JP2013067783A - Porous film roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous film roll, wherein decrease in planarity of a film due to wrinkles generated upon winding is improved.SOLUTION: The porous film roll is obtained by winding a porous film around a winding core, wherein when measuring hardness at an interval of 10 mm in the width direction across the full width and assuming that an average value is Ha and hardness at an optional measuring point is Hi, at least two parts having high hardness which satisfies the following formula (1): (1) 1.1×Ha≤Hi≤2.0×Ha.

Description

  The present invention relates to a porous film roll formed by winding a porous film around a winding core. More specifically, the present invention relates to a porous film roll in which the flatness of a product roll is improved by controlling the hardness distribution in the width direction of the porous film roll to a range satisfying a specific relational expression.

  Porous films are used in various applications such as separators for batteries and electrolytic capacitors, various separation membranes, clothing, and moisture-permeable waterproof membranes in medical applications. However, since the porous film is weaker than the general film and easily deforms, the flatness is likely to deteriorate. In particular, in a high temperature environment such as in a warehouse in summer, stress between layers due to thermal expansion / contraction behavior of the film is generated, and the flatness is further deteriorated.

  About the flatness improvement of a film, the method of reducing the thickness unevenness of the width direction of a film is described as a flatness improvement method of the optical film for liquid crystal display devices, for example (patent document 1). However, in this method, if the film is wound in a long length, the film may be crushed by its own weight, and the physical properties of the film in the winding core portion may be deteriorated and the productivity may be deteriorated. Moreover, when the preservation | save in the high temperature environment or heat processing was performed, the deterioration of the flatness of the film was not avoided. In addition, as a method for improving the flatness of a film made of an organic polymer for a magnetic recording medium, a method for controlling humidity when storing a film roll is described (Patent Document 2). However, in the porous film, the influence of the atmospheric humidity on the flatness is small, and it has been difficult to improve the flatness by the same method. Moreover, the method of controlling an orientation angle is described by making the tension | tensile_strength after a tenter high about the polypropylene film for print lamination (patent document 3). However, when a porous film is produced, if the tension after the tenter is increased, the pores may be deformed and the porosity and air permeability may be lowered, so that it is difficult to use the same method.

JP 2006-175616 A JP-A-9-71669 Japanese Patent Laid-Open No. 11-240067

  An object of the present invention is to solve the above-described problems. That is, an object of the present invention is to provide a porous film roll in which the flatness of the final product roll is improved.

  The above-described problem is a porous film roll formed by winding a porous film around a winding core, and when the hardness is measured at intervals of 10 mm in the width direction over the entire width, the average value is Ha, at an arbitrary measurement point. When the hardness is Hi, there is a problem to be solved by a porous film roll having two or more high hardness portions satisfying the following formula (1).

  1.1 × Ha ≦ Hi ≦ 2.0 × Ha (1)

  ADVANTAGE OF THE INVENTION According to this invention, the porous film roll which can obtain the product roll with which planarity was improved, and the product roll can be provided.

It is the schematic for demonstrating one embodiment of this invention. 3 is a schematic graph showing the hardness distribution of the porous film roll of Example 2. FIG.

  The porous film of the present invention is preferably made of a thermoplastic resin, and examples of the thermoplastic resin include resins such as polyester, polyamide, and polyolefin. Among these, polyolefin is preferably used.

  Examples of the monomer component constituting the polyolefin here include ethylene, propylene, 1-butene, 1-pentene, 3-methylpentene-1, 3-methyl-1-butene, 1-hexene and 4-methyl. -1-pentene, 5-ethyl-1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-eicosene, vinyl And cyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2-norbornene, and the like. These homopolymers and at least two kinds of copolymers selected from the above monomer components, A blend or a blend of copolymers can be used. Of course, it is not limited to these. In addition to the above monomer components, for example, vinyl alcohol, maleic anhydride, acrylic acid compounds and the like may be copolymerized or graft polymerized, but are not limited thereto. Among the polyolefins obtained from the constituents mentioned above, polypropylene is preferably used because it has excellent properties such as permeability and low specific gravity.

  The polypropylene resin used in the present invention is preferably an isotactic polypropylene resin having a melt flow rate (hereinafter referred to as MFR) of 2 to 30 g / 10 min from the viewpoint of extrusion moldability and uniform formation of pores. Here, MFR is an index indicating the melt viscosity of a resin defined in JIS K 7210 (1995), and is a physical property value indicating the characteristics of a polyolefin resin. In the present invention, it refers to a value measured at 230 ° C. and 2.16 kg.

  In the present invention, the isotactic index of the polypropylene resin is preferably in the range of 90 to 99.9%. When the isotactic index is less than 90%, the crystallinity of the resin is lowered, and the film-forming property may be lowered, or the strength of the film may be insufficient.

  The porous film in the present invention has a plurality of through holes that penetrate both surfaces of the film and have air permeability.

  As a method for forming the through-hole in the film, either a wet method or a dry method may be used, but a dry method is desirable because the process can be simplified.

  Moreover, it is preferable that the porous film roll of this invention removes an edge part by a slit at a film forming process, winds up as an intermediate roll, and makes it a porous film roll.

  In addition, the porous film in the present invention is preferably a stretched film, but in this case, the residual stress of the film immediately after film formation tends to be large, and since the porous film is a porous film, the dimensional change caused by the residual stress Is likely to occur. In particular, in a film having a high porosity, the strength of the film may be reduced, and the dimensional change may be increased. If a dimensional change occurs after being wound on a roll, local tightening may occur, which may lead to deterioration of flatness when the film is unwound. As a result of intensive studies to prevent such deterioration of flatness, it has been found that it is effective to provide two or more high-hardness portions in the width direction in the intermediate roll. That is, since the residual stress is relieved in the portion sandwiched between the two high-hardness portions and the winding becomes difficult to tighten, the flatness of the film due to wrinkles generated during winding by selectively slitting the portion is cut out. It is possible to obtain an improved film roll (hereinafter sometimes referred to as a product roll).

  From the viewpoint described above, when the hardness of the porous film roll of the present invention is measured at intervals of 10 mm in the width direction over the entire width, when the average value is Ha and the hardness at any measurement point is Hi, the following formula (1 It is important that there are two or more high-hardness portions satisfying the above.

1.1 × Ha ≦ Hi ≦ 2.0 × Ha (1)
Formula (1) is more preferably 1.3 × Ha ≦ Hi ≦ 1.8 × Ha, and more preferably 1.5 × Ha ≦ Hi ≦ 1.8 × Ha. In the case of 1.1 × Ha> Hi, the residual stress between the high hardness portions is not sufficiently relaxed, and the planarity may be lowered. Moreover, when Hi> 2.0 × Ha, the winding shape becomes unstable, and flatness and productivity may be lowered.

  As a method for obtaining the porous film roll described above, for example, when winding the biaxially stretched film around an intermediate roll, it can be achieved by a method of co-winding the film slit in the width direction. It will be described later.

  Here, when the hardness is measured at intervals of 10 mm in the width direction over the entire width of the porous film roll and there are continuous measurement points satisfying the formula (1), the entire measurement point is regarded as one high hardness part. It is defined as

  There are no particular limitations as long as the number of high-hardness parts satisfying the formula (1) is two or more, but if the number of places is large, the area of the flat portion sandwiched between the two high-hardness parts becomes small. Productivity may be reduced. Also, if the number of high hardness parts is small, when winding on a wide intermediate roll, the residual stress is insufficiently relaxed near the center between the high hardness parts because the width between the high hardness parts becomes too large, The flatness of the film may decrease.

  The width between the high hardness portions is preferably 0.05 m or more from the viewpoint of productivity, more preferably 0.1 m or more, and further preferably 0.2 m or more. The upper limit of the width is not particularly defined, but it is preferably adjusted within a range in which the flatness is not deteriorated due to the excessively wide width between the high hardness portions.

  The porous film roll of the present invention is preferably one obtained by continuously winding (winding) a film on the winding core in the longitudinal direction by at least 100 m or more. The film length in the longitudinal direction is preferably 200 to 10,000 m. If the winding is too long, the circumference of the high hardness portion becomes large and the winding shape may become unstable. Therefore, it is more preferably 300 to 5,000 m, and more preferably 500 to 3,000 m. 500 to 2,500 m is particularly preferable.

  The winding core for winding the porous film roll of the present invention is cylindrical, and the material thereof is not particularly limited, and paper, resin, metal, and a combination thereof can be used. The length of the core is not particularly limited as long as it is not less than the film width.

  In addition, although it is preferable from a viewpoint of productivity that the ratio of the measurement point which satisfy | fills Formula (1) among all the measurement points is 20% or less, 15% or less is more preferable and 10% or less is more preferable. When the ratio of the measurement points satisfying the formula (1) is larger than 20%, the area of the portion having good flatness sandwiched between the two high hardness portions becomes small, and thus the productivity may be lowered.

  In the porous film roll of the present invention, the hardness is measured at intervals of 10 mm in the width direction over the entire width, and the hardness Hj at an arbitrary measurement point sandwiched between two adjacent high hardness portions satisfying the formula (1) is expressed by the following formula ( It is preferable to satisfy 2).

Hj ≦ 1.0 × Ha (2)
Hj in the formula (2) is preferably in the range of Hj ≦ 1.0 × Ha from the viewpoint of relaxation of residual stress, but more preferably in the range of Hj ≦ 0.9 × Ha. When Hj is in a range of Hj> 1.0 × Ha, the residual stress between the high hardness portions is not sufficiently relaxed, and the planarity may be lowered.

  The porous film of the present invention preferably has a porosity of 40 to 90% from the viewpoint of ion conductivity when used as a separator. If the porosity is less than 40%, the electrical resistance increases when used as a separator, and the energy loss may increase when used for high-power applications. On the other hand, when the porosity exceeds 90%, the strength of the film becomes too low, and the handleability may be inferior, for example, the film may be broken when wound together with the electrode to be stored inside the battery. From the standpoint of achieving both excellent battery characteristics and strength, the porosity of the film is more preferably 45 to 90%, and particularly preferably 45 to 75%.

  Such a porous film having a high porosity may decrease the strength of the film and increase the dimensional change. When a dimensional change occurs after winding on the winding core, stress concentrates on the tightened portion and may lead to a decrease in flatness when the film is unwound. However, by providing two or more high hardness portions in the width direction in the film roll, the residual stress can be alleviated without tightening the film sandwiched between the two locations, and then the higher hardness portion is removed. By slitting, it is possible to wind up a product roll having improved film flatness due to wrinkles generated during winding.

  As a method for controlling the porosity of the porous film within such a range, for example, when a polypropylene resin is used as a matrix resin, a β crystal method capable of forming voids usually by biaxial stretching can be mentioned. From the viewpoint of efficiently forming voids, the polypropylene resin used preferably has a β-crystal forming ability of 40 to 90%. 60 to 85% is more preferable, and 65 to 80% is more preferable. If the β crystal forming ability is less than 40%, the amount of β crystal 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, the film has poor permeability. There is a case. On the other hand, in order to make the β crystal forming ability exceed 90%, it is necessary to add a large amount of a β crystal nucleating agent described later, or to make the stereoregularity of the polypropylene resin to be used extremely high. Industrial practical value is low, such as a decrease in stability.

  The β crystal fraction is an existing ratio of β crystals formed in the polypropylene resin. The β crystal fraction is preferably 40% or more. In order to achieve a β crystal fraction of 40% or more, it is preferable to use an additive having a function of assisting the formation of β crystals by adding to a polypropylene resin, generally called a β crystal nucleating agent.

  Examples of the β crystal nucleating agent include alkali or alkaline earth metal salts of carboxylic acids such as sodium benzoate, calcium 1,2-hydroxystearate, magnesium succinate, and N, N′-dicyclohexyl-2,6-naphthalene. Preferred examples include amide compounds represented by carboxyamide, aromatic sulfonic acid compounds such as sodium benzenesulfonate and sodium naphthalenesulfonate, imide carboxylic acid derivatives, phthalocyanine pigments, and quinacridone pigments. Among these, amide compounds represented by the following chemical formulas (A) and (B) and typified by N, N′-dicyclohexyl-2,6-naphthalenedicarboxyamide can be cited as particularly preferred β crystal nucleating agents. .

R ² —NHCO—R ¹ —CONH—R ³ (A)
Here, R ¹ in the formula is a saturated or unsaturated aliphatic dicarboxylic acid residue having 1 to 24 carbon atoms, a saturated or unsaturated alicyclic dicarboxylic acid residue having 4 to 28 carbon atoms, or 6 carbon atoms. Represents an aromatic dicarboxylic acid residue having ˜28, and R ² and R ³ are the same or different cycloalkyl groups having 3 to 18 carbon atoms, cycloalkenyl groups having 3 to 12 carbon atoms, or derivatives thereof.

R ⁵ —CONH—R ⁴ —NHCO—R ⁶ (B)
Here, R ⁴ in the formula is a saturated or unsaturated aliphatic diamine residue having 1 to 24 carbon atoms, a saturated or unsaturated alicyclic diamine residue having 4 to 28 carbon atoms, or 6 to 12 carbon atoms. A heterocyclic diamine residue or an aromatic diamine residue having ⁶ to 28 carbon atoms, wherein R ⁵ and R ⁶ are the same or different cycloalkyl groups having 3 to 12 carbon atoms and cycloalkenyl groups having 3 to 12 carbon atoms. Or these derivatives.

  Specific examples of such a particularly preferred β crystal nucleating agent or β resin-added polypropylene resin include β crystal nucleating agent “NJESTER” (type name: NU-100, etc.) manufactured by Shin Nippon Rika Co., Ltd. .

  A method for producing a porous polypropylene film that can be preferably used in the present invention will be specifically described below.

  First, polypropylene resin is supplied to an extruder and melted at a temperature of 200 to 320 ° C. After passing through a filtration filter, extruded from a slit-shaped die, cast on a cooling metal drum, cooled and solidified into a sheet, and unstretched A sheet.

  Here, in order to produce a large amount of β crystals in the unstretched sheet, the melt extrusion temperature is preferably low, but if it is less than 200 ° C., an unmelted material is generated in the molten polymer discharged from the die. , It may cause a process failure such as tearing in the subsequent stretching process. Moreover, when it exceeds 320 degreeC, the thermal decomposition of a polypropylene will become intense and it may be inferior to the film characteristics, for example, a Young's modulus, breaking strength, etc. of the porous polypropylene film obtained.

  Further, the temperature of the cooling metal drum is set to 60 to 130 ° C., the film is crystallized under moderately slow cooling conditions, β crystals are generated in a large amount and uniformly, and a highly permeable porous polypropylene film after stretching To do. If the temperature of the metal drum for cooling is less than 60 ° C, the β crystal fraction of the first run of the obtained unstretched sheet may be reduced. If the temperature exceeds 130 ° C, the solidification of the sheet on the drum is insufficient. Thus, it may be difficult to uniformly separate the sheet from the cooling metal drum. Moreover, the permeability of the obtained porous polypropylene film tends to increase as it approaches the upper limit in the temperature range described above, and tends to decrease as it approaches the lower limit. This depends on the amount of β crystals in the unstretched sheet obtained, respectively. It is estimated that Here, the amount of β crystals in the unstretched sheet corresponds to the β crystal fraction obtained from the first run caloric curve obtained by using the unstretched sheet as a sample and using a differential scanning calorimeter. In the case of a highly permeable porous polypropylene film, the cooling metal drum temperature is preferably 100 to 125 ° C.

  The time for the unstretched sheet to contact the cooling metal drum (hereinafter referred to as the contact time to the drum) is preferably 6 to 60 seconds. Here, the contact time with the drum is the time required until the unstretched sheet peels from the drum, with the start time (= 0 seconds) when the molten polymer first lands on the drum in the casting step. Means. In addition, when the casting process is composed of a plurality of drums, the total time when the unstretched sheet comes into contact with these drums is the contact time with the cooling metal drum. When the contact time with the cooling metal drum is less than the above range, although depending on the temperature, the unstretched sheet sticks at the time of peeling, or there are few β crystals generated in the unstretched sheet (β crystals of the unstretched sheet) Therefore, the porosity of the film after biaxial stretching may be lowered to an insufficient level. When the contact time with the cooling metal drum exceeds the above range, although depending on the size of the cooling metal drum, the peripheral speed of the cooling metal drum is unnecessarily low, and the productivity may be significantly deteriorated. Usually, the contact time of 10 minutes or more may not be substantially removed. The contact time with the metal drum is more preferably 7 to 45 seconds, and further preferably 8 to 40 seconds.

  In addition, as an adhesion method to the cooling metal drum, any one of an electrostatic application (pinning) method, an adhesion method using the surface tension of water, an air knife method, a press roll method, an underwater casting method, etc. is used. However, it is preferable to use an air knife method or an electrostatic application method in which the thickness uniformity is good and the cooling rate can be controlled by the temperature of the blowing air. Here, in the air knife method, air is blown from the non-drum surface (the surface that does not contact the drum), and the temperature is preferably 10 to 200 ° C., and the surface is controlled by controlling the cooling rate of the surface. It is possible to control the amount of β crystal and thus the surface porosity, that is, to control the permeability of the resulting porous polypropylene film.

  In addition, in the case of forming a laminate in which the second and third layers are coextruded and laminated on at least one surface of the porous polypropylene film, each of the desired resins is prepared as necessary in addition to the above-described polypropylene. The resin is supplied to separate extruders, melted at a desired temperature, passed through a filtration filter, merged in a short tube or a die, extruded from a slit-like die at each desired laminated thickness, and a cooling metal drum It can be cast into a sheet and cooled and solidified into a sheet shape to obtain a laminated unstretched sheet.

  Next, the obtained unstretched sheet is biaxially stretched to form pores (through holes) in the film. As a biaxial stretching method, the film is stretched in the longitudinal direction of the film and then stretched in the width direction, or the sequential biaxial stretching method of stretching in the longitudinal direction after stretching in the width direction, or the longitudinal direction and the width direction of the film are stretched almost simultaneously. The simultaneous biaxial stretching method can be used, but it is preferable to adopt the sequential biaxial stretching method in that it is easy to obtain a highly air-permeable film, and in particular, it is possible to stretch in the width direction after stretching in the longitudinal direction. preferable.

  As specific stretching conditions, first, the unstretched sheet is controlled to a temperature at which it can be stretched 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 adopted. As the stretching temperature in the longitudinal direction, it is preferable to employ a temperature of 110 to 140 ° C., more preferably 120 to 135 ° C., from the viewpoint of film characteristics and uniformity. The draw ratio is preferably 3 to 6 times, more preferably 4 to 6 times, and still more preferably 4.5 to 5.8 times. If the draw ratio is less than 3 times, the air permeability may be lowered, and the productivity may be lowered. The air permeability increases as the stretching ratio is increased. However, if the stretching ratio exceeds 6 times, the film may be easily broken in the next transverse stretching step.

  Next, the uniaxially stretched polypropylene film is introduced into a tenter stretcher while gripping the film end, and stretched in the width direction to obtain a biaxially stretched film. The stretching temperature is preferably 130 to 155 ° C, and more preferably 145 to 150 ° C because high air permeability is obtained. The stretching ratio in the width direction is preferably 4 to 12 times, more preferably 6 to 10 times. When the draw ratio is less than 4 times, the porosity may be lowered to deteriorate battery characteristics, and the productivity may be lowered. Further, the productivity is improved as the stretching ratio is increased. However, when the stretching ratio is more than 12 times, the film may be easily broken. The transverse stretching speed at this time is preferably 500 to 6,000% / min, more preferably 1,000 to 5,000% / min. It is particularly preferable that the stretching speed is as low as 2,000% / min or less.

  Subsequently, heat setting is performed in the tenter as it is, and the temperature is preferably from the transverse stretching temperature to 165 ° C., and the heat setting time is preferably 1 to 30 seconds. Further, the heat setting may be performed while relaxing in the longitudinal direction and / or the width direction of the film. In particular, the relaxation rate in the width direction is preferably 7 to 20% from the viewpoint of thermal dimensional stability.

  Next, the porous polypropylene film of the present invention is obtained by slitting the biaxially stretched porous polypropylene film in a winding process into a predetermined width and winding it around the core as an intermediate roll.

  As described above, as a method for obtaining a porous film roll satisfying the formula (1), for example, as shown in FIG. This can be achieved by co-winding two or more places in the direction.

  Although the raw material of the film to wind together is not specifically limited, It is preferable to use the same kind of film as the porous film wound up as an intermediate roll. As the method, the cost can be reduced by using a film trimmed by a winder, and it is not necessary to separate unnecessary portions even at the time of slitting, and can be easily collected and reused.

  The thickness of the co-winding film is preferably 0.4 to 1.5 times the thickness of the porous film wound up as an intermediate roll, and more preferably 0.6 to 1.2 times. When the thickness is less than 0.4 times, the relaxation of the residual stress between the high hardness portions becomes insufficient, and the effect of the present invention may not be exhibited. Moreover, when thickness exceeds 1.5 times, a winding form becomes unstable and planarity and productivity may fall.

  It is preferable that the film roll to be wound together is one in which the film is continuously wound (wound up) by at least 100 m in the longitudinal direction on the core. The film length in the longitudinal direction is more preferably 200 to 10,000 m. Moreover, the film width of the film used for co-winding is preferably 5 to 50 mm. More preferably, it is 5-30 mm, More preferably, it is 5-15 mm. When the film width is less than 5 mm, the co-winding portion is liable to be wound and the flatness may be lowered. On the other hand, when the film width exceeds 50 mm, the area of a portion having good flatness sandwiched between two adjacent high-hardness portions becomes small, so that productivity may be lowered.

  It is preferable to provide two or more high hardness portions. Since there is no portion sandwiched between the high hardness portions at one location, the effect of the present invention cannot be exhibited. In addition, when the number of high hardness portions is large, the area of a portion having good flatness sandwiched between two high hardness portions becomes small, so that productivity may be lowered. Also, if the number of high hardness parts is small, when winding on a wide intermediate roll, the width between the high hardness parts becomes too large and the residual stress is not sufficiently relaxed near the center between the high hardness parts. The effects of the invention may not be manifested.

  Since the porous film roll of the present invention has improved flatness of the film due to wrinkles generated during winding, and has high quality and high productivity, it can be used for packaging, hygiene, agricultural, and construction. Although it can be used for supplies, medical supplies, separation membranes, light diffusing plates, and reflective sheets, it can be preferably used as a separator for an electricity storage device because it is particularly excellent in output characteristics, process suitability and long-term storage. 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.

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

(1) Hardness of film roll Shimadzu rubber hardness tester 200 type (stock) according to JIS-K-6301-1975 spring type hardness test A type at intervals of 10 mm across the entire width of the wound porous film roll in the width direction. Measures the hardness (unit: degree) to 2 digits after the decimal point, puts the average value into Ha, the hardness of the high hardness part to Hi, and sandwiches it between the adjacent high hardness parts The values of Hi / Ha and Hj / Ha were determined with the given hardness as Hj.

(2) Porosity The 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 was measured in an atmosphere at a room temperature of 23 ° C. and a relative humidity of 65%. The measurement was performed three times, and the average value was defined as the specific gravity ρ of the film.

  Next, the measured film was hot-pressed at 280 ° C. and 5 MPa, and then rapidly cooled with water at 25 ° C. to prepare a sheet in which pores were completely erased. The specific gravity of this sheet was measured in the same manner as described above, and the average value was defined as the specific gravity (d) of the resin. In the examples described later, the specific gravity d of the resin was 0.91 in any case. From the specific gravity of the film and the specific gravity of the resin, the porosity was calculated by the following formula.

Porosity (%) = [(d−ρ) / d] × 100
(3) β-crystal forming ability, β-crystal fraction 5 mg of resin or film was sampled, loaded into an aluminum pan as a sample, and measured using a differential scanning calorimeter (DSC, RDC220 manufactured by Seiko Denshi Kogyo Co., Ltd.). did. First, the temperature is raised from room temperature to 240 ° C. at 10 ° C./min (first run) in a nitrogen atmosphere, held for 10 minutes, and then cooled to 30 ° C. at 10 ° C./min. About the melting peak observed when the temperature is raised (second run) again at 10 ° C./min after holding for 5 minutes, the melting having a peak in the temperature range of 145 to 157 ° C. is the melting peak of β crystal, 158 ° C. or more The melting at which the peak is observed is defined as the melting peak of the α crystal, and the amount of heat of fusion is determined from the base line drawn on the high temperature side flat portion of the DSC curve and the area of the region surrounded by the peak. Assuming that the heat of fusion of the α crystal is ΔHα and the heat of fusion of the β crystal is ΔHβ, the value calculated by the following formula is the β crystal forming ability. In addition, calibration of the heat of fusion was performed using indium.

β crystal forming ability (%) = [ΔHβ / (ΔHα + ΔHβ)] × 100
In addition, the value which computed the abundance ratio of (beta) crystal similarly from the melting peak observed by a first run has shown the (beta) crystal fraction in the state of the sample. The test was performed 3 times, and the average value was evaluated.

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

(5) Planarity evaluation A slit was made into a width of 100 mm centering on an intermediate position between adjacent high-hardness portions, and the obtained product roll was heat-treated for 200 hours in an atmosphere of temperature 40 ° C. and humidity 60% RH. Unwind the film by 1m from the product roll and add free tension (in the state where it is hung in the vertical direction by its own weight) and tension of 1kg / m and 3kg / m to check for flatness such as dents and swells. confirmed. The presence or absence of deterioration of flatness was confirmed visually by the following method.

  (Double-circle): There is no location where flatness deteriorated by free tension.

  ○: The flatness was deteriorated in the free tension, and disappeared with the tension of 1 kg / m width.

  Δ: Locations with deteriorated flatness are observed with a tension of 1 kg / m width, and disappear with a tension of 3 kg / m width.

  X: The portion where the flatness deteriorates does not disappear even with a tension of 3 kg / m width.

(Reference example)
As a raw material resin for porous polypropylene film, 95 parts by mass of homopolypropylene resin FLX80E4 manufactured by Sumitomo Chemical Co., Ltd., Engage 8411 (MFR: 18 g / 10 min) manufactured by Dow Chemical Co., which is an ethylene / α-olefin copolymer, is 5 In addition to parts by mass, 0.2 part by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide (Shin Nippon Rika Co., Ltd., Nu-100) which is a β crystal nucleating agent, and further antioxidant The raw materials are supplied from the weighing hopper to the twin screw extruder so that IRGANOX1010 and IRGAFOS168 manufactured by Ciba Specialty Chemicals are mixed at a ratio of 0.15 and 0.1 parts by mass, respectively, and melt kneaded at 300 ° C. And discharged from the die in a strand shape, cooled and solidified in a water bath at 25 ° C., cut into a chip shape and chipped. As a raw material. It was 163 degreeC when melting | fusing point was measured about the obtained chip | tip raw material using the differential scanning calorimeter.

  This chip is supplied to a single screw extruder and melt extruded at 220 ° C. After removing foreign matter with a 30 μm cut sintered filter, it is discharged from a T-die to a cast drum whose surface temperature is controlled at 120 ° C. An unstretched sheet was obtained by casting for 15 seconds. Next, preheating was performed using a ceramic roll heated to 120 ° C., and the film was stretched 5 times in the longitudinal direction of the film. After cooling, the end was then held by a clip and introduced into a tenter type stretching machine, and stretched in the film width direction at 150 ° C., 8 times at a stretching rate of 1,500% / min. Then, the film was heat-fixed and then subjected to relaxation treatment at 160 ° C. and a relaxation rate of 10% to obtain a porous film having a thickness of 20 μm. The obtained porous film was slit to a width of 20 mm to obtain a porous film a for co-winding.

Example 1
As a raw material resin for porous polypropylene film, 95 parts by mass of homopolypropylene resin FLX80E4 manufactured by Sumitomo Chemical Co., Ltd., Engage 8411 (MFR: 18 g / 10 min) manufactured by Dow Chemical Co., which is an ethylene / α-olefin copolymer, is 5 In addition to parts by mass, 0.2 part by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide (Shin Nippon Rika Co., Ltd., Nu-100) which is a β crystal nucleating agent, and further antioxidant The raw materials are supplied from the weighing hopper to the twin screw extruder so that IRGANOX1010 and IRGAFOS168 manufactured by Ciba Specialty Chemicals are mixed at a ratio of 0.15 and 0.1 parts by mass, respectively, and melt kneaded at 300 ° C. And discharged from the die in a strand shape, cooled and solidified in a water bath at 25 ° C., cut into a chip shape and chipped. As a raw material. It was 163 degreeC when melting | fusing point was measured about the obtained chip | tip raw material using the differential scanning calorimeter.

  This chip is supplied to a single screw extruder and melt extruded at 220 ° C. After removing foreign matter with a 30 μm cut sintered filter, it is discharged from a T-die to a cast drum whose surface temperature is controlled at 120 ° C. An unstretched sheet was obtained by casting for 15 seconds. Next, preheating was performed using a ceramic roll heated to 120 ° C., and the film was stretched 5 times in the longitudinal direction of the film. After cooling, the end was then held in a tenter type stretching machine with a clip and introduced, and the film was stretched in the film width direction at 150 ° C. 8 times at a stretching speed of 1,500% / min. As it was, heat setting was performed at 160 ° C., and then relaxation treatment was performed at 160 ° C. and a relaxation rate of 10% to obtain a 20 μm porous film. Subsequently, when the edge portion is slit in the winder and wound as an intermediate roll having a width of 0.5 m, the co-winding porous film a obtained in the reference example is wound in two places on both ends of the intermediate roll. A porous film roll was obtained. The porous film roll had a winding length of 2,000 m, a winding tension of 12 N / m, and a core used was a paper tube with an inner diameter of 6 inches. Hi / Ha and Hj / Ha were evaluated about the obtained porous film roll. Here, there were two high hardness portions satisfying 1.1 × Ha ≦ Hi ≦ 2.0 × Ha at both ends of the porous film roll. Thereafter, the porous film roll was slit into a width of 100 mm with the intermediate position between adjacent high hardness portions as the center, and the porosity and flatness of the obtained product roll were measured, and the results are shown in Table 1 ( The same applies to the following examples and comparative examples).

(Example 2)
In Example 1, the porous film a for co-winding obtained in the reference example was subjected to the same operation as in Example 1 except that the co-winding was performed at three positions on both ends and the center of the intermediate roll. A roll and a product roll were obtained, and each physical property value is shown in Table 1. A graph obtained by measuring the value of Hi / Ha in the width direction is shown in FIG. Here, the high hardness part which satisfy | fills 1.1 * Ha <= Hi <= 2.0 * Ha existed in three places, the both ends of a porous film roll, and the center part.

(Example 3)
In the reference example, the discharge amount of the extruder was adjusted to obtain a co-winding porous film b having a thickness of 15 μm. In Example 1, instead of the co-winding porous film a, the co-winding porous film b The same operation as Example 1 was performed except having used, the porous film roll and the product roll were obtained, and each physical-property value was shown in Table 1. Here, there were two high hardness portions satisfying 1.1 × Ha ≦ Hi ≦ 2.0 × Ha at both ends of the porous film roll.

Example 4
In Example 1, the co-winding porous film a was co-wound from the beginning of winding at two locations on both ends of the intermediate roll for 1/3 of the total winding length of the porous film roll. A roll and a product roll were obtained, and each physical property value is shown in Table 1. Here, there were two high hardness portions satisfying 1.1 × Ha ≦ Hi ≦ 2.0 × Ha at both ends of the porous film roll.

(Example 5)
In Example 1, the same operation as in Example 1 was performed except that the longitudinal draw ratio of the porous polypropylene film was changed to 3.0 times, and each physical property value is shown in Table 1. Here, there were two high hardness portions satisfying 1.1 × Ha ≦ Hi ≦ 2.0 × Ha at both ends of the porous film roll.

(Comparative Example 1)
In Example 1, the same operation as in Example 1 was performed except that the porous film roll and the product roll were obtained without performing the co-winding, and each physical property value is shown in Table 1. The porosity and flatness were evaluated using a product roll in which the central portion of the porous film roll was slit to a width of 100 mm. Here, there was one high hardness portion satisfying 1.1 × Ha ≦ Hi ≦ 2.0 × Ha.

(Comparative Example 2)
In Example 3, the same operation as in Example 3 was carried out except that the co-winding porous film b was overlapped and co-rolled to obtain a porous film roll and a product roll. Are shown in Table 1. Here, high hardness portions satisfying Hi> 2.0 × Ha exist at two positions on both ends of the porous film roll, and high hardness portions satisfying 1.1 × Ha ≦ Hi ≦ 2.0 × Ha are films. It was not present across the entire width.

  The porous film roll of the present invention can be provided as a porous film roll in which deterioration of the flatness of the film due to wrinkles generated during winding is improved.

DESCRIPTION OF SYMBOLS 1 Porous film roll 2 Porous film for co-winding 3 Porous film roll for co-winding

Claims (7)

A porous film roll formed by winding a porous film around a winding core. When the hardness is measured at intervals of 10 mm in the width direction over the entire width, the average value is Ha, and the hardness at an arbitrary measurement point is Hi. A porous film roll having two or more high-hardness portions satisfying the following formula (1).
1.1 × Ha ≦ Hi ≦ 2.0 × Ha (1) 2. The porous film roll according to claim 1, wherein the hardness Hj at an arbitrary measurement point sandwiched between two adjacent high-hardness portions satisfying the formula (1) satisfies the following formula (2).
Hj ≦ 1.0 × Ha (2)   The porous film roll according to claim 2, wherein 5 or more measurement points satisfying the formula (2) are present continuously.   The porous film roll in any one of Claims 1-3 whose ratio of the measurement point which satisfy | fills Formula (1) is 20% or less among all the measurement points.   The porous film roll in any one of Claims 1-4 whose porosity of a porous film is 40 to 90%.   The film roll wound by performing a slit from the part pinched | interposed into the high hardness part in the porous film roll in any one of Claims 1-5. An electricity storage device using the porous film of claim 6 as a separator.

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