JP2000248088A - Polyolefin microporous membrane and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly safe microporous polyolefin membrane having a moderately high air permeability, a low porosity, an appropriate pore diameter, and excellent in battery characteristics when used as a battery separator. . A polyolefin microporous membrane comprising an ultrahigh molecular weight polyolefin (A) having a weight average molecular weight of 500,000 or more or a composition (B) containing an ultrahigh molecular weight polyolefin having a weight average molecular weight of 500,000 or more, Degree is 1000
~ 2000sec / 100cc, bubble point value is 1
A microporous polyolefin membrane characterized by being at least 0 kg / cm ² and a method for producing the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microporous membrane made of an ultrahigh molecular weight polyolefin, and more particularly to a microporous polyolefin membrane for a battery separator.

[0002]

2. Description of the Related Art Microporous polyolefin membranes are insoluble in organic solvents and stable against electrolytes and electrode active materials.
Separators for secondary batteries, separators for large batteries such as electric vehicles, separators for capacitors, various separation membranes, water treatment membranes, ultrafiltration membranes, microfiltration membranes, reverse osmosis filtration membranes, various filters, moisture-permeable waterproof clothing or Is widely used as the base material. Conventionally, a method for obtaining a microporous film by mixing a polyolefin with an organic medium and an inorganic powder such as finely divided silica, melt-molding the polyolefin, and extracting the organic medium and the inorganic powder has been known. However, a step of extracting an inorganic substance was required, and the permeability of the obtained membrane largely depended on the particle size of the inorganic powder, and it was difficult to control the permeability.

[0003] Also, various methods for producing a high-strength microporous membrane using an ultrahigh molecular weight polyolefin have been proposed. For example, JP-A-60-242035 and JP-A-61-1
No. 95132, JP-A-61-195133,
JP-A-63-39602, JP-A-63-2736
No. 51, JP-A-3-64334, JP-A-3-64334
Japanese Patent No. 105851 discloses a method for producing a microporous film by forming a gel-like sheet from a solution obtained by heating and dissolving a polyolefin composition containing an ultra-high-molecular-weight polyolefin in a solvent, heating and stretching the gel-like sheet and extracting and removing the solvent. Although a method is described, the microporous polyolefin membrane by these techniques is characterized by a narrow pore size distribution and a small pore size, and is used for a battery separator and the like.

[0004] Recent lithium ion batteries have battery characteristics,
It is required to improve battery safety and battery productivity. In particular, it is very important to balance battery safety and productivity improvement. It is important to reduce the process failure rate to improve productivity, and it is necessary to prevent voltage drop due to self-discharge.Moreover, during battery production, even if the separator is pressed by the electrode edge or impurities mixed on the electrode, a small discharge phenomenon Preferably do not occur. In order to maintain safety, a separator that is difficult to contact between electrodes in a destructive test such as a crush test, or a separator that reduces the short-circuit current even if short-circuited is preferable. In order to suppress a decrease in short circuit, the pore diameter is preferably a certain size or less.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a battery separator having a moderately high air permeability, a low porosity, and a suitable pore diameter in order to solve the above-mentioned problems. It is to provide a highly safe polyolefin microporous membrane excellent in battery characteristics.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, using ultra-high molecular weight polyolefin or a polyolefin composition containing the same, from a solution having a specific concentration with a solvent. The obtained gel-like molded product is
In the production method obtained by stretching, solvent removal and heat setting, it has been found that by optimizing the stretching conditions, heat setting conditions and the like, a polyolefin microporous membrane having a good balance between air permeability and pore diameter can be obtained. I thought.

That is, according to the present invention, the weight average molecular weight is 5
A polyolefin microporous membrane comprising a composition (B) containing an ultrahigh molecular weight polyolefin (A) having a molecular weight of at least 500,000 or an ultrahigh molecular weight polyolefin having a weight average molecular weight of at least 500,000, having an air permeability of 1000 to 2000 sec / 100 cc;
A microporous polyolefin membrane having a bubble point value of 10 kg / cm ² or more.

Further, the present invention relates to an ultrahigh molecular weight polyolefin (A) having a weight average molecular weight of 500,000 or more or a composition (B) containing an ultrahigh molecular weight polyolefin having a weight average molecular weight of 500,000 or more and a solvent 95%. From a solution consisting of ６５65% by weight, a gel was obtained by melt extrusion, the gel was stretched 3 × 3 times or more, and then the solvent was removed.
A method for producing a microporous polyolefin membrane, comprising performing heat setting after drying, wherein the heat setting temperature after removing the solvent is 122 to 130 ° C. .

Preferred embodiments of the present invention are described below. (1) The microporous polyolefin membrane described above, wherein the ultrahigh molecular weight polyolefin having a weight average molecular weight of 500,000 or more is made of polyethylene or polypropylene. (2) The composition (B) containing an ultrahigh molecular weight polyolefin having a weight average molecular weight of 500,000 or more is composed of an ultrahigh molecular weight polyolefin (B-1) having a weight average molecular weight of 1,000,000 or more and a weight average molecular weight of 100,000 or more and less than 500,000. The microporous polyolefin membrane comprising high-density polyethylene (B-2). (3) The polyolefin microporous membrane, wherein the average through-hole diameter is 0.01 to 0.05 µm. (4) The polyolefin microporous membrane, wherein the piercing strength is 500 g / 25 μm or more. (5) The microporous polyolefin membrane having a tensile strength of 1000 kg / cm ² or more. (6) The polyolefin microporous membrane, wherein the porosity is 25 to 35%. (7) The polyolefin microporous membrane, wherein the heat shrinkage is 5% or less. (8) The method for producing a microporous polyolefin membrane according to claim 5, wherein the heat setting temperature is higher than the stretching temperature, and the difference between the heat setting temperature and the stretching temperature is 5 to 10 ° C.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The polyolefin microporous membrane of the present invention will be described in detail below with respect to constituent components, physical properties, and a production method. 1. Polyolefin The ultrahigh molecular weight polyolefin (A) used in the microporous polyolefin membrane of the present invention is an ultrahigh molecular weight polyolefin having a weight average molecular weight of 500,000 or more, preferably an ultrahigh molecular weight polyolefin having a weight average molecular weight of 1,000,000 to 15,000,000. . The weight average molecular weight of the polyolefin (A) is 50
If it is less than 10,000, the strength of the film is undesirably reduced.

The composition (B) containing an ultrahigh molecular weight polyolefin having a weight average molecular weight of 500,000 or more is not particularly limited.
An ultrahigh molecular weight polyolefin (B-1) having a weight average molecular weight of preferably 1.5 million or more, more preferably 1.5 million to 15 million, and a weight average molecular weight of 10,000 or more and less than 500,000, preferably 100,000 More than 50
A polyolefin composition (B) comprising less than 10,000 polyolefins (B-2). 1% by weight of ultrahigh molecular weight polyolefin (B-1) having a weight average molecular weight of 1,000,000 or more
It must be contained as described above. When the content of the ultrahigh molecular weight polyolefin (B-1) is less than 1% by weight, entanglement of the molecular chain of the ultrahigh molecular weight polyolefin is hardly formed, and a high-strength microporous film cannot be obtained. When the weight average molecular weight of the polyolefin (B-2) is less than 10,000, the resulting microporous membrane is easily broken, and the desired microporous membrane cannot be obtained.

Examples of the polyolefin include a crystalline homopolymer, a two-stage polymer or a copolymer obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-pentene-1, 1-hexene and the like. These blends are exemplified. Among these, polypropylene, polyethylene and their compositions are preferred, especially,
A composition comprising an ultrahigh molecular weight polyethylene (B-1) having a weight average molecular weight of 1,000,000 or more and a high density polyethylene (B-2) having a weight average molecular weight of 100,000 or more and less than 500,000 is preferable.

The molecular weight distribution (weight average molecular weight / number average molecular weight) of the polyolefin or polyolefin composition is preferably 300 or less, more preferably 5 to 50. If the molecular weight distribution exceeds 300, breakage due to low molecular weight components occurs, and the strength of the entire film is reduced, which is not preferable. When a polyolefin composition is used, an appropriate amount of an ultrahigh molecular weight polyolefin having a weight average molecular weight of 1,000,000 or more and a polyolefin having a weight average molecular weight of 100,000 or more and less than 500,000 are mixed so that the molecular weight distribution falls within the above range. The polyolefin composition may be one obtained by multi-stage polymerization or a composition comprising two or more polyolefins, as long as it has the above-mentioned molecular weight and molecular weight distribution.

The above-mentioned polyolefin or polyolefin composition may contain, if necessary, various additives such as an antioxidant, an ultraviolet absorber, an antiblocking agent, a pigment, a dye, an inorganic filler, and the like. When the membrane is used as a separator for a lithium battery or the like, a polymer capable of providing a shutdown function at a low temperature can be added within a range that does not impair the object of the present invention.

2. Polyolefin microporous membrane (1) Physical properties The polyolefin microporous membrane of the present invention has the following physical properties. Air permeability The air permeability of the polyolefin microporous membrane of the present invention is 1000
~ 2000sec / 100cc, preferably 1200 ~
It is 1800 sec / 100 cc. Air permeability 1000
If the polyolefin microporous membrane is used as a battery separator, the self-discharge phenomenon cannot be suppressed when the polyolefin microporous membrane is less than sec / 100 cc, and if it exceeds 2000 sec / 100 cc, the impedance becomes too high and the battery characteristics deteriorate. In such cases, it cannot be used as a battery separator.

Bubble Point The bubble point of the microporous polyolefin membrane of the present invention is:
It is 10 kg / cm ² or more, preferably 15 kg / cm ² or more. When the bubble point is less than 10 kg / cm ² , when the microporous polyolefin membrane is used as a battery separator, the pores become too large, and the voltage drop or self-discharge due to dendrite growth increases, and the battery cannot be used as a battery separator.

Porosity The porosity of the microporous polyolefin membrane of the present invention is from 25 to 3
5% is preferred. When the porosity is less than 25%, when the polyolefin microporous membrane is used as a battery separator,
The ion conductivity is poor, and the battery characteristics such as the battery capacity and the cycle characteristics at low temperatures are particularly poor. On the other hand, if it exceeds 35%, the balance between the safety as a battery and the impedance cannot be maintained.

Puncture Strength The puncture strength of the microporous polyolefin membrane of the present invention is 500.
g / 25 μm or more, preferably 650 g / 25 μm or more. When the puncture strength is less than 500 g / 25 μm, when a polyolefin microporous membrane is used as a battery separator, there is a problem that a short circuit is minutely generated due to compression of the separator caused by electrode irregularities or burrs.

Tensile strength The tensile strength of the microporous polyolefin membrane of the present invention is 100
0 kg / cm ² or more, particularly 1300 kg / c
m ² or more. Tensile strength 1000k
When it is at least g / cm ² , when a polyolefin microporous membrane is used as a battery separator, there is no fear of membrane breakage, which is preferable.

Heat Shrinkage The heat shrinkage of the microporous polyolefin membrane of the present invention is preferably 5% or less. When the heat shrinkage exceeds 5%, when the polyolefin microporous membrane is used as a battery separator,
Exposure of the electrodes during abnormal temperature rise of the battery can be suppressed.

Average Through-pore Diameter The average through-pore diameter of the microporous polyolefin membrane of the present invention is preferably 0.01 to 0.05 μm. When the average through-hole diameter is less than 0.01 μm, the permeability is significantly reduced,
If the thickness exceeds 05 μm, dendrite growth cannot be suppressed.

The microporous polyolefin membrane of the present invention has the specific air permeability and bubble point of the above requirements, and when used as a battery separator, reduces self-discharge causing battery process defects, and performs a battery destruction test. In such a case, a short circuit is unlikely to occur, and heat generation at the time of a short circuit can be suppressed low. In particular, the piercing strength is 500 g / 25 μm or more,
Tensile strength of 1000 kg / cm ² or more, porosity of 25 to
A polyolefin microporous membrane having a heat shrinkage of 35% or less is preferably 35% or less, and can be suitably used as a battery separator, a liquid filter, and the like.

(2) Production of Microporous Polyolefin Membrane The microporous polyolefin membrane of the present invention is obtained by adding an organic liquid or a resin component obtained by adding a polyolefin or a polyolefin composition to a polymer or the like that imparts a low-temperature shutdown effect, if necessary. Mix solids, extrude after melt kneading,
It can be obtained by stretching, solvent removal, drying and heat setting. As a preferred method of obtaining the polyolefin microporous membrane of the present invention, a good solvent of the polyolefin is supplied to the polyolefin or the polyolefin composition to prepare a solution of the polyolefin or the polyolefin composition, and the solution is formed into a sheet from a die of an extruder. After extrusion, the mixture is cooled to form a gel composition, and the gel composition is heated and stretched to remove the remaining solvent, dried, and then heat-set.

In the present invention, a solution of the polyolefin or the polyolefin composition as a raw material is prepared by heating and dissolving the above-mentioned polyolefin or the polyolefin composition in a solvent. The solvent is not particularly limited as long as it can sufficiently dissolve the polyolefin. For example, Nonan, Decane, Undecane, Dodecane,
Examples include aliphatic or cyclic hydrocarbons such as liquid paraffin, and mineral oil fractions whose boiling points correspond to these.To obtain a stable gel-like molded product, a non-volatile solvent such as liquid paraffin is used. preferable.

The heating dissolution is carried out with stirring at a temperature at which the polyolefin or the polyolefin composition is completely dissolved in the solvent, or by a method of uniformly mixing and dissolving in an extruder. In the case of dissolving while stirring in a solvent, the temperature varies depending on the polymer and the solvent to be used. For example, in the case of a polyethylene composition, the temperature is in the range of 140 to 250 ° C. When producing a microporous membrane from a high-concentration solution of the polyolefin composition, it is preferable to dissolve it in an extruder.

When dissolving in an extruder, first, the above-mentioned polyolefin or polyolefin composition is supplied to the extruder and melted. The melting temperature depends on the type of polyolefin used, but the melting point of polyolefin + 30
-100 ° C is preferred. For example, in the case of polyethylene, the temperature is preferably 160 to 230 ° C, particularly 170 to 200 ° C, and in the case of polypropylene, the temperature is preferably 190 to 270 ° C, particularly 190 to 250 ° C. Next, a liquid solvent is supplied to the molten polyolefin or polyolefin composition from the middle of the extruder.

The mixing ratio of the polyolefin or the polyolefin composition and the solvent is 5 to 35% by weight based on 100% by weight of the total of the polyolefin or the polyolefin composition and the solvent.
It is preferably 20 to 30% by weight, and the solvent is 95 to 65% by weight.
%, Preferably 80 to 70% by weight. If the polyolefin or the polyolefin composition is less than 5% by weight (the solvent exceeds 95% by weight), when forming into a sheet, the swell and neck-in are large at the die exit, making the sheet formability and self-supporting difficult. In addition, it takes too much time to remove the solvent, and the productivity is reduced. On the other hand, when the polyolefin or the polyolefin composition exceeds 35% by weight (the solvent is less than 65% by weight), a desired microporous film cannot be obtained, and the moldability decreases. By changing the concentration in this range, the permeability of the membrane can be controlled.

Next, the heated solution of the polyolefin or the polyolefin composition thus melt-kneaded is directly or through another extruder so that the final product has a thickness of 5 to 250 μm from a die or the like. And extruded. As the die, a sheet die having a rectangular base shape is usually used, but a double cylindrical hollow die, an inflation die, or the like can also be used. The die gap when a sheet die is used is usually 0.1 to 5 mm, and the material is heated to 140 to 250 ° C during extrusion molding.
At this time, the extrusion speed is usually 20 to 30 cm / min to 15 m / min.

The solution extruded from the die is formed into a gel-like molded product by cooling. The cooling is performed by cooling the die or cooling the gel-like sheet. Cooling is performed at a rate of at least 50 ° C / min to 90 ° C or less, preferably to 80 to 30 ° C. As a method of cooling the gel-like sheet, a method of directly contacting with cold air, cooling water, or another cooling medium, a method of contacting with a roll cooled by a refrigerant, and the like can be used, but a method using a cooling roll is preferable.

Next, this gel-like molded product is biaxially stretched.
The stretching is performed at a predetermined magnification by heating the gel-like molded product and using a usual tenter method, roll method, rolling or a combination of these methods. The biaxial stretching may be either vertical or horizontal simultaneous stretching or sequential stretching, but simultaneous biaxial stretching is particularly preferred. The stretching temperature is not particularly limited, but in order to obtain a higher-strength polyolefin microporous membrane, in the case of a composition of ultra-high-molecular-weight polyethylene and high-density polyethylene, 11
0-125 degreeC is preferable, More preferably, it is 110-12.
0 ° C. The stretching ratio is 3 times (3 × 3 times) or more in the MD and TD directions. If the stretching ratio is less than 3 times, a sufficient piercing strength of the microporous polyolefin membrane cannot be obtained.

Further, the molded product obtained above is washed with a solvent to remove the remaining solvent. Examples of the cleaning solvent include hydrocarbons such as pentane, hexane, and heptane; chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride; fluorinated hydrocarbons such as ethane trifluoride; and ethers such as diethyl ether and dioxane. Volatile ones can be used. These solvents are appropriately selected according to the solvent used for dissolving the polyolefin composition, and used alone or as a mixture. The washing method can be performed by a method of immersing in a solvent for extraction, a method of showering the solvent, a method of a combination thereof, or the like. Cleaning as described above,
The process is performed until the residual solvent in the molded product is less than 1% by weight. Thereafter, the washing solvent is dried, and the washing solvent can be dried by a method such as heat drying or air drying.

Next, the microporous membrane obtained by removing the solvent is heat-set at 122 to 130 ° C. The heat setting temperature is preferably higher than the stretching temperature, and the difference from the stretching temperature is preferably 5 to 10 ° C. When the heat setting temperature is lower than 122 ° C., only a microporous membrane having a value lower than the predetermined air permeability of the present invention can be obtained, and 130 ° C.
If it exceeds, a microporous membrane having a value higher than the predetermined air permeability of the present invention is obtained, which is inappropriate in any case. When the heat setting temperature is higher than the stretching temperature and the difference from the stretching temperature is 5 to 10 ° C., the advantage is obtained that the microporous membrane having the predetermined air permeability of the present invention can be obtained while maintaining the strength. Having.

By the above-mentioned method, a microporous polyolefin membrane having the above-mentioned physical properties can be produced. The obtained microporous polyolefin membrane may be further subjected to plasma irradiation, surfactant impregnation, Surface modification such as hydrophilic treatment such as surface grafting can be performed.

[0034]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not particularly limited to the examples. In addition, the test method in an Example is as follows. (1) Weight average molecular weight and molecular weight distribution: using GPC apparatus manufactured by Waters Co., Ltd., GMH-6 manufactured by Tosoh Corporation, o-dichlorobenzene as a solvent, a temperature of 135 ° C., and a flow rate of 1.0 ml. Per minute by gel permission chromatography (GPC). (2) Film thickness: Measured using a stylus-type film thickness meter Mitutoyolitematic. (3) Air permeability: Measured according to JIS P8117. (4) Average through-hole diameter: Measured with a Coulter porometer (manufactured by Coulter). (5) Porosity: measured by a gravimetric method. (6) Puncture strength: 2 needles with a diameter of 1 mm (0.5 mmR)
It pierced at mm / sec and the load at the time of breaking was measured. (7) Tensile strength: The breaking strength of a 10 mm wide strip test piece was measured in accordance with ASTM D822. (8) Bubble point: Measured in ethanol according to ASTM E-128-61. In addition, when exceeding the limit value, it was described as "≧ 15". (10) Thermal shrinkage: The shrinkage in the MD and TD directions after exposure for 12 hours in an atmosphere at 80 ° C. was measured.

(11) Electrode intrusion distance: Using a Kikusui partial discharge measuring device with a variable interelectrode distance, a minute discharge phenomenon caused by a minute void was detected, and a discharge starting distance and a voltage were measured. Specifically, when the electrode was made to enter under the condition of an applied voltage of 0.4 kV, the distance at which partial discharge occurred was measured as the electrode entry distance. When the electrode penetration distance is 5 μm or more, there is an effect of suppressing dendrite growth, which is effective in suppressing a battery process defect. (12) Partial discharge starting voltage: In the same manner as in the measurement of the electrode penetration distance, the partial discharge starting voltage was measured under the condition of an applied voltage of 0.8 kV when the distance between the electrodes was a film thickness. When the partial discharge starting voltage is 0.5 kV or more, there is an effect of suppressing dendrite growth, which is effective in suppressing a battery process defect.

Example 1 20% by weight of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2.0 × 10 ⁶ and high density polyethylene (HDPE) 80 having a weight average molecular weight of 3.5 × 10 ⁵
A polyethylene composition was obtained by adding 0.375 parts by weight of an antioxidant to 100 parts by weight of the polyethylene composition to the polyethylene composition consisting of 100% by weight. 20 parts by weight of the obtained polyethylene composition was placed in a twin-screw extruder (58 mmφ, L / D
= 42, strong kneading type), 80 parts by weight of liquid paraffin was supplied from the side feeder of this twin-screw extruder, and melt-kneaded at 200 ° C and 200 rpm to prepare a polyethylene solution in the extruder. A gel-like sheet was formed while extruding the final product from a T-die set at the tip of the extruder so as to have a thickness of 50 to 60 μm, and taking it off with a cooling roll adjusted to 50 ° C. Subsequently, this gel-like sheet was biaxially stretched at 116 ° C. so as to be 5 × 5 times to obtain a stretched sheet. After the obtained sheet was washed with methylene chloride to extract and remove the remaining liquid paraffin, drying was performed, and heat setting was further performed at 125 ° C. for 10 seconds.
A 25 μm-thick microporous polyethylene membrane was obtained. Table 1 shows the results of evaluating the physical properties of this polyethylene microporous membrane.

Examples 2 to 5 A microporous polyethylene membrane was prepared in the same manner as in Example 1 except that UHMWPE and HDPE shown in Table 1 were used in the proportions shown in Table 1 and the stretching temperature and the stretching ratio shown in Table 1 were used. Obtained. Table 1 shows the physical properties of the obtained microporous polyethylene membrane.

[0038]

[Table 1]

Comparative Examples 1 to 6 Polyethylene was used in the same manner as in Example 1 except that UHMWPE and HDPE shown in Table 2 were used in the proportions shown in Table 2 and the stretching temperature, stretching ratio and heat setting temperature shown in Table 2 were used. A microporous membrane was obtained. Table 2 shows the physical properties of the obtained microporous polyethylene membrane.
Shown in

[0040]

[Table 2]

[0041]

As described in detail above, the microporous polyolefin membrane of the present invention comprises an ultrahigh molecular weight polyolefin,
Because it is a microporous membrane with a good balance of air permeability and bubble point, it is a highly safe polyolefin microporous membrane with excellent battery characteristics when used as a battery separator, and as a battery separator, liquid filter, etc. It can be suitably used.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08J 9/00 CES C08J 9/00 CESA 9/28 CES 9/28 CES H01M 2/16 H01M 2/16 P // B29K 23:00 105: 04 B29L 7:00 (72) Inventor Shigeaki Kobayashi 3-27-1-342 Baba, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture (72) Inventor Koichi Kono 3-29, Mihara, Asaka-shi, Saitama -10-404 F term (reference) 4D006 GA16 MA03 MA22 MA24 MA31 MB15 MB16 MB17 MB20 MC22 MC22X MC23 MC83 MC88 NA01 NA10 NA14 NA50 NA63 NA68 NA70 PB12 PC80 4F071 AA15 AA20 AA81 AE19 AF08Y AF14Y AF15Y AF36 AF61Y AH12 BC 4F074 AA16 AA17 AA24 AB01 AD01 CB37 CC02X CC04Z CC29Y CC32Z CC42 DA10 DA49 5H021 BB01 BB02 BB05 BB13 CC00 EE01 EE04 HH00 HH01 HH06 HH07

Claims (5)

[Claims] 1. A microporous polyolefin membrane comprising an ultrahigh molecular weight polyolefin (A) having a weight average molecular weight of 500,000 or more or a composition (B) containing an ultrahigh molecular weight polyolefin having a weight average molecular weight of 500,000 or more, Temper 1000
~ 2000sec / 100cc, bubble point value is 1
A polyolefin microporous membrane characterized by being at least 0 kg / cm ² . 2. A battery separator using the microporous polyolefin membrane according to claim 1. 3. A battery using the microporous polyolefin membrane according to claim 1 as a battery separator. 4. A filter using the microporous polyolefin membrane according to claim 1. 5. An ultrahigh molecular weight polyolefin having a weight average molecular weight of 500,000 or more (A) or a composition containing an ultrahigh molecular weight polyolefin having a weight average molecular weight of 500,000 or more (B) 5-35.
From a solution consisting of 95% by weight and 95% by weight of a solvent, a gel is obtained by melt-extrusion, the gel is stretched 3 × 3 times or more, and then the solvent is removed. A method for producing a microporous polyolefin membrane, comprising:
The method for producing a microporous polyolefin membrane according to claim 1, wherein the temperature is 22 to 130 ° C.