JP2011228056A - Microporous membrane and cell separator including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microporous membrane having excellent mechanical characteristics, liquid permeability and melt-down characteristics.SOLUTION: The microporous membrane made of a resin composition containing 4-methyl-1-pentene polymer having weight average molecular weight of 1.0 x 10or more is provided.

Description

  The present invention relates to a microporous membrane and its use. In particular, the present invention relates to a microporous membrane excellent in heat resistance, including a 4-methyl-1-pentene polymer; and a battery separator including the same and having excellent meltdown characteristics.

  Polyolefin microporous membranes include battery separators used for lithium ion batteries, nickel-hydrogen batteries, nickel-cadmium batteries, polymer batteries, etc., separators for electrolytic capacitors, reverse osmosis filtration membranes, ultrafiltration membranes, microfiltration membranes, etc. It is widely used for various filters, moisture-permeable and waterproof clothing, medical materials, etc. When the polyolefin microporous membrane is used as a battery separator, particularly as a lithium ion battery separator, the performance of the polyolefin microporous membrane is deeply related to the characteristics, productivity and safety of the battery. Therefore, it is said that the polyolefin microporous membrane used as a battery separator preferably has excellent mechanical characteristics, heat resistance, permeability, dimensional stability, shutdown characteristics, meltdown characteristics, and the like.

  The shutdown characteristic refers to a characteristic that can prevent the temperature inside the battery from being increased by blocking the ionic conduction inside the battery by closing the micropores when the temperature becomes high. For this reason, the lower the shutdown temperature, the better the shutdown characteristics. The meltdown characteristic means a characteristic in which breakage due to melting hardly occurs. For this reason, the higher the meltdown temperature, the better the meltdown characteristics.

  The shutdown temperature means the lowest temperature at which the separator loses its permeability due to the collapse of the microporous material due to deformation of the material and the termination of the battery reaction. The meltdown temperature means a minimum temperature at which the separator maintains its original shape at a high temperature exceeding the shutdown temperature and can withstand breakage and breakage due to melting.

  In general, a microporous film made only of polyethylene has a low meltdown temperature, whereas a microporous film made only of polypropylene has a high meltdown temperature. Therefore, a microporous membrane combining polyethylene and polypropylene has been proposed for battery separators (for example, Patent Documents 1 to 4).

  Among these, in Patent Document 1, as a polyolefin microporous film having excellent safety and strength, a microporous film A containing polyethylene and polypropylene as essential components and a microporous film B made of polyethylene are laminated and integrated. A polyolefin microporous membrane having a three-layer structure of microporous membrane A / microporous membrane B / microporous membrane A or microporous membrane B / microporous membrane A / microporous membrane B has been proposed.

  Patent Document 2 includes a laminate of two or more layers containing polyethylene and polypropylene as essential components, and a polypropylene mixing ratio of at least one surface layer is more than 50% by mass to 95% by mass, and polyethylene for the entire film. A polyolefin laminated film having a content of 50% by mass to 95% by mass has been proposed.

JP 2002-321323 A International Publication No. 2004/089627 Pamphlet JP-A-3-105851 Special table 2010-502471

  However, the polyolefin microporous membranes of Patent Documents 1 to 4 do not necessarily have good meltdown characteristics. For this reason, a microporous membrane for battery separators having higher heat resistance than polyethylene and polypropylene and having excellent meltdown characteristics is desired.

  Polyolefin having high heat resistance includes poly-4-methyl-1-pentene. However, since poly-4-methyl-1-pentene is relatively brittle, it easily breaks during stretching, and it is difficult to stretch at a high draw ratio (low stretchability). If sufficient stretching is not possible, not only sufficient mechanical strength cannot be obtained, but also the micropermeability cannot be sufficiently formed, so that the liquid permeability is also lowered.

  Thus, there is a demand for a microporous membrane having excellent meltdown characteristics while maintaining mechanical strength and liquid permeability. The present invention has been made in view of the above circumstances, and provides a microporous membrane excellent in mechanical properties, liquid permeability, dimensional stability and heat resistance (particularly heat resistance), and further the microporous membrane. An object of the present invention is to provide a battery separator and a battery excellent in mechanical characteristics, permeability, and meltdown characteristics.

As a result of intensive studies, the inventors have made the weight-average molecular weight of the 4-methyl-1-pentene polymer 1.0 × 10 ⁶ or more, thereby increasing the meltdown temperature and further improving the stretchability. And found that the film can be stretched at a high magnification. Thus, it has been found that a microporous membrane having high mechanical strength, sufficient microporosity, and excellent liquid permeability can be obtained by being stretchable at a high magnification. The present invention has been made based on such knowledge.

[1] A microporous membrane comprising a resin composition containing a 4-methyl-1-pentene polymer having a weight average molecular weight of 1.0 × 10 ⁶ or more.
[2] The microporous membrane according to [1], wherein the 4-methyl-1-pentene polymer has a weight average molecular weight of 1.5 × 10 ⁶ or more and 2.3 × 10 ⁶ or less.
[3] The microporous membrane according to [1] or [2], wherein the porosity is 25% or more and 80% or less, and the meltdown temperature is 170 ° C or more.
[4] The 4-methyl-1-pentene polymer is derived from a structural unit derived from 4-methyl-1-pentene and an α-olefin having 2 to 20 carbon atoms other than the 4-methyl-1-pentene. The microporous film according to any one of [1] to [3], which is a 4-methyl-1-pentene copolymer containing a structural unit.
[5] The microporous structure according to [4], wherein the content of the structural unit derived from the α-olefin having 2 to 20 carbon atoms in the 4-methyl-1-pentene copolymer is 10% by mass or less. film.
[6] The microporous membrane is a biaxially stretched film made of the resin composition, and any one of [1] to [5], wherein the biaxially stretched surface stretch ratio is 9 times or more. A microporous membrane according to 1.
[7] A battery separator having the microporous membrane according to any one of [1] to [6].

  The microporous membrane of the present invention is excellent in heat resistance, mechanical strength and liquid permeability. For this reason, the microporous membrane of the present invention is preferably used as a separator for a battery such as a lithium ion battery having particularly excellent meltdown characteristics.

  The microporous membrane of the present invention is formed from a resin composition containing a 4-methyl-1-pentene polymer having a certain weight average molecular weight.

1. Resin composition containing 4-methyl-1-pentene polymer 4-methyl-1-pentene polymer is a crystalline polymer mainly composed of 4-methyl-1-pentene, and 4-methyl-1 -A pentene homopolymer or a copolymer of 4-methyl-1-pentene and an α-olefin having 2 to 20 carbon atoms other than 4-methyl-1-pentene.

  The content of structural units derived from 4-methyl-1-pentene in the 4-methyl-1-pentene copolymer is 80% by mass or more, preferably 90% by mass or more, more preferably 92% by mass or more and 98% by mass. Hereinafter, it is 94 to 97 mass% more preferably.

  Examples of α-olefins having 2 to 20 carbon atoms other than 4-methyl-1-pentene include ethylene, propylene, 1-butene, 1-hexene, 1-octene, 1-decene, 1-tetradecene, and 1 -Including octadecene. These may be used alone or in combination of two or more. Of these, 1-decene, 1-tetradecene and 1-octadecene are preferred because they have good copolymerizability with 4-methyl-1-pentene and good toughness can be obtained.

  In the 4-methyl-1-pentene copolymer, the content of structural units derived from an α-olefin having 2 to 20 carbon atoms other than 4-methyl-1-pentene is preferably 10% by mass or less. .

The weight average molecular weight of the 4-methyl-1-pentene polymer is 1.0 × 10 ⁶ or more and 2.3 × 10 ⁶ or less, preferably 1.5 × 10 ⁶ or more and 2.3 × 10 ⁶ or less. . By using a 4-methyl-1-pentene polymer having a weight average molecular weight of 1.0 × 10 ⁶ or more, a microporous film having a high melting point and a high meltdown temperature can be obtained. Furthermore, the moldability can be improved and the draw ratio can be increased.

  The weight average molecular weight of the 4-methyl-1-pentene polymer is measured by GPC (gel permeation chromatography) using an orthodichlorobenzene solvent at 140 ° C.

  The 4-methyl-1-pentene polymer can be produced by any method, but can be produced using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. The crystal structure of the resulting 4-methyl-1-pentene polymer may be isotactic or syndiotactic. For example, as described in JP-A-2003-105022, 4-methyl-1-pentene is homopolymerized in the presence of a catalyst, or 4-methyl-1-pentene and the α-olefin are co-polymerized. By polymerization, a powdery 4-methyl-1-pentene polymer can be obtained.

  The content of 4-methyl-1-pentene polymer in the resin composition constituting the microporous membrane is preferably 0.1 to 100% by mass, more preferably 20 to 80% by mass, and still more preferably. Is 40-60 mass%.

  In addition to the 4-methyl-1-pentene polymer, the resin composition constituting the microporous film may further contain other resins, additives, and the like as long as the effects of the present invention are not impaired.

  Examples of other resins include polymers and copolymers having polyethylene, ultrahigh molecular weight polyethylene, polypropylene, polybutene, and other α-olefins having 2 to 20 carbon atoms as constituent units. In order to lower the shutdown temperature of the microporous membrane, resins having a shutdown temperature lower than that of 4-methyl-1-pentene polymer, such as polyethylene and ultrahigh molecular weight polyethylene, are preferable.

  When the resin composition constituting the microporous film further contains polyethylene or polypropylene, it may further contain a compatibilizing agent in order to enhance the compatibility between the 4-methyl-1-pentene polymer and polyethylene or polypropylene. . Such compatibilizers include polyolefin elastomers such as ethylene-α-olefin copolymers and propylene-α-olefin copolymers.

  Examples of the additive include an antioxidant, an ultraviolet absorber, an antiblocking agent, a pore forming agent, an inorganic filler, a pigment, a dye, and the like. Examples of the pore forming agent include finely divided silicic acid.

2. Production method of microporous membrane The microporous membrane of the present invention is prepared by mixing (for example, melt-kneading) a resin composition containing at least (1) 4-methyl-1-pentene polymer and a diluent (for example, melt-kneaded). (2) a step of extruding the melt-kneaded product, (3) a step of cooling the obtained molded body to obtain a gel-like sheet, (4) a step of stretching the gel-like sheet to obtain a stretched sheet, (5) After the diluent is removed from the stretched sheet, it is produced through a step of drying to obtain a microporous film.

  After the step (5), if necessary, (6) a step of heat-treating the microporous membrane, (7) a step of laminating with another microporous membrane, (8) a step of crosslinking by ionizing radiation, and / or ) (9) Other steps such as a hydrophilic treatment step and (10) a surface coating step with an aramid resin may be performed.

(1) Preparation of Melt-Kneaded Product A diluent is added to the resin composition containing the aforementioned 4-methyl-1-pentene polymer, and mixed by, for example, melt-kneading to prepare a melt-kneaded product.

  The diluent to be added is not particularly limited, but may be a liquid solvent that is liquid at room temperature. By using a liquid solvent, it is possible to stretch at a relatively high magnification. Examples of the liquid solvent include chain or cyclic aliphatic hydrocarbons such as nonane, decane, decalin, paraxylene, undecane, dodecane, and liquid paraffin; mineral oil fractions having boiling points equivalent to these; phthalates that are liquid at room temperature And acid esters (for example, dibutyl phthalate and dioctyl phthalate). These may be used alone or in combination of two or more. In order to obtain a gel-like sheet with little change in the content of the liquid solvent with time, it is preferable to use a non-volatile liquid solvent such as liquid paraffin.

  The diluent may further contain a solid solvent together with the liquid solvent. The solid solvent means a solvent that is solid at room temperature but is miscible with the 4-methyl-1-pentene polymer in the melt-kneaded state. Examples of the solid solvent include stearyl alcohol, seryl alcohol, and paraffin wax.

  The total content of the resin component containing 4-methyl-1-pentene polymer in the melt-kneaded product is preferably 1 to 50% by mass, more preferably 10 to 50% by mass, and further preferably 20 to 20% by mass. 40% by mass.

  Although melt kneading is not particularly limited, it is preferably performed by a twin screw extruder. Melt kneading with a twin screw extruder is suitable for preparing a highly concentrated polyolefin solution. The ratio (L / D) of the screw length (L) to the diameter (D) of the twin screw extruder is preferably in the range of 20 to 100, and more preferably in the range of 35 to 70.

(2) Extrusion molding The obtained melt-kneaded product may be directly extruded from a die to obtain a “gel-like molded product”; once the melt-kneaded product is cooled and pelletized, the pellet is melted again It may be kneaded and extruded from a die to obtain a “gel-like molded product”.

  The die may be a T-die shaped sheet die, a double cylindrical hollow die, an inflation die, or the like.

(3) Production of gel-like sheet The obtained gel-like molded body can be cooled to, for example, room temperature (25 ° C.) or less to obtain a “gel-like sheet”. Thereby, the micro resin phase (4-methyl-1-pentene polymer in the gel-like sheet) separated by the diluent is immobilized.

  It is preferable to cool the gel-like molded body at a rate of 50 ° C./min or more until at least the gelation temperature of the melt-kneaded product is reached. The gel-like molded body can be cooled to 25 ° C. or lower. The method for cooling the gel-like molded body is not particularly limited, and may be a method of directly contacting a cooling medium such as cold air or cooling water; a method of contacting a roll cooled with a refrigerant, or the like.

(4) Production of Stretched Sheet After the obtained gel-like sheet is heated, it is stretched in a uniaxial direction or a biaxial direction to obtain a “stretched sheet”. By stretching, the mechanical strength of the sheet can be improved and the thickness can be reduced.

  The stretching method is not particularly limited, and may be, for example, a tenter method, a roll method, an inflation method, a rolling method, or a method combining these. The stretching may be uniaxial stretching or biaxial stretching, but is preferably biaxial stretching. The biaxial stretching may be any of simultaneous biaxial stretching, sequential stretching and multistage stretching (for example, a combination of simultaneous biaxial stretching and sequential stretching), and simultaneous biaxial stretching is particularly preferable.

  The stretching ratio in uniaxial stretching is preferably 2 times or more, and more preferably 3 to 30 times. The stretching ratio in biaxial stretching is preferably 3 × 3 times or more, that is, the surface stretching ratio is preferably 9 times or more, and the surface stretching ratio is more preferably 16 times or more. Thus, in order to enable stretching at a high stretching ratio, the above-described 4-methyl-1-pentene polymer may have a weight average molecular weight of a certain value or more.

  When the resin contained in the gel-like sheet is composed only of 4-methyl-1-pentene polymer, the stretching temperature is preferably 100 to 250 ° C, more preferably 120 to 220 ° C, and further preferably 170. It is -200 degreeC, Most preferably, it is 180 degreeC. When the resin contained in the gel-like sheet is a mixture of 4-methyl-1-pentene polymer and polyethylene or polypropylene, the stretching temperature is preferably the melting point Tm + 10 ° C. or less of polyethylene or polypropylene. Specifically, about 120 ° C. is preferable.

(5) Removal of diluent to preparation of microporous membrane The obtained stretched sheet is washed with a washing solvent or the like to remove the diluent from the stretched sheet. If the polymer phase (for example, 4-methyl-1-pentene polymer phase) in the stretched sheet is phase-separated from the diluent, fine pores are formed by removing the liquid solvent.

  The method of cleaning the stretched sheet is not particularly limited, and may be a method of immersing the stretched sheet in a cleaning solvent, a method of showering the stretched sheet with the cleaning solvent, a combination thereof, or the like. The washing with the washing solvent is preferably performed until the residual amount of diluent in the stretched sheet is less than 1% by mass of the content before washing. The usage-amount of a washing | cleaning solvent can be 300-30000 mass parts with respect to 100 mass parts of extending | stretching sheets.

Examples of washing solvents include saturated hydrocarbons such as pentane, hexane and heptane; chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride; ethers such as diethyl ether and dioxane; ketones such as methyl ethyl ketone; C ₆ F ₁₄ , C ₇ F _{16 and the} like chain fluorocarbons; C ₅ H ₃ F _{7 and} other cyclic hydrofluorocarbons; C ₄ F ₉ OCH ₃ and C ₄ F ₉ OC ₂ H _{5 and} other hydrofluoroethers; C Easily volatile solvents such as perfluoroethers such as ₄ F ₉ OCF ₃ and C ₄ F ₉ OC ₂ F ₅ are included.

  By drying the stretched sheet obtained by removing the diluent, a “microporous membrane” can be obtained. The drying method may be a heat drying method, an air drying method, or the like.

(6) Heat treatment It is preferable to heat-treat the microporous membrane obtained by drying. The heat treatment method is appropriately selected according to the required physical properties, and may be, for example, a heat stretching process, a heat setting process, a heat shrinking process, or the like. The heat treatment temperature can be about 100 to 250 ° C., for example.

(7) Lamination Another resin film may be further laminated on the dried microporous film or the heat-treated microporous film. The other resin film is preferably a microporous film made of a resin having a melting point lower than that of 4-methyl-1-pentene polymer, such as a microporous film made of polyethylene or ultrahigh molecular weight polyethylene. This is because the shutdown temperature of the microporous membrane containing 4-methyl-1-pentene polymer can be lowered, and the shutdown characteristics of the battery can be improved.

  The method for laminating such other resin films is not particularly limited, but the thermal laminating method is preferable. Examples of the heat lamination method include a heat sealing method, an impulse sealing method, an ultrasonic lamination method, and the like, but a heat sealing method is preferable. As the heat sealing method, a method using a heat roll is preferable.

(8) Crosslinking treatment The obtained microporous membrane may be subjected to a crosslinking treatment by irradiating with ionizing radiation such as α-rays, β-rays, γ-rays, and electron beams. Thereby, the resin which comprises a microporous film can be bridge | crosslinked, and the mechanical strength and meltdown temperature of a microporous film can be raised.

(9) Hydrophilization treatment The obtained microporous membrane may be subjected to a hydrophilic treatment. The hydrophilic treatment may be, for example, monomer graft, surfactant treatment, plasma treatment, corona discharge, or the like. For the surfactant treatment, any of a nonionic surfactant, a cationic surfactant, an anionic surfactant, and a zwitterionic surfactant can be used, but a nonionic surfactant is preferably used.

  The surfactant treatment is performed by immersing the microporous membrane in a solution in which the surfactant is dissolved in water or a lower alcohol solvent; by applying the solution to the microporous membrane by the doctor blade method, or the like. Can do. The lower alcohol solvent may be methanol, ethanol, isopropyl alcohol or the like. If necessary, other coating methods may be used in combination.

(10) Coating treatment The obtained microporous membrane may be coated with a heat-resistant resin in order to further enhance the heat resistance and the like. Examples of heat-resistant resins include polyimide, polyamideimide, aromatic polyamide (also called aramid), polycarbonate, polyacetal, polysulfone, polyphenyl sulfide, polyether ether ketone, aromatic polyester, polyether sulfone, and polyether imide Etc. are included.

  The microporous membrane of the present invention thus obtained has high meltdown characteristics because it contains a 4-methyl-1-pentene polymer having a weight average molecular weight of a certain level or more. The meltdown temperature of the microporous membrane is 170 ° C. or higher, preferably 170 to 240 ° C. The meltdown temperature can be measured by a penetration method using TMA (Thermo Mechanical Analysis) according to JIS K7196. Specifically, a test load of 50 g is applied to a 0.5 mmφ needle-inserted probe and the sample is placed on a microporous membrane sample having a thickness of 20 μm. Then, the temperature of the sample is increased at a temperature increase rate of 5.0 ° C./min, and the temperature when the penetration probe penetrates 20 μm can be set as the “meltdown temperature”.

  The microporous membrane of the present invention can have high shutdown characteristics by further including polyethylene in addition to the 4-methyl-1-pentene polymer. The shutdown temperature of the microporous membrane is preferably 120 to 220 ° C. The shutdown temperature can be measured by TMA. Specifically, the temperature at the inflection point of the TMA curve obtained by heating the sample near the melting point can be set as the “shutdown temperature”.

  The average through-hole diameter of the microporous membrane is preferably 0.001 to 0.1 μm. The average through-hole diameter of the microporous membrane can be measured using a through-pore diameter evaluation apparatus according to the half dry method (ASTM E1294-89).

  The porosity of the microporous membrane is preferably 25 to 80%. If the porosity is less than 25%, the liquid permeability of the microporous membrane may be insufficient, and the electrolyte may be difficult to impregnate. On the other hand, if the porosity exceeds 80%, the electrolyte can be easily impregnated, so that the impedance of the battery can be reduced. However, the mechanical strength of the microporous film is easily impaired, and the battery is short-circuited. Safety may be impaired.

The porosity can be measured by, for example, a gravimetric method. Specifically, when the sample thickness of the microporous membrane is T (μm), the sample mass is M (g), the sample area is S (cm ² ), and the resin density is ρ (g / cm ³ ), respectively. Can be obtained by fitting the value of
Porosity (%) = [1- (10000 * M / ρ) / (S * T)] × 100

  The microporous membrane of the present invention can be used for various primary batteries and secondary batteries (for example, nickel-hydrogen batteries, nickel-cadmium batteries, nickel-zinc batteries, silver-zinc batteries, lithium primary batteries, lithium ion secondary batteries, lithium polymer batteries). It can be preferably used as a battery separator for secondary batteries, particularly lithium ion secondary batteries.

  The thickness of the microporous membrane used as the battery separator is preferably 3 to 200 μm, more preferably 5 to 50 μm, although it depends on the type of battery.

EXAMPLES Examples according to the present invention will be specifically described below, but the present invention is not limited to these examples.
[Weight average molecular weight measurement]
The weight average molecular weight of the 4-methyl-1-pentene polymer was measured by GPC (gel permeation chromatography) using an orthodichlorobenzene solvent at 140 ° C.
[Meltdown temperature measurement]
The meltdown temperature of the microporous membrane was measured by a penetration method using TMA according to JIS K7196. Specifically, a test load of 50 g was applied to a 0.5 mmφ needle probe and the sample was placed on a microporous membrane sample. The temperature of the sample was raised at a rate of temperature rise of 5.0 ° C./min, and the temperature when the penetration probe penetrated 20 μm was defined as “meltdown temperature”.

[Preparation of solid catalyst component]
750 g of anhydrous magnesium chloride, 2800 g of decane and 3080 g of 2-ethylhexyl alcohol were reacted by heating at 130 ° C. for 3 hours to obtain a uniform solution. Thereafter, 220 ml of 2-isobutyl-2-isopropyl-1,3-dimethoxypropane was added to the solution, and the mixture was further stirred and mixed at 100 ° C. for 1 hour.

  The homogeneous solution thus obtained was cooled to room temperature, and 3000 ml of this homogeneous solution was then added dropwise into 800 ml of titanium tetrachloride maintained at −20 ° C. over 45 minutes with stirring. After the insertion, the temperature of the mixture was raised to 110 ° C. over 4.5 hours, and when it reached 110 ° C., 5.2 ml of 2-isobutyl-2-isopropyl-1,3-dimethoxypropane was added, The mixture was stirred and reacted at the same temperature for 2 hours. After completion of the reaction, the solid part was collected by hot filtration. This solid part was resuspended in 1000 ml of titanium tetrachloride, and then reacted again at 110 ° C. for 2 hours. After completion of the reaction, the solid part was again collected by hot filtration, and sufficiently washed with 90 ° C. decane and hexane until no free titanium compound was detected in the washing solution.

  The solid titanium catalyst component prepared by the above operation was stored as a decant slurry. Among these, some solid titanium catalyst components were sampled and dried, and the catalyst composition was measured. The composition of the obtained solid titanium catalyst component was as follows: titanium 3.0% by mass, magnesium 17.0% by mass, chlorine 57% by mass, 2-isobutyl-2-isopropyl-1,3-dimethoxypropane 18.8% by mass. And 2-ethylhexyl alcohol was 1.3% by mass.

[Synthesis of 4-methyl-1-pentene copolymer (A)]
In a SUS polymerization tank with a stirrer with an internal volume of 150 liters, 100 liters of decane, 26 kg of 4-methyl-1-pentene, 230 g of a mixture of 1-hexadecene and 1-octadecene, 6.75 liters under a nitrogen atmosphere Of hydrogen, 67.5 mmol of triethylaluminum, and 0.27 mol of the above solid titanium catalyst component in terms of titanium atom were charged. And the polymerization reaction of 4-methyl-1-pentene, 1-hexadecene and 1-octadecene was carried out for 5 hours while keeping the inside of the polymerization tank at 60 ° C. The powdery polymer was taken out from the polymerization tank, filtered and washed, and then dried to obtain a powdery 4-methyl-1-pentene copolymer (A).

The yield of the obtained 4-methyl-1-pentene copolymer (A) was 26 kg. The obtained 4-methyl-1-pentene copolymer (A) has a weight average molecular weight of 1.1 × 10 ⁶ by GPC measurement, and is measured by NMR. 1) -hexadecene and 1-octadecene content was 6.0% by mass in total.

[Synthesis of 4-methyl-1-pentene copolymer (B)]
Instead of 230 g of 1-hexadecene and 1-octadecene mixture and 6.75 liters of hydrogen, 230 g of 1-decene and 4.0 liters of hydrogen were used, except that 4-methyl-1 described above was used. A powdery 4-methyl-1-pentene copolymer (B) composed of 4-methyl-1-pentene and 1-decene was obtained in the same manner as in the pentene copolymer (A).

The weight average molecular weight of the 4-methyl-1-pentene copolymer (B) by GPC measurement was 2.0 × 10 ⁶ , and the 1-decene content was 3.3% by mass.

The resin components used in the examples and comparative examples are summarized in Table 1.

[Example 1]
Preparation of microporous membrane 40 parts by mass of 4-methyl-1-pentene copolymer (A), 60 parts by mass of liquid paraffin P-350P (manufactured by MORESCO) as a diluent, tetrakis [methylene as an antioxidant -3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] 0.2 parts by mass of methane was blended and kneaded in a lab plast mill for 10 minutes at 240 ° C. and 50 rpm.

  The obtained gel-like substance was inserted into a 1 mm-thick mold, and after pressurizing to 10 MPa at a press temperature of 240 ° C. using a press molding machine and preheating for 5 minutes; depressurization and pressurization (10 MPa) steps Repeated 10 times. Next, the pressure was again increased to 10 MPa and held for 5 minutes, and then the pressure was released. Then, it cooled by pressurizing to 10 Mpa at the press temperature of 50 degreeC using the press molding machine, and obtained the gel-like sheet | seat of thickness 1mm.

  The obtained gel-like sheet | seat was 120 degreeC and 2 mm / min. Biaxial stretching was performed under the same conditions. Stretching was uniformly stretchable up to 3 × 3 times.

  The stretched sheet stretched 3 × 3 times was fixed to a tenter for deparaffinization treatment and immersed in hexane at 23 ° C. for 10 minutes to obtain a microporous membrane. The meltdown temperature by TMA of the obtained microporous film was 212 ° C.

[Example 2]
After obtaining a gel-like sheet in the same manner as in Example 1 except that 4-methyl-1-pentene copolymer (B) was used instead of 4-methyl-1-pentene copolymer (A), Simultaneous biaxial stretching.

  Simultaneous biaxial stretching was capable of stretching up to 5 × 5 times. Further, the stretched sheet stretched 5 × 5 times was subjected to deparaffinization treatment in the same manner as in Example 1 to obtain a microporous membrane. The melt-down temperature by TMA of the obtained microporous film was 215 degreeC.

[Example 3]
10 parts by mass of 4-methyl-1-pentene copolymer (B), 30 parts by mass of ultra high molecular weight polyethylene MIPELON XM-220 (manufactured by Mitsui Chemicals), liquid paraffin P-350P ((stock) ) MORSCO) 60 parts by mass, tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane 0.2 parts by mass as an antioxidant, Similarly, after obtaining a gel-like sheet, it was simultaneously biaxially stretched.

  Simultaneous biaxial stretching was capable of stretching up to 5 × 5 times or more. Further, the stretched sheet stretched 5 × 5 times was subjected to deparaffinization treatment in the same manner as in Example 1 to obtain a microporous membrane. The meltdown temperature by TMA of the obtained microporous film was 170 ° C.

[Example 4]
20 parts by mass of 4-methyl-1-pentene copolymer (B), 20 parts by mass of ultra high molecular weight polyethylene miperon XM-220 (Mitsui Chemicals), and liquid paraffin P-350P ((stock) ) MORSCO) 60 parts by weight, tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane 0.2 parts by weight as an antioxidant, Similarly, after obtaining a gel-like sheet, it was simultaneously biaxially stretched.

  Simultaneous biaxial stretching was capable of stretching up to 5 × 5 times or more. Further, the stretched sheet stretched 5 × 5 times was subjected to deparaffinization treatment in the same manner as in Example 1 to obtain a microporous membrane. The meltdown temperature by TMA of the obtained microporous film was 200 ° C.

[Example 5]
30 parts by mass of 4-methyl-1-pentene copolymer (B), 10 parts by mass of ultra high molecular weight polyethylene MIPELON XM-220 (manufactured by Mitsui Chemicals), and liquid paraffin P-350P ((stock) ) MORSCO) 60 parts by weight, tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane 0.2 parts by weight as an antioxidant, Similarly, after obtaining a gel-like sheet, it was simultaneously biaxially stretched.

  Simultaneous biaxial stretching was capable of stretching up to 5 × 5 times or more. Further, the stretched sheet stretched 5 × 5 times was subjected to deparaffinization treatment in the same manner as in Example 1 to obtain a microporous membrane. The meltdown temperature by TMA of the obtained microporous film was 210 ° C.

[Comparative Example 1]
Ultra high molecular weight polyethylene MIPELON XM-220 (manufactured by Mitsui Chemicals) 40 parts by mass, liquid paraffin P-350P (manufactured by MORESCO) as a diluent, 60 parts by mass, tetrakis [methylene-3 as an antioxidant -(3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] 0.2 parts by mass of methane was blended to obtain a gel-like sheet in the same manner as in Example 1, and then biaxially stretched simultaneously.

  In simultaneous biaxial stretching, stretching was possible up to 5 × 5 times or more. Further, the stretched sheet stretched 5 × 5 times was subjected to deparaffinization treatment in the same manner as in Example 1 to obtain a microporous membrane. The meltdown temperature by TMA of the obtained microporous film was 140 ° C.

[Comparative Example 2]
40 parts by mass of 4-methyl-1-pentene copolymer (C) (Mitsui Chemicals Co., Ltd. RT18, weight average molecular weight 5.6 × 10 ⁵ ) as a diluent, liquid paraffin-P350P (manufactured by MORESCO) ) And 60 parts by mass of tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane as an antioxidant, and the same as in Example 1. A gel-like sheet was obtained.

  The obtained gel-like sheet was measured at 120 ° C. and 2 mm / min. When simultaneously biaxially stretched under the above conditions, the gel sheet could not be stretched up to 2 × 2 times and the gel sheet was broken in the stretching step. For this reason, a microporous film could not be obtained.

[Comparative Example 3]
40 parts by mass of poly-4-methyl-1-pentene copolymer (D) (Mitsui Chemicals Co., Ltd., MX002 weight average molecular weight 6.0 × 10 ⁵ ) as a diluent, liquid paraffin-P350P (manufactured by MORESCO) ) And 60 parts by mass of tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane as an antioxidant, and gel as in Example 1. A sheet was obtained.

  The obtained gel-like sheet was measured at 120 ° C. and 2 mm / min. When simultaneously biaxially stretched under the above conditions, the gel sheet could not be stretched up to 2 × 2 times and the gel sheet was broken in the stretching step. For this reason, a microporous membrane could not be obtained.

Table 2 shows the evaluation results of Examples 1 to 5 and Comparative Examples 1 to 3.

As shown in Table 2, the gel-like sheets of Examples 1 to 5 containing a 4-methyl-1-pentene copolymer having a weight average molecular weight of 10 ⁶ or more can be stretched to a high stretch ratio. It was found that the down temperature was as high as about 170 ° C. or higher.

On the other hand, although the gel-like sheet of Comparative Example 1 that does not contain 4-methyl-1-pentene copolymer can be stretched to a high stretch ratio, it is understood that the meltdown temperature is low. On the other hand, the gel sheets of Comparative Examples 2 to 3 containing a 4-methyl-1-pentene copolymer having a weight average molecular weight of less than 10 ⁶ could not be stretched to a high stretch ratio.

  ADVANTAGE OF THE INVENTION According to this invention, the microporous film excellent in heat resistance, mechanical strength, and liquid permeability can be provided. For this reason, the microporous membrane of the present invention is preferably used as a separator for a battery such as a lithium ion battery having particularly excellent meltdown characteristics.

Claims (7)

A microporous membrane comprising a resin composition containing a 4-methyl-1-pentene polymer having a weight average molecular weight of 1.0 × 10 ⁶ or more. 2. The microporous membrane according to claim 1, wherein the 4-methyl-1-pentene polymer has a weight average molecular weight of 1.5 × 10 ⁶ or more and 2.3 × 10 ⁶ or less.   The microporous membrane according to claim 1 or 2, wherein the porosity is 25% or more and 80% or less, and the meltdown temperature is 170 ° C or more.   The 4-methyl-1-pentene polymer is a structural unit derived from 4-methyl-1-pentene and a structural unit derived from an α-olefin having 2 to 20 carbon atoms other than the 4-methyl-1-pentene. The microporous membrane according to any one of claims 1 to 3, which is a 4-methyl-1-pentene copolymer containing:   5. The microporous membrane according to claim 4, wherein the content of the structural unit derived from the α-olefin having 2 to 20 carbon atoms in the 4-methyl-1-pentene copolymer is 10% by mass or less. The microporous membrane is a biaxially stretched film of the resin composition,
The microporous membrane according to any one of claims 1 to 5, wherein a surface stretch ratio of the biaxial stretching is 9 times or more. The battery separator which has the microporous film as described in any one of Claims 1-6.