Method for the preparation of porous polymer membranes

Abstract

The method for preparing a porous polymer membrane according to an embodiment of the present invention may include: stretching a polymer sheet containing oil to prepare a primary porous polymer membrane, irradiating the primary porous polymer membrane with an electron beam to prepare a cross-linked porous polymer membrane, extracting oil from the cross-linked porous polymer membrane and performing thermal fixation.

Description

Technical Field

[0001] This invention relates to a method for preparing a porous polymer membrane. Background Technology

[0002] Porous polymer membranes are used in a variety of fields. For example, they can be used in electronic devices such as battery separators, electrolytic capacitor separators, and insulators for electronic devices; in biological fields such as pleural membranes for artificial lungs, plasma purification membranes, and breathable medical clothing; as separation filters for separating trace organic matter and viruses from water; and as separators for gas mixtures or filters for air purifiers.

[0003] Porous polymer membranes can be prepared by various methods. For example, a low-crosslinked porous polymer membrane can be further crosslinked as needed to be used as a porous polymer membrane.

[0004] Previously, porous polymer membranes were prepared by using a roll-to-roll process to move the membrane along its path and then irradiating it with an electron beam to cure it.

[0005] However, the method described above cannot rapidly produce high-quality porous polymer membranes, so there is a need to develop a device that can simultaneously improve the production speed and quality of porous polymer membranes. Summary of the Invention

[0006] (a) Technical problems to be solved One technical problem of the present invention is to provide a method for preparing a porous polymer membrane with improved efficiency.

[0007] (II) Technical Solution The method for preparing a porous polymer membrane according to the present invention may include: stretching a polymer sheet containing oil to prepare a primary porous polymer membrane, irradiating the primary porous polymer membrane with an electron beam to prepare a cross-linked porous polymer membrane, extracting oil from the cross-linked porous polymer membrane and performing thermal fixation.

[0008] In one embodiment, the accelerating voltage of the electron beam can be from 0.2 MeV to 2.5 MeV.

[0009] In one embodiment, the cumulative irradiation dose of the electron beam on the primary porous polymer membrane can be from 25 kGy to 200 kGy.

[0010] In one embodiment, the polymer sheet can be prepared by a method comprising the steps of: mixing the oil with a polymer resin to prepare a melt; and extruding the melt and shaping it into a sheet form.

[0011] In one embodiment, the polymer sheet may contain the oil at a content of 60% to 90% by weight of the total weight.

[0012] In one embodiment, the stretching can be performed at a temperature of 100°C to 200°C and at a magnification of 4 to 400 times.

[0013] In one embodiment, the heat fixation can be performed at a temperature of 100°C to 200°C.

[0014] In one embodiment, a heat treatment step may be further included after the electron beam irradiation step and before the oil extraction step.

[0015] In one embodiment, the heat treatment can be performed at a temperature of 50°C to 150°C.

[0016] In one embodiment, a porous polymer membrane with a high load melt index (HLMI) of less than 0.5 g / 10 min, as measured according to ASTM D 1238 at a temperature of 190°C and a load of 21.6 kg, can be prepared.

[0017] In one embodiment, a porous polymer membrane with a high-temperature strain increase rate (SR) of less than 6, as defined by Equation 1, can be prepared: [Formula 1] High-temperature strain increase rate (SR) = ΔS / ΔT In Equation 1, ΔS is the strain change in the temperature-strain diagram between 155°C and 170°C obtained by thermomechanical analysis (TMA) under a load of 0.02N, heating the porous polymer membrane from room temperature at a heating rate of 5°C / min, and measuring the strain. ΔT is the temperature change.

[0018] (III) Beneficial Effects According to the method for preparing porous polymer membranes of the present invention, a porous polymer membrane with improved mechanical and physical properties at high temperatures can be provided.

[0019] The method for preparing porous polymer membranes according to the present invention can improve the production speed of the porous polymer membranes.

[0020] According to the method for preparing porous polymer membranes of the present invention, the quality of porous polymer membranes can be improved even by simply changing the position of the equipment. Attached Figure Description

[0021] Figure 1This is a flowchart of a method for preparing a porous polymer membrane according to an embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram illustrating a system for preparing a porous polymer membrane according to one embodiment. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings. However, this is merely exemplary, and the present invention is not limited to the specific embodiments described herein.

[0024] Figure 1 This is a process flow diagram of a method for preparing a porous polymer membrane according to an embodiment of the present invention.

[0025] Reference Figure 1 Primary porous polymer membrane S10 can be prepared by stretching an oil-containing polymer sheet.

[0026] In one embodiment, the polymer sheet can be prepared by the following method.

[0027] Oil can be mixed with polymer resin to prepare a melt. The oil can block direct contact between the polymer surface and air, thus preventing a decrease in the quality of the porous polymer membrane. The primary porous polymer membrane formed from the melt retains oil within the pores, thereby reducing contact with air.

[0028] The polymer resin is not limited as long as it can be cured by electron beam irradiation. The polymer resin may include polyolefin-based resins such as polyethylene, polypropylene, and polymethylpentene; polyesters such as nylon and polyethylene terephthalate; polycarbonate; styrene-based resins; fluorine-based resins such as polytetrafluoroethylene and polyvinylidene fluoride; and vinyl chloride resins. These resins may be used alone or in combination of two or more.

[0029] In one embodiment, the polymer resin may include at least one selected from polyethylene (PE), polypropylene (PP), polybutene, polypentene, polymethylpentene, polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride-trifluorochloroethylene (PVDF-CTFE), polyvinylidene fluoride-ethylene tetrafluoroethylene (PVDF-ETFE), polyacrylonitrile (PAN), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyimide (PI), polyphenylene sulfide (PPS), polysulfone, polyethersulfone (PES), ethylene-vinyl acetate copolymer (EVA), and polycarbonate (PC).

[0030] The polymer resin may contain a weight-average molecular weight of 10.5 g / mol to 10 6 The polymer has a weight-average molecular weight of g / mol. For example, the polymer resin may contain a weight-average molecular weight of 5 g / mol. 10 5 g / mol to 2 10 6 g / mol polyethylene.

[0031] In one embodiment, the oil may include phthalic acid esters other than paraffin oil, mineral oil, or wax; aromatic ethers; palmitic acid; fatty acids with 10 to 20 carbon atoms; fatty alcohols with 10 to 20 carbon atoms; and at least one of one or more fatty acids of saturated and unsaturated fatty acids with 4 to 26 carbon atoms forming an ester bond with an alcohol having 1 to 8 hydroxyl groups and 1 to 10 carbon atoms.

[0032] In one embodiment, the kinematic viscosity of the oil at 40°C can be from 80 cST to 150 cST.

[0033] According to one embodiment, the kinematic viscosity of the oil at 40°C can be from 90 cST to 100 cST.

[0034] For example, the kinematic viscosity can be measured according to ASTM D445 or ISO 3104 standards. Alternatively, the kinematic viscosity can be measured using a glass capillary viscometer via the capillary method, but is not limited thereto.

[0035] The melt can be prepared by mixing and kneading the polymer resin and the oil in a weight ratio of 2:8 to 5:5. For example, the melt can be prepared in a compounding machine, such as a twin-screw compounding machine.

[0036] The melt can be extruded and formed into a sheet. For example, the melt can be continuously extruded from a die to provide a polymer sheet. The thickness of the extruded polymer sheet can be 100-4000 µm before stretching, but is not limited to this.

[0037] In one embodiment, the polymer sheet may contain the oil at a content of 60% to 90% by weight of the total weight.

[0038] According to one embodiment, the polymer sheet may contain the oil at a content of 65% to 80% by weight of the total weight.

[0039] The polymer sheet can be stretched. The polymer chain spacing of the extruded polymer sheet is very small, and it can have a high density. The stretching process can reduce the thickness and density of the polymer film. Therefore, a primary porous polymer film containing oil within the pores of the prepared porous film can be provided.

[0040] The direction and magnification of the stretching can be adjusted as needed. For example, the stretching can be biaxial stretching, including a first stretching process along the length direction (MD) and a second stretching process along the width direction (TD). The order of the stretching steps is not particularly limited and can be changed as needed.

[0041] According to one embodiment, the stretching ratio can be from 4 to 400 times. For example, in the case of biaxial stretching, the stretching can be from 2 to 20 times along the length direction and / or from 2 to 20 times along the width direction.

[0042] In one embodiment, when performing uniaxial stretching, the stretching ratio can be more than 16 times, more than 20 times, more than 30 times, more than 50 times, or more than 60 times, and can be less than 350 times, less than 250 times, less than 200 times, less than 185 times, less than 150 times, or less than 100 times.

[0043] In one embodiment, in the case of uniaxial tension, the stretching ratio can be from 16 to 400 times or from 16 to 185 times.

[0044] In one embodiment, in the case of biaxial stretching, the stretching ratio can be 2 to 18 times, 2 to 15 times, 2 to 14 times, 4 to 14 times, or 4 to 10 times along the length direction, and can be 2 to 18 times, 2 to 15 times, 2 to 14 times, 4 to 14 times, or 4 to 10 times along the width direction.

[0045] In one embodiment, the stretch ratio in the length direction may be the same as or different from the stretch ratio in the width direction.

[0046] In one embodiment, the stretching can be performed at a temperature of 100°C to 200°C or 110°C to 130°C. Therefore, the flexibility of the polymer film can be improved, allowing the stretching process to be performed quickly with less force.

[0047] Figure 2 This is a schematic diagram illustrating a system for preparing a porous polymer membrane according to one embodiment.

[0048] The porous polymer membrane preparation system may include: a stretching section A1, which prepares a primary porous polymer membrane by stretching a polymer sheet containing oil; an electron beam irradiation section A2, which prepares a cross-linked porous polymer membrane by irradiating the primary porous polymer membrane with an electron beam; an oil extraction section A3, which extracts oil from the cross-linked porous polymer membrane; and a heat-fixing section A4, which heat-fixes the cross-linked porous polymer membrane from which the oil has been extracted.

[0049] In other words, the stretching section A1 can be configured to prepare a primary porous polymer membrane by stretching a polymer sheet containing oil. The electron beam irradiation section A2 can be configured to prepare a cross-linked porous polymer membrane by irradiating the primary porous polymer membrane with an electron beam. The oil extraction section A3 can be configured to extract oil from the cross-linked porous polymer membrane. The heat-fixing section A4 can be configured to heat-fix the cross-linked porous polymer membrane from which the oil has been extracted.

[0050] The preparation system includes, for example, multiple conveying units that are sequentially connected to the stretching section, the electron beam irradiation section, the oil extraction section, and the heat-fixing section, and the conveying direction of the conveying units is the direction of movement from the stretching section to the heat-fixing section.

[0051] In some implementations, the conveying unit can convey the membranes in an in-line manner.

[0052] The conveying section may include, for example, a guide roller or a conveyor belt that moves the film along the conveying direction.

[0053] Reference Figure 2 The polymer sheet can be stretched in the stretching section A1. The stretching section A1 may include a uniaxial or biaxial stretching device, which can stretch the sheet sequentially or simultaneously, for example, by means of a roller or a tenter frame.

[0054] For example, a polymer sheet provided in the form of a roller R1 can be stretched in the stretching section A1. The density of the polymer sheet can be reduced through the stretching process.

[0055] The stretching section A1 can stretch the polymer sheet, for example, along the machine direction (MD) and the transverse direction (TD), and the machine direction (MD) can be the same as the conveying direction.

[0056] Figure 2 The polymer sheet is shown to be supplied in the form of a roller R1. However, it is not limited to this; the polymer sheet can also be supplied continuously after forming to the stretching process.

[0057] Crosslinked porous polymer membranes can be prepared by irradiating the primary porous polymer membrane with an electron beam (e.g., Figure 1 (S20).

[0058] According to one embodiment, the primary porous polymer membrane may have a pore size of less than 100 nm, for example, a pore size of 40 nm to 100 nm, 40 nm to 90 nm, 40 nm to 70 nm, or 40 nm to 60 nm. The pore size may refer to the average pore diameter.

[0059] As a non-limiting example, the pore size can be measured using a pore size analyzer according to ASTM F316-03. For example, the pore size analyzer can be a capillary flow porometer, a gas adsorption analyzer (BET, BJH, etc.), or a gas displacement hydrometer (e.g., a helium hydrometer).

[0060] The primary porous polymer membrane may comprise a structure in which linear polymer chains are intertwined in a separated state to form pores between the chains, and the interior of these pores is impregnated with oil to prevent contact between the surfaces of the polymer chains and air. Electron beam irradiation can cause cross-linking and curing of the linear polymer chains, resulting in a cross-linked porous polymer membrane comprising a network formed by the bonded polymer chains. The term "bonded" can refer to the presence of covalent chemical bonds connecting two linear polymer chains. The network of bonded polymer chains can represent a three-dimensional interconnected network structure with multiple covalent bonds between the polymer chains, which can lead to increased heat resistance as mechanical stability increases with temperature.

[0061] Refer again Figure 2 In the electron beam irradiation unit A2, the electron beam irradiation device (DB) can irradiate an electron beam. The primary porous polymer membrane can pass through the electron beam irradiation unit A2 while traveling and can be continuously supplied to the oil extraction unit described below.

[0062] In one embodiment, the accelerating voltage of the electron beam can be from 0.2 MeV to 2.5 MeV.

[0063] According to one embodiment, the accelerating voltage of the electron beam can be from 0.5 MeV to 1.5 MeV. The accelerating voltage of the electron beam can be adjusted according to the type of polymer, the thickness of the primary porous polymer film, the energy required for curing, the travel speed, etc.

[0064] In one embodiment, the primary porous polymer membrane can be irradiated with an electron beam one or two or more times to prepare a cross-linked porous polymer membrane.

[0065] In one embodiment, the cumulative irradiation dose of the electron beam on the primary porous polymer membrane can be from 25 kGy to 200 kGy.

[0066] According to one embodiment, the cumulative irradiation dose of the electron beam on the primary porous polymer membrane can be from 50 kGy to 200 kGy. The cumulative irradiation dose of the electron beam can be adjusted according to the type of polymer, the thickness of the primary porous polymer membrane, the energy required for curing, the travel speed, etc.

[0067] For example, the cumulative irradiation dose of the electron beam can be the average cumulative irradiation dose per unit area of ​​the primary porous polymer membrane. For example, the cumulative irradiation dose can be calculated based on a single irradiation dose of the electron beam, the area of ​​the membrane irradiated by the electron beam in any region, the irradiation depth of the electron beam, and the number of passes. The electron beam irradiation process can be carried out while the primary porous polymer membrane contains oil. Therefore, the polymer chains can undergo cross-linking reactions without exposure to air (especially oxygen). During electron beam irradiation, the high thermal energy and electron beam energy can cause highly reactive elements to form free radicals or undergo side reactions. In particular, oxygen in the air forms free radicals, which may reduce the quality of the polymer membrane; however, according to the present invention, by irradiating the polymer chains with an electron beam without contact with oxygen, a polymer membrane with further improved quality can be provided.

[0068] In one embodiment, a heat treatment may be performed after the electron beam irradiation. This heat treatment can further promote the reaction of residual free radicals or highly reactive chemicals generated by the electron beam irradiation that are used for crosslinking. Therefore, it can prevent the degradation of the porous polymer sheet quality caused by the reaction of these residual free radicals in the oil extraction process described below.

[0069] In one embodiment, the heat treatment can be performed at a temperature of 50°C to 150°C.

[0070] In one embodiment, the heat treatment may be carried out at a temperature of 50°C to 150°C for more than 1 minute and less than 20 minutes. Preferably, the heat treatment may be carried out at a temperature of 100°C to 130°C for more than 1 minute and less than 10 minutes.

[0071] According to the preparation method described above, oil can be extracted from the cross-linked porous polymer membrane (e.g., ...). Figure 1 (S30). After the electron beam crosslinking, oil can be removed from the pores of the porous polymer membrane.

[0072] The oil extraction process can use conventional solvent extraction methods such as immersion, solution spray, and ultrasonic treatment alone, or it can combine two or more processes, but is not particularly limited thereto.

[0073] Refer again Figure 2 The cross-linked porous polymer membrane supplied from the electron beam irradiation unit A2 can enter the oil extraction unit A3, where oil can be removed.

[0074] In the oil extraction section A3, the oil can be extracted by treating the cross-linked porous polymer membrane with an organic solvent.

[0075] The organic solvent may be, for example, methyl ethyl ketone, dichloromethane, hexane, etc., which have high extraction efficiency and fast drying, but is not limited to these.

[0076] Extraction can remove more than 99% by weight of the total weight of the oil contained in the cross-linked porous polymer membrane.

[0077] According to the preparation method described, after oil extraction, heat fixation can be performed (e.g., Figure 1 (S40). Heat fixation can improve the network strength of cross-linked polymer chains at high temperatures, preventing the membrane's own support from decreasing due to the removal of oil present between the cross-linked polymer chains.

[0078] Refer again Figure 2 The porous polymer membrane supplied from the oil extraction section A3 can enter the heat-fixing section A4 and be heat-treated in the heat-fixing section A4, so that the porous polymer membrane can be prepared into a roller body R2.

[0079] The thermal fixation can include, for example, thermal fixation or thermal relaxation. Through this thermal fixation, residual stress in the porous polymer membrane can be reduced or eliminated.

[0080] In one embodiment, the heat fixation can be performed at a temperature of 100°C to 200°C.

[0081] According to one embodiment, the heat setting can be performed at a temperature between 110°C and 130°C. The heat setting temperature can be adjusted according to the type of polymer, the viscosity of the oil being removed, the film thickness, the travel speed, etc.

[0082] In one embodiment, the high load melt index (HLMI) of the porous polymer membrane prepared by the method can be below 0.5 g / 10 min.

[0083] According to one embodiment, the HLMI of the porous polymer membrane prepared by the method can be below 0.1 g / 10 min. Within this range, the mechanical and physical properties of the porous polymer membrane at high temperatures can be improved.

[0084] HLMI can, for example, refer to the mass (g / 10 min) of molten polymer measured when the porous polymer membrane is cut to prepare a sample and then extruded under a load of 21.6 kg at a temperature of 190°C for 10 minutes.

[0085] The HLMI is the weight of the porous polymer membrane measured when 3g of the membrane is placed in a perforated chamber at 190°C and subjected to a load of 21.6kg for 10 minutes. The HLMI can be expressed in g / 10 minutes.

[0086] For example, the HLMI can be measured according to ASTM D 1238.

[0087] In one embodiment, the high-temperature strain increase rate (SR) of the porous polymer membrane prepared by the method, as defined by Formula 1, can be less than 6.

[0088] [Formula 1] High-temperature strain increase rate (SR) = ΔS / ΔT In Equation 1, ΔS is the strain change in the temperature-strain diagram between 155°C and 170°C obtained by thermomechanical analysis (TMA) under a load of 0.02N, heating the porous polymer membrane from room temperature at a heating rate of 5°C / min, and measuring the strain. ΔT is the temperature change.

[0089] According to one embodiment, the high-temperature strain increase rate of the porous polymer membrane prepared by the method can be less than 5.

[0090] Within the aforementioned range, the mechanical and physical properties of the porous polymer membrane at high temperatures can be improved. For example, the rate of degradation of the mechanical and physical properties of the porous polymer membrane in the temperature range of approximately 155°C to 170°C can be reduced, thus enabling the porous polymer membrane to be used even in extremely high temperature environments.

[0091] The high-temperature strain increase rate can be the slope value of the interval where the strain increases linearly in the range of 155℃ to 170℃ in the temperature-strain graph (horizontal axis is temperature, in ℃, vertical axis is strain, in %) obtained by measuring the strain of the porous polymer membrane during the heating process.

[0092] The thermomechanical analysis can be performed, for example, using a TMA 450 instrument from TA Instruments.

[0093] In the thermomechanical analysis, strain can be measured, for example, along MD or TD.

[0094] In the thermomechanical analysis, strain can be measured, for example, along the MD.

[0095] Porous polymer membranes can be applied in a variety of fields. For example, they can be used in the electrical / electronic field for secondary battery separators and the purification of chemicals required for semiconductor processes; in the biological field for hemodialysis, acting as artificial kidneys; in the field for pleural membranes for artificial lungs, plasma purification membranes, and breathable medical clothing; in the water treatment field for the separation of pathogens and bacteria in water treatment plants and seawater desalination; and in the petrochemical field for the purification of chemicals or organic solvents and the separation of gases produced in petrochemical processes.

[0096] In one embodiment of the present invention, a system for preparing the porous polymer membrane can be provided. As described above, a system for preparing the porous polymer membrane can be provided. Figure 2 The illustrated system is a porous polymer membrane preparation system according to one embodiment.

[0097] The porous polymer membrane preparation system can be a roll-to-roll system comprising a polymer sheet roller R1 and a porous polymer membrane roller R2.

[0098] Within the travel interval of the polymer sheet roller R1 and the porous polymer membrane roller R2, the polymer sheet can travel from the polymer sheet roller R1 to the porous polymer membrane roller R2, and can pass through the stretching section A1, the electron beam irradiation section A2, the oil extraction section A3 and the heat-fixing section A4 arranged in sequence.

[0099] In one embodiment, the system may further include an extrusion section for preparing a polymer sheet by extruding a melt containing a polymer resin and an oil. The extrusion section may be located upstream of the stretching section A1. The extrusion section may include a die, such as a T-die, for extruding and forming the melt into a polymer sheet, and may further include a mixing device for mixing the polymer resin and oil at the front end of the die, and a cooling device for cooling the extruded polymer sheet at the rear end of the die. The cooling device may include, for example, a device for discharging cooling gas or a cooling roller. The cooling gas may be, for example, air, nitrogen, helium, etc., and may have a temperature of 0-80°C, but is not limited thereto.

[0100] According to embodiments of the present invention, the high load melt index (HLMI) of the porous polymer membrane, measured under ASTM D 1238 at a temperature of 190°C and a load of 21.6 kg, can be less than 0.5 g / 10 min, and the high temperature strain increase rate (SR) defined by Equation 1 can be less than 6. [Formula 1] High-temperature strain increase rate (SR) = ΔS / ΔT In Equation 1, ΔS(%) is the strain change in the temperature-strain diagram between 155℃ and 170℃ obtained by thermomechanical analysis (TMA) under a load of 0.02N, heating the porous polymer membrane from room temperature at a heating rate of 5℃ / min, and measuring the strain. ΔT(℃) is the temperature change.

[0101] The porous polymer membrane can be prepared by the above preparation method and / or the above preparation system.

[0102] The porous polymer membrane is prepared by curing a primary porous polymer membrane containing oil by electron beam irradiation and then extracting the oil. The porous polymer membrane may contain a cured product that is cured by electron beam irradiation before the oil extraction.

[0103] Since the electron beam irradiation process is performed on the primary porous polymer membrane while it contains oil, the porous polymer membrane may contain a cured product in which the polymer chains are cross-linked without exposure to air (especially oxygen). During electron beam irradiation, the high thermal energy and electron beam energy can cause highly reactive elements to form free radicals or induce side reactions. In particular, the formation of free radicals from oxygen in the air may degrade the quality of the polymer membrane; however, according to the present invention, by irradiating the polymer chains with an electron beam while they are not in contact with oxygen, a porous polymer membrane with further improved quality can be provided.

[0104] For example, a porous polymer membrane with a gel content of 80% or more, such as 90% or more, as measured by the method described in section (3) Gel Content, can be provided. This increased gel content can indicate a significant improvement in the thermophysical and mechanophysical properties of the porous polymer membrane, and this may be related to factors such as the crosslinking structure, crosslinking density, and the type of covalent bonds contained in the crosslinking structure.

[0105] In one embodiment, the thickness of the porous polymer membrane can be, for example, from 5 μm to 100 μm. As a non-limiting example, the thickness of the porous polymer membrane can be measured using a TESA Mu-Hite Electronic Height Gauge from TESA at a measuring pressure of 0.63 N.

[0106] The embodiments of the present invention will be further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only for illustrating the present invention and are not intended to limit the scope of the claims. Various changes and modifications can be made to the embodiments within the scope of the present invention and its technical concept, which is obvious to those skilled in the art, and such variations and modifications naturally fall within the scope of the claims.

[0107] Example 1 The weight-average molecular weight is 6.0. 10 5 High-density polyethylene and paraffin oil with a kinematic viscosity of 95 cST at 40°C were mixed at a weight ratio of 30:70 and compounded using a twin-screw mixer to prepare a melt. The melt was extruded using a T-die and formed into sheets, which were then subjected to a 36-fold (6-fold) reaction at 115°C. 6) The membrane was stretched using a biaxial stretching ratio of 6 in both the MD and TD directions. The stretched membrane was then irradiated with an electron beam (accelerating voltage of 1 MeV, irradiation dose of 100 kGy). Paraffin oil was extracted and heat-fixed (120°C, 2 minutes) to prepare a porous polymer membrane (9 μm thick).

[0108] Example 2 A porous polymer membrane (9 μm thick) was prepared using the same method as in Example 1, except that the electron beam irradiation dose was changed to 50 kGy.

[0109] Example 3 A porous polymer membrane (9 μm thick) was prepared using the same method as in Example 1, except that the electron beam irradiation dose was changed to 150 kGy.

[0110] Example 4 A porous polymer membrane (9 μm thick) was prepared using the same method as in Example 1, except that it underwent a subsequent heat treatment (110 °C, 2 min) after electron beam irradiation.

[0111] Comparative Example 1 A porous polymer membrane (9 μm thick) was prepared using the same method as in Example 1, except that the electron beam irradiation process and heat treatment were omitted.

[0112] Comparative Example 2 A porous polymer membrane (9 μm thick) was prepared using the same method as in Example 1, except that paraffin oil was extracted from the stretched membrane, heat-fixed to prepare a porous membrane, and then the porous membrane was irradiated with an electron beam (accelerating voltage of 1 MeV and irradiation dose of 100 kGy).

[0113] Comparative Example 3 A porous polymer membrane (9 μm thick) was prepared using the same method as in Example 1, except that the paraffin oil was extracted from the stretched membrane, irradiated with an electron beam (accelerating voltage of 1 MeV and irradiation dose of 100 kGy), and then heat-fixed.

[0114] Comparative Example 4 A porous polymer membrane (9 μm thick) was prepared using the same method as in Example 1, except that paraffin oil was extracted from the stretched membrane, heat-fixed to prepare a porous membrane, and then the porous membrane was irradiated with an electron beam (accelerating voltage of 1 MeV, irradiation dose of 100 kGy). Subsequent heat treatment was then performed (110°C, 2 minutes).

[0115] [Table 1] Experimental Example The physical properties of the porous polymer membranes of the Examples and Comparative Examples were evaluated using the following methods, and the results are shown in Table 2 below.

[0116] (1) Thermomechanical properties Using a TMA 450 instrument from TA Instruments, under temperature ramp mode and a preload of 0.02 N, the strain of the porous polymer films of the examples and comparative examples was measured from 40 °C to 200 °C at a heating rate of 5 °C / min. A graph was obtained with temperature (in °C) on the horizontal axis and strain (in %) on the vertical axis. In the graph, the slope value of the interval where strain increases linearly from 155 °C to 170 °C is measured as the high-temperature strain increase rate. The high-temperature strain increase rate was calculated according to Mathematical Formula 1 described above, and the calculated value was used for the evaluation of the thermomechanical properties.

[0117] (2) HLMI Three g of the porous polymer membranes from the examples and comparative examples were placed in a perforated chamber at 190°C, and a load of 21.6 kg was applied for 10 minutes. The weight of the melt from the porous polymer membranes was measured, and the high load melt index (HLMI) was measured according to ASTM D1238. At this time, the diameter and length of the pores were the same as those of the standard mold (orifice), forming 2.095 ± 0.005 mm and 8.000 ± 0.025 mm, respectively.

[0118] (3) Gel content Three g of the porous polymer membranes from the examples and comparative examples were immersed in xylene at 135°C for 3 hours. The percentage of undissolved residual solids relative to the initial added mass (3 g) was then calculated as the gel content. A mixture of xylene isomers was used for impregnation, but it is not limited to this; one or more xylene isomers selected from o-xylene, m-xylene, or p-xylene can be used.

[0119] [Table 2] Referring to Table 2, the porous polymer membranes of the embodiments can provide improved mechanical and physical properties at high temperatures and can provide a gel content of over 92%.

[0120] On the other hand, the mechanical and physical properties of the porous polymer membrane in the comparative example deteriorated significantly at high temperatures, and the gel content dropped to below 40%.

Claims

1. A method for preparing a porous polymer membrane, comprising the following steps: Stretching an oil-containing polymer sheet to prepare a primary porous polymer membrane; The primary porous polymer membrane is irradiated with an electron beam to prepare a cross-linked porous polymer membrane; Oil was extracted from the cross-linked porous polymer membrane; as well as Heat-setting step.

2. The method for preparing the porous polymer membrane according to claim 1, wherein, The accelerating voltage of the electron beam is from 0.2 MeV to 2.5 MeV.

3. The method for preparing a porous polymer membrane according to claim 1, wherein, The cumulative irradiation dose of the electron beam on the primary porous polymer membrane is 25 kGy to 200 kGy.

4. The method for preparing a porous polymer membrane according to claim 1, wherein, The polymer sheet is prepared by a method comprising the following steps: The oil is mixed with a polymer resin to prepare a melt; and The molten material is extruded and shaped into a sheet.

5. The method for preparing a porous polymer membrane according to claim 1, wherein, The polymer sheet contains the oil at a content of 60% to 90% by weight of the total weight.

6. The method for preparing a porous polymer membrane according to claim 1, wherein, The stretching is performed at a temperature of 100°C to 200°C and at a magnification of 4 to 400 times.

7. The method for preparing a porous polymer membrane according to claim 1, wherein, The heat fixation is performed at a temperature of 100°C to 200°C.

8. The method for preparing a porous polymer membrane according to claim 1, wherein, The process further includes a heat treatment step after the electron beam irradiation step and before the oil extraction step.

9. The method for preparing a porous polymer membrane according to claim 8, wherein, The heat treatment temperature is between 50°C and 150°C.

10. The method for preparing a porous polymer membrane according to claim 1, wherein, The high load melt index (HLMI) of the prepared porous polymer membrane, measured according to ASTM D 1238 at a temperature of 190°C and a load of 21.6 kg, was less than 0.5 g / 10 min.

11. The method for preparing a porous polymer membrane according to claim 1, wherein, The high-temperature strain increase rate (SR) of the prepared porous polymer membrane, as defined by Equation 1, is less than 6. [Formula 1] High-temperature strain increase rate (SR) = ΔS / ΔT In Equation 1, ΔS is the strain change in the temperature-strain diagram between 155°C and 170°C obtained by thermomechanical analysis (TMA) under a load of 0.02N, heating the porous polymer membrane from room temperature at a heating rate of 5°C / min, and measuring the strain. ΔT is the temperature change.

12. A system for preparing a porous polymer membrane, comprising: A stretching section, wherein a primary porous polymer membrane is prepared by stretching an oil-containing polymer sheet; An electron beam irradiation unit prepares a cross-linked porous polymer membrane by irradiating the primary porous polymer membrane with an electron beam; An oil extraction section, wherein the oil extraction section extracts oil from the cross-linked porous polymer membrane; A heat-fixing section is provided for heat-fixing the cross-linked porous polymer membrane of the extracted oil. as well as Multiple conveying units, which are sequentially connected to the stretching unit, the electron beam irradiation unit, the oil extraction unit, and the heat-fixing unit. The conveying direction of the conveying unit is the direction of movement from the stretching unit to the heat-fixing unit.

13. The porous polymer membrane preparation system according to claim 12, wherein, The preparation system further includes an extrusion section for preparing polymer sheets by extruding a melt containing polymer resin and oil, wherein the extrusion section is located upstream of the stretching section.

14. A porous polymer membrane having a high-load melt index (HLMI) of less than 0.5 g / 10 min, measured according to ASTM D 1238 at a temperature of 190 °C and a load of 21.6 kg, and a high-temperature strain increase rate (SR) of less than 6, as defined by Equation 1. [Formula 1] High-temperature strain increase rate (SR) = ΔS / ΔT In Equation 1, ΔS is the strain change in the temperature-strain diagram between 155℃ and 170℃ obtained by thermomechanical analysis (TMA) under a load of 0.02N, heating the porous polymer membrane from room temperature at a heating rate of 5℃ / min, and measuring the strain. The unit is %, and ΔT is the temperature change, which is in℃.

15. The porous polymer membrane according to claim 14, wherein, The porous polymer membrane is prepared by curing a primary porous polymer membrane containing oil by electron beam irradiation and then extracting the oil, and the porous polymer membrane contains a cured product that is cured by electron beam irradiation before the oil is extracted.

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