JP2015017249A - Olefinic resin microporous film roll, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an olefinic resin microporous film roll in which the occurrence of curvature in the unwound olefinic resin microporous film, is highly suppressed.SOLUTION: An olefinic resin microporous film roll is provided, which is formed by drawing an olefinic resin film and winding the drawn olefinic resin film having a length of 400 m or more, around a core body, and which is characterized by that the difference between the maximum outer peripheral length and the minimum outer peripheral length thereof, is 3 mm or less.

Description

  The present invention relates to an olefin resin 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 olefinic resin microporous film is manufactured by stretching an olefinic resin film in order to obtain porosity and mechanical strength.

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

  However, the olefin resin microporous film unwound from the olefin resin microporous film roll may be curved in the length direction. Such a curved olefin resin microporous film may have poor running stability during conveyance by a roll-to-roll method or the like, and positioning may be difficult during battery assembly.

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

JP 2011-140633 A

  An object of the present invention is to provide an olefin resin microporous film roll in which the occurrence of bending in the unrolled olefin resin microporous film is highly suppressed, and a method for producing the roll.

The olefin-based resin microporous film roll of the present invention is formed by stretching an olefin-based resin film, and the olefin-based resin microporous film having a length of 400 m or more is wound around a core. A perforated film roll,
The difference between the maximum outer peripheral length and the minimum outer peripheral length of the olefin resin microporous film roll is 3 mm or less.

Furthermore, the manufacturing method of the olefin resin microporous film roll of the present invention includes the following steps:
The olefin-based resin film is supplied to an extruder, melt-kneaded, and extruded from a die attached to the tip of the extruder, so that the thickness of the central portion in the width direction is thicker than the thickness of both ends in the width direction. An extrusion process to obtain;
A curing process for curing the olefin-based resin film obtained in the extrusion process,
A stretching process for forming micropores by uniaxial stretching of the olefin-based resin film after the curing process;
An annealing step of shrinking the olefinic resin microporous film after the stretching step at a shrinkage of 0.1 to 10% by heating at a surface temperature of 100 to 175 ° C;
A winding step of obtaining an olefinic resin microporous film roll by winding a olefinic resin microporous film having a length of 400 m or more after the annealing step around a core;
It is characterized by having.

  ADVANTAGE OF THE INVENTION According to this invention, the generation | occurrence | production of the curvature in the unrolled olefin resin microporous film can be provided highly, and the olefin resin microporous film roll can be provided.

The thickness distribution in the width direction of the homopolypropylene microporous film obtained in Example 1 is shown. The thickness distribution in the width direction of the homopolypropylene microporous film obtained in Example 2 is shown. The thickness distribution in the width direction of the homopolypropylene microporous film obtained in Example 6 is shown. The thickness distribution in the width direction of the homopolypropylene microporous film obtained in Example 7 is shown. It is a figure which shows roughly the principle of the measurement of the curvature amount of a homo polypropylene microporous film.

  The olefinic resin microporous film roll of the present invention is formed by winding an olefinic resin microporous film having a length of 400 m or more around a core, which is formed by stretching the olefinic resin film.

  In the olefin resin microporous film roll of the present invention, the length of the olefin resin microporous film wound around the core is 400 m or more. On the other hand, when an olefin resin microporous film that is too long is wound on a core, wrinkles may occur due to tightening. Therefore, the length of the olefin resin microporous film wound around the core is preferably 400 to 5000 m, and more preferably 400 to 3500 m.

  The width of the olefin-based resin microporous film wound around the core is not particularly limited, but is preferably 3 cm to 3 m, and more preferably 5 cm to 2 m. If the width of the olefin resin microporous film is too narrow, the film may break during transportation. 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. The length of a core should just be more than the width | variety of an olefin resin microporous film.

  The difference between the maximum outer peripheral length and the minimum outer peripheral length of the olefin-based resin microporous film roll is limited to 3 mm or less, preferably 2.5 mm or less, and more preferably 2 mm or less. In such an olefin-based resin microporous film roll, the olefin-based resin microporous film is wound with a uniform winding tension. Therefore, the olefin-based resin microporous film roll unwound from the olefin-based resin microporous film roll It can reduce highly that a film curves to a longitudinal direction. In the olefin resin microporous film roll in which the difference between the maximum outer peripheral length and the minimum outer peripheral length exceeds 3 mm, the olefin resin microporous film unwound from this may be bent in the longitudinal direction. The curved olefinic resin microporous film has a reduced running stability during transportation, causing creases and wrinkles, and the olefinic resin microporous film meanders. In addition, the curved olefin resin microporous film may make positioning difficult during battery assembly.

In the present invention, the difference between the maximum outer peripheral length and the minimum outer peripheral length of the olefin-based resin microporous film roll can be measured as follows. First, the outer peripheral length of the olefin resin microporous film roll is measured at intervals of 1 cm in the axial direction of the core in the olefin resin microporous film roll (width direction of the olefin resin microporous film). Then, the difference (C ₁ −C ₂ ) between the maximum outer peripheral length (C ₁ ) and the minimum outer peripheral length (C ₂ ) obtained in this way is obtained. The measurement of the outer peripheral length of the olefin resin microporous film roll can be performed using a non-contact type laser displacement meter.

  The thermal shrinkage in the length direction of the olefinic resin microporous film after heating the olefinic resin microporous film at 105 ° C. for 1 hour is preferably 4% or less, more preferably 3.5% or less. In the olefin resin microporous film roll using the olefin resin microporous film having a heat shrinkage rate of 4% or less, the curvature of the olefin resin microporous film unrolled from the roll can be reduced to a high level.

  The standard deviation of the heat shrinkage in the length direction of the olefinic resin microporous film after heating the olefinic resin microporous film at 105 ° C. for 1 hour is preferably 1% or less, and more preferably 0.8% or less. In the olefin-based resin microporous film roll using the olefin-based resin microporous film having a standard deviation of the heat shrinkage rate of 1% or less, the curvature of the olefin-based resin microporous film to be unwound from this can be highly 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 position in the olefin-based 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 central portion on one short side of the test piece and the central portion on 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 heat shrinkage rate is measured for each of the 30 test pieces, and the arithmetic average value is defined as the heat shrinkage rate (%) of the olefin resin microporous film.
Thermal contraction rate (%) = 100 × (8−L ₁ ) / 8

  In addition, the standard deviation of the heat shrinkage rate of the olefinic resin microporous film was determined by measuring the heat shrinkage rate of each of the 30 test pieces prepared from the olefinic resin microporous film in the same procedure as described above. The value is calculated based on the measured value.

  The air permeability of the olefinic 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 olefinic 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 the film is high.

  In the present invention, the air permeability of the olefin-based 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.

  In the olefin-based resin microporous film roll of the present invention, the olefin-based resin microporous film wound around the core includes micropores formed by stretching the olefin-based resin film.

  The surface opening ratio of the olefin resin microporous film is preferably 10 to 55%, more preferably 20 to 55%, particularly preferably 25 to 55%, and most preferably 30 to 50%. The olefin-based resin microporous film having a surface opening ratio within the above range is imparted with excellent air permeability while reducing a decrease in mechanical strength.

  In addition, the surface opening rate of an olefin resin microporous film can be measured in the following way. First, in an arbitrary part of the surface of the olefin-based resin microporous film, a measurement part having a plane rectangular shape of 9.6 μm × 12.8 μm is defined, and this measurement part 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 porosity of the olefin resin microporous film is preferably 30 to 70%, more preferably 35 to 67%. The olefin resin microporous film having a porosity in the above range is excellent in air permeability and mechanical strength.

In addition, the porosity of an olefin resin microporous film can be measured in the following way. First, a test piece having a plane square shape (area 100 cm ² ) measuring 10 cm in length and 10 cm in width is obtained by cutting the olefin-based resin microporous film. Next, the weight W (g) and thickness T (cm) of the test piece are measured, and the apparent density ρ (g / cm ³ ) is calculated by the following formula (I). In addition, the thickness of a test piece measures 15 thickness of a test piece using a dial gauge (for example, signal ABS Digimatic indicator by Mitutoyo Corporation), and makes it the arithmetic mean value. Then, using this apparent density ρ (g / cm ³ ) and the density ρ ₀ (g / cm ³ ) of the olefin resin itself, the porosity P (% of the olefin resin microporous film based on the following formula (II) ) Can be calculated.
Apparent density ρ (g / cm ³ ) = W / (100 × T) (I)
Porosity P [%] = 100 × [(ρ ₀ −ρ) / ρ ₀ ] (II)

  The olefin resin microporous film used in the olefin resin microporous film roll of the present invention is formed by stretching an olefin resin film.

  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 having excellent 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 is excellent in film formation stability and can provide an olefin resin microporous film in which micropores are more uniformly formed.

  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 to 8420000, manufactured by TOSOH)
Elution conditions: 145 ° C
SEC temperature: 145 ° C

As a manufacturing method of the olefin resin microporous film roll, the following steps,
The olefin-based resin film is supplied to an extruder, melt-kneaded, and extruded from a die attached to the tip of the extruder, so that the thickness of the central portion in the width direction is thicker than the thickness of both ends in the width direction. An extrusion process to obtain;
A curing process for curing the olefin-based resin film obtained in the extrusion process,
A stretching process for forming micropores by uniaxial stretching of the olefin-based resin film after the curing process;
An annealing step of shrinking the olefinic resin microporous film after the stretching step at a shrinkage of 0.1 to 10% by heating at a surface temperature of 100 to 175 ° C;
A winding step of obtaining an olefinic resin microporous film roll by winding a olefinic resin microporous film having a length of 400 m or more after the annealing step around a core;
A method having the following is preferably used.

(Extrusion process)
In the extrusion process, the olefin resin is supplied to the extruder, melted and kneaded, and then extruded from a die attached to the tip of the extruder to produce an olefin resin film.

  The temperature of the olefin resin when the olefin resin is melt-kneaded by an extruder is preferably 20 ° C. higher than the melting point of the olefin resin and 100 ° C. higher than the melting point of the olefin resin. More preferably, the temperature is 25 ° C. higher than the melting point of the olefin resin and 80 ° C. higher than the melting point of the olefin resin, more preferably 25 ° C. higher than the melting point of the olefin resin and higher than the melting point of the olefin resin. A temperature not higher than 50 ° C. is particularly preferable. By setting the temperature of the olefin resin at the time of melt kneading to a temperature that is 20 ° C. higher than the melting point of the olefin resin, an olefin resin microporous film having a uniform thickness can be obtained. Moreover, the orientation of an olefin resin can be improved and the production | generation of a lamella can be accelerated | stimulated by making the temperature of the olefin resin at the time of melt-kneading into the temperature below 100 degreeC higher than melting | fusing point of an olefin resin.

  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.

  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 refers to a value obtained by dividing the clearance of the lip of the die by the thickness of the olefin resin film extruded from the die. The clearance of the die lip is measured by measuring the clearance of the die lip at 10 or more locations using a clearance gauge (for example, JIS clearance gauge manufactured by Nagai Gauge Manufacturing Co., Ltd.) in accordance with JIS B7524. It can be done by seeking.

  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. In addition, by setting the film forming speed of the olefin resin film to 300 m / min or less, the film forming stability of the olefin resin film is improved, and an olefin resin microporous film having a uniform thickness and width is obtained. Can do.

  The olefin-based resin film extruded from the die makes the thickness of the central portion in the width direction thicker than the thickness of both end portions, but it is preferable that the thickness gradually increases from both ends in the width direction toward the center. By stretching the olefin resin film having such a variation in thickness in a stretching process described later, an olefin resin microporous film having a uniform thickness with little variation in residual stress can be obtained. By using this olefin resin microporous film, an olefin resin microporous film roll having a small difference between the maximum outer peripheral length and the minimum outer peripheral length can be obtained.

  10-100 micrometers is preferable and, as for the thickness of the center part in the width direction of an olefin resin film, 15-60 micrometers is more preferable. The olefin-based resin film having a too thin central portion may be non-uniform in thickness after stretching. In such a case, the olefin-based resin micropore in which the difference between the maximum outer peripheral length and the minimum outer peripheral length is reduced. There is a possibility that a film roll cannot be obtained. Moreover, in the olefin resin film whose thickness of a center part is too thick, there exists a possibility of reducing the air permeability of the olefin resin microporous film obtained.

  The rate of increase in the thickness of the central portion in the width direction relative to the thickness of both end portions in the width direction of the olefin-based resin film is preferably 0.3 to 7.5%, more preferably 0.5 to 7%, and more preferably 1 to 5 % Is particularly preferable, and 2 to 4% is most preferable. Since the olefin resin film having an increase rate within the above range has a uniform thickness after stretching, an olefin resin microporous film roll having a small difference between the maximum outer peripheral length and the minimum outer peripheral length can be provided.

  In addition, in this invention, the center part in the width direction of an olefin resin film means the range of a total of 10% which spread equally 5% from the center point in the width direction of an olefin resin film to right and left. 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.

  The thickness of the center part or the edge part in the width direction of the olefin resin film can be measured as follows. First, a virtual straight line is drawn on the olefin resin film from one end to the other end in the width direction. And on this virtual straight line, the thickness of the center part in the width direction of an olefin resin film is measured at least five places, and let the arithmetic mean value be the thickness of the center part in the width direction of an olefin resin film. Moreover, on the said virtual straight line, the thickness of the edge part in the width direction of an olefin resin film is measured at least five places, and let the arithmetic mean value be the thickness of the edge part in the width direction of an olefin resin film. The thickness of the olefin-based resin film can be measured using a digital thickness meter (for example, a product name “Signal ABS Digimatic Indicator” manufactured by Mitutoyo Corporation) having an accuracy of 1/1000 mm.

Moreover, the increase rate (R [%]) of the center part in the width direction with respect to each thickness of the both ends in the width direction of the olefin resin film is the center part in the width direction of the olefin resin film as described above. The thickness (C [μm]) and the end thickness (E [μm]) are measured, and the values are obtained based on the following formula.
Increase rate (R [%]) = 100 × (CE) / E

  And the fluctuation | variation of the thickness in the width direction of an olefin resin film can be measured as follows. First, an imaginary straight line is drawn on the olefin resin film from one end to the other end in the width direction. And on this virtual straight line, the thickness variation of the olefin resin film in the width direction is measured by measuring the thickness of the olefin resin film at intervals of 2% with respect to the entire width of the olefin resin film. be able to.

  The thickness of the olefin resin film extruded from the die can be controlled by adjusting the temperature distribution of the die or adjusting the lip clearance of the die.

  And the olefin resin which comprises the olefin resin film is cooled by cooling the olefin resin film extruded from die | dye until the surface temperature becomes below 100 degreeC lower than melting | fusing point of the said olefin 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 process is performed by curing the olefin resin film obtained by the extrusion process at a temperature not lower than 30 ° C. lower than the melting point of the olefin resin and not higher than 5 ° C. lower than the melting point of the olefin resin. Is preferred.

  The curing temperature of the olefin resin film is preferably 30 ° C. lower than the melting point of the olefin resin and 5 ° C. lower than the melting point of the olefin resin, preferably 25 ° C. lower than the melting point of the olefin resin. And a temperature lower by 10 ° C. than the melting point of the olefin resin is more preferable. By making the curing temperature of the olefin resin film 30 ° C. lower than the melting point of the olefin resin, the crystallization of the olefin resin film is promoted, and between the lamellae of the olefin resin film in the stretching process described later. It is possible to facilitate the formation of the minute hole portion. In addition, by setting the curing temperature of the olefin resin film to 5 ° C. or lower than the melting point of the olefin resin, the lamellar structure is destroyed due to relaxation of the molecular orientation of the olefin resin constituting the olefin resin film. Can be reduced.

  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 | stretching process of uniaxially stretching the olefin resin film after a curing process and forming a micropore part is implemented. The stretching process includes the following processes:
A first stretching step of uniaxially stretching the 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 olefin-based resin film stretched in the first stretching step is 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. It is preferable to have the 2nd extending | stretching process of extending | stretching uniaxially at a draw ratio of 1.05 to 3 time at a draw speed of 15 to 150% / min.

(First stretching process)
In the first stretching step, the olefin-based resin film after the curing step is uniaxially stretched at a stretch rate of 20 to 3000% / min at a surface temperature of -20 to 100 ° C and a stretch 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, a fine crack is efficiently generated independently in the non-crystalline part 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 1.2 to 1.6 times, and particularly preferably 1.25 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. Moreover, a micropore part can be uniformly formed in an olefin resin microporous film by making the draw ratio of an olefin resin film 1.6 times or less.

  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 speed in the first stretching step of the olefin resin film is preferably 20 to 3000% / min, and more preferably 20 to 1000% / 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-based 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 stretching method of the olefin resin film in the first stretching step is not particularly limited as long as the olefin resin film can be uniaxially stretched. The olefin resin film can be stretched using a stretching roll. For example, a method of uniaxially stretching an olefin-based resin film at a predetermined temperature using a uniaxial stretching apparatus having a plurality of stretching rolls having different rotational speeds.

(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 the stretching treatment 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 lower by 10 to 100 ° C. 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, it is possible to grow the micropores while suppressing the blockage of the micropores, and to improve the air permeability of the olefin resin microporous film.

  In the second stretching step, the stretching ratio of the olefin resin film is preferably 1.05 to 3 times, and preferably 1.2 to 3 times. By setting the draw ratio of the olefin-based resin film to 1.05 times or more, the micropores formed in the olefin-based resin film during the first stretching step are grown to have excellent air permeability. A film can be provided. Moreover, the obstruction | occlusion of the micropore part formed in the olefin resin film in a 1st extending | stretching process can be suppressed by making the draw ratio of an olefin resin film into 3 times or less.

  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 stretching method of the olefin resin film in the second stretching step is not particularly limited as long as the olefin resin film can be uniaxially stretched. The olefin resin film can be stretched using a stretching roll. For example, a method of uniaxially stretching an olefin-based resin film at a predetermined temperature using a uniaxial stretching apparatus having a plurality of stretching rolls having different rotational speeds.

(Annealing process)
Next, the annealing process which anneal-treats to the olefin resin film in which the uniaxial stretching was given in the 2nd extending process is performed. 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.

  Although the surface temperature of the olefin resin film in an annealing process is limited to 100-175 degreeC, 130-170 degreeC is 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.

  The shrinkage ratio of the olefin resin film in the annealing step is 0.1 to 10%, preferably 0.1 to 8%. If the shrinkage rate is too low, the residual stress generated in the olefin resin film in the stretching process cannot be alleviated as a whole, and the thickness of the resulting olefin resin microporous film may be uneven. There is. In the olefin resin microporous film roll using such an olefin resin microporous film, the olefin resin microporous film is partially wound and 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 olefinic 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.

(Winding process)
Next, the winding process which obtains an olefin resin microporous film roll by winding the olefin resin microporous film whose length after an annealing process is 400 m or more around a core body is implemented.

  Since the olefin resin microporous film after the annealing step described above has a uniform thickness distribution, such an olefin resin microporous film can be wound around the core with a uniform winding tension. There is very little difference between the maximum perimeter and the minimum perimeter. The olefinic resin microporous film unwound from such an olefinic resin microporous film roll is highly reduced in the occurrence of curvature in its length direction. Therefore, the olefin-based resin microporous film is excellent in running stability, the occurrence of wrinkles and meandering under conveyance is highly reduced, and can be easily positioned during battery assembly.

  Furthermore, since the residual stress of the olefin-based resin microporous film is highly relaxed and the residual stress that remains slightly is uniformly dispersed, the thermal shrinkage rate and its standard deviation can be reduced. .

  In the winding process, when the olefinic resin microporous film is wound around the core, the winding tension of the olefinic resin microporous film is preferably 0.1 to 200 N / m, preferably 1 to 100 N / m, per unit width. m is more preferable. By setting the winding tension within the above range, the olefin resin microporous film can be wound at a substantially constant winding speed.

  In the present invention, the winding tension of the olefin resin microporous film can be measured using a conventionally known tension detector.

  In the winding process, the length of the olefin resin microporous film wound on the core is 400 m or more, preferably 400 to 5000 m, and more preferably 400 to 3500 m.

  In the winding process, the width of the olefin 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.

(Slit process)
In the method of the present invention, the olefin-based resin microporous film is unwound from the olefin-based resin microporous film roll obtained in the winding step described above, and the olefin-based resin microporous film is cut in its length direction. It is preferable to further perform a slitting process in which the cut olefin resin microporous film is wound around the core again after being adjusted to a desired width.

  By performing a slit process, the olefin resin microporous film roll by which the narrow olefin resin microporous film adjusted to the desired width was wound can be obtained. However, if the thickness distribution and the occurrence of residual stress are non-uniform in the olefin resin microporous film made narrow by performing the slit process, it is particularly easy to bend after being wound. . However, according to the method of the present invention, as described above, an olefin-based resin microporous film in which the residual stress is relaxed high and the remaining residual stress is evenly dispersed and the thickness distribution is uniform. Can be obtained. Therefore, even when the olefinic resin microporous film obtained by the method of the present invention is cut into a narrow width in the slit process and wound around the core again, the narrowed olefinic resin microporous film is curved. This can be suppressed to a high level.

  In the slitting process, when winding the narrow olefin resin microporous film around the core, the winding tension of the narrow olefin resin microporous film is preferably 0.1 to 200 N / m per unit width. 1 to 100 N / m is more preferable. By setting the winding tension within the above range, it is possible to wind the olefin-based resin microporous film at a substantially constant winding speed without generating residual stress.

  In the olefin-based resin microporous film roll, the width of the cut olefin-based resin microporous film is not particularly limited and may be determined according to the application.

  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. The core used in the annealing process and the slit process is as described above.

  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 427,000, number average molecular weight Mn 45,100, melting point 165 ° C., heat of fusion 93 mJ / mg) was supplied to the extruder and melt-kneaded at a resin temperature of 200 ° C. Thereafter, the homopolypropylene was extruded into a film form from a T-die attached to the tip of the extruder, and cooled to a surface temperature of 30 ° C. to obtain a long homopolypropylene film (width 500 mm). The extrusion rate was 10 kg / hour, the film formation rate was 22 m / min, and the draw ratio was 83. Moreover, the thickness of the center part in the width direction of a homopolypropylene film is 28.3 micrometers, each thickness of the both ends in the width direction is 27.7 micrometers, and the increase rate of the thickness of the center part with respect to each thickness of both ends Was 2.2%. Furthermore, the thickness of the homopolypropylene film gradually increased from both ends in the width direction toward the center.

(Curing process)
Next, a cylindrical core body having an outer diameter of 178 mm is prepared, the core body is rotated in the circumferential direction around the axis core, and a long homopolypropylene film is wound around the core body in a roll shape. A homopolypropylene film roll was obtained by taking. 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 process)
Next, the homopolypropylene film is continuously unwound from the homopolypropylene film roll after the curing process so that the surface temperature of the homopolypropylene film is 23 ° C., and the draw ratio is 600% / min. It was uniaxially stretched 1.4 times only in the extrusion direction.

(Second stretching step)
Subsequently, after the surface temperature of the homopolypropylene film was set to 125 ° C., the film was uniaxially stretched only in the extrusion direction at a stretch ratio of 2.5 times at a stretch rate of 50% / min.

(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 155 ° C. and no tension is applied to the homopolypropylene film. In this way, the homopolypropylene film is annealed by being conveyed in a hot stove for 1 minute, and the homopolypropylene film is contracted to a shrinkage rate of 4% in the stretching direction (conveying direction). A homopolypropylene microporous film (width 450 mm) was obtained.

(Winding process)
Next, a paper-made cylindrical core body (inner diameter 6 inches, wall thickness 13 mm) is prepared. A homopolypropylene microporous film roll was obtained by winding a polypropylene microporous film (length 900 m) in a roll shape at a winding tension of 6.7 N / m per unit width.

[Example 2]
In the extrusion process, by adjusting the clearance of the lip of the T die, the thickness of the central portion in the width direction is 28.1 μm, the thickness of both end portions in the width direction is 27.8 μm, and the thickness of each end portion A homopolypropylene microporous film roll was obtained according to the same procedure as in Example 1 except that a homopolypropylene film having an increase rate of 1.1% in the thickness of the central portion was obtained. In addition, the thickness of the homopolypropylene film obtained in the extrusion process gradually increased from both ends in the width direction toward the center.

[Example 3]
In the second stretching step, a homopolypropylene microporous film roll was obtained according to the same procedure as in Example 1 except that the stretching speed of the homopolypropylene film was 30% / min.

[Example 4]
In the annealing step, a homopolypropylene microporous film roll was obtained according to the same procedure as in Example 1 except that the surface temperature of the homopolypropylene film was 165 ° C.

[Example 5]
In the annealing step, a homopolypropylene microporous film roll was obtained according to the same procedure as in Example 1, except that the homopolypropylene film was shrunk to a shrinkage rate of 7% in the stretching direction (conveyance direction).

[Example 6]
In the extrusion process, by adjusting the clearance of the lip of the T die, the thickness at the center in the width direction is 28.0 μm, the thickness at both ends in the width direction is 27.9 μm, and the thickness at each end A homopolypropylene microporous film roll was obtained according to the same procedure as in Example 1, except that a homopolypropylene film having an increase rate of 0.4% in the thickness of the central portion was obtained. In addition, the thickness of the homopolypropylene film obtained in the extrusion process gradually increased from both ends in the width direction toward the center.

[Example 7]
In the extrusion process, by adjusting the clearance of the lip of the T die, the thickness of the central portion in the width direction is 28.5 μm, the thickness of each end portion in the width direction is 26.6 μm, and the thickness of each end portion A homopolypropylene microporous film roll was obtained according to the same procedure as in Example 1 except that a homopolypropylene film having a thickness increase rate of 7.1% with respect to the center was obtained. In addition, the thickness of the homopolypropylene film obtained in the extrusion process gradually increased from both ends in the width direction toward the center.

[Comparative Example 1]
In the extrusion process, by adjusting the clearance of the lip of the T die, the thickness of the central portion in the width direction is 27.9 μm, the thickness of both end portions in the width direction is 28.2 μm, and the thickness of each end portion According to the same procedure as in Example 1, except that the increase rate of the thickness of the central portion with respect to is -1.1%, and a homopolypropylene film having a thickness gradually decreasing from both ends in the width direction toward the center is obtained. A homopolypropylene microporous film roll was obtained.

[Evaluation]
For the homopolypropylene microporous film roll, the difference between the maximum outer peripheral length and the minimum outer peripheral length was measured according to the method described above. Further, the homopolypropylene microporous film was unwound from the homopolypropylene microporous film roll, and the heat shrinkage rate in the length direction after heating for 1 hour at 105 ° C., its standard deviation, and air permeability. , Surface aperture ratio, and porosity were measured according to the method described above. These results are shown in Table 1.

  About the homopolypropylene film obtained in the extrusion process of Examples 1, 2, 6, and 7, the fluctuation | variation of the thickness in the width direction was measured based on the method mentioned above. The obtained measurement results are shown in FIGS. As is clear from these, the thicknesses of the homopolypropylene films obtained in the extrusion steps of Examples 1, 2, 6 and 7 gradually increased from both ends in the width direction toward the center.

[Curved]
In accordance with the following procedure, the homopolypropylene microporous film roll was unwound from the homopolypropylene microporous film roll, and after the slit process was performed on the homopolypropylene microporous film, the amount of bending generated in the narrow homopolypropylene microporous film was measured. .

(Slit process)
The homopolypropylene microporous film is continuously unwound from the homopolypropylene microporous film roll, and the slitter unit cuts off the homopolypropylene microporous film after cutting off the edge portions at a distance of 15 mm from both ends in the width direction. Then, the homopolypropylene microporous film in the width direction was continuously cut in the length direction to obtain a narrow homopolypropylene microporous film (width 210 mm, length 800 m). Thereafter, a paper-made cylindrical core (inner diameter 6 inches, wall thickness 13 mm) is prepared, and the core is rotated in the circumferential direction around the axial core to obtain a narrow homopolypropylene microporous film. Two homopolypropylene microporous film rolls were obtained by rewinding in a roll shape at a winding tension of 47.6 N / m per unit width.

(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 from the homopolypropylene microporous film roll after the slitting process. At this time, the length direction of the test piece 10 was set to be the length direction of the homopolypropylene microporous film. 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. 5, a straight line L connecting both ends of the measurement side 10c of the test piece 10 is drawn, and the center in the length direction of the straight line L and the center in the length direction of the measurement side 10c of the test piece 10 are drawn. The distance D (mm) was measured with a caliper as the amount of bending. Ten test pieces 10 were prepared from the homopolypropylene microporous film, the amount of bending of each test piece 10 was measured according to the above procedure, and the arithmetic average value of these was taken as the amount of bending of the homopolypropylene microporous film. For each of the two homopolypropylene microporous film rolls, the bending amount of the homopolypropylene microporous film was measured according to the above procedure, and the results are shown in Table 1.

10 Test piece 10a Short side of test piece 10b Long side of test piece 10c Long side of test piece

Claims (8)

An olefin-based resin microporous film roll formed by stretching an olefin-based resin film and having a length of 400 m or more and an olefin-based resin microporous film wound around a core body,
A difference between the maximum outer peripheral length and the minimum outer peripheral length of the olefin resin microporous film roll is 3 mm or less.   2. The olefin-based resin microporous film roll according to claim 1, wherein the thermal shrinkage in the length direction of the olefin-based resin microporous film after heating at 105 ° C. for 1 hour is 4% or less.   The olefin resin micropore according to claim 1 or 2, wherein the standard deviation of the heat shrinkage rate in the length direction of the olefin resin micropore film after heating at 105 ° C for 1 hour is 1% or less. Film roll.   The olefin resin microporous film roll according to any one of claims 1 to 3, wherein the air permeability of the olefin resin microporous film is 100 to 600 sec / 100 mL.   The olefin resin microporous film roll according to any one of claims 1 to 4, wherein the surface opening ratio of the olefin resin microporous film is 10 to 55%.   An olefinic resin microporous film cut out from the olefinic resin microporous film roll according to any one of claims 1 to 5. The olefin resin is supplied to an extruder, melted and kneaded, and extruded from a die attached to the tip of the extruder, so that the thickness of the central portion in the width direction is thicker than the thickness of both ends in the width direction. An extrusion process to obtain,
Curing process for curing the olefin resin film obtained in the extrusion process,
Stretching process for forming micropores by uniaxially stretching the olefin resin film after the curing process,
An annealing step of shrinking the olefin-based resin microporous film after the stretching step at a shrinkage of 0.1 to 10% by heating at a surface temperature of 100 to 175 ° C;
A winding step of obtaining an olefinic resin microporous film roll by winding the olefinic resin microporous film having a length of 400 m or more after the annealing step around a core;
The manufacturing method of the olefin resin microporous film roll characterized by having. The stretching step is
A first stretching step of uniaxially stretching the 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 olefin-based resin film stretched in the first stretching step is 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 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;
The manufacturing method of the olefin resin microporous film roll of Claim 7 characterized by the above-mentioned.

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