JP2001176484A - Porous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous film having superior heat resistance, while maintaining high mechanical strength. SOLUTION: This porous film is obtained by using super macromolecular weight of polyolefin and polyolefin having cross-linking ability, with the percentage of gel components being 40-70%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous film having excellent heat resistance, and more particularly, to a porous film which is preferably used as a battery separator or the like which is disposed between a positive electrode and a negative electrode of a battery to isolate them. About.

[0002]

2. Description of the Related Art Various types of batteries have been put to practical use. In recent years, in order to cope with a cordless electronic device, a lightweight, high electromotive force, high energy, and self-dischargeable battery is obtained. There are few lithium batteries that are attracting attention. A separator is interposed between the positive and negative electrodes to prevent a short circuit between the positive and negative electrodes. A porous membrane having a large number of micropores is used as the separator to ensure ion permeability between the positive and negative electrodes. Is done.

[0003] As a method for producing such a porous membrane, conventionally, a gel-like sheet is prepared from a solution obtained by heating and dissolving an ultra-high-molecular-weight polyolefin or an ultra-high-molecular-weight polyolefin in a solvent, and removing the gel before and after stretching. Various methods have been proposed for performing a solvent treatment, performing a stretching treatment, and removing a residual solvent.

[0004] The porous membrane thus obtained can be suitably used as a battery separator. However, in recent years, as the capacity of the battery has increased, severe damage such as abnormalities in the battery such as external short-circuit or overcharge has occurred. A porous film with excellent heat resistance that exhibits a so-called shutdown function that closes the pores and interrupts the current even in difficult situations, maintains that state at a higher temperature, and does not cause internal short-circuiting due to a rupture of the membrane, etc. Have been.

As a method for improving heat resistance, for example, a porous film obtained by crosslinking polyethylene with an electron beam or the like has been reported. However, these porous membranes have a form composed of fibrous fibrils and lamella existing around the fibrils, and the fibrils forming the skeleton of the porous membrane are cut by cross-linking treatment by electron beam irradiation. There is a disadvantage that it is easy to be done. Therefore, when a porous film containing a polyolefin resin such as polyethylene is cross-linked by electron beam irradiation, heat resistance is improved, but mechanical strength is reduced, and the film cannot be suitably used as a battery separator. In particular, a molecular weight of 50 useful as a battery separator
When using ultrahigh molecular weight polyethylene of 10,000 or more, there is a tendency that the mechanical strength is significantly reduced by electron beam irradiation. For example, Japanese Patent Application Laid-Open No. 10-7831 discloses a high-strength, high-heat-resistant porous polyethylene film in which the molecular weight between crosslinking points is controlled by electron beam irradiation and the molecular weight is 200,000 or less. Although the molecular weight of polyethylene used for the porous membrane is described as 100,000 to 4,000,000,
Examples of ultrahigh molecular weight polyethylene are not shown, and when ultrahigh molecular weight polyethylene is actually used, there is a concern that the practical strength may be reduced by electron beam irradiation.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a porous membrane having excellent heat resistance while maintaining high mechanical strength.

[0007]

SUMMARY OF THE INVENTION The gist of the present invention relates to a porous membrane obtained by using an ultra-high molecular weight polyolefin and a polyolefin having a crosslinking ability and having a gel fraction of 40 to 70%. .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, an ultrahigh molecular weight polyolefin is a polyolefin having a weight average molecular weight of 500,000 or more. The weight average molecular weight is preferably 1,000,000 to 20,000,000, more preferably 1,000,000 to 15,000,000.

The ultra-high molecular weight polyolefin that can be used in the present invention is not particularly limited as long as it has been conventionally used for a porous membrane. For example, ethylene, propylene, 1-butene, 4- Examples thereof include homopolymers and copolymers of olefins such as methyl-1-pentene and 1-hexene, and mixtures thereof. Among these, from the viewpoint of increasing the strength of the obtained porous membrane, an ultrahigh molecular weight A crystalline polymer resin such as polyethylene is preferably used.

The content of the ultrahigh molecular weight polyolefin in the porous membrane is preferably 30 to 70% by weight, and more preferably 40 to 70% by weight.
60% by weight is more preferred.

[0011] The porous membrane of the present invention further contains a polyolefin having a crosslinking ability. In the present invention, there is one great feature in using the polyolefin having the cross-linking ability, and by performing a cross-linking treatment on the porous film containing such a resin, the heat resistance is excellent while maintaining the mechanical strength. A porous membrane can be manufactured.

The polyolefin having a crosslinking ability includes
There is no particular limitation as long as the resin has good compatibility with the ultrahigh molecular weight polyolefin, and examples thereof include silane crosslinkable polyolefin, styrene-butadiene rubber, natural rubber, isoprene rubber, butadiene rubber, and ethylene-propylene rubber. Among them, silane-crosslinkable polyethylene is particularly preferable because it does not cause a decrease in molecular weight due to electron beam irradiation or the like and can be efficiently crosslinked under mild conditions such as steam and hot water. The silanol group composed of silane of the silane crosslinkable polyethylene is crosslinked by forming a siloxane bond by a dehydration reaction with water or steam. The silane crosslinkable polyethylene preferably has a melt flow rate (MFR) of 0.03 to 10. These crosslinkable polyolefins can be used alone or
A combination of more than one species may be used.

The content of the crosslinkable polyolefin in the porous membrane is 30 to 70% by weight, preferably 40 to 60% by weight. The lower limit of the content is 30% by weight or more from the viewpoint of improving the heat resistance of the porous membrane, and the upper limit is preferably 70% by weight or less from the viewpoint of maintaining mechanical strength such as needle penetration strength. .

The porous membrane of the present invention having the above structure has a gel fraction of 40 to 70%. In the present invention, the gel fraction indicates a measure of the crosslinked structure of the porous membrane. The higher the value of the gel fraction, the higher the shape retention ability of the porous membrane when exposed to high temperatures. In the present invention, when the gel fraction is 40 to 70%, the effect that the porous film has high mechanical strength and excellent heat resistance is exhibited. The gel fraction is preferably 50 to 7
0%, more preferably 60 to 70%. The gel fraction is 40% or more from the viewpoint of heat resistance, and 70% or less from the viewpoint of mechanical strength. Here, the gel fraction refers to a value measured by a method described in Examples described later.

Next, a method for producing a porous film according to the present invention will be described. For the production of the porous film according to the present invention, known methods such as a dry film forming method and a wet film forming method can be used. For example, the ultra-high molecular weight polyolefin, a resin composition comprising a polyolefin having a cross-linking ability and the like, mixed with a solvent, formed by melting and kneading, then rolling, stretching in one or more axial directions, and extracting and removing the solvent, It can be produced by a crosslinking treatment.

Any solvent may be used as long as it is excellent in the solubility of the resin composition. Examples of the solvent include aliphatic or cyclic hydrocarbons such as nonane, decane, undecane, dodecane, decalin, and liquid paraffin, and boiling points. Corresponding mineral oil fractions and the like are mentioned, and non-volatile solvents containing a large amount of alicyclic hydrocarbons such as liquid paraffin are preferred.

The mixing ratio between the resin composition and the solvent cannot be unconditionally limited depending on the type of the solvent, the solubility of the resin composition in the solvent, and the like. The mixing ratio of the composition is preferably from 5 to 30% by weight of the mixture, more preferably from 8 to 20% by weight. For example, when a crystalline ultrahigh molecular weight polyolefin having a weight average molecular weight of 500,000 or more is used as a component of the resin composition from the viewpoint of exhibiting mechanical strength as a porous film, the mixing ratio of the compound is 5% by weight of the mixture. It is preferable that it is above. Further, the mixing ratio of the solvent, for example,
Preferably 70-95% by weight of the mixture, more preferably 80-92% by weight.

The step of dissolving and kneading the mixture of the resin composition and the solvent and molding can be carried out by a known method. For example, the mixed solution which has been uniformly dispersed in advance with a Henschel mixer or the like to form a slurry is banned. mixer,
It may be melt-kneaded in a batch system using a kneader or the like, and then molded using an extruder equipped with a T die or the like, or may be sandwiched between cooled metal plates and rapidly cooled to form by rapid crystallization. Alternatively, the mixture may be directly melt-kneaded with a twin-screw extruder or a continuous kneader using a gravimetric feeder or a liquid addition pump, and may be formed with a T die attached to the tip of the kneader. The kneading may be performed under appropriate temperature conditions.
Although not particularly limited, it is preferably 100 to 200 ° C.

The shape of the molded product thus obtained may be a sheet, a round bar, a tube, or the like. Above all, the thickness of the sheet-like or tube-like molded product is not particularly limited, but is preferably 3 to 30 mm, and 5 to 20 mm.
mm is more preferable. The thickness is preferably 3 mm or more from the viewpoint of maintaining the strength of the film (solvent extraction film) after extracting the solvent, and is preferably 30 mm or less from the viewpoint of efficiently reducing the thickness in the rolling step.

The step of rolling the obtained molded product can be performed by a pressing method using a double belt press or the like, an in-die rolling method using a die having a predetermined shape, or the like. In particular, a tube-shaped die can be applied to the tube-shaped molded product, and in that case, it is preferable to perform rolling by appropriately adjusting the tensile strength-to-width ratio in the direction in which the die is pulled.

The thickness of the rolled sheet (rolled sheet) thus obtained is not particularly limited, but is preferably, for example, 0.2 to 3 mm, more preferably 0.2 to 2 mm. The thickness is preferably 0.2 mm or more from the viewpoint of easy thinning by rolling, and preferably 3 mm or less from the viewpoint of productivity of the porous film. Further, the rolling temperature is not particularly limited, but the melting point of the kneaded material is -1.
0-30 ° C is preferred. The rolling temperature is preferably −30 ° C. or more of the melting point of the kneaded material from the viewpoint of facilitating thinning by the rolling process, and −10 ° C. of the melting point of the kneaded material from the viewpoint of obtaining the mechanical strength and homogeneity required for a battery separator. The following is preferred. Further, the total pressurizing time when using the pressing method is not particularly limited, but is preferably 1 to 5 minutes. The time is preferably 1 minute or more from the viewpoint of obtaining a rolled sheet having a predetermined thickness, and is preferably 5 minutes or less from the viewpoint of excellent productivity.

The method of stretching the rolled sheet is not particularly limited, but may be a usual tenter method,
A roll method, an inflation method or a combination of these methods may be used, and any method such as uniaxial stretching and biaxial stretching can be applied. In the case of biaxial stretching, either vertical or horizontal simultaneous stretching or sequential stretching may be used. The temperature of the stretching treatment is preferably 100 to 140 ° C.

The desolvation treatment is a step of forming a microporous structure by removing the solvent from the stretched sheet (stretched sheet). For example, by removing the residual solvent by washing the stretched sheet with a solvent. It can be carried out. Examples of the solvent include hydrocarbons such as pentane, hexane, heptane, and decane; chlorine hydrocarbons such as methylene chloride and carbon tetrachloride; fluorinated hydrocarbons such as ethane trifluoride; and ethers such as diethyl ether and dioxane. Volatile solvents can be mentioned, and these can be used alone or in combination of two or more. The washing method using such a solvent is not particularly limited, and examples thereof include a method of immersing the stretched sheet in the solvent to extract the solvent and a method of showering the solvent on the stretched sheet.

Next, after obtaining a desolvated film (desolvation film), the resin composition constituting the desolvation film can be cross-linked to obtain a porous film. For crosslinking, depending on the type of polyolefin having crosslinking ability used,
Heat, electron beam, radiation, steam, hot water, or the like can be used. Among these, the cross-linking treatment using steam or hot water does not cause cutting of ultra-high molecular weight polyolefin fibrils, maintains high mechanical strength, and greatly improves heat resistance (film rupture resistance at high temperatures). It is preferable in that it can be performed.
Cross-linking treatment using steam, for example, in a thermo-hygrostat,
A process performed at a humidity of 80% or more can be given. The condition is
The gel fraction is appropriately selected to be 40 to 70%,
The temperature is preferably from 80 to 110 ° C. The temperature is preferably 80 ° C. or higher from the viewpoint of sufficient progress of crosslinking, and is preferably 110 ° C. or lower from the viewpoint of maintaining an appropriate porosity.
The temperature of the crosslinking treatment using hot water is 70 to 100 ° C.
Is preferred. The time for these crosslinking treatments is preferably 0.1 to 2 hours.

After the above-mentioned cross-linking treatment step, the porous membrane is generally heat-set (heat-fixed) to prevent heat shrinkage.
May be. In particular, in the present invention, by performing the cross-linking treatment using heat as described above, depending on the processing conditions, substantially heat setting is also possible, but when the heat setting is insufficient, the heat shrinkage is reduced. For better prevention, heat setting may be performed by further heating after the crosslinking treatment. The heat setting may be performed, for example, at 110 to 140 ° C. for about 0.5 to 2 hours.

The thickness of the porous membrane obtained as described above is preferably 1 to 60 μm, more preferably 5 to 45 μm. The porosity is preferably 20 to 80%, and
75% is more preferred.

As the mechanical strength of the porous membrane, for example, the needle penetration strength is preferably 300 gf / 25 μm or more,
0 gf / 25 μm or more is more preferable. As the heat resistance, the heat resistance temperature is preferably 160 ° C. or higher, more preferably 180 ° C. or higher. In addition, as a method of measuring the needle penetration strength and the heat resistant temperature, the method described in Examples described later can be used.

The porous membrane of the present invention can be used as a battery separator having excellent mechanical strength and high resistance to rupture at high temperatures as described above, and can be used in various sizes and applications of batteries. Can be expected to further improve safety.

[0029]

The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. In addition, various characteristics were measured in the following manner.

(Thickness) The thickness was measured from a 1 / 10,000 mm thickness gauge and a 10,000 × scanning electron micrograph of the cross section of the porous membrane.

(Porosity) The obtained porous membrane is
The thickness was determined with a 1/1000 mm thickness gauge, the weight was weighed with an electronic balance, and the porosity was determined by the following formula. The density of the resin component was 0.940 g /
ml. Porosity (%) = pore volume × 100 / total membrane volume

(Gel Fraction) The obtained porous membrane was extracted in boiling para-xylene for 8 hours using a Soxhlet extractor, and the gel fraction was determined from the following equation. Gel fraction (%) = 100 × residual weight (g) / sample weight (g)

(Needle penetration strength) Using a handy compression tester "KES-G5" manufactured by Kato Tech Co., Ltd., the needle has a diameter of 1.0 mm, the tip shape R is 0.5 mm, and the holder diameter is 11.
The measurement was performed at 3 mm at a pushing speed of 2 mm / sec, and the maximum load until the film was broken was defined as the needle penetration strength. All values are 25μ
m.

(Heat-resistant temperature) Positive electrode plate (made of platinum, 14 m in diameter)
m), between the negative electrode plate (made of platinum, 16 mm in diameter)
The temperature of the measuring jig sandwiching the porous membrane of 5 mm was increased at 5 ° C./min, and the temperature at which short-circuit occurred was measured with a thermocouple connected to the positive electrode plate, and the temperature was defined as the heat-resistant temperature.

Example 1 Ultra high molecular weight polyethylene 5 having a weight average molecular weight of 2,000,000
Weight%, melt flow rate 0.5, density 0.942
10% by weight of silane-crosslinkable polyethylene (manufactured by Mitsubishi Chemical Corporation, trade name: Linklon, the same applies hereinafter), and liquid paraffin as a solvent (kinematic viscosity at 40 ° C. is 59 mm
^A solution consisting of 85% by weight of a ² / s solvent) was uniformly mixed in a slurry form at 160 ° C. and a twin screw extruder (cylinder diameter 40
mm, L / D = 42), using a T-die (lip thickness 5 mm) at the tip of the twin-screw extruder,
The mixture was formed into a sheet at ℃ and quenched by a water bath. Thereafter, the obtained sheet-like molded product was preheated to 115 ° C. and then pressed at a molding temperature of 115 ° C. for 3 minutes to obtain a rolled sheet having a thickness of 0.5 mm. Then, the batch type simultaneous biaxial stretching machine 11
After stretching 3.5 × 3.5 times at 5 ° C., desolvation treatment was performed with heptane to obtain a desolvation film having a thickness of 35 μm and a porosity of 60%. The obtained membrane was subjected to a crosslinking treatment in a thermo-hygrostat at a temperature of 90 ° C. and a humidity of 95% for 4 hours. 110 ° C
For 0.5 hour at a thickness of 26 μm and a porosity of 4
A 2% porous membrane was obtained.

Example 2 Ultra high molecular weight polyethylene 1 having a weight average molecular weight of 2,000,000
0% by weight, melt flow rate 0.5, density 0.94
20% by weight of silane-crosslinkable polyethylene 2 and liquid paraffin as a solvent (kinematic viscosity at 40 ° C. is 59 m
A solution consisting of 70% by weight (m ² / s solvent) was uniformly mixed in a slurry form at 160 ° C. and a twin-screw extruder (cylinder diameter 4
0 mm, L / D = 42), melt-kneaded, formed into a sheet at 160 ° C. with a T die (lip thickness 5 mm) at the tip of a twin-screw extruder, and quenched in a water bath. Thereafter, the obtained sheet-like molded product was preheated to 115 ° C., and then a molding temperature of 1
Pressing was performed at 15 ° C. for 3 minutes to obtain a rolled sheet having a thickness of 0.5 mm. After that, the batch type simultaneous biaxial stretching machine was used to adjust the temperature to 1
After stretching 3.5 × 3.5 times in length and width at 15 ° C., desolvation treatment was performed with heptane to obtain a desolvation film having a thickness of 42 μm and a porosity of 58%. The obtained film was heated in a thermo-hygrostat at a temperature of 90 ° C.
Crosslinking treatment was performed at a humidity of 95% for 4 hours. The treated membrane is
Heat setting was performed at 0.5 ° C. for 0.5 hour to obtain a porous film having a thickness of 28 μm and a porosity of 40%.

Example 3 Ultra high molecular weight polyethylene 1 having a weight average molecular weight of 2,000,000
0% by weight, melt flow rate 0.5, density 0.94
20% by weight of silane-crosslinkable polyethylene 2 and liquid paraffin as a solvent (kinematic viscosity at 40 ° C. is 59 m
A solution consisting of 70% by weight (m ² / s solvent) was uniformly mixed in a slurry form at 160 ° C. and a twin-screw extruder (cylinder diameter 4
0 mm, L / D = 42), melt-kneaded, formed into a sheet at 160 ° C. with a T die (lip thickness 5 mm) at the tip of a twin-screw extruder, and quenched in a water bath. Thereafter, the obtained sheet-like molded product was preheated to 115 ° C., and then a molding temperature of 1
Pressing was performed at 15 ° C. for 3 minutes to obtain a rolled sheet having a thickness of 0.5 mm. Thereafter, the temperature was adjusted to 11 by a batch-type simultaneous biaxial stretching machine.
After stretching 3.5 × 3.5 times at 5 ° C., desolvation treatment was performed with heptane to obtain a desolvation film having a thickness of 42 μm and a porosity of 58%. The obtained film was subjected to a crosslinking treatment in a thermo-hygrostat at a temperature of 90 ° C. and a humidity of 95% for 1 hour. 110 ° C
For 0.5 hour at a thickness of 26 μm and a porosity of 4
A 3% porous membrane was obtained.

Comparative Example 1 Ultra-high molecular weight polyethylene 5 having a weight average molecular weight of 2,000,000
Weight%, melt flow rate 0.6, density 0.964
A solution consisting of 10% by weight of high-density polyethylene and 85% by weight of a liquid paraffin as a solvent (solvent having a kinematic viscosity of 59 mm ² / s at 40 ° C.) is uniformly mixed in a slurry form, and biaxially heated at a temperature of 160 ° C. Extruder (cylinder diameter 40
mm, L / D = 42), melt-kneaded, formed into a sheet at 160 ° C. with a T-die (lip thickness 5 mm) at the tip of a twin-screw extruder, and quenched in a water bath. Thereafter, the obtained sheet-like molded product was preheated to 115 ° C., and then a molding temperature of 11 ° C.
Pressing was performed at 5 ° C. for 3 minutes to obtain a rolled sheet having a thickness of 0.5 mm. Then, using a batch type simultaneous biaxial stretching machine, 115
After stretching 3.5 × 3.5 times in length and width at ° C., desolvation treatment was performed with heptane to obtain a desolvation film having a thickness of 35 μm and a porosity of 60%. The obtained membrane was subjected to a crosslinking treatment in a thermo-hygrostat at a temperature of 90 ° C. and a humidity of 95% for 4 hours. The treated film was heat-set at 110 ° C. for 0.5 hour, and had a porosity of 42 μm and a thickness of 26 μm.
% Of the porous membrane was obtained.

Comparative Example 2 Ultra high molecular weight polyethylene 1 having a weight average molecular weight of 2,000,000
0% by weight, melt flow rate 0.5, density 0.94
20% by weight of silane-crosslinkable polyethylene 2 and liquid paraffin as a solvent (kinematic viscosity at 40 ° C. is 59 m
A solution consisting of 70% by weight (m ² / s solvent) was uniformly mixed in a slurry form at 160 ° C. and a twin-screw extruder (cylinder diameter 4
0 mm, L / D = 42), using a T-die (lip thickness 5 mm) at the tip of the twin-screw extruder,
It was formed into a sheet at 0 ° C. and quenched by a water bath. Thereafter, the obtained sheet-like molded product was preheated to 115 ° C. and then pressed at a molding temperature of 115 ° C. for 3 minutes to obtain a rolled sheet having a thickness of 0.5 mm. After that, the film is stretched 3.5 × 3.5 times horizontally and vertically at a temperature of 115 ° C. by a batch-type simultaneous biaxial stretching machine, and then subjected to a desolvation treatment with heptane to form a desolvation film having a thickness of 42 μm and a porosity of 58%. Obtained. The obtained film is heated at a temperature of 80 in a thermo-hygrostat.
Cross-linking treatment was carried out at 95 ° C. and a humidity of 95% for 1 hour. 1 treated membrane
Heat setting was performed at 10 ° C. for 0.5 hour to obtain a porous film having a thickness of 30 μm and a porosity of 41%.

Comparative Example 3 Ultra high molecular weight polyethylene 2 having a weight average molecular weight of 2,000,000
Weight%, melt flow rate 0.5, density 0.942
18% by weight of silane-crosslinkable polyethylene, and liquid paraffin as a solvent (kinematic viscosity at 40 ° C. is 59 mm
^A solution consisting of 80% by weight of a ² / s solvent) was uniformly mixed in a slurry form at 160 ° C. and a twin screw extruder (cylinder diameter 40
mm, L / D = 42), using a T-die (lip thickness 5 mm) at the tip of the twin-screw extruder,
The mixture was formed into a sheet at ℃ and quenched by a water bath. Thereafter, the obtained sheet-like molded product was preheated to 115 ° C. and then pressed at a molding temperature of 115 ° C. for 3 minutes to obtain a rolled sheet having a thickness of 0.5 mm. Then, the batch type simultaneous biaxial stretching machine 11
After stretching 3.5 × 3.5 times at 5 ° C., desolvation treatment was performed with heptane to obtain a desolvation film having a thickness of 42 μm and a porosity of 58%. The obtained film was subjected to a crosslinking treatment at a temperature of 80 ° C. and a humidity of 95% for 4 hours in a thermo-hygrostat. 110 ° C
For 0.5 hour at a thickness of 27 μm and a porosity of 3
A 6% porous membrane was obtained.

Table 1 shows the gel fraction, heat resistance temperature and needle penetration strength of the porous membranes obtained in Examples 1 to 3 and Comparative Examples 1 to 3.

[0042]

[Table 1]

From the results shown in Table 1, all of the porous membranes obtained in Examples 1 to 3 had an appropriate porosity, and the gel fraction was in the range of 40 to 70%. It can be seen that both the heat resistant temperature and the needle penetration strength are higher than those of the porous membranes obtained in Examples 1 to 3.

[0044]

The porous membrane of the present invention has a high heat-resistant temperature without impairing the needle penetration strength at room temperature, and can be used as a battery separator to maintain the shape of the separator as the temperature rises. Performance can be improved.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shunsuke Nomi 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Tomoaki Ichikawa 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko (72) Inventor Hideyuki Emori 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 4F070 AA12 AA14 AA15 AB07 AB11 AB12 AB22 AC75 AE08 GA01 GB03 GC02 4F074 AA16 AA16H AB01 BB22 CA02 CA03 CA04 CC02Y CC06Z CC27Z CC28Z CC29Z DA04 DA22 DA49 5H021 CC00 EE04 HH01

Claims (2)

[Claims] 1. A gel fraction obtained by using an ultrahigh molecular weight polyolefin and a crosslinkable polyolefin having a gel fraction of 4
A porous membrane, which is 0 to 70%. 2. The porous membrane according to claim 1, wherein the crosslinkable polyolefin is a silane crosslinkable polyolefin.