JP5727747B2 - Laminated porous film, battery separator and battery - Google Patents

Description

  The present invention relates to a laminated porous film, and can be used as a packaging product, sanitary product, livestock product, agricultural product, building product, medical product, separation membrane, battery separator, and particularly suitably used as a nonaqueous electrolyte battery separator. Is.

  The polymer porous film with many fine communication holes is used for separation membranes used for the production of ultrapure water, purification of chemicals, water treatment, waterproof and moisture permeable films used for clothing and sanitary materials, and batteries. It is used in various fields such as battery separators.

Secondary batteries are widely used as power sources for portable devices such as OA, FA, household electric appliances and communication devices. In particular, portable devices using lithium ion secondary batteries are increasing because they have good volumetric efficiency when mounted on devices, leading to miniaturization and weight reduction of the devices.
On the other hand, large-scale secondary batteries are being researched and developed in many fields related to energy / environmental issues, including road leveling, UPS, electric vehicles, etc., and are excellent in large capacity, high output, high voltage and long-term storage. Therefore, the use of lithium ion batteries, which are a type of non-aqueous electrolyte secondary battery, is expanding.

The working voltage of a lithium ion secondary battery is usually designed with 4.1V to 4.2V as the upper limit. This is because the aqueous solution causes electrolysis at such a high voltage and cannot be used as an electrolytic solution. Therefore, so-called non-aqueous electrolytes using organic solvents are used as electrolytes that can withstand high voltages.
As the solvent for the non-aqueous electrolyte, a high dielectric constant organic solvent capable of making more lithium ions exist is used, and organic carbonates such as polypropylene carbonate and ethylene carbonate are mainly used as the high dielectric constant organic solvent. Have been trying. As a supporting electrolyte that becomes a lithium ion source in a solvent, a highly reactive electrolyte such as lithium hexafluorophosphate is dissolved in a solvent and used.

  In the lithium ion secondary battery, a separator is interposed between the positive electrode and the negative electrode from the viewpoint of preventing an internal short circuit. Of course, the separator is required to have insulating properties due to its role. Moreover, it is necessary to have a fine pore structure in order to provide air permeability as a lithium ion passage and a function of diffusing and holding the electrolyte. A porous film is used as a separator to satisfy these requirements.

With the recent increase in battery efficiency, the importance of battery safety is increasing. As a characteristic that contributes to the safety of the battery separator, there is a shutdown characteristic (hereinafter sometimes referred to as “SD characteristic”). This SD characteristic is a function of preventing the subsequent increase in temperature inside the battery because the micropores are closed when the temperature is about 100 to 140 ° C., and as a result, ion conduction inside the battery is blocked. When used as a battery separator, it is necessary to have this SD characteristic.
The SD characteristic is an important characteristic that contributes to safety when a battery separator is incorporated in a lithium ion secondary battery. For example, in a battery separator having a shutdown characteristic when the battery becomes abnormal due to an abnormal temperature, the micropores are closed, and ion conduction inside the battery is blocked, thereby preventing a subsequent increase in temperature inside the battery. In particular, with the recent increase in capacity of batteries, the importance for battery safety has increased, and the need for this characteristic has further increased.

Another characteristic that contributes to safety is a breakdown characteristic (hereinafter sometimes referred to as “BD characteristic”). This BD characteristic is a function in which heat generation does not stop due to the expression of the SD characteristic, and even when the temperature becomes higher (for example, 160 ° C. or higher), the film does not break and keeps the positive electrode and the negative electrode separated. . If it has BD characteristics, insulation can be maintained even at high temperatures, and a wide range of short-circuits between electrodes can be prevented, thereby preventing accidents such as ignition due to abnormal heat generation of the battery. For this reason, when used as a battery separator, it is preferable to have this BD characteristic, and the breakdown temperature (hereinafter sometimes referred to as “BD temperature”) is preferably higher.
Here, “BD temperature” refers to the lowest temperature among the temperatures at which the laminated porous film of the present invention breaks when heated by the method described in the Examples.

  In recent years, separators that simultaneously achieve both safety and strength improvement have been demanded in order to achieve both high performance of the battery and improvement of production efficiency.

  Various techniques as shown below have been proposed as a technique for forming a film having this kind of fine pores. For example, Patent Document 1 discloses two stages by changing the temperature of a laminated film of polyethylene and polypropylene in a uniaxial direction. There has been proposed a method for producing a battery separator, characterized in that it is made porous by stretching.

  On the other hand, various methods for obtaining a porous film by stretching a polypropylene sheet containing β crystals have been proposed. A feature of this method for producing a porous film is that a β-crystal is used to obtain a porous structure, and it is preferable to obtain a porous structure by stretching a sheet containing many β-crystals before stretching. . In addition, this method is a general biaxial stretching method, and is characterized in that productivity is very good as a method for obtaining a porous film.

  For example, Patent Document 2 proposes a manufacturing method in which a porous film is obtained by forming a sheet of a resin composition containing a predetermined amount of a filler and a β-crystal nucleating agent in polypropylene and stretching the resin composition under specific stretching conditions. Patent Document 3 proposes a superporous polypropylene microporous film obtained by biaxial stretching from an original polypropylene film having a high β crystal content.

  Patent Document 4 discloses a method for producing a polypropylene porous film by containing a specific amide compound in polypropylene, crystallizing under specific conditions to obtain a solidified product containing β crystals, and stretching the solidified product. Proposed.

  Further, Patent Document 5 proposes a battery separator including a polypropylene microporous membrane manufactured from a β-nucleus-containing precursor, and further provides a function of improving safety such as a blocking function as another layer. It is described.

  Patent Document 6 discloses a laminated porous film in which at least two porous layers are laminated, in which one of the porous layers is a layer containing a polypropylene-based resin, and the other layer is the polypropylene-based film. A laminated porous film is proposed which is a shutdown layer made of a composition having a crystal melting peak temperature lower than the crystal melting peak temperature of the resin composition of the resin-containing layer, and has β activity and / or β crystal forming ability. In addition, it is described that the film is a porous film having a shutdown characteristic (SD characteristic) in order to ensure the safety of the battery while having the breakdown characteristic (BD characteristic) of the polypropylene resin.

Japanese Patent No. 2883726 Japanese Patent No. 1953202 Japanese Patent No. 2509030 Japanese Patent No. 3443934 JP 2000-30683 A JP 2008-311220 A

  However, the manufacturing method described in Patent Document 1 requires strict control of manufacturing conditions and is difficult to say that productivity is good. For example, when creating a laminated film before making it porous, film formation is performed while controlling the higher order structure with a high draft ratio, but it is very difficult to form a stable film with such a high draft ratio. Have difficulty. Further, in order to develop a porous structure, it is necessary to perform multi-stage stretching in two steps, a low temperature region and a high temperature region, at a small stretching speed, the stretching speed is greatly limited, and productivity is very poor. Furthermore, the separator manufactured by the manufacturing method is very weak against tearing in the same direction as the stretching direction, and has a problem that a tear is likely to occur in the stretching direction.

  Moreover, since the polypropylene porous film of the said patent documents 2-4 is high in the crystal melting temperature of a polypropylene, in the BD characteristic, it is superior to a polyethylene porous film. However, fortunately, the above characteristics cannot be exhibited at all with respect to the SD characteristics. Therefore, using these porous films as battery separators has a problem in ensuring the safety of the battery.

In addition, the battery separator including the polypropylene microporous membrane manufactured from the β-nucleus-containing precursor described in Patent Document 5 is not described in Examples with a blocking function, and the safety of the battery is improved only by providing a polyethylene layer. It was difficult to give the function to make it.
In addition, the laminated porous film described in Patent Document 6 has both a breakdown characteristic (BD characteristic) of a polypropylene resin and a shutdown characteristic (SD characteristic) as an index of battery safety. It is hard to say that the pin stab strength is sufficient.

  The present invention has been made to solve the above problems, and has a shutdown characteristic which is an important characteristic in terms of ensuring safety while having excellent air permeability characteristics contributing to electrical performance, and a pin. It is an object to provide a laminated porous film having excellent puncture strength.

  In order to solve the above-described problems, the present invention alternately comprises a layer A composed of a porous layer mainly composed of a polypropylene resin composition and a layer B composed of a porous layer mainly composed of a polyethylene resin composition. A laminated porous film having a laminated structure, wherein the B layer has at least 5 layers and has β activity.

  In the present invention, the layer A preferably contains a β crystal nucleating agent.

  In the present invention, the B layer preferably contains a crystal nucleating agent.

  In the present invention, the B layer may contain at least one compound X selected from a modified polyolefin resin, an alicyclic saturated hydrocarbon resin or a modified product thereof, an ethylene copolymer, or a wax. preferable.

  In the present invention, the air permeability is preferably 5 to 3000 seconds / 100 ml, and the pin penetration strength is preferably 1.5 N or more.

The laminated porous film of the present invention has a structure in which A layer composed of a porous layer mainly composed of polypropylene resin and B layer composed of a porous layer mainly composed of polyethylene resin are laminated alternately. Since the layer B is a laminated porous film having at least 5 layers and having β activity, an appropriate temperature range is maintained while maintaining the breakdown characteristics of a conventional polypropylene resinous laminated porous film. It has a shutdown characteristic that closes the hole.
Furthermore, since the laminated porous film of the present invention has β activity, it has fine pores, can ensure sufficient communication, and can exhibit excellent electrical characteristics.
Moreover, the laminated porous film of the present invention does not require strict control of production conditions, and can be produced simply and efficiently.

It is a partially broken perspective view of the nonaqueous electrolyte battery which has stored the lamination porous film of the present invention as a battery separator. It is a figure explaining the fixing method of the lamination | stacking porous film in the air permeability measurement after heating for 5 second at 135 degreeC, and a wide angle X-ray-diffraction measurement. 2 is a cross-sectional SEM photograph of the nonporous film-like material of Example 1. 2 is a cross-sectional SEM photograph of the laminated porous film of Example 1.

Hereinafter, embodiments of the laminated porous film of the present invention will be described in detail.
In the present invention, the expression “main component” includes the intention to allow other components to be contained within a range that does not interfere with the function of the main component, unless otherwise specified. Although the content ratio of the component is not specified, the main component includes 50% by mass or more, preferably 70% by mass or more, particularly preferably 90% by mass or more (including 100% by mass) in the composition. To do.
In addition, when described as “X to Y” (X and Y are arbitrary numbers), “X is preferably greater than X” and “preferably smaller than Y” together with the meaning of “X to Y” unless otherwise specified. Is included. Here, even if the upper limit and lower limit of the numerical range in the present invention are slightly out of the numerical range characterized by the present invention, as long as the same effects as those in the numerical range are provided, the present invention. It is included in the equivalent range.

  The laminated porous film of the present invention has a β activity, and has a structure in which an A layer mainly composed of a polypropylene resin composition and a B layer mainly composed of a polyethylene resin composition are alternately laminated, The layer B is a laminated porous film having at least 5 layers, and the laminated porous film has β activity.

The laminated porous film of the present invention is characterized by having the β activity.
The β activity can be regarded as an index indicating that the polypropylene resin composition produced β crystals in the film-like material before stretching. If the polypropylene-based resin in the film-like material before stretching produces β crystals, fine pores are formed by subsequent stretching, so that a separator having air permeability can be obtained.

The presence or absence of β activity of the laminated porous film can be determined by conducting a differential thermal analysis of the laminated porous film using a differential scanning calorimeter and detecting a crystal melting peak temperature derived from β crystals of polypropylene resin. Judgment is based on no.
Specifically, the laminated porous film is heated at a heating rate of 10 ° C./min from 25 ° C. to 240 ° C. for 1 minute in a differential scanning calorimetric system, and then cooled at a cooling rate of 10 ° C. from 240 ° C. to 25 ° C. When the temperature is held again for 1 minute after cooling down at a rate of 10 minutes per minute, and when the temperature is raised again from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./minute, the crystal melting peak temperature (Tmβ) derived from the β crystals of polypropylene at the time of temperature rise Is detected, it is determined to have β activity.

In addition, the β activity of the laminated porous film is calculated by the following formula using the heat of crystal melting derived from the α crystal of the polypropylene resin (ΔHmα) and the heat of crystal melting derived from the β crystal (ΔHmβ). Yes.
β activity (%) = [ΔHmβ / (ΔHmβ + ΔHmα)] × 100
For example, in the case of homopolypropylene, the heat of crystal melting derived from β crystal (ΔHmβ) mainly detected in the range of 145 to 160 ° C., and the crystal derived from α crystal mainly detected at 160 ° C. to 175 ° C. It can be calculated from the heat of fusion (ΔHmα). Further, for example, in the case of random polypropylene copolymerized with 1 to 4 mol% of ethylene, the amount of heat of crystal melting (ΔHmβ) derived from the β crystal detected mainly at 120 ° C. or more and less than 140 ° C. is mainly 140. It can be calculated from the crystal melting calorie (ΔHmα) derived from the α crystal detected in the range of from 0 ° C. to 165 ° C.

The β activity is preferably larger. Specifically, the β activity is preferably 20% or more, more preferably 40% or more, and particularly preferably 60% or more. If the β activity is 20% or more, it indicates that a lot of β crystals of the polypropylene resin composition can be generated even in the film-like material before stretching, and many fine and uniform holes are formed by stretching, As a result, a laminated porous film having high mechanical strength and excellent air permeability can be obtained.
The upper limit value of β activity is not particularly limited, but the higher the β activity, the more effective it is obtained from the above effects, so the closer it is to 100%, the better.

  As a method for obtaining the above β activity, a method of molding a molten polypropylene resin with a high draft, a method of not adding a substance that promotes the formation of α crystals of the polypropylene resin, and a method described in Japanese Patent No. 3739481 Examples thereof include a method of adding a polypropylene-based resin that has been subjected to a treatment for generating peroxide radicals, and a method of adding a β crystal nucleating agent to the resin composition. Among them, it is preferable to obtain a β activity by adding a β crystal nucleating agent to the resin composition. By adding the β crystal nucleating agent, it is possible to more uniformly and efficiently promote the generation of β crystals of the polypropylene resin, and to obtain a laminated porous film having a layer having β activity.

Below, the detail of the component of each layer which comprises the laminated porous film of this invention is demonstrated. The laminated porous film of the general embodiment has a structure in which an A layer composed of a porous layer mainly composed of polypropylene resin and a B layer composed of a porous layer mainly composed of a polyethylene resin composition are alternately stacked. The layer B has at least 5 layers and has β activity, and is a laminated porous film.
[A layer]
Next, the A layer in the present invention will be described. The A layer in the present invention contains a polypropylene resin composition as a main component.

(Polypropylene resin composition)
As the polypropylene resin composition in the present invention, homopolypropylene (propylene homopolymer), or propylene and ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene or 1 -Random copolymers or block copolymers with α-olefins such as decene. Among these, when used for a battery separator, homopolypropylene is more preferably used from the viewpoint of mechanical strength.

Moreover, as a polypropylene-type resin composition, it is preferable that the isotactic pentad fraction which shows stereoregularity is 80 to 99%, More preferably, it is 83 to 98%, More preferably, it is 85 to 97%. Use things. If the isotactic pentad fraction is too low, the mechanical strength of the laminated porous film may be reduced. On the other hand, the upper limit of the isotactic pentad fraction is defined by the upper limit that can be obtained industrially at present, but this is not the case when a more regular resin is developed in the industrial level in the future. is not.
The isotactic pentad fraction is a three-dimensional structure in which five methyl groups that are side chains are located in the same direction with respect to the main chain of carbon-carbon bonds composed of arbitrary five consecutive propylene units. Or the ratio is meant. Signal assignment of the methyl group region is as follows. Zambelli et at al. (Macromol. 8, 687 (1975)).

  Moreover, it is preferable that Mw / Mn which is a parameter which shows molecular weight distribution of a polypropylene resin composition is 1.5-10.0. More preferably, 2.0 to 8.0, and still more preferably 2.0 to 6.0 is used. This means that the smaller the Mw / Mn, the narrower the molecular weight distribution. However, if the Mw / Mn is less than 1.5, problems such as a decrease in extrusion moldability occur, and it is difficult to produce industrially. There are many cases. On the other hand, when Mw / Mn exceeds 10.0, low molecular weight components increase, and the mechanical strength of the resulting laminated porous film tends to decrease. Mw / Mn is obtained by GPC (gel per emission chromatography) method.

  Further, the melt flow rate (MFR) of the polypropylene resin composition is not particularly limited, but usually the MFR is preferably 0.1 to 15 g / 10 min, and preferably 0.5 to 10 g / 10 min. It is more preferable that When the MFR is less than 0.1 g / 10 minutes, the melt viscosity of the resin during the molding process is high, and the productivity is lowered. On the other hand, when it exceeds 15 g / 10 minutes, practical problems such as insufficient strength of the obtained laminated porous film tend to occur. MFR is measured under the conditions of a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210.

  Examples of the polypropylene resin composition include trade names “Novatech PP” “WINTEC” (manufactured by Nippon Polypro Co., Ltd.), “Versify” “Notio” “Toughmer XR” (manufactured by Mitsui Chemicals), “Zeras” “Thermo Run” ( "Mitsubishi Chemical Co., Ltd.", "Sumitomo Noblen" "Tough Selenium" (manufactured by Sumitomo Chemical Co., Ltd.), "Prime TPO" (manufactured by Prime Polymer Co., Ltd.), "Adflex" "Adsyl", "HMS-PP (PF814)" (manufactured by Sun Allomer) ), “Inspire” (manufactured by Dow Chemical Co., Ltd.), and other commercially available products can be used.

(Β activity)
In order to have β activity, the following are used as β crystal nucleating agents in the present invention. However, the β crystal nucleating agent is not particularly limited as long as it increases the formation and growth of β crystals of the polypropylene resin composition. Instead, two or more types may be mixed and used.
Examples of the β crystal nucleating agent include amide compounds; tetraoxaspiro compounds; quinacridones; iron oxides having a nanoscale size; potassium 1,2-hydroxystearate, magnesium benzoate or magnesium succinate, magnesium phthalate, etc. Alkali or alkaline earth metal salts of carboxylic acids typified by: aromatic sulfonic acid compounds typified by sodium benzene sulfonate or sodium naphthalene sulfonate; di- or triesters of dibasic or tribasic carboxylic acids; phthalocyanines Phthalocyanine pigments typified by blue and the like; a two-component compound comprising component a which is an organic dibasic acid and a component b which is an oxide, hydroxide or salt of a Group IIA metal of the periodic table; a cyclic phosphorus compound; A group consisting of magnesium compounds Things and the like.

  Specific examples of preferable β crystal nucleating agents include β crystal nucleating agent “NJESTER NU-100” manufactured by Shin Nippon Rika Co., Ltd., and specific examples of polypropylene resins to which β crystal nucleating agents are added include polypropylene “ Bepol B-022SP ”, polypropylene manufactured by Borealis“ Beta (β) -PP BE60-7032 ”, polypropylene manufactured by mayzo“ BNX BETAPP-LN ”, and the like. Specific types of other nucleating agents are described in JP-A No. 2003-306585, JP-A No. 06-228966, and JP-A No. 09-194650.

  In the present invention, the β crystal nucleating agent is preferably blended in the polypropylene resin composition. The ratio of the β-crystal nucleating agent added to the polypropylene resin needs to be appropriately adjusted depending on the type of the β-crystal nucleating agent or the composition of the polypropylene-based resin. The nucleating agent is preferably 0.0001 to 5.0 parts by mass, more preferably 0.01 to 3 parts by mass, and still more preferably 0.1 to 3 parts by mass. If it is 0.0001 part by mass or more, β crystals of polypropylene resin can be sufficiently produced and grown at the time of production, and desired air permeability characteristics can be obtained by stretching. Moreover, if it is 5.0 mass parts or less, it becomes economically advantageous, and since troubles due to bleeding out of the β crystal nucleating agent are less likely to occur, it is preferable.

It is important that the A layer is mainly composed of a polypropylene resin composition. Specifically, when a polypropylene resin and a β crystal nucleating agent are used, the total mass of the polypropylene resin composition and the β crystal nucleating agent is 70% by mass or more, preferably 80% by mass or more based on the total mass of the A layer. More preferably, it accounts for 90% by mass or more.
The layer A may contain additives or other components that are generally blended into the resin composition within a range that does not impair the purpose of the present invention and the properties of the layer A as described above. Examples of the additive include recycling resin, silica, talc, kaolin, calcium carbonate, which is added for the purpose of improving and adjusting molding processability, productivity, and various physical properties of the laminated porous film. Inorganic particles such as, pigments such as titanium oxide and carbon black, flame retardants, weathering stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers, crosslinking agents, lubricants, nucleating agents, plasticizers, anti-aging agents, Examples thereof include additives such as antioxidants, light stabilizers, ultraviolet absorbers, neutralizers, antifogging agents, antiblocking agents, slip agents, and coloring agents. Specifically, as antioxidants, amine-based antioxidants such as copper halides and aromatic amines, triethylene glycol bis [3- (3-t-butyl-5methyl-4-hydroxyphenyl) propionate] and the like And phenolic antioxidants. A commercially available product is “Irganox B225” (manufactured by Ciba Special). In addition, UV absorbers described in P178 to P182 of “Plastics compounding agents”, surfactants as antistatic agents described in P271 to P275, lubricants described in P283 to P294, etc. Is mentioned.

[B layer]
Next, the B layer in the present invention will be described. B layer in this invention has a polyethylene-type resin composition as a main component.

(Polyethylene resin composition)
B layer is a layer which has a polyethylene-type resin composition as a main component. The layer B has any structure / configuration as long as it has a large number of fine pores communicating in the thickness direction and is composed of a composition mainly composed of a polyethylene resin composition as described above. May be. For example, a structure in which the fine pores are provided in a film-like material made of a polyethylene-based resin composition may be used, or particulate or fibrous fine materials may be aggregated to form a layer. A structure in which the gap is the fine hole may be employed. The B layer of the present invention preferably has the former structure in which uniform fine holes can be formed and the air efficiency and the like can be easily controlled.
The thermal characteristics of the polyethylene resin composition, which is the main component of the composition constituting the B layer, is important. That is, it is necessary to select the polyethylene resin so that the crystal melting peak temperature of the composition constituting the B layer is lower than the crystal melting peak temperature of the resin composition constituting the A layer. Specifically, the layer B is preferably a polyethylene resin composition having a crystal melting peak temperature of 100 ° C. or higher and 150 ° C. or lower.
This crystal melting peak temperature is a peak value of the crystal melting temperature when the temperature is raised from 25 ° C. at a heating rate of 10 ° C./min using a differential scanning calorimeter in accordance with JIS K7121.

  The polyethylene-based resin composition in the present invention includes a low-density polyethylene, a linear low-density polyethylene, a linear ultra-low-density polyethylene, a medium-density polyethylene, a high-density polyethylene, and a copolymer mainly composed of ethylene, that is, ethylene and propylene. , Butene-1, pentene-1, hexene-1, heptene-1, octene-1, etc., α-olefins having 3 to 10 carbon atoms; vinyl esters such as vinyl acetate and vinyl propionate; methyl acrylate, ethyl acrylate Copolymer or multi-component copolymer with one or more comonomers selected from unsaturated carboxylic acid esters such as methyl methacrylate and ethyl methacrylate, and unsaturated compounds such as conjugated and non-conjugated dienes A coalescence or a mixed composition thereof may be mentioned. The ethylene unit content of the ethylene polymer is usually more than 50% by mass.

  Among these polyethylene resins, at least one polyethylene resin selected from low density polyethylene, linear low density polyethylene, and high density polyethylene is preferable, and high density polyethylene is most preferable.

Density of the polyethylene resin composition is preferably 0.910~0.970g / cm ^3, more preferably 0.930~0.970g / cm ^3, 0.940~0.970g More preferably, it is / cm ³ . A density of 0.910 g / cm ³ or more is preferable because a layer having appropriate SD characteristics can be formed. On the other hand, 0.970 g / cm ³ or less is preferable in that a layer having an appropriate SD characteristic can be formed and stretchability is maintained. The density in the present invention is a value measured according to JIS K7112 using a density gradient tube method.

  The melt flow rate (MFR) of the polyethylene resin composition is not particularly limited, but usually the MFR is preferably 0.03 to 15 g / 10 minutes, and preferably 0.3 to 10 g / 10 minutes. It is preferable. When the MFR is within the above range, the back pressure of the extruder does not become too high during the molding process, and the productivity is excellent. The MFR in the present invention is a measured value under the conditions of a temperature of 190 ° C. and a load of 2.16 kg in accordance with JIS K7210.

  The production method of the polyethylene resin is not particularly limited, and is a known polymerization method using a known olefin polymerization catalyst, for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene catalyst. A polymerization method using a single site catalyst may be mentioned.

(Crystal nucleating agent)
The crystal nucleating agent is preferably added because it has an effect of controlling the crystal structure of the polyethylene resin composition and making the porous structure fine at the time of stretching and opening.
The crystal nucleating agent in the present invention refers to a material that has an effect of nucleation for crystal growth during the cooling process from the molten state of the polyethylene resin. Specifically, during the cooling of the polyethylene resin from the molten state, the crystal nucleating agent becomes a site for nucleation for crystal growth, has an ordered and faster crystal structure, and has many sites for nucleation. By doing so, more small and homogeneous crystals are produced. When a crystal nucleating agent is added to a polyethylene-based resin, the crystallization speed of the polyethylene-based resin is increased. For example, in the differential scanning calorimetry (DSC), the crystallization peak and the crystal melting peak become sharp. Show.

  The crystal nucleating agent in the present invention is only required to have an effect of nucleation for crystal growth during the cooling process from the molten state having the above-mentioned characteristics. For example, a dibenzylidene sorbitol (DBS) compound, 1,3-O -Bis (3,4-dimethylbenzylidene) sorbitol, dialkylbenzylidene sorbitol, diacetal of sorbitol having at least one chlorine or bromine substituent, di (methyl or ethyl substituted benzylidene) sorbitol, bis having a substituent forming a carbocycle (3,4-dialkylbenzylidene) sorbitol, aliphatic, alicyclic, and aromatic carboxylic acids, dicarboxylic acids or polybasic polycarboxylic acids, corresponding anhydrides and metal salts of organic acids such as metal salts, Cyclic bis-phenol phosphate, disodium bicycl [2.2.1] Bicyclic dicarboxylic acids and salt compounds such as heptene dicarboxylic acids, saturated metal or organic bicyclic dicarboxylates such as bicyclo [2.2.1] heptane-dicarboxylate Salt compound, 1,3: 2,4-O-dibenzylidene-D-sorbitol, 1,3: 2,4-bis-O- (m-methylbenzylidene) -D-sorbitol, 1,3: 2,4 -Bis-O- (m-ethylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (m-isopropylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O -(Mn-propylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (mn-butylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O -(P-methylbenz Den) -D-sorbitol, 1,3: 2,4-bis-O- (p-ethylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (p-isopropylbenzylidene) -D -Sorbitol, 1,3: 2,4-bis-O- (pn-propylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (pn-butylbenzylidene) -D -Sorbitol, 1,3: 2,4-bis-O- (2,3-dimethylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (2,4-dimethylbenzylidene) -D -Sorbitol, 1,3: 2,4-bis-O- (2,5-dimethylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (3,4-dimethylbenzylidene) -D -Sorbitol, 1,3: 2,4-Bi Su-O- (3,5-dimethylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (2,3-diethylbenzylidene) -D-sorbitol, 1,3: 2,4- Bis-O- (2,4-diethylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (2,5-diethylbenzylidene) -D-sorbitol, 1,3: 2,4- Bis-O- (3,4-diethylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (3,5-diethylbenzylidene) -D-sorbitol, 1,3: 2,4- Bis-O- (2,4,5-trimethylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (3,4,5-trimethylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (2,4,5-to Ethylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (3,4,5-triethylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (p- Methyloxycarbonylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (p-ethyloxycarbonylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (p- Isopropyloxycarbonylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (on-propyloxycarbonylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- ( on-butylbenzylidene) -D-sorbitol, 1,3: 2,4-bis-O- (o-chlorobenzylidene) -D-sorbitol, 1,3: 2,4-bis-O (P-chlorobenzylidene) -D-sorbitol, 1,3: 2,4-bis-O-[(5,6,7,8, -tetrahydro-1-naphthalene) -1-methylene] -D-sorbitol, 1,3: 2,4-bis-O-[(5,6,7,8, -tetrahydro-2-naphthalene) -1-methylene] -D-sorbitol, 1,3-O-benzylidene-2,4 -Op-methylbenzylidene-D-sorbitol, 1,3-Op-methylbenzylidene-2,4-O-benzylidene-D-sorbitol, 1,3-O-benzylidene-2,4-O-p -Ethylbenzylidene-D-sorbitol, 1,3-O-p-ethylbenzylidene-2,4-O-benzylidene-D-sorbitol, 1,3-O-benzylidene-2,4-Op-chlorobenzylidene- D-So Bitol, 1,3-O-p-chlorobenzylidene-2,4-O-benzylidene-D-sorbitol, 1,3-O-benzylidene-2,4-O- (2,4-dimethylbenzylidene) -D- Sorbitol, 1,3-O- (2,4-dimethylbenzylidene) -2,4-O-benzylidene-D-sorbitol, 1,3-O-benzylidene-2,4-O- (3,4-dimethylbenzylidene ) -D-sorbitol, 1,3-O- (3,4-dimethylbenzylidene) -2,4-O-benzylidene-D-sorbitol, 1,3-Op-methyl-benzylidene-2,4-O -P-ethylbenzylidene sorbitol, 1,3-p-ethyl-benzylidene-2,4-p-methylbenzylidene-D-sorbitol, 1,3-Op-methyl-benzylidene-2,4 Diacetal compounds such as Op-chlorobenzylidene-D-sorbitol, 1,3-Op-chloro-benzylidene-2,4-Op-methylbenzylidene-D-sorbitol, sodium 2,2′-methylene- Bis- (4,6-di-tert-butylphenyl) phosphate, aluminum bis [2,2′-methylene-bis- (4-6-di-tert-butylphenyl) phosphate], 2,2-methylenebisphosphate ( 4,6-di-tert-butylphenyl) sodium, oleic acid amide, erucic acid amide, stearic acid amide, hebeninic acid amide, etc., aliphatic amides having 11 to 22 carbon atoms, 2 sodium hexahydrophthalic acid, silica, talc , Kaolin, calcium carbide and other inorganic particles, glycerol, glycerin monoester, etc. Higher fatty acid esters, and the like.

  In the present invention, the crystal nucleating agent is preferably 0.00001 to 5.0 parts by mass with respect to 100 parts by mass of the polyethylene resin. 0.0001-3.0 mass parts is more preferable, and 0.001-1 mass part is still more preferable. Within such a range, when the polyethylene-based resin is crystallized in the cooling process from the molten state, the number of crystal nuclei increases, and as a result, the spherulite size becomes fine. The crystal nucleating agent is preferable because it does not bleed on the surface of the film.

  Specific examples of commercially available crystal nucleating agents include “Gelall D” (manufactured by Shin Nippon Rika Co., Ltd.), “Adeka Stub” series (manufactured by Asahi Denka Kogyo Co., Ltd.), “Millad” (manufactured by Milliken Chemical Co., Ltd.), “Hyperform”. (Manufactured by Milliken Chemical Co., Ltd.), “IRGACLEAR D” (manufactured by Ciba Special Chemicals Co., Ltd.) and the like, and as a master batch of the crystal nucleating agent, “Rike Master CN” (manufactured by Riken Vitamin Co., Ltd.) series and the like can be mentioned.

(Compound X)
Moreover, it is preferable to add the substance which promotes porosity and expression of SD characteristic to the said B layer. In particular, the B layer preferably contains at least one compound X selected from a modified polyolefin resin, an alicyclic saturated hydrocarbon resin or a modified product thereof, or a wax. By adding the compound X, a porous structure can be obtained more efficiently, and the shape and diameter of the pores can be easily controlled.

  The modified polyolefin resin in the present invention refers to a resin mainly composed of an unsaturated carboxylic acid or an anhydride thereof, or a polyolefin modified with a silane coupling agent. Examples of unsaturated carboxylic acids or their anhydrides include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, citraconic acid, citraconic anhydride, itaconic acid, itaconic anhydride or monoepoxy compounds of these derivatives and the above acids. Ester compounds, and polymers having a group capable of reacting with these acids in the molecule and an acid-reactive organism. These metal salts can also be used. Among these, maleic anhydride is more preferably used. Moreover, these copolymers can be used individually or in mixture of 2 or more types, respectively.

  Examples of the silane coupling agent include vinyltriethoxysilane, methacryloyloxytrimethoxysilane, and γ-methacryloyloxypropyltriacetyloxysilane.

  In order to produce the modified polyolefin resin, for example, these modified monomers can be copolymerized in the stage of polymerizing the polymer in advance, or these modified monomers can be graft copolymerized with the polymer once polymerized. Further, for modification, these modified monomers are used alone or in combination, and those having a content in the range of 0.1% by mass or more and 5% by mass or less are preferably used. Of these, those that have been graft-modified are preferably used.

  Examples of commercially available modified polyolefin resins include “Admer” (manufactured by Mitsui Chemicals), “Modic” (manufactured by Mitsubishi Chemical), “Modiper” (manufactured by NOF Corporation), and the like.

  Examples of the alicyclic saturated hydrocarbon resin and the modified product thereof in the present invention include petroleum resins, rosin resins, terpene resins, coumarone resins, coumarone-indene resins, and modified products thereof.

  The petroleum resin in the present invention is a C4 to C10 alicyclic olefin or diolefin obtained from a by-product such as by thermal decomposition of naphtha, or a C8 or more aromatic compound having an olefinically unsaturated bond. An aliphatic, aromatic and copolymer petroleum resin obtained by singly or copolymerizing one or more of the compounds contained therein.

  Examples of the petroleum resin include an aliphatic petroleum resin mainly composed of a C5 fraction, an aromatic petroleum resin mainly composed of a C9 fraction, a copolymer petroleum resin thereof, and an alicyclic petroleum resin. . Examples of terpene resins include terpene resins and terpene-phenol resins from β-pinene. Examples of rosin resins include rosin resins such as gum rosin and wood rosin, and esterified rosin resins modified with glycerin and pentaerythritol. it can. The alicyclic saturated hydrocarbon resin and the modified product thereof are preferable because they exhibit relatively good compatibility when mixed with a polyethylene resin, and a petroleum resin is more preferable from the viewpoint of color change and thermal stability. More preferred are petroleum resins.

  Hydrogenated petroleum resin is obtained by hydrogenating petroleum resin by a conventional method. Examples thereof include hydrogenated aliphatic petroleum resins, hydrogenated aromatic petroleum resins, hydrogenated copolymer petroleum resins and hydrogenated alicyclic petroleum resins, and hydrogenated terpene resins. Of the hydrogenated petroleum resins, hydrogenated alicyclic petroleum resins obtained by copolymerizing and hydrogenating a cyclopentadiene compound and an aromatic vinyl compound are preferable. Commercially available hydrogenated petroleum resins include the “Arcon” (Arakawa Chemical Industries) series.

  Next, the wax in the present invention will be described. The wax in the present invention refers to an organic compound having a melting point of 40 to 200 ° C. and a melt viscosity of 50 Pa · s or less at a temperature 10 ° C. higher than the melting point.

  The wax in the present invention includes polar or nonpolar wax, polypropylene wax, polyethylene wax, and wax modifier. Specifically, polar wax and nonpolar wax. Fischer-Tropsch wax, oxidized Fischer-Trips wax, hydroxy stearamide wax, functionalized wax, polypropylene wax, polyethylene wax, wax modifier, amorphous wax, carnauba wax, castor oil wax, microcrystalline wax, honey Wax, carnauba wax, castor wax, plant wax, candeki wax, Japanese wax, our wax, douglas fur bark wax, rice bran wax, jojoba wax, bayberry wax, montan wax, ozokerite wax, ceresin wax, petroleum wax, paraffin These include waxes, chemically modified hydrocarbon waxes, substituted amide waxes, and combinations and derivatives thereof. Among these, paraffin wax, polyethylene wax, and microcrystalline wax are preferable from the viewpoint that the porous structure can be efficiently formed, and microcrystalline wax is most preferable because the pore diameter can be reduced.

  Specific examples of commercially available waxes include the “Mitsui High Wax” (Mitsui Chemicals) series and the “metallocene wax” (Clariant Japan) series as polyethylene waxes, and the microcrystalline waxes include “ Hi-Mic "(manufactured by Nippon Seiwa Co., Ltd.) series and the like.

  As the ethylene-based copolymer, one having an MFR (JIS K7210, temperature: 190 ° C., load: 2.16 kg) of 0.1 g / 10 min to 10 g / 10 min is preferably used. If the MFR is 0.1 g / 10 min or more, the extrudability can be maintained satisfactorily. On the other hand, if the MFR is 10 g / 10 min or less, the strength of the film is hardly lowered.

  The ethylene-based copolymer includes “Evaflex” (manufactured by Mitsui DuPont Polychemical Co., Ltd.), “Novatech EVA” (manufactured by Nippon Polyethylene Co., Ltd.), and ethylene-acrylic acid copolymer as “ethylene-vinyl acetate copolymer”. NUC Copolymer ”(manufactured by Nihon Unicar),“ Rex Pearl EAA ”(manufactured by Nippon Ethylene Co., Ltd.),“ Elvalloy ”(manufactured by Mitsui DuPont Polychemical Co., Ltd.),“ Lex Pearl ”as an ethylene- (meth) -acrylic acid copolymer "EMA" (produced by Nippon Ethylene Co., Ltd.), "Lex Pearl EEA" (produced by Nippon Ethylene Co., Ltd.) as an ethylene-ethyl acrylate copolymer, "Aclift" (produced by Sumitomo Chemical Co., Ltd.), ethylene-methyl (meth) acrylic acid, ethylene “Vodyne” (manufactured by Sumitomo Chemical Co., Ltd.), ethylene as a vinyl acetate-maleic anhydride terpolymer Glycidyl methacrylate copolymer, ethylene-vinyl acetate-glycidyl methacrylate terpolymer, and "bond first" (manufactured by Sumitomo Chemical Co., Ltd.) are commercially available as ethylene-ethyl acrylate-glycidyl methacrylate terpolymer. Available at:

  The compound X exhibits relatively good compatibility with the polyethylene resin, and is compatible when the polyethylene resin is melted. When the polyethylene resin crystallizes, the compound X bleeds at the crystal interface. It is considered that the compound to be worked out more effectively due to the shutdown property, and from this viewpoint, an alicyclic saturated hydrocarbon resin and a modified product thereof, or a wax are more preferable, and a wax is more preferable from the viewpoint of moldability.

  The compounding amount of the compound X is 1 mass as a lower limit with respect to 100 parts by mass of the polyethylene resin composition contained in the B layer when the interface between the polyethylene resin composition and the compound X is peeled to form micropores. Part or more, preferably 5 parts by weight or more, more preferably 10 parts by weight or more. On the other hand, the upper limit is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and still more preferably 30 parts by mass or less. When the compounding amount of the compound X is 1 part by mass or more with respect to 100 parts by mass of the polyethylene-based resin composition, an effect of expressing a desired good porous structure is sufficiently obtained. Moreover, the more stable moldability is securable because the compounding quantity of the compound X shall be 50 mass parts or less.

  In the B layer in the present invention, in addition to the polyethylene resin composition and the compound X that promotes porosity, if necessary, a thermoplastic resin is used as long as the thermal characteristics of the laminated porous film, specifically, the shutdown characteristics are not impaired. It may be used. Other thermoplastic resins that can be mixed with the above-mentioned polyethylene resin composition include styrene resins such as styrene, AS resin, or ABS resin, fluorine resins, polyethylene terephthalate, polybutylene terephthalate, polycarbonate, poly Ester resins such as arylates; ether resins such as polyacetal, polyphenylene ether, polysulfone, polyethersulfone, polyetheretherketone, or polyphenylene sulfide; polyamide resins such as 6 nylon, 6-6 nylon, and 6-12 nylon These thermoplastic resins can be mentioned.

  Moreover, you may add what is called rubber components, such as a thermoplastic elastomer, to the B layer in this invention as needed. Examples of the thermoplastic elastomer include styrene / butadiene, polyolefin, urethane, polyester, polyamide, 1,2-polybutadiene, polyvinyl chloride, and ionomer.

  In the B layer, in addition to the above-mentioned compound X, a metal soap or synthetic hydrotalcite compound as a catalyst neutralizer, a phenol-based antioxidant generally marketed as an antioxidant, or a phosphorus-based oxidation as necessary. From one or more selected from polyhydric alcohol fatty acid ester, alkyldiethanolamine, linear alkyl alcohol, polyoxyethylene alkylamine fatty acid ester, polyoxyethylene alkylamine compound, etc. The compound which becomes, a hindered amine light stabilizer, a weather resistance agent, an antifogging agent, an antiblocking agent, and another transparent nucleating agent can be added.

  The B layer may contain other additives or other components as long as the properties of the laminated porous film are not impaired. The additive is not particularly limited, but recycled resin generated from trimming loss such as ears, inorganic particles such as silica, talc, kaolin and calcium carbide, pigments such as titanium oxide and carbon black, flame retardants, Weather resistance stabilizer, antistatic agent, crosslinking agent, lubricant, plasticizer, anti-aging agent, antioxidant, light stabilizer, UV absorber, neutralizer, antifogging agent, antiblocking agent, slip agent, or coloring An additive such as an agent can be mentioned.

[Configuration of laminated porous film]
Then, the structure of a laminated porous film is demonstrated. The laminated porous film of the present invention has a structure in which A layer composed of a porous layer mainly composed of polypropylene resin and B layer composed of a porous layer mainly composed of polyethylene resin are laminated alternately. The B layer has at least 5 layers. The simplest configuration is B layer / A layer / B layer / A layer / B layer / A layer / B layer / A layer / B layer, then the simplest configuration is A layer / B layer / A layer / B Layer / A layer / B layer / A layer / B layer / A layer / B layer, A layer / B layer / A layer / B layer / A layer / B layer / A layer / B layer / A layer / B layer / A layer. In addition, B layer / A layer / B layer / A layer / B layer / A layer / B layer / A layer / B layer / A layer and B layer / A layer / B layer / A layer / B layer / A It may be layer / B layer / A layer / B layer / A layer / B layer. The number of layers is not particularly limited as long as at least 5 layers B are present, and may be increased as necessary to 10 layers, 11 layers, 12 layers, and 13 layers.
When the B layer has 5 layers or more, sufficient pin penetration strength can be secured, and among them, the B layer preferably has 10 layers or more, more preferably 15 layers or more.
Moreover, if the structure of the laminated porous film is symmetrical with respect to the thickness direction, such as A layer / B layer /... / B layer / A layer, the degree of curl and surface smoothness of the obtained laminated porous film It is particularly excellent because of good properties.

  The stacking ratio of the A layer and the B layer can be appropriately adjusted according to the use and purpose, and is not particularly limited, but the B layer (the total thickness of the B layer) with respect to the thickness 100 of all layers. The ratio is preferably 1 to 40, more preferably 1 to 30. Within such a range, the air permeability at 25 ° C. is good, and the air permeability after heating at 135 ° C. for 5 seconds can be sufficiently increased.

In addition, it is possible to adopt a form of three types and three layers in combination with layers having other functions as required. Other layers may be laminated or may be appropriately treated, and is not particularly limited to a laminated structure consisting of only the A layer and the B layer.
When other layers other than the A layer and the B layer exist, it is necessary to provide the other layers so that the relationship between the A layer and the B layer does not deviate from the above-described relationship. The total thickness of the other layers is preferably 0.1 to 0.5, more preferably 0.1 to 0.3, with respect to the thickness 1 of all layers.

[Form and physical properties of laminated porous film]
The form of the laminated porous film of the present invention may be either flat or tube-like, but it is preferable from the viewpoint of productivity that several products can be taken, and further processing of inner surface cords and the like The surface is more preferable because it is simple to apply.
The thickness of the laminated porous film of the present invention is preferably 1 to 500 μm, more preferably 5 to 300 μm, still more preferably 5 to 100 μm, particularly preferably 7 to 50 μm, and most preferably 10 to 40 μm. A thickness of 1 μm or more is preferable because substantially sufficient air permeability characteristics can be obtained and there is no problem in terms of mechanical strength. Moreover, if thickness is 500 micrometers or less, since sufficient mechanical strength can be obtained and it does not become a problem also from a viewpoint of an air permeability characteristic, it is preferable.

In addition, the laminated porous film of the present invention is also characterized in that there are many fine pores having communication in the thickness direction and has excellent air permeability.
As an index thereof, when the laminated porous film of the present invention is used for a battery separator, the air permeability at 25 ° C. is preferably 5 to 3000 seconds / 100 ml.
The upper limit of the air permeability is preferably 3000 seconds / 100 ml or less, more preferably 2000 seconds / 100 ml or less, still more preferably 1000 seconds / 100 ml or less, and particularly preferably 500 seconds / 100 ml or less. That is, if the air permeability is 3000 seconds / 100 ml or less, it is suggested that the air permeability is sufficient and has sufficient air permeability characteristics. And sufficient battery characteristics can be obtained.
On the other hand, the lower limit of the air permeability is not particularly limited, but is preferably 5 seconds / 100 ml or more, more preferably 20 seconds / 100 ml or more, and further preferably 50 seconds / 100 ml or more. When the air permeability is 5 seconds / 100 ml or more, the pore diameter is moderately small and the mechanical strength can be maintained sufficiently high. When used as a battery separator, troubles such as an internal short circuit can be avoided.
The air permeability represents the difficulty in passing through the air in the thickness direction of the porous film, and is specifically expressed in the number of seconds required for 100 ml of air to pass through the porous film. Therefore, it means that the smaller the numerical value is, the easier it is to pass through, and the higher numerical value is, the more difficult it is to pass through. That is, the smaller the value means that the connectivity in the thickness direction of the porous film is better, and the larger the value means that the connectivity in the thickness direction of the porous film is worse. The term “communication” refers to the degree of connection of pores in the thickness direction of the porous film. The low air permeability of the present invention means that, when used as a battery separator, it means that ions can be easily transferred and is excellent in electrical characteristics. The air permeability is measured by the method described in the examples.

The laminated porous film of the present invention preferably has shutdown characteristics when used as a battery separator. Specifically, the air permeability after heating at 135 ° C. for 5 seconds is preferably 10,000 seconds / 100 ml or more, more preferably 25000 seconds / 100 ml or more, and further preferably 50000 seconds / 100 ml or more. By setting the air permeability after heating at 135 ° C for 5 seconds to 10000 seconds / 100ml or more, the holes are quickly closed and the current is cut off during abnormal heat generation, thus avoiding problems such as battery rupture. be able to.
The shutdown characteristic depends on the porosity and the hole diameter. Although not limited to the following contents, for example, the air permeability after heating at 135 ° C. for 5 seconds can be controlled by increasing the number of the B layers to refine the crystal of the polyethylene-based resin. it can. Further, for example, by adding the compound X to a polyethylene resin and adjusting the type and blending amount of the compound X, or adding a crystal nucleating agent to make the crystal of the polyethylene resin finer, 135 ° C. The air permeability after heating for 5 seconds can be controlled.
In the production method, the air permeability after heating at 135 ° C. for 5 seconds can be set to 10,000 seconds / 100 ml or more by adjusting the draw ratio and the drawing temperature.

  In the laminated porous film of the present invention, the porosity is preferably 5 to 80%, more preferably 20 to 70%. The porosity is an important factor for defining the porous structure. If the porosity is less than 5%, it is difficult to substantially obtain communication. On the other hand, if the porosity is higher than 80%, handling becomes difficult from the viewpoint that the mechanical strength of the film becomes weak. The porosity is measured by the method of the example.

In the laminated porous film of the present invention, the pin puncture strength is preferably 1.5 N or more, more preferably 2.0 N or more, and further preferably 3.0 N or more, regardless of the thickness.
Pin puncture strength greatly contributes to short-circuiting and productivity during battery production, particularly when the laminated porous film of the present invention is used as a battery separator. If the pin puncture strength is lower than 1.5N, the probability of occurrence of a short circuit due to film breakage due to foreign matter or the like during battery production may increase. On the other hand, the upper limit value of the pin puncture strength is not particularly specified, but usually 10N or less is used.

[Method for producing laminated porous film]
Next, although the manufacturing method of the laminated porous film of this invention is demonstrated, this invention is not limited only to the laminated porous film manufactured by the manufacturing method which concerns.
The manufacturing method of the laminated porous film of this invention is divided roughly into the following three by the order of porous formation and lamination.
(A) A method of producing a porous film of A layer and a porous film of B layer, and then laminating at least the porous film of A layer and the porous film of B layer.
(B) A method of forming a laminated nonporous film-like material of A layer and B layer and then making the nonporous film-like material porous.
(C) A method in which one of the two layers of the A layer and the B layer is made porous, and then laminated with another layer of a non-porous film to make it porous.

Examples of the method (a) include a method of thermally laminating the porous film of the A layer and the porous film of the B layer, and a method of laminating with an adhesive or the like.
As the method (b), a non-porous film of layer A and a non-porous film of layer B are prepared, and the non-porous film of layer A and the non-porous film of layer B are heated. Examples thereof include a method of making porous after laminating with a laminate or an adhesive, or a method of making porous after forming a laminated nonporous film-like material having at least an A layer and a B layer by coextrusion.
As the method (c), the A-layer porous film and the B-layer nonporous film, or the A-layer nonporous film and the B-layer porous film are laminated with a thermal laminate or an adhesive. The method of making it.
In the present invention, the method (b) is preferable from the viewpoint of simplicity of the process and productivity, and a method using coextrusion is more preferable.

  As a preferable form of the laminated porous film of the present invention, a B layer mainly composed of a mixed resin composition containing an A layer mainly composed of a polypropylene resin having β activity and a polyethylene resin and a crystal nucleating agent. A laminated nonporous film-like material having a layer is prepared. Subsequently, there is a production method characterized in that a number of fine pores having connectivity in the thickness direction are formed by stretching the laminated non-porous film-like material.

The method for producing the laminated non-porous film is not particularly limited, and a known method may be used. For example, the resin composition is melted using an extruder, extruded from a T die, and cooled and solidified with a cast roll. A method is mentioned. Further, a method of cutting a film produced by a tubular method into a flat shape can be applied.
Examples of the stretching method for the laminated nonporous film-like material include a roll stretching method, a rolling method, a tenter stretching method, and a biaxial stretching method such as simultaneous biaxial stretching and sequential biaxial stretching. Biaxial stretching is performed in combination of two or more.

  As a more preferred embodiment, a laminated non-porous film-like shape is formed by coextrusion from a T die using a mixed resin composition containing a polypropylene resin forming the A layer, a polyethylene resin forming the B layer, and a crystal nucleating agent. The manufacturing method which makes a porous thing by producing a thing and biaxially stretching the said laminated nonporous film-like thing is mentioned.

  Specifically, first, the respective resin compositions constituting the A layer and the B layer are mixed using a Henschel mixer, a super Henschel mixer, a tumbler mixer, or the like, and then a single screw extruder, a twin screw extruder, a kneader. Etc., and pelletized after melt kneading. The resin composition constituting the A layer contains at least a polypropylene resin and a β crystal nucleating agent, and the resin composition constituting the B layer contains a polyethylene X resin composition containing a compound X and a crystal nucleating agent as required. Also good.

  Next, the obtained pellets of the resin composition are supplied to separate extruders. In the extruder, the resin melted by heating to the melting point or higher is homogenized with a gear pump or the like, and foreign matter or modified resin is removed through a filter or the like. The resin composition constituting the A layer and the resin composition constituting the B layer sent out from different flow paths using these two or more extruders are then sent to the multilayer laminating apparatus. As the multilayer laminating apparatus, a multi-manifold die, a feed block, a static mixer, or the like can be used. Moreover, you may combine these arbitrarily. A structure in which the A layer composed of a porous layer mainly composed of a polypropylene resin, which is a feature of the present invention, and the B layer composed of a porous layer mainly composed of a polyethylene resin are laminated, In order to achieve a laminated porous film having at least 5 layers and having β activity, it is preferable to use a feed block having at least one member having many fine slits. When such a feed block is used, the flow path through which the molten resin composition passes does not become extremely long, so there is little resin modification or foreign matter due to thermal degradation, and even when the number of layers is large, highly accurate lamination Is possible. It is also possible to form an arbitrary layer thickness configuration.

  Next, the molten laminated body formed in a desired layer configuration in this way is then formed into a desired shape by a die. And the sheet | seat laminated | stacked by the multilayer discharged | emitted from die | dye is extruded on cooling bodies, such as a casting drum, and is cooled and solidified, and a casting sheet is obtained. The gap of the die is determined from various conditions such as the film pressure of the laminated porous film finally required, stretching conditions, draft rate, etc., but is generally preferably about 0.1 to 3.0 mm, more preferably Is 0.5 to 2.0 mm. When the gap is 0.1 mm or more, a more sufficient production rate can be ensured. On the other hand, when the thickness is 3.0 mm or less, sufficient sex difference stability can be ensured.

  When it is extruded onto a cooling body such as a casting drum and cooled and solidified, it is brought into close contact with the cooling body such as a casting drum by electrostatic force and rapidly solidified by using an electrode such as a wire, tape, needle or knife. Is preferred. In addition, there are also methods in which air is blown out from a slit-like, spot-like, or planar device and brought into close contact with a cooling body such as a casting drum, or cooled by being brought into close contact with the cooling body with a nip roll.

In extrusion molding, the extrusion processing temperature is appropriately adjusted depending on the flow characteristics and moldability of the resin composition, but is generally preferably 180 to 300 ° C, and more preferably in the range of 200 to 280 ° C. An extrusion temperature of 180 ° C. or higher is preferable because the viscosity of the molten resin is sufficiently low and the back pressure during melt extrusion does not increase, and the moldability is excellent. On the other hand, it is preferable to set the temperature at 300 ° C. or lower because deterioration of the resin composition, and hence mechanical strength of the laminated porous film can be suppressed.
The cooling and solidification temperature by the cast roll is important in the present invention, and the β crystal of the polypropylene resin can be generated and grown to adjust the β crystal ratio in the B layer.
The cooling and solidifying temperature of the cast roll is preferably 80 to 150 ° C, more preferably 90 to 140 ° C, and still more preferably 100 to 130 ° C. It is preferable to set the cooling and solidification temperature to 80 ° C. or higher because the ratio of β crystals in the B layer that has been cooled and solidified can be sufficiently increased. Further, it is preferable to set the temperature to 150 ° C. or lower because troubles such as the molten resin extruded and sticking to the cast roll hardly occur and film formation can be efficiently performed.

By setting the cast roll in the temperature range, the β crystal ratio of the B layer before stretching is preferably adjusted to 30 to 100%, more preferably 40 to 100%, still more preferably 50 to 100%, 60 ˜100% is particularly preferred. By setting the β crystal ratio of the polypropylene-based resin in the B layer before stretching to 30% or more, a porous sheet is easily formed by a subsequent stretching operation, and a sheet having good air permeability can be obtained.
The β crystal ratio in the B layer before stretching is detected when the B layer is heated from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min using a differential scanning calorimeter. It is calculated by the following equation using the heat of crystal melting derived from the α crystal of the resin (ΔHmα) and the heat of crystal melting derived from the β crystal (ΔHmβ).
β crystal ratio (%) = [ΔHmβ / (ΔHmβ + ΔHmα)] × 100

  Subsequently, the obtained laminate is subjected to uniaxial stretching or biaxial stretching. The uniaxial stretching method may be longitudinal uniaxial or transverse uniaxial stretching. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. Among these, sequential biaxial stretching is more preferable because the stretching conditions can be selected in each stretching step and the porous structure can be easily controlled. In addition, the extending | stretching to the take-up (flow) direction of a film-like thing is called "longitudinal stretching", and the extending | stretching to the perpendicular direction is called "lateral stretching."

When the sequential biaxial stretching method is used, the stretching temperature needs to be appropriately selected depending on the composition of the resin composition to be used, the crystal melting peak temperature, the crystallization temperature, etc., but the control of the porous structure is relatively easy, The strength is preferable because it can balance with other physical properties such as shrinkage.
The stretching temperature in the longitudinal stretching is generally preferably 10 to 130 ° C, more preferably 15 to 125 ° C. The longitudinal draw ratio is preferably 2 to 10 times, more preferably 3 to 8 times. By performing longitudinal stretching within the above range, it is possible to develop an appropriate pore starting point while controlling breakage during stretching.
The stretching temperature in the transverse stretching is generally preferably 90 to 150 ° C, more preferably 95 to 130 ° C, still more preferably 100 ° C to 125 ° C. The transverse draw ratio is preferably 1.5 to 3 times, more preferably 1.8 to 2.5 times, and still more preferably 1.8 to 2.3 times. By performing transverse stretching within the above range, the pore starting point formed by longitudinal stretching can be appropriately expanded and a fine porous structure can be expressed.
Further, the stretching speed in the stretching step is preferably 500 to 12000% / min, more preferably 750 to 10,000% / min, and still more preferably 1000 to 80000% / min. By stretching at a stretching speed within the above range, a fine porous structure can be developed without forming pores such as a large defect structure.

  The laminated porous film thus obtained is preferably heat-treated at a temperature of about 100 to 150 ° C., more preferably about 110 to 140 ° C. for the purpose of improving dimensional stability. In addition, you may perform a 1-30% relaxation process as needed during a heat treatment process. After the heat treatment, the laminated porous film of the present invention is obtained by uniformly cooling and winding up.

[Battery separator]
Next, a nonaqueous electrolyte battery containing the laminated porous film of the present invention as a battery separator will be described with reference to FIG.
Both electrodes of the positive electrode plate 21 and the negative electrode plate 22 are wound in a spiral shape so as to overlap each other via the battery separator 10, and the outside is stopped with a winding tape to form a wound body. When winding in this spiral shape, the battery separator 10 preferably has a thickness of 5 to 40 μm, particularly preferably 5 to 30 μm. By making the thickness 5 μm or more, the battery separator is hardly broken, and by making the thickness 40 μm or less, it is possible to increase the battery area when wound in a predetermined battery can and to increase the battery capacity. it can.

  A wound body in which the positive electrode plate 21, the battery separator 10 and the negative electrode plate 22 are integrally wound is housed in a bottomed cylindrical battery case and welded to the positive and negative electrode lead bodies 24 and 25. Next, the electrolyte is injected into the battery can, and after the electrolyte has sufficiently penetrated into the battery separator 10 or the like, the positive electrode lid 27 is sealed around the opening periphery of the battery can via the gasket 26, and precharging and aging are performed. A cylindrical non-aqueous electrolyte battery is manufactured.

As the electrolytic solution, an electrolytic solution in which a lithium salt is used as an electrolytic solution and is dissolved in an organic solvent is used. The organic solvent is not particularly limited, but for example, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, esters such as dimethyl carbonate, methyl propionate or butyl acetate, and nitriles such as acetonitrile. 1,2-dimethoxyethane, 1,2-dimethoxymethane, dimethoxypropane, 1,3-dioxolane, ethers such as tetrahydrofuran, 2-methyltetrahydrofuran or 4-methyl-1,3-dioxolane, or sulfolane These may be used alone or in combination of two or more.
Among them, an electrolyte obtained by dissolving lithium hexafluorophosphate (LiPF ₆₎ at a rate of 1.0 mol / L in a solvent obtained by mixing 2 parts by mass of methyl ethyl carbonate relative to ethylene carbonate 1 part by weight is preferred.

As the negative electrode, an alkali metal or a compound containing an alkali metal integrated with a current collecting material such as a stainless steel net is used. Examples of the alkali metal include lithium, sodium, and potassium. Examples of the compound containing an alkali metal include an alloy of an alkali metal and aluminum, lead, indium, potassium, cadmium, tin or magnesium, a compound of an alkali metal and a carbon material, a low potential alkali metal and a metal oxide, and the like. Or a compound with a sulfide or the like.
When a carbon material is used for the negative electrode, the carbon material may be any material that can be doped and dedoped with lithium ions, such as graphite, pyrolytic carbons, cokes, glassy carbons, a fired body of an organic polymer compound, Mesocarbon microbeads, carbon fibers, activated carbon and the like can be used.

  In this embodiment, as a negative electrode, a carbon material having an average particle size of 10 μm is mixed with a solution in which vinylidene fluoride is dissolved in N-methylpyrrolidone to form a slurry, and this negative electrode mixture slurry is passed through a 70-mesh net. After removing the large particles, uniformly apply to both sides of the negative electrode current collector made of a strip-shaped copper foil having a thickness of 18 μm and dry, and then compression-molded with a roll press machine, cut, strip-shaped negative electrode plate and We use what we did.

  As the positive electrode, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, manganese dioxide, metal oxide such as vanadium pentoxide or chromium oxide, metal sulfide such as molybdenum disulfide, etc. are used as active materials. , These positive electrode active materials are combined with conductive additives and binders such as polytetrafluoroethylene as appropriate, and finished with a current collector material such as a stainless steel mesh as a core material. It is done.

In the present embodiment, a strip-like positive electrode plate produced as follows is used as the positive electrode. In other words, lithium graphite oxide (LiCoO ₂ ) was added with phosphorous graphite as a conductive additive at a mass ratio of 90: 5 (lithium cobalt oxide: phosphorous graphite) and mixed, and this mixture and polyvinylidene fluoride were mixed with N -Mix with a solution dissolved in methylpyrrolidone to make a slurry. This positive electrode mixture slurry is passed through a 70-mesh net to remove large particles, and then uniformly applied to both sides of a positive electrode current collector made of an aluminum foil having a thickness of 20 μm, dried, and then compressed by a roll press. After forming, it is cut into a strip-like positive electrode plate.

  Examples and Comparative Examples are shown below, and the laminated porous film of the present invention will be described in more detail. However, the present invention is not limited at all. In addition, the various measured value and evaluation about the laminated porous film displayed in this specification were performed as follows. Here, the take-up (flow) direction of the laminated porous film from the extruder is referred to as a vertical direction, and the orthogonal direction is referred to as a horizontal direction.

(1) Thickness The obtained laminated porous film was measured unspecified in five locations with a 1/1000 mm dial gauge, and the average was taken as the thickness.

(2) Porosity The substantial amount W1 of the obtained laminated porous film is measured, and the mass W0 in the case of 0% porosity is calculated from the density and thickness of the resin composition. Based on calculation.
Porosity (%) = {(W0−W1) / W0} × 100

(3) Air permeability (Gurley value)
A sample was cut out from the obtained laminated porous film with a diameter of 40 mm, and the air permeability (second / 100 ml) was measured according to JIS P8117.

(4) Pin puncture strength test Using a FUDOH THEO METER made by Leotech Co., Ltd., in accordance with the Japanese National Agricultural Standards Notification No. 1019, the pin diameter is φ1 mm, the tip is 0.5 R, and the pin puncture speed is 300 mm / min. The maximum intensity (N) was measured.

(5) Air permeability after heating at 135 ° C for 5 seconds (shutdown characteristics)
The obtained laminated porous film was cut into a 60 mm × 60 mm square, and an aluminum plate (material: JIS standard A5052, size: vertical) with a circular hole of φ40 mm in the center as shown in FIG. 2 (A). It sandwiched between two sheets (60 mm, 60 mm in width, 1 mm in thickness), and as shown in FIG. 2 (B), the periphery was filled with glycerin (first grade manufactured by Nacalai Tesque) until it reached 100 mm from the bottom. A film in a state of being fixed with two aluminum plates was immersed in the center of an oil bath (manufactured by AS ONE, OB-200A) at 135 ° C. and heated for 5 seconds. Immediately after heating, separately filled with 25 ° C. glycerin, immersed in a cooling bath and cooled for 5 minutes, washed with 2-Punopanol (manufactured by Nacalai Tesque, special grade) and 15 minutes in an air atmosphere at 25 ° C. After drying, the measurement was performed according to the method of (3) above.

Further, the obtained laminated porous film was evaluated for β activity as follows.
(6) Differential scanning calorimetry (DSC)
The resulting laminated porous film was heated from 25 ° C. to 240 ° C. at a scanning rate of 10 ° C./min for 1 minute using a differential scanning calorimeter (DSC-7) manufactured by Perkin Elmer, and then held for 1 minute. The temperature was lowered from 240 ° C. to 25 ° C. at a scanning rate of 10 ° C./min and held for 1 minute, and then the temperature was raised again from 25 ° C. to 240 ° C. at a scanning rate of 10 ° C./min. The presence or absence of β activity was evaluated based on whether or not a peak was detected at 145 to 160 ° C., which is a crystal melting peak temperature (Tmβ) derived from the β crystal of polypropylene at the time of reheating.
○: When Tmβ is detected within the range of 145 ° C to 160 ° C (with β activity)
X: When Tmβ is not detected within the range of 145 ° C to 160 ° C (no β activity)
The β activity was measured with a sample amount of 10 mg under a nitrogen atmosphere.

(7) Wide angle X-ray diffraction measurement (XRD)
As in the case of the measurement of the shutdown characteristic, the film was cut into a 60 mm long × 60 mm wide square and fixed as shown in FIGS.
The film in a state of being restrained by two aluminum plates is placed in a ventilation constant temperature thermostatic device (manufactured by Yamato Scientific Co., Ltd., model: DKN602) having a set temperature of 180 ° C. and a display temperature of 180 ° C., and then held for 3 minutes. Then, it was gradually cooled to 100 ° C. over 10 minutes or more. When the display temperature reaches 100 ° C., the film is taken out and cooled in an atmosphere of 25 ° C. for 5 minutes while being restrained by two aluminum plates. Wide-angle X-ray diffraction measurement was performed on a 40 mmφ circular portion.
-Wide-angle X-ray diffraction measurement device: manufactured by Mac Science, model number: XMP18A
X-ray source: CuKα ray, output: 40 kV, 200 mA
Scanning method: 2θ / θ scan, 2θ range: 5 ° to 25 °, scanning interval: 0.05 °, scanning speed: 5 ° / min
About the obtained diffraction profile, the presence or absence of β activity was evaluated from the peak derived from the (300) plane of the β crystal of polypropylene as follows.
○: When a peak is detected in the range of 2θ = 16.0 to 16.5 ° (with β activity)
X: When no peak was detected in the range of 2θ = 16.0 to 16.5 ° (no β activity)
When the film piece cannot be cut into a 60 mm × 60 mm square, the sample may be prepared by adjusting so that the film is placed in a circular hole of 40 mmφ in the center.

Example 1
As a resin composition constituting the A layer, 3,9-bis [4- as a β crystal nucleating agent with respect to 100 parts by mass of a polypropylene resin (Prime Polymer Co., Ltd., Prime Polypro F300SV, MFR: 3 g / 10 min). (N-cyclohexylcarbamoyl) phenyl] -2,4,8,10-tetraoxaspiro [5.5] undecane 0.3 parts by mass was added, and the same direction twin screw extruder manufactured by Toshiba Machine Co., Ltd. (caliber φ40 mm, L / D = 32) was used to obtain a resin composition A1 melt-kneaded at 280 ° C. and processed into pellets.
In addition, as a mixed resin composition constituting the B layer, a crystal is formed on 100 parts by mass of high-density polyethylene (manufactured by Nippon Polytech Co., Ltd., Novatec HD HF560, density: 0.963 g / cm ³ , MFR: 7.0 g / 10 min). Add 0.04 parts by mass of glycerin monoester and 10 parts by mass of microcrystalline wax (Nippon Seiwa Co., Ltd., Hi-Mic 1080) as a nucleating agent, and melt at 230 ° C. using the same type of unidirectional twin screw extruder. A resin composition B1 kneaded and processed into a pellet was obtained.
Resin compositions A1 and B1 were extruded at 200 ° C. with separate extruders, and A1 / B1 / A1 / B1 /... / A1 so that the A1 layer would be the front and back through a 65-layer feed block. Split extrusion was carried out, followed by extrusion at 200 ° C. from a single-layer hanger coat die having a die width of 300 mm and a lip gap of 2 mm. The extrusion ratio of the A1 layer and the B1 layer was extruded so that the total extrusion amount was A1 / B1 = 83/17% by mass. Thereafter, the film was cooled and solidified by adhering to a casting roll at 125 ° C. for about 30 seconds at a line speed of 3 m / sec, to obtain a laminated non-porous film having a thickness of 210 μm. A cross-sectional SEM photograph of the laminated non-porous membrane is shown in FIG. The thickness of the A1 layer of the laminated non-porous membrane is about 7.5 μm, and the thickness of the B1 layer is about 1.5 μm.
The laminated nonporous film-like material was stretched 1.5 times in the machine direction at 20 to 100 ° C. by a roll stretching machine, and then stretched 4.0 times in the machine direction at 100 ° C., for a total machine draw ratio of 6. After stretching to 0 times, a laminated porous film having a thickness of 40 μm was obtained by sequentially biaxially stretching 2.0 times at 100 ° C. in the transverse direction with a tenter stretching machine. Various physical properties and evaluation of the obtained laminated porous film were performed, and the results are summarized in Table 1. The SEM photograph of the cross section of the laminated porous film is shown in FIG.

(Example 2)
The thickness of the laminated non-porous membrane was 97 μm, and the obtained laminated non-porous membrane was stretched 1.4 to 1.3 times in the longitudinal direction at 40 to 100 ° C. and then stretched at 120 ° C. A laminated porous film having a thickness of 37 μm was obtained in the same manner as in Example 1 except that the film was stretched twice and stretched so that the total longitudinal stretching ratio was 4.0 times. Various physical properties and evaluation of the obtained laminated porous film were performed, and the results are summarized in Table 1.

(Example 3)
The thickness of the laminated non-porous membrane was 97 μm, and the obtained laminated non-porous membrane was stretched 1.4 to 1.3 times in the longitudinal direction at 40 to 100 ° C. and then stretched at 120 ° C. A laminated porous film having a thickness of 28 μm was obtained in the same manner as in Example 1 except that the film was stretched 0 times and stretched so that the total longitudinal stretching ratio was 5.5 times. Various physical properties and evaluation of the obtained laminated porous film were performed, and the results are summarized in Table 1.

Example 4
The thickness of the laminated non-porous membrane was 97 μm, and the obtained laminated non-porous membrane was stretched 1.5 times in the longitudinal direction at 100 ° C. and then stretched 3.0 times at 120 ° C. for total longitudinal stretching. A laminated porous film having a thickness of 39 μm was obtained in the same manner as in Example 1 except that the film was stretched so that the magnification was 4.5 times. Various physical properties and evaluation of the obtained laminated porous film were performed, and the results are summarized in Table 1.

(Comparative Example 1)
A laminated porous film will be obtained in the same manner as in Example 1 except that the resin composition constituting the A layer is only a polypropylene resin (Prime Polymer, Prime Polypro F300SV, MFR: 3 g / 10 min). However, since it did not have β activity, it was broken during longitudinal stretching, and a film could not be obtained.

(Comparative Example 2)
For the resin composition constituting the B layer, the resin composition A1 is used as an alternative to the resin composition B1, so that it is substantially in the state of a single A layer, and the thickness is 37 μm under the same conditions as in Example 1. A porous film was obtained. Various physical properties and evaluation of the obtained porous film were performed, and the results are summarized in Table 1. Although the air permeability was developed by stretching, it was confirmed that there was no shutdown characteristic because the air permeability after heating at 135 ° C. for 5 seconds was not substantially changed.

From Table 1, it turns out that the laminated porous film of Examples 1-4 prescribed | regulated by this invention is a laminated porous film with favorable air permeability characteristics, and the air permeability after heating at 135 degreeC for 5 second is 10000. Since the second / 100 ml or more, it was found to have excellent shutdown characteristics. On the other hand, when it did not have β activity as in Comparative Example 1, the film was broken during longitudinal stretching, and a laminated porous film could not be obtained.
In addition, when only the A layer was used as in Comparative Example 2, the air permeability after heating at 135 ° C. for 5 seconds was less than 10,000 seconds / 100 ml, although it could have excellent air permeability characteristics. The shutdown characteristic could not be expressed.

  The laminated porous film of the present invention is a film having excellent air permeability characteristics contributing to electrical performance, and having shutdown characteristics, which is an important characteristic in ensuring safety, and having excellent pin penetration strength. Therefore, it can be suitably used as a battery separator.

DESCRIPTION OF SYMBOLS 10 Battery separator 20 Nonaqueous electrolyte battery 21 Positive electrode plate 22 Negative electrode plate 24 Positive electrode lead body 25 Negative electrode lead body 26 Gasket 27 Positive electrode cover 31 Aluminum plate 32 Film 33 Clip 34 Film longitudinal direction 35 Film lateral direction

Claims (4)

Layer A composed of a porous layer mainly composed of a polypropylene resin composition, and at least one selected from polyethylene resin as a main component, crystal nucleating agent, alicyclic saturated hydrocarbon or modified product thereof, or wax And a B layer composed of a porous layer containing Nb, and a B layer having at least 15 layers, having β activity, and a pin piercing strength of 5.7 N or more. Porous film. The laminated porous film according to claim 1, wherein the total thickness of the B layer is 1 to 40 with respect to the total thickness 100. The laminated porous film according to claim 1 or 2 , wherein the A layer contains a β crystal nucleating agent. A battery separator comprising the laminated porous film according to any one of claims 1 to 3 , and having an air permeability of 5 to 3000 seconds / 100 ml.

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