JP5439772B2 - Porous film and power storage device - Google Patents

Description

  The present invention relates to a porous film. More specifically, the present invention relates to a porous film having high air permeability, high heat resistance, and good workability, which can be suitably used for a separator used in a nonaqueous solvent battery or a capacitor.

  A non-aqueous solvent battery such as a lithium battery or a lithium ion battery has a problem that the electrolytic solution used is an organic solvent and is inferior in safety against heat generation of the battery as compared with an aqueous solvent of an aqueous battery. Therefore, conventionally, in order to improve the safety of non-aqueous solvent batteries, particularly lithium ion batteries having a large energy density, a separator using a microporous porous film of an olefin-based material mainly composed of polyethylene has been used. Polyethylene is mainly used because polyethylene can be used in an organic solvent, and when the battery abnormally generates heat due to a short circuit, etc., the polyethylene melts at an appropriate temperature (around 130 ° C) and the porous structure is blocked. This is because safety can be ensured by doing (shutdown).

  However, in recent years, large batteries such as hybrid vehicle (HEV) batteries and tool batteries have been increased in output and rapidly rise to temperatures higher than 130 ° C. The function of shutting down is not always required, and heat resistance is required. Further, in order to increase the output of the battery and to use it for a lithium ion capacitor, it is necessary to reduce the resistance of the separator alone, so that a high porosity and high air permeability of the separator are required. Further, it is important for HEV batteries to be able to guarantee a long life of 10 years and more stringent safety. Moreover, in a battery having high energy and high power, such as a battery for HEV, the amount of heat generated at the time of thermal runaway is large, and if the temperature continues to rise even when the shutdown temperature is exceeded, the film breaks due to the thermal contraction of the separator. There is a risk that both poles will short circuit and cause further heat generation.

  A separator using polyethylene has a problem in that it is inferior in heat resistance such as heat generation due to a short circuit between the electrodes due to a tendency to shrink at a temperature of 140 ° C. or less for a battery high temperature test. Therefore, a separator using a polypropylene porous film having higher heat resistance than polyethylene has been proposed (for example, Patent Document 1). However, since there is no stiffness of the film, workability when assembling a battery having a winding process may be poor.

  Moreover, the proposal which uses the polypropylene nonwoven fabric excellent in heat resistance and suitable for high output uses like a large sized battery for a separator is also made (for example, patent document 2). However, in this case, since the base material is a non-woven fabric made of fibers, it has a large average pore diameter of about several μm, so that a fine short circuit is likely to occur, and a long life like a battery for HEVs. And it was not enough for even more stringent safety. Furthermore, as long as the nonwoven fabric is used, the film thickness becomes large and the volume increase is inevitable, and there is also a problem that goes against the trend of the era of battery miniaturization and weight reduction.

  In addition, a composite porous membrane filled with resin particle aggregates from the surface to the inside of a porous substrate has been proposed (for example, Patent Document 3). In this case, the fine particles may be aggregated, and the fine particle aggregate portion becomes rigid and the workability of the battery is deteriorated. In addition, there is a possibility that defects may occur or the particles may fall off due to the aggregation of the fine particles. In addition, a fine short circuit is likely to occur, and it is not sufficient for a long life like a battery for HEV and a further severe safety.

In addition, proposals have been made to apply organic particles or inorganic filler layers having a high softening point to the surface of a porous substrate (for example, Patent Document 4). In addition, proposals have been made to apply a polyimide, aramid, and polyamideimide layer in which an inorganic filler is dispersed on the surface of a polyethylene porous film (for example, Patent Documents 5 and 6). In addition, a proposal has been made in which an aramid layer is applied to the surface of a polyethylene porous film, and further, polypropylene and polyethylene particles are applied (for example, Patent Document 7). In these cases, there is a problem that the workability of the battery is deteriorated because the polyimide, aramid, polyamideimide, and aramid layer to be applied are rigid.
Japanese Patent Laid-Open No. 01-103634 JP-A-60-52 JP 2006-286111 A JP 2007-273443 A JP 2006-164873 A JP 2006-348280 A JP 2002-151044 A

  An object of the present invention is to solve the above-described problems. That is, an object is to provide a porous film that has good heat resistance and processability and exhibits excellent characteristics when used as a separator.

In order to achieve the above object, the present invention comprises a porous layer containing an inorganic filler on at least one surface, has a Gurley air permeability of 10 to 600 seconds / 100 ml, and a loop stiffness in terms of thickness 25 μm of 1000 to 2000 μN / cm. Oh it is,
A water-soluble polymer is contained in the porous layer;
The porous layer is characterized in that the porous layer contains a oxirane ring-containing compound and / or a polymer thereof, and cellulose and / or a salt thereof .

  The porous film of the present invention has good heat resistance, high porosity, high air permeability, appropriate pore diameter, workability, and can be provided as a porous film exhibiting excellent characteristics when used as a separator. it can.

  From the viewpoint of workability, the porous film of the present invention is required to have a loop stiffness in terms of thickness of 25 μm of 800 to 2000 μN / cm. When the loop stiffness is less than 800 μN / cm, there are cases where the assemblability of the battery is deteriorated such that the film is not stiff, wrinkles are easily formed, and cutting defects are likely to occur when the separator is cut. When it is higher than 2000 μN / cm, the film is not flexible, and in the wound type battery, the assembling property of the battery may be deteriorated such that the winding tension becomes too high due to the hard separator. More preferably, it is 1000-2000 micron / cm, More preferably, it is 1000-1800 micron / cm from a viewpoint of the assembly property of a battery.

  Hereinafter, a porous film having a loop stiffness converted to a thickness of 25 μm and having a stiffness of 800 to 2000 μN / cm will be described.

  As a means for achieving a loop stiffness in terms of thickness of 25 μm of 800 to 2000 μN / cm, for example, a method of biaxial stretching using a high-rigidity polymer to form a film, a method of applying a high-rigidity layer to a porous resin film, There is a method of making a multilayer film by laminating highly rigid layers.

  As the high-rigidity polymer, a polymer such as polysulfone, polyamide, polyimide, polyamideimide, aromatic polyamide, and fluorine resin may be used alone, or a mixture of several kinds may be used.

  The method of applying a highly rigid layer to the porous resin film is a method of applying a porous layer made of a highly rigid polymer such as polyamide, polyimide, polyamideimide, aromatic polyamide, and fluorine resin to the porous resin film, inorganic There are a method of applying a porous layer in which a filler is arranged, or a method of applying a porous layer made of a highly rigid polymer and an inorganic filler.

  As a method of laminating a highly rigid layer to form a multilayer film, there is a method of laminating a porous film using a highly rigid polymer such as polyamide, polyimide, polyamideimide, aromatic polyamide, or fluorine resin.

  From the viewpoint of production cost, high porosity, high air permeability, and battery processability, a method of applying a highly rigid layer to the porous resin film is preferable. Furthermore, a method of applying a porous layer formed by arranging an inorganic filler on a porous resin film is preferable from the viewpoint of production cost and battery processability.

  The porous film of the present invention is preferably formed by arranging a porous layer containing an inorganic filler having a thickness of 2 to 6 μm on at least one surface of a porous resin film serving as a substrate. With only a porous resin film, it is difficult to control the loop stiffness in terms of a thickness of 25 μm within the range of the present invention, the film is not stiff, and the battery has poor assemblability such that cutting failure tends to occur when the separator is cut. There is a case.

  The inorganic filler used in the present invention is preferably high in electrical insulation and electrochemically stable from the viewpoint of use as a separator for an electricity storage device. When electrical insulation is low, there is a possibility of short-circuiting when a lithium ion battery is assembled. When electrochemically unstable, for example, a side reaction occurs during the charge / discharge reaction, and sufficient energy cannot be obtained.

  Examples of the inorganic filler include oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide and iron oxide, and nitride ceramics such as silicon nitride, titanium nitride and boron nitride, and silicon. Carbide, calcium carbonate, aluminum sulfate, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amicite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, Examples include ceramics such as diatomaceous earth and silica sand, and ceramics such as glass fiber. From the viewpoint of electrochemical stability, it is preferable to use oxide ceramics, which may be used alone, Mix multiple It may be used Te.

  When adding an inorganic filler, it is preferable that the average particle diameter is 0.1-5 micrometers. If the average particle size is less than 0.1 μm, the pores existing in the porous film may be clogged, resulting in poor air permeability. On the other hand, when the thickness exceeds 5 μm, coarse protrusions are formed, the surface property is deteriorated, and the assembling property of the battery such as winding deviation may deteriorate. More preferably, it is 0.1-3 micrometers from a viewpoint of the assembly property of a battery.

  When applying an inorganic filler, the inorganic filler is dispersed in a high-boiling organic solvent such as N-methylpyrrolidone (hereinafter sometimes abbreviated as NMP), and a water-insoluble polymer such as polyvinylidene fluoride is used as a binder. Often applied. In the above case, since the organic solvent has a high boiling point, it is difficult to dry the organic solvent. The organic solvent may be present in the porous layer even after drying.

  Therefore, in the present invention, a water-soluble polymer is preferable from the viewpoint that it is easy to dry, and after applying a porous layer formed by arranging an inorganic filler in the porous film, no moisture remains after drying. Examples of the water-soluble polymer include cellulose and / or cellulose salt, acrylic resin, polyvinyl alcohol, polyvinyl pyrrolidone, resin and the like and salts thereof.

  In the present invention, an oxirane ring-containing compound and / or a polymer thereof is preferably present in the porous layer in order to improve the adhesion between the porous resin film and the porous layer made of an inorganic filler. Examples of the oxirane ring-containing compound include various epoxy resins, epoxy group-containing (meth) acrylates such as glycidyl (meth) acrylate, and epoxy group-containing organosilicon compounds such as Y-glycidoxypropylmethyldiethoxysilane. From the viewpoint of liquidity, an epoxy resin is preferably used. Specific examples of the epoxy resin include bisphenol A type epoxy resin, tetramethylbisphenol A type epoxy resin, bisphenol F type epoxy resin, tetramethylbisphenol F type epoxy resin, bisphenol S type epoxy resin, fluorene type epoxy resin, and biphenyl type epoxy. Examples thereof include resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, polyethylene oxide type epoxy resins, and polypropylene oxide type epoxy resins. These can be used as one kind or a mixture of two or more kinds. Moreover, it is preferable to use a bifunctional or higher functional epoxy resin from the viewpoint of electrolytic solution resistance. From the viewpoint of flexibility, an epoxy equivalent of 100 or higher is preferable, and 300 or higher is more preferable. From the viewpoint of environment and workability, it is preferable to use a water-soluble epoxy resin. Sorbitol polyglycidoxy ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, polypropylene glycol diglycidyl ether, polyethylene Bifunctional or higher aliphatic epoxy resins such as glycol diglycidyl ether can be used, and one or a mixture of two or more can be used. Among these, an oxirane ring-containing compound represented by the following general formula (1) is preferable from the viewpoint of electrolytic solution resistance and flexibility.

(R ^{1 to} R ⁴ represent a substituent selected from an alkyl group having 6 or less carbon atoms, hydrogen, a hydroxyl group, a halogen, a halogenated alkyl group, and a glycidoxy group, and a different substituent may be selected depending on the repeating unit. Represents an integer of 1 or more.)
Specifically, water-soluble epoxy resins such as polypropylene glycol diglycidyl ether and polyethylene glycol diglycidyl ether are particularly preferable. Further, for the purpose of imparting flexibility, phenol ethylene oxide glycidyl ether (particularly preferably having a repeating unit of ethylene oxide chain of about 5 to 10), lauryl alcohol ethylene oxide glycidyl ether (repeating unit of ethylene oxide chain of about 10 to 18). Even if a monoepoxy compound such as epoxidized vegetable oil or the like is used, an epoxy emulsion such as a cresol novolac type epoxy can also be used.

  Further, various curing catalysts may be used in combination for the purpose of promoting the curing of the oxirane ring-containing compound and curing at a low temperature. Curing agents include acids such as Lewis acids, phthalic anhydride, hexahydrophthalic anhydride, nadic anhydride, acid anhydrides such as methyl nadic anhydride, various metal complex compounds such as aluminum acetylacetonate, metal alkoxides, Alkali metal organic carboxylates and carbonates, aliphatic amines such as diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, diethylaminopropylamine, modified aliphatic polyamines, modified aromatic polyamines, triethylamine, benzyldimethylamine, tributylamine Tertiary amines such as tris (dimethylamino) methylphenol, aromatic amines such as m-phenylenediamine, diaminodiphenylmethane and diaminodiphenylsulfone, cyclic amines such as aminoethylpiperazine, 2-methyl Examples include imidazole compounds such as ru-4-ethylimidazole and 2-methylimidazole, quaternary ammonium salts such as triethylbenzylammonium chloride and tetramethylammonium chloride, boron trifluoride, boron trifluoride-monoethylamine complex, and the like. These can be used alone or as a mixture of two or more. The amount of the curing agent used and the curing conditions are not particularly limited, and are determined experimentally as appropriate. The polymer of the oxirane ring-containing compound referred to in the present invention is only required to contain the oxirane ring-opening residue of the oxirane ring-containing compound in the repeating unit of the polymer, and is not composed of the oxirane ring-containing compound alone. It doesn't matter. For example, there is no particular limitation such as ring-opening polymerization of an oxirane ring, polyaddition or polycondensation with diols, diamines, isocyanates, or the like. Moreover, what was polymerized as a crosslinking component of resin with active hydrogen may be used. Furthermore, alcohol, acetal, acetylene, alkyl halide, 2-aminothiol, carbamyl chloride, ethyleneimine, halohydrin, ketone, phosphine, phosphorus oxychloride, sodium sulfite, thioisocyanate, thiol, acetoacetate, acyl halide, oxirane ring, Amide, ammonia, acid, carbon dioxide, cyanoacetate, benzene, hydrocyanic acid, nitrosyl chloride, phthalimide, thiocyanic acid, thionyl chloride, acetonitrile, aldehyde, carbon disulfide, diborane, Grignard reagent, hydrogen sulfide, phosgene, phosphorous acid, It may be polymerized by various polymerization methods after reacting a substance such as silicon tetrachloride, sulfuryl chloride, thiolic acid or water.

  In the present invention, it is also preferable to add an adhesive, for example, polyvinylidene chloride, polyvinylidene fluoride, cellulose and / or cellulose salt, acrylic resin, polyvinyl butyral, polyethylene, polyvinyl alcohol, polytetrafluoroethylene, polyvinylpyrrolidone. Polyimide, polyamide, polysulfide, polyvinyl methyl ether, polyethylene oxide, polypropylene oxide, melamine resin, polyvinyl pyridine, higher alcohols, and salts thereof can be used in combination. Among these resins, cellulose and / or cellulose salt are preferably used from the viewpoint of reactivity with the oxirane ring-containing compound and / or polymer thereof. Cellulose and / or cellulose salt are not particularly limited, but preferred specific examples include hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, and sodium salts and ammonium salts thereof. Especially, it is especially preferable from a reactive viewpoint to contain at least 1 sort (s) selected from the group which consists of carboxymethylcellulose or its salt, and hydroxyethylcellulose or its salt.

  As a method for applying the porous layer, any generally performed method may be used. For example, a dispersion prepared by dispersing a thermoplastic resin in a solvent or the like may be used as a reverse coating method, a bar coating method, or a gravure coating. A coating layer may be formed by coating on a film by a coating method such as a coating method, a rod coating method, a die coating method, or a spray coating method. Further, when adjusting the dispersion, a dispersant or the like may be appropriately added in order to prevent uneven distribution of particles in the coating layer.

  Next, the porous resin film will be described. The porous resin film constituting the porous film of the present invention has many fine through-holes that penetrate both surfaces of the film and have air permeability. The resin constituting the porous resin film may be any of polyolefin resin, polycarbonate, polyamide, polyimide, polyamideimide, aromatic polyamide, fluorine resin, etc., but heat resistance, moldability, production cost reduction, chemical resistance From the viewpoints of properties, oxidation resistance and reduction resistance, polyolefin resins are desirable.

  Examples of the monomer component constituting the polyolefin resin include ethylene, propylene, 1-butene, 1-pentene, 3-methylpentene-1, 3-methyl-1-butene, 1-hexene and 4-methyl. -1-pentene, 5-ethyl-1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-eicosene, vinyl And cyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2-norbornene, and the like. These homopolymers and at least two kinds of copolymers selected from the above monomer components, Examples include, but are not limited to, blends of copolymers and copolymers. In addition to the above monomer components, for example, vinyl alcohol, maleic anhydride or the like may be copolymerized or graft polymerized, but is not limited thereto. Among these, polypropylene is preferable from the viewpoints of heat resistance, air permeability, porosity, and the like.

  As a method for forming a through-hole in a film, either a wet method or a dry method may be used, but a dry method is desirable because the process can be simplified, and in particular, while the film is biaxially oriented to make physical properties uniform and thin. In view of maintaining high strength, it is preferable to use the β crystal method.

  In order to form through-holes in the film using the β crystal method, it is important to form 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, a crystallization nucleating agent that selectively forms β crystals is preferably used as an additive. Examples of the β crystal nucleating agent include known pigment compounds and amide compounds. In particular, amide compounds disclosed in JP-A-5-310665 can be preferably used. The addition amount of the β crystal nucleating agent is preferably 0.05 to 0.5 parts by mass, more preferably 0.1 to 0.3 parts by mass when the entire polypropylene resin is 100 parts by mass. .

  The polypropylene resin constituting the porous polypropylene film of the present invention is 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. It is preferable that If the MFR is out of the above preferred range, it may be difficult to obtain a biaxially 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 high air permeability is achieved. May be difficult. A commercially available resin can be used as the isotactic polypropylene resin.

  Of course, a homopolypropylene resin can be used for the polypropylene film of the present invention, and from the viewpoints of stability in the film-forming process, film-forming properties, and uniformity of physical properties, the ethylene component, butene, hexene, You may copolymerize alpha olefin components, such as an octene, in 5 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, and for example, polypropylene resins PF814, PF633, and PF611 manufactured by Basel, polypropylene resin WB130HMS manufactured by Borealis, and polypropylene resins D114 and D206 manufactured by Dow can be used.

In the polypropylene resin constituting the polypropylene film of the present invention, the void formation efficiency at the time of stretching is improved, and the air permeability is improved by increasing the pore diameter. Therefore, an ethylene / α-olefin copolymer is added to the polypropylene resin in an amount of 1 to It is preferable to add 10% by 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.
The polypropylene porous film of the present invention preferably has a Gurley air permeability of 10 to 600 seconds / 100 ml. When the Gurley air permeability is less than 10 seconds / 100 ml, the porosity is increased or the pore diameter is too large, and the strength may not be sufficiently maintained, or the battery life is shortened when used as a separator. There is a case. On the other hand, if it exceeds 600 seconds / 100 ml, the characteristics when used as a separator will be insufficient. More preferably, it is 10-300 seconds / 100ml, More preferably, it is 10-200 seconds / 100ml from a viewpoint of a separator characteristic. Here, the Gurley air permeability is an index of the air permeability of the sheet and is shown in JIS P 8117 (1998). Gurley permeability is the balance of the amount of β-crystal nucleating agent or β-crystal nucleating agent-added polypropylene and ultra-low-density polyethylene added to the polypropylene constituting the film. Crystallization conditions for solidifying the polymer (metal drum temperature, peripheral speed of the metal drum, thickness of the unstretched sheet to be obtained, etc.) and stretching conditions in the stretching process (stretching direction (longitudinal or lateral), stretching method (vertical or lateral) Uniaxial stretching, longitudinal-lateral or lateral-longitudinal sequential biaxial stretching, simultaneous biaxial stretching, re-stretching after biaxial stretching, etc.), stretching ratio, stretching speed, stretching temperature, etc.).

  Moreover, in this invention, it is preferable that the average hole diameter of a through-hole is 40-150 nm. If the thickness is less than 40 nm, the characteristics when used as a separator are insufficient. If the thickness exceeds 150 nm, particles are likely to fall off or slightly short-circuit, which may cause problems such as adversely affecting the battery life. More preferably, it is 40-100 nm from the viewpoint of the life of the battery because it is difficult for particles to fall off or slightly short circuit. The average pore size is increased by increasing the addition amount of β crystal nucleating agent or β crystal nucleating agent-added polypropylene or ultra-low density polyethylene within a preferable range. The hole diameter becomes smaller.

  The method for producing the porous resin film in the present invention will be specifically described below. In addition, the manufacturing method of the film of this invention is not limited to this. 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 raw material is prepared by mixing 0.2 parts by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide and 2 parts by mass in advance using a twin-screw extruder. At this time, the melting temperature is preferably 270 to 300 ° C.

  Next, the mixed raw material is supplied to a single-screw melt extruder, and melt extrusion is performed at 200 to 230 ° C. 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. At this time, 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. Further, air may be blown over the entire surface using an air knife as necessary from the close contact state of the entire sheet on the drum.

  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 120 ° C, more preferably 95 to 110 ° C. As a draw ratio, it is 3-6 times, More preferably, it is 3-5 times. When the film is stretched in the longitudinal direction, a so-called neck-down phenomenon is observed in which the film width decreases. In order to achieve high air permeability, the neck-down ratio (film width after stretching / before stretching) The film width is preferably 30 to 70%. Considering stretching in the width direction, 40 to 65% is more preferable. 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 100 to 1,000% / minute, more preferably 100 to 600% / minute. Subsequently, heat setting is performed in the stenter as it is, and the temperature is preferably from the transverse stretching temperature to 160 ° C. Furthermore, it may be carried out 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 7 to 12% from the viewpoint of thermal dimensional stability.

  Next, a coating liquid containing particles is applied onto the obtained polypropylene porous film. The particle concentration of the coating liquid is preferably 5 to 20% by mass. If the particle concentration is less than 5% by mass, the air permeability which is outside the range of the loop stiffness of the present invention may be deteriorated. If the particle concentration is higher than 20% by mass, the particles may fall off. The adhesive organic resin concentration of the coating liquid is preferably 1 to 10% by mass. When the adhesive organic resin concentration is less than 1% by mass, the adhesion with the porous resin film may be insufficient, or the particles may drop off. When the adhesive organic resin concentration is 10% by mass or more, air permeability may be deteriorated. Further, when adjusting the dispersion, in order to prevent uneven distribution of particles in the coating layer, a cellosolve-based dispersant or the like may be added as appropriate.

  The particle concentration / binder concentration ratio is preferably 15-30. If the particle concentration / binder concentration ratio is less than 15, the gas permeability may be deteriorated. If the particle concentration / binder concentration ratio is 30 or more, particles may fall off.

  When the coating liquid is applied, a surface treatment such as a corona discharge treatment may be applied to the coated surface of the film, if necessary, in air, nitrogen, or a mixed atmosphere of carbon dioxide and nitrogen. As a coating method, for example, a dispersion prepared by dispersing particles in a solvent or the like is applied onto a film by a coating method such as a reverse coating method, a bar coating method, a gravure coating method, a rod coating method, a die coating method, or a spray coating method. It can be applied and dried to form a coating layer. As drying conditions, the drying temperature is preferably 80 to 100 ° C., and the drying time is preferably 10 seconds to 10 minutes. If the drying temperature is less than 80 ° C., the coating liquid may become undried. Moreover, when drying temperature becomes higher than 100 degreeC, shrinkage | contraction of a porous resin film will become large and air permeability may worsen. If the drying time is less than 10 seconds, the coating liquid may become undried. Moreover, when drying temperature becomes longer than 10 minutes, the shrinkage | contraction of a porous resin film may become large, or air permeability may worsen.

  Since the porous film of the present invention can hold an organic solvent, it can be used as a separator for an electricity storage device that uses an organic solvent as an electrolytic solution. In addition, the polypropylene porous film of the present invention has a high porosity and high air permeability, so the resistance as a separator is low, and it can be preferably used for lithium ion batteries and lithium ion capacitors among the above electricity storage devices. .

  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 hole diameter of through holes POROUS MATERIALS, Inc. Using an automatic pore size distribution measuring device “PERM-POROMETER” manufactured by the manufacturer, the porous layer surface was measured as the upper side. Measurement conditions are as follows.
Test solution: 3M “Fluorinert” FC-40
Test temperature: 25 ° C
Test gas: Air analysis software: Capwin
Measurement conditions: Automatic measurement based on default conditions of Capillary Flow Porometry-Wet up, Dry down Note that the following relational expression holds between the pore diameter (pore diameter) and the test pressure.
d = Cγ / P × 10 ³
[However, d: pore diameter (nm), C: constant, γ: surface tension of fluorinate (16 mN / m), P: pressure (Pa). ]
Here, based on the above, the average pore diameter was calculated from the 1/2 half-wetting curve using the data analysis software attached to the apparatus. However, the measurement limit was set to 37 nm due to the problem of the upper limit of pressure during measurement. The same measurement was performed for the same sample five times at different locations, and the average value of the average pore diameters obtained was taken as the average pore diameter of the through holes in the sample.

(2) β crystal forming ability and β crystal fraction resin or 5 mg of a film was sampled in an aluminum pan and measured using a differential scanning calorimeter (RDC220 manufactured by Seiko Denshi Kogyo). First, the temperature is raised from room temperature to 240 ° 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. About the melting peak observed when the temperature is increased (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 of the α crystal is the melting peak of the α crystal, the melting peak of the α crystal is taken as the melting peak of the base, and the area of the region surrounded by the peak drawn from the flat portion on the high temperature side. When the heat of fusion of ΔHα and β crystals is ΔHβ, the value calculated by the following formula is β crystal forming ability. The heat of fusion was calibrated using indium.
β crystal forming ability (%) = [ΔHβ / (ΔHα + ΔHβ)] × 100
In addition, the β crystal fraction in the state of the sample can be calculated by calculating the abundance ratio of the β crystal in the same manner from the melting peak observed in the first run.

(3) Sample thickness The sample thickness t (μm) was obtained by using a dial gauge in accordance with JIS K7130 (1992) A-2 method with the porous layer as the upper surface and 10 samples stacked. The thickness was measured at any five locations. The average value was divided by 10 to obtain the sample thickness t.

(4) When calculating the loop stiffness (bending strength index) M in a thickness of 25 μm of the loop stiffness film, the sample was cut into a length of 150 mm and a width of 10 mm in the measurement direction, and a loop stiffness tester manufactured by Toyo Seiki Seisakusho Co., Ltd. was used. The bending stress M1 (μN) was measured. In addition, when the porous layer was present only on one side, the measurement was performed with the porous layer on the outside. Moreover, when the porous layer was coated on both sides, the measurement was performed with the larger porous layer as the outer side. The loop length was 50 mm and the crushing distance was 5 mm. A loop stiffness M (μN / cm) having a thickness of 25 μm was determined from the measured value M1 (N) of the bending stress and the sample thickness t (μm) using the following formula.
M = M1 × (25 / t) ³ /(1.0)
The measurement was performed using 20 samples having different sampling positions in the longitudinal direction and the width direction, and the average value was obtained.

(5) Gurley air permeability Measured according to the method B of JIS P 8117 (1998) at 23 ° C. and 65% RH with the porous layer surface facing upward (unit: seconds / 100 ml). The same measurement was performed for the same sample five times at different locations, and the average value of the obtained Gurley air permeability was taken as the Gurley air permeability of the sample. At this time, those having an average value of Gurley air permeability exceeding 7,200 seconds / 100 ml were regarded as having substantially no air permeability, and were set to infinity (∞) seconds / 100 ml.

(6) Heat resistance test A sample film was cut into a 3 × 3 cm square and 1 × 3 cm under the conditions of a heating temperature of 200 ° C., a heating time of 10 seconds, and a load of 0.1 MPa using a heat seal tester manufactured by Tester Sangyo Co., Ltd. The area of was heated.
The film which performed the said process was evaluated on the following references | standards.
○: The shape of the film is maintained, and there is no formation of holes by visual observation. X: There is formation of holes in the film. Preparation of Electrolyte Solution After dissolving LiC ₄ F ₉ SO ₃ in trimethyl phosphate, propylene carbonate was added and mixed, and LiC ₄ F ₉ was added to a mixed solvent having a volume ratio of propylene carbonate to trimethyl phosphate of 1: 2. An organic electrolyte solution in which SO ₃ was dissolved at 0.6 mol / liter was prepared. In order to investigate the flash point of the organic electrolyte solution thus obtained, the electrolyte solution was heated to a predetermined temperature, and a fire was brought close to the liquid surface to investigate whether it would ignite. In the tests at 100 ° C., 150 ° C., and 200 ° C., there was no ignition, and it was found that the flash point of this electrolyte was 200 ° C. or higher.

B. Production of Battery A positive electrode having a lithium cobalt oxide (LiCoO ₂ ) thickness of 40 μm manufactured by Hosen Co., Ltd. was used and cut into a width of 200 mm and a length of 4,000 mm. Further, a graphite negative electrode having a thickness of 50 μm manufactured by Hosen Co., Ltd. was used and cut into a width of 200 mm and a length of 4,000 mm.

  Next, the above belt-like positive electrode is overlapped with the sheet-like negative electrode through the separator film of each Example / Comparative Example and wound into a spiral to form a spiral electrode body, and then a bottomed cylindrical battery After filling the case and welding the positive and negative electrode lead bodies, the electrolyte was poured into the battery case. The opening of the battery case was sealed and the battery was precharged to produce a cylindrical organic electrolyte secondary battery. 100 batteries were prepared for each of the examples and comparative examples.

C. The number of defects caused by the separator in the process of producing 100 battery-workable spiral electrode bodies was examined. The defective contents are the breakage of the separator at the time of producing the spiral electrode body, the wrinkle of the separator, the short circuit due to the defect of the separator, and the short circuit due to the dropping of the fine particles contained in the separator.
○: 0 △: 1 ×: 2 or more Battery characteristics For each secondary battery produced, charge and discharge operations were performed under an atmosphere of 25 ° C. to charge the battery to 4.2 V at 1,600 mA for 3.5 hours and to discharge to 2.7 V at 1,600 mA. The capacity was examined. Further, a charge / discharge operation of charging at 1,600 mA to 4.2 V for 3.5 hours and discharging at 1,600 mA to 2.7 V was performed 100 times, and the discharge capacity at the 100th time was examined.
[(Discharge capacity at the 100th time) / (Discharge capacity at the first time)] × 100 The value obtained by the calculation formula was evaluated according to the following criteria.
○: 85% or more Δ: 80% or more and less than 85% ×: less than 80% or less The present invention will be described more specifically based on examples, but it goes without saying that the present invention is not limited thereto. .

Example 1
First, the following composition was compounded at 300 ° C. with a twin-screw extruder to prepare a resin A chip.
<Polypropylene resin A>
92 parts by mass of Sumitomo Chemical Co., Ltd. homopolypropylene FSX80E4 (hereinafter referred to as PP-1), 1 part by mass of Basel polypropylene PF-814 (hereinafter referred to as HMS-PP), which is a high melt tension polypropylene resin, Engage 8411 (melt index: 18 g / 10 min., Hereinafter simply referred to as PE) made by Dow Chemical, which is an ethylene-octene-1 copolymer, is added to 7 parts by mass, and N, N′-, which is a β crystal nucleating agent. 0.2 parts by mass of dicyclohexyl-2,6-naphthalenedicarboxamide (manufactured by Shin Nippon Rika Co., Ltd., Nu-100, hereinafter simply referred to as β crystal nucleating agent) and Ciba Specialty, an antioxidant Chemicals IRGANOX1010 and IRGAFOS168 are each 0.15 and 0.1 parts by mass (hereinafter simply referred to as acid-proofing agents, Unless mounting 3: Using 2 weight ratio)
Chips made of polypropylene resin A are fed to a single screw extruder, melted and kneaded at 220 ° C, passed through a 400-mesh single plate filter, extruded from a slit-shaped base heated to 200 ° C, and heated to a surface temperature of 120 ° C. The film was cast into a cooling metal drum, heated to 120 ° C. using an air knife from the non-drum surface side of the film, and formed into a sheet shape while being blown into close contact with hot air to obtain an unstretched sheet. The contact time with the cooling metal drum at this time was 40 seconds.

The obtained unstretched sheet is preheated through a roll group maintained at 105 ° C., passed between rolls maintained at 105 ° C. and provided with a circumferential speed difference, stretched 6 times in the longitudinal direction at 105 ° C., and then at 127 ° C. for 1 second. Hold and cool to 95 ° C. After cooling, it was introduced into a tenter while holding both ends with clips, preheated at 150 ° C., and stretched 7 times in the transverse direction at 150 ° C. Next, heat-fixed at 155 ° C. while giving 5% relaxation in the transverse direction in the tenter, uniformly cooled, cooled to room temperature, wound up, 21 μm thick, Gurley air permeability 200 seconds / 100 ml of porous film was obtained.
Next, 15 parts by mass of Quartron “PL-20” (average particle size 370 nm) manufactured by Fuso Chemical Industry Co., Ltd., which is silica particles, and Nagase Kasei Kogyo Co., Ltd., which is an oxirane ring-containing compound and / or a polymer thereof, are used as the coating agent. 1.0 part by mass of Denacol "EX-861" manufactured by Co., Ltd. and 0.5 part by mass of "CMC Daicel 2240" manufactured by Daicel Chemical Industries, Ltd., which is cellulose and / or cellulose salt, and 83.5 A suspension mixed with parts by mass was prepared. The coating agent was No. A porous film having a total thickness of 25 μm is coated on one side of a porous film with 14 Meyer bars, then dried in a hot air oven at 80 ° C. for 1 minute, and further dried in a hot air oven at 80 ° C. for 12 hours or more. A film was obtained.
The obtained film was measured for Gurley air permeability, heat resistance test, battery assembly, and battery characteristics. The results are shown in Tables 1 and 2. The obtained film had both high processability and air permeability equivalent to that of the base film, separator characteristics, and excellent battery.

(Example 2)
20 parts by mass of Quatron “PL-20” manufactured by Fuso Chemical Industry Co., Ltd., which is the silica particle of the coating agent, and Denacol “EX-861” manufactured by Nagase Chemical Industries Co., Ltd., which is a polymer and / or a polymer thereof. The same operation as in Example 1 except that 2 parts by mass and 1 part by mass of “CMC Daicel 2240” manufactured by Daicel Chemical Industries, Ltd., which is cellulose and / or cellulose salt, were changed to 77 parts by mass of ion-exchanged water. The physical property values are shown in Tables 1 and 2. The obtained film had both high processability and air permeability equivalent to that of the base film, separator characteristics, and excellent battery.

(Example 3)
The same operation as in Example 1 was performed except that the cellulose and / or cellulose salt of the coating agent was changed to “HEC Daicel SP600” manufactured by Daicel Chemical Industries, Ltd. The obtained film had both high processability and air permeability equivalent to that of the base film, separator characteristics, and excellent battery.

Example 4
The same operation as in Example 1 was carried out except that the oxirane ring-containing compound of the coating agent and / or the polymer thereof was changed to Denacor “EX-841” manufactured by Nagase Chemical Industries, Ltd. It was shown to. The obtained film had both high processability and air permeability equivalent to that of the base film, separator characteristics, and excellent battery.

(Example 5)
The coating agent described in Example 1 was No. The same operation as in Example 1 was carried out except that the porous film was coated on both sides with an 8 Meyer bar, and the physical property values are shown in Tables 1 and 2. The obtained film had both high processability and air permeability equivalent to that of the base film, separator characteristics, and excellent battery.

(Example 6)
The same operation as in Example 1 was carried out except that the cellulose and / or cellulose salt of the coating agent was changed to “Sunrose A” manufactured by Nippon Paper Chemicals Co., Ltd. The obtained film had both high processability and air permeability equivalent to that of the base film, separator characteristics, and excellent battery.

(Example 7)
The same operation as in Example 1 was carried out except that the oxirane ring-containing compound and / or polymer thereof in the coating agent was changed to “YD-128” manufactured by Toto Kasei Co., Ltd. It was. The obtained film had both high processability and air permeability equivalent to that of the base film, separator characteristics, and excellent battery.

(Example 8)
The same physical properties as in Example 1 were performed except that the coating particles were changed to “AKP-G008” (average particle size 3 μm) manufactured by Sumitomo Chemical Co., Ltd., which is alumina particles. Indicated. The obtained film had both high processability and air permeability equivalent to that of the base film, separator characteristics, and excellent battery.

Example 9
Except for changing the particles of the coating to “TTO-55” (average particle diameter of 100 nm) manufactured by Ishihara Sangyo Co., Ltd., which is a titania particle, the same physical properties as in Example 1 were performed. Indicated. The obtained film had both high processability and air permeability equivalent to that of the base film, separator characteristics, and excellent battery.

(Example 10)
The same physical property values as in Example 1 were carried out except that the coating particles were changed to “W-0.1V” (average particle size 2 μm) manufactured by Daiichi Rare Element Chemical Co., Ltd., which are zirconia particles. Are shown in Tables 1 and 2. The obtained film had both high processability and air permeability equivalent to that of the base film, separator characteristics, and excellent battery.

(Example 11)
The same operation as in Example 1 was carried out except that the coating particles were changed to “AKP-G008” (average particle size 2.5 μm) manufactured by Sumitomo Chemical Co., Ltd., which is magnesia particles. It was shown in 2. The obtained film had both high processability and air permeability equivalent to that of the base film, separator characteristics, and excellent battery.

(Example 12)
The same physical properties as in Example 1 were carried out except that the coating particles were changed to “HM-5” (average particle size 1 μm) manufactured by Sanyo Ceratech Co., Ltd., which is silicon nitride. Indicated. The obtained film had both high processability and air permeability equivalent to that of the base film, separator characteristics, and excellent battery.

(Example 13)
The same operation as in Example 1 was performed except that the base film was changed to “Hypore” manufactured by Asahi Kasei Chemicals Corporation. The obtained film had both high processability and air permeability equivalent to that of the base film, separator characteristics, and excellent battery.

( Reference Example 14)
As a coating agent, 20 parts by mass of Quartron “PL-20” manufactured by Fuso Chemical Industry Co., Ltd., which is a silica particle, and 5 parts by mass of “FLX-5010” manufactured by BASF Co., Ltd., which is an acrylic resin emulsion, and ion-exchanged water. A suspension was prepared by mixing 75 parts by mass. The coating agent was No. A porous film having a total thickness of 25 μm is coated on one side of a porous film with 14 Meyer bars, then dried in a hot air oven at 80 ° C. for 1 minute, and further dried in a hot air oven at 80 ° C. for 12 hours or more. A film was obtained. The obtained film had both high processability and air permeability equivalent to that of the base film, separator characteristics, and excellent battery.

( Reference Example 15)
As a coating agent, 20 parts by mass of quartz particle “PL-20” manufactured by Fuso Chemical Industry Co., Ltd., which is silica particles, and 5 parts by mass of “# 1320” manufactured by Kureha Chemical Co., Ltd., which is a dispersion of PVDF, are ion-exchanged water. A suspension was prepared by mixing 75 parts by mass. The coating agent was No. A porous film having a total thickness of 25 μm is coated on one side of a porous film with 14 Meyer bars, then dried in a hot air oven at 80 ° C. for 1 minute, and further dried in a hot air oven at 80 ° C. for 12 hours or more. A film was obtained. The obtained film had both high processability and air permeability equivalent to that of the base film, separator characteristics, and excellent battery.

(Comparative Example 1)
Except that the coating agent was not applied, the same operation as in Example 1 was performed, and the physical property values are shown in Tables 1 and 2. In this case, although having high air permeability and separator characteristics, the heat resistance at 200 ° C. was insufficient, the loop stiffness was low, and the processability was insufficient.

(Comparative Example 2)
15 parts by mass of Fukuro Chemical Co., Ltd. Quartron “PL-20”, which is silica particles, and 0.5 mass of “CMC Daicel 2240”, Daicel Chemical Industries, Ltd., which is cellulose and / or cellulose salt. The physical properties were shown in Tables 1 and 2 in the same manner as in Example 1 except that 84.5 parts by mass of the parts and ion-exchanged water were used. In this case, although it had high air permeability and heat resistance at 200 ° C., the loop stiffness was low, the processability was insufficient, the particles dropped out, and the separator characteristics were also insufficient.

(Comparative Example 3)
0.5 parts by mass of “CMC Daicel 2240” manufactured by Daicel Chemical Industries, Ltd., which is a cellulose and / or cellulose salt, and Denacor manufactured by Nagase Kasei Kogyo Co., Ltd., which is an oxirane ring-containing compound and / or a polymer thereof. The same physical properties as in Example 1 were carried out except that 1.0 part by mass of “EX-861” and 98.5 parts by mass of ion-exchanged water were used. In this case, the coating film was formed into a film, lacking air permeability, low loop stiffness, insufficient workability, and insufficient separator characteristics.

(Comparative Example 4)
14 parts by mass of Quatron “PL-20” manufactured by Fuso Chemical Industry Co., Ltd., which is a silica particle, and an oxirane ring-containing compound and / or a polymer thereof, Denacol “EX-861” manufactured by Nagase Chemical Industries, Ltd. The same physical properties as in Example 1 were performed except that 1.0 part by mass and 85 parts by mass of ion-exchanged water were used. In this case, although it had high air permeability and heat resistance at 200 ° C., the loop stiffness was low, the processability was insufficient, the particles dropped out, and the separator characteristics were also insufficient.

(Comparative Example 5)
Synthesis of para-aramid solution Synthesis of poly (paraphenylene terephthalamide) (hereinafter abbreviated as PPTA) using a 5 liter (l) separable flask having a stirring blade, thermometer, nitrogen inlet tube and powder addition port went. The flask was sufficiently dried, charged with 4200 g of NMP, 272.65 g of calcium chloride dried at 200 ° C. for 2 hours was added, and the temperature was raised to 100 ° C. After calcium chloride was completely dissolved, the temperature was returned to room temperature, and 132.91 g of paraphenylenediamine (hereinafter abbreviated as PPD) was added and completely dissolved. While maintaining this solution at 20 ± 2 ° C., 243.32 g of terephthalic acid dichloride (hereinafter abbreviated as TPC) was added in 10 divided portions every about 5 minutes. Thereafter, the solution was aged for 1 hour while maintaining at 20 ± 2 ° C., and stirred for 30 minutes under reduced pressure in order to remove bubbles.

  Next, 100 g of this polymerization solution was weighed into a 500 ml separable flask having a stirring blade, a thermometer, a nitrogen inlet tube and a liquid addition port, and the NMP solution was gradually added. Finally, a PPTA solution having a PPTA concentration of 2.0% by weight was prepared, and this was used as a P solution. A porous film made of PE (polyethylene) (film thickness 25 μm, air permeability 700 sec / 100 cc, average pore radius (mercury intrusion method) 0.04 μm) was used. Using a bar coater manufactured by Tester Sangyo Co., Ltd. (gap: 200 μm), P solution, which is a heat-resistant resin solution, is applied onto the PE porous membrane placed on a glass plate and held in a draft in the laboratory for about 20 minutes. As a result, PPTA was precipitated, and a cloudy film was obtained on the PE porous film. The PE porous membrane with the membrane attached thereto was immersed in ion-exchanged water, and after 5 minutes, the membrane was peeled from the glass plate, washed thoroughly with flowing ion-exchanged water, and then freed of water. . This membrane was sandwiched between nylon cloths and further sandwiched between aramid felts. In a state where the PE porous membrane with the film attached is sandwiched between nylon cloth and aramid felt, place an aluminum plate, cover it with nylon film, seal the nylon film and aluminum plate with gum, A conduit for decompression was attached.

  A composite in which the whole is put into a heat oven and the membrane is dried while reducing the pressure at 60 ° C., and a shutdown layer made of a PE porous membrane and a heat resistant porous layer made of an aramid porous membrane (thickness: 5 μm) are laminated. A film was obtained. The prepared composite film was placed on a glass plate, and carboxymethylcellulose [Daiichi Kogyo Seiyaku Co., Ltd., trade name: Serogen 4H] was dissolved in ion-exchanged water using a bar coater (gap 10 μm) manufactured by Tester Sangyo Co., Ltd. Fine particles [manufactured by Nippon Aerosil Co., Ltd., trade name: Alumina C, particle size 0.013 μm] were dispersed and applied to the surface of the aramid porous layer side adjusted to a solid content of 1.5% by adding ion exchange water. After that, it was naturally dried. In this case, although it had high air permeability and heat resistance at 200 ° C., the loop stiffness was low, the processability was insufficient, the particles dropped out, and the separator characteristics were also insufficient.

(Comparative Example 6)
In dehydrated N-methyl-2-pyrrolidone, 2-chloroparaphenylenediamine corresponding to 80 mol% with respect to the total amount of diamine and 4,4′-diaminodiphenyl ether corresponding to 20 mol% with respect to the total amount of diamine are dissolved. Then, 2-chloroterephthalic acid chloride corresponding to 98.5 mol% was added thereto, polymerized by stirring for 2 hours, neutralized with lithium carbonate, and an aromatic polyamide solution having a polymer concentration of 11% by weight was obtained. . This solution was reprecipitated with water to obtain a polymer 1. 15% by weight of this polymer 1, 75% by weight of N-methyl-2-pyrrolidone and 10% by weight of polyethylene glycol having a number average molecular weight of 20,000 were taken, and the polymer was dissolved in N-methyl-2-pyrrolidone. Then, polyethylene glycol was added to obtain a uniformly and completely compatible polymer solution. This polymer solution was formed into a film of about 50 μm on a glass plate using a bar coater, allowed to stand in an oven adjusted to 90 ° C. for 3 minutes, and then placed in an oven adjusted to 150 ° C. for 3 minutes. Separated and deposited to form a film. The solvent evaporation rate at this time was 60%. This film was peeled from the glass plate, and the solvent, polyethylene glycol and impurities were extracted in a 50 ° C. water bath for 1 hour. Thereafter, it was fixed to an aluminum frame, air-dried for 1 hour, and then heat-treated at 320 ° C. for 1 minute.

  In this case, although it had high air permeability and heat resistance at 200 ° C., the loop stiffness was high and the workability was insufficient.

  The porous film according to the present invention can be provided as a porous film having good heat resistance and good separator characteristics.

Claims (5)

Comprising a porous layer containing at least one surface of the inorganic filler, a Gurley air permeability 10 to 600 sec / 100 ml, Ri loop stiffness is 1000~2000μN / cm der thickness 25μm terms,
A water-soluble polymer is contained in the porous layer;
A porous film comprising an oxirane ring-containing compound and / or a polymer thereof, and cellulose and / or a salt thereof in the porous layer. The oxirane ring-containing compound is an epoxy resin, and the cellulose and / or salt thereof includes at least one selected from the group consisting of carboxymethyl cellulose or a salt thereof, and hydroxyethyl cellulose or a salt thereof. The porous film according to claim 1 . The porous film of Claim 1 or 2 used for an electrical storage device separator. An electricity storage device using the porous film according to claim 3 as an electricity storage device separator. The electrical storage device of Claim 4 whose electrical storage device is a lithium ion battery.