Continuous production apparatus and production method of e-PTFE biaxially stretched tubular film

Abstract

The application discloses a continuous production equipment and method of e-PTFE bidirectional stretching tubular membrane, belongs to the technical field of filter membranes, and comprises a control system, a conveying device, an extruder, a degreasing stretching box, a traction machine, a fixed jacket, a jacket assembly device, a radial stretching core rod, a core rod assembly device, a high-temperature stretching box, a core rod dismounting device and a jacket dismounting device; the continuous production equipment of the e-PTFE bidirectional stretching tubular membrane is high in automation, can realize twice axial stretching and once radial stretching of a tubular body in combination with a specific method, and prepares the e-PTFE bidirectional stretching tubular membrane which is more uniform in three-dimensional fluffy membrane hole, node and fiber distribution, higher in porosity and better in interception effect.

Description

Technical Field

[0001] This invention belongs to the field of filtration membrane technology, specifically relating to continuous production equipment and production method for e-PTFE biaxially oriented tubular membranes. Background Technology

[0002] e-PTFE (expanded polytetrafluoroethylene) is an indispensable synthetic polymer material in modern science and industry. Due to the presence of highly energetic FC bonds in its molecular structure, it possesses advantages such as acid and alkali resistance, high and low temperature resistance, corrosion resistance, oxidation resistance, low coefficient of friction, and good chemical stability. It is widely used in filtration and separation fields such as solid-liquid separation, membrane contactors, and membrane reactors. The production method of e-PTFE generally involves processes such as paste extrusion, degreasing, and stretching.

[0003] Tubular membranes are widely used in the filtration and separation membrane field due to their high packing density, small footprint, and low cost. However, due to the unique characteristics of the stretching process, most tubular membranes on the market are prepared using the uniaxial stretching method. This method produces polytetrafluoroethylene hollow fiber membranes with larger pore sizes and lower bubble points, making them unsuitable for high-precision separation and filtration. It only yields a pore structure with alternating axial filaments and nodes, and the axial pore length is much greater than the radial pore length. Biaxial stretching, on the other hand, can produce a three-dimensional, double-batch network structure with comparable axial and radial dimensions, which is more conducive to the control of the filtration and separation process.

[0004] In the prior art, researchers have focused on methods for preparing biaxially stretched tubular separation membranes, but these methods all have some drawbacks. For example, Chinese patent document CN104190268A discloses a biaxial stretching device and method for polytetrafluoroethylene (PTFE) hollow fiber membranes. This invention extends the mandrel and increases its diameter after the high-temperature zone. The unstretched product is pushed by the force of the extruder through the extended mandrel, passing over the area with the increased mandrel diameter to complete the transverse stretching. Then, it is wound around the speed-regulating guide wheel for longitudinal stretching, thereby achieving biaxial stretching and improving the porosity of the PTFE hollow fiber membrane. However, the expanded mandrel may cause quality instability issues. In addition, the sudden and brief stretching action of the speed-regulating guide wheel can lead to poor performance in the main application direction of the tubular membrane.

[0005] Chinese patent document CN102266725A discloses a polytetrafluoroethylene (PTFE) hollow fiber membrane and its preparation method. The PTFE hollow fiber membrane comprises PTFE hollow fibers with a pore size range of 0.5-2 μm and at least one microporous PTFE flat sheet membrane layer with a pore size range of 0.02-0.5 μm and a thickness of 5-100 μm disposed on the outer ring wall of the PTFE hollow fibers. This invention involves wrapping one or more layers of microporous PTFE strip-shaped flat sheet membranes around the outer ring wall of tubular PTFE hollow fibers, followed by heat treatment and sintering at 270-300℃ to form a PTFE hollow fiber membrane for filtration. However, this method involves a cumbersome wrapping process, making it difficult to remove filter residues adhering to the tube wall and the PTFE hollow fiber membrane after filtration, resulting in poor reusability and high cost.

[0006] Chinese patent document CN103481528A discloses a biaxially stretched porous expanded polytetrafluoroethylene (PTFE) hollow tubular membrane and its preparation method. This invention first prepares a biaxially stretched PTFE microporous flat sheet membrane, then winds multiple layers to the target thickness and sintersties them into the finished product. However, this method easily forms dead volume cavities between membrane layers during the rewinding process, making cleaning difficult. Furthermore, it easily causes separation between layers during use, affecting the membrane's mechanical properties. Summary of the Invention

[0007] This invention provides a continuous production equipment for e-PTFE biaxially oriented tubular membranes, which has a high degree of automation and can achieve two axial stretchings and one radial stretching of the tubular body to prepare e-PTFE biaxially oriented tubular membranes with three-dimensional fluffy membrane pores, more uniform distribution of nodes and fibers, higher porosity, and better retention effect.

[0008] The specific technical solution adopted is as follows:

[0009] A continuous production line for e-PTFE biaxially oriented tubular film includes a control system, a conveying device, an extruder, a degreasing and stretching box, a traction machine, a fixed jacket, a jacket assembly device, a radially stretching mandrel, a mandrel assembly device, a high-temperature stretching box, a mandrel disassembly device, and a jacket disassembly device.

[0010] The extruder is used to extrude a preform containing polytetrafluoroethylene into a tubular shape; the degreasing and stretching box performs high-temperature degreasing and the first axial stretching on the tubular shape;

[0011] After the first axial stretch, the traction machine pulls the tubular body and assembles it with the fixed sleeve under the action of the clamp fitting device to fix the tubular body;

[0012] The core rod assembly device engages a tubular body with a fixed sleeve and a radially tensioning core rod to radially stretch the tubular body;

[0013] After the tubular body is subjected to a second axial stretching and shaping in a high-temperature stretching chamber under radial stretching, it is separated from the radial stretching core rod by the action of the core rod disassembly device and the jacket disassembly device, and the fixed jacket is removed to obtain the e-PTFE biaxially stretched tubular membrane.

[0014] The control system is communicatively connected to the conveying device, the extruder, the degreasing and stretching box, the traction machine, the fixed jacket, the jacket assembly device, the radial stretching mandrel, the mandrel assembly device, the high-temperature stretching box, the mandrel disassembly device, and the jacket disassembly device.

[0015] The extruder, degreasing stretching box, traction machine, fixed jacket, jacket assembly device, radial stretching mandrel, mandrel assembly device, high temperature stretching box, mandrel disassembly device and jacket disassembly device are all connected by a conveying device;

[0016] The radial tension mandrel includes an integrally connected column and a cone, with evenly distributed vent holes on its surface. The diameter of the cone decreases as it moves away from the column.

[0017] The device of this invention can achieve bidirectional stretching of a tubular body first in the axial direction, then in the radial direction, and then in the axial direction again. Through the action of the fixed sleeve and the radial stretching core rod, it overcomes the rebound force during high-temperature stretching, ensuring the high mechanical properties of the e-PTFE bidirectional stretched tubular membrane in the main direction and its membrane pore structure.

[0018] Preferably, the fixing sleeve includes a clamping collar and a sleeve, and the clamping collar and the sleeve are engaged by threads or bayonet.

[0019] Preferably, the conveying device includes a first conveying device and a second conveying device. The first conveying device is used to automatically convey the fixed jacket, and the second conveying device is used to convey the tubular body in a radially stretched state through a high-temperature stretching chamber.

[0020] Preferably, the core rod assembly device includes a fixing accessory, which cooperates with a fixing sleeve to perform a second axial stretching on the tubular body in the radially stretched state by adjusting the fixing accessory.

[0021] Preferably, the outer diameter of the cylindrical portion of the radial tensioning mandrel is adjustable, and radial tension of the tubular body is achieved by increasing the outer diameter of the cylindrical portion; or the radial tensioning mandrel is made of an elastic material, and its outer diameter expands under the action of a given internal air pressure or hydraulic pressure, thereby achieving radial tension of the tubular body. Under the above preferred conditions, the radial tensioning effect can be improved.

[0022] Preferably, the cone angle of the cone in the radially stretched core rod is <30°, and the length of the column portion in the radially stretched core rod is >1.2 times the length of the tubular body.

[0023] More preferably, the cone angle of the cone in the radial tension core is <10°, and the length of the column portion in the radial tension core is >1.5 times the length of the tubular body; this facilitates the radial tension core passing through the tubular body and the second axial tension.

[0024] The present invention also provides a method for producing an e-PTFE biaxially oriented tubular membrane, comprising the following steps:

[0025] (1) Mix polytetrafluoroethylene powder with liquid lubricant, keep warm in a sealed container, and then press into a blank;

[0026] (2) Using the continuous production equipment for the e-PTFE biaxially stretched tubular film, the billet is extruded into a tubular body and then degreased in a degreasing and stretching box at a temperature of 240-300℃, and then subjected to the first axial stretching at a temperature of 350-380℃. The first axial stretching ratio is 1:1-8.

[0027] (3) After the tubular body is assembled with the fixed clamp after the first axial stretching, the radial stretching core rod passes through the tubular body within 10s-10min. At the same time, the friction is reduced by the air venting through the exhaust hole, so that the tubular body is completely fitted on the outer surface of the cylindrical part of the radial stretching core rod to complete the radial stretching (stop the air supply through the exhaust hole after assembly). The radial stretching ratio is 1:1-8.

[0028] (4) Adjust the fixing accessories so that the radially stretched tubular body is subjected to a second axial stretching in a high-temperature stretching box at 100-400℃. The second axial stretching ratio is 1:1-8. After the second axial stretching, it is separated from the radially stretched core rod. The fixing sleeve is removed to obtain the e-PTFE biaxially stretched tubular membrane.

[0029] Preferably, the average particle size of the polytetrafluoroethylene powder is 50-1000 micrometers, and the liquid lubricant is paraffin wax, petroleum ether, kerosene, etc.; the ratio of polytetrafluoroethylene powder to liquid lubricant is 1-500:1.

[0030] Preferably, in step (2), the first axial stretching ratio is 1:3-4, in step (3), the radial stretching ratio is 1:2.5-4, and in step (4), the second axial stretching ratio is 1:1-3. Under the above parameters, it is beneficial to prepare an e-PTFE biaxially stretched tubular membrane with three-dimensional fluffy membrane pores, more uniform distribution of nodes and fibers, higher porosity, and better retention effect.

[0031] According to the national standard "Determination of Pore Size of Separation Membranes - Bubble Point and Average Flow Rate Method" (GB / T32361-2015), the preferred e-PTFE biaxially stretched tubular membrane has a maximum equivalent pore size of 50 nm-1 μm, an average equivalent pore size of 30 nm-0.8 μm, and a porosity >50%.

[0032] More preferably, the e-PTFE biaxially oriented tubular membrane has a maximum equivalent pore size of 80nm-800nm, an average equivalent pore size of 50nm-500nm, and a porosity of >80%.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] (1) The continuous production equipment for e-PTFE biaxially stretched tubular membrane in this invention can realize two axial stretchings and one radial stretching of the tubular body, and prepare e-PTFE biaxially stretched tubular membrane with three-dimensional fluffy membrane pores, more uniform distribution of nodes and fibers, higher porosity and better retention effect. Moreover, the second axial stretching and radial stretching occur simultaneously, reducing the risk of excessive cracking due to radial stretching and making the nodes more uniform.

[0035] (2) The vent holes set on the radial stretching core rod reduce friction and alleviate axial tension when the tubular body and the radial stretching core rod cooperate with each other, ensuring axial uniformity when the radial stretching core rod is inserted into the tubular membrane. The shape setting of the radial stretching core rod and the specific speed make the tubular body generate axial reshaping while being radially stretched, reforming the polytetrafluoroethylene microfiber, improving elasticity, fiber orientation and pore structure. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of the continuous production equipment for the e-PTFE biaxially oriented tubular membrane.

[0037] Figure 2 This is a schematic diagram of the core rod assembly device.

[0038] Figure 3 This is a schematic diagram of the fixed jacket structure.

[0039] Figure 4 This is a cross-sectional structural diagram of the cylindrical portion of a radially stretched core rod.

[0040] The attached figures are labeled as follows: 1 Control system, 21 First conveying device, 22 Second conveying device, 3 Extruder, 4 Degreasing and stretching box, 5 Traction machine, 6 Fixed clamp, 61 Clamping collar, 62 Sleeve, 7 Clamp assembly device, 8 Radial stretching mandrel, 81 Inner support rod, 82 Inner cantilever, 83 Outer cantilever, 84 Outer support tube, 9 Mandrel assembly device, 91 Fixing accessories, 92 Screw, 93 Motor, 10 High temperature stretching box, 11 Mandrel disassembly device, and 12 Clamp disassembly device. Detailed Implementation

[0041] The present invention will be further illustrated below with reference to the embodiments and accompanying drawings. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0042] like Figure 1 As shown, a continuous production equipment for e-PTFE biaxially oriented tubular film includes a control system 1, a conveying device (including a first conveying device 21 and a second conveying device 22), an extruder 3, a degreasing and stretching box 4, a traction machine 5, a fixed jacket 6, a jacket assembly device 7, a radial stretching mandrel 8, a mandrel assembly device 9, a high-temperature stretching box 10, a mandrel disassembly device 11, and a jacket disassembly device 12.

[0043] The extruder 3 is used to extrude the preform containing polytetrafluoroethylene into a tubular body; the degreasing and stretching box 4 performs high-temperature degreasing and first axial stretching on the tubular body; the traction machine 5 pulls the tubular body after the first axial stretching and assembles it with the fixed jacket 6 under the action of the jacket assembly device 7 to fix the tubular body; the core rod assembly device 9 cooperates with the tubular body with the fixed jacket 6 and the radial stretching core rod 8 to perform radial stretching on the tubular body; after the tubular body is radially stretched and then subjected to a second axial stretching and shaping in the high-temperature stretching box 10, it is separated from the radial stretching core rod under the action of the core rod disassembly device 11 and the jacket disassembly device 12, and the fixed jacket is removed to obtain the e-PTFE biaxially stretched tubular film.

[0044] The control system 1 is communicatively connected to the conveying device, extruder 3, degreasing and stretching box 4, traction machine 5, fixed jacket 6, jacket assembly device 7, radial stretching mandrel 8, mandrel assembly device 9, high temperature stretching box 10, mandrel disassembly device 11, and jacket disassembly device 12.

[0045] The extruder 3, degreasing stretching box 4, traction machine 5, fixed jacket 6, jacket assembly device 7, radial stretching mandrel 8, mandrel assembly device 9, high temperature stretching box 10, mandrel disassembly device 11 and jacket disassembly device 12 are all connected by a conveying device.

[0046] The conveying device includes a first conveying device 21 and a second conveying device 22. The first conveying device 21 is used to automatically convey the fixed jacket 6, and the second conveying device 22 is used to convey the tubular body in a radially stretched state through the high-temperature stretching box 10.

[0047] like Figure 2 As shown, the core rod assembly device 9 includes a fixing accessory 91 (clamping fixing bracket), a screw 92 and a motor 93. The fixing accessory 91 can adjust the distance between the two fixing clamps within a certain range to perform a second axial stretching on the tubular body in the radial stretching state, thereby overcoming the axial springback force during high temperature stretching.

[0048] like Figure 3 As shown, the fixed clamping sleeve 6 includes a clamping ring 61 and a sleeve 62, which are engaged by threads or bayonet.

[0049] The radial tension core rod 8 includes an integrally connected column part and a cone body, with evenly distributed vent holes on its surface. The diameter of the cone body decreases as it moves away from the column part.

[0050] Optionally, the outer diameter of the cylindrical portion of the radial tension mandrel is adjustable, and the cross-sectional structure is as follows: Figure 4 As shown, the variable-diameter cylindrical portion of the radially stretching core rod 8 includes an inner support rod 81, several telescopic cantilever arms, and an outer support tube 84. The outer wall of the inner support rod 81 is connected to the outer support tube 84 via the telescopic cantilever arms. Specifically, the cantilever arms include an inner cantilever arm 82 and an outer cantilever arm 83, which are folded together. Radial stretching of the tubular body is achieved by increasing the outer diameter of the cylindrical portion; or the radially stretching core rod is made of an elastic material, and its outer diameter expands under a given internal air or hydraulic pressure, thus achieving radial stretching of the tubular body.

[0051] The cone angle of the cone in the radially stretched core rod is <30°, and the length of the column portion in the radially stretched core rod is >1.2 times the length of the tubular body.

[0052] Example 1

[0053] (1) Mix polytetrafluoroethylene powder (average particle size of 500μm) with kerosene at a mass ratio of 85:15. After mixing, keep it at 25°C for 2 hours in a sealed container, and then press it into a blank at 25°C.

[0054] (2) Using the continuous production equipment for the e-PTFE biaxially stretched tubular film (the cone angle of the cone in the radial stretching mandrel is 9°), the billet is extruded into a tubular body at 35°C with a compression ratio of 1:500. Then, it is degreased at 280°C in a degreasing and stretching box, and then subjected to the first axial stretching at 370°C. The first axial stretching ratio is 1:3.5.

[0055] (3) After the tubular body is assembled with the fixed clamp after the first axial stretching, the radial stretching core rod passes through the tubular body in 30s. At the same time, the friction is reduced by the air outlet through the exhaust hole, so that the tubular body is completely fitted on the outer surface of the column part of the radial stretching core rod to complete the radial stretching. The radial stretching ratio is 1:3.

[0056] (4) The radially stretched tubular body is passed through a high-temperature stretching box at 390°C and held for 120 seconds while the fixing accessories are adjusted for a second axial stretching. The second axial stretching ratio is 1:1.5. After the second axial stretching, it is separated from the radially stretched core rod and the fixing sleeve is removed to obtain the e-PTFE biaxially stretched tubular membrane.

[0057] Example 2

[0058] The only difference between this embodiment and embodiment 1 is that a radial stretching mandrel with a cone angle of 15° is used instead. In step (3), after the tubular body after the first axial stretching is assembled with the fixing clamp, the radial stretching mandrel passes through the tubular body in 10s. At the same time, the friction is reduced by the air outlet through the exhaust hole, so that the tubular body is completely fitted on the outer surface of the cylindrical part of the radial stretching mandrel to complete the radial stretching. The radial stretching ratio is 1:2. In step (4), the tubular body after radial stretching is passed through a high temperature stretching box at 350°C and held for 60s for the second axial stretching. The second axial stretching ratio is 1:1.2, and the e-PTFE biaxially stretched tubular membrane is obtained.

[0059] Example 3

[0060] The only difference between this embodiment and embodiment 1 is that a radial stretching mandrel with a cone angle of 20° is used instead; in step (3), after the tubular body after the first axial stretching is assembled with the fixing clamp, the radial stretching mandrel passes through the tubular body for 60s, and at the same time, the friction is reduced by the air outlet through the exhaust hole, so that the tubular body is completely fitted on the outer surface of the cylindrical part of the radial stretching mandrel to complete the radial stretching, and the radial stretching ratio is 1:4; in step (4), the tubular body after radial stretching is passed through a high temperature stretching box at 300°C and held for 30s for the second axial stretching, and the second axial stretching ratio is 1:2, to obtain the e-PTFE biaxially stretched tubular membrane.

[0061] Comparative Example 1

[0062] In this embodiment, the tubular body after the first axial stretching in Example 1 is directly used as the tubular membrane for comparison.

[0063] Sample Analysis

[0064] The performance of the e-PTFE tubular membranes in Examples 1-3 and Comparative Example 1 was tested, and the results are shown in Table 1.

[0065] The maximum equivalent pore size and average equivalent pore size of the e-PTFE tubular membrane were tested according to the national standard "Determination of Pore Size of Separation Membranes - Bubble Point and Average Flow Rate Method" (GB / T32361-2015); the porosity was tested according to the weight loss method, i.e., [(Wet membrane tube weight - Dry membrane tube weight) / water density] / membrane tube volume; when a diatomaceous earth suspension with a mass concentration of 1 g / L and a medium particle size of 20-30 μm was filtered under a constant pressure of 15 kPa, the average filtration rate within 5 minutes from the start of filtration was the high turbidity liquid permeability A; and the average filtration rate within 5 minutes after 55 minutes from the start of filtration was the high turbidity liquid permeability B.

[0066] Table 1. Performance of the e-PTFE tubular membranes in Examples 1-3 and Comparative Example 1

[0067]

[0068] The embodiments described above provide a detailed explanation of the technical solutions of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A continuous production line for e-PTFE biaxially oriented tubular membranes, characterized in that, It includes a control system (1), a conveying device, an extruder (3), a degreasing and stretching box (4), a traction machine (5), a fixed jacket (6), a jacket assembly device (7), a radial stretching mandrel (8), a mandrel assembly device (9), a high-temperature stretching box (10), a mandrel disassembly device (11), and a jacket disassembly device (12). The extruder (3) is used to extrude a preform containing polytetrafluoroethylene into a tubular body; the degreasing and stretching box (4) performs high-temperature degreasing and first axial stretching on the tubular body; The traction machine (5) pulls the tubular body after the first axial stretch and assembles it with the fixing sleeve (6) under the action of the clamp fitting device (7) to fix the tubular body; The core rod assembly device (9) engages the tubular body with the fixed sleeve and the radially stretched core rod (8) to perform radial stretching on the tubular body; After the tubular body is subjected to a second axial stretching and shaping in a high-temperature stretching box (10) under radial stretching, it is separated from the radial stretching core rod by the action of the core rod disassembly device (11) and the jacket disassembly device (12), and the fixed jacket is removed to obtain the e-PTFE biaxially stretched tubular membrane. The radial tension core rod (8) includes an integrally connected cylindrical part and a cone, with evenly distributed vent holes on its surface. The diameter of the cone decreases in the direction away from the cylindrical part. The core rod assembly device (9) includes a fixing accessory (91), which cooperates with the fixing sleeve (6). By adjusting the fixing accessory (91), the tubular body in the radially stretched state is subjected to a second axial stretch. The outer diameter of the cylindrical part of the radial tensioning core rod (8) is adjustable, and the radial tension of the tubular body is achieved by increasing the outer diameter of the cylindrical part; or the radial tensioning core rod (8) is made of elastic material, and the outer diameter expands under the action of a given internal air pressure or hydraulic pressure to achieve the radial tension of the tubular body.

2. The continuous production equipment for e-PTFE biaxially oriented tubular membranes according to claim 1, characterized in that, The fixed clamp (6) includes a clamping ring (61) and a sleeve (62), which are engaged by threads or bayonet.

3. The continuous production equipment for e-PTFE biaxially oriented tubular membranes according to claim 1, characterized in that, The conveying device includes a first conveying device (21) and a second conveying device (22). The first conveying device is used to automatically convey the fixed jacket (6), and the second conveying device is used to convey the tubular body in radial tension state through the high temperature tension box (10).

4. The continuous production equipment for e-PTFE biaxially oriented tubular membrane according to claim 1, characterized in that, The cone angle of the cone in the radial tension core rod (8) is <30°, and the length of the column part in the radial tension core rod is >1.2 times the length of the tubular body.

5. A method for producing an e-PTFE biaxially oriented tubular membrane, characterized in that, Includes the following steps: (1) Mix polytetrafluoroethylene powder with liquid lubricant, keep warm in a sealed container, and then press into a blank; (2) Using the continuous production equipment for e-PTFE biaxially stretched tubular film according to any one of claims 1-4, after the billet is extruded into a tubular body, it is first degreased in a degreasing and stretching box (4) at a temperature of 240-300°C, and then subjected to a first axial stretching at a temperature of 350-380°C. The first axial stretching ratio is 1:1-8. (3) After the tubular body is assembled with the fixed sleeve (6) after the first axial stretching, the radial stretching core rod (8) passes through the tubular body within 10s-10min. At the same time, the friction is reduced by the air outlet through the exhaust hole, so that the tubular body is completely fitted on the outer surface of the column part of the radial stretching core rod (8) to complete the radial stretching. The radial stretching ratio is 1:1-8. (4) Adjust the fixing accessories (91) so that the radially stretched tubular body is subjected to a second axial stretching in a high temperature stretching box (10) at 100-400℃. The second axial stretching ratio is 1:1-8. After the second axial stretching, it is separated from the radial stretching core rod, and the fixing sleeve is removed to obtain the e-PTFE biaxially stretched tubular membrane.

6. The method for producing e-PTFE biaxially oriented tubular membrane according to claim 5, characterized in that, The average particle size of the polytetrafluoroethylene powder is 50-1000 micrometers, and the liquid lubricant includes paraffin wax, petroleum ether, or kerosene; the ratio of the polytetrafluoroethylene powder to the liquid lubricant is 1-500:

1.

7. The method for producing e-PTFE biaxially oriented tubular membrane according to claim 5, characterized in that, In step (2), the first axial stretching ratio is 1:3-4; in step (3), the radial stretching ratio is 1:2.5-4; and in step (4), the second axial stretching ratio is 1:1-3.

8. The method for producing e-PTFE biaxially oriented tubular membrane according to claim 5, characterized in that, The e-PTFE biaxially stretched tubular membrane has a maximum equivalent pore size of 50 nm-1 μm, an average equivalent pore size of 30 nm-0.8 μm, and a porosity of >50%.

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