Porous polymer membrane

Abstract

The porous polymer membrane according to an embodiment of the present invention has a crosslinking reactivity degree of 1.0 or higher as defined by Formula 1. [Formula 1] Crosslinking reactivity degree = ((AB) / 10000) - C (In Formula 1, A is the temperature at which the porous polymer membrane breaks when it is heated to 220°C at a heating rate of 5°C / min while a force of 0.015N is applied, i.e., the melt fracture temperature (°C); B is the percentage of the mass of undissolved residual solids after the porous polymer membrane has been immersed in xylene at 135°C for 3 hours divided by the initial mass, i.e., the gel content (%); C is the high load melt index (HLMI) (g / 10 min) of the porous polymer membrane measured according to ASTM D 1238 at a temperature of 190°C and a load of 21.6 kg.)

Description

Technical Field

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

[0002] Porous polymer membranes containing micropores and exhibiting low reactivity are used in a variety of fields. For example, porous polymer membranes are used as separators in batteries, gas separation processes and / or equipment, permeation membranes, etc., for the physical and electrical separation of components or to prevent remixing of refined products.

[0003] With applications in various fields, there is a need for porous polymer membranes that exhibit high durability even in extreme environments. For example, porous polymer membranes with improved durability are required in environments with extremely high temperatures, extremely low temperatures, excessive static electricity, and high external forces.

[0004] Techniques have been proposed to improve the durability of conventional porous polymer membranes through surface treatment or post-processing. However, there is still a need for a porous polymer membrane with sufficiently high chemical resistance and mechanical-physical properties. Summary of the Invention

[0005] (a) Technical problems to be solved One technical problem of the present invention is to provide a porous polymer membrane with improved chemical and physical properties and mechanical and physical properties.

[0006] (II) Technical Solution The porous polymer membrane according to an embodiment of the present invention can have a crosslinking reactivity degree of 1.0 or higher as defined by Formula 1 below.

[0007] [Formula 1] Crosslinking reactivity = ((A) B) / 10000)-C In Equation 1, A is the temperature at which the porous polymer membrane breaks when it is heated to 220°C at a heating rate of 5°C / min and a force of 0.015N is applied while it is stretched by thermomechanical analysis (TMA), i.e., the melt fracture temperature (°C); B is the percentage of the mass of undissolved residual solids divided by the initial mass after the porous polymer membrane is immersed in xylene at 135°C for 3 hours, i.e., the gel content (%); and C is the high load melt index (HLMI) (g / 10 min) of the porous polymer membrane measured according to ASTM D 1238 at a temperature of 190°C and a load of 21.6 kg.

[0008] According to one implementation scheme, in Formula 1, A can be above 160°C.

[0009] According to one implementation scheme, in Equation 1, B can be 80% or more.

[0010] According to one implementation, in Formula 1, C can be less than 0.2 g / 10 minutes.

[0011] According to one embodiment, the porous polymer membrane can have a porosity of 10% to 80%.

[0012] According to one embodiment, the porous polymer membrane may comprise 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).

[0013] The separator for secondary batteries according to embodiments of the present invention may include the above-mentioned porous polymer membrane.

[0014] The gas separation diaphragm according to an embodiment of the present invention may include the above-described porous polymer membrane.

[0015] (III) Beneficial Effects The porous polymer membrane according to embodiments of the present invention can have improved solvent resistance. Therefore, damage to the porous polymer membrane caused by contact with organic solvents can be suppressed or reduced.

[0016] The porous polymer membrane according to embodiments of the present invention can have improved heat resistance. Therefore, the polymer membrane can effectively suppress or reduce thermal damage and mechanical damage caused by external forces under high-temperature environments, and can maintain operational reliability over long periods of time.

[0017] The method for manufacturing a porous polymer membrane according to an embodiment of the present invention can suppress or reduce side reactions caused by oxygen during the crosslinking process of the polymer, thereby providing a porous polymer membrane with improved physical properties. Attached Figure Description

[0018] Figure 1 This is a schematic process flow diagram of a method for preparing a porous polymer membrane according to one embodiment. Detailed Implementation

[0019] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, so that those skilled in the art to which this invention pertains can readily implement it. However, this is merely exemplary, and the present invention is not limited to the exemplary embodiments described.

[0020] The porous polymer membrane according to an embodiment of the present invention can have a crosslinking reactivity degree of 1.0 or higher as defined by Formula 1 below.

[0021] [Formula 1] Crosslinking reactivity = ((A) B) / 10000)-C In Equation 1, A is the temperature at which the porous polymer membrane breaks when it is heated to 220°C at a heating rate of 5°C / min and a force of 0.015N is applied while it is stretched by thermomechanical analysis (TMA), i.e., the melt fracture temperature (°C); B is the percentage of the mass of undissolved residual solids divided by the initial mass after the porous polymer membrane is immersed in xylene at 135°C for 3 hours, i.e., the gel content (%); and C is the high load melt index (HLMI) (g / min) of the porous polymer membrane measured according to ASTM D 1238 at a temperature of 190°C and a load of 21.6 kg.

[0022] The thermomechanical analysis can be performed, for example, using a thermomechanical analysis apparatus (thermomechanical analyzer). The temperature can be increased while stretching the porous polymer membrane after fixing both ends within the thermomechanical analysis apparatus. For example, with both ends of the porous polymer membrane fixed or clamped, a force of 0.015 N can be applied while the temperature is increased from 25°C to 220°C at a rate of 5°C / min. During the heating process under tensile force, the temperature at which the porous polymer membrane fractures can be used as the melting fracture temperature. For example, the cross-sectional area of ​​the specimen has a width of approximately 3 mm to 5 mm and a length of approximately 10 mm to 20 mm; as a non-limiting example, the specimen can have a width of 4 mm and a length of 16 mm.

[0023] For example, the thermomechanical analysis equipment may be the TMA450 model from TA Instruments, but is not limited to this.

[0024] For example, the higher the durability of the porous polymer membrane at high temperatures, the higher its melt fracture temperature can be.

[0025] According to one implementation scheme, in Formula 1, A can be above 160°C.

[0026] According to one implementation, in Formula 1, A can be 160°C to 250°C or 160°C to 200°C.

[0027] Within the aforementioned range, the high-temperature durability of the porous polymer membrane can be further improved.

[0028] In Formula 1, B can be the percentage of the mass of undissolved residual solids after immersing a sample (e.g., 3g) of the porous polymer membrane in xylene at 135°C for 3 hours, divided by the initial mass before immersion. The xylene can be, for example, o-xylene, m-xylene, or p-xylene, but is not limited thereto. For example, for B, 200ml of xylene can be heated to 135°C, and then 3g of the porous polymer membrane can be added to the xylene. After 3 hours from the time of addition, the solids are filtered and dried, and then the weight is measured. B can be calculated as a percentage by converting the ratio of the residual solids mass to the initial added mass (3g). For example, the higher the solvent resistance of the porous polymer membrane to organic solvents, the higher its gel content can be.

[0029] According to one implementation scheme, in Equation 1, B can be 80% or more.

[0030] According to one implementation scheme, in Formula 1, B can be 85% or more, 90% or more, or 95% or more. For example, B can be 95% to 100%.

[0031] Within the aforementioned range, the solvent resistance of the porous polymer membrane to organic solvents can be further improved. When the porous polymer membrane is immersed in a hydrophobic organic solvent, its solvent resistance can be significantly improved even with increased temperature.

[0032] According to one embodiment, the solubility of the porous polymer membrane in xylene can refer to the proportion of the dissolved portion to the total added amount, which can be defined as 100 minus the gel content, and can be calculated using the formula: solubility = 100 - B (%). For example, the solubility of the porous polymer membrane in xylene can be less than 20%, less than 15%, less than 10%, or less than 5%.

[0033] In Formula 1, C refers to the High Load Melt Index (HLMI). For example, C can refer to the HLMI of the mass (g / 10 min) of the molten polymer after the porous polymer membrane is cut to prepare a sample and extruded under a load of 21.6 kg at a temperature of 190°C for 10 minutes.

[0034] In addition, for example, C can refer to the high load melt index (HLMI) in g / 10 minutes, which is the weight of the porous polymer membrane measured when 3 g of the porous polymer membrane is placed in a porous chamber at a temperature of 190°C and discharged under a load of 21.6 kg for 10 minutes.

[0035] In addition, for example, C can be measured according to ASTM D 1238.

[0036] The higher the processability of the porous polymer membrane, the higher the HLMI can be.

[0037] According to one implementation, in Formula 1, C can be less than 0.2 g / 10 minutes.

[0038] According to one embodiment, in Formula 1, C can be less than 0.1 g / 10 minutes, less than 0.05 g / 10 minutes, less than 0.03 g / 10 minutes, or less than 0.02 g / 10 minutes. Furthermore, for example, if C is converted to an hourly value, 0.1 g / 10 minutes can correspond to 0.6 g / hour, and 0.02 g / 10 minutes can correspond to 0.12 g / hour.

[0039] Within the aforementioned range, the processability of the porous polymer membrane can be further improved.

[0040] When the porous polymer membrane has a crosslinking degree of less than 1.0, its processability, solvent resistance, and / or high-temperature durability may be reduced. Therefore, the porous polymer membrane may be difficult to apply in various fields.

[0041] In one embodiment, the porous polymer membrane may have a crosslinking degree of 1.5 to 3. Therefore, while the mechanical strength of the porous polymer membrane is increased, improved resistance to organic solvents can be achieved even at elevated temperatures, thus providing improved mechanical properties and durability.

[0042] According to one embodiment, the porous polymer membrane can have a porosity of 10% to 80%.

[0043] According to one embodiment, the porous polymer membrane can have a porosity of 30% to 60%. Within this range, the porous polymer membrane can possess sufficient air permeability while maintaining an appropriate level of mechanical and physical properties. When the porous polymer membrane is used in a lithium secondary battery and immersed in a liquid electrolyte, improved ionic conductivity can be achieved.

[0044] According to one embodiment, the porous polymer membrane can have a puncture strength of 0.15 N / μm or higher. The puncture strength of the porous polymer membrane can vary depending on the material.

[0045] The porous polymer membrane is not limited as long as it can be cured by electron beam irradiation. The polymer resin may include polyolefin resins such as polyethylene, polypropylene, and polymethylpentene; polyesters such as nylon and polyethylene terephthalate; polycarbonate; styrene resins; fluorine resins such as polytetrafluoroethylene and polyvinylidene fluoride; and vinyl chloride resins. These resins may be used alone or in combination of two or more.

[0046] According to one embodiment, the porous polymer membrane may contain at least one selected from, for example, 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).

[0047] The polyolefin-based resin may include polypropylene-based resin, polyethylene-based resin, etc.

[0048] For example, the porous polymer membrane may contain a polyethylene resin.

[0049] When the porous membrane contains at least one of the polymers listed above, it may have improved processability.

[0050] For example, during electron beam irradiation, chemical bonds within polymer chains break, potentially generating highly reactive free radicals, which may temporarily reduce the polymer's mechanical strength. Subsequently, these free radicals can form new bonds between dissimilar polymer chains under an inert atmosphere, thereby restoring mechanical strength and forming crosslinks. This crosslinking can create a three-dimensional network structure with improved thermal and chemical stability, including increased solvent resistance and melt fracture temperature. Because the generated free radicals are highly reactive, they may be annihilated upon contact with oxygen; therefore, an inert atmosphere is preferred for effective crosslinking. Furthermore, the formation of crosslinks may be weakened in the presence of oxygen concentrations similar to those in the surrounding air, potentially resulting in reduced thermal and chemical stability of the polymer.

[0051] Figure 1 This is a schematic process flow diagram of a method for preparing a porous polymer membrane according to one embodiment.

[0052] The method for preparing the porous polymer membrane may include: extruding and stretching a raw material containing a polymer to form a primary porous polymer membrane (step S10); forming an oxygen-displaced primary porous polymer membrane, wherein the oxygen content in the total gas contained in the pores of the primary porous polymer membrane is less than 9% by volume (step S20); embedding and sealing the oxygen-displaced primary porous polymer membrane within an oxygen-impermeable outer material (step S30); irradiating the oxygen-displaced primary porous polymer membrane with an electron beam from the outside of the oxygen-impermeable outer material to prepare a porous polymer membrane (step S40).

[0053] First, a primary porous polymer membrane can be prepared. This primary porous polymer membrane can be prepared by purchasing or by manufacturing.

[0054] For example, a primary porous polymer membrane can be prepared by stretching a polymer-containing particle or melt after extrusion. For instance, raw resin particles can be extruded using an extruder at a temperature above 200°C to form a resin sheet, and the resin sheet can be cooled to prepare an unstretched sheet. The unstretched sheet can then be stretched to form a primary porous polymer membrane. The stretching method can include simultaneous biaxial stretching, sequential biaxial stretching, multi-segment stretching, multiple stretching, etc.

[0055] The primary porous polymer membrane is not limited as long as it can be cured by electron beam irradiation. The primary porous polymer membrane may contain polyolefin 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 can be used alone or in combination of two or more.

[0056] The primary porous polymer membrane may contain at least one selected from, for example, 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). For example, the primary porous polymer membrane may contain a polyethylene-based resin.

[0057] The primary porous polymer membrane may comprise an assembly of linear polymer chains. These linear polymer chains may not be bonded together in a direction perpendicular to their length, thus the primary porous polymer membrane can possess very high processability and low mechanical and physical properties.

[0058] In one embodiment, the pore size of the primary porous polymer membrane can be below 100 nm, for example, it can be 40 nm to 100 nm, 40 nm to 90 nm, 40 nm to 70 nm, or 40 nm to 60 nm. The pore size can 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 the ASTM F316-03 standard. The pore size analyzer can be, for example, a capillary flow porometer, a gas adsorption analyzer (BET, BJH, etc.), or a helium pycnometer.

[0060] For example, the pores of the primary porous polymer membrane may be filled with air. The oxygen concentration in the air may be approximately 21% by volume.

[0061] For example, the oxygen content in the total gas contained in the pores of the oxygen-displaced primary porous polymer membrane can be less than 9% by volume, less than 8.5% by volume, less than 7% by volume, less than 5% by volume, or less than 4.5% by volume.

[0062] For example, the oxygen-displaced primary porous polymer membrane can be prepared by replacing 57% or more, 60% or more, 70% or more, 80% or more, or 85% or more of oxygen, based on the total oxygen volume contained in the pores of the primary porous polymer membrane, with an inert gas. That is, the oxygen displacement degree of the oxygen-displaced primary porous polymer membrane can be 57% or more, 60% or more, 70% or more, 80% or more, or 85% or more.

[0063] The primary porous polymer membrane contains multiple pores, which may contain gas, such as air. When the oxygen content in the total gas contained in the pores is too high, impurities may form during subsequent crosslinking, or the crosslinking reaction sites between polymer chains may react with oxygen, resulting in insufficient crosslinking.

[0064] In one embodiment, the primary porous polymer membrane can be placed in a vacuum atmosphere and then in an inert gas atmosphere to form the oxygen-displaced primary porous polymer membrane.

[0065] According to one embodiment, the primary porous polymer membrane can be made with a density of less than 10. -2 Place the sample in a near-vacuum environment with a pressure close to 0 for 30 minutes to 2 hours. The near-vacuum environment refers to an environment with a pressure close to 0, and may include environments close to a vacuum.

[0066] When the primary porous polymer membrane is placed in the vacuum-like environment, the oxygen-containing gas (e.g., air) present inside the pores can be removed and the primary porous polymer membrane is deformed into a compressed form.

[0067] Then, an inert gas can be supplied. Therefore, the inert gas can permeate into the pores of the primary porous polymer membrane, and some or all of the space previously occupied by oxygen before vacuum or near-vacuum treatment can be filled by the inert gas.

[0068] In one embodiment, the inert gas can be supplied at a flow rate of 0.5 L / min to 1.5 L / min.

[0069] For example, the inert gas is not particularly limited, but may include N2, He, Ar, Ne, etc.

[0070] Therefore, it is possible to prepare an oxygen-displacement primary porous polymer membrane that reduces the oxygen content in the total gas filling the pores.

[0071] As used in this specification, "oxygen displacement degree" can refer to a percentage value representing the ratio of the total oxygen content removed from the pores to the total oxygen content contained within the pores of the primary porous polymer membrane. The method for measuring the respective total oxygen content is not particularly limited; for example, it can be measured using the number of moles of oxygen or a volume ratio. For instance, when the oxygen displacement degree is calculated using the total number of moles of oxygen as the total oxygen content, the oxygen displacement degree can refer to a percentage value representing the ratio of the total number of moles of oxygen removed from the pores of the porous polymer membrane to the total number of moles of oxygen contained within the pores of the primary porous polymer membrane.

[0072] For example, the oxygen displacement degree can be a percentage value calculated as the ratio of the total number of moles of oxygen removed from the pores of the membrane after being placed in the vacuum or vacuum-like environment to the total number of moles of oxygen present in the pores of the primary porous polymer membrane before being provided with the vacuum or vacuum-like environment.

[0073] As a non-limiting example, the total number of moles (n) of oxygen present in the pores of the primary porous polymer membrane before the chamber containing the vacuum or near-vacuum atmosphere is introduced. I The following calculation can be performed. For example, the pores of a membrane stored or prepared in an atmospheric atmosphere before the membrane is added to the chamber can be filled with air. The total volume (V) of the primary porous polymer membrane can be calculated. F Multiply by porosity (R) P To calculate the pore volume (V) P ), the pore volume (V P Substituting the atmospheric absolute pressure of approximately 101.325 kPa, the room temperature of approximately 298.15 K, and the gas constant (R) into the ideal gas law (PV = nRT), the total number of moles of gas within the pores (n) can be calculated. T At this point, no special temperature restriction is required; the temperature measured under the atmosphere in which the membrane is stored or prepared can be substituted into the ideal gas law. The total number of moles of gas within the pores (n) T Multiply by the mole fraction of oxygen in the atmosphere (n) O (approximately 0.21), thus allowing the calculation of the total number of moles of oxygen present in the stomata (n). I At this point, the gas constant R is a known constant, which can be approximately 8.314 J / mol·K.

[0074] As a non-limiting example, the total number of moles (n) of oxygen removed from the pores of the primary porous polymer membrane. F The following calculation can be performed.

[0075] For example, an oxygen analyzer can be installed in the chamber to measure the increase in partial pressure of oxygen (P). O The increase in the partial pressure of oxygen (P) O ), the effective volume of the chamber (V) C The internal temperature of the chamber (T) C Substituting the gas constant (R) and the total number of moles of oxygen removed from the pores (n) into the ideal gas law, we can calculate the total number of moles of oxygen removed from the pores (n). F )".

[0076] The oxygen analyzer can be used to measure the increase in oxygen partial pressure (P). OThe apparatus, if needed, can also measure the partial pressure of oxygen. The oxygen analyzer can be, for example, a residual gas analyzer (RGA, mass spectrometer), a paramagnetic oxygen analyzer, a zirconia oxygen analyzer, a galvanic cell type, or other electrochemical oxygen analyzers, as long as it can measure the partial pressure of oxygen (or the increase in partial pressure over time). The structure or materials of the apparatus are not particularly limited. Furthermore, the increase in the partial pressure of oxygen (P...) O The oxygen partial pressure can be calculated as follows: by measuring the oxygen concentration (volume %) and the total pressure of the chamber, multiplying the two to calculate the oxygen partial pressure, and then calculating the difference from the initial oxygen partial pressure.

[0077] For example, the oxygen-displacing primary porous polymer membrane can be embedded and sealed within an oxygen-impermeable outer material.

[0078] Even without external force, gases exhibit a high diffusion rate. Unless the gas is blocked, oxygen may diffuse into the space inside the pores over time. By embedding and sealing the oxygen-dispatch primary porous polymer membrane within the oxygen-impermeable outer material, oxygen can be prevented from permeating into the pores during subsequent processes.

[0079] In one embodiment, the oxygen-impermeable outer casing material, measured according to ASTM D 3985 method at 23°C and 0% relative humidity, has an oxygen permeability of 1 ml (cc) / m³. 2 Below / day / standard atmosphere (atm). The lower the oxygen permeability, the better the oxygen blocking characteristics, therefore its lower limit is not particularly limited. The oxygen permeability can be, for example, 0.9 ml / m³. 2 / day / below standard atmosphere, 0.5 ml / m 2 / day / below standard atmosphere, 0.3 ml / m 2 / day / below standard atmospheres.

[0080] As a non-limiting example, the oxygen permeability can be measured using an oxygen permeability testing machine, such as a Mocon OX-TRAN device.

[0081] In one embodiment, the oxygen-impermeable outer material may comprise at least one selected from polyamide-imide, polycarbonate, polypropylene, polyvinyl chloride, polyester, polyamide, polyurethane, and a mixture of polyethylene and paraffin.

[0082] For example, as a film containing the mixture of the polyethylene and alkanes, a paraffin sealing film, etc., can be used.

[0083] For example, the material of the outer casing is not particularly limited, but can be a material that will not deform during the electron beam crosslinking and subsequent heat treatment processes. For example, the outer casing material may partially comprise aluminum foil, stainless steel, etc.

[0084] An electron beam is irradiated from the outside of the oxygen-impermeable outer material, causing crosslinking. The oxygen-displaced primary porous polymer membrane can be crosslinked in a sealed state, thus enabling the preparation of porous polymer membranes with improved mechanical and physical properties.

[0085] In one embodiment, the subsequent heat treatment can be performed while the oxygen-impermeable outer casing is sealed.

[0086] According to one embodiment, the electron beam can be irradiated with an accelerating voltage of 0.1 MeV to 10 MeV. According to some embodiments, the electron beam can be irradiated with an accelerating voltage of 0.1 MeV to 5 MeV or 0.2 MeV to 2.5 MeV.

[0087] Within the aforementioned range, it is possible to suppress the decomposition of polymer chains while appropriately carrying out cross-linking between polymer chains.

[0088] In one embodiment, the oxygen-impermeable outer material may be irradiated with an electron beam once or twice or more.

[0089] According to one embodiment, the electron beam can irradiate with a cumulative exposure dose of 10 kGy to 300 kGy. According to some embodiments, the electron beam can irradiate with a cumulative exposure dose of 25 kGy to 150 kGy or 75 kGy to 150 kGy.

[0090] For example, the cumulative irradiation dose of the electron beam can be the average cumulative irradiation dose per unit area of ​​the oxygen-displaced primary porous polymer membrane. For example, the cumulative irradiation dose can be calculated based on the 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.

[0091] Within the aforementioned range, cross-linking between polymer chains can be performed more appropriately while further suppressing polymer chain decomposition.

[0092] According to one embodiment, the exterior of the oxygen-impermeable outer material can be an atmospheric atmosphere or an inert gas atmosphere.

[0093] According to one embodiment, after the crosslinking is performed, heat energy can be applied from the outside of the oxygen-impermeable outer material for subsequent heat treatment. Therefore, further crosslinking of residual free radicals in the polymer chains can be promoted, and the mechanical and physical properties of the porous polymer membrane can be further improved.

[0094] The subsequent heat treatment can be carried out in a sealed state. Therefore, the diffusion of oxygen can be continuously prevented, and further side reactions of the free radicals can be prevented.

[0095] According to one embodiment, the ratio of the porosity of the primary porous polymer membrane to the porosity of the porous polymer membrane can be greater than 1 and less than 10. Through the crosslinking process, the pore volume of the primary porous polymer membrane can be reduced, and a porous polymer membrane with improved mechanical and physical properties can be provided.

[0096] The porosity of primary porous polymer membranes and porous polymer membranes can be calculated, for example, by calculating the space within the membrane (pore volume ratio).

[0097] The porosity of the membrane can be measured, for example, by mass- and size-based methods, liquid permeation methods, etc.

[0098] As a non-limiting example, in the mass- and size-based method, porosity can be calculated as follows: First, prepare a membrane sample, measure its mass using a precision balance, and measure its thickness and area. Measure the skeletal density of the polymer using a helium hydrometer or similar device. Divide the measured mass of the sample by the product of the thickness, area, and skeletal density to calculate the volume ratio of solids within the membrane. Subtract this ratio from the total volume to calculate the porosity (%).

[0099] As a non-limiting example, in the liquid permeation method, porosity can be calculated as follows: The sample is thoroughly immersed in a solvent, filling the pores with solvent. The mass of the immersed sample and the mass of the dried sample are then measured separately. The measured mass difference is multiplied by the density of the solvent to calculate the volume filled in the pores, and this difference is compared with the total volume of the membrane to calculate the porosity.

[0100] The porous polymer membrane according to embodiments of the present invention can be applied to various electrochemical devices, including separators for secondary batteries, and can be provided, for example, as a membrane for separators.

[0101] A secondary battery separator according to an embodiment of the present invention may include the aforementioned porous polymer membrane. The secondary battery separator may further include, for example, a coating containing a gas adsorbent. The gas adsorbent may, for example, comprise zeolite, and may further comprise one or more porous inorganic particles selected from, for example, aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), aluminum oxide (Al2O3), magnesium oxide (MgO), calcium oxide (CaO), barium sulfate (BaSO4), boehmite, titanium dioxide (TiO2), silicon dioxide (SiO2), and clay. As a non-limiting example, the average size (D) of the gas adsorbent... 50 The size can range from 0.01 to 5 μm.

[0102] The coating may further comprise, for example, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer (polyethylene-co-vinyl acetate), polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. At least one binder selected from propionate, cyanoethyl pullullan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullullan, carboxyl methyl cellulose, and polyvinyl alcohol.

[0103] In one embodiment, the thickness of the separator for the secondary battery can be from 10 μm to 100 μm.

[0104] A gas separation membrane according to an embodiment of the present invention may include the aforementioned porous polymer membrane. The gas separation membrane may further include, for example, a selective layer. The selective layer may contain graphene oxide, metal-organic frameworks (MOFs), hydrotalcite, zirconate, calcium oxide, etc., but is not limited thereto. The gas separation membrane may further include an intermediate layer containing siloxane-based polymers and / or polyacetylene-based polymers between the porous polymer membrane and the selective layer; this intermediate layer may function as an adhesive layer. The aforementioned gas separation membrane can selectively separate gases such as carbon dioxide, hydrogen, helium, nitrogen, oxygen, and olefins.

[0105] 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.

[0106] Example 1 A 10 μm thick polyethylene (PE) porous membrane was used in an environment with a density of less than 10 μm. -2 The gas was placed in a vacuum chamber at a pressure of 1 hour, and then N2 gas was supplied for 3 minutes to replace the oxygen inside the pores with an oxygen replacement rate of more than 80% by volume.

[0107] An oxygen-displacing PE porous membrane is embedded within an outer material that can block oxygen and then sealed.

[0108] In a sealed state, an electron beam is irradiated in an atmospheric environment with an accelerating voltage of 1 MeV until the cumulative irradiation reaches 100 kGy, thereby preparing a porous polymer membrane.

[0109] The oxygen displacement degree is calculated as follows, before the membrane is added to the vacuum chamber, by measuring the total volume (V) of each membrane. F Multiply by porosity (R) P To calculate the pore volume (V) P ), the pore volume (V P Substituting the atmospheric absolute pressure of approximately 101.325 kPa, the room temperature of approximately 298.15 K, and the gas constant (R) of 8.314 J / mol·K into the ideal gas law (PV=nRT), we can calculate the total number of moles of gas in the pores (n). T )".

[0110] The total number of moles of gas in the pores (n) TMultiply by the mole fraction of oxygen in the atmosphere (n) O That is, approximately 0.21, thus calculating the total number of moles of oxygen present in the stomata (n). I )".

[0111] In the vacuum chamber, the increase in partial pressure of oxygen (P) caused by the removal of oxygen from the membrane is measured. O ).

[0112] The increase in the partial pressure of the oxygen (P) O The effective volume (V) of the vacuum chamber C The internal temperature of the vacuum chamber (T) C Substituting the gas constant (R) of 8.314 J / mol·K into the ideal gas law, calculate the total number of moles of oxygen removed from the pores (n). F )".

[0113] The total number of moles of oxygen removed from the stomata (n) F ) and the total number of moles of oxygen present in the stomata (n) T The proportion of (n) F / n I The percentage of oxygen replacement is calculated as the oxygen replacement rate. The oxygen replacement rate will be calculated using the same method below.

[0114] Example 2 The porous polymer membrane was prepared using the same method as in Example 1, except that the electron beam was irradiated until the cumulative irradiation dose reached 25 kGy.

[0115] Example 3 The porous polymer membrane was prepared using the same method as in Example 1, except that the electron beam was irradiated until the cumulative irradiation dose reached 150 kGy.

[0116] Comparative Example 1 The porous polymer membrane was prepared using the same method as in Example 1, except that displacement was performed to make the oxygen displacement of the membrane 50%.

[0117] Comparative Example 2 The porous polymer membrane was prepared using the same method as in Example 1, except that a 10 μm thick PE porous membrane was placed in an atmospheric environment for 1 hour and then irradiated with an electron beam in a 99.999% nitrogen atmosphere without being sealed in an outer casing that could block oxygen.

[0118] Comparative Example 3 The porous polymer membrane was prepared using the same method as in Example 1, except that a 10 μm thick PE porous membrane was placed in an atmospheric environment for 1 hour, then embedded in an outer material that could block oxygen, and then irradiated with an electron beam in an atmospheric atmosphere.

[0119] Comparative Example 4 The porous polymer membrane was prepared using the same method as in Example 1, except that the oxygen-displaced PE porous membrane was not sealed and was irradiated with an electron beam in an atmospheric environment.

[0120] Reference example A PE porous membrane with a thickness of 10 μm was used.

[0121] Table 1 below shows the preparation conditions for the examples and comparative examples.

[0122] [Table 1] In Table 1, a sealed condition is indicated by “O” and an unsealed condition is indicated by “X”.

[0123] Measurement example For the porous polymer membranes of the Examples and Comparative Examples, measurements were performed using the following methods, as shown in Table 2, and the degree of crosslinking reactivity was calculated according to Formula 1 above.

[0124] (1) Melt fracture temperature The porous polymer membranes of the examples and comparative examples were stretched using a thermomechanical analysis apparatus, with the temperature increased from 25°C to 220°C at a rate of 5°C / min while a force of 0.015 N was applied. The temperature at which the membrane ruptured was measured and taken as the melt fracture temperature.

[0125] (2) 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, and the percentage of undissolved residual solids relative to the initial added amount (3 g) was calculated as the gel content.

[0126] (3) 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 discharge for 10 minutes. The weight of the melt of the porous polymer membrane was measured and taken as the high load melt index (HLMI). 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.

[0127] At this point, when all 3g of porous polymer membrane added 10 minutes prior has been discharged, the HLMI is calculated based on the elapsed time up to that point.

[0128] (4) Porosity The porosity of porous polymer membranes is calculated by measuring the space within the membrane. Specifically, the porous polymer membrane is cut into rectangles of D1cm × D2cm (thickness: T, μm), and then the porosity is determined using the mass (M, g) measured by a precision balance and the PE skeleton density (ρ, g / cm³). 3 ), and is calculated using the following formula.

[0129] Porosity = {1 - (M × 10000) / (D1 × D2 × T × ρ)} (5) Pore diameter The pore diameter of the porous polymer membrane was measured according to ASTM F316-03 using a capillary flow porosimeter (CFP-1500-AEL, PMI). Measurements were performed using a half-dry method. The test solution used to fill the pores was Galwick solution (surface tension: 15.9 dynes / cm = 15.9 mN / m) supplied by PMI.

[0130] [Table 2] Experimental Example: Evaluation of Penetration Durability The puncture strength of the porous polymer membranes of the examples and comparative examples was measured using an INSTRON Universal TestMachine (model name: 3345). An indentation probe with a pin tip of 1.0 mm in diameter and 0.5 mm radius of curvature was used in the test, and the indentation speed was set to 120 mm / min.

[0131] Cut the porous polymer membrane sample into 50mm × 50mm pieces and fix it flat on the lower clamp of the testing machine. Use the clamp to hold the edges of the sample in place, ensuring the sample does not detach and is wrinkle-free.

[0132] The indentation probe is moved in a direction perpendicular to the membrane surface, and the resulting force-displacement curve is recorded. The puncture strength is evaluated by dividing the maximum load (N) at the location of the first membrane rupture by the membrane thickness (μm) (N / μm).

[0133] All samples were stabilized for at least 24 hours at 25±2℃ and 50±5% relative humidity before measurement and then used for testing.

[0134] [Table 3] Referring to Tables 2 and 3, the porous polymer membranes of the embodiments having a crosslinking reactivity degree of 1.5 or higher provide improved mechanical and physical properties compared to the membranes of the comparative examples due to the suppression of polymer chain decomposition. Furthermore, as shown in Table 2, the porous polymer membranes of the embodiments exhibit improved physical properties after electron beam irradiation while maintaining a puncture strength at the same level as the reference examples.

[0135] On the other hand, the porous polymer membranes of the comparative examples with a crosslinking degree of less than 1.0 exhibited significantly reduced puncture strength or lower durability at high temperatures, resulting in deteriorated physical properties.

[0136] Although polyethylene (PE) is used in the examples for preparing porous polymer membranes, other types of polymers described in this specification can also form porous polymer membranes with a crosslinking reactivity of 1.0 or more as defined by Formula 1 above when prepared under the same or similar preparation conditions.

Claims

1. A porous polymer membrane having a crosslinking reactivity degree of 1.0 or higher as defined in Formula 1: [Formula 1] Crosslinking reactivity = ((A) B) / 10000)-C In Equation 1, A represents the temperature at which the porous polymer membrane breaks when it is heated to 220°C at a heating rate of 5°C / min and a force of 0.015N is applied simultaneously using thermomechanical analysis (TMA). The temperature is the melt fracture temperature, expressed in °C. B represents the gel content, expressed as a percentage (%), calculated by dividing the mass of the undissolved residual solids of the porous polymer membrane after immersion in xylene at 135°C for 3 hours by the initial mass. C represents the high load melt index (HLMI) of the porous polymer membrane, measured according to ASTM D 1238 at a temperature of 190°C and a load of 21.6 kg, in g / 10 min.

2. The porous polymer membrane according to claim 1, wherein, In Equation 1, A is above 160°C.

3. The porous polymer membrane according to claim 1, wherein, In Equation 1, B is 80% or more.

4. The porous polymer membrane according to claim 1, wherein, In Formula 1, C is less than 0.2 g / 10 minutes.

5. The porous polymer membrane according to claim 1, wherein, The porous polymer membrane has a porosity of 10% to 80%.

6. The porous polymer membrane according to claim 1, wherein, The porous polymer membrane comprises 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).

7. A separator for a secondary battery, comprising the porous polymer membrane of claim 1.

8. A gas separation diaphragm comprising the porous polymer membrane of claim 1.

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