JP5707961B2 - Storage device separator - Google Patents

Description

  The present invention relates to an electrical storage device separator having excellent electrical characteristics and safety. Specifically, by providing a particle-containing layer containing inorganic particles and thermoplastic resin particles in a polyolefin-based porous film, not only has excellent heat-resistant dimensional stability, but also has excellent electrical characteristics of the polyolefin-based porous film, The present invention relates to a highly safe separator for an electricity storage device that can be suitably used for a high-power lithium ion secondary battery capable of losing ionic conductivity by a shutdown function during abnormal heat generation of the electricity storage device.

  Polyolefin-based porous films are widely used in separator applications for lithium ion secondary batteries because they are excellent in mechanical properties in addition to electrical insulation and ion permeability. With increasing energy density, studies have been made on increasing the diameter of a film, reducing the thickness of the film, increasing the porosity, and the like (see, for example, Patent Documents 1 and 2). In addition, in order to ensure safety when using these films, proposals have been made to provide a layer composed of a binder and low-melting point resin particles or inorganic particles on the outermost layer of the film (for example, Patent Documents 3 to 3). 5). However, when the above layer is provided on the film, there is a problem in that the air permeability resistance is lowered as compared with the film used for the substrate, and the battery characteristics when used as a separator are adversely affected. In addition, although proposals have been made to maintain air permeability resistance by configuring the above layer only with low-melting point resin particles (for example, Patent Document 6), the heat resistance when used as a separator is low and safety is improved. There was a problem that it could not be secured. As a method for laminating the particle-containing layer, a method of applying a fixing agent to a polyolefin-based porous film (for example, Patent Document 7) has been proposed, but the coating liquid penetrates into the film from the open surface of the polyolefin-based porous film. However, there has been a problem that air permeability resistance becomes high.

Japanese Patent Laid-Open No. 11-302434 International Publication WO2005 / 61599 Pamphlet JP 2005-285385 A JP 2007-95575 A JP 2009-091118 A JP 2007-324073 A JP 2002-166218 A

  An object of the present invention is to solve the above-described problems. That is, the object of the present invention is to provide a particle-containing layer on a polyolefin-based porous film, thereby suppressing deterioration of air permeability resistance and suitable for a separator for an electricity storage device that achieves both excellent battery performance and safety at a high level. It is to provide a porous film.

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

A particle-containing layer containing inorganic particles is formed on at least one surface of the polyolefin-based porous film, and the particle-containing layer has a laminate structure of at least two layers, and the air resistance change rate (Gd) defined below. Is a porous film having an air permeability resistance (Ga) of 50 to 500 seconds / 100 ml.

Gd = {(Ga−Gb) / Gb} × 100
Gd: Permeability change rate (%)
Ga: Air permeability resistance of the porous film (second / 100 ml)
Gb: Air permeation resistance of polyolefin-based porous film (sec / 100 ml)

  The polyolefin-based porous film of the present invention has good heat resistance, high air permeability, and good shutdown properties, and can be provided as a porous film that exhibits excellent characteristics when used as a separator.

  The polyolefin-based porous film used in the present invention has many fine through holes that penetrate both surfaces of the film and have 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 dimensions when the particle-containing layer 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 heat-resistant resin other than the polyolefin resin. In that case, ion conductivity, which is a basic characteristic as a separator, is required. 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 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. 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, 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 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.

  The air resistance of the polyolefin-based porous film is preferably 50 to 500 seconds / 100 ml. When the air permeation resistance is less than 50 seconds / 100 ml, it is difficult to completely close the pores even if the particles are softened, and the shutdown property is insufficient. Moreover, when it exceeds 500 seconds / 100 ml, it exists in the tendency for the battery characteristic at the time of using a porous film as a separator to deteriorate.

  The air resistance of the polyolefin-based porous film is preferably 80 to 400 seconds / 100 ml, more preferably 100 to 300 seconds / 100 ml, and still more preferably 150 to 250 seconds / 100 ml, although it depends on the application.

  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 by heating 5 mg of polypropylene resin or polypropylene film at a rate of 10 ° C./min from room temperature to 240 ° C. in a nitrogen atmosphere using a differential scanning calorimeter and holding 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 + ΔHββ] × 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 porous film used in the present invention preferably has a porosity of 60 to 90%. If it is less than 60%, the characteristics when a polyolefin-based porous film is used as a separator may be insufficient. If it exceeds 90%, it may be insufficient from the viewpoint of separator characteristics and strength. The porosity of the polyolefin-based porous film can be obtained from the following formula from the specific gravity (ρ) of the polyolefin-based porous film and the specific gravity (d) of the polyolefin-based resin.

Porosity (%) = [(d−ρ) / d] × 100
The polyolefin-based porous film used in 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 preferably has an average pore diameter of 40 to 400 nm. If the thickness is less than 40 nm, the characteristics when used as a separator are insufficient. If the thickness exceeds 400 nm, particles are likely to fall off or slightly short-circuit, which may cause problems such as adversely affecting the battery life.

  In the porous film of the present invention, a particle-containing layer containing inorganic particles and thermoplastic resin particles is provided on at least one surface of the above-described polyolefin-based porous film. By providing the particle-containing layer, the polyolefin porous film can have excellent heat resistance and mechanical properties. The particle-containing layer will be described in detail below.

  The particle-containing layer of the porous film of the present invention contains inorganic particles.

  The types of inorganic particles include, for example, 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 thereof 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 several It may be used.

  Furthermore, from the viewpoint of stability in the lithium ion battery, inorganic particles having a water content of 1% by mass or less are preferable. More preferably, the water content is preferably 0.5% by mass or less.

  In the present invention, the inorganic particles having a water content of 1% by mass or less are preferably inorganic particles having a dense structure having no 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. Alumina, silica produced by a dry method, and zirconia produced by a dry method may be subjected to a silane coupling treatment.

  About these inorganic particles, it is preferable that an average particle diameter is 0.05-2 micrometers from a viewpoint of coexistence of the air permeability of a particle content layer, and a dynamic characteristic, and it is more preferable if it is 0.05-1 micrometers. Especially preferably, it is 0.1-0.6 micrometer. If the average particle size is less than 0.05 μm, the particles may permeate into the film from the open surface of the polyolefin porous film, and the air permeation resistance of the polyolefin porous film may increase. On the other hand, if the average particle diameter exceeds 2 μm, the gap between the particles becomes large, and the mechanical properties of the particle-containing layer may be lowered. Here, the method for measuring the average particle diameter of the inorganic particles will be described in detail later, but the mass average diameter is calculated and adopted using the equivalent circle diameter obtained by image processing from the transmission electron micrograph of the particles.

  It is preferable to use thermoplastic resin particles having a melting point of 100 to 140 ° C. in the particle-containing layer of the porous film of the present invention from the viewpoint of imparting shutdown property to the film. If the melting point of the thermoplastic resin particles is less than 100 ° C, the operating environment will shut down the through-holes of the film at a low temperature of about 100 ° C, which is not a problem for other materials of the electricity storage device, and will malfunction Will occur. On the other hand, if the melting point exceeds 140 ° C., a self-heating reaction may start in the electricity storage device before shutting down. In the case of a cobalt-based positive electrode that is often used in lithium ion batteries, the shutdown preferably functions at 125 to 140 ° C. from the viewpoint of thermal stability of the positive electrode, and therefore the melting point of the thermoplastic resin particles is 120 to 140 ° C. More preferably, the melting point is preferably changed in consideration of the thermal stability of the positive electrode. When the thermoplastic resin particles have a plurality of melting points, the highest temperature melting point may be within the above range.

  The thermoplastic resin particles used in the present invention are not particularly limited as long as they are made of a thermoplastic resin having a melting point within the above range, but particles made of a polyolefin resin are preferred. Thermoplastic resin particles made of a polyolefin resin such as a polymer, polypropylene, and a polypropylene copolymer are preferred. The average particle size of the thermoplastic resin particles is preferably 0.5 to 5 μm, more preferably 0.8 to 3 μm.

  In the present invention, an oxirane ring-containing compound is preferably present in the particle-containing layer in order to improve the adhesion between the porous film and the particle-containing layer. 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.

  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). Monoepoxy compounds such as epoxidized vegetable oil and the like can be used, and epoxy emulsions such as 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.

  As a method for forming the particle-containing layer in the present invention, a method of applying a coating liquid containing inorganic particles, thermoplastic resin particles, an oxirane ring-containing compound, or the like is preferably employed. As a method of coating, any generally performed method may be used.For example, a particle suspension prepared by dispersing an oxirane ring-containing compound in ion-exchanged water or the like is a reverse coating method, a bar coating method, What is necessary is just to apply | coat on a film by application methods, such as a gravure coat method, a rod coat method, a die coat method, and a spray coat method, and to make it a coating layer (particle content layer). Further, when preparing the suspension, a dispersant or the like may be appropriately added in order to prevent uneven distribution of particles in the coating layer.

  In the present invention, the air resistance of the porous film is preferably 50 to 500 seconds / 100 ml. When the air permeation resistance is less than 50 seconds / 100 ml, it is difficult to completely close the pores even if the particles are softened, and the shutdown property is insufficient. Moreover, when it exceeds 500 seconds / 100 ml, it exists in the tendency for the battery characteristic at the time of using a porous film as a separator to deteriorate.

  The air resistance of the porous film is preferably 80 to 400 seconds / 100 ml, more preferably 100 to 300 seconds / 100 ml, still more preferably 150 to 250 seconds / 100 ml, although it depends on the application.

  In the present invention, the rate of change in air permeability (Gd) calculated from the air resistance of the polyolefin-based porous film and the air resistance of the porous film is preferably 10% or less. The air resistance change rate (Gd) is defined by the following equation.

Gd = {(Ga−Gb) / Gb} × 100
Here, Gd means the air resistance change rate (%), Ga means the air resistance (second / 100 ml) of the porous film, and Gb means the air resistance (second / 100 ml) of the polyolefin-based porous film. If Gd exceeds 10%, the coating solution used to form the particle-containing layer on the polyolefin-based porous film may permeate into the film from the opening surface of the polyolefin-based porous film and block the opening. The battery characteristics may be worse than that of the polyolefin-based porous film. From the above viewpoint, Gd is preferably 10% or less, and more preferably 5% or less.

  In the present invention, the particle-containing layer preferably has a layer structure of at least two layers. In order to make the particle-containing layer have a laminate structure of at least two layers, one particle-containing layer is provided on at least one surface of the polyolefin-based porous film, and then the particle-containing layer is further laminated on the particle-containing layer. By having a laminated structure of two or more layers, it is possible to suppress coating omission that occurs when a particle-containing layer is formed by coating as described later, and to improve safety when used as a battery separator. it can. When the particle-containing layer has a single-layer structure consisting of only one layer, it may not be possible to repair a coating omission part generated in the coating process.

  In the above, when the layer on the polyolefin-based porous film side of the particle-containing layer is A layer and the outermost layer side is B layer, the viscosity of the coating liquid for forming the A layer is 20 Pa · s to 50 Pa · s at 25 ° C. Preferably, the viscosity of the coating liquid for forming the B layer is 0.001 Pa · s to 20 Pa · s at 25 ° C., and the particle-containing layer is preferably formed using the coating liquid. By using the above-mentioned method, the compatibility between the polyolefin-based porous film and the coating liquid is improved, the adhesion between the polyolefin-based porous film and the particle-containing layer is improved, and the viscosity of the coating liquid is controlled, thereby applying the coating liquid. It is possible to suppress the clogging of the opening portion of the polyolefin-based porous film. When a coating liquid having a viscosity of less than 20 Pa · s is used as the coating liquid for forming the A layer, the fluidity of the coating liquid is improved, and the opening of the polyolefin-based porous film may be clogged. Moreover, since the fluidity | liquidity of a coating liquid will deteriorate when the viscosity exceeds 50 Pa * s, obstruction | occlusion of the aperture part by thickness spots, coating spots, and a coating liquid will occur, and a part with high air permeability resistance will generate | occur | produce. If the coating liquid for forming the B layer is more than 20 Pa · s, the fluidity of the coating liquid is lowered, and the effect of repairing a portion where the coating is lost in the coating process may be reduced. From the above viewpoint, the viscosity of the coating liquid for forming the A layer is 20 Pa · s or more and 50 Pa · s or less at 25 ° C., and the viscosity of the coating liquid for forming the B layer is 0.001 Pa · s or more at 25 ° C. The viscosity of the coating liquid for forming the A layer is preferably 30 Pa · s to 40 Pa · s at 25 ° C., and the viscosity of the coating liquid for forming the B layer is 25 ° C. More preferably, it is 0.001 Pa · s or more and 15 Pa · s or less.

  In the present invention, the ratio of the coating liquid viscosity for forming the A layer and the B layer forming the particle-containing layer (the coating viscosity for the A layer / the coating viscosity for the B layer) is 1.5 to 10. Is preferable, and it is more preferable that it is 2-5. When the ratio of the coating liquid viscosity for forming the A layer and the B layer is out of the above range, the effect of suppressing the blockage of the pores of the polyolefin-based porous film due to the application of laminating the particle-containing layer and the coating omission The suppression effect may be reduced.

  The viscosity of the coating agent can be adjusted by changing the solid component content in the coating solution or adding a known thickener to the coating solution. Moreover, the drying property of a coating liquid can also be adjusted by use of a thickener.

  In the present invention, a compound that can be dispersed or melted in water is preferably added to the coating liquid for forming the particle-containing layer from the viewpoint of porosity. Examples of the compound that can be dispersed or melted in water include polyvinylidene chloride, polyvinylidene fluoride (PVDF), acrylic, cellulose and / or cellulose salt, acrylic resin, ethylene vinyl alcohol (EVA: structural unit derived from vinyl acetate, 20 to 35 mol%), ethylene-acrylic acid copolymer such as ethylene-ethyl acrylate copolymer (EEA), fluorine rubber, styrene butadiene rubber (SBR), cross-linked acrylic resin, polyurethane, polyvinyl butyral, polyethylene, polyvinyl Alcohol, polytetrafluoroethylene, polyvinyl pyrrolidone, polyimide, polyamide, polysulfide, polyvinyl methyl ether, polyethylene oxide, polypropylene oxide, melamine resin, polyvinyl pyridine, higher alcohol And resins such as these and salts thereof. These compounds can bind other materials (between particles, between particles and a substrate, etc.). As the compound that can be dispersed or melted in water, one of the exemplified compounds may be used, or two or more may be used in combination. Among these resins, it is preferable to use at least one selected from the group consisting of cellulose and / or cellulose salt and a compound that can be dispersed or melted in water other than cellulose and / or cellulose salt. Cellulose and / or cellulose salt can adjust the viscosity of the coating composition by adjusting the molecular weight of cellulose. 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. Among them, it is particularly preferable to include at least one selected from the group consisting of carboxymethyl cellulose or a salt thereof and hydroxyethyl cellulose or a salt thereof.

  In the present invention, as drying conditions after coating, the drying temperature is preferably 80 to 120 ° C., and the drying time is preferably 1 to 10 minutes. When the drying temperature is less than 80 ° C., the particle-containing layer may be undried, and the particle-containing layer may contain a large amount of moisture. When the drying temperature is higher than 120 ° C., the thermoplastic resin particles melt and the porous film Air permeability may deteriorate. When the drying time is less than 1 minute, the particle-containing layer becomes undried, and the particle-containing layer may contain a large amount of moisture. When the drying time is longer than 10 minutes, the thermoplastic resin particles melt and the porous film penetrates. Temper may worsen. More preferably, from the viewpoint of air permeability of the porous film, the drying temperature is preferably 90 to 110 ° C., and the drying time is preferably 2 to 5 minutes.

  The total thickness of the porous film of the present invention is preferably 15 to 40 μm, and more preferably 18 to 35 μm. Among these, the thickness of the polyolefin-based porous film is more preferably 12 to 35 μm in terms of electrical characteristics as a separator, and more preferably 15 to 30 μm. Moreover, it is preferable that it is 1-9 micrometers from the viewpoint of heat resistance and a dynamic characteristic, and, as for the lamination | stacking thickness of a particle content layer, it is more preferable if it is 3-7 micrometers.

  In this invention, it is preferable that the lamination | stacking thickness of A layer in a particle | grain content layer is 1-3 micrometers. When this range is exceeded, the porous film after drying becomes brittle and cracks may occur or air permeability resistance may deteriorate. Moreover, it is preferable from a viewpoint of the homogenization of a porous film that the lamination | stacking thickness of B layer is 2-4 micrometers.

  In the porous film of the present invention, it is preferable to provide particle-containing layers on both sides of the polyolefin-based porous film. If the particle-containing layer is only on one side, the separator (porous film) may be curled, resulting in poor handleability.

  The polyolefin-based porous film constituting the porous film of the present invention includes an antioxidant, a heat stabilizer, an antistatic agent, a lubricant composed of inorganic or organic particles, and an anti-blocking agent as long as the effects of the present invention are not impaired. Various additives such as an agent, a filler and an incompatible polymer may be contained. In particular, it is preferable to contain 0.01 to 0.5 parts by mass of an antioxidant with respect to 100 parts by mass of the polypropylene resin for the purpose of suppressing oxidative deterioration due to the thermal history of the polypropylene resin.

  Below, the manufacturing method of the polyolefin-type porous film which comprises the porous film of this invention, and the manufacturing method of a porous film are 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 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. 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 110 to 140 ° C, more preferably 120 to 135 ° C, and still more preferably 123 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 130-155 degreeC, More preferably, it is 145-153 degreeC, and it extends | stretches 4 to 12 times in the width direction, More preferably, it is 6 to 11 times, More preferably, it is 6.5 to 10 times. The transverse stretching speed at this time is preferably 300 to 5,000% / min, more preferably 500 to 3,000% / min. Subsequently, heat setting is performed in the stenter as it is, and the temperature is preferably from the transverse stretching temperature to 160 ° C. Further, the heat setting may be performed while relaxing in the longitudinal direction and / or the width direction of the film, and in particular, the relaxation rate in the width direction is preferably 5 to 20% from the viewpoint of thermal dimensional stability.

  15 parts by mass of silica particles produced by a dry method as inorganic particles in the porous film produced by the above production method, 10 parts by mass of polyethylene particles as thermoplastic resin particles, 2.0 parts by mass of an oxirane ring-containing compound, and carboxymethylcellulose 2 0.0 parts by mass and 71 parts by mass of ion-exchanged water are mixed and adjusted so that the viscosity is 35 Pa · s. After stirring this coating liquid for 4 hours, it is apply | coated on a porous film with the application | coating method using a die coater, and it is made to dry at 100 degreeC for 1 minute, and it is set as the A layer of a particle | grain containing layer whose laminated thickness is 1-3 micrometers. Further, 15 parts by mass of silica particles, 10 parts by mass of polyethylene particles as thermoplastic resin particles, 2.0 parts by mass of an oxirane ring-containing compound, 1.0 part by mass of carboxymethyl cellulose, and 71 parts by mass of ion-exchanged water are added to the film. The coating thickness was adjusted to a viscosity of 10 Pa · s, stirred for 4 hours, and then coated on the porous film by a coating method using a die coater, and dried at 100 ° C. for 1 minute to obtain a laminated thickness. Let it be B layer of a 2-4 micrometers particle | grain containing layer.

  The porous film of the present invention not only has excellent air permeability and mechanical properties, but also has shutdown properties and meltdown resistance, so that it is particularly suitable for non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries. It can be preferably used as a battery separator.

  Since the porous film of the present invention has both excellent air permeability and mechanical properties, and also has melt-down resistance, 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.

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

(1) 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
(2) Melting point of thermoplastic resin particles The melting point of thermoplastic resin particles is obtained by collecting an appropriate amount of a dispersion liquid in which particles before adjusting to a coating material for a particle-containing layer are dispersed, and drying at 70 ° C. in a hot air oven. Collect solids only. A solid content of 5 mg was taken as a sample in an aluminum pan and measured using a differential scanning calorimeter (RDC220 manufactured by Seiko Denshi Kogyo). Regarding the melting peak observed when the temperature is increased from room temperature to 200 ° C. at 20 ° C./min under a nitrogen atmosphere, the peak temperature on the highest temperature side is defined as the melting point of the thermoplastic resin particles.

  Further, even after the thermoplastic resin particles are adjusted to the coating material for the particle-containing layer or after being applied on the porous film, the measurement is performed with a differential scanning calorimeter in the same manner as described above, The melting point of the plastic resin particles can be determined. In addition, after apply | coating on a porous film, the melting | fusing point of a thermoplastic resin particle can be determined by extract | collecting a sample by scraping only a particle-containing layer from the film surface, and measuring on the same conditions.

(3) Air permeability resistance, rate of change in air resistance resistance Using a B-shaped Gurley tester of JIS P 8117 (2009) using a 100 mm square cut from a polyolefin-based porous film or porous film as a sample. The permeation time of 100 ml of air was measured three times at 23 ° C. and 65% relative humidity. The average value of the permeation time was taken as the air permeation resistance of the polyolefin-based porous film or porous film.

  Further, the air resistance change rate (Gd) defined below was calculated and evaluated according to the following criteria.

Gd = {(Ga−Gb) / Gb} × 100
Here, Gd means the air resistance change rate (%), Ga means the air resistance (second / 100 ml) of the porous film, and Gb means the air resistance (second / 100 ml) of the polyolefin-based porous film.

◎: Gd is 2% or less ○: Gd is greater than 2% and 5% or less △: Gd is greater than 5% and less than 10% ×: Gd is greater than 10% (4) Average pore diameter of through holes Mercury intrusion method The average pore diameter of the polyolefin-based porous film was measured with a porosimeter (Shimadzu Corporation 9220 type). A sample was cut out about 25 mm square, taken in a standard cell, and measured under conditions of an initial pressure of about 20 kPa. The said measurement was implemented about arbitrary 5 places and made the average value of the average hole diameter the average hole diameter of the through-hole in the said sample.

(5) Coating liquid viscosity Using a B-type viscometer (manufactured by Tokyo Keiki Co., Ltd.), in accordance with JIS K7117 (1999), spindle no. 4 was measured at 25 ° C. at a rotation speed of 60 rpm, and the viscosity was determined.

(6) Lamination thickness of particle-containing layer About the central portion in the width direction of the film before applying the particle-containing layer, a dial gauge thickness meter (manufactured by PEACOCK) at a total of 10 locations in the longitudinal direction with a sense of at least 5 cm. Measured with UPRIGHT DIAL GAUGE (No. 25)), and the average value is defined as the thickness (la) of the olefinic porous film.

  Next, with the particle-containing layer side of the film dried after coating the particle-containing layer as the upper surface, the central part in the width direction of the film, a total of 10 arbitrary places in the longitudinal direction with a dial gauge thickness gauge The thickness was measured, and the average value was taken as the thickness (lb) of the porous film.

  The lamination thickness of the particle-containing layer was calculated from the following formula from la and lb.

Lamination thickness of particle-containing layer = lb-la
The lamination thickness of each layer of the particle-containing layer was measured using the above method every time each layer was laminated.

Use qualifier: 10 mmφ flat standard probe (No101117)
Load: 50g
(7) Omission of coating With a defect detector equipped with an unwinder and a winder, the amount of transmitted light for a width of 50 mm was measured at the center in the width direction of the obtained porous film. A cylindrical rod lens having a length of 750 mm and a diameter of 10 mm was used as the light source, and light from a 250 W metal halide light source was incident from the end surface of the rod lens. A light source was placed 250 mm away from one side of the film, and the amount of irradiated light was detected from the other side. The distance between the detector and the film was 15 mm. As a detector, a CCD line sensor camera E7450D manufactured by Electrosensory Devices Co., Ltd. and a camera lens AiMicro-Nikkor 55mmF2.8S manufactured by Nikon Corporation were used, and the inspection was performed under the following conditions. The porous film was run at 6 m / min, and the amount of light transmitted through the film was measured as 40 m long × 50 mm wide. In the table, the number of portions where the transmitted light amount is 2.5 times or more compared to the average transmitted light amount was measured. Here, for the average transmitted light amount, the transmitted light amount for a length of 1 m was measured for each of the core portion and the unwinding portion of the film, and the average value was used.

Width direction resolution: 20 μm / pixel
Longitudinal resolution: 20 μm / pixel
Field of view width: 200 mm width at the center Scan rate: 9,500
Aperture: 8F
○: No coating omission.

      ×: One or more missing coatings.

(8) Heat resistance test The porous film was cut into a 3 × 3 cm square and 1 × under 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. A 3 cm area was heated.

  The porous film which performed the said process was evaluated on the following references | standards.

      ○: The shape of the porous film is maintained. No hole formation by visual inspection.

      X: The flatness of the porous film is poor. There is a hole formation by melting.

Example 1
As a raw material resin for polyolefin-based porous film, 94 parts by mass of homopolypropylene FLX80E4 (hereinafter referred to as PP-1) manufactured by Sumitomo Chemical Co., Ltd., Basel polypropylene PF-814 (hereinafter referred to as HMS-) which is a high melt tension polypropylene resin. 1 part by mass of PP-1) and Engage 8411 (melt index: 18 g / 10 min, hereinafter simply referred to as PE-1) made by Dow Chemical, which is an ethylene-octene-1 copolymer, is added to 5 parts by mass. N, N′-dicyclohexyl-2,6-naphthalene dicarboxyamide (Nippon Rika Co., Ltd., Nu-100, hereinafter simply referred to as β crystal nucleating agent), which is a β crystal nucleating agent, is 0.2. Part by mass, and IRGANOX1010 and IRGAFOS168 made by Ciba Specialty Chemicals, which are antioxidants, respectively .15, 0.1 parts by mass (hereinafter simply referred to as an antioxidant, and used at a mass ratio of 3: 2 unless otherwise specified) from the weighing hopper to the twin screw extruder so as to be mixed at this ratio The raw material was supplied to the substrate, melted and kneaded at 300 ° C., discharged from the die in a strand shape, cooled and solidified in a water bath at 25 ° C., and cut into a chip shape to obtain a chip raw material.

  This chip is supplied to a single screw extruder and melt extruded at 220 ° C. After removing foreign matter with a 25 μm cut sintered filter, it is discharged from a T-die onto a cast drum whose surface temperature is controlled at 120 ° C. An unstretched sheet was obtained by casting for 15 seconds. 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 8% in the width direction to obtain a polyolefin-based porous film having a thickness of 23 μm.

  On one side of the porous film (the surface that contacted the drum during melt extrusion, hereinafter referred to as the D surface), a layer A coating solution was applied using a die coater so that the laminated thickness after drying was 2 μm. For 1 minute. Next, the layer B coating solution is applied to the surface on which the layer A is laminated using a die coater so that the layer thickness after drying is 4 μm, and dried at 100 ° C. for 1 minute to form a two-layer structure of A / B A porous film was prepared by forming a particle-containing layer.

<Composition of coating liquid for particle-containing layer>
(1) Layer A coating liquid (coating liquid viscosity: 35 Pa · s)
Silica particles (“SFP20” manufactured by Denki Kagaku Kogyo Co., Ltd.) 15 parts by mass Polyethylene particles (Chemical “W100” manufactured by Mitsui Chemicals, Inc.) 10 parts by mass 861 ") 2.0 parts by mass Carboxymethylcellulose (" CMC Daicel 2240 "manufactured by Daicel Chemical Industries, Ltd.)
2.0 parts by mass Ion-exchanged water 71 parts by mass (2) B layer coating liquid (coating liquid viscosity 10 Pa · s)
Silica particles (“SFP20” manufactured by Denki Kagaku Kogyo Co., Ltd.) 15 parts by mass Polyethylene particles (Chemical “W100” manufactured by Mitsui Chemicals, Inc.) 10 parts by mass 861 ") 2.0 parts by mass Carboxymethylcellulose (" CMC Daicel 2240 "manufactured by Daicel Chemical Industries, Ltd.)
1.0 part by mass 71 parts by mass of ion-exchanged water (Example 2)
In Example 1, for the layer A of the particle-containing layer, a coating liquid having the following composition was prepared so that the coating liquid viscosity was 45 Pa · s, and a porous film was produced in the same manner as in Example 1.

<Composition of coating liquid for particle-containing layer>
・ A layer coating solution (viscosity viscosity 45Pa ・ s)
Silica particles (“SFP20” manufactured by Denki Kagaku Kogyo Co., Ltd.) 15 parts by mass Polyethylene particles (Chemical “W100” manufactured by Mitsui Chemicals, Inc.) 10 parts by mass Oxirane ring-containing compound (Denacol “EX- manufactured by Nagase Chemical Industries, Ltd.”) 861 ") 2.0 parts by mass Carboxymethylcellulose (" CMC Daicel 2240 "manufactured by Daicel Chemical Industries, Ltd.)
2.5 parts by mass 71 parts by mass of ion-exchanged water (Example 3)
In Example 1, a coating film having the following composition was prepared for the layer A of the particle-containing layer so that the coating liquid viscosity was 25 Pa · s, and a porous film was produced in the same manner as in Example 1.

<Composition of coating liquid for particle-containing layer>
・ A layer coating solution (viscosity viscosity 25Pa ・ s)
Silica particles (“SFP20” manufactured by Denki Kagaku Kogyo Co., Ltd.) 15 parts by mass Polyethylene particles (Chemical “W100” manufactured by Mitsui Chemicals, Inc.) 10 parts by mass Oxirane ring-containing compound (Denacol “EX- manufactured by Nagase Chemical Industries, Ltd.”) 861 ") 2.0 parts by mass Carboxymethylcellulose (" CMC Daicel 2240 "manufactured by Daicel Chemical Industries, Ltd.)
1.5 parts by mass Ion-exchanged water 71 parts by mass (Example 4)
In Example 1, for the B layer of the particle-containing layer, a coating liquid having the following composition was prepared so that the coating liquid viscosity was 17 Pa · s, and a porous film was produced in the same manner as in Example 1.

<Composition of coating liquid for particle-containing layer>
・ B layer coating solution (viscosity viscosity 17Pa ・ s)
Silica particles (“SFP20” manufactured by Denki Kagaku Kogyo Co., Ltd.) 15 parts by mass Polyethylene particles (Chemical “W100” manufactured by Mitsui Chemicals, Inc.) 10 parts by mass 861 ") 2.0 parts by mass Carboxymethylcellulose (" CMC Daicel 2240 "manufactured by Daicel Chemical Industries, Ltd.)
1.3 parts by mass 71 parts by mass of ion-exchanged water (Example 5)
In Example 1, for the layer A of the particle-containing layer, a coating solution having the following composition was prepared so that the coating solution viscosity was 36 Pa · s, and a porous film was produced in the same manner as in Example 1.

<Composition of coating liquid for particle-containing layer>
・ A layer coating liquid (coating liquid viscosity: 36 Pa · s)
Silica particles (“SFP20” manufactured by Denki Kagaku Kogyo Co., Ltd.) 15 parts by mass Polyethylene particles (Chemical “W100” manufactured by Mitsui Chemicals, Inc.) 10 parts by mass Oxirane ring-containing compound (Denacol “EX- manufactured by Nagase Chemical Industries, Ltd.”) 861 ") 2.0 parts by mass Carboxymethylcellulose (" CMC Daicel 2240 "manufactured by Daicel Chemical Industries, Ltd.)
1.5 parts by mass PVDF / acrylic water dispersion (“Kyner Aquatech” manufactured by Arkema Co., Ltd., solid content concentration 40%) 2.5 parts by mass Ion-exchanged water 69 parts by mass (Example 6)
In Example 1, a coating solution having the following composition was prepared so that the coating solution viscosity was 36 Pa · s for the particle-containing layer A and the coating solution viscosity was 12 Pa · s for the B layer. A porous film was prepared in the same manner as described above.

<Composition of coating liquid for particle-containing layer>
・ A layer coating liquid (coating liquid viscosity: 36 Pa · s)
Silica particles (“SFP20” manufactured by Denki Kagaku Kogyo Co., Ltd.) 15 parts by mass Polyethylene particles (Chemical “W100” manufactured by Mitsui Chemicals, Inc.) 10 parts by mass Oxirane ring-containing compound (Denacol “EX- manufactured by Nagase Chemical Industries, Ltd.”) 861 ") 2.0 parts by mass Carboxymethylcellulose (" CMC Daicel 2240 "manufactured by Daicel Chemical Industries, Ltd.)
1.5 parts by mass PVDF / acrylic water dispersion (Arkema “Kyner Aquatech” solid content concentration 40%) 2.5 parts by mass Ion-exchanged water 69 parts by mass ・ B layer coating liquid (coating liquid viscosity 12 Pa · s)
Silica particles (“SFP20” manufactured by Denki Kagaku Kogyo Co., Ltd.) 15 parts by mass Polyethylene particles (Chemical “W100” manufactured by Mitsui Chemicals, Inc.) 10 parts by mass Oxirane ring-containing compound (Denacol “EX- manufactured by Nagase Chemical Industries, Ltd.”) 861 ") 2.0 parts by mass Carboxymethylcellulose (" CMC Daicel 2240 "manufactured by Daicel Chemical Industries, Ltd.)
0.5 parts by mass PVDF / acrylic water dispersion (“Kayner Aquatech” manufactured by Arkema Co., Ltd., solid content concentration 40%) 1.25 parts by mass Ion-exchanged water 71.25 parts by mass (Comparative Example 1)
In Example 1, for the layer A of the particle-containing layer, a coating liquid having the following composition was prepared so that the coating liquid viscosity was 10 Pa · s, and a porous film was produced in the same manner as in Example 1.

<Composition of coating liquid for particle-containing layer>
・ A layer coating liquid (coating liquid viscosity: 10 Pa · s)
Silica particles (“SFP20” manufactured by Denki Kagaku Kogyo Co., Ltd.) 15 parts by mass Polyethylene particles (Chemical “W100” manufactured by Mitsui Chemicals, Inc.) 10 parts by mass Oxirane ring-containing compound (Denacol “EX- manufactured by Nagase Chemical Industries, Ltd.”) 861 ") 2.0 parts by mass Carboxymethylcellulose (" CMC Daicel 2240 "manufactured by Daicel Chemical Industries, Ltd.)
1.0 part by mass Ion-exchanged water 71 part by mass (Comparative Example 2)
In Example 1, the coating liquid having the following composition was used for the layer A of the particle-containing layer so that the coating liquid viscosity was 10 Pa · s, and for the B layer, the coating liquid viscosity was 35 Pa · s. And a porous film was produced in the same manner as in Example 1.

<Composition of coating liquid for particle-containing layer>
(1) Coating liquid for layer A (coating liquid viscosity 10 Pa · s)
Silica particles (“SFP20” manufactured by Denki Kagaku Kogyo Co., Ltd.) 15 parts by mass Polyethylene particles (Chemical “W100” manufactured by Mitsui Chemicals, Inc.) 10 parts by mass 861 ") 2.0 parts by mass Carboxymethylcellulose (" CMC Daicel 2240 "manufactured by Daicel Chemical Industries, Ltd.)
1.0 part by mass Ion-exchanged water 71 parts by mass (2) B layer coating liquid (coating liquid viscosity: 35 Pa · s)
Silica particles (“SFP20” manufactured by Denki Kagaku Kogyo Co., Ltd.) 15 parts by mass Polyethylene particles (Chemical “W100” manufactured by Mitsui Chemicals, Inc.) 10 parts by mass 861 ") 2.0 parts by mass Carboxymethylcellulose (" CMC Daicel 2240 "manufactured by Daicel Chemical Industries, Ltd.)
2.0 parts by mass Ion-exchanged water 71 parts by mass (Comparative Example 3)
On one side of the porous film of Example 1 (the surface in contact with the drum during melt extrusion, hereinafter referred to as D surface), a coating liquid having the following composition was applied using a die coater so that the laminated thickness after drying was 6 μm. Then, it was dried at 100 ° C. for 1 minute to form a particle-containing layer having a single layer structure, and a porous film was produced.

・ Particle-containing layer coating liquid (coating liquid viscosity: 35 Pa · s)
Silica particles (“SFP20” manufactured by Denki Kagaku Kogyo Co., Ltd.) 15 parts by mass Polyethylene particles (Chemical “W100” manufactured by Mitsui Chemicals, Inc.) 10 parts by mass Oxirane ring-containing compound (Denacol “EX- manufactured by Nagase Chemical Industries, Ltd.”) 861 ") 2.0 parts by mass Carboxymethylcellulose (" CMC Daicel 2240 "manufactured by Daicel Chemical Industries, Ltd.)
2.0 parts by mass Ion-exchanged water 71 parts by mass (Comparative Example 4)
On one side of the porous film of Example 1 (the surface in contact with the drum during melt extrusion, hereinafter referred to as D surface), a coating liquid having the following composition was applied using a die coater so that the laminated thickness after drying was 6 μm. Then, it was dried at 100 ° C. for 1 minute to form a particle-containing layer having a single layer structure, and a porous film was produced.

・ Particle-containing layer coating liquid (viscosity viscosity: 10 Pa · s)
Silica particles (“SFP20” manufactured by Denki Kagaku Kogyo Co., Ltd.) 15 parts by mass Polyethylene particles (Chemical “W100” manufactured by Mitsui Chemicals, Inc.) 10 parts by mass Oxirane ring-containing compound (Denacol “EX- manufactured by Nagase Chemical Industries, Ltd.”) 861 ") 2.0 parts by mass Carboxymethylcellulose (" CMC Daicel 2240 "manufactured by Daicel Chemical Industries, Ltd.)
1.0 part by mass Ion-exchanged water 71 parts by mass (Comparative Example 5)
The porous film before applying the particle-containing layer of Example 1 was evaluated as it was.

  Since the porous film of the present invention suppresses the deterioration of air resistance due to heat resistance and the provision of a particle-containing layer in a polyolefin-based porous film, and has both excellent battery performance and safety at a high level, It can be suitably used as a separator for an electricity storage device, particularly a lithium ion battery that is a non-aqueous electrolyte secondary battery.

Claims (10)

A particle-containing layer containing inorganic particles is formed on at least one surface of the polyolefin-based porous film, and the particle-containing layer has a laminate structure of at least two layers, and the air resistance change rate (Gd) defined below. Is a porous film having an air permeability resistance (Ga) of 50 to 500 seconds / 100 ml.
Gd = {(Ga−Gb) / Gb} × 100
Gd: Permeability change rate (%)
Ga: Air permeability resistance of the porous film (second / 100 ml)
Gb: Air permeation resistance of polyolefin-based porous film (sec / 100 ml) The porous film according to claim 1, wherein the particle-containing layer contains thermoplastic resin particles and has a melting point of 100 to 140 ° C. The porous film according to claim 1 or 2, wherein the polyolefin-based porous film has an average pore diameter of 40 to 400 nm. The porous film according to claim 1, wherein the air permeation resistance of the polyolefin-based porous film is 50 to 500 seconds / 100 ml. The porous film according to any one of claims 1 to 4, wherein the polyolefin-based porous film is a film stretched in at least a uniaxial direction. The porous film according to any one of claims 1 to 5, wherein the polyolefin-based porous film is made of polypropylene resin. The porous film according to claim 6, wherein the polypropylene resin has a β-crystal forming ability of 40 to 90%. The porous film according to any one of claims 1 to 7, wherein the particle-containing layer contains an oxirane ring compound. The separator for electrical storage devices formed using the porous film in any one of Claims 1-8 . An electricity storage device using the electricity storage device separator according to claim 9 .