JP2015063639A - Production method of heat-resistant propylene resin microporous film, heat-resistant propylene resin microporous film, separator for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-resistant propylene resin microporous film and a production method of the film which is excellent in both transmitting property for ions such as a lithium ion and heat resistance, and which prevents contamination in a production line.SOLUTION: The production method of a heat-resistant propylene resin microporous film includes the steps of: (I) applying a composition comprising a radical polymerizable monomer containing a polyfunctional acrylic monomer having 3 or more functional groups and a photopolymerization initiator on a surface of a propylene resin microporous film so as to deposit 5 to 25 pts.wt. of the radical polymerizable monomer and 0.1 to 2.5 pts.wt. of the photopolymerization initiator on 100 pts.wt. of the propylene resin microporous film; and (II) irradiating the propylene resin microporous film after the step (I) with UV rays in an integrated luminous quantity of 1000 to 5000 mJ/cm.

Description

  The present invention relates to a method for producing a heat-resistant propylene-based resin microporous film used for a separator of a secondary battery such as a lithium ion battery, a heat-resistant propylene-based resin microporous film, a non-aqueous electrolyte secondary battery separator, The present invention relates to a water electrolyte secondary battery.

  Conventionally, lithium ion secondary 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 electrical short circuit between electrodes is prevented.

  When the lithium ion battery is charged, lithium ions are released from the positive electrode and move into 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.

  As the separator, a propylene-based resin microporous film is used because it is excellent in insulation and cost. However, the microporous film of propylene-based resin undergoes large thermal shrinkage near the melting point of the propylene-based resin. For example, when the separator is damaged due to the inclusion of a metal foreign substance or the like and a short circuit occurs, the battery temperature rises due to the generation of reaction heat of the electrolytic solution, thereby causing the propylene-based resin microporous film to thermally shrink. Due to the shrinkage of the propylene-based resin microporous film, heat of reaction of the electrolytic solution is further generated and the battery temperature rises.

  In recent years, lithium-ion batteries have been desired to have high output and secure excellent safety. Therefore, the separator is also required to improve heat resistance.

  Patent Document 1 discloses a lithium secondary battery separator that is processed by electron beam irradiation and has a thermomechanical analysis (TMA) value at 100 ° C. of 0% to −1%. However, the heat resistance of the lithium secondary battery separator is insufficient only by treatment with electron beam irradiation.

  Patent Document 2 discloses a porous film in which divinylbenzene or a crosslinked polymer composed of divinylbenzene and ethylvinylbenzene is held on at least a part of the surface of the porous film composed of polyethylene or polypropylene. Yes. This porous membrane is used as a separation membrane in the water purification field, the blood treatment field, the air purification field, the food industry field and the like.

  However, when the technique disclosed in Patent Document 2 is simply applied to a separator, the separator cannot be sufficiently crosslinked, and sufficient heat resistance cannot be imparted to the separator.

  Therefore, when the amount of divinylbenzene held in the separator is increased in order to give sufficient heat resistance to the separator, the holes in the separator are extremely smaller than the holes in the separation membrane. As a result, the lithium ion permeability decreases. Such a separator cannot be used for a lithium ion battery.

  Further, Patent Document 3 includes a porous base material having a large number of pores, and a porous coating layer coated on at least one surface of the porous base material and containing inorganic particles and a binder. A separator in which is cross-linked is disclosed.

  However, when the separator is manufactured, the inorganic particles contained in the porous coating layer fall off from the surface of the porous substrate and contaminate the production line.

JP 2003-22793 A Japanese Patent Laid-Open No. 3-193125 Special table 2011-505663 gazette

  The present invention provides a method for producing a heat-resistant propylene-based resin microporous film that is excellent in both the permeability and heat resistance of ions such as lithium ions and that does not cause contamination of the production line. Furthermore, the present invention provides a heat-resistant propylene-based resin microporous film obtained by the above production method, a non-aqueous electrolyte secondary battery separator using the heat-resistant propylene-based resin microporous film, and a non-aqueous electrolyte secondary Provide batteries.

The method for producing the heat-resistant propylene-based resin microporous film of the present invention is as follows:
A composition containing a radical polymerizable monomer containing a trifunctional or higher polyfunctional acrylic monomer and a photopolymerization initiator is applied to the surface of the propylene resin microporous film, and 100 parts by weight of the propylene resin microporous film is applied. The step (I) of attaching 5 to 25 parts by weight of the radical polymerizable monomer and 0.1 to 2.5 parts by weight of the photopolymerization initiator, and 1000 on the propylene-based resin microporous film after the step (I) A step (II) of irradiating ultraviolet rays with an integrated light quantity of ˜5000 mJ / cm ²
It is characterized by having.

  The propylene-based resin microporous film used in the present invention contains a propylene-based resin. Further, the propylene-based resin microporous film includes micropores penetrating the film front and back surfaces. The fine pores can impart excellent ion permeability to the heat-resistant propylene-based resin microporous film. As a result, the heat-resistant propylene-based resin microporous film can transmit ions such as lithium ions in the thickness direction.

  The thickness of the propylene-based resin microporous film is preferably 5 to 100 μm, and more preferably 10 to 50 μm.

  In the present invention, the thickness of the propylene-based resin microporous film can be measured according to the following procedure. That is, the arbitrary 10 places of a propylene-type resin microporous film are measured using a dial gauge, and let the arithmetic mean value be the thickness of a propylene-type resin microporous film.

  The air permeability of the propylene-based resin microporous film is preferably 100 to 600 sec / 100 mL, and more preferably 120 to 300 sec / 100 mL. A propylene-based resin microporous film having an air permeability within the above range is excellent in both mechanical strength and ion permeability.

  The air permeability of the propylene-based resin microporous film was measured at 10 points at 10 cm intervals in the length direction of the propylene-based resin microporous film in accordance with JIS P8117 in an atmosphere of a temperature of 23 ° C. and a relative humidity of 65%. And it is set as the value obtained by calculating the arithmetic mean value.

  The surface opening ratio of the propylene-based resin microporous film is preferably 25 to 55%, more preferably 30 to 50%. A propylene-based resin microporous film having a surface opening ratio within the above range is excellent in both mechanical strength and ion permeability.

  In addition, the surface opening ratio of a propylene-type resin microporous film can be measured in the following way. First, in a desired portion of the surface of the microporous propylene-based resin film, a measurement portion having a plane rectangular shape of 9.6 μm in length and 12.8 μm in width is defined, 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 whose one of the long side and the short side is parallel to the extending direction. 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 across the measurement part and the part which is not a measurement part, only the part which exists in a measurement part among micropores is set as a measuring object.

  The maximum major axis of the open end of the micropore in the propylene-based resin microporous film is preferably 1 μm or less, and more preferably 100 nm to 800 nm. A propylene-based resin microporous film having a maximum long diameter of 1 μm or less at the opening end of the microporous portion is excellent in mechanical strength and has uniform ion permeability. Such a propylene-based resin microporous film can reduce the occurrence of minute internal short circuits (dendritic short circuits) due to the growth of dendrites (dendritic crystals).

  The average major axis of the open ends of the micropores in the propylene-based resin microporous film is preferably 500 nm or less, and more preferably 200 nm to 500 nm. The propylene-based resin microporous film having an average major axis at the opening end of the micropore portion of 500 nm or less has uniform ion permeability, thereby reducing the occurrence of minute internal short circuit (dendritic short). .

  In addition, the maximum major axis and the average major axis of the open end of the micropores in the propylene-based resin microporous film are measured as follows. First, the surface of the propylene resin microporous film is coated with carbon. Next, 10 arbitrary positions on the surface of the propylene-based resin microporous film are photographed at a magnification of 10,000 using a scanning electron microscope. The photographing range is a plane rectangular range of 9.6 μm long × 12.8 μm wide on the surface of the propylene-based resin microporous film.

  The major axis of the opening end of each micropore appearing in the obtained photograph is measured. Among the long diameters of the opening ends in the microhole portion, the maximum long diameter is set as the maximum long diameter of the opening end of the microhole portion. The arithmetic mean value of the major axis of the open end in each micropore is defined as the average major axis of the open end of the micropore. The major axis of the open end of the microhole is defined as the diameter of a perfect circle having the smallest diameter that can surround the open end of the microhole. Micropores that exist across the imaging range and the non-imaging range are excluded from the measurement target.

The pore density of the propylene-based resin microporous film is preferably 15 / μm ² or more, and more preferably 17 / μm ² or more. A propylene-based resin microporous film having a pore density of 15 / μm ² or more is excellent in ion permeability.

In addition, the pore density of a propylene-type resin microporous film is measured in the following way. First, in a desired portion of the surface of the microporous propylene-based resin film, a measurement portion having a plane rectangular shape of 9.6 μm in length and 12.8 μm in width is defined, and this measurement portion is photographed at a magnification of 10,000 times. Then, the number of micropores is measured in the measurement part, and the pore density can be calculated by dividing this number by 122.88 μm ² (9.6 μm × 12.8 μm).

  The propylene-based resin microporous film contains a propylene-based resin. Examples of the propylene-based resin include homopolypropylene and copolymers of propylene and other olefins. Of these, homopolypropylene is preferable. Propylene-type resin may be used independently, or 2 or more types may be used together. The copolymer of propylene and another olefin may be a block copolymer or a random copolymer.

  Examples of the olefin copolymerized with propylene include α such as ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-nonene and 1-decene. -An olefin etc. are mentioned, Ethylene is preferable.

As an index indicating the crystallinity of homopolypropylene, there is an isotactic pendart fraction (mmmm fraction) measured by ¹³ C-NMR method. The isotactic pendart fraction measured by ¹³ C-NMR method of homopolypropylene is a side chain with respect to the main chain formed by the carbon-carbon bond composed of any five consecutive propylene units. The ratio of the three-dimensional structure in which all of the methyl groups are located in the same direction occupies the whole molecular chain of homopolypropylene.

90% or more is preferable and, as for the isotactic pendart fraction measured by the ¹³ C-NMR method of homopolypropylene, 95% or more is more preferable. By setting the isotactic pendart fraction to 90% or more, it is possible to provide a propylene-based resin microporous film in which micropores are uniformly formed.

  The weight average molecular weight of the propylene-based resin is preferably 250,000 to 500,000, and more preferably 280,000 to 480,000. According to the propylene-based resin having a weight average molecular weight within the above range, it is possible to provide a propylene-based resin microporous film that is excellent in film forming stability and in which micropores are uniformly formed.

  The molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) of the propylene-based resin is preferably 7.5 to 12, and more preferably 8 to 11. According to the propylene-based resin having a molecular weight distribution within the above range, a propylene-based resin microporous film having a high surface opening ratio, excellent ion permeability, and excellent mechanical strength is provided. Can do.

  Here, the weight average molecular weight and the number average molecular weight of the propylene-based resin are polystyrene-converted values measured by a GPC (gel permeation chromatography) method. Specifically, 6-7 mg of propylene-based resin was sampled, and the collected propylene-based resin was supplied to a test tube, and then 0.05 wt% BHT (dibutylhydroxytoluene) o-DCB (ortho) was added to the test tube. Dichlorobenzene) solution is added to dilute the propylene resin concentration to 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 propylene resin is dissolved in an o-DCB solution of BHT to obtain a measurement sample. Using this measurement sample, the weight average molecular weight and the number average molecular weight of the propylene-based resin can be measured by the GPC method.

The weight average molecular weight and number average molecular weight in the propylene-based resin can be measured, for example, with the following measuring apparatus and measurement conditions.
Product name “HLC-8121GPC / HT” manufactured by TOSOH
Measurement conditions Column: TSKgelGMHHR-H (20) HT x 3
TSK guard column-HHR (30) HT x 1
Mobile phase: o-DCB 1.0 mL / min
Sample concentration: 1 mg / mL
Detector: Bryce refractometer
Standard substance: 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 propylene-type resin, 160-165 degreeC is more preferable. According to the propylene resin having a melting point within the above range, it is possible to provide a propylene resin microporous film excellent in film forming stability and suppressed in mechanical strength at high temperature.

  The production method of the propylene-based resin microporous film is not particularly limited, and a conventionally known wet method or stretching method is used. In the wet method, for example, a process of obtaining a propylene resin film by molding a resin composition containing a propylene resin and a filler or a plasticizer, and the filler or plasticizer is extracted from the propylene resin film. And a step of obtaining a propylene-based resin microporous film in which micropores are formed. On the other hand, the stretching method has a step of obtaining a propylene-based resin microporous film in which micropores are formed by uniaxially stretching or biaxially stretching a propylene-based resin film.

  As the propylene resin microporous film, a propylene resin microporous film produced by a stretching method is more preferable. The propylene-based resin microporous film produced by the stretching method is particularly susceptible to thermal shrinkage at high temperatures due to residual strain generated by stretching. Therefore, the effect of the production method of the present invention can be particularly exhibited by using such a propylene-based resin microporous film in the production method of the present invention.

  As a method for producing a propylene resin microporous film by a stretching method, specifically, (1) a process of obtaining a propylene resin film by extruding a propylene resin and generating lamellar crystals in the propylene resin film And a step of growing, and a step of obtaining a propylene-based resin microporous film in which micropores are formed by stretching a propylene-based resin film and separating lamella crystals; and (2) propylene-based A step of obtaining a propylene-based resin film by extruding a propylene-based resin composition containing a resin and a filler, and an interface between the propylene-based resin and the filler by uniaxially or biaxially stretching the propylene-based resin film Propylene-based resin microporous film in which micropores are formed by peeling And a method and a that step. The method (1) is preferable because a propylene-based resin microporous film in which a large number of micropores are uniformly formed is obtained.

As a method for producing a propylene-based resin microporous film, particularly preferably, the following steps:
The propylene-based resin was melt-kneaded in an extruder at a temperature not lower than 20 ° C. higher than the melting point of the propylene-based resin and not higher than 100 ° C. higher than the melting point of the propylene-based resin, and attached to the tip of the extruder. An extrusion step of obtaining a propylene-based resin film by extruding from a die;
Curing step for curing the propylene-based resin film after the extrusion step at a temperature of 30 ° C. lower than the melting point of the propylene-based resin and 1 ° C. lower than the melting point of the propylene-based resin;
A first stretching step in which the propylene-based resin film after the curing step is uniaxially stretched at a stretching ratio of 1.2 to 1.6 times at a surface temperature of −20 ° C. or more and less than 100 ° C .;
A second stretching step in which the propylene-based resin film stretched in the first stretching step is uniaxially stretched at a surface magnification of 1.2 to 2.2 times at a surface temperature of 100 to 150 ° C;
And an annealing step of annealing the propylene-based resin film that has been stretched in the second stretching step.

  According to the above method, it is possible to obtain a propylene-based resin microporous film in which a large number of micropores penetrating the film front and back surfaces are formed. According to such a propylene-based resin microporous film, there is provided a heat-resistant propylene-based resin microporous film that has excellent air permeability and can smoothly and uniformly transmit ions such as lithium ions. can do. Therefore, according to such a heat-resistant propylene-based resin microporous film, the internal resistance of the secondary battery can be reduced. Such a secondary battery can be charged and discharged at a high current density even in a high output application such as a vehicle such as an electric vehicle. In addition, even when the inside of the secondary battery becomes hot due to occurrence of an abnormal situation such as overcharge, the electrical safety between the electrodes can be suppressed to a high level. Is secured.

(Extrusion process)
A propylene-based resin film containing a propylene-based resin can be produced by supplying a propylene-based resin to an extruder, melt-kneading, and then extruding from a T-die attached to the tip of the extruder.

  The temperature of the propylene-based resin when melt-kneading the propylene-based resin with an extruder is preferably 20 ° C. higher than the melting point of the propylene-based resin and 100 ° C. lower than the melting point of the propylene-based resin. More preferably, the temperature is 25 ° C. higher than the melting point of the propylene resin and 80 ° C. higher than the melting point of the propylene resin, and the temperature is 25 ° C. higher than the melting point of the propylene resin. It is particularly preferable that the temperature be 50 ° C. or higher than the melting point. By setting the temperature of the propylene-based resin at the time of melt-kneading to a temperature that is 20 ° C. higher than the melting point of the propylene-based resin, a propylene-based resin microporous film having a uniform thickness can be obtained. In addition, by controlling the temperature of the propylene-based resin at the time of melt-kneading to not more than 100 ° C. higher than the melting point of the propylene-based resin, the orientation of the propylene-based resin can be improved and the generation of lamellae can be promoted.

  50-300 are preferable, as for the draw ratio at the time of extruding a propylene-type resin into a film form from an extruder, 65-250 are more preferable, and 70-250 are especially preferable. By setting the draw ratio to 50 or more, the tension applied to the propylene-based resin can be improved. As a result, the propylene-based resin can be sufficiently oriented to promote the generation of lamellae. Moreover, the film-forming stability of a propylene-type resin film can be improved by making a draw ratio into 300 or less. This makes it possible to obtain a propylene-based resin microporous film having a uniform thickness and width.

  The draw ratio means a value obtained by dividing the clearance of the lip of the T die by the thickness of the propylene-based 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. The thickness of the propylene-based resin film extruded from the T-die is 10 or more in the thickness of the propylene-based resin film extruded from the T-die using a dial gauge (for example, signal ABS Digimatic indicator manufactured by Mitutoyo Corporation). It can be performed by measuring and calculating the arithmetic mean value.

  The film forming speed of the propylene-based resin film is preferably 10 to 300 m / min, more preferably 15 to 250 m / min, and particularly preferably 15 to 30 m / min. By setting the film-forming speed of the propylene-based resin film to 10 m / min or more, the tension applied to the propylene-based resin can be improved. This makes it possible to sufficiently align the propylene-based resin molecules and promote the generation of lamellae. Moreover, the film-forming stability of a propylene-type resin film can be improved by making the film-forming speed | rate of a propylene-type resin film into 300 m / min or less. This makes it possible to obtain a propylene-based resin microporous film having a uniform thickness and width.

  Then, the propylene resin film constituting the propylene resin film is cooled by cooling the propylene resin film extruded from the T-die until the surface temperature becomes 100 ° C. or lower than the melting point of the propylene resin. Crystallizes and lamella is highly produced. In the present invention, the propylene-based resin film constituting the propylene-based resin film is oriented in advance by extruding the melt-kneaded propylene-based resin, and then the propylene-based resin film is cooled. Thereby, the portion where the propylene-based resin is oriented can promote the generation of lamellae.

  The surface temperature of the cooled propylene-based resin film is preferably not more than 100 ° C. lower than the melting point of the propylene-based resin, more preferably 140 to 110 ° C. lower than the melting point of the propylene-based resin, and more than the melting point of the propylene-based resin. Also, a temperature lower by 135 to 120 ° C. is particularly preferable. By cooling the surface temperature of the propylene-based resin film to the above range, the propylene-based resin can be crystallized to highly generate lamellae.

(Curing process)
Subsequently, the propylene-type resin film obtained by the extrusion process mentioned above is cured. This propylene-based resin curing step is performed in order to grow the lamella formed in the propylene-based resin film in the extrusion step. 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 propylene-based resin film. It is possible to generate a crack between lamellas, not within the lamella, and to form a minute through hole (microhole part) starting from this crack.

  The curing step is performed by curing the propylene-based resin film obtained by the extrusion step at a temperature that is 30 ° C. lower than the melting point of the propylene-based resin and 5 ° C. lower than the melting point of the propylene-based resin.

  The curing temperature of the propylene-based resin film is preferably 30 ° C. or lower than the melting point of the propylene-based resin and 5 ° C. lower than the melting point of the propylene-based resin, preferably 25 ° C. lower than the melting point of the propylene-based resin. And a temperature lower by 8 ° C. than the melting point of the propylene-based resin is more preferable. By setting the curing temperature of the propylene-based resin film to a temperature 30 ° C. lower than the melting point of the propylene-based resin, crystallization of the propylene-based resin film can be sufficiently promoted. Moreover, collapse of the lamellar structure due to relaxation of the molecular orientation of the propylene resin can be reduced by setting the curing temperature of the propylene resin film to 5 ° C. or lower than the melting point of the propylene resin.

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

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

  When curing the propylene-based resin film while running on the propylene-based resin film, the curing time of the propylene-based resin film is preferably 1 minute or more, and more preferably 5 minutes to 60 minutes.

  When curing the propylene-based resin film in a roll-up state, the curing time is preferably 1 hour or longer, and more preferably 15 hours or longer. By curing the propylene-based resin film wound in a roll shape with such a curing time, the curing of the propylene-based resin film as a whole can be performed sufficiently with the curing temperature described above. Thereby, the lamella can be sufficiently grown in the propylene-based resin film. Moreover, from a viewpoint of reducing the thermal deterioration of a propylene-type resin film, 35 hours or less are preferable and 30 hours or less are more preferable.

  If the propylene-based resin film is cured in the form of a roll, the propylene-based resin film is unwound from the propylene-based resin film roll after the curing step, and the stretching step and the annealing step described later are performed. Good.

(First stretching process)
Next, a first stretching process is performed on the propylene-based resin film after the curing process, in which the surface temperature is -20 ° C. or higher and lower than 100 ° C., and uniaxial stretching is performed at a stretching ratio of 1.2 to 1.6 times. In the first stretching step, the propylene-based resin film is preferably uniaxially stretched only in the extrusion direction. In the first stretching step, the lamellae in the propylene-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 are reliably formed starting from this crack.

  In the first stretching step, the surface temperature of the propylene-based resin film is preferably −20 ° C. or higher and lower than 100 ° C., more preferably 0 to 80 ° C., and particularly preferably 10 to 40 ° C. By setting the surface temperature of the propylene-based resin film to −20 ° C. or higher, breakage of the propylene-based resin film during stretching can be reduced. Moreover, by setting the surface temperature of the propylene-based resin film to less than 100 ° C., it is possible to generate cracks in the non-crystalline part between lamellae.

  In the first stretching step, the stretching ratio of the propylene-based resin film is preferably 1.2 to 1.6 times, and more preferably 1.25 to 1.5 times. By setting the draw ratio to 1.2 times or more, micropores can be formed in the non-crystalline part between lamellae. Moreover, a micropore part can be uniformly formed in a propylene-type resin microporous film by making a draw ratio into 1.6 times or less.

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

  The stretching speed in the first stretching step of the propylene-based resin film is preferably 20% / min or more, more preferably 20 to 500% / min, and particularly preferably 20 to 70% / 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 500% / min or less, the breakage of the propylene-based resin film in the first stretching step can be suppressed.

  In addition, in this invention, the extending | stretching speed of a propylene-type resin film means the change rate of the dimension in the extending | stretching direction of the propylene-type resin film per unit time.

  The method for stretching the propylene-based resin film in the first stretching step is not particularly limited as long as the propylene-based resin film can be uniaxially stretched. For example, the propylene-based resin film can be stretched at a predetermined temperature using a uniaxial stretching device. Examples thereof include a uniaxial stretching method.

(Second stretching step)
Next, a second stretching step is performed in which the propylene-based resin film after the first stretching step is subjected to a uniaxial stretching treatment at a surface temperature of 100 to 150 ° C. and a stretching ratio of 1.2 to 2.2 times. Also in the second stretching step, the propylene-based resin film is preferably uniaxially stretched only in the extrusion direction. By performing the stretching process in the second stretching step, a large number of micropores formed in the propylene-based resin film in the first stretching step can be grown.

  In the second stretching step, the surface temperature of the propylene-based resin film is preferably 100 to 150 ° C, and more preferably 110 to 140 ° C. By setting the surface temperature of the propylene-based resin film to 100 ° C. or higher, the micropores formed in the propylene-based resin film in the first stretching step can be highly grown. Further, by setting the surface temperature of the propylene-based resin film to 150 ° C. or less, it is possible to reduce the blockage of the micropores formed in the propylene-based resin film in the first stretching step.

  In the second stretching step, the stretching ratio of the propylene-based resin film is preferably 1.2 to 2.2 times, and more preferably 1.5 to 2 times. By setting the draw ratio of the propylene-based resin film to 1.2 times or more, micropores formed in the propylene-based resin film during the first stretching step can be grown. Thereby, the propylene-type resin microporous film which has the outstanding air permeability can be provided. Moreover, it becomes possible by suppressing the draw ratio of a propylene-type resin film to 2.2 times or less to block | close the micropore part formed in the propylene-type resin film in a 1st extending | stretching process.

  In the second stretching step, the stretching speed of the propylene-based resin film is preferably 500% / min or less, more preferably 400% / min or less, and particularly preferably 15 to 60% / min. By setting the stretching speed of the propylene-based resin film within the above range, micropores can be formed uniformly in the propylene-based resin film.

  The method for stretching the propylene-based resin film in the second stretching step is not particularly limited as long as the propylene-based resin film can be uniaxially stretched. For example, the propylene-based resin film can be stretched at a predetermined temperature using a uniaxial stretching device. Examples thereof include a uniaxial stretching method.

(Annealing process)
Next, an annealing process is performed in which the propylene-based 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 propylene-based resin film due to the stretching applied in the above-described stretching step, and to suppress the heat shrinkage caused by heating in the resulting propylene-based resin microporous film. Is called.

  The surface temperature of the propylene-based resin film in the annealing step is preferably not less than the surface temperature of the propylene-based resin film in the second stretching step and 10 ° C. lower than the melting point of the propylene-based resin. By setting the surface temperature of the propylene-based resin film to be equal to or higher than the surface temperature of the propylene-based resin film at the time of the second stretching step, the strain remaining in the propylene-based resin film can be sufficiently relaxed. This makes it possible to improve the dimensional stability during heating of the propylene-based resin microporous film. Moreover, the blockage | closure of the micropore part formed at the extending | stretching process can be suppressed by making the surface temperature of a propylene-type resin film 10 degrees C or less lower than melting | fusing point of a propylene-type resin.

  The shrinkage ratio of the propylene-based resin film in the annealing step is preferably 25% or less. By setting the shrinkage rate of the propylene-based resin film to 25% or less, it is possible to reduce the occurrence of sagging of the propylene-based resin film and uniformly anneal the propylene-based resin film.

  The shrinkage ratio of the propylene-based resin film is obtained by dividing the shrinkage length of the propylene-based resin film in the stretching direction during the annealing step by the length of the propylene-based resin film in the stretching direction after the second stretching step. The value multiplied by.

(Process (I))
In the method of the present invention, the step (I) of applying a composition containing a radical polymerizable monomer containing a trifunctional or higher polyfunctional acrylic monomer and a photopolymerization initiator onto the surface of the above-mentioned propylene resin microporous film. To implement.

  The radical polymerizable monomer means a monomer having a functional group having a radical polymerizable unsaturated bond that can be radically polymerized by irradiation with ultraviolet rays in the presence of a photopolymerization initiator. The radically polymerizable monomer includes at least a trifunctional or higher polyfunctional acrylic monomer.

  The trifunctional or higher polyfunctional acrylic monomer contains at least three functional groups having a radical polymerizable unsaturated bond that can be radically polymerized by irradiation with ultraviolet rays in the presence of a photopolymerization initiator, and It only needs to contain an acryloyl group or a methacryloyl group. The functional group having a radical polymerizable unsaturated bond capable of radical polymerization is preferably an acryloyl group or a methacryloyl group.

  As the polyfunctional acrylic monomer, a trifunctional or higher polyfunctional acrylic monomer is used, and a trifunctional to hexafunctional polyfunctional acrylic monomer is preferably used. In addition, trifunctional or more polyfunctional acrylic monomers may be used alone or in combination of two or more.

  The trifunctional polyfunctional acrylic monomer is not particularly limited. For example, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, ethoxylated isocyanuric acid triacrylate, ε- Examples include caprolactone-modified tris- (2-acryloxyethyl) isocyanurate and ethoxylated glycerin triacrylate.

  The tetrafunctional polyfunctional acrylic monomer is not particularly limited. For example, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, ditrimethylolpropane tetraacrylate, ditrimethylolpropane tetramethacrylate, ethoxylated pentaerythritol tetraacrylate, and ethoxy And pentaerythritol tetramethacrylate.

  The hexafunctional polyfunctional acrylic monomer is not particularly limited, and examples thereof include dipentaerythritol hexaacrylate and dipentaerythritol hexamethacrylate.

  Of these, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and dipentaerythritol hexaacrylate are preferable as the trifunctional or higher polyfunctional acrylic monomer.

  The radical polymerizable monomer may further contain a bifunctional polyfunctional acrylic monomer. The bifunctional polyfunctional acrylic monomer contains two functional groups having a radical polymerizable unsaturated bond that can be radically polymerized by irradiation with ultraviolet rays in the presence of a photopolymerization initiator, and an acryloyl group. Or what is necessary is just to contain the methacryloyl group. The functional group having a radical polymerizable unsaturated bond capable of radical polymerization is preferably an acryloyl group or a methacryloyl group.

  Examples of the bifunctional polyfunctional acrylic monomer include 1,9-nonanediol dimethacrylate, 1,9-nonanediol diacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, tripropylene glycol diacrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,10-decanediol methacrylate, Neopentyl glycol dimethacrylate, glycerin dimethacrylate and the like can be mentioned. The bifunctional polyfunctional acrylic monomer may be used alone or in combination of two or more.

  The content of the trifunctional or higher polyfunctional acrylic monomer in the radical polymerizable monomer is preferably 10% by weight or more, more preferably 30% by weight or more, particularly preferably 80% by weight or more, and most preferably 100% by weight. . By using a radically polymerizable monomer containing 10% by weight or more of a trifunctional or higher polyfunctional acrylic monomer, the resulting heat resistant propylene resin microporous film has excellent heat resistance without reducing air permeability. Can be granted.

  It is preferable that the composition contains a high molecular weight substance in addition to the radical polymerizable monomer and the photopolymerization initiator. A high molecular weight body means the product by superposition | polymerization. High molecular weight substances include polymers and oligomers. Examples of the high molecular weight body include a butadiene oligomer and an imide polymer. A high molecular weight body may be used individually by 1 type, and may use 2 or more types together. By using a high molecular weight body, it is possible to form a packed layer having excellent toughness despite having high hardness. According to such a filling layer, the heat resistance and puncture strength of the heat resistant synthetic resin microporous film can be further improved.

  Examples of the butadiene oligomer include 1,2-butadiene oligomer, 1,3-butadiene oligomer, epoxidized butadiene oligomer, and butadiene (meth) acrylate oligomer. Examples of the butadiene (meth) acrylate oligomer include butadiene (meth) acrylate oligomers represented by the following formula (I).

（式中、ｏは、繰り返し単位の数であって、２以上の整数であり、Ｒは、下記式（II）で示される基である。）

(In the formula, o is the number of repeating units and is an integer of 2 or more, and R is a group represented by the following formula (II).)

  Examples of the imide-based polymer include polyamideimide and soluble polyimide.

  500-30000 is preferable and, as for the number average molecular weight of a high molecular weight body, 1000-10000 are more preferable. A high molecular weight polymer having a number average molecular weight within the above range has excellent compatibility with a propylene-based resin, and therefore can highly reduce the blockage of the micropores of the propylene-based resin microporous film during coating. it can.

In addition, in this invention, the number average molecular weight of a high molecular weight body is the value converted into polystyrene measured by GPC (gel permeation chromatography) method. For example, it can be measured with the following measuring apparatus and measurement conditions.
<Measurement device>
Wateres product name “Waters 2690”
<Measurement conditions>
Column: Shodex GPC LF-404 (4.6mm ID x 250mm) x 2 Column temperature: 40 ° C
Mobile phase: THF (0.3 mL / min)
Sample concentration: 0.2% by weight
Detector: Product name “2414” manufactured by RI waters

  10-100 weight part is preferable with respect to 100 weight part of radically polymerizable monomers, and, as for content of the high molecular weight body in a composition, 20-50 weight part is more preferable. By using a composition having a high molecular weight content within the above range, a filling layer can be uniformly formed on the wall surface of the microporous portion of the synthetic resin microporous film without blocking the microporous portion. Thus, a heat-resistant synthetic resin microporous film having further improved heat resistance and puncture strength can be provided.

  Examples of the photopolymerization initiator include benzophenone, benzyl, methyl-o-benzoylbenzoate, and anthraquinone.

  The content of the photopolymerization initiator in the composition is preferably 2 to 10 parts by weight and more preferably 3 to 8 parts by weight with respect to 100 parts by weight of the radical polymerizable monomer. When there is too much content of a photoinitiator, deterioration of a propylene resin microporous film may be promoted. Moreover, when there is too little content of a photoinitiator, strong ultraviolet irradiation is required for superposition | polymerization of a radically polymerizable monomer, and deterioration of a propylene resin microporous film may be promoted similarly to the case where it is too much.

  In the method of the present invention, a composition containing a radical polymerizable monomer, a photopolymerization initiator, and, if necessary, a high molecular weight substance is applied to a propylene-based resin microporous film. At this time, the composition may be applied directly to the surface of the propylene resin microporous film. However, a radically polymerizable monomer and a photopolymerization initiator, and if necessary, a high molecular weight material is dispersed or dissolved in a solvent to obtain a coating solution, and this coating solution is applied to a propylene-based resin microporous film. It is preferable. By using such a coating liquid, the radical polymerizable monomer and the photopolymerization initiator can be uniformly attached to the entire resin surface including the wall surface of the microporous portion of the propylene-based resin microporous film. This makes it possible to produce a heat-resistant propylene-based resin microporous film having high and improved heat resistance. Furthermore, by using a radically polymerizable monomer as the coating liquid, it is possible to highly reduce the blockage of micropores in the propylene-based resin microporous film by the radically polymerizable monomer. Therefore, it is possible to improve the heat resistance of the heat-resistant propylene-based resin microporous film without reducing the air permeability.

  The solvent used in the coating solution is not particularly limited as long as it can dissolve or disperse the radical polymerizable monomer and the photopolymerization initiator. For example, alcohols such as methanol, ethanol, propanol, isopropyl alcohol, acetone, Examples thereof include ketones such as methyl ethyl ketone and methyl isobutyl ketone, ethers such as tetrahydrofuran and dioxane, toluene, ethyl acetate and chloroform. Of these, ethyl acetate, ethanol, methanol, toluene, and acetone are preferable. These solvents can be removed smoothly after the coating liquid is applied to the surface of the propylene-based resin microporous film. Furthermore, the solvent has low reactivity with an electrolyte solution constituting a secondary battery such as a lithium ion battery, and is excellent in safety.

  85-97 weight% is preferable and, as for content of the solvent in a coating liquid, 88-95 weight% is more preferable. By setting the content of the solvent within the above range, the filling layer can be uniformly formed on the wall surface of the microporous portion without blocking the microporous portion of the propylene-based resin microporous film, and thus the air permeability is reduced. A heat-resistant propylene-based resin microporous film with improved heat resistance can be produced without reducing it.

  The method for applying the composition to the propylene-based resin microporous film is not particularly limited. For example, (1) a method of applying the composition to the propylene-based resin microporous film; (2) propylene-based in the composition A method of immersing a resin microporous film and coating a propylene-based resin microporous film with a radically polymerizable monomer; (3) a radically polymerizable monomer and a photopolymerization initiator, and if necessary, a high molecular weight substance in a solvent (4) radicals, wherein a coating solution is prepared by dissolving or dispersing in a coating solution, and the coating solution is applied to a propylene-based resin microporous film and then the solvent is removed by heating the propylene-based resin microporous film; A polymerizable monomer, a photopolymerization initiator, and, if necessary, a high molecular weight material are dissolved or dispersed in a solvent to prepare a coating liquid, and a propylene-based resin microporous film is added to the coating liquid. By immersing Lum, after applying a coating liquid to the propylene resin microporous film in, and a method of removing a solvent by heating the propylene resin microporous film. Of these, the methods (3) and (4) are preferred. According to these methods, the radical polymerizable monomer can be uniformly applied to the wall surface of the microporous portion of the propylene-based resin microporous film.

  In the methods (3) and (4) above, the heating temperature of the propylene-based resin microporous film for removing the solvent can be set according to the type and boiling point of the solvent used. The heating temperature of the propylene-based resin microporous film for removing the solvent is preferably 50 to 140 ° C, more preferably 70 to 130 ° C. By setting the heating temperature within the above range, the coated solvent can be efficiently removed while highly reducing thermal shrinkage and blockage of the micropores of the propylene-based resin microporous film.

  In the methods (3) and (4) above, the heating time of the propylene-based resin microporous film for removing the solvent is not particularly limited, and can be set according to the type and boiling point of the solvent used. The heating time of the propylene-based resin microporous film for removing the solvent is preferably 0.02 to 60 minutes, more preferably 0.1 to 30 minutes.

  As described above, by applying the composition or coating liquid to the propylene-based resin microporous film, the propylene-based resin microporous film is provided with a radical polymerizable monomer and a photopolymerization initiator, and, if necessary, a high molecular weight body. Can be attached.

  The adhesion amount of the radical polymerizable monomer to the propylene resin microporous film is limited to 3 to 30 parts by weight with respect to 100 parts by weight of the propylene resin microporous film. -23 parts by weight is more preferred. By setting the adhesion amount of the radical polymerizable monomer within the above range, the filling layer can be uniformly formed on the wall surface of the microporous portion without blocking the microporous portion of the propylene-based resin microporous film. This makes it possible to produce a heat-resistant propylene-based resin microporous film with improved heat resistance without reducing air permeability.

  The adhesion amount of the photopolymerization initiator to the propylene resin microporous film is limited to 0.1 to 2.5 parts by weight with respect to 100 parts by weight of the propylene resin microporous film. 0.0 part by weight is preferable, and 0.5 to 1.5 part by weight is more preferable. By setting the adhesion amount of the photopolymerization initiator within the above range, the radical polymerizable monomer can be sufficiently polymerized.

  The adhesion amount of the high molecular weight body to the propylene-based resin microporous film is preferably 1 to 25 parts by weight, more preferably 2 to 15 parts by weight with respect to 100 parts by weight of the propylene-based resin microporous film. Part is particularly preferred. By making the adhesion amount of the high molecular weight material within the above range, the filling layer can be uniformly formed on the wall surface of the microporous portion without blocking the microporous portion of the propylene-based resin microporous film. This makes it possible to produce a heat-resistant propylene-based resin microporous film with improved heat resistance without reducing air permeability.

(Process (II))
Next, in the method of the present invention, the propylene-based resin microporous film coated with the composition or the coating liquid is irradiated with ultraviolet rays at an integrated light amount of 1000 to 5000 mJ / cm ² . As a result, the radical polymerizable monomer is polymerized, and the packed layer containing the polymer of the radical polymerizable monomer is integrally formed on at least a part of the propylene-based resin microporous film, preferably the entire wall surface of the microporous part. be able to.

  As described above, the packed layer includes a polymer of a radical polymerizable monomer including a polyfunctional acrylic monomer having three or more functions. By using the packed layer including such a polymer, It is possible to provide a heat-resistant propylene-based resin microporous film having a high heat shrinkage and having excellent heat resistance. In addition, since the trifunctional or higher polyfunctional acrylic monomer has excellent compatibility with the propylene resin microporous film, a filling layer can be formed without blocking the micropores of the propylene resin microporous film. Can do. Therefore, according to the packed bed, excellent heat resistance can be imparted to the propylene-based resin microporous film without reducing the air permeability.

  Moreover, in this invention, after applying the radically polymerizable monomer containing the polyfunctional acrylic monomer more than trifunctional to the propylene-type resin microporous film, it irradiates with an ultraviolet-ray. At this time, since ultraviolet rays have a moderately high energy, the ionizing radiation reaches the propylene resin microporous film, and radicals are also generated in the propylene resin in the propylene resin microporous film. Can be made. Thereby, a part of the propylene-based resin and a part of the polymer of the radical polymerizable monomer can be chemically bonded. By forming such chemical bonds, it is possible to form a packed layer that is firmly integrated with the propylene-based resin microporous film. This can further improve the heat resistance of the propylene-based resin microporous film.

  Furthermore, by irradiating the propylene-based resin microporous film with ultraviolet rays, a part of the propylene-based resin is decomposed to lower the molecular weight, and as a result, the stress relaxation of the propylene-based resin microporous film can proceed. It is considered that such stress relaxation effectively prevents thermal shrinkage of the heat-resistant propylene-based resin microporous film at high temperatures. Examples of the propylene-based resin microporous film that can achieve such an effect include a polypropylene-based resin microporous film.

Integrated quantity of ultraviolet light for propylene resin microporous film is limited to 1000~5000mJ / cm ^2, preferably ^{1000~4000mJ / cm 2, 1500~3700mJ / cm} 2 is more preferable. If the cumulative amount of ultraviolet light is too low, the amount of ultraviolet light that reaches the propylene resin microporous film decreases, and therefore the chemical reaction between the propylene resin in the propylene resin microporous film and the polymer of the radical polymerizable monomer. May not form sufficient bonds. Moreover, when the irradiation intensity | strength of an ultraviolet-ray is too high, the propylene-type resin in a propylene-type resin microporous film may deteriorate, and the mechanical strength of the heat-resistant propylene-type resin microporous film obtained may be reduced.

  After irradiating the propylene-based resin microporous film with ultraviolet rays, the propylene-based resin microporous film is preferably heated at 100 to 150 ° C. Thereby, the radically polymerizable monomer remaining in the film can be removed by volatilization or thermal decomposition without contributing to the polymerization reaction due to the irradiation of ultraviolet rays. By removing the remaining radical polymerizable monomer, coloring and thermal decomposition of the non-aqueous electrolyte due to the remaining radical polymerizable monomer is suppressed, thereby improving safety and extending the life of the non-aqueous electrolyte. A secondary battery can be provided. The heating temperature of the propylene-based resin microporous film is preferably 100 to 150 ° C, more preferably 100 to 130 ° C.

  The rate of increase in the air permeability of the heat-resistant propylene resin microporous film relative to the air permeability of the propylene resin microporous film is preferably 30% or less, preferably 20% or less, and particularly preferably 10% or less. In the method of the present invention, as described above, a trifunctional or higher polyfunctional acrylic monomer is used as the radical polymerizable monomer. By using such a polyfunctional acrylic monomer, it is possible to form a packed layer without blocking the micropores of the propylene resin microporous film, and therefore, to the air permeability of the propylene resin microporous film. The increase rate of the air permeability of the heat resistant propylene resin microporous film can be lowered as described above.

The air permeability of the heat-resistant propylene resin microporous film can be measured in the same manner as the measurement method described above for the air permeability of the propylene resin microporous film. The rate of increase () of the air permeability (A ₁ ) of the heat-resistant propylene resin microporous film relative to the air permeability (A ₀ ) of the propylene resin microporous film can be calculated based on the following formula. it can.
Air permeability increase rate (%) = 100 × (A ₁ −A ₀ ) / A ₀

According to the method of the present invention described above, a heat-resistant propylene-based resin microporous film having excellent heat resistance can be provided. Such heat-resistant propylene-based resin microporous film is
A propylene-based resin microporous film containing a propylene-based resin;
A packing layer that is formed integrally with the wall surface of the micropores of the propylene-based resin microporous film and includes a polymer of a radically polymerizable monomer that includes a trifunctional or higher polyfunctional acrylic monomer. In addition, a part of the propylene resin and a part of the polymer of the radical polymerizable monomer are chemically bonded.

  The packed layer includes a polymer of a radical polymerizable monomer including a trifunctional or higher polyfunctional acrylic monomer. A part of the polymer in the packed bed and a part of the propylene resin in the propylene resin microporous film are chemically bonded. By using such a packed layer containing a polymer, as described above, it is possible to provide a heat-resistant propylene-based resin microporous film that has high heat shrinkage at high temperatures and has excellent heat resistance, as described above. .

  Moreover, when a high molecular weight body is used in the formation of the filling layer, the filling layer further includes a high molecular weight body. When a high molecular weight body having a radical polymerizable unsaturated bond is used, such a high molecular weight body and a radical polymerizable monomer may be polymerized to form a polymer. You may chemically couple | bond with a part of propylene-type resin fine in a propylene-type resin microporous film. A butadiene oligomer is mentioned as a high molecular weight body which has a radically polymerizable unsaturated bond.

The filling layer can improve the heat resistance of the heat-resistant propylene resin microporous film without using inorganic particles. Therefore, it is preferable that the packed bed does not contain inorganic particles. Examples of the inorganic particles include inorganic particles generally used for porous coating layers. Examples of the material constituting the inorganic particles include Al ₂ O ₃ , SiO ₂ , TiO ₂ , and MgO.

  In addition, by using a polyfunctional acrylic monomer having three or more functional groups, it is possible to form a filling layer without blocking the micropores of the propylene-based resin microporous film. The air permeability of the conductive propylene-based resin microporous film is highly reduced.

  Part of the polymer in the packed bed and part of the propylene resin in the propylene resin microporous film are chemically bonded. Such chemical bonds are not particularly limited, and include covalent bonds, ionic bonds, and intermolecular bonds.

  The content of the packed layer in the heat-resistant propylene-based resin microporous film is preferably 3 to 30 parts by weight, more preferably 5 to 25 parts by weight, and more preferably 10 to 25 parts per 100 parts by weight of the propylene-based resin microporous film. Part by weight is particularly preferred. By setting the content of the packed layer within the above range, excellent heat resistance can be imparted to the resulting heat-resistant propylene-based resin microporous film without reducing air permeability.

  The air permeability of the heat-resistant propylene-based resin microporous film is not particularly limited, but is preferably 50 to 300 sec / 100 mL, and more preferably 75 to 250 sec / 100 mL. As described above, the heat-resistant propylene-based resin microporous film of the present invention has a high reduction in air permeability due to the formation of the packed layer. Therefore, the air permeability of the heat-resistant propylene-based resin microporous film of the present invention can be within the above range. The air permeability of the heat-resistant propylene-based resin microporous film can be measured by the same method as the method for measuring the air permeability of the propylene-based resin microporous film described above.

  The heat shrinkage ratio after heating the heat-resistant propylene-based resin microporous film at 130 ° C. for 1 hour is preferably 8% or less. The heat-resistant propylene-based resin microporous film is provided with excellent heat resistance by the packed layer. Therefore, the heat-resistant propylene-based resin microporous film can have a heat shrinkage rate of 8% or less.

  The heat-resistant propylene-based resin microporous film of the present invention includes a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery, a nonaqueous electrolyte primary battery such as a lithium primary battery, and a nonaqueous electrolyte solution such as an electric double layer capacitor. However, it is preferably used as a separator for non-aqueous electrolyte secondary batteries and more preferably as a separator for lithium ion secondary batteries. Since the heat-resistant propylene-based resin microporous film of the present invention is excellent in heat resistance, the use of such a heat-resistant propylene-based resin microporous film as a separator resulted in a case where the temperature inside the battery became high. Even in such a case, it is possible to provide a non-aqueous electrolyte secondary battery in which an electrical short circuit between the electrodes is highly suppressed.

A nonaqueous electrolytic solution is an electrolytic solution in which an electrolyte salt is dissolved in a solvent that does not contain water. Examples of the non-aqueous electrolyte used in the lithium ion secondary battery include a non-aqueous electrolyte obtained by dissolving a lithium salt in an aprotic organic solvent. Examples of the aprotic organic solvent include a mixed solvent of a cyclic carbonate such as propylene carbonate and ethylene carbonate and a chain carbonate such as diethyl carbonate, methyl ethyl carbonate, and dimethyl carbonate. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , and LiN (SO ₂ CF ₃ ) ₂ .

  The heat-resistant synthetic resin microporous film of the present invention has a packed layer containing a polymer of a radical polymerizable monomer containing a trifunctional or higher polyfunctional acrylic monomer. According to this filled layer, the wettability of the heat-resistant propylene-based resin microporous film with respect to the nonaqueous electrolytic solution can be improved. Therefore, the heat-resistant propylene-based resin microporous film easily allows the nonaqueous electrolytic solution to enter the micropores, and can uniformly hold a large amount of the nonaqueous electrolytic solution. Accordingly, by using a heat-resistant propylene-based resin microporous film as a separator, it is possible to provide a non-aqueous electrolyte secondary battery that is excellent in productivity and has a high reduction in lifetime due to deterioration of the electrolyte. Can do.

  According to the method for producing a propylene-based resin microporous film of the present invention, as described above, a heat-resistant propylene-based resin microporous film having improved heat resistance without reducing ion permeability such as lithium ions is produced. be able to. Therefore, according to such a heat-resistant propylene-based resin microporous film, it is possible to provide a non-aqueous electrolyte secondary battery capable of charging and discharging at a high current density while reducing the internal resistance. . In addition, such a non-aqueous electrolyte secondary battery can reduce the electrical short circuit between the electrodes to a high level even when the internal temperature becomes high due to abnormal heat generation due to overcharging or the like.

  The heat-resistant propylene-based resin microporous film produced by the method for producing a propylene-based resin microporous film of the present invention does not need to use a porous coating layer containing inorganic particles, and thus is excellent in lightness. Contamination of the production line due to falling off of inorganic particles during the production process does not occur.

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

Example 1
1. Production of homopolypropylene microporous film (extrusion process)
Homopolypropylene (weight average molecular weight 413,000, number average molecular weight 44,300, melting point 163 ° C.) was supplied to the extruder, melted and kneaded at a resin temperature of 200 ° C., and then attached to the tip of the extruder. The film was extruded from the die into a film and cooled until the surface temperature reached 30 ° C. to obtain a long homopolypropylene film (thickness 30 μm, width 200 mm). The extrusion rate was 12 kg / hour, the film forming speed was 22 m / min, and the draw ratio was 70.

(Curing process)
Next, a homopolypropylene film roll was obtained by winding a long homopolypropylene film around a core in a roll shape. While maintaining this homopolypropylene film roll so that its axial direction is horizontal, the homopolypropylene film roll was installed while rotating at a rotational speed of 0.1 rpm in the circumferential direction around the axial core of the core. It was allowed to stand for 24 hours in a hot air oven where the ambient temperature was 155 ° C.

(First stretching process)
Next, the homopolypropylene film is continuously unwound from the cured homopolypropylene film roll at an unwinding speed of 0.5 m / min so that the surface temperature of the homopolypropylene film becomes 23 ° C. and 50% / min. The film was uniaxially stretched using a uniaxial stretching apparatus only in the extrusion direction at a stretching ratio of 1.2 times at a stretching speed of.

(Second stretching step)
Subsequently, the homopolypropylene film was uniaxially stretched only in the extrusion direction at a stretching ratio of 2 times at a stretching rate of 42% / min so that the surface temperature was 120 ° C. using a uniaxial stretching apparatus (second stretching step). .

(Annealing process)
Thereafter, the homopolypropylene film was supplied to the hot air furnace, and the homopolypropylene film was allowed to run for 1 minute so that the surface temperature was 130 ° C. and no tension was applied to the homopolypropylene film. A long homopropylene microporous film (thickness: 25 μm) was obtained by annealing the film. The shrinkage ratio of the homopolypropylene film in the annealing process was 5%.

The open end of the micropores in the homopropylene microporous film had a maximum major axis of 610 nm and an average major axis of 360 nm. The homopropylene microporous film had a surface opening ratio of 38%, a pore density of 20 / μm ² , and a porosity of 48%.

2. Preparation of packed layer (Step (I))
A coating solution was prepared by dissolving 100 parts by weight of trimethylolpropane triacrylate (TMPTA) and 5 parts by weight of benzophenone in 1900 parts by weight of ethyl acetate as a solvent. This coating solution was applied to the surface of a homopolypropylene microporous film. Thereafter, the homopolypropylene microporous film was heated at 80 ° C. for 2 minutes to evaporate and remove the solvent. In the homopolypropylene microporous film, trimethylolpropane triacrylate and benzophenone were attached in an amount shown in Table 1 with respect to 100 parts by weight of the homopolypropylene microporous film.

(Process (II))
Next, after irradiating the homopolypropylene microporous film with ultraviolet rays in a vacuum at an integrated light quantity of 1700 mJ / cm ² , the homopolypropylene microporous film was heated to ° C. Thereby, trimethylolpropane triacrylate was polymerized, and a packed layer containing a polymer of trimethylolpropane triacrylate was integrally formed on the entire resin surface including the inner wall surface of the microporous portion of the homopolypropylene microporous film. . Moreover, a part of homopolypropylene contained in the homopolypropylene microporous film and a part of the polymer contained in the packed layer were chemically bonded. The heat-resistant homopolypropylene microporous film had the thickness shown in Table 1.

(Example 2)
A heat-resistant homopolypropylene microporous film was obtained in the same procedure as in Example 1 except that the cumulative amount of ultraviolet light was 2400 mJ / cm ² in step (II).

(Example 3)
A heat-resistant homopolypropylene microporous film was obtained in the same procedure as in Example 1 except that in step (II), the cumulative amount of ultraviolet light was 3600 mJ / cm ² .

Example 4
A heat-resistant homologue was prepared in the same procedure as in Example 1 except that the blending amount of benzophenone in the coating liquid in step (I) was 3 parts by weight and the cumulative amount of ultraviolet light was 3600 mJ / cm ² in step (II). A polypropylene microporous film was obtained.

(Example 5)
A heat-resistant homologue was prepared in the same manner as in Example 1 except that the blending amount of benzophenone in the coating liquid in step (I) was 8 parts by weight and the cumulative amount of ultraviolet light was 3400 mJ / cm ² in step (II). A polypropylene microporous film was obtained.

(Example 6)
As a solvent, 2375 parts by weight of ethyl acetate, 100 parts by weight of trimethylolpropane triacrylate, a butadiene (meth) acrylate oligomer represented by the above formula (I) (number average molecular weight 2500, trade name “TE-2000” manufactured by Nippon Soda Co., Ltd.) 25 parts by weight and 5 parts by weight of benzophenone were dissolved to prepare a coating solution. A heat-resistant homopolypropylene microporous film was obtained in the same procedure as in Example 1 except that this coating solution was used in step (I) and the cumulative amount of ultraviolet light was changed to 3400 mJ / cm ² in step (II).

  In addition, in the homopolypropylene microporous film after the step (I), trimethylolpropane triacrylate, butadiene (meth) acrylate oligomer and benzophenone are shown in Table 1 with respect to 100 parts by weight of the homopolypropylene microporous film. Only the amount was attached. In the heat-resistant homopolypropylene microporous film, the packed layer contained a copolymer of trimethylolpropane triacrylate and butadiene (meth) acrylate oligomer. And a part of homopolypropylene contained in the homopolypropylene microporous film and a part of the copolymer contained in the packed layer were chemically bonded.

(Example 7)
As solvent, 2375 parts by weight of ethyl acetate, 100 parts by weight of trimethylolpropane triacrylate, 25 parts by weight of 1,2-butadiene oligomer (number average molecular weight 1100, trade name “B-1000” manufactured by Nippon Soda Co., Ltd.), and 5 parts by weight of benzophenone Part was dissolved to prepare a coating solution. A heat-resistant homopolypropylene microporous film was obtained in the same procedure as in Example 1 except that this coating solution was used in step (I) and the cumulative amount of ultraviolet light was changed to 3600 mJ / cm ² in step (II).

  In addition, in the homopolypropylene microporous film after the step (I), trimethylolpropane triacrylate, 1,2-butadiene oligomer and benzophenone are shown in Table 1 with respect to 100 parts by weight of the homopolypropylene microporous film. Only the amount was attached. In the heat resistant homopolypropylene microporous film, the packed layer contained a copolymer of trimethylolpropane triacrylate and 1,2-butadiene oligomer. And a part of homopolypropylene contained in the homopolypropylene microporous film and a part of the copolymer contained in the packed layer were chemically bonded.

(Example 8)
As solvent, 1188 parts by weight of ethanol and 1188 parts by weight of toluene, 100 parts by weight of trimethylolpropane triacrylate, polyamideimide (glass transition temperature: 260 ° C., number average molecular weight: 6000, trade name “HR15ET” manufactured by Toyobo Co., Ltd.) 25 parts by weight And 5 parts by weight of benzophenone were dissolved to prepare a coating solution. A heat-resistant homopolypropylene microporous film was obtained in the same procedure as in Example 1 except that this coating solution was used in step (I) and the cumulative amount of ultraviolet light was changed to 3400 mJ / cm ² in step (II). Polyamideimide was dissolved in a mixed solvent of ethanol and toluene.

  In addition, in the homopolypropylene microporous film after the step (I), trimethylolpropane triacrylate, polyamideimide and benzophenone are attached in an amount shown in Table 1 with respect to 100 parts by weight of the homopolypropylene microporous film. It was. In the heat resistant homopolypropylene microporous film, the packed layer contained a polymer of trimethylolpropane triacrylate and polyamideimide. And a part of homopolypropylene contained in the homopolypropylene microporous film and a part of the polymer contained in the packed layer were chemically bonded.

Example 9
As a solvent, 1044 parts by weight of ethanol and 1044 parts by weight of toluene, 100 parts by weight of trimethylolpropane triacrylate, polyamideimide (glass transition temperature: 260 ° C., number average molecular weight: 6000, trade name “HR15ET” manufactured by Toyobo Co., Ltd.) 33 parts by weight And 5 parts by weight of benzophenone were dissolved to prepare a coating solution. A heat-resistant homopolypropylene microporous film was obtained in the same procedure as in Example 1 except that this coating solution was used in step (I) and the cumulative amount of ultraviolet light was changed to 3600 mJ / cm ² in step (II). Polyamideimide was dissolved in a mixed solvent of ethanol and toluene.

  In addition, in the homopolypropylene microporous film after the step (I), trimethylolpropane triacrylate, polyamideimide and benzophenone are attached in an amount shown in Table 1 with respect to 100 parts by weight of the homopolypropylene microporous film. It was. In the heat resistant homopolypropylene microporous film, the packed layer contained a polymer of trimethylolpropane triacrylate and polyamideimide. And a part of homopolypropylene contained in the homopolypropylene microporous film and a part of the polymer contained in the packed layer were chemically bonded.

(Comparative Example 1)
In the same manner as in Example 1, a homopolypropylene microporous film was produced. In addition, process (I) and process (II) were not performed to this homopolypropylene microporous film.

(Comparative Example 2)
A commercially available homopolypropylene microporous film (trade name “# 2500” manufactured by Celgard) was prepared. This homopolypropylene microporous film does not have a packed layer.

(Comparative Example 3)
A heat-resistant homopolypropylene microporous film was obtained in the same procedure as in Example 1 except that in step (II), the cumulative amount of ultraviolet light was 5400 mJ / cm ² .

(Evaluation)
The air permeability of the heat-resistant homopolypropylene microporous film was measured in the same manner as the above-described method for measuring the air permeability of the propylene-based resin microporous film. Table 1 shows the results obtained by measuring the heat shrinkage rate and puncture strength of the heat-resistant homopolypropylene microporous film in the following manner.

(Heat shrinkage)
From the heat-resistant homopolypropylene microporous film, 5 test pieces each having a flat rectangular shape measuring 2 cm long × 10 cm wide were cut out. At this time, the lateral direction of the test piece was made parallel to the length direction (extrusion direction) of the microporous film. Next, a marked line having a length of 8 cm (L ₀ ) is drawn in the lateral direction of the test piece, the test piece is heated at 130 ° C. or 150 ° C. for 1 hour and left at room temperature for 30 minutes, and then the length of the marked line is measured. (L) was measured. And the heat-shrinkage rate was computed based on the following formula, and the arithmetic mean value of five samples was made into the heat-shrinkage rate.
Thermal contraction rate (%) = 100 × (L ₀ −L ₁ ) / L ₀

(Puncture strength)
Five flat square test pieces having a side of 40 mm were cut out from the heat-resistant homopolypropylene microporous film. Using a tensile tester (trade name “RTC-1310A” manufactured by Orientec Co., Ltd.), measured at a load cell of 25 N and a speed of 50 mm / min, the arithmetic average value of the maximum stress at the time of piercing of five samples was determined as the piercing strength. did.

Claims (11)

A composition containing a radical polymerizable monomer containing a trifunctional or higher polyfunctional acrylic monomer and a photopolymerization initiator is applied to a propylene resin microporous film, and the propylene resin microporous film is added to 100 parts by weight of the propylene resin microporous film. Step (I) for adhering 3 to 30 parts by weight of a radical polymerizable monomer and 0.1 to 2.5 parts by weight of the photopolymerization initiator, and 1000 to 100% of the propylene-based resin microporous film after the step (I) Step (II) of irradiating ultraviolet rays with an integrated light quantity of 5000 mJ / cm ² ,
A method for producing a heat-resistant propylene-based resin microporous film, comprising:   The method for producing a heat-resistant propylene resin microporous film according to claim 1, wherein the content of the trifunctional or higher polyfunctional acrylic monomer in the radical polymerizable monomer is 10% by weight or more.   The heat-resistant propylene resin microporous composition according to claim 1 or 2, wherein the composition is a coating liquid in which a radical polymerizable monomer and a photopolymerization initiator are dissolved or dispersed in a solvent. A method for producing a film.   The heat-resistant propylene resin microporous film according to any one of claims 1 to 3, wherein, in step (II), the propylene resin microporous film after being irradiated with ultraviolet rays is heated to 100 to 150 ° C. A method for producing a porous film.   The increase rate of the air permeability of the heat-resistant propylene resin microporous film with respect to the air permeability of the propylene resin microporous film is 30% or less, according to any one of claims 1 to 4. The manufacturing method of the heat-resistant propylene-type resin microporous film of description. A propylene resin microporous film containing a propylene resin and having micropores;
A packing layer containing a polymer of a radical polymerizable monomer which is integrally formed on the wall surface of the micropore portion of the propylene resin microporous film and which contains a trifunctional or higher polyfunctional acrylic monomer. A heat-resistant propylene-based resin microporous film, wherein a part of the propylene-based resin and a part of the polymer of the radical polymerizable monomer are chemically bonded.   The heat-resistant propylene-based resin microporous film according to claim 6, wherein the air permeability is 50 to 300 sec / 100 mL.   The heat-shrinkable propylene-based resin microporous film according to claim 6 or 7, wherein a heat shrinkage rate after heating at 130 ° C for 1 hour is 8% or less.   The increase rate of the air permeability of the heat-resistant propylene resin microporous film with respect to the air permeability of the propylene resin microporous film is 30% or less, according to any one of claims 6 to 8, The heat-resistant propylene-based resin microporous film described.   A separator for a non-aqueous electrolyte secondary battery comprising the heat-resistant propylene-based resin microporous film according to any one of claims 6 to 9.   A non-aqueous electrolyte secondary battery using the separator for a non-aqueous electrolyte secondary battery according to claim 10.