Microporous membrane

Abstract

To provide a microporous film that has high strength, can be made thinner, is excellent in shutdown characteristics, and useful especially as a separator for a secondary battery.SOLUTION: A microporous film is made of a composition that contains at least polyethylene of a weight average molecular weight of 500,000 or less of 5-5,000 pts.wt. relative to 100 pts.wt. of an ultrahigh-molecular weight polyethylene copolymer that has an intrinsic viscosity of 10-50 dL / g, a molecular weight distribution of 4 or less, and the number of short chain branches of 1-10 per 1,000 carbons. The microporous film has at least 1) a film thickness of 0.001-1 mm, 2) a piercing strength of 3-5 N / 10 μm, 3) a thermal shrinkage of 2- 10%, and 4) a heat treatment temperature of 100-130°C when air permeability is over 9,999 seconds measured under conditions of a measurement temperature of 23°C and an air passage amount of 100 m in an air permeability measurement device.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a specific microporous membrane, and more particularly to a microporous membrane made of a specific ultra-high molecular weight polyethylene copolymer composition that is expected to be applied as a separator for secondary batteries because it has high strength, can be made into a thin film, and exhibits particularly excellent shutdown characteristics by maintaining mechanical strength and having excellent occlusion properties above a certain temperature. [Background technology]

[0002] Ultra-high molecular weight polyethylene has an extremely high molecular weight, equivalent to over 1 million in viscosity-average molecular weight (Mv), resulting in excellent impact resistance, self-lubricating properties, wear resistance, weather resistance, chemical resistance, and dimensional stability, possessing high physical properties comparable to engineering plastics. For this reason, various molding methods are being used to explore its application in lining materials, line components for the food industry, machine parts, artificial joints, sporting goods, microporous membranes, separators, and more.

[0003] However, due to its high molecular weight, ultra-high molecular weight polyethylene has extremely low fluidity when melted, making it difficult to mold by kneading and extrusion like ordinary polyethylene, which has a molecular weight in the range of tens of thousands to about 300,000. Therefore, ultra-high molecular weight polyethylene is molded by methods such as direct sintering of the polymer powder obtained by polymerization, compression molding, molding using a ram extruder that extrudes while intermittently compressing, and extrusion molding while dispersed in a solvent, followed by removal of the solvent.

[0004] In the molding method in which the material is extruded while dispersed in a solvent, and then the solvent is removed, it is known that porous membranes can be produced by uniaxial and biaxial stretching before and after the removal of the solvent. This ultra-high molecular weight polyethylene microporous membrane is expected to have excellent physical properties such as heat resistance, strength, and impact resistance due to the high molecular weight of ultra-high molecular weight polyethylene. However, ultra-high molecular weight polyethylene produced by commercially available Ziegler catalysts has a molecular weight distribution (Mw / Mn), which is the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn), that is greater than 4, and the molecular weight distribution is broad. As a result, the strength of the molded article is not sufficiently improved, and it cannot be said that it exhibits the expected performance.

[0005] On the other hand, methods have been proposed to produce ultra-high molecular weight ethylene polymers with a narrow molecular weight distribution using metallocene catalysts or post-metallocene catalysts (see, for example, Patent Documents 1 and 2), and to improve moldability by adding low molecular weight polyethylene such as high-density polyethylene to ultra-high molecular weight polyethylene (see, for example, Patent Document 3).

[0006] Furthermore, polyolefin microporous membranes are used in filters and as isolation materials for various batteries, and are particularly used as separators for lithium-ion batteries due to their excellent mechanical strength. Recently, with the rapid spread of electric vehicles, automotive lithium-ion batteries are required to be larger, have higher capacity and higher output compared to lithium-ion batteries for mobile phones and personal computers, and the safety requirements for separators have also changed, such as the need to improve the shutdown characteristics of lithium-ion batteries. Shutdown characteristics refer to the ability to ensure the safety of a battery by melting the separator and closing the pores to interrupt the battery reaction when the inside of the battery overheats in an overcharge state. The lower the shutdown temperature, the greater the safety effect and the better the shutdown characteristics. Methods have been proposed to lower the shutdown temperature of microporous membranes by using ethylene-α-olefin copolymers, which have a lower melting point than ethylene homopolymers (see, for example, Patent Documents 4 and 5).

[0007] Furthermore, ultra-high molecular weight polyethylene compositions and microporous membranes made therefrom have been proposed, including one containing 5 to 5,000 parts by weight of polyethylene with an intrinsic viscosity of 500,000 or less and an Mw / Mn ratio of 4 or less per 100 parts by weight of ultra-high molecular weight polyethylene with an intrinsic viscosity of 10 dl / g or more and 80 dl / g or less, and a microporous membrane made therefrom (see, for example, Patent Document 6). Also proposed are ultra-high molecular weight polyethylene microporous membranes containing ultra-high molecular weight polyethylene with an intrinsic viscosity of 4 to 10 dL / g and an Mw / Mn ratio of 4 or less, with a film thickness of 0.001 to 1 mm, a heat shrinkage rate of 2 to 3%, and a puncture strength (PS) of 2 to 5 N / 10 μm (see, for example, Patent Document 7). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 4868853 [Patent Document 2] Japanese Patent Publication No. 2006-36988 [Patent Document 3] Japanese Patent Publication No. 2003-105121 [Patent Document 4] Japanese Patent Publication No. 2001-72788 [Patent Document 5] Japanese Patent Publication No. 2021-102744 [Patent Document 6] Japanese Patent Publication No. 2017-145386 [Patent Document 7] Japanese Patent Publication No. 2022-20963 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, Patent Documents 1 and 2 merely propose ultra-high molecular weight polyethylene and do not propose anything regarding films, or even microporous films. Furthermore, these ultra-high molecular weight polyethylenes have problems with moldability, and when films are manufactured, they have poor moldability and stretchability. Even if stretching is possible, it is limited to the production of films with low stretch ratios, and the productivity and performance are not sufficient.

[0010] Furthermore, in the proposal in Patent Document 3, even when low molecular weight polyethylene was added, it only resulted in a film with a low stretching ratio, and the productivity was not sufficiently improved.

[0011] Furthermore, while the polyolefin microporous membrane proposed in Patent Document 4 lowers the shutdown temperature, its low stretching ratio results in low productivity, and the proposal in Patent Document 5, although excellent in mechanical strength, does not achieve sufficient shutdown performance.

[0012] Furthermore, the proposals in Patent Documents 6 and 7 lacked specific consideration regarding mechanical properties, the balance between heat resistance and shutdown properties (pore occlusion), and particular ultra-high molecular weight polyethylene copolymers.

[0013] Therefore, the present invention aims to provide a microporous membrane that can provide a secondary battery such as a lithium-ion battery that has excellent shutdown characteristics and superior safety while maintaining mechanical strength. [Means for solving the problem]

[0014] As a result of intensive research to solve the above problems, the inventors of the present invention have made a composition using a ultra-high molecular weight polyethylene copolymer having a specific molecular weight and molecular weight distribution, and made a microporous membrane having specific properties, thereby maintaining mechanical strength while exhibiting particularly excellent shutdown properties. When employed as a separator for a lithium-ion battery, a runaway reaction caused by overcharging of the lithium-ion battery, short circuit between the positive electrode and the negative electrode, etc. is suppressed by closing the pores of the microporous membrane at a lower temperature, and thermal runaway of the lithium-ion battery can be prevented at a lower temperature, resulting in a microporous membrane with excellent safety, and thus the present invention has been completed.

[0015] That is, the present invention relates to a composition containing at least 5 to 5,000 parts by weight of polyethylene having a weight average molecular weight (hereinafter, may also be referred to as Mw) of 500,000 or less with respect to 100 parts by weight of a ultra-high molecular weight polyethylene copolymer having an intrinsic viscosity (hereinafter, may also be referred to as [η]) of 10 to 50 dL / g, a molecular weight distribution (hereinafter, may also be referred to as Mw / Mn) of 4 or less, and 1 to 10 short-chain branches per 1,000 carbons, and relates to a microporous membrane characterized by satisfying at least any one of the following 1) to 4). 1) The film thickness is 0.001 to 1 mm. 2) The puncture strength measured under the measurement conditions of a temperature of 23°C and a puncture speed of 50 mm / min in the compression mode of a tensile tester equipped with a needle having a diameter of 1 mm and a curvature radius of 0.5 mm is 3 to 5 N / 10 μm. 3) The heat shrinkage rate measured under the heat treatment conditions of 105°C for 1 hour is 2 to 10%. 4) After performing a heat treatment for 1 hour, when the air permeability is measured with an air permeability measuring device under the measurement conditions of a temperature of 23°C and an air passage amount of 100 ml, the heat treatment temperature when the air permeability exceeds 9,999 seconds is 100 to 130°C.

[0016] The present invention will be described in detail below.

[0017] The microporous membrane of the present invention is made of a composition containing at least polyethylene in a ultra-high molecular weight polyethylene copolymer.

[0018] The high molecular weight polyethylene copolymer is a ultra-high molecular weight polyethylene copolymer having short chain branches, such as ultra-high molecular weight ethylene-propylene copolymer, ultra-high molecular weight ethylene-1-butene copolymer, ultra-high molecular weight ethylene-1-hexene copolymer, ultra-high molecular weight ethylene-1-octene copolymer, ultra-high molecular weight ethylene-4-methyl-1-pentene copolymer and other ultra-high molecular weight ethylene-α-olefin copolymers; etc. can be cited. And, [η] is 10 to 50 dL / g. Here, when [η] is less than 10 dL / g, the obtained microporous membrane will be mechanically inferior. On the other hand, when [η] exceeds 50 dL / g, due to the extremely high molecular weight, its molding processability as a composition will be inferior. In addition, [η] in the present invention can be measured by a method of measuring at 135 °C in a solution with a polymer concentration of 0.0005 to 0.01% using, for example, an Ubbelohde viscometer with decahydronaphthalene as a solvent. Also, Mw / Mn is 4 or less, and particularly preferably 2.5 or more and 4 or less. Here, when Mw / Mn exceeds 4, the obtained microporous membrane will be mechanically inferior. In addition, Mw, the number average molecular weight (hereinafter sometimes referred to as Mn), can be measured by a method of calculating as linear polyethylene conversion from an elution curve by, for example, ultra-high temperature gel permeation chromatography.

[0019] Furthermore, the ultra-high molecular weight polyethylene copolymer has 1 to 10 short chain branches per 1000 carbons, preferably 1 to 7. Also, there is no limit to the number of carbons in the short chain branches. Among them, particularly because it becomes a microporous membrane with an excellent balance between pore blockage and heat resistance, it is preferably 1 to 10, and particularly preferably 2 to 6. And, when the number of short chain branches per 1000 carbons is less than 1, when the obtained composition is made into a microporous membrane, the temperature at which the microporous membrane melts and the pores are blocked becomes high, so the shutdown characteristics are inferior. On the other hand, when the number of short chain branches per 1000 carbons exceeds 10, when the obtained composition is made into a microporous membrane, the melting point of the microporous membrane becomes low and the heat resistance is inferior. The number of short chain branches in the present invention is 13 C-NMR, 1It can be calculated from the number of methyl groups measured by H-NMR, infrared spectroscopy, etc.

[0020] The ultra-high molecular weight polyethylene copolymer preferably has a particle shape, as this improves operability, such as good particle fluidity when forming microporous membranes and excellent filling efficiency in storage equipment, storage containers, and hoppers, and the bulk density in this case is 130 to 700 kg / m³. 3 This is preferable, and when forming a microporous film, it offers particularly excellent processability, so a density of 200-600 kg / m² is desirable. 3 This is preferable. The bulk density can be measured, for example, by a method compliant with JIS K6760 (1995).

[0021] Furthermore, since the ultra-high molecular weight polyethylene copolymer can suppress discoloration (yellowing) and oxidative degradation caused by titanium, resulting in a good color tone and excellent weather resistance, it is preferable that the titanium content be low, and in particular, a titanium content of 0.5 ppm or less or below the detection limit is preferred. The titanium content can be determined by measurement using chemical titration, X-ray fluorescence analysis, ICP emission analysis, etc.

[0022] The ultra-high molecular weight polyethylene copolymer is preferable to have an average particle size of 1 to 1000 μm, as it exhibits excellent flowability as a powder, as well as superior moldability and physical properties. The average particle size can be measured by methods such as the sieving test method using a standard sieve specified in JIS Z8801.

[0023] Furthermore, the ultra-high molecular weight polyethylene copolymer is preferably a metallocene catalyst-based ultra-high molecular weight polyethylene copolymer, as it is easier to satisfy the above-mentioned properties, and is particularly preferably an ultra-high molecular weight polyethylene copolymer or its particles as described below.

[0024] Any method can be used to produce the ultra-high molecular weight polyethylene copolymer. For example, a method can be used in which ethylene is copolymerized with other olefins using a polyethylene production catalyst. Examples of α-olefins in this method include propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene, with 1-butene and 1-hexene being preferred. Examples of polymerization methods include solution polymerization, bulk polymerization, gas-phase polymerization, and slurry polymerization. Among these, slurry polymerization is particularly preferred because it enables the production of ultra-high molecular weight polyethylene copolymers with uniform particle shapes and allows for the efficient and stable production of ultra-high molecular weight polyethylene copolymers that provide microporous membranes with excellent shutdown properties while maintaining mechanical strength. Any commonly used organic solvent can be used as the solvent in slurry polymerization. Examples include benzene, toluene, xylene, pentane, hexane, and heptane. Liquefied gases such as isobutane and propane, and olefins such as 1-butene and 1-hexene can also be used as solvents.

[0025] Furthermore, any catalyst for polyethylene production used to produce the ultra-high molecular weight polyethylene copolymer can be used as long as it enables the production of the ultra-high molecular weight polyethylene copolymer. Examples include metallocene catalysts obtained from at least a transition metal compound (A), an organically modified clay modified with an aliphatic salt (B), and an organoaluminum compound (C).

[0026] Examples of the transition metal compound (A) include a transition metal compound having a (substituted) cyclopentadienyl group and a (substituted) fluorenyl group, a transition metal compound having a (substituted) cyclopentadienyl group and a (substituted) indenyl group, and a transition metal compound having a (substituted) indenyl group and a (substituted) fluorenyl group. Examples of the transition metal include zirconium and hafnium. Among these, zirconium compounds having a (substituted) cyclopentadienyl group and an amino group-substituted fluorenyl group, and hafnium compounds having a (substituted) cyclopentadienyl group and an amino group-substituted fluorenyl group are particularly preferred because they enable the efficient production of ultra-high molecular weight polyethylene copolymers.

[0027] More specifically, for example, diphenylmethylene (1-indenyl)(9-fluorenyl) zirconium dichloride, diphenylmethylene (1-indenyl)(2,7-di-t-butyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (4-phenyl-1-indenyl)(2,7-di-t-butyl-9-fluorenyl) zirconium dichloride, diphenylsilanediyl (cyclopentadienyl)(2-(dimethylamino)-9-fluorenyl) zirconium dichloride, diphenylsilanediyl (cyclopentadienyl) (2-(diethylamino)-9-fluorenyl) zirconium dichloride, diphenylsilanediyl (cyclopentadienyl) (2-(dibenzylamino)-9-fluorenyl) zirconium dichloride, diphenylsilanediyl (cyclopentadienyl) (2,7-bis(dimethylamino)-9-fluorenyl) zirconium dichloride, diphenylsilanediyl (cyclopentadienyl) (2,7-bis(diethylamino)-9-fluorenyl) zirconium dichloride, diphenylsilanediyl (cyclopentadienyl) (2,7 -Bis(dibenzylamino)-9-fluorenyl) zirconium dichloride, diphenylsilanediyl(cyclopentadienyl)(4-(dimethylamino)-9-fluorenyl) zirconium dichloride, diphenylsilanediyl(cyclopentadienyl)(4-(diethylamino)-9-fluorenyl) zirconium dichloride, diphenylsilanediyl(cyclopentadienyl)(4-(dibenzylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene(cyclopentadienyl)(2-(dimethylamino)-9- Fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl) (2-(diethylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl) (2-(diisopropylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl) (2-(dibenzylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl) (4-(dimethylamino)-9-fluorenyl) zirconium dichloride,Diphenylmethylene (cyclopentadienyl)(4-(diethylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl)(2-(diisopropylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl)(4-(dibenzylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl)(2,7-bis(dimethylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene ( Cyclopentadienyl)(2,7-bis(diethylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene(cyclopentadienyl)(2,7-bis(di-n-propylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene(cyclopentadienyl)(2,7-bis(diisopropylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene(cyclopentadienyl)(2,7-bis(di-n-butyl-amino)-9-fluorenyl) zirconium dichloride, dif Diphenylmethylene (cyclopentadienyl)(2,7-bis(diisobutylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl)(2,7-bis(di-t-butylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl)(2,7-bis(dibenzylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl)(3,6-bis(dimethylamino)-9-fluorenyl) zirconium dichloride , diphenylmethylene (cyclopentadienyl)(3,6-bis(diethylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl)(2,5-bis(dimethylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl)(2,5-bis(diethylamino)-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl)(2-(dimethylamino)-7-methyl-9-fluorenyl) zirconium dichloride,Diphenylmethylene (cyclopentadienyl)(2-(diethylamino)-7-methyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl)(2-(diisopropylamino)-7-methyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl)(2-(dibenzylamino)-7-methyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl)(2-(dimethylamino)-7-ethyl-9-fluorenyl) zirconium dichloride Zirconium dichloride, diphenylmethylene (cyclopentadienyl) (2-(diethylamino)-7-ethyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl) (2-(diisopropylamino)-7-ethyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl) (2-(dibenzylamino)-7-ethyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl) (2-(dimethylamino)-7-n-propyl- 9-Fluorenyl) Zirconium Dichloride, Diphenylmethylene (Cyclopentadienyl) (2-(Diethylamino)-7-n-propyl-9-Fluorenyl) Zirconium Dichloride, Diphenylmethylene (Cyclopentadienyl) (2-(Diisopropylamino)-7-n-propyl-9-Fluorenyl) Zirconium Dichloride, Diphenylmethylene (Cyclopentadienyl) (2-(Dibenzylamino)-7-n-propyl-9-Fluorenyl) Zirconium Dichloride, Diphenylmethylene (Cyclopentadienyl) (2-(dimethylamino)-7-isopropyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl) (2-(diethylamino)-7-isopropyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl) (2-(diisopropylamino)-7-isopropyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl) (2-(dibenzylamino)-7-isopropyl-9-fluorenyl) zirconium dichloride,Diphenylmethylene (cyclopentadienyl)(2-(dimethylamino)-7-n-butyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl)(2-(diethylamino)-7-n-butyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl)(2-(diisopropylamino)-7-n-butyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl)(2-(dibenzo (Dimethylamino)-7-n-butyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl) (2-(dimethylamino)-7-isobutyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl) (2-(diethylamino)-7-isobutyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl) (2-(diisopropylamino)-7-isobutyl-9-fluorenyl) zirconium Dichloride, diphenylmethylene (cyclopentadienyl) (2-(dibenzylamino)-7-isobutyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl) (2-(dimethylamino)-7-t-butyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl) (2-(diethylamino)-7-t-butyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (cyclopentadienyl) (2- Examples of zirconium compounds include (diisopropylamino)-7-t-butyl-9-fluorenyl) zirconium dichloride and diphenylmethylene(cyclopentadienyl)(2-(dibenzylamino)-7-t-butyl-9-fluorenyl) zirconium dichloride; zirconium compounds obtained by changing the dichloro form of these compounds to dimethyl, diethyl, dihydro, diphenyl, or dibenzyl forms; and hafnium compounds obtained by changing the zirconium in these compounds to hafnium.

[0028] Examples of organically modified clays (B) modified with the aliphatic salt include N,N-dimethyl-behenylamine hydrochloride, N-methyl-N-ethyl-behenylamine hydrochloride, N-methyl-Nn-propyl-behenylamine hydrochloride, N,N-dioleyl-methylamine hydrochloride, N,N-dimethyl-behenylamine hydrofluoride, N-methyl-N-ethyl-behenylamine hydrofluoride, N-methyl-Nn-propyl-behenylamine hydrofluoride, N,N-dioleyl-methylamine hydrofluoride, and N,N-dimethyl-behenylamine hydrofluoride. Iamine hydrobromide, N-methyl-N-ethyl-behenylamine hydrobromide, N-methyl-Nn-propyl-behenylamine hydrobromide, N,N-dioleyl-methylamine hydrobromide, N,N-dimethyl-behenylamine hydroiodide, N-methyl-N-ethyl-behenylamine hydroiodide, N-methyl-Nn-propyl-behenylamine hydroiodide, N,N-dioleyl-methylamine hydroiodide, N,N-dimethyl-behenylamine sulfate, N-methyl-N-ethyl-behenylamine sulfate Salts, aliphatic amine salts such as N-methyl-Nn-propyl-behenylamine sulfate and N,N-dioleyl-methylamine sulfate; P,P-dimethyl-behenylphosphine hydrochloride, P,P-diethyl-behenylphosphine hydrochloride, P,P-dipropyl-behenylphosphine hydrochloride, P,P-dimethyl-behenylphosphine hydrofluoride, P,P-diethyl-behenylphosphine hydrofluoride, P,P-dipropyl-behenylphosphine hydrofluoride, P,P-dimethyl-behenylphosphine hydrobromide, P,P- Examples of clays modified with aliphatic salts include diethyl-behenylphosphine hydrobromide, P,P-dipropyl-behenylphosphine hydrobromide, P,P-dimethyl-behenylphosphine hydroiodide, P,P-diethyl-behenylphosphine hydroiodide, P,P-dipropyl-behenylphosphine hydroiodide, P,P-dimethyl-behenylphosphine sulfate, P,P-diethyl-behenylphosphine sulfate, and P,P-dipropyl-behenylphosphine sulfate.

[0029] Furthermore, the clay compound constituting the organically modified clay (B) can be any compound belonging to the category of clay compounds. Generally, it is formed by stacking many layers called silicate layers, which are composed of tetrahedral sheets of silica tetrahedra arranged in a two-dimensional continuous arrangement and octahedral sheets of alumina octahedra or magnesia octahedra arranged in a two-dimensional continuous arrangement in a 1:1 or 2:1 ratio. Some of the Si in the silica tetrahedra are isomorphically substituted with Al, the Al in the alumina octahedra with Mg, and the Mg in the magnesia octahedra with Li, resulting in a deficiency of positive charge within the layer, and the layer as a whole is negatively charged. To compensate for this negative charge, Na is present between the layers. + or Ca 2+ These are known to contain cations such as . As for the clay compound, there are natural or synthetic products such as kaolinite, talc, smectite, vermiculite, mica, brittle mica, and blemish, and these can be used, but among them smectite is preferred due to its availability and ease of organic modification, and among smectite, hectorite or montmorillonite is even more preferred.

[0030] The organically modified clay (B) can be obtained by introducing the aliphatic salt between layers of the clay compound to form an ionic complex. When preparing the organically modified clay (B), it is preferable to select conditions such as a clay compound concentration of 0.1 to 30% by weight and a processing temperature of 0 to 150°C for processing. The aliphatic salt may be prepared as a solid and dissolved in a solvent for use, or a solution of the aliphatic salt may be prepared by a chemical reaction in the solvent and used as is. Regarding the reaction ratio of the clay compound to the aliphatic salt, it is preferable to use an amount of aliphatic salt equivalent to or greater than the exchangeable cations of the clay compound. As processing solvents, for example, aliphatic hydrocarbons such as pentane, hexane, and heptane; aromatic hydrocarbons such as benzene and toluene; alcohols such as ethyl alcohol and methyl alcohol; ethers such as ethyl ether and n-butyl ether; halogenated hydrocarbons such as methylene chloride and chloroform; acetone; 1,4-dioxane; tetrahydrofuran; water, etc. Preferably, alcohols or water are used alone or as one component of the solvent.

[0031] Furthermore, there are no restrictions on the particle size of the organically modified clay (B) that constitutes the catalyst for polyethylene production, but it is preferable that it be 1 to 100 μm in size, as this provides excellent efficiency during catalyst preparation and polyethylene production. There are also no restrictions on the method of adjusting the particle size; large particles may be crushed to an appropriate size, small particles may be granulated to an appropriate size, or a combination of crushing and granulation may be used. In addition, the particle size may be adjusted either in the clay before organic modification or in the organically modified clay after modification.

[0032] Any organoaluminum compound (C) can be used as long as it belongs to the category known as organoaluminum compounds, and examples include alkylaluminum compounds such as trimethylaluminum, triethylaluminum, and triisobutylaluminum.

[0033] Regarding the proportion of the transition metal compound (A) (hereinafter sometimes referred to as component (A)), the organically modified clay (B) (hereinafter sometimes referred to as component (B)), and the organoaluminum compound (C) (hereinafter sometimes referred to as component (C)) that constitute the polyethylene production catalyst, there are no restrictions as long as they can be used as a catalyst for polyethylene production. In particular, since it is a polyethylene production catalyst that can produce ultra-high molecular weight polyethylene copolymers with high production efficiency, the molar ratio per metal atom of component (A) to component (C) is preferably in the range of component (A):component (C) = 100:1 to 1:100000, and especially preferably in the range of 1:1 to 1:10000. Furthermore, the weight ratio of component (A) to component (B) is preferably in the range of component (A):component (B) = 10:1 to 1:10000, and especially preferably in the range of 3:1 to 1:1000.

[0034] Regarding the method for preparing the polyethylene production catalyst, any method may be used as long as it is possible to prepare a polyethylene production catalyst containing component (A), component (B), and component (C). For example, a method may be used in which each of components (A), (B), and (C) is mixed in an inert solvent or using a monomer for polymerization as the solvent. There are no restrictions on the order in which these components are reacted, nor on the temperature or time of the treatment. It is also possible to prepare a polyethylene production catalyst using two or more types of each of components (A), (B), and (C).

[0035] The polymerization conditions for producing the ultra-high molecular weight polyethylene copolymer, such as polymerization temperature, polymerization time, polymerization pressure, and monomer concentration, can be arbitrarily selected. Among these, polymerization is preferably carried out within the range of a polymerization temperature of 0 to 100°C, a polymerization time of 10 seconds to 20 hours, and a polymerization pressure of atmospheric pressure to 100 MPa. It is also possible to adjust the molecular weight using hydrogen or other means during polymerization. Polymerization can be carried out by batch, semi-continuous, or continuous methods, and it is also possible to carry out the polymerization in two or more stages by changing the polymerization conditions. Furthermore, the ultra-high molecular weight polyethylene copolymer obtained after polymerization can be separated and recovered from the polymerization solvent by conventionally known methods and dried.

[0036] The polyethylene constituting the microporous membrane of the present invention may be any polyethylene prepared with a Ziegler-Natta catalyst, metallocene catalyst, etc., as long as its Mw is 500,000 or less, preferably 50,000 to 500,000. However, if the polyethylene has an Mw exceeding 500,000, the viscosity of the resulting composition becomes high, resulting in poor moldability and making it difficult to form a microporous membrane.

[0037] Furthermore, the polyethylene can be exemplified not only by ethylene homopolymers but also by copolymers of ethylene and α-olefins. Examples of α-olefins include propylene, 1-butene, 1-hexene, and 1-octene.

[0038] The composition constituting the microporous membrane of the present invention contains at least 5 to 5000 parts by weight of polyethylene per 100 parts by weight of the ultra-high molecular weight polyethylene copolymer, preferably 20 to 2000 parts by weight. Here, if the polyethylene is less than 5 parts by weight, the resulting composition will have poor moldability, and it will not be easy to obtain a microporous membrane with the desired stretch ratio when making a stretched microporous membrane. In addition, the resulting microporous membrane will have poor mechanical strength. On the other hand, if it exceeds 5000 parts by weight, the resulting microporous membrane will have poor mechanical strength.

[0039] The method for preparing the composition can be any method that allows for the mixing of the ultra-high molecular weight polyethylene copolymer with polyethylene to obtain an ultra-high molecular weight polyethylene copolymer system composition. Examples include extrusion kneading or roll kneading in a molten state, or dissolving in a solvent, then extrusion kneading, roll kneading, or stirring and mixing using a stirring blade, followed by removal of the solvent by solvent distillation or solvent extraction. Furthermore, when dissolving in an organic solvent, the mixture obtained can be used as is, in conjunction with the mixing reaction with the organic solvent described later. Examples of solvents used in this process include linear or branched saturated or unsaturated aliphatic compounds such as hexane, heptane, decane, dodecane, tetradecane, octadecane, eicosane, liquid paraffin, and isoparaffin; saturated or unsaturated alicyclic compounds such as cyclohexane, cyclodecane, tetrahydronaphthalene, and decahydronaphthalene; aromatic compounds such as benzene, toluene, xylene, naphthalene, and anthracene; and halogenated hydrocarbon compounds such as methylene chloride, 1,2-dichloroethane, 1,1,2-trichloroethane, chlorobenzene, and dichlorobenzene.

[0040] The microporous membrane of the present invention is made of a composition containing at least the ultra-high molecular weight polyethylene copolymer and polyethylene, and without departing from the object of the present invention, it may also contain known additives such as heat stabilizers, weather stabilizers, antistatic agents, antifogging agents, antiblocking agents, slip agents, lubricants, nucleating agents, pigments, etc.; inorganic fillers or reinforcing agents such as carbon black, talc, glass powder, glass fiber, metal powder, etc.; organic fillers or reinforcing agents; flame retardants; neutron shielding agents, etc. Furthermore, it may also contain resins such as polypropylene resins, poly-1-butene, poly-4-methyl-1-pentene, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polystyrene, and maleic anhydride grafts thereof. Methods for adding such additives include blending them with the ultra-high molecular weight polyethylene copolymer or polyethylene, blending them during molding of the ultra-high molecular weight polyethylene copolymer or polyethylene, pre-dry blending or melt blending, etc.

[0041] The microporous membrane of the present invention satisfies all of the following characteristics: 1) a film thickness of 0.001 to 1 mm; 2) a puncture strength of 3 to 5 N / 10 μm measured in compression mode on a tensile testing machine equipped with a needle with a diameter of 1 mm and a radius of curvature of 0.5 mm at a temperature of 23°C and a puncture speed of 50 mm / min; 3) a thermal shrinkage rate of 2 to 10% measured at a heat treatment condition of 105°C for 1 hour; and 4) a heat treatment temperature of 100 to 130°C at which the air permeability exceeds 9999 seconds when measured using an air permeability measuring device at a temperature of 23°C and an air passage volume of 100 ml after 1 hour of heat treatment.

[0042] Here, if the film thickness is less than 0.001 mm, the film strength will be inferior. On the other hand, if the film thickness exceeds 1 mm, the permeability to gases, etc., will be inferior. Also, if the puncture strength is less than 3 N / 10 μm, the mechanical properties will be inferior and the durability will be poor. On the other hand, if it exceeds 5 N / 10 μm, the flexibility will be inferior and the film properties will be poor. Furthermore, if the thermal shrinkage rate exceeds 10%, when the microporous film is incorporated into a battery as a separator, the high shrinkage rate will cause the microporous film to rupture, leading to thermal runaway due to a short circuit between the positive and negative electrodes, resulting in inferior durability and safety. On the other hand, if the thermal shrinkage rate is less than 2%, the fluctuations in response to heat will be small and it is likely to have poor shutdown properties. The film thickness (mm) can be determined, for example, by measuring the film thickness at 30 points on the microporous film using a contact-type film thickness gauge and taking the average value. Puncture strength can be measured using the compression mode of a tensile testing machine. For example, an 8cm square microporous membrane can be punctured using a needle with a diameter of 1mm and a radius of curvature of 0.5mm at a puncture speed of 10-200mm / min. Thermal shrinkage can be determined by heating an 8cm square microporous membrane at 105°C for 1 hour, allowing it to cool for 24 hours, and then measuring the shrinkage rate.

[0043] Furthermore, the microporous membrane of the present invention is characterized by a heat treatment temperature of 100 to 130°C, preferably 105 to 125°C, at which the air permeability exceeds 9999 seconds when the membrane is heat-treated at a specific heat treatment temperature for 1 hour and measured using an air permeability measuring device under measurement conditions of a temperature of 23°C and an air passage volume of 100 ml. Here, if the heat treatment temperature at which the air permeability exceeds 9999 seconds at a measurement temperature of 23°C is lower than 100°C, when the microporous membrane is incorporated into a battery as a separator, the pores of the microporous membrane tend to become clogged even within the normal operating temperature range of the battery, resulting in inferior battery performance. On the other hand, if the heat treatment temperature exceeds 130°C when the air permeability at a measurement temperature of 23°C exceeds 9999 seconds, then when a microporous membrane is incorporated into a battery as a separator, the temperature at which the pores close will be higher. This raises the temperature at which runaway reactions caused by battery overcharging or short circuits between the positive and negative electrodes are suppressed, accelerating the temperature rise inside the battery due to the runaway reaction, thus compromising safety. Air permeability can be measured, for example, using a Gahl-type densometer at a measurement temperature of 23°C, by measuring the time it takes for 100 ml of air to pass through a microporous membrane sandwiched in an opening with a diameter of 28.6 mm.

[0044] Furthermore, the microporous membrane has an excellent balance between membrane strength and membrane resistance, which affects permeability, so a porosity of 10-80% is preferred, and a microporous membrane with a porosity of 20-70% is particularly preferred. The air permeability is preferably 100-500 seconds, and particularly preferably 100-400 seconds. The air permeability can be measured by the same method as described above. Moreover, the average pore diameter is preferably 1-1000 nm, and particularly preferably 10-500 nm. Here, the porosity is, for example, porosity (V, %) = 100 - 10 × (weight of an 8cm square microporous membrane) (W, g) / (true density of the microporous membrane (g / cm³) 3 Area of ​​a microporous membrane (cm²) × 8cm square 2 The average pore size can be determined by multiplying the thickness of the microporous membrane (d, mm) by the number of pores. In addition, the average pore size can be determined by nitrogen adsorption, mercury intrusion, or by image analysis from images obtained by scanning electron microscopy.

[0045] There are no particular limitations on the method for producing the microporous membrane of the present invention. For example, a method may be described that involves mixing a composition containing at least an ultra-high molecular weight polyethylene copolymer and polyethylene with an organic solvent at a temperature of 50 to 300°C to form a sheet, followed by a step of removing the organic solvent from the sheet, and when producing a stretched microporous membrane, a step of stretching such as uniaxial stretching, simultaneous biaxial stretching, or sequential biaxial stretching.

[0046] Examples of organic solvents used include high-boiling-point aliphatic or alicyclic hydrocarbons such as octane, decane, dodecane, octadecane, decahydronaphthalene, and tetrahydronaphthalene; aromatic hydrocarbons such as benzene, toluene, xylene, and naphthalene; halogenated hydrocarbons such as dichloroethane, trichloroethane, chlorobenzene, and trichlorobenzene; linear or branched liquid paraffins; paraffin waxes; higher alcohols with 5 or more carbon atoms; phthalate esters, or mixtures thereof. When mixing the ultra-high molecular weight polyethylene composition with the organic solvent, a concentration of 0.5 to 60 wt% of the ultra-high molecular weight polyethylene composition is preferred, and 5 to 40 wt%, in order to efficiently obtain a microporous film with excellent uniformity and smoothness. When mixing the composition with the organic solvent, examples of methods include mixing in a reaction vessel equipped with a stirring blade, extrusion kneading in a single-screw or twin-screw extruder, and extrusion kneading after mixing in a reactor. The resulting mixture is then molded into a sheet-like material containing an organic solvent by methods such as compression molding, extrusion from a T-die or circular die, or inflation molding.

[0047] Furthermore, steps to remove the organic solvent from the sheet-like material include, for example, drying by heating, solvent extraction with a low-melting-point aliphatic or alicyclic hydrocarbon, alcohol, halogenated hydrocarbon, etc., followed by drying.

[0048] Furthermore, the stretching process, particularly the biaxial stretching process, can include, for example, simultaneous biaxial stretching in the longitudinal and transverse directions, or sequential biaxial stretching in the longitudinal and transverse directions, respectively. The stretching speed and temperature may be constant or vary in multiple stages. The stretching ratio is preferably 2 to 20 times in the longitudinal direction and 2 to 20 times in the transverse direction, and is particularly preferable to 5 to 15 times in the longitudinal direction and 5 to 15 times in the transverse direction, as this results in a thin film with high strength and high stretchability. The stretching temperature is preferably 0 to 200°C. The order of the organic solvent removal process and the stretching process is arbitrary; for example, the organic solvent may be removed before stretching, or after stretching, or both may be performed simultaneously. Annealing may also be performed after stretching.

[0049] Furthermore, the microporous membrane of the present invention can be applied to various electrode separators, such as battery separators and electrolytic membranes. In particular, it is suitable as a separator for lithium-ion secondary batteries due to its excellent mechanical strength and shutdown characteristics. When this microporous membrane is applied to a lithium-ion secondary battery, it not only results in miniaturization and weight reduction through thinning, but also provides excellent emergency shutdown capabilities and safety. When using the microporous membrane of the present invention as a separator for a lithium-ion secondary battery, it is preferable to have a film thickness of 15 μm or less.

[0050] When using a lithium-ion secondary battery, examples of the positive electrode include lithium metal oxides such as cobalt-manganese-nickel composite oxide-lithium, examples of the negative electrode include carbon materials such as graphite, and examples of the electrolytic solution include a 1M LiPF6 ethyl carbonate / diethyl carbonate solution. When applying these to a lithium-ion secondary battery, a constant current discharge corresponding to 0.5C (the current value for discharging the discharge capacity of the lithium-ion secondary battery in 2 hours), 1C (the current value for discharging the discharge capacity of the lithium-ion secondary battery in 1 hour), and 2C (the current value for discharging the discharge capacity of the lithium-ion secondary battery in 0.5 hours) was performed for 10 seconds on a lithium-ion secondary battery in a charged state corresponding to 50% of the total capacity, then the current was stopped, the voltage rise at that time was measured, and the DC resistance value calculated from the current value dependence (IR loss) of this voltage drop was 10Ω·m 2 Preferably, it is a separator that can achieve 500 or more charge-discharge cycles when performing constant current charge-discharge at a current value (0.5C) for discharging the discharge capacity of the lithium-ion battery in 2 hours.

[0051] Since the microporous membrane of the present invention is excellent in mechanical strength and shutdown characteristics, it can be used as a separator for lithium-ion batteries (LIBs), lead-acid batteries, nickel-metal hydride batteries, alkaline batteries, etc.

Advantages of the Invention

[0052] By providing a microporous membrane with high membrane strength and excellent shutdown characteristics, which is excellent in durability and safety, it becomes possible to improve the productivity of the microporous membrane, extend the continuous use time of the battery, miniaturize the battery, and improve safety.

Examples

[0053] Examples are shown below to explain the present invention in more detail, but the present invention is not limited by these examples.

[0054] Unless otherwise specified, commercially available reagents or those synthesized according to known methods were used.

[0055] A jet mill (manufactured by Seishin Corporation, product name CO-JET SYSTEM α MARK III) was used to pulverize the organically modified clay, and the particle size after pulverization was measured using a Microtrac particle size distribution analyzer (manufactured by Nikkiso Co., Ltd., product name MT3000) with ethanol as a dispersant.

[0056] The preparation of the catalyst for polyethylene production, the production of polyethylene, and the solvent purification were all carried out under an inert gas atmosphere. A hexane solution of triisobutylaluminum (20 wt%) was used, manufactured by Tosoh FineChem Co., Ltd.

[0057] Furthermore, the physical properties of the ultra-high molecular weight polyethylene copolymer in the production example and the microporous membrane in the example were measured by the method described below.

[0058] ~Measurement of intrinsic viscosity ([η])~ The viscosity was measured using an Ubbelohde viscometer with decahydronaphthalene as the solvent at 135°C, at a concentration of 0.005 wt% ultra-high molecular weight polyethylene copolymer.

[0059] ~Measurement of Mw and Mn~ Measurements were performed using an ultra-high temperature gel permeation chromatography system (Senshu Chemicals, product name SSC-7110) equipped with a column (Tosoh Corporation, product name TSKgel GMHHR-H(S)HT), with 1-chloronaphthalene as the eluent, at a column temperature of 210°C, a sample concentration of 0.5 mg / ml, and an injection volume of 0.2 ml. The molecular weight calibration curve was calibrated using standard polystyrene samples, and Mw and Mn were converted to linear polyethylene values.

[0060] ~Measurement of short-chain branching number~ The ultra-high molecular weight polyethylene copolymer is dissolved in deuterated tetrachloroethane (tetrachloroethane-d2) and heated at 130°C. 1 The number of methyl groups (corresponding to the terminal methyl groups of short-chain branches) was measured by 1H-NMR and determined as the number of short-chain branches.

[0061] ~Measurement of bulk density~ Measurements were taken using a method compliant with JIS K6760 (1995).

[0062] ~Measurement of Titanium Content~ The titanium content in the ultra-high molecular weight polyethylene copolymer was measured using an ICP emission spectrometer (PerkinElmer Corporation, product name Optima3000XL) prepared by ashing and alkali fusion of the ultra-high molecular weight polyethylene copolymer.

[0063] ~Measurement of average particle size~ Using nine types of sieves specified in JIS Z8801 (mesh openings: 710 μm, 500 μm, 425 μm, 300 μm, 212 μm, 150 μm, 106 μm, 75 μm, 53 μm), 100 g of ultra-high molecular weight polyethylene copolymer was classified. The average particle size was determined by measuring the particle size at which the weight of the particles remaining in each sieve, obtained by integrating the weights from the largest mesh opening side, into an integral curve.

[0064] ~Measurement of film thickness and porosity of microporous membranes~ The film thickness (d, mm) of the microporous membrane was measured at 30 points on the membrane using a contact-type film thickness gauge, and the average value was taken. The porosity (V, %) was determined by measuring the weight (W, g) of an 8 cm square microporous membrane, and the true density (ρ, g / cm³) of the microporous membrane was determined. 3 ), was calculated using the following formula (1).

[0065] V(%) = 100 - W / (0.064 × ρ × d) (1) ~Measurement of pore size in microporous membranes~ Using an automatic specific surface area / pore size distribution analyzer (manufactured by Nippon Bell Co., Ltd., product name BELSORP-miniII), the volume-based mode diameter was measured by nitrogen adsorption and defined as the average pore diameter.

[0066] ~Measurement of thermal shrinkage rate~ An 8cm square microporous membrane was heated at 105°C for 1 hour, and then allowed to cool at room temperature for 24 hours. The percentage change in length and width was calculated and used as the average value.

[0067] ~Measuring puncture resistance~ An 8cm square microporous membrane was left standing at 23°C for 48 hours. Then, the puncture strength was determined by a puncture test using a tensile testing machine (Toyo Seiki Seisakusho Co., Ltd., product name: Strograph E3) in compression mode, at a measurement temperature of 23°C, with a needle of 1mm diameter and radius of curvature of 0.5mm, at a puncture speed of 50mm / min.

[0068] ~Measuring air permeability~ An 8cm square microporous membrane was left standing at 23°C for 48 hours. Then, using an air permeability measuring device (Toyo Seiki Seisakusho Co., Ltd., product name: Gale-type Densometer G-B3C), the membrane was placed in an opening with a diameter of 28.6mm, and the time it took for 100ml of air to pass through was measured at a temperature of 23°C to determine the air permeability.

[0069] ~Heat treatment of microporous membranes~ An 8cm square microporous membrane was heated at a predetermined temperature for 1 hour and then allowed to cool at room temperature for 24 hours. Subsequently, the air permeability measurement was performed, and the heat treatment temperature at which the air permeability exceeded 9999 seconds was determined.

[0070] Manufacturing Example 1 (1) Preparation of organically modified clay 300 ml of industrial alcohol (manufactured by Nippon Alcohol Sales Co., Ltd., product name: Ekinen F-3) and 300 ml of distilled water were placed in a 1 liter flask. 15.0 g of concentrated hydrochloric acid and 42.4 g (120 mmol) of dimethylbehenylamine (manufactured by Lion Specialty Chemicals, product name: Lipomin DM22D) were added. The mixture was heated to 45°C to disperse 100 g of synthetic hectorite (manufactured by BYK Additives Limited, product name: Laponite RDS). The temperature was then raised to 60°C and the mixture was stirred for 1 hour while maintaining that temperature. After filtering the slurry, it was washed twice with 600 ml of 60°C warm water and dried in an oven at 85°C for 12 hours to obtain 125 g of organically modified clay. This organically modified clay was pulverized using a jet mill to a median diameter of 10 μm.

[0071] (2) Preparation of a suspension of the catalyst for polyethylene production After purging a 300 ml flask equipped with a thermometer and reflux tubing with nitrogen, 25.0 g of the organically modified clay obtained in (1) and 108 ml of hexane were added, followed by 0.715 g of diphenylmethylene (cyclopentadienyl) (2-(diethylamino)-7-t-butyl-9-fluorenyl) hafnium dichloride and 142 ml of a hexane solution of 20 wt% triisobutylaluminum. The mixture was stirred at 60°C for 3 hours. After cooling to 45°C, the supernatant was removed, washed twice with 200 ml of hexane, and then 200 ml of hexane was added to obtain a suspension of the catalyst for polyethylene production (solid weight: 10.9 wt%).

[0072] (3) Production of ultra-high molecular weight polyethylene copolymer In a 2-liter autoclave, 1.2 liters of hexane, 1.0 ml of a hexane solution of 20 wt% triisobutylaluminum, and 1003 mg (equivalent to 109 mg of solids) of the polyethylene production catalyst suspension obtained in (2) were added. After heating to 60°C, ethylene partial pressure was maintained at 0.67 MPa, 1.5 g of 1-butene was added, and ethylene and hydrogen were continuously supplied to maintain a hydrogen concentration of 2500 ppm relative to ethylene in the gas phase of the autoclave, and slurry polymerization of ethylene was carried out. After 120 minutes, the pressure was removed, the slurry was filtered off, and dried to obtain ultra-high molecular weight polyethylene copolymer (1). The physical properties of the obtained ultra-high molecular weight polyethylene copolymer (1) are shown in Table 1.

[0073] Manufacturing Examples 2-10 (1) Preparation of organically modified clay and (2) preparation of a suspension of the catalyst for polyethylene production were carried out in the same manner as in Production Example 1.

[0074] (3) Production of ultra-high molecular weight polyethylene copolymer Ultra-high molecular weight polyethylene copolymers (2) to (10) were obtained by the same method as in Production Example 1, except that the concentrations of 1-butene and the hydrogen in the gas phase of the autoclave were changed as shown in Table 1. The physical properties of the obtained ultra-high molecular weight polyethylene copolymers (2) to (10) are shown in Table 1.

[0075] Manufacturing Example 11 (1) Preparation of organically modified clay and (2) preparation of a suspension of the catalyst for polyethylene production were carried out in the same manner as in Production Example 1.

[0076] (3) Production of ultra-high molecular weight polyethylene In a 2-liter autoclave, 1.2 liters of hexane, 1.0 ml of a hexane solution of 20 wt% triisobutylaluminum, and 883 mg (equivalent to 96 mg of solids) of the polyethylene production catalyst suspension obtained in (2) were added. After heating to 60°C, ethylene and hydrogen were continuously supplied to maintain an ethylene partial pressure of 0.67 MPa and a hydrogen concentration in the gas phase of the autoclave at 2800 ppm relative to ethylene, and slurry polymerization of ethylene was carried out. After 120 minutes, the pressure was removed, the slurry was filtered off, and dried to obtain ultra-high molecular weight polyethylene (11), a homopolymer of ethylene. The physical properties of the obtained ultra-high molecular weight polyethylene (11) are shown in Table 1.

[0077] Manufacturing examples 12, 13 (1) Preparation of organically modified clay and (2) preparation of a suspension of the catalyst for polyethylene production were carried out in the same manner as in Production Example 1.

[0078] (3) Production of ultra-high molecular weight polyethylene Ultra-high molecular weight polyethylene (12) and (13), which are homopolymers of ethylene, were obtained by the same method as in Production Example 11, except that the hydrogen concentration in the gas phase of the autoclave was changed as shown in Table 1. The physical properties of the obtained ultra-high molecular weight polyethylene (12) and (13) are shown in Table 1.

[0079] [Table 1]

[0080] Manufacturing Example 14 (1) Preparation of solid catalyst components In a 1-liter glass flask equipped with a thermometer and reflux tubing, 50 g (2.1 mol) of metallic magnesium powder and 210 g (0.62 mol) of titanium tetrabutoxide were added. 320 g (4.3 mol) of n-butanol in which 2.5 g of iodine was dissolved was added over 2 hours at 90°C. The mixture was then stirred under a nitrogen seal at 140°C for 2 hours while removing the generated hydrogen gas to obtain a homogeneous solution. Next, 2100 ml of hexane was added to dilute the solution. 90 g of this component (equivalent to 0.095 mol of magnesium) was placed in a separately prepared 500 ml glass flask, 59 ml of hexane was added, and 106 ml of a hexane solution containing 0.29 mol of isobutylaluminum dichloride was added dropwise over 2 hours at 45°C. The mixture was then stirred at 70°C for 1 hour to obtain a solid catalyst component. Unreacted materials and by-products were removed using a gradient method with hexane, and the composition was analyzed to find a titanium content of 8.6 wt%.

[0081] (2) Production of ultra-high molecular weight polyethylene copolymer In a 2-liter autoclave, 1.2 liters of hexane, 1.0 ml of a hexane solution of 20 wt% triisobutylaluminum, and 9.0 mg of the solid catalyst component obtained in (1) were added. After raising the temperature to 70°C, 12.3 g of 1-butene and hydrogen were supplied to a concentration of 300 ppm, and ethylene was continuously supplied to maintain a partial pressure of 0.5 MPa. After 90 minutes, the pressure was removed, the slurry was filtered off, and the mixture was dried to obtain the ultra-high molecular weight polyethylene copolymer (14). The properties of the obtained ultra-high molecular weight polyethylene copolymer (14) are shown in Table 2.

[0082] Manufacturing examples 15-25 (1) The preparation of the solid catalyst components was carried out in the same manner as in Production Example 14.

[0083] (2) Production of ultra-high molecular weight polyethylene (co)polymer Ultra-high molecular weight polyethylene (co)polymers (15) to (25) were obtained by the same method as in Production Example 15, except that the concentrations of 1-butene and the hydrogen in the gas phase of the autoclave were changed as shown in Table 2. The physical properties of the obtained ultra-high molecular weight polyethylene (co)polymers (15) to (25) are shown in Table 2.

[0084] [Table 2]

[0085] Manufacturing example 26 (1) The preparation of the solid catalyst components was carried out in the same manner as in Production Example 14.

[0086] (2) Manufacturing of polyethylene In a 2-liter autoclave, 1.2 liters of hexane, 1.0 ml of a hexane solution of 20 wt% triisobutylaluminum, and 9.0 mg of the solid catalyst component obtained in (1) were added. After heating to 80°C, hydrogen was supplied to a pressure of 0.2 MPa, and ethylene was continuously supplied to a partial pressure of 0.6 MPa. After 90 minutes, the pressure was removed, the slurry was filtered off, and the mixture was dried to obtain polyethylene. The Mw of the obtained polyethylene was 400,000.

[0087] Example 1 3.8 g of ultra-high molecular weight polyethylene copolymer (1) produced in Production Example 1, 8.9 g of polyethylene produced in Production Example 26, 29.6 g of liquid paraffin (MORESCO, product name: Moresco White P-350P), and 0.03 g of (product name: Irganox 1010, manufactured by BASF) and 0.03 g of (product name: Irgafos 168, manufactured by BASF) as antioxidants were placed in a 70 ml batch-type kneader (Toyo Seiki Seisakusho Co., Ltd., product name: Laboplast Mill 4C150), and kneaded at a kneading temperature of 190 °C and a rotation speed of 30 rpm for 15 minutes to obtain a kneaded product of ultra-high molecular weight polyethylene composition.

[0088] The resulting mixture was compressed and molded at a press temperature of 190°C to form a sheet with a thickness of 0.6 mm.

[0089] This sheet-like material was sequentially biaxially stretched at 115°C using a biaxial stretching machine (manufactured by Toyo Seiki Seisakusho Co., Ltd., product name EX10-B) so that the stretching ratio was 6x6x in both the longitudinal and transverse directions. The stretched material was then washed with methylene chloride to remove liquid paraffin, and dried to produce a stretched microporous membrane.

[0090] The resulting stretched microporous membrane showed no holes or tears visible to the naked eye. Table 3 shows the film thickness, thermal shrinkage rate, puncture strength, porosity, air permeability, average pore diameter, and heat treatment temperature at which the air permeability exceeded 9999 seconds for this stretched microporous membrane.

[0091] Examples 2-9 A kneaded ultra-high molecular weight polyethylene composition was prepared in the same manner as in Example 1, except that ultra-high molecular weight polyethylene copolymers (2) to (9) produced in Production Examples 2 to 9 were used instead of ultra-high molecular weight polyethylene copolymer (1), and a stretched microporous membrane was produced.

[0092] The resulting stretched microporous membrane showed no holes or tears visible to the naked eye. Table 3 shows the film thickness, thermal shrinkage rate, puncture strength, porosity, air permeability, average pore diameter, and heat treatment temperature at which the air permeability exceeded 9999 seconds for this stretched microporous membrane.

[0093] Comparative Example 1 A kneaded ultra-high molecular weight polyethylene composition was prepared in the same manner as in Example 1, except that the ultra-high molecular weight polyethylene copolymer (10) produced in Production Example 10 was used instead of the ultra-high molecular weight polyethylene copolymer (1), and a stretched microporous membrane was produced.

[0094] The resulting stretched microporous membrane showed no holes or tears visible to the naked eye. Table 3 shows the film thickness, thermal shrinkage rate, puncture strength, porosity, air permeability, average pore diameter, and heat treatment temperature at which the air permeability exceeded 9999 seconds for this stretched microporous membrane.

[0095] Comparative Examples 2-4 A kneaded ultra-high molecular weight polyethylene composition was prepared in the same manner as in Example 1, except that ultra-high molecular weight polyethylene (11) to (13) produced in Production Examples 11 to 13 was used instead of ultra-high molecular weight polyethylene copolymer (1), and a stretched microporous membrane was produced.

[0096] The resulting stretched microporous membrane showed no holes or tears visible to the naked eye. Table 3 shows the film thickness, thermal shrinkage rate, puncture strength, porosity, air permeability, average pore diameter, and heat treatment temperature at which the air permeability exceeded 9999 seconds for this stretched microporous membrane.

[0097] [Table 3]

[0098] Comparative Examples 5-16 A kneaded ultra-high molecular weight polyethylene composition was prepared and a microporous membrane was manufactured by the same method as in Example 1, except that ultra-high molecular weight polyethylene (co)polymers (14) to (25) produced in Production Examples 14 to 25 were used instead of ultra-high molecular weight polyethylene copolymer (1).

[0099] The resulting microporous membrane showed no holes or tears visible to the naked eye. Table 4 shows the film thickness, thermal shrinkage rate, puncture strength, porosity, air permeability, average pore diameter, and heat treatment temperature at which the air permeability exceeded 9999 seconds for this stretched microporous membrane.

[0100] [Table 4] [Industrial applicability]

[0101] The microporous membrane of the present invention exhibits excellent mechanical strength and shutdown characteristics, and can be used as a separator for lithium-ion batteries (LIBs), lead-acid batteries, nickel-metal hydride batteries, alkaline batteries, electrolytic cells, and the like.

Claims

1. It is a composition containing at least 5 to 5,000 parts by weight of polyethylene with a weight average molecular weight of 500,000 or less per 100 parts by weight of a ultra-high molecular weight polyethylene copolymer having an intrinsic viscosity of 10 to 50 dL / g, a molecular weight distribution of 4 or less, and 1 to 10 short-chain branches per 1,000 carbons, and is characterized by satisfying at least any one of the following 1) to 4): 1) The film thickness is 0.001 to 1 mm. 2) The puncture strength measured using a tensile testing machine equipped with a needle with a diameter of 1 mm and a radius of curvature of 0.5 mm in compression mode at a temperature of 23°C and a puncture speed of 50 mm / min was 3 to 5 N / 10 μm. 3) The thermal shrinkage rate measured under heat treatment conditions of 105°C for 1 hour was 2-10%. 4) After a 1-hour heat treatment, the heat treatment temperature at which the air permeability exceeds 9999 seconds when measured using an air permeability measuring device under the conditions of a temperature of 23°C and an air passage volume of 100 ml is 100 to 130°C.

2. The microporous membrane with good shutdown properties according to claim 1, characterized in that the heat treatment temperature in 4) is 105 to 125°C.

3. The microporous membrane with good shutdown properties according to claim 1 or 2, characterized in that the ultra-high molecular weight polyethylene copolymer is a metallocene catalyst-based ultra-high molecular weight polyethylene copolymer.

4. Furthermore, the good-shutdown microporous membrane according to claim 1 or 2 is characterized in that it also satisfies the condition that 5) the porosity is 10 to 80%.

5. Furthermore, the good shut-off microporous membrane according to claim 1 or 2 is characterized in that it also satisfies the condition that 6) the air permeability at a measurement temperature of 23°C is 100 to 500 seconds, as measured by an air permeability measuring device.

6. A microporous membrane with good shutdown properties according to claim 1 or 2, characterized in that it is a stretched microporous membrane.

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