JP4338164B2 - Porous film and method for producing the same - Google Patents

Description

【００６６】
表１の結果より、実施例１及び２の多孔質フィルムは、ラミネート積層した比較例１の多孔質フィルムに比べ、熱破断温度が高く、また積層強度が高いため、非架橋層内で剥離が発生したことから、架橋性樹脂添加による架橋の方が、電子線照射よりも耐熱性に優れた多孔質フィルムを得られることがわかる。
【００６７】
【発明の効果】
本発明により、架橋層および非架橋層をそれぞれ少なくとも１層存在する構造を有し、それらの層間の積層強度が高く、且つ高温で優れた耐熱膜破断性を有する多孔質フィルムを得ることができる。[0001]
BACKGROUND OF THE INVENTION
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 that is preferably used as a battery separator or the like that is disposed between the positive and negative electrodes of a battery to isolate them, a method for producing the same, a battery using the porous film, and a capacitor.
[0002]
[Prior art]
In recent years, lithium batteries that are lightweight as batteries, have high electromotive force and high energy, and have low self-discharge are attracting attention in order to cope with cordless electronic devices. A separator is provided between the positive electrode and the negative electrode of the lithium battery to prevent a short circuit between the positive electrode and the negative electrode. As the separator, a large number of micropores are formed to ensure the permeation of ions between the positive electrode and the negative electrode. A porous film is used. Among them, what has a so-called shutdown function (SD function) in which when an abnormal current occurs due to an incorrect connection of the battery, the resin is thermally deformed as the internal temperature of the battery rises to block 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 polyethylene microporous film or a microporous film having a multilayer structure of polyethylene and polypropylene is known.
[0003]
However, due to recent advances in lithium ion secondary batteries, etc., not only the SD function, but also the heat resistant element, that is, when the temperature further rises after shutdown, the separator itself melts or melts. If it breaks, there is a risk of battery ignition and explosion. Therefore, a separator that does not break or break even at higher temperatures is desired. In particular, as the capacity of the battery and the internal resistance of the battery decrease, it becomes more and more important because elements that increase heat generation increase.
[0004]
As a method for achieving both heat resistance and SD characteristics, as disclosed in the specification of Japanese Patent No. 2768745, at least two polyethylene porous films are laminated, and at least of these laminated porous films. It has been found that a separator in which one sheet is crosslinked and at least one sheet is uncrosslinked is effective. In this method, lamination was possible without laminating micropores by laminating a porous film in a specific temperature range, but the laminating temperature was low, so the lamination strength between the films was not sufficiently high, and peeling was not possible. In order to prevent this, it was necessary to pay attention to the handling of the film after production. Moreover, for example, when an electron beam is irradiated after lamination, a non-crosslinked layer cannot be obtained, and there arises a problem that heat resistance and SD characteristics cannot be compatible.
[0005]
Therefore, in order to obtain a separator having both heat resistance and SD characteristics, a porous film that is porous after lamination, has a crosslinked layer and a non-crosslinked layer at least one layer, and does not peel between the layers, and a method for producing the same are desired. It was.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a porous film having at least one cross-linked layer and a non-cross-linked layer, a high lamination strength between those layers, and an excellent anti-breaking film rupture resistance even at high temperatures, the production method thereof, It is providing the battery and capacitor which use a porous film.
[0007]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above-mentioned problems, the present inventors have found that high lamination strength can be obtained even after film formation by laminating gel-like molded products containing high-molecular-weight polyolefins before phase separation. . Further, the present inventors have found that by adding a crosslinkable resin to at least one layer, crosslinking occurs by heat treatment after film formation and the like and a high heat resistant layer is formed.
[0008]
  That is, the gist of the present invention is as follows.
[1] A porous film formed by laminating a layer containing polyolefin (resin layer A) and a layer containing both polyolefin and a crosslinkable resin (resin layer B)The porous film is a resin in which the crosslinkable resin has a double bond and a hydrogen atom is bonded to the α-position carbon.,
[2] The porous film according to [1], wherein the resin layer B has a crosslinked structure;
[3] A method for producing a porous film, characterized by laminating a gel-like molded product containing polyolefin and a gel-like molded product containing both polyolefin and a crosslinkable resin to form a film.The method for producing a porous film, wherein the crosslinkable resin has a double bond and a hydrogen atom is bonded to the α-position carbon.,
[4] A battery using the porous film according to [1] or [2].,
[5] A capacitor using the porous film according to [1] or [2]And
[6] Battery separator comprising the porous film of [1] or [2]
It is about.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The porous film of the present invention is formed by laminating a layer containing polyolefin (resin layer A) and a layer containing both 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.
[0010]
The polyolefin used in the resin layers A and B preferably has a weight average molecular weight of 5 × 10.^FiveExamples of the high molecular weight polyolefin include a homopolymer obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and the like, a blend thereof, and the like. Among them, high molecular weight polyethylene that has excellent mechanical strength and high crystallinity is desirable as a material. The weight average molecular weight of the high molecular weight polyolefin is further 1 × 10⁶The above ultra-high molecular weight is preferable, 1.5 × 10⁶The above is more preferable.
[0011]
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, and more preferably 20 to 100% by weight. The lower limit of the content is preferably 5% by weight or more from the viewpoint of sufficient strength of the film formed.
[0012]
The resin layer A has a weight average molecular weight of 5 × 10 5 as other resins.^FiveLess than polyolefin, thermoplastic elastomer, 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 Toray DuPont), “Septon” (manufactured by Kuraray Co., Ltd.), and the like. Examples of the hydrogenated polybutadiene resin include “DYNARON” (manufactured by Nippon Synthetic Rubber). Examples of the modified olefin resin include “Evaflex” (manufactured by Mitsui DuPont Polychemical Co., Ltd.), “Modiper” (manufactured by Nippon Oil & Fats Co., Ltd.), and the like. Examples of EPDM include “Esprene” (manufactured by Sumitomo Chemical Co., Ltd.).
[0013]
The content of other resins 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.
[0014]
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 α-position carbon, and can form a crosslinked structure by at least heat treatment. Not. For example, an unsaturated condensed alicyclic compound derivative is obtained by ring-opening polymerization, and a resin having an aliphatic ring and a double bond derived from the monomer unit in the main chain (for example, polynorbornene) or a terminal Resin having a structure in which a methylene group is bonded to the main chain (for example, polybutadiene) 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 Is mentioned. Among these, from the viewpoint of dispersibility, polynorbornene is preferable, and the weight average molecular weight is 2 × 10.⁶The above polynorbornene is particularly preferred.
[0015]
The content of the crosslinkable resin in the resin layer B is 1 to 50% by weight, preferably 3 to 40% by weight, and more preferably 5 to 35% by weight. The content is preferably 1% by weight or more from the viewpoint of effective addition of the crosslinkable resin, and from the viewpoint of obtaining a high air permeability with a high porosity of the porous film, it is 50% by weight or less. preferable. Therefore, the content of polyolefin in the resin layer B is 50 to 99% by weight, preferably 60 to 97% by weight, more preferably 65 to 95% by weight.
[0016]
In the present invention, the order in which the resin layers A and B having these components are laminated is not particularly limited, but the resin layers A and B are preferably laminated alternately. 1-50 micrometers is preferable and, as for the thickness of each layer, 5-50 micrometers is more preferable. In addition, since each of these layers is laminated in a molten state, it is considered that molecules of each other layer penetrate each other and are firmly bonded to the whole.
[0017]
The porous film of the present invention is obtained by, for example, extruding a mixture obtained by adding a solvent to a resin component containing polyolefin or a resin component containing both polyolefin and a crosslinkable resin, and then extruding it into a sheet. It can be obtained by subjecting a sheet-like molded product obtained by laminating the two kinds of gel-like molded products to a film forming process including a stretching process and a solvent removal process. In the present invention, the film formation treatment refers to a treatment step of forming a porous film in which the resin layer A and the resin layer B are laminated by a treatment such as stretching, desolvation, and rolling if necessary. .
[0018]
The solvent is not particularly limited as long as it has excellent solubility in each resin component. For example, nonane, decane, undecane, dodecane, decalin, liquid paraffin and other aliphatic or cyclic hydrocarbons, or mineral oils having boiling points corresponding to these. A non-volatile solvent such as liquid paraffin is preferable.
[0019]
The compounding amount of the resin component and the solvent varies depending on the type of resin, solubility, kneading temperature, etc., and thus cannot be determined unconditionally. However, as long as the resulting slurry mixture can be melt-kneaded and formed into a sheet shape There is no particular limitation. For example, the blending amount of the resin component is preferably 5 to 30% by weight in the mixture, more preferably 10 to 30% by weight, and still more preferably 10 to 25% by weight. The blending amount of the resin component is preferably 5% by weight or more from the viewpoint of improving the strength of the obtained porous film, and the polyolefin can be sufficiently dissolved in a solvent and kneaded to near the fully extended state. From the viewpoint of obtaining sufficient entanglement of the polymer chain, it is preferably 30% by weight or less.
[0020]
The amount of the solvent in the mixture is preferably 70 to 95% by weight, more preferably 70 to 90% by weight, and even more preferably 75 to 90% by weight. The blending amount is preferably 70% by weight or more from the viewpoint of moderate kneading torque, rolling and stretching stress, and excellent productivity, and necking-in does not occur at the die outlet when extrusion, and molding is easy. From this viewpoint, the content is preferably 95% by weight or less.
[0021]
In addition, an additive such as an antioxidant, an ultraviolet absorber, a dye, a nucleating agent, a pigment, and an antistatic agent may be added to the mixture as necessary, as long as the object of the present invention is not impaired. it can.
[0022]
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, in the melt kneading of the mixture in the present invention, a kneader or a biaxial kneader capable of giving a strong shearing force to the mixture is usually preferably used.
[0023]
The temperature at which the mixture is melt-kneaded is preferably within the range of the temperature at which the solvent starts to dissolve the high-molecular-weight polyolefin (dissolution start 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 hardly causing the resin to decompose. In addition, when a resin having a melting point higher than that of the high-molecular-weight polyolefin is added, it is preferable to knead at a temperature higher than the temperature at which the added resin starts to dissolve. In order to suppress decomposition of the high molecular weight polyolefin, the temperature may be lowered to the extent that the film characteristics are not deteriorated during kneading after dissolution.
[0024]
Next, at least one kind of gel-like molded product (resin layer B) containing a crosslinkable resin obtained by extruding the melt-kneaded product into a sheet shape and a gel-like molded product (resin layer A) containing no crosslinkable resin are obtained. Laminate one by one to form a laminate.
[0025]
In the present invention, by laminating two types of gel-like products obtained by extruding the melt-kneaded material into a sheet, entanglement of molecules between layers is formed at the interface, and the fusion is strengthened. Since the separation proceeds after fusion, a porous structure similar to the bulk is formed at the interface, and the excellent effect of not reducing the air permeability is exhibited.
[0026]
The method for extruding the melt-kneaded material into a sheet is not particularly limited, and examples thereof include a method using an extruder equipped with a T die or the like.
[0027]
The lamination method may be either a batch method or a continuous method. 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 falls below 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 inhibits the adhesion of each layer. . In the continuous type, for example, two or more kneaders can be used and bonded together using a roll in the vicinity of the die, or bonded at a discharge pressure just before the die outlet. In particular, a method of bonding in a die is preferable because there is no biting of impurities or air.
[0028]
In the present invention, the obtained laminate is preferably sandwiched between metal plates cooled to 0 ° C. or less, more preferably −10 ° C. or less, and then rapidly cooled to form a sheet.
[0029]
The thickness of the sheet-like molded product thus obtained is usually preferably 0.5 to 20 mm.
[0030]
Next, the obtained sheet-like molded product is stretched. The stretching method is not particularly limited, and may be a normal tenter method, a roll method, or a combination of these methods. In addition, any method such as uniaxial stretching or biaxial stretching can be applied. In the case of biaxial stretching, either longitudinal or transverse simultaneous stretching or sequential stretching may be used, but longitudinal and transverse simultaneous stretching is preferable.
[0031]
The temperature during the stretching treatment is preferably a temperature of the melting point of the high-molecular-weight polyolefin + 5 ° C. or less from the viewpoint of good uniformity of stretching and sufficient film strength.
[0032]
Next, a solvent removal treatment is performed on the sheet-like molded product after the stretching treatment.
The solvent removal treatment is a step of removing the solvent from the sheet-like molded product to form a porous structure, and can be performed, for example, by washing the sheet-like molded product with a solvent to remove the remaining solvent. The solvent can be appropriately selected according to the solvent used for the preparation of the resin composition. Specifically, hydrocarbons such as pentane, hexane, heptane and decane, chlorination such as methylene chloride and carbon tetrachloride, etc. Examples include hydrocarbons, ethers such as diethyl ether and dioxane, and readily volatile solvents such as alcohols. These may be used alone or in admixture of two or more. The method of desolvation treatment using such a solvent is not particularly limited, and examples thereof include a method of extracting a solvent by immersing a sheet-like molded product in a solvent, a method of showering the solvent on the sheet-like molded product, and the like. . The solvent removal treatment may be performed before stretching. For example, the sheet-like composition may be subjected to a solvent removal treatment and then subjected to a stretching treatment. Alternatively, the solvent removal treatment may be performed before the stretching treatment, and the solvent removal treatment may be performed again after the stretching treatment.
[0033]
In the present invention, rolling treatment may be further performed before and after the stretching and desolvation treatment. For example, the sheet-shaped molded product may be subjected to a rolling treatment as it is and then subjected to a stretching treatment and a solvent removal treatment (any of stretching and solvent removal may be performed first). Alternatively, the rolling treatment may be performed between the stretching treatment and the solvent removal treatment. For example, the solvent removal treatment is performed before the rolling treatment, and the stretching treatment and the solvent removal treatment are again performed after the rolling treatment (the order of the stretching and the solvent removal is any May be performed first) to remove the residual solvent.
[0034]
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 part of the double bond derived from the crosslinkable resin disappears, and in the resin layer B of the resulting porous film, the crosslinkable resins or between the crosslinkable resin and the polyolefin Cross-linking occurs and heat resistance is greatly improved.
[0035]
In addition, although the ratio which makes the said double bond lose | disappear is suitably selected in consideration of desired heat resistance, the disappearance rate of 80 to 100% (calculated based on the magnitude | size of IR peak) is preferable.
The disappearance of all or part of the double bond by heat treatment in the presence of oxygen can be confirmed by observing the infrared absorption spectrum. This indicates that the resin layer B has a crosslinked structure. I mean.
[0036]
The atmosphere during the heat treatment is particularly preferably an air atmosphere from the viewpoints of economy and stability. The heat treatment method may be a one-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 heat treatment is performed at a higher temperature, or a temperature increase method in which heat treatment is performed while the temperature is increased. Although a heat treatment method may be used, it is desirable to perform the treatment without impairing the original characteristics of the porous film such as air permeability. In the case of the one-stage heat treatment method, although it depends on the composition of the porous film, it is preferably 40 ° C to 140 ° C. In addition, if heat treatment is started from a low temperature and then the treatment temperature is raised, the heat resistance gradually improves with the cross-linking of the resin layer B of the porous film. It becomes possible to be exposed to high temperature without impairing Therefore, in order to complete the heat treatment in a short time without impairing various characteristics, a multistage type or a temperature rising type heat treatment method is preferable. The heat treatment time in this case cannot be determined unconditionally because the rate of disappearance of the double bond varies depending on the temperature. For example, if it is 115 ° C., it is preferably 30 minutes or longer.
[0037]
The first heat treatment temperature of the multi-stage heat treatment method depends on the composition of the porous film, but preferably 40 to 90 ° C. The second heat treatment temperature depends on the composition of the porous film, but preferably Is 90-140 ° C. Moreover, you may perform the heat processing after the 3rd step | paragraph after a further short time at further high temperature as needed. The treatment time depends on the composition of the porous film, but is preferably about 3 to 48 hours for the first heat treatment and about 0.5 to 6 hours for the heat treatment at the second higher temperature. In the case of the temperature raising type heat treatment method, it may be performed under the conditions according to the multistage heat treatment method.
As a specific heat treatment method, a known method such as fixing the four corners of the porous film into the oven, winding it into a roll and putting it into the oven, fixing the area with a tenter and continuously passing through the oven is used. It is done.
[0038]
The mechanism of the crosslinking reaction by heat treatment in the presence of oxygen is complicated and not necessarily clear, but the reason for the improvement of the heat resistance of the porous film is estimated as follows.
[0039]
First, a polymer radical generated by the action of oxygen is added to the double bond of the crosslinkable resin, and at this time, a crosslink reaction occurs between the crosslinkable resins or between the crosslinkable resin and the polyolefin. It is thought that this is because of the three-dimensionalization.
[0040]
Secondly, it is conceivable that the glass transition temperature is greatly increased by the disappearance of the C═C double bond of the crosslinkable resin and conversion to a saturated C—C bond. 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 to a saturated C—C bond, it becomes hundreds of tens of ° C. It is supposed to be. The reason why the C = C double bond is converted to a saturated C—C bond and the glass transition temperature is increased is because the main chain has an aliphatic ring, and the porous film after treatment in the present invention is usually used. Such a rise in glass transition temperature is presumed to be a major factor in having higher heat resistance than that of the crosslinkable rubber.
[0041]
Thirdly, since polar groups such as hydroxyl groups, ester groups, and carboxyl groups are generated in the porous film due to the oxidation action, pseudo-crosslinking based on these contributes to the factor that improves heat resistance. It seems to have become.
[0042]
In the porous film of the present invention, it is considered that the heat resistance is greatly improved by complicatedly entwining these functions and effects.
[0043]
Moreover, when performing the said heat processing, an ultraviolet-ray, visible light, etc. may be irradiated as needed, and bridge | crosslinking may be accelerated | stimulated.
[0044]
In the present invention, the porous film obtained in this way may be subjected to heat-setting treatment or the like for preventing thermal shrinkage of the film as necessary before or after the crosslinking treatment, and the shape may be fixed. .
[0045]
The porous film obtained as described above has high lamination strength and exhibits excellent heat resistance due to the presence of a crosslinked layer. Since the required strength differs depending on the separator handling method, the lamination strength cannot be defined unconditionally, but most preferably when a T peel test is performed, a non-crosslinked layer (resin layer A) or a crosslinked layer (resin layer B) It is sufficient if the strength is sufficient to cause delamination. As an index of heat resistance, the thermal fracture temperature of the porous film is preferably 180 ° C. or higher, and more preferably 200 ° C. or higher.
[0046]
The thickness of the porous film of the present invention is 2 to 60 μm, preferably 5 to 45 μm. The thickness of each layer is 1 to 50 μm, preferably 2 to 40 μm, and the porosity is 20 to 80%, preferably Is 25-75%, air permeability is 100-1000sec / 100cm^Three, Preferably 200 to 900 sec / 100 cm^ThreeThe SD temperature is desirably 120 to 150 ° C, preferably 130 to 140 ° C. Lamination strength, thermal rupture temperature, thickness, porosity and air permeability can be measured using the methods described in the examples described later.
[0047]
The SD (shutdown) temperature can be measured as follows. That is, a SUS cell having a cylindrical test chamber of 25 mmφ and capable of sealing the test chamber is used, and a platinum plate (thickness: 1.0 mm) of 20 mmφ is used for the lower electrode and 10 mmφ is used for the upper electrode. A measurement sample punched to 24 mmφ is immersed in an electrolytic solution, impregnated with the electrolytic solution, sandwiched between electrodes, and set in a cell. A certain surface pressure is applied to the electrode 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 a resistance meter are connected to the cell so that the temperature and resistance can be measured. The temperature and resistance are measured by placing the cell in a 180 ° C. thermostat. The average temperature increase rate from 100 to 150 ° C. is 10 ° C./min, and this measurement shows that the resistance is 100 Ω · cm.²The temperature at which the temperature is reached is defined as the SD temperature.
[0048]
The porous film of the present invention having such characteristics has a high lamination strength between the resin layer A (non-crosslinked layer) and the resin layer B (crosslinked layer), and the crosslinked layer has sufficient heat resistance, so that the heat breaking temperature. And can be suitably used for battery separators and the like.
[0049]
Like the conventional separator, the porous film of the present invention can be used in the state of being interposed between the positive electrode and the negative electrode to assemble a battery. In this case, the material of the positive electrode, the negative electrode, the battery case, the electrolytic solution, etc. and the arrangement structure of these components are not required to be special, and may be the same as the conventional one, for example, as disclosed in JP-A-63-205048. May be street.
[0050]
The porous film of the present invention can be used in the state of being interposed between a pair of electrodes in the same manner as a conventional separator to assemble a capacitor. In this case, the material of the electrode, electrolyte, case, etc. and the arrangement structure of these components are not required to be special, and may be the same as in the past. For example, in an electric double layer capacitor, an activated carbon electrode formed by using polytetrafluoroethylene (PTFE) as a binder as an electrode, and 0.5 M Et in propylene carbonate as an electrolyte_FourBF_FourA solution to which can be added can be used.
[0051]
【Example】
The present invention will be described in more detail based on examples and comparative examples, but the present invention is not limited to only such examples. Various characteristics are measured as follows.
[0052]
(Melting point)
Using a differential scanning calorimeter “DSC-200” manufactured by Seiko Denshi Kogyo Co., Ltd., the temperature was raised from room temperature to 200 ° C. at a rate of 10 ° C./min. The onset temperature of the endothermic peak in this temperature rising process was defined as the melting point. To do.
[0053]
(Weight average molecular weight)
A gel permeation chromatograph “GPC-150C” manufactured by Waters Co., Ltd. is used, o-dichlorobenzene is used as a solvent, and “Shodex-80M” manufactured by Showa Denko KK is used as a column at 135 ° C. Data processing is performed using a data processing system manufactured by TRC. The molecular weight is calculated based on polystyrene.
[0054]
(Film thickness)
It was measured with a 1/10000 thickness gauge.
[0055]
(Porosity)
A porous film to be measured is cut out into a circle having a diameter of 6 cm, and its volume and weight are obtained, and calculation is performed using the following formula from the obtained results.
[0056]
Porosity (volume%) = 100 × [volume (cm^Three) -Weight (g) / average density of resin component (g / cm^Three]] / Volume (cm^Three)
[0057]
(Air permeability (Gurley value))
It measured based on JISP8117.
[0058]
(Heat rupture temperature (heat resistance))
A strip-shaped sample having a width of 3 mm was attached with a chuck interval of 10 mm, set in a thermal stress strain analyzer “TMA / SS100” manufactured by Seiko Electronics, and heated at a temperature rising rate of 2 ° C./min. Evaluation was made based on the temperature rising state, and when the strip-shaped sample broke, the temperature at this time was defined as the heat breaking temperature.
[0059]
(Lamination strength)
A porous film was cut into a width of 1 cm as a test piece, and a T peel test was performed at a speed of 300 mm / min. The temperature was room temperature (25 ° C.). The value at which the peel strength became almost steady was taken as the lamination strength.
[0060]
Example 1
Weight average molecular weight 2 × 10⁶High molecular weight polyethylene (melting point: 134 ° C., hereinafter the same) 30% by weight and weight average molecular weight 2 × 10^FiveHigh molecular weight polyethylene (melting point: 127 ° C.) 60% by weight, ring-opening polymer powder of norbornene (manufactured by Nippon Zeon Co., Ltd., Nosolex NB, weight average molecular weight 2 × 10⁶Above, the same shall apply hereinafter) 20 parts by weight of a polyolefin composition comprising 10% by weight and 80 parts by weight of liquid paraffin (solidifying point: −15 ° C., kinematic viscosity at 40 ° C .: 59 cst, the same shall apply hereinafter) in a slurry state, Melt kneading was performed at 160 ° C. using a biaxial kneader. Furthermore, the weight average molecular weight 2 × 10⁶High molecular weight polyethylene 33% by weight and weight average molecular weight 2 × 10^Five20 parts by weight of a polyolefin composition consisting of 67% by weight of high molecular weight polyethylene and 80 parts by weight of liquid paraffin were uniformly mixed in a slurry state and melt kneaded at 160 ° C. using a biaxial kneader. Two layers of the above-mentioned two kinds of melt-kneaded products 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 shape having a thickness of 5 mm. At this time, the thickness of each layer was 2.5 mm. This quenched sheet is heat-pressed at 115 ° C. until the thickness becomes 0.7 mm, and after solvent removal using heptane, simultaneous longitudinal and transverse biaxial stretching is performed at 115 ° C. to 3.5 × 3.5 times. went. 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, the double bond of the norbornene ring-opening polymer was 97% lost.
[0061]
Example 2
Weight average molecular weight 2 × 10⁶20 parts by weight of a polyolefin composition comprising 90% by weight of a high molecular weight polyethylene and 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 state, and a biaxial kneader at 160 ° C. Was melt-kneaded. Furthermore, the weight average molecular weight 2 × 10⁶20 parts by weight of high molecular weight polyethylene and 80 parts by weight of liquid paraffin were uniformly mixed in a slurry state and melt-kneaded at 160 ° C. using a biaxial kneader. Two layers of the above-mentioned two types of melt-kneaded products 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. The thickness of each layer at this time was 2.5 mm. This quenched sheet was heat-pressed at 115 ° C. until the thickness became 0.7 mm, and was simultaneously biaxially stretched 3.5 × 3.5 times at 125 ° C. and subjected to solvent removal using heptane. Thereafter, the obtained porous film was heat-treated in air at 85 ° C. for 1 hour and further at 130 ° C. for 1 hour to obtain a porous film of the present invention. In addition, when the infrared absorption spectrum of the obtained porous film was observed, 99% of the double bond of the norbornene ring-opening polymer disappeared.
[0062]
Comparative Example 1
Weight average molecular weight 2 × 10⁶High molecular weight polyethylene 33% by weight and weight average molecular weight 2 × 10^Five20 parts by weight of a polyolefin composition comprising 67% by weight of high molecular weight polyethylene and 80 parts by weight of liquid paraffin were uniformly mixed in a slurry state, melt-kneaded at 160 ° C. using a twin-screw kneader, and extruded from a die. . The obtained gel-like molded product was sandwiched between metal plates cooled to 0 ° C. and rapidly cooled into a sheet having a thickness of 3 mm. This quenched sheet was heat-pressed at 115 ° C. until the thickness became 0.4 mm, and after solvent removal using heptane, simultaneous longitudinal and transverse biaxial stretching at 115 ° C. to 3.5 × 3.5 times was performed. I did it.
[0063]
This uncrosslinked film was irradiated with an electron beam of 30 MRad in a nitrogen atmosphere to obtain a crosslinked film. The crosslinked film and the uncrosslinked film were heat-set at 85 ° C. for 1 hour and further at 115 ° C. for 1 hour to prevent thermal shrinkage, and then superposed one by one, temperature 100 ° C., pressure 0.3 kg / cm (linear pressure) ) Was laminated with a laminator to obtain a porous film. In addition, since the crosslinkable resin was not used for the obtained porous film, even if it observed the infrared absorption spectrum, there was no change.
[0064]
Table 1 shows the film thickness, porosity, air permeability, thermal fracture temperature, and lamination strength of the porous films obtained in Examples 1 and 2 and Comparative Example 1.
[0065]
[Table 1]

[0066]
From the results shown in Table 1, the porous films of Examples 1 and 2 have higher thermal fracture temperatures and higher lamination strength than the laminated laminated porous film of Comparative Example 1, and therefore, peeling occurs in the non-crosslinked layer. From the occurrence, it can be seen that crosslinking by addition of a crosslinkable resin can provide a porous film having better heat resistance than electron beam irradiation.
[0067]
【The invention's effect】
According to the present invention, it is possible to obtain a porous film having a structure in which at least one cross-linked layer and a non-cross-linked layer are present, a high lamination strength between these layers, and excellent heat-resistant film breakability at high temperatures. .

Claims (9)

A porous film in which a layer containing polyolefin (resin layer A) and a layer containing both polyolefin and a crosslinkable resin (resin layer B) are laminated , wherein the crosslinkable resin has a double bond A porous film which is a resin in which a hydrogen atom is bonded to the α-position carbon . The porous film according to claim 1, wherein the polyolefin of the resin layer A and the resin layer B contains a high molecular weight polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more.   The porous film according to claim 1 or 2, wherein the polyolefin is polyethylene. The porous film according to any one of claims 1 to 3 , wherein the crosslinkable resin is polynorbornene or polybutadiene. The porous film in which the resin layer B has a crosslinked structure in the porous film according to any one of claims 1 to 4 . A method for producing a porous film, characterized by laminating a gel-like molded product containing polyolefin and a gel-like molded product containing both polyolefin and a crosslinkable resin , wherein the crosslinkability A method for producing a porous film, wherein the resin has a double bond and a hydrogen atom is bonded to the α-position carbon . Batteries comprising a porous film according to any one claims 1-5. Capacitor comprising a porous film according to any one claims 1-5. A battery separator comprising the porous film according to claim 1 .