JP2002036459A - Porous film and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous film having at least one crosslinking layer and one non-crosslinking layer so that a laminating strength between the layers is high and excellent film breakage resistance is incorporated even at a high temperature, a method for manufacturing the same, a battery and a capacitor using the porous film. SOLUTION: The porous film comprises a layer (resin layer A) containing a polyolefin, and a layer (resin layer B) containing both the polyolefin and a crosslinkable resin and laminated on the layer A. The method for manufacturing the porous film comprises the steps of laminating the porous film having the resin layer B including a crosslinking structure, a gel-like molding containing the polyolefin, and the gel-like molding containing both the polyolefin and the crosslinkable resin, and treating to form a film. The battery using the porous film, and the capacitor using the porous film are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a porous film and a method for producing the same. More specifically, the present invention relates 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 and isolates them, a method for producing the same, a battery and a capacitor using the porous film.

[0002]

2. Description of the Related Art In recent years, lithium batteries that are lightweight, have high electromotive force and high energy, and have low self-discharge have been attracting attention in order to cope with cordless electronic devices. Between the positive electrode and the negative electrode of this lithium battery, a separator is provided to prevent short circuit of the positive electrode and the negative electrode, and as this separator, a large number of microporous holes were formed in order to ensure the transmission of ions between the positive electrode and the negative electrode. A porous film has been used. Among them, those having a so-called shutdown function (SD function), in which when an abnormal current is generated due to incorrect connection of the battery, the resin is thermally deformed as the battery internal temperature rises to close the micropores and stop the battery reaction. It is adopted from the viewpoint of improving safety. As the separator having such an SD function, for example, a microporous film made of polyethylene, a microporous film having a multilayer structure of polyethylene and polypropylene, and the like are known.

However, due to recent advances in lithium ion secondary batteries and the like, not only the SD function described above, but also a heat-resistant element, that is, the separator itself melts when the temperature rises after shutdown. Or, if a state of plasticization and breakage occurs, there is a risk of ignition and explosion of the battery. Therefore, there is a strong demand for a separator that does not break or break to higher temperatures. In particular, as the capacity of batteries with higher capacity and the reduction of battery internal resistance progress,
This is increasingly important because the factors that generate heat increase.

As a method for achieving both the heat resistance and the SD characteristics, as disclosed in Japanese Patent No. 2768745, at least two polyethylene porous films are laminated, and the laminated porous films are laminated. It has been found that a separator in which at least one sheet is crosslinked and at least one sheet is not crosslinked is effective. In this method, lamination of a porous film in a specific temperature range enabled lamination without closing micropores.However, since the lamination temperature was low, the lamination strength between the films was not sufficiently high. In order to prevent this, care must be taken in handling the film after production. In addition, if, for example, an electron beam is irradiated after lamination, a problem arises in that a non-crosslinked layer cannot be obtained, and heat resistance and SD characteristics cannot be compatible.

Accordingly, in order to obtain a separator having both heat resistance and SD characteristics, a porous film which is porous after lamination, has at least one cross-linked layer and one non-cross-linked layer, and has no delamination between layers, and a method for producing the same Was desired.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide at least one crosslinked layer and at least one non-crosslinked layer, to have a high lamination strength between the layers and to have excellent rupture resistance at high temperatures. An object of the present invention is to provide a porous film, a method for producing the same, and a battery and a capacitor using the porous film.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, by laminating gel-like molded products containing a high-molecular-weight polyolefin before phase separation, a high level is obtained even after film formation. It has been found that lamination strength can be obtained. Further, they have found that by adding a crosslinkable resin to at least one of them, crosslinking occurs by heat treatment after film formation and the like, and a high heat-resistant layer is formed, and the present invention has been accomplished.

That is, the gist of the present invention is to provide a porous film in which [1] a layer containing a polyolefin (resin layer A) and a layer containing both a polyolefin and a crosslinkable resin (resin layer B) are laminated; [2] The porous film according to the above [1], wherein the resin layer B has a crosslinked structure, [3] a gel molded product containing a polyolefin, and a gel molded product containing both a polyolefin and a crosslinkable resin. And a method for producing a porous film, characterized in that a film is formed by laminating the above, [4] a battery using the porous film according to [1] or [2], and [5] the [ The present invention relates to a capacitor using the porous film according to 1) or 2).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The porous film of the present invention is formed by laminating a layer containing a polyolefin (resin layer A) and a layer containing both a polyolefin and a crosslinkable resin (resin layer B). . In this specification, the resin layer A
Is also referred to as a non-crosslinked layer, and the resin layer B is also referred to as a crosslinked layer.

The polyolefin used in the resin layers A and B is
Preferably, it is a high molecular weight polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more, for example, a homopolymer or copolymer obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and the like. And blends thereof. Among them, excellent mechanical strength,
High-molecular-weight polyethylene, from which high crystallinity can be obtained, is desirable as a material. The weight average molecular weight of the high molecular weight polyolefin, more preferably has 1 × 10 ⁶ or more ultra-high molecular weight, and more preferably 1.5 × 10 ⁶ or more.

The content of the high molecular weight polyolefin in the resin layer A is 5 to 100% by weight, preferably 10 to 100% by weight, more preferably 20 to 100% by weight. The lower limit of the content is preferably 5% by weight or more from the viewpoint that the strength of the formed film is sufficient.

In the resin layer A, as other resins, a polyolefin having a weight average molecular weight of less than 5 × 10 ⁵ , a thermoplastic elastomer, a hydrogenated polybutadiene resin,
Modified olefin resin, ethylene propylene diene monomer rubber (EPDM) and the like may be contained. Examples of the thermoplastic elastomer resin include “TPE” (manufactured by Sumitomo Chemical Co., Ltd.), “Hytrel” (manufactured by Dupont Toray), and “Septon” (manufactured by Kuraray Co., Ltd.). As the hydrogenated polybutadiene resin, "DYNA
RON "(made by Japan Synthetic Rubber) and the like. Examples of the modified olefin resin include “Evaflex” (manufactured by DuPont-Mitsui Polychemicals) and “Modiper”
(Manufactured by NOF Corporation) and the like. As the EPDM, for example, “Esprene” (manufactured by Sumitomo Chemical Co., Ltd.) and the like can be mentioned.

The content of the other resin in the resin layer A is preferably 0 to 95% by weight, more preferably 0 to 90% by weight, and still more preferably 0 to 80% by weight.

The crosslinkable resin used in the resin layer B in the present invention is a resin having a double bond and a hydrogen atom bonded to the carbon at the α-position, and at least forming a crosslinked structure by heat treatment. If there is, it is not limited. For example, a resin obtained by ring-opening polymerization of an unsaturated condensed alicyclic compound derivative and having an aliphatic ring derived from its monomer unit and a double bond in the main chain (for example, polynorbornene), Resin (for example, polybutadiene), which is obtained by polymerizing a monomer having a structure in which a terminal hydrogen atom of a lower hydrocarbon having a double bond is substituted with an ethylene group, and having a structure in which a methylene group is bonded to a main chain. Is mentioned. Among these, polynorbornene is preferable from the viewpoint of dispersibility, and polynorbornene having a weight average molecular weight of 2 × 10 ⁶ or more is particularly preferable.

The content of the crosslinkable resin in the resin layer B is 1
-50% by weight, preferably 3-40% by weight, more preferably 5-35% by weight. The content is preferably 1% by weight or more from the viewpoint that the addition action of the crosslinkable resin is effective, and 50% by weight or less from the viewpoint of high porosity of the porous film and high air permeability. preferable. Therefore, the content of the polyolefin in the resin layer B is 50 to 99% by weight, preferably 60 to 97% by weight, more preferably 65 to 99% by weight.
~ 95% by weight.

In the present invention, the order of laminating the resin layers A and B having these components is not particularly limited, but it is preferable that the resin layers A and B are alternately laminated. The thickness of each layer is preferably from 1 to 50 μm, more preferably from 5 to 50 μm. In addition, since these layers are laminated in a molten state, it is considered that molecules of the layers penetrate each other, and the layers are firmly fused as a whole.

The porous film of the present invention is prepared by, for example, melting and kneading a mixture obtained by adding a solvent to a resin component containing a polyolefin or a resin component containing both a polyolefin and a crosslinkable resin, and then forming a sheet. It can be obtained by subjecting a sheet-like molded product obtained by laminating two types of gel-like molded products obtained by extrusion to a film-forming treatment including a stretching treatment and a desolvation treatment. In the present invention, the film forming process refers to a process step of forming a porous film in which the resin layer A and the resin layer B are laminated by a process such as stretching, desolvation, and, if necessary, rolling of the laminated sheet-like molded product. .

The solvent may be any solvent that is excellent in the solubility of each resin component. For example, aliphatic or cyclic hydrocarbons such as nonane, decane, undecane, dodecane, decalin, liquid paraffin and the like, or those having a boiling point of Corresponding mineral oil fractions may be mentioned, but non-volatile solvents such as liquid paraffin are preferred.

The amount of the resin component and the solvent varies depending on the type of the resin, the solubility, the kneading temperature and the like, and cannot be unconditionally determined. However, the amount of the obtained slurry-like mixture can be melt-kneaded and formed into a sheet. If it is, there is no particular limitation. For example, the compounding amount of the resin component is preferably 5 to 30% by weight of the mixture, more preferably 10 to 30% by weight, and
0-25% by weight is more preferred. From the viewpoint of improving the strength of the obtained porous film, the amount of the resin component is preferably 5% by weight or more. In addition, the polyolefin can be sufficiently dissolved in a solvent and kneaded to near the stretched state. From the viewpoint of obtaining sufficient entanglement of the polymer chains, the content is preferably 30% by weight or less.

The amount of the solvent in the mixture is preferably from 70 to 95% by weight, more preferably from 70 to 90% by weight,
More preferably, it is 5 to 90% by weight. The compounding amount is preferably 70% by weight or more from the viewpoint that the kneading torque, rolling and stretching stress are moderate and the productivity is excellent, and neck-in does not occur at the die exit when extruding, and molding is easy. From the viewpoint, it is preferably 95% by weight or less.

If necessary, additives such as an antioxidant, an ultraviolet absorber, a dye, a nucleating agent, a pigment, and an antistatic agent are added to the mixture as long as the object of the present invention is not impaired. can do.

The melt-kneading of the mixture is preferably performed by applying a sufficient shearing force to the mixture in order to obtain sufficient entanglement of the polymer chains of the high-molecular-weight polyolefin. Therefore, for melt-kneading the mixture in the present invention, usually, a kneader or a twin-screw kneader capable of giving a strong shearing force to the mixture is preferably used.

The temperature at which the mixture is melt-kneaded is preferably in the range of a temperature at which the solvent starts dissolving the high molecular weight polyolefin (dissolution starting temperature) to + 60 ° C. The temperature is preferably equal to or higher than the dissolution start temperature from the viewpoint of efficiently dispersing the high-molecular-weight polyolefin, and is preferably equal to or lower than the dissolution start temperature + 60 ° C from the viewpoint of preventing the resin from being easily decomposed. When resins having a melting point higher than that of the high-molecular-weight polyolefin are added, kneading is preferably performed at a temperature at which the added resins start melting or higher. In addition, in order to suppress the decomposition of the high molecular weight polyolefin, at the time of kneading after dissolution,
The temperature may be lowered to such an extent that the film characteristics are not deteriorated.

Next, a gel-like molded product containing a crosslinkable resin obtained by extruding the melt-kneaded product into a sheet (resin layer B)
And at least one type of gel-like molded product (resin layer A) containing no crosslinkable resin is laminated to form a laminate.

In the present invention, by laminating two types of gel-like molded products obtained by extruding the melt-kneaded product into a sheet, molecules are entangled between the layers at the interface, and the fusion is strengthened. In addition, since the phase separation proceeds after fusion, a porous structure similar to the bulk is formed at the interface, and an excellent effect that the air permeability is not reduced is exhibited.

The method of extruding the melt-kneaded material into a sheet is as follows.
There is no particular limitation, and examples thereof include a method using an extruder equipped with a T-die or the like.

As a lamination method, either a batch method or a continuous method may be used. In the batch method, for example, at least one type of gel-like molded product can be bonded in an arbitrary order using a biaxial roll. At this time, the temperature of the adhesive surface of the gel is preferably not lower than the temperature at which phase separation starts. When the temperature is lower than the temperature at which the resin is deposited, a solvent such as liquid paraffin emerges on the surface of the gel-like molded product and hinders the adhesion of each layer. . In the continuous method, for example, two or more kneaders can be used to bond together using a roll in the vicinity of a die, or can be bonded by a discharge pressure immediately before a die outlet. In particular, a method of bonding in a die is preferable because it does not involve the entry of impurities or air.

In the present invention, the obtained laminate is desirably sandwiched between metal plates cooled to preferably 0 ° C. or lower, more preferably -10 ° C. or lower, and quenched to form a sheet.

The thickness of the sheet-like molded product thus obtained is usually preferably 0.5 to 20 mm.

Next, the obtained sheet-like molded product is subjected to a stretching treatment. The method of the stretching treatment is not particularly limited,
Ordinary tenter method, roll method or a combination of these methods may be used. In addition, 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, but vertical and horizontal simultaneous stretching is preferred.

The temperature at the time of the stretching treatment is preferably a temperature not higher than the melting point of the high-molecular-weight polyolefin + 5 ° C. from the viewpoint that the uniformity of the stretching is good and sufficient film strength is obtained.

Next, the sheet-like molded product after the stretching treatment is subjected to a desolvation treatment. The solvent removal treatment is a step of forming a porous structure by removing the solvent from the sheet-like molded product, and can be performed, for example, by washing the sheet-like molded product with a solvent to remove the residual solvent. The solvent can be appropriately selected according to the solvent used in the preparation of the resin composition.Specifically, pentane, hexane, heptane, hydrocarbons such as decane, methylene chloride, chlorination of carbon tetrachloride, etc. Examples include volatile solvents such as hydrocarbons, ethers such as diethyl ether and dioxane, and alcohols, and these can be used alone or in combination of two or more. The method of desolvation treatment using such a solvent is not particularly limited, and examples thereof include a method of immersing a sheet-like molded product in a solvent to extract the solvent, a method of showering the solvent to the sheet-like molded product, and the like. . The desolvation treatment may be performed before stretching. For example, the sheet-like composition may be subjected to a desolvation treatment and then subjected to a stretching treatment, or a desolvation treatment may be performed before the stretching treatment and the desolvation treatment may be performed again after the stretching treatment.

In the present invention, a rolling treatment may be further performed before and after the stretching and the desolvation treatment. For example, a sheet-like molded product may be subjected to a rolling treatment as it is, and then subjected to a stretching treatment and a desolvation treatment (the stretching and the desolvation may be performed in any order). Alternatively, a rolling process may be performed between the stretching process and the desolvation process. For example, a desolvation process is performed before the rolling process, and the stretching process and the desolvation process are performed again after the rolling process. May be performed first) to remove the residual solvent.

Next, it is preferable to perform a thermal oxidation treatment of the crosslinkable resin. Specifically, heat treatment is performed in the presence of oxygen or ozone. By performing the heat treatment, all or some of the double bonds derived from the crosslinkable resin disappear, and the crosslinkable resins in the resin layer B of the obtained porous film, or between the crosslinkable resin and the polyolefin, Crosslinking occurs and heat resistance is greatly improved.

The ratio of eliminating the double bond is as follows:
It is appropriately selected in consideration of the desired heat resistance.
A disappearance rate of 0% (calculated based on the size of the IR peak) is preferable. The disappearance of all or a part of the double bonds due to the heat treatment in the presence of oxygen can be confirmed by observing an infrared absorption spectrum, which indicates that the resin layer B has a crosslinked structure. Means.

The atmosphere for the heat treatment is particularly preferably an air atmosphere from the viewpoint of economy and stability. As the heat treatment method, a single-stage heat treatment method in which heat treatment is performed once, a multi-stage heat treatment method in which heat treatment is first performed at a low temperature and then a heat treatment at a higher temperature may be performed, or a temperature-rise heat treatment method in which heat treatment is performed while increasing the temperature Although a heat treatment method may be used, it is desirable to carry out the treatment without impairing the original properties of the porous film such as air permeability. In the case of the single-stage heat treatment method, the temperature is preferably from 40 ° C to 140 ° C, although it depends on the composition of the porous film. Also, when the heat treatment is started at a low temperature and then increased, the heat resistance gradually increases with the crosslinking of the resin layer B of the porous film. Can be exposed to high temperatures without damaging the Therefore, in order to complete the heat treatment in a short time without deteriorating various characteristics, a multi-stage or elevated temperature heat treatment is preferable. The heat treatment time in this case cannot be unconditionally determined because the rate of disappearance of the double bond varies depending on the temperature, but it is preferably 30 minutes or more at 115 ° C., for example.

The initial heat treatment temperature in the multistage heat treatment depends on the composition of the porous film, but is preferably 4
The temperature of the second heat treatment is preferably from 90 to 140 ° C., although it depends on the composition of the porous film. If necessary, heat treatment at a higher temperature and for a shorter time in the third and subsequent stages may be performed. The treatment time depends on the composition of the porous film, but is 3 to 4 for the first heat treatment.
About 8 hours, 0.5-
About 6 hours are preferable. In the case of the elevated temperature heat treatment, the heat treatment may be performed under the same conditions as those of the above-described multi-stage heat treatment. As a specific heat treatment method, a known method such as fixing the four corners of the porous film into the oven, winding into a roll and putting into the oven, or fixing the area with a tenter and continuously passing through the oven is used. Can be

The mechanism of the crosslinking reaction by the heat treatment in the presence of oxygen is complicated and not always clear, but the reason for the improvement in the heat resistance of the porous film is presumed as follows.

First, a polymer radical generated by the action of oxygen is added to a double bond of the crosslinkable resin, and at this time, a crosslinking reaction between the crosslinkable resins or between the crosslinkable resin and the polyolefin is caused. It is thought that this occurs because the structure becomes three-dimensional.

Second, it is conceivable that the C = C double bond of the crosslinkable resin disappears and is converted into a saturated C—C bond, thereby greatly increasing the glass transition temperature. For example,
When polynorbornene is used as the crosslinkable resin, its glass transition temperature is 35 ° C., but when the C ＝ C double bond is hydrogenated and converted into a saturated C—C bond, the glass transition temperature is over one hundred and several tens of degrees Celsius.
It is supposed to be. The reason why the C = C double bond is converted into a saturated CC bond and the glass transition temperature is increased is that the main chain has an aliphatic ring. It is presumed that such a rise in glass transition temperature is also a major factor in having a higher heat resistance than that of the crosslinkable rubber.

Third, since polar groups such as a hydroxyl group, an ester group, and a carboxyl group are generated in the porous film by the oxidizing action, pseudo-crosslinking based on these groups also contributes to improve heat resistance. It seems to be a factor to do.

It is considered that the porous film of the present invention has a great improvement in heat resistance due to the complicated effects of these effects.

In the case of performing the heat treatment, if necessary, irradiation with ultraviolet rays, visible rays, or the like may be performed to promote crosslinking.

In the present invention, the porous film thus obtained is subjected to a heat setting treatment or the like before or after the cross-linking treatment, if necessary, to prevent heat shrinkage of the film, thereby fixing the shape. You may.

The porous film obtained as described above has a high lamination strength and exhibits excellent heat resistance due to the presence of the crosslinked layer. The lamination strength cannot be specified unconditionally because the required strength varies depending on the method of handling the separator. However, most preferably, a non-crosslinked layer (resin layer A) or a crosslinked layer (resin layer B) when a T-peel test is performed. It is sufficient if the strength is such that the in-layer peeling occurs. As an index of heat resistance, the thermal rupture temperature of the porous film is preferably 180 ° C. or higher, more preferably 200 ° C. or higher.

The thickness of the porous film of the present invention is 2
６０60 μm, preferably 5 to 45 μm, and the thickness of each layer is 1 to 50 μm, preferably 2 to 40 μm.
μm, porosity is 20 to 80%, preferably 25 to 75
%, Air permeability is 100 to 1000 sec / 100 cm ³ ,
Preferably, 200 to 900 sec / 100 cm ³ , SD
Temperature is 120-150 ° C, preferably 130-140 ° C
Are respectively desirable. Lamination strength, thermal rupture temperature, thickness, porosity, and air permeability can be measured using the methods described in Examples described later.

The SD (shutdown) temperature can be measured as follows. That is, 25 mm
It has a cylindrical test chamber of φ, uses a SUS cell that can seal the test chamber, the lower electrode is 20 mmφ, and the upper electrode is 10 mm.
A platinum plate of mmφ (thickness: 1.0 mm) is used. 24m
A measurement sample punched to mφ is immersed in an electrolyte to impregnate the electrolyte, sandwiched between electrodes, and set in a cell. The electrodes are applied with a constant surface pressure by a spring provided in the cell. As the electrolytic solution, a solution obtained by dissolving lithium borofluoride to a concentration of 1.0 mol / L in a solvent in which propylene carbonate and dimethoxyethane are mixed at a volume ratio of 1: 1 is used. A thermocouple thermometer and an ohmmeter are connected to this cell so that temperature and resistance can be measured.
Put into a constant temperature oven and measure the temperature and resistance. 100 ~
The average temperature rise rate at 150 ° C. is 10 ° C./min, and the temperature at which the resistance reaches 100 Ω · cm ²
D temperature.

The porous film of the present invention having such characteristics has a resin layer A (non-crosslinked layer) and a resin layer B (crosslinked layer).
Has a high laminating strength, and has a high thermal rupture temperature because the crosslinked layer has sufficient heat resistance, and can be suitably used for a battery separator and the like.

The battery can be assembled by using the porous film of the present invention in a state of being interposed between the positive electrode and the negative electrode, similarly to the conventional separator. At this time, the materials of the positive electrode, the negative electrode, the battery case, the electrolytic solution and the like and the arrangement structure of these components are not required to be exceptional, and may be the same as conventional ones, for example, as shown in JP-A-63-205048. May be street.

Further, the capacitor can be assembled by using the porous film of the present invention in a state of being interposed between a pair of electrodes, similarly to a conventional separator. At this time, the materials of the electrodes, the electrolytic solution, the case, and the like and the arrangement structure of these components are not required to be exceptional, and may be the same as the conventional one. For example, in an electric double layer capacitor, an activated carbon electrode formed of polytetrafluoroethylene (PTFE) as a binder can be used as an electrode, and a solution obtained by adding 0.5 M Et ₄ BF ₄ to propylene carbonate can be used as an electrolyte.

[0051]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to only these Examples. In addition, about various characteristics, it measures as follows.

(Melting point) Using a differential scanning calorimeter “DSC-200” manufactured by Seiko Denshi Kogyo KK, the temperature was changed from room temperature to 200 ° C.
The temperature is raised at a rate of 10 ° C./min up to this temperature, and the onset temperature of the endothermic peak in this temperature rising process is defined as the melting point.

(Weight average molecular weight) A gel permeation chromatograph "GPC-150C" manufactured by Waters was used, o-dichlorobenzene was used as a solvent, and "Shodex-80M" manufactured by Showa Denko KK was used as a column. 13
Measure at 5 ° C. Data processing is performed using a data processing system manufactured by TRC. The molecular weight is calculated based on polystyrene.

(Film Thickness) Measured using a 1/10000 thickness gauge.

(Porosity) The porous film to be measured is cut out in a circular shape having a diameter of 6 cm, the volume and weight are obtained, and the obtained result is calculated by the following equation.

Porosity (% by volume) = 100 × [Volume (cm)
³ ) -weight (g) / average density of resin component (g / c)
m ³ )] / volume (cm ³ )

(Air permeability (Gurley value)) JIS P811
7 was measured.

(Thermal Rupture Temperature (Heat Resistance)) A strip sample having a width of 3 mm was attached with a chuck space of 10 mm, and a thermal stress strain analyzer “TMA / SS10” manufactured by Seiko Electronics Co., Ltd.
0 "and the temperature was raised at a rate of 2 ° C / min.
Evaluation was made from the state at the time of the temperature rise. When the strip-shaped sample was broken, the temperature at this time was defined as the thermal break temperature.

(Lamination strength) As a test piece, a porous film was cut into a width of 1 cm, and T was cut at a speed of 300 mm / min.
A peel test was performed. The temperature was room temperature (25 ° C.). The value at which the peel strength became almost steady was defined as the lamination strength.

Example 1 High molecular weight polyethylene having a weight average molecular weight of 2 × 10 ⁶ (melting point: 134 ° C., the same applies hereinafter) and 30% by weight and high molecular weight polyethylene having a weight average molecular weight of 2 × 10 ⁵ (melting point: 127 ° C.)
60% by weight of a powder of a ring-opening polymer of norbornene (manufactured by Zeon Corporation, Nosorex NB, weight average molecular weight 2)
× 10 ⁶ or more, the same applies hereinafter) 20 parts by weight of a polyolefin composition consisting of 10% by weight and liquid paraffin (freezing point: −
80 parts by weight of a kinematic viscosity at 15 ° C. and 40 ° C .: 59 cst;
The mixture was melt-kneaded using a twin-screw kneader at ℃. Furthermore, 33% by weight of a high molecular weight polyethylene having a weight average molecular weight of 2 × 10 ^{6 and} a high molecular weight polyethylene 67 having a weight average molecular weight of 2 × 10 ⁵ were used.
In a slurry, 20 parts by weight of a polyolefin composition of 80% by weight and 80 parts by weight of liquid paraffin were uniformly mixed and melt-kneaded at 160 ° C. using a twin-screw kneader. 2 above
Two kinds of the melt-kneaded material were extruded from a die, and the obtained laminate (thickness: 10 mm) was sandwiched between metal plates cooled to 0 ° C., and rapidly cooled into a sheet having a thickness of 5 mm. At this time, the thickness of each layer was 2.5 mm. This quenched sheet is
After heat pressing at 0.7 ° C. until the thickness becomes 0.7 mm, desolvation treatment was performed using heptane.
Simultaneous vertical and horizontal biaxial stretching was performed 5 × 3.5 times. Thereafter, the obtained porous film was heat-treated in air at 85 ° C. for 1 hour and further at 115 ° C. for 1 hour to obtain a porous film of the present invention. When the infrared absorption spectrum of the obtained porous film was observed, 97% of the double bonds of the ring-opened polymer of norbornene had disappeared.

Example 2 High molecular weight polyethylene 90 having a weight average molecular weight of 2 × 10 ⁶
20 parts by weight of a polyolefin composition consisting of 10% by weight of a powder of a ring-opening polymer of norbornene and 80 parts by weight of liquid paraffin are uniformly mixed in a slurry form at 160 ° C.
Was melt-kneaded using a twin-screw kneader. Further, 20 parts by weight of a high-molecular-weight polyethylene having a weight-average molecular weight of 2 × 10 ⁶ and 80 parts by weight of liquid paraffin were uniformly mixed in a slurry form, and melt-kneaded at 160 ° C. using a biaxial kneader. 2 above
Two kinds of the melt-kneaded material were extruded from a die, and the obtained laminate (thickness: 10 mm) was sandwiched between metal plates cooled to 0 ° C., and rapidly cooled into a sheet having a thickness of 5 mm. At this time, the thickness of each layer was 2.5 mm. This quenched sheet is 11
Heat press at 5 ° C until the thickness becomes 0.7 mm.
The film was stretched simultaneously and vertically and horizontally by 3.5 × 3.5 at 25 ° C., and subjected to a solvent removal treatment using heptane. Then, the obtained porous film was further heated at 85 ° C.
C. for 1 hour to obtain a porous film of the present invention.
When the infrared absorption spectrum of the obtained porous film was observed, 99% of the double bonds of the ring-opened polymer of norbornene had disappeared.

Comparative Example 1 High molecular weight polyethylene 33 having a weight average molecular weight of 2 × 10 ⁶
In a slurry, 20 parts by weight of a polyolefin composition composed of 67% by weight of a high-molecular-weight polyethylene having a weight-average molecular weight of 2 × 10 ⁵ and 80 parts by weight of liquid paraffin are uniformly mixed in a slurry form, and the mixture is mixed at 160 ° C. using a biaxial kneader. The mixture was melt-kneaded and extruded from a die. The obtained gel-like molded product was cooled to 0 ° C.
And rapidly quenched into a sheet having a thickness of 3 mm. The quenched sheet is heated at 115 ° C. to a thickness of 0.4
mm, and subjected to a desolvation treatment using heptane, followed by simultaneous vertical and horizontal biaxial stretching of 3.5 × 3.5 at 115 ° C.

The uncrosslinked film was treated under nitrogen atmosphere for 30 minutes.
Irradiation with MRad electron beam was performed to obtain a crosslinked film. The crosslinked film and the uncrosslinked film are each at 85 ° C. for 1 hour,
After heat-setting at 115 ° C. for 1 hour to prevent heat shrinkage, the sheets were superposed one by one, at a temperature of 100 ° C. and a pressure of 0.1 ° C.
Lamination was performed with a laminator under the condition of 3 kg / cm (linear pressure) to obtain a porous film. Since no crosslinkable resin was used in the obtained porous film, there was no change in infrared absorption spectrum observation.

Table 1 shows the film thickness, porosity, air permeability, thermal rupture temperature and lamination strength of the porous films obtained in Examples 1 and 2 and Comparative Example 1.

[0065]

[Table 1]

From the results shown in Table 1, the porous films of Examples 1 and 2 have higher thermal rupture temperatures and higher lamination strengths than the porous films of Comparative Example 1 laminated and laminated. , It can be seen that the cross-linking by the addition of the cross-linkable resin can obtain a porous film having better heat resistance than the electron beam irradiation.

[0067]

According to the present invention, a porous film having a structure having at least one cross-linked layer and at least one non-cross-linked layer, having high lamination strength between the layers and excellent heat-resistant film rupture properties at high temperatures. Can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 65/00 C08L 65/00 H01M 2/16 H01M 2/16 L // C08J 9/26 CES C08J 9 / 26 CES 102 102 (72) Inventor Mutsuko Yamaguchi 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Yoshihiro Uetani 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Hideyuki Emori 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 4F074 AA09 AA16 AA17 AB01 BB25 CA03 CB03 CB16 CC02Y CC02Z CC06Z DA02 DA49 4F100 AK01B AK02B AK03A AK03B04 AK03B04A AL05B BA02 BA08 BA10A BA10B BA16 DJ10A DJ10B EJ05B EJ37 GB43 JA07A JA07B JJ03 JK01 JK06 JM10A JM10B YY00A YY00B 4J002 AC032 BB031 BB121 BB171 CE002 GQ00 5H021 CC04 EE02 EE04

Claims (10)

[Claims] 1. Layer containing polyolefin (resin layer A)
And a layer (resin layer B) containing both a polyolefin and a crosslinkable resin. 2. The porous film according to claim 1, wherein the polyolefins of the resin layers A and B each contain a high molecular weight polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more. 3. The porous film according to claim 1, wherein the polyolefin is polyethylene. 4. The resin according to claim 1, wherein the crosslinkable resin has a double bond, and a hydrogen atom is bonded to the α-position carbon.
The porous film according to any one of the above. 5. The porous film according to claim 1, wherein the crosslinkable resin is polynorbornene or polybutadiene. 6. The porous film according to claim 1, wherein the resin layer B has a crosslinked structure. 7. The porous film according to claim 6, wherein all or some of the double bonds of the crosslinkable resin have disappeared. 8. A gel-like molded product containing a polyolefin,
A method for producing a porous film, comprising laminating a polyolefin and a gel-like molded product containing both of a crosslinkable resin and performing a film forming treatment. 9. A battery comprising the porous film according to claim 1. 10. A capacitor using the porous film according to claim 1.