JPH1017693A - Manufacture of poly olefin porous membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a porous membrane comprising a polyolefin and having mechanical strengths, especially a high Young's modulus, applicable to various usages. SOLUTION: This manufacturing method of a porous membrane from a polyolefin includes filming of a mixed composition of a polyolefin and a plasticizer and a primary drawing process, a secondary drawing process, and a plasticizer extraction process. In this case, the film is drawn (primary drawing), at a temperature of -100-50 deg.C, 1.5-3.0 times to at least one direction. The porous membrane has a Young's modulus of not less than 40kg/mm<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a porous film made of a polyolefin resin. More specifically, when a porous film made of a polyolefin resin is produced by a production method including a first stretching, a second stretching and a step of extracting a plasticizer, a porous film having a high Young's modulus is obtained by performing the first stretching under specific conditions. It relates to a method of manufacturing.

[0002]

2. Description of the Related Art Conventionally, various porous membranes have been developed.
These applications cover a wide variety of applications, such as battery separators, electrolytic capacitor partitions, various filters, moisture permeable waterproof membranes, ultrafiltration membranes, and microfiltration membranes. The required performance varies depending on each application. A typical production method of these porous membranes is a method of mixing and dispersing a liquid or a solid which is more easily extracted with a solvent than a synthetic resin into a synthetic resin, and extracting with a solvent. Japanese Patent Publication No. 5-62130 discloses (A) poly-
4-methylpentene-1 or poly-3-methylbutene-
Component 9 having a lower melting point than resin used as component (A) at room temperature solid selected from aliphatic compounds and alicyclic compounds (B) for 10 to 90% by weight of resin 9
A porous permeable film formed by forming a film from a resin composition comprising 0 to 10% by weight and stretching the film and then subjecting the component (B) to extraction or stretching after the component (B) extraction Is described. In addition, Japanese Unexamined Patent Publication No.
Japanese Patent No. 240036 discloses that a component having a molecular weight of 7 × 10 ⁵ or more is contained in an amount of 1% by weight or more and (weight-average molecular weight / number-average molecular weight) is 10 to 300% by weight.
And a solution comprising 50 to 90% by weight of a solvent, and extruding the solution from a die to form an unstretched gel-like composition by cooling. The gel-like composition is dispersed at a crystal dispersion temperature of the polyolefin. The film is stretched at least 1.2 to 10 times in the uniaxial direction at the following temperature, and subsequently, at a temperature of from the crystal dispersion temperature to the melting point + 10 ° C.
A method for producing a microporous polyolefin membrane by stretching the film to 0 times and then removing the residual solvent is described.

[0003] One of the uses of these porous membranes is a separator comprising a laminate of a high-melting-point polyolefin-based resin porous membrane layer and a low-melting-point polyolefin-based resin porous membrane layer described in JP-A-2-77108. There is. According to the present invention, when a short circuit occurs, an excessive current flows in the battery and heat is generated, the low-melting-point polyolefin-based resin porous membrane layer is closed and sealed by melting the resin constituting the low-melting-point polyolefin-based resin layer. It has a function (shutdown) to stop the flow and suppress overheating. It also describes that the high-melting-point polyolefin-based resin porous membrane layer has a function of holding the low-melting-point polyolefin-based resin porous membrane layer that has been melt-clogged and preventing the occurrence of a short circuit again (breakdown). It is described that this separator is manufactured by a plasticizer extraction method.

Further, the separator needs to be thinner from the viewpoint of increasing the energy density of the battery, but needs to have a certain thickness from the viewpoint of preventing contact between the electrodes. Therefore, it is desired that the separator for a non-aqueous solvent battery has low impedance.

[0005] A battery having such a function has a form in which a positive electrode material, a separator, and a negative electrode material are stacked and rolled in a necessary number of times. In this winding operation, a laminated body in which a positive electrode material, a separator and a negative electrode material are stacked is wound around a pin a required number of times, and then the pin is pulled out to obtain a wound body. At this time, if the mechanical strength of the separator, especially Young's modulus is insufficient, the winding of the positive electrode material, the separator and the negative electrode material is finished, and the pin does not come out when pulling out the pin, or in extreme cases Such a defect as cracking of the separator and a defect such as short-circuiting of the positive and negative electrodes due to the separator being displaced from between the electrodes occur.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a porous film having a mechanical strength, particularly a high Young's modulus, and a low impedance, which can be used for various applications as a porous film made of polyolefin. To provide.

[0007]

Means for Solving the Problems The inventors of the present invention have made intensive studies to achieve the above object, and as a result, formed a mixed composition comprising a polyolefin resin and a plasticizer into a film and stretched the film. In the method for producing a porous film comprising a polyolefin including a step of extracting a plasticizer, it has been found that a porous film having a high Young's modulus and a low apparent impedance can be obtained by performing the first stretching under specific conditions. Thus, the present invention has been completed.

That is, the present invention comprises a polyolefin comprising a step of forming a mixed composition comprising a polyolefin resin and a plasticizer into a film, first stretching, second stretching, and extracting a plasticizer. In the method for producing a porous membrane, there is provided a method for producing a polyolefin porous membrane, wherein the film is stretched in at least one direction by 1.5 to 3.0 times (first stretching) at a temperature of -10 to 50 ° C. It is. The polyolefin porous membrane obtained by the above method has a Young's modulus of 40 kg / mm ² or more, and preferably has an apparent impedance of 25 Ω · cm ² or less.

The present invention also provides a method for producing a polyolefin laminated porous membrane comprising at least two layers (A) and (B) in which the film has different melting points in the above invention. Further, the present invention provides (1) a step of melt-extruding the mixed composition to form a film, and (2) a step of forming the film from at least one direction at a temperature of -10 to 50 ° C in at least one direction.
3.0-stretching (first stretching), (3) extracting a plasticizer from the first stretched film, (4) a temperature lower than the melting point of the film, or the film is a laminate. In the case of the present invention, there is provided a method for producing a porous membrane, comprising a step of stretching by 1.2 to 2.5 times (second stretching) at a temperature lower than the melting point of the layer having the lowest melting point among those layers. .

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The polyolefin resin used in the present invention is poly-3-
Methylbutene-1, polybutene-1, polypropylene,
Poly (4-methylpentene-1), polyethylene, or a mixed resin of these resins may be used. Among them, poly (4-methylpentene-1) resin is particularly preferable as a porous film requiring a high melting point.

In the present invention, poly (4-methylpentene)
1) The resin includes a homopolymer of 4-methylpentene-1 or a copolymer using an α-olefin having 2 to 12 carbon atoms as a copolymerization component. Specific examples of the copolymer component include ethylene, propylene, butene-1, hexene-1, 3-methylbutene-1, octene-1, styrene, and vinylcyclohexene. These copolymer components are 40% by mass or less, preferably 20% by mass in the polymer.
It is desirable that: In addition, it is desirable that the porous film itself has a melting point of preferably 180 ° C. or more from the viewpoint of maintaining the shape of the film stably with a rise in temperature. Among the polyolefin resins, the melting point of a resin selected from polyethylene (including a copolymer with an α-olefin mainly composed of ethylene), an ethylene-propylene copolymer, and poly (butene-1) is preferably 100. ~ 140
C. layer and a layer of a resin having a higher melting point than those described above can also be used. As the polyolefin resin constituting the layer having a high melting point, poly (4-methylpentene-1) resin is preferable.

The resin constituting the single layer of the porous membrane may be a mixed resin of polyolefin. In the case of a mixed resin, it is desirable to determine the mixing ratio so that the resin having a high melting point occupies more than 50% by mass of the total of the mixed resins among the mixed resins constituting the layer. Here, the melting point is an endothermic peak temperature accompanying melting when 10 mg of a sample is measured from a room temperature at a heating rate of 10 ° C./min under a nitrogen stream using a differential scanning calorimeter (DSC30, manufactured by Mettler). Means When the layer is made of a mixed resin, a plurality of endothermic peaks may appear, and the temperature of the peak having the largest peak area among the peaks is defined as the melting point of the layer.

The plasticizer used in the present invention is for plasticizing a polyolefin resin such as poly (4-methylpentene-1), polybutene-1, and polyethylene. Examples of the plasticizer include phthalic acid, dimethyl phthalate, and phthalate. Diethyl phthalate, dibutyl phthalate, diisopentyl phthalate,
Phthalic acid diesters such as dioctyl phthalate and didodecyl phthalate; aliphatic dialcohols having 2 to 4 carbon atoms; and aliphatic dicarboxylic acids having 2 to 9 carbon atoms (the aliphatic dialcohols having 2 to 4 carbon atoms include ethylene glycol). Propylene glycol, 1,4-butanediol, 1,2-butanediol and the like. Examples of the aliphatic dicarboxylic acid having 2 to 6 carbon atoms include oxalic acid, malonic acid, succinic acid, glutaric acid, adipine Acids, azelaic acid, etc.) and lactones (propiolactone, butyrolactone, δ-valerolactone, ε-caprolactone, etc.)
And aliphatic polyesters such as ring-opening polymerization polymers, phosphate esters, glycol esters, and epoxy compounds. Of these, phthalic acid diester is preferred. Furthermore, mixtures of two or more of the above plasticizers can be used.

A mixed composition is obtained by blending a plasticizer with the polyolefin resin. The mixing method is not particularly limited as long as the plasticizer is uniformly mixed. For example, there is a method of mixing with a ribbon blender, a Henschel mixer, a fixed V-type blender, a tumbler, a ball mill, and the like, followed by melt kneading with an extruder, or a method of simultaneously charging both into an extruder and directly melting and kneading. In the case of a laminated porous film, preferably, a polyolefin resin for forming one layer having a melting point of 150 ° C. or more and 100 to 140 ° C. different from this.
What is necessary is just to prepare a separate mixed composition in which a plasticizer is added to each of the polyolefin resin for forming another layer having the melting point of the above and a plasticizer. The mixing ratio of the resin and the plasticizer is preferably 50 to 12 parts with respect to 100 parts by mass of the resin.
0 parts by mass, more preferably 60 to 100 parts by mass,
Particularly preferably, it is 70 to 90 parts by mass.

The mixture composition is pelletized if necessary, and then extruded at a temperature of 180 to 340 ° C., preferably 200 ° C.
It can be melt-extruded at ~ 280 ° C and formed into a film (film). In the case of a laminated film, it may be formed by a melt coextrusion method or may be laminated outside a die. At this point, the thickness of the film may be 200 to 2 depending on the subsequent stretching ratio.
0 μm is preferred, and more preferably 150 to 30 μm
It is.

Next, the obtained film is stretched (first stretching). Stretching is performed by a tenter method, a roll method, an inflation method, a rolling method, or the like. The stretching may be either uniaxial stretching or biaxial stretching. In the case of biaxial stretching, simultaneous stretching or sequential stretching may be used. The first stretching temperature is -10 to 50C, preferably 0 to 40C, more preferably 5 to 30C. By setting the stretching temperature higher than −10 ° C., the occurrence of breakage during stretching is reduced,
By setting the temperature within a range not exceeding ℃, stretching is unlikely to be uneven. The first stretching ratio is 1.5 to 1.5 in at least one direction.
Stretching is performed at 3.0 times, preferably 1.8 to 3.0 times.
When the stretching ratio is 1.5 times or more, the Young's modulus of the porous film obtained does not decrease, and when the stretching ratio is less than 3.0 times, the tearing phenomenon of the film hardly occurs. In the case of biaxial stretching, the area magnification is preferably 2 to 9
And more preferably 4 to 9 times. The Young's modulus of the porous film obtained under the first stretching condition is maintained at 40 kg / mm ² or more, although the reason is unknown, and the apparent impedance is maintained at 25 Ω · cm ² or less.

A plasticizer is extracted from the first stretched or second stretched film or laminated film. The solvent for this purpose is not particularly limited as long as it does not dissolve the polyolefin resin serving as a film material such as poly (4-methylpentene-1), poly (butene-1) or polyethylene and can dissolve the plasticizer. For example, solvents such as haloalkanes such as trichloromethane and trichloroethane, ketones such as acetone and methyl ethyl ketone, lower carboxylic acid esters such as ethyl acetate, lower alcohols such as methanol and isopropyl alcohol, and aromatic hydrocarbons such as toluene and xylene can be exemplified. .

The extraction method using a solvent is preferably carried out at a temperature of 5 to 5.
In an extraction solvent at 150 ° C, more preferably 10 to 100 ° C, particularly preferably 15 to 50 ° C, preferably 0.5 to 3 ° C.
It is left for 60 minutes, more preferably for 3 to 120 minutes, particularly preferably for 5 to 60 minutes. In addition, extraction can be accelerated by appropriately applying vibration. After the extraction of the plasticizer, it is preferable to perform a heat treatment at a temperature of 40 to 120 ° C. for a time of 0.25 to 360 minutes for drying the porous membrane.

The stretched film or laminated film after the extraction of the plasticizer is further stretched at a stretching ratio of 1.2 to 2.5 times, preferably 1.5 to 2.0 times (second stretching). Is done. Second
By setting the stretching ratio of stretching to 1.2 times or more, the apparent impedance of the stretched porous membrane can be kept in a low range, and by setting the stretching ratio to 2.5 times or less, tearing or breaking of the film (film) may occur. Can be avoided.

The stretching temperature of the second stretching is preferably a temperature below the melting point of the film or, if the film is a laminate, a temperature below the melting point of the layer having the lowest melting point among those layers. It is preferred that The laminate is made of, for example, poly (4
-In the case of a layer composed of a methylpentene-1) resin and a layer composed of a poly (butene-1) resin, preferably 0 to 120
° C, more preferably 5-80 ° C, particularly preferably 10-80 ° C.
50 ° C. When the stretching temperature of the second stretching is 0 ° C. or higher, breakage during stretching hardly occurs, and when the temperature is 120 ° C. or lower, the stretching hardly becomes uneven. In the case of a laminated film, the temperature of 120 ° C. or lower is also desirable in that the holes in the low-melting-point polyolefin resin layer are partially blocked to prevent reduction in through-holes.

The form of the porous membrane of the present invention may be at least two layers of a porous membrane made of a polyolefin resin alone or a layer (A) having a melting point of 150 ° C. or more and a layer (B) having a melting point of 100 to 140 ° C. Membrane. As an example of the application, when a porous membrane of poly (4-methylpentene-1) resin is used as a separator for a battery, a laminated porous membrane may be used from the viewpoint of facilitating shutdown and preventing breakdown. preferable. As the laminated porous film, a laminate of a porous film (layer A) made of poly (4-methylpentene-1) resin and a layer (B) of the porous film is preferable. The layer configuration of the laminated porous membrane is not limited to the number or order of lamination, and has a two-layer configuration of (A) layer / (B) layer, (A layer)
/ (B) layer / (A) layer, (B) layer / (A) layer / (B) layer, and the like. Above all, (A layer) /
(B) layer / (A) layer is preferred. Further, it is preferable that each of the single-layer porous membrane and the multilayer porous membrane is used in a stretched form.

When a laminated porous membrane is used as a battery separator, a poly (4-methylpentene-1) porous membrane (A
The thickness of the layer is preferably from 3 to 20 μm, and more preferably from 5 to 15 μm, from the viewpoint of ease of forming a laminated structure, not being excessively thick as a laminated structure, or reducing the possibility of occurrence of a short circuit. It is more preferred that there be.

Examples of the polyolefin resin constituting the layer (B) include polyethylene, ethylene-propylene copolymer, and poly (butene-1). Among these, polyethylene and poly (butene-1) are preferred, and poly (butene-1) is more preferred. The thickness of the polyolefin resin porous membrane layer is preferably 3 μm or more, more preferably 5 to 15 μm. Further, as long as the shutdown function is not impaired, the resin may be mixed with another resin (for example, polypropylene).

The porous membrane of the present invention is preferably 10 to 50 μm, more preferably 15 μm, regardless of whether it is a single layer or a laminated porous membrane.
It is desirable to have a thickness of ３０30 μm. When the thickness of the porous membrane exceeds about 50 μm, for example, when the porous membrane is used for a battery separator, the number of windings of the laminate of the two electrodes and the separator per battery decreases, and the battery capacity decreases. Not preferred. The thickness is 10 μm
If it is smaller, the mechanical strength of the film becomes insufficient, which is not preferable.

The porous membrane obtained by the production method of the present invention has a Young's modulus of 40 kg / mm ² or more, preferably 50 kg / mm ² or more. Here, the Young's modulus is
It is a tensile modulus determined by the calculation method described in JIS K7127. When the Young's modulus of the porous membrane is smaller than 40 kg / mm ² , when the separator is used as a battery separator, the operation of winding both electrodes and the separator during the battery production is difficult. It is not preferable because a pin dropout easily occurs, and when winding at a high speed, winding is likely to occur and productivity is significantly reduced.

The apparent impedance together with the Young's modulus is preferably 25 Ω · cm ² or less, more preferably 20 Ω · cm ² or less. 25Ω apparent impedance
-If it exceeds cm ² , it is difficult to obtain sufficient charge / discharge characteristics when used in a battery, which is not preferable. In the present invention, the apparent impedance means that at room temperature (23 ° C.), a porous membrane is coated with a non-aqueous solvent-based electrolyte solution (1 mol / liter perchloric acid in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane at a volume ratio of 1: 1). (Impregnated with lithium oxide dissolved) and then applying an alternating current (100 KHz, 0.1 V) with electrodes (Pt electrodes) in contact with both surfaces of the porous membrane, and measuring the resistance (Ω · cm ² ). And measured in a form including the resistance component of the non-aqueous solvent-based electrolyte.

The porosity of the obtained porous membrane is preferably 25 to 60%, more preferably 30 to 45%. The porosity in the present invention means a porosity of a single layer in the case of a single-layer porous film made of, for example, poly (4-methylpentene-1) resin or poly (4-methylpentene-1).
1) In the case of a laminated porous film including a layer made of a resin, it means the average porosity of all the laminated porous films.

[0028]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. In addition, the measurement in the Example and the comparative example was based on the following method. 1. Porosity A sample (5 cm x 5 cm) was mixed with mineral oil (Aldri)
(manufactured by Ch. Co., Ltd.) for 6 hours, and the weight (W2) after sufficiently wiping the mineral oil on the surface was measured. The pores were determined from the weight (W1) of the sample before immersion and the density (ρ) of the mineral oil. The volume (V1) is calculated by the following equation: V1 = (W2-W1) /
ρ. The porosity (P) is determined by the apparent volume (V
2: Value calculated by thickness and dimensions) and pore volume (V
From 1), the following equation: P = (V1 / V2) × 100 (%)
Was calculated by

2. Using a Young's modulus tensile strength / elongation measuring instrument (Tensilon RTM-100 manufactured by Orientec Co., Ltd.), width 10 mm × length 10
A test piece of a 0 mm porous film or a laminated porous film was measured for tensile strength and elongation under the conditions of a distance between chucks of 50 mm and a tensile speed of 20 mm / min, and the Young's modulus was obtained by a calculation method described in JIS K7127.

3. Impedance The obtained laminated porous membrane is impregnated with an electrolytic solution (1 mol / L of lithium perchlorate dissolved in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane at a volume ratio of 1: 1). The sample was fixed by sandwiching it between two 5 cm ² platinum electrodes to form a measurement cell. This measurement cell is connected to an LCR meter (Yokogawa Hewlett Packard).
1004 between the electrodes of the measuring cell
KHz, 0.1V AC is applied and AC electric resistance (Ω ・
cm2) was measured. The AC electric resistance at this time was defined as the apparent impedance of the porous film. When the impregnating property of the non-aqueous solvent-based electrolyte is poor, the porous membrane is impregnated with 1,2-dimethoxyethane in advance, and the 1,2-dimethoxyethane in the porous membrane is mixed with the non-aqueous solvent-based electrolyte. It is desirable to measure by replacing.

4. Pin-out test 43 mm wide and 5 mm long from a porous membrane obtained under the same manufacturing conditions
Five samples cut into 00 mm were prepared. 4.5 diameter
The end of the two porous membranes is sandwiched between the slit portions (C) of a SUS split pin having a length of 60 mm, a length of 60 mm and a slit width of 1 mm. First, only the porous membrane is wound around a 50 mm pin, and then the width is 38 mm, the length is 400 mm, and the thickness is 150 μm.
m is wound around a pin at a speed of 2 seconds / 1 rotation, and a layered product obtained by stacking two copper plates having a thickness of 2 m to form a porous film / copper plate / porous film / copper plate is fixed with an adhesive tape. This was evaluated as a roll (D). A split pin (C) was pulled out from the completed roll (D), and a pin pull test was performed. When the pin was pulled out and the split pin (C) came off without breaking the shape of the entrapment (D), ○, the porous membrane at the center of the entrapment (D) came off while being pulled by the split pin (C), When the entrapment (D) was mushroom-shaped or when the split pin (C) did not come off from the entrapment (D), it was evaluated as x. The evaluation was performed using five rolls (D) made of a porous membrane obtained under the same manufacturing conditions.
When three or more times were ○, the result was ○. When three or more times were ×, the result was ×.

(Examples 1-2 and Comparative Example 1) 100 parts by mass of poly (4-methylpentene-1) (trade name: TPX, manufactured by Mitsui Petrochemical Industries, Ltd., melting point: 235 ° C.)
0 parts by mass of dioctyl phthalate was melt-mixed at 260 ° C. and pelletized. The obtained pellet was melt-molded into a film at a temperature of 240 ° C. using an extruder equipped with a T-die having a width of 270 mm, and cooled on a chill roll at 140 ° C. to obtain a raw (film-like) film. . After the raw film is stretched (first stretching) in the MD direction (length direction of the raw material) at a temperature of 20 ° C. between metal rolls at a stretching ratio shown in Table 1 (indicated in the column of the first stretching ratio). Then, a 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 treatment while applying ultrasonic waves in isopropyl alcohol at 30 ° C. for 5 minutes. Furthermore, after treating in acetone for 1 minute, it was air-dried. After that, the temperature 2 between the metal rolls
5 ° C., stretching ratio shown in Table 1 (displayed in the column of the second stretching ratio)
The film was stretched in the same direction as the stretching before the plasticizer extraction (second stretching). Thereafter, heat treatment was performed on a metal roll at a temperature of 70 ° C. for 1 minute to obtain a porous film. The thickness of the obtained porous membrane, porosity,
The Young's modulus and impedance were measured, and a pin-out test was performed. The results are shown in Table 1.

(Comparative Example 2) The same procedure as in Example 1 was performed except that the first stretching temperature was 70 ° C. The results are shown in Table 1.

(Examples 3 to 6, Comparative Examples 3 to 5) (Layer B)
Poly (butene-1) (manufactured by Mitsui Petrochemical Co., Ltd., trade name: Buron, melting point 123 ° C.) 1
With respect to 00 parts by mass, 100 parts by mass of dioctyl phthalate was melt-mixed at 230 ° C. using a twin-screw extruder and pelletized. Similarly, to form (A layer), 70 parts by mass of 100 parts by mass of poly (4-methylpentene-1) (manufactured by Mitsui Petrochemical Industries, Ltd., trade name: TPX, melting point: 235 ° C.)
A mass part of dioctyl phthalate was similarly melt-mixed at 260 ° C. and pelletized. The obtained pellet is 370 mm
Using a three extruder equipped with a three-layer co-extrusion T-die having a width, it is melt-molded into a film at a temperature of 240 ° C. in a laminated structure of A layer / B layer / A layer, and cooled on a chill roll at 140 ° C. Thus, a laminated film was obtained. The laminated film is heated at a temperature of 20 between rolls.
After stretching in the MD direction (first stretching) at a stretching temperature (shown in the column of the first stretching ratio) shown in Table 2 at a temperature of 70 ° C., a heat treatment was performed on a metal roll at a temperature of 70 ° C. for 1 minute to obtain a laminated porous membrane. Was. The ratio of the thickness of each layer constituting the laminated porous membrane was A layer / B layer / A layer = 2: 1: 2. The thickness, porosity, Young's modulus, and impedance of the obtained laminated porous film were measured, and a pin detachment test was performed. The results are shown in Table 2.

Example 7 In order to form a layer (B), 100 parts by mass of poly (butene-1) (manufactured by Mitsui Petrochemical Industries, Ltd., trade name: Buron, melting point 123 ° C.)
100 parts by mass of dioctyl phthalate was melt-mixed at 230 ° C. using a twin-screw extruder and pelletized. (A
Layer) to form poly (4-methylpentene-1)
70 parts by mass of dioctyl phthalate was similarly melt-mixed at 260 ° C. and pelletized with 100 parts by mass (manufactured by Mitsui Petrochemical Industries, Ltd., trade name: TPX, melting point: 235 ° C.). The obtained pellets were melt-molded into a film at a temperature of 240 ° C. in a layered structure of layer A / layer B / layer A at a temperature of 240 ° C. using three extruders provided with a three-layer co-extrusion T-die having a width of 370 mm.
It was cooled on a chill roll at 0 ° C. to obtain a laminated film. The laminated film is successively biaxially stretched by a tenter method at a temperature of 18 ° C., a stretching ratio of 2.5 times in the TD direction (perpendicular to the length direction of the raw material), and a stretching ratio of 1.5 times in the MD direction (the tenth method). After 1 stretching), a heat treatment was performed on a metal roll at a temperature of 70 ° C. for 1 minute. The stretched laminated film was continuously treated in isopropyl alcohol at 30 ° C. for 5 minutes while applying ultrasonic waves. After drying, the film was 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 obtain a laminated porous film. The ratio of the thickness of each layer constituting the laminated porous membrane is A layer
/ B layer / A layer = 2: 1: 2. The thickness of the obtained laminated porous film was 33 μm, the Young's modulus was 61 kg / mm ² , the impedance was 11 Ω · cm ² , and the porosity was 33%. The results are shown in Table 2.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

When a porous film is produced from a mixed composition comprising a polyolefin resin and a plasticizer according to the present invention, the conditions for the first stretching are a temperature of -10 to 50 ° C and a temperature of 1.5 to 3 in at least one direction. By stretching by a factor of 0.0, a porous film having a high Young's modulus and a low impedance could be obtained. As a specific example, a porous layer made of poly (4-methylpentene-1) resin, a porous layer made of poly (4-methylpentene-1) resin, and poly (butene-
The laminated porous membrane with the porous membrane of 1) has a high Young's modulus and a low impedance, and the battery separator made of these porous membranes can improve productivity by preventing pin dropout failure during manufacturing. It has a shutdown function and a breakdown prevention function, which are required for a battery, and contributes to higher energy density of the battery and improvement of the safety of the battery. Moreover, the method is a method for producing a porous film that can be used for applications other than battery separators because of its high Young's modulus.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location // C08L 23:02 (72) Inventor Tomoo Susa Nakanomachi, Nakorai-machi, Nakoso-machi, Iwaki-shi, Fukushima 30- 157 (72) Inventor Binya Mizuno 13-1-201 Higashizaki-cho, Tsuchiura-shi, Ibaraki

Claims (7)

[Claims] 1. A method for forming a porous composition comprising a polyolefin comprising a step of forming a mixed composition comprising a polyolefin resin and a plasticizer into a film, a first drawing step, a second drawing step, and a step of extracting a plasticizer. In the manufacturing method, -10 to 5
At a temperature of 0 ° C., 1.5 to 3.0 times in at least one direction,
A method for producing a polyolefin porous membrane, comprising stretching (first stretching). 2. The method for producing a polyolefin laminated porous membrane according to claim 1, wherein the membrane comprises at least two layers having different melting points: a layer (A) and a layer (B). 3. The method according to claim 2, wherein the film comprises a layer (A) having a melting point of 150 ° C. or higher and a layer (B) having a melting point of 100 to 140 ° C. 4. A method for producing a polyolefin laminated porous membrane wherein the resin constituting the layer (A) according to claim 3 is poly (4-methylpentene-1). 5. The method for producing a polyolefin porous membrane according to claim 1 or 2, comprising the following steps: 1) a step of melt-extruding the mixed composition to form a film; Stretching in at least one direction 1.5 to 3.0 times at a temperature of 1 ° C. (first stretching); 3) extracting a plasticizer from the first stretched film; 4) less than the melting point of the film At a temperature of less than the melting point of the layer having the lowest melting point among the layers when the film is a laminate (second stretching) Process. 6. The method for producing a polyolefin porous membrane according to claim 5, wherein the film is a laminated film comprising at least a layer made of poly (4-methylpentene-1) and a layer made of polybutene-1. . 7. The method for producing a polyolefin porous membrane according to claim 1, wherein the first stretching is biaxial stretching.