A preparation method of large-pore polytetrafluoroethylene membrane and large-pore polytetrafluoroethylene membrane

Abstract

A method for preparing a large-pore polytetrafluoroethylene membrane comprises the following steps: S1 mixing, S2 aging, S3 compacting, S4 calendering, S5 degreasing, S6 stretching, and S7 heat setting. Step S1 mixing involves uniformly mixing polytetrafluoroethylene dispersion resin powder, an extrusion aid, and pure water to form a polytetrafluoroethylene material, wherein the mass of the pure water is 1% to 3% of the total mass of the pure water and the extrusion aid. The polytetrafluoroethylene membrane obtained using this preparation method has a maximum pore size range of 30 to 70 microns, breaking the limitation of conventional polytetrafluoroethylene membranes that the pore size is difficult to exceed 10 microns. This significantly increases the pore size, resulting in better water flux and significantly improved filtration efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of polytetrafluoroethylene membranes, and in particular to a preparation method of a large-pore polytetrafluoroethylene membrane and a large-pore polytetrafluoroethylene membrane. Background Art

[0002] Filtration membranes primarily include microfiltration, ultrafiltration, nanofiltration, and reverse osmosis membranes. All utilize pressure differentials as a driving force for membrane separation. When a certain pressure differential is applied across the membrane, some solvents and components smaller than the membrane pore size are allowed to pass through, while particles, macromolecules, and salts are retained by the membrane, achieving separation.

[0003] Microfiltration membranes are primarily used to remove suspended solids, microorganisms, and organic matter from liquids while retaining dissolved matter. Microfiltration membranes typically have pore sizes larger than 0.1 micrometers, making them effective at removing larger particles and microorganisms, but unable to remove small molecules such as bacteria and viruses.

[0004] Generally speaking, the larger the pore size of the filter membrane, the lower the filter membrane's ability to retain impurities, because larger pores cannot effectively block smaller particles. However, at the same time, the larger the pore size of the filter membrane, the higher the water flux. This is because a filter membrane with a larger pore size allows more water molecules to pass through, thereby increasing water flux. Therefore, when the particulate impurities that need to be filtered out are large in size, a filter membrane with a larger pore size is often selected. As long as the pore size of the filter membrane is smaller than the size of the particulate impurities themselves, a normal and reliable filtration effect can be ensured. On this basis, the larger the pore size, the further the water flux can be improved, thereby improving filtration efficiency.

[0005] However, the pore size range of most microfiltration membranes is generally between 0.1 microns and 10 microns. Therefore, even when the filter material is particulate impurities with a size much larger than 10 microns, the maximum pore size of the filter membrane that can be selected is only about 10 microns.

[0006] Polytetrafluoroethylene (PTFE) membranes are commonly used in microfiltration. Due to their excellent physical and chemical properties, they play a vital role in numerous industries requiring filtration and separation technologies, enjoying a wide range of applications. PTFE membranes are typically manufactured using a polytetrafluoroethylene dispersion resin through specialized processes such as premixing, extrusion, calendering, and stretching. Their pore sizes typically range from 0.02 to 15 microns. However, conventionally manufactured PTFE membranes typically have a maximum pore size exceeding 10 microns.

[0007] A polytetrafluoroethylene membrane that is easy to prepare and has a larger pore size would certainly have certain market application value. However, the existing technology has not yet studied how to increase the pore size of polytetrafluoroethylene membranes. Therefore, how to obtain polytetrafluoroethylene membranes with larger pore sizes has become an urgent problem to be solved. Summary of the Invention

[0008] In order to overcome the shortcomings of the background technology, the present invention provides a method for preparing a large-pore polytetrafluoroethylene membrane and a large-pore polytetrafluoroethylene membrane.

[0009] The technical solution adopted by the present invention is a method for preparing a large-pore polytetrafluoroethylene membrane, comprising the following steps in sequence: S1 mixing, S2 aging, S3 pressing, S4 calendering, S5 degreasing, S6 stretching and S7 heat setting.

[0010] Among them, step S1 mixing is to uniformly mix the polytetrafluoroethylene dispersion resin powder, extrusion aid and pure water to form a polytetrafluoroethylene material, the mass of pure water is 1% to 3% of the total mass of pure water and extrusion aid, and the total mass of pure water and extrusion aid is 20% to 30% of the mass of the polytetrafluoroethylene dispersion resin powder.

[0011] The aging treatment temperature in step S2 is 40-80°C and the time is 8-12 hours.

[0012] Step S3 of the green compaction process includes pre-pressing and pushing. The aging raw material is first pre-pressed at a pressing speed of 50 to 100 mm / min to obtain a pre-pressed green body, and then the pre-pressed green body is pushed at a pushing speed of 200 to 400 mm / min to obtain a PTFE rod.

[0013] The temperature of the pressing rollers in step S4 is 40-60°C.

[0014] The degreasing temperature in step S5 is 200°C.

[0015] Step S6 stretching includes longitudinal stretching and transverse stretching in sequence, wherein the stretching ratio of the longitudinal stretching is 4 to 6 times; and the stretching ratio of the transverse stretching is 8 to 12 times.

[0016] The heat setting temperature in step S7 is 320-340° C., and the heat setting time is 30-60 seconds.

[0017] In the above preparation method, a small amount of pure water is additionally added at the same time as the extrusion aid is added, and the polytetrafluoroethylene dispersed resin powder, the extrusion aid, and the pure water are uniformly mixed. The extrusion aid can uniformly penetrate into the polytetrafluoroethylene resin, thereby reducing frictional resistance while increasing adhesion between polytetrafluoroethylene particles. Pure water and the extrusion aid are immiscible with each other. After mixing, water molecules can be evenly distributed between polytetrafluoroethylene particles, thereby increasing the distance between polytetrafluoroethylene particles and ultimately achieving the purpose of increasing the pore size.

[0018] A large-pore polytetrafluoroethylene membrane is prepared by the above-mentioned preparation method, and its maximum pore diameter can reach 30 microns to 70 microns.

[0019] The present invention has the beneficial effect of adding a small amount of pure water for uniform mixing compared to conventional PTFE membrane preparation methods. This pure water increases the spacing between PTFE particles, thereby increasing the pore size. The large-pore PTFE membrane produced using the present invention has a maximum pore size of 30 to 70 microns, breaking the limitation of conventional PTFE membranes that pores cannot exceed 10 microns. This significantly increases the pore size, resulting in better water flux and significantly improved filtration efficiency. DETAILED DESCRIPTION

[0020] The technical solution of the present invention will be further described below with reference to the embodiments. Example 1

[0021] A method for preparing a large-pore polytetrafluoroethylene membrane comprises the following steps:

[0022] S1 Mixing: Add 10 kg of polytetrafluoroethylene (PTFE) dispersion resin powder, 1.98 kg of extrusion aid, and 0.02 kg of pure water to a double-cone mixer. Rotate the mixer clockwise for 20 minutes, let it rest for 3 minutes, and then rotate it counterclockwise for 20 minutes. The mixing temperature is 15°C. The polytetrafluoroethylene (PTFE) dispersion resin powder, extrusion aid, and pure water are uniformly mixed to form a polytetrafluoroethylene material. The weight ratio of pure water to extrusion aid is 1:99. The extrusion aid is preferably kerosene.

[0023] S2 aging: placing the uniformly mixed polytetrafluoroethylene material in an oven for aging at a temperature of 40° C. for 12 hours.

[0024] S3 pressing: The aging treated polytetrafluoroethylene material is pre-pressed at a pressing speed of 75 mm / min to obtain a pre-pressed green body, and then the obtained pre-pressed green body is pushed at a pushing speed of 300 mm / min to obtain a PTFE rod.

[0025] S4 calendering: calendering the prepared PTFE rod material, with the temperature of the pressing roller being 40° C., and obtaining the base tape after calendering.

[0026] S5 Degreasing: Place the calendered base tape into a degreasing machine for heat treatment at 200°C to remove the extrusion aid and pure water.

[0027] S6 stretching: The degreased base tape is stretched, and the stretching process includes longitudinal stretching and transverse stretching in sequence to obtain a biaxially stretched base film. The longitudinal stretching ratio is 4 times, and the transverse stretching ratio is 11 times.

[0028] S7 heat setting: The stretched film is heat-set at a temperature of 330°C for 30 seconds.

[0029] After the polytetrafluoroethylene membrane is prepared by the above method, three samples are taken from different parts of the polytetrafluoroethylene membrane, and then the pore sizes of the three samples are measured.

[0030] Through pore size measurement, it was found that the maximum pore size of the first sample was approximately 32 microns, the maximum pore size of the second sample was approximately 30 microns, and the maximum pore size of the third sample was approximately 30 microns. Example 2

[0031] A large-pore polytetrafluoroethylene membrane, the preparation method of which comprises the following steps:

[0032] S1 Mixing: Add 10 kg of polytetrafluoroethylene (PTFE) dispersion resin powder, 2.165 kg of extrusion aid, and 0.035 kg of pure water to a double-cone mixer. Rotate the mixer clockwise for 20 minutes, let it rest for 3 minutes, and then rotate it counterclockwise for 20 minutes. The mixing temperature is 15°C. The polytetrafluoroethylene (PTFE) dispersion resin powder, extrusion aid, and pure water are uniformly mixed to form a polytetrafluoroethylene material. The weight ratio of pure water to extrusion aid is approximately 1.5:98.5. The extrusion aid is preferably kerosene.

[0033] S2 aging: placing the uniformly mixed polytetrafluoroethylene material in an oven for aging at a temperature of 50° C. for 11 hours.

[0034] S3 pressing: The aging treated polytetrafluoroethylene material is pre-pressed at a pressing speed of 60 mm / min to obtain a pre-pressed green body, and then the obtained pre-pressed green body is pushed at a pushing speed of 250 mm / min to obtain a PTFE rod material.

[0035] S4 calendering: calender the prepared PTFE rod material with the temperature of the pressing roller being 50° C. to obtain a base tape.

[0036] S5 Degreasing: Place the calendered base tape into a degreasing machine for heat treatment at 200°C to remove the extrusion aid and pure water.

[0037] S6 stretching: The degreased base tape is stretched, the stretching process sequentially including longitudinal stretching and transverse stretching to obtain a biaxially stretched base film. The longitudinal stretching has a stretching ratio of 5 times, and the transverse stretching has a stretching ratio of 10 times.

[0038] S7 heat setting: The stretched film is heat-set at a temperature of 320°C and a heat-setting time of 600s.

[0039] After the polytetrafluoroethylene membrane is prepared by the above method, three samples are taken from different parts of the polytetrafluoroethylene membrane, and then the pore sizes of the three samples are measured.

[0040] After pore size measurement, it was found that the maximum pore size of the first sample was approximately 42 microns, the maximum pore size of the second sample was approximately 39 microns, and the maximum pore size of the third sample was approximately 38 microns. Example 3

[0041] A large-pore polytetrafluoroethylene membrane, the preparation method of which comprises the following steps:

[0042] S1 Mixing: Add 10 kg of polytetrafluoroethylene (PTFE) dispersion resin powder, 2.35 kg of extrusion aid, and 0.05 kg of pure water to a double-cone mixer. Rotate the mixer clockwise for 20 minutes, let it rest for 3 minutes, and then rotate it counterclockwise for 20 minutes. The mixing temperature is 15°C. The polytetrafluoroethylene (PTFE) dispersion resin powder, extrusion aid, and pure water are uniformly mixed to form a polytetrafluoroethylene material. The weight ratio of pure water to extrusion aid is approximately 2:98. The extrusion aid is preferably kerosene.

[0043] S2 aging: placing the uniformly mixed polytetrafluoroethylene material in an oven for aging at a temperature of 60° C. for 10 hours.

[0044] S3 pressing: The aging treated polytetrafluoroethylene material is pre-pressed at a pressing speed of 50 mm / min to obtain a pre-pressed green body, and then the obtained pre-pressed green body is pushed at a pushing speed of 200 mm / min to obtain a PTFE rod material.

[0045] S4 calendering: calender the prepared PTFE rod material with the temperature of the pressing roller being 50° C. to obtain a base tape.

[0046] S5 Degreasing: Place the calendered base tape into a degreasing machine for heat treatment at 200°C to remove the extrusion aid and pure water.

[0047] S6 stretching: The degreased base tape is stretched, the stretching process sequentially including longitudinal stretching and transverse stretching to obtain a biaxially stretched base film. The longitudinal stretching has a stretching ratio of 4 times, and the transverse stretching has a stretching ratio of 12 times.

[0048] S7 heat setting: The stretched film is heat-set at a temperature of 330°C and a heat-setting time of 40 seconds.

[0049] After the polytetrafluoroethylene membrane is prepared by the above method, three samples are taken from different parts of the polytetrafluoroethylene membrane, and then the pore sizes of the three samples are measured.

[0050] Through pore size measurement, it was found that the maximum pore size of the first sample was approximately 53 microns, the maximum pore size of the second sample was approximately 50 microns, and the maximum pore size of the third sample was approximately 51 microns. Example 4

[0051] A large-pore polytetrafluoroethylene membrane, the preparation method of which comprises the following steps:

[0052] S1 Mixing: Add 10 kg of polytetrafluoroethylene (PTFE) dispersion resin powder, 2.73 kg of extrusion aid, and 0.07 kg of pure water to a double-cone mixer. Rotate the mixer clockwise for 20 minutes, let it rest for 3 minutes, and then rotate it counterclockwise for 20 minutes. The mixing temperature is 15°C. The polytetrafluoroethylene (PTFE) dispersion resin powder, extrusion aid, and pure water are uniformly mixed to form a polytetrafluoroethylene material. The weight ratio of pure water to extrusion aid is 2.5:97.5. The extrusion aid is kerosene.

[0053] S2 aging: placing the uniformly mixed polytetrafluoroethylene material in an oven for aging at a temperature of 70° C. for 9 hours.

[0054] S3 pressing: The aging treated polytetrafluoroethylene material is pre-pressed at a pressing speed of 100 mm / min to obtain a pre-pressed green body, and then the obtained pre-pressed green body is pushed at a pushing speed of 400 mm / min to obtain a PTFE rod material.

[0055] S4 calendering: calender the prepared PTFE rod material with the temperature of the pressing roller being 60° C. to obtain a base tape.

[0056] S5 Degreasing: Place the calendered base tape into a degreasing machine for heat treatment at 200°C to remove the extrusion aid and pure water.

[0057] S6 stretching: The degreased base tape is stretched, the stretching process sequentially including longitudinal stretching and transverse stretching to obtain a biaxially stretched base film. The longitudinal stretching has a stretching ratio of 5 times, and the transverse stretching has a stretching ratio of 8 times.

[0058] S7 heat setting: The stretched film is heat-set at a temperature of 330°C for 60 seconds.

[0059] After the polytetrafluoroethylene membrane is prepared by the above method, three samples are taken from different parts of the polytetrafluoroethylene membrane, and then the pore sizes of the three samples are measured.

[0060] After pore size measurement, it was found that the maximum pore size of the first sample was approximately 59 microns, the maximum pore size of the second sample was approximately 61 microns, and the maximum pore size of the third sample was approximately 59 microns. Example 5

[0061] A large-pore polytetrafluoroethylene membrane, the preparation method of which comprises the following steps:

[0062] S1 Mixing: Add 10 kg of polytetrafluoroethylene (PTFE) dispersion resin powder, 2.91 kg of extrusion aid, and 0.09 kg of pure water to a double-cone mixer. Rotate the mixer clockwise for 20 minutes, let it rest for 3 minutes, and then rotate it counterclockwise for 20 minutes. The mixing temperature is 15°C. The polytetrafluoroethylene (PTFE) dispersion resin powder, extrusion aid, and pure water are uniformly mixed to form a polytetrafluoroethylene material. The weight ratio of pure water to extrusion aid is 3:97. The extrusion aid is kerosene.

[0063] S2 aging: placing the uniformly mixed polytetrafluoroethylene material in an oven for aging at a temperature of 80° C. for 8 hours.

[0064] S3 pressing: The aging treated polytetrafluoroethylene material is pre-pressed at a pressing speed of 80 mm / min to obtain a pre-pressed green body, and then the obtained pre-pressed green body is pushed at a pushing speed of 320 mm / min to obtain a PTFE rod material.

[0065] S4 calendering: calender the prepared PTFE rod material with the temperature of the pressing roller being 60° C. to obtain a base tape.

[0066] S5 Degreasing: Place the calendered base tape into a degreasing machine for heat treatment at 200°C to remove the extrusion aid and pure water.

[0067] S6 stretching: The degreased base tape is stretched, and the stretching process includes longitudinal stretching and transverse stretching in sequence to obtain a biaxially stretched base film. The longitudinal stretching has a stretching ratio of 6 times, and the transverse stretching has a stretching ratio of 9 times.

[0068] S7 heat setting: The stretched film is heat-set at a temperature of 340°C for 30 seconds.

[0069] After the polytetrafluoroethylene membrane is prepared by the above method, three samples are taken from different parts of the polytetrafluoroethylene membrane, and then the pore sizes of the three samples are measured.

[0070] After pore size measurement, it was found that the maximum pore size of the first sample was approximately 68 microns, the maximum pore size of the second sample was approximately 70 microns, and the maximum pore size of the third sample was approximately 65 microns.

[0071] Compared with the existing conventional preparation method of polytetrafluoroethylene membrane, the preparation methods of the above five embodiments all add a small amount of pure water during the mixing process, that is, the polytetrafluoroethylene dispersed resin powder, extrusion aid and pure water are evenly mixed. Among them, the mass of the added pure water accounts for 1% to 3% of the total mass of pure water and extrusion aid.

[0072] During the preparation of polytetrafluoroethylene membranes, adding extrusion aids can increase lubricity, reduce thrust resistance and improve production efficiency. That is, the extrusion aids can evenly penetrate into the polytetrafluoroethylene resin, reducing friction resistance while increasing the adhesion between polytetrafluoroethylene particles, thereby ensuring the preparation and molding of the polytetrafluoroethylene membrane.

[0073] In addition to kerosene as used in the embodiment, other extrusion aids such as paraffin oil may be used instead of the extrusion aid. However, pure water and these extrusion aids are generally immiscible with each other. When the polytetrafluoroethylene dispersion resin powder, the extrusion aid, and the pure water are evenly mixed, the pure water cannot dissolve in the polytetrafluoroethylene dispersion resin powder and the extrusion aid and can only be evenly distributed between the polytetrafluoroethylene particles. This increases the spacing between the polytetrafluoroethylene particles, thereby ultimately achieving the purpose of increasing the pore size.

[0074] The five examples described above demonstrate that the maximum pore diameter of the prepared PTFE membrane is significantly larger than that of conventional PTFE membranes. Furthermore, the pore diameter increases with increasing amounts of pure water. This is because more pure water increases the number of water molecules between PTFE particles, and the spacing between them also increases. Of course, the amount of pure water should not be too high, as it can prevent the PTFE particles from adhering reliably and hindering the proper preparation and molding of the PTFE membrane. At the same time, the amount of pure water should not be too low, as it can easily lead to uneven distribution of water molecules. An optimal amount of pure water is 1% to 3% of the total mass of pure water and extrusion aid.

[0075] Except for the additional addition of pure water during mixing in step S1, the other steps include S2 aging, S3 pressing, S4 calendering, S5 degreasing, S6 stretching and S7 heat setting. In fact, there is no substantial difference from the existing conventional technology and it is only a preferred option.

[0076] The aging treatment temperature in step S2 is 40-80° C. and the time is 8-12 hours to ensure that the extrusion aid can be evenly penetrated into the polytetrafluoroethylene resin.

[0077] Step S3, the green compaction process, includes pre-pressing and pushing. The aged raw material is first pre-pressed at a pressing speed of 50 to 100 mm / min to obtain a pre-pressed green body. The pre-pressed green body is then pushed at a pushing speed of 200 to 400 mm / min to obtain a PTFE rod. Pre-pressing is first performed at a lower pressing speed to ensure that air can slowly escape. Then, pushing is performed at a faster pushing speed to ensure uniform compaction of the material, avoid the generation of bubbles and defects, and thus improve the strength of the membrane.

[0078] The temperature of the pressing rollers in step S4 is 40-60°C.

[0079] The degreasing temperature in step S5 is 200° C. to reliably remove the extrusion aid and pure water.

[0080] Step S6 stretching includes longitudinal stretching and transverse stretching in sequence, wherein the stretching ratio of the longitudinal stretching is 4 to 6 times; the stretching ratio of the transverse stretching is 8 to 12 times, so as to ensure uniform stretching of the polytetrafluoroethylene film.

[0081] The heat setting temperature in step S7 is 320-340° C. and the heat setting time is 30-60 seconds, which ensures that the polytetrafluoroethylene membrane structure is stable and reliable, reduces defects, and ensures good product quality.

[0082] The large-pore polytetrafluoroethylene membrane prepared by the preparation method of the present invention has a maximum pore size range of 30 microns to 70 microns, breaking the limitation that the pore size of existing conventional polytetrafluoroethylene membranes is difficult to exceed 10 microns, greatly increasing the pore size, and can be used in scenarios where larger-sized particles are filtered. It has better water flux and can greatly improve filtration efficiency.

[0083] Technical personnel should note: Although the present invention has been described according to the above specific implementation methods, the inventive concept of the present invention is not limited to this invention. Any modification using the inventive concept will be included in the scope of protection of this patent right.

Claims

1. A method for preparing a large-pore polytetrafluoroethylene membrane, comprising the following steps: S1 mixing, S2 aging, S3 pressing, S4 calendering, S5 degreasing, S6 stretching, and S7 heat setting; characterized in that: In step S1, the mixing step is to uniformly mix the polytetrafluoroethylene dispersed resin powder, the extrusion aid, and pure water to form a polytetrafluoroethylene material, wherein the mass of the pure water is 1% to 3% of the total mass of the pure water and the extrusion aid.

2. The method for preparing a large-pore polytetrafluoroethylene membrane according to claim 1, characterized in that: The total mass of the pure water and the extrusion aid is 20% to 30% of the mass of the polytetrafluoroethylene dispersion resin powder.

3. The method for preparing a large-pore polytetrafluoroethylene membrane according to claim 1, characterized in that: The aging treatment temperature in step S2 is 40-80°C and the time is 8-12 hours.

4. The method for preparing a large-pore polytetrafluoroethylene membrane according to claim 1, wherein: Step S3 of the green compaction process includes pre-pressing and pushing. The aging raw material is first pre-pressed at a pressing speed of 50 to 100 mm / min to obtain a pre-pressed green body, and then the pre-pressed green body is pushed at a pushing speed of 200 to 400 mm / min to obtain a PTFE rod.

5. The method for preparing a large-pore polytetrafluoroethylene membrane according to claim 1, characterized in that: The temperature of the pressing rollers in step S4 is 40-60°C.

6. The method for preparing a large-pore polytetrafluoroethylene membrane according to claim 1, characterized in that: The degreasing temperature in step S5 is 200°C.

7. The method for preparing a large-pore polytetrafluoroethylene membrane according to claim 1, characterized in that: Step S6 stretching includes longitudinal stretching and transverse stretching in sequence, wherein the stretching ratio of the longitudinal stretching is 4 to 6 times; and the stretching ratio of the transverse stretching is 8 to 12 times.

8. The method for preparing a large-pore polytetrafluoroethylene membrane according to claim 1, characterized in that: The heat setting temperature in step S7 is 320-340° C., and the heat setting time is 30-60 seconds.

9. A large-pore polytetrafluoroethylene membrane prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The maximum pore size of the polytetrafluoroethylene membrane is 30 microns to 70 microns.