Preparation method of large-aperture polytetrafluoroethylene membrane and large-aperture polytetrafluoroethylene membrane

Abstract

The invention discloses a preparation method of a large-aperture polytetrafluoroethylene film. The preparation method comprises the following steps in sequence: S1, mixing materials; S2, curing; S3, compacting; the material mixing in the step S1 is that polytetrafluoroethylene dispersion resin powder, an extrusion aid and pure water are uniformly mixed to form a polytetrafluoroethylene material, and the mass of the pure water is 1%-3% of the total mass of the pure water and the extrusion aid. According to the polytetrafluoroethylene membrane obtained by adopting the preparation method, the maximum aperture range can reach 30-70 microns, the limitation that the aperture of the conventional polytetrafluoroethylene membrane is difficult to exceed 10 microns is broken through, and the aperture size is greatly increased, so that the polytetrafluoroethylene membrane has better water flux and can greatly improve the filtering 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 mainly include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes. All of them are membrane separation technologies that use pressure difference as a driving force. When a certain pressure difference is applied on both sides of the membrane, some solvents and components smaller than the membrane pore size can pass through the membrane, while particles, macromolecules, salts, etc. are retained by the membrane, thereby achieving the purpose of separation.

[0003] Among them, the main function of microfiltration membrane is to remove suspended matter, microorganisms and organic matter from liquids while retaining dissolved matter. The pore size of microfiltration membrane is generally larger than 0.1 micron, which makes it effective in removing larger particles and microorganisms, but cannot 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 a larger pore size cannot effectively block smaller particles. However, at the same time, the larger the pore size of the filter membrane, the greater the water flux. This is because a filter membrane with a larger pore size can allow more water molecules to pass through, thereby increasing the water flux. Therefore, when the particle impurities that need to be filtered out are large in size, a filter membrane with a larger pore size is often chosen, because as long as the pore size of the filter membrane can be guaranteed to be smaller than the size of the particle impurities themselves, a normal and reliable filtering effect can be ensured. On this basis, as long as the pore size is larger, the water flux can be further increased, and the filtering efficiency can be improved.

[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) membrane is a commonly used microfiltration membrane. Due to its excellent physical and chemical properties, it plays an important role in many industries that require filtration and separation technology, and has a very wide range of applications. Polytetrafluoroethylene membranes are usually made of polytetrafluoroethylene dispersed resin, and are produced and processed through special processes such as premixing, extrusion, calendering, and stretching. The pore size range is generally between 0.02 microns and 15 microns. However, in fact, the maximum pore size of polytetrafluoroethylene membranes prepared by existing conventional methods is generally difficult to exceed 10 microns.

[0007] If there is a polytetrafluoroethylene membrane that is easy to prepare and has a larger pore size, it must have certain market application value. However, there is no research in the prior art on how to increase the pore size of polytetrafluoroethylene membranes. Therefore, how to obtain a polytetrafluoroethylene membrane with a larger pore size 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 dispersed resin powder, extrusion aid and pure water to form a polytetrafluoroethylene material, the mass of pure water is 1%~3% of the total mass of pure water and extrusion aid, and the total mass of pure water and extrusion aid is 20%~30% of the mass of the polytetrafluoroethylene dispersed resin powder.

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

[0012] Step S3 of pressing 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 body, and then the obtained pre-pressed body is pushed at a pushing speed of 200 to 400 mm / min to obtain a PTFE rod.

[0013] The temperature of the calendering 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 multiple of the longitudinal stretching is 4 to 6 times; and the stretching multiple 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 while adding the extrusion aid, and the polytetrafluoroethylene dispersed resin powder, the extrusion aid and the pure water are uniformly mixed, wherein the extrusion aid can be uniformly penetrated into the polytetrafluoroethylene resin, while reducing the friction resistance, it can also increase the adhesion between the polytetrafluoroethylene particles, while the pure water and the extrusion aid are immiscible with each other, and after mixing, the water molecules can be uniformly distributed between the polytetrafluoroethylene particles, thereby increasing the distance between the polytetrafluoroethylene particles, and finally 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 size can reach 30 microns to 70 microns.

[0019] The beneficial effect of the present invention is that compared with the conventional preparation method of the existing polytetrafluoroethylene membrane, a small amount of pure water is added for uniform mixing, and the pure water can increase the spacing between the polytetrafluoroethylene particles, thereby achieving the purpose of increasing the pore size. The large-pore polytetrafluoroethylene membrane prepared by the preparation method of the present invention can have a maximum pore size of 30 microns to 70 microns, breaking the limitation that the pore size of the conventional polytetrafluoroethylene membrane is difficult to exceed 10 microns, greatly increasing the pore size, thereby having a better water flux, and can greatly improve the filtration efficiency. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described below in conjunction with embodiments. Example 1

[0021] A method for preparing a large-pore polytetrafluoroethylene membrane comprises the following steps: S1 Mixing: Add 10kg of polytetrafluoroethylene dispersion resin powder, 1.98kg of extrusion aid and 0.02kg of pure water into a double cone mixer, rotate clockwise for 20min, stand still for 3min, and then rotate counterclockwise for 20min. The mixing temperature is 15°C. The polytetrafluoroethylene 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, and the extrusion aid is specifically selected from kerosene.

[0022] S2 Ripening: The uniformly mixed polytetrafluoroethylene material is placed in an oven for aging, the aging treatment temperature is 40° C., and the time is 12 hours.

[0023] S3 pressing: the aging treated polytetrafluoroethylene material is pre-pressed at a pressing speed of 75 mm / min to obtain a pre-pressed body, and then the obtained pre-pressed body is pushed at a pushing speed of 300 mm / min to obtain a PTFE rod.

[0024] S4 calendering: the prepared PTFE rod material is calendered, the temperature of the pressing roller is 40°C, and the base tape is obtained after calendering.

[0025] S5 degreasing: The calendered base tape is placed in a degreasing machine for heat treatment at 200°C to remove the extrusion aid and pure water.

[0026] S6 stretching: the degreased base tape is stretched, the stretching process includes longitudinal stretching and transverse stretching in sequence, to obtain a biaxially stretched base film. The longitudinal stretching has a stretching multiple of 4 times; the transverse stretching has a stretching multiple of 11 times.

[0027] S7 heat setting: The stretched film is heat set at a temperature of 330°C and a heat setting time of 30 seconds.

[0028] 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.

[0029] After 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

[0030] A large-pore polytetrafluoroethylene membrane, the preparation method of which comprises the following steps: S1 Mixing: Add 10kg of polytetrafluoroethylene dispersion resin powder, 2.165kg of extrusion aid and 0.035kg of pure water into a double cone mixer, rotate clockwise for 20min, stand still for 3min, and then rotate counterclockwise for 20min. The mixing temperature is 15°C. The polytetrafluoroethylene 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 about 1.5:98.5, and the extrusion aid is specifically selected from kerosene.

[0031] S2 Ripening: The uniformly mixed polytetrafluoroethylene material is placed in an oven for aging, the aging treatment temperature is 50° C., and the time is 11 hours.

[0032] S3 pressing: the aging treated polytetrafluoroethylene material is pre-pressed at a pressing speed of 60 mm / min to obtain a pre-pressed body, and then the obtained pre-pressed body is pushed at a pushing speed of 250 mm / min to obtain a PTFE rod.

[0033] S4 calendering: the prepared PTFE rod material is calendered, and the temperature of the pressing roller is 50° C. to obtain a base tape.

[0034] S5 degreasing: The calendered base tape is placed in a degreasing machine for heat treatment at 200°C to remove the extrusion aid and pure water.

[0035] S6 stretching: the degreased base tape is stretched, the stretching process includes longitudinal stretching and transverse stretching in sequence, to obtain a biaxially stretched base film. The longitudinal stretching has a stretching multiple of 5 times, and the transverse stretching has a stretching multiple of 10 times.

[0036] S7 heat setting: The stretched film is heat set at a temperature of 320°C and a heat setting time of 600s.

[0037] 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.

[0038] 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

[0039] A large-pore polytetrafluoroethylene membrane, the preparation method of which comprises the following steps: S1 Mixing: Add 10kg of polytetrafluoroethylene dispersion resin powder, 2.35kg of extrusion aid and 0.05kg of pure water into a double cone mixer, rotate clockwise for 20min, stand still for 3min, and then rotate counterclockwise for 20min. The mixing temperature is 15°C. The polytetrafluoroethylene 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 about 2:98, and the extrusion aid is specifically selected from kerosene.

[0040] S2 Ripening: The uniformly mixed polytetrafluoroethylene material is placed in an oven for aging, the aging treatment temperature is 60° C., and the time is 10 hours.

[0041] 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.

[0042] S4 calendering: the prepared PTFE rod material is calendered, and the temperature of the pressing roller is 50° C. to obtain a base tape.

[0043] S5 degreasing: The calendered base tape is placed in a degreasing machine for heat treatment at 200°C to remove the extrusion aid and pure water.

[0044] S6 stretching: the degreased base tape is stretched, the stretching process includes longitudinal stretching and transverse stretching in sequence, to obtain a biaxially stretched base film. The longitudinal stretching has a stretching multiple of 4 times, and the transverse stretching has a stretching multiple of 12 times.

[0045] S7 heat setting: The stretched film is heat set at a temperature of 330°C and a heat setting time of 40 seconds.

[0046] 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.

[0047] After 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

[0048] A large-pore polytetrafluoroethylene membrane, the preparation method of which comprises the following steps: S1 Mixing: Add 10kg of polytetrafluoroethylene dispersion resin powder, 2.73kg of extrusion aid and 0.07kg of pure water into a double cone mixer, rotate clockwise for 20min, stand still for 3min, and then rotate counterclockwise for 20min. The mixing temperature is 15°C. The polytetrafluoroethylene 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, and the extrusion aid is specifically selected from kerosene.

[0049] S2 Ripening: The uniformly mixed polytetrafluoroethylene material is placed in an oven for aging, the aging treatment temperature is 70° C., and the time is 9 hours.

[0050] 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.

[0051] S4 calendering: the prepared PTFE rod material is calendered, and the temperature of the pressing roller is 60° C. to obtain a base tape.

[0052] S5 degreasing: The calendered base tape is placed in a degreasing machine for heat treatment at 200°C to remove the extrusion aid and pure water.

[0053] S6 stretching: the degreased base tape is stretched, the stretching process includes longitudinal stretching and transverse stretching in sequence, to obtain a biaxially stretched base film. The longitudinal stretching has a stretching multiple of 5 times, and the transverse stretching has a stretching multiple of 8 times.

[0054] S7 heat setting: The stretched film is heat set at a temperature of 330°C and a heat setting time of 60s.

[0055] 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.

[0056] 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

[0057] A large-pore polytetrafluoroethylene membrane, the preparation method of which comprises the following steps: S1 Mixing: Add 10kg of polytetrafluoroethylene dispersion resin powder, 2.91kg of extrusion aid and 0.09kg of pure water into a double cone mixer, rotate clockwise for 20min, stand still for 3min, and then rotate counterclockwise for 20min. The mixing temperature is 15°C. The polytetrafluoroethylene 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, and the extrusion aid is specifically selected from kerosene.

[0058] S2 Ripening: The uniformly mixed polytetrafluoroethylene material is placed in an oven for aging, the aging treatment temperature is 80° C., and the time is 8 hours.

[0059] 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.

[0060] S4 calendering: the prepared PTFE rod material is calendered, and the temperature of the pressing roller is 60° C. to obtain a base tape.

[0061] S5 degreasing: The calendered base tape is placed in a degreasing machine for heat treatment at 200°C to remove the extrusion aid and pure water.

[0062] S6 stretching: the degreased base tape is stretched, the stretching process includes longitudinal stretching and transverse stretching in sequence, to obtain a biaxially stretched base film. The longitudinal stretching has a stretching multiple of 6 times, and the transverse stretching has a stretching multiple of 9 times.

[0063] S7 heat setting: The stretched film is heat set at a temperature of 340°C and a heat setting time of 30 seconds.

[0064] 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.

[0065] 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.

[0066] 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, wherein the mass of the added pure water accounts for 1% to 3% of the total mass of the pure water and the extrusion aid.

[0067] In the preparation process of polytetrafluoroethylene film, adding extrusion aid can increase lubricity, reduce thrust resistance and improve production efficiency. That is, the extrusion aid can evenly penetrate into the polytetrafluoroethylene resin, while reducing friction resistance, it can also increase the adhesion between polytetrafluoroethylene particles, ensuring the preparation and molding of the polytetrafluoroethylene film.

[0068] In addition to kerosene in the embodiment, the extrusion aid may be replaced by other extrusion aids such as paraffin oil. Pure water and these extrusion aids are usually immiscible with each other. When the polytetrafluoroethylene dispersed resin powder, the extrusion aid and the pure water are evenly mixed, the pure water cannot be dissolved in the polytetrafluoroethylene dispersed resin powder and the extrusion aid, and can only be evenly distributed between the polytetrafluoroethylene particles. Therefore, the distance between the polytetrafluoroethylene particles is increased, and finally the purpose of increasing the pore size is achieved.

[0069] According to the above five embodiments, the maximum pore size of the prepared polytetrafluoroethylene membrane is significantly larger than the pore size of the existing conventional polytetrafluoroethylene membrane, and the pore size increases with the increase of the amount of pure water, because the more pure water there is, the more water molecules there are between the polytetrafluoroethylene particles, and the larger the spacing between the polytetrafluoroethylene particles. Of course, the amount of pure water should not be too much, because too much pure water will cause the polytetrafluoroethylene particles to be unable to adhere reliably, affecting the normal preparation and molding of the polytetrafluoroethylene membrane. At the same time, the amount of pure water should not be too little, because too little pure water will easily cause the water molecules to be unable to be evenly distributed. When the mass of the added pure water accounts for 1% to 3% of the total mass of the pure water and the extrusion aid, it is the best choice.

[0070] Except for adding pure water during mixing in step S1, other steps include S2 aging, S3 pressing, S4 calendering, S5 degreasing, S6 stretching and S7 heat setting, which are actually no different from the existing conventional technology and are only preferred options.

[0071] The aging treatment temperature in step S2 is 40-80° C. and the time is 8-12 hours, so as to ensure that the extrusion aid can be uniformly infiltrated into the polytetrafluoroethylene resin.

[0072] Step S3, the green sheet pressing 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 sheet, and then the obtained pre-pressed green sheet is pushed at a pushing speed of 200 to 400 mm / min to obtain a PTFE rod. The pre-pressing is first performed at a lower pressing speed to ensure that the air can slowly escape, and then the pushing is performed at a faster pushing speed to ensure that the material is evenly compacted, avoid the generation of bubbles and defects, and thus improve the strength of the membrane.

[0073] The temperature of the calendering rollers in step S4 is 40-60°C.

[0074] The degreasing temperature in step S5 is 200° C. to reliably remove the extrusion aid and pure water.

[0075] Step S6 stretching includes longitudinal stretching and transverse stretching in sequence, wherein the stretching multiple of the longitudinal stretching is 4 to 6 times; and the stretching multiple of the transverse stretching is 8 to 12 times, so as to ensure uniform stretching of the polytetrafluoroethylene film.

[0076] 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 film structure is stable and reliable, reduces defects, and ensures good product quality.

[0077] 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 conventional polytetrafluoroethylene membranes is difficult to exceed 10 microns, greatly increasing the pore size, and being suitable for filtering larger-sized particles. It has better water flux and can greatly improve the filtration efficiency.

[0078] Technical personnel should note that: 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, and 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: Step S1 of mixing is to uniformly mix polytetrafluoroethylene dispersed resin powder, extrusion aid and pure water to form polytetrafluoroethylene material, wherein the mass of pure water is 1% to 3% of the total mass of pure water and 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 dispersed resin powder.

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

4. The method for preparing a large-pore polytetrafluoroethylene membrane according to claim 1, characterized in that: Step S3 of pressing 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 body, and then the obtained pre-pressed 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 calendering 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 multiple of the longitudinal stretching is 4 to 6 times; and the stretching multiple 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.