytetrafluoroethylene microporous membrane comprises the following steps:

[0031] (1) By weight, 100 parts of polytetrafluoroethylene resin powder, 5 parts of non-porous silica and 10 parts of hydrogenated C9 petroleum resin powder are mixed uniformly by a three-dimensional rotary mixer; in this embodiment, the silica needs to be treated with a silane coupling agent KH550 so that its surface contains amino groups; the hydrogenated C9 petroleum resin powder is obtained by dissolving hydrogenated C9 petroleum resin pellets in N'N-dimethylformamide solution, then adding excess deionized water, and flocculating the solution;

[0032] (2) 25 parts of auxiliary oil are added to the uniformly mixed material to obtain a mixed material, and the mixed material is pre-pressed into a cylindrical blank with a diameter of 2.5 cm and a height of 3 cm at room temperature, and then the cylindrical blank is passed through a calender and calendered at 60° C. to obtain a polytetrafluoroethylene casting sheet with a thickness of 800 μm, and then aged at 90° C. for 6 hours; the auxiliary oil in this embodiment is a uniform single isoparaffin auxiliary;

[0033] (3) The aging polytetrafluoroethylene casting sheet was longitudinally stretched at 180°C, with a stretching ratio of 6 and a stretching rate of 50% / s, and then transversely stretched at 140°C, with a stretching ratio of 9 and a stretching rate of 50% / s, and then high-temperature sintered at 360°C for 10 minutes to obtain a heat-set polytetrafluoroethylene microporous membrane;

[0034] (4) immersing the heat-set polytetrafluoroethylene microporous membrane in a mixed solution of dioxane and deionized water containing trimesaldehyde at a molar concentration of 0.06 mol / L and oscillating at multiple frequencies for 70 h, the temperature of the mixed solution being 120° C., and the volume ratio of dioxane to deionized water in the mixed solution being 10:3;

[0035] (5) The polytetrafluoroethylene microporous membrane was taken out, and the polytetrafluoroethylene microporous membrane was washed with dioxane, deionized water and anhydrous ethanol respectively, dried and rolled up to obtain the polytetrafluoroethylene microporous membrane.

[0036] Example 2

[0037] A method for preparing a polytetrafluoroethylene microporous membrane comprises the following steps:

[0038] (1) By weight, 110 parts of polytetrafluoroethylene resin powder, 10 parts of mesoporous silica and 15 parts of aromatic hydrogenated petroleum resin powder are mixed uniformly by a three-dimensional rotary mixer; in this embodiment, the silica needs to be treated with a silane coupling agent KH550 so that its surface contains amino groups; the aromatic hydrogenated petroleum resin powder is obtained by dissolving aromatic hydrogenated petroleum resin pellets in N'N-dimethylformamide solution, then adding excess deionized water, and flocculating the solution;

[0039] (2) 30 parts of auxiliary oil are added to the uniformly mixed material to obtain a mixed material, and the mixed material is pre-pressed into a cylindrical blank with a diameter of 2.5 cm and a height of 3 cm at room temperature, and then the cylindrical blank is passed through a calender and calendered at 60° C. to obtain a polytetrafluoroethylene casting sheet with a thickness of 800 μm, and then aged at 110° C. for 8 hours; in this embodiment, the auxiliary oil is a mixture of multiple isoparaffin additives, and different isoparaffin additives are pre-frozen into ice cubes in liquid nitrogen and then blended for use; compared with the good applicability of a single isoparaffin additive under specific preparation conditions, this embodiment changes the parameters such as the aging temperature, sintering temperature, and solution concentration, and multiple mixed isoparaffin additives can better adapt to the preparation conditions;

[0040] (3) The aging polytetrafluoroethylene casting sheet was longitudinally stretched at 180°C, with a stretching ratio of 6 and a stretching rate of 50% / s, and then transversely stretched at 140°C, with a stretching ratio of 9 and a stretching rate of 50% / s, and then high-temperature sintered at 320°C for 20 minutes to obtain a heat-set polytetrafluoroethylene microporous membrane;

[0041] (4) immersing the heat-set polytetrafluoroethylene microporous membrane in a mixed solution of dioxane and deionized water containing trimesaldehyde at a molar concentration of 0.075 mol / L and oscillating at multiple frequencies for 75 h, the temperature of the mixed solution being 130° C., and the volume ratio of dioxane to deionized water in the mixed solution being 10:2;

[0042] (5) The polytetrafluoroethylene microporous membrane was taken out, and the polytetrafluoroethylene microporous membrane was washed with dioxane, deionized water and anhydrous ethanol respectively, dried and rolled up to obtain the polytetrafluoroethylene microporous membrane.

[0043] Example 3

[0044] A method for preparing a polytetrafluoroethylene microporous membrane comprises the following steps:

[0045] (1) By weight, 110 parts of polytetrafluoroethylene resin powder, 12 parts of hollow silica and 5 parts of hydrogenated C5 / C9 petroleum resin powder are mixed uniformly by a three-dimensional rotary mixer; in this embodiment, the silica needs to be treated with a silane coupling agent KH550 so that its surface contains amino groups; the hydrogenated C5 / C9 petroleum resin powder is obtained by dissolving hydrogenated C5 / C9 petroleum resin pellets in N'N-dimethylformamide solution, then adding excess deionized water, and flocculating the solution;

[0046] (2) 20 parts of auxiliary oil are added to the uniformly mixed material to obtain a mixed material, and the mixed material is pre-pressed into a cylindrical blank with a diameter of 2.5 cm and a height of 3 cm at room temperature, and then the cylindrical blank is passed through a calender and calendered at 60° C. to obtain a polytetrafluoroethylene casting sheet with a thickness of 800 μm, and then aged at 50° C. for 12 hours; in this embodiment, the auxiliary oil is a mixture of multiple isoparaffin auxiliary agents, and different isoparaffin auxiliary agents are pre-frozen into ice cubes in liquid nitrogen before being blended for use;

[0047] (3) The aging polytetrafluoroethylene casting sheet was longitudinally stretched at 180°C, with a stretching ratio of 6 and a stretching rate of 50% / s, and then transversely stretched at 140°C, with a stretching ratio of 9 and a stretching rate of 50% / s, and then high-temperature sintered at 370°C for 5 minutes to obtain a heat-set polytetrafluoroethylene microporous membrane;

[0048] (4) immersing the heat-set polytetrafluoroethylene microporous membrane in a mixed solution of dioxane and deionized water containing trimesaldehyde at a molar concentration of 0.07 mol / L and oscillating at multiple frequencies for 80 h, the temperature of the mixed solution being 130° C., and the volume ratio of dioxane to deionized water in the mixed solution being 10:2;

[0049] (5) The polytetrafluoroethylene microporous membrane was taken out, and the polytetrafluoroethylene microporous membrane was washed with dioxane, deionized water and anhydrous ethanol respectively, dried and rolled up to obtain the polytetrafluoroethylene microporous membrane.

[0050] Example 4

[0051] A method for preparing a polytetrafluoroethylene microporous membrane comprises the following steps:

[0052] (1) By weight, 120 parts of polytetrafluoroethylene resin powder, 1 part of hollow silica and 5 parts of hydrogenated C5 petroleum resin powder are mixed uniformly by a three-dimensional rotary mixer; in this embodiment, the silica needs to be treated with a silane coupling agent KH550 so that its surface contains amino groups; the hydrogenated C5 petroleum resin powder is obtained by dissolving hydrogenated C5 petroleum resin pellets in N'N-dimethylformamide solution, then adding excess deionized water, and flocculating the solution;

[0053] (2) 30 parts of auxiliary oil are added to the uniformly mixed material to obtain a mixed material, and the mixed material is pre-pressed into a cylindrical blank with a diameter of 2.5 cm and a height of 3 cm at room temperature, and then the cylindrical blank is passed through a calender and calendered at 60° C. to obtain a polytetrafluoroethylene casting sheet with a thickness of 800 μm, and then aged at 70° C. for 10 hours; the auxiliary oil in this embodiment is a mixture of multiple isoparaffin auxiliary agents, and different isoparaffin auxiliary agents are pre-frozen into ice cubes in liquid nitrogen before blending and use;

[0054] (3) The aging polytetrafluoroethylene casting sheet was longitudinally stretched at 180°C, with a stretching ratio of 6 and a stretching rate of 50% / s, and then transversely stretched at 140°C, with a stretching ratio of 9 and a stretching rate of 50% / s, and then high-temperature sintered at 350°C for 15 minutes to obtain a heat-set polytetrafluoroethylene microporous membrane;

[0055] (4) immersing the heat-set polytetrafluoroethylene microporous membrane in a mixed solution of dioxane and deionized water containing trimesaldehyde at a molar concentration of 0.05 mol / L and oscillating at multiple frequencies for 60 h, the temperature of the mixed solution being 100° C., and the volume ratio of dioxane to deionized water in the mixed solution being 10:5;

[0056] (5) The polytetrafluoroethylene microporous membrane was taken out, and the polytetrafluoroethylene microporous membrane was washed with dioxane, deionized water and anhydrous ethanol respectively, dried and rolled up to obtain the polytetrafluoroethylene microporous membrane.

[0057] Comparative Example 1

[0058] The difference between Comparative Example 1 and Example 1 is that: hydrogenated petroleum resin powder is not added to the raw material for preparing the polytetrafluoroethylene microporous membrane, and in step (1), 100 parts of polytetrafluoroethylene resin powder and 5 parts of non-porous silica are mixed uniformly by a three-dimensional rotary mixer, and then mixed with 25 parts of auxiliary oil to obtain a mixed material;

[0059] The remaining steps are the same as those in Example 1.

[0060] Comparative Example 2

[0061] The difference between Comparative Example 2 and Example 1 is that: no non-porous silica is added to the raw material for preparing the polytetrafluoroethylene microporous membrane, and in step (1), 100 parts of polytetrafluoroethylene resin powder and 10 parts of hydrogenated C9 petroleum resin powder are uniformly mixed by a three-dimensional rotary mixer, and then mixed with 25 parts of auxiliary oil to obtain a mixed material;

[0062] The remaining steps are the same as those in Example 1.

[0063] Comparative Example 3

[0064] The difference between Comparative Example 3 and Example 2 is that:

[0065] In step (1), 110 parts of polytetrafluoroethylene resin powder and 10 parts of mesoporous silica are uniformly mixed by a three-dimensional rotary mixer without adding aromatic hydrogenated petroleum resin powder, and then mixed with 30 parts of auxiliary oil to obtain a mixed material;

[0066] The remaining steps are the same as those in Example 2.

[0067] Comparative Example 4

[0068] The difference between Comparative Example 4 and Example 2 is that:

[0069] In step (1), 110 parts of polytetrafluoroethylene resin powder and 15 parts of aromatic hydrogenated petroleum resin powder are uniformly mixed by a three-dimensional rotary mixer without adding mesoporous silica, and then mixed with 30 parts of auxiliary oil to obtain a mixed material;

[0070] The remaining steps are the same as those in Example 2.

[0071] Comparative Example 5

[0072] The difference between Comparative Example 5 and Example 3 is that:

[0073] In step (1), 110 parts of polytetrafluoroethylene resin powder and 5 parts of hydrogenated C5 / C9 petroleum resin powder are uniformly mixed by a three-dimensional rotary mixer without adding hollow silica, and then mixed with 20 parts of auxiliary oil to obtain a mixed material;

[0074] The remaining steps are the same as those in Example 3.

[0075] Comparative Example 6

[0076] The difference between Comparative Example 6 and Example 3 is that:

[0077] In step (1), 110 parts of polytetrafluoroethylene resin powder and 12 parts of hollow silica are uniformly mixed by a three-dimensional rotary mixer without adding hydrogenated C5 / C9 petroleum resin powder, and then mixed with 20 parts of auxiliary oil to obtain a mixed material;

[0078] The remaining steps are the same as those in Example 3.

[0079] Comparative Example 7

[0080] The difference between Comparative Example 7 and Example 4 is that:

[0081] In step (1), 120 parts of polytetrafluoroethylene resin powder and 1 part of hollow silica are uniformly mixed by a three-dimensional rotary mixer without adding hollow silica, and then mixed with 30 parts of auxiliary oil to obtain a mixed material;

[0082] The remaining steps are the same as those in Example 4.

[0083] Comparative Example 8

[0084] The difference between Comparative Example 8 and Example 4 is that:

[0085] In step (1), 120 parts of polytetrafluoroethylene resin powder and 5 parts of hydrogenated C5 petroleum resin powder are uniformly mixed by a three-dimensional rotary mixer without adding hydrogenated C5 petroleum resin powder, and then mixed with 30 parts of auxiliary oil to obtain a mixed material;

[0086] The remaining steps are the same as those in Example 4.

[0087] The polytetrafluoroethylene microporous membranes prepared by the methods of Examples 1-4 and Comparative Examples 1-8 were characterized, and the characterization items and methods are as follows:

[0088] 1. Water contact angle:

[0089] The water contact angle is measured by the drop method according to "GBT 30693 "Measurement of the contact angle of water on plastic film". The water contact angle on the surface of the PTFE microporous membrane is measured using a static water contact angle meter.

[0090] 2. High temperature resistance:

[0091] The high temperature resistance test is carried out by placing the sample at different temperatures (200-500°C) for 1 hour and measuring its contact angle after cooling to room temperature.

[0092] Generally, heating at a higher temperature will cause the film to be in a state of melting and refreezing, thereby reducing the surface roughness and partially destroying the micro-nano structure. This state reduces the water contact angle. When the temperature reaches a certain temperature, microcracks will form on the film surface and the surface cohesion will be lost, causing the water contact angle of the material to decrease sharply. The temperature below the critical temperature of the transition from hydrophobic state to hydrophilic state is called its heat resistance temperature.

[0093] 3. Tensile strength:

[0094] The tensile strength is tested in accordance with "GB / T 1040.3 "Test method for tensile strength of plastic films"".

[0095] 4. Long-term anti-infiltration performance:

[0096] Long-term anti-wetting property was measured by subjecting the PTFE microporous membrane to water shock for 4 h and measuring the change in water contact angle.

[0097] The specific characterization results are shown in Table 1 below:

[0098] Table 1

[0099]

[0100] In summary, the polytetrafluoroethylene microporous membranes obtained by the methods provided in Examples 1-4 of the present invention all satisfy the contact angle greater than 90°, are hydrophobic materials, have heat-resistant temperatures higher than 300°C, have excellent high-temperature resistance, have a tensile strength ≥35MPa for high strength, and have good anti-infiltration properties if the contact angle variation is less than 5%. At the same time, they meet the high-performance evaluation factors of hydrophobicity, high-temperature resistance, high strength and anti-infiltration properties, and are polytetrafluoroethylene microporous membranes with excellent high-temperature resistance, high strength and long-term anti-infiltration properties.

[0101] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a polytetrafluoroethylene microporous membrane, characterized in that: The following steps are involved: (1) By weight, 100 to 120 parts of polytetrafluoroethylene resin powder, 1 to 12 parts of silicon dioxide, and 5 to 15 parts of hydrogenated petroleum resin powder are mixed uniformly; (2) adding 20 to 30 parts of auxiliary oil to the uniformly mixed material to obtain a mixed material, pre-pressing the mixed material into a cylindrical billet, and then rolling the cylindrical billet through a calender to obtain a polytetrafluoroethylene casting sheet, which is then aged; (3) the matured polytetrafluoroethylene casting sheet is subjected to asynchronous biaxial stretching and high-temperature sintering to obtain a heat-set polytetrafluoroethylene microporous membrane; (4) immersing the heat-set polytetrafluoroethylene microporous membrane in a mixed solution of dioxane containing an aldehyde monomer and deionized water and oscillating the mixture at multiple frequencies for 70 to 80 hours; (5) The polytetrafluoroethylene microporous membrane was taken out, and the polytetrafluoroethylene microporous membrane was washed with dioxane, deionized water and anhydrous ethanol respectively, dried and rolled up to obtain the polytetrafluoroethylene microporous membrane.

2. The method for preparing a polytetrafluoroethylene microporous membrane according to claim 1, characterized in that: In the step (1), the silicon dioxide is pretreated with a silane coupling agent so that its surface contains amino groups; the silicon dioxide is non-porous, mesoporous or hollow.

3. The method for preparing a polytetrafluoroethylene microporous membrane according to claim 1, characterized in that: The hydrogenated petroleum resin powder in step (1) is obtained by dissolving hydrogenated petroleum resin pellets in N'N-dimethylformamide solution, adding excess deionized water, and flocculating the solution; the hydrogenated petroleum resin is one or more of hydrogenated C5 petroleum resin, hydrogenated C9 petroleum resin or aromatic hydrogenated petroleum resin.

4. The method for preparing a polytetrafluoroethylene microporous membrane according to claim 1, characterized in that: The auxiliary agent oil in the step (2) is a uniform single isoparaffin auxiliary agent or a mixture of multiple isoparaffin auxiliary agents.

5. The method for preparing a polytetrafluoroethylene microporous membrane according to claim 4, characterized in that: When the auxiliary oil is a mixture of multiple isoparaffin auxiliary agents, the different isoparaffin auxiliary agents are frozen into ice cubes in liquid nitrogen before being blended for use.

6. The method for preparing a polytetrafluoroethylene microporous membrane according to claim 1, characterized in that: In the step (2), the aging temperature is 50 to 110° C. and the aging time is 6 to 12 hours.

7. The method for preparing a polytetrafluoroethylene microporous membrane according to claim 1, characterized in that: In the step (3), the high temperature sintering temperature is 320-370° C., and the high temperature sintering time is 5-20 minutes.

8. The method for preparing a polytetrafluoroethylene microporous membrane according to claim 1, characterized in that: In the step (4), the aldehyde monomer is an aromatic compound having a difunctional group or a trifunctional group, and the molar concentration of the aldehyde monomer solution is 0.05 to 0.075 mol / L.

9. The method for preparing a polytetrafluoroethylene microporous membrane according to claim 1, characterized in that: The temperature of the mixed solution in step (4) is 100-130° C., and the volume ratio of dioxane to deionized water in the mixed solution is 10:2-10:

5.

10. A polytetrafluoroethylene microporous membrane prepared according to the preparation method according to any one of claims 1 to 9.

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