WO1998001502A1

WO1998001502A1 - Porous membrane comprising poly(4-methylpentene-1) resin and battery separator

Info

Publication number: WO1998001502A1
Application number: PCT/JP1997/002307
Authority: WO
Inventors: Kazuhiro Meguro; Tomoo Susa; Toshiya Mizuno; Yoshikichi Teramoto; Hiroshi Sato
Original assignee: Kureha Chemical Industry Co., Ltd.
Priority date: 1996-07-03
Filing date: 1997-07-03
Publication date: 1998-01-15
Also published as: JPH1017692A

Abstract

A porous membrane comprising a poly(4-methylpentene-1) resin and having an apparent impedance of not more than 25 Φ.cm2 and a Young's modulus of not less than 40 kg/mm2; a laminated porous membrane comprising a laminate of at least two layers of a porous membrane layer (A) comprising a poly(4-methylpentene-1) resin and a porous membrane layer (B) comprising a polyolefin resin different from the resin constituting the layer (A) and having a melting point of 100 to 400 °C, wherein the laminate has an apparent impedance of not more than 25 Φ.cm2 and a Young's modulus of not less than 40 kg/mm2; a battery separator comprising the above porous membrane; and a process for preparing the same.

Description

Field of the Invention Field of technology for porous membranes made of poly (4-methylpentene-1) resin and separation for batteries

The present invention relates to a porous membrane made of a poly (4-methylpentene-11) resin. The present invention also relates to a separator for a pond comprising the porous membrane and a method for producing the porous membrane. More specifically, a porous film made of poly (4-methylpentene-11) resin having a specific multiplication impedance and a specific Young's modulus, and a porous film made of poly (4-methylpentene-11) resin and a specific film made of another polyolefin resin The present invention relates to a porous membrane having at least two particles with a porous membrane layer having a melting point range, a separator for a battery comprising the porous membrane, and a method for producing the porous membrane. Background art

Conventionally, various porous membranes have been developed, and these applications cover a wide variety of applications, such as separation for batteries, partition walls for electrolytic capacitors, various filters, moisture-permeable waterproof membranes, ultrafiltration membranes, and microfiltration membranes. . The required performance varies depending on each application. For example, a battery separator has a structure in which at least one pair of electrodes are opposed to each other and an electrolytic solution is interposed between the electrodes.However, from the viewpoint of increasing the electric capacity of the battery and reducing the size of the battery. It is desirable that the distance between the electrodes is small. When the distance between the positive electrodes is small, it is common practice to interpose a separator made of a porous film between the positive electrodes to prevent contact between the electrodes and to retain the electrolyte.

In particular, in lithium batteries and lithium ion batteries, contact between the positive and negative electrodes due to the formation of dendritic lithium metal crystals (dendrites) during charge and discharge, contact between the positive and negative electrodes due to contraction of the separator, and one-time 1 pole caused by insufficient piercing strength It is necessary to ensure safety against overheating of the pond, which is caused by contact of the fr'ii pole due to poverty. As a device that imparts this safety, a separator composed of a laminate of a high-melting-point polyolefin-based resin porous membrane layer and a low-melting-point polyolefin-based resin porous membrane 11 described in JP-A-2-77108 is used. I can do it.

According to the present invention, even if a short circuit occurs and an excessive current flows in the battery, the heat generated at that time melts the polyolefin-based resin constituting the low-melting-point polyolefin-based resin porous membrane waste and seals the plug. The effect is that the flow of current is stopped to suppress overheating (short-down), and the high-melting-point polyolefin-based resin porous membrane waste is laminated to retain the melt-clogged low-melting-point polyolefin-based resin porous membrane ^. It is understood that this has the effect of preventing the occurrence (breakdown).

Further, the separator needs to be thinner from the viewpoint of increasing the energy density of the battery, but needs to have a certain degree from the viewpoint of preventing contact between the electrode and the electrode. For this reason, the non-aqueous solvent type ¾Ikegawa Separe Ichiichi has a low in-between.

Non-aqueous solvent type batteries can be said to be representative of electrochemical devices because of their narrow electrodes, from the viewpoint of increasing the battery capacity. Electrochemical devices with a narrow electrode spacing, especially lithium-ion and lithium-ion batteries, generate electricity by increasing the capacity of the battery by stacking the positive electrode material, separator, and negative electrode material and rolling them in as many times as necessary. I am saying. When manufacturing a non-aqueous solvent type battery, the winding operation between the electrode and the separator is as follows: the positive electrode material, the separator electrode and the negative electrode material are rolled up and wound around the pin as many times as necessary, then the pin is pulled out and wound Gaining body. For the entrainment, the separator is longer than the electrode, and only the separator is involved at the beginning of the entrainment. In such a manufacturing method, since the positive electrode material, the separator, and the electrode material are wrapped around the electrodes, the electrodes are pressed against each other, that is, the electrode and the separator are mutually pressed, and the separator applies a tensile force. Below. At this time, the mechanical strength of Separee overnight, especially Young's modulus If the material is insufficient, the winding of the positive electrode material, separator and negative electrode material will end, and the pin will not come out when the pin is pulled out, or in extreme cases, a crack will occur over a short period of time. And the separator is displaced from the electrode and shorts both the positive and negative electrodes. An object of the present invention is to prevent the above-described pin disconnection failure during battery production, and furthermore, a porous membrane having a function of increasing the energy density of the battery, and a shutdown function as a separator. An object of the present invention is to provide a multi-layer membrane having a function of preventing breakdown, a battery separator comprising the same, and a method for producing a porous membrane.

Disclosure of the invention

The present inventors have conducted intensive studies to improve the above problems, and as a result, have an apparent impedance of 25 Ω · cm ² or less and a Young's modulus of 40 kg made of poly (4-methylpentene-11) resin. The inventors have found that a porous membrane having a thickness of / mm ² or more can solve such a problem, and have completed the present invention. That is, the first aspect of the present invention provides a polyporous membrane made of poly (4-methylpentene-11) resin having an apparent impedance of 25 Ω · c or less and a Young's modulus of 40 kg / mm ² or more. A second aspect of the present invention is a layer (A) of a porous membrane made of poly (4-methylpentene-11) resin, and a polyolefin resin different from the resin constituting the layer (A). A laminate of at least two layers with porous membrane debris (B) having a melting point of ° C, wherein the laminate has an apparent impedance of 25 Ω · cm ² or less and a Young's modulus of 40 kg / mm ² or more. A porous membrane is provided. Furthermore, a third aspect of the present invention provides a battery separator comprising the porous membranes of the first and second aspects, and a fourth aspect provides a method for producing the porous membranes of the first and second aspects. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail. The first aspect of the present invention relates to a porous membrane made of a poly (4-methylpentene-11) resin having an apparent impedance of 25 Ω · cm ² or less and a Young's modulus of 40 kg / mm ² or less. The poly (4-methylpentene-11) resin used in the present invention includes a copolymer obtained by using a homopolymer of 4-methylpentene-11 or a 1-year-old olefin having 2 to 12 carbon atoms as a co-JE synthetic component. In. Examples of co-synthetic components include ti-butyl ethylene, propylene, butene-1, hexene-11, 3-methylbutene-11, octene-11, styrene, vinylcyclohexene, and the like. It is desirable that the content of these copolymers be 40% by mass or less, preferably 20% by mass or less in the polymer.

Further, it is preferable that the porous film itself has a melting point of preferably 200 ° C. or higher, and in the past, 230 ° C. or higher, in order to stably maintain the shape of the film with increasing temperature. As physical properties possessed by the porous membrane of the present invention,兌掛only impedance 25 Ω · cm ² or more de, preferably 20 Ω · cm ² or less. If the apparent impedance exceeds 25 Ω · cm ² , it is not preferable because sufficient charge / discharge characteristics cannot be obtained when used in batteries. In the present invention, the convertible impedance means that at room temperature (23 ° C.), a nonaqueous solvent-based electrolytic solution (a mixture of propylene carbonate and 1,2-dimethoxetane in a 1: 1 volume ratio of lithium perchlorate) (At a concentration of 1 mol / liter), and then apply AC (100 KHz, 0.4 IV) while the electrodes (Pt electrodes) are in contact with both sides of the porous membrane. It is the measured resistance (Ω · cm ² ), which is measured in a form that includes the resistance component of the non-aqueous solvent-based electrolyte. The Young's modulus in the present invention was determined by the calculation method described in JIS K7127. 'a ji Zhang modulus, requires 40 k gz mm ² or more, preferably 50 kgmm ² or more. If the Young's modulus of the porous film is used as the ¾ pond for separator Isseki first and 40 kg / mm ² is less than, susceptible to failure omission pin rolling operation between both electrodes and the separator Isseki during ^ pond manufacturing, history When winding at high speed, wrinkles are likely to occur. / |-: Productivity is significantly reduced, which is not preferable. The porosity of the porous removal according to the present invention is preferably 25 to 60%, more preferably 30 to 45%. If the porosity is greater than 60%, the mechanical strength will decrease.If the porosity is less than 25% / J, the apparent impedance will increase, and when used as a pond separator, the pond volume M will decrease. Absent. The porosity in the present invention means, for example, the porosity of a single-piece porous membrane made of poly (4-methylpentene-11) resin, or the porosity of poly (4-methylpentene-1-ene). 1) In the case of a porous membrane containing layers made of resin, it means the average porosity of all the debris in the laminated porous membrane. The second aspect of the present invention is a porous membrane made of poly (4-methylpentene-11) resin (A) and a polyolefin resin different from the resin constituting the refuse (A) and having a melting point of 100 to 140 ° C. The present invention relates to a porous membrane having at least two layers with the porous membrane waste (B), wherein the stackable body has a convertible impedance of 25 Ω · cm ² or less and a Young's modulus of 40 kg / mm ² or more. As the poly (4-methylpentene-11) resin, the same resins as those described in the first invention can be used. Layer (A) of a porous membrane made of poly (4-methylpentene-1) resin and layer of a porous membrane made of a polyolefin resin different from the resin constituting the layer (A) and having a melting point of 100 to 140 ° C ( By having at least two layers with B), the following functions are provided. That is, this laminated porous membrane receives a thermal history When the temperature reaches or exceeds the melting point of (B), the micropores of (B) are melted and closed, but the layer (A) has a higher melting point than the layer (B), so it retains its shape as a porous stack membrane. It has been done. Examples of the polyolefin resin that can be used as the resin of the layer (B) in the present invention include polyethylene having a melting point of 100 to 140 ° C., preferably 110 to 135 ° C. Examples thereof include a copolymer with refine), an ethylene-propylene copolymer, and poly (butene-1). Of these polyolefin resins, polyethylene and polybutene-11 are preferred. Here, the “melting point” refers to a value obtained by measuring a sample 10018 at a temperature of 10 ° CZ under a nitrogen flow at a temperature rate of 10 ° CZ using a small difference scanning calorimeter (eg, DSC 30, manufactured by Mettler). Endothermic peak temperature created by melting. If ^ is composed of a mixed resin, multiple endothermic peaks may appear, and the temperature of the peak with the largest peak area of the peaks is the melting point of ^. A third aspect of the present invention relates to a battery separator composed of the first and second porous films. The feature of the present invention is that it has a low convertible impedance (25 Ω · cm ² or less) and a Young's modulus of 40 kg / mm ² or more, thereby satisfying the electrical properties (low impedance) required for battery separators. In addition, it is possible to prevent the occurrence of defective pins during manufacturing by specifying the Young's modulus. A fourth aspect of the present invention relates to a method for producing a porous membrane and a laminated porous membrane according to the first and second aspects of the present invention. The manufacturing method will be described below. A plasticizer is blended with poly (4-methylpentene-1) resin to obtain a composite composition. The mixing method is not particularly limited as long as the plasticizer is uniformly mixed. For example, melt-kneading with an extruder after mixing with a ribbon blender, hensile mixer, fixed V-type blender, tumbler, ball mill, etc. And directly melt-kneaded. In the case of a laminated porous membrane, a poly (4-methylpentene-1) resin and a polyolefin resin having a melting point of 100 to 140 ° C (for example, polybutene-1) are used. Use separate mixed compositions, each containing a plasticizer. The mixing ratio of the resin and the plasticizer is 50 to 150 parts by mass of the plasticizer to 100 parts by mass of the resin, preferably 60 to 120 parts by mass, and more preferably 70 to 1 part by mass. 0 0 It is a mass part. The plasticizer used in the present invention plasticizes polyolefin resins such as poly (4-methylpentene-1) and polybutene-11, and includes, for example, phthalic acid, dimethyl phthalate, getyl phthalate, and phthalate. Diesters such as dibutyl acid, diisopentyl phthalate, dioctyl phthalate, and didodecyl phthalate; aliphatic dialcohols having 2 to 4 carbon atoms and aliphatic dicarboxylic acids having 2 to 9 carbon atoms (fats having 2 to 4 carbon atoms) Examples of the aliphatic dialcohols include ethylene glycol, propylene glycol, 1,4-butanediol, and 1,2-butanediol. Examples of the aliphatic dicarboxylic acids having 2 to 9 carbon atoms include oxalic acid and malonic acid. Condensed polymers with acids, succinic acid, glutaric acid, adipic acid, azelaic acid, etc., lactones Examples include aliphatic polyesters such as ring-opening polymer molecules of ton, butyrolactone, (—pa'relolactone, £ -prolactone, etc.), phosphate esters, glycolesters, and epoxy compounds. A diester is preferred, and a mixture of two or more of the above plasticizers can also be used.This mixture composition is optionally pelletized and then extruded at a temperature of 180 to 34 ° C., preferably. Can be formed into a melt-extruded film (film) at 200 to 280 ° C. In the case of a laminated film, it may be formed by a melt co-extrusion method or may be formed outside the die. The thickness of the film at this point depends on the subsequent stretching ratio, but is preferably 200 to 20 2. m is preferable, and more preferably 150 to 30 m. Next, the obtained film is stretched (first stretching). Stretching, Teng evening one method, roll method, inflation one Deployment汰-,) ^T:. Conducted in casting method or the like. Stretching may be either uniaxial stretching or biaxial stretching. In the case of biaxial stretching, either temporary stretching or sequential stretching may be used. The temperature for the first stretching is from 110 to 50 ° C, preferably from 0 to 40 ° C, and more preferably from 5 to 30 ° C. If the first stretching temperature is lower than 110 ° C, breakage will occur during stretching, and if it exceeds 50 ° C, the stretching will not be uneven. The first draw ratio is at least 1.5 to 3.0 times, preferably 2.0 to 2.5 times in one direction. By stretching in at least one direction within the range of the first stretching temperature at a stretching ratio of 1.5 to 3.0, the Young's modulus can be increased and the apparent impedance can be reduced. Can be. On the other hand, if the ratio of the first stretching exceeds 3.0 times, the film is likely to be torn. Next, a plasticizer is extracted from the first spread film or the stacked film. The solvent for this purpose is not particularly limited as long as it does not dissolve polyolefin resin such as poly (4-methylpentene-1) or poly (butene-11) and can dissolve nj plastic. For example, haloalkanes such as trichloromethane and trichloromethane, ketones such as acetone and methylethyl ketone, lower carboxylic acid esters such as ethyl acetate, lower alcohols such as methanol and isopropyl alcohol, and aromatics such as toluene and xylene. Solvents such as aromatic hydrocarbons can be used.

The extraction method using a solvent is preferably performed at a temperature of 5 to 150 ° C, more preferably 10 to 100 ° C, particularly preferably 15 to 50 ° C, preferably 0.5 to 3 ° C. It is released for 60 minutes, more preferably for 3 to 120 minutes, particularly preferably for 5 to 60 minutes. In addition, the extraction can be accelerated by applying appropriate vibration. "After extracting the plasticizer, dry the perforated crotch Heat treatment may be performed at a temperature of 40 to 120 ° C for a time of 0.25 to 360 minutes, or after treatment with a volatile solvent such as acetone, and air drying. After the extraction of the efficacious agent, the film is further stretched (second stretching). Stretching can be performed by the same type of stretching method as in the first stretching, and may be either uniaxial stretching or biaxial stretching. In the case of biaxial stretching, either simultaneous stretching or sequential stretching may be used. The stretching temperature of the second stretching is 0 to 120 ° C, preferably 5 to 80 ° C, and more preferably 10 to 50 ° C. If the stretching temperature of the second stretching is lower than 0 ° C., breakage occurs during stretching. 1 If the temperature exceeds 20 ° C, stretching tends to be uneven, and in the case of a laminate / film, the pores of the low-melting polyolefin resin are partially blocked and the number of through-holes is reduced, resulting in a higher impedance. . The magnification of the second stretching is 1.2 to 2.5 times, preferably 1.5 to 2.0 times. If the second factor is less than 1.2 times, the apparent impedance cannot be lowered, and if it is more than 2.5 times, the film tends to tear or break. The form of the porous membrane of the present invention may be a porous membrane made of poly (4-methylpentene-11) resin alone or a layer of a porous membrane made of poly (4-methylpentene-1) resin.

(A) and a porous membrane layer (B) made of a polyolefin resin different from the resin constituting the layer (A) and having a melting point of 100 to 140 ° C. I can do it. If a poly (4-methylpentene-11) resin porous membrane is used as the separation for the pond, a laminated porous membrane is preferable from the viewpoint of easy down-sizing. The porous membrane is made of poly (4-methylpentene)

1) It is preferable to use a stack of the resin-made porous crotch (Al i) and the porous membrane layer (B). There is no limitation on the number or order of the products in the layer structure of the ¾ layer porous membrane. (A) Layer Z (B) Two-layer structure, (AM / (B) layer / (A) polishing, (B) m / (A) m, (B) three polishing, etc. Among them, (Afei) / (B ) Layer, ./ (A) layer is preferable from the viewpoint of safety If a porous membrane is used as the battery separator, the thickness of the poly (4-methylpentene 1) porous membrane (layer A) The thickness is preferably 3 to 20〃m, from the viewpoint of ease of forming the stack structure, not being excessively thick as the stack structure, or reducing the possibility of occurrence of short circuit, and 5 to 15 / m. More preferably, the polyolefin resin constituting the layer (B) includes polyethylene, ethylene-propylene copolymer, and poly (butene-11). Polyethylene and poly (butene-1) are preferred, and poly (butene-1) is more preferred. The thickness of the porous membrane layer is preferably 3 / m or more, more preferably 5 to 15 m.

Furthermore, the polyolefin resin may be mixed with another resin (for example, polypropylene) to form a layer as long as the shirt-down function is not impaired. The porous membrane of the present invention preferably has a thickness of preferably 10 to 50 m, more preferably 20 to 35 m, regardless of whether it is a single-layer or laminated porous membrane. When the thickness of the porous membrane exceeds about 50 m, for example, when the porous membrane is used for the separation of the pond, the number of layers of the ¾ layer between the two electrodes and the separation of the pond per one pond decreases. Since the battery capacity is reduced, the battery capacity becomes low, which is not preferable. On the other hand, if the thickness is less than 10 // m, the mechanical strength of the film becomes insufficient, which is not preferable. Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto. Not something. The measurements in the projecting examples and the comparative examples depended on the following methods.

1. Porosity

The sample (5 cm x 5 cm) was immersed in mineral oil (manufactured by A1drich) for 6 hours, and the weight (W2) after sufficiently wiping the surface mineral oil was measured. The weight (W2) of the sample before immersion was measured. The pore volume (V 1) was determined from the following equation: V 1 = (W2-W1) Z p from W1) and the density (p) of the mineral oil. The porosity (P) is calculated from the apparent body 嵇 (V2: a value calculated from the thickness and dimensions) and the porosity 秸 (VI) as follows: P = (VI V V 2) X 100 (%).

2. Young's modulus

Using a tensile strength and elongation measuring instrument (Tensilon RTM-100 manufactured by Orientec Co., Ltd.), a test piece of a porous film or a laminated porous film with a width of 101 ^ 11 and a length of 100 mm is inserted into a chuck. The tensile strength and elongation were measured under the conditions of a distance of 50 mm and a tension speed of 20 mm / min, and the Young's modulus was calculated by the calculation method described in d of JISK7127.

3. Apparent impedance

Lithium perchlorate was dissolved at a concentration of 1 mol Z liter in a mixed solvent of 1: 1 electrolyte (the ratio of propylene carbonate and 1,2-dimethylxetane) in the obtained stack of porous membranes. ), And fixed with ^two 5 cm ² platinum electrodes to obtain a measurement cell. Using a LCR meter (Yokogawa Hewlett Packard, Model 4274), apply an alternating current of 100 KHz and 0.1 V between the electrodes of the measuring cell and apply an AC electric resistance ( Ω · cm ² ) was measured. The AC electrical resistance at this time was defined as the apparent impedance of the porous membrane. When the impregnating property of the non-aqueous solvent-based electrolyte is poor, the porous membrane is impregnated with 1,2-dimethylxetane beforehand, and the 1,2-dimethoxyethane in the porous membrane is impregnated with the non-aqueous solvent-based electrolyte. Replace with measurement It is ^one thing to do.

4. Pin missing test

Five samples cut from the perforated crotch obtained under the same manufacturing conditions to a width of 43 mm and a ji of 500 mm were prepared. Insert the end of the two porous membranes into the slit (C) of a SS pin made of SUS with a diameter of 4.5 mm, length of 60 mm and slit fe'l mm. First, wrap only the porous membrane around a 5 Omm pin, and then wrap two copper plates 38 mm wide, 400 mm long, and 150 μπι thick so that they become porous membrane Ζ copper plate / porous copper plate. Τ Wrap the rolled product around the pin at a speed of 2 seconds / 1 In. Roll, fix the finished roll with adhesive tape, and use it for evaluation roll (D. Finished roll ( A test was conducted in which the split pin (C) was pulled out from D), that is, a bin pull-out test, where the split pin (C) came off without breaking the shape of the wound material (D) when the pin was pulled out. The porous film at the center of the wound (D) is pulled out by the split pin (C) and comes off, and the wound (D) is shaped like a mushroom, or the wound (D) is split from the split pin (C). The sample that did not come off was designated as X. The evaluation was performed using five rolls (D) made with a porous membrane obtained under the manufacturing conditions. There, the case three or more times was 〇 and 〇, 3i9: the case more than j was X was X.

(Examples 1-2, Comparative Examples 1-3)

Poly (4-methylpentene-1) (manufactured by Ino Petrochemical Industry Co., Ltd., trade name: T PX, melting point 235 ° C) For 100 parts by mass, 70 parts by mass of dioctyl phthalate are melt-mixed at 260 ° C, Pelletized. The obtained pellets were melt-molded into a film at a temperature of 240 "C using an extruder with a T-die of 270 mm width and cooled on a chill roll at 140 ° C. The raw film was placed between the metal rolls at a temperature of 20 ° (:) at the draw ratio shown in Table 1 (shown in the first draw ratio column). After stretching in the direction (the length direction of the raw fabric) (first stretching), heat treatment was performed on a metal roll at a temperature of 70 ° C for 1 minute. The stretched film was subjected to a plasticizer extraction process while applying ultrasonic waves in isopropyl alcohol at 30 ° C for 5 minutes. Furthermore, after treating in Ryoton for 1 minute, it was air-dried. Then, the film was stretched (second stretching) between the metal rolls at the temperature of 25 ° C and the stretching ratio shown in Table 1 (shown in the column of the second stretching ratio) in the same direction as the stretching before extracting the plasticizer. Thereafter, heat treatment was performed on the metal roll at a temperature of 70 ° C for 1 minute to obtain a porous film. The thickness, porosity, Young's modulus, and convertible impedance of the obtained porous film were measured, and a pin removal test was performed. The results are shown in Table 1.

(Comparative Example 4)

The same operation as in Example 1 was performed except that the first stretching temperature was 70 ° C. The results are shown in Table 1.

(Examples 3-6, Comparative Examples 5-8)

Poly (butene-1) (Mitsui Petrochemical Co., Ltd., trade name: Buron, melting point 123 ° C) to form (Layer B) 100 parts by mass, 100 parts by mass of dioctyl phthalate of 100 quality The mixture was melt-mixed at 230 ° C using a twin-screw extruder and pelletized. In order to form the same (layer A), poly (4-methylpentene) (manufactured by Mitsui Petrochemical Industry Co., Ltd., trade name: TPX, melting point: 235 ° C) A part of dioctyl furoate was similarly melt-mixed at 260 ° C and pelletized. The obtained pellets were melt-molded into a film at a temperature of 240 ° C using a three-layer extruder equipped with a 370 mm wide three-layer co-extrusion T die at a temperature of 240 ° C with a layered structure of A layer, ZB layer and ZA layer. It was cooled on a chill roll at ° C to obtain a laminated film. The laminated film is stretched in the MD direction (first stretching) at a stretching ratio (shown in the column of the first stretching ratio) shown in Table 2 at a temperature of 20 between the rolls, and then heated on a metal roll at a temperature of 70%. Heat treatment was performed for 1 minute at ° C. This The stretched debris film was continuously extracted in isopropyl alcohol at 30 ° C for 5 minutes while applying ultrasonic waves. After drying, the film is stretched in the same direction as the first stretching (2 stretching) at a stretching ratio (shown in the column of 2nd stretching ratio) shown in ¾2 at a temperature of 25 between the rolls. Heat treatment was performed at 70 ° C for 1 minute to obtain a laminated porous material. The ratio of the thicknesses of the respective layers constituting the laminated porous film was A layer / anode layer A = 2: 1: 2. The thickness, porosity, Young's modulus, and apparent impedance of the obtained laminated porous film were measured, and a pin loss test was performed. The results are shown in Table 2.

(Example 7)

Poly (butene one 1) to form a layer (B): to (Nii Petrochemical Industries, Ltd., trade name views one Ron, mp 123 ° C) 1 00 quality S unit, 100 ^gamma portion of the lid Le Dioctyl acid was melt-mixed at 230 ° C using a twin-screw extruder and pelletized. To form the same (AIi), poly (4-methylpentene-1) (manufactured by ^ don Petrochemical Industry Co., Ltd., trade name: TPX, melting point 235 ° C) Dioctyl phthalate was similarly melt-mixed at 260 ° C and pelletized. The obtained pellets were melt-molded into a film with a laminated structure of A layer, ZB layer and A layer at a temperature of 240 ° C using three extruders equipped with a 370 mm wide three-layer co-extrusion T die. and it cooled on the chill roll 140 ^D C, to obtain a laminated membrane-like bodies. The debris film was heated at 18 ° C in the TD direction (¾ in the length direction of the raw material) at a draw ratio of 2.5 times and a draw ratio of 1.5 in the MD direction. After the axial stretching (first stretching), a heat treatment was performed on a metal roll at a temperature of 70 ° C. for 1 minute. The stretched dust film was continuously subjected to extraction treatment in isopropyl alcohol at 30 ° C. for 5 minutes while applying ultrasonic waves. After drying, the film is stretched in the MD direction (second stretching) at a temperature of 25 ° C and a stretching ratio of 1.3 between rolls, and then heat-treated at 70 ° C for 2 minutes on a metal roll to form a laminated porous membrane. Obtained. The thickness ratio of each layer constituting the laminated porous membrane was A layer / B) / A layer = 2: 1: 2. The thickness of the obtained porous porous membrane was 33 m, the Young's modulus was 61 kg / mm, the impedance was 11 Ω · cm ² , and the porosity was 33%. Table 2 shows the results.

1

Table 2

Industrial applicability

According to the present invention, a porous membrane made of poly (4-methylpentene-11) resin and a product of a layer made of poly (4-methylpentene-11) resin and a porous membrane made of another polyolefin resin have a low impedance and a relatively high Young's strength. ^ Rate. Pond separators consisting of these porous membranes are designed to prevent pin dropout during production. Producibility 1: Productivity required for battery separators, breakdown function, break-down It is equipped with a prevention function, which contributes to improving the safety of the pond. In addition, it is possible to increase the energy density of the pond.

Claims

The scope of the claims

1. Poly (4-methylpentene one 1)兑掛only impedance consists resin 2 5 Ω. C rn ^ or less, a porous membrane that冇the Young's modulus 40 kg / mm ² or more h.

2. ^ (A) and layer of porous membrane made of poly (4-methylpentene-1) resin

(A) a laminate of at least 2% of a porous membrane layer (Β) made of a polyolefin resin having a melting point of 100 to 140 ° C. and having an apparent impedance of 25%.多孔 · cm ² or less, Young's modulus 40 kg / mm ² or more.

3. A porous membrane, wherein the resin constituting the layer (B) according to claim 2 is polybutene-11.

4. A battery separator composed of the porous ceramics described in claim 1 or claim 3.

5. A process of melt-extruding a mixed composition comprising 100 parts by mass of a poly (4-methylpentene-1) resin and 50 to 150 parts by mass of a plasticizer to form a film, wherein the crotch is -10 to 50 ° 1.5 to 3. (stretching to Mfi (first stretching) at least in the-direction at a temperature of C, extracting plasticizer from the first stretched film, further 0 to 120 ° of the film 2. The method for producing a porous membrane according to claim 1, comprising a step of stretching (second stretching) 1.2 to 2.5 times at a temperature of C.

6. A polyolefin resin that is different from poly (4-methylpentene-11) resin in a composition consisting of 100 parts by mass of poly (4-methylpentene-1) resin and 50 to 120 parts by mass of plastic, A step of melt-extruding a composition of at least two poles of a composition comprising 100 parts by mass of a resin having a melting point and 50 to 150 parts by mass of an agent to form a laminated film; Stretching at least in the-direction at a temperature of ° C by 1.5 to 3.0 times (first stretching); extracting plasticizer from the first stretched laminated film; The object is further heated at a temperature of 0 to 120 ° C 1.2 to 2.

3. The method for producing a porous film according to claim 2, comprising a step of stretching by 5 times (second stretching).