Porous membrane and manufacturing method and application thereof

Abstract

The invention provides a porous membrane and a manufacturing method and application thereof. The porous membrane comprises a plurality of filtering holes, the porous membrane comprises polyethylene and an antioxidant, and the mass-average molecular weight of the polyethylene is in a range of 1 million to 10 million; wherein the polyethylene comprises a first polyethylene material and a second polyethylene material, the mass-average molecular weight of the first polyethylene material is smaller than that of the second polyethylene material, and the mass ratio of the first polyethylene material in the polyethylene is larger than that of the second polyethylene material in the polyethylene. Therefore, the aperture of the filtering holes of the porous membrane is reduced, the filtering precision of the porous membrane is improved, and the tensile strength of the porous membrane is improved; and moreover, the manufacturing cost of the porous membrane is reduced.

Description

Technical Field

[0001] This application relates to the technical field of membrane materials, and particularly relates to a porous membrane, a manufacturing method thereof, and an application thereof. Background Art

[0002] UPE (Ultra-high molecular Weight Polyethylene) refers to linear structure polyethylene with a mass average molecular weight ≥ 1 million. Due to the properties of UPE such as wear resistance, impact resistance, self-lubrication, and high chemical stability, porous membranes made of UPE for filtration and separation are widely used. The industry usually uses a single type of UPE to make porous membranes, but the pore size of the porous membranes made in this way is relatively large, and the filtration accuracy of the porous membranes is relatively small, which cannot meet the requirements of practical applications. Summary of the Invention

[0003] This application provides a porous membrane, a manufacturing method thereof, and an application thereof. The porous membrane provided by this application is made of a first polyethylene material and a second polyethylene material, which is not only conducive to reducing the pore size of the filtration pores of the porous membrane, improving the filtration accuracy of the porous membrane, and increasing the tensile strength of the porous membrane; moreover, it is conducive to reducing the manufacturing cost of the porous membrane.

[0004] In a first aspect, an embodiment of this application provides a porous membrane. The porous membrane includes a plurality of filtration pores, and the porous membrane includes polyethylene and an antioxidant. The mass average molecular weight of the polyethylene is in the range of 1 million - 10 million; wherein, the polyethylene includes a first polyethylene material and a second polyethylene material, the mass average molecular weight of the first polyethylene material is less than that of the second polyethylene material, and the mass percentage of the first polyethylene material in the polyethylene is greater than that of the second polyethylene material in the polyethylene.

[0005] In the manufacturing process of the porous membrane provided by this application, it is necessary to first obtain a melt by melt blending the first polyethylene material, the second polyethylene material, the antioxidant, and a pore-forming agent, cool the melt to obtain a cast sheet, stretch the cast sheet and then perform extraction to remove the pore-forming agent, and then perform heat setting to obtain the porous membrane; wherein, both the melt and the cast sheet are porous structures. Since the mass average molecular weight of the polyethylene is in the range of 1 million - 10 million, the polyethylene has strong wear resistance, high strength, and stable chemical properties. The porous membrane made of polyethylene with a mass average molecular weight in the range of 1 million - 10 million has high heat resistance, wear resistance, good mechanical properties, and large tensile strength.

[0006] More importantly, compared with the porous membrane made of a single polyethylene material in the prior art, the porous membrane of the present application is made of a first polyethylene material and a second polyethylene material. The weight-average molecular weight of the first polyethylene material is less than that of the second polyethylene material, and the mass percentage of the first polyethylene material in the polyethylene is greater than that of the second polyethylene material in the polyethylene. This design is conducive to appropriately increasing the polyethylene content in the melt during the production process, ensuring that the melt forms pores with smaller diameters, thereby facilitating the formation of smaller pore diameters in the filtration pores of the porous membrane formed, improving the filtration accuracy of the porous membrane, and increasing the tensile strength of the porous membrane. Moreover, it can avoid excessive polyethylene content in the melt during the production process, prevent the melt viscosity from being too high, which increases the difficulty of melt blending of the first polyethylene material, the second polyethylene material, the antioxidant, and the pore-forming agent, and further reduces the requirements for the mechanical equipment for melt blending, thus facilitating the reduction of the production cost of the porous membrane.

[0007] In a possible implementation, the weight-average molecular weights of both the first polyethylene material and the second polyethylene material are in the range of 1 million - 5 million.

[0008] The design that the weight-average molecular weights of both the first polyethylene material and the second polyethylene material are in the range of 1 million - 5 million is conducive to reducing the difficulty of regulating the polyethylene content in the melt, thereby facilitating the adjustment of the pore diameter of the filtration pores of the porous membrane and the adjustment of the filtration accuracy of the porous membrane.

[0009] In a possible implementation, the weight-average molecular weight of the first polyethylene material is in the range of 1 million - 3 million, and the weight-average molecular weight of the second polyethylene is in the range of 4 million - 5 million; the mass percentage of the first polyethylene material in the polyethylene is in the range of 60% - 80%, and the mass percentage of the second polyethylene material in the polyethylene is in the range of 20% - 40%.

[0010] The design that the weight-average molecular weight of the first polyethylene material is in the range of 1 million - 3 million, the weight-average molecular weight of the second polyethylene is in the range of 4 million - 5 million; the mass percentage of the first polyethylene material in the polyethylene is in the range of 60% - 80%, and the mass percentage of the second polyethylene material in the polyethylene is in the range of 20% - 40% ensures a more appropriate polyethylene content in the melt formed, is conducive to the melt forming pores with smaller diameters, is conducive to reducing the pore diameter of the filtration pores of the porous membrane, and is conducive to improving the filtration accuracy of the porous membrane.

[0011] In a possible implementation, in the porous membrane, the total mass percentage of polyethylene is 20% - 50%.

[0012] In the porous membrane, a design with the total mass percentage of polyethylene being 20%-50% ensures an appropriate polyethylene content in the porous membrane, which is beneficial to improving the mechanical properties of the porous membrane. Moreover, on the basis of facilitating the melt blending of the first polyethylene material, the second polyethylene material, the antioxidant, and the pore-forming agent, ensuring that the melt has a higher content of polyethylene is conducive to the formation of more pores in the melt, increasing the porosity of the pores formed by the melt, and further improving the porosity of the filtration pores of the porous membrane, which is beneficial to enhancing the filtration rate and filtration efficiency of the porous membrane.

[0013] In a possible implementation manner, the antioxidant includes at least one of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dibutylhydroxytoluene, and tert-butylhydroquinone.

[0014] The design that the antioxidant includes at least one of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dibutylhydroxytoluene, and tert-butylhydroquinone is beneficial to reducing the risk of calcification of polyethylene during the formation of the melt, improving the processing efficiency of the formed melt, enhancing the processing efficiency of the porous membrane, and reducing the processing cost of the porous membrane.

[0015] In a possible implementation manner, the porous membrane includes a first surface and a second surface arranged opposite to each other, and the filtration pores include a first opening and a second opening arranged opposite to each other. The first opening is located on the first surface, the second opening is located on the second surface, and the pore diameter of the first opening is equal to the pore diameter of the second opening.

[0016] The design that the pore diameter of the first opening is equal to the pore diameter of the second opening is beneficial to simplifying the structure of the porous membrane while ensuring the filtration accuracy and filtration efficiency of the porous membrane, ensuring the simplicity of the structure of the porous membrane, and reducing the processing cost of the porous membrane.

[0017] In a possible implementation manner, the pore diameter of the filtration pores is less than 0.02 μm.

[0018] The design that the pore diameter of the filtration pores is less than 0.02 μm ensures that the porous membrane has a high filtration accuracy. The porous membrane can intercept particles with a particle size of not less than 2 nm, greatly increasing the concentration of particles with a particle size less than 2 nm in the solution filtered through the porous membrane, and ensuring that the porous membrane can filter a solution containing particles with a particle size of not less than 2 nm.

[0019] In a possible implementation manner, among all the filtration pores of the porous membrane per square μm, the proportion of the number of filtration pores with a pore diameter in the range of 16 nm - 20 nm is not less than 90%.

[0020] In all the filtration pores of the porous membrane per square μm, the design where the proportion of the number of filtration pores with pore diameters in the range of 16 nm - 20 nm is not less than 90% ensures that the pore size distribution of the filtration pores of the porous membrane is concentrated. This not only ensures that the porous membrane can stably retain particles with a particle size of not less than 2 nm, guarantees that the porous membrane has better filtration accuracy and filtration efficiency, but also is conducive to increasing the speed of the solution passing through the porous membrane and improving the filtration speed of the porous membrane.

[0021] In a possible implementation, the porosity of the porous membrane is greater than or equal to 50%.

[0022] The porosity of the porous membrane refers to the ratio of the volume of the filtration pores of the porous membrane to the volume of the porous membrane. The design with the porosity of the porous membrane being greater than or equal to 50% ensures that the porous membrane not only has high tensile strength, but also has a fast filtration speed, a large flow rate, a high dirt-holding capacity, can retain more impurity particles, has a long service life, and a low cost.

[0023] In a possible implementation, the pore density of the porous membrane is in the range of 60 pores / μm 2 - 300 pores / μm 2 range.

[0024] The pore density of the porous membrane refers to the number of filtration pores in each square μm of the porous membrane. The design with the pore density of the porous membrane in the range of 60 pores / μm 2 - 300 pores / μm 2 range ensures that the porous membrane not only has high tensile strength, but also has a fast filtration speed, a large flow rate, a high dirt-holding capacity, can retain more impurity particles, has a long service life, and a low cost.

[0025] In a possible implementation, the filtration accuracy of the porous membrane is less than 2 nm, and the filtration efficiency of the porous membrane is greater than 99.9%.

[0026] The filtration accuracy refers to the particle size of the largest particles that the porous membrane can retain. The filtration efficiency refers to the ratio of the number of particles retained by the porous membrane to the number of particles contained in the solution during the process of filtering the solution through the porous membrane. The design with the filtration accuracy of the porous membrane less than 2 nm ensures that the porous membrane can effectively filter out impurity particles with a particle size of not less than 2 nm to ensure that the solution filtered through the porous membrane meets the expectations. The design with the filtration efficiency of the porous membrane greater than 99.9% ensures that the porous membrane can effectively filter out impurity particles and guarantees that the cleanliness of the solution filtered through the porous membrane is higher and more in line with the expectations.

[0027] In a possible implementation, the pure water flux of the porous membrane is greater than 0.1 ml / min / cm 2 .

[0028] The pure water flux refers to the volume of pure water passing through a porous membrane per unit area of the porous membrane per unit time at 25°C under an environment of 0.1 Mpa. The pure water flux of the porous membrane is greater than 0.1 ml / min / cm 2 The design ensures that the porous membrane has a relatively fast filtration speed, a large flow rate, which is conducive to reducing the time cost of filtration.

[0029] In a second aspect, the embodiments of the present application also provide a method for manufacturing a porous membrane. The manufacturing method includes:

[0030] Melting and kneading polyethylene, an antioxidant, and a pore-forming agent and then extruding to obtain a melt;

[0031] After cooling the melt, a cast film is obtained;

[0032] Stretching the cast film and then performing extraction to remove the pore-forming agent, and then performing heat setting to obtain a porous membrane;

[0033] Among them, the weight-average molecular weight of the polyethylene is in the range of 1 million to 10 million. The polyethylene includes a first polyethylene material and a second polyethylene material. The weight-average molecular weight of the first polyethylene material is less than that of the second polyethylene material, and the mass ratio of the first polyethylene material in the polyethylene is greater than the mass ratio of the second polyethylene material in the polyethylene.

[0034] For the porous membrane prepared by the method provided by the present application, during its manufacturing process, it is necessary to first obtain a melt by melting and kneading the first polyethylene material, the second polyethylene material, an antioxidant, and a pore-forming agent, cool the melt to obtain a cast film, stretch the cast film and then perform extraction to remove the pore-forming agent, and then perform heat setting to obtain a porous membrane; among them, both the melt and the cast film are porous structures. Since the weight-average molecular weight of the polyethylene is in the range of 1 million to 10 million, the polyethylene has strong wear resistance, high strength, and stable chemical properties. The porous membrane made of polyethylene with a weight-average molecular weight in the range of 1 million to 10 million has high heat resistance, wear resistance, good mechanical properties, and a large tensile strength.

[0035] More importantly, compared with the porous membrane made of a single polyethylene material in the prior art, the porous membrane of the present application is made of a first polyethylene material and a second polyethylene material. The weight-average molecular weight of the first polyethylene material is less than that of the second polyethylene material, and the mass percentage of the first polyethylene material in polyethylene is greater than that of the second polyethylene material in polyethylene. This design is conducive to appropriately increasing the polyethylene content in the melt during the production process, ensuring that the melt forms pores with smaller diameters, thereby facilitating the formation of smaller pore diameters in the filtration pores of the porous membrane formed, improving the filtration accuracy of the porous membrane, and increasing the tensile strength of the porous membrane. Moreover, it can avoid excessive polyethylene content in the melt during the production process, preventing the melt viscosity from being too high, which may increase the difficulty of melt blending of the first polyethylene material, the second polyethylene material, the antioxidant, and the pore-forming agent, and further lead to high requirements for the mechanical equipment for melt blending. This is beneficial to reducing the production cost of the porous membrane.

[0036] In a possible implementation, the mass percentage of polyethylene in the melt ranges from 10% to 50%.

[0037] The design with the mass percentage of polyethylene in the melt ranging from 10% to 50% ensures a higher polyethylene content in the melt while facilitating the melt blending of the first polyethylene material, the second polyethylene material, the antioxidant, and the pore-forming agent. This is conducive to the melt forming more pores, increasing the porosity of the pores formed by the melt, and further improving the porosity of the filtration pores of the porous membrane, as well as enhancing the filtration speed and efficiency of the porous membrane.

[0038] In a possible implementation, the weight-average molecular weight of the first polyethylene material ranges from 1 million to 3 million, and the weight-average molecular weight of the second polyethylene material ranges from 4 million to 5 million; the mass percentage of the first polyethylene material in polyethylene ranges from 60% to 80%, and the mass percentage of the second polyethylene material in polyethylene ranges from 20% to 40%.

[0039] The design with the weight-average molecular weight of the first polyethylene material ranging from 1 million to 3 million, the weight-average molecular weight of the second polyethylene ranging from 4 million to 5 million, the mass percentage of the first polyethylene material in polyethylene ranging from 60% to 80%, and the mass percentage of the second polyethylene material in polyethylene ranging from 20% to 40% ensures a more appropriate polyethylene content in the melt formed, facilitating the melt to form pores with smaller diameters, reducing the pore diameters of the filtration pores of the porous membrane, and improving the filtration accuracy of the porous membrane.

[0040] In a possible implementation, the pore-forming agent includes at least one of liquid paraffin, solid paraffin, dioctyl phthalate, and dibutyl phthalate; and / or, the antioxidant includes at least one of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dibutylhydroxytoluene, and tert-butylhydroquinone.

[0041] The design that the pore-forming agent includes at least one of liquid paraffin, solid paraffin, dioctyl phthalate, and dibutyl phthalate ensures that the melt obtained after the melting and mixing of polyethylene and the antioxidant with the pore-forming agent is easy to form pores, facilitating the subsequent easy obtaining of a porous membrane with smaller pore diameters of the filter pores, higher uniformity of the distribution of the filter pores, and higher tensile strength.

[0042] The design that the antioxidant includes at least one of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dibutylhydroxytoluene, and tert-butylhydroquinone is beneficial to reducing the risk of calcification of polyethylene during the formation of the melt due to degradation, beneficial to improving the processing efficiency of forming the melt, beneficial to improving the processing efficiency of the porous membrane, and beneficial to reducing the processing cost of the porous membrane.

[0043] In a possible implementation, the cooling temperature is in the range of -25°C to 50°C.

[0044] The design that the cooling temperature is in the range of -25°C to 50°C is beneficial to increasing the cooling rate of the melt, beneficial to reducing the pore diameter of the pores formed by the melt, beneficial to improving the uniformity of the distribution of the pores formed by the melt, beneficial to ensuring that the pore diameter of the pores formed by the melt is more concentrated, and thus beneficial to reducing the pore diameter of the filter pores of the porous membrane, beneficial to improving the uniformity of the distribution of the filter pores of the porous membrane, beneficial to making the pore diameter of the filter pores of the porous membrane more concentrated, and beneficial to improving the filtration accuracy and filtration efficiency of the porous membrane.

[0045] In a possible implementation, the thickness of the cast film is in the range of 1 mm to 10 mm.

[0046] The design that the thickness of the cast film is in the range of 1 mm to 10 mm ensures that the cast film has a relatively large thickness, the cast film can be stretched at a relatively large magnification, and ensures that the stretched cast film has strong tensile strength, and thus ensures that the porous membrane has strong tensile strength.

[0047] In a possible implementation, "stretching the cast film" specifically means: simultaneously performing transverse stretching and longitudinal stretching on the cast film; wherein, the stretching temperature of the transverse stretching and the stretching temperature of the longitudinal stretching are in the range of 110°C to 125°C, the stretching ratio of the transverse stretching and the stretching ratio of the longitudinal stretching are in the range of 6 to 12 times, and the stretching rate of the transverse stretching and the stretching rate of the longitudinal stretching are in the range of 1 mm / s to 30 mm / s.

[0048] The cast film formed after the melt is cooled has a porous structure. The design of simultaneously performing transverse stretching and longitudinal stretching on the cast film ensures that the elongation at break of the stretched cast film is the same in the transverse and longitudinal directions, which is beneficial to improving the overall structural consistency of the cast film, reducing the pore size of the stretched cast film, ensuring that the pore sizes of the pores in the stretched cast film are more concentrated, and the distribution of the pores in the stretched cast film is more uniform. Furthermore, it ensures that the pore sizes of the filtration pores of the porous membrane are smaller and more concentrated, and the distribution of the filtration pores of the porous membrane is more uniform.

[0049] In a possible implementation manner, the extractant used in the extraction includes at least one of dichloromethane, acetone, methanol, ethanol, glycerol, tetrafluoroethane, and isopropanol.

[0050] The design that the extractant used in the extraction includes at least one of dichloromethane, acetone, methanol, ethanol, glycerol, tetrafluoroethane, and isopropanol ensures that the pore-forming agent in the stretched cast film can be removed, so as to obtain a porous membrane.

[0051] In a possible implementation manner, the temperature of the heat setting is in the range of 100°C - 120°C, and the time of the heat setting is in the range of 1h - 2h.

[0052] The design that the temperature of the heat setting is in the range of 100°C - 120°C and the time of the heat setting is in the range of 1h - 2h ensures that the molecular chains in the stretched cast film are fully relaxed and crystallized, and the internal stress of the molecular chains can be fully released, thereby avoiding stress concentration and being beneficial to improving the mechanical strength and structural reliability of the prepared porous membrane.

[0053] In a third aspect, the embodiments of the present application further provide an application of the porous membrane according to any one of the first aspects in the filtration field and battery separators.

[0054] In a possible implementation manner, the porous membrane is used to filter a solution containing particles with a particle size of not less than 2 nm.

[0055] In a fourth aspect, the embodiments of the present application further provide a filtration device. The filtration device includes a cavity and the porous membrane according to any one of the first aspects, and the porous membrane is disposed in the cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the background art, the following will describe the drawings required to be used in the embodiments of the present application or the background art.

[0057] Figure 1 is a schematic structural diagram of a filtration device provided by an embodiment of the present application;

[0058] Figure 2 is Figure 1Partial structural schematic diagram of part A of the porous membrane of the filtering device shown from another angle;

[0059] Figure 3 is Figure 1 Partial structural schematic diagram of part A of the porous membrane of the filtering device shown from yet another angle;

[0060] Figure 4 Schematic flow chart of a method for fabricating a porous membrane provided by an embodiment of the present application. Detailed implementation manners

[0061] An embodiment of the present application provides a porous membrane, a method for fabricating the same, and an application thereof. The porous membrane can be applied to a filtering device and a battery. The porous membrane provided by the present application is made of a first polyethylene material and a second polyethylene material, which is not only beneficial to reducing the pore diameter of the filtering pores of the porous membrane, improving the uniformity of the distribution of the filtering pores of the porous membrane, increasing the tensile strength of the porous membrane, and improving the filtering accuracy of the porous membrane; moreover, it is beneficial to reducing the manufacturing cost of the porous membrane.

[0062] The embodiments of the present application will be described below with reference to the accompanying drawings in the embodiments of the present application.

[0063] Please refer to Figure 1 、 Figure 2 and Figure 3 , Figure 1 Schematic structural diagram of a filtering device 100 provided by an embodiment of the present application. Figure 2 is Figure 1 Partial structural schematic diagram of part A of the porous membrane 20 of the filtering device 100 shown from another angle. Figure 3 is Figure 1 Partial structural schematic diagram of part A of the porous membrane 20 of the filtering device 100 shown from yet another angle. It should be noted that the dotted line with an arrow in the figure indicates the flow direction of the solution.

[0064] An embodiment of the present application provides a filtering device 100, which is used to filter a solution. Exemplarily, the filtering device 100 is a capsule filter. In some other embodiments, the filtering device 100 can also be other types of filters. The filtering device 100 includes a cavity 10 and a porous membrane 20. The porous membrane 20 is disposed in the cavity 10. Wherein, the cavity 10 is generally cylindrical. The cavity 10 includes a receiving cavity 11, an inlet 12 and an outlet 13. In the axial direction of the cavity 10, the inlet 12 and the outlet 13 are located on opposite sides of the receiving cavity 11 and are both communicated with the receiving cavity 11. The porous membrane 20 is bent into a bag shape. The porous membrane 20 is installed in the receiving cavity 11 by means including but not limited to bonding, gluing or fasteners. Wherein, the bag mouth of the porous membrane 20 in the shape of a bag faces the inlet 12. The inlet 12 is used for the solution to flow into the receiving cavity 11. The porous membrane 20 is used to filter the solution. The outlet 13 is used for the solution filtered by the porous membrane 20 to flow out of the receiving cavity 11. The filtering device 100 filters the solution through the porous membrane 20. That is to say, the porous membrane 20 is applied to the filtering device 100, and this embodiment provides an application of the porous membrane 20 in the filtering field.

[0065] In this embodiment, the solution includes target particles and impurity particles. The particle size of the target particles is less than 2 nm, and the particle size of the impurity particles is not less than 2 nm. The porous membrane 20 filters the solution, and can intercept impurity particles with a particle size not less than 2 nm. The target particles with a particle size less than 2 nm can pass through the porous membrane 20 and flow out of the receiving cavity 11 with the solvent from the outlet 13. By the porous membrane 20, the concentration and particle cleanliness of the target particles with a particle size less than 2 nm in the solution can be improved. That is to say, the porous membrane 20 is used to filter a solution containing particles with a particle size not less than 2 nm (i.e., impurity particles). The porous membrane 20 can improve the concentration and particle cleanliness of the particles with a particle size less than 2 nm in the solution.

[0066] Exemplarily, the solution flowing into the receiving cavity 11 from the inlet 12 can be a photoresist. Wherein, the target particles are photoresist particles with a particle size less than 2 nm. The porous membrane 20 can improve the concentration and cleanliness of the photoresist particles with a particle size less than 2 nm, so as to improve the performance of the photoresist material made of the photoresist. In some other embodiments, the solution flowing into the receiving cavity 11 from the inlet 12 can also be a drug solution or other solutions.

[0067] In some embodiments, the porous membrane 20 includes a first surface 21 and a second surface 22. In the thickness direction of the porous membrane 20, the first surface 21 and the second surface 22 are arranged opposite to each other. In other words, the porous membrane 20 includes a first surface 21 and a second surface 22 arranged opposite to each other. The first surface 21 faces the inlet 12, and the second surface 22 faces away from the inlet 12.

[0068] The porous membrane 20 is provided with a plurality of filtration holes 23. In other words, the porous membrane 20 includes a plurality of filtration holes 23. Each filtration hole 23 penetrates the porous membrane 20 along the thickness direction of the porous membrane 20. The plurality of filtration holes 23 are arranged at intervals. Among them, the filtration hole 23 includes a first opening 231 and a second opening 232 which are arranged opposite to each other. The first opening 231 is located on the first surface 21, and the second opening 232 is located on the second surface 22. The aperture of the first opening 231 is equal to the aperture of the second opening 232. In some other embodiments, the aperture of the first opening 231 and the aperture of the second opening 232 may not be equal. The porous membrane 20 filters the solution flowing into the accommodation cavity 11 from the inlet 12 through the plurality of filtration holes 23. The design that the aperture of the first opening 231 is equal to the aperture of the second opening 232 is beneficial to simplifying the structure of the porous membrane 20 on the basis of ensuring the filtration accuracy and filtration efficiency of the porous membrane 20, ensuring the simple structure of the porous membrane 20, and is beneficial to reducing the processing cost of the porous membrane 20.

[0069] In some embodiments, the porous membrane 20 includes polyethylene and an antioxidant. The weight average molecular weight of the polyethylene is in the range of 1 million to 10 million; among them, the polyethylene includes a first polyethylene material and a second polyethylene material. The weight average molecular weight of the first polyethylene material is less than that of the second polyethylene material, and the mass ratio of the first polyethylene material in the polyethylene is greater than the mass ratio of the second polyethylene material in the polyethylene.

[0070] In the production process of the porous membrane 20 provided in the present application, it is necessary to first melt and mix the first polyethylene material, the second polyethylene material, the antioxidant and the pore-forming agent to obtain a melt, cool the melt to obtain a cast sheet, stretch the cast sheet and then extract it to remove the pore-forming agent, and then perform heat setting to obtain the porous membrane 20; among them, both the melt and the cast sheet are porous structures. Since the weight average molecular weight of the polyethylene is in the range of 1 million to 10 million, the polyethylene has strong wear resistance, high strength and stable chemical properties. The porous membrane 20 made of polyethylene with a weight average molecular weight in the range of 1 million to 10 million has high heat resistance, wear resistance, good mechanical properties and large tensile strength.

[0071] More importantly, compared with the porous membrane 20 made of a single polyethylene material in the prior art, the porous membrane 20 of the present application is made of a first polyethylene material and a second polyethylene material. The weight-average molecular weight of the first polyethylene material is less than that of the second polyethylene material, and the mass ratio of the first polyethylene material in polyethylene is greater than that of the second polyethylene material in polyethylene. This design is conducive to appropriately increasing the polyethylene content in the melt during the production process, ensuring that the melt forms pores with smaller diameters, and then facilitating the formation of smaller-diameter filtration pores 23 in the formed porous membrane 20, improving the filtration accuracy of the porous membrane 20, and increasing the tensile strength of the porous membrane 20. Moreover, it can prevent the polyethylene content in the melt from being too high during the production process, avoiding excessive viscosity of the melt, which increases the difficulty of melt-blending the first polyethylene material, the second polyethylene material, the antioxidant, and the pore-forming agent, and further reducing the requirements for melt-blending machinery and equipment, thus facilitating the reduction of the production cost of the porous membrane 20.

[0072] In some embodiments, the weight-average molecular weights of both the first polyethylene material and the second polyethylene material are in the range of 1 million - 5 million. In some other embodiments, the weight-average molecular weights of the first polyethylene material and the second polyethylene material can also be in the range of 5 million - 10 million. The design where the weight-average molecular weights of both the first polyethylene material and the second polyethylene material are in the range of 1 million - 5 million is conducive to reducing the difficulty of regulating the polyethylene content in the melt, and then facilitating the adjustment of the pore diameter of the filtration pores 23 of the porous membrane 20 and the adjustment of the filtration accuracy of the porous membrane 20.

[0073] In some embodiments, the weight-average molecular weight of the first polyethylene material is in the range of 1 million - 3 million, and the weight-average molecular weight of the second polyethylene is in the range of 4 million - 5 million. The mass ratio of the first polyethylene material in polyethylene is in the range of 60% - 80%. The mass ratio of the second polyethylene material in polyethylene is in the range of 20% - 40%. The design where the weight-average molecular weight of the first polyethylene material is in the range of 1 million - 3 million, the weight-average molecular weight of the second polyethylene is in the range of 4 million - 5 million, the mass ratio of the first polyethylene material in polyethylene is in the range of 60% - 80%, and the mass ratio of the second polyethylene material in polyethylene is in the range of 20% - 40% ensures a more appropriate polyethylene content in the formed melt, is conducive to the melt forming pores with smaller diameters, is conducive to reducing the pore diameter of the filtration pores 23 of the porous membrane 20, and is conducive to improving the filtration accuracy of the porous membrane 20.

[0074] Among them, the weight-average molecular weight of the first polyethylene material can be, including but not limited to, 1 million, 1.2 million, 1.5 million, 1.8 million, 2 million, 2.2 million, 2.5 million, 2.8 million or 3 million. The mass ratio of the first polyethylene material in the polyethylene can be, including but not limited to, 60%, 65%, 70%, 75% or 80%. The weight-average molecular weight of the second polyethylene material can be, including but not limited to, 4 million, 4.2 million, 4.5 million, 4.8 million or 5 million. The mass ratio of the second polyethylene material in the polyethylene can be, including but not limited to, 20%, 25%, 30%, 35% or 40%.

[0075] In some embodiments, in the porous membrane 20, the total mass ratio of polyethylene is 20%-50%, and the total mass ratio of the antioxidant is less than 1%. The design that the total mass ratio of polyethylene in the porous membrane 20 is 20%-50% ensures that the content of polyethylene in the porous membrane 20 is appropriate, which is beneficial to improving the mechanical properties of the porous membrane 20; moreover, on the basis of facilitating the melt blending of the first polyethylene material, the second polyethylene material, the antioxidant and the pore-forming agent, ensuring that the melt has a higher content of polyethylene is beneficial to the formation of more pores in the melt, beneficial to increasing the porosity of the pores formed by the melt, and thus beneficial to increasing the porosity of the filtration pores 23 of the porous membrane 20 and beneficial to improving the filtration speed and filtration efficiency of the porous membrane 20. Specifically, the total mass ratio of polyethylene can be, including but not limited to, 20%, 30%, 40% or 50%, and the total mass ratio of the antioxidant can be, including but not limited to, 0.03%, 0.05%, 0.07% or 0.09%.

[0076] In some embodiments, the antioxidant includes at least one of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dibutylhydroxytoluene, and tert-butylhydroquinone. The design that the antioxidant includes at least one of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dibutylhydroxytoluene, and tert-butylhydroquinone is beneficial to reducing the risk of calcification of polyethylene due to degradation during the formation of the melt, beneficial to improving the processing efficiency of forming the melt, beneficial to improving the processing efficiency of the porous membrane 20, and beneficial to reducing the processing cost of the porous membrane 20.

[0077] In some embodiments, the pore diameter of the filtration pores 23 is less than 0.02 μm. Target particles in the solution with a particle size less than 2 nm can flow through the porous membrane 20 via the filtration pores 23; impurity particles in the solution with a particle size not less than 2 nm cannot flow through the porous membrane 20 via the filtration pores 23. The design with the pore diameter of the filtration pores 23 less than 0.02 μm ensures that the porous membrane 20 has a high filtration accuracy. The porous membrane 20 can retain particles with a particle size not less than 2 nm, greatly increasing the concentration of particles with a particle size less than 2 nm in the solution filtered by the porous membrane 20, and ensuring that the porous membrane 20 can filter a solution containing particles with a particle size not less than 2 nm.

[0078] It can be understood that the filtration accuracy of the porous membrane 20 is less than 2 nm. The filtration accuracy refers to the particle size of the largest particles that the porous membrane 20 can retain. The design with the filtration accuracy of the porous membrane 20 less than 2 nm ensures that the porous membrane 20 can effectively filter out impurity particles not less than 2 nm, so as to ensure that the solution filtered by the porous membrane 20 meets the expectations.

[0079] Among them, the pore diameter of the filtration pores 23 is greater than 0.01 μm and less than 0.02 μm. Specifically, the pore diameter of the filtration pores 23 can be, including but not limited to, 0.012 μm, 0.014 μm, 0.016 μm, 0.018 μm or 0.02 μm. In some other embodiments, the pore diameter of the filtration pores 23 can also be less than 0.01 μm or equal to 0.01 μm.

[0080] In some embodiments, among all the filtration pores 23 of the porous membrane 20 per square μm, the proportion of the number of filtration pores 23 with a pore diameter in the range of 16 nm - 20 nm is not less than 90%. The design with the proportion of the number of filtration pores 23 with a pore diameter in the range of 16 nm - 20 nm among all the filtration pores 23 of the porous membrane 20 per square μm not less than 90% ensures that the pore diameter distribution of the filtration pores 23 of the porous membrane 20 is concentrated. It not only ensures that the porous membrane 20 can stably retain particles with a particle size not less than 2 nm, ensures that the porous membrane 20 has better filtration accuracy and filtration efficiency, but also is conducive to increasing the speed of the solution passing through the porous membrane 20 and is conducive to increasing the filtration speed of the porous membrane 20.

[0081] Specifically, among all the filtration pores 23 of the porous membrane 20 per square μm, the proportion of the number of filtration pores 23 with pore diameters in the range of 16 nm - 20 nm is within the range of 90% - 95%. Among them, among all the filtration pores 23 of the porous membrane 20 per square μm, the proportion of the number of filtration pores 23 with pore diameters in the range of 16 nm - 20 nm can be, including but not limited to, 90%, 91%, 92%, 93%, 94% or 95%. In some other embodiments, among all the filtration pores 23 of the porous membrane 20 per square μm, the proportion of the number of filtration pores 23 with pore diameters in the range of 16 nm - 20 nm can also be greater than 95%. That is to say, the pore diameter concentration of the filtration pores 23 within the range of 16 nm - 20 nm is not less than 90%.

[0082] Exemplarily, a PMI (Porometer Installation) device can be used to obtain the pore diameter distribution of the filtration pores 23 of the porous membrane 20 through the gas-liquid method. Specifically, based on the principle of gas-liquid displacement technology, the PMI device completely wets the 1 μm 2 porous membrane 20 with an immersion liquid until all the filtration pores 23 in the porous membrane 20 are completely filled with the wetting liquid, and then the immersion liquid filled in the filtration pores 23 is extruded by gas (dry method) and liquid (wet method) respectively. As the flow rate of the gas or liquid increases, the pressure exerted by the gas or liquid on the immersion liquid filled in the filtration pores 23 also gradually increases. The immersion liquid filled in the filtration pore 23 with the largest pore diameter is extruded first, the immersion liquid filled in the filtration pores 23 with smaller pore diameters is extruded more slowly, and the immersion liquid filled in the filtration pore 23 with the smallest pore diameter is extruded last.

[0083] The pore diameter of each filtration pore 23 can be obtained according to the following formula:

[0084] D = 4γcosθ / p

[0085] where D is the pore diameter of the filtration pore 23, γ is the liquid surface tension, θ is the liquid contact angle, and p is the gas pressure.

[0086] The pore diameter distribution number of each filtration pore 23 can be obtained according to the following formula:

[0087]

[0088] where fw i is the flow rate of the liquid passing through the porous membrane 20 at the first pressure, fd i is the flow rate of the gas passing through the porous membrane 20 at the first pressure, fw0 is the flow rate of the liquid passing through the porous membrane 20 at the second pressure, fd0 is the flow rate of the gas passing through the porous membrane 20 at the second pressure, the second pressure is less than the first pressure, and Q iis the number of pore diameters of the filter holes 23 corresponding to the first pressure, and Q0 is the number of pore diameters of the filter holes 23 corresponding to the second pressure.

[0089] Thus, the pore diameter of the filter hole 23 and the corresponding pore diameter distribution number can be obtained, that is, the pore diameter range in which the pore diameters of the filter holes 23 are concentrated and the proportion of the number of filter holes 23 with pore diameters in this range among all the filter holes 23 per square μm of the porous membrane 20 can be determined, that is, the pore diameter concentration.

[0090] In some embodiments, the porosity of the porous membrane 20 is greater than or equal to 50%. The design with a porosity of the porous membrane 20 greater than or equal to 50% ensures that the porous membrane 20 not only has high tensile strength, but also has a fast filtration speed, a large flow rate, a high dirt-holding capacity, can intercept more impurity particles, has a long service life, and a low cost.

[0091] Specifically, the porosity of the porous membrane 20 is greater than or equal to 50% and less than or equal to 70%. Among them, the porosity of the porous membrane 20 can be, including but not limited to, 50%, 52%, 55%, 58%, 60%, 63%, 66%, or 70%. The porosity of the porous membrane 20 refers to the ratio of the volume of the filter holes 23 of the porous membrane 20 to the volume of the porous membrane 20. The porosity of the filter holes 23 of the porous membrane 20 can be tested by methods including but not limited to mercury intrusion method, density method, or dry-wet membrane weighing method, etc.

[0092] In some embodiments, the pore density of the porous membrane 20 is within 60 pores / μm 2 - 300 pores / μm 2 In the range. The design with the pore density of the porous membrane 20 within 60 pores / μm 2 - 300 pores / μm 2 in the range ensures that the porous membrane 23 not only has high tensile strength, but also has a fast filtration speed, a large flow rate, a high dirt-holding capacity, can intercept more impurity particles, has a long service life, and a low cost.

[0093] Specifically, the pore density of the porous membrane 20 can be, including but not limited to, 60 pores / μm 2 , 100 pores / μm 2 , 120 pores / μm 2 , 140 pores / μm 2 , 160 pores / μm 2 , 180 pores / μm 2 , 200 pores / μm 2 , 220 pores / μm 2 , 240 pores / μm 2 , 260 pores / μm 2 , 280 pores / μm 2 or 300 pores / μm2 The pore density of the porous membrane 20 refers to the number of filtration pores 23 in each square μm of the porous membrane 20.

[0094] In some embodiments, the filtration efficiency of the porous membrane 20 is greater than 99.9%. The design with a filtration efficiency of the porous membrane 20 greater than 99.9% ensures that the porous membrane 20 can effectively filter out impurity particles, ensuring that the solution filtered by the porous membrane 20 is more in line with expectations. Specifically, the filtration efficiency of the porous membrane 20 can be, including but not limited to, 99.91%, 99.915%, 99.92%, 99.925%, 99.93%, 99.94%, 99.95% or 99.96%. The filtration efficiency refers to the ratio of the number of particles intercepted by the porous membrane 20 to the number of particles contained in the solution during the process of filtering the solution through the porous membrane 20.

[0095] In some embodiments, the pure water flux of the porous membrane 20 is greater than 0.1 ml / min / cm 2 The pure water flux of the porous membrane 20 is greater than 0.1 ml / min / cm 2 The design ensures that the porous membrane 20 has a relatively fast filtration speed, which is conducive to reducing the time cost of filtration. Further, the pure water flux of the porous membrane 20 is greater than 0.2 ml / min / cm 2 Among them, the pure water flux of the porous membrane 20 can be, including but not limited to, 0.12 ml / min / cm 2 、0.15 ml / min / cm 2 、0.18 ml / min / cm 2 、0.22 ml / min / cm 2 、0.25 ml / min / cm 2 or 0.3 ml / min / cm 2 The pure water flux refers to the volume of pure water passing through the unit area of the porous membrane 20 per unit time at 25°C under an environment of 0.1 Mpa.

[0096] Please refer to Figure 4 , and in combination with Figure 1 and Figure 2 , Figure 4 is a schematic flow chart of a method for manufacturing a porous membrane 20 provided by an embodiment of the present application.

[0097] The embodiment of the present application also provides a method for manufacturing a porous membrane 20. The manufacturing method includes:

[0098] S1. Melt and mix polyethylene, antioxidant and pore-forming agent and then extrude to obtain a melt.

[0099] S2. After cooling the melt, obtain a cast film;

[0100] S3. After stretching the cast film, perform extraction to remove the pore-forming agent, and then perform heat setting to obtain the porous membrane 20;

[0101] Among them, the weight-average molecular weight of polyethylene is in the range of 1 million to 10 million. The polyethylene includes a first polyethylene material and a second polyethylene material. The weight-average molecular weight of the first polyethylene material is less than that of the second polyethylene material, and the mass ratio of the first polyethylene material in the polyethylene is greater than that of the second polyethylene material in the polyethylene.

[0102] In the process of manufacturing the porous membrane 20 provided by this application, first, a melt is obtained by melt blending a first polyethylene material, a second polyethylene material, an antioxidant, and a pore-forming agent. After cooling the melt, a cast film is obtained. After stretching the cast film, perform extraction to remove the pore-forming agent, and then perform heat setting to obtain the porous membrane 20; among them, both the melt and the cast film are porous structures. Since the weight-average molecular weight of polyethylene is in the range of 1 million to 10 million, polyethylene has strong wear resistance, high strength, and stable chemical properties. The porous membrane 20 made of polyethylene with a weight-average molecular weight in the range of 1 million to 10 million has high heat resistance, wear resistance, good mechanical properties, and high tensile strength.

[0103] More importantly, compared with the porous membrane 20 made of a single polyethylene material in the prior art, the porous membrane 20 of this application is made of a first polyethylene material and a second polyethylene material. The design that the weight-average molecular weight of the first polyethylene material is less than that of the second polyethylene material and the mass ratio of the first polyethylene material in the polyethylene is greater than that of the second polyethylene material in the polyethylene is conducive to appropriately increasing the polyethylene content in the melt during the manufacturing process, conducive to ensuring that the melt forms pores with smaller diameters, and thus conducive to making the pore diameter of the filtration pores 23 in the formed porous membrane 20 smaller, conducive to improving the filtration accuracy of the porous membrane 20, and conducive to increasing the tensile strength of the porous membrane 20; moreover, it can avoid the excessive polyethylene content in the melt during the manufacturing process, avoid the too high viscosity of the melt, resulting in an increase in the difficulty of melt blending the first polyethylene material, the second polyethylene material, the antioxidant, and the pore-forming agent, and further resulting in high requirements for the melt blending machinery and equipment, which is conducive to reducing the manufacturing cost of the porous membrane 20.

[0104] In some embodiments, the weight-average molecular weight of the first polyethylene material is in the range of 1 million to 3 million, and the weight-average molecular weight of the second polyethylene material is in the range of 4 million to 5 million; the mass percentage of the first polyethylene material in the polyethylene is in the range of 60% to 80%, and the mass percentage of the second polyethylene material in the polyethylene is in the range of 20% to 40%. The design that the weight-average molecular weight of the first polyethylene material is in the range of 1 million to 3 million, the weight-average molecular weight of the second polyethylene is in the range of 4 million to 5 million; the mass percentage of the first polyethylene material in the polyethylene is in the range of 60% to 80%, and the mass percentage of the second polyethylene material in the polyethylene is in the range of 20% to 40% ensures that the polyethylene content in the prepared melt is more appropriate, which is conducive to the melt forming pores with smaller diameters, reducing the pore diameter of the filtration pores of the porous membrane, and improving the filtration accuracy of the porous membrane.

[0105] Among them, the weight-average molecular weight of the first polyethylene material can be, including but not limited to, 1 million, 1.2 million, 1.5 million, 1.8 million, 2 million, 2.2 million, 2.5 million, 2.8 million or 3 million. The mass percentage of the first polyethylene material in the polyethylene can be, including but not limited to, 60%, 65%, 70%, 75% or 80%. The weight-average molecular weight of the second polyethylene material can be, including but not limited to, 4 million, 4.2 million, 4.5 million, 4.8 million or 5 million. The mass percentage of the second polyethylene material in the polyethylene can be, including but not limited to, 20%, 25%, 30%, 35% or 40%.

[0106] In some embodiments, the mass percentage of polyethylene in the melt is in the range of 10% to 50%. The design that the mass percentage of polyethylene in the melt is in the range of 10% to 50% ensures that, on the basis of facilitating the melt mixing of the first polyethylene material, the second polyethylene material, the antioxidant and the pore-forming agent, the melt has a higher content of polyethylene, which is conducive to the melt forming more pores, increasing the porosity of the pores formed by the melt, and further improving the porosity of the filtration pores of the porous membrane 20, and improving the filtration speed and filtration efficiency of the porous membrane 20. Specifically, the mass percentage of polyethylene in the melt can be, including but not limited to, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%.

[0107] In some embodiments, the pore-forming agent includes at least one of liquid paraffin, solid paraffin, dioctyl phthalate and dibutyl phthalate. The design that the pore-forming agent includes at least one of liquid paraffin, solid paraffin, dioctyl phthalate and dibutyl phthalate ensures that the melt obtained after the melt mixing of polyethylene, antioxidant and pore-forming agent is easy to form pores, facilitating the subsequent easy obtaining of a porous membrane 20 with smaller pore diameters of the filtration pores 23, higher uniformity of the distribution of the filtration pores 23 and higher tensile strength.

[0108] In some embodiments, the antioxidant includes at least one of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dibutylhydroxytoluene, and tert-butylhydroquinone. The design that the antioxidant includes at least one of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dibutylhydroxytoluene, and tert-butylhydroquinone is beneficial to reducing the risk of calcification of polyethylene due to degradation during the formation of the melt, beneficial to improving the processing efficiency of forming the melt, beneficial to improving the processing efficiency of the porous membrane 20, and beneficial to reducing the processing cost of the porous membrane 20.

[0109] In some embodiments, "after melting and kneading polyethylene, an antioxidant, and a pore-forming agent and then extruding to obtain a melt" specifically means: mixing and stirring the first polyethylene material and the second polyethylene material to form polyethylene; putting polyethylene, an antioxidant, and a pore-forming agent into a kneading device through a powder weigher and a piston pump, then heating, melting, and kneading, and extruding the melt from the die head of the kneading device. Among them, the kneading device is a device that can provide shearing, mixing, heating, and optional granulation and material conveying. Exemplarily, the kneading device is a twin-screw extruder. Polyethylene, an antioxidant, and a pore-forming agent are melted, kneaded, and extruded into a melt through a twin-screw extrusion process. In some other embodiments, the kneading device can also be a single-screw extruder or other melt extruders.

[0110] The temperature of melting and kneading is 190°C - 200°C. Specifically, the temperature of melting and kneading can be, including but not limited to, 190°C, 193°C, 195°C, 198°C, or 200°C. The melt is a uniform sheet. Exemplarily, the melt can be, including but not limited to, a round sheet, a rectangular sheet, or other shaped sheets. The melt is a porous structure, and the pores of the melt are covered by the pore-forming agent in the melt.

[0111] In some embodiments, "after cooling the melt, a cast film is obtained" specifically means: the melt is cooled by rolling with a condensation roller to obtain a cast film. Among them, the temperature of the condensation roller is between -25°C and 50°C. That is to say, the cooling temperature is in the range of -25°C to 50°C. The design of the cooling temperature in the range of -25°C to 50°C is beneficial to increasing the cooling rate of the melt, beneficial to reducing the pore diameter of the pores formed by the melt, beneficial to increasing the uniformity of the distribution of the pores formed by the melt, beneficial to ensuring that the pore diameter of the pores formed by the melt is more concentrated, and further beneficial to reducing the pore diameter of the filtration pores 23 of the porous membrane 20, beneficial to increasing the uniformity of the distribution of the filtration pores 23 of the porous membrane 20, beneficial to making the pore diameter of the filtration pores 23 of the porous membrane 20 more concentrated, and beneficial to increasing the filtration accuracy and filtration efficiency of the porous membrane 20. Specifically, the cooling temperature (i.e., the temperature of the condensation roller) can be, including but not limited to, -25°C, -10°C, 0°C, 10°C, 20°C, 30°C, 40°C or 50°C. In some other embodiments, the melt can also be placed in a cooling box, and the melt can be cooled by adjusting the temperature inside the cooling box.

[0112] The shape of the cast film can be, including but not limited to, circular sheet, rectangular sheet or various special-shaped sheets. The thickness of the cast film is in the range of 1 mm to 10 mm. The design of the thickness of the cast film in the range of 1 mm to 10 mm ensures that the cast film has a relatively large thickness, the cast film can be stretched at a relatively large magnification, and the stretched cast film has strong tensile strength, and further ensures that the porous membrane 20 has strong tensile strength. Specifically, the thickness of the cast film can be, including but not limited to, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm. The cast film is a porous structure, and the pores of the cast film are covered by a pore-forming agent in the cast film.

[0113] In some embodiments, in "after stretching the cast film, extraction is performed to remove the pore-forming agent, and then heat setting is performed to obtain a porous membrane", "stretching the cast film" specifically means: the cast film is simultaneously stretched horizontally and vertically. Simultaneously stretching the cast film horizontally and vertically can be performed in a stretching device. The stretching device can be, including but not limited to, a biaxial stretching machine.

[0114] Among them, the stretching temperature of the horizontal stretching and the stretching temperature of the vertical stretching are in the range of 110°C to 125°C. Specifically, the stretching temperature of the horizontal stretching is equal to the stretching temperature of the vertical stretching, and the stretching temperature of the horizontal stretching and the stretching temperature of the vertical stretching can both be, including but not limited to, 110°C, 115°C, 120°C or 125°C.

[0115] The draw ratio of the transverse stretching and the draw ratio of the longitudinal stretching are in the range of 6 to 12 times. Specifically, the draw ratio of the transverse stretching is equal to the draw ratio of the longitudinal stretching, and the draw ratios of the transverse stretching and the longitudinal stretching may both be, including but not limited to, 6 times, 7 times, 8 times, 9 times, 10 times, 11 times or 12 times.

[0116] The stretching rate of the transverse stretching and the stretching rate of the longitudinal stretching are in the range of 1 mm / s to 30 mm / s. Specifically, the stretching rate of the transverse stretching is equal to the stretching rate of the longitudinal stretching, and the stretching rates of the transverse stretching and the longitudinal stretching may both be, including but not limited to, 1 mm / s, 5 mm / s, 10 mm / s, 15 mm / s, 20 mm / s, 25 mm / s or 30 mm / s.

[0117] The cast film formed after the melt is cooled has a porous structure. The design of simultaneously performing transverse stretching and longitudinal stretching on the cast film ensures that the elongation at break of the stretched cast film is consistent in the transverse and longitudinal directions, which is beneficial to improving the overall structural consistency of the cast film, reducing the pore diameter of the stretched cast film, ensuring that the pore diameters of the pores in the stretched cast film are more concentrated, and the distribution of the pores in the stretched cast film is more uniform. Furthermore, it ensures that the pore diameters of the filtration pores of the porous membrane are smaller and more concentrated, and the distribution of the filtration pores of the porous membrane is more uniform.

[0118] In some embodiments, in "extracting to remove the pore-forming agent after stretching the cast film and then performing heat setting to obtain the porous membrane", "extracting after stretching the cast film" specifically means: immersing the stretched cast film into an extraction tank containing an extractant until the pore-forming agent dissolves in the extractant and forms a raw membrane, and then taking out the raw membrane from the extraction tank. Among them, the extractant used for extraction includes at least one of dichloromethane, acetone, methanol, ethanol, glycerol, tetrafluoroethane and isopropanol. The design that the extractant used for extraction includes at least one of dichloromethane, acetone, methanol, ethanol, glycerol, tetrafluoroethane and isopropanol ensures that the pore-forming agent in the stretched cast film can be removed to prepare the porous membrane 20. The raw membrane has a porous structure, and the pores of the raw membrane are exposed to the outside.

[0119] In some embodiments, in the process of "performing stretching on the cast film, then performing extraction to remove the pore-forming agent, and then performing heat setting to obtain a porous membrane", the specific operation of "then performing heat setting" is as follows: putting the original film into an oven within the temperature range of 100°C - 120°C and staying for 1h - 2h to perform heat setting on the original film, and then obtaining the porous membrane 20. It can be understood that the heat setting temperature is within the range of 100°C - 120°C. The design with the heat setting temperature within the range of 100°C - 120°C and the heat setting time within the range of 1h - 2h ensures that the molecular chains in the stretched cast film are fully relaxed and crystallized, and the internal stress of the molecular chains can be fully released, thereby avoiding stress concentration and being beneficial to improving the mechanical strength and structural reliability of the prepared porous membrane 20. The structure and performance of the porous membrane 20 can be referred to as described above and will not be elaborated here. Specifically, the heat setting temperature (i.e., the temperature of the oven) can be, including but not limited to, 100°C, 105°C, 110°C, 115°C or 120°C. The heat setting time is within the range of 1h - 2h. Specifically, the heat setting time (i.e., the time the original film stays in the oven) can be, including but not limited to, 1h, 1.5h or 2h.

[0120] The following further describes the embodiments of the present application through multiple embodiments.

[0121] Embodiment 1

[0122] Mix and stir a first polyethylene material with a weight average molecular weight of 1 million and a second polyethylene material with a weight average molecular weight of 4 million in a mass ratio of 60:40 to prepare polyethylene. Put the polyethylene, tert-butylhydroquinone (i.e., antioxidant) and liquid paraffin (i.e., pore-forming agent) into a twin-screw extruder through a powder scale and a plunger pump, and after melting and kneading at 190°C, extrude from the die head of the twin-screw extruder to form a uniform sheet-like melt; wherein, the mass proportion of polyethylene in the melt is 35%. Cool the melt by rolling with a cooling roll to obtain a cast film; wherein, the temperature of the cooling roll (i.e., the cooling temperature) is -25°C.

[0123] Put the cast film into a biaxial stretching machine and simultaneously perform longitudinal stretching and transverse stretching at 110°C; wherein, the stretching ratio of longitudinal stretching and the stretching ratio of transverse stretching are both 6 times, and the stretching rate of longitudinal stretching and the stretching rate of transverse stretching are both 10 mm / s. It can be understood that the stretching temperature of longitudinal stretching and the stretching temperature of transverse stretching are both 110°C. Immerse the stretched cast film into an extraction tank containing dichloromethane (i.e., extractant) until the liquid paraffin (i.e., pore-forming agent) dissolves in the dichloromethane (i.e., extractant) to form the original film, and then take out the original film from the extraction tank. Put the original film into an oven at 110°C and stay for 1h to perform heat setting on the original film, and then obtain the porous membrane 20. Among them, the parameters involved in preparing the porous membrane 20 in Embodiment 1 are summarized in Table 1.

[0124] Example 2

[0125] Mix and stir a first polyethylene material with a weight-average molecular weight of 1.5 million and a second polyethylene material with a weight-average molecular weight of 4.5 million in a mass ratio of 70:30 to make polyethylene. Put the polyethylene, tert-butylhydroquinone (i.e., antioxidant), and liquid paraffin (i.e., pore former) into a twin-screw extruder through a powder weigher and a plunger pump, and after melting and kneading at 195 °C, extrude it from the die head of the twin-screw extruder into a uniform sheet-like melt; among them, the mass ratio of polyethylene in the melt is 25%. Cool the melt by rolling it with a cooling roll to obtain a cast film; among them, the temperature of the cooling roll (i.e., the cooling temperature) is 0 °C.

[0126] Put the cast film into a biaxial stretching machine and simultaneously perform longitudinal stretching and transverse stretching at 110 °C; among them, the stretching ratio of longitudinal stretching and the stretching ratio of transverse stretching are both 9 times, and the stretching rate of longitudinal stretching and the stretching rate of transverse stretching are both 15 mm / s. It can be understood that the stretching temperature of longitudinal stretching and the stretching temperature of transverse stretching are both 110 °C. Immerse the stretched cast film into an extraction tank containing dichloromethane (i.e., extractant) until the liquid paraffin (i.e., pore former) dissolves in the dichloromethane (i.e., extractant) to form a primary film, and then take out the primary film from the extraction tank. Put the primary film into an oven at 110 °C and stay for 1 h to thermally set the primary film to obtain a porous membrane 20. Among them, the parameters involved in preparing the porous membrane 20 of Example 2 are summarized in Table 1.

[0127] Example 3

[0128] Mix and stir a first polyethylene material with a weight-average molecular weight of 2.5 million and a second polyethylene material with a weight-average molecular weight of 5 million in a mass ratio of 80:20 to make polyethylene. Put the polyethylene, tert-butylhydroquinone (i.e., antioxidant), and liquid paraffin (i.e., pore former) into a twin-screw extruder through a powder weigher and a plunger pump, and after melting and kneading at 200 °C, extrude it from the die head of the twin-screw extruder into a uniform sheet-like melt; among them, the mass ratio of polyethylene in the melt is 25%. Cool the melt by rolling it with a cooling roll to obtain a cast film; among them, the temperature of the cooling roll (i.e., the cooling temperature) is 10 °C.

[0129] The cast film is put into a biaxial stretching machine, and longitudinal stretching and transverse stretching are carried out synchronously at 115 °C; among them, the magnification of longitudinal stretching and the stretching magnification of transverse stretching are both 12 times, and the stretching rate of longitudinal stretching and the stretching rate of transverse stretching are both 20 mm / s. It can be understood that the stretching temperature of longitudinal stretching and the stretching temperature of transverse stretching are both 115 °C. The stretched cast film is immersed in an extraction tank containing dichloromethane (i.e., the extractant) until the liquid paraffin (i.e., the pore-forming agent) dissolves in dichloromethane (i.e., the extractant) to form a primary film, and then the primary film is taken out from the extraction tank. The primary film is put into an oven at 110 °C and left for 1 h to thermally set the primary film, and then the porous membrane 20 is obtained. Among them, the parameters related to the preparation of the porous membrane 20 in Example 3 are summarized in Table 1.

[0130] Comparative Example 1

[0131] The polyethylene material, tert-butylhydroquinone (i.e., antioxidant) and liquid paraffin (i.e., pore-forming agent) are put into a twin-screw extruder through a powder scale and a piston pump, and after melting and kneading at 190 °C, they are extruded from the die head of the twin-screw extruder into a uniform sheet-like melt; among them, the mass proportion of polyethylene in the melt is 35%, and the polyethylene is the first polyethylene material with a weight-average molecular weight of 1 million. The melt is cooled by rolling with a cooling roll to obtain a cast film; among them, the temperature of the cooling roll (i.e., the cooling temperature) is -25 °C.

[0132] The cast film is put into a biaxial stretching machine, and longitudinal stretching and transverse stretching are carried out synchronously at 110 °C; among them, the magnification of longitudinal stretching and the stretching magnification of transverse stretching are both 6 times, and the stretching rate of longitudinal stretching and the stretching rate of transverse stretching are both 10 mm / s. It can be understood that the stretching temperature of longitudinal stretching and the stretching temperature of transverse stretching are both 110 °C. The stretched cast film is immersed in an extraction tank containing dichloromethane (i.e., the extractant) until the liquid paraffin (i.e., the pore-forming agent) dissolves in dichloromethane (i.e., the extractant) to form a primary film, and then the primary film is taken out from the extraction tank. The primary film is put into an oven at 110 °C and left for 1 h to thermally set the primary film, and then the porous membrane 20 is obtained. Among them, the parameters related to the preparation of the porous membrane 20 in Comparative Example 1 are summarized in Table 1.

[0133] The porous membranes 20 provided in each example and comparative example are tested for pore structure and filtration performance, and the results are summarized in Table 1 below.

[0134] Table 1

[0135]

[0136]

[0137] As can be learned from Table 1, the pore diameter of the filtration pores 23 of the porous membrane 20 provided in the embodiments of the present application is smaller, with the pore diameter being less than 0.02 μm. The pore diameter concentration of the filtration pores 23 within the range of 16 nm - 20 nm is higher, and the pore diameter concentration is not less than 90%. The porosity of the porous membrane 20 is higher, with the porosity being greater than or equal to 50%. The pore density of the porous membrane 20 is higher, and the pore density is within the range of 60 pores / μm 2 - 300 pores / μm 2 . The filtration accuracy of the porous membrane 20 is higher, and the porous membrane 20 can filter out particles with a particle size of not less than 2 nm. The filtration efficiency of the porous membrane 20 is higher, and the filtration efficiency can be increased to more than 99%. The pure water flux of the porous membrane 20 is higher, and the pure water flux can be increased to 0.2 ml / min / cm 2 or more.

[0138] Next, specific examples of the application of the above-mentioned porous membrane in filtration are provided. Specifically, the embodiments of the present application provide a filtration method for a filtration device 100. The filtration method includes: pouring a solution to be filtered (a solution containing particles with a particle size of not less than 2 nm) into the receiving cavity 11 of the filtration device 100, so that the porous membrane 20 disposed in the receiving cavity 11 filters the solution to be filtered.

[0139] Specifically, the solution to be filtered is poured into the receiving cavity 11 of the filtration device 100 from the inlet 12 of the filtration device 100, so that the porous membrane 20 disposed in the receiving cavity 11 filters the solution to be filtered, and the solution filtered by the porous membrane 20 flows out of the receiving cavity 11 from the outlet 13 of the filtration device 100.

[0140] In some embodiments, the content of particles with a particle size of not less than 2 nm is within the range of 0.002×10 -5 mol / L - 6×10 -5 mol / L. Specifically, the content of particles with a particle size of not less than 2 nm can include but is not limited to 0.002×10 -5 mol / L, 0.1×10 -5 mol / L, 0.5×10 -5 mol / L, 1×10 -5 mol / L, 2×10 -5 mol / L, 3×10 -5 mol / L, 4×10 -5 mol / L, 5×10 -5 mol / L or 6×10 -5 mol / L. Exemplarily, the particles with a particle size of not less than 2 nm are metal particles. Specifically, the particles with a particle size of not less than 2 nm can be copper particles, aluminum particles or other metal particles. In some other embodiments, the particles with a particle size of not less than 2 nm can also be non-metal particles.

[0141] In some embodiments, before "pouring the solution to be filtered (a solution containing particles with a particle size of not less than 2 nm) into the receiving cavity 11 of the filtering device 100", a dispersion aid is added to the solution to be filtered. The design of the dispersion aid ensures that the particles with a particle size of not less than 2 nm can be evenly dispersed in the solution, ensuring the stability of the solution, and can prevent the particles with a particle size of not less than 2 nm from precipitating or aggregating, facilitating the filtering of the porous membrane 20, and being conducive to improving the filtering efficiency and filtering speed. Among them, the dispersion aid is mercaptosuccinic acid (MSA). In some other embodiments, the dispersion aid can also be sodium citrate. The concentration of the dispersion aid is in the range of 0 mol / L - 1 mol / L. Specifically, the concentration of the dispersion aid can be, including but not limited to, 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 0.8 mol / L or 1 mol / L.

[0142] In some embodiments, the flow rate of the solution to be filtered is in the range of 3 ml / min - 30 ml / min. The design of the flow rate of the solution to be filtered in the range of 3 ml / min - 30 ml / min ensures that the porous membrane 20 can effectively filter out the particles with a particle size of not less than 2 nm, which is conducive to improving the filtering efficiency of the porous membrane 20 for the solution. Specifically, the flow rate of the solution added with the dispersion aid can be, including but not limited to, 3 ml / min, 5 ml / min, 10 ml / min, 15 ml / min, 20 ml / min or 30 ml / min.

[0143] In some other embodiments, the porous membrane 20 can also be used as a battery separator in a battery. In other words, an application of the porous membrane 20 in a battery separator is provided. The porous membrane 20 is disposed between the positive and negative electrodes of the battery, can isolate the positive and negative electrodes of the battery, the porous membrane 20 can intercept the electrons in the battery, and allows the ions in the battery to freely shuttle between the positive and negative electrodes.

Claims

1. A porous membrane, characterized in that, The porous membrane includes a plurality of filtration pores, and the porous membrane includes polyethylene and an antioxidant, wherein the weight-average molecular weight of the polyethylene is in the range of 1 million to 10 million; Among them, the polyethylene includes a first polyethylene material and a second polyethylene material, the weight-average molecular weight of the first polyethylene material is less than that of the second polyethylene material, and the mass percentage of the first polyethylene material in the polyethylene is greater than that of the second polyethylene material in the polyethylene.

2. The porous membrane according to claim 1, wherein The weight-average molecular weights of the first polyethylene material and the second polyethylene material are both in the range of 1 million to 5 million.

3. The porous membrane according to claim 1 or 2, characterized in that, The weight-average molecular weight of the first polyethylene material is in the range of 1 million to 3 million, and the weight-average molecular weight of the second polyethylene is in the range of 4 million to 5 million; the mass percentage of the first polyethylene material in the polyethylene is in the range of 60% to 80%, and the mass percentage of the second polyethylene material in the polyethylene is in the range of 20% to 40%.

4. The porous membrane according to any one of claims 1 to 3, characterized in that, In the porous membrane, the total mass percentage of the polyethylene is 20% to 50%.

5. The porous membrane according to any one of claims 1 to 4, characterized in that, The antioxidant includes at least one of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dibutylhydroxytoluene, and tert-butylhydroquinone.

6. The porous membrane according to any one of claims 1 to 5, characterized in that, The porous membrane includes a first surface and a second surface arranged opposite to each other, the filtration pores include a first opening and a second opening arranged opposite to each other, the first opening is located on the first surface, the second opening is located on the second surface, and the pore diameter of the first opening is equal to that of the second opening.

7. The porous membrane according to any one of claims 1 to 6, characterized in that, The pore diameter of the filtration pore is less than 0.02 μm.

8. The porous membrane according to claim 7, wherein, Among all the filtration pores of the porous membrane per square μm, the proportion of the number of filtration pores with a pore diameter in the range of 16 nm to 20 nm is not less than 90%.

9. The porous membrane according to any one of claims 1 to 8, characterized in that, The porosity of the porous membrane is greater than or equal to 50%.

10. The porous membrane according to any one of claims 1 to 9, characterized in that, The pore density of the porous membrane is within 60 pores / μm 2 - 300 pores / μm 2 .

11. The porous membrane according to any one of claims 1 to 10, characterized in that, The filtration accuracy of the filtration membrane is less than 2 nm, and the filtration efficiency of the porous membrane is greater than 99.9%.

12. The porous membrane according to any one of claims 1 to 11, characterized in that, The pure water flux of the porous membrane is greater than 0.1 ml / min / cm 2 .

13. A method for manufacturing a porous membrane, characterized in that, The manufacturing method includes: Melting and kneading polyethylene, an antioxidant, and a pore-forming agent and then extruding to obtain a melt; After cooling the melt, a cast sheet is obtained; Stretching the cast sheet and then extracting to remove the pore-forming agent, and then performing heat setting to obtain a porous membrane; Among them, the weight-average molecular weight of the polyethylene is in the range of 1 million to 10 million, the polyethylene includes a first polyethylene material and a second polyethylene material, the weight-average molecular weight of the first polyethylene material is less than that of the second polyethylene material, and the mass percentage of the first polyethylene material in the polyethylene is greater than that of the second polyethylene material in the polyethylene.

14. The manufacturing method according to claim 13, wherein, The mass percentage of the polyethylene in the melt is in the range of 10% to 50%.

15. The manufacturing method according to claim 13 or 14, characterized in that, The weight-average molecular weight of the first polyethylene material is in the range of 1 million to 3 million, and the weight-average molecular weight of the second polyethylene material is in the range of 4 million to 5 million; the mass percentage of the first polyethylene material in the polyethylene is in the range of 60% to 80%, and the mass percentage of the second polyethylene material in the polyethylene is in the range of 20% to 40%.

16. The manufacturing method according to any one of claims 13 to 15, characterized in that The pore former includes at least one of liquid paraffin, solid paraffin, dioctyl phthalate, and dibutyl phthalate; And / or, the antioxidant includes at least one of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dibutylhydroxytoluene, and tert-butylhydroquinone.

17. The manufacturing method according to any one of claims 13 to 16, characterized in that, The temperature of the cooling is in the range of -25°C to 50°C.

18. The manufacturing method according to any one of claims 13 to 17, characterized in that, The thickness of the cast film is in the range of 1 mm to 10 mm.

19. The manufacturing method according to any one of claims 13 to 18, characterized in that, The "stretching the cast film" specifically means: simultaneously performing transverse stretching and longitudinal stretching on the cast film; Wherein, the stretching temperature of the transverse stretching and the stretching temperature of the longitudinal stretching are in the range of 110°C to 125°C, the stretching ratio of the transverse stretching and the stretching ratio of the longitudinal stretching are in the range of 6 to 12 times, and the stretching rate of the transverse stretching and the stretching rate of the longitudinal stretching are in the range of 1 mm / s to 30 mm / s.

20. The manufacturing method according to any one of claims 13 to 19, characterized in that, The extractant used for the extraction includes at least one of dichloromethane, acetone, methanol, ethanol, glycerol, tetrafluoroethane, and isopropanol.

21. The manufacturing method according to any one of claims 13 to 20, characterized in that, The temperature of the heat setting is in the range of 100°C to 120°C, and the time of the heat setting is in the range of 1 h to 2 h.

22. The application of the porous membrane according to any one of claims 1 to 12 in the field of filtration and battery separators.

23. The application according to claim 22, characterized in that, The porous membrane is used for filtering a solution containing particles with a particle size of not less than 2 nm.

24. A filtering device, characterized in that, The filtration device includes a cavity and the porous membrane according to any one of claims 1 to 12, and the porous membrane is disposed in the cavity.

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