JP3250894B2 - Method for producing microporous polyolefin membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a microporous membrane made of polyolefin, and more particularly, to a method for efficiently producing a microporous polyolefin membrane having excellent strength, good permeability and stable pore size. It relates to a method of manufacturing.

[0002]

2. Description of the Related Art Microporous membranes include separators for batteries, diaphragms for electrolytic capacitors,
It is used for various applications such as various filters, moisture-permeable waterproof clothing, reverse osmosis filtration membranes, ultrafiltration membranes, and microfiltration membranes.

[0003] Conventionally, as a method for producing a microporous polyolefin membrane, for example, a pore-forming agent composed of fine powder of a different polymer or the like is mixed with polyolefin and micro-dispersed.
A mixed extraction method for extracting a pore-forming agent, a phase separation method for forming a porous structure by separating a polyolefin phase into a microphase with a solvent, and applying a strain such as stretching to a polyolefin molded article in which different solids are micro-dispersed, An elongation method or the like has been used in which a heterogeneous solid is broken down at the interface to generate pores and make the pores porous. However, there is a limit to thinning and high strength by stretching.

Recently, ultrahigh molecular weight polyolefins that can be formed into high strength and high elasticity films have been developed, and various methods for producing high strength microporous membranes have been proposed. For example, JP-A-58-5228 discloses that an ultrahigh molecular weight polyolefin is dissolved in a non-volatile solvent, a gel such as a fiber or a film is formed from the solution, and the gel containing the solvent is extracted with a volatile solvent. A method of heating and stretching is disclosed. However, a gel having a porous structure highly swollen with a non-volatile solvent cannot be stretched in a high orientation even if it is stretched in two directions, and is easily broken due to expansion of a network structure, and the obtained film has low strength. In addition, there is a disadvantage that the pore size distribution of the formed pores becomes large. On the other hand, in the gel dried after extracting the non-volatile solvent with the volatile solvent, the network structure shrinks and densifies, but the non-uniform evaporation of the volatile solvent easily causes warpage of the film raw material, and the shrinking and densification causes However, there is a drawback that stretching at a high magnification cannot be performed.

On the other hand, a gel-like sheet is formed from a solution obtained by heating and dissolving an ultra-high-molecular-weight polyolefin having a weight-average molecular weight of 7 × 10 ⁵ or more in a solvent, and the amount of the solvent in the gel-like sheet is reduced by desolvation treatment. Various methods have been proposed for producing microporous membranes of ultra-high molecular weight polyolefin (polyethylene) by preparing, then heat-stretching, and then removing the residual solvent (JP-A-60-242035, JP-A-60-242035). 61-4
95132, JP-A-61-195133, JP-A-63-39602, JP-A-63-273651).

[0006] However, in the above method, the higher the concentration of the polyolefin solution, the longer it takes to prepare the solution. Therefore, there is a problem that the polyolefin is easily oxidized and deteriorated, and it is difficult to make the concentration of the solution uniform.

JP-A-62-223245 discloses a high molecular weight polyolefin (A) having an intrinsic viscosity [μ] of 3 dl / g or more in decalin at 135 ° C. of 5 to 70% by weight, and a melting point of (A) or more. Plasticizer (B) having a boiling point and soluble in a solvent of 95 to 30
% By weight, and extruded into a cylinder using a circular die to form a film, and the resulting film is treated with a solvent to extract and remove component (B). A method for producing a porous polyolefin membrane having permeability is disclosed. However, since the film extruded from the annular die is immediately subjected to inflation molding, crystallization of polyolefin is insufficient, and orientation by stretching and stable fine fibrillation of polyolefin crystal are not always sufficient.

Accordingly, an object of the present invention is to provide a method for efficiently producing a microporous polyolefin membrane having good permeability, stable openness with a fine pore size and high strength .
For battery using microporous membrane obtained by the method
And filters .

[0009]

As a result of intensive studies in view of the above-mentioned object, the present inventors have melted a polyolefin containing an ultrahigh molecular weight component in an extruder and supplied a good solvent for the polyolefin to the melt. After preparing a solution of polyolefin by extruding this solution from the annular die,
By cooling to form a raw gel tube, heating and stretching the raw gel tube, and then removing the remaining solvent, a polyolefin fine material having an appropriate fine pore diameter, stable openability and high strength. A porous membrane can be manufactured, and according to such a method, the time required for preparing a high-concentration solution of a polyolefin can be significantly shortened as compared with the conventional art, and oxidative deterioration of the polyolefin can be prevented. At the same time, they have found that the manufacturing efficiency can be greatly improved, and arrived at the present invention.

That is, the method for producing a microporous polyolefin membrane of the present invention comprises the steps of: (a) melting a polyolefin containing 1% by weight or more of a component having a weight average molecular weight of 7 × 10 ⁵ or more in an extruder; 90 to 20% by weight of a liquid solvent (a good solvent for the polyolefin) at a temperature of the molten polyolefin and 90 to 20% by weight is supplied to the melted polyolefin at a temperature of 10 to 80% by weight, and melt-kneaded. c) The obtained kneaded material is extruded from an annular die, cooled to form a raw gel tube, (d) the raw gel tube is heated and stretched, and (e) the remaining solvent is removed. It is characterized by the following.

The present invention will be described in detail below. [1] Polyolefin The microporous polyolefin membrane produced by the method of the present invention comprises a polyolefin containing 1% by weight or more of a component having a weight average molecular weight of 7 × 10 ⁵ or more.

The polyolefin has a weight average molecular weight of 7 × 10
^If the content of ⁵ or more components is less than 1% by weight, the entanglement of the molecular chain of the ultra-high molecular weight polyolefin that contributes to the improvement of the stretchability becomes insufficient, so that it is difficult to sufficiently improve the strength. On the other hand, the upper limit of the content of the ultrahigh molecular weight component is not particularly limited. However, if the content exceeds 90% by weight, it is difficult to achieve a desired polyolefin solution with a high concentration and to stretch the polyolefin solution, which is not preferable. The polyolefin preferably does not substantially contain a component having a weight average molecular weight of 1 × 10 ³ or less.

The polyolefin has a molecular weight distribution (weight average molecular weight / number average molecular weight) of 5 to 300, especially 5 to 300.
Preferably it is ~ 50. If the molecular weight distribution exceeds 300, low molecular weight components are broken during stretching, and the strength of the entire film is lowered, which is not preferable.

The polyolefin includes ethylene,
Propylene, 1-butene, 4-methyl-1-pentene, crystalline homopolymer obtained by polymerizing 1-hexene, etc., two-stage polymer,
Alternatively, a copolymer and a blend thereof may be used.
Among these, polypropylene, polyethylene (particularly high-density polyethylene), and compositions thereof are preferred.

If the polyolefin has the above-mentioned weight average molecular weight and molecular weight distribution, even if it is produced by a reactor blend (multi-stage polyolefin), it may have a molecular weight of 2 or less.
It may be a composition of at least one kind of polyolefin.

[0016] In the case of the reactor blend, for example, a weight flat
To be produced by multi-stage polymerization so as to contain 1% by weight or more of an ultrahigh molecular weight component having an average molecular weight of 7 × 10 ⁵ or more and a molecular weight distribution (weight average molecular weight / number average molecular weight) of 5 to 300. Can be. As the multistage polymerization method, it is preferable to adopt a method of producing a high molecular weight portion and a low molecular weight portion by two-stage polymerization.

In the case of a composition comprising two or more kinds of polyolefins, an ultrahigh molecular weight polyolefin having a weight average molecular weight of 7 × 10 ⁵ or more, which is a homopolymer or copolymer of the olefin, and a weight average molecular weight of 7 × 10 ⁵ It can be obtained by mixing an appropriate amount of less than polyolefin such that the weight average molecular weight / number average molecular weight falls within the above range.

In the case of the composition, the content of the ultrahigh molecular weight polyolefin in the polyolefin composition is preferably 1% by weight or more, based on 100% by weight of the whole polyolefin composition. When the content of the ultrahigh molecular weight polyolefin is less than 1% by weight, the portion contributing to the improvement of stretchability is insufficient. On the other hand, the upper limit is not particularly limited.

The lower limit of the weight average molecular weight of the polyolefin (polyolefin having a weight average molecular weight of less than 7 × 10 ⁵ ) other than the ultrahigh molecular weight polyolefin in the polyolefin composition is preferably 1 × 10 ⁴ or more. It is not preferable to use a polyolefin having a weight average molecular weight of less than 1 × 10 ⁴ , since breakage is likely to occur during stretching and a desired microporous film cannot be obtained. Therefore, it is preferable to blend a polyolefin having a weight average molecular weight of 1 × 10 ⁴ or more and less than 7 × 10 ⁵ with the ultrahigh molecular weight polyolefin.

The above-mentioned polyolefin containing an ultrahigh molecular weight component may contain, if necessary, an antioxidant, an ultraviolet absorber, an antiblocking agent, a pigment, a dye, an inorganic filler, an antibacterial agent, a deodorant. Various additives such as far-infrared radiating agents can be added within a range that does not impair the object of the present invention.

[2] Manufacturing Method Next, a method for manufacturing the microporous polyolefin membrane of the present invention using the above-described ultrahigh molecular weight component-containing polyolefin will be described.

FIG. 1 is a schematic diagram showing an example of an inflation film forming apparatus to which the method for producing a microporous polyolefin film of the present invention can be applied. In FIG. 1, the inflation film forming apparatus 1 includes a hopper 21, a solvent tank 23, and the solvent tank 23.
Feeder 22 that supplies the solvent from the middle of the extruder
, A gear pump 3 provided at the tip of the extruder 2, an annular die 4, a cooling ring 5, a pair of rolls 20, 20 ', and a pair of first nip rolls 6, 6'.
And a heating device 7, a blower 8, a pair of second nip rolls 9, 9 ', a reversing device 10, a slitter 11, a cleaning device 12, a drying device 15, and a winder 16, Cleaning equipment 12
Is equipped with felt rolls 13 and 13 '
4, 14 '.

The microporous polyolefin membrane is manufactured as follows using the apparatus having the above-described structure.

First, the above-mentioned polyolefin is supplied from the hopper 21 to the extruder 2 and melted. The melting temperature varies depending on the type of polyolefin used, but generally, the melting point of the polyolefin + 10 ° C to + 120 ° C is preferable. here
The melting point is measured by DSC based on JIS K 7121.
(Hereinafter the same). For example, in the case of polyethylene, the temperature is preferably + 130 ° C. to + 260 ° C., particularly + 140 ° C. to + 240 ° C., and in the case of polypropylene, it is + 180 ° C. to + 240 ° C.
The temperature is preferably 290 ° C, in particular + 180 ° C to + 270 ° C.

Next, a liquid solvent in the molten state (a good solvent for the above-mentioned polyolefin) is supplied to the polyolefin in the molten state from the middle of the extruder (side feeder 22). When simultaneously supplying a polyolefin containing an ultra-high molecular weight polyolefin and a solvent,
Mixing cannot be performed because the viscosity difference is too large, and the polyolefin and the screw of the extruder co-rotate. Therefore, a desired solution cannot be prepared. As the solvent, for example, an aliphatic or cyclic hydrocarbon such as nonane, decane, decalin, p-xylene, undecane, dodecane, and liquid paraffin, or a mineral oil fraction having a boiling point corresponding to these can be used.

The mixing ratio of the polyolefin and the solvent is 10 to 80% by weight, preferably 10 to 60% by weight, and the solvent is 90 to 20% by weight, with the total of the polyolefin and the solvent being 100% by weight. Preferably it is 90 to 40% by weight. If the polyolefin content is less than 10% by weight (the solvent content exceeds 90% by weight), the swell and neck-in at the outlet of the annular die 4 are large, making it difficult to form a gel-like sheet. On the other hand, if the polyolefin exceeds 80% by weight (the solvent is less than 20% by weight), it is difficult to prepare a uniform solution.

By adding a solvent to the polyolefin in a molten state and kneading the mixture in an extruder, a high-concentration polyolefin solution having a uniform concentration can be prepared in a short time. For this purpose, it is preferable to use a twin-screw extruder.

Next, the heated solution of the polyolefin thus melt-kneaded is extruded from the annular die 4. The annular die 4 preferably has a die gap of 0.1 to 5 mm, and is heated to 110 to 250 ° C. during extrusion.

Incidentally, between the extruder 2 and the annular die 4,
In order to prevent the resin supplied from the extruder from pulsating, it is preferable to provide the gear pump 3 as in this embodiment. A plurality of the gear pumps 3 may be provided. Further downstream, it is preferable to provide a static ball mixer to disperse the laminar flow and improve the mixing.

The solution extruded from the annular die 4 is cooled by the cooling ring 5 to form a raw gel tube 30a. Cooling methods include cold air,
A method of directly contacting with cooling water or another cooling medium, a method of contacting with a roll cooled by a refrigerant, or the like can be used.

The raw material of the gel-like tube is made of rolls 20 and 20 '.
After passing through the first nip rolls 6 and 6 ′, heating is performed by the heating device 7. As the heating device 7, it is preferable to use a ceramic far-infrared irradiation device or the like from the viewpoint of stretchability. The heating temperature is below the melting point of polyolefin + 10 ° C.
Preferably, it is in the range from the crystal dispersion temperature to less than the melting point. This
Here, the crystal dispersion temperature is defined as the melt viscoelasticity based on ASTM D 4065.
It means the value determined by the property measurement (hereinafter the same). For example, in the case of polyethylene at 90 to 140 ° C. , more preferably 10
It ranges from 0 to 130 ° C. If the stretching temperature exceeds the melting point + 10 ° C., it is not preferable because effective melting of the resin does not allow effective molecular chain orientation. On the other hand, if the stretching temperature is lower than the crystal dispersion temperature, the resin is insufficiently softened, the film is easily broken in stretching, and high-magnification stretching cannot be performed.

After the heating, the film is stretched. Stretching is
1.5 to 12 times the diameter of the tube stock, 1.5 to the flow direction
The magnification is 12 times and the area magnification is 2.2 to 144 times, preferably 3 to 36 times. If the areal magnification is less than 2.2 times, stretching is insufficient and porosity is high, and a highly elastic and high strength microporous film cannot be obtained. Meanwhile, 14
If it exceeds 4 times, there will be restrictions on the stretching apparatus, stretching operation, and the like. The blow-up ratio is preferably set to 2 to 6.

The obtained stretched product 30b is twisted at 180 to 340 ° by the reversing device 10 to remove wrinkles and slacks, and then split by the slitter 11.

Subsequently, the stretched product 30b passes through felt rolls 13 and 13 'to remove excess solvent. Thereafter, the remaining solvent is completely removed by showering the cleaning solvent from the cleaning solvent shower devices 14 and 14 '.
The washing solvent can be appropriately selected depending on the solvent used. Examples thereof include hydrocarbons such as pentane, hexane, and heptane; chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride; and fluorocarbons such as ethane trifluoride. Ethers such as hydrogen, diethyl ether and dioxane, N-methyl-2
-Pyrrolidone and the like. These solvents are appropriately selected according to the solvent used for dissolving the polyolefin, and used alone or as a mixture. Further, if necessary, it can be diluted with water or the like before use. The washing method can be appropriately selected and used, such as a method of immersing in a solvent and extracting, or a method of a combination thereof, in addition to a method of showering a solvent as in this embodiment.

The washing as described above is performed until the residual solvent in the stretch molded product becomes less than 1% by weight. Thereafter, the cleaning solvent is dried by the drying device 15 and wound up by the winder 16, whereby the microporous film 30c can be obtained. Drying of the washing solvent can be performed by a method such as heat drying or air drying.
The dried microporous membrane 30c is desirably heat-set at a temperature in the range of the crystal dispersion temperature to the melting point. This heat setting can be performed at once by adjusting the drying temperature and time in the drying device.

The microporous polyolefin membrane produced as described above has a porosity of 35-95% and an average through-pore diameter of 0.00
1 to 0.5 μm and a tensile strength at break of 300 kg / cm ² or more. The thickness of the polyolefin microporous membrane of the present invention,
Although it can be appropriately selected according to the application, it is generally 0.1 to 50 μm, preferably 2 to 40 μm.

The obtained microporous polyolefin membrane can be further subjected to a surface treatment such as a plasma irradiation, a surfactant impregnation, or a hydrophilic treatment such as surface grafting, if necessary.

[0038]

In the present invention, a polyolefin containing an ultrahigh molecular weight component is melted in an extruder, and a solvent is supplied thereto to prepare a polyolefin solution, which is extruded from an annular die and cooled to form a gel. The raw material tube is formed, and the raw material gel tube is heated and stretched, and then the remaining solvent is removed to produce a microporous polyolefin membrane. By such a method, the polyolefin microporous membrane is not deteriorated by oxidation,
It can be manufactured much more efficiently than in the past.

Although it is not always clear why such an effect is obtained, it takes a long time to prepare a polyolefin solution containing an ultrahigh molecular weight component.
It is difficult to equalize the concentration of the solution, and there is a problem that the solution is easily deteriorated.However, a solvent is supplied to the polyolefin containing the ultrahigh molecular weight component in a molten state in an extruder,
It is considered that this is because a homogeneous solution of a high-concentration polyolefin can be prepared in a short time by kneading to prepare a solution. In addition, since such a high-concentration polyolefin solution is extruded in a ring shape, and the polyolefin is crystallized by cooling, the tubular raw material is heated and stretched. And sufficient fibrillation by cleavage of polyolefin crystals by stretching is stably performed. Therefore, it is considered that a microporous polyolefin membrane having excellent mechanical strength such as tensile rupture strength and piercing strength in addition to good permeability and stable pore opening property is obtained.

[0040]

Examples of the present invention will be described below. In addition, the test method in an Example is as follows. (1) Film thickness: The cross section was measured by a scanning electron microscope (unit: μm). (2) Average pore diameter: Measured with a nitrogen adsorption / desorption type pore diameter measuring instrument (manufactured by Nikkaki Co., Ltd.) (unit: μm). (3) Tensile breaking strength: Measured according to ASTM D882 (unit: kg / cm ² ). (4) Air permeability: Air permeability measured in accordance with JIS P8117 (unit: sec / 100 cc) (5) Piercing strength: A needle with 0.5 mmR and 1 mmφ needles was used to fix a fixed membrane with a measurement area of 1 cm ^2. The load at the time of piercing was shown (unit: g).

Example 1 24 parts by weight of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight (Mw) of 2.5 × 10 ^{6 and} a weight average molecular weight (Mw)
w) Raw material resin (melting point 135 ° C, crystal dispersion temperature 90 ° C) with 76 parts by weight of 3.5 × 10 ⁵ high-density polyethylene (HDPE ), and 2,6-di-t-butyl-p-cresol as an antioxidant (BHT,
0.05 parts by weight of Sumitomo Chemical Co., Ltd.) and 0.1 parts by weight of tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxylphenyl) -propionate] methane (Irganox 1010, Ciba-Geigy) Was dry blended, and this was charged into a twin screw extruder (45 mmφ, L / D = 48, strong kneading type). Liquid paraffin (30 Cst / 40 ° C.) was supplied from two side feeders of the twin-screw extruder so that the concentration of the resin component was 17% by weight (resin component + liquid paraffin = 100% by weight), and 200 rpm was supplied. Melt and knead with
A polyethylene solution was prepared in an extruder.

Subsequently, a stable discharge is performed by a gear pump installed at the tip of the extruder, and further, the laminar flow is eliminated by passing through a static ball mixer (not shown). ℃) to 185
The mixture was extruded at a temperature of ° C and rapidly cooled with cooling water (water temperature of 30 ° C) to form a gel-like tube. Subsequently, the gel-like tube was heated to 120 ° C. by a far-infrared ceramic heater, and was simultaneously biaxially stretched at a take-up speed of 5 m / min and a condition of 5 times and a blow-up ratio of 5. The obtained stretched membrane was washed with methylene chloride to extract and remove the remaining liquid paraffin, and then dried to obtain a polyethylene microporous membrane.

Table 1 shows the composition and production conditions of the microporous polyethylene membrane. The thickness, average pore size, tensile rupture strength and air permeability of this microporous polyethylene membrane were measured. The results are shown in Table 1.

Examples 2 and 3 and Comparative Examples 1 and 2 The same procedures as in Example 1 were carried out except that the ratio of the ultrahigh molecular weight polyethylene in the raw material resin and the concentration of the polyethylene solution were variously changed as shown in Table 1. To produce a polyethylene microporous membrane. In addition, for each raw material resin
However, the melting point was 135 ° C and the crystal dispersion temperature was 90 ° C.

Table 1 shows the composition and production conditions of the microporous polyethylene membrane. The thickness, average pore size, tensile rupture strength and air permeability of this microporous polyethylene membrane were measured. The results are shown in Table 1.

Table 1 Composition Example 1 Example 2 Example 3 UHMWPE (parts by weight) 24 26 30 HDPE (parts by weight) 76 74 70 Concentration (% by weight) Polyethylene ⁽¹⁾ 17 35 50 Liquid paraffin 83 65 50 Production Condition Rotation speed of extruder (rpm) 200 200 220 Extruder temperature (° C) 185 185 190 Stretching temperature (° C) 120 120 125 Stretching ratio (times) 5 × 5 5 × 5 5 × 5 Physical film thickness (μm) 34 34 35 Average pore size (μm) 0.03 0.04 0.03 Tensile breaking strength ⁽²⁾ 540 980 1150 Breathability ⁽³⁾ 600 850 950 Puncture strength ⁽⁴⁾ 530 570 600

[0047] of Table 1 (Continued) Composition Comparative Example 1 Comparative Example 2 UHMWPE (parts by weight) 35 2 HDPE (parts by weight) 50 3 Concentration (wt%) polyethylene ⁽¹⁾ 85 5 Liquid paraffin 15 95 production conditions extruder Rotation speed (rpm) 200 200 Extruder temperature (° C) 195 185 Stretching temperature (° C)- ^{* 1- * 2} Stretching ratio (times)- ^{* 1- * 2} Physical film thickness (μm)- ^{* 1- * 2} Average Pore size (μm)- ^{* 1- * 2} Tensile breaking strength ⁽²⁾ - ^{* 1- * 2} Breathability ⁽³⁾ - ^{* 1- * 2} Piercing strength ⁽⁴⁾ - ^{* 1- * 2} Note) (1) UHMWPE And HDPE. (2) Unit: kg / cm ² . (3) Unit: second / 100cc. (4) Unit: g. * 1: The polyethylene solution could not be extruded from the annular die to form a sheet. * 2: The swell was too large to be formed.

As is apparent from Table 1, the microporous polyethylene membranes obtained by the methods of Examples 1 to 4 had microporosity, and had good strength and air permeability.

[0049]

As described above in detail, according to the present invention, a polyolefin containing an ultrahigh molecular weight component is melted in an extruder, and a solvent is supplied thereto to prepare a polyolefin solution. Is extruded from an annular die and cooled to form a raw gel-like tube, and this raw gel-like tube is heated and stretched, and then the remaining paraffin oil is removed to produce a microporous polyolefin membrane. It is possible to efficiently produce a polyolefin microporous membrane having excellent permeability, stable pore opening, and particularly excellent strength.

The microporous polyolefin membrane according to the method of the present invention can be used as a separator for a battery such as a lithium battery, a diaphragm for an electrolytic capacitor, an ultra-fine filtration membrane, an ultrafiltration membrane, various filters, a porous material for a moisture-permeable waterproof clothing. Suitable for various applications such as membranes.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an inflation film forming apparatus to which the method of the present invention can be applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Inflation film-forming apparatus 2 ... Extruder 3 ... Gear pump 4 ... Annular die 5 ... Cooling ring 6, 6 '... First nip roll 7 ... Heating device 8.・ Blower 9, 9 ′ ・ ・ ・ Second nip roll 10 ・ ・ ・ Reversing device 11 ・ ・ ・ Slitter 12 ・ ・ ・ Cleaning device 13, 13 ′ ・ ・ ・ Felt roll 14 ・ ・ ・ Shower device 15 ・ ・ ・ Drying device 16 ... Winder 30a ... Raw gel tube 30b ... Stretched product 30c ... Microporous membrane

Claims (3)

(57) [Claims] 1. An extruder is used to melt (a) a polyolefin containing 1% by weight or more of a component having a weight average molecular weight of 7 × 10 ⁵ or more, and (b) 10 to 80% by weight of the polyolefin in the molten state. 90 to 20% by weight of a liquid solvent (a good solvent for the polyolefin) at the temperature of the molten polyolefin is supplied from the middle of the extruder and melt-kneaded, and (c) the obtained kneaded material is extruded from an annular die. Cooling to form a raw gel tube, (d) heating and stretching the raw gel tube, and (e) removing the solvent remaining thereafter, thereby producing a microporous polyolefin membrane. . 2. A method for producing a poly (method ) according to claim 1.
Battery separator using olefin microporous membrane. 3. A method for producing a poly (polypropylene) produced by the method according to claim 1.
A filter using a microporous olefin membrane.