JP5267754B1 - Porous polyolefin film and electricity storage device - Google Patents

Abstract

Provided is a porous polyolefin film having improved wrinkling and flatness in a pre-drying process of LIB and EDLC assembly. The porous polyolefin film of the present invention has the following relationship between the Young's modulus f ₍₂₃₎ (MPa) in the longitudinal direction at 23 ° C. and the Young's modulus f ₍₁₀₅₎ (MPa) in the longitudinal direction at 105 ° C. (1) It is characterized by satisfy | filling Formula and (2) Formula.
f ₍₁₀₅₎ > 80 (1)
f ₍₂₃₎ -f ₍₁₀₅₎ <450 (2)

Description

  The present invention relates to a porous polyolefin film and an electricity storage device.

  Porous polyolefin films are being developed for use in a wide variety of applications, including separators for batteries and electrolytic capacitors, various separation membranes, clothing, moisture-permeable waterproof membranes for medical applications, reflectors for flat panel displays, and thermal transfer recording sheets. Yes. Among them, lithium ion batteries (LIBs) widely used in mobile devices such as notebook personal computers, mobile phones, and digital cameras, and electric double layer capacitors (EDLC) used as storage devices for stationary and backup power supplies A porous film is suitable as a separator for lithium ion capacitors (LIC). In particular, in recent years, LIB has been used in electric vehicles and hybrid vehicles, and separators with good air permeability and thin thickness have been demanded as batteries have higher output and capacity. In addition, as a separator for EDLC, a cellulose separator having low cost and good air permeability has been conventionally used. However, in recent years, it is desired to reduce the thickness of the separator in order to improve electric capacity.

  As a porous polyolefin film, α-type crystal (α crystal) and β-type crystal (β crystal), which are polymorphs of polypropylene, are formed by a dry process that can be manufactured at low cost with a wide, large area by biaxial stretching. A so-called β crystal method has been proposed in which voids are formed in a film using the difference in crystal density and crystal transition (see Patent Documents 1 to 3). In addition, in order to improve the air permeability by the β crystal method in response to the demand for higher output of the battery, a fibril is formed by forming a polypropylene resin and a second component resin domain that is not completely compatible with the polypropylene resin. There has also been a proposal for promoting cleavage (see Patent Document 4).

Although the porous film using the polyolefin described in Patent Documents 1 to 4 can be thinned, the moisture in the battery adversely affects the battery characteristics in LIB, LIC, and EDLC applications (Patent Document 5). And 6), a drying process may be provided in which the separator is dried at around 100 ° C. to remove moisture in advance, and wrinkles are generated or flatness is reduced due to the transport tension and drying temperature in this drying process. There was a case.
In these applications, since the size of the battery is increased and the area used is increased, cost reduction is also strongly desired.

JP-A 63-199742 JP-A-6-100720 Japanese Patent Laid-Open No. 9-255804 International Publication No. 2007/046225 JP 2003-297428 A JP 2007-287781 A

  An object of the present invention is to solve the above-described problems. That is, an object of the present invention is to provide a porous polyolefin film in which the generation of wrinkles and the decrease in flatness are improved in the pre-drying process of LIB or EDLC assembly.

To solve the above problems and achieve the object, porous polyolefin film of the present invention, the longitudinal direction of the Young's modulus f at _{23 ℃ (23) (MPa)} , in the longitudinal direction at 105 ° C. Young's modulus f _{( 105)} The relationship with (MPa) satisfies the following formulas (1) and (2).
f ₍₁₀₅₎ > 80 (1)
f ₍₂₃₎ -f ₍₁₀₅₎ <450 (2)

Further, the porous polyolefin film of the present invention has a relationship between the longitudinal Young's modulus f ₍₂₃₎ (MPa) at ₂₃ ° C. and the longitudinal Young's modulus f ₍₁₀₅₎ (MPa) at 105 ° C. (1 ) And (3) are satisfied.
f ₍₁₀₅₎ > 80 (1)
f ₍₂₃₎ / f ₍₁₀₅₎ <6 (3)

  The porous polyolefin film of the present invention is suitable as a separator for LIB, LIC, and EDLC with high output because wrinkles and flatness are reduced in the pre-drying process of LIB, LIC, and EDLC assembly. Can be used.

FIG. 1 is a diagram illustrating a method for evaluating the degree of occurrence of wrinkles.

In the porous polyolefin film of the present invention, the relationship between the longitudinal Young's modulus f ₍₂₃₎ (MPa) at ₂₃ ° C and the longitudinal Young's modulus f ₍₁₀₅₎ (MPa) at 105 ° C is expressed by the following formula (1). And (2) is satisfied.
f ₍₁₀₅₎ > 80 (1)
f ₍₂₃₎ -f ₍₁₀₅₎ <450 (2)
In the present application, a direction parallel to the film forming direction is referred to as a film forming direction, a longitudinal direction, or an MD direction, and a direction perpendicular to the film forming direction in the film plane is referred to as a width direction or a TD direction. When the Young's modulus f ₍₁₀₅₎ in the longitudinal direction at 105 ° C. is 80 MPa or less, when heated to around 100 ° C. in order to remove moisture in the pre-drying step of LIB or EDLC assembly, the porous polyolefin film is dried in the drying oven. May be deformed and wrinkles may occur or flatness may be reduced. f ₍₁₀₅₎ is more preferably 90 MPa or more, and further preferably 100 MPa or more. The upper limit of f ₍₁₀₅₎ is not particularly provided, but if it is 500 MPa or more, the permeability may be deteriorated and may not be suitable for high-power applications.

If the difference between the Young's modulus f ₍₂₃₎ in the longitudinal direction at 23 ° C. and the Young's modulus f ₍₁₀₅₎ in the longitudinal direction at 105 ° C. in Formula (2) exceeds 450 MPa, the porous polyolefin film is introduced into the drying oven. When this is done, wrinkles may occur or flatness may be reduced. A general drying apparatus unwinds a porous polyolefin film from an unwinder at room temperature, introduces the porous polyolefin film into a drying oven to dry water and an organic solvent, and then winds the porous polyolefin film at room temperature. At this time, since the tension of the conveyed porous polyolefin film is controlled by a tension system installed in the vicinity of the unwinder and the winder, the tension applied to the porous polyolefin film before and after the drying oven is constant. That is, in Formula (2), when the difference between the Young's modulus f ₍₂₃₎ in the longitudinal direction at 23 ° C. and the Young's modulus f ₍₁₀₅₎ in the longitudinal direction at 105 ° C. becomes large, the porous polyolefin film before entering the drying oven The deformation behavior of the porous polyolefin film in the drying oven is greatly different. In a film having no general pores, this difference in deformation behavior does not greatly affect the wrinkle and flatness of the film, but since the porous polyolefin film is easily deformed, wrinkles may occur or It is thought to cause a decline in sex. From the above viewpoint, the difference between the Young's modulus f ₍₂₃₎ in the longitudinal direction at 23 ° C. and the Young's modulus f ₍₁₀₅₎ in the longitudinal direction at 105 ° C. is preferably 400 MPa or less, more preferably 350 MPa or less.

Further, the porous polyolefin film of the present invention has a relationship between the longitudinal Young's modulus f ₍₂₃₎ (MPa) at ₂₃ ° C. and the longitudinal Young's modulus f ₍₁₀₅₎ (MPa) at 105 ° C. (1 ) And (3) are satisfied.
f ₍₁₀₅₎ > 80 (1)
f ₍₂₃₎ / f ₍₁₀₅₎ <6 (3)
In Formula (3), when the Young's modulus ratio f ₍₂₃₎ / f ₍₁₀₅₎ between 23 ° C. and 105 ° C. exceeds 6, when the porous polyolefin film is introduced into the drying oven, wrinkles are generated or flatness is reduced. May decrease. The Young's modulus ratio f ₍₂₃₎ / f ₍₁₀₅₎ is more preferably less than 5, and most preferably less than 4.5.

  As a method for obtaining a porous polyolefin film satisfying the above formulas (1) and (2), that is, having a high Young's modulus at the drying temperature and a small difference between the Young's modulus at room temperature and the drying temperature, Add a predetermined amount of a β crystal nucleating agent, a polypropylene resin (A), an ethylene / α-olefin copolymer (B) and a dispersing agent (C), which will be described later, and the conditions during stretching shall be within the range described later. It can be controlled by.

  The porous polyolefin film of the present invention has pores that penetrate both surfaces of the film and have air permeability (hereinafter referred to as through-holes). As a method for obtaining the porous polyolefin film having through-holes, as long as the above characteristics are satisfied, the production method and the material are not particularly limited, and a known method can be adopted. It is preferable to use polyolefin as the material of the porous polyolefin film because the material cost can be reduced and the separator can be manufactured at low cost. As a production method, it is preferable to use the β crystal method described later, because the film can be formed with high productivity by biaxial stretching.

  Hereinafter, preferred embodiments of the porous polyolefin film of the present invention will be described by taking the β crystal method as an example.

  The porous polyolefin film of the present invention preferably contains a polypropylene resin (A) having a β crystal forming ability of 40% or more as a main component. The “main component” means that the proportion of a specific component in all components is preferably 50% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and most preferably 95% by mass or more. It means that there is.

  The β crystal method is a method in which a β crystal formed in a cast sheet is used as fibrils oriented in the film forming direction by longitudinal stretching, and a porous polypropylene film is obtained by forming a network while cleaving the fibrils by transverse stretching. Although it is a method, conventionally, it has been difficult to highly uniformly cleave fibrils oriented in the film forming direction by transverse stretching. When non-uniform fibril cleavage occurs, thick fibrils that bear the strength in the longitudinal direction of the porous polyolefin film are reduced, and the strength is considered to be lowered. In the present invention, by adopting the raw materials and film forming conditions described later, fibrils strongly oriented in the longitudinal direction are uniformly generated, that is, the Young's modulus at the drying temperature is high, and the difference between the Young's modulus at the normal temperature and the drying temperature. Led to a small film.

  As a method for improving air permeability in the β crystal method, polypropylene resin (A) and an ethylene / α-olefin system that promotes fibril cleavage by forming a domain that is not completely compatible with the polypropylene resin (A). A porous polypropylene film using the copolymer (B) is known (for example, see WO2007 / 046225). However, when this method is used, the air permeability is improved, but the uniformity of fibril cleavage in the transverse stretching step is insufficient.

  In the present invention, in addition to the polypropylene resin (A) and the ethylene / α-olefin copolymer (B), the domain of the ethylene / α-olefin copolymer (B) is fine and uniform as the third component. When the film-forming conditions described later are employed using the dispersing agent (C) for dispersing in the pores, the pore structure becomes uniform, coarse pores due to stretching can be reduced, and the difference in mechanical properties between high temperature and room temperature. Can be reduced, which is preferable.

  First, raw materials used for the porous polyolefin film of the present invention will be described.

  In order to form through holes in the film using the β crystal method, a polyolefin composition having β crystal forming ability is used as a material for the porous polyolefin film. The polyolefin composition is preferably a polypropylene composition containing a polypropylene resin (A) as a main component, and the β crystal-forming ability of the polypropylene composition is preferably 40% or more. If the β-crystal forming ability is less than 40%, the amount of β-crystals is small at the time of film production, so the number of voids formed in the film is reduced by utilizing the transition to α-crystal, and as a result, only films with low permeability are obtained. It may not be possible. On the other hand, in order to make the β crystal forming ability exceed 90%, it is necessary to add a large amount of a β crystal nucleating agent described later or to make the stereoregularity of the polypropylene resin (A) to be used extremely high. The industrial practical value is low, for example, the film forming stability is lowered. Industrially, β-crystal forming ability is preferably 60 to 90%, particularly preferably 65 to 85%.

  In order to control the β crystal forming ability to 40 to 90%, a polypropylene resin (A) having a high isotactic index is used, or it is added to a polypropylene resin (A) called a β crystal nucleating agent. A crystallization nucleating agent that selectively forms β crystals is preferably used as an additive.

  Examples of the β crystal nucleating agent include alkali or alkaline earth metal salts of carboxylic acids such as calcium 1,2-hydroxystearate and magnesium succinate, and N, N′-dicyclohexyl-2,6-naphthalenedicarboxyamide. Amide compounds, tetraoxaspiro compounds such as 3,9-bis [4- (N-cyclohexylcarbamoyl) phenyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, benzenesulfonic acid Preferable examples include aromatic sulfonic acid compounds such as sodium and sodium naphthalene sulfonate, imide carboxylic acid derivatives, phthalocyanine pigments, and quinacridone pigments. Particularly, amides disclosed in JP-A-5-310665 Compounds can be preferably usedThe content of the β crystal nucleating agent is preferably 0.05 to 0.5% by mass, more preferably 0.1 to 0.3% by mass, based on the entire polypropylene composition. . If it is less than 0.05% by mass, formation of β crystals becomes insufficient, and the air permeability of the porous polyolefin film may be lowered. If it exceeds 0.5% by mass, coarse voids are formed, and in the drying process of the assembly process of LIB, LIC and EDLC, film deformation is likely to occur due to the transport tension and drying temperature, causing wrinkles and flatness. It can be.

  For the polypropylene resin (A) used in the present invention, it is possible to use an isotactic polypropylene resin having a melt flow rate (hereinafter referred to as MFR) of 2 to 30 g / 10 minutes in order to achieve extrudability and uniform pore formation. It is preferable from the viewpoint. Here, MFR is an index indicating the melt viscosity of a resin defined in JIS K 7210 (1995), and is a physical property value indicating the characteristics of a polyolefin resin. In the present invention, it refers to a value measured at 230 ° C. and 2.16 kg. In the present invention, the isotactic index of the polypropylene resin (A) is preferably in the range of 90 to 99.9%. More preferably, it is 95 to 99%. When the isotactic index is less than 90%, the crystallinity of the resin is lowered, and the film forming property may be deteriorated or the strength of the film may be insufficient.

  As a polypropylene composition for forming the porous polyolefin film of the present invention, not only homopolypropylene can be used, but also from the viewpoint of stability in the film-forming process, film-forming property, and uniformity of physical properties. In addition, a resin obtained by copolymerizing an ethylene component and an α-olefin component such as butene, hexene, and octene in an amount of 5% by mass or less, more preferably 2.5% by mass or less can also be used.

  When the polypropylene composition forming the porous polyolefin film of the present invention is biaxially stretched to form a through-hole, from the viewpoint of improving the air permeability due to the improvement of void formation efficiency at the time of stretching and the pore diameter being enlarged. It is preferable to contain an ethylene / α-olefin copolymer (B) as the second component. Here, examples of the ethylene / α-olefin copolymer (B) include linear low-density polyethylene and ultra-low-density polyethylene. Among them, octene-1 is copolymerized, and the melting point is 60 to 90 ° C. Copolymer polyethylene resin (copolymer PE resin) can be preferably used. Examples of the copolymer polyethylene include commercially available resins such as “Engage (registered trademark)” (type names: 8411, 8452, 8100, etc.) manufactured by Dow Chemical.

  The polypropylene composition forming the porous polyolefin film of the present invention may contain 10% by mass or less of the ethylene / α-olefin copolymer (B) when the entire polypropylene composition is 100% by mass. It is preferable from the viewpoint of improving air permeability. From the viewpoint of the mechanical strength of the porous polyolefin film, it is more preferably 1 to 7% by mass, and further preferably 1 to 4% by mass.

The porous polyolefin film of the present invention includes, as a polypropylene composition forming the porous polyolefin film, the above-described polypropylene resin (A), an ethylene / α-olefin copolymer (B), and a dispersant (C) thereof. When the film forming conditions described below are further employed, the pore structure becomes uniform, the fibril cleavage in the transverse stretching becomes uniform, and the coarse pores due to stretching decrease, thereby reducing the Young's modulus f in the longitudinal direction at 105 ° C. ₍₁₀₅₎ is preferred because the strength in the longitudinal direction can be improved and the difference in mechanical properties between high temperature and room temperature can be reduced. The porous polyolefin film of the present invention has a uniform structure, and the difference between the Young's modulus f ₍₂₃₎ in the longitudinal direction at 23 ° C. and the Young's modulus f ₍₁₀₅₎ in the longitudinal direction at 105 ° C. is smaller than a predetermined value. Therefore, when heated near 100 ° C. in order to remove moisture in the preliminary drying step, deformation of the film in the drying oven and generation of wrinkles can be prevented.

  The dispersant (C) used in the present invention is not particularly limited as long as the dispersibility of the ethylene / α-olefin copolymer (B) in the polypropylene resin (A) can be enhanced. By the way, International Publication No. 2007/046225 discloses an ethylene / α-olefin copolymer incompatible with polypropylene resin, melting at a predetermined temperature, addition of a compatibilizing agent, or high shearing force during extrusion. It is described that fine pores can be formed and the porosity and air permeability can be improved by dispersing them in a polypropylene resin, etc. However, no specific compound or the like is described for the compatibilizer, and a polypropylene composition containing a polypropylene resin (A) and an ethylene / α-olefin copolymer (B) is melted at a predetermined temperature. However, it is difficult to disperse the ethylene / α-olefin copolymer (B) to a predetermined dispersion diameter and to make the pore structure of the polypropylene film highly uniform only by extruding by applying a high shear force. It is. The present inventors have a highly compatible segment (for example, a polypropylene segment, an ethylene butylene copolymer segment) and a highly compatible segment (B) with the polypropylene resin (A) ( An ethylene / α-olefin copolymer having a dispersion diameter in a predetermined range in the polypropylene resin (A) by blending a block copolymer having a polyethylene segment, etc.) into the polypropylene composition as a dispersant (C). It was found that a cast sheet in which the coalesced (B) was dispersed was obtained, and the pore structure of the porous polyolefin film could be made uniform by stretching the cast sheet. Examples of the dispersant (C) include commercially available resins such as olefin crystal, ethylene butylene, olefin crystal block polymer (hereinafter referred to as CEBC) “DYNARON (registered trademark)” manufactured by JSR (type name: 6100P, 6200P, etc.) and olefin block copolymer “INFUSE OBC (registered trademark)” manufactured by Dow Chemical Company. The addition amount of the dispersant (C) is preferably 1 to 50 parts by mass, more preferably 5 to 33 parts by mass with respect to 100 parts by mass of the ethylene / α-olefin copolymer (B). . From the viewpoint of improving the dispersibility of the ethylene / α-olefin copolymer (B) in the polypropylene resin (A) and improving the uniformity of pore formation, the melting point of the dispersant (C) is ethylene / α. -It is preferable that it is 0-60 degreeC higher than melting | fusing point of an olefin type copolymer (B), and it is more preferable that it is 15-30 degreeC higher.

  The polypropylene composition for forming the porous polyolefin film of the present invention includes an antioxidant, a heat stabilizer, an antistatic agent, a lubricant composed of inorganic or organic particles, and further an anti-blocking agent, as long as the effects of the present invention are not impaired. Various additives such as an agent, a filler and an incompatible polymer may be contained. In particular, it is preferable to add an antioxidant for the purpose of suppressing oxidative deterioration due to the thermal history of the polypropylene resin (A). The addition amount of the antioxidant is preferably 2 parts by mass or less, more preferably 1 part by mass or less, still more preferably 0.5 parts by mass or less with respect to 100 parts by mass of the polypropylene composition.

The amount of the ethylene component contained in the porous polyolefin film of the present invention is preferably less than 10 parts by mass when the porous polyolefin film is 100 parts by mass. When the amount of the ethylene component is 10 parts by mass or more, the heat resistance is lowered because many low-melting-point components are contained, and the Young's modulus f ₍₁₀₅₎ (MPa) in the longitudinal direction at 105 ° C. is lowered. When the film is introduced into the drying oven, wrinkles may occur or flatness may be reduced. The amount of the ethylene component is more preferably less than 5 parts by mass, and still more preferably less than 3 parts by mass.

  The polypropylene composition for forming the porous polyolefin film of the present invention may contain a pore-forming aid composed of inorganic or organic particles as long as the effects of the present invention are not impaired. The content is preferably 5 parts by mass or less with respect to 100 parts by mass of the polypropylene composition, more preferably 2 parts by mass or less, and still more preferably 1 part by mass or less. When the amount exceeds 5 parts by mass, when used as a separator, the dropped particles may deteriorate battery performance, increase raw material costs, and decrease productivity.

  The porous polyolefin film of the present invention is preferably 10 to 200 seconds / 100 ml. If the air permeation resistance is less than 10 seconds / 100 ml, the strength of the film becomes insufficient, the film is deformed in the drying oven, wrinkles may occur, and flatness may be lowered. When it exceeds 200 seconds / 100 ml, the permeability is lowered, and particularly when used as a separator for EDLC, the required output characteristics may not be obtained. The air resistance is more preferably 50 to 170 seconds / 100 ml, and further preferably 70 to 140 seconds / 100 ml. The air permeation resistance is the addition amount of a β crystal nucleating agent, an ethylene / α-olefin copolymer (B) and a dispersing agent (C) described later, the temperature of the cast drum, the stretching ratio and temperature in the longitudinal direction, and the transverse stretching speed. The temperature and time in the heat treatment step and the relaxation rate in the relaxation zone can be controlled within the ranges described later.

  The porous polyolefin film of the present invention preferably has an air resistance per thickness of 20 seconds / 100 ml / μm or less. If it exceeds 20 seconds / 100 ml / μm, the permeability decreases, and particularly when used as a separator for EDLC, the required output characteristics may not be obtained even if the separator is thinned.

  The porous polyolefin film of the present invention preferably has a total film thickness of 20 μm or less. When the thickness exceeds 20 μm, the permeability decreases. Particularly when used as a separator for EDLC, the required output characteristics cannot be obtained, or the volume ratio of the porous polyolefin film in the electricity storage device becomes too high, resulting in high energy. The density cannot be obtained. From the viewpoint of achieving both film strength and output characteristics, the total film thickness is more preferably 3 to 18 μm, and even more preferably 5 to 15 μm.

  The porous polyolefin film of the present invention preferably has a thermal shrinkage in the width direction at 105 ° C. of 5% or less. When the thermal shrinkage in the width direction exceeds 5%, the change in the film width becomes large in the drying oven, and wrinkles may occur or flatness may be deteriorated. The thermal contraction rate in the width direction is more preferably 3% or less, and further preferably 1% or less. The smaller the heat shrinkage rate, the better. However, the lower limit is substantially about 0.1%. The heat shrinkage ratio is the amount of β-crystal nucleating agent, ethylene / α-olefin copolymer (B) and dispersant (C) added, the temperature of the cast drum, the stretching ratio and temperature in the longitudinal direction, and the temperature in the heat treatment step. And the time and the relaxation rate in the relaxation zone can be controlled within the range described later.

  The porous polyolefin film of the present invention preferably has a porosity of 60 to 80%. When the porosity is less than 60%, the permeability decreases, and particularly when used as an EDLC separator, the required output characteristics may not be obtained. On the other hand, when the porosity exceeds 80%, the mechanical strength of the porous film becomes too low, the film is deformed in the drying oven, and wrinkles may occur or the flatness may be lowered. The porosity is more preferably 62 to 75%, and particularly preferably 65 to 70%. The porosity is the amount of β-crystal nucleating agent, ethylene / α-olefin copolymer (B) and dispersant (C) added, the temperature of the cast drum, the stretching ratio and temperature in the longitudinal direction, the temperature in the heat treatment step. And the time and the relaxation rate in the relaxation zone can be controlled within the range described later.

  The porous polyolefin film of the present invention may have a laminated structure for the purpose of imparting various effects as long as the effects of the present invention are not impaired. The number of stacked layers may be a two-layer stack, a three-layer stack, or a larger number of stacks. As a lamination method, either a feed block method by co-extrusion or a multi-manifold method, or a method of laminating porous films by lamination may be used. As a laminated structure, for example, a layer containing polyethylene can be laminated for the purpose of imparting shutdown properties at low temperatures, or a layer containing particles can be laminated for the purpose of imparting strength and heat resistance. In the case of a laminated structure, it is preferable that the resin constituting the surface layer does not contain a polyethylene resin or an ethylene copolymer resin. When an ethylene component is present in the surface layer, the oxidation resistance may decrease when used as a battery separator.

  Below, the manufacturing method of the porous polyolefin film of this invention is demonstrated based on a specific example. In addition, the manufacturing method of the film of this invention is not limited to this.

  As the polypropylene resin (A), 99.5 parts by mass of a commercially available homopolypropylene resin with an MFR of 8 g / 10 min, as the β crystal nucleating agent, 0.3 parts by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxyamide, oxidation The raw material is supplied from the weighing hopper to the twin screw extruder so that 0.2 parts by mass of the inhibitor is mixed at this ratio, melted and kneaded, discharged from the die in a strand shape, and cooled and solidified in a 25 ° C. water tank. Then, it is cut into chips to prepare a polypropylene raw material (a). At this time, the melting temperature is preferably 270 to 300 ° C. Similarly, 64.8 parts by mass of the above-described homopolypropylene resin as the polypropylene resin (A) and a commercially available MFR 18 g / 10 min ultra low density polyethylene resin ethylene octene as the ethylene / α-olefin copolymer (B) 30 parts by mass of 1 copolymer, 5 parts by mass of commercially available CEBC as a dispersant (C), and 0.2 parts by mass of an antioxidant are fed to the twin screw extruder from the weighing hopper, Melt-kneading is performed at 240 ° C., discharged from a die in a strand shape, cooled and solidified in a water bath at 25 ° C., and cut into a chip shape to prepare a polypropylene raw material (b).

Next, 90 parts by mass of the polypropylene raw material (a) and 10 parts by mass of the polypropylene raw material (b) are mixed by dry blending and supplied to a uniaxial melt extruder, and melt extrusion is performed at 200 to 230 ° C. Next, after removing foreign substances, modified polymers, and the like with a filter installed in the middle, they are discharged from a T-die onto a cast drum to obtain an unstretched cast sheet. In the present invention, in order to obtain a uniform pore structure, it is important to control the domain shape and dispersion state of the ethylene / α-olefin copolymer (B) in the cast sheet. In addition, it is preferable to set the shear rate at the die to 100 to 1000 sec ⁻¹ during the extrusion. More preferably, it is 150-800 sec < ^-1 >, More preferably, it is 200-600 sec < ^-1 >. The shear rate at the die is expressed by equation (3). When the shear rate at the die is less than 100 sec ⁻¹ , shearing is not sufficiently performed and it may be difficult to control the domain shape. Further, when the shear rate at the die exceeds 1000 sec ⁻¹ , the domain is sheared more than necessary, and it may be difficult to control the domain shape.
Shear rate (sec ⁻¹ ) = 6Q / ρWt ² (3)
Q: Flow rate (kg / sec)
ρ: specific gravity (kg / cm ³ )
W: Groove width (cm)
t: Groove gap (cm)

  By making the shear rate of the die within a preferable range as described above, the domain (ethylene-α-olefin copolymer (B)) mainly composed of the ethylene / α-olefin copolymer (B) in the cast sheet. Can be dispersed finely and uniformly. Here, the domain diameter of the TD / ZD cross section is preferably 5 to 100 nm, more preferably 10 to 90 nm, and still more preferably 15 to 80 nm. However, the TD / ZD cross section indicates a cross section when the film is cut along a plane passing through a straight line parallel to the thickness direction and a straight line parallel to the width direction. When the domain diameter is less than 5 nm, the effect of promoting fibril cleavage at the time of stretching is small, and air permeability may be lowered. If the domain diameter exceeds 100 nm, the size of the pores may increase and the mechanical strength may be inferior. Normally, when trying to control the domain diameter only by die shearing, the domain diameter becomes smaller near the surface layer in the thickness direction where shearing is easily applied, but the domain diameter becomes larger near the center in the thickness direction, resulting in a uniform pore structure. In the present invention, by using the dispersant (C) described above, a porous polyolefin film in which fibril cleavage in lateral stretching is uniformed by forming a film in the above range is obtained. can get.

  The flow rate of the polymer, the groove width of the T die, and the groove gap are appropriately adjusted so that the shear rate of the die is in the above-described range. The flow rate of the polymer is preferably in the range of 40 to 500 kg / hr from the viewpoint of extrusion stability. The groove width of the T die is preferably in the range of 200 to 1000 mm from the viewpoint of productivity. The groove width of the T die is preferably in the range of 0.8 to 2 mm from the viewpoint of internal pressure in the extrusion system and casting accuracy. The cast drum preferably has a surface temperature of 105 to 130 ° C from the viewpoint of controlling the β crystal fraction of the cast sheet to be high. At this time, particularly, the forming of the end portion of the sheet affects the subsequent stretchability, and therefore it is preferable that the end portion is sprayed with spot air to be in close contact with the drum. Further, air may be blown over the entire surface using an air knife as necessary from the state in which the entire sheet is in close contact with the drum.

  Next, the obtained cast sheet is biaxially oriented to form pores in the film. As a biaxial orientation method, the film is stretched in the longitudinal direction of the film and then stretched in the width direction, or the sequential biaxial stretching method in which the film is stretched in the width direction and then stretched in the longitudinal direction. The simultaneous biaxial stretching method can be used, but it is preferable to adopt the sequential biaxial stretching method from the viewpoint that it is easy to obtain a film having a good balance between air permeability and film mechanical properties, and in particular, stretching in the longitudinal direction. Then, it is preferable to extend in the width direction.

  Specific stretching conditions will be described by taking a sequential biaxial stretching method of stretching in the film longitudinal direction and then stretching in the width direction as an example. As a temperature control method for stretching the cast sheet in the longitudinal direction, a method using a temperature-controlled rotating roll, a method using a hot air oven, or the like can be adopted. The stretching temperature in the longitudinal direction is preferably 90 to 140 ° C. If it is less than 90 degreeC, a film may fracture | rupture. If it exceeds 140 ° C., the pore structure may become non-uniform or the air permeability may be reduced. A higher longitudinal stretching temperature tends to have a higher Young's modulus in the longitudinal direction. From this viewpoint, it is more preferably 110 to 135 ° C, and particularly preferably 120 to 130 ° C. As a draw ratio, it is preferable that it is 3-6 times. As the draw ratio is increased, the Young's modulus in the longitudinal direction is improved. However, if the draw ratio is more than 6 times, the film may be easily broken in the next transverse drawing step. The draw ratio is more preferably 4.5 to 6 times.

Subsequently, in order to stretch in the width direction, the end of the film after longitudinal stretching is gripped with a clip, and transverse stretching is performed with a lateral stretching machine, but in the longitudinal direction when gripping the film after longitudinal stretching with a clip It is preferable to start stretching in the longitudinal direction while applying tension and stretching the film in the longitudinal direction because the Young's modulus f ₍₁₀₅₎ in the longitudinal direction at 105 ° C. of the resulting porous polyolefin film can be improved. Specific methods include forming a film by adding a difference (draw) between the final roll speed of the longitudinal stretching machine and the line speed of the transverse stretching machine, or using a simultaneous biaxial stretching machine, For example, a method of slightly stretching in the direction and performing lateral stretching while applying tension can be used. Here, the draw is preferably 103 to 120%, more preferably 105 to 110%. If the draw is lower than 103%, the Young's modulus f ₍₁₀₅₎ in the longitudinal direction at 105 ° C. decreases, and the difference from the Young's modulus f ₍₂₃₎ at room temperature increases, so that the porous film of the present invention can be used as LIB, LIC, and When used as an EDLC separator, the film may be deformed in the pre-drying step of assembly, and wrinkles may occur or flatness may be reduced. On the other hand, if the draw exceeds 120%, the film may break in the section between the longitudinal stretching machine and the transverse stretching machine during film formation.

  The transverse stretching temperature in the case of conducting transverse stretching while maintaining the tension in the longitudinal direction is preferably 130 to 155 ° C. If it is less than 130 degreeC, a film may fracture | rupture, and if it exceeds 155 degreeC, air permeability may fall. More preferably, it is 145-155 degreeC. The draw ratio in the width direction is preferably 2 to 12 times. If it is less than 2 times, the air permeability may decrease or the planarity in the width direction may decrease. If it exceeds 12 times, the film may break. When the draw ratio in the width direction is too high, the Young's modulus in the longitudinal direction may be lowered, and therefore it is preferably 3 to 8 times, more preferably 4 to 6 times. The transverse stretching speed at this time is preferably 500 to 6,000% / min, more preferably 1,000 to 5,000% / min. The area magnification (longitudinal stretching magnification × lateral stretching magnification) is preferably 30 to 60 times.

  Subsequent to the transverse stretching, a heat treatment step is performed with the width after the transverse stretching. Here, the heat treatment step is a heat setting zone (hereinafter referred to as HS1 zone) in which heat treatment is performed with the width after transverse stretching, and the heat treatment is performed while the film is relaxed in the width direction by narrowing the clip width in the width direction after transverse stretching. It is divided into three zones: a relaxation zone (hereinafter referred to as Rx zone) to be performed, and a heat setting zone (hereinafter referred to as HS2 zone) in which heat treatment is performed with the width after relaxation, which is compatible with air permeability and mechanical properties. Furthermore, it is preferable from the viewpoint of low heat yield.

  The temperature of the HS1 zone is preferably 140 to 165 ° C. If it is lower than 140 ° C., the thermal shrinkage in the width direction may increase. If the temperature exceeds 165 ° C, the orientation of the film is too relaxed, the relaxation rate cannot be increased in the subsequent Rx zone, and it is difficult to achieve both air permeability and mechanical strength. Resistance may increase. If it is 150-160 degreeC from a viewpoint of coexistence of air permeability and mechanical strength, it is more preferable.

  The heat treatment time in the HS1 zone is preferably 0.1 seconds or longer and 10 seconds or shorter from the viewpoint of achieving both a heat shrinkage ratio in the width direction and productivity.

  In the present invention, the relaxation rate in the Rx zone is preferably 13 to 35%. If the relaxation rate is less than 13%, the thermal contraction rate in the width direction may increase. If it exceeds 35%, the air permeability may decrease, or the thickness unevenness or flatness in the width direction may decrease. From the viewpoint of improving air permeability and reducing heat shrinkage, it is more preferably 15 to 25%.

  The temperature of the Rx zone is preferably 155 to 170 ° C. When the temperature of the Rx zone is lower than 155 ° C., the shrinkage stress for relaxation is lowered, and the above-described high relaxation rate may not be achieved or the thermal shrinkage rate in the width direction may be increased. If the temperature exceeds 170 ° C., the polymer around the pores may melt at a high temperature and the air permeability may be lowered. From the viewpoint of improving air permeability and reducing the heat shrinkage rate, it is more preferably 160 to 165 ° C.

  The relaxation rate in the Rx zone is preferably 100 to 1,000% / min. When the relaxation rate is less than 100% / min, it is necessary to slow down the film forming rate or lengthen the tenter length, which may be inferior in productivity. If it exceeds 1,000% / min, the speed at which the film shrinks becomes slower than the speed at which the rail width of the tenter shrinks, the film flutters in the tenter and breaks, or the physical properties in the width direction are uneven and the flatness is lowered. There is a case. The relaxation rate is more preferably 150 to 500% / min.

The temperature of the HS2 zone is preferably 155 to 165 ° C. If the temperature is lower than 155 ° C., the tension of the film after thermal relaxation becomes insufficient, resulting in uneven physical properties and flatness in the width direction, and may increase the heat shrinkage rate in the width direction. Also, the higher the HS2 temperature, the higher the Young's modulus f ₍₁₀₅₎ in the longitudinal direction at 105 ° C. tends to be higher, and f ₍₁₀₅₎ may be insufficient below 155 ° C. When the temperature exceeds 165 ° C., the polymer around the pores may melt at a high temperature, and the air permeability may be lowered. From the viewpoint of achieving both air permeability and mechanical strength, the temperature of the HS2 zone is more preferably 160 to 165 ° C.

  In the present invention, the heat treatment time in the HS2 zone is preferably from 0.1 second to 10 seconds from the viewpoint of mechanical strength, physical property unevenness in the width direction, and compatibility between flatness and productivity. The film after the heat setting step is made into a product by removing the ears gripped by the clips of the transverse stretching machine.

  Since the porous polyolefin film of the present invention is excellent in strength and heat resistance, it can be used for packaging products, sanitary products, agricultural products, building products, medical products, separation membranes, light diffusion plates, reflective sheets, In particular, because the Young's modulus at the drying temperature is high and the difference in Young's modulus between the normal temperature and the drying temperature is small, wrinkles and flatness are improved in the pre-drying process of LIB and EDLC assembly. It can use suitably as a separator for electrical storage devices. Moreover, it can use suitably also as a base material for the heat-resistant separator formed by coating and drying a ceramic or a heat-resistant resin layer. The separator made of the porous polypropylene film of the present invention is provided between the positive electrode and the negative electrode of the electricity storage device, and can efficiently permeate ions in the electrolytic solution while preventing contact between the electrodes. Here, examples of the electricity storage device include a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery, a lithium ion capacitor, and an electric double layer capacitor. Since such an electricity storage device can be repeatedly used by charging and discharging, it can be used as a power supply device for industrial devices, household equipment, electric vehicles, hybrid electric vehicles, and the like. The electricity storage device using the separator using the porous film of the present invention can be suitably used for power supplies of industrial equipment and automobiles because of the excellent characteristics of the separator.

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

(1) Film thickness A total of 10 arbitrary positions were measured with a contact-type film thickness meter, Mitsutyo Lightmatic VL-50A (10.5 mmφ carbide spherical surface probe, measurement load 0.06 N), and the average The value was taken as the thickness of the porous polyolefin film.

(2) Young's modulus in the longitudinal direction at 23 ° C .; f ₍₂₃₎
The measurement was performed according to the measurement method defined in JIS K7127 (1999). A porous polyolefin film was cut into a rectangle having a length of 150 mm in the film forming direction and a length of 10 mm in the width direction, and used as a sample. Using a tensile tester (Orientec Tensilon UCT-100), the tensile test was performed in the longitudinal direction of the film under an atmosphere of 23 ° C. and 65% RH at an initial chuck distance of 50 mm and a tensile speed of 300 mm / min. . The measurement was performed 5 times while changing the sample, and the average value of Young's modulus was obtained.
The film thickness was measured as follows. Cut out into a rectangular shape with a length of 150 mm and a width of 10 mm. Contact type film thickness meter Mitutoyo's Lightmatic VL-50A (10.5 mmφ super hard spherical surface probe, measurement at an arbitrary 5 positions within the initial chuck distance of 50 mm. The load was measured at 0.06 N), and the average value was defined as the thickness of the porous polyolefin film.

(3) Young's modulus in the longitudinal direction at 105 ° C .; f ₍₁₀₅₎
The measurement was performed according to the measurement method defined in JIS K7127 (1999). A sample obtained by cutting the porous polyolefin film to the same size as in (2) above is set in a tensile tester (Orientec Tensilon UCT-100), and the chuck is put into an oven heated to 105 ° C. for 1 minute. After heating, the tensile test was performed in the longitudinal direction of the film at an initial chuck distance of 50 mm and a tensile speed of 300 mm / min. The measurement was performed 5 times while changing the sample, and the average value of Young's modulus was obtained.
The film thickness was measured by the same method as in (2) above.

(4) β crystal forming ability 5 mg of polypropylene in the porous polyolefin film was sampled on an aluminum pan and measured using a differential scanning calorimeter (RDC220 manufactured by Seiko Denshi Kogyo). First, the temperature is raised from room temperature to 260 ° C. at a rate of 10 ° C./minute (first run) in a nitrogen atmosphere, held for 10 minutes, and then cooled to 20 ° C. at a rate of 10 ° C./minute. After holding for 5 minutes, the melting peak observed when the temperature is raised again at 10 ° C./min (second run) is the melting peak of the β crystal at 145 ° C. to 157 ° C., 158 ° C. The melting at which the peak is observed is defined as the melting peak of the α crystal, and the melting heat amount of the α crystal is obtained from the baseline and the area of the region surrounded by the peak drawn from the flat portion on the high temperature side. Is the ΔHα, and the heat of fusion of the β crystal is ΔHβ, the value calculated by the following formula is the β crystal forming ability. The heat of fusion was calibrated using indium.
β crystal forming ability (%) = [ΔHβ / (ΔHα + ΔHβ)] × 100
In addition, the β crystal fraction in the state of the sample can be calculated by calculating the abundance ratio of the β crystal in the same manner from the melting peak observed in the first run.

(5) Air permeability resistance A square having a size of 100 mm × 100 mm was cut out from the porous polyolefin film and used as a sample. Using a JIS P 8117 (1998) B-type Gurley tester, the permeation time of 100 ml of air was measured at 23 ° C. and a relative humidity of 65%. The measurement was performed three times with the sample changed, and the average value of the permeation time was defined as the air permeability of the film. In addition, it can confirm that the through-hole is formed in the film that this air permeability value is a finite value.

(6) 105 ° C. thermal shrinkage (width direction)
Five rectangles each having a size of 10 mm × 200 mm were cut out from the porous polyolefin film and used as samples. In addition, the length direction of 200 mm was match | combined with the width direction of the film. Mark the position 25 mm from both ends of the sample to make the test length 150 mm (l ₀ ). Next, it is hung in an oven kept at 105 ° C. with a load of 3 g, taken out after heating for 1 hour, cooled at room temperature, measured for dimensions (l ₁ ), and calculated by the following formula. The average value was defined as the heat shrinkage rate.
Thermal contraction rate = {(l ₀ −l ₁ ) / l ₀ } × 100 (%)

(7) Wrinkle occurrence (23 ° C)
A porous polyolefin film is sampled at 300 mm in the longitudinal direction and 200 mm in the width direction to prepare Sample 1 of the porous polyolefin film. As shown in FIG. 1, both end portions 30 mm in the longitudinal direction of the sample 1 are sandwiched between two metal plates 2 in full width, and the lower metal plate 2 and the weight 3 in the longitudinal direction are combined so that a load of 2 kgf is obtained. Apply a load. At this time, the two metal plates 2 are fixed so that the position of the separator does not shift when suspended. The sample was lifted in an atmosphere of 23 ° C. and 65% RH, and the degree of occurrence of wrinkles was determined according to the following criteria in 10 seconds of observation. ○, Δ is acceptable ○: No wrinkles can be confirmed Δ: One or two wrinkles can be confirmed ×: Three or more wrinkles

(8) Wrinkle generation degree (105 ° C)
In the same manner as in (7) above, a sample with a load of 0.5 kgf was suspended in a gear oven heated to an atmosphere of 105 ° C., and the degree of wrinkle generation was determined based on the following criteria in 10 seconds of observation. ○, Δ is acceptable ○: No wrinkles can be confirmed Δ: One or two wrinkles can be confirmed ×: Three or more wrinkles

(9) Wrinkle generation degree when passing through heating oven When a roll sample having a width of 300 mm is prepared, unrolled at 23 ° C., and passed through a tunnel-shaped oven having an internal temperature of 105 ° C., the wrinkle generation state of the sample at the outlet of the oven Was judged according to the following criteria. The transport tension was 0.5 kgf, the oven length was 2 m, and the transport speed was 15 m / min. Guide rolls were set at the entrance and exit of the tunnel oven. The sample was passed through a tunnel oven in advance, and was maintained in a state where it was transported for 15 seconds after the start of transportation in order to stabilize the transportation state, and then judged when it was passed through for 20 seconds. ○ and △ are acceptable.
○: No wrinkles can be confirmed Δ: One or two wrinkles can be confirmed ×: Three or more wrinkles

(10) Measurement of dispersion diameter (domain diameter) of different components in cast sheet Using a microtome method, an ultrathin section having a cross section (TD / ZD cross section) in the width direction-thickness direction of the cast sheet was collected. The collected sections were stained with RuO ₄ and the cross section was observed using a transmission electron microscope (TEM) under the following conditions. At this time, for example, the ethylene-α-olefin polymer (B) having lower crystallinity than polypropylene resin is dyed blacker than polypropylene.
-Apparatus: Transmission electron microscope (TEM) H-7100FA manufactured by Hitachi, Ltd.
・ Acceleration voltage: 100 kV
-Observation magnification: 20,000 times.
Images obtained by continuously observing from one surface of the cast sheet to the other surface in the thickness direction were collected. A straight line is drawn on the obtained image at an interval of 1 μm parallel to the thickness direction of the cast sheet, and the dispersion diameter of all the ethylene-α-olefin polymers (B) existing between the two straight lines is determined. Measured (unit: nm). The dispersion diameter existing between the two straight lines was averaged, the average value in the thickness direction was calculated, and the obtained average dispersion diameter was taken as the dispersion diameter of the ethylene-α-olefin polymer (B).

Example 1
As the polypropylene resin (A), 99.5 parts by mass of Homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd. having a melting point of 165 ° C. and an MFR of 7.5 g / 10 min, N, N′-dicyclohexyl-2 which is a β crystal nucleating agent , 6-Naphthalenedicarboxyamide (manufactured by Shin Nippon Rika Co., Ltd., NU-100), 0.3 parts by mass, and IRGANOX 1010 and IRGAFOS168 by Ciba Specialty Chemicals, which are antioxidants, each by 0.1 part by mass The raw material is fed from the weighing hopper to the twin screw extruder so that the mixture is mixed at this ratio, melt kneaded at 300 ° C., discharged from the die in a strand shape, cooled and solidified in a 25 ° C. water tank, and chip-shaped. To obtain a polypropylene composition (I).

  Next, 64.8 parts by mass of homopolypropylene FLX80E4 as the polypropylene resin (A), and ethylene-α-octene-1 copolymer (Deng Chemical “Engage” as the ethylene / α-olefin copolymer (B) (Registered Trademark) "8411, Melt Index: 18 g / 10 min) 30 parts by mass, Dispersant (C) Olefin Crystal / Ethylene Butylene / Olefin Crystal Block Polymer (CEBC)“ DYNARON ”(Registered Trademark) (Type name: 6200P), and 0.1 parts by mass of “Irganox (registered trademark)” 1010 and “Irgaphos (registered trademark)” 168 manufactured by Ciba Specialty Chemicals, which are antioxidants. Raw material from weighing hopper to twin screw extruder to be mixed at this ratio Feeding, and were melt-kneaded at 240 ° C., is ejected from the die into strands, it cooled and solidified at 25 ° C. water bath, was obtained by cutting into chips the polypropylene composition (II).

  90 parts by mass of the obtained polypropylene composition (I) and 10 parts by mass of the polypropylene composition (II) were dry blended, supplied to a single screw melt extruder, melt extruded at 220 ° C., and sintered at 25 μm cut. After removing the foreign matter with a filter, it was discharged from a T-die onto a cast drum whose surface temperature was controlled at 120 ° C. to obtain an unstretched sheet. The domain diameter in the unstretched sheet was 75 nm. In addition, as for the domain diameter, many domains of about 80 nm were observed near the surface layer in the thickness direction, and many domains of about 70 nm were observed in the central part. Next, preheating was performed using a ceramic roll heated to 125 ° C., and the film was stretched 5.0 times in the longitudinal direction of the film. Next, with the draw speed of 105% applied to the roll speed after the longitudinal stretching, the end of the film was held with a clip and introduced into a horizontal stretching machine, and 5.0 times at 150 ° C., a stretching speed of 1,800% / Stretched in minutes. The heat treatment is performed at 160 ° C. in the HS1 zone while holding the width direction as it is, and the heat treatment is subsequently performed at 162 ° C. while relaxing 20% in the width direction. Finally, the heat treatment is performed at 162 ° C. in the HS2 zone while holding the width direction. Heat treatment was performed to obtain a porous polypropylene film having a thickness of 12 μm.

(Example 2)
As the polypropylene resin (A), 54.8 parts by mass of homopolypropylene FLX80E4, and as the ethylene-α-olefin-based polymer (B), ethylene-octene-1 copolymer (“Engage (registered trademark)” 8411 manufactured by Dow Chemical, Melt index: 18 g / 10 min) as 30 parts by mass, dispersant (C) as olefin crystal / ethylene butylene / olefin crystal block polymer (CEBC) “DYNARON (registered trademark)” manufactured by JSR (type name: 6200P) 15 parts by weight, and 0.1 parts by weight of “Irganox (registered trademark)” 1010 and “Irgaphos (registered trademark)” 168 manufactured by Ciba Specialty Chemicals, which are antioxidants, are mixed in this ratio. Feed the raw material from the weighing hopper to the twin screw extruder, Melt kneading was carried out at 0 ° C., the strand was discharged from the die, solidified by cooling in a water bath at 25 ° C., and cut into chips to obtain a polypropylene composition (III). 10 parts by mass of the obtained polypropylene composition (III) and 90 parts by mass of the polypropylene composition (I) used in Example 1 were dry blended and supplied to a uniaxial melt extruder. Under the conditions, a porous polypropylene film having a thickness of 12 μm was obtained.

(Examples 3, 4, and 5)
In the production conditions shown in Table 1, the MD temperature during stretching from the conditions of Example 1 was 103% for the roll speed after longitudinal stretching (Example 3), the MD stretch ratio was 5.5 times (Example 4), The transverse draw ratio was changed to 6.5 times (Example 5), and a 12 μm thick porous polypropylene film was obtained.

(Comparative Example 1)
As the polypropylene resin (A), 69.8 parts by mass of homopolypropylene FLX80E4, and as the ethylene-α-olefin polymer (B), an ethylene-octene-1 copolymer (“Engage (registered trademark)” 8411 manufactured by Dow Chemical Co., Ltd. , Melt Index: 18 g / 10 min), 30 parts by mass, and 0.1 parts by mass of “Irganox (registered trademark)” 1010 and “Irgaphos (registered trademark)” 168 manufactured by Ciba Specialty Chemicals, which are antioxidants. The raw material is supplied from the weighing hopper to the twin screw extruder so that the parts are mixed at this ratio, melt kneaded at 240 ° C., discharged from the die in a strand shape, cooled and solidified in a 25 ° C. water tank, and chips The polypropylene composition (IV) was obtained by cutting into a shape. 10 parts by mass of the obtained polypropylene composition (IV) and 90 parts by mass of the polypropylene composition (I) used in Example 1 were dry blended and supplied to a uniaxial melt extruder. The draw rate with respect to the roll speed after stretching is 100%, the relaxation rate after transverse stretching is 15%, the HS1, Rx zone, and HS2 zone are each changed to 160 ° C., and the porosity is substantially 12 μm and contains no dispersant. A conductive polypropylene film was obtained. The domain diameter in the unstretched sheet was 120 nm. In addition, with regard to the domain diameter, many domains of about 100 nm were observed near the surface layer in the thickness direction, and many domains of about 150 nm were observed in the central part. The film of this comparative example had a large difference between the Young's modulus in the longitudinal direction at 105 ° C. and the Young's modulus in the longitudinal direction at 23 ° C.

(Comparative Example 2)
In the production conditions shown in Table 1, the HS1 zone, the Rx zone, and the HS2 zone after transverse stretching were each changed to 155 ° C. from the conditions of Example 1, the relaxation treatment rate was changed to 5%, and a porous polypropylene film having a thickness of 12 μm was obtained. Obtained. The film of Comparative Example 2 was a film having an insufficient Young's modulus in the longitudinal direction at 105 ° C. and a very large difference from the Young's modulus at 23 ° C.

  In the examples satisfying the requirements of the present invention, not only are the air permeability and thermal dimensional stability excellent, but also the Young's modulus in the longitudinal direction at 105 ° C. is high and the Young's modulus difference in the longitudinal direction at 23 ° C. is small. It can be considered that it can be suitably used as a separator for a battery. On the other hand, in the comparative example, the Young's modulus in the longitudinal direction at 105 ° C. is insufficient, and the difference from the Young's modulus at 23 ° C. is so large that it is difficult to use as a separator for an electricity storage device.

  The porous polyolefin film of the present invention can be suitably used as an electrical storage device separator for automobiles because wrinkles and flatness are improved in the pre-drying process of LIB, LIC, and EDLC assembly. .

1: Sample 2: Metal plate 3: Weight

Claims (7)

The relationship between the Young's modulus f ₍₂₃₎ (MPa) in the longitudinal direction at 23 ° C. and the Young's modulus f ₍₁₀₅₎ (MPa) in the longitudinal direction at 105 ° C. satisfies the following formulas (1) and (2). A porous polyolefin film characterized by
f ₍₁₀₅₎ > 80 (1)
f ₍₂₃₎ -f ₍₁₀₅₎ <450 (2) The relationship between the longitudinal Young's modulus f ₍₂₃₎ (MPa) at ₂₃ ° C. and the longitudinal Young's modulus f ₍₁₀₅₎ (MPa) at 105 ° C. satisfies the following formulas (1) and (3). A featured porous polyolefin film.
f ₍₁₀₅₎ > 80 (1)
f ₍₂₃₎ / f ₍₁₀₅₎ <6 (3)   The porous polyolefin film according to claim 1 or 2, wherein the thermal shrinkage in the width direction at 105 ° C is 5% or less.   Air permeability resistance is 10-200 seconds / 100ml, The porous polyolefin film according to any one of claims 1 to 3 characterized by things.   The porous polyolefin film according to any one of claims 1 to 4, wherein an air resistance per thickness is 20 seconds / 100 ml / µm or less.   The porous polyolefin film according to any one of claims 1 to 5, comprising a polypropylene having a β-crystal forming ability of 40% or more as a main component. In an electricity storage device provided with a separator that is provided between a positive electrode and a negative electrode and transmits ions in an electrolyte while preventing contact between the two,
The said separator was formed using the porous polyolefin film as described in any one of Claims 1-6, The electrical storage device characterized by the above-mentioned.

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