JP5434661B2 - Porous film and power storage device - Google Patents

Description

  The present invention relates to a porous film and an electricity storage device. More specifically, the present invention relates to a porous film having a high porosity and excellent workability, which can be suitably used for a non-aqueous solvent battery or a separator used in a capacitor, and an electricity storage device using the porous film as a separator.

  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 to shut down is not always required, and high safety is required. Furthermore, it is important for HEV batteries to be able to guarantee a long service life of 10 years or more and more stringent safety.

  A separator using polyethylene has been proposed as a separator for a non-aqueous solvent battery such as a lithium ion battery (for example, Patent Documents 1 and 2). However, the porosity and air permeability are low, and it is not suitable for a high output battery such as a HEV battery.

  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 3). However, due to the high porosity and high air permeability, the strength in the thickness direction is low, and in processes where the roll is passed or wound with high tension that applies pressure in the thickness direction, process passability and battery processability are reduced. There is a case.

  In addition, a proposal has been made to use a polypropylene non-woven fabric that is excellent in heat resistance and suitable for high-power applications such as a large battery as a separator (for example, Patent Document 4). However, in this case, since the base material is a nonwoven fabric made of fibers, it has a large average pore diameter of about several μm, so there is a possibility that it has a defect due to the through hole. It is very high, and it is suggested that a fine short circuit is likely to occur, an initial failure at the time of winding the battery is likely to occur, and it is not possible to sufficiently compensate for a long life as in the HEV battery and a further severe 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 5). In this case, although the strength in the thickness direction is increased by the filled resin particles, the porosity and air permeability are low, and it is not suitable for a high output battery such as a HEV battery.

  In addition, proposals have been made to apply organic particles or inorganic particle layers having a high softening point to the surface of a porous substrate (for example, Patent Document 6). In this case, the strength in the thickness direction is increased by the organic particle or inorganic particle layer, but the porosity and air permeability are low, and it is not suitable for a high output battery such as a HEV battery.

JP-A-11-130899 JP-A-11-130900 Japanese Patent Laid-Open No. 01-103634 JP-A-60-52 JP 2006-286111 A JP 2007-273443 A

  An object of the present invention is to solve the above-described problems. That is, it aims at providing the porous film which is excellent in the workability at the time of winding, and shows the characteristic outstanding when used as a separator.

The present invention for achieving the above objective is a cushion of not more than 30%, a porosity of Ri 60% to 90% der, and has a three-layer structure in which the surface layer B is laminated on both sides of the inner layer A The inner layer A contains 1 to 20% by mass of an elastomer having a melting point or softening temperature of less than 100 ° C., and the surface layer B is characterized by a porous film having a smaller amount of the elastomer than the inner layer A.

  The porous film of the present invention is excellent in workability at the time of winding, and can provide a porous film that exhibits excellent characteristics when used as a separator.

  When the porous film of the present invention has a cushion ratio of 30% or less and a porosity within a range of 60 to 90%, the processability of the porous film, when producing a wound battery From the viewpoints of battery workability, reduction of internal resistance of the battery, and improvement of output density. Conventionally, when the porosity is in the range of 60 to 90%, the cushion rate is high, the strength in the thickness direction is low, and when the pressure in the thickness direction is applied, the surface unevenness due to the surface fibrils becomes smooth. Since the friction coefficient increases, the processability of the porous film and the workability when producing a wound battery may be reduced. Further, when the cushion rate is 30% or less, the porosity is lowered, the internal resistance of the battery is high, and the output density may not be increased. That is, in the past, it was difficult to achieve both a cushion ratio and a porosity in the above range. However, in the present invention, for example, organic particles are coated at a specific timing, or a composite structure of three or more layers is formed. The surface layer can be achieved by making the porosity lower than that of the inner layer. Details will be described later.

  First, the porous film will be described. The porous film in this invention has many fine through-holes which penetrate the both surfaces of a film and express air permeability. The resin constituting the porous 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 In view of 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.

  The method for forming through-holes in the porous film of the present invention can be roughly classified into a wet method and a dry method. In the wet method, polypropylene is used as the matrix resin, the extractables extracted after sheeting are added and mixed, and only the additive is extracted using the good solvent of the extractables. There is a method of generating holes. On the other hand, as a dry method, for example, by adopting low-temperature extrusion and a high draft ratio at the time of melt extrusion, the lamella structure in the film before stretching formed into a sheet is controlled, and this is uniaxially stretched so that at the lamella interface There is a method called a lamellar stretching method for generating cleavage and forming voids. There is also a method in which a large amount of incompatible resin is added as particles to inorganic particles or polypropylene as a matrix resin, and a sheet is formed and stretched to cause cleavage at the particle-resin interface to form voids. It can be illustrated. Furthermore, it is called the β crystal method, in which voids are formed in the film by utilizing the crystal density difference and crystal transition between α type crystal (α crystal) and β type crystal (β crystal), which are polymorphs of polypropylene. A method can also be adopted.

  Since the porous film of the present invention can simplify the process, the dry method is desirable. Among them, the β crystal method is used from the viewpoint that the film can be biaxially oriented and the physical properties can be uniformed and high strength can be maintained while being a thin film. preferable. 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 pigment-based compounds and amide-based compounds. Particularly, amide-based 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 β crystal forming ability is preferably 50 to 100%. More preferably, it is 60 to 100%. If the β-crystal forming ability is less than 50%, the β crystal fraction is low at the initial stage of film production, and voids in the film are not easily formed even if the crystal transition from β crystal to α crystal is performed in the stretching process.

  When the porous film of the present invention is constituted by using a polypropylene resin, the polypropylene resin has 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 minutes. It is preferable that it is an isotactic polypropylene resin. 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.

  Further, the isotactic index of the isotactic polypropylene resin is preferably 90 to 99.9%, and if the isotactic index is less than 90%, the resin has low crystallinity and achieves high air permeability. It can be difficult. As the isotactic polypropylene resin, a commercially available resin can be used.

  As the polypropylene resin used in the present invention, it is possible to use a homopolypropylene resin, as well as from the viewpoint of stability in the film-forming process, film-forming properties, and uniformity of physical properties, polypropylene with an ethylene component or butene, Resins obtained by copolymerizing α-olefin components such as hexene and octene in the range of 5% by mass or less can also be used. The form of introduction of the comonomer (copolymerization component) into polypropylene may be either random copolymerization or block copolymerization.

  When the polypropylene resin used in the present invention is biaxially stretched to form a through-hole, 80 to 99 parts by mass of polypropylene is used from the viewpoint of improving void formation efficiency during stretching and improving air permeability by increasing the hole diameter. The melting point or softening temperature is preferably a mixture having a mass ratio of 20 to 1 part by mass of an elastomer having a temperature of 100 ° C. or less. However, 80 to 99 parts by mass of polypropylene and the melting point or softening temperature are not immediately closed at the melting point or softening temperature of the elastomer as a mixture in which the mass ratio of the elastomer of less than 100 ° C. is 20 to 1 part by mass, In many cases, the pores are closed in the range of (melting point−20 ° C.) to (melting point + 10 ° C.) of polypropylene. If the melting point or softening temperature is less than 100 ° C. and the amount of the elastomer is 20 parts by mass or more, the film-forming property is deteriorated and the separator is closed before the heat setting step with a stenter necessary for imparting preferable heat resistance. It becomes difficult to be used as.

  Here, an elastomer having a melting point or softening temperature of 100 ° C. or less is an olefin-based elastomer, polybutene, ethylene-vinyl acetate-acrylic, isoprene rubber, styrene / butadiene rubber, hydrogenated styrene / butadiene rubber, styrene / butylene / styrene copolymer. And styrene / ethylene / butylene / styrene copolymer. Of these, olefin elastomers are preferred, and ethylene / α-olefin copolymers are more preferred. Examples of the ethylene / α-olefin copolymer include linear low-density polyethylene and ultra-low-density polyethylene. Among them, a copolymer polyethylene resin (copolymer) having a melting point of 60 to 90 ° C. obtained by copolymerizing octene-1. Polymerized PE resin) can be preferably used. Examples of the copolymerized polyethylene include commercially available resins such as “Engage (registered trademark)” (type names: 8411, 8452, 8100, etc.) manufactured by Dow Chemical.

  The copolymer polyethylene resin contains 1 to 10% by mass when the entire polypropylene resin constituting the film of the present invention is 100% by mass, and the porosity and average through-hole diameter described below are controlled within a preferable range. Since it becomes easy to do, it is preferable. From the viewpoint of the mechanical properties of the film, it is more preferably 1 to 7% by mass. In the polypropylene resin constituting the porous film, the void formation efficiency at the time of stretching is improved, and the air permeability is improved by increasing the pore diameter. Therefore, 1 to 10 mass of ethylene / α-olefin copolymer is added to the polypropylene resin. % Addition is preferable.

  In the present invention, in order to set the cushion rate to 30% or less and the porosity to be in the range of 60 to 90%, for example, a porous film is coated with organic particles, or a composite configuration of three or more layers is used. The surface layer may be a layer having a lower porosity than the internal layer. When the composite structure has three or more layers, it is preferable that the porosity of at least one surface layer is lower than the porosity of the inner layer.

  When coating organic particles, by coating and drying the organic particles, the organic particles infiltrate in the thickness direction of the film and melt and solidify in the process, forming a pillar that becomes the trunk in the thickness direction of the film, Cushion rate decreases. Further, by coating a small amount of organic particles, the cushion rate can be reduced without reducing the porosity. In the case of a laminated film having a composite structure of three layers or more, if the porosity of the surface layer is made smaller than the porosity of the inner layer, the stiffness of the surface layer increases and the cushion rate decreases. When the surface layer is equal to or higher than the porosity of the inner layer, the cushion rate may exceed the above range and become high. In order to set the cushion rate to 30% or less and the porosity to be in the range of 60 to 90%, the porosity of the surface layer is preferably 50 to 70%, more preferably 60 to 70%. In view of the above, the porosity of the inner layer is preferably 65 to 90%, more preferably 70 to 85% from the viewpoint of separator characteristics.

  On the other hand, in the case of a single membrane configuration, the porosity may be less than 60% in order to achieve a cushion rate of 30% or less.

  As a method for laminating a composite structure of three or more layers, there is a method of forming a laminated film by a method of forming sheets laminated by a coextrusion method and sequentially forming a film by biaxial stretching. As a method of coextrusion, there is a method of laminating using a feed block method or a multi-manifold method.

  Moreover, as a method of making the porosity of the surface layer smaller than the porosity of the inner layer, the melting point or softening temperature contained in the inner layer is 1 to 20 parts by mass, more preferably 1 to 20 parts by mass of elastomer. The method is preferably 1 to 10 parts by mass, and the melting point or softening temperature of the surface layer is preferably such that the amount of elastomer below 100 ° C. is not more than the inner layer, and the surface layer is more preferably free of elastomer. Particularly, in the case of a three-layer composite structure, the surface layer B is laminated on both surfaces of the inner layer A, the inner layer A contains 1 to 20% by mass of an elastomer having a melting point or softening temperature of less than 100 ° C. An embodiment with less than the inner layer A is preferred. In this case, it is more preferable that the surface layer B does not contain the elastomer.

  Further, in order to make the cushion rate 30% or less and the porosity within the range of 60 to 90%, as the lamination ratio, the thickness of the inner layer is 1/3 to 15 / The range of 17 is preferable, and more preferably 1/4 to 10/12.

  In the above, the material of the organic particles to be coated is not particularly limited as long as it is a resin that can be softened or melted at 150 to 170 ° C., for example, high after application of the coating liquid. Polyolefin resins such as density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene and copolymers thereof, and polyacryl resins such as polystyrene and styrene / acrylonitrile copolymers are preferably used. Here, the organic particles that are softened or melted at a predetermined temperature are those in which a coating agent is applied to a glass plate and heated in an oven controlled to the temperature for 60 seconds, the particles are deformed by heat and the particle height. Means that the particle height is less than half of the original particle height.

  As a method for coating the above organic particles, any generally performed method may be used.For example, a dispersion prepared by dispersing a thermoplastic resin in a solvent or the like, a reverse coating method, a bar coating method, What is necessary is just to apply | coat on a film by application | coating 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. 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.

In the above, as a method of forming a composite structure of three or more layers, different types of resin compositions are molded into a laminated film by a co-extrusion method consisting of a T-die molding method or an inflation molding method, and then the laminated film is stretched There is a method of making it porous.
The porous film of the present invention preferably has a cushion rate of 30% or less from the viewpoint of strength in the thickness direction of the porous film. If the cushion rate is higher than 30%, the strength in the thickness direction is low, and when the pressure in the thickness direction is applied, surface unevenness due to the surface fibrils becomes smooth, or the process passability of the porous film and In some cases, the workability when producing a wound battery is lowered. The cushion rate is more preferably 25% or less. The lower limit of the cushion rate is not particularly provided, but is preferably 10% or more and more preferably 20% from the viewpoint of volume change relaxation of expansion / contraction of the positive and negative electrodes during charge / discharge. Here, the cushion rate is an index indicating the strength in the thickness direction of the porous film, and the cushion rate can be lowered by strengthening the fibrils forming the porous film. Specifically, the cushion ratio can be lowered by coating the porous film with organic particles or laminating a layer having a lower porosity than the inner layer on the surface. In the case of a laminated film having a composite structure of three or more layers, when the porosity of the surface layer is smaller than the porosity of the inner layer, when the load is applied in the thickness direction, the surface layer with a low porosity will accept the load. At present, it is considered that the load is dispersed in the inner layer having a high porosity, but the cushion ratio can be lowered even with a high porosity. Moreover, it is thought that the processability of a porous film and the workability at the time of producing a winding type battery increase because the cushion ratio increases and the unevenness of the film surface remains even under a high load.

  The porous film of the present invention preferably has a porosity in the range of 60 to 90% from the viewpoint of reducing the internal resistance of the battery and further improving the output density. If it is less than 60%, the characteristics when used as a separator may be insufficient. If it exceeds 90%, it may be insufficient from the viewpoint of separator characteristics and strength. More preferably, it is 70 to 85%. The porosity can be increased by controlling the stretching temperature and stretching speed to lower the tensile strength of the film during stretching.

  The porous film of the present invention preferably has a Gurley air permeability in the range of 10 to 400 seconds / 100 ml from the viewpoint of reducing the internal resistance of the battery and further improving the output density. 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 400 seconds / 100 ml, the characteristics when used as a separator will be insufficient. More preferably, it is 10-300 seconds / 100 ml, More preferably, it is 10-230 seconds / 100 ml, More preferably, it is 10-200 seconds / 100 ml 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 determined by the stretching conditions (stretching direction (longitudinal or transverse), stretching method (longitudinal or transverse uniaxial stretching, longitudinal-transverse or transverse-longitudinal biaxial stretching, simultaneous biaxial stretching, biaxial stretching). It can be controlled by re-stretching later), stretching ratio, stretching speed, stretching temperature, and the like. Compared to the case of uniaxial stretching, the air permeability is higher in the case of biaxial stretching, the air permeability is increased when the stretching ratio is increased, and the air permeability is decreased when the stretching ratio is decreased.

  Below, the manufacturing method of the porous film of this invention is demonstrated concretely. In addition, the manufacturing method of the film of this invention is not limited to this.

  First, as a polypropylene resin constituting the porous film, 87 to 98 parts by mass of a commercially available homopolypropylene resin having an MFR of 8 g / 10 minutes, 1 to 3 parts by mass of a commercially available MFR of 2.5 g / 10 minutes and a high melt tension polypropylene resin, and a commercially available MFR of 8 g. / 10 minutes Ultra low density polyethylene resin 1 to 10 parts by weight, N, N'-dicyclohexyl-2,6-naphthalenedicarboxamide 0.2 part by weight is mixed, and using a twin-screw extruder, a predetermined ratio is obtained in advance. , 87 to 99 parts by mass of commercially available homopolypropylene resin MFR 8 g / 10 min, 1 to 3 parts by mass of high melt tension polypropylene resin MFR 2.5 g / 10 min, commercially available MFR 8 g / 10 min. N, N′-dicyclohexyl-2,6-naphthalenedicarboxyamide 0 to 9 parts by mass of a density polyethylene resin Part by mass, to prepare a raw material B that was premixed at a predetermined ratio by using a twin-screw extruder.

  Next, the raw material A is supplied to a single screw extruder for the A layer, and the raw material B is supplied to a single screw extruder for the B layer, and melt extrusion is performed at 200 to 230 ° C. Then, after removing foreign substances and modified polymer with a filter installed in the middle of the polymer tube, the lamination ratio of the porous film 1/10/1 with the multi-manifold type B layer / A layer / B layer composite T-die And discharged onto a cast drum to obtain a laminated unstretched sheet having a layer structure of B layer / A layer / B layer. 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, 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 be in close contact with the drum. Further, air may be blown over the entire surface using an air knife as necessary based on the state of close contact of the entire sheet on the drum.

  Next, the obtained laminated 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, a temperature at which the laminated unstretched sheet is stretched in the longitudinal direction is controlled. 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 130 ° C, more preferably 100 to 120 ° C. As a draw ratio, it is 3-6 times, More preferably, it is 3-5 times.

  After stretching in the longitudinal direction, the film end is held by a stenter-type stretching machine and introduced. And it heats to 130-155 degreeC preferably, and extends 6 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 5,000% / min, more preferably 1,000 to 4,000% / min. Subsequently, heat setting is performed in the stenter as it is, and preferable heat resistance is imparted. The temperature is preferably from the transverse stretching temperature to 165 ° C., more preferably from 150 to 160 ° C. Furthermore, during heat setting, the film may be relaxed in the longitudinal direction and / or the width direction of the film. In particular, the relaxation rate in the width direction is preferably 3 to 15% from the viewpoint of thermal dimensional stability.

  Although the manufacturing method is described above, it cannot be overemphasized that this invention is not limited to these.

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

  Examples of the electricity storage device of the present invention include a non-aqueous electrolyte secondary battery using an organic solvent and an electric double layer capacitor. In particular, a lithium ion battery is suitable from the balance of battery capacity and output density. Since it can be used repeatedly by charging and discharging, it can be used for power supplies of IT equipment, daily life equipment, hybrid cars, electric cars and the like. In particular, a lithium ion battery is suitable for the above-mentioned use from the balance of battery capacity and output density. Since the electricity storage device using the porous film of the present invention has a high porosity and high air permeability, it can be suitably used for a power source such as a hybrid vehicle and an electric vehicle.

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

(1) Cushion ratio A 10 mmφ flat standard measuring element (No101117) is attached to a dial gauge (Mitoyo Seisakusho No. 2109-10), and the thickness when 50 g load is applied is the thickness when T1 (μm) and 500 g load are applied. The thickness was determined by the following formula after measuring T2 (μm).

Cushion rate (%) = (1−T2 / T1) × 100
The thickness was measured 30 seconds after applying the load. In this measurement, the measurement position was changed, 10 points were measured, and the average value was used.

(2) Porosity The sample film was cut into a 3 × 3 cm square, and the mass W (g) was measured using an electronic balance (Electronic pan balance manufactured by Shimadzu Corporation, UW220H). Also, a dial gauge thickness gauge (JIS B 7503 (1997), UPAIGHT DIAL GAUGE (No. 25) manufactured by PEACOCK was attached with a 5 mmφ flat type probe, 125 g load was applied, the thickness was measured at five points, and the average The thickness was defined as D (cm), and the porosity was determined from the following equation.

Porosity = 100− (100 (W / ρ) / (9 × D))
Ρ in the above formula indicates the specific gravity of the film before stretching or the specific gravity of the film obtained by making the porous film non-porous by pressing. ρ was measured according to JIS K 7112 (1999), method D, 23 ± 1 ° C., and the solvent of the gradient tube was ethanol / water.

However, the porosity of each layer was calculated as follows. The porous film is cut in the thickness direction using a leather blade, ion-coated using an IB-5 type ion coater manufactured by Eiko Engineering, and using a field emission scanning electron microscope (JSM-6700F) manufactured by JEOL. The cross section of each layer was observed at a photographing magnification of 3000 times. For each layer, the obtained image data (the image of only the observation part without the display of the scale bar or the like) was transferred to Image-ProPlus Ver. Image analysis was performed using 4.5, and the area ratio of the aperture was calculated. As an image analysis method, first, a flattening filter (dark, 10 pixels) was executed once to correct luminance spots, and then a median filter (kernel size 3 × 3) was executed once to remove noise. Next, the local equalization filter (logarithmic distribution, small window 100, step 1) was executed once to brightly emphasize areas other than the apertures, and contrast adjustment (contrast 100) was performed. Finally, spatial calibration is performed, and in the count / size item, the lower limit value of area detection is set to 0.5 μm ² and counting is performed to remove only the apertures from which black spots (noise) of 0.5 μm ² or less are removed. Detected. The area ratio of the opening portion was calculated for each layer by obtaining the area ratio of the detected opening portion with respect to the total area by counting the area ratio of the count / size item.
The area ratio of the open area was calculated by applying a calibration curve of the open area area ratio and the porosity prepared in advance for a single porous film as the porosity of each layer.

  In addition, the preparation methods of a single membrane porous film are shown below. The resin of each layer is supplied to an extruder, melt-extruded at 220 ° C., foreign matter is removed with a 25 μm cut sintered filter, and then discharged onto a cast drum whose surface temperature is controlled at 120 ° C. with a T-die. The film was cast so as to be indirect for 15 seconds, and was formed into a sheet shape by blowing hot air heated to 120 ° C. using an air knife from the non-drum surface side of the film to obtain an unstretched sheet. The obtained unstretched sheet was preheated through a roll group maintained at 105 ° C., passed between rolls maintained at 105 ° C. and provided with a circumferential speed difference, stretched five times in the longitudinal direction at 105 ° C., and then at 127 ° C. Hold for 1 second, cool to 95 ° C, hold both ends with clips and introduce into tenter, preheat at 150 ° C, stretch 7 times in the transverse direction at 150 ° C, 5% in the transverse direction in the tenter The film was heat-set at 160 ° C. while being relaxed, and then uniformly cooled and then cooled to room temperature and wound up to obtain a porous film having a thickness of 25 μm.

(3) Gurley air permeability Measured at 23 ° C. and 65% RH in accordance with JIS P 8117 (1998), method B (unit: second / 100 ml). The same measurement was performed on the laminated samples 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.

(4) β-crystal forming ability 5 mg of resin or film was sampled on an aluminum pan and measured using a differential scanning calorimeter (DSC) (Seiko Denshi Kogyo RDC220). First, the temperature is raised from 20 ° C. to 250 ° C. at 20 ° C./min in a nitrogen atmosphere, and kept as it is for 5 minutes. Next, the temperature is lowered to 25 ° C. at 20 ° C./min, and kept for 5 minutes. And it heated up to 250 degreeC again at 20 degree-C / min, and measured. With respect to the β-crystal melting peak of polypropylene in the temperature range of 145 to 157 ° C. observed at the second temperature increase and the α-crystal melting peak of polypropylene observed at 158 ° C. or higher, the flat portion on the high temperature side is drawn as a reference. The amount of heat of fusion was calculated from the area of the region surrounded by the baseline and peak. The heat of fusion is calibrated using indium. The β crystal forming ability is calculated from the β crystal melting heat (ΔHβ) and α crystal melting heat (ΔHα) by the following formula.
β crystal forming ability (%) = [ΔHβ / (ΔHα + ΔHβ)] × 100
In addition, when obtaining a laminated film and measuring the β crystal forming ability of each layer, it is possible to collect and measure the components constituting each layer by scraping each layer of the film according to the laminated thickness. .

(5) Lamination ratio The lamination ratio of the porous film was cut in the thickness direction using a leather blade, and the cut surface was 10,000 times using a field emission scanning electron microscope of JSM-6700F manufactured by JEOL Ltd. Surface observation is performed, and the thickness of each layer is measured using “measurement between two points” in the software of JEOL PC-SEM 6700. The same measurement was performed for the same sample five times at different locations, and the average value of the obtained thicknesses was taken as the thickness of the layer, and the lamination ratio was calculated using this. Measurement conditions are as shown below.

Acceleration voltage: 1 kV
Objective aperture: 4
Secondary electron detection key: ON
Mode: 2
Emission: 10 μm
Auto reset: OFF
Observation mode: LEM
Scan rotation: 0
Dynamic focus: 0
(6) Battery characteristics 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. LiPF ₆ was dissolved as a solute in a mixed solvent of propylene carbonate: dimethyl carbonate = 3: 7 (volume ratio) to a concentration of 1 mol / liter to obtain an electrolytic solution.

  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. For each of the examples and comparative examples, 200 batteries were produced.

A. Battery processability A defect due to the separator in the process of producing 200 spiral electrode bodies was examined. The defective contents are the position shift of the separator, the wrinkle of the separator, and the breakage of the separator at the time of producing the spiral electrode body. Evaluation was performed according to the following criteria depending on the number of defective electrode bodies.

○: 0 △: 1 or 2 ×: 3 or more Output characteristics For each of the fabricated secondary batteries, charging and discharging operations were performed under an atmosphere of 25 ° C. with charging at 1,600 mA up to 4.2 V for 3.5 hours and discharging at 1,600 mA up to 2.7 V. The capacity was examined. Further, a charging / discharging operation was performed in which charging was performed at 1,600 mA to 4.2 V for 3.5 hours, and discharging was performed at 16,000 mA to 2.7 V, and the discharge capacity was examined.

  The value obtained by the formula of [(discharge capacity at 16,000 mA) / (discharge capacity at 1,600 mA)] × 100 was evaluated according to the following criteria. In addition, 20 test pieces were measured, and the average value was evaluated.

○: 85% or more Δ: 80% or more and less than 85% ×: less than 80% C.I. Leaving test A positive electrode having a thickness of 50 μm made of lithium cobalt oxide (LiCoO ₂ ) manufactured by Hosen Co., Ltd. was used and cut into a width of 60 mm and a length of 900 mm. Further, a graphite negative electrode having a thickness of 60 μm manufactured by Hosen Co., Ltd. was used and cut into a width of 60 mm and a length of 920 mm. LiPF ₆ was dissolved as a solute in a mixed solvent of propylene carbonate: dimethyl carbonate = 3: 7 (volume ratio) to a concentration of 1 mol / liter to obtain an electrolytic solution.

  Next, the above-mentioned belt-like positive electrode is overlapped with the above-mentioned sheet-like negative electrode through the separator film of each Example / Comparative Example and wound in a spiral shape 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. Twenty batteries were produced for each example and comparative example. For each of the fabricated secondary batteries, charging and discharging operations were performed in an atmosphere of 25 ° C. to charge the battery up to 4.2 V at 1,400 mA for 1.5 hours and to discharge to 2.7 V at 1,400 mA. Examined. Further, the battery was charged at 1,400 mA to 4.2 V for 1.5 hours, then left at 60 ° C. for 2 months, and then discharged at 1,400 mA to 2.7 V.

  The value obtained by the formula of [(discharge capacity after standing) / (initial discharge capacity)] × 100 was evaluated according to the following criteria. In addition, 20 test pieces were measured, and the average value was evaluated.

○: 85% or more Δ: 80% or more and less than 85% ×: Less than 80% or one or more is less than 20% The factors that cause the discharge capacity to be less than 80% are scratches on the separator when the spiral electrode body is manufactured. .

  Hereinafter, 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 chips of resins A and B.

<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, melting point 72 ° C., 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 is a β crystal nucleating agent. , N′-dicyclohexyl-2,6-naphthalenedicarboxamide (manufactured by Shin Nippon Rika Co., Ltd., Nu-100, hereinafter simply referred to as β crystal nucleating agent) is 0.2 part by mass, and further an antioxidant. Ciba Specialty Chemicals IRGANOX1010 and IRGAFOS168 are 0.15 and 0.1 parts by mass (hereinafter simply referred to as an antioxidant). It noted, unless otherwise 3: the use) with 2 mass ratio compounded to 280 ° C. in a twin-screw extruder after the dry blend was a chip.

<Polypropylene resin B>
99 parts by mass of homopolypropylene FSX80E4 (hereinafter referred to as PP-1) manufactured by Sumitomo Chemical Co., Ltd., 1 part by mass of Basel polypropylene PF-814 (hereinafter referred to as HMS-PP) which is a high melt tension polypropylene resin, 0.2 parts by mass of 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 Further, IRGANOX 1010 and IRGAFOS 168 manufactured by Ciba Specialty Chemicals, which are antioxidants, are 0.15 and 0.1 parts by mass (hereinafter simply referred to as acid inhibitors, unless otherwise specified, in a mass ratio of 3: 2). Used) was dry blended and then compounded at 280 ° C. with a twin screw extruder to obtain chips.

  Supply polypropylene resin A chips for layer A and polypropylene resin B chips to separate single screw extruders for layer B, melt extrude at 220 ° C, and remove foreign matter with a 25μm cut sintered filter , The multi-manifold type B layer / A layer / B layer composite T die is laminated so that the porous film has a lamination ratio of 1/10/1, and is discharged onto a cast drum whose surface temperature is controlled at 120 ° C. The film was cast so as to be indirectly on the drum for 15 seconds, and heated to 120 ° C. by using an air knife from the non-drum surface side of the film, and formed into a sheet while being in close contact with hot air to obtain an unstretched sheet. Subsequently, it was brought into contact with a cooling metal drum having a surface temperature of 80 ° C. The contact 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 peripheral speed difference, stretched 5 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, the film was heat-set at 160 ° C. while giving a relaxation of 5% in the transverse direction in the tenter, uniformly cooled, then cooled to room temperature and wound up to obtain a porous film having a thickness of 25 μm. The physical property values are shown in Tables 1 and 2.

  The obtained porous film had high processability and excellent battery characteristics, and the porous film had high air permeability.

(Example 2)
A porous film having a thickness of 25 μm was obtained in the same manner as in Example 1 except that the heat setting temperature was changed to 162 ° C. Each physical property value is shown in Tables 1 and 2.

  The obtained porous film had high processability and excellent battery characteristics, and the porous film had high air permeability.

(Example 3)
Supply polypropylene resin A chips for layer A and polypropylene resin B chips to separate single screw extruders for layer B, melt extrude at 220 ° C, and remove foreign matter with a 25μm cut sintered filter , Except that the multi-manifold type B layer / A layer / B layer composite T-die was laminated so that the porous film would be 1/4/1 and discharged onto a cast drum whose surface temperature was controlled at 120 ° C. The same operation as in Example 1 was performed to obtain a porous film having a thickness of 25 μm. Each physical property value is shown in Tables 1 and 2.

  The obtained porous film had high processability and excellent battery characteristics, and the porous film had high air permeability.

Example 4
Supply polypropylene resin A chips for layer A and polypropylene resin B chips to separate single screw extruders for layer B, melt extrude at 220 ° C, and remove foreign matter with a 25μm cut sintered filter , Except that multi-manifold type B layer / A layer / B layer composite T-die was laminated so that the porous film would be 1/2/1 and discharged to a cast drum whose surface temperature was controlled at 120 ° C The same operation as in Example 1 was performed to obtain a porous film having a thickness of 25 μm. Each physical property value is shown in Tables 1 and 2.

  The obtained porous film had high processability and excellent battery characteristics, and the porous film had high air permeability.

(Example 5)
Supply polypropylene resin A chips for layer A and polypropylene resin B chips to separate single screw extruders for layer B, melt extrude at 220 ° C, and remove foreign matter with a 25μm cut sintered filter , Except that the multi-manifold type B layer / A layer / B layer composite T-die was laminated so that the porous film would be 1/12/1 and discharged onto a cast drum whose surface temperature was controlled at 120 ° C. The same operation as in Example 1 was performed to obtain a porous film having a thickness of 25 μm. Each physical property value is shown in Tables 1 and 2.

  The obtained porous film had high processability and excellent battery characteristics, and the porous film had high air permeability.

(Example 6)
<Polypropylene resin C>
98 parts by mass of homopolypropylene FSX80E4 manufactured by Sumitomo Chemical Co., Ltd., 1 part by mass of Basel polypropylene PF-814 which is a high melt tension polypropylene resin, and 1 mass of Engage 8411 manufactured by Dow Chemical which is an ethylene-octene-1 copolymer. 0.2 part by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxyamide (Shin Nihon Rika Co., Ltd., Nu-100), which is a β crystal nucleating agent, and an antioxidant Each of IRGANOX1010 and IRGAFOS168 manufactured by Ciba Specialty Chemicals, which were 0.15 and 0.1 parts by mass, was dry blended and then compounded at 280 ° C. with a twin screw extruder to obtain chips.

  A polypropylene resin A chip is supplied to a single screw extruder for layer A and a polypropylene resin C chip is supplied to a separate single screw extruder for layer B, melt extruded at 220 ° C., and a 25 μm cut sintered filter After removing the foreign matter, the multi-manifold type B layer / A layer / B layer composite T die was laminated so that the porous film was 1/4/1, and the cast drum whose surface temperature was controlled at 120 ° C. Except for discharging, the same operation as in Example 1 was performed to obtain a porous film having a thickness of 25 μm. Each physical property value is shown in Tables 1 and 2.

  The obtained porous film had high processability and excellent battery characteristics, and the porous film had high air permeability.

(Example 7)
<Polypropylene resin D>
92 parts by mass of homopolypropylene FSX80E4 manufactured by Sumitomo Chemical Co., Ltd., 1 part by mass of Basel polypropylene PF-814, which is a high melt tension polypropylene resin, and low-density polyethylene by a metallocene catalyst method (Sumitomo Chemical ( Co., Ltd., “Excellen FX” CX5016; MFR: 17 g / 10 min (190 ° C., Tm: 91 ° C.) is added to 7 parts by mass, and β, crystal nucleating agent N, N′-dicyclohexyl-2,6 -0.2 parts by mass of naphthalene dicarboxyamide (manufactured by Shin Nippon Rika Co., Ltd., Nu-100), and IRGANOX 1010 and IRGAFOS 168 by Ciba Specialty Chemicals, which are antioxidants, 0.15 and 0.1 mass, respectively After dry blending, compound with a twin screw extruder at 280 ° C. Tsu was a flop.

  The polypropylene resin D chip is supplied to the single-layer extruder for the A layer and the polypropylene resin B chip for the B layer, melt-extruded at 220 ° C., and foreign matter is removed with a 25 μm cut sintered filter. Example except that the multi-manifold type B layer / A layer / B layer composite T-die was laminated so that the porous film would be 1/10/1 and discharged onto a cast drum whose surface temperature was controlled at 120 ° C. The same operation as 1 was performed to obtain a porous film having a thickness of 25 μm. Each physical property value is shown in Tables 1 and 2.

  The obtained porous film had high processability and excellent battery characteristics, and the porous film had high air permeability.

( Reference Example 8)
Polypropylene resin A is supplied to a single screw extruder, melt extruded at 220 ° C., foreign matter is removed with a 25 μm cut sintered filter, and then discharged from a T-die onto a cast drum whose surface temperature is controlled at 120 ° C. After the directional stretching, corona discharge treatment was performed on one side of the obtained porous film (the side in contact with the drum during melt extrusion, hereinafter referred to as the D side). As a coating agent, a suspension prepared by mixing 10 parts by mass of Chemipearl “WP100” manufactured by Mitsui Chemicals, Inc. and 90 parts by mass of ion-exchanged water was prepared. The coating was coated with Meyer bar # 4. Subsequently, both ends were introduced into a tenter while being gripped by clips, preheated at 150 ° C., and stretched 7 times in the transverse direction at 150 ° C. Next, the film was heat-set at 160 ° C. while giving a relaxation of 5% in the transverse direction in the tenter, uniformly cooled, then cooled to room temperature and wound up to obtain a porous film having a thickness of 25 μm. Each physical property value is shown in Tables 1 and 2.

( Reference Example 9)
Polypropylene resin A is supplied to a single screw extruder, melt extruded at 220 ° C., foreign matter is removed with a 25 μm cut sintered filter, and then discharged from a T-die onto a cast drum whose surface temperature is controlled at 120 ° C. After the directional stretching, corona discharge treatment was performed on one side of the obtained porous film (the side in contact with the drum during melt extrusion, hereinafter referred to as the D side). As a coating agent, a suspension prepared by mixing 5 parts by mass of Chemipearl “WP100” manufactured by Mitsui Chemicals, Inc. and 95 parts by mass of ion-exchanged water was prepared. The coating was coated with Meyer bar # 4. Subsequently, both ends were introduced into a tenter while being gripped by clips, preheated at 150 ° C., and stretched 7 times in the transverse direction at 150 ° C. Next, the film was heat-set at 160 ° C. while giving a relaxation of 5% in the transverse direction in the tenter, uniformly cooled, then cooled to room temperature and wound up to obtain a porous film having a thickness of 25 μm. Each physical property value is shown in Tables 1 and 2.

(Comparative Example 1)
Except for supplying polypropylene resin A to a single screw extruder, performing melt extrusion at 220 ° C., removing foreign matter with a 25 μm cut sintered filter, and then discharging it from a T-die to a cast drum whose surface temperature was controlled at 120 ° C. The same operation as in Example 1 was performed to obtain a porous film having a thickness of 25 μm. Each physical property value is shown in Tables 1 and 2.

  Although the obtained porous film had excellent battery characteristics, the obtained porous film had insufficient processability.

(Comparative Example 2)
Except for supplying polypropylene resin D to a single screw extruder, performing melt extrusion at 220 ° C, removing foreign matter with a 25 µm cut sintered filter, and then discharging it from a T-die to a cast drum whose surface temperature was controlled at 120 ° C. The same operation as in Example 1 was performed to obtain a porous film having a thickness of 25 μm. Each physical property value is shown in Tables 1 and 2.

  Although the obtained porous film had excellent battery characteristics, the obtained porous film had insufficient processability.

(Comparative Example 3)
A polypropylene resin B chip is supplied to a single screw extruder, melt extruded at 220 ° C., foreign matter is removed with a 25 μm-cut sintered filter, and a cast drum whose surface temperature is controlled to 120 ° C. with a T-die. Discharge, cast indirectly on the drum for 15 seconds, heat to 120 ° C using an air knife from the non-drum surface side of the film, blow into hot air, and form into a sheet shape to obtain an unstretched sheet It was. Subsequently, the contact time with the cooling metal drum having a surface temperature of 80 ° C. was 40 seconds.

  The obtained unstretched sheet was preheated through a roll group maintained at 105 ° C., passed between rolls maintained at 105 ° C. and provided with a peripheral speed difference, stretched four times in the longitudinal direction at 135 ° C., and then at 135 ° 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, the film was heat-set at 162 ° C. while giving 5% relaxation in the transverse direction in the tenter, uniformly cooled, then cooled to room temperature and wound up to obtain a porous film having a thickness of 25 μm. Each physical property value is shown in Tables 1 and 2.

  Although the obtained porous film had high processability, the output characteristics were insufficient.

(Comparative Example 4)
Supply polypropylene resin A chips for layer A and polypropylene resin B chips to separate single screw extruders for layer B, melt extrude at 220 ° C, and remove foreign matter with a 25μm cut sintered filter The multi-manifold type B layer / A layer / B layer composite T-die is laminated so that the porous film becomes 1/10/1, and discharged onto a cast drum whose surface temperature is controlled at 120 ° C. The film was cast so as to be indirect for 15 seconds, heated to 120 ° C. using an air knife from the non-drum surface side of the film, and then formed into a sheet shape while sprayed with hot air to obtain an unstretched sheet. Subsequently, the contact time with the cooling metal drum having a surface temperature of 80 ° C. was 40 seconds.

  The obtained unstretched sheet was preheated through a roll group maintained at 105 ° C., passed between rolls maintained at 105 ° C. and provided with a peripheral speed difference, stretched four times in the longitudinal direction at 135 ° C., and then at 135 ° 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, the film was heat-set at 162 ° C. while giving 5% relaxation in the transverse direction in the tenter, uniformly cooled, then cooled to room temperature and wound up to obtain a porous film having a thickness of 25 μm. Each physical property value is shown in Tables 1 and 2.

  Although the obtained porous film had high processability, the output characteristics were insufficient.

(Comparative Example 5)
Polypropylene resin A chips are supplied to separate single screw extruders for A layer and B layer, melt extruded at 220 ° C., foreign matter is removed with a 25 μm cut sintered filter, and multi-manifold type B layer / The same operation as in Example 1 was performed except that the porous film was laminated with an A layer / B layer composite T die so that the porous film became 1/10/1 and was discharged onto a cast drum whose surface temperature was controlled at 120 ° C. A porous film having a thickness of 25 μm was obtained. Each physical property value is shown in Tables 1 and 2.

  The obtained porous film had excellent battery characteristics, and the porous film had high air permeability but had insufficient workability.

(Comparative Example 6)
Supply polypropylene resin B chips to separate single screw extruders for A layer and polypropylene resin A chips for B layer, melt extrude at 220 ° C, remove foreign matter with a 25μm cut sintered filter, Example 1 except that the porous film was laminated with a manifold type B layer / A layer / B layer composite T die so that the porous film would be 1/10/1 and discharged onto a cast drum whose surface temperature was controlled at 120 ° C. The same operation was performed to obtain a porous film having a thickness of 25 μm. Each physical property value is shown in Tables 1 and 2.

  The obtained porous film had excellent battery characteristics, and the porous film had high air permeability but had insufficient workability.

(Comparative Example 7)
<Polypropylene resin E>
92 parts by mass of homopolypropylene FSX80E4 manufactured by Sumitomo Chemical Co., Ltd., 1 part by mass of polypropylene PF-814 manufactured by Basell, which is a high melt tension polypropylene resin, high density polyethylene (manufactured by Prime Polymer Co., Ltd., “Hi-X” HA2200J; 5.2 g / 10 min (190 ° C., Tm: 132 ° C.) was added to 7 parts by mass, and β-crystal nucleating agent N, N′-dicyclohexyl-2,6-naphthalenedicarboxyamide (Shin Nippon Rika ( Co., Ltd., Nu-100) 0.2 parts by weight, and further, 0.15 parts by weight of IRGANOX 1010 and IRGAFOS 168 by Ciba Specialty Chemicals, which are antioxidants, and 0.1 parts by weight after dry blending with a twin screw extruder Compounded at 280 ° C. to form a chip.

  Supply polypropylene resin E chip for A layer and polypropylene resin B chip for separate single screw extruders for B layer, melt extrusion at 220 ° C, remove foreign matter with a 25μm cut sintered filter, Example 1 except that the porous film was laminated with a manifold type B layer / A layer / B layer composite T die so that the porous film would be 1/10/1 and discharged onto a cast drum whose surface temperature was controlled at 120 ° C. The same operation was performed to obtain a porous film having a thickness of 25 μm. Each physical property value is shown in Tables 1 and 2.

  Although the obtained porous film had high processability, the output characteristics were insufficient.

  The porous film according to the present invention is excellent in workability during winding and can provide a porous film having excellent characteristics when used as a separator.

Claims (10)

And the cushion factor than 30%, a porosity of Ri 60% to 90% der, and has a three-layer structure in which the surface layer B is laminated on both sides of the inner layer A, the melting point or softening temperature in the inner layer A 100 A porous film containing 1 to 20% by mass of an elastomer having a temperature of less than 0 ° C., and the amount of the elastomer is smaller in the surface layer B than in the inner layer A It is lower than the porosity of the inner layer even without least porosity of one of the surface layer, the porous film according to claim 1, wherein. The porous film of Claim 1 or 2 in which the porous film contains polyolefin resin. The porous film in any one of Claims 1-3 whose Gurley air permeability is 10-400 second / 100ml. The porous film according to claim 3 or 4, wherein the polyolefin resin is a polypropylene resin having a β crystal forming ability of 50 to 100%. The porous film in any one of Claims 1-5 in which the surface layer B does not contain the said elastomer. The porous film according to any one of claims 1 to 6 , wherein at least one surface is coated with a resin that softens or melts at 150 to 170 ° C. As used in the electric storage device separator, the porous film according to any one of claims 1-7. An electricity storage device using the porous film according to claim 8 as an electricity storage device separator. The electricity storage device according to claim 9 , wherein the electricity storage device is a lithium ion battery.