JP5354132B2 - Porous polypropylene film and power storage device - Google Patents

Abstract

Provided are a porous polypropylene film with excellent productivity, air permeability, mechanical properties, and heat resistance, and an electrical storage device. The present invention is a porous polypropylene film including a polypropylene resin having beta-crystal-forming capability, characterized in having a thickness of 10-30 mum, a hole rate of 55-85%, air-permeability resistance of 70-300 seconds/100 ml, puncture strength per 1 mum thickness of 0.18-0.50 N/mum, and a thermal contraction rate of 12% or less in the width direction when processed for 60 minutes at 135°C.

Description

  The present invention relates to a porous polypropylene film excellent in productivity, air permeability, mechanical properties, and heat resistance, and an electricity storage device using the porous polypropylene film as a separator for an electricity storage device.

  Porous polypropylene films are being considered for use in a wide range 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 these, a porous polypropylene film is suitable as a separator for lithium ion batteries widely used in mobile devices such as notebook personal computers, mobile phones, and digital cameras, electric vehicles, and hybrid vehicles.

  The characteristics required for porous films for separators include high productivity and low cost, excellent air permeability and high output characteristics when used as a battery, and piercing as an index of dendrite resistance. It is necessary that the strength is high and that the battery is excellent in safety, and further, the heat resistance of the porous film is high, and the safety is ensured even if the temperature of the battery rises during an abnormality. However, in order to increase the mechanical properties and heat resistance, it is necessary to increase the amount of resin per separator thickness to improve the strength, and the porosity and air permeability are reduced. It was difficult to satisfy the characteristics and safety at the same time.

  Further, in recent years, a layer made of inorganic particles or heat-resistant resin is coated on the surface of the porous film to study heat resistance, but when the Young's modulus or elongation at break of the porous film is low, Since wrinkles may occur or break when the coating is conveyed, high mechanical strength is required. However, it was difficult to satisfy productivity, air permeability, and mechanical strength at the same time.

  Various proposals have been made as methods for making a polypropylene film porous. Porous methods can be broadly classified into wet methods and dry methods. In the wet method, polyethylene or polypropylene is used as the matrix resin, and the extractables are added and mixed as additives to form a sheet, and then only the additive is extracted using the good solvent of the extractables in the matrix resin. In this method, various proposals have been made (for example, see Patent Document 1). When this method is used, the resin viscosity at the time of extrusion can be lowered by containing a solvent, and film formation with a high molecular weight raw material becomes possible, so that mechanical properties such as puncture strength and tensile strength are improved. The solvent extraction process requires time and labor, and it is difficult to improve productivity.

  On the other hand, as a dry method, for example, by adopting low temperature extrusion and high draft ratio at the time of melt extrusion, the lamella structure in the film before stretching is controlled, and this is uniaxially stretched to cause cleavage at the lamella interface And a method of forming voids (so-called lamellar stretching method) has been proposed (see, for example, Patent Document 2). The method does not require an extraction step, and thus has higher productivity than the wet method. However, since it is uniaxial stretching, it is difficult to widen the product, and it is necessary to reduce the stretching speed. It was difficult. In addition, since the mechanical properties in the film forming direction and the width direction are greatly different due to the uniaxial stretching, there are cases where improvement is required such as low strength in the width direction and easy tearing in the film forming direction.

  As a porous polypropylene film formed by biaxial stretching by a dry method, the difference in crystal density between crystals of polymorphs of α-type crystals (α crystals) and β-type crystals (β crystals), which are polymorphs of polypropylene, and crystals Many proposals have been made of a so-called β crystal method in which voids are formed in a film using transition (see, for example, Patent Documents 3 to 12). This method is excellent in productivity because it is formed by dry biaxial stretching, but the resin viscosity at the time of extrusion is high, so there is an upper limit on the molecular weight of the polypropylene resin, and mechanical properties such as puncture strength and tensile strength are high. It was difficult to do. Furthermore, in order to increase the mechanical properties, it is necessary to form a film having a low porosity and a high air resistance, and it is difficult to achieve a balance with the air permeability. For example, Patent Document 3 describes a porous polypropylene film having high puncture strength. However, since the porosity is high and the thickness is large, the air permeability is poor, and the output characteristics may be insufficient. On the other hand, Patent Documents 4 to 11 describe porous polypropylene films having good air permeability. However, although these porous polypropylene films are excellent in output characteristics, the puncture strength is low and the dendrite resistance may be lowered. Patent Document 12 also describes a porous polypropylene film having good air permeability in the β crystal method. However, these porous polypropylene films have a high porosity in order to improve the air permeability, and the mechanical strength and thermal characteristics may be deteriorated in some cases.

Japanese Patent Laid-Open No. 55-131028 Japanese Patent Publication No.55-32531 JP 2000-30683 A JP 2008-307890 A JP 2008-311220 A JP 2009-39910 A JP 2009-45771 A JP 2010-111182 A JP 2010-171003 A International Publication No. 2010/147149 International Publication No. 2010/008003 International Publication No. 2007/046225

  An object of the present invention is to solve the above-described problems. That is, the object is to provide a porous polypropylene film excellent in productivity, output characteristics and safety when used as a battery separator.

  In order to solve the above-described problems and achieve the object, the porous polypropylene film of the present invention is a porous polypropylene film containing a polypropylene resin having β-crystal forming ability, and has a thickness of 10 to 30 μm and a porosity. Is 55 to 85%, air permeability is 70 to 300 seconds / 100 ml, puncture strength per 1 μm thickness is 0.18 to 0.50 N / μm, and heat shrinkage in the width direction when treated at 135 ° C. for 60 minutes. It is characterized by being 12% or less.

  Since the porous polypropylene film of the present invention is excellent in productivity, air permeability, mechanical strength, and heat resistance, it exhibits excellent ionic conductivity suitable for a separator for an electricity storage device, and is also safe and inexpensive. It can be suitably used as a separator.

FIG. 1 is an equivalent circuit used for measuring the separator resistance.

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

  The porous polypropylene 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 a porous polypropylene film having this through-hole, it is preferable to use the β crystal method described later, since it can be formed with high productivity by biaxial stretching.

  The porous polypropylene film of the present invention has a total film thickness of 10 to 30 μm. If the total thickness is less than 10 μm, the film may break during use, and if it exceeds 30 μm, the air permeability decreases and the separator is used as a separator. May become too high, making it impossible to obtain a high energy density. The total film thickness is more preferably 12 to 25 μm, and still more preferably 15 to 20 μm.

  The porous polypropylene film of the present invention has a porosity of 55 to 85%. When the porosity is less than 55%, the electrical resistance may increase particularly when used as a separator for a high-power battery. On the other hand, when the porosity exceeds 85%, mechanical strength such as puncture strength of a film, which is an index of dendrite resistance, may be lowered. From the viewpoint of achieving both excellent battery characteristics and strength, the porosity of the film is more preferably 57 to 80%, and particularly preferably 60 to 75%.

  The porosity is determined by the amount of β crystal nucleating agent, ethylene / α-olefin copolymer (B) and dispersant (C) added later, the temperature of the cast drum, the draw ratio and temperature in the longitudinal direction, and the heat treatment step. It is possible to control by controlling the temperature and time of the heat and the relaxation rate in the relaxation zone within the ranges described later.

  The porous polypropylene film of the present invention has an air resistance of 70 to 300 seconds / 100 ml. More preferably, it is 80-250 seconds / 100 ml, More preferably, it is 100-200 seconds / 100 ml. If the air permeability resistance is less than 70 seconds / 100 ml, mechanical strength such as puncture strength of the film, which is an index of dendrite resistance, may be lowered. When the air resistance exceeds 300 seconds / 100 ml, the output characteristics may be deteriorated particularly when used as a separator for a high-power battery.

  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 polypropylene film of the present invention has a puncture strength of 0.18 to 0.50 N / μm per 1 μm thickness measured according to JIS Z 1707 (1997) (needle entry speed: 50 mm / min). More preferably, it is 0.20-0.45 N / micrometer, More preferably, it is 0.22-0.40 N / micrometer, Most preferably, it is 0.25-0.35 N / micrometer. The puncture strength is preferably 0.18 N / μm or more from the viewpoint of safety when used as a power storage device separator. From the viewpoint of safety, the higher the puncture strength, the better. However, in the porous polypropylene film obtained by the β crystal method, in order to increase the puncture strength to more than 0.50 N / μm, it is necessary to reduce the porosity and air permeability. In particular, when used as a separator for high-power batteries, the output characteristics may deteriorate.

  The puncture strength is the amount of β crystal nucleating agent, ethylene / α-olefin copolymer (B) and dispersant (C) to be described later, the temperature of the cast drum, the draw ratio and temperature in the longitudinal direction, the transverse draw ratio, 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 polypropylene film of the present invention has a heat shrinkage in the width direction of 12% or less when treated at 135 ° C. for 60 minutes. More preferably, it is 0.5-11%, More preferably, it is 1-10%. When the thermal shrinkage rate at 135 ° C. exceeds 12%, for example, when a shutdown layer containing polyethylene is applied to the surface of the porous polyolefin film of the present invention by coating or the like, the polyethylene melts around 135 ° C. to form pores. When the plug is closed, the porous polyolefin film as the base material may contract and the battery may be short-circuited.

  The heat shrinkage ratio is determined by the addition amount of the β crystal nucleating agent, the ethylene / α-olefin copolymer (B) and the dispersing agent (C) described later, the temperature of the cast drum, the stretching ratio and temperature in the longitudinal direction, and the heat treatment step. It is possible to control by controlling the temperature and time of the heat and the relaxation rate in the relaxation zone within the ranges described later.

  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.

  Conventionally, in a porous polypropylene film obtained by the β crystal method, there are known methods for individually controlling the five physical properties of thickness, porosity, air permeability resistance, puncture strength, and heat shrinkage within the above-mentioned ranges. ing. However, for example, if the thickness is decreased to increase air permeability, the porosity is increased, or the air resistance is decreased, the amount of resin per thickness decreases, the pore structure becomes brittle, and the piercing strength Low thermal conductivity, thermal shrinkage ratio increases, satisfies all five physical properties at the same time, and has high output characteristics and safety when used as a separator with both air permeability and mechanical strength. Could not get. In the extraction method, it is possible to improve the strength by increasing the molecular weight. However, in the β crystal method, which is formed by a dry process, there is a limitation in increasing the molecular weight from the viewpoint of filtration pressure during extrusion. It was difficult to achieve both temper and mechanical strength.

  The β-crystal method is a method of forming a β-crystal of polypropylene on a cast sheet, forming α-crystal fibrils oriented in the film-forming direction by longitudinal stretching, and forming a network while cleaving the fibrils by transverse stretching. This is a method for obtaining a polypropylene film. In the β crystal method, there is room for improvement in the uniformity of cleavage in the transverse stretching, and the same was true for the uniformity of the pore size of the resulting film. In the porous polypropylene film obtained by the β crystal method, in order to improve the puncture strength and the tensile strength, it is necessary to improve the uniformity of the pores and reduce the coarse pores. In the present invention, the pore structure of a porous polypropylene film obtained by a β crystal method, that is, a porous polypropylene film containing a polypropylene resin (A) having β crystal forming ability is remarkably obtained by adopting raw materials and film forming conditions described later. It has been made uniform to achieve both air permeability, mechanical strength, and heat resistance. In addition, a cast sheet shows the unstretched sheet | seat which shape | molded the polypropylene composition containing the molten polypropylene resin (A) on the cast drum.

  As a method for improving air permeability in a porous polypropylene film obtained by the β crystal method, the first component is a polypropylene resin (A) and the second component is a domain that is not completely compatible with the polypropylene resin (A). There is known an example using an ethylene / α-olefin copolymer (B) that promotes fibril cleavage by forming a polymer (for example, International Publication No. 2007/046225 pamphlet). However, when this method is used, the air permeability is improved, but the uniformity of the pore size is insufficient, and it is difficult to achieve high strength at the same time.

  In the present invention, the dispersion diameter of the domain in the TD / ZD cross section of the ethylene / α-olefin copolymer (B), which is the second component that is not completely compatible with the polypropylene resin (A) in the cast sheet, is less than 100 nm. Therefore, it is preferable because the pore structure is made uniform and both high air permeability and mechanical strength can be achieved. Specifically, the domains of the polypropylene resin (A) having the ability to form β crystals, the ethylene / α-olefin copolymer (B), and the ethylene / α-olefin copolymer (B) are fine and uniform. It is preferable to form a propylene composition containing a dispersant (C) for dispersion in a film under the film forming conditions described later, since the pore structure is uniformized and both high air permeability and mechanical strength can be achieved. Also, the heat shrinkage rate can be improved. This is considered to be due to the uniform relaxation of the pore structure and uniform relaxation in the heat setting step after transverse stretching. Here, the TD / ZD cross section refers to 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.

Next, the raw materials used for the porous polypropylene film of the present invention will be described.
In order to form a through-hole in the film using the β crystal method, it is preferable that the β crystal forming ability of the polypropylene composition is 40 to 90%. 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 a film with low permeability is 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 to be used extremely high. Industrial practical value is low, such as a decrease in stability. Industrially, β-crystal forming ability is preferably 60 to 85%, 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 polypropylene film may be lowered. If it exceeds 0.5 mass%, coarse voids are formed, and the puncture strength and tensile strength may be reduced.

  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 of the polypropylene resin (A) is less than 90%, the crystallinity of the resin is lowered, and the film-forming property may be deteriorated or the film strength may be insufficient.

  As the polypropylene resin (A) for forming the porous polypropylene film of the present invention, it is possible to use homopolypropylene as well as from the viewpoint of stability in the film forming process, film forming properties, and uniformity of physical properties. A resin obtained by copolymerizing polypropylene with an α-olefin component such as an ethylene component, butene, hexene, or octene in an amount of 5% by mass or less, more preferably 2.5% by mass or less can also be used. The polypropylene resin (A) may be a combination of homopolypropylene and / or polypropylene copolymer and high molecular weight polypropylene. The polypropylene resin (A) preferably contains a high molecular weight polypropylene in the range of 0.5 to 30% by mass from the viewpoint of improving the strength. The high molecular weight polypropylene is a polypropylene having an MFR of 0.1 to 2 g / 10 min. For example, polypropylene resin D101 manufactured by Sumitomo Chemical Co., Ltd., polypropylene resins E111G, B241, E105GM manufactured by Prime Polymer Co., etc. can be preferably used.

  The polypropylene composition for forming the porous polypropylene film of the present invention is biaxially stretched to form through-holes, from the viewpoint of improving void formation efficiency during stretching and improving air permeability by increasing the pore diameter. 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 copolymerized polyethylene include commercially available resins such as “Engage (registered trademark)” (type names: 8411, 8452, 8100, etc.) manufactured by Dow Chemical.

  The ethylene / α-olefin copolymer (B) is contained in an amount of 10% by mass or less when the entire polypropylene composition constituting the porous polypropylene film of the present invention is 100% by mass, from the viewpoint of improving air permeability. To preferred. From the viewpoint of the mechanical properties of the film, it is more preferably 1 to 7% by mass, and more preferably 1 to 4% by mass.

  The polypropylene composition for forming the porous polypropylene film of the present invention includes an ethylene / α-olefin copolymer (B) in addition to the polypropylene resin (A) and the ethylene / α-olefin copolymer (B). It is preferable to contain the dispersant (C) because the pore structure is made uniform and both high air permeability and mechanical strength can be achieved.

  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, in the pamphlet of International Publication No. 2007/046225, an ethylene / α-olefin copolymer incompatible with polypropylene resin is melted at a predetermined temperature, a compatibilizing agent is added, or a high shearing force at the time of 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 compatibilizing agent, and a polypropylene composition containing the polypropylene resin (A) and the ethylene / α-olefin copolymer (B) is prepared at a predetermined temperature. 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 uniform only by melting, extruding with high shearing force, etc. is there. 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 polypropylene 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.

  In the polypropylene composition forming the porous polypropylene film of the present invention, 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 polypropylene composition for forming the porous polypropylene 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 polypropylene film of the present invention preferably has a puncture strength of 4.0 to 8.0N. More preferably, it is 4.2-7.0N, More preferably, it is 4.5-6.0N. When the puncture strength is 4.0 N or more, it can be preferably used as a separator for a high-power, high-capacity electricity storage device that requires particularly high safety such as for vehicles. From the viewpoint of safety, the higher the puncture strength, the better. However, in order to make the puncture strength higher than 8.0 N in the porous polypropylene film obtained by the β crystal method, it is necessary to lower the porosity and air permeability. In particular, when used as a separator for high-power batteries, the output characteristics may deteriorate.

  The puncture strength is determined by setting the addition amount of the β crystal nucleating agent, the ethylene / α-olefin copolymer (B) and the dispersing agent (C) within the above range, the temperature of the cast drum, the draw ratio and the temperature in the longitudinal direction. 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.

In the porous polypropylene film of the present invention, the relationship between porosity ε (%), thickness T (μm), and puncture strength S (N) is expressed by the following formula (1) from the viewpoint of achieving both air permeability and mechanical strength. It is preferable to satisfy.
S / (T × (100−ε) / 100) ≧ 0.45 (1)
If the puncture strength per amount of resin in the thickness direction, which is the value on the left side of the equation (1), is less than 0.45 N / μm, the air permeability of the film is low and the output characteristics deteriorate when used as a separator, or the puncture strength May decrease. The puncture strength per resin amount in the thickness direction is more preferably 0.5 N / μm or more.

  The porous polypropylene film of the present invention preferably has a tensile strength in the width direction of 60 to 200 MPa. More preferably, it is 70-180 MPa, More preferably, it is 80-160 MPa. If the tensile strength is less than 60 MPa, wrinkles are likely to occur in the transport process during film formation, and the yield may be reduced when used as a separator for an electricity storage device. From the viewpoint of safety, the higher the tensile strength, the better. However, in order to make the tensile strength larger than 200 MPa in the porous polypropylene film obtained by the β crystal method, it is necessary to lower the porosity and air permeability. When used as a separator for high-power batteries, output characteristics may deteriorate.

  For the tensile strength in the width direction, the addition amount of the β crystal nucleating agent, the ethylene / α-olefin copolymer (B) and the dispersing agent (C) is within the above range, the temperature of the cast drum, and the stretching in the longitudinal direction. The magnification and temperature, the stretching ratio in the width direction, and the temperature and time in the heat treatment step can be controlled within the ranges described later.

  The porous polypropylene film of the present invention preferably has a Young's modulus in the width direction of 0.5 to 2.0 GPa. More preferably, it is 0.6-1.8 GPa, More preferably, it is 0.7-1.6 GPa. When the Young's modulus in the width direction is less than 0.5 GPa, when tension is applied in the film-forming direction during film conveyance in film formation or coating, the film may be easily deformed in the width direction and wrinkled. From the viewpoint of film formation stability, the higher the Young's modulus in the width direction, the better. However, in order to make the Young's modulus in the width direction larger than 2.0 GPa in the porous polypropylene film obtained by the β crystal method, The air permeability needs to be lowered, and the output characteristics may be deteriorated particularly when used as a separator for a high-power battery. In general, when the Young's modulus of the film is increased, the elongation at break may be lowered.

  The Young's modulus in the width direction is determined by adjusting the addition amount of the β crystal nucleating agent, the ethylene / α-olefin copolymer (B) and the dispersing agent (C), the temperature of the cast drum, and the stretching in the longitudinal direction. The magnification and temperature, the stretching ratio in the width direction, and the temperature and time in the heat treatment step can be controlled within the ranges described later.

  The porous polypropylene film of the present invention preferably has a breaking elongation in the width direction of 20 to 100%. More preferably, it is 25-100%, More preferably, it is 30-100%. When the elongation at break is less than 20%, film breakage tends to occur in the film forming process, the battery assembling process, etc., and the film forming stability and productivity may be lowered. From the viewpoint of film formation stability, the higher the breaking elongation, the better. However, in order to make the breaking elongation in the width direction larger than 100% in the porous polypropylene film obtained by the β crystal method, the porosity and air permeability In particular, when used as a separator for high-power batteries, the output characteristics may deteriorate. In general, when the breaking elongation of the film is increased, the Young's modulus may be decreased.

  The breaking elongation in the width direction is determined by adjusting the addition amount of the β crystal nucleating agent, the ethylene / α-olefin copolymer (B) and the dispersing agent (C), the temperature of the cast drum, and the longitudinal direction. The stretching ratio and temperature, the stretching ratio and stretching temperature in the width direction, and the temperature and time in the heat treatment step can be controlled within the ranges described below.

  The porous polypropylene film of the present invention preferably has a tensile strength in the film forming direction of 60 to 200 MPa. More preferably, it is 70-180 MPa, More preferably, it is 80-160 MPa. When the tensile strength is less than 60 MPa, the film is likely to be broken in the conveying step during film formation, and the yield may be lowered when used as a separator for an electricity storage device. From the viewpoint of safety, the higher the tensile strength, the better. However, in order to make the tensile strength larger than 200 MPa in the porous polypropylene film obtained by the β crystal method, it is necessary to lower the porosity and air permeability. When used as a separator for high-power batteries, output characteristics may deteriorate.

  The tensile strength in the film forming direction is determined by adjusting the addition amount of the β crystal nucleating agent, the ethylene / α-olefin copolymer (B) and the dispersing agent (C), the temperature of the cast drum, and the longitudinal direction. The stretching ratio and temperature, the stretching ratio in the width direction, the relaxation rate in the heat treatment step, the temperature and the time can be controlled within the ranges described below.

  The porous polypropylene film of the present invention preferably has a Young's modulus in the film forming direction of 0.4 to 2.0 GPa. More preferably, it is 0.45-1.8 GPa, Most preferably, it is 0.5-1.6 GPa. If the Young's modulus in the film forming direction is less than 0.4 GPa, the film is likely to be deformed by the tension in the film forming process, and as a result, wrinkles may be easily formed. From the viewpoint of safety, higher Young's modulus is preferable, but in order to make Young's modulus larger than 2.0 GPa in the porous polypropylene film obtained by the β crystal method, it is necessary to lower the porosity and air permeability. In particular, when used as a separator for high-power batteries, the output characteristics may deteriorate.

  The Young's modulus in the film forming direction is determined by adjusting the addition amount of the β crystal nucleating agent, the ethylene / α-olefin copolymer (B) and the dispersing agent (C), the temperature of the cast drum, and the longitudinal direction. The stretching ratio and temperature, the stretching ratio and stretching temperature in the width direction, and the temperature and time in the heat treatment step can be controlled within the ranges described below.

  The porous polypropylene film of the present invention preferably has a breaking elongation in the film forming direction of 50 to 200%. More preferably, it is 60 to 200%, and most preferably 70 to 200%. When the breaking elongation in the film forming direction is less than 50%, film tearing is likely to occur when a transfer tension is applied in the film forming direction in the film forming process or the battery assembling process, and the film forming stability and productivity are increased. May decrease. From the viewpoint of film formation stability, the higher the elongation at break, the better. However, in the porous polypropylene film obtained by the β crystal method, in order to make the elongation at break in the film formation direction larger than 200%, the porosity and permeability It is necessary to lower the temper, and the output characteristics may be deteriorated particularly when used as a separator for a high-power battery. In general, when the breaking elongation of the film is increased, the Young's modulus may be decreased.

  The elongation at break in the film forming direction is determined by adjusting the addition amount of the β crystal nucleating agent, the ethylene / α-olefin copolymer (B) and the dispersing agent (C), the temperature of the cast drum, and the longitudinal direction. The stretching ratio and temperature, the stretching ratio and stretching temperature in the width direction, and the temperature and time in the heat treatment step can be controlled within the ranges described below.

  The porous polypropylene film of the present invention preferably has a maximum pore size of 0.04 to 1.0 μm. More preferably, it is 0.04-0.08 micrometer. When the maximum pore diameter exceeds 1.0 μm, a portion having a large pore diameter exists, so that the Young's modulus and the breaking elongation of the porous polypropylene film may be lowered. When the maximum pore diameter is less than 0.04 μm, the air permeability is lowered, and the air permeability of the present invention may not be obtained.

  For the maximum pore size, the addition amount of the β crystal nucleating agent, the ethylene / α-olefin copolymer (B) and the dispersing agent (C) is within the above range, the temperature of the cast drum, the draw ratio and the temperature in the longitudinal direction. The stretching ratio and stretching temperature in the width direction and the temperature and time in the heat treatment step can be controlled within the ranges described below.

  The porous polypropylene film of the present invention may have a laminated structure for the purpose of imparting various effects. 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. Therefore, when using the above-mentioned ethylene / α-olefin copolymer (B) or dispersant (C), it is possible to take a laminated structure in which a layer using these additives is an inner layer and a layer not used is a surface layer. preferable.

  Below, the manufacturing method of the porous polypropylene 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 polypropylene resin (A), 94.5 parts by mass of commercially available homopolypropylene resin (A1) with an MFR of 8 g / 10 min, 5 parts by mass of commercially available homopolypropylene resin (A2) with an MFR of 0.5 g / 10 min, as a β crystal nucleating agent Feed the raw material from the metering hopper to the twin screw extruder so that 0.3 parts by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxyamide and 0.2 parts by mass of the antioxidant are mixed at this ratio. Melt-kneading is performed, it discharges from a die | dye in strand shape, it cools and solidifies in a 25 degreeC water tank, cuts into a chip shape, and prepares a polypropylene raw material (a). At this time, the melting temperature is preferably 270 to 300 ° C. Similarly, 58.3 parts by mass of the homopolypropylene resin (A1), 6.5 parts by mass of the homopolypropylene resin (A2), and 18 g of a commercially available MFR as an ethylene / α-olefin copolymer (B). / 10 min ultra low density polyethylene resin 30 parts by mass of ethylene / octene-1 copolymer, 5 parts by mass of commercially available CEBC as dispersant (C), 0.2 parts by mass of antioxidant are mixed in this ratio The raw material is fed from the weighing hopper to the twin screw extruder, melt kneaded at 240 ° C., discharged from the die in a strand shape, cooled and solidified in a 25 ° C. water tank, cut into a chip shape, and then the polypropylene raw material (b Prepare).

Next, 89.7 parts by mass of the raw material (a), 10 parts by mass of the raw material (b), and 0.3 parts by mass of the antioxidant were mixed by dry blending and supplied to a single screw melt extruder. Perform melt extrusion at 0 ° 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 a 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 1,000 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 (2). 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, if the shear rate at the die exceeds 1,000 sec ⁻¹ , the domain may be sheared more than necessary, and it may be difficult to control the domain shape.
Shear rate (sec ⁻¹ ) = 6Q / ρWt ² (2)
Q: Flow rate (kg / sec)
ρ: specific gravity (kg / cm ³ )
W: Groove width (cm)
t: Groove gap (cm)

  By making the die shear rate within the preferred range as described above, the domain (olefin copolymer (B) mainly comprising the ethylene / α-olefin copolymer (B) in the cast sheet before stretching is used. It is possible to finely and uniformly disperse the main component (mixed with the dispersant (C)). Here, the average domain diameter (dispersion 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. 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. When the domain diameter exceeds 100 nm, the size of the hole increases and the puncture 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. However, in the present invention, a porous polypropylene film having a highly uniform pore structure is obtained by forming the film in the above range using the dispersant (C) described above. Both air permeability and mechanical strength can be achieved.

  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 1,000 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 in that it is easy to obtain a film having a good balance between air permeability and piercing characteristics, and in particular, after stretching in the longitudinal direction. The film is preferably stretched 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 air permeability may decrease. From the viewpoint of achieving both air permeability and puncture strength, the temperature is more preferably 100 to 130 ° C, and particularly preferably 115 to 125 ° C. As a draw ratio, it is preferable that it is 3-7 times. As the draw ratio is increased, the air permeability is improved. However, if the film is stretched more than 7 times, the film is easily broken in the next transverse stretching process, or the air permeability becomes too high and the puncture strength is lowered. There is a case. From the viewpoint of achieving both air permeability and puncture strength, the draw ratio is more preferably 4.5 to 6 times.

  Next, in order to stretch in the width direction, the film end is held by a tenter type stretching machine and introduced. The transverse stretching temperature 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. From the viewpoint of achieving both air permeability and puncture strength, the temperature is more preferably 145 to 155 ° C. 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 tensile strength in the width direction may decrease. If it exceeds 12 times, the film may break. From the viewpoint of improving tensile strength, the film is more preferably stretched 7 to 11 times, and more preferably 7 to 10 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.

  Following the transverse stretching, a heat treatment step is performed in the tenter. Here, the heat treatment step includes a heat setting zone (hereinafter referred to as HS1 zone) in which heat treatment is performed with the width after transverse stretching, and a relaxation zone (hereinafter referred to as Rx zone) in which heat treatment is performed while relaxing the film by narrowing the width of the tenter. It is preferable that the heat treatment zone (hereinafter referred to as the “HS2 zone”) is subjected to heat treatment with the width after relaxation to be divided into three zones, from the viewpoint of both air permeability and mechanical properties, and 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 puncture strength, or the polymer around the pores melts at high temperatures, resulting in air resistance. May become larger. If it is 150-160 degreeC from a viewpoint of coexistence of air permeability and puncture 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. When the temperature is lower than 155 ° C., the tension of the film after thermal relaxation becomes insufficient, which may cause uneven physical properties in the width direction and a decrease in flatness, or increase the heat shrinkage rate in the width direction. In addition, the higher the HS2 temperature, the higher the puncture strength tends to be. If the temperature is lower than 155 ° C., the puncture strength may be insufficient. 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 puncture 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 0.1 seconds or more and 10 seconds or less from the viewpoint of physical property unevenness in the width direction and flatness and productivity. The film after the heat setting step is removed by slitting the ears gripped by the tenter clip, and wound around the core with a winder to obtain a product.

  The porous polypropylene film of the present invention not only has excellent air permeability and productivity, but also has excellent puncture strength, heat resistance, and extrusion stability, so that it can be used for packaging, hygiene, agricultural, building, medical, and separation. Although it can be used for a film, a light diffusing plate, and a reflective sheet, it can be preferably used particularly as a separator for an electricity storage device. 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, and an electric double layer capacitor such as a lithium ion capacitor. Since such an electricity storage device can be repeatedly used by charging and discharging, it can be used as a power supply device for industrial devices, household equipment, electric vehicles, hybrid electric vehicles, and the like.

  The electricity storage device using the separator using the porous polypropylene film of the present invention can be suitably used for industrial equipment and automobile power supply devices 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) Thickness The thickness of the porous polypropylene film was measured with a contact-type film thickness meter, Mitsutyo Lightmatic VL-50A (10.5 mmφ carbide spherical surface probe, measurement load 0.06 N). The measurement was performed 10 times at different locations, and the average value was taken as the thickness of the porous polypropylene film.

(2) Air permeability resistance A square having a size of 100 mm × 100 mm was cut from a porous polypropylene film and used as a sample. Using a B-type Gurley tester of JIS P 8117 (1998), the permeation time of 100 ml of air was measured for the sample at 23 ° C. and a relative humidity of 65%. The measurement was performed three times by changing the sample, and the average value of the permeation time was taken as the air resistance of the film.

(3) Porosity A porous polypropylene film was cut into a size of 40 mm × 50 mm and used as a sample. Using an electronic hydrometer (SD-120L manufactured by Mirage Trading Co., Ltd.), the specific gravity was measured in an atmosphere at a room temperature of 23 ° C. and a relative humidity of 65%. The measurement was performed three times, and the average value was defined as the specific gravity ρ of the film.
Next, the measured film was hot-pressed at 280 ° C. and 5 MPa, and then rapidly cooled with water at 25 ° C. to prepare a sheet in which pores were completely erased. The specific gravity of this sheet was measured in the same manner as described above, and the average value was defined as the specific gravity (d) of the resin. In the examples described later, the specific gravity d of the resin was 0.91 in any case. From the specific gravity of the film and the specific gravity of the resin, the porosity was calculated by the following formula.
Porosity (%) = [(d−ρ) / d] × 100

(4) Puncture strength Using a universal testing machine (Shimadzu Autograph AG-IS), measurement was performed at 23 ° C. according to JIS Z 1707 (1997). The load applied to the film when the sample broke was read and used as the puncture strength (N). The measurement was performed 5 times for each sample, and the average value was evaluated. The puncture strength (N / μm) per 1 μm thickness was a value divided by the film thickness of the sample before the test measured by the above method (1).

(5) Heat shrinkage rate A porous polypropylene film was cut into a rectangular shape having a length of 150 mm and a width of 10 mm as a sample. In addition, the length direction of 150 mm was matched with the width direction of the film. Mark lines were drawn at 100 mm intervals in the center of the sample, and the distance L ₀ between the mark lines before heating was measured. The upper end of the sample was gripped, a weight of 3 g was applied to the lower end, the sample was suspended in a hot air oven heated to 135 ° C. and left to stand for 60 minutes for heat treatment. After the heat treatment, allowed to cool, after removing the weight, the gauge length L ₁ after heating was measured and the value calculated by the following formula was heat shrinkage. The measurement was performed 5 times for each sample, and the average value is shown in Table 1.
Thermal contraction rate (%) = (L ₀ −L ₁ ) / L ₀ × 100

(6) β crystal forming ability 5 mg of a porous polypropylene film was sampled in an aluminum pan and measured using a differential scanning calorimeter (Seiko Denshi Kogyo RDC220). First, the temperature is raised from room temperature to 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. About the melting peak observed when the temperature is increased (second run) again at 10 ° C./min after holding for 5 minutes, the melting having a peak in the temperature range of 145 to 157 ° C. is the melting peak of β crystal, 158 ° C. or more The melting of the α crystal is the melting peak of the α crystal, the melting peak of the α crystal is taken as the melting peak of the base, and the area of the region surrounded by the peak drawn from the flat portion on the high temperature side. When the heat of fusion of ΔHα and β crystals is ΔHβ, the value calculated by the following formula is β crystal forming ability. The heat of fusion was calibrated using indium.
β crystal forming ability (%) = [ΔHβ / (ΔHα + ΔHβ)] × 100

However, in the above method, there is a melting peak having an apex at 140 to 160 ° C., but when it is unclear whether it is caused by melting of the β crystal, the apex of the melting peak exists at 140 to 160 ° C. The sample prepared under the following conditions has β crystal forming ability when the K value calculated from each diffraction peak intensity of the diffraction profile obtained by 2θ / θ scan by the wide angle X-ray diffraction method is 0.3 or more. Judge that it is.
The sample preparation conditions and the measurement conditions of the wide angle X-ray diffraction method are shown below.

·sample:
The direction of the film is aligned, and the samples are stacked so that the sample thickness after hot press preparation is about 1 mm. This sample is sandwiched between two aluminum plates having a thickness of 0.5 mm, and is hot-pressed at 280 ° C. for 3 minutes to be melted and compressed to make the polymer chain substantially non-oriented. The obtained sheet is crystallized by being immersed in boiling water at 100 ° C. for 5 minutes immediately after being taken out together with the aluminum plate. Then, a sample obtained by cutting a sheet obtained by cooling in an atmosphere at 25 ° C. is used for measurement.
・ Wide-angle X-ray diffraction method measurement conditions:
X-ray generator: 4036A2 (tube type) manufactured by Rigaku Corporation
X-ray source: CuKα ray (using Ni filter)
Output: 40kV, 20mA
Optical system: Rigaku Denki Co., Ltd., pinhole optical system (2mmφ)
Goniometer: Rigaku Electric Corporation slit system: 2mmφ (above) -1 ° -1 °
Detector: Scintillation counter counting recording device: RAD-C type measurement method manufactured by Rigaku Corporation Co., Ltd. Measuring method: Transmission type 2θ / θ scan: Step scan, 2θ range 10-55 °, 0.05 ° step, integration time 2 seconds

In accordance with the above conditions, an X-ray diffraction profile is obtained by 2θ / θ scanning.
Here, the K value is observed in the vicinity of 2θ = 16 °, and is observed in the diffraction peak intensity of the (300) plane (referred to as Hβ1) due to the β crystal and in the vicinity of 2θ = 14, 17, 19 °, and α From the diffraction peak intensities (referred to as Hα1, Hα2, and Hα3, respectively) of the (110), (040), and (130) planes due to the crystal, it can be calculated by the following mathematical formula. The K value is an empirical value indicating the ratio of β crystals. For details of the K value, such as the calculation method of each diffraction peak intensity, see A. Turner Jones et al., “Macromoleculare Chemie” (Macromoleculare Chemie). ), 75, pages 134-158 (1964).
K = Hβ1 / {Hβ1 + (Hα1 + Hα2 + Hα3)}
The structure of the polypropylene crystal type (α crystal, β crystal), the obtained wide-angle X-ray diffraction profile, etc. are described in, for example, Edward P. Moore Jr. Written by "Polypropylene Handbook", Industrial Research Committee (1998), p. 135-163; Hiroyuki Tadokoro, “Structure of Polymer”, Kagaku Dojin (1976), p. 393; A. Turner Jones et al., “Macromoleculare Chemie”, 75, 134-158 (1964), and there are many reports including references cited therein. You can refer to it.

(7) Melting point (Tm)
The raw material polypropylene resin was measured by the same method as the method for measuring the β crystal forming ability, and the peak temperature (α crystal) of the second run was taken as the melting point (Tm). However, the melting point was measured using a polypropylene raw material to which no β crystal nucleating agent was added.

(8) Melt flow rate (MFR)
The MFR of the polypropylene resin was measured according to the condition M (230 ° C., 2.16 kg) of JIS K 7210 (1995). The polyethylene resin was measured according to the condition D (190 ° C., 2.16 kg) of JIS K 7210 (1995).

(9) Tensile strength, Young's modulus, elongation at break A porous polypropylene film was cut into a rectangle having a length of 150 mm and a width of 10 mm and used as a sample. When measuring the strong elongation (tensile strength, Young's modulus, breaking elongation) in the film forming direction, the length direction of 150 mm is aligned with the film forming direction of the film, and the strong elongation in the width direction (tensile strength). , Young's modulus, elongation at break), the length direction of 150 mm was matched with the width direction of the film. Using a tensile tester (Orientec Tensilon UCT-100), a tensile test was performed according to JIS K 7127 (1999, specimen type 2), and tensile strength, Young's modulus, and elongation at break were measured. The initial chuck distance was 50 mm, and the tensile speed was 300 mm / min. The measurement was performed 5 times for each sample, and the average value was evaluated.

(10) Maximum pore diameter POROUS MATERIALS, Inc. The maximum pore diameter of the porous polypropylene film was measured according to ASTM E-128-61 using an automatic pore diameter distribution measuring device “PERM-POROMETER”. Measurement conditions are as follows. About the same sample, it changed 5 places and performed, and made the average value of the obtained maximum hole diameter the maximum hole diameter of the through-hole in the said sample.
Test solution: 3M “Fluorinert” FC-40
Test temperature: 25 ° C
Test gas: Air

(11) Measurement of dispersion diameter (domain diameter) of ethylene-α-olefin polymer (B) in cast sheet Using a microtome method, the cast sheet has a cross section (TD / ZD cross section) in the width direction-thickness direction. Ultrathin sections were 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) 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).

(12) Separator resistance evaluation A porous polypropylene film was punched into a diameter of 24 mm. From the bottom, a SUS plate having a diameter of 16 mm, a porous polypropylene film, and a SUS plate having a diameter of 16 mm were stacked in this order and stored in a small stainless steel container with a lid (HS cell, spring cell 2.5 kgf). The container and the lid are insulated, and the container and the lid are in contact with the SUS plate. In this container, an electrolytic solution in which LiPF ₆ was dissolved as a solute in a mixed solvent of propylene carbonate: diethyl carbonate = 1: 1 (volume ratio) to a concentration of 1 mol / liter was injected and sealed, and the cell for evaluation Was made.
For each of the fabricated cells for evaluation, the AC impedance was measured under the conditions of a voltage amplitude of 10 mV and a frequency of 10 Hz to 100 kHz in a 25 ° C. atmosphere, and the Cole-Cole plot was calculated using the equivalent circuit of FIG. Asked. The measurement was performed 5 times with different samples, and the separator resistance R was defined as the average value of the separator resistance, and evaluation was performed according to the following criteria.
◎: R is 4Ω or less ○: R is larger than 4Ω, 5Ω or less Δ: R is larger than 5Ω, 6Ω or less ×: R is larger than 6Ω

(13) Strength evaluation The mechanical properties of the porous polypropylene film were evaluated according to the following criteria.
○: When the puncture strength per 1 μm thickness is 0.18 N / μm or more and the tensile strength in the width direction is 60 MPa or more Δ: The puncture strength per 1 μm thickness is 0.18 N / μm or more and the tensile in the width direction When the strength is less than 60 MPa or the puncture strength per 1 μm thickness is less than 0.18 N / μm and the tensile strength in the width direction is 60 MPa or more ×: The puncture strength per 1 μm thickness is less than 0.18 N / μm, And the tensile strength in the width direction is less than 60 MPa

Example 1
As the polypropylene resin (A), 99.7 parts by mass of homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd., melting point 165 ° C., MFR = 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), 0.1 parts by mass of IRGANOX 1010 and IRGAFOS 168 by Ciba Specialty Chemicals, which are antioxidants, respectively. 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, 60 parts by mass of a homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd. having a melting point of 165 ° C. and MFR = 7.5 g / 10 min as the polypropylene resin (A), and ethylene as the ethylene-α-olefin polymer (B). -30 parts by mass of octene-1 copolymer ("Engage (registered trademark)" 8411 manufactured by Dow Chemical, melt index: 18 g / 10 min, melting point 70 ° C), CEBC (JSR) as the dispersant (C) 10 parts by mass of “DYNARON (registered trademark)” 6200P (melting point: 91 ° C.) manufactured by Co., Ltd. and “Irganox (registered trademark)” 1010 manufactured by Ciba Specialty Chemicals, which is an antioxidant, “Irgaphos (registered trademark)” ”Raw material from the weighing hopper to the twin screw extruder so that 0.1 parts by mass of 168 are 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).

  Furthermore, as polypropylene resin (A), 70 parts by mass of homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd., melting point 165 ° C., MFR = 7.5 g / 10 min, and melting point 162 ° C., MFR = 0.5 g / 10 min. 30 parts by weight of homopolypropylene D101 manufactured by Sumitomo Chemical Co., Ltd., and 0.1 parts by weight of “Irganox (registered trademark)” 1010 and “Irgaphos (registered trademark)” 168 manufactured by Ciba Specialty Chemicals, which are antioxidants. Feed the raw material from the weighing hopper to the twin screw extruder so that the parts are mixed at this ratio, perform melt kneading at 240 ° C., discharge the strands from the die, solidify by cooling in a 25 ° C. water bath, A polypropylene composition (III) was obtained by cutting into chips.

  The obtained polypropylene composition (I) 73.3 parts by mass, polypropylene composition (II) 10 parts by mass and polypropylene composition (III) 16.7 parts by mass were dry blended and uniaxial melt extrusion for layer A The polypropylene composition (I) is supplied to a single-screw melt extruder for the B layer, melt-extruded at 220 ° C., and foreign matter is removed with a 60 μm cut sintered filter. A B / A / B composite T die was laminated at a thickness ratio of 1/8/1 and discharged onto a cast drum whose surface temperature was controlled at 125 ° C. to obtain a cast sheet. The domain diameter in the A layer of the cast sheet was 50 nm. Further, the domain diameter in the A layer was about 50 nm both in the vicinity of the surface layer and in the center of the A layer, and was uniform in the thickness direction. Subsequently, it preheated using the ceramic roll heated at 120 degreeC, and stretched 5 times in the longitudinal direction of the film. Next, the edge part was hold | gripped with the clip and it extended | stretched 9 times in the width direction at 150 degreeC.

In the subsequent heat treatment process, heat treatment was performed at 150 ° C. for 2 seconds while maintaining the distance between the clips after stretching (HS1 zone), and further relaxed at 163 ° C. with a relaxation rate of 17% and a relaxation rate of 200% / min (Rx zone). Then, heat treatment was performed at 163 ° C. for 5 seconds while maintaining the distance between the clips after relaxation (HS2 zone).
Then, the ear | edge part of the film hold | gripped with the clip was cut and removed, and the 17-micrometer-thick porous polypropylene film was obtained.

(Example 2)
80 parts by mass of the polypropylene composition (I) obtained in Example 1, 10 parts by mass of the polypropylene composition (II) and 10 parts by mass of the polypropylene composition (III) were dry blended to produce a uniaxial melt extruder for the A layer. In addition, the polypropylene composition (I) is supplied to a uniaxial melt extruder for the B layer, melt extruded at 220 ° C., and foreign matters are removed with a 60 μm cut sintered filter. A B / A / B composite T die was laminated at a thickness ratio of 1/8/1 and discharged onto a cast drum whose surface temperature was controlled at 120 ° C. to obtain a cast sheet. Next, preheating was performed using a ceramic roll heated to 124 ° C., and the film was stretched 4.8 times in the longitudinal direction of the film. Next, the edge part was hold | gripped with the clip and it extended | stretched 8.5 times in the width direction at 151 degreeC.

In the subsequent heat treatment process, heat treatment was performed at 151 ° C. for 2 seconds while maintaining the distance between the clips after stretching (HS1 zone), and further relaxation was performed at 163 ° C. with a relaxation rate of 15% and a relaxation rate of 180% / min (Rx zone). Then, heat treatment was performed at 163 ° C. for 5 seconds while maintaining the distance between the clips after relaxation (HS2 zone).
Then, the ear | edge part of the film hold | gripped with the clip was cut and removed, and the 20-micrometer-thick porous polypropylene film was obtained.

(Example 3)
80 parts by mass of the polypropylene composition (I) obtained in Example 1, 10 parts by mass of the polypropylene composition (II) and 10 parts by mass of the polypropylene composition (III) were dry blended to produce a uniaxial melt extruder for the A layer. The melt was extruded at 220 ° C., and foreign matter was removed with a 60 μm cut sintered filter, which was then discharged onto a cast drum whose surface temperature was controlled at 120 ° C. using a T die to obtain a cast sheet. Next, preheating was performed using a ceramic roll heated to 120 ° C., and the film was stretched 5.0 times in the longitudinal direction of the film. Next, the edge part was hold | gripped with the clip and it extended | stretched 7.6 times in the width direction at 150 degreeC.
In the subsequent heat treatment process, heat treatment was performed at 150 ° C. for 2 seconds while maintaining the distance between the clips after stretching (HS1 zone), and at 164 ° C., relaxation was performed at a relaxation rate of 20% and a relaxation rate of 240% / min (Rx zone). Then, heat treatment was performed at 164 ° C. for 5 seconds while maintaining the distance between the clips after relaxation (HS2 zone).
Then, the ear | edge part of the film hold | gripped with the clip was cut and removed, and the 12-micrometer-thick porous polypropylene film was obtained.

Example 4
80 parts by mass of the polypropylene composition (I) obtained in Example 1, 10 parts by mass of the polypropylene composition (II) and 10 parts by mass of the polypropylene composition (III) were dry blended to produce a uniaxial melt extruder for the A layer. In addition, the polypropylene composition (I) is supplied to a uniaxial melt extruder for the B layer, melt extruded at 220 ° C., and foreign matters are removed with a 60 μm cut sintered filter. A B / A / B composite T die was laminated at a thickness ratio of 1/8/1 and discharged onto a cast drum whose surface temperature was controlled at 120 ° C. to obtain a cast sheet. Then, preheating was performed using a ceramic roll heated to 123 ° C., and the film was stretched 4.8 times in the longitudinal direction of the film. Next, the edge part was hold | gripped with the clip and it extended | stretched 8.5 times in the width direction at 151 degreeC.
In the subsequent heat treatment process, heat treatment was performed at 151 ° C. for 2 seconds while maintaining the distance between the clips after stretching (HS1 zone), and further relaxation was performed at 163 ° C. with a relaxation rate of 15% and a relaxation rate of 180% / min (Rx zone). Then, heat treatment was performed at 163 ° C. for 5 seconds while maintaining the distance between the clips after relaxation (HS2 zone).
Then, the ear | edge part of the film hold | gripped with the clip was cut and removed, and the 15-micrometer-thick porous polypropylene film was obtained.

(Comparative Example 1)
As polypropylene resin (A), 70 parts by mass of homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd. having a melting point of 165 ° C. and MFR = 7.5 g / 10 min, and ethylene-octene-as ethylene-α-olefin polymer (B) 30 parts by mass of 1 copolymer (“Engage (registered trademark)” 8411 manufactured by Dow Chemical, melt index: 18 g / 10 min), and “Irganox (manufactured by Ciba Specialty Chemicals), an antioxidant. (Registered trademark) "1010" and "Irgaphos (registered trademark)" 168 are fed to the twin-screw extruder from the weighing hopper so that 0.1 parts by mass are mixed at this ratio, and melt-kneaded at 240 ° C. It is discharged from the die in the form of a strand, cooled and solidified in a water bath at 25 ° C., cut into chips, and a polypropylene assembly To obtain a thing (IV).
90 parts by mass of the polypropylene composition (I) obtained in Example 1 and 10 parts by mass of the polypropylene composition (IV) were dry blended and supplied to a single-screw melt extruder for the A layer, and the polypropylene composition (I ) Is supplied to a single-axis melt extruder for the B layer, melt extruded at 220 ° C., foreign matter is removed with a sintered filter of 60 μm cut, and then a feed block type B / A / B composite T die is used. The laminate was laminated at a thickness ratio of 1/8/1 and discharged onto a cast drum whose surface temperature was controlled at 120 ° C. to obtain a cast sheet. The domain diameter in the A layer of the cast sheet was 120 nm. In addition, the domain diameter in the A layer has a tendency that the domain of about 100 nm is often observed near the surface of the A layer, the domain of about 150 nm is frequently observed in the central part of the A layer, and the domain diameter tends to increase toward the central part. there were. Next, preheating was performed using a ceramic roll heated to 118 ° C., and the film was stretched 5.0 times in the longitudinal direction of the film. Next, the edge part was hold | gripped with the clip and it extended | stretched 4.0 time in the width direction at 150 degreeC.
In the subsequent heat treatment step, relaxation was performed at 160 ° C. with a relaxation rate of 10% and a relaxation rate of 120% / min (Rx zone).
Then, the ear | edge part of the film hold | gripped with the clip was cut and removed, and the porous polypropylene film with a thickness of 24 micrometers was obtained.

(Comparative Example 2)
While 90 parts by mass of the polypropylene composition (I) obtained in Example 1 and 10 parts by mass of the polypropylene composition (IV) obtained in Comparative Example 1 were dry-blended and supplied to a uniaxial melt extruder for the A layer. The polypropylene composition (I) was supplied to a single-axis melt extruder for layer B, melt-extruded at 220 ° C., foreign matters were removed with a 60 μm cut sintered filter, and a feed block type B / A / A B composite T die was laminated at a thickness ratio of 1/8/1 and discharged onto a cast drum whose surface temperature was controlled at 120 ° C. to obtain a cast sheet. 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, the edge part was hold | gripped with the clip and it extended | stretched 4.2 times in the width direction at 150 degreeC.
In the subsequent heat treatment step, relaxation was performed at 160 ° C. with a relaxation rate of 10% and a relaxation rate of 120% / min (Rx zone).
Then, the ear | edge part of the film hold | gripped with the clip was cut and removed, and the 20-micrometer-thick porous polypropylene film was obtained.

  Examples that satisfy the requirements of the present invention are not only excellent in air permeability and productivity but also excellent in puncture strength and heat resistance, and thus can be suitably used as a separator for an electricity storage device. On the other hand, in the comparative example, it is difficult to use as a separator for an electricity storage device, such as poor mechanical properties or poor air permeability.

  Since the porous propylene film of the present invention is excellent in productivity, gas permeability, mechanical properties, and heat resistance, it can be suitably used as a separator for an electricity storage device.

Claims (4)

Β-crystal forming ability of 40-90%, thickness 10-30 μm, porosity 55-85%, air permeability resistance 70-300 sec / 100 ml, puncture strength per 1 μm thickness 0.18- A porous polypropylene film having a thermal shrinkage of 12% or less in the width direction when treated at 0.50 N / μm and 135 ° C. for 60 minutes.   The porous polypropylene film according to claim 1, wherein the porous polypropylene film has a tensile strength in the width direction of 60 to 200 MPa. The relationship between porosity ε (%), thickness T (μm), and puncture strength S (N) of the porous polypropylene film satisfies the following expression (1): 2. The porous polypropylene film according to 2.
S / (T × (100−ε) / 100) ≧ 0.45 (1) 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 electrical storage device characterized by the said separator being formed using the porous polypropylene film as described in any one of Claims 1-3 .

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