KR20140081808A - Porous polypropylene film, layered porous film, and electricity-storage device - Google Patents

Abstract

The present invention provides a porous polypropylene film, a laminated porous film and a power storage device which are excellent in organic solvent resistance and durability and have little change in physical properties when a functional layer such as a heat resistant layer is coated. The porous polypropylene film of the present invention is a porous polypropylene film containing a polypropylene resin having the ability to form a crystal, and has a durability of 1,000 sec / 100 ml or less and a rate of change of thickness before and after the acetone immersion treatment of 20% or less .

Description

TECHNICAL FIELD [0001] The present invention relates to a porous polypropylene film, a laminated porous film, and a battery device. [0002] POROUS POLYPROPYLENE FILM, LAYERED POROUS FILM, AND ELECTRICITY-STORAGE DEVICE [

The present invention relates to a porous polypropylene film, a laminated porous film, and a battery device using the same.

The porous polypropylene film is considered to be developed for various applications such as separators for batteries and electrolytic capacitors, various separating membranes, waterproofing membranes for medical applications (medical applications), reflectors for flat panel displays, and thermal transfer recording sheets. . Among them, a porous film is suitable as a separator for a lithium ion battery which is widely used in a notebook personal computer, a mobile phone such as a cellular phone, a digital camera, and the like. Particularly in recent years, lithium ion batteries have been used in electric vehicles and hybrid cars, and studies have been actively conducted to coat an inorganic particle layer or a heat-resistant resin layer on a porous film in accordance with the increase in output and capacity of batteries (for example, 2). In addition, since the size of the battery is increased and the area used is increased, low cost is strongly demanded.

A variety of proposals have been made on the method of repacking a polypropylene film. Among them, the β-crystallization method is a drying method and a method capable of forming a film with good productivity by biaxial stretching. The β-crystallization method is a method of forming voids in a film by using a difference in crystal density between the α-form crystals (α-form crystals) and β-form crystals (β-form crystals), which are crystalline polymorphs of polypropylene, and crystal transition, and a number of proposals have been made (See, for example, Patent Documents 3 to 5). A number of proposals have been made for a method of coating a functional layer such as a heat-resistant layer on the surface of a porous polypropylene film by a β-crystallization method (see, for example, Patent Documents 6 to 14).

However, when the organic solvent such as acetone is applied and dried in the porous polypropylene film obtained by the β-crystallization method, the pore structure may be changed to change the thickness or the durability of the porous film. Therefore, as described in Patent Documents 6 to 14, Is limited to a water system, and it is difficult to improve the productivity by using an organic solvent having a high drying speed.

Japanese Patent Application Laid-Open No. 2007-273443 Japanese Patent Application Laid-Open No. 2006-164873 Japanese Patent Application Laid-Open No. 63-199742 Japanese Unexamined Patent Application Publication No. 6-100720 Japanese Patent Application Laid-Open No. 9-255804 Japanese Patent Application Laid-Open No. 2009-19118 Japanese Patent Application Laid-Open No. 2009-114434 Japanese Patent Application Laid-Open No. 2009-226746 Japanese Patent Application Laid-Open No. 2009-227819 Japanese Patent Application Laid-Open No. 2010-65088 Japanese Patent Application Laid-Open No. 2010-219037 Japanese Patent Laid-Open No. 1110704 Japanese Patent Application Laid-Open No. 2011-126275 International Publication No. 2010/008003

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a porous polypropylene film which can be suitably used as a separator for power storage devices, which has excellent organic solvent resistance and pourability and exhibits little change in physical properties when a functional layer, A multilayer porous film, and a battery device using the same.

In order to solve the above problems and to achieve the object, the porous polypropylene film according to the present invention is a porous polypropylene film comprising a polypropylene resin having a capability of forming a crystal, and has a durability of 1,000 sec / 100 ml or less, And the thickness change ratio before and after the treatment is 20% or less.

The porous polypropylene film of the present invention is excellent in organic solvent resistance and pourability and can be suitably used as a separator for power storage devices because the change in physical properties is small when a functional layer such as a heat resistant layer is coated.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view of a sample before acetone immersion treatment in measurement of change in physical properties accompanied by acetone immersion and drying treatment. Fig.
Fig. 2 is a schematic view of a sample after being immobilized on a metal frame in measurement of changes in physical properties accompanying acetone immersion and drying treatment. Fig.
Fig. 3 is a schematic view of a sample after acetone immersion drying treatment in measurement of change in physical properties accompanied by acetone immersion and drying treatment. Fig.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a porous polypropylene film, a multilayer porous film and a battery device according to the present invention will be described in detail with reference to the drawings. The present invention is not limited by these embodiments.

The porous polypropylene film according to the present embodiment includes a polypropylene resin having the ability to form? Crystals as a first component. Here, the polypropylene resin is preferably the main component in the porous polypropylene film. Here, the term "main component" means that the specific component accounts for 50% by mass or more of the total components, more preferably 80% by mass or more, further preferably 90% by mass or more, and particularly preferably 95% it means.

The porous polypropylene film according to the present embodiment has holes (hereafter referred to as through holes) having permeability through both surfaces of the film. As a method for obtaining the porous polypropylene film having the through-hole, it is preferable that the method is a β-crystallization method described later in that a film can be formed with good productivity by biaxial stretching.

In order to form a through hole in the film by using the? crystallization method, it is preferable that the porous polypropylene film has a? crystal forming ability of 40% or more. When the? -crystal-forming ability is less than 40%, the amount of? crystals is small at the time of film production, so that the number of voids formed in the film is reduced by using the transition to? crystals, and as a result, only a film with low transparency may be obtained. On the other hand, the upper limit of the? -Crystal-forming ability is not particularly limited, but if it exceeds 99.9%, it is necessary to add a large amount of the? -Crystalline nucleating agent to be described later or to make the stereoregularity of the polypropylene resin to be used extremely high , The film forming stability is lowered, and the industrial practical value is low. The β-crystal forming ability is industrially preferably 65 to 99.9%, particularly preferably 70 to 95%.

In order to control the? -crystalline forming ability to 40% or more, a polypropylene resin having a high isotactic index is used, or a crystallization nucleating agent for selectively forming a? crystal is added to a polypropylene resin called? It 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 Tetraoxaspiro compounds such as the representative amide compounds, 3,9-bis [4- (N-cyclohexylcarbamoyl) phenyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, Aromatic sulfonic acid compounds such as sodium sulfonate and sodium naphthalenesulfonate, imidecarboxylic acid derivatives, phthalocyanine-based pigments and quinacridone-based pigments can be preferably used. Particularly, Japanese Patent Laid-Open Publication No. 5-310665 Amide-based compounds can be preferably used. The amount of the? crystal nucleating agent to be added is preferably 0.05 to 0.5% by mass, more preferably 0.1 to 0.3% by mass based on the whole polypropylene resin. When the amount is less than 0.05% by mass, the formation of the? -Crystal becomes insufficient, and the porosity of the porous polypropylene film may deteriorate in some cases. If it exceeds 0.5% by mass, coarse voids may be formed, which may result in a large change in physical properties during application and drying of the organic solvent.

The polypropylene resin constituting the porous polypropylene film according to the present embodiment preferably has a melt flow rate (hereinafter referred to as MFR, measurement conditions: 230 ° C, 2.16 kg) in the range of 2 to 30 g / 10 min, Further, it is preferable that it is an isotactic polypropylene resin. If the MFR is less than 2 g / 10 min, 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 is excessively low, so that film breakage tends to occur at the time of stretching, and the productivity may be lowered. More preferably, the MFR is 3 to 20 g / 10 min.

When an isotactic polypropylene resin is used, the isotacticity index is preferably 90 to 99.9%, and more preferably 95 to 99%. If the isotacticity index is less than 90%, the crystallinity of the resin is low and it may be difficult to achieve high specularity.

As the polypropylene resin to be used in the present embodiment, homopolypropylene resin can be used. In addition, from the viewpoints of stability in film forming process, film formability, and uniformity of physical properties, it is possible to use an ethylene component, a butene, a hexene, Of the? -Olefin component in the range of 5% by mass or less, more preferably 2.5% by mass or less. The mode of introduction of the comonomer (copolymerization component) to the polypropylene may be either random copolymerization or block copolymerization.

The above-mentioned polypropylene resin may contain a high molecular weight polypropylene in some cases from the viewpoints of safety improvement and film formability improvement. The content is preferably in the range of 0.5 to 30 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 and E105GM manufactured by Prime Polymer.

In addition, it is preferable that the above-mentioned polypropylene resin contains a low melting point polypropylene in view of safety improvement and improvement of film formability. The content is preferably in the range of 0.5 to 30 mass%. The low melting point polypropylene is polypropylene having a melting point Tm of 130 to 155 占 폚, for example, polypropylene resin S131 or FS3611 made by Sumitomo Chemical Co., Ltd. can be used.

The polypropylene resin used in the present embodiment is a mixture of 80 to 99 parts by mass of polypropylene and 20 to 1 part by mass of ethylene /? - olefin copolymer in terms of void formation efficiency at the time of biaxial stretching . As the ethylene /? - olefin copolymer, there may be mentioned linear low density polyethylene or ultra low density polyethylene. Of these, a copolymerized polyethylene resin (copolymerized PE resin) copolymerized with octene-1 and having a melting point of 60 to 90 ° C is preferably used Can be used. Examples of the copolymerized polyethylene include commercially available resins such as "Engage (registered trademark)" (type name: 8411, 8452, 8100, etc.) manufactured by DOW CHEMICAL.

When the content of the copolymerized polyethylene resin is 10% by mass or less based on 100% by mass of the entire polypropylene resin constituting the film of the present embodiment, the porosity and the average through-hole diameter are set within a preferable range And therefore it is preferable. From the viewpoint of the mechanical properties of the film, 1 to 7 mass% is more preferable, and 1 to 2.5 mass% is more preferable.

The polypropylene resin used in the present embodiment is preferably added with a dispersant in addition to the ethylene /? - olefin copolymer described above from the viewpoint of uniformizing the pore structure and suppressing the change in physical properties after acetone immersion treatment. The dispersant may be one which can increase the dispersibility of the ethylene /? - olefin-based copolymer to the polypropylene resin. As described in WO 2007/046225, a polypropylene resin and an ethylene /? - olefin- For example, an ethylene / propylene random copolymer generally used as a compatibilizing agent of a polypropylene resin and a polyethylene resin does not function as a dispersant for uniformizing the pore structure in the present embodiment. Examples of the dispersant preferably used in the present embodiment include a segment (polypropylene segment, ethylene butylene copolymer segment) having high compatibility with polypropylene and a segment (polyethylene segment or the like) having high compatibility with polyethylene Block copolymer is preferable. As a resin having such a structure, commercially available resins such as olefin crystal, ethylene butylene, olefin crystal block polymer (hereinafter referred to as CEBC) "DYNARON (registered trademark)" : 6100P, 6200P, etc.) and the olefin block copolymer "INFUSE OBC (registered trademark)" manufactured by DOW CHEMICAL CO., LTD. The amount of the dispersant to be added 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 /? - olefin copolymer. From the viewpoints of improving the dispersibility of the ethylene /? - olefin-based copolymer to the polypropylene resin and improving the uniformity of pore formation, the melting point of the dispersing agent is preferably from 0 to 60 Deg.] C, and more preferably 15 to 30 [deg.] C.

The polypropylene resin forming the porous polypropylene film according to the present embodiment may contain additives such as an antioxidant, a heat stabilizer, a neutralizer, an antistatic agent, a lubricant containing inorganic or organic particles, Various additives such as filler, filler, and incompatible polymer may be added. Particularly, it is preferable to add an antioxidant for the purpose of suppressing oxidative deterioration due to thermal history of the polypropylene resin. However, the amount of the antioxidant to be added to 100 parts by mass of the polypropylene composition is preferably 2 parts by mass or less, more preferably 2 parts by mass or less 1 part by mass or less, and more preferably 0.5 part by mass or less.

The porous polypropylene film of the present embodiment has a thickness change ratio of 20% or less before and after the acetone immersion treatment. When the thickness change ratio exceeds 20%, that is, when the thickness exceeds 20%, shrinkage or swelling, when the functional layer such as the heat resistant layer is applied by coating, the thickness changes according to the drying condition, Or the output resistance may decrease due to the increase of the dumping resistance. The rate of change in thickness before and after the acetone immersion treatment is preferably 14% or less, more preferably 7% or less. The rate of change in the thickness before and after the acetone immersion treatment may be determined by adjusting the addition amount of the above-mentioned? -Crystalline nucleus agent, ethylene /? - olefin copolymer or dispersant within the above range, the temperature, the longitudinal stretching magnification and temperature, The temperature and time in the heat treatment process, and the relaxation rate in the relaxation zone within the range described later.

The porous polypropylene film according to the present embodiment can be used as a separator in a power storage device provided with, for example, a separator provided between a positive electrode and a negative electrode to prevent contact between the positive electrode and the negative electrode and to transmit ions in the electrolyte solution.

The porous polypropylene film of the present embodiment has a dumping resistance of 1,000 sec / 100 mL or less. More preferably 10 to 1,000 seconds / 100 ml, more preferably 50 to 500 seconds / 100 ml, and most preferably 80 to 350 seconds / 100 ml. When the durability exceeds 1,000 seconds, the output characteristics may be lowered when the porous polypropylene film is used in the separator of the power storage device. From the viewpoint of the output characteristics, the lower the durability is, the better. However, when the durability is less than 10 seconds, the mechanical strength of the film is lowered and handling properties are lowered, and electrical characteristics such as cycle characteristics are lowered when used in the separator. In the case of controlling the durability by the β-crystallization method, the longitudinal stretching conditions such as the longitudinal stretching magnification and the longitudinal stretching temperature, or the transverse stretching temperature and the transverse stretching conditions such as the transverse stretching speed and the transverse stretching ratio, Control can be performed.

However, in the case of controlling the durability by the operating conditions, when the durability is lowered, the porosity of the porous polypropylene film is increased and the physical properties and dimensions after the acetone immersion treatment are increased. Therefore, in the present embodiment, besides the use of the raw materials described above, by setting the conditions after the heat treatment conditions after the transverse stretching to the specific conditions as described below, the durability is low and the change in physical properties and dimensions due to the acetone treatment is small A porous polypropylene film was obtained, and both the organic solvent and the output characteristics were made compatible. The heat treatment conditions will be described below.

In the β-crystallization method, it is possible to obtain a porous polypropylene film by forming holes by transverse stretching in a tenter after the longitudinal stretching. 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 is heat-set and relaxed after stretching. (Tm-10) DEG C to (Tm-5) DEG C when the melting point of the polypropylene resin is Tm. In this embodiment, the relaxation rate is about 2 to 10% (Tm-2) 占 폚 to (Tm + 5) 占 폚 by taking the temperature at that time as a high value of 15 to 35% A porous polypropylene film having a small change can be obtained.

The porous polypropylene film of the present embodiment preferably has a film thickness of 5 to 50 mu m. If the thickness is less than 5 mu m, the film may be broken at the time of use. If the thickness exceeds 50 mu m, the volume ratio of the porous polypropylene film in the electrical storage device may become excessively high, and high energy density may not be obtained. The film thickness is more preferably 10 to 30 mu m, and further preferably 12 to 25 mu m.

The porosity of the porous polypropylene film according to the present embodiment is preferably 40 to 85%. If the porosity is less than 40%, the electrical resistance may be increased particularly when used as a separator for a high output battery. On the other hand, when the porosity exceeds 85%, the physical properties and dimensional changes after acetone treatment may increase. The porosity of the film is more preferably from 42 to 75%, and particularly preferably from 45 to 70% from the viewpoint of achieving excellent cell characteristics and organic solvent resistance. The porosity may be determined by adjusting the addition amount of the above-mentioned? -Crystalline nucleus, ethylene /? - olefin copolymer or dispersant within the above range, the temperature of the casting drum, the stretching magnification and temperature in the longitudinal direction, the transverse stretching magnification, And the relaxation rate in the relaxation zone within the range described below.

In the porous polypropylene film of the present embodiment, it is preferable that the rate of dimensional change in the width direction before and after the acetone immersion treatment is 2% or less. Herein, the acetone immersion treatment refers to a treatment in which the 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 DEG C for 1 minute to remove acetone. When the dimension in the width direction after the acetone treatment is contracted by more than 2% before the acetone treatment, when the functional layer such as the heat resistant layer is applied by coating, the durability is increased or the width is decreased to increase the thickness have. On the other hand, when the dimension in the width direction after the acetone treatment is expanded to more than 2% before the acetone treatment, the resin constituting the porous polypropylene film is swollen or dissolved when a functional layer such as a heat resistant layer is applied by coating, The pores of the polypropylene film are coarsened and the electrical characteristics such as the cycle characteristics may be lowered. The dimensional change ratio in the width direction is more preferably 1.5% or less, more preferably the dimensional shrinkage ratio in the width direction before and after the acetone immersion treatment is preferably 0 to 1.5%, and most preferably the shrinkage ratio in the width direction before and after the acetone immersion treatment is 0 to 1%. The rate of dimensional change in the transverse direction before and after the acetone immersion treatment may be determined by adjusting the addition amount of the β-crystal nucleus agent, the ethylene / α-olefin copolymer or the dispersant within the above-mentioned range, the temperature and the stretching magnification and temperature in the casting drum, It is possible to control the temperature and time in the heat treatment process, the relaxation rate in the relaxation zone within the range described later, and particularly, the control of the temperature, time, and relaxation rate in the heat treatment process is important.

In the present invention, the direction parallel to the direction in which the film is formed is referred to as a film forming direction, the longitudinal direction, or the MD direction, and the direction orthogonal to the film forming direction within the film surface is referred to as a width direction, a lateral direction, or a TD direction.

In the porous polypropylene film of the present embodiment, it is preferable that the change rate of the durability before and after the acetone immersion treatment is 15% or less. When the rate of change of the dumping resistance exceeds 15%, that is, when the durability is reduced or increased by more than 15%, when the functional layer such as the heat resistant layer is applied by coating, the durability is changed by the drying condition, The durability is increased, the durability of the durability is increased, the output characteristics are decreased, and the durability of the durability of the durability of the durability is increased. The change rate of the dumping resistance before and after the acetone immersion treatment is preferably 10% or less, more preferably 7% or less. The rate of change of the durability before and after the acetone immersion treatment is determined by adjusting the addition amount of the above-mentioned? -Crystalline nucleus agent, ethylene /? - olefin copolymer or dispersant within the above range, the temperature of the casting drum, the stretching magnification and temperature in the longitudinal direction, The magnification, the temperature and time in the heat treatment process, and the relaxation rate in the relaxation zone within the range described below.

In the porous polypropylene film according to the present embodiment, when the maximum value and the minimum value of the thickness change ratio before and after the acetone immersion treatment are measured at intervals of 70 mm in the width direction as T _max (%) and T _min (% (T _max -T _min ) is preferably 3% or less. More preferably, it is 2% or less. When the value of (T _max -T _min ) is more than 3%, the thickness variation ratio in the width direction is large, so that the thickness unevenness in the width direction of the product may become large when coating is performed using an organic solvent. (T _max -T _min ) is determined by setting the addition amount of the above-mentioned? -Crystalline nucleus agent, ethylene /? - olefin copolymer or dispersant within the above range, the temperature of the casting drum and the relaxation rate in the relaxation zone To be within a range.

The porous polypropylene film according to the present embodiment preferably has a laminated structure in view of compatibility between the organic solvent and the air permeability. As the laminated structure, it is preferable that either one of the layers contains a polypropylene resin having a carboxyl group or a modified polyolefin made of an unsaturated dicarboxylic acid, more preferably a polypropylene resin having a carboxyl group as the surface layer or an unsaturated dicarboxylic acid It is preferable that it contains a modified polyolefin by an acid. The polypropylene resin having a carboxyl group or the polyolefin modified with an unsaturated dicarboxylic acid is preferably contained in an amount of 0.1 to 50%, more preferably 1 to 10%, in the layer contained. As a method for 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 its acid derivatives and monoolefin dicarboxylic acids, anhydrides thereof and monoesters thereof. Specific examples of (meth) acrylic acid and its ester derivatives include (meth) acrylic acid; (Meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl Examples of the monoolefin dicarboxylic acid include maleic acid, chloromaleic acid, citraconic acid, itaconic acid, glutaconic acid, 3-methyl-2-pentene diacid, - pentene-diacid, 2-hexene-diacid, and the like. These polypropylene resins also preferably have a? -Crystalline forming ability, and more preferably have a? -Crystalline forming ability of 40% or more.

The laminated water may be a laminate of two layers, a laminate of three layers, or a laminated layer of any of them. The lamination method may be a feed block method by co-extrusion or a method of bonding porous polypropylene films by lamination. Any method may be used, but from the viewpoint of productivity, a laminate by coextrusion desirable.

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

99.5 parts by mass of a commercially available homopolypropylene resin having an MFR of 8 g / 10 minutes as a polypropylene resin, 0.3 parts by mass of N, N'-dicyclohexyl-2,6-naphthalenedicarboxyamide as a crystal nucleating agent, and 0.2 parts by mass of an antioxidant The raw material is fed from a weighing hopper to the twin screw extruder so as to be mixed in this ratio, melt-kneaded, discharged from the die onto a strand, cooled and solidified in a water bath at 25 캜 and cut into chips to prepare a raw material for polypropylene (a) . At this time, the melting temperature is preferably 270 to 300 캜.

Similarly, 59.8 parts by mass of the above-mentioned homopolypropylene resin, 30 parts by mass of an ethylene /? -Olefin copolymer having an MFR of 18 g / 10 minutes as an ethylene /? - olefin copolymer, 10 parts by mass of CEBC and 0.2 parts by mass of an antioxidant were mixed at this ratio. The raw materials were fed from a weighing hopper to a twin-screw extruder, melt-kneaded at 240 DEG C, discharged from the die onto a strand, 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 minutes, 30 parts by mass of a commercially available homopolypropylene having an MFR of 0.5 g / 10 minutes and 0.2 parts by mass of an antioxidant at this ratio The raw material was fed from a weighing hopper to a twin screw extruder so as to be melt-kneaded at 240 DEG C, discharged from the die onto a strand, cooled and solidified in a water bath at 25 DEG C and cut into chips to prepare a polypropylene raw material (c) do.

Subsequently, 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 part by mass of the antioxidant were mixed by dry blending, On the other hand, 99 parts by mass of the polypropylene raw material (a) and 1 part by mass of a polypropylene resin having a carboxyl group or a modified polyolefin with an unsaturated dicarboxylic acid are dry-blended and fed to the single-screw extruder of the B layer. Then, melt extrusion is performed at 200 to 230 캜 from a single-screw extruder of the A-layer and a single-screw extruder of the B-layer. Further, the foreign substances and the modified polymer are removed by a filter installed in the middle of the polymer tube, and then discharged from the feed block type B / A / B composite T die onto the casting drum to obtain an unstretched laminated cast sheet. The casting drum preferably has a surface temperature of 105 to 130 DEG C from the viewpoint of controlling the beta crystal fraction of the casting sheet to a high level. At this time, it is particularly preferable that the end portion of the sheet affects the subsequent stretchability, so that spot air is sprayed to the end portion so as to adhere to the drum. In addition, air may be sprayed from the close contact state of the entire sheet on the drum with the use of an air knife on the entire surface, if necessary. The casting sheet refers to an unstretched sheet obtained by forming a molten polypropylene resin into a sheet on a casting drum.

Then, the obtained casting sheet is biaxially oriented to form pores in the sheet. As a biaxial orientation method, there are a sequential biaxial stretching method in which the casting sheet is stretched in the width direction, then in the width direction, or in the width direction and then in the longitudinal direction, or in the longitudinal direction and the width direction of the casting sheet A simultaneous biaxial stretching method in which stretching is performed at substantially the same time, or the like can be used. From the viewpoints of the durability and the organic solvent resistance, it is preferable to adopt a biaxial stretching method of a sequential order. In particular, it is preferable to stretch in the longitudinal direction and then in the width direction.

As specific stretching conditions, first, the temperature of the casting sheet is controlled to a temperature at which stretching is performed in the longitudinal direction. As the temperature control method, a method using a temperature-controlled rotary 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. Below 90 DEG C, the casting sheet may be broken or the porosity may become excessively high, resulting in a large change in physical properties and dimensions after the acetone treatment. On the other hand, if it exceeds 140 캜, the durability may decrease. The stretching temperature in the longitudinal direction is more preferably 110 to 135 占 폚, particularly preferably 125 to 130 占 폚. The stretching magnification is preferably 3 to 7 times. If it is less than 3 times, the durability is low and the output characteristic may be lowered. The higher the draw ratio, the better the durability. However, when the draw ratio exceeds 7 times, the porosity becomes excessively high and the change in the physical properties and dimensions after acetone treatment may become large. The draw ratio is more preferably from 4.5 to 6 in view of compatibility between high specularity and organic solvent resistance.

Then, the end portion of the sheet drawn in the longitudinal direction is gripped and introduced into the tenter-type stretching machine. The transverse stretching temperature is preferably 130 to 155 占 폚. If the temperature is less than 130 캜, the stretched sheet in the longitudinal direction may break, or the physical properties and dimensions of the film after the transverse stretching may change significantly after the acetone treatment. If the temperature exceeds 155 캜, . The transverse drawing temperature is more preferably from 140 to 155 DEG C from the viewpoint of compatibility between the air permeability and the organic solvent resistance. The stretching ratio in the width direction is preferably 4 to 12 times. If it is less than 4 times, the durability may deteriorate and the output characteristics may be lowered. If it is more than 12 times, the physical properties and dimensional changes after acetone treatment may increase. From the viewpoint of compatibility between the output property and the 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 magnification x transverse stretching magnification) is preferably 30 to 60 times. Thus, a film (porous polypropylene film) is obtained by stretching the cast sheet.

Following the transverse stretching, a heat treatment step is performed in the tenter. Here, the heat treatment process is a heat-setting zone (hereinafter referred to as HS1 zone) in which heat treatment is performed as it is after the transverse stretching, a relaxation zone (hereinafter referred to as Rx zone) in which the width of the tenter is narrowed, (Hereinafter referred to as the HS2 zone) in which the heat treatment is carried out as it is in the width after the heat treatment and in the organic solvent resistance control.

The temperature of the zone HS1 is preferably between 140 and 165 ° C. If the temperature of the zone HS1 is less than 140 DEG C, the change in physical properties and dimensions after the acetone treatment may become large. On the other hand, when the temperature of the HS1 zone exceeds 165 DEG C, the surface of the porous polypropylene film is melted to increase the durability, or the porous polypropylene film shrinks in the width direction and breaks in the HS1 zone, have. From the viewpoint of compatibility between the output characteristics and the organic solvent resistance, the temperature of the HS1 zone is more preferably 150 to 160 deg.

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

In the present embodiment, the relaxation ratio in the Rx region is preferably 13 to 35%. If the relaxation ratio is less than 13%, the heat shrinkage ratio in the width direction may become large. On the other hand, when the relaxation rate exceeds 35%, the durability is lowered and the output characteristics are lowered, and the thickness irregularity in the width direction and the heat shrinkage rate become uneven. From the viewpoint of compatibility between the output characteristics and the low heat shrinkage ratio, the relaxation ratio is more preferably 15 to 25%.

The temperature of the Rx zone is preferably 155-170 < 0 > C. If the temperature in the Rx zone is less than 155 占 폚, the shrinkage stress for relaxation is lowered and the above-mentioned high relaxation ratio can not be achieved, or the physical properties and dimensional changes after acetone treatment may increase. On the other hand, if the temperature in the Rx zone exceeds 170 캜, the polymer around the hole may melt due to the high temperature, thereby reducing the durability. From the viewpoint of the output characteristics and the organic solvent resistance, the temperature of the Rx zone is more preferably 160 to 165 占 폚.

The relaxation speed in the Rx zone is preferably 100 to 1,000% / min. If the relaxation speed is less than 100% / minute, it is necessary to slow down the film forming speed or to increase the tenter length, which may result in poor productivity. On the other hand, if the relaxation speed exceeds 1,000% / minute, the rate at which the film shrinks is slower than the rate at which the rail width of the tenter decreases, so that the film is flaked and broken in the tenter, May be increased or planarity may be lowered. The relaxation speed is more preferably 150 to 500% / min.

The temperature of the HS2 zone is preferably between 155 and 165 ° C. If the temperature of the HS2 zone is less than 155 占 폚, the tension of the film after heat relaxation becomes insufficient, and the variation rate of the thickness after the acetone treatment may become ununiform in the width direction or cause a decrease in planarity. On the other hand, if the temperature of the zone HS2 exceeds 165 DEG C, the polymer around the hole melts due to the high temperature, resulting in deterioration of the durability and the output characteristics may be deteriorated. From the viewpoint of compatibility between the output characteristics and the organic solvent resistance, the temperature of the HS2 zone is more preferably 160 to 165 占 폚. The film after the heat fixing step is slit and removed by a clip held by a clip of the tenter, and wound on a core by a winder to obtain a product.

Thereafter, a coating layer may be provided on at least one side of the porous polypropylene film to obtain a laminated porous film. Since the porous polypropylene film of the present embodiment has excellent organic solvent resistance, it is possible to maintain high air permeability even when coating is carried out using an organic solvent. As the coating method, a known method can be used. For example, at least one organic solvent selected from acetone, ethanol, tetrahydrofuran, N-methyl-2-pyrrolidone and the like is used as the solvent, and heat-resistant resin or inorganic particles and a binder An additive may be added to prepare a coating agent, and coating may be performed on at least one surface of the porous polypropylene film using a die coating method or a gravure coating method. Thereafter, the laminated porous film can be obtained by drying the solvent using a drying oven.

The porous polypropylene film according to the present embodiment is excellent in productivity, low in durability, and small in changes in physical properties and dimensions after the acetone treatment. Therefore, the porous polypropylene film can be used as packaging articles, sanitary articles, agricultural articles, , A light diffusing plate, and a reflection sheet, but it is particularly suitable in terms of being capable of satisfying the output characteristics and the organic solvent resistance when used as a separator for a power storage device. Examples of the electrical storage device include a non-aqueous electrolyte secondary battery typified by a lithium ion secondary battery and an electric double layer capacitor such as a lithium ion capacitor. Such a power storage device can be used repeatedly by charging and discharging, so that it can be used as a power supply device for an industrial device, a living appliance, an electric car or a hybrid electric car. Particularly, the electrical 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 functional layer such as a heat resistant layer on the surface layer. The laminated porous film to which the heat resistant layer is applied to the porous polypropylene film according to the present embodiment can be suitably used for a nonaqueous electrolyte secondary battery for electric vehicles because of its excellent output characteristics and safety.

<Examples>

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

(1) β crystal formation ability

5 mg of the porous polypropylene film was taken as a sample into a pan made of aluminum and measured using a differential scanning calorimeter (RDC220, manufactured by Seiko Denshi Kogyo). First, the temperature is raised from the room temperature to 260 占 폚 in a nitrogen atmosphere at 10 占 폚 / min (first run), held for 10 minutes, and then cooled to 40 占 폚 at 10 占 폚 / min. The melt having a peak in a temperature range of 145 to 157 DEG C is added to the melting peak observed at a temperature rise (second run) at 10 DEG C / , Melting at which peaks are observed at 158 占 폚 or higher is defined as the melting peak of the? Crystal, and the respective amounts of heat of fusion are determined from the areas of the regions surrounded by the base line and the peak based on the flat portion on the high temperature side, And the heat of fusion of the? Crystal is? H ?, the value calculated by the following formula is defined as the ability to form? Crystals. Calibration of the heat of fusion was carried out using indium.

β crystal formation ability (%) = [ΔHβ / (ΔHα + ΔHβ)] × 100

Further, the β crystal fraction in the sample state can be calculated by calculating the existence ratio of β crystal similarly from the melting peak observed in the first run.

(2) Melting point (Tm)

The polypropylene resin was measured in the same manner as the method for measuring the? -Crystalline forming ability, and the peak temperature (? Crystal) of the second run was set as the melting point (Tm).

(3) Change in physical properties accompanying immersion in acetone and drying treatment

The porous polypropylene film was cut into a rectangular shape having a length of 140 mm and a width of 70 mm to obtain a sample (2) (see Fig. 1). The dimension of the center portion in the longitudinal direction with respect to the width direction of the cut porous polypropylene film was measured to obtain the length L _TD1 (mm) in the width direction before the treatment. The film thickness at the center of the sample 2 was measured by the method according to the following (8), and the thickness before processing was set to T1 (占 퐉). The durability of the cut sample (2) was measured according to the method described in the following (6). The measurement position 1 of the dumping resistance was made two at the center passing through the center in the width direction and centered on a point 30 mm inward from two sides parallel to the width direction. The specular resistance was measured at these measurement positions (1), and the average value thereof was set as a speculative resistance G1 before processing.

The metal frame 3 made of stainless steel having an inner frame of 80 mm x 80 mm and an outer frame of 100 mm x 100 mm (see Fig. 2) And only the longitudinal direction of the sample 2 was fixed by inserting two portions per one side with a double clip (C ratio TP-CL-104) (4). The sample 2 was set so as not to be wrinkled or loosened at the time of fixing the sample 2 and the 5g weight of the cylindrical shape having a contact surface of 0.785 cm 2 was placed at the center of the fixed sample 2, It was confirmed that the warping amount was 1 mm or less. The sample 2 immersed in the longitudinal direction only in the metal frame was immersed in acetone (Kanto Kagaku Kogyo Co., Ltd.) for 1 minute and then heated in a hot air oven at 80 캜 (PHH-100 made by Espex (former TABAI) Setting) for one minute, removed from the oven, allowed to stand for 5 minutes, cooled to room temperature, and then the sample (2) was removed from the metal frame.

The sample 2, which was removed from the hot air oven, was measured for the shrunken position with respect to the width direction of the sample 2, and the length thereof was taken as the length L _TD2 (mm) in the width direction after processing (see FIG. The film thickness at the center of the most shrunken place in the width direction was measured by the method according to the following (8), and the thickness after processing was determined as T2 (占 퐉). The durability of the specimen 2 is measured based on the most shrunk place (measurement position 5 of drip resistance) in the width direction of the sample 2, G2 (Fig. 3).

The rate of change of each physical property was calculated based on the following expression.

Width direction dimensional change ratio (%) = | L _TD1 -L _TD2 | / L _TD1 100

Thickness change ratio (%) = | T1-T2 | / T1100

Gurley Rate of change in speculative resistance (%) = | G1-G2 | / G1 100

(4) Width direction unevenness of the rate of change of thickness before and after acetone immersion treatment

As a sample for measurement, a sample having a width of 70 mm from one end in the width direction of the porous polypropylene film to the other end was cut across the entire width of the porous polypropylene film at a center line interval of 70 mm. Further, in the case where an end water of less than 70 mm was generated at the other end, a sample having a length of 70 mm, which is in contact with the other end, was sampled from a portion adjacent to the longitudinal direction. The thickness variation before and after immersing in acetone was measured for each sample in the same manner as in (3) above to determine the rate of thickness change. (T _max -T _min ) was obtained by setting the maximum value of the rate of change of thickness of each measurement value as T _max and the minimum value of the rate of change of thickness as T _min .

(5) Melt flow rate (MFR)

The MFR of the polypropylene resin was measured according to the condition M (230 DEG C, 2.16 kg) of JIS K7210 (1995). The MFR of the polyethylene resin was measured according to the condition D (190 DEG C, 2.16 kg) of JIS K 7210 (1995).

(6) Speculative resistance

The porous polypropylene film was measured for the permeation time of 100 ml of air at 23 DEG C and a relative humidity of 65% using a B type gluing tester of JIS P 8117 (1998). Further, the fact that a through hole is formed in the film can be confirmed by confirming that the permeability has a finite value.

(7) Public rate

The porous polypropylene film was cut into a size of 30 mm x 40 mm to obtain a sample. The specific gravity (rho) was measured in an atmosphere at room temperature of 23 DEG C and relative humidity of 65% using an electronic specific gravity meter (SD-120L manufactured by Mirajo Boo Co., Ltd.).

Then, the measured film was hot-pressed at 280 占 폚 and 5 MPa, and then quenched with water at 25 占 폚 to produce a sheet which was completely blanked. The specific gravity of the 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 any of the examples described later, the specific gravity d of the resin was 0.91. From the specific gravity of the film and the specific gravity of the resin, the porosity was calculated by the following formula.

The porosity (%) = [(d-p) / d] x 100

(8) Film thickness

The thickness was measured using a dial gauge thickness meter (JIS B-7503 (1997), UPRIGHT DIAL GAUGE (0.001 x 2 mm) manufactured by PEACOCK, No. 25, equilibrium measuring 10 mmφ, load of 50 gf).

(Example 1)

99.7 parts by mass of a homopolypropylene FLX80E4 available from Sumitomo Chemical Co., Ltd. as a polypropylene resin having a melting point of 165 占 폚 and MFR = 7.5 g / 10 minutes, N, N'-dicyclohexyl-2,6-naphthalene , 0.3 part by mass of dicarboxyamide (NU-100, manufactured by Shin-Nippon Rika KK), 0.1 part by mass of each of antioxidant IRGANOX 1010 and IRGAFOS 168, , And the mixture was melt-kneaded at 300 占 폚. Then, the melt-kneaded material was discharged from the die into a strand, cooled and solidified in a water bath at 25 DEG C, and cut into chips to obtain a polypropylene composition (I).

Then, 70 parts by mass of homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd., having a melting point of 165 占 폚 and an MFR of 7.5 g / 10 minutes, an ethylene-octene-1 copolymer (DOW CHEMICAL INC. 8411, 30 parts by mass as a polymerization initiator, 30 parts by mass as a polymerization initiator, and 30 parts by mass as a melt index: 18 g / 10 minutes), 0.1 parts by mass of Ciba Specialty Chemicals Glygannox 1010 and Irgaphos 168 as antioxidants, And melt-kneaded at 240 占 폚. Then, the melt-kneaded material was discharged from the die into a strand shape, cooled and solidified in a water bath at 25 ° C, and cut into chips to obtain a polypropylene raw material (II).

As a polypropylene resin, 70 parts by mass of homopolypropylene FLX80E4, 30 parts by mass of homopolypropylene D101 (trade name, manufactured by Sumitomo Chemical Co., Ltd.) having a melting point of 162 占 폚 and MFR of 0.5 g / 10 minutes and 30 parts by mass of Ciba Specialty Chemicals Knox 1010 and Irgafos 168 were respectively fed into a twin-screw extruder from a weighing hopper such that 0.1 parts by mass thereof was mixed in this ratio, and melt-kneaded at 240 ° C. Then, the melt-kneaded material was discharged from the die onto the strand, cooled and solidified in a water bath at 25 DEG C, and cut into chips to obtain a polypropylene composition (III).

73.3 parts by mass of the obtained polypropylene composition (I), 10 parts by mass of the polypropylene composition (II) and 16.7 parts by mass of the polypropylene composition (III) were dry-blended and fed to the single-shaft melt extruder for layer A, ) And 1 part by mass of Adomer QF500 manufactured by Mitsui Chemicals, Inc., a polypropylene resin having a carboxyl group or a modified polyolefin having an unsaturated dicarboxylic acid, were fed to a single-shaft melt extruder for the B layer. Then, melt extrusion was carried out at 220 占 폚 from a single-shaft melt extruder for layer A and a single-shaft melt extruder for layer B. After removal of foreign matter by a sintering filter of 60 占 퐉 cutting, a feed block type B / A / B composite T And then discharged onto a casting drum controlled at a surface temperature of 122 캜 to obtain a cast sheet. Subsequently, preheating was carried out using a ceramic roll heated to 120 占 폚, and the cast sheet was stretched five times in the longitudinal direction at a stretching temperature of 120 占 폚. The sheet thus stretched in the longitudinal direction was introduced into the tenter-type stretching machine by gripping the ends thereof with a clip, preheated at 155 DEG C for 3 seconds, stretched at 150 DEG C at 8.0 DEG and at a stretching rate of 1,800% . In addition, the distance between the clips in the width direction of the tenter inlet was 150 mm.

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

Thereafter, the portion of the film held by the tenter clip was slit and removed, and a 500 mm wide porous polypropylene film having a width of 500 mm and a thickness of 25 탆 was wound on the core with a width of 500 mm wound on the core, .

(Example 2)

59.8 parts by mass of homopolypropylene FLX80E4, 30 parts by mass of an ethylene-octene-1 copolymer (Dow Chemical Industries, Inc., 8411, melt index: 18 g / 10 minutes) as a copolymerized PE resin, 30 parts by mass of CEBC 10 parts by mass of Ciba Specialty Chemicals, 10 parts by mass of Ciba Specialty Chemicals, 10 parts by mass of Irganox 1010 and 10 parts by mass of Irgaphos 168 were mixed at the same ratio in a proportion of 10 parts by mass, Followed by melt kneading. Then, the melt-kneaded material was discharged from the die into a strand shape, cooled and solidified in a water bath at 25 DEG C, and cut into chips to obtain a polypropylene raw material (IV).

73.3 parts by mass of the obtained polypropylene composition (I), 10 parts by mass of the polypropylene composition (IV) and 16.7 parts by mass of the polypropylene composition (III) were dry-blended and fed to a single-shaft melt extruder for layer A, ) And 1 part by mass of Adomer QF500 manufactured by Mitsui Chemicals, Inc., a polypropylene resin having a carboxyl group or a modified polyolefin with an unsaturated dicarboxylic acid, were fed to a single-shaft melt extruder for the B layer. Then, melt extrusion was carried out at 220 占 폚 from a single-shaft melt extruder for layer A and a single-shaft melt extruder for layer B. After removal of foreign matter by a sintering filter of 60 占 퐉 cutting, a feed block type B / A / B composite T And then discharged onto a casting drum controlled at a surface temperature of 120 DEG C to obtain a cast sheet. Subsequently, preheating was carried out using a ceramic roll heated to 120 占 폚, and the cast sheet was stretched five times in the longitudinal direction at a stretching temperature of 120 占 폚. Subsequently, the longitudinally stretched sheet was gripped by a clip at its ends and preheated at 155 DEG C for 3 seconds, stretched at 150 DEG C to 8.4 times at a stretching speed of 1,800% / minute to obtain a film . Further, the distance between the clips in the width direction of the tenter inlet was 150 mm.

In the subsequent heat treatment step, the film was heat-treated at 150 DEG C for 3 seconds (HS1 region) while maintaining the distance between the clips after stretching, and further relaxed at 164 DEG C and a relaxation rate of 15% (Rx region) And a heat treatment was performed at 164 占 폚 for 5 seconds (HS2 zone) while maintaining the temperature at 164 占 폚, to obtain a porous polypropylene film having a width of 500 mm and a thickness of 25 占 퐉 under the same conditions as in Example 1.

(Example 3)

With respect to Example 2, relaxation was performed at 164 DEG C and a relaxation rate of 20% (Rx zone). A porous polypropylene film having a width of 500 mm and a thickness of 25 탆 was obtained under the same conditions as in Example 2. [

(Example 4)

Example 1 was preheated using a ceramic roll heated to 120 占 폚, and the cast sheet was stretched five times in the longitudinal direction at a stretching temperature of 120 占 폚. Then, the end portion of the sheet drawn in the longitudinal direction was gripped and introduced into a tenter-type stretching machine by a clip, preheated at 155 ° C for 3 seconds, and then stretched at 150 ° C to 8.4 times at a stretching rate of 1,100% / min. A porous polypropylene film having a width of 500 mm and a thickness of 25 탆 was obtained under the same conditions as in Example 1. [

(Example 5)

72.3 parts by mass of the prepared polypropylene composition (I), 10 parts by mass of the polypropylene composition (IV), 16.7 parts by mass of the polypropylene composition (III), and a polypropylene resin or unsaturated dicarboxylic acid 1 part by mass of Adomer QF500 manufactured by Mitsui Chemicals, Inc., which is a modified polyolefin with a carboxylic acid, was dry-blended and fed to a single-screw melt extruder. Then, the melt was extruded from the single-screw extruder at 220 ° C, the foreign substances were removed by a sintering filter having a cutting length of 60 μm, and then discharged onto a casting drum controlled at a surface temperature of 120 ° C. by a T-die to obtain a cast sheet . A porous polypropylene film having a width of 500 mm and a thickness of 25 탆 was obtained under the same conditions as in Example 1. [

(Comparative Example 1)

90 parts by mass of the prepared polypropylene composition (I) and 10 parts by mass of the polypropylene composition (II) were dry blended in the same manner as in Example 1 and fed to a single-shaft melt extruder for the A layer. The polypropylene composition (I) Lt; / RTI &gt; melt-extruder. Then, melt extrusion was carried out at 220 占 폚 from a single-shaft melt extruder for layer A and a single-shaft melt extruder for layer B. After removal of foreign matter by a sintering filter of 60 占 퐉 cutting, a feed block type B / A / B composite T And the mixture was discharged onto a casting drum controlled at a surface temperature of 120 DEG C and cast on a drum for 15 seconds to obtain a cast sheet. Subsequently, preheating was carried out using a ceramic roll heated to 120 占 폚, and the cast sheet was stretched five times in the longitudinal direction at a stretching temperature of 120 占 폚. Subsequently, the longitudinally stretched sheet was gripped by a clip at its ends and preheated at 155 DEG C for 3 seconds, stretched at 150 DEG C to 8.4 times at a stretching speed of 1,800% / minute to obtain a film . In addition, the distance between the clips in the width direction of the tenter inlet was 150 mm.

In the subsequent heat treatment step, the film was subjected to heat treatment (HS1 zone) at 150 캜 for 3 seconds while maintaining the distance between the clips after stretching, and further relaxed at 160 캜 and a relaxation rate of 10% (Rx zone) And heat treatment was performed at 160 DEG C for 5 seconds (HS2 zone).

Thereafter, the portion of the film held by the tenter clip was slit and removed, and a 500 mm wide porous polypropylene film having a width of 500 mm and a thickness of 25 탆 was wound on the core with a width of 500 mm wound on the core, .

(Comparative Example 2)

Preheating was carried out using a ceramic roll heated to 127 占 폚, and the cast sheet was stretched five times in the longitudinal direction at a draw temperature of 127 占 폚. A porous polypropylene film having a width of 500 mm and a thickness of 25 탆 was obtained under the same conditions as in Comparative Example 1 except for this.

(Comparative Example 3)

Film formation was carried out in accordance with the following method described as Example 1 in Japanese Patent Application Laid-Open No. 2008-248231. 94 parts by mass of a homopolypropylene WF836DG3 (MFR: 7 g / 10 min., Isotacticity index: 97%) manufactured by Sumitomo Chemical Co., Ltd. as a polypropylene resin, and a high melt tension homopolypropylene Pro-fax PF814 1 part by mass of ethylene /? - olefin copolymer (MFR: 2.5 g / 10 min., Isotacticity index: 97%) and 5 parts by mass of ethylene /? - olefin copolymer 0.2 part by mass of N, N'-dicyclohexyl-2,6-naphthalenedicarboxamide (Nu-100 made by Shin-Nippon Rika Co., Ltd.) as a crystal nucleating agent was added to the twin screw extruder, To perform melt kneading. Then, the melt-kneaded material was extruded into a strand shape, cooled and solidified in a water bath at 25 ° C, and cut into chips to obtain a polyolefin resin raw material.

The polyolefin resin was supplied to a single-screw extruder and subjected to melt extrusion at 220 占 폚. Foreign substances were removed by a sintering filter and then discharged from a T-die onto a casting drum controlled at a surface temperature of 120 占 폚, To obtain a cast sheet. Subsequently, the cast sheet was heated using a roll heated to 95 DEG C, and stretched four times at a stretching temperature of 95 DEG C in the machine direction. After the sheet drawn in the longitudinal direction was once cooled, the sheet was stretched 6 times at a stretching speed of 1,500% / minute in a width direction at 145 DEG C by a tenter type transverse stretching machine, heat set at 155 DEG C for 5 seconds, And relaxed at 140 캜 for 5 seconds at a relaxation rate of 10% to obtain a porous polypropylene film having a thickness of 28 탆.

(Comparative Example 4)

In Example 1, heat treatment was carried out at 160 캜 for 5 seconds (HS 2 zone) while relaxation at 160 캜 and relaxation rate of 10% in the relaxation of the heat treatment process (Rx zone) and maintaining the distance between clips after relaxation. Otherwise, a porous polypropylene film having a width of 500 mm and a thickness of 25 탆 was obtained under the same conditions as in Example 1.

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

The embodiment satisfying the requirements of the present invention is suitable as a separator for power storage devices having little change in physical properties when a functional layer such as a heat resistant layer is coated because of low durability, high porosity and excellent solvent resistance It is possible to use it. On the other hand, the comparative example was insufficient as a separator for a power storage device which coated a functional layer such as a heat-resistant layer, since both the low dumping resistance and the solvent resistance were insufficient.

The porous polypropylene film of the present invention can be suitably used as a separator for power storage devices because of its excellent organic solvent resistance and durability, and has little physical property change when a functional layer such as a heat resistant layer is coated.

1: Measurement position of speculative resistance
2: Samples
3: Metal frame
4: Double clip (C ratio TP-CL-104)
5: Measurement position of speculative resistance

Claims (8)

a porous polypropylene film comprising a polypropylene resin having? crystal formation ability, wherein the porous polypropylene film has a durability of 1,000 seconds / 100 ml or less and a rate of change in thickness before and after the acetone immersion treatment is 20% or less. The porous polypropylene film according to claim 1, wherein the rate of dimensional change 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 a rate of change in durability before and after the acetone immersion treatment is 15% or less. 4. The method according to any one of claims 1 to 3, wherein the maximum value and the minimum value when the thickness change rate before and after the acetone immersion treatment are measured at intervals of 70 mm in the width direction are T _max (%) and T _min (%) , The value of (T _max -T _min ) is 3% or less. The porous polypropylene film according to any one of claims 1 to 4, wherein the porous polypropylene film has a? Crystal forming ability of 40% or more. A laminated porous film comprising a porous polypropylene film according to any one of claims 1 to 5 and a coating layer provided on the porous polypropylene film. A power storage device provided with a separator provided between a positive electrode and a negative electrode for transmitting ions in an electrolyte while preventing contact between them,
Wherein the separator is formed using the porous polypropylene film according to any one of claims 1 to 5. A power storage device provided with a separator provided between a positive electrode and a negative electrode for transmitting ions in an electrolyte while preventing contact between them,
Wherein the separator is formed using the multilayer porous film according to claim 6.

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