JP4801705B2 - Laminated porous film for separator and method for producing the same - Google Patents

Description

  The present invention relates to a laminated porous film and can be used as a battery separator, and can be particularly suitably used as a nonaqueous electrolyte battery separator.

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 a high volumetric efficiency when mounted on devices, leading to a reduction in size and weight of the devices.
On the other hand, large-sized secondary batteries are being researched and developed in many fields related to energy / environmental issues, including road leveling, UPS, and electric vehicles, and are excellent in large capacity, high output, high voltage, and long-term storage. Therefore, the use of lithium ion secondary batteries, which are a kind of non-aqueous electrolyte secondary battery, is expanding.

The working voltage of a lithium ion secondary battery is usually designed with an upper limit of 4.1 to 4.2V. At such a high voltage, the aqueous solution causes electrolysis and cannot be used as an electrolyte. 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 causing more lithium ions to be present is used, and organic carbonates such as polypropylene carbonate and ethylene carbonate are mainly used as the high dielectric constant organic solvent. in use. As a supporting electrolyte that becomes a lithium ion source in the solvent, a highly reactive electrolyte such as lithium hexafluorophosphate is dissolved in the 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 microporous structure in order to provide air permeability as a lithium ion passage and a function of diffusing and holding the electrolyte. In order to satisfy these requirements, a porous film is used as a separator.

With the recent increase in battery capacity, the importance of battery safety has increased.
As a characteristic that contributes to the safety of the battery separator, there is a shutdown characteristic (hereinafter 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.

Another characteristic that contributes to safety is a breakdown characteristic (hereinafter referred to as “BD characteristic”). This BD characteristic is a function in which heat generation does not stop due to the development of the SD characteristic and the film does not break even when the temperature is higher (160 ° C. or higher) and the positive electrode and the negative electrode are kept 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. Therefore, when it is used as a battery separator, it preferably has this BD characteristic, and the breakdown temperature (hereinafter 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 response to such a demand, Japanese Patent No. 2883726 (Patent Document 1) is characterized in that a laminated film of polyethylene and polypropylene is made porous by changing the temperature in one axial direction and stretching in two stages. A separator manufacturing method has been proposed.
However, this manufacturing method requires strict control of manufacturing conditions, and it 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. In addition, in order to develop a porous structure, it is necessary to perform multistage stretching at two stages, a low temperature region and a high temperature region, at a low stretching speed, and the stretching speed is greatly limited, resulting in extremely poor productivity. .
Furthermore, the separator manufactured by the manufacturing method is very weak against tearing in a direction perpendicular to the stretching direction, and there is a problem that a tear is easily generated in the stretching direction.

  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 porous structure is obtained by using β crystals, and it is preferable that a lot of β crystals are contained in the sheet before stretching to obtain a porous structure. 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, in Japanese Patent No. 1953202 (Patent Document 2), a manufacturing method for obtaining a porous film 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. Has been proposed. In addition, Japanese Patent No. 2509030 (Patent Document 3) proposes a superporous polypropylene microporous film obtained by biaxial stretching from an original polypropylene film having a high β crystal content (K> 0.5). . In Japanese Patent No. 3443934 (Patent Document 4), a specific amide compound is contained in polypropylene, and crystallized under specific conditions to obtain a solidified product containing β crystals. A method for producing a film has been proposed.

  These polypropylene porous films are superior to the polyethylene porous film in BD characteristics because of the high crystal melting temperature of polypropylene. However, since the above characteristics are adversely affected and the SD characteristics cannot be exhibited at all, there is a problem in securing the safety of the battery in order to use these porous films as battery separators.

  Therefore, Japanese Patent Laid-Open No. 2000-30683 (Patent Document 5) proposes a battery separator including a polypropylene microporous membrane manufactured from a β-nucleus-containing precursor, and further, as another layer, a blocking function or the like. It is described that a function for improving safety is imparted. However, there is no description of the example which provided the interruption | blocking function, and it was difficult to provide the function which improves the safety | security of a battery only by providing a polyethylene layer.

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

  The present invention has been made in view of the above-mentioned problems, and has a superior electrical resistance that contributes to battery performance, and a separator laminated film having an important shutdown characteristic in terms of ensuring safety, and its production The challenge is to provide a method.

The order to solve the problems, the present invention comprises a substrate layer in which the polypropylene-based resin and 50 wt% or more, the shutdown layer where the port Riechiren based resin and 50 wt% or more (hereinafter referred to as "SD layer" And a laminated porous film having two or more layers ,
It is assumed that the laminated porous film has β activity by blending a β-type nucleating agent with the polypropylene resin of the base material layer ,
There is provided a laminated porous film for a separator having an electrical resistance of 10Ω or less at 25 ° C. and an electrical resistance of 100Ω or more after heating at 135 ° C. for 5 seconds .

The SD layer is composed of the polyethylene resin as a main component and has a shutdown temperature (hereinafter referred to as “SD temperature”) lower than that of the base material layer.
In the present invention, “SD temperature” refers to the lowest temperature at which the micropores are blocked. Specifically, when the laminated porous film for a separator of the present invention is heated by the method described in the examples, The lowest temperature among the temperatures at which the resistance becomes 10 times or more the electrical resistance before heating.

Since at least one base material layer of the laminated porous film for a separator of the present invention has β activity, a fine porous layer can be provided and excellent electrical characteristics can be exhibited.

In the laminated porous film for a separator of the present invention, the presence or absence of “β activity” is determined when the crystal melting peak temperature derived from the β crystal is detected by a differential scanning calorimeter described later, or the X-ray diffraction measurement described later. When a diffraction peak derived from β crystals is detected by measurement using an apparatus, it is determined that β activity is present.
The β activity of the laminated porous film according to the present invention is the laminated porous film in any case where the laminated porous film for a separator of the present invention is composed of only the base material layer and the SD layer, and when another porous layer is laminated. It is measured in the state.

  Further, the SD layer preferably contains at least one compound selected from a modified polyolefin resin, an alicyclic saturated hydrocarbon resin or a modified product thereof, an ethylene copolymer, or a wax. .

The laminated porous film for a separator of the present invention preferably has an MD tensile strength / TD tensile strength ratio of 0.3 to 15.
About MD tensile strength / TD tensile strength ratio, it measures by the method as described in the below-mentioned Example.

The present invention provides a method for producing a laminated porous film for a separator as described above, wherein the polypropylene resin is 50% by mass or more and 0.0001 to 5.0 parts by mass of β crystal with respect to 100 parts by mass of the polypropylene resin. A manufacturing method characterized by laminating a base material layer containing a nucleating agent and a shutdown layer containing 50 mass% or more of a polyethylene resin into two or more layers by coextrusion and biaxially stretching to make it porous. Is provided.

The laminated porous film for a separator of the present invention is a laminated porous film having a base layer mainly composed of a polypropylene resin and a shutdown layer mainly composed of a polyethylene resin and having β activity. Yes, the electrical resistance at 25 ° C. is 10Ω or less, and the electrical resistance after heating at 135 ° C. for 5 seconds is 100Ω or more. Since it includes a base material layer mainly composed of a polypropylene resin and a shutdown layer mainly composed of a polyethylene resin, while maintaining the breakdown characteristics of the conventional laminated porous film made of polypropylene resin, It has a shutdown characteristic that closes the hole in an appropriate temperature range.
Furthermore, since the laminated porous film for a separator of the present invention has β activity, it has fine pores, can ensure sufficient communication, and can maintain strength with the base material layer, Excellent mechanical strength such as pin puncture strength and tear strength. Therefore, it is useful for battery separators from the viewpoint of structure maintenance and impact resistance.
Moreover, the laminated porous film for a separator of the present invention does not require strict control of production conditions, and can be produced simply and efficiently.

Hereinafter, embodiments of the laminated porous film for a separator 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. The content ratio of the components is not specified, but the main component includes 50% by mass or more, preferably 70% by mass or more, particularly preferably 90% by mass or more (including 100%) in the composition. It is.
Further, when “X to Y” (X and Y are arbitrary numbers) is described, “X to Y” is intended unless otherwise specified, and “it is preferably larger than X and smaller than Y”. Includes intentions.

  The laminated porous film for a separator of this embodiment is a laminated porous film in which at least two porous layers are laminated, and one of the two porous layers is based on a polypropylene resin as a main component. It is a material layer, the other layer is a shutdown layer (SD layer) whose main component is a polyethylene resin, and the laminated porous film has β activity.

The laminated porous film for a separator 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 has 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 for separator is determined by performing differential thermal analysis of the laminated porous film using a differential scanning calorimeter, and the crystal melting peak temperature derived from the β crystal of the polypropylene resin is detected. It is judged by whether or not.
Specifically, the laminated porous film is heated at a heating rate of 10 ° C./min from 25 ° C. to 240 ° C. for 1 minute with a differential scanning calorimeter, and then cooled from 240 ° C. to 25 ° C. at a cooling rate of 10 ° C. / When the temperature is lowered for 1 minute and held for 1 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 crystal of polypropylene is If detected, it is determined to have β activity.

In addition, the β activity of the laminated porous film for a separator is calculated by the following formula using the crystal heat of fusion derived from the α crystal of the polypropylene resin (ΔHmα) and the heat of crystal melt derived from the β crystal (ΔHmβ). is doing.
β activity (%) = [ΔHmβ / (ΔHmβ + ΔHmα)] × 100
For example, in the case of homopolypropylene, the heat of crystal melting derived from β crystal (ΔHmβ) detected mainly in the range of 145 ° C. or higher and lower than 160 ° C. and the α crystal derived from α crystal detected mainly at 160 ° C. or higher and 175 ° C. or lower. It can be calculated from the heat of crystal fusion (ΔHmα). Further, for example, in the case of random polypropylene copolymerized with 1 to 4 mol% of ethylene, the crystal melting heat amount (ΔHmβ) derived from the β crystal detected mainly in the range of 120 ° C. or more and less than 140 ° C., and 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 of the laminated porous film for a separator is preferably large, and the β activity is preferably 20% or more. More preferably, it is 40% or more, and particularly preferably 60% or more. If the laminated porous film has a β activity of 20% or more, it indicates that a large amount of β crystals of polypropylene resin can be produced in the film-like material before stretching, and fine and uniform pores are formed by stretching. Many layers are formed, and as a result, a laminated porous film excellent in electrical performance can be obtained.
The upper limit of β activity is not particularly limited, but the higher the β activity, the more effective the effect is obtained.

The presence or absence of the β activity can also be determined by a diffraction profile obtained by X-ray diffraction measurement of a laminated porous film subjected to a specific heat treatment.
Specifically, X-ray diffraction measurement was performed on a laminated porous film for a separator that was subjected to heat treatment at 170 to 190 ° C., which is a temperature exceeding the melting point of the polypropylene resin, and was slowly cooled to produce and grow β crystals. When the diffraction peak derived from the (300) plane of the β-crystal of the resin is detected in the range of 2θ = 16.0 ° to 16.5 °, it is determined that there is β activity.
For details on the β crystal structure and X-ray diffraction measurement of polypropylene resins, see Macromol. Chem. 187, 643-652 (1986), Prog. Polym. Sci. Vol. 16, 361-404 (1991), Macromol. Symp. 89, 499-511 (1995), Macromol. Chem. 75, 134 (1964), and references cited therein. A detailed evaluation method of β activity will be described in Examples described later.

As a method for obtaining β activity of the above-mentioned laminated porous film for a separator are gaining β activity by adding the β crystal nucleating agent to the resin composition before Kimoto material layer. By adding a β crystal nucleating agent, it is possible to promote the generation of β crystals of polypropylene resin more uniformly and efficiently, and to obtain a lithium ion battery separator having a porous layer having β activity. it can.

  Below, the detail of the component of each layer which comprises the laminated porous film of this invention is demonstrated.

[Description of base material layer]
First, the base material layer will be described in detail below.
(Description of polypropylene resin)
Examples of the polypropylene resin contained in the base material layer include homopropylene (propylene homopolymer), or propylene and ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-octene, Examples thereof include random copolymers or block copolymers with α-olefins such as nonene and 1-decene. Among these, homopolypropylene is more preferably used from the viewpoint of the mechanical strength of the laminated porous film.

Moreover, as a polypropylene resin, it is preferable that the isotactic pentad fraction (mmmm fraction) which shows stereoregularity is 80 to 99%. More preferably 83-98%, still more preferably 85-97%. If the isotactic pentad fraction is too low, the mechanical strength of the 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 the present time, 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 (mmmm fraction) is the same direction for all five methyl groups that are side chains with respect to the main chain of carbon-carbon bonds composed of arbitrary five consecutive propylene units. Means the three-dimensional structure located at or its proportion. Signal assignment of the methyl group region is as follows. It conforms to Zambelli et al (Macromolecules 8,687, (1975)).

  Moreover, it is preferable that Mw / Mn which is a parameter which shows molecular weight distribution of a polypropylene resin is 2.0-10.0. 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 is, the narrower the molecular weight distribution is. However, when the Mw / Mn is less than 2.0, problems such as a decrease in extrusion moldability occur, and it is difficult to produce industrially. . On the other hand, when Mw / Mn exceeds 10.0, low molecular weight components increase, and the mechanical strength of the laminated porous film tends to decrease. Mw / Mn is obtained by GPC (gel permeation chromatography) method.

  Further, the melt flow rate (MFR) of the polypropylene resin is not particularly limited, but usually the MFR is preferably 0.1 to 15 g / 10 minutes, and preferably 0.5 to 10 g / 10 minutes. It is more preferable. When the MFR is less than 0.1 g / 10 minutes, the melt viscosity of the resin at the time of molding is high and the productivity is lowered. On the other hand, if it exceeds 15 g / 10 minutes, the mechanical strength of the film is insufficient, and problems are likely to occur in practice. MFR is measured according to JIS K7210 under conditions of a temperature of 230 ° C. and a load of 2.16 kg.

(Description of β crystal nucleating agent)
Examples of the β crystal nucleating agent used in the present invention include those shown below, but are not particularly limited as long as they increase the formation and growth of β crystals of polypropylene resin, and two or more types are mixed. May be 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 represented by: aromatic sulfonic acid compounds represented by sodium benzenesulfonate or sodium naphthalenesulfonate; di- or triesters of dibasic or tribasic carboxylic acids; phthalocyanine blue Phthalocyanine pigments typified by: 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; Made of magnesium compound Such as the formation thereof.

  Specific examples of commercially available 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 Aristech. Examples include polypropylene “Bepol B-022SP”, Borealis polypropylene “Beta (β) -PP BE60-7032,” Mayzo polypropylene “BNX BETAPP-LN”, and the like.

  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. 0.0001 to 5.0 parts by mass of the agent is preferred. 0.001-3.0 mass parts is more preferable, and 0.01-1.0 mass part is still more preferable. 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 to ensure sufficient β activity, and sufficient β activity is ensured even when a laminated porous film is formed. And desired air permeability can be obtained. On the other hand, addition of 5.0 parts by mass or less is preferable because it is economically advantageous and there is no bleeding of the β crystal nucleating agent on the film surface.

It is important that the base material layer is mainly composed of a polypropylene resin. Specifically, when using a polypropylene resin and a β crystal nucleating agent, the total mass of the polypropylene resin 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 base material layer. More preferably, it occupies 90 mass% or more.
The base material layer may contain additives or other components that are generally blended in the resin composition within a range not impairing the object of the present invention and the properties of the base material layer as described above. Examples of the additive include recycling resin, silica, talc, kaolin, carbonic acid, etc., which are added for the purpose of improving / adjusting the processability, productivity, and various physical properties of the laminated porous film. Inorganic particles such as calcium, 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 And additives such as antioxidants, light stabilizers, ultraviolet absorbers, neutralizers, antifogging agents, antiblocking agents, slip agents, and coloring agents. Specifically, as antioxidants, copper halides, amine-based antioxidants such as 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 294, etc. Is mentioned.

[Description of Shutdown Layer (SD Layer)]
Next, the shutdown layer (SD layer) will be described.

(Description of polyethylene resin)
The SD layer of the present invention is a shutdown layer mainly composed of a polyethylene resin. The SD layer 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 as described above. Good. For example, it may have a structure in which the fine pores are provided in a film-like material made of a polyethylene resin composition, or a particulate or fibrous fine material aggregates to form a layer, A structure in which the gap is the fine hole may be used. The SD layer of the present invention preferably has the former structure in which uniform fine pores can be formed and the porosity and the like can be easily controlled.

The thermal properties of the polyethylene resin, which is the main component of the composition constituting the SD 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 SD layer is lower than the crystal melting peak temperature of the composition constituting the base material layer. Specifically, the SD layer is preferably a polyethylene resin 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.

  Specific types of polyethylene resins include not only polyethylene resins such as ultra low density polyethylene, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, or ultra high density polyethylene alone, but also ethylene. Examples thereof include a propylene copolymer or a mixture of a polyethylene resin and another polyolefin resin. Among these, a polyethylene resin alone is preferable.

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

Further, the melt flow rate (MFR) of the polyethylene-based resin 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 more preferable. If the MFR is 0.03 g / 10 min or more, the melt viscosity of the resin during the molding process is sufficiently low, which is excellent in productivity and preferable. On the other hand, if it is 15 g / 10 minutes or less, since it is close to the melt viscosity of the polypropylene resin to be mixed, dispersibility is improved, resulting in a homogeneous laminated porous film, which is preferable.
MFR is measured in accordance with JIS K7210 under conditions of a temperature of 190 ° C. and a load of 2.16 kg.

  The production method of the polyethylene resin is not particularly limited, and 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. And a polymerization method using a single site catalyst.

(Description of Compound (X))
It is preferable to add a substance that promotes porosity and expression of SD characteristics to the SD layer. Among them, the SD layer more preferably contains 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. 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 anhydrides thereof 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. Examples include ester compounds, reaction products of a polymer having a group capable of reacting with these acids in the molecule and an acid. 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. 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) and “Modic” (manufactured by Mitsubishi Chemical).

  Examples of alicyclic saturated hydrocarbon resins and modified products thereof include petroleum resins, rosin resins, terpene resins, coumarone resins, indene resins, coumarone-indene resins, and modified products thereof.

  The petroleum resin in the present invention is a C4 to C10 aliphatic olefin or diolefin obtained from a by-product of naphtha pyrolysis or the like, or a C8 or higher aromatic compound having an olefinically unsaturated bond. An aliphatic, aromatic or copolymer petroleum resin obtained by singly or copolymerizing one or more of the compounds contained in the above.

  Examples of petroleum resins include aliphatic petroleum resins mainly containing C5 fraction, aromatic petroleum resins mainly containing C9 fraction, copolymer petroleum resins thereof, and alicyclic petroleum resins. . Examples of terpene resins include terpene resins and terpene-phenol resins derived from β-pinene, and examples of rosin resins include rosin resins such as gum rosin and utdrodine, and esterified rosin resins modified with glycerin and pentaerythritol. The alicyclic saturated hydrocarbon resin and the modified product thereof have relatively good compatibility when mixed with a polyethylene resin, but a petroleum resin is more preferable in terms of color tone and thermal stability, and a hydrogenated petroleum resin is used. More preferably.

  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. Among hydrogenated petroleum resins, hydrogenated alicyclic petroleum resins obtained by copolymerizing and hydrogenating a cyclopentadiene compound and an aromatic vinyl compound are particularly preferable. Examples of commercially available hydrogenated petroleum resins include “ALCON” (manufactured by Arakawa Chemical Industries).

  The ethylene copolymer in the present invention is a compound obtained by copolymerizing ethylene and one or more of vinyl acetate, unsaturated carboxylic acid, unsaturated carboxylic acid anhydride, or carboxylic acid ester. It is.

  The ethylene copolymer preferably has an ethylene monomer unit content of 50% by mass or more, more preferably 60% by mass or more, and still more preferably 65% by mass or more. On the other hand, regarding the upper limit, the content of ethylene monomer units is preferably 95% by mass or less, more preferably 90% by mass or less, and further preferably 85% by mass or less. If the content of the ethylene monomer unit is within a predetermined range, a porous structure can be formed more efficiently.

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

  The ethylene-based copolymer is “EVAFLEX” (Mitsui / DuPont Polychemical Co., Ltd.), “Novatech EVA” (Nihon Polyethylene Co., Ltd.) as an ethylene-vinyl acetate copolymer, and “NUC” as an ethylene-acrylic acid copolymer. Copolymer ”(Nippon Unicar), Everflex-EAA (Mitsui / DuPont Polychemical),“ REXPEARL EAA ”(Japan Ethylene),“ ELVALOY ”(Mitsui) as an ethylene- (meth) acrylic acid copolymer -DuPont Polychemical Co., Ltd.), "REXPEARL EMA" (Nippon Ethylene Co., Ltd.), ethylene-ethyl acrylate copolymer as "REXPEARL EEA" (Nihon Ethylene Co., Ltd.), ethylene-methyl (meth) acrylic acid copolymer "Aclift" (manufactured by Sumitomo Chemical), "Bondyne" (manufactured by Sumitomo Chemical Co., Ltd.) as an ethylene-vinyl acetate-maleic anhydride terpolymer , "Bond first" (manufactured by Sumitomo Chemical Co., Ltd.) as ethylene-glycidyl methacrylate copolymer, ethylene-vinyl acetate-glycidyl methacrylate terpolymer, ethylene-ethyl acrylate-glycidyl methacrylate terpolymer Are commercially available.

The wax in the present invention is an organic compound that satisfies the following properties (a) and (b).
(A) The melting point is 40 ° C to 200 ° C.
(A) The melt viscosity at a temperature 10 ° C. higher than the melting point is 50 Pa · s or less.

  For waxes, polar or nonpolar waxes, polypropylene waxes, polyethylene waxes and wax modifiers are included. Specifically, polar wax, nonpolar wax, Fischer-Tropsch wax, oxidized Fischer-Tropsch wax, hydroxy stearamide wax, functionalized wax, polypropylene wax, polyethylene wax, wax modifier, amorphous wax, carnauba wax , Castor oil wax, microcrystalline wax, beeswax, carnauba wax, castor wax, plant wax, candelilla wax, Japanese wax, ouricury wax, douglas fur bark wax, rice bran wax, jojoba wax, bay wax, montan wax, ozo Kelite wax, ceresin wax, petroleum wax, paraffin wax, chemically modified hydrocarbon wax, substituted amide wax, and combinations and derivatives thereof Body, and the like. Among these, paraffin wax, polyethylene wax, and microcrystalline wax are preferable from the viewpoint of efficiently forming a porous structure, and microcrystalline wax that can further reduce the pore diameter is more preferable from the viewpoint of SD characteristics. Examples of commercially available polyethylene wax include “FT-115” (manufactured by Nippon Seiwa), and examples of microcrystalline wax include “Hi-Mic” (manufactured by Nippon Seiwa).

  Among the compounds (X), alicyclic saturated hydrocarbon resin or a modified product thereof, an ethylene copolymer, or a wax is more preferable as the SD property works more effectively, and the wax is further from the viewpoint of moldability. preferable.

  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 contained in the SD layer when the interface between the polyethylene resin 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, an effect of expressing a desired good porous structure is sufficiently obtained. Moreover, the more stable moldability is securable because the compounding quantity of compound (X) shall be 50 mass parts or less.

  In the SD layer, in addition to the polyethylene resin and the compound (X) for promoting porosity, if necessary, a thermoplastic resin is used as long as the thermal characteristics of the laminated porous film, specifically, the SD characteristics are not impaired. Also good. Examples of other thermoplastic resins that can be mixed with the polyethylene resin include styrene resins such as styrene, AS resin, and ABS resin: polyvinyl chloride, fluorine resin, polyethylene terephthalate, polybutylene terephthalate, and polycarbonate. Or ester resins such as polyarylate; ether resins such as polyacetal, polyphenylene ether, polysulfone, polyethersulfone, polyetheretherketone or polyphenylene sulfide; polyamides such as 6 nylon, 6-6 nylon and 6-12 nylon Examples thereof include thermoplastic resins such as resins.

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

In the SD layer, in addition to the polyethylene resin and the compound (X) that promotes porosity, an additive or other component that is generally blended in the resin composition may be included. Examples of the additive include recycling resin, silica, talc, kaolin, carbonic acid, etc., which are added for the purpose of improving / adjusting the processability, productivity, and various physical properties of the laminated porous film. Inorganic particles such as calcium, 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 And additives such as antioxidants, light stabilizers, ultraviolet absorbers, neutralizers, antifogging agents, antiblocking agents, slip agents, and coloring agents.
Among them, the nucleating agent is preferable because it has an effect of controlling the crystal structure of the polyethylene resin and reducing the porous structure at the time of stretching and opening. Examples of commercially available products include “Gelall D” (manufactured by Shin Nippon Chemical Co., Ltd.), “Adeka Stub” (manufactured by Asahi Denka Kogyo Co., Ltd.), “Hyperform” (manufactured by Milliken Chemical Co., Ltd.), or “IRGACLEAR D” (Ciba Special Chemicals). Etc.). Moreover, as a specific example of the polyethylene resin to which the nucleating agent is added, “Rike Master” (manufactured by Riken Vitamin Co., Ltd.) and the like are commercially available.

[Description of laminated structure]
The laminated structure of the laminated porous film of the present invention will be described.
There is no particular limitation as long as there is at least a base material layer and an SD layer that form a basic configuration. The simplest structure is a two-layer structure of a base material layer and an SD layer, and the next simple structure is a two-kind three-layer structure of both outer and middle layers, which are preferable structures. In the case of two types and three layers, it may be a base layer / SD layer / base layer or an SD layer / base layer / SD layer. In addition, it is possible to adopt a form of three types and three layers in combination with layers having other functions as required. Further, the number of layers may be increased as necessary to 4 layers, 5 layers, 6 layers, and 7 layers. Among them, when the resin starts to flow at a high temperature, it may be sucked into the porous structure of the negative electrode. Therefore, it is preferable to select a base material layer mainly composed of polypropylene resin as the outer layer.
About the total thickness ratio of the base material layer and the SD layer, the value of the base material layer / SD layer is preferably 0.05 to 20, more preferably 0.1 to 15, and 0.5 to More preferably, it is 12. By setting the value of the base material layer / SD layer to 0.05 or more, the BD characteristics and strength of the base material layer can be sufficiently exhibited. Moreover, by setting it to 20 or less, for example, when applied to a battery, SD characteristics can be sufficiently exhibited, and safety can be ensured. Moreover, when other layers other than the SD layer and the base material layer are present, the total thickness of the other layers is preferably 0.05 to 0.5 with respect to the total thickness 1, and preferably 0.1 to 0.3. Is more preferable.

[Description of shape and physical properties of laminated porous film]
The form of the laminated porous film may be either flat or tube-like, but it is possible to take several products as a product in the width direction, so that the productivity is good and the inner surface can be treated with a coat or the like From the viewpoint of being able to do so, a planar shape is more preferable.
The thickness of the laminated porous film of the present invention is preferably 50 μm or less, more preferably 40 μm or less, and still more preferably 30 μm or less. On the other hand, the lower limit is preferably 5 μm or more, more preferably 10 μm or more, and further preferably 15 μm or more. When used as a battery separator, if the thickness is 50 μm or less, the electrical resistance of the laminated porous film can be reduced, so that the battery performance can be sufficiently ensured. Further, if the thickness is 5 μm or more, substantially necessary electrical insulation can be obtained. For example, even when a large voltage is applied, short-circuiting is difficult and excellent safety is achieved.

The physical properties of the laminated porous film of the present invention can be freely adjusted by the composition of the base material layer or the SD layer, the number of laminated layers and the lamination ratio, combinations with layers having other properties, and the production method.
The lower limit of the SD temperature of the laminated porous film of the present invention is preferably 100 ° C or higher, more preferably 110 ° C, and still more preferably 120 ° C or higher. On the other hand, the upper limit is preferably 140 ° C. or lower. When SD characteristics are manifested at 100 ° C. or lower, for example, when the laminated porous film of the present invention is used as a battery separator and the battery is left in a car in summer, the temperature may be close to 100 ° C. depending on the location. Since it may rise, it is not preferable that the battery does not function in this state. On the other hand, a temperature higher than 140 ° C. is not sufficient in terms of ensuring safety as a battery.
Effective means for adjusting the SD temperature include selecting a thermoplastic resin having a crystal melting peak temperature close to the desired SD temperature as the thermoplastic resin contained in the SD layer, and increasing the layer ratio of the SD layer. It is.

The laminated porous film of the present invention is also characterized by exhibiting BD characteristics at 160 ° C. or higher. That is, the BD temperature of the laminated porous film of the present invention is 160 ° C. or higher, preferably 180 ° C. or higher, more preferably 200 ° C. or higher. When the BD temperature is less than 160 ° C., there is no difference between the SD temperature and the BD temperature. For example, when the laminated porous film of the present invention is used as a battery separator, a battery with sufficiently secured safety cannot be provided. On the other hand, although there is no restriction | limiting in particular about the high temperature side of BD temperature, Preferably it is 300 degrees C or less.
As means for adjusting the BD temperature, means such as increasing the layer ratio of the base material layer are effective.

(Electric resistance at 25 ° C)
The laminated porous film of the present invention needs to have an electric resistance of 10Ω or less at 25 ° C., preferably 5.0Ω or less, more preferably 3.0Ω or less. By using 10Ω or less, when used as a battery separator, the battery performance can be sufficiently excellent when used at room temperature.
In addition, the low electrical resistance at 25 ° C. of the laminated porous film means that the charge can be easily transferred when used as a battery separator, and is preferable because of excellent battery performance.
On the other hand, the lower limit is not particularly limited, but is preferably 0.1Ω or more, more preferably 0.5Ω or more, and further preferably 1.0Ω or more. If the electrical resistance at 25 ° C. is 0.1Ω or more, troubles such as an internal short circuit can be avoided when used as a battery separator.

(Electric resistance after heating at 135 ° C for 5 seconds)
It is important that the laminated porous film of the present invention exhibits SD characteristics when used as a battery separator. Accordingly, the electric resistance after heating at 135 ° C. for 5 seconds needs to be 100Ω or more, preferably 200Ω or more, more preferably 1000Ω or more. By setting the electrical resistance after heating at 135 ° C. for 5 seconds to 100Ω or more, it is possible to avoid troubles such as battery rupture due to the rapid closure of the pores during abnormal heat generation.
In order to set the electric resistance after heating at 135 ° C. for 5 seconds to 100Ω or more, it depends on the hole diameter and the porosity. Although not limited to the following contents, for example, the compound (X) is added to the polyethylene resin, and the kind and blending amount of the compound (X) is adjusted, or the nucleating agent is added to crystal the polyethylene resin. By miniaturizing, the electrical resistance after heating at 135 ° C. for 5 seconds can be controlled.
In the production method, the electrical resistance after heating at 135 ° C. for 5 seconds can be made 100Ω or more by adjusting the stretching conditions.
On the other hand, the upper limit is not particularly limited, but is preferably 100000Ω or less.

  The porosity is an important factor for defining the porous structure, and is a numerical value indicating the proportion of the space portion in the film. In the laminated porous film of the present invention, the porosity is preferably 5% or more, more preferably 20% or more, still more preferably 30% or more, and particularly preferably 40% or more. On the other hand, the upper limit is preferably 80% or less, more preferably 70% or less, and even more preferably 65% or less. If the porosity is 5% or more, it is possible to obtain a laminated porous film having sufficient communication properties and excellent air permeability. Moreover, if the porosity is 80% or less, the mechanical strength of the laminated porous film can be sufficiently maintained, which is preferable from the viewpoint of handling.

Moreover, in the laminated porous film of this invention, it is preferable that the anisotropy is small from a viewpoint of film physical property. As an anisotropy index, it can be expressed by the ratio of the tensile strength of MD and TD and the ratio of the tear strength of MD and TD. MD denotes the film take-up (flow) direction, and TD denotes the MD perpendicular direction.
For example, taking tensile strength as an example, the ratio of the ratio is preferably “MD tensile strength / TD tensile strength ratio” of 0.3 or higher, more preferably 0.5 or higher, and still more preferably 1.0 or higher. It is. On the other hand, the upper limit of “MD tensile strength / TD tensile strength ratio” is preferably 15 or less, more preferably 10 or less, and still more preferably 8 or less. By setting the value of “MD tensile strength / TD tensile strength ratio” within a specified range, the film has a sufficiently balanced handling and physical properties, and has a porous structure with less anisotropy.
The MD tensile strength is preferably 25 MPa or more, more preferably 30 MPa or more, and still more preferably 40 MPa or more. If it is 25 MPa or more, it is sufficient strength in handling the film. Although there is no particular upper limit, a range in which the balance with TD tensile strength does not deviate from the above range is preferable.
The TD tensile strength is preferably 25 MPa or more, more preferably 30 MPa or more, and still more preferably 40 MPa or more. If it is 25 MPa or more, it is sufficient strength in handling the film. Although there is no particular upper limit, a range in which the balance with the MD tensile strength does not deviate from the above range is preferable.
The tensile strength is measured by the method described in the examples.

   The laminated porous film of the present invention is preferably biaxially stretched. Biaxial stretching reduces the anisotropy, and a laminated porous film with a sufficient balance between handling and physical properties can be obtained.

  In the laminated porous film of the present invention, other physical properties can be freely adjusted by the composition of the resin composition constituting the base layer and the SD layer, the layer configuration, the production method, and the like.

[Description of manufacturing method]
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 this manufacturing method.
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 porous film of a base material layer mainly composed of a polypropylene resin (hereinafter referred to as “porous film PP”) and a porous film of a shutdown layer mainly composed of a polyethylene resin (hereinafter referred to as “ A method of laminating at least the porous film PP and the porous film SD.
(B) A film-like material mainly composed of polypropylene resin (hereinafter referred to as “non-porous film-like product PP”) and a film-like material mainly composed of polyethylene resin (hereinafter referred to as “non-porous film-like material SD”). A laminated non-porous film-like material comprising at least two layers, and then making the non-porous film-like material porous.
(C) One of the two layers of the base material layer mainly composed of polypropylene resin and the shutdown layer (SD layer) mainly composed of polyethylene resin is made porous, and then the other layer is non-porous. A method of laminating with a film and making it porous.

Examples of the method (a) include a method of laminating the porous film PP and the porous film SD, and a method of laminating with an adhesive or the like.
As the method (b), a non-porous film product PP and a non-porous film product SD are respectively produced, and the non-porous film product PP and the non-porous film product SD are laminated with a laminate or an adhesive. Examples thereof include a method for forming a porous structure, and a method for forming a laminated nonporous film by coextrusion and then forming a porous structure.
Examples of the method (c) include a method of laminating the porous film PP and the nonporous film SD or the nonporous film PP and the porous film SD, and a method of laminating with an adhesive or the like.
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.

The production method of the laminated porous film of the present invention can be classified by the SD layer porous method separately from the above classification.
That is, when the base material layer has β activity, micropores can be easily formed by stretching. On the other hand, as a method for making the SD layer porous, a known method such as a stretching method, a phase separation method, an extraction method, a chemical treatment method, an irradiation etching method, a foaming method, or a combination of these techniques can be used. Of these, the stretching method is preferably used in the present invention.

The stretching method is a method in which a non-porous layer or a non-porous film-like material is formed using a composition in which a compound is mixed with a resin, and the interface between the resin and the compound is separated by stretching to form micropores. is there.
The phase separation method is a technique called a conversion method or a microphase separation method, and is a method of forming pores based on a phase separation phenomenon of a polymer solution. Specifically, it is roughly classified into (a) a method of forming micropores by phase separation of polymer, and (b) a method of forming pores while forming micropores during polymerization. As the former method, there are a solvent gelation method using a solvent and a hot melt rapid solidification method, and either method may be used.

In the extraction method, an additive that can be removed in a later step is mixed with the thermoplastic resin composition constituting the SD layer to form a nonporous layer or a nonporous film, and then the additive is extracted with a chemical or the like. This is a method for forming fine holes. Examples of the additive include a polymer additive, an organic additive, and an inorganic additive.
As an example using a polymer additive, a non-porous layer or a non-porous film-like material is formed using two types of polymers having different solubility in an organic solvent, and only one of the two types of polymers is used. A method of extracting the one polymer by immersing in a dissolving organic solvent is mentioned. More specifically, a method of forming a nonporous layer or a nonporous film made of polyvinyl alcohol and polyvinyl acetate, and extracting polyvinyl acetate using acetone and n-hexane, or a block or graft copolymer And a method of forming a non-porous layer or a non-porous film-like material by containing a hydrophilic polymer and removing the hydrophilic polymer with water.

As an example using an organic substance additive, a non-porous layer or a non-porous film-like material is formed by blending a soluble substance in an organic solvent in which the thermoplastic resin constituting the SD layer is insoluble, There is a method of extracting and removing the substance by dipping.
Examples of the substance include higher aliphatic alcohols such as stearyl alcohol or seryl alcohol, n-alkanes such as n-decane or n-dodecane, paraffin wax, liquid paraffin, or kerosene. These include isopropanol, ethanol, It can be extracted with an organic solvent such as hexane. In addition, water-soluble substances such as sucrose and sugar can also be mentioned as the substances, and these have the advantage of reducing the burden on the environment because they can be extracted with water.

The chemical treatment method is a method of forming micropores by chemically cleaving the bond of the polymer substrate or conversely performing a bonding reaction. More specifically, a method of forming micropores by chemical treatment such as redox agent treatment, alkali treatment, acid treatment, and the like can be mentioned.
The irradiation etching method is a method of forming minute holes by irradiating with neutron beam or laser.
The fusion method is a method of using a polymer fine powder such as polytetrafluoroethylene, polyethylene, or polypropylene and sintering the polymer fine powder after molding.
Examples of the foaming method include a mechanical foaming method, a physical foaming method, and a chemical foaming method, and any of them can be used in the present invention.

  As a preferred embodiment of the method for producing a laminated porous film of the present invention, a resin composition containing as a main component a polypropylene resin having β activity, and a resin containing compound (X) containing a polyethylene resin as a main component Using the composition, a laminated non-porous film-like material composed of at least two layers of a base material layer and an SD layer is produced, and the laminated non-porous film-like material is stretched to form micropores having connectivity in the thickness direction. A method for producing a laminated porous film characterized in that a large number of films are formed.

The production method of 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, coextruded from a T die, and cooled and solidified with a cast roll. Is mentioned. Moreover, the method of cutting open the film manufactured by the tubular method and making it flat is also applicable.
As a method for stretching the laminated nonporous film-like material, there are methods such as a roll stretching method, a rolling method, a tenter stretching method, and a simultaneous biaxial stretching method, and biaxial stretching is performed by combining these alone or in combination of two or more. Among these, biaxial stretching is preferable from the viewpoint of controlling the porous structure.

  As a more preferred embodiment, a resin composition containing as a main component a polypropylene resin having β activity constituting the base material layer, and a compound (X) containing as a main component a polyethylene resin constituting the SD layer. A laminated nonporous film-like material having a two-layer / three-layer structure is produced by coextrusion from a T die so as to make a porous structure by using a resin composition containing A method for producing a laminated porous film that is made porous by biaxially stretching is described below.

  The resin composition constituting the base material layer preferably contains at least a polypropylene resin and a β crystal nucleating agent. These raw materials are preferably mixed using a Henschel mixer, a super mixer, a tumbler type mixer or the like, or mixed by hand blending with all ingredients in a bag, and then preferably a single screw or twin screw extruder, a kneader, etc. Is pelletized after melt-kneading with a twin screw extruder.

  When preparing the resin composition that constitutes the SD layer, the raw materials such as the polyethylene resin, compound (X) and other additives as described in the description of the SD layer, Henschel mixer, super mixer, tumbler mixer, etc. After mixing by using, it is melt-kneaded with a single-screw or twin-screw extruder, a kneader or the like, preferably a twin-screw extruder, and then pelletized.

The pellets of the resin composition for the base layer and the pellets of the resin composition for the SD layer are put into an extruder and extruded from a die for co-extrusion with a T die. The type of T-die may be a multi-manifold type for type 2 and 3 layers or a feed block type for type 2 and 3 layers.
The gap of the T die to be used is determined from the final required film thickness, stretching conditions, draft rate, various conditions, etc., but is generally about 0.1 to 3.0 mm, preferably 0.5. -1.0 mm. If it is less than 0.1 mm, it is not preferable from the viewpoint of production speed, and if it is more than 3.0 mm, it is not preferable from the viewpoint of production stability because the draft rate increases.

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 150 to 300 ° C, and more preferably 180 to 280 ° C. When the temperature is 150 ° C. or higher, the viscosity of the molten resin is preferably sufficiently low and excellent in moldability. On the other hand, at 300 ° C. or lower, the deterioration of the resin composition can be suppressed.
The cooling and solidification temperature by the cast roll is very important in the present invention, and β crystals in the film-like material before stretching can be generated and grown, and the β-crystal ratio in the film-like material can be adjusted. The cooling and solidification 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. By setting the cooling and solidification temperature to 80 ° C. or higher, the β crystal ratio in the film-like material cooled and solidified can be sufficiently increased, which is preferable. Further, it is preferable to set the temperature to 150 ° C. or lower because troubles such as the extruded molten resin sticking to and wrapping around the cast roll hardly occur and the film can be efficiently formed into a film.

It is preferable to adjust the β crystal ratio of the obtained film-like material before stretching to 30 to 100% by setting a cast roll in the temperature range. 40 to 100% is more preferable, 50 to 100% is still more preferable, and 60 to 100% is particularly preferable. By setting the β crystal ratio of the film-like material before stretching to 30% or more, it is possible to obtain a porous film that is easily made porous by the subsequent stretching operation, has excellent electrical characteristics, and has β activity.
The β crystal ratio of the film-like material before stretching is detected when the film-like material is heated from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min using a differential scanning calorimeter. The crystal melting calorie (ΔHmα) derived from the α crystal and the crystal melting calorie (ΔHmβ) derived from the β crystal are calculated by the following formula.
β crystal ratio (%) = [ΔHmβ / (ΔHmβ + ΔHmα)] × 100

  Next, the obtained laminated nonporous membrane is biaxially stretched. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. In the case of producing a laminated porous film excellent in SD characteristics, which is the object of the present invention, sequential biaxial stretching is more preferred 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 (MD) of a film-like thing is called "longitudinal stretching", and the extending | stretching to the perpendicular direction (TD) is called "lateral stretching."

  When using sequential biaxial stretching, it is necessary to select the stretching temperature according to the composition of the resin composition to be used, the crystal melting peak temperature, the crystallinity, etc., but the control of the porous structure is easy, and the mechanical strength and shrinkage rate It is easy to balance with other physical properties. The stretching temperature in the longitudinal stretching is generally controlled in the range of 20 ° C to 130 ° C, preferably 40 ° C to 120 ° C, more preferably 60 ° C to 110 ° C. The longitudinal draw ratio is preferably 2 to 10 times, more preferably 3 to 8 times, and still more preferably 4 to 7 times. By performing longitudinal stretching within the above range, it is possible to develop an appropriate pore starting point while suppressing breakage during stretching. On the other hand, the stretching temperature in transverse stretching is generally 100 to 160 ° C, preferably 110 to 150 ° C, and more preferably 120 to 140 ° C. The transverse draw ratio is preferably 2 to 10 times, more preferably 3 to 8 times, and further preferably 4 to 7 times. By transversely 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. The stretching speed in the stretching step is preferably 500 to 12000% / min, more preferably 1500 to 10,000% / min, and further preferably 2500 to 8000% / min.

  The laminated porous film thus obtained is subjected to heat treatment at a temperature of preferably about 100 ° C. to 150 ° C., more preferably about 110 ° C. to 140 ° C. for the purpose of improving dimensional stability. During the heat treatment step, 1 to 30% relaxation treatment may be performed as necessary. The laminated porous film of the present invention can be obtained by uniformly cooling and winding after this heat treatment.

[Explanation of 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. 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 1.4 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. That is, lithium graphite oxide (LiCoO ₂ ) is 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 are 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.

[Description of Examples]
Next, although an Example and a comparative example are shown and it demonstrates in detail about the laminated porous film of this invention, this invention is not limited to these.

Example 1
3,9-bis [4- (N-cyclohexylcarbamoyl) phenyl] -2 as a β crystal nucleating agent with respect to 100 parts by mass of a polypropylene resin (Prime Polymer, Prime Polypro F300SV, MFR: 3 g / 10 min) , 4,8,10-tetraoxaspiro [5.5] undecane is added in an amount of 0.1 part by mass, and 280 using a same-direction twin screw extruder (caliber φ40 mm, L / D = 32) manufactured by Toshiba Machine Co., Ltd. Resin composition A1 melt-kneaded at 0 ° C. and processed into pellets was obtained.
Moreover, as a polyethylene resin, hydrogenated petroleum resin (Arakawa Chemical Industries, Ltd.) is added to 80 parts by mass of high density polyethylene (manufactured by Prime Polymer, Hi-ZEX3300F, density: 0.950 g / cm ³ , MFR: 1.1 g / 10 min). Manufactured, Alcon P115) 20 parts by mass was added, and a resin composition B1 processed into a pellet by melt-kneading at 230 ° C. using the same type of unidirectional twin screw extruder was obtained.
Resin compositions A1 and B1 were extruded at 210 ° C. with separate extruders, extruded from a T-die for multilayer molding through a feed block of two types and three layers, and the film thickness ratio after stretching was A1 / B1 / A1 = 3 / After laminating to 1/3, it was cooled and solidified with a casting roll at 125 ° C. to obtain a laminated nonporous film-like material having a thickness of 80 μm.
The laminated non-porous membrane was biaxially stretched sequentially at 100 ° C. by MD to 5.5 times, then at 100 ° C. by 2.5 times, and then thermally relaxed by 100% at 100 ° C. to obtain a laminated porous film. Got.
Various characteristics of the obtained laminated porous film were measured and evaluated, and the results are summarized in Table 1.

(Example 2)
As polyethylene-based resin, 80 parts by mass of high-density polyethylene (Prime Polymer, Hi-ZEX3300F, density: 0.950 g / cm ³ , MFR: 1.1 g / 10 min), maleic anhydride-modified linear low-density polyethylene 20 parts by mass (Mitsui Chemicals Co., Ltd., Admer NF308) was added, and a resin composition B2 processed into a pellet by melting and kneading at 230 ° C. using the same type of unidirectional twin screw extruder was obtained.
Using the resin composition B2 as an alternative to the resin composition B1, a laminated non-porous film having a thickness of 80 μm was obtained under the same extrusion conditions as in Example 1.
The laminated non-porous film was successively biaxially stretched at 100 ° C. to MD 4.0 times, then at 100 ° C. 2.5 times to TD, and then thermally relaxed 4% at 100 ° C. to obtain a laminated porous film. Got.
Various characteristics of the obtained laminated porous film were measured and evaluated, and the results are summarized in Table 1.

(Example 3)
As a polyethylene-based resin, 80 parts by mass of high-density polyethylene (manufactured by Prime Polymer, Hi-ZEX3300F, density: 0.950 g / cm ³ , MFR: 1.1 g / 10 min), ethylene-methyl methacrylate copolymer ( Sumitomo Chemical Co., Ltd., ACLIFT CM8014) 20 parts by mass was added, and a resin composition B3 processed into a pellet by melt-kneading at 230 ° C. using the same type of unidirectional twin screw extruder was obtained. A laminated porous film was obtained in the same manner as in Example 2 except that the resin composition B3 was used as an alternative to the resin composition B2.
Various characteristics of the obtained laminated porous film were measured and evaluated, and the results are summarized in Table 1.

Example 4
For 100 parts by mass of polypropylene resin (manufactured by Prime Polymer, Prime Polypro F300SV, MFR: 3 g / 10 min) as an antioxidant (C255, manufactured by Ciba Specialty Chemicals, IRGAFOS168 / IRGANOX1010 = 1/1) 0.2 And 0.1 part by mass of 3,9-bis [4- (N-cyclohexylcarbamoyl) phenyl] -2,4,8,10-tetraoxaspiro [5.5] undecane as a β crystal nucleating agent was added. Using a same-direction twin-screw extruder manufactured by Toshiba Machine Co., Ltd. (caliber 40 mmφ, L / D = 32), a resin composition A2 melted and kneaded at 270 ° C. and processed into a pellet was obtained.
As polyethylene-based resin, 80 parts by mass of high-density polyethylene (manufactured by Prime Polymer, Hi-ZEX3300F, density: 0.950 g / cm ³ , MFR: 1.1 g / 10 min), microcrystalline wax (manufactured by Nippon Seiwa Co., Ltd.) , Hi-Mic1090) 20 parts by mass, and 0.3 parts by mass of dibenzylidene sorbitol (manufactured by Nippon Nippon Chemical Co., Ltd., Gelol D) as a nucleating agent were added and melted at 230 ° C. using the same type of unidirectional twin screw extruder. A resin composition B4 kneaded and processed into a pellet was obtained. A laminated porous film was obtained in the same manner as in Example 2 except that the resin composition A2 was used as an alternative to the resin composition A1 and the resin composition B4 was used as an alternative to the resin composition B2.
Various characteristics of the obtained laminated porous film were measured and evaluated, and the results are summarized in Table 1.

(Example 5)
As polyethylene-based resin, 80 parts by mass of high-density polyethylene (manufactured by Prime Polymer, Hi-ZEX3300F, density: 0.950 g / cm ³ , MFR: 1.1 g / 10 min), ethylene-vinyl acetate copolymer (Japan) Resin composition processed into a pellet by melting and kneading at 230 ° C. using a same-direction twin-screw extruder, adding 20 parts by mass (made by polyethylene, Novatec EVA, LV151, MFR: 3.0 g / 10 min) Product B5 was obtained.
Using the resin composition B5 as an alternative to the resin composition B2, a laminated non-porous film having a thickness of 80 μm was obtained under the same extrusion conditions as in Example 2.
The laminated non-porous film was successively biaxially stretched at 100 ° C. to MD 4.5 times, then at 100 ° C. to TD 2.0 times, and then thermally relaxed at 100 ° C. for 5% to obtain a laminated porous film. Got.
Various characteristics of the obtained laminated porous film were measured and evaluated, and the results are summarized in Table 1.

(Comparative Example 1)
50 parts by mass of high-density polyethylene (manufactured by Prime Polymer, Hi-ZEX2200J, density: 0.964 g / cm ³ , MFR: 1.1 g / 10 min) and barium sulfate (“B-” manufactured by Sakai Chemical Industry Co., Ltd.) as a filler 55 ”, particle size: 0.66 μm) and 50 parts by weight of hardened castor oil (Hyokusato Oil Co., Ltd., HY-CASTROIL, molecular weight: 938) are added, and the same type of same-direction twin screw extruder is used. The resin composition B6 was melt-kneaded at 230 ° C. and processed into pellets.
Using the resin composition B6 as an alternative to the resin composition B1, a laminated non-porous film having a thickness of 80 μm was obtained under the same extrusion conditions as in Example 1.
The laminated non-porous film was successively biaxially stretched at 100 ° C. to MD 3.0 times, then at 100 ° C. to TD 3.7 times, and then thermally relaxed at 100 ° C. for 5% to obtain a laminated porous film. Got.
Various characteristics of the obtained laminated porous film were measured and evaluated, and the results are summarized in Table 1.

(Comparative Example 2)
As an alternative to the resin composition A1, only a polypropylene resin (Prime Polymer Co., Prime Polypro F300SV, MFR: 3 g / 10 min) was used, and it was the same as in Example 1 except that it was cooled and solidified with a 110 ° C. casting roll. A laminated non-porous film having a thickness of 80 μm was obtained under the extrusion conditions.
Attempts were made to stretch the laminated nonporous membrane-like material 4.0 times to MD at 100 ° C., but the film was broken and a laminated porous film could not be obtained. The β crystal ratio of the laminated film was 0%.

  About the film of the obtained Example and the comparative example, various characteristics were measured and evaluated as follows.

(1) Layer ratio A cross section of the laminated porous film was cut out and observed with a scanning electron microscope (S-4500, manufactured by Hitachi, Ltd.), and the layer ratio was measured from the layer configuration and thickness.
(2) Thickness A thickness of 1/1000 mm was used to measure 30 in-plane thicknesses unspecified, and the average was taken as the thickness.
(3) Porosity The substantial amount W1 of the laminated porous film was measured, the mass W0 in the case of the porosity of 0% was calculated from the density and thickness of the resin composition, and calculated from these values based on the following formula. .
Porosity (%) = {(W0−W1) / W0} × 100
(4) Tensile strength Measured according to JIS K7127. Specifically, both MD and TD were measured at a width of 15 mm, a length of 80 mm, a distance between chucks of 40 mm, and a crosshead speed of 200 mm / min, and the tensile strength at the breaking point was recorded.
(5) Electric resistance at 25 ° C. Laminated porous film is cut into 3.5 cm × 3.5 cm square in an air atmosphere at 25 ° C. and placed in a glass petri dish, propylene carbonate containing 1M lithium perchlorate: ethyl Methyl carbonate = 1: 1 (v / v) solution (manufactured by Kishida Chemical Co., Ltd.) was added to the extent that the porous film was immersed, and the solution was soaked. The porous film was taken out, the excess electrolyte solution was wiped off, and placed in the center of a stainless steel dish having a diameter of 60 mm. A 100 g stainless steel weight having a bottom surface of φ30 mm was slowly placed, a terminal was connected to the petri dish and the weight, and the electrical resistance was measured using a HIKI LCR HiTESTER (manufactured by Hioki Electric Co., Ltd., model number 3522-50).
(6) Electrical resistance after heating at 135 ° C. for 5 seconds A laminated porous film was cut into a 60 mm vertical x 60 mm horizontal square, and an aluminum plate with a circular hole of φ40 mm in the center as shown in FIG. 2 (A) (Material: JIS standard A5052, size: 60 mm long, 60 mm wide, 1 mm thick) Clip between the two pieces as shown in Fig. 2 (B). Double clip "Kuri-J35" manufactured by KOKUYO. ). Next, glycerin (manufactured by Nacalai Tesque, grade 1) was filled up to 100 mm from the bottom, and was fixed to the center of a 135 ° C. oil bath (manufactured by ASONE, OB-200A) with two aluminum plates. The film in the state was immersed and heated for 5 seconds. Immediately after the heating, the sample is immersed in a separately prepared cooling bath filled with 25 ° C. glycerin and cooled for 5 minutes, then washed with 2-propanol (manufactured by Nacalai Tesque, special grade), and 15 in a 25 ° C. air atmosphere. Dried for minutes. The electric resistance of the dried film was measured according to the method (5) above.
(7) BD characteristics As in the measurement of (6) above, the film was cut into a 60 mm long x 60 mm wide square and fixed as shown in FIGS.
The film fixed with two aluminum plates is placed in an oven set at 200 ° C (Tabai Espec, Tabai Gear Oven “GPH200”, damper closed), and the oven set temperature reaches 200 ° C again. 2 minutes later, the film was evaluated for the presence or absence of BD characteristics.
○: When the shape is maintained (with BD characteristics)
×: When the shape cannot be maintained and the film breaks (no BD characteristics)
If the film piece cannot be cut into a 60 mm × 60 mm square, the sample may be prepared by adjusting the film so that the film is placed in a circular hole having a central portion of φ40 mm.

  Further, the obtained laminated porous film was evaluated for β activity as follows.

(8) Differential scanning calorimetry (DSC)
Using a differential scanning calorimeter (DSC-7) manufactured by Perkin Elmer, the film was heated from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min and held for 1 minute, and then from 240 ° C. to 25 ° C. The temperature was lowered at a cooling rate of 10 ° C./min, held for 1 minute, and further heated from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min. The presence or absence of β activity was evaluated as follows depending on whether a peak was detected at 145 ° C. to 160 ° C., which is the 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.

(9) X-ray diffraction measurement As in the case of the measurement of the BD characteristics, the laminated porous film was cut into a 60 mm long x 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 thermostat (model DKN602, manufactured by Yamato Kagaku Co., Ltd.) having a set temperature of 180 ° C. and a display temperature of 180 ° C., and held for 3 minutes. The temperature was changed and gradually cooled to 100 ° C. over 10 minutes. 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. X-ray diffraction measurement was performed on a circular portion having a diameter of 40 mm.
-X-ray diffraction measurement device: manufactured by Mac Science Co., Ltd. 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)
If the film piece cannot be cut into a 60 mm × 60 mm square, the sample may be prepared by adjusting the film so that the film is placed in a circular hole having a central portion of φ40 mm.

Table 1 shows the physical property values obtained in each Example and Comparative Example.
It turns out that the laminated porous film of the Example comprised within the range prescribed | regulated by this invention has the shutdown characteristic outstanding compared with the film of the comparative example comprised by the range other than prescribed | regulated by this invention.
On the other hand, it can be seen from Comparative Example 1 that when the resin composition obtained by mixing barium sulfate as a filler in high-density polyethylene is disposed as the SD layer, the shutdown characteristics are not exhibited.
Further, from Comparative Example 2, when the laminated non-porous film had a β crystal ratio of 0% and no β activity, it could not be made porous by stretching. That is, when it does not have β activity, it turns out that the laminated porous film of the present invention cannot be produced.

  Since the laminated porous film of the present invention has excellent electrical resistance and has shutdown characteristics, it can be suitably used as a battery separator.

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 film in the electrical resistance after heating for 5 second at 135 degreeC, BD characteristic, and a X-ray-diffraction measurement.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Battery separator 20 Lithium ion battery 21 Positive electrode plate 22 Negative electrode plate 31 Aluminum plate 32 Film 33 Clip 34 Film vertical direction 35 Film horizontal direction

Claims (5)

It consists of a laminated porous film of two or more layers including a base material layer containing 50% by mass or more of a polypropylene resin and a shutdown layer containing 50% by mass or more of a polyethylene resin, and the polypropylene resin of the base material layer Β-nucleating agent is added to the laminated porous film having β activity ,
A laminated porous film for a separator, wherein the electrical resistance at 25 ° C. is 10Ω or less and the electrical resistance after heating at 135 ° C. for 5 seconds is 100Ω or more.   The shutdown layer contains 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. The laminated porous film for a separator according to claim 1.   3. The laminated porous film for a separator according to claim 1, wherein an MD tensile strength / TD tensile strength ratio is 0.3 or more and 15 or less.   The laminated porous film for a separator according to any one of claims 1 to 3, wherein the laminated porous film is biaxially stretched. A base material layer containing a polypropylene resin in an amount of 50% by mass or more and 0.0001 to 5.0 parts by mass of a β crystal nucleating agent with respect to 100 parts by mass of the polypropylene resin, and 50% by mass of the polyethylene resin. The production of the laminated porous film for a separator according to any one of claims 1 to 3, wherein the shutdown layer as described above is laminated into two or more layers by coextrusion and biaxially stretched to make it porous. Method.

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