WO2013054932A1

WO2013054932A1 - Porous polypropylene film, layered porous film, and electricity-storage device

Info

Publication number: WO2013054932A1
Application number: PCT/JP2012/076549
Authority: WO
Inventors: 啓生駒; 久万　琢也; 大倉　正寿
Original assignee: 東レ株式会社
Priority date: 2011-10-14
Filing date: 2012-10-12
Publication date: 2013-04-18
Also published as: CN103890062A; JPWO2013054932A1; JP5354131B2; KR20140081808A; CN103890062B

Abstract

Provided are: a porous polypropylene film that exhibits excellent gas permeability and resistance to organic solvents, wherein when said film is coated with a functional layer such as a heat-resistance layer, the physical properties of said film do not change much; a layered porous film; and an electricity-storage device. Said porous polypropylene film, which contains a polypropylene resin that can form a beta crystal structure, is characterized by a gas permeation resistance of 1,000 sec/100 ml or less and further characterized in that an acetone-immersion treatment changes the thickness of the porous polypropylene film by no more than 20%.

Description

Porous polypropylene film, laminated porous film, and electricity storage device

The present invention relates to a porous polypropylene film, a laminated porous film, and an electricity storage device using these.

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 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. In particular, in recent years, lithium-ion batteries have been used in electric vehicles and hybrid vehicles, and as the output of batteries increases and the capacity increases, studies on coating porous films with inorganic particle layers and heat-resistant resin layers are actively conducted. (For example, refer to Patent Documents 1 and 2). Further, since the size of the battery is increased and the area to be used is increased, cost reduction is also strongly desired.

Various proposals have been made as a method for making a polypropylene film porous. Among them, a β-crystal method can be cited as a dry method and a method capable of forming a film with high productivity by biaxial stretching. The β crystal method is a method in which voids are formed in a film by utilizing the difference in crystal density and crystal transition between α type crystal (α crystal) and β type crystal (β crystal), which are polymorphs of polypropylene. Many proposals have been made (see, for example, Patent Documents 3 to 5). Furthermore, many proposals have been made on a method of coating a functional layer such as a heat-resistant layer on the surface of a porous polypropylene film by the β crystal method (see, for example, Patent Documents 6 to 14).

However, the porous polypropylene film by the β crystal method may change the pore structure and change the thickness and air resistance when an organic solvent such as acetone is applied and dried. As described above, the coating agent for coating is limited to an aqueous system, and it has been difficult to improve productivity by using an organic solvent having a high drying rate.

JP 2007-273443 A JP 2006-164873 A Japanese Unexamined Patent Publication No. 63-199742 Japanese Patent Application Laid-Open No. 6-100720 Japanese Patent Laid-Open No. 9-255804 JP 2009-19118 A JP 2009-114434 A JP 2009-226746 A JP 2009-227819 A JP 2010-65088 A JP 2010-219037 A JP 2011-110704 A JP 2011-126275 A International Publication No. 2010/008003

The present invention has been made in view of the above, and is suitably used as a separator for an electricity storage device, which has excellent organic solvent resistance and air permeability, and has little change in physical properties when coating a functional layer such as a heat-resistant layer. An object of the present invention is to provide a porous polypropylene film, a laminated porous film, and an electricity storage device using these.

In order to solve the above-described problems and achieve the object, the porous polypropylene film according to the present invention is a porous polypropylene film containing a polypropylene resin having β-crystal forming ability, and has an air resistance of 1,000 seconds. / 100 ml or less, the thickness change rate before and after acetone immersion treatment is 20% or less.

The porous polypropylene film of the present invention is excellent in organic solvent resistance and air permeability, and can be suitably used as a separator for an electricity storage device because it has little change in physical properties when coating a functional layer such as a heat-resistant layer.

It is the schematic of the sample before the acetone immersion process in the physical-property change measurement accompanying acetone immersion and a drying process. It is the schematic of the sample after fixing to the metal frame in the physical-property change measurement accompanying acetone immersion and a drying process. It is the schematic of the sample after the acetone immersion drying process in the physical-property change measurement accompanying acetone immersion and a drying process.

Hereinafter, embodiments of a porous polypropylene film, a laminated porous film, and an electricity storage device according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

The porous polypropylene film according to the present embodiment includes a polypropylene resin having β-crystal forming ability as the first component. Here, the polypropylene resin is preferably the main component in the porous polypropylene film. Here, the “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, further preferably 90% by mass or more, and most preferably Means 95% by mass or more.

The porous polypropylene film according to the present embodiment 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.

In order to form through holes in the film using the β crystal method, the β crystal forming ability of the porous polypropylene film 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 a film with low permeability is obtained. It may not be possible. On the other hand, the upper limit of β-crystal forming ability is not particularly limited, but it exceeds 99.9% by adding a large amount of the β-crystal nucleating agent described later or the stereoregulation of the polypropylene resin to be used. The industrial practical value is low, for example, the film forming stability is lowered. Industrially, the β-crystal forming ability is preferably 65 to 99.9%, particularly preferably 70 to 95%.

In order to control the β-crystal forming ability to 40% or more, a polypropylene resin with a high isotactic index is used, or a β crystal is selectively formed by adding it to a polypropylene resin called a β crystal nucleating agent. The crystallization nucleating agent to be used is preferably used as an additive. Examples of β crystal nucleating agents 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 are preferred. Compounds can be preferably usedThe addition amount 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 whole polypropylene resin. 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% by mass, coarse voids are formed, and physical property changes during application of organic solvents and drying may increase.

The polypropylene resin constituting the porous polypropylene film according to the present embodiment has a melt flow rate (hereinafter referred to as MFR, measurement conditions are 230 ° C., 2.16 kg) in the range of 2 to 30 g / 10 minutes. It is preferable that it is an isotactic polypropylene resin. When the MFR is less than 2 g / 10 minutes, the melt viscosity of the resin becomes high and high-precision filtration becomes difficult, and the quality of the film may be lowered. When the MFR exceeds 30 g / 10 min, the molecular weight becomes too low, so that the film is easily broken during stretching, and the productivity may be lowered. More preferably, the MFR is 3 to 20 g / 10 minutes.

In the case of using an isotactic polypropylene resin, the isotactic index is preferably 90 to 99.9%, more preferably 95 to 99%. If the isotactic index is less than 90%, the crystallinity of the resin is low, and it may be difficult to achieve high air permeability.

As a polypropylene resin used in the present embodiment, a homopolypropylene resin can be used, as well as an ethylene component in polypropylene from the viewpoint of stability in film forming process, film forming property, and uniformity of physical properties. It is also possible to use a resin obtained by copolymerizing an α-olefin component such as, butene, hexene, octene or the like in an amount of 5% by mass or less, more preferably 2.5% by mass or less. The form of introduction of the comonomer (copolymerization component) into polypropylene may be either random copolymerization or block copolymerization.

In addition, it may be preferable for the above-mentioned polypropylene resin to contain high molecular weight polypropylene from the viewpoint of improving safety and improving film forming property. The content is preferably in the range of 0.5 to 30% by mass. The high molecular weight polypropylene is a polypropylene having an MFR of 0.1 to 1 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 used.

In addition, it may be preferable for the above-mentioned polypropylene resin to contain a low melting point polypropylene from the viewpoint of improving safety and improving film forming property. The content is preferably in the range of 0.5 to 30% by mass. The low melting point polypropylene is a polypropylene having a melting point Tm of 130 to 155 ° C., and for example, polypropylene resins S131 and FS3611 manufactured by Sumitomo Chemical Co., Ltd. can be used.

The polypropylene resin used in the present embodiment has a mass ratio of 80 to 99 parts by mass of polypropylene and 20 to 1 part by mass of the ethylene / α-olefin copolymer from the viewpoint of void formation efficiency during biaxial stretching. A mixture is preferred. Here, examples of the ethylene / α-olefin copolymer include linear low-density polyethylene and ultra-low-density polyethylene, and among them, a copolymer polyethylene obtained by copolymerizing octene-1 and having a melting point of 60 to 90 ° C. A resin (copolymerized 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.

When the total amount of the polypropylene resin constituting the film according to the present embodiment is 100% by mass, the copolymer polyethylene resin contains 10% by mass or less, and the porosity and average through-hole diameter described later are controlled within a preferable range. Since it becomes easy to do, it is preferable. From the viewpoint of the mechanical properties of the film, it is more preferably 1 to 7% by mass, still more preferably 1 to 2.5% by mass.

The polypropylene resin used in the present embodiment may be added with a dispersant in addition to the above-described ethylene / α-olefin copolymer from the viewpoint of uniformizing the pore structure and suppressing physical property changes after the acetone immersion treatment. preferable. Any dispersing agent may be used as long as it can increase the dispersibility of the ethylene / α-olefin copolymer in the polypropylene resin. As described in International Publication No. 2007/046225, the polypropylene resin and the ethylene · The compatibility of the α-olefin copolymer is good. For example, the ethylene / propylene random copolymer generally used as a compatibilizing agent for polypropylene resin and polyethylene resin is dispersed for uniform pore structure in this embodiment. Does not function as an agent. As a dispersant preferably used in the present embodiment, blocks each having a highly compatible segment with polypropylene (for example, a polypropylene segment, an ethylene butylene copolymer segment) and a highly compatible segment with polyethylene (such as a polyethylene segment). A copolymer is preferred. As a resin having such a structure, a commercially available resin such as olefin crystal, ethylene butylene, olefin crystal block polymer (hereinafter referred to as CEBC) “DYNARON (registered trademark)” (type name) manufactured by JSR Corporation : Olefin block copolymer "INFUSE OBC (registered trademark)" manufactured by Dow Chemical Co., Ltd. The addition amount of the dispersant 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. From the viewpoint of improving the dispersibility of the ethylene / α-olefin copolymer in polypropylene resin and improving the uniformity of pore formation, the melting point of the dispersant is higher than the melting point of the ethylene / α-olefin copolymer. The temperature is preferably 0 to 60 ° C., more preferably 15 to 30 ° C.

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

The porous polypropylene film according to the present embodiment has a thickness change rate of 20% or less before and after the acetone immersion treatment. When the thickness change rate exceeds 20%, that is, when the thickness exceeds 20% and shrinks or swells, when the functional layer such as a heat-resistant layer is applied by coating, the thickness changes depending on the drying conditions, thereby controlling the product thickness. May become difficult, or air resistance may increase and output characteristics may deteriorate. The thickness change rate before and after the acetone immersion treatment is preferably 14% or less, and more preferably 7% or less. The rate of change in thickness before and after the acetone immersion treatment is determined by adjusting the amount of the β-crystal nucleating agent, ethylene / α-olefin copolymer and dispersant described above within the above range, the temperature of the cast drum, and the stretching ratio in the longitudinal direction. And the temperature, 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 below.

The porous polypropylene film according to the present embodiment is provided, for example, between a positive electrode and a negative electrode, and as a separator in an electricity storage device including a separator that transmits ions in an electrolytic solution while preventing contact between the two. Can be used.

The porous polypropylene film according to the present embodiment has an air resistance of 1,000 seconds / 100 ml or less. More preferably, it is 10 to 1,000 seconds / 100 ml, more preferably 50 to 500 seconds / 100 ml, and most preferably 80 to 350 seconds / 100 ml. If the air permeation resistance exceeds 1,000 seconds, the output characteristics may deteriorate when the porous polypropylene film is used as a separator for an electricity storage device. From the viewpoint of output characteristics, the air permeability resistance is preferably as low as possible. However, if it is less than 10 seconds, the mechanical strength of the film is lowered and the handling property is lowered, or the electric characteristics such as the cycle characteristics are lowered when the separator is used. There is a case. When controlling permeation resistance by the β crystal method, operating conditions such as longitudinal stretching conditions such as longitudinal stretching ratio and longitudinal stretching temperature, or transverse stretching conditions such as transverse stretching temperature, transverse stretching speed and transverse stretching ratio are changed. Thus, the air resistance can be controlled.

However, when controlling the air resistance according to the operating conditions, if the air resistance is reduced, the porosity of the porous polypropylene film increases, and the change in physical properties and dimensions after the acetone immersion treatment may increase. It was. Therefore, in the present embodiment, in addition to using the above-mentioned raw materials, by setting the conditions after the heat treatment conditions after transverse stretching to specific conditions as described later, the air resistance is low and by acetone treatment. A porous polypropylene film with small changes in physical properties and dimensions was obtained, and both organic solvent resistance and output characteristics were compatible. The heat treatment conditions are described below.

In the β crystal method, pores are formed by transverse stretching with a tenter following longitudinal stretching, and a porous polypropylene film can be obtained. The transverse stretching process in the tenter can be divided into three processes: a preheating process, a transverse stretching process, and a heat treatment process. In the heat treatment process, the film after stretching is thermally fixed and relaxed. The relaxation rate of a general film is about 2 to 10%, and the temperature at that time is about (Tm-10) ° C to (Tm-5) ° C, where the melting point of the polypropylene resin is Tm. In this embodiment, the relaxation rate is set to a high value of 15 to 35%, and further, the air resistance is reduced by taking the heat treatment temperature condition of (Tm−2) ° C. to (Tm + 5) ° C. In addition, a porous polypropylene film having small changes in physical properties and dimensions after acetone treatment can be obtained.

The porous polypropylene film according to the present embodiment preferably has a film thickness of 5 to 50 μm. If the thickness is less than 5 μm, the film may break during use. If the thickness exceeds 50 μm, the volume ratio of the porous polypropylene film in the electricity storage device becomes too high, and it may not be possible to obtain a high energy density. . The film thickness is more preferably 10 to 30 μm, and still more preferably 12 to 25 μm.

The porous polypropylene film according to this embodiment preferably has a porosity of 40 to 85%. When the porosity is less than 40%, the electrical resistance may increase particularly when used as a separator for a high-power battery. On the other hand, if the porosity exceeds 85%, there may be a large change in physical properties and dimensions after acetone treatment. From the viewpoint of achieving both excellent battery characteristics and organic solvent resistance, the film porosity is more preferably 42 to 75%, and particularly preferably 45 to 70%. The porosity is determined by setting the addition amount of the above-mentioned β crystal nucleating agent, ethylene / α-olefin copolymer and dispersing agent within the above range, the temperature of the cast drum, the stretching ratio and temperature in the longitudinal direction, and the transverse stretching. The magnification, 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 according to the present embodiment preferably has a dimensional change rate in the width direction of 2% or less before and after the acetone immersion treatment. Here, the acetone immersion treatment is a method in which a porous polypropylene film is fixed by frame attachment only in the film forming direction, immersed in acetone for 1 minute, and then dried in a hot air oven at 80 ° C. for 1 minute to remove acetone. Shows the processing to be performed. If the dimension in the width direction after acetone treatment shrinks by more than 2% compared to that before acetone treatment, the air resistance increases or the width decreases when a functional layer such as a heat-resistant layer is applied by coating. As a result, the thickness may increase. On the other hand, when the dimension in the width direction after the acetone treatment exceeds 2% with respect to that before the acetone treatment, the resin constituting the porous polypropylene film swells when a functional layer such as a heat-resistant layer is applied by coating. Or it melt | dissolves and the hole of a porous polypropylene film coarsens and electrical characteristics, such as cycling characteristics, may fall. The width direction dimensional change rate is more preferably 1.5% or less, more preferably the width direction dimensional shrinkage before and after the acetone immersion treatment is preferably 0 to 1.5%, and most preferably the acetone immersion treatment. The front-rear width direction dimensional shrinkage is 0 to 1%. The rate of dimensional change in the width direction before and after the acetone immersion treatment is determined by setting the amount of the β crystal nucleating agent, ethylene / α-olefin copolymer and dispersant described above within the above range, the temperature of the cast drum, and the longitudinal direction. The draw ratio and temperature, 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 below, especially the temperature, time, and relaxation rate in the heat treatment step. Control is important.

In the present application, the direction parallel to the film forming direction is referred to as the film forming direction, the longitudinal direction or the MD direction, and the direction perpendicular to the film forming direction in the film plane is the width direction, the lateral direction or the TD direction. Called.

The porous polypropylene film according to the present embodiment preferably has a change rate of air permeability resistance before and after the acetone immersion treatment of 15% or less. When the change rate of the air resistance exceeds 15%, that is, when the air resistance decreases or increases beyond 15%, when the functional layer such as a heat-resistant layer is applied by coating, the air resistance depends on the drying conditions. May change, making control difficult, increasing air resistance and reducing output characteristics, and increasing air resistance unevenness after drying, which may deteriorate battery characteristics. The change rate of the air resistance before and after the acetone immersion treatment is preferably 10% or less, and more preferably 7% or less. The rate of change in air resistance before and after the acetone immersion treatment is determined based on the addition amount of the β crystal nucleating agent, ethylene / α-olefin copolymer and dispersing agent described above, the temperature of the cast drum, and the longitudinal direction. The stretching ratio and temperature, the transverse stretching 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 below.

In the porous polypropylene film according to the present embodiment, the maximum value when the thickness change rate before and after the acetone immersion treatment was measured at intervals of 70 mm in the width direction was T _max (%), and the minimum value was T _min (%). In this case, the value of (T _max −T _min ) is preferably 3% or less. More preferably, it is 2% or less. When the value of (T _max -T _min ) exceeds 3%, the thickness variation rate variation in the width direction is large, and therefore, when coating with an organic solvent, the thickness variation in the width direction of the product becomes large. May end up. The value of (T _max -T _min ) depends on the amount of addition of the β crystal nucleating agent, ethylene / α-olefin copolymer and dispersant described above within the above range, the temperature of the cast drum, and the relaxation zone. It is possible to control the relaxation rate by setting the relaxation rate within the range described later.

The porous polypropylene film according to the present embodiment preferably has a laminated structure from the viewpoint of achieving both organic solvent resistance and air permeability. As the laminated structure, it is preferable that any layer contains a polypropylene resin having a carboxyl group or a modified polyolefin by an unsaturated dicarboxylic acid, and more preferably a polypropylene resin having a carboxyl group in the surface layer or an unsaturated dicarboxylic acid. It preferably contains a modified polyolefin. The polypropylene resin having a carboxyl group or the polyolefin modified with an unsaturated dicarboxylic acid is preferably contained in an included layer in an amount of 0.1 to 50%, more preferably 1 to 10%. Is preferred. As a method of introducing a carboxyl group into a polypropylene resin, there is a method of graft copolymerizing a polar monomer having a carboxyl group. Examples of the polar monomer having a carboxyl group include (meth) acrylic acid and acid derivatives thereof, and monoolefin dicarboxylic acid, anhydrides and monoesters thereof. Specific examples of (meth) acrylic acid and ester derivatives thereof include, for example, (meth) acrylic acid; methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, (meth) acrylic Isopropyl acid, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, etc. Examples of monoolefin dicarboxylic acids include maleic acid, chloromaleic acid, citraconic acid , Itaconic acid, glutaconic acid, 3-methyl-2-pentene diacid, 2-methyl-2-pentene diacid, 2-hexene diacid, and the like. In addition, it is preferable that these polypropylene resins also have β crystal forming ability, and β crystal forming ability is more preferably 40% or more.

The number of stacked layers may be a two-layer stack, a three-layer stack, or a larger number of stacks. The lamination method may be either a feed block method by coextrusion or a method of laminating porous polypropylene films by lamination, but from the viewpoint of productivity, lamination by coextrusion is preferred.

Hereinafter, a method for producing a porous polypropylene film according to the present embodiment will be described based on a specific example. In addition, the manufacturing method of the porous polypropylene film of this invention is not limited to this.

99.5 parts by mass of a commercially available homopolypropylene resin with an MFR of 8 g / 10 min as a polypropylene resin, 0.3 parts by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxyamide as a β-crystal nucleating agent, an antioxidant 0 The raw material is fed from the weighing hopper to the twin screw extruder so that 2 parts by mass are mixed at this ratio, melt kneaded, discharged from the die in the form of strands, cooled and solidified in a 25 ° C. water bath, and chips A polypropylene raw material (a) is prepared by cutting into a shape. At this time, the melting temperature is preferably 270 to 300 ° C.

Similarly, 59.8 parts by mass of the above-mentioned homopolypropylene resin, 30 parts by mass of a commercially available MFR 18 g / 10 min ultra low density polyethylene resin ethylene / octene-1 copolymer as an ethylene / α-olefin copolymer, As raw materials, 10 parts by weight of commercially available CEBC and 0.2 parts by weight of antioxidant are mixed at this ratio, and the raw material is supplied from the weighing hopper to the twin screw extruder, melt kneaded at 240 ° C. Discharge, solidify by cooling in a water bath at 25 ° C., and cut into chips to prepare a polypropylene raw material (b).

Further, as a polypropylene resin, 70 parts by mass of a commercially available homopolypropylene resin having an MFR of 8 g / 10 min, 30 parts by mass of a commercially available homopolypropylene having an MFR of 0.5 g / 10 min, and 0.2 parts by mass of an antioxidant The raw material is supplied from the weighing hopper to the twin screw extruder so as to be 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 formed into chips. Cut to prepare a polypropylene raw material (c).

Next, 73 parts by mass of the polypropylene raw material (a), 10 parts by mass of the polypropylene raw material (b), 16.7 parts by mass of the polypropylene raw material (c), and 0.3 parts by mass of the antioxidant are mixed by dry blending, Supplied to a single screw extruder of layer A, while dry blending 99 parts by weight of the polypropylene raw material (a) and 1 part by weight of a polypropylene resin having a carboxyl group or a modified polyolefin with unsaturated dicarboxylic acid, Supply to the extruder. Then, melt extrusion is performed at 200 to 230 ° C. from the single-axis extruder for the A layer and the single-screw extruder for the B layer. Furthermore, after removing foreign substances and modified polymer with a filter installed in the middle of the polymer tube, the mixture is discharged onto a cast drum from a feed block type B / A / B composite T die to obtain an unstretched laminated cast sheet. . The surface temperature of the cast drum is preferably 105 to 130 ° C. from the viewpoint of controlling the β crystal fraction of the cast 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. The cast sheet refers to an unstretched sheet obtained by molding a molten polypropylene resin into a sheet shape on a cast drum.

Next, the obtained cast sheet is biaxially oriented to form pores in the sheet. The biaxial orientation method includes stretching the cast sheet in the longitudinal direction and then stretching in the width direction, or the successive biaxial stretching method of stretching in the longitudinal direction after stretching in the width direction, or the longitudinal direction and width of the cast sheet. A simultaneous biaxial stretching method in which the directions are stretched almost simultaneously can be used. From the viewpoint of air permeability and organic solvent resistance, it is preferable to employ a sequential biaxial stretching method, and in particular, stretching in the longitudinal direction and then stretching in the width direction are preferred.

As specific stretching conditions, first, the temperature of the cast sheet is controlled to a temperature for stretching in the longitudinal direction. As a temperature control method, a method using a temperature-controlled rotating roll, a method using a hot air oven, or the like can be employed. The stretching temperature in the longitudinal direction is preferably 90 to 140 ° C. If it is less than 90 degreeC, a cast sheet may fracture | rupture or a porosity will become high too much, and the change of the physical property and dimension after acetone processing may become large. On the other hand, if it exceeds 140 ° C., the air permeability may decrease. The stretching temperature in the longitudinal direction is more preferably 110 to 135 ° C, particularly preferably 125 to 130 ° C. The draw ratio is preferably 3 to 7 times. If it is less than 3 times, the air permeability is low, and the output characteristics may deteriorate. As the draw ratio is increased, the air permeability is improved. However, if the draw ratio is more than 7 times, the porosity becomes too high, and the physical properties and dimensional changes after the acetone treatment may increase. From the viewpoint of achieving both high air permeability and organic solvent resistance, the draw ratio is more preferably 4.5 to 6 times.

Next, the end of the sheet stretched in the longitudinal direction is introduced into the tenter type stretching machine by gripping. The transverse stretching temperature is preferably 130 to 155 ° C. If the temperature is lower than 130 ° C, the sheet stretched in the longitudinal direction may break, or the physical properties and dimensional changes after the acetone treatment of the film after transverse stretching may increase. If the temperature exceeds 155 ° C, the air permeability decreases and the output characteristics. May decrease. From the viewpoint of achieving both air permeability and organic solvent resistance, a more preferred transverse stretching temperature is 140 to 155 ° C. The draw ratio in the width direction is preferably 4 to 12 times. If it is less than 4 times, the air permeability may be lowered and the output characteristics may be lowered. When it exceeds 12 times, the change in physical properties and dimensions after acetone treatment may be large. From the viewpoint of achieving both output characteristics and organic solvent resistance, the draw ratio is more preferably 4 to 10 times, and still more preferably 4 to 7 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 ratio (longitudinal stretching ratio × lateral stretching ratio) is preferably 30 to 60 times. Thus, a film (porous polypropylene film) is obtained by extending a cast sheet.

続い Following 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 from the viewpoint of control of air permeability and organic solvent resistance that it is divided into three zones, a heat setting zone (hereinafter referred to as HS2 zone) in which heat treatment is performed with the width after relaxation.

The temperature of the HS1 zone is preferably 140 to 165 ° C. If the temperature of the HS1 zone is lower than 140 ° C., the physical properties and dimensional changes after the acetone treatment may increase. On the other hand, when the temperature of the HS1 zone exceeds 165 ° C., the porous polypropylene film surface is melted and air permeability resistance is increased, and further, the porous polypropylene film contracts in the width direction and breaks in the HS1 zone, Productivity may be reduced. From the viewpoint of achieving both output characteristics and organic solvent resistance, the temperature of the HS1 zone is more preferably 150 to 160 ° C.

The heat treatment time in the HS1 zone is preferably 0.1 second or more and 10 seconds or less, more preferably 3 seconds or more and 8 seconds or less from the viewpoint of achieving both Young's modulus in the width direction and productivity.

In the present embodiment, 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. On the other hand, if the relaxation rate exceeds 35%, the air permeability may be lowered to deteriorate the output characteristics, or the thickness unevenness in the width direction and the heat shrinkage rate unevenness may be increased. From the viewpoint of achieving both output characteristics and a low heat shrinkage rate, the relaxation rate 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 less than 155 ° C., the shrinkage stress for relaxation becomes low, and the above-described high relaxation rate may not be achieved, or physical properties and dimensional changes after acetone treatment may increase. On the other hand, if the temperature of the Rx zone exceeds 170 ° C., the polymer around the pores may melt due to the high temperature and the air permeability may be lowered. From the viewpoint of output characteristics and organic solvent resistance, the temperature of the Rx zone 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. On the other hand, when the relaxation rate exceeds 1,000% / min, the rate at which the film shrinks becomes slower than the rate at which the tenter rail width shrinks, the film flutters in the tenter and tears, or the rate of change in thickness after acetone treatment In some cases, the unevenness in the width direction increases or the flatness deteriorates. 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 of the HS2 zone is less than 155 ° C., the tension of the film after thermal relaxation becomes insufficient, and unevenness in the width direction of the thickness change rate after the acetone treatment may increase, or flatness may be deteriorated. On the other hand, when the temperature of the HS2 zone exceeds 165 ° C., the polymer around the pores melts due to the high temperature, and the gas permeability may be reduced, resulting in a decrease in output characteristics. From the viewpoint of achieving both output characteristics and organic solvent resistance, the temperature of the HS2 zone is more preferably 160 to 165 ° C. 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.

Thereafter, a coated layer may be provided on at least one surface of the porous polypropylene film to form a laminated porous film. Since the porous polypropylene film according to the present embodiment is excellent in resistance to organic solvents, high air permeability can be maintained even when coating is performed using an organic solvent. As a coating method, a known method can be used. For example, using at least one organic solvent selected from acetone, ethanol, tetrahydrofuran, N-methyl-2-pyrrolidone, etc. as a solvent, and adding a heat-resistant resin, inorganic particles, and additives such as a binder as necessary May be prepared and applied to at least one surface of the porous polypropylene film using a die coating method or a gravure coating method. Then, a laminated porous film can be obtained by drying the solvent using a drying oven.

The porous polypropylene film according to the present embodiment has excellent productivity, low air resistance, and small changes in physical properties and dimensions after acetone treatment, so that it is a packaging product, sanitary product, agricultural product, and building product. It can be used for medical supplies, separation membranes, light diffusing plates, and reflective sheets, but is particularly suitable when used as a separator for an electricity storage device because both output characteristics and organic solvent resistance can be achieved. 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. In particular, the electricity storage device using the separator using the porous polypropylene film according to the present embodiment is suitable as a porous film for a substrate for coating a surface layer with a functional layer such as a heat-resistant layer. Furthermore, the laminated porous film provided with a heat resistant layer on the porous polypropylene film according to the present embodiment is excellent in output characteristics and safety, and therefore can be suitably used for a non-aqueous electrolyte secondary battery for an electric vehicle. .

Hereinafter, Examples 1 to 5 of the present invention will be described in detail. The characteristics of Examples 1 to 5 and Comparative Examples 1 to 4 were measured and evaluated by the following methods. Of course, the present invention is not limited to these.

(1) β-crystal forming ability 5 mg of a porous polypropylene film was taken as a sample 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 10 ° C./min (first run) in a nitrogen atmosphere, held for 10 minutes, and then cooled to 40 ° C. at 10 ° C./min. The melting peak observed when the temperature is raised again (second run) at 10 ° C / min after holding for 5 minutes is the melting peak of 145 ° C to 157 ° C. 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
In addition, the β crystal fraction in the state of the sample can be calculated by calculating the abundance ratio of the β crystal from the melting peak observed in the first run.

(2) Melting point (Tm)
The 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).

(3) Change in physical properties accompanying acetone immersion and drying treatment A porous polypropylene film was cut into a rectangle of 140 mm in the longitudinal direction and 70 mm in the width direction as Sample 2 (see FIG. 1). The dimension of the center part in the longitudinal direction was measured in the width direction of the cut-out porous polypropylene film, and it was _defined as a width direction length L _TD1 (mm) before processing. Moreover, the film thickness in the center part of the sample 2 was measured by the method according to following (8), and it was set as thickness T1 (micrometer) before a process. The air resistance of the sample 2 cut out was measured according to the method described in the following (6). The measurement position 1 of the air permeation resistance was set at two locations centering on a point which passed through the center in the width direction and entered 30 mm inside from two sides parallel to the width direction. The air resistance was measured at these measurement positions 1, and the average value was defined as the pre-treatment air resistance G1.

For the stainless steel metal frame 3 having an inner frame of 80 mm × 80 mm and an outer frame of 100 mm × 100 mm (see FIG. 2), the sample 2 is folded back by 20 mm at the top and bottom in the longitudinal direction at the outer frame part of the metal frame. BiTP-CL-104) 4 was clamped at two locations per side to fix only the longitudinal direction of sample 2. When fixing, set the sample 2 so that it does not wrinkle or sag. At the same time, place a cylindrical 5 g weight with a contact cross section of 0.785 cm ^{2 on} the center of the fixed sample 2 It was confirmed that the amount of deflection was 1 mm or less. Sample 2 fixed only in the longitudinal direction on a metal frame is immersed in acetone (special grade made by Kanto Chemical) for 1 minute, and then heated in an 80 ° C hot air oven (Espec Corp. (formerly TABAI) PHH-100, wind control set to 6) The sample 2 was removed from the metal frame after being dried for 1 minute, taken out of the oven and allowed to stand for 5 minutes, cooled to room temperature.

About the sample 2 removed from the hot air oven, the place where the sample 2 contracted most in the width direction was measured, and the length was _defined as a width direction length L _TD2 (mm) after processing (see FIG. 3). Moreover, the film thickness in the center of the place shrink | contracted most in the width direction was measured by the method according to following (8), and it was set as post-process thickness T2 (micrometer). Further, by the method according to the following (6), the air resistance is measured around the most contracted place (the air resistance measurement position 5) in the width direction of the sample 2, and the value is processed and the air resistance G2 after processing. (FIG. 3).

The change rate of each physical property was calculated based on the following formula.
Dimensional change rate in width direction (%) = | L _TD1 −L _TD2 | / L _TD1 × 100
Thickness change rate (%) = | T1-T2 | / T1 × 100
Change rate of Gurley air resistance (%) = | G1-G2 | / G1 × 100

(4) Unevenness in the width direction of the rate of change in thickness before and after acetone immersion treatment As a measurement sample, a sample having a width of 70 mm from one end to the other end in the width direction of the porous polypropylene film was set, and the center line interval was set to 70 mm. And cut out across the entire width of the porous polypropylene film. When a fraction of less than 70 mm was generated at the other end, a 70 mm square sample in contact with the other end was taken from a site adjacent in the longitudinal direction and used as a sample. About each sample, the thickness before and behind acetone immersion was measured by the method similar to said (3), and thickness change rate was calculated | required. The maximum thickness change rate of each measured value was T _max , and the minimum thickness change rate was T _min, and the value of (T _max −T _min ) was determined.

(5) 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 MFR of the polyethylene resin was measured according to the condition D (190 ° C., 2.16 kg) of JIS K 7210 (1995).

(6) Air permeation resistance With respect to the porous polypropylene film, the permeation time of 100 ml of air was measured at 23 ° C. and relative humidity 65% using a B-type Gurley tester of JIS P 8117 (1998). In addition, it can confirm that the through-hole is formed in the film that this air permeability value is a finite value.

(7) Porosity A porous polypropylene film was cut into a size of 30 mm × 40 mm and used as a sample. Using an electronic hydrometer (SD-120L manufactured by Mirage Trading Co., Ltd.), the specific gravity (ρ) was measured in an atmosphere having a room temperature of 23 ° C. and a relative humidity of 65%.

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 from 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

(8) Film thickness Using a dial gauge thickness gauge (JIS B-7503 (1997), PEACOCK UPRIGHT DIAL GAUGE (0.001 × 2 mm), No. 25, measuring element 10 mmφ flat, 50 gf load) Was measured.

Example 1
As the polypropylene resin, 99.7 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 N, N′-dicyclohexyl-2,6 which is a β crystal nucleating agent -0.3 parts by mass of naphthalene dicarboxyamide (manufactured by Shin Nippon Rika Co., Ltd., NU-100), and 0.1 parts by mass of IRGANOX 1010 and IRGAFOS 168 made by Ciba Specialty Chemicals, which are antioxidants. The raw materials were supplied from the weighing hopper to the twin screw extruder so as to be mixed at this ratio, and melt kneading was performed at 300 ° C. Then, the melt-kneaded material was discharged from the die in a strand shape, cooled and solidified in a water bath at 25 ° C., and cut into a chip shape to obtain a polypropylene composition (I).

Next, 70 parts by mass of Sumitomo Chemical Co., Ltd. homopolypropylene FLX80E4 having a melting point of 165 ° C. and MFR = 7.5 g / 10 min, and an ethylene-octene-1 copolymer (engage 8411 manufactured by Dow Chemical Co., Ltd.) as a copolymer PE resin. , Melt index: 18 g / 10 min) from the weighing hopper so that 0.1 parts by mass of IRGANOX 1010 and IRGAFOS 168 manufactured by Ciba Specialty Chemicals, which are antioxidants, are mixed at this ratio. The raw material was supplied to a twin screw extruder and melt kneaded at 240 ° C. Then, the melt-kneaded material was discharged from the die in a strand shape, cooled and solidified in a water bath at 25 ° C., and cut into a chip shape to obtain a polypropylene raw material (II).

As polypropylene resin, 70 parts by mass of homopolypropylene FLX80E4, 30 parts by mass of homopolypropylene D101 made by Sumitomo Chemical Co., Ltd., melting point 162 ° C. and MFR = 0.5 g / 10 min, and Ciba Specialty which is an antioxidant -Chemicals IRGANOX 1010 and IRGAFOS 168 were each fed to the twin screw extruder from the weighing hopper so that 0.1 parts by mass of each were mixed at this ratio, and melt kneaded at 240 ° C. Then, the melt-kneaded material was discharged from the die in a strand shape, cooled and solidified in a water bath at 25 ° C., and cut into a chip shape to obtain a polypropylene composition (III).

The resulting 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 to melt uniaxially for the A layer. On the other hand, 99 parts by mass of the polypropylene composition (I) and 1 part by mass of Admer QF500 manufactured by Mitsui Chemicals, which is a modified polyolefin with a polypropylene resin having a carboxyl group or an unsaturated dicarboxylic acid, are mixed with B The uniaxial melt extruder for the layer was fed. Then, melt extrusion is performed at 220 ° C. from a single-axis melt extruder for the A layer and a single-axis melt extruder for the B layer, and after removing foreign matters with a 60 μm cut sintered filter, a feed block type B / The 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 122 ° C. to obtain a cast sheet. Next, preheating was performed using a ceramic roll heated to 120 ° C., and the cast sheet was stretched 5 times in the longitudinal direction at a stretching temperature of 120 ° C. Next, the sheet stretched in the longitudinal direction was introduced into a tenter-type stretching machine by gripping the end with a clip, preheated at 155 ° C. for 3 seconds, then 8.0 times at 150 ° C., and a stretching speed of 1,800 The film was obtained by stretching at% / min. The distance between the clips in the width direction at the entrance of the tenter was 150 mm.

In the subsequent heat treatment step, the film was heat treated for 3 seconds at 150 ° C while maintaining the distance between the stretched clips (HS1 zone), and further relaxed at 164 ° C and a relaxation rate of 15% (Rx zone). Heat treatment was performed at 164 ° C. for 5 seconds while keeping the distance (HS2 zone).

Thereafter, the ears of the film held by the tenter clip were removed by slitting, and the porous polypropylene film having a width of 500 mm was wound around the core by a winder by 500 m to obtain a porous polypropylene film having a width of 500 mm and a thickness of 25 μm.

(Example 2)
59.8 parts by mass of homopolypropylene FLX80E4, 30 parts by mass of ethylene-octene-1 copolymer (engage 8411 manufactured by Dow Chemical, melt index: 18 g / 10 min) as a copolymer PE resin, and CEBC (JSR) as a dispersant DYNARON 6200P (manufactured by Co., Ltd.) and biaxial extrusion from a weighing hopper so that 0.1 parts by mass of IRGANOX 1010 and IRGAFOS 168 manufactured by Ciba Specialty Chemicals, which are antioxidants, are mixed at this ratio. The raw material was supplied to the machine and melt kneaded at 240 ° C. The melt-kneaded material was discharged from the die in the form of a strand, cooled and solidified in a water bath at 25 ° C., and cut into a chip to obtain a polypropylene raw material (IV).

The resulting polypropylene composition (I) 73.3 parts by mass, polypropylene composition (IV) 10 parts by mass and polypropylene composition (III) 16.7 parts by mass were dry blended and uniaxial melt extrusion for layer A On the other hand, 99 parts by mass of the polypropylene composition (I) and 1 part by mass of Admer QF500 manufactured by Mitsui Chemicals, Ltd., which is a modified polyolefin with a polypropylene resin having a carboxyl group or an unsaturated dicarboxylic acid, are used for the B layer. To a single screw melt extruder. Then, melt extrusion is performed at 220 ° C. from a single-axis melt extruder for the A layer and a single-axis melt extruder for the B layer, and after removing foreign matters with a 60 μm cut sintered filter, a feed block type B / The 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 120 ° C., and the cast sheet was stretched 5 times in the longitudinal direction at a stretching temperature of 120 ° C. Next, the sheet stretched in the longitudinal direction was introduced into a tenter-type stretching machine by gripping the end with a clip, preheated at 155 ° C. for 3 seconds, then 8.4 times at 150 ° C., and a stretching speed of 1,800 The film was obtained by stretching at% / min. The distance between the clips in the width direction at the entrance of the tenter was 150 mm.

In the subsequent heat treatment step, the film was heat treated for 3 seconds at 150 ° C while maintaining the distance between the stretched clips (HS1 zone), and further relaxed at 164 ° C and a relaxation rate of 15% (Rx zone). A porous polypropylene film having a width of 500 mm and a thickness of 25 μm was obtained under the same conditions as in Example 1 except that heat treatment was performed at 164 ° C. for 5 seconds (HS2 zone) while keeping the distance.

(Example 3)
In contrast to Example 2, relaxation was performed at 164 ° C. and a relaxation rate of 20% (Rx zone). Except this, under the same conditions as in Example 2, a porous polypropylene film having a width of 500 mm and a thickness of 25 μm was obtained.

(Example 4)
For Example 1, preheating was performed using a ceramic roll heated to 120 ° C., and the cast sheet was stretched 5 times in the longitudinal direction at a stretching temperature of 120 ° C. Next, the end of the sheet stretched in the longitudinal direction is introduced into a tenter-type stretching machine by holding it with a clip, preheated at 155 ° C. for 3 seconds, then 8.4 times at 150 ° C., stretching speed 1,100 Stretched at% / min. Except this, under the same conditions as in Example 1, a porous polypropylene film having a width of 500 mm and a thickness of 25 μm was obtained.

(Example 5)
Polypropylene composition (I) 72.3 parts by mass, polypropylene composition (IV) 10 parts by mass, polypropylene composition (III) 16.7 parts by mass and polypropylene having a carboxyl group, prepared in the same manner as in Example 1. One part by mass of ADMER QF500 manufactured by Mitsui Chemicals, Inc., which is a modified polyolefin by resin or unsaturated dicarboxylic acid, was dry blended and supplied to a single screw melt extruder. Then, melt extrusion is performed at 220 ° C. from the single-screw melt extruder, foreign matter is removed with a 60 μm cut sintered filter, and then discharged onto a cast drum whose surface temperature is controlled at 120 ° C. with a T die. Got. Except this, under the same conditions as in Example 1, a porous polypropylene film having a width of 500 mm and a thickness of 25 μm was obtained.

(Comparative Example 1)
90 parts by mass of the polypropylene composition (I) prepared in the same manner as in Example 1 and 10 parts by mass of the polypropylene composition (II) were dry-blended and supplied to a uniaxial melt extruder for layer A, while polypropylene The composition (I) was supplied to a uniaxial melt extruder for the B layer. Then, melt extrusion is performed at 220 ° C. from a single-axis melt extruder for the A layer and a single-axis melt extruder for the B layer, and after removing foreign matters with a 60 μm cut sintered filter, a feed block type B / The A / B composite T die was laminated at a thickness ratio of 1/8/1, discharged onto a cast drum whose surface temperature was controlled at 120 ° C., and cast onto the drum for 15 seconds to obtain a cast sheet. Next, preheating was performed using a ceramic roll heated to 120 ° C., and the cast sheet was stretched 5 times in the longitudinal direction at a stretching temperature of 120 ° C. Next, the sheet stretched in the longitudinal direction was introduced into a tenter-type stretching machine by gripping the end with a clip, preheated at 155 ° C. for 3 seconds, then 8.4 times at 150 ° C., and a stretching speed of 1,800 The film was obtained by stretching at% / min. The distance between the clips in the width direction at the entrance of the tenter was 150 mm.

In the subsequent heat treatment step, the film was heat treated at 150 ° C for 3 seconds while maintaining the distance between the stretched clips (HS1 zone), and further relaxed at 160 ° C and a relaxation rate of 10% (Rx zone). Heat treatment was performed at 160 ° C. for 5 seconds while keeping the distance (HS2 zone).

(Comparative Example 2)
Preheating was performed using a ceramic roll heated to 127 ° C., and the cast sheet was stretched 5 times in the longitudinal direction at a stretching temperature of 127 ° C. Except for this, a porous polypropylene film having a width of 500 mm and a thickness of 25 μm was obtained under the same conditions as in Comparative Example 1.

(Comparative Example 3)
Film formation was performed according to the following method described as Example 1 in JP-A-2008-248231. As a polypropylene resin, 94 parts by mass of homopolypropylene WF836DG3 (MFR: 7 g / 10 min, isotactic index: 97%) manufactured by Sumitomo Chemical Co., Ltd., high melt tension homopolypropylene Pro-fax PF814 (MFR: manufactured by Basell) 2.5 g / 10 min, isotactic index: 97%) 1 part by mass, and ethylene / α-olefin copolymer Engage 8411 (melt index: 18 g / 10 min) manufactured by Dow Chemical Co., Ltd. 2 parts by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide (Nu-100 manufactured by Shin Nippon Rika Co., Ltd.), which is a β crystal nucleating agent, was added to the mixture. It supplied to the screw extruder and melt-kneaded at 220 degreeC. The melt-kneaded material was extruded into a strand shape, cooled and solidified in a 25 ° C. water tank, and cut into a chip shape to obtain a polyolefin resin raw material.

This polyolefin resin is supplied to a single screw extruder, melt extruded at 220 ° C., foreign matter is removed by a sintered filter, and then discharged from a T-die onto a cast drum whose surface temperature is controlled at 120 ° C. Cast for 15 seconds to obtain a cast sheet. Next, the cast sheet was heated using a roll heated to 95 ° C., and stretched 4 times in the longitudinal direction at a stretching temperature of 95 ° C. The sheet stretched in the longitudinal direction is once cooled, and then stretched 6 times in the width direction at 145 ° C. at a stretching speed of 1,500% / min with a stenter-type transverse stretching machine, and heat-fixed at 155 ° C. for 5 seconds. Then, relaxation was performed at 140 ° C. and a relaxation rate of 10% for 5 seconds to obtain a porous polypropylene film having a thickness of 28 μm.

(Comparative Example 4)
Compared to Example 1, in the relaxation of the heat treatment step, relaxation was performed at 160 ° C. and a relaxation rate of 10% (Rx zone), and heat treatment was performed at 160 ° C. for 5 seconds while maintaining the distance between the clips after relaxation (HS2 zone) ). Except for this, a porous polypropylene film having a width of 500 mm and a thickness of 25 μm was obtained under the same conditions as in Example 1.

The characteristics of Examples 1 to 5 and Comparative Examples 1 to 4 are shown in Table 1 below.

In the examples satisfying the requirements of the present invention, the air permeability resistance is low, the porosity is high, and the solvent resistance is excellent. Therefore, the separator for an electricity storage device has little change in physical properties when coating a functional layer such as a heat-resistant layer. Can be suitably used. On the other hand, in the comparative example, since both low air permeability resistance and solvent resistance were insufficient, it was insufficient as a power storage device separator for coating a functional layer such as a heat resistant layer.

Since the porous polypropylene film of the present invention is excellent in organic solvent resistance and gas permeability, it can be suitably used as a separator for an electricity storage device because there is little change in physical properties when coating a functional layer such as a heat-resistant layer. .

1 Measurement position of air resistance 2 Sample 3 Metal frame 4 Double clip (C Bi TP-CL-104)
5 Measurement position of air resistance

Claims

A porous polypropylene film containing a polypropylene resin having β-crystal forming ability, wherein the air permeability resistance is 1,000 seconds / 100 ml or less, and the rate of change in thickness before and after the acetone immersion treatment is 20% or less. Polypropylene film.
The porous polypropylene film according to claim 1, wherein the dimensional change rate in the width direction before and after the acetone immersion treatment is 2% or less.
The porous polypropylene film according to claim 1 or 2, wherein the rate of change in air resistance before and after the acetone immersion treatment is 15% or less.
When the maximum value when the thickness change rate before and after the acetone immersion treatment is measured at intervals of 70 mm in the width direction is T max (%) and the minimum value is T min (%), the value of (T max −T min ) is The porous polypropylene film according to any one of claims 1 to 3, which is 3% or less.
5. The porous polypropylene film according to claim 1, wherein the β-crystal forming ability of the porous polypropylene film is 40% or more.
A laminated porous film obtained by providing a coating layer on the porous polypropylene film according to any one of claims 1 to 5.
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 electricity storage device, wherein the separator is formed using the porous polypropylene film according to any one of claims 1 to 5.
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 is formed using the laminated porous film of Claim 6, The electrical storage device characterized by the above-mentioned.