JP2016027139A - Microporous film roll and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microporous film roll capable of reducing occurrence of curvature and sag on a taken-out olefin-based resin microporous film.SOLUTION: Provided is a microporous film roll which is formed by winding an olefin-based resin microporous film around a lead body, in which difference of adjacent outer peripheral lengths is equal to or less than 1.5 mm on outer peripheral length of the microporous film roll measured for 10 mm interval from one end to the other end, difference between maximum outer peripheral length and minimum outer peripheral length is equal to or less than 3 mm, and the microporous film roll satisfies the formula (1): [(D/2-d/2)/w]×[(h-h)/t]<200. (In the formula, D is average outer diameter (mm) of the microporous film roll, d is average outer diameter (mm) of the lead body, w is average width (mm) of the olefin-based resin microporous film, his maximum outer peripheral length of the microporous film roll, his minimum outer peripheral length of the microporous film roll, and t is average thickness (mm) of the olefin-based resin microporous film).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a microporous film roll and a method for producing the same.

  Conventionally, lithium ion batteries have been used as power sources for portable electronic devices. This lithium ion battery is generally configured by disposing a positive electrode, a negative electrode, and a separator in an electrolytic solution. The positive electrode is formed by applying lithium cobalt oxide or lithium manganate to the surface of the aluminum foil. The negative electrode is formed by applying carbon to the surface of the copper foil. And the separator is arrange | positioned so that a positive electrode and a negative electrode may be partitioned off, and the short circuit with a positive electrode and a negative electrode is prevented.

  When the lithium ion battery is charged, lithium ions are released from the positive electrode and enter the negative electrode. On the other hand, when the lithium ion battery is discharged, lithium ions are released from the negative electrode and move to the positive electrode. Such charging / discharging is repeated in the lithium ion battery. Therefore, the separator used for the lithium ion battery is required to allow lithium ions to permeate well.

  As such a separator, an olefin resin microporous film is used. The olefin resin microporous film is manufactured by stretching an olefin resin film in order to obtain porosity and mechanical strength.

  In order to improve productivity and transportability, the olefin resin microporous film is used as a roll. Such a microporous film roll is obtained by winding a long olefin resin microporous film around a core body.

  However, the olefin resin microporous film unwound from the microporous film roll may be bent in the length direction or may be slack. The olefin-based resin microporous film that is curved or slackened in this way has poor running stability during conveyance by a roll-to-roll method or the like, and positioning becomes difficult during battery assembly.

  Therefore, Patent Document 1 discloses a porous polypropylene film roll in which the amount of bending and the amount of slackening at a film length of 1 m are both 3 mm or less. However, the porous polypropylene film roll of Patent Document 1 still cannot sufficiently reduce the occurrence of bending and slack.

JP 2011-140633 A

  An object of this invention is to provide the microporous film roll by which the generation | occurrence | production of the curve and the slack in the rolled olefin resin microporous film was reduced, and its manufacturing method.

The microporous film roll of the present invention is a microporous film roll formed by winding a long olefinic resin microporous film formed by stretching an olefinic resin film on a core body. ,
In the outer peripheral length of the microporous film roll measured at intervals of 10 mm from one end to the other end of the microporous film roll, the difference between adjacent outer peripheral lengths is 1.5 mm or less, and the maximum outer peripheral length and the minimum outer peripheral length The difference from the length is 3 mm or less, and the relationship of the following formula (1) is satisfied.
[(D / 2−d / 2) / w] × [(h ₁ −h ₂ ) / t] <200 (1)
(In the formula, D is the average outer diameter (mm) of the microporous film roll, d is the average outer diameter (mm) of the core, and w is the average width (mm of the olefin-based resin microporous film). H ₁ is the maximum outer peripheral length (mm) of the microporous film roll, h ₂ is the minimum outer peripheral length (mm) of the microporous film roll, and t is the olefin resin microporous film. Average thickness (mm).)

  In the microporous film roll, the average length of the olefin-based resin microporous film wound around the core is preferably 400 m or more. On the other hand, when the olefin resin microporous film that is too long is wound around the core, wrinkles may occur due to tightening. Therefore, the length of the olefin-based resin microporous film wound around the core is preferably 400 to 5000 m, more preferably 400 to 3500 m, and particularly preferably 400 to 1500 m.

  In addition, the average length of an olefin resin microporous film can be measured as follows. The length is measured for at least 10 arbitrary positions in the olefin-based resin microporous film, and the arithmetic average value is defined as the average length of the olefin-based resin microporous film.

  The average width of the olefin-based resin microporous film wound around the core is not particularly limited, but is preferably 2 cm to 3 m, more preferably 2 cm to 1 m, further preferably 2 cm to 70 cm, and particularly preferably 2 cm to 50 cm. . In an olefin resin microporous film having a width that is too narrow, the film may be bent or slack after being unwound from a roll. Moreover, in the olefin resin microporous film which is too wide, there is a possibility that wrinkles are generated when the film is wound around the core.

  The material of the core is not particularly limited, and examples thereof include paper, synthetic resin, and metal. Moreover, the shape of a core should just be able to wind an olefin resin microporous film around the outer surface, and a cylindrical shape is preferable.

  In the outer peripheral length of the microporous film roll measured at intervals of 10 mm from one end to the other end of the microporous film roll, the difference between adjacent outer peripheral lengths is preferably 1.5 mm or less, more preferably 1.0 mm or less. . The difference between the adjacent outer peripheral lengths means the absolute value of the difference between the adjacent outer peripheral lengths. In the olefin resin microporous film in the microporous film roll, the winding tension applied in the roll circumferential direction at the time of winding remains. When the difference between the adjacent outer peripheral lengths exceeds 1.5 mm, the winding tension remaining in the olefin resin microporous film in the microporous film roll may not be uniform. The produced olefin resin microporous film may be bent in the longitudinal direction. The curved olefin-based resin microporous film is deteriorated in running stability at the time of conveyance, and folds and wrinkles are generated, and the olefin-based resin microporous film meanders. In addition, a curved olefin resin microporous film may make positioning difficult during battery assembly.

In the outer peripheral length of the microporous film roll measured at intervals of 10 mm from one end to the other end of the microporous film roll, the difference between the maximum outer peripheral length (h ₁ ) and the minimum outer peripheral length (h ₂ ) (h ₁ − h ₂ ) is preferably 3 mm or less, more preferably 2.5 mm or less, and particularly preferably 2 mm or less. If the difference between the maximum outer peripheral length and the minimum outer peripheral length exceeds 3 mm, the winding tension remaining in the olefin-based resin microporous film in the microporous film roll may not be uniform. Therefore, the microporous film roll The olefin-based resin microporous film unwound from may be bent in the longitudinal direction.

The microporous film roll satisfies the relationship of the following formula (1), but preferably satisfies the relationship of the following formula (2), and more preferably satisfies the relationship of the following formula (3).
[(D / 2−d / 2) / w] × [(h ₁ −h ₂ ) / t] <200 (1)
[(D / 2−d / 2) / w] × [(h ₁ −h ₂ ) / t] ≦ 150 (2)
[(D / 2−d / 2) / w] × [(h ₁ −h ₂ ) / t] ≦ 100 (3)
(In the formulas (1) to (3), D is the average outer diameter (mm) of the microporous film roll, d is the average outer diameter (mm) of the core, and w is the olefin resin microporous film. The average width (mm), h ₁ is the maximum outer peripheral length (mm) of the microporous film roll, h ₂ is the minimum outer peripheral length (mm) of the microporous film roll, and t is the microporous olefin resin. (The average thickness (mm) of the film.)

In the left side of the above formula (1), the first term [(D / 2−d / 2) / w] means the ratio of the film winding height to the film width in the microporous film roll, and the second term [(h ₁₋ h ₂ ) / t] means the ratio between the maximum difference in the outer peripheral length of the microporous film roll and the film thickness. As a result of various studies on the above-mentioned problems in the present invention, the detailed reason is not clear, but there is a correlation between the ratio indicated by the first term and the ratio indicated by the second term, and the product of these ratios. It was found that by making the value less than 200, it is possible to provide a microporous film roll in which the occurrence of bending and slack in the unrolled olefin resin microporous film is reduced.

  In addition, the outer periphery length of a microporous film roll means the length of the outer periphery of the microporous film roll in the direction orthogonal to the axial center direction of a core. The measurement of the outer peripheral length of the microporous film roll can be performed using, for example, a non-contact type laser displacement meter. Then, in the microporous film roll, the outer peripheral length of the microporous film roll is measured at intervals of 10 mm from one end to the other end in the axial direction of the core, and the measured values obtained are adjacent to each other. The difference between the outer peripheral length, the maximum outer peripheral length, the minimum outer peripheral length, and the difference between the maximum outer peripheral length and the minimum outer peripheral length can be obtained.

  The average outer diameter of the microporous film roll, the average outer diameter of the core, the average width of the olefin resin microporous film, and the average thickness of the olefin resin microporous film can be measured as follows. it can. In the microporous film roll, the olefin resin microporous film unwound from the microporous film roll and the core, at least 10 locations are selected as measurement locations, and the outer diameter and core of the microporous film roll are selected at each measurement location. The outer diameter of the body, the width of the olefin resin microporous film, and the thickness of the olefin resin microporous film are measured. And the arithmetic average value of each measured value of the outer diameter of the microporous film roll, the outer diameter of the core, the width of the olefin resin microporous film, and the thickness of the olefin resin microporous film, respectively, The average outer diameter of the roll, the average outer diameter of the core, the average width of the olefin resin microporous film, and the average thickness of the olefin resin microporous film.

  The outer diameter of the microporous film roll is the cross-section of the microporous film roll in a direction orthogonal to the axial center direction of the core body, and the both ends of the microporous film roll pass through the axis of the core body of the microporous film roll. It means the length of an arbitrary straight line existing on the outer periphery of the cross section. In addition, the measurement of the outer diameter of a microporous film roll can be performed using a non-contact type laser displacement meter etc., for example.

  The outer diameter of the core body is an arbitrary straight line passing through the axis of the core body and having both ends on the outer periphery of the cross section of the core body in the cross section of the core body in a direction orthogonal to the axial direction of the core body. It means length. In addition, the outer diameter of a core can be performed using a non-contact type laser displacement meter etc., for example.

  The width of the olefin-based resin microporous film means the length in the direction orthogonal to the length direction (stretching direction) of the olefin-based resin microporous film. In addition, the width | variety of an olefin resin microporous film can be performed using a caliper etc., for example.

  The measurement of the thickness of the olefin-based resin microporous film at a measurement location arbitrarily selected in the microporous film roll can be performed as follows. In a cross section of the microporous film roll in a direction orthogonal to the axial direction of the core body, one end is present on the axial center of the core body of the microporous film roll, and the other end is on the outer periphery of the cross section. Is measured as a measurement region, and in this measurement region, the total thickness and the number of laminated olefinic resin microporous films are measured, and the total thickness is divided by the number of laminations to obtain the thickness of the olefinic resin microporous film. Can be calculated. The total thickness of the olefin resin microporous film can be measured using, for example, a dial gauge.

  The heat shrinkage in the length direction of the olefin resin microporous film after heating the olefin resin microporous film at 105 ° C. for 1 hour is preferably 4% or less, more preferably 3.5% or less. In the microporous film roll using the olefin-based resin microporous film having a heat shrinkage rate of 4% or less, the occurrence of bending or slack in the olefin-based resin microporous film to be unwound from this can be reduced.

In addition, the measurement of the thermal contraction rate of an olefin resin microporous film can be performed in the following ways. First, 30 plane rectangular test pieces having a width of 2 cm and a length of 10 cm are cut out from an arbitrary portion of the olefin-based resin microporous film. At this time, the length direction (stretching direction) of the olefin resin microporous film is set to be the length direction of the test piece. A 8 cm long marked line is drawn on a straight imaginary line connecting the center of one short side of the test piece and the center of the other short side of the test piece. Next, the test piece is placed in a thermostat having an internal temperature of 105 ° C. and heated for 1 hour, and then the test piece is left in an atmosphere at a temperature of 23 ° C. for 5 minutes. Next, the length (L ₁ [cm]) of the marked line drawn on the test piece is measured, and the heat shrinkage rate (%) is calculated based on the following formula. Then, in the same procedure as described above, the thermal shrinkage rate is measured for each of the 30 test pieces, and the arithmetic average value is defined as the thermal shrinkage rate (%) of the propylene-based resin microporous film.
Thermal contraction rate (%) = 100 × (8−L ₁ ) / 8

  In the microporous film roll of the present invention, the olefin resin microporous film wound around the core includes micropores formed by stretching the olefin resin film. It does not specifically limit as an extending | stretching method of an olefin resin film, Uniaxial stretching or biaxial stretching can be illustrated.

  The air permeability of the olefin-based resin microporous film is preferably 100 to 600 sec / 100 mL, more preferably 100 to 500 s / 100 mL, and particularly preferably 100 to 400 s / 100 mL. The olefin-based resin microporous film having an air permeability within the above range has a high porosity and excellent lithium ion permeability because the ratio of the gas passing through it is high.

  In the present invention, the air permeability of the olefin resin microporous film refers to a value measured in an environment of a temperature of 23 ° C. and a relative humidity of 65% in accordance with JIS P8117.

  The surface opening ratio of the olefin-based resin microporous film is preferably 10 to 55%, more preferably 25 to 55%, and particularly preferably 30 to 50%. The olefin-based resin microporous film having a surface opening ratio in the above range is imparted with excellent air permeability while reducing a decrease in mechanical strength.

  The surface opening ratio of the olefin resin microporous film can be measured in the following manner. First, in an arbitrary portion of the surface of the olefin-based resin microporous film, a measurement portion having a plane rectangular shape of 9.6 μm in length and 12.8 μm in width is determined, and this measurement portion is photographed at a magnification of 10,000 times.

Next, each micropore formed in the measurement portion is surrounded by a rectangle. The rectangle is adjusted so that both the long side and the short side have the minimum dimension. Let the area of the said rectangle be an opening area of each micropore part. The total opening area S (μm ² ) of the micropores is calculated by summing the opening areas of the micropores. This is the total opening area S of the minute hole ([mu] m ²⁾ of 122.88μm ² (9.6μm × 12.8μm) surface porosity values multiplied by 100 and divided by the (%). In addition, about the micropore part which exists over the measurement part and the part which is not a measurement part, only the part which exists in a measurement part among micropores is made into a measuring object.

  The natural shrinkage ratio in the length direction (stretching direction) of the olefin resin microporous film after storing the olefin resin microporous film in an atmosphere at a temperature of 23 ° C. and a relative humidity of 50% for 7 days is 0 .3% or less is preferable, and 0.2% or less is more preferable. In the microporous film roll using the olefin resin microporous film having a natural shrinkage rate of 0.3% or less, the occurrence of bending or slack of the olefin resin microporous film unwound from this can be reduced.

In addition, the measurement of the natural shrinkage | contraction rate of the length direction of an olefin resin microporous film can be performed in the following ways. First, 30 plane rectangular test pieces having a width of 2 cm and a length of 10 cm are cut out from an arbitrary portion of the olefin resin microporous film. At this time, the length direction (extrusion direction) of the olefin resin microporous film is set to be the length direction of the test piece. A 8 cm long marked line is drawn on a straight imaginary line connecting the center of one short side of the test piece and the center of the other short side of the test piece. Next, the test piece is placed in a thermostatic chamber having a temperature of 23 ° C. and a relative humidity of 50%, and stored for 7 days. Next, the length (L ₂ [cm]) of the marked line drawn on the test piece is measured, and the natural shrinkage rate (%) is calculated based on the following formula. Then, in the same procedure as described above, the natural shrinkage rate is measured for each of the 30 test pieces, and the arithmetic average value thereof is defined as the natural shrinkage rate (%) of the olefin-based resin microporous film.
Natural shrinkage (%) = 100 × (8−L ₂ ) / 8

  Examples of the olefin resin used for the olefin resin film include an ethylene resin and a propylene resin. Of these, propylene-based resins are preferable. According to the propylene resin, it is possible to provide an olefin resin microporous film excellent in heat resistance.

  Examples of the propylene-based resin include a propylene homopolymer, a copolymer of propylene and another olefin, and the like. Propylene-type resin may be used independently, or 2 or more types may be used together. Further, the copolymer of propylene and other olefins may be either a block copolymer or a random copolymer. Examples of the olefin copolymerized with propylene include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-nonene, and 1-decene. Examples include α-olefins.

  The weight average molecular weight of the olefin resin is not particularly limited, but is preferably 250,000 to 500,000, and more preferably 280,000 to 480,000. An olefin resin having a weight average molecular weight within the above range can provide an olefin resin microporous film having excellent film forming stability, a uniform thickness, and a uniform formation of micropores.

  The molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) of the olefin resin is not particularly limited, but is preferably 7.5 to 12.0, more preferably 8.0 to 11.5, and more preferably 8.0 to 11 0.0 is particularly preferred. According to the olefin resin having a molecular weight distribution within the above range, it is possible to provide an olefin resin microporous film having a high surface opening ratio while suppressing a decrease in mechanical strength.

  Here, the weight average molecular weight and number average molecular weight of the olefin resin are polystyrene-converted values measured by a GPC (gel permeation chromatography) method. Specifically, after collecting 6 to 7 mg of olefin resin, supplying the collected olefin resin to a test tube, o-DCB containing 0.05% by weight of BHT (dibutylhydroxytoluene) in the test tube ( (Orthodichlorobenzene) solution is added and diluted so that the concentration of the olefin resin is 1 mg / mL to prepare a diluted solution.

  The dilution liquid is shaken for 1 hour at a rotation speed of 25 rpm at 145 ° C. using a dissolution filter, and the olefin resin is dissolved in an o-DCB solution containing BHT to obtain a measurement sample. Using this measurement sample, the weight average molecular weight and number average molecular weight of the olefin resin can be measured by the GPC method.

The weight average molecular weight and the number average molecular weight in the olefin resin can be measured, for example, with the following measuring apparatus and measurement conditions.
<Measurement device>
Product name "HLC-8121GPC / HT" manufactured by TOSOH
<Measurement conditions>
Column: TSKgelGMHHR-H (20) HT x 3
TSKguardcolumn-HHR (30) HT x 1 Mobile phase: o-DCB 1.0 mL / min Sample concentration: 1 mg / mL
Detector: Blythe refractometer Standard material: Polystyrene (Molecular weight: 500-8420000, manufactured by TOSOH)
Elution conditions: 145 ° C
SEC temperature: 145 ° C

  160-170 degreeC is preferable and, as for melting | fusing point of olefin resin, 160-165 degreeC is more preferable. According to the olefin resin having a melting point within the above range, it is possible to provide an olefin resin microporous film having excellent film forming stability, a uniform thickness, and a uniform formation of micropores.

  In the present invention, the melting point of the olefin-based resin can be measured using a differential scanning calorimeter (for example, a device name “DSC220C”, manufactured by Seiko Instruments Inc.) according to the following procedure. First, 10 mg of an olefin resin is heated from 25 ° C. to 250 ° C. at a heating rate of 10 ° C./min, and held at 250 ° C. for 3 minutes. Next, the olefin-based resin is cooled from 250 ° C. to 25 ° C. at a temperature decrease rate of 10 ° C./min, and held at 25 ° C. for 3 minutes. Subsequently, the olefin resin is reheated from 25 ° C. to 250 ° C. at a rate of temperature increase of 10 ° C./min, and the temperature at the top of the endothermic peak in this reheating step is defined as the melting point of the olefin resin.

As a manufacturing method of the microporous film roll of the present invention,
An extrusion step of obtaining a long olefin-based resin film by supplying an olefin-based resin to an extruder, melt-kneading, and extruding from a T-die attached to the tip of the extruder;
Curing process for curing the olefin resin film obtained in the extrusion process,
A stretching step for uniaxially stretching the olefin-based resin film after the curing step;
Annealing step to obtain a long olefin resin microporous film by annealing the olefin resin film after the stretching step;
Winding process;
A method having the following is preferably used.

And in the method of the present invention, the winding step is
A winding step (I) for obtaining a microporous film roll by winding the olefin resin microporous film after the annealing step around a core, or the olefin resin microporous film after the annealing step as a core A raw film roll is obtained by winding, and after the olefin resin microporous film is unwound from the raw film roll, the olefin resin microporous film is cut in the length direction thereof, and the cut olefin Winding process to obtain a microporous film roll by winding a porous resin microporous film around a core (II)
Have

(Extrusion process)
In the extrusion step, an olefin resin film is obtained by supplying an olefin resin to an extruder, melt-kneading, and then extruding from a T die attached to the tip of the extruder.

  The temperature of the olefin resin when melt-kneading the olefin resin with an extruder is preferably (Tm + 20) ° C. to (Tm + 100) ° C., more preferably (Tm + 25) ° C. to (Tm + 80) ° C., and (Tm + 50) ° C. to (Tm + 80) ° C. is particularly preferred. By setting the temperature of the olefin resin at the time of melt-kneading within the above range, the orientation of the olefin resin can be improved and the generation of lamellae can be promoted. “Tm” means the melting point of the olefin resin.

  50-300 are preferable, as for the draw ratio at the time of extruding an olefin resin from an extruder to a film form, 65-250 are more preferable, and 70-250 are especially preferable. By making the draw ratio when extruding the olefin resin from the extruder into a film shape be 50 or more, the tension applied to the olefin resin is improved, thereby sufficiently orienting the olefin resin molecules to produce lamellae. Can be promoted. Moreover, the film forming stability of the olefin resin film is improved by making the draw ratio when extruding the olefin resin from the extruder into a film to 300 or less, and the olefin resin has a uniform thickness and width. A microporous film can be obtained.

  The draw ratio is a value obtained by dividing the clearance of the lip of the T die by the average thickness of the olefin resin film extruded from the T die. The clearance of the lip of the T die is measured by measuring the clearance of the lip of the T die at 10 or more locations using a clearance gauge in conformity with JIS B7524 (for example, JIS clearance gauge manufactured by Nagai Gauge Manufacturing Co., Ltd.), and the arithmetic average thereof This can be done by determining the value. In addition, the average thickness of the olefin resin film extruded from the T die is 10 thicknesses of the olefin resin film extruded from the T die using a dial gauge (for example, signal ABS Digimatic Indicator manufactured by Mitutoyo Corporation). This can be done by measuring as described above and calculating the arithmetic mean value.

  The film forming rate of the olefin resin film is preferably 10 to 300 m / min, more preferably 15 to 250 m / min, and particularly preferably 15 to 150 m / min. By setting the film forming rate of the olefin resin film to 10 m / min or more, the tension applied to the olefin resin can be improved, and thereby the olefin resin molecules can be sufficiently oriented to promote the production of lamellae. Also, by forming the olefin-based resin film at a rate of 300 m / min or less, the film-forming stability of the olefin-based resin film is improved, and an olefin-based resin microporous film having a uniform thickness and width is obtained. Can do.

  The olefin-based resin film extruded from the T die has a surface temperature at both ends in the width direction of (Tm + 10) ° C. to (Tm + 100) ° C., and a surface temperature at the center in the width direction is higher than the surface temperature at both ends. It is set to be 3 to 50 ° C. lower. In the stretching step to be described later, micropores are formed by stretching the olefin resin film, but in the stretching step, the central portion is more easily stretched than both ends of the olefin resin film, and the thickness of the central portion is It tends to be thinner than both ends. Such a thickness distribution remains in the olefin resin microporous film. Even if such a microporous film is wound up to form a microporous film roll, the outer peripheral length of the microporous film roll is not uniform.

  In the method of the present invention, in the extrusion step, by setting the surface temperature of the olefin resin film extruded from the T die as described above, the olefin resin molecules in the central portion are oriented higher than the both ends, The generation of lamellae can be promoted. By stretching such an olefin resin film, an olefin resin microporous film having a uniform thickness can be obtained. By winding up the olefin-based resin microporous film, a microporous film roll having a uniform outer peripheral length can be obtained. By setting it as uniform outer periphery length, generation | occurrence | production of the curve of the olefin resin microporous film unwound from the microporous film roll and slackening can be reduced.

  Although the surface temperature of the both ends in the width direction of the olefin resin film extruded from the T die is (Tm + 10) ° C. to (Tm + 100) ° C., (Tm + 20) ° C. to (Tm + 90) ° C. is preferable. By setting the surface temperature of both ends within the above range, the olefin resin molecules contained in both ends can be sufficiently oriented to generate lamellae.

  The surface temperature of the center part in the width direction of the olefin resin film extruded from the T die is 3 to 50 ° C., preferably 3 to 40 ° C., more preferably 3 to 15 than the surface temperature of both ends in the width direction. Decrease the temperature. If the surface temperature of the central part is too low, the olefin resin molecules contained in the central part may not be sufficiently oriented. Moreover, when the surface temperature of a center part is too high, the orientation of the olefin resin molecule contained in the center part is relaxed, and it may be unable to fully orient.

  In addition, in this invention, the center part in the width direction of an olefin resin film means the range of a total of 80% which spread by 40% equally from the center point in the width direction of an olefin resin film. Moreover, the edge part in the width direction of an olefin resin film means the range extended 10% toward the center from the edge in the width direction of an olefin resin film.

  As a method for controlling the surface temperatures of both end portions and the central portion in the width direction of the olefin resin film extruded from the T die, for example, a T die or an air knife can be used.

  When using a T die, a heater is built in the T die, and the surface temperature of both ends and the center in the width direction of the olefin-based resin film extruded from the T die is controlled by adjusting the heating temperature by the heater. be able to.

  In the case of using an air knife, a plurality of air supply pipes each having a heater installed therein are connected to the air knife, and by adjusting the heating temperature by each heater, an air flow having a predetermined temperature distribution is supplied from the air knife to the T die. By spraying on the olefin resin film extruded from the surface, the surface temperature of both ends and the center in the width direction of the olefin resin film can be controlled.

  Next, by cooling the olefin resin film extruded from the T-die until the surface temperature becomes 100 ° C. or lower than the melting point of the olefin resin, the olefin resin constituting the olefin resin film is formed. The resin crystallizes to produce lamellae. In the present invention, the olefin resin is cooled by extruding the melt-kneaded olefin resin to orient the olefin resin molecules constituting the olefin resin film in advance and then cooling the olefin resin film. The portion where the is oriented can promote the formation of lamellae.

(Curing process)
Subsequently, the olefin resin film obtained by the extrusion process described above is cured. The curing process of the olefin resin is performed to grow the lamella formed in the olefin resin film in the extrusion process. Thereby, it is possible to form a laminated lamella structure in which crystallized portions (lamellar) and amorphous portions are alternately arranged in the extrusion direction of the olefin-based resin film. A crack is generated not between the lamellas but between the lamellae, and a minute through hole (microhole part) can be formed starting from this crack.

  The curing temperature of the olefin resin film is (Tm-30) ° C to (Tm-5) ° C, but (Tm-25) ° C to (Tm-10) ° C is preferable. By setting the curing temperature of the olefin resin film to a temperature of (Tm-30) ° C. or higher, crystallization of the olefin resin film is promoted, and micropores are formed between lamellae of the olefin resin film in the stretching step described later. Can be easily formed. In addition, by reducing the curing temperature of the olefin resin film to a temperature of (Tm-5) ° C. or less, it is possible to reduce the collapse of the lamellar structure due to the relaxation of the molecular orientation of the olefin resin constituting the olefin resin film. be able to.

  In addition, the curing temperature of an olefin resin film is the surface temperature of an olefin resin film. However, when the surface temperature of the olefin resin film cannot be measured, for example, when the olefin resin film is cured in a roll shape, the curing temperature of the olefin resin film is the atmospheric temperature and To do. For example, when curing is performed in a state where the olefin-based resin film is wound into a roll inside a heating apparatus such as a hot stove, the temperature inside the heating apparatus is set as the curing temperature.

  The curing of the olefin-based resin film may be performed while the olefin-based resin film is running, or may be performed in a state where the olefin-based resin film is wound into a roll.

  When the curing of the olefin resin film is performed while running the olefin resin film, the curing time of the olefin resin film is preferably 1 minute or more, and more preferably 5 minutes to 60 minutes.

  When the olefin-based resin film is cured in a rolled state, the curing time is preferably 1 hour or longer, and more preferably 15 hours or longer. By curing the olefin-based resin film in the state of being wound up in such a curing time, the temperature of the olefin-based resin film is entirely cured from the surface to the inside of the roll with the above-described curing temperature. And the lamellae of the olefin resin film can be sufficiently grown. Moreover, in order to suppress the thermal deterioration of an olefin resin film, the curing time is preferably 35 hours or less, and more preferably 30 hours or less.

  In addition, what is necessary is just to unwind an olefin resin film from the olefin resin film roll after a curing process, and to implement the extending | stretching process and annealing process which are mentioned later when curing is performed by the said method.

(Stretching process)
Next, the extending process which forms a micropore part by carrying out uniaxial stretching or biaxial stretching of the olefin resin film after a curing process is implemented. The method of uniaxially stretching or biaxially stretching the olefin resin film is not particularly limited. Other than the uniaxial stretching method described later, a biaxial stretching method of stretching the olefin-based resin film in the extrusion direction and the direction orthogonal to the extrusion direction may be used. The biaxial stretching method is not particularly limited, and is a simultaneous biaxial stretching method in which an olefin resin film is simultaneously stretched in an extrusion direction and a direction perpendicular to the extrusion direction, and the olefin resin film is stretched in the extrusion direction and then orthogonal to the extrusion direction. Examples include a sequential biaxial stretching method in which stretching is performed in the direction of stretching, and can be appropriately selected according to the shape of the micropores to be formed.

The stretching process for forming micropores by uniaxial stretching of the olefin-based resin film after the curing process is as follows:
A first stretching step of uniaxially stretching an olefin-based resin film at a stretching temperature of 20 to 3000% / min at a surface temperature of -20 to 100 ° C and a stretching ratio of 1.05 to 1.6 times;
The surface temperature of the olefinic resin film stretched in the first stretching step is higher than the surface temperature of the olefinic resin film in the first stretching step and lower by 10 to 100 ° C. than the melting point of the olefinic resin. A second stretching step of uniaxial stretching at a stretching rate of 15 to 150% / min and a stretching ratio of 1.05 to 3 times;
It is preferable to have.

(First stretching step)
In the first stretching step, the olefin-based resin film after the curing step is uniaxially stretched at a stretching rate of 20 to 3000% / min at a surface temperature of -20 to 100 ° C and a stretching ratio of 1.05 to 1.6 times. Apply. In the first stretching step, the olefin resin film is preferably uniaxially stretched only in the extrusion direction. In the first stretching step, the lamellae in the olefin-based resin film are hardly melted, and by separating the lamellae by stretching, the fine cracks are efficiently generated independently in the non-crystalline portion between the lamellae. A large number of micropores can be reliably formed starting from this crack.

  In the first stretching step, the surface temperature of the olefin resin film is preferably -20 to 100 ° C, more preferably 0 to 80 ° C, and particularly preferably 10 to 40 ° C. By setting the surface temperature of the olefin-based resin film to −20 ° C. or higher, breakage of the olefin-based resin film during stretching can be reduced. Moreover, a crack can be generated in the amorphous part between lamellae by setting the surface temperature of the olefin-based resin film to 100 ° C. or less.

  In the first stretching step, the stretching ratio of the olefin resin film is preferably 1.05 to 1.6 times, more preferably 1.1 to 1.5 times. By setting the draw ratio of the olefin-based resin film to 1.05 times or more, micropores are formed in the non-crystalline part between lamellas, thereby providing excellent air permeability and low resistance when lithium ions permeate. -Based resin microporous film can be provided. On the other hand, when the stretching ratio of the olefin resin film exceeds 1.6 times, the stretching stress applied to the central portion of the olefin resin film becomes excessive and the thickness becomes thin, and the olefin resin fine film having a uniform thickness becomes thin. A porous film may not be obtained. Even when such an olefin-based resin microporous film is wound, a microporous film roll having a uniform outer peripheral length may not be obtained.

  In addition, in this invention, the draw ratio of an olefin resin film means the value which remove | divided the length of the olefin resin film after extending | stretching by the length of the olefin resin film before extending | stretching.

  The stretching rate in the first stretching step of the olefin resin film is preferably 20 to 3000% / min, more preferably 20 to 1000% / min, and particularly preferably 100 to 500% / min. By setting the stretching speed to 20% / min or more, the micropores can be formed uniformly in the non-crystalline part between lamellae. By setting the stretching speed to 3000% / min or less, it is possible to suppress breakage of the olefin resin film in the first stretching step.

  In addition, in this invention, the extending | stretching speed of an olefin resin film means the change rate of the dimension in the extending | stretching direction of the olefin resin film per unit time.

  The method for stretching the olefinic resin film in the first stretching step is not particularly limited as long as the olefinic resin film can be uniaxially stretched. For example, the olefinic resin film includes a plurality of stretching rolls having different rotation speeds. And a method of uniaxial stretching at a predetermined temperature using a uniaxial stretching apparatus.

(Second stretching step)
In the second stretching step, the surface temperature of the olefin resin film after the first stretching step is higher than the surface temperature of the olefin resin film in the first stretching step and lower by 10 to 100 ° C. than the melting point of the olefin resin. In the following, a uniaxial stretching process is performed at a stretching ratio of 15 to 150% / min and a stretching ratio of 1.05 to 3 times. Also in the second stretching step, the olefin resin film is preferably uniaxially stretched only in the extrusion direction. By performing such a stretching process in the second stretching step, a large number of micropores formed in the olefin resin film in the first stretching step can be grown.

  In the second stretching step, the surface temperature of the olefin-based resin film is preferably higher than the surface temperature of the olefin-based resin film in the first stretching step and 10 to 100 ° C. lower than the melting point of the olefin-based resin. A temperature not higher than the surface temperature of the olefin resin film in the process and 15 to 80 ° C. lower than the melting point of the olefin resin is more preferable. By setting the surface temperature of the olefin resin film within the above range, the micropores can be grown while suppressing the blockage of the micropores, and the air permeability of the olefin resin microporous film can be improved.

  In the second stretching step, the stretching ratio of the olefin resin film is preferably 1.05 to 3 times, and more preferably 1.5 to 2.5 times. By setting the draw ratio of the olefin-based resin film to 1.05 times or more, the microporous portion formed in the olefin-based resin film is grown during the first stretching step, and the olefin-based resin microporous having excellent air permeability. A film can be provided. On the other hand, when the stretching ratio of the olefin resin film exceeds 3 times, the stretching stress applied to the central portion of the olefin resin film becomes excessive and the thickness becomes thin, and the olefin resin microporous film has a uniform thickness. May not be obtained. Even when such an olefin-based resin microporous film is wound, a microporous film roll having a uniform outer peripheral length may not be obtained.

  In the second stretching step, the stretching speed of the olefin resin film is preferably 15 to 150% / min, more preferably 15 to 100% / min, and particularly preferably 15 to 60% / min. By setting the stretching speed within the above range, micropores can be uniformly formed in the olefin-based resin film.

  The method for stretching the olefin resin film in the second stretching step is not particularly limited as long as the olefin resin film can be uniaxially stretched. For example, the olefin resin film has a plurality of stretching rolls having different rotation speeds. Examples thereof include a method of uniaxial stretching at a predetermined temperature using a uniaxial stretching apparatus.

(Annealing process)
Next, an annealing process is performed in which the olefin resin film that has been uniaxially stretched in the second stretching process is annealed. This annealing step is performed to alleviate the residual strain generated in the olefin resin film due to the stretching applied in the stretching step described above, and to suppress the heat shrinkage caused by heating in the resulting olefin resin microporous film. Is called.

  100-175 degreeC is preferable and, as for the surface temperature of the olefin resin film in an annealing process, 130-170 degreeC is more preferable. By setting the surface temperature of the olefin resin film to 100 ° C. or higher, the strain remaining in the olefin resin film can be sufficiently relaxed. Moreover, the obstruction | occlusion of the micropore part formed at the extending process can be suppressed by making the surface temperature of an olefin resin film into 175 degrees C or less.

  0.1-15% is preferable and, as for the shrinkage | contraction rate of the olefin resin film in an annealing process, 0.1-10% is more preferable. If the shrinkage rate is too low, the residual stress generated in the olefin resin film in the stretching process cannot be alleviated uniformly, and the resulting olefin resin microporous film has non-uniform residual stress. There is a possibility that. In a microporous film roll using such an olefin resin microporous film, the olefin resin microporous film may be partially wound due to non-uniform residual stress in the olefin resin microporous film, which may cause a large difference in outer peripheral length. . On the other hand, if the shrinkage rate is too high, the micropores may be blocked, and the air permeability and porosity of the resulting olefin meter resin microporous film may be reduced.

  The shrinkage rate of the olefin resin film in the annealing process is obtained by dividing the shrinkage length of the propylene resin film in the stretching direction during the annealing process by the length of the propylene resin film in the stretching direction after the stretching process. A value multiplied by 100.

  Next, in the method of the present invention, after the annealing step, either a winding step (I) or a winding step (II) described later is performed. The olefin resin microporous film after the annealing step has a uniform thickness distribution, the residual stress is relaxed, and the remaining residual stress is also uniformly dispersed. Therefore, by winding such an olefin-based resin microporous film around the core in the winding step (I) or winding step (II) described later, the microporous film roll can be uniformly wound and tightened. Therefore, the difference between the maximum outer peripheral length and the minimum outer peripheral length of the microporous film roll can be extremely reduced. Olefin-based resin microporous film unwound from such a microporous film roll has reduced occurrence of bending and slack in the length direction. Therefore, the olefin-based resin microporous film is excellent in running stability, reduces the occurrence of wrinkles and meandering under conveyance, and can be easily positioned during battery assembly.

(Winding process (I))
In the winding process (I), the microporous film roll is obtained by winding the olefin-based resin microporous film after the annealing process around the core.

  In the winding step (I), when winding the olefin resin microporous film around the core, the winding tension of the olefin resin microporous film is preferably 0.1 to 200 N / m per unit width. -100 N / m is more preferable. By setting the winding tension within the above range, it is possible to wind the olefin resin microporous film at a substantially constant winding speed without generating residual stress.

  In the winding step (I), the average length of the olefin-based resin microporous film wound around the core is preferably 400 m or more, more preferably 400 to 5000 m, further preferably 400 to 3500 m, and particularly preferably 400 to 1500 m. preferable.

  In the winding step (I), the average width of the olefin-based resin microporous film wound around the core is not particularly limited, but is preferably 2 cm to 3 m, more preferably 2 cm to 1 m.

(Winding process (II))
In the winding process (II), an olefin-based resin microporous film is obtained by winding the olefin-based resin microporous film after the annealing process on a core, and the olefin-based resin microporous film is unwound from the raw film roll, A microporous film roll is obtained by cutting an olefin resin microporous film in the length direction and winding the cut olefin resin microporous film around a core.

  In the winding process (II), the olefin resin microporous film after the annealing process is cut and adjusted to a desired width, and then the cut olefin resin microporous film is wound to roll the microporous film roll. Can be obtained. However, in the winding process (II), if the cut olefin resin microporous film has nonuniform thickness distribution and residual stress, it is particularly likely to bend and loosen after being wound. . However, according to the method of the present invention, as described above, the thickness distribution is uniform, the residual stress is relaxed, and the residual stress slightly remaining is uniformly dispersed. Can be obtained. Therefore, even if the olefinic resin microporous film obtained by the method of the present invention is cut into a narrow width in the winding step (II) and wound again around the core, the curvature in the cut olefinic resin microporous film And the occurrence of slack can be reduced.

  In the winding step (II), when the raw film roll is obtained by winding the olefin resin microporous film around the core, the winding tension of the olefin resin microporous film is 0.1 per unit width. -200 N / m are preferable, 1-100 N / m are more preferable, and 35-70 N / m are especially preferable. By setting the winding tension within the above range, it is possible to wind the olefin resin microporous film at a substantially constant winding speed without generating residual stress.

  The average length of the olefin-based resin microporous film wound around the core in the raw film roll is preferably 400 m or more, more preferably 400 to 5000 m, further preferably 400 to 3500 m, and particularly preferably 400 to 1500 m. .

  In the raw film roll, the average width of the olefin-based resin microporous film wound around the core is not particularly limited, but is preferably 3 cm to 3 m, more preferably 5 cm to 2 m.

  In the winding process (II), when the microporous film roll is obtained by winding the cut olefin resin microporous film around the core, the winding tension of the cut olefin resin microporous film is per unit width. 0.1 to 200 N / m is preferable, 1 to 100 N / m is more preferable, and 1 to 30 N / m is particularly preferable. By setting the winding tension within the above range, it is possible to wind up the olefin-based resin microporous film cut at a substantially constant winding speed without generating residual stress.

  In the microporous film roll, the average length of the cut olefin resin microporous film is preferably 400 m or more, more preferably 400 to 5000 m, further preferably 400 to 3500 m, and particularly preferably 400 to 1500 m.

  In the microporous film roll, the average width of the cut olefin-based resin microporous film only needs to be thinner than the width of the olefin-based resin microporous film wound around the core in the raw film roll, Although not particularly limited, 2 cm to 1 m is preferable, 2 cm to 70 cm is more preferable, and 2 cm to 50 cm is particularly preferable. Even if the olefin resin microporous film having a small width is wound up, the method of the present invention allows the curvature or slack of the narrow olefin resin microporous film unwound from the microporous film roll. Can be reduced.

  In order to cut the olefin-based resin microporous film in the length direction thereof, a conventionally known apparatus such as a slitter apparatus can be used.

  In the winding step (II), when the olefin resin microporous film is cut in the length direction, both side portions in the width direction of the olefin resin microporous film may be cut and removed.

  ADVANTAGE OF THE INVENTION According to this invention, the microporous film roll by which the generation | occurrence | production of the curve and the slack in the olefin resin microporous film unwound was reduced can be provided.

It is a figure which shows roughly the measurement principle of the curvature amount of a homo polypropylene microporous film. It is a schematic sectional drawing of the measuring apparatus of the amount of slack of a homo polypropylene microporous film.

  Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto.

[Example 1]
(Extrusion process)
Homopolypropylene (weight average molecular weight (Mw) 413,000, number average molecular weight (Mn) 44,300, molecular weight distribution (Mw / Mn) 9.3, melting point 163 ° C., heat of fusion 96 mJ / mg) was fed to the extruder. The mixture was melt kneaded at a resin temperature of 230 ° C. Thereafter, the homopolypropylene was extruded into a film from a T die attached to the tip of the extruder to obtain a molten homopolypropylene film. At this time, by adjusting the temperature of the heater built in the T die, the surface temperature of both ends in the width direction of the melted homopolypropylene film extruded from the T die is set to 200 ° C., and the surface of the center portion in the width direction The temperature was 195 ° C. Then, it cooled and solidified until the surface temperature of the both ends and center part in the width direction of a melted homo polypropylene film became 30 degreeC, and obtained the elongate homo polypropylene film. The extrusion rate was 10 kg / hour, the film formation rate was 22 m / min, and the draw ratio was 83.

(Curing process)
Next, a cylindrical core body having an average outer diameter of 178 mm is prepared, and the core body is rotated in the circumferential direction around the shaft core, so that a long homopolypropylene film is rolled into the core body. A homopolypropylene film roll was obtained by winding. This homopolypropylene film roll was allowed to stand for 24 hours in a hot air oven in which the atmosphere temperature in the place where the polypropylene film roll was installed was 150 ° C. At this time, the temperature of the homopolypropylene film was entirely the same as the temperature inside the hot stove from the surface to the inside of the homopolypropylene film roll.

(First stretching step)
Next, the homopolypropylene film is continuously unwound from the homopolypropylene film roll after the curing process, and the surface temperature of the homopolypropylene film is set to 20 ° C., and then sequentially passed to the first stretching roll and the second stretching roll, By rotating the peripheral speed of the second stretching roll so as to be larger than the peripheral speed of the first stretching roll, the homopolypropylene film is stretched at a stretching ratio of 1.2 times at a stretching speed of 140% / min only in the extrusion direction. Uniaxial stretching was performed.

(Second stretching step)
Subsequently, the homopolypropylene film fed from the second stretching roll was supplied into the heating furnace, the surface temperature of the homopolypropylene film was set to 120 ° C., and the seven stretching rolls installed in the heating furnace were The homopolypropylene film is 42% / min by passing it up and down in a zigzag manner in the conveyance direction and rotating the respective peripheral speeds of the drawing rolls so as to increase sequentially in the conveyance direction of the homopolypropylene film. The film was uniaxially drawn only in the extrusion direction at a draw ratio of 1.8 times at a drawing speed of.

(Annealing process)
After that, the homopolypropylene film is sequentially supplied to the first roll and the second roll arranged vertically in the hot air furnace so that the surface temperature of the homopolypropylene film becomes 140 ° C. and no tension is applied to the homopolypropylene film. In this way, the homopolypropylene film is annealed by being conveyed in the hot stove for 10 minutes, and the homopolypropylene film is contracted to have a contraction rate of 10% in the stretching direction (conveying direction). A homopolypropylene microporous film (thickness 25 μm) was obtained.

(Winding process (II))
Next, a paper-made cylindrical core (average inner diameter: 6 inches, average thickness: 13 mm) is prepared, and this core is rotated in the circumferential direction around the axis, so that the core is elongated. A raw film roll was obtained by winding a homopolypropylene microporous film (average length: 1320 m, average width: 450 mm) in a roll shape at a winding tension of 47.6 N / m per unit width.

  Thereafter, the homopolypropylene microporous film is continuously unwound from the original film roll, and the homopolypropylene microporous film is cut and removed on both sides (each average width of 15 mm) in the width direction with a slitter device. The center in the width direction of the polypropylene microporous film is continuously cut in the length direction, and the homopolypropylene microporous film cut (hereinafter, the cut homopolypropylene microporous film is also simply referred to as “homopolypropylene microporous film A”). ) Thereafter, two paper-made cylindrical cores (average outer diameter: 92.2 mm) were prepared, and each core was rotated in the circumferential direction around the axis to obtain the homopolypropylene microporous film A, respectively. Two microporous film rolls (average outer diameter of 224 mm) were obtained by rewinding into a roll shape at a winding tension of 10 N / m per unit width.

[Examples 2 to 4 and Comparative Examples 1 to 4]
The surface temperature of the central portion in the width direction of the melted homopolypropylene film extruded from the T-die in the extrusion step, and the average widths of both sides of the homopolypropylene microporous film cut and removed in the winding step (II), Except for changing the winding tension when winding the homopolypropylene microporous film A around the core and the average length of the homopolypropylene microporous film A wound around the core as shown in Table 1, respectively. A microporous film roll was obtained in the same manner as in Example 1.

[Evaluation]
About the microporous film roll, the average outer diameter of the microporous film roll, the average outer diameter of the core, the average width of the homopolypropylene microporous film A, and the average thickness of the homopolypropylene microporous film A were measured according to the above-described procedure. Moreover, the homopolypropylene microporous film A was unwound from the obtained microporous film roll, and the average length was measured according to the above-described procedure. These results are shown in Table 1.

  The outer peripheral length was measured at intervals of 10 mm from one end of the microporous film roll to the other end in accordance with the above-described procedure, and the difference between the adjacent outer peripheral lengths was calculated. Table 1 shows the maximum difference between adjacent outer peripheral lengths among the calculated differences between adjacent outer peripheral lengths. Table 1 shows the difference between the maximum outer peripheral length and the minimum outer peripheral length in the measured outer peripheral length.

  Further, the homopolypropylene microporous film A is unwound from the microporous film roll, and this homopolypropylene microporous film A is heated at 105 ° C. for 1 hour, and then heat shrinkage, air permeability, and temperature 23 in the length direction. The natural shrinkage in the length direction after being stored for 7 days under an atmosphere of 50 ° C. and a relative humidity of 50% was measured according to the above-mentioned procedure, and the results are shown in Table 1.

(Measurement of bending amount)
A test piece 10 having a width of 210 mm and a length of 2 m was obtained by unwinding and cutting the homopolypropylene microporous film A from the microporous film roll. At this time, the length direction of the test piece 10 was set to be the length direction of the homopolypropylene microporous film A. The test piece 10 had a pair of short sides 10a and 10a facing each other and a pair of curved long sides 10b and 10c connecting the opposing edges of the short sides 10a and 10a. The long side has a long side 10b having a long length and a long side 10c having a short length. In the following measurement, the long side 10c having a shorter length (hereinafter, also referred to as "measurement side") Was measured. First, the test piece 10 was placed on a horizontal flat plate so that the entire lower surface of the test piece 10 was in close contact with the upper surface of the flat plate. Next, as shown in FIG. 1, to draw a straight line L ₃ connecting the two ends of the measuring edge 10c of the test piece 10, and the center in the length direction of the straight line L _3, the length direction in the measurement edges 10c of the test piece 10 The distance M ₁ (mm) from the center of was measured with a scale as the amount of bending. Ten test pieces 10 were prepared from the homopolypropylene microporous film A, the bending amount of each test piece 10 was measured according to the above procedure, and the arithmetic average value thereof was taken as the bending amount of the homopolypropylene microporous film A. The results are shown in Table 1.

(Measurement of maximum slack)
After unrolling the homopolypropylene microporous film A from the microporous film roll, a test piece 20 having a width of 210 mm and a length of 2.3 m was cut out from the homopolypropylene microporous film A. At this time, the length direction of the test piece 20 was set to be the length direction of the homopolypropylene microporous film A. After both ends (length 10 cm) in the length direction of the test piece 20 are folded while being curved in a cylindrical shape on the upper surface side of the test piece 20, the folded tip is attached to the upper surface of the test piece 20 with adhesive tapes 30a and 30b. The weight mounting cylindrical portions were formed at both ends of the test piece 20 by fixing with the above.

  Next, as shown in FIG. 2, the center part of the length direction of the test piece 20 was spanned between a pair of rod-like support members 40a and 40b arranged in parallel with each other at an interval of 2 m, By inserting rod-shaped weights 50a, 50b (length: 250 mm, diameter: 12 mm, weight: 222 g) made of stainless steel into the weight mounting cylindrical portion of the test piece suspended from these rod-shaped support members 40a, 40b, A tension was applied to the test piece 20 in the length direction.

Then, the amount of looseness of the test piece to which tension was applied was measured according to the following procedure. First, a pair of rod-like support member 40a, from the longitudinal midpoint of the imaginary line L ₄ connecting the 40b apexes of the position of height 50mm upward, the longitudinal direction of rectangular pillar metrics member 60 Was arranged so as to be parallel to the width direction of the test piece 20. Next, the distance M ₂ (mm) in the vertical direction between the test piece 20 and the lower surface of the measurement reference member 60 is measured with a scale at intervals of 10 mm from one end to the other end in the width direction of the test piece. The absolute value of the difference between the distance M ₂ and 50 (mm) was calculated as the amount of slack. Table 1 shows the maximum amount of sag calculated.

10 specimens
10a short side
10b Long side
10c long side
10c Measuring edge
20 specimens
30a, 30b adhesive tape
40a, 40b Rod support member
50a, 50b weight
60 Measurement reference member L ₃ straight line L ₄ virtual straight line M ₁ distance M ₂ distance

Claims (9)

A microporous film roll formed by winding a long olefinic resin microporous film formed by stretching an olefinic resin film on a core body,
In the outer peripheral length of the microporous film roll measured at intervals of 10 mm from one end to the other end of the microporous film roll, the difference between adjacent outer peripheral lengths is 1.5 mm or less, and the maximum outer peripheral length and the minimum outer peripheral length A microporous film roll having a difference from the length of 3 mm or less and satisfying a relationship of the following formula (1).
[(D / 2−d / 2) / w] × [(h ₁ −h ₂ ) / t] <200 (1)
(In the formula, D is the average outer diameter (mm) of the microporous film roll, d is the average outer diameter (mm) of the core, and w is the average width (mm of the olefin-based resin microporous film). H ₁ is the maximum outer peripheral length (mm) of the microporous film roll, h ₂ is the minimum outer peripheral length (mm) of the microporous film roll, and t is the olefin resin microporous film. Average thickness (mm).)   The microporous film roll according to claim 1, wherein the average length of the olefin-based resin microporous film is 400 m or more.   The microporous film roll according to claim 1 or 2, wherein the olefin resin microporous film is formed by uniaxially or biaxially stretching an olefin resin film.   The microporous film according to any one of claims 1 to 3, wherein a heat shrinkage rate in the length direction of the olefin-based resin microporous film after heating at 105 ° C for 1 hour is 4% or less. roll.   The microporous film roll according to any one of claims 1 to 4, wherein the air permeability of the olefin-based resin microporous film is 100 to 600 sec / 100 mL.   The natural shrinkage in the length direction of the olefin-based resin microporous film after being stored for 7 days under an atmosphere of a temperature of 23 ° C. and a relative humidity of 50% is 0.3% or less. The microporous film roll according to any one of claims 1 to 5.   An olefin-based resin microporous film cut out from the microporous film roll according to any one of claims 1 to 6. After melt-kneading the olefin-based resin with an extruder, by extruding from a T die attached to the tip of the extruder, the surface temperature at both ends in the width direction is (Tm + 10) ° C. to (Tm + 100) ° C., And the extrusion process which obtains the long olefin resin film whose surface temperature of the central part in the width direction is 3-50 ° C lower than the surface temperature of the above-mentioned both ends,
A curing process for curing the olefin-based resin film after the extrusion process at a temperature of (Tm-30) ° C. to (Tm-5) ° C .;
A stretching step for uniaxially stretching the olefin-based resin film after the curing step;
Annealing step to obtain a long olefin resin microporous film by annealing the olefin resin film after the stretching step;
Winding process;
(Wherein, Tm is the melting point (° C.) of the olefin resin),
The above winding process
A winding step (I) for obtaining a microporous film roll by winding the olefin resin microporous film after the annealing step around a core, or the olefin resin microporous film after the annealing step as a core A raw film roll is obtained by winding, and after the olefin resin microporous film is unwound from the raw film roll, the olefin resin microporous film is cut in the length direction thereof, and the cut olefin Winding process to obtain a microporous film roll by winding a porous resin microporous film around a core (II)
The manufacturing method of the microporous film roll characterized by having. The stretching process
A first stretching step in which the olefin-based resin film after the curing step is uniaxially stretched at a stretching rate of 20 to 3000% / min at a surface temperature of −20 to 100 ° C. and a stretching ratio of 1.05 to 1.6 times;
The surface temperature of the olefinic resin film stretched in the first stretching step is higher than the surface temperature of the olefinic resin film in the first stretching step and lower by 10 to 100 ° C. than the melting point of the olefinic resin. The method for producing a microporous film roll according to claim 8, further comprising a second stretching step of uniaxially stretching at a stretching rate of 15 to 150% / min and a stretching ratio of 1.05 to 3 times.

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