JP2012131990A - Separator for use in electricity-storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyolefin-based porous film excellent in safety at a low temperature.SOLUTION: This polyolefin-based porous film includes a polyolefin-based resin, a thermoplastic elastomer, and particles, and has such an elongation retention of 70% or more as is calculated by the following formula: elongation retention (%)={thrust elongation (mm) at -30°C/thrust elongation (mm) at 25°C}×100.

Description

  The present invention relates to an electricity storage device separator that is excellent in safety at low temperatures. In particular, the present invention relates to a highly safe separator for an electricity storage device that improves puncture characteristics at a low temperature and has the excellent electrical performance of a polyolefin-based porous film and can be suitably used for a lithium ion secondary battery.

  Polyolefin-based porous films are widely used especially for separators of lithium ion secondary batteries because they have excellent mechanical properties in addition to electrical insulation and ion permeability.

  Although there are many items to be provided as a separator for a lithium ion secondary battery, film properties suitable mainly for higher battery capacity, higher output, and safety are required. Among them, in recent years, maintenance of safety and battery performance when the use temperature of the battery becomes low is required. In conventional techniques, methods for improving mechanical properties at room temperature (for example, piercing properties and tensile strength / elongation) have been studied (for example, Patent Documents 1 to 3). However, these methods improve properties at room temperature. Even if possible, there was a problem that the physical properties at low temperature were not improved.

  In addition, as a method for improving the mechanical properties of a general film at a low temperature, a technique of adding an elastomer component to a resin composition has been reported (Patent Document 4). There was a problem that it was not done enough.

JP 2008-521964 A JP 2003-20357 A JP 2007-112855 A JP 2000-129051 A

  An object of the present invention is to solve the above-described problems. That is, an object of the present invention is to provide an olefin-based porous film suitable for use as a separator for an electricity storage device that suppresses a decrease in elongation in a puncture test at a low temperature and has excellent battery performance and safety at a low temperature. is there.

  In order to achieve the above object, the present invention has the following features.

  A polyolefin-based porous film comprising a polyolefin-based resin, a thermoplastic elastomer, and particles, and having an elongation retention calculated by the following formula of 70% or more.

    Elongation retention (%) = {Puncture elongation at −30 ° C. (mm) / Puncture elongation at 25 ° C. (mm)} × 100

  The polyolefin-based porous film of the present invention has a good puncture elongation at a low temperature, and can be provided as a porous film exhibiting excellent characteristics when used as a separator.

  The polyolefin-based porous film of the present invention penetrates both surfaces of the film and has many fine through holes having air permeability. As a method for forming a through-hole in the film, either a wet method or a dry method may be used, but a dry method is desirable because the process can be simplified.

  Polyolefins constituting the polyolefin-based porous film include single polyolefin resins such as polyethylene, polypropylene, polybutene-1 and poly-4-methylpentene-1, mixtures of these resins, and random copolymerization of monomers. Alternatively, a block copolymerized resin can be used.

  The polyolefin-based porous film preferably has a melting point of 155 to 180 ° C. from the viewpoint of heat resistance. When the melting point is lower than 155 ° C., the porous film may change in dimensions when a particle-containing layer described later is laminated on the polyolefin-based porous film. On the other hand, in order to set the melting point of the polyolefin-based porous film to a temperature exceeding 180 ° C., it is necessary to add a large amount of a heat-resistant resin other than the polyolefin resin. In that case, the ion conductivity that is a basic characteristic as a separator is obtained. There is a case where it drops significantly. The melting point of the polyolefin-based porous film refers to the melting point of course when showing a single melting point, but when the polyolefin-based porous film has a plurality of melting points, for example, the polyolefin-based porous film is composed of a mixture of polyolefins. Of these, the melting point appearing on the highest temperature side is defined as the melting point of the polyolefin-based porous film. The melting point of the polyolefin-based porous film is more preferably 160 to 180 ° C., further preferably 165 to 180 ° C. from the viewpoint of heat resistance. Moreover, as above-mentioned, when a polyolefin-type porous film shows several melting | fusing point, it is preferable that all of them exist in the said range.

  In order to realize excellent battery characteristics, the polyolefin-based porous film is preferably made of a polypropylene resin, and is particularly preferably a porous film manufactured using a porosification method called a β crystal method. In order to form through-holes in the film using the β crystal method, it is important to generate a large amount of β crystals in the polypropylene resin. For this purpose, it is added to the polypropylene resin, which is called a β crystal nucleating agent. Thus, it is preferable to use a crystallization nucleating agent that selectively generates β crystals as an additive. Examples of the β crystal nucleating agent include various pigment compounds and amide compounds. In particular, amide compounds disclosed in JP-A-5-310665 can be preferably used. As content of (beta) crystal nucleating agent, when the whole polypropylene resin is 100 mass parts, it is preferable that it is 0.05-0.5 mass part, and more preferable if it is 0.1-0.3 mass part. .

  The polypropylene resin constituting the polyolefin-based porous film may be an isotactic polypropylene resin having a melt flow rate (hereinafter referred to as MFR, measurement conditions are 230 ° C., 2.16 kg) in the range of 2 to 30 g / 10 min. preferable. If the MFR is out of the above preferred range, it may be difficult to obtain a stretched film. More preferably, the MFR is 3 to 20 g / 10 minutes. The isotactic index of the isotactic polypropylene resin is preferably 90 to 99.9%. If the isotactic index is less than 90%, the crystallinity of the resin is low, and it may be difficult to achieve high air permeability. A commercially available resin can be used as the isotactic polypropylene resin.

  Of course, homopolypropylene resin can be used for the polyolefin-based porous film, and from the viewpoint of stability in the film-forming process, film-forming property, and uniformity of physical properties, polypropylene may contain an ethylene component, butene, hexene, octene. The α-olefin component such as may be copolymerized within a range of 5% by mass or less. The form of the comonomer introduced into the polypropylene may be either random copolymerization or block copolymerization. Moreover, it is preferable that said polypropylene resin contains a high melt tension polypropylene in 0.5-5 mass% at the point of film forming property improvement. High melt tension polypropylene is a polypropylene resin whose tension in the molten state is increased by mixing a high molecular weight component or a component having a branched structure into the polypropylene resin or by copolymerizing a long-chain branched component with polypropylene. However, among these, it is preferable to use a polypropylene resin copolymerized with a long chain branching component. This high melt tension polypropylene is commercially available. For example, polypropylene resins PF814, PF633, and PF611 manufactured by Basell, polypropylene resin WB130HMS manufactured by Borealis, and polypropylene resins D114 and D206 manufactured by Dow can be used.

  In this invention, it is preferable that the density | concentration of the polypropylene resin which comprises a polyolefin-type porous film is 85 mass% or more, More preferably, it is 90 mass% or more. When the polypropylene resin concentration is less than 85% by mass, void formation efficiency during stretching may be impaired.

  In the polypropylene resin constituting the polyolefin-based porous film, the void formation efficiency at the time of stretching is increased, and the air permeability is improved by expanding the pore diameter. Therefore, 1 to 10 ethylene / α-olefin copolymer is added to the polypropylene resin. It is preferable to add mass%. Here, examples of the ethylene / α-olefin copolymer include linear low density polyethylene and ultra-low density polyethylene. Among them, ethylene / octene-1 copolymer obtained by copolymerization of octene-1 is preferably used. be able to. A commercially available resin can be used for the ethylene-octene-1 copolymer.

  In this invention, a film raw material means the raw material used when manufacturing a polyolefin-type porous film. Specifically, the above-described polyolefin resin, nucleating agent, additive and the like are blended.

  The polyolefin porous film of the present invention has an elongation retention calculated by the following formula of 70% or more. Preferably they are 70% or more and 100% or less.

Elongation retention (%) = {Puncture elongation at −30 ° C. (mm) / Puncture elongation at 25 ° C. (mm)} × 100
In the above formula and the present invention, the piercing elongation is the movement of the pin tip from when the pin tip comes into contact with the film until the piercing break occurs in the measurement of the piercing strength measured according to JIS Z 1707 (1997). Say distance. When the above-described elongation retention is less than 70%, when a polyolefin-based porous film is used as a separator, battery performance at low temperatures may be deteriorated, or the separator may be damaged by impact or friction. Further, the higher the elongation retention, the better the safety when using a polyolefin-based porous film as a separator. In addition, since it is preferable that there is little change in physical properties at low temperatures, the elongation retention is preferably 70% or more and 100% or less. The elongation retention is more preferably 75% or more and 100% or less, further preferably 80% or more and 100% or less, further preferably 85% or more and 100% or less, and more preferably 90% or more and 100% or less.

  The polyolefin-based porous film of the present invention preferably has a puncture elongation at 25 ° C. of 2.5 mm or more, more preferably 2.5 mm or more and 10 mm or less, and further preferably 3.0 mm or more and 10 mm or less. . If it is smaller than 2.5 mm, the separator may be damaged by impact or friction when used as a separator. In addition, when larger than 10 mm, when using a polyolefin-type porous film as a separator, it may become easy to deform | transform by external force.

  In the present invention, in order to make the piercing elongation at 25 ° C. 2.5 mm or more, the polypropylene resin constituting the polyolefin-based porous film is different from this regardless of the presence of an ethylene / α-olefin copolymer. It is preferable to contain a thermoplastic elastomer. The thermoplastic elastomer is preferably a styrene elastomer or a diene elastomer. Examples of the styrene elastomer include styrene-butadiene-styrene type, styrene-isoprene-styrene type, styrene-ethylene-butylene-styrene type, styrene-ethylene-propylene-styrene type, and a combination type of polystyrene and vinyl-polyisoprene. Styrenic thermoplastic elastomer, styrene-butadiene rubber, hydrogenated styrene-butadiene rubber and styrene-ethylene-butylene-olefin crystal block copolymer, and any mixed rubber of these, which are block copolymers having polystyrene blocks and rubber intermediate blocks However, the present invention is not limited to this. Examples of the diene elastomer include butadiene, isoprene, piperylene, 1,3-pentadiene and the like, but are not limited thereto.

  In this invention, it is preferable that content of the thermoplastic elastomer contained in a polyolefin-type porous film is 0.1-10 mass parts with respect to 100 mass parts of polypropylene resins which comprise a film, 0.5-7 It is more preferable that it is a mass part, More preferably, it is 2-6 mass parts. If the thermoplastic elastomer is added in excess of 10 parts by mass, film formation may be inhibited. Moreover, the puncture characteristic in low temperature may deteriorate that it is less than 0.1 mass part.

  In the present invention, it is effective to disperse the thermoplastic elastomer with the particles as nuclei in order to make the elongation retention 70% or more. The thermoplastic elastomer is dispersed with the particles as the core to form a dispersion (domain), so that a stronger network structure is created in the polyolefin-based porous film while suppressing dropout of the particles, improving the piercing characteristics at low temperatures can do. The structure of the domain is a structure formed only of a thermoplastic elastomer, or when the film contains an ethylene / α-olefin copolymer, the ethylene / α-olefin copolymer is formed of a thermoplastic elastomer. Any of the coexisting structures may be used.

  In the present invention, the structure of the domain of the thermoplastic elastomer can be confirmed by observing the cross section of the polyolefin-based porous film with an electron microscope.

  In the present invention, any of organic particles or inorganic particles can be suitably used. Examples of inorganic particles include oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide and iron oxide, nitride ceramics such as silicon nitride, titanium nitride and boron nitride, silicon carbide, and carbonic acid. Calcium, aluminum sulfate, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amicite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth Organic particles, such as ceramics such as silica sand, ceramics such as glass fiber, etc., are obtained by crosslinking a polymer compound with a crosslinking agent. For example, crosslinked particles of a polymethoxysilane compound, crosslinked particles of a polystyrene compound, Cross-linked particles of ril-based compounds, cross-linked particles of polyurethane-based compounds, cross-linked particles of polyester-based compounds, cross-linked particles of fluoride-based compounds, and the like. From the viewpoint of electrochemical stability, oxide-based ceramics are used. It is preferable. In the present invention, these particles may be used alone or in combination. Of course, the particles may be a composite of an inorganic material and an organic material.

  Furthermore, from the viewpoint of stability in the lithium ion battery, the water content of the particles is preferably 1% by mass or less. More preferably, the water content is preferably 0.5% by mass or less. In the present invention, the water content means the amount of water contained in the particle surface and the pores of the particle. The water content can be measured according to JIS K5101 (2004).

  In the present invention, particles having a moisture content of 1% by mass or less are preferably particles having a dense structure that does not have pores inside. For example, alumina, silica produced by dry method, oxide ceramics such as zirconia produced by dry method, nitride ceramics such as silicon nitride, titanium nitride, boron nitride, silicon carbide, calcium carbonate, aluminum sulfate silica Examples include ceramics such as sand, ceramics such as glass fiber, etc. From the viewpoint of electrochemical stability, it is preferable to use alumina, silica produced by a dry method, zirconia produced by a dry method, May be used alone, or a plurality may be used in combination.

  In the present invention, the average particle diameter (average area circle equivalent diameter) of the particles used is preferably in the range of 50 to 500 nm. When the average particle diameter exceeds 500 nm, pore formation of the film may be inhibited. On the other hand, when the thickness is less than 50 nm, defects due to aggregation of particles in the resin increase. More preferably, it is 100-400 nm.

  In this invention, 0.1-10 mass parts is preferable with respect to 100 mass parts of polypropylene resins, and, as for content of the particle | grains contained in a polyolefin-type porous film, More preferably, it is 0.1-8 mass parts, Preferably it is 0.1-6 mass parts. If the content is less than 0.1 parts by mass, the particles serving as the core of the thermoplastic elastomer may be insufficient, and the mechanical strength at low temperatures may be reduced. Further, when added in an amount exceeding 10 parts by mass, the film becomes brittle when the film is formed, the particles easily fall off, the volume ratio of the nucleus in the domain of the thermoplastic elastomer becomes too large, and the diameter of the domain Therefore, the air permeability may be deteriorated because the formation of through holes in the polyolefin-based porous film is inhibited.

  In the present invention, the surface-treated particles can also be used. Although the thing by a silane coupling agent and a saturated and unsaturated fatty acid is mentioned as a kind of process, A silane coupling agent is used suitably from a heat resistant viewpoint.

  Examples of the silane coupling agent include vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ- ( 2-aminoethyl) aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltrimethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-methacryloxypropylmethyldimethoxysilane , Γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane N-β (aminoethyl) γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl- γ-aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, bis- (3- [triethoxysilyl]- Propyl) -tetrasulfane (TESPT), bis- (3- [triethoxysilyl] -propyl) -disulphane and the like. In particular, a silane coupling agent having a boiling point of 150 ° C. or higher is preferable from the viewpoint of heat resistance.

  In the present invention, as a method of dispersing the thermoplastic elastomer in the polyolefin-based porous film with the particles as nuclei, a master batch obtained by kneading the particles and the thermoplastic elastomer in advance and then diluting with a polyolefin-based resin at an arbitrary concentration is used. A method of producing and adding at the time of film production can be mentioned, but the method is not limited thereto.

  The masterbatch is prepared by supplying thermoplastic elastomer and particles as raw materials to an extruder having a vent, melt-kneading while degassing by vacuum suction from the vent, and dispersing the particles in the thermoplastic elastomer. A method is available. The gut-like particle-containing thermoplastic elastomer discharged from the extruder can be cooled in a water bath or the like by a conventional method and then cut to obtain pellets (hereinafter sometimes referred to as elastomer pellets). Next, the elastomer pellets and polyolefin resin as raw materials are supplied to an extruder having a vent, and melted and kneaded while degassing by vacuum suction from the vent to disperse the thermoplastic elastomer containing particles in the polyolefin resin. Let The gut-like polymer discharged from the extruder is cooled in a water bath or the like by a conventional method, and then cut into a master batch in which a thermoplastic elastomer is dispersed in a polyolefin resin with particles as nuclei. Furthermore, it is also a preferable method to provide a filtration apparatus between the extruder and the die and remove coarse particles in the kneaded polymer.

  In the present invention, in order to improve the compatibility between the thermoplastic elastomer and the polyolefin resin, it is preferable to add a modified polypropylene resin at the time of producing the master batch. Examples of the modified polypropylene resin include an unsaturated compound having one or more carboxylic acid groups, an unsaturated compound having one or more carboxylic anhydride groups, and derivatives thereof by propylene homopolymer, propylene, and graft copolymerization or radical copolymerization. It is obtained by introducing it into a so-called polypropylene resin which is a copolymer with α-olefin or a mixture thereof.

  The air permeation resistance of the polyolefin-based porous film of the present invention is preferably 50 to 500 seconds / 100 ml, more preferably 65 to 450 seconds / 100 ml, still more preferably 80 to 400 seconds / 100 ml, although it depends on the application. If the air permeability resistance is less than 50 seconds / 100 ml, the film strength is low, and pinholes are easily generated when used as a separator, causing a short circuit or tearing when wound for storage inside the battery. May be inferior in handleability. Further, if the air resistance exceeds 500 seconds / 100 ml, the ion conductivity is inferior.

  As a method for controlling the air resistance to such a preferable range, it becomes easy to achieve by using a resin in which a polypropylene resin and an ethylene / α-olefin copolymer are mixed at a specific ratio, and further, a specific biaxial to be described later It can be effectively achieved by adopting stretching conditions.

  Since the polyolefin-based porous film is preferably made porous by the β crystal method, the β crystal forming ability of the polypropylene resin constituting (included) in the film is preferably 40 to 90%.

  Here, the β crystal-forming ability indicates the ratio of β crystals existing in the polypropylene resin under certain conditions, measured under the following conditions, and is a value indicating how much β crystals are formed. is there. The β crystal-forming ability was measured after 5 mg of polypropylene resin or polypropylene film was heated from room temperature to 240 ° C. at a rate of 10 ° C./min (first run) using a differential scanning calorimeter and held for 10 minutes. Cool to 30 ° C. at 10 ° C./min. About the melting peak observed when the temperature is raised (second run) again at 10 ° C./min after holding for 5 minutes, the melting having a peak in the temperature range of 145 to 157 ° C. is the melting peak of β crystal, 158 ° C. or more The melting at which the peak is observed is the melting peak of the α crystal, and the heat of fusion is determined. The heat of fusion of the α crystal is ΔHα and the heat of fusion of the β crystal is ΔHβ. Crystal formation ability.

β crystal forming ability (%) = [ΔHβ / (ΔHα + ΔHβ] × 100
If the β-crystal forming ability is less than 40%, the amount of β-crystal is small at the time of film production, so the number of voids formed in the film is reduced by utilizing the transition to α-crystal, and as a result, only a film with low permeability is obtained. There may not be. In addition, when the β-crystal forming ability exceeds 90%, coarse pores are formed, and the function as a power storage device separator may not be provided. In order to make the β crystal forming ability in the range of 40 to 90%, it is preferable to use a polypropylene resin having a high isotactic index and to add the above-mentioned β crystal nucleating agent. The β crystal forming ability is more preferably 45 to 80%.

  In addition to the above β crystal method, a method for producing a polyolefin-based porous film is to use polypropylene as a matrix resin, add a material to be extracted when mixing into a sheet, mix, and use a good solvent for the material to be extracted. By extracting only the additives, a so-called extraction method that forms voids in the matrix resin, low-temperature extrusion at the time of melt extrusion, and using a high draft ratio, a lamellar structure in the pre-stretched film formed into a sheet There is a method called a lamellar stretching method in which cleavage at the lamella interface is generated by controlling the uniaxial stretching to form a void, and any of them can be used.

  The polyolefin-based porous film used in the present invention preferably has a porosity of 45 to 90%, more preferably 50 to 80%. If it is less than 45%, battery performance may be insufficient when a polyolefin-based porous film is used as a separator. If it exceeds 90%, it may be insufficient from the viewpoint of separator characteristics and strength.

  The method for controlling the porosity of the film to such a preferable range can be achieved by employing specific biaxial stretching conditions described later.

  The polyolefin-based porous film of the present invention is preferably stretched at least in a uniaxial direction. When an unstretched film is used, the porosity and mechanical strength of the film may be insufficient. As a method for stretching the polyolefin-based porous film in at least a uniaxial direction, it is preferable to stretch the film at a predetermined magnification by heating, a tenter method, a roll method, an inflation method, or a combination thereof. The stretching may be uniaxial stretching or biaxial stretching. In the case of biaxial stretching, any of simultaneous biaxial stretching, sequential stretching, and multistage stretching (for example, a combination of simultaneous biaxial stretching and sequential stretching) may be used, but sequential biaxial stretching is preferable.

  The polyolefin-based porous film of the present invention may be a laminated film formed by laminating a plurality of layers having different compositions or the same composition. A laminated film is preferable because the film surface characteristics and the overall film characteristics may be individually controlled within a preferable range. In that case, an A | B | A type three-layer stack is preferable, but there is no problem even if it is an A | B type two-layer stack or a multilayer stack of four or more layers. The lamination thickness ratio is not particularly limited as long as the effects of the present invention are not impaired.

  Below, the manufacturing method of the polyolefin-type porous film of this invention is demonstrated concretely. In addition, although the manufacturing method of the polyolefin-type porous film of this invention is not limited to this, the polypropylene porous film by (beta) crystal method is demonstrated as an example.

  As a polypropylene resin, 94 parts by mass of a commercially available homopolypropylene resin with an MFR of 8 g / 10 minutes, 1 part by mass of a commercially available MFR of 2.5 g / 10 minutes with a high melt tension polypropylene resin, and an ultra low density polyethylene resin 5 with a melt index of 18 g / 10 minutes. A polypropylene resin raw material prepared by mixing 0.2 parts by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide with parts by mass and mixing in advance at a predetermined ratio using a twin screw extruder is prepared. At this time, the melting temperature is preferably 270 to 300 ° C.

  Further, 79.8% by mass of a commercially available thermoplastic elastomer, 20% by mass of commercially available organic or / and inorganic particles, and 0.2% by mass of a commercially available antioxidant are mixed, and a twin screw extruder at a melting temperature of 170 to 200 ° C. Were kneaded to prepare elastomer pellets. 40% by mass of this elastomer pellet, 59.8% by mass of a commercially available homopolypropylene resin with an MFR of 8 g / 10 min, and 0.2% by mass of a commercially available antioxidant were mixed, and a twin screw extruder was used at a melting temperature of 170 to 200 ° C. Use and knead to make a master batch of thermoplastic elastomer.

  Next, with respect to 100 parts by mass of the above-mentioned polypropylene resin raw material, the master batch is weighed so that the particles are 0.1 to 10 parts by mass and the elastomer is 0.1 to 10 parts by mass. Supply and melt extrusion at 200-230 degreeC. And after removing a foreign material, a modified polymer, etc. with the filter installed in the middle of the polymer pipe | tube, it discharges on a cast drum from T-die, and an unstretched sheet is obtained. At this time, the surface temperature of the cast drum is preferably 105 to 130 ° C. from the viewpoint of controlling the β crystal fraction of the cast film to be high. In particular, since the forming of the end portion of the sheet affects the subsequent stretchability, it is preferable that the end portion is sprayed with spot air to adhere to the drum. Note that the polymer may be brought into close contact with the cast drum using a method in which air is blown over the entire surface from the contact state of the entire sheet on the drum using an air knife or an electrostatic application method as necessary.

  Next, the obtained unstretched sheet is biaxially oriented to form pores in the film. As a biaxial orientation method, the film is stretched in the longitudinal direction of the film and then stretched in the width direction, or the sequential biaxial stretching method in which the film is stretched in the width direction and then stretched in the longitudinal direction. The simultaneous biaxial stretching method can be used, but it is preferable to adopt the sequential biaxial stretching method in that it is easy to obtain a highly air-permeable film, and in particular, it is possible to stretch in the width direction after stretching in the longitudinal direction. preferable.

  As specific stretching conditions, first, the temperature is controlled so that the unstretched sheet is stretched in the longitudinal direction. As a temperature control method, a method using a temperature-controlled rotating roll, a method using a hot air oven, or the like can be adopted. The stretching temperature in the longitudinal direction is preferably 90 to 135 ° C, more preferably 100 to 130 ° C. The stretching ratio is 3 to 6 times, more preferably 4 to 5.5 times. Next, after cooling, the end of the film is gripped and introduced into a stenter type stretching machine. And it heats to 140-155 degreeC preferably, and extends 5 to 12 times in the width direction, More preferably, it extends 6 to 10 times. The transverse stretching speed at this time is preferably 300 to 5,000% / min, more preferably 500 to 3,000% / min. Next, heat setting is performed in the stenter as it is, and the temperature is preferably not less than the transverse stretching temperature and not more than 168 ° C. Furthermore, it may be performed while relaxing in the longitudinal direction and / or the width direction of the film at the time of heat setting, and in particular, the relaxation rate in the width direction is preferably 3 to 20% from the viewpoint of thermal dimensional stability.

  Since the polyolefin-based porous film of the present invention has excellent air permeability and piercing characteristics at low temperatures, it can be suitably used as a separator for an electricity storage device.

  Here, examples of the electricity storage device include a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery, and an electric double layer capacitor such as a lithium ion capacitor. Since such an electricity storage device can be repeatedly used by charging and discharging, it can be used as a power supply device for industrial devices, household equipment, electric vehicles, hybrid electric vehicles, and the like. The electricity storage device used as the separator of the present invention can be suitably used for power supplies for industrial equipment and automobiles because of the excellent characteristics of the separator.

  Moreover, the polyolefin-based porous film of the present invention is excellent in leakage resistance and mechanical strength in addition to excellent breathability and moisture permeability in addition to the separator of the electricity storage device, moisture permeable waterproof clothing, sanitary goods, It is very useful as a material used in the fields of absorbent articles such as disposable diapers, sanitary goods, building materials, various packaging materials, synthetic paper, filtration membranes and separation membranes, and agricultural multi-sheets.

  Hereinafter, the present invention will be described in detail by way of examples. The characteristics were measured and evaluated by the following methods.

(1) Average particle diameter of particles The average particle diameter of particles is obtained by taking a photograph with a magnification of 20,000 times for randomly extracted particles using a scanning electron microscope SEM.

  The average particle diameter (D) is obtained from the following formula by obtaining the area equivalent circle diameter (Di) of 100 particles from the above photograph. Here, the area equivalent circle diameter (Di) is the diameter of each circumscribed circle.

(2) Air permeability resistance A 100 mm square from one side of a polyolefin-based porous film was cut out, and a B-shaped Gurley tester of JIS P 8117 (2009) was used at 23 ° C. and 65% relative humidity. Measurement of the permeation time of 100 ml of air was performed three times. The average value of the permeation time was taken as the air resistance of the polyolefin-based porous film.

(3) Porosity A polyolefin-based porous film was cut into a size of 30 mm × 40 mm and used as a sample. Using an electronic hydrometer (SD-120L manufactured by Mirage Trading Co., Ltd.), the specific gravity was measured in an atmosphere at a room temperature of 23 ° C. and a relative humidity of 65%. The measurement was performed three times, and the average value was defined as the specific gravity ρ of the film.

  Next, the measured film was hot-pressed at 280 ° C. and 5 MPa, and then rapidly cooled with water at 25 ° C. to prepare a sheet from which pores were completely erased. The specific gravity of this sheet was measured in the same manner as described above, and the average value was defined as the specific gravity (d) of the resin. In the examples described later, the specific gravity d of the resin was 0.91 in any case. From the specific gravity of the film and the specific gravity of the resin, the porosity was calculated by the following formula.

Porosity (%) = [(d−ρ) / d] × 100
(4) β-crystal forming ability 5 mg of the resin constituting the polyolefin-based porous film or the polyolefin-based porous film itself was sampled in an aluminum pan and measured using a differential scanning calorimeter (Seiko Denshi Kogyo RDC220). First, the temperature is raised from room temperature to 280 ° C. at 10 ° C./min (first run) in a nitrogen atmosphere, held for 10 minutes, and then cooled to 30 ° C. at 10 ° C./min. After holding for 5 minutes, the melting peak observed when the temperature is raised again at 10 ° C./min (second run) is the melting peak of the β crystal at 145 ° C. to 157 ° C., 158 ° C. The melting at which the peak is observed is defined as the melting peak of the α crystal, and the melting heat amount of the α crystal is obtained from the baseline and the area of the region surrounded by the peak drawn from the flat portion on the high temperature side. Is the ΔHα, and the heat of fusion of the β crystal is ΔHβ, the value calculated by the following formula is the β crystal forming ability. The heat of fusion was calibrated using indium.

β crystal forming ability (%) = [ΔHβ / (ΔHα + ΔHβ)] × 100
(5) Puncture elongation and elongation retention rate Using a universal testing machine (Autograph AG-IS, manufactured by Shimadzu Corporation), measurement is performed at 25 ° C. and −30 ° C. according to JIS Z1707 (1997), and the tip of the pin is a film. The moving distance of the tip of the pin from the point of contact to the point of puncture and breakage was read and taken as the puncture elongation at that temperature. In the measurement at −30 ° C., a thermostatic bath (TCR2L manufactured by Shimadzu Corporation) was used. The puncture elongation obtained from the above measurement was substituted into the following formula to calculate the elongation retention.

Elongation retention (%) = {Puncture elongation at −30 ° C. (mm) / Puncture elongation at 25 ° C. (mm)} × 100
(6) Safety evaluation at low temperature Using a positive electrode with a lithium cobalt oxide (LiCoO ₂ ) thickness of 40 μm manufactured by Hosen Co., Ltd., punched into a circle with a diameter of 15.9 mm, and manufactured by Hosen Co., Ltd. A graphite negative electrode having a thickness of 50 μm was used and punched into a circle having a diameter of 16.2 mm, and then a polyolefin-based porous film was punched to a diameter of 24 mm. The negative electrode, metal particles (average particle diameter 11 μm, Alfa Aesar aluminum particles) 1 mg, polyolefin porous film, positive electrode are stacked in this order so that the surface of the positive electrode active material and the negative electrode active material face each other. It was stored in a container (manufactured by Hosen Co., Ltd., HS cell, spring pressure 10 kgf). The container and the lid are insulated, the container is in contact with the negative electrode copper foil, and the lid is in contact with the positive electrode aluminum foil. Into this container, an electrolytic solution in which LiPF ₆ was dissolved as a solute in a mixed solvent of propylene carbonate: diethyl carbonate = 3: 7 (volume ratio) to a concentration of 1 mol / liter was injected and sealed to produce a battery. did.

  Each of the fabricated secondary batteries was charged in an atmosphere of 25 ° C. to 4.2 V at 1.6 mA for 3.5 hours and left in an atmosphere of 25 ° C. for 1 week, and then 1.6 mA to 2.7 V. Discharge was performed and the discharge capacity was measured.

  In addition, the battery was charged at 1.6 mA to 4.2 V at 25 ° C. for 3.5 hours, left at −30 ° C. for 1 week, then left at room temperature for 3 hours, and then at 1.6 mA. The battery was discharged to 2.7 V and the discharge capacity was measured.

  [(Discharge capacity after standing at −30 ° C.) / (Discharge capacity after standing at 25 ° C.)] × 100 The value obtained by the calculation formula was evaluated according to the following criteria. In addition, 50 test pieces were measured, and the average value was evaluated.

○: 85% or more Δ: 80% or more and less than 85% ×: less than 80% or one or more and less than 20% (7) Domain structure of thermoplastic elastomer The polyolefin-based porous film can be seen in the longitudinal section of the film In addition, an ultrathin section was prepared at −100 ° C. using an ultramicrotome (RM2265, manufactured by Leica). The sample was stained with RuO ₄ and observed at a magnification of 10,000 using a transmission electron microscope (H7100FA, manufactured by Hitachi, Ltd.). In the observed image, the structure of 100 thermoplastic elastomer domains extracted at random was confirmed.

Example 1
94.55% by mass of homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd., Dow Chemical's Engage 8411 (melt index: 18 g / 10 min), an ethylene-octene-1 copolymer, as the main raw material resin for polyolefin-based porous film Is added to 5% by mass, and N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide (Nu-100, manufactured by Shin Nippon Rika Co., Ltd., hereinafter simply referred to as β crystal nucleating agent). ), 0.2% by weight, and IRGANOX1010 and IRGAFOS168 manufactured by Ciba Specialty Chemicals, which are antioxidants, are mixed at a ratio of 0.15 and 0.1% by weight from the weighing hopper to be twin-screw extruded. The raw material is supplied to the machine, melted and kneaded at 300 ° C, discharged from the die into strands, and a 25 ° C water tank And solidified by cooling, and cut into chips to obtain a polypropylene resin raw material.

  80% by mass of Asahi Kasei Chemicals Co., Ltd., which is a styrene / butadiene block copolymer, raw material for elastomer pellets, and 20% by mass of silica particles SFP-20 (average particle diameter 200 nm) manufactured by Denki Kagaku Kogyo Co., Ltd. as particles. The raw material is supplied from the weighing hopper to the twin-screw extruder so as to be mixed at this ratio, melt kneaded at 190 ° C., discharged from the die in a strand shape, cooled and solidified in a 25 ° C. water tank, and chip-shaped To give elastomer pellets (A).

  In order to prepare a masterbatch, 59.8% by mass of homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd., 40% by mass of elastomer pellets (A), 0.1% by mass of IRGANOX1010 and IRGAFOS168, each in this ratio The raw material is fed from the weighing hopper to the twin screw extruder so that it is mixed in the melt, melt-kneaded at 190 ° C, discharged from the die in a strand shape, cooled and solidified in a 25 ° C water bath, and cut into chips. To obtain a master batch (a).

  A film raw material was prepared by mixing 93.55% by mass of polypropylene resin raw material, 6.25% by mass of master batch (a), 0.1% by mass of IRGANOX1010 and IRGAFOS168. This film raw material is supplied to a single screw extruder, melt extruded at 220 ° C., foreign matter is removed with a 25 μm cut sintered filter, and then discharged from a T die to a cast drum whose surface temperature is controlled at 120 ° C. To give an unstretched sheet. Next, preheating was performed using a ceramic roll heated to 120 ° C., and the film was stretched 4.5 times in the longitudinal direction of the film. After cooling, the end portion was introduced into a tenter type stretching machine by holding it with a clip, and stretched 6 times at 145 ° C. As it was, heat treatment was performed at 155 ° C. for 6 seconds while relaxing 5% in the width direction to obtain a polyolefin-based porous film 1 having a thickness of 23 μm.

  When the structure of the thermoplastic elastomer domain of the polyolefin-based porous film 1 was evaluated, more than half of the domains contained particles in the domain.

(Example 2)
A polypropylene resin raw material and a masterbatch (a) were produced using the same method as in Example 1, and 87.3% by mass of the polypropylene resin raw material, 12.5% by mass of the masterbatch (a), IRGANOX 1010, and IRGAFOS168 were each set to 0.000. 1% by mass was mixed to prepare a film raw material.

  This film raw material was formed into a film using the same method as in Example 1 to obtain a polyolefin-based porous film 2 having a thickness of 23 μm.

  When the structure of the domain of the thermoplastic elastomer of the polyolefin-based porous film 2 was evaluated, more than half of the domains had a structure containing particles in the domain.

Example 3
A polypropylene resin raw material and a masterbatch (a) were prepared using the same method as in Example 1, and 74.8% by weight of the polypropylene resin raw material and 25% by weight of the masterbatch (a), IRGANOX 1010 and IRGAFOS168 were each 0.1% by weight. % Was mixed to prepare a film raw material.

  This film raw material was formed into a film using the same method as in Example 1 to obtain a polyolefin-based porous film 3 having a thickness of 23 μm.

  When the structure of the domain of the thermoplastic elastomer of the polyolefin-based porous film 3 was evaluated, more than half of the domains had a structure including particles in the domain.

Example 4
A polypropylene resin raw material was produced using the same method as in Example 1. As a raw material for elastomer pellets, 67% by mass of Asahi Kasei Chemicals Co., Ltd., which is a styrene / butadiene block copolymer, Tuftec (registered trademark) H1052, and 33% by mass of silica particles SFP-20 (average particle size 200 nm) manufactured by Denki Kagaku Kogyo as particles. The raw material is supplied from the weighing hopper to the twin-screw extruder so as to be mixed at this ratio, melt kneaded at 190 ° C., discharged from the die in a strand shape, cooled and solidified in a 25 ° C. water tank, and chip-shaped To give elastomer pellets (I).

  In order to prepare a masterbatch, 59.8% by mass of homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd., 40% by mass of elastomer pellets (I), 0.1% by mass of IRGANOX1010 and IRGAFOS168, each in this ratio The raw material is fed from the weighing hopper to the twin screw extruder so that it is mixed in the melt, melt-kneaded at 190 ° C, discharged from the die in a strand shape, cooled and solidified in a 25 ° C water bath, and cut into chips. To obtain a master batch (b).

  A film raw material was prepared by mixing 85% by mass of a polypropylene resin raw material, 14.8% by mass of masterbatch (b), 0.1% by mass of IRGANOX1010 and IRGAFOS168. This film raw material was formed into a film using the same method as in Example 1 to obtain a polyolefin-based porous film 4 having a thickness of 23 μm.

  When the structure of the domain of the thermoplastic elastomer of the polyolefin-based porous film 4 was evaluated, more than half of the domains contained particles in the domain.

(Example 5)
A polypropylene resin raw material was produced using the same method as in Example 1. As a raw material for elastomer pellets, Asahi Kasei Chemicals Co., Ltd., which is a styrene / butadiene block copolymer, 50% by mass of Tuftec (registered trademark) H1052, and 50% by mass of silica particles SFP-20 (average particle diameter 200 nm) manufactured by Denki Kagaku Kogyo Co., Ltd. as particles. The raw material is supplied from the weighing hopper to the twin-screw extruder so as to be mixed at this ratio, melt kneaded at 190 ° C., discharged from the die in a strand shape, cooled and solidified in a 25 ° C. water tank, and chip-shaped To give elastomer pellets.

  In order to prepare a masterbatch, 59.8% by mass of homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd., 40% by mass of elastomer pellets (U), 0.1% by mass of IRGANOX1010 and IRGAFOS168, each in this ratio The raw material is fed from the weighing hopper to the twin screw extruder so that it is mixed in the melt, melt-kneaded at 190 ° C, discharged from the die in a strand shape, cooled and solidified in a 25 ° C water bath, and cut into chips. To obtain a master batch (c).

  A film raw material was prepared by mixing 79.8% by mass of a polypropylene resin raw material, 20% by mass of a master batch (c), 0.1% by mass of IRGANOX 1010 and IRGAFOS168. This film raw material was formed into a film using the same method as in Example 1 to obtain a polyolefin-based porous film 5 having a thickness of 23 μm.

  When the structure of the domain of the thermoplastic elastomer of the polyolefin-based porous film 5 was evaluated, more than half of the domains had a structure including particles in the domain.

(Example 6)
A polypropylene resin raw material was produced using the same method as in Example 1. As a raw material for the elastomer pellets, 33% by mass of Asahi Kasei Chemicals Co., Ltd., which is a styrene / butadiene block copolymer, and 67% by mass of silica particles SFP-20 (average particle size 200 nm) manufactured by Denki Kagaku Kogyo Co., Ltd. as particles. The raw material is supplied from the weighing hopper to the twin-screw extruder so as to be mixed at this ratio, melt kneaded at 190 ° C., discharged from the die in a strand shape, cooled and solidified in a 25 ° C. water tank, and chip-shaped To give elastomer pellets.

  In order to prepare a masterbatch, 59.8% by mass of homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd., 40% by mass of elastomer pellets (E), 0.1% by mass of IRGANOX1010 and IRGAFOS168, each in this ratio The raw material is fed from the weighing hopper to the twin screw extruder so that it is mixed in the melt, melt-kneaded at 190 ° C, discharged from the die in a strand shape, cooled and solidified in a 25 ° C water bath, and cut into chips. To obtain a master batch (d).

  A film material was prepared by mixing 69.9% by mass of a polypropylene resin raw material, 29.9% by mass of a master batch (d), 0.1% by mass of IRGANOX 1010 and IRGAFOS168. This film raw material was formed into a film using the same method as in Example 1 to obtain a polyolefin-based porous film 6 having a thickness of 23 μm.

  When the structure of the domain of the thermoplastic elastomer of the polyolefin-based porous film 6 was evaluated, more than half of the domains contained particles in the domain.

(Comparative Example 1)
94.55% by mass of homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd., Dow Chemical's Engage 8411 (melt index: 18 g / 10 min), an ethylene-octene-1 copolymer, as the main raw material resin for polyolefin-based porous film Is added to 5% by mass, and N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide (Nu-100, manufactured by Shin Nippon Rika Co., Ltd., hereinafter simply referred to as β crystal nucleating agent). ), 0.2% by weight, and IRGANOX1010 and IRGAFOS168 manufactured by Ciba Specialty Chemicals, which are antioxidants, are mixed at a ratio of 0.15 and 0.1% by weight from the weighing hopper to be twin-screw extruded. The raw material is supplied to the machine, melted and kneaded at 300 ° C, discharged from the die into strands, and a 25 ° C water tank Then, it was solidified by cooling, and cut into chips to obtain a polypropyne resin raw material. This film raw material is supplied to a single screw extruder, melt extruded at 220 ° C., foreign matter is removed with a 25 μm cut sintered filter, and then discharged from a T-die to a cast drum whose surface temperature is controlled at 120 ° C. To give an unstretched sheet. Next, preheating was performed using a ceramic roll heated to 120 ° C., and the film was stretched 4.5 times in the longitudinal direction of the film. After cooling, the end portion was introduced into a tenter type stretching machine by holding it with a clip, and stretched 6 times at 145 ° C. As it was, heat treatment was performed at 155 ° C. for 6 seconds while relaxing 5% in the width direction to obtain a polyolefin-based porous film 7 having a thickness of 23 μm.

(Comparative Example 2)
A polypropylene resin raw material was produced using the same method as in Example 1. In order to prepare a masterbatch, 59.8% by mass of homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd., Asahi Kasei Chemicals Co., Ltd., which is a styrene / butadiene block copolymer, 40% by mass of Tuftec (registered trademark) H1052, IRGANOX 1010 and IRGAFOS 168 are each fed with raw materials from a measuring hopper to a twin screw extruder so that 0.1% by mass is mixed at this ratio, melt kneaded at 190 ° C., discharged from a die in a strand shape, and 25 ° C. And solidified by cooling in a water tank and cut into chips to obtain a master batch (e).

  A film raw material was prepared by mixing 89.8% by mass of a polypropylene resin raw material, 10% by mass of a master batch (e), 0.1% by mass of IRGANOX 1010 and IRGAFOS168. This film raw material was formed into a film using the same method as in Example 1 to obtain a polyolefin-based porous film 8 having a thickness of 23 μm.

(Comparative Example 3)
A polypropylene resin raw material was produced using the same method as in Example 1. In order to prepare a master batch, 69.8% by mass of homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd., 30% by mass of silica particles SFP-20 (average particle size 200 nm) manufactured by Denki Kagaku Kogyo as particles, IRGANOX 1010, IRGAFOS 168 is supplied to a twin screw extruder from a weighing hopper so that 0.1% by mass of each is mixed at this ratio, melt kneaded at 190 ° C., discharged from a die in a strand shape, and 25 ° C. The mixture was cooled and solidified in a water tank and cut into chips to obtain a master batch (f).

  A film raw material was prepared by mixing 91.5% by mass of a polypropylene resin raw material, 8.3% by mass of a master batch (f), 0.1% by mass of IRGANOX 1010 and IRGAFOS168. This film raw material was formed into a film using the same method as in Example 1 to obtain a polyolefin-based porous film 9 having a thickness of 23 μm.

(Comparative Example 4)
As the main raw material resin for polyolefin-based porous film, 89.55% by mass of homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd., Dow Chemical Engage 8411 which is an ethylene-octene-1 copolymer (melt index: 18 g / 10 min) Is added to 10% by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide (Nu-100, manufactured by Shin Nippon Rika Co., Ltd., hereinafter simply referred to as β crystal nucleating agent) ), 0.2% by weight, and IRGANOX1010 and IRGAFOS168 manufactured by Ciba Specialty Chemicals, which are antioxidants, are mixed at a ratio of 0.15 and 0.1% by weight from the weighing hopper to be twin-screw extruded. The raw material is supplied to the machine, melt kneaded at 300 ° C, discharged from the die into strands, and water at 25 ° C It was cooled and solidified in a tank and cut into chips to obtain a polypropyne resin raw material. This film raw material is supplied to a single screw extruder, melt extruded at 220 ° C., foreign matter is removed with a 25 μm cut sintered filter, and then discharged from a T-die to a cast drum whose surface temperature is controlled at 120 ° C. To give an unstretched sheet. Next, preheating was performed using a ceramic roll heated to 120 ° C., and the film was stretched 4.5 times in the longitudinal direction of the film. After cooling, the end portion was introduced into a tenter type stretching machine by holding it with a clip, and stretched 6 times at 145 ° C. As it was, heat treatment was performed at 155 ° C. for 6 seconds while relaxing 5% in the width direction to obtain a polyolefin-based porous film 10 having a thickness of 23 μm.

(Comparative Example 5)
A polypropylene resin raw material was produced using the same method as in Example 1. In order to produce a thermoplastic elastomer masterbatch, 59.8% by mass of homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd. The raw material is supplied from the weighing hopper to the twin screw extruder so that 0.1% by mass of each of the mass%, IRGANOX 1010, and IRGAFOS 168 are mixed at this ratio, melt-kneaded at 190 ° C., and discharged from the die in a strand shape. Then, it was cooled and solidified in a water bath at 25 ° C. and cut into chips to obtain a master batch (g). Further, in order to prepare a particle master batch, 59.8% by mass of homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd., 40% by mass of silica particles SFP-20 (average particle size 200 nm) manufactured by Denki Kagaku Kogyo, IRGANOX1010 and IRGAFOS168 The raw material is supplied from the weighing hopper to the twin screw extruder so that 0.1% by mass of each is mixed at this ratio, melt kneaded at 190 ° C., discharged from the die in a strand shape, and in a 25 ° C. water tank. The mixture was cooled and solidified and cut into chips to obtain a master batch (h). A film raw material was prepared by mixing 79.8% by mass of a polypropylene resin raw material, 10% by mass of a master batch (g), 10% by mass of a master batch (h), 0.1% by mass of IRGANOX 1010 and IRGAFOS168. This film raw material was formed into a film using the same method as in Example 1 to obtain a polyolefin-based porous film 11 having a thickness of 23 μm.

  When the structure of the domain of the thermoplastic elastomer of the polyolefin-based porous film 11 was evaluated, there were many structures having no particle in the domain as compared with the structure having a particle in the domain.

  In Table 1, the raw material composition value (mass%) in the porous film is an approximate value.

  The porous film of the present invention can improve the elongation in a piercing test at low temperature by containing a thermoplastic elastomer and particles in a polyolefin-based porous film, and can maintain safety in a wide temperature range. In particular, it can be suitably used as a separator of a lithium ion battery which is a nonaqueous electrolyte secondary battery.

Claims (11)

A polyolefin-based porous film comprising a polyolefin-based resin, a thermoplastic elastomer, and particles, and having an elongation retention calculated by the following formula of 70% or more.
Elongation retention (%) = {Puncture elongation at −30 ° C. (mm) / Puncture elongation at 25 ° C. (mm)} × 100 The polyolefin based porous film according to claim 1, wherein the piercing elongation at 25 ° C. is 2.5 mm or more. The polyolefin-based porous film according to claim 1 or 2, comprising 0.1 to 10 parts by mass of particles with respect to 100 parts by mass of the polyolefin-based resin. The polyolefin-based porous film according to any one of claims 1 to 3, wherein the average particle diameter of the particles is 50 to 500 nm. The polyolefin based porous film according to any one of claims 1 to 4, wherein the particles are silica. The polyolefin porous film according to any one of claims 1 to 5, wherein the thermoplastic elastomer is a styrene elastomer or a diene elastomer. The polyolefin-based porous film according to any one of claims 1 to 6, wherein the air permeability resistance is 50 to 500 seconds / 100 ml. The polyolefin porous film according to any one of claims 1 to 7, wherein the porosity is 45 to 90%. The polyolefin porous film according to any one of claims 1 to 8, wherein the polyolefin porous film contains 85% by mass or more of polypropylene resin. The polyolefin-based porous film according to claim 9, wherein the polypropylene resin has a β-crystal forming ability of 40 to 90%. The separator for electrical storage devices which uses the polyolefin-type porous film in any one of Claims 1-10.