A polytetrafluoroethylene fiber composite membrane and its preparation method

Abstract

This invention discloses a polytetrafluoroethylene (PTFE) fiber composite membrane and its preparation method. By adding a foaming agent to the curing material, the foaming agent molecules decompose during the longitudinal stretching of the PTFE roll, reducing the membrane size nodes and thus increasing the membrane flux. Adding a fluorinated emulsion for bonding during thermal lamination further improves the membrane flux and filtration accuracy. Furthermore, subjecting the PTFE membrane to ultra-low temperature freezing treatment increases the membrane's strength. In summary, the PTFE fiber composite membrane prepared by the method of this invention can ensure high flux while maintaining a small pore size.

Description

Technical Field

[0001] This invention relates to the field of membrane preparation, and more particularly to a polytetrafluoroethylene fiber composite membrane and its preparation method. Background Technology

[0002] Polytetrafluoroethylene (PTFE) is a highly crystalline polymer of tetrafluoroethylene monomer, a white thermoplastic with a waxy feel. PTFE fiber composite membranes are prepared by mixing PTFE dispersion resin with additives, followed by extrusion molding, stretching, and shaping. They possess excellent physical and mechanical properties and chemical stability, and have significant application prospects in textiles, air filtration, biomedicine, membrane separation, and other fields.

[0003] In the semiconductor field, the purity of hydrofluoric acid used in chip etching is extremely critical. Therefore, corrosion-resistant polytetrafluoroethylene (PTFE) fiber composite membranes are used to filter the etching solution before chip etching. This requires the PTFE fiber composite membrane to have a pore size of several nanometers to tens of nanometers and high flux. However, currently available PTFE fiber composite membranes prepared by biaxial stretching have relatively large nodes and it is difficult to balance flux and pore size. They cannot guarantee high flux at small pore sizes, making them unsuitable for semiconductor filtration, especially for filtering chip etching solutions.

[0004] For example, patent application publication number CN 116510537 A discloses a multilayer polytetrafluoroethylene (PTFE) composite film and its preparation method. A calendered preform of PTFE is online laminated with a cast preform of a thermoplastic polymer, and the resulting composite preform is then prepared into a multilayer PTFE composite film with a gradient structure using a biaxial stretching method. However, the pore size of this PTFE microporous film is relatively large, making it unsuitable for use in the semiconductor field. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a polytetrafluoroethylene fiber composite membrane and its preparation method. The prepared polytetrafluoroethylene fiber composite membrane can balance flux and pore size, ensuring high flux even with small pore sizes.

[0006] The technical solution of the present invention to solve the above problems is as follows:

[0007] A method for preparing a polytetrafluoroethylene fiber composite membrane includes the following steps:

[0008] S1. Dissolve the first foaming agent in alkane oil, mix the polytetrafluoroethylene dispersion resin and alkane oil evenly in proportion, and cure to obtain the first cured material; make the first cured material into a first polytetrafluoroethylene roll, and stretch it longitudinally at a stretch ratio a1 to obtain a first polytetrafluoroethylene tape; stretch the first polytetrafluoroethylene tape transversely at a stretch ratio b1, and then heat set, wind up, and freeze at ultra-low temperature to obtain a low-grammage polytetrafluoroethylene fiber film.

[0009] S2. Dissolve the second foaming agent in alkane oil, mix the polytetrafluoroethylene dispersion resin and alkane oil in a certain proportion, and cure to obtain a second cured material; make the second cured material into a second polytetrafluoroethylene roll, stretch it longitudinally at a stretch ratio a2 to obtain a second polytetrafluoroethylene tape, stretch the second polytetrafluoroethylene tape transversely at a stretch ratio b2, and then perform heat setting, winding, and ultra-low temperature freezing to obtain a high-grammage polytetrafluoroethylene fiber film; wherein a1 > a2, b1 > b2.

[0010] S3. Spray fluoropolymer emulsion onto both sides of the high-grammage polytetrafluoroethylene fiber membrane, and then composite it with the low-grammage polytetrafluoroethylene fiber membrane. Wrap it up and freeze it at ultra-low temperature to obtain a polytetrafluoroethylene fiber composite membrane.

[0011] Preferably, both the first and second foaming agents are selected from one or more of azodicarbonamide, N,N-dinitrospentamethylenetetramine, and trihydrazine.

[0012] Preferably, the alkane oils used in steps S1 and S2 are selected from ISOPAR. TM One or more of the following isoparaffin solvents: G, H, and L.

[0013] Preferably, the fluoropolymer emulsion is selected from one or more of water-in-oil polytetrafluoroethylene emulsion and polytetrafluoroethylene-co-hexafluoropropylene emulsion; the fluoropolymer emulsion in S3 needs to be diluted with a small molecule polar solvent.

[0014] Preferably, the mass ratio of polytetrafluoroethylene dispersion resin to alkane oil in steps S1 and S2 is 10:(2-3.5); the mass of foaming agent in steps S1 and S2 is 0.5-2.5% of the mass of alkane oil.

[0015] Preferably, the longitudinal stretching temperature in both steps S1 and S2 is 220–300°C; the longitudinal stretching ratio in both steps S1 and S2 is 6–10 times, and the longitudinal stretching ratio in step S2 is less than the longitudinal stretching ratio in step S1.

[0016] Preferably, the temperature for both transverse and longitudinal stretching in steps S1 and S2 is 80–200°C; the transverse stretching ratio in both steps S1 and S2 is 4–10 times, and the transverse stretching ratio in step S2 is less than the transverse stretching ratio in step S1; the heat setting temperature in both steps S1 and S2 is 330–420°C.

[0017] Preferably, the curing temperature in steps S1 and S2 is 40–80°C and the curing time is 6–12 h; the ultra-low temperature freezing temperature in steps S1 and S2 is -140–-170°C and the freezing time is 20–28 h.

[0018] Preferably, the fluoropolymer emulsion used in step S3 during compounding is 1–3 g / m³. 2 The composite temperature is 310-350℃, the composite pressure is 0.05-0.2MPa, and the composite speed is 6-12m / min; the ultra-low temperature freezing temperature in step S3 is -140--170℃, and the freezing time is 20-28h.

[0019] Another object of the present invention is to provide a polytetrafluoroethylene fiber composite membrane prepared by the above-mentioned method for preparing polytetrafluoroethylene fiber composite membrane.

[0020] Polytetrafluoroethylene (PTFE) generally has a high degree of crystallinity. In PTFE molecules, the CF2 units are arranged in a zigzag shape. Because the radius of fluorine atoms is larger than that of hydrogen atoms, adjacent CF2 units cannot be completely cross-oriented, but instead form a helical twisted chain. When the temperature is below 19°C, a 13 / 6 helix will be formed. After ultra-low temperature freezing treatment, the helix will be further intensified, and even the spatial conformation at the microscopic level will be united, thereby making the entanglement between molecules tighter and increasing the strength of the PTFE film.

[0021] The present invention has the following beneficial effects:

[0022] This invention improves membrane flux by adding a foaming agent to the curing material, causing the foaming agent molecules to decompose during the longitudinal stretching of the PTFE roll, thus reducing the membrane size nodes. Adding a fluorinated emulsion during thermal lamination further enhances the membrane flux and filtration accuracy. Furthermore, subjecting the PTFE membrane to ultra-low temperature freezing treatment increases its strength. In summary, the PTFE fiber composite membrane prepared by this invention ensures high flux while maintaining a small pore size. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the polytetrafluoroethylene fiber composite structure of the present invention.

[0024] In the diagram: 1-Large weight polytetrafluoroethylene membrane, 2-Small weight polytetrafluoroethylene membrane, 3-Fluoropolymer emulsion. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to specific embodiments. However, the specific details of the embodiments are only for illustrating the present invention and do not represent all technical methods under the concept of the present invention. Therefore, they should not be construed as limiting the overall technical solution of the present invention.

[0026] Example 1

[0027] (1) Dissolve the foaming agent azodicarbonamide in alkane oil ISOPAR TM In G, the foaming agent mass is 2.5% of the alkane oil mass. Then, polytetrafluoroethylene dispersion resin (DuPont PTFE 601X) and alkane oil ISOPAR are mixed. TM After mixing G at a mass ratio of 10:3.5, it is cured at 80℃ for 6 hours to obtain cured material. The cured material is then extruded and calendered into polytetrafluoroethylene (PTFE) rolls by a preformer, an extruder, and a calender. The rolls are then stretched longitudinally 10 times at 300℃ to obtain PTFE vinyl tape. The PTFE vinyl tape is then stretched transversely 10 times at 80℃, heat-set at 420℃, wound up, and then placed in an ultra-low temperature freezer at -160℃ for 24 hours to obtain a low-grammage PTFE fiber membrane.

[0028] (2) Dissolve the foaming agent N,N-dinitrospentamethylenetetramine in alkane oil ISOPAR TM In H, the foaming agent mass is 1.5% of the alkane oil mass. Then, polytetrafluoroethylene dispersion resin (Chenguang PTFE 1009) and alkane oil ISOPAR are mixed. TM After mixing H at a mass ratio of 10:3, the mixture is cured at 60℃ for 8 hours to obtain cured material. The cured material is then extruded through a compact press, an extruder, and a calender to form polytetrafluoroethylene (PTFE) rolls. The rolls are then stretched longitudinally by 8 times at 250℃ to obtain PTFE vinyl tape. The PTFE vinyl tape is stretched transversely by 5 times at 80℃, heat-set at 330℃, and then wound up and placed in an ultra-low temperature freezer at -160℃ for 24 hours to obtain a high-grammage PTFE fiber membrane.

[0029] (3) A water-in-oil PTFE emulsion diluted with isopropanol is sprayed onto one side of a high-weight PTFE fiber membrane, and then laminated with a low-weight PTFE fiber membrane using a thermal laminator (the low-weight PTFE fiber membrane is in contact with a metal rod with heating function); then the other side of the high-weight PTFE fiber membrane is sprayed with a water-in-oil PTFE emulsion diluted with isopropanol, and then laminated again with the low-weight PTFE fiber membrane using a thermal laminator (the low-weight PTFE fiber membrane is in contact with a metal rod with heating function); wherein the fluoropolymer emulsion content is 3 g / m² during each lamination. 2The thermal bonding temperature is 350℃, the thermal bonding pressure is 0.1MPa, and the thermal bonding speed is 8m / min. Finally, the wound polytetrafluoroethylene composite film is placed in an ultra-low temperature freeze at -160℃ for 24 hours, and then taken out to obtain the polytetrafluoroethylene composite film.

[0030] Example 2

[0031] (1) Dissolve the foaming agent trihydrazine in alkane oil ISOPAR TM In L, the foaming agent mass is 2.0% of the alkane oil mass. Then, polytetrafluoroethylene dispersion resin (Chenguang PTFE 216) and alkane oil are mixed according to ISO PAR... TM The L-irradiation material is mixed evenly at a mass ratio of 10:3.0 and cured at 40℃ for 12 hours to obtain cured material. The cured material is then extruded and calendered into polytetrafluoroethylene (PTFE) rolls by a preformer, an extruder, and a calender. The rolls are then stretched longitudinally by 8 times at 250℃ to obtain PTFE vinyl tape. The PTFE vinyl tape is stretched transversely by 6 times at 120℃, heat-set at 400℃, and then wound up and placed in an ultra-low temperature freezer at -160℃ for 24 hours to obtain a low-grammage PTFE fiber membrane.

[0032] (2) Dissolve the foaming agent hydrazine in alkane oil ISOPAR TM In L, the foaming agent mass is 1.0% of the alkane oil mass. Then, polytetrafluoroethylene dispersion resin (Chenguang PTFE 1009) and alkane oil ISOPAR are mixed. TM L is mixed evenly at a mass ratio of 10:2 and cured at 80℃ for 10 hours to obtain cured material; the cured material is then extruded and calendered into polytetrafluoroethylene (PTFE) rolls by passing them through a preformer, an extruder, and a calender, and then stretched longitudinally by 6 times at 300℃ to obtain PTFE vinyl tape; the PTFE vinyl tape is stretched transversely by 4 times at 200℃, heat-set at 360℃, wound up, and then placed in an ultra-low temperature freezer at -160℃ for 24 hours to obtain a high-grammage PTFE fiber film.

[0033] (3) A polytetrafluoroethylene-co-hexafluoropropylene emulsion diluted with isopropanol is sprayed onto one side of a high-weight polytetrafluoroethylene fiber membrane, and then laminated with a low-weight polytetrafluoroethylene fiber membrane using a thermal laminating machine (the low-weight polytetrafluoroethylene fiber membrane is in contact with a metal rod with heating function); then the other side of the high-weight polytetrafluoroethylene fiber membrane is sprayed with an oil-in-water polytetrafluoroethylene emulsion diluted with isopropanol, and then laminated with the low-weight polytetrafluoroethylene fiber membrane again using a thermal laminating machine (the low-weight polytetrafluoroethylene fiber membrane is in contact with a metal rod with heating function); wherein the fluoropolymer emulsion content is 2 g / m² during each lamination. 2The thermal lamination temperature is 310℃, the thermal lamination pressure is 0.15MPa, and the thermal lamination speed is 10m / min. Finally, the wound polytetrafluoroethylene composite film is placed in an ultra-low temperature freeze at -160℃ for 24 hours, and then taken out to obtain the polytetrafluoroethylene composite film.

[0034] Example 3

[0035] (1) Dissolve the foaming agent azodicarbonamide in alkane oil ISOPAR TM In G, the foaming agent mass is 0.5% of the alkane oil mass, and then polytetrafluoroethylene dispersion resin (DuPont PTFE 601X) and ISOPAR are added. TM G is mixed evenly at a mass ratio of 10:3.5 and cured at 70℃ for 12 hours to obtain cured material; the cured material is then extruded and calendered into polytetrafluoroethylene (PTFE) rolls by passing them through a compact press, an extruder, and a calender, and then stretched longitudinally by 8 times at 200℃ to obtain PTFE vinyl tape; the PTFE vinyl tape is stretched transversely by 8 times at 200℃, heat-set at 400℃, wound up, and then placed in an ultra-low temperature freezer at -160℃ for 24 hours to obtain a low-grammage PTFE fiber membrane.

[0036] (2) Dissolve the foaming agent N,N-dinitrospentamethylenetetramine in alkane oil ISOPAR TM In G, the foaming agent mass is 1.5% of the alkane oil mass. Then, polytetrafluoroethylene dispersion resin (Chenguang PTFE 1009) and alkane oil ISOPAR are mixed. TM G is mixed evenly at a mass ratio of 10:3 and cured at 60℃ for 8 hours to obtain cured material; the cured material is then extruded and calendered into polytetrafluoroethylene (PTFE) rolls by passing them through a preformer, an extruder, and a calender, and then stretched longitudinally by 8 times at 250℃ to obtain PTFE vinyl tape; the PTFE vinyl tape is then stretched transversely by 5 times at 80℃, heat-set at 330℃, wound up, and placed in an ultra-low temperature freezer at -160℃ for 24 hours to obtain a high-grammage PTFE fiber membrane.

[0037] (3) A water-in-oil PTFE emulsion diluted with isopropanol is sprayed onto one side of a high-weight PTFE fiber membrane, and then laminated with a low-weight PTFE fiber membrane using a thermal laminator (the low-weight PTFE fiber membrane is in contact with a metal rod with heating function); then the other side of the high-weight PTFE fiber membrane is sprayed with a water-in-oil PTFE emulsion diluted with isopropanol, and then laminated again with the low-weight PTFE fiber membrane using a thermal laminator (the low-weight PTFE fiber membrane is in contact with a metal rod with heating function); wherein the fluoropolymer emulsion content is 1 g / m² during each lamination. 2The thermal lamination temperature is 350℃, the thermal lamination pressure is 0.2MPa, and the thermal lamination speed is 12m / min. Finally, the wound polytetrafluoroethylene composite film is placed in an ultra-low temperature freeze at -160℃ for 24 hours, and then taken out to obtain the polytetrafluoroethylene composite film.

[0038] Example 4

[0039] (1) Dissolve the foaming agent N,N-dinitrospentamethylenetetramine in alkane oil ISOPAR TM In H, the foaming agent mass is 2.0% of the alkane oil mass. Then, polytetrafluoroethylene dispersion resin (DuPont PTFE 601X) and alkane oil ISOPAR are mixed. TM H is mixed evenly at a mass ratio of 10:2.5 and cured at 60℃ for 10 hours to obtain cured material; the cured material is then extruded and calendered into polytetrafluoroethylene (PTFE) rolls by passing them through a preformer, an extruder, and a calender, and then stretched longitudinally by 7 times at 200℃ to obtain PTFE vinyl tape; the PTFE vinyl tape is then stretched transversely by 7 times at 150℃, heat-set at 380℃, wound up, and placed in an ultra-low temperature freezer at -160℃ for 24 hours to obtain a low-grammage PTFE fiber membrane.

[0040] (2) The foaming agent N,N-dinitrospentamethylenetetramine is dissolved in alkane oil ISOPAR TM In L, the foaming agent mass is 1.0% of the alkane oil mass. Then, polytetrafluoroethylene dispersion resin (Chenguang PTFE 1009) and alkane oil ISOPAR are mixed. TM L is mixed evenly at a mass ratio of 10:2 and cured at 80℃ for 10 hours to obtain cured material; the cured material is then extruded and calendered into polytetrafluoroethylene (PTFE) rolls by passing them through a preformer, an extruder, and a calender, and then stretched longitudinally by 6 times at 300℃ to obtain PTFE vinyl tape; the PTFE vinyl tape is stretched transversely by 5 times at 200℃, heat-set at 380℃, wound up, and then placed in an ultra-low temperature freezer at -160℃ for 24 hours to obtain a high-grammage PTFE fiber membrane.

[0041] (3) A polytetrafluoroethylene-co-hexafluoropropylene emulsion diluted with isopropanol is sprayed onto one side of a high-weight polytetrafluoroethylene fiber membrane, and then laminated with a low-weight polytetrafluoroethylene fiber membrane using a thermal laminating machine (the low-weight polytetrafluoroethylene fiber membrane is in contact with a metal rod with heating function); then the other side of the high-weight polytetrafluoroethylene fiber membrane is sprayed with an oil-in-water polytetrafluoroethylene emulsion diluted with isopropanol, and then laminated with the low-weight polytetrafluoroethylene fiber membrane again using a thermal laminating machine (the low-weight polytetrafluoroethylene fiber membrane is in contact with a metal rod with heating function); wherein the fluoropolymer emulsion content is 2 g / m² during each lamination. 2The thermal lamination temperature is 310℃, the thermal lamination pressure is 0.15MPa, and the thermal lamination speed is 10m / min. Finally, the wound polytetrafluoroethylene composite film is placed in an ultra-low temperature freeze at -160℃ for 24 hours, and then taken out to obtain the polytetrafluoroethylene composite film.

[0042] Comparative Example 1

[0043] The foaming agent azodicarbonamide is dissolved in alkane oil ISOPAR. TM In G, the foaming agent mass is 2.5% of the alkane oil mass. Then, polytetrafluoroethylene dispersion resin (DuPont PTFE 601X) and alkane oil ISOPAR are mixed. TM G is mixed evenly at a mass ratio of 10:3.5 and cured at 80℃ for 6 hours to obtain cured material. The cured material is then extruded and calendered into PTFE rolls by a preformer, an extruder, and a calender. The rolls are then stretched longitudinally 10 times at 300℃ to obtain PTFE vinyl tape. The PTFE vinyl tape is stretched transversely 10 times at 80℃, heat-set at 420℃, and then wound up and placed in a -160℃ ultra-low temperature freezer for 24 hours to obtain a low-grammage PTFE fiber membrane. The obtained membrane is then hot-pressed using a thermal laminator at a temperature of 350℃, a pressure of 0.1MPa, and a speed of 8m / min. Finally, the wound PTFE membrane is placed in a -160℃ ultra-low temperature freezer for 24 hours to obtain the PTFE fiber membrane.

[0044] Comparative Example 2

[0045] The foaming agent N,N-dinitrospentamethylenetetramine was dissolved in the lubricant ISOPAR. TM In step H, the foaming agent mass is 1.5% of the alkane oil mass. Then, polytetrafluoroethylene dispersion resin (Chenguang PTFE 1009) and alkane oil are mixed evenly at a mass ratio of 10:3 and cured at 60℃ for 8 hours to obtain cured material. The cured material is then extruded and calendered into polytetrafluoroethylene rolls through a preformer, extruder, and calender. The rolls are then stretched longitudinally by 8 times at 250℃ to obtain polytetrafluoroethylene tape. The polytetrafluoroethylene tape is stretched transversely by 5 times at 80℃, heat-set at 330℃, and then wound up and placed in a -160℃ ultra-low temperature freezer for 24 hours to obtain a high-grammage polytetrafluoroethylene fiber membrane. The obtained membrane is then hot-pressed using a thermal laminating machine at a temperature of 350℃, a pressure of 0.1MPa, and a speed of 8m / min. Finally, the wound polytetrafluoroethylene membrane is placed in a -160℃ ultra-low temperature freezer for 24 hours and then removed to obtain a polytetrafluoroethylene fiber membrane.

[0046] Comparative Example 3

[0047] (1) Mix polytetrafluoroethylene dispersion resin (Chenguang PTFE 216) and alkane oil at a mass ratio of 10:3.0 and cure at 40°C for 12 hours to obtain cured material; pass the cured material through a preformer, an extruder and a calender to form polytetrafluoroethylene rolls, and then stretch them longitudinally by 8 times at 250°C to obtain polytetrafluoroethylene vinyl tape; stretch the polytetrafluoroethylene vinyl tape transversely by 6 times at 120°C, heat set at 400°C and wind it up to obtain a small-gram weight polytetrafluoroethylene fiber film.

[0048] (2) Mix polytetrafluoroethylene dispersion resin (Chenguang PTFE 1009) and alkane oil at a mass ratio of 10:2 and cure at 80°C for 10 hours to obtain cured material; pass the cured material through a preformer, an extruder and a calender to form polytetrafluoroethylene rolls, and then stretch them longitudinally by 6 times at 300°C to obtain polytetrafluoroethylene vinyl tape; stretch the polytetrafluoroethylene vinyl tape transversely by 4 times at 200°C, heat set at 360°C and wind it up to obtain a high-grammage polytetrafluoroethylene fiber film.

[0049] (3) The large-weight polytetrafluoroethylene fiber membrane is laminated with the small-weight polytetrafluoroethylene fiber membrane using a thermal laminating machine (the small-weight polytetrafluoroethylene fiber membrane is in contact with a metal rod with heating function); then the other side of the large-weight polytetrafluoroethylene fiber membrane is laminated with the small-weight polytetrafluoroethylene fiber membrane again using a thermal laminating machine (the small-weight polytetrafluoroethylene fiber membrane is in contact with a metal rod with heating function) to form a polytetrafluoroethylene composite membrane, wherein the thermal laminating temperature is 330℃, the thermal laminating pressure is 0.15MPa, and the thermal laminating speed is 10m / min.

[0050] The polytetrafluoroethylene fiber composite membranes prepared in Examples 1-4 and Comparative Examples 1-3 were tested. The basis weight and thickness of the polytetrafluoroethylene fiber composite membranes were tested according to GB / T20220-2006, the bubble point of the polytetrafluoroethylene fiber composite membranes was tested according to GB / T32361-2015, and the gas flux of the polytetrafluoroethylene fiber composite membranes was tested according to GB / T 1038-2000. The test results are shown in Table 1.

[0051] Table 1: Test Results of Polytetrafluoroethylene Fiber Composite Membrane

[0052]

[0053] The bubble point test involves completely immersing the polytetrafluoroethylene (PTFE) fiber composite membrane in a test liquid, slowly increasing the gas pressure on the membrane side, observing the bubbling of the gas passing through the membrane, and detecting the gas pressure at the time of bubbling. The bubble point is the pressure corresponding to the maximum pore size of the PTFE fiber composite membrane, and the full bubble point is the pressure corresponding to the average pore size of the PTFE fiber composite membrane.

[0054] As can be seen from Table 1, the gas flux of Examples 1 to 4 is slightly less than that of Comparative Examples 1 to 2, but the bubble point of Examples 1 to 4 is much greater than that of Comparative Examples 1 to 2. The larger the bubble point, the smaller the pore size of the polytetrafluoroethylene membrane. That is, the pore size of Examples 1 to 4 is much smaller than that of Comparative Examples 1 to 2.

[0055] Table 1 also shows that the bubble point of Examples 1 to 4 is greater than that of Comparative Example 3, that is, the pore size of Examples 1 to 4 is smaller than that of Comparative Example 3, and the gas flux of Examples 1 to 4 is much greater than that of Comparative Example 3.

[0056] In summary, the polytetrafluoroethylene fiber composite membranes prepared in Examples 1-4 can balance flux and pore size, ensuring high flux even with small pore size.

Claims

1. A method for preparing a polytetrafluoroethylene fiber composite membrane, characterized in that, Includes the following steps: S1. Dissolve the first foaming agent in alkane oil, mix the polytetrafluoroethylene dispersion resin and alkane oil in proportion and cure to obtain the first cured material. The first cured material is made into a first polytetrafluoroethylene roll, which is longitudinally stretched at a stretch ratio a1 to obtain a first polytetrafluoroethylene tape; the first polytetrafluoroethylene tape is transversely stretched at a stretch ratio b1, and then heat-set, wound up, and cryogenically frozen to obtain a low-grammage polytetrafluoroethylene fiber film. S2. Dissolve the second foaming agent in alkane oil, mix the polytetrafluoroethylene dispersion resin and alkane oil in proportion, and mature to obtain the second matured material. The second cured material is made into a second polytetrafluoroethylene roll, which is longitudinally stretched at a stretch ratio a2 to obtain a second polytetrafluoroethylene tape. The second polytetrafluoroethylene tape is then transversely stretched at a stretch ratio b2. Subsequently, it is heat-set, wound up, and cryogenically frozen to obtain a high-grammage polytetrafluoroethylene fiber film. Wherein a1 > a2, b1 > b2. S3. Spray fluoropolymer emulsion onto both sides of the high-grammage polytetrafluoroethylene fiber membrane and composite it with the low-grammage polytetrafluoroethylene fiber membrane. Then, wind it up and freeze it at ultra-low temperature to obtain a polytetrafluoroethylene fiber composite membrane. In steps S1 and S2, the longitudinal stretching temperature is 220–300℃, the longitudinal stretching ratio is 6–10 times, the transverse stretching temperature is 80–200℃, the transverse stretching ratio is 4–10 times, the heat setting temperature is 330–420℃, the curing temperature is 40–80℃, the curing time is 6–12 h, the ultra-low temperature freezing temperature is -170–-140℃, and the freezing time is 20–28 h. In step S3, the fluoropolymer emulsion used for compounding is 1–3 g / m³. 2 The composite temperature is 310–350℃, the composite pressure is 0.05–0.2 MPa, the composite speed is 6–12 m / min, the ultra-low temperature freezing temperature is -170–-140℃, and the freezing time is 20–28 h.

2. The method for preparing a polytetrafluoroethylene fiber composite membrane according to claim 1, characterized in that, Both the first and second foaming agents are selected from one or more of azodicarbonamide, N,N-dinitrospentamethylenetetramine, and trihydrazine.

3. The method for preparing a polytetrafluoroethylene fiber composite membrane according to claim 1, characterized in that, The alkane oils used in steps S1 and S2 are both selected from ISOPAR. TM One or more of the following isoparaffin solvents: G, H, and L.

4. The method for preparing a polytetrafluoroethylene fiber composite membrane according to claim 1, characterized in that, The fluoropolymer emulsion is selected from one or more of the following: oil-in-water polytetrafluoroethylene emulsion and polytetrafluoroethylene-co-hexafluoropropylene emulsion; the fluoropolymer emulsion in S3 needs to be diluted with a small molecule polar solvent.

5. The method for preparing a polytetrafluoroethylene fiber composite membrane according to claim 1, characterized in that, In steps S1 and S2, the mass ratio of polytetrafluoroethylene dispersion resin to alkane oil is 10:(2-3.5); in steps S1 and S2, the mass of foaming agent is 0.5-2.5% of the mass of alkane oil.

6. The polytetrafluoroethylene fiber composite membrane prepared by the method for preparing a polytetrafluoroethylene fiber composite membrane according to any one of claims 1 to 5.

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