JP2016088976A - Method for producing heat-resistant synthetic resin microporous film, heat-resistant synthetic resin microporous film, separator for nonaqueous electrolytic solution secondary battery, and nonaqueous electrolytic solution secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-resistant synthetic resin microporous film which is excellent in both of permeability of ions such as a lithium ion and heat resistance and hardly causes pollution of a production line, and to provide a method for producing the heat-resistant synthetic resin microporous film.SOLUTION: The method for producing the heat-resistant synthetic resin microporous film comprises the steps of: applying a polymerizable compound having two or more radically-polymerizable functional groups in one molecule thereof to the surface of a synthetic resin microporous film; and performing remote type plasma treatment on the synthetic resin microporous film. According to this production method, the heat-resistant synthetic resin microporous film, the heat resistance of which is improved without deteriorating the permeability of ions such as the lithium ion, can be produced.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a heat-resistant synthetic resin microporous film used for a separator of a secondary battery such as a lithium ion secondary battery, a heat-resistant synthetic resin microporous film, a nonaqueous 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 secondary 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 secondary 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 secondary battery is discharged, lithium ions are released from the negative electrode and move to the positive electrode. Therefore, the separator is required to have excellent ion permeability such as lithium ions.

  As the separator, a polyolefin-based resin microporous film is used because it is excellent in insulation and cost. However, the polyolefin resin microporous film undergoes large thermal shrinkage near the melting point of the polyolefin resin. For example, when the separator is damaged due to the mixing of metal foreign matter or the like and a short circuit occurs between the electrodes, the battery temperature rises due to the generation of Joule heat, which causes the polyolefin resin microporous film to thermally shrink. Due to the shrinkage of the polyolefin resin microporous film, a short circuit between the electrodes further occurs and the battery temperature rises.

  In recent years, lithium ion secondary batteries have been desired to be able to ensure high output and 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 secondary 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 battery 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 is a heat-resistant synthetic resin microporous film that is excellent in both permeability and heat resistance of ions such as lithium ions, does not cause contamination of the production line, and has good suitability for battery production lines, and a method for producing the same I will provide a. Furthermore, this invention provides the separator for nonaqueous electrolyte secondary batteries and the nonaqueous electrolyte secondary battery using the said heat resistant synthetic resin microporous film.

  The method for producing the heat-resistant synthetic resin microporous film of the present invention comprises the steps of applying a polymerizable compound having two or more radically polymerizable functional groups in one molecule on the surface of the synthetic resin microporous film, and then forming the synthetic resin microporous film. A remote plasma treatment is performed on the film.

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

  5-100 micrometers is preferable and, as for the thickness of a synthetic resin microporous film, 10-50 micrometers is more preferable.

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

The air permeability of the synthetic resin microporous film is preferably 20 to 600 sec / 100 mL.
0-400 sec / 100 mL is more preferable, and 70-300 sec / 100 mL is more preferable. A synthetic 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 synthetic resin microporous film was measured at 10 points at 10 cm intervals in the length direction of the synthetic resin microporous film in accordance with JIS P8117 in an atmosphere of a temperature of 23 ° C. and a relative humidity of 65%. The value obtained by calculating the arithmetic mean value is used.

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

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

Next, each micropore formed in the measurement portion is surrounded by a rectangle 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 synthetic resin microporous film is preferably 1 μm or less, and more preferably 100 nm to 800 nm. A synthetic resin microporous film having a maximum long diameter of 1 μm or less at the opening end of the micropore portion is excellent in mechanical strength and has uniform ion permeability. Such a synthetic 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 synthetic resin microporous film is preferably 500 nm or less, and more preferably 200 nm to 500 nm. A synthetic resin microporous film having an average major axis at the opening end of the micropores of 500 nm or less has a uniform ion permeability, which can reduce the occurrence of minute internal short circuits (dendritic shorts).

  In addition, the maximum major axis and the average major axis of the open ends of the micropores in the synthetic resin microporous film are measured as follows. First, the surface of the synthetic resin microporous film is coated with carbon. Next, 10 arbitrary positions on the surface of the synthetic 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 synthetic 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 synthetic resin microporous film is preferably 15 / μm ² or more, and more preferably 17 / μm ² or more. A synthetic resin microporous film having a pore density of 15 / μm ² or more is excellent in ion permeability.

The pore density of the synthetic resin microporous film is measured in the following manner. First, in an arbitrary portion of the surface of the synthetic resin microporous film, a measurement portion having a plane rectangular shape of 9.6 μm in length and 12.8 μm in width is determined, and this measurement portion is photographed at a magnification of 10,000. 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 synthetic resin microporous film can be used without particular limitation as long as it is a porous film used as a separator in a conventional secondary battery such as a lithium ion secondary battery. As the synthetic resin microporous film, an olefin resin microporous film is preferable. The olefin-based resin microporous film is likely to be deformed or contracted due to melting of the olefin-based resin at a high temperature. On the other hand, according to the coating layer of the present invention, excellent heat resistance can be imparted to the olefin-based resin microporous film as described later. Therefore, the effect of this invention can be exhibited more by forming a membrane | film | coat layer integrally in an olefin resin microporous film.

  The olefin resin microporous film contains an olefin resin. As the olefin resin, ethylene resin and propylene resin are preferable, and propylene resin is more preferable.

  Examples of the propylene-based resin include homopolypropylene and copolymers of propylene and other olefins. When the synthetic resin microporous film is produced by the stretching method described later, 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 pentad fraction (mmmm fraction) measured by ¹³ C-NMR method. The isotactic pentad fraction measured by the ¹³ C-NMR method of homopolypropylene is a side chain with respect to the main chain formed by a 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.

The isotactic pentad fraction measured by the ¹³ C-NMR method of homopolypropylene is preferably 90% or more, and more preferably 95% or more. By setting the isotactic pentad fraction to 90% or more, a synthetic resin microporous film in which micropores are uniformly formed can be provided.

  The weight average molecular weight of the olefin resin is preferably 250,000 to 500,000, and more preferably 280,000 to 480,000. According to the olefin resin having a weight average molecular weight within the above range, it is possible to provide an olefin resin microporous film having excellent film forming stability and having uniform micropores.

  The molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) of the olefin resin is preferably 7.5 to 12, and more preferably 8 to 11. According to the olefin resin having a molecular weight distribution within the above range, an olefin 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 number average molecular weight of the olefin resin are polystyrene-converted values measured by a GPC (gel permeation chromatography) method. Specifically, 6 to 7 mg of olefin resin was sampled, and the collected olefin 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 solution is shaken for 1 hour at 145 ° C. and a rotation speed of 25 rpm using a dissolution filter, and the olefin resin is dissolved in the BHT o-DCB solution 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.
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 olefin resin, 160-165 degreeC is more preferable. According to the olefin resin having a melting point within the above range, it is possible to provide an olefin resin microporous film that has excellent film forming stability and suppresses a decrease in mechanical strength at high temperatures.

  As a synthetic resin microporous film, the olefin resin microporous film manufactured by the extending | stretching method is more preferable. The olefin-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 an olefin-based resin microporous film in the production method of the present invention.

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

As the method for producing an olefin-based resin microporous film, particularly preferably, the following steps:
The olefin resin was melt-kneaded at a temperature not lower than 20 ° C. higher than the melting point of the olefin resin and not higher than 100 ° C. higher than the melting point of the olefin resin in an extruder, and attached to the tip of the extruder. An extrusion step of obtaining an olefin-based resin film by extruding from a die;
Curing step for curing the olefin resin film after the extrusion step at a temperature 30 ° C. lower than the melting point of the olefin resin and 1 ° C. lower than the melting point of the olefin resin;
A first stretching step in which the olefin 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 olefin-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 olefin-based resin film that has been stretched in the second stretching step.

  According to the above method, it is possible to obtain an olefin resin microporous film in which a large number of micropores penetrating the film front and back surfaces are formed. According to such an olefin-based resin microporous film, there is provided a heat-resistant synthetic resin microporous film that has excellent air permeability and can smoothly and uniformly transmit ions such as lithium ions. be able to. Therefore, according to such a heat resistant synthetic 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)
The olefin-based resin film containing the olefin-based resin can be manufactured by supplying the olefin-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 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-based resin and 80 ° C. higher than the melting point of the olefin-based resin. It is particularly preferable that the temperature be 50 ° C. or higher than the melting point. 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.

  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 setting the draw ratio to 50 or more, the tension applied to the olefin resin can be improved. As a result, the olefin resin can be sufficiently oriented to promote the production of lamellae. Moreover, the film-forming stability of an olefin resin film can be improved by making a draw ratio into 300 or less. This makes it possible to obtain an olefin-based resin microporous film having a uniform thickness and width.

  The draw ratio refers to a value obtained by dividing the clearance of the lip of the T die by the thickness of the olefin resin film extruded from the T die. The clearance of the lip of the T die is measured by measuring the clearance of the lip of the T die at 10 or more locations using a clearance gauge in conformity with JIS B7524 (for example, JIS clearance gauge manufactured by Nagai Gauge Manufacturing Co., Ltd.), and the arithmetic average thereof This can be done by determining the value. The thickness of the olefin resin film extruded from the T die is 10 or more in the thickness of the olefin 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 olefin 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 olefin resin film to 10 m / min or more, the tension applied to the olefin resin can be improved. As a result, the olefin resin molecules can be sufficiently oriented to promote the formation of lamellae. Moreover, the film-forming stability of an olefin resin film can be improved by making the film-forming speed | rate of an olefin resin film into 300 m / min or less. This makes it possible to obtain an olefin-based resin microporous film having a uniform thickness and width.

  And the olefin resin which comprises the olefin resin film is cooled by cooling the olefin resin film extruded from T-die until the surface temperature becomes below 100 degreeC lower than melting | fusing point of the said olefin resin. Crystallizes and lamella is highly produced. The olefin resin film constituting the olefin resin film is oriented in advance by extruding the melt-kneaded olefin resin, and then the olefin resin film is cooled. Thereby, the part in which the olefin resin is oriented can promote the generation of lamellae.

  The surface temperature of the cooled olefin resin film is preferably 100 ° C. or lower than the melting point of the olefin resin, more preferably 140 to 110 ° C. lower than the melting point of the olefin resin, and more than the melting point of the olefin resin. Also, a temperature lower by 135 to 120 ° C. is particularly preferable. By cooling the surface temperature of the olefin resin film to the above range, the olefin resin can be crystallized and a lamella can be highly produced.

(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. As a result, 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. 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 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 1 ° C. lower than the melting point of the olefin resin.

  The curing temperature of the olefin resin film is preferably 30 ° C. lower than the melting point of the olefin resin and 1 ° 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 setting the curing temperature of the olefin resin film to 30 ° C. lower than the melting point of the olefin resin, crystallization of the olefin resin film can be sufficiently promoted. Moreover, collapse of the lamella structure by relaxation of the molecular orientation of an olefin resin can be reduced by making the curing temperature of an olefin resin film below 1 degreeC lower than melting | fusing point of an olefin resin.

  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 curing 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 a state wound in such a curing time, the curing of the olefin-based resin film as a whole can be performed sufficiently with the curing temperature described above. Thereby, a lamella can be fully grown in an olefin resin film. Moreover, from a viewpoint of reducing the thermal deterioration of an olefin resin film, the curing time is preferably 35 hours or less, and more preferably 30 hours or less.

  If the olefin resin film is cured in a roll shape, the olefin resin film is unwound from the olefin resin film roll after the curing process, and the stretching process and the annealing process described later are performed. Good.

(First stretching process)
Next, a first stretching step is performed on the olefin-based resin film after the curing step, 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 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 are reliably formed starting from this crack.

  In the first stretching step, the surface temperature of the olefin 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 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 resin film to less than 100 ° C.

  In the first stretching step, the stretching ratio of the olefin 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 an olefin resin microporous film by making a draw ratio into 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% / 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, it is possible to suppress breakage of the olefin resin film in the first stretching step.

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

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

(Second stretching step)
Next, a second stretching step is performed in which the olefin resin film after the first stretching step is subjected to a uniaxial stretching process 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 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 resin film is preferably 100 to 150 ° C, and more preferably 110 to 140 ° C. By setting the surface temperature of the olefin resin film to 100 ° C. or higher, the micropores formed in the olefin resin film in the first stretching step can be highly grown. Moreover, the obstruction | occlusion of the micropore part formed in the olefin resin film in a 1st extending | stretching process can be highly reduced by making the surface temperature of an olefin resin film into 150 degrees C or less.

  In the second stretching step, the stretching ratio of the olefin-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 olefin resin film to 1.2 times or more, the micropores formed in the olefin resin film during the first drawing step can be grown. Thereby, the olefin resin microporous film having excellent air permeability can be provided. Moreover, it becomes possible by suppressing the draw ratio of an olefin resin film to 2.2 times or less to block | close the micropore part formed in the olefin resin film in a 1st extending | stretching process.

  In the second stretching step, the stretching speed of the olefin 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 olefin resin film within the above range, micropores can be uniformly formed in the olefin resin film.

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

(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.

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

  The shrinkage ratio of the olefin resin film in the annealing step is preferably 25% or less. By setting the shrinkage rate of the olefin resin film to 25% or less, the occurrence of sagging of the olefin resin film can be reduced, and the olefin resin film can be annealed uniformly.

  The shrinkage of the olefin-based resin film is 100 by dividing the shrinkage length of the olefin-based resin film in the stretching direction during the annealing step by the length of the olefin-based resin film in the stretching direction after the second stretching step. The value multiplied by.

(Coating process)
In the method of the present invention, a polymerizable compound having two or more radical polymerizable functional groups in one molecule (hereinafter referred to as “two radical polymerizable functional groups in one molecule” on the surface of the above-mentioned synthetic resin microporous film. The above-mentioned polymerizable compound "may be simply referred to as" polymerizable compound "). The polymerizable compound has two or more radical polymerizable functional groups in one molecule, but preferably has three or more radical polymerizable functional groups in one molecule. The radical polymerizable functional group is a functional group containing a radical polymerizable unsaturated bond capable of radical polymerization by plasma irradiation. Although it does not restrict | limit especially as a radically polymerizable functional group, For example, a (meth) acryloyl group, a vinyl group, etc. are mentioned, A (meth) acryloyl group is preferable.

  As the polymerizable compound, a polyfunctional acrylic monomer having two or more radical polymerizable functional groups in one molecule, a vinyl oligomer having two or more radical polymerizable functional groups in one molecule, Modified polyfunctional (meth) acrylate having two or more (meth) acryloyl groups, dendritic polymer having two or more (meth) acryloyl groups in one molecule, and two (meth) acryloyl groups in one molecule The urethane (meth) acrylate oligomer which has the above is mentioned. A polymeric compound may be used independently and may use 2 or more types together.

  In the present invention, (meth) acrylate means acrylate or methacrylate. (Meth) acryloyl means acryloyl or methacryloyl. Moreover, (meth) acrylic acid means acrylic acid or methacrylic acid.

  The polyfunctional acrylic monomer only needs to have two or more radical polymerizable functional groups in one molecule, but it has three or more functional groups having three or more radical polymerizable functional groups in one molecule. A polyfunctional acrylic monomer is preferable, and a trifunctional to hexafunctional polyfunctional acrylic monomer having 3 to 6 radical polymerizable functional groups in one molecule is particularly preferable.

As a polyfunctional acrylic monomer,
1,9-nonanediol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, tripropylene glycol di (meth) acrylate, 2-hydroxy-3 -Acryloyloxypropyl di (meth) acrylate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, neopentyl glycol Bifunctional polyfunctional acrylic monomers such as di (meth) acrylate, tricyclodecane dimethanol di (meth) acrylate, and glycerin di (meth) acrylate;
Trimethylolpropane tri (meth) acrylate, trimethylolpropane ethoxytri (meth) acrylate, pentaerythritol tri (meth) acrylate, ethoxylated isocyanuric acid tri (meth) acrylate, ε-caprolactone modified tris- (2-acryloxyethyl) Trifunctional or higher polyfunctional acrylic monomers such as isocyanurate and ethoxylated glycerin tri (meth) acrylate;
Tetrafunctional polyfunctional acrylic monomers such as pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, and ethoxylated pentaerythritol tetra (meth) acrylate;
Pentafunctional polyfunctional acrylic monomers such as dipentaerythritol penta (meth) acrylate;
6-functional polyfunctional acrylic monomers such as dipentaerythritol hexa (meth) acrylate;
Etc. can be illustrated.

  It does not specifically limit as a vinyl-type oligomer, For example, a polybutadiene-type oligomer etc. can be illustrated. The polybutadiene oligomer means an oligomer having a butadiene skeleton. Examples of the polybutadiene oligomer include a polymer containing a butadiene component as a monomer component. Examples of the monomer component of the polybutadiene oligomer include a 1,2-butadiene component and a 1,3-butadiene component. Of these, a 1,2-butadiene component is preferred.

  The vinyl oligomer may have a hydrogen atom at both ends of the main chain, and the terminal hydrogen atom is substituted with a hydroxyalkyl group such as a hydroxy group, a carboxy group, a cyano group, or a hydroxyethyl group. It may be a thing. Moreover, as a vinyl-type oligomer, you may have radically polymerizable functional groups, such as an epoxy group, a (meth) acryloyl group, and a vinyl group, in the side chain or terminal of a molecular chain.

As polybutadiene oligomer,
Polybutadiene oligomers such as poly (1,2-butadiene) oligomers and poly (1,3-butadiene) oligomers;
An epoxidized polybutadiene oligomer in which an epoxy group is introduced into the molecule by epoxidizing at least a part of the carbon-carbon double bond contained in the butadiene skeleton;
A polybutadiene (meth) acrylate oligomer having a butadiene skeleton and having a (meth) acryloyl group at a side chain or a terminal of the main chain;
Etc. can be illustrated.

  A commercially available product can be used as the polybutadiene oligomer. Examples of the poly (1,2-butadiene) oligomer include “B-1000”, “B-2000”, and “B-3000” manufactured by Nippon Soda Co., Ltd. Examples of the polybutadiene oligomer having a hydroxyl group at both ends of the main chain include trade names “G-1000”, “G-2000”, and “G-3000” manufactured by Nippon Soda Co., Ltd. As the epoxidized polybutadiene oligomer, trade names “JP-100” and “JP-200” manufactured by Nippon Soda Co., Ltd. can be exemplified. Examples of the polybutadiene (meth) acrylate oligomer include “TE-2000”, “EA-3000”, and “EMA-3000” manufactured by Nippon Soda Co., Ltd.

  The polyfunctional (meth) acrylate modified product only needs to have two or more radical polymerizable functional groups in one molecule, but has three or more radical polymerizable functional groups in one molecule. A polyfunctional (meth) acrylate modified product having a functionality or higher is preferable, and a trifunctional to 6 functional polyfunctional (meth) acrylate modified product having 3 to 6 radical polymerizable functional groups in one molecule is more preferable. preferable.

  Preferred examples of the modified polyfunctional (meth) acrylate include an alkylene oxide modified product of a polyfunctional (meth) acrylate and a caprolactone modified product of a polyfunctional (meth) acrylate.

  The alkylene oxide modified product of polyfunctional (meth) acrylate is preferably obtained by esterifying an adduct of polyhydric alcohol and alkylene oxide with (meth) acrylic acid. The polyfunctional (meth) acrylate-modified caprolactone is preferably obtained by esterifying an adduct of a polyhydric alcohol and caprolactone with (meth) acrylic acid.

  Examples of the polyhydric alcohol in the alkylene oxide modified product and the caprolactone modified product include trimethylolpropane, glycerol, pentaerythritol, ditrimethylolpropane, and tris (2-hydroxyethyl) isocyanuric acid.

  Examples of the alkylene oxide in the modified alkylene oxide include ethylene oxide, propylene oxide, isopropylene oxide, and butylene oxide.

  Examples of caprolactone in the modified caprolactone include ε-caprolactone, δ-caprolactone, and γ-caprolactone.

  In the alkylene oxide modified product of polyfunctional (meth) acrylate, the average addition mole number of alkylene oxide may be 1 mol or more per radical polymerizable functional group. The average added mole number of alkylene oxide is preferably 1 mol or more and 4 mol or less, more preferably 1 mol or more and 3 mol or less per radical polymerizable functional group.

As a trifunctional polyfunctional (meth) acrylate modified product,
Trimethylolpropane tri (meth) acrylate modified with ethylene oxide, trimethylolpropane tri (meth) acrylate modified with propylene oxide, trimethylolpropane tri (meth) acrylate modified with isopropylene oxide, trimethylolpropane tri (meth) Of butylene oxide modified by acrylate, and trimethylolpropane tri (meth) acrylate modified by alkylene oxide such as ethylene oxide / propylene oxide modified by trimethylolpropane tri (meth) acrylate, and trimethylolpropane tri (meth) acrylate Modified caprolactone;
Glyceryl tri (meth) acrylate modified with ethylene oxide, glyceryl tri (meth) acrylate modified with propylene oxide, glyceryl tri (meth) acrylate modified with isopropylene oxide, glyceryl tri (meth) acrylate modified with butylene oxide, and An alkylene oxide modified product of glyceryl tri (meth) acrylate such as ethylene oxide / propylene oxide modified product of glyceryl tri (meth) acrylate, and a caprolactone modified product of glyceryl tri (meth) acrylate;
Pentaerythritol tri (meth) acrylate modified with ethylene oxide, pentaerythritol tri (meth) acrylate modified with propylene oxide, pentaerythritol tri (meth) acrylate modified with propylene oxide, pentaerythritol tri (meth) acrylate butylene oxide A modified product, and an alkylene oxide modified product of pentaerythritol tri (meth) acrylate, such as an ethylene oxide / propylene oxide modified product of pentaerythritol tri (meth) acrylate, and a caprolactone modified product of pentaerythritol tri (meth) acrylate;
Tris- (2-acryloxyethyl) isocyanurate modified with ethylene oxide, Tris- (2-acryloxyethyl) isocyanurate modified with propylene oxide, Tris- (2-acryloxyethyl) isocyanurate modified with isopropylene oxide , Tris- (2-acryloxyethyl) isocyanurate modified with butylene oxide, and tris- (2-acryloxyethyl) isocyanurate modified with ethylene oxide / propylene oxide, tris- (2-acryloxyethyl) The alkylene oxide modified product of isocyanurate, the caprolactone modified product of tris- (2-acryloxyethyl) isocyanurate, and the like can be mentioned.

As a tetrafunctional polyfunctional (meth) acrylate modified product,
Pentaerythritol tetra (meth) acrylate modified with ethylene oxide, pentaerythritol tetra (meth) acrylate modified with propylene oxide, pentaerythritol tetra (meth) acrylate modified with propylene oxide, pentaerythritol tetra (meth) acrylate butylene oxide Modified products, and alkylene oxide modified products of pentaerythritol tetra (meth) acrylates such as ethylene oxide / propylene oxide modified products of pentaerythritol tetra (meth) acrylate, and caprolactone modified products of pentaerythritol tetra (meth) acrylate; and ditrimethylol Propane tetra (meth) acrylate modified with ethylene oxide, ditrimethylolprop Of propylene oxide of tetra- (meth) acrylate, isopropylene oxide of ditrimethylolpropane tetra (meth) acrylate, butylene oxide of ditrimethylolpropane tetra (meth) acrylate, and ditrimethylolpropane tetra (meth) acrylate Examples thereof include alkylene oxide modified products of ditrimethylolpropane tetra (meth) acrylate such as ethylene oxide / propylene oxide modified products, and caprolactone modified products of ditrimethylolpropane tetra (meth) acrylate.

As a polyfunctional (meth) acrylate modified product of 5 or more functions, specifically,
Dipentaerythritol poly (meth) acrylate modified with ethylene oxide, dipentaerythritol poly (meth) acrylate modified with propylene oxide, dipentaerythritol poly (meth) acrylate modified with propylene oxide, dipentaerythritol poly (meth) Butylene oxide modified products of acrylate, and alkylene oxide modified products of dipentaerythritol poly (meth) acrylate such as ethylene oxide / propylene oxide modified product of dipentaerythritol poly (meth) acrylate, and dipentaerythritol poly (meth) acrylate And caprolactone-modified products.

  Commercially available products can also be used as the modified polyfunctional (meth) acrylate.

  Examples of the modified ethylene oxide of trimethylolpropane tri (meth) acrylate include trade names “SR454”, “SR499” and “SR502” manufactured by Sartomer, trade names “Biscoat # 360” manufactured by Osaka Organic Chemical Co., Ltd., and Miwon. Examples include trade names “Miramer M3130”, “Miramer M3160”, and “Miramer M3190” manufactured by the company. Examples of the modified propylene oxide of trimethylolpropane tri (meth) acrylate include trade names “SR492” and “CD501” manufactured by Sartomer, and “Miramer M360” manufactured by Miwon. As an isopropylene oxide modified product of trimethylolpropane tri (meth) acrylate, trade name “TPA-330” manufactured by Nippon Kayaku Co., Ltd. may be mentioned.

  Examples of the ethylene oxide modified product of glyceryl tri (meth) acrylate include trade names “A-GYL-3E” and “A-GYL-9E” manufactured by Shin-Nakamura Chemical Co., Ltd. Examples of the propylene oxide-modified product of glyceryl tri (meth) acrylate include trade names “SR9020” and “CD9021” manufactured by Sartomer. Examples of the glyceryl tri (meth) acrylate modified isopropylene oxide include trade name “GPO-303” manufactured by Nippon Kayaku Co., Ltd.

  Examples of the caprolactone-modified product of tris- (2-acryloxyethyl) isocyanurate include trade names “A-9300-1CL” and “A-9300-3CL” manufactured by Shin-Nakamura Chemical Co., Ltd.

  Examples of the modified ethylene oxide of pentaerythritol tetra (meth) acrylate include “Miramer M4004” manufactured by Miwon. Examples of the ethylene oxide modified product of ditrimethylolpropane tetra (meth) acrylate include trade name “AD-TMP-4E” manufactured by Shin-Nakamura Chemical Co., Ltd.

  Examples of the ethylene oxide-modified product of dipentaerythritol polyacrylate include “A-DPH-12E” manufactured by Shin-Nakamura Chemical Co., Ltd. As an isopropylene oxide modified product of dipentaerythritol polyacrylate, trade name “A-DPH-6P” manufactured by Shin-Nakamura Chemical Co., Ltd. may be mentioned.

  The dendritic polymer having two or more (meth) acryloyl groups in one molecule means a spherical macromolecule in which branch molecules having (meth) acryloyl groups are radially assembled.

  The dendritic polymer having a (meth) acryloyl group includes a dendrimer having two or more (meth) acryloyl groups in one molecule, and a hyperbranched polymer having two or more (meth) acryloyl groups in one molecule. Can be mentioned.

  A dendrimer means a spherical polymer obtained by integrating (meth) acrylates in a spherical shape with (meth) acrylates as branch molecules.

  The dendrimer may have two or more (meth) acryloyl groups in one molecule, but a trifunctional or more functional dendrimer having three or more (meth) acryloyl groups in one molecule is preferable. A polyfunctional dendrimer having 5 to 20 (meth) acryloyl groups in one molecule is more preferable.

  The weight average molecular weight of the dendrimer is preferably 1000 to 50000, more preferably 1500 to 25000. By setting the weight average molecular weight of the dendrimer within the above range, the bond density in the dendrimer molecule and the bond density between the dendrimer molecules become “dense” and “coarse”. A film layer having excellent elasticity and elongation can be formed.

  In addition, let the weight average molecular weight of a dendrimer be the value converted with polystyrene using the gel permeation chromatography (GPC).

  As a dendritic polymer having two or more (meth) acryloyl groups in one molecule, a commercially available product can be used. As dendrimers having two or more (meth) acryloyl groups in one molecule, trade names “CN2302”, “CN2303” and “CN2304” manufactured by Sartomer, and trade names “V1000” and “SUBARU” manufactured by Osaka Organic Chemical Co., Ltd. -501 "," SIRIUS-501 ", and trade name" A-HBR-5 "manufactured by Shin-Nakamura Chemical Co., Ltd.

  A hyperbranched polymer having two or more (meth) acryloyl groups in one molecule is an ABx type polyfunctional monomer (where A and B are functional groups that react with each other, and the number X of B is 2 or more). It means a spherical polymer obtained by modifying the surface and the inside of a hyperbranched structure having an irregular branch structure obtained by polymerization with a (meth) acryloyl group.

  The urethane (meth) acrylate oligomer having a (meth) acryloyl group has two or more (meth) acryloyl groups in one molecule.

  The urethane acrylate oligomer is obtained, for example, by reacting a polyisocyanate compound, a (meth) acrylate having a hydroxyl group or an isocyanate group, and a polyol compound.

  Examples of the urethane acrylate oligomer include (1) a urethane acrylate obtained by further reacting a hydroxyl group-containing (meth) acrylate with a terminal isocyanate group-containing urethane prepolymer obtained by reacting a polyol compound and a polyisocyanate compound. And (2) urethane acrylate oligomers obtained by further reacting a (meth) acrylate having an isocyanate group with a terminal hydroxyl group-containing urethane prepolymer obtained by reacting a polyol compound and a polyisocyanate compound.

  Examples of the polyisocyanate compound include isophorone diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, and diphenylmethane-4,4 ′. -Diisocyanate etc. are mentioned.

Examples of the (meth) acrylate having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and Examples include polyethylene glycol (meth) acrylate. Examples of the (meth) acrylate having an isocyanate group include methacryloyloxyethyl isocyanate.

  As a polyol compound, polyol compounds, such as an alkylene type, a polycarbonate type, a polyester type, or a polyether type, are mentioned, for example. Specific examples include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polycarbonate diol, polyester diol, and polyether diol.

  Commercially available products can also be used as urethane (meth) acrylate oligomers having two or more (meth) acryloyl groups in one molecule. For example, product name “UA-122P” manufactured by Shin-Nakamura Chemical Co., Ltd., product name “UF-8001G” manufactured by Kyoeisha Chemical Co., Ltd., product names “CN977”, “CN999”, “CN963”, “CN985” manufactured by Sartomer Company. , “CN970”, “CN133”, “CN975” and “CN997”, trade names “IRR214-K” manufactured by Daicel Ornex, and trade names “UX-5000”, “UX-5102D” manufactured by Nippon Kayaku Co., Ltd. -M20 "," UX-5005 ", and" DPHA-40H ". Further, as the polymerizable compound, an aliphatic special oligomer such as a trade name “CN113” manufactured by Sartomer Co., Ltd. may be used.

  In the present invention, among the polymerizable compounds described above, polyfunctional acrylic monomers are preferable, and trimethylolpropane tri (meth) acrylate, trimethylolpropane ethoxytri (meth) acrylate, pentaerythritol tri (meth) acrylate, penta Erythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and ditrimethylolpropane tetra (meth) acrylate are preferred. In addition, an alkylene oxide modified product of the polyfunctional acrylic monomer is also preferably used. According to these, excellent heat resistance can be imparted to the heat-resistant synthetic resin microporous film without reducing the mechanical strength.

  When a polyfunctional acrylic monomer is used as the polymerizable compound, the content of the polyfunctional acrylic monomer in the polymerizable compound is preferably 30% by weight or more, more preferably 80% by weight or more, and particularly 100% by weight. preferable. By using a polymerizable compound containing 30% by weight or more of a polyfunctional acrylic monomer, excellent heat resistance can be imparted to the resulting heat-resistant microporous film without reducing air permeability.

  A polymerizable compound having two or more radical polymerizable functional groups in one molecule is applied to the surface of the synthetic resin microporous film. At this time, the polymerizable compound may be directly applied to the surface of the synthetic resin microporous film. However, it is preferable to disperse or dissolve the polymerizable compound in a solvent to obtain a coating solution, and to apply this coating solution to the surface of the synthetic resin microporous film. As described above, by using the polymerizable compound as the coating liquid, the polymerizable compound can be uniformly attached to the surface of the synthetic resin microporous film. This makes it possible to produce a heat-resistant synthetic resin microporous film having a uniform coating layer and high heat resistance. Furthermore, by using the polymerizable compound as the coating liquid, it is possible to highly reduce the blockage of the micropores in the synthetic resin microporous film by the polymerizable compound. Therefore, it is possible to improve the heat resistance of the heat-resistant synthetic 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 polymerizable compound, for example, alcohols such as methanol, ethanol, propanol, isopropyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, and the like. Ketones, ethers such as tetrahydrofuran and dioxane, ethyl acetate, chloroform and the like. Of these, ethyl acetate, ethanol, methanol, and acetone are preferable. These solvents can be removed smoothly after the coating solution is applied to the surface of the synthetic resin microporous film. Furthermore, the solvent has low reactivity with an electrolyte solution constituting a secondary battery such as a lithium ion secondary battery, and is excellent in safety.

  The content of the polymerizable compound in the coating liquid is preferably 3 to 20% by weight, and more preferably 5 to 15% by weight. By setting the content of the polymerizable compound within the above range, a coating layer can be uniformly formed on the surface of the synthetic resin microporous film without clogging the micropores, and thus without reducing the air permeability. A heat-resistant synthetic resin microporous film having improved heat resistance can be produced.

  The method for applying the polymerizable compound to the surface of the synthetic resin microporous film is not particularly limited. For example, (1) a method of applying the polymerizable compound to the surface of the synthetic resin microporous film; (2) in the polymerizable compound A method of immersing a synthetic resin microporous film in the surface and coating the surface of the synthetic resin microporous film with a polymerizable compound; (3) preparing a coating solution by dissolving or dispersing the polymerizable compound in a solvent; A method in which the coating liquid is applied to the surface of the synthetic resin microporous film, and then the synthetic resin microporous film is heated to remove the solvent; and (4) the coating liquid is dissolved or dispersed in the solvent. After the synthetic resin microporous film is immersed in this coating liquid and the coating liquid is applied in the synthetic resin microporous film, the synthetic resin microporous film is heated to remove the solvent. Is mentioned. Of these, the methods (3) and (4) are preferred. According to these methods, the polymerizable compound can be uniformly applied to the surface of the synthetic resin microporous film.

  In the methods (3) and (4) above, the heating temperature of the synthetic 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 synthetic 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 heat shrinkage and blockage of the micropores of the synthetic resin microporous film.

  In the methods (3) and (4) above, the heating time of the synthetic 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 synthetic resin microporous film for removing the solvent is preferably 0.02 to 60 minutes, more preferably 0.1 to 30 minutes.

  As described above, the polymerizable compound can be attached to the surface of the synthetic resin microporous film by applying the polymerizable compound or the coating liquid to the surface of the synthetic resin microporous film.

  The amount of the polymerizable compound attached to the synthetic resin microporous film is preferably 1 to 80 parts by weight, more preferably 2 to 60 parts by weight, and 3 to 50 parts by weight with respect to 100 parts by weight of the synthetic resin microporous film. More preferred is 5 to 40 parts by weight. By setting the adhesion amount of the polymerizable compound within the above range, the coating layer can be uniformly formed on the surface of the synthetic resin microporous film without blocking the micropores. This makes it possible to produce a heat-resistant synthetic resin microporous film with improved heat resistance without reducing air permeability.

(Plasma treatment process)
Next, in the method of the present invention, a plasma treatment is performed on the synthetic resin microporous film coated with the polymerizable compound. Thereby, the polymerizable compound is polymerized, and the coating layer containing the polymer of the polymerizable compound can be integrally formed on at least a part of the surface of the synthetic resin microporous film, preferably the entire surface.

  As described above, the coating layer contains a polymer of a polymerizable compound, and by using the coating layer containing such a polymer, heat shrinkage at high temperatures is reduced and excellent heat resistance is achieved. It is possible to provide a heat-resistant synthetic resin microporous film having the same. Moreover, since a polymeric compound is excellent in the adaptability with respect to a synthetic resin microporous film, a membrane | film | coat layer can be formed, without obstruct | occluding the micropore part of a synthetic resin microporous film. Therefore, according to the coating layer, excellent heat resistance can be imparted to the synthetic resin microporous film without reducing air permeability.

  In the present invention, the plasma treatment is performed after a polymerizable compound is applied to the surface of the synthetic resin microporous film. At this time, since the plasma has high energy, the plasma also reaches the synthetic resin microporous film, and the C—C bonds in the synthetic resin contained in the surface portion of the synthetic resin microporous film Synthetic resins can also be activated to generate radicals by molecular chain cleavage such as C—H bonds. Thereby, a part of the synthetic resin and a part of the polymer of the polymerizable compound can be chemically bonded. Although details are not clear, the polymer of the polymerizable compound contained in the coating layer is graft-polymerized to the synthetic resin contained in the surface portion of the synthetic resin microporous film by chemical bonding. Conceivable. By forming such chemical bonds, it is possible to form a coating layer that is firmly integrated with the surface of the synthetic resin microporous film. Thereby, the heat resistance of the synthetic resin microporous film can be further improved.

  Furthermore, by subjecting the synthetic resin microporous film to plasma treatment, a part of the synthetic resin is decomposed to lower the molecular weight, and as a result, the stress relaxation of the synthetic resin microporous film can proceed. It is considered that such stress relaxation effectively prevents thermal shrinkage of the heat-resistant synthetic resin microporous film at high temperatures. Moreover, since plasma has a moderately high energy, it can suppress the fall of the mechanical strength of the synthetic resin microporous film by excessive decomposition | disassembly of a synthetic resin. Examples of the synthetic resin microporous film that can provide a stress relaxation effect include polypropylene resin microporous films.

  As the plasma processing, a direct type in which a plasma processing object is disposed inside a discharge space between a pair of electrodes and a plasma processing is performed, and a plasma processing object is disposed outside between the electrodes and plasma is generated between the electrodes. There is known a remote type in which a plasma process is performed by spraying the processed gas into a plasma processing object.

  In the present invention, either direct plasma treatment or remote plasma treatment can be used, but remote plasma treatment is preferred. By adopting the remote type plasma treatment, it is possible to suppress a decrease in the mechanical strength of the synthetic resin microporous film as compared with the case where the direct type plasma treatment is adopted.

FIG. 1 is a schematic diagram of a remote type plasma processing apparatus. The remote plasma processing apparatus (1) shown in FIG. 1 has a processing head (10) and a plasma generation gas supply source (13).
The processing head (10) is provided with a pair of electrodes (11, 11) facing each other. A solid dielectric layer (not shown) is formed on the opposing surface of each electrode (11). One electrode (11) is connected to a power source (12). The other electrode (11) is electrically grounded. By the voltage supply from the power source (12), the space between the electrodes (11, 11) becomes a discharge space (17) near atmospheric pressure.

  A plasma generation gas supply source (13) is connected to the discharge space (17) via a connecting tube (not shown) so that the plasma generation gas is supplied into the discharge space (17). It is configured.

  At the bottom of the processing head (10), a blow-out port (15) for discharging a plasma-ized processing gas is provided. Furthermore, it is preferable that an electric field shielding member (14) is provided at the bottom of the processing head (10). In the form shown in FIG. 1, a through-hole is formed in the electric field blocking member (14) to serve as a blowout port (14). The electric field shielding member (14) is made of metal and is electrically grounded. The electric field shielding member (14) shields the electric field from the electrode (11) connected to the power source (12), and as a result, the arc discharge falls from the electrode (11) to the synthetic resin microporous film (A). Can be prevented. Thereby, it can prevent that a synthetic resin microporous film (A) receives an electric field damage (generation | occurrence | production of the pinhole by arc discharge, etc.).

  Next, a method for plasma-treating the synthetic resin microporous film (A) coated with the polymerizable compound using the plasma treatment apparatus (1) described above will be described. First, a synthetic resin microporous film (A) is conveyed on a movable sample stand (16) by a conveyance means (not shown). By applying a pulse wave or continuous wave voltage from the power source (12) to the electrodes (11, 11), a space between the pair of electrodes (11, 11) is defined as a discharge space (17). On the other hand, plasma generating gas is blown out from the gas supply source (13) to the discharge space (17) through the connecting tube. As a result, the plasma generating gas is turned into plasma in the discharge space (17). Next, plasma treatment can be performed by blowing the plasma-ized processing gas onto the surface of the synthetic resin microporous film (A) from the blowout port (15) of the processing head (10).

  The remote plasma treatment can be performed by spraying the plasma generated by the discharge in the plasma generating gas onto the synthetic resin microporous film (A) coated with the polymerizable compound. By such plasma treatment, the polymerizable compound can be radically polymerized.

The plasma treatment step can be performed in an atmospheric pressure atmosphere or a vacuum (reduced pressure) atmosphere, but is preferably performed in an atmospheric pressure atmosphere. The plasma treatment process under an atmospheric pressure atmosphere does not require equipment or time required for decompression, and can improve productivity. When the plasma treatment step is performed under an atmospheric pressure atmosphere, the pressure in the discharge space (17) is preferably 1.013 × 10 ^{4 to} 50.663 × 10 ⁴ Pa, and 1.333 × 10 ^{4 to} 10.664 ×. 10 ⁴ Pa is more preferable, and 9.331 × 10 ^{4 to} 10.9797 × 10 ⁴ Pa is particularly preferable.

  The voltage may be supplied to either one of the pair of electrodes (11, 11), or may be supplied to both. The voltage supplied to the electrode (11) is not limited to a pulse wave shape, but may be a continuous wave shape such as a sine wave, but a pulse wave shape is preferable.

  The rise time of the pulse wave voltage is preferably 100 μs or less. Thereby, the plasma generating gas can be efficiently converted into plasma. On the other hand, the falling time of the pulse wave voltage is preferably 100 μs or less. Thereby, the plasma generating gas can be efficiently converted into plasma. In the present invention, the rise time of the pulse wave voltage means a time during which the voltage change is continuously positive. In the present invention, the falling time of the pulse wave voltage means a time during which the voltage change is continuously negative.

  From the viewpoint of efficiently converting the plasma generating gas into plasma, the electric field strength of the pulse wave voltage is preferably 10 to 1000 kV / cm. From the same viewpoint, the frequency of the pulse wave voltage is preferably 0.5 to 100 kHz.

Plasma energy density to a synthetic resin microporous film the polymerizable compound is applied is preferably 5~300J / cm ^2, more preferably 10~250J / cm ^2, more preferably 20~200J / cm ^2. If the energy density of the plasma is too low, the amount of plasma that reaches the synthetic resin microporous film is reduced, so that the chemical bond between the synthetic resin in the synthetic resin microporous film and the polymer of the polymerizable compound is sufficient. Sometimes it cannot be formed. Moreover, when the energy density of plasma is too high, the synthetic resin in the synthetic resin microporous film may deteriorate, and the mechanical strength of the resulting heat-resistant synthetic resin microporous film may be reduced.

  The distance (WD) between the synthetic resin microporous film (A) coated with the polymerizable compound and the tip of the outlet (15) has a correlation with the amount of plasma reaching the synthetic resin microporous film, and is far away. As a result, the amount of plasma that reaches is reduced, and there may be a case where a chemical bond between the synthetic resin in the synthetic resin microporous film and the polymer of the polymerizable compound cannot be sufficiently formed. Therefore, the distance between the synthetic resin microporous film coated with the polymerizable compound and the tip of the outlet (15) is preferably 10 mm or less, more preferably 7 mm or less, and even more preferably 5 mm or less. In addition, it is better that the distance between the synthetic resin microporous film (A) and the tip of the air outlet (15) is as short as possible, but considering the reality, it is preferably 0.05 mm or more and 0.1 mm or more. Is more preferable. By setting the distance to 0.1 mm or more, the occurrence of defects such as wrinkles and tears can be reduced in the heat-resistant synthetic resin microporous film.

  According to the method of the present invention described above, a heat-resistant synthetic resin microporous film having good battery production line suitability and excellent heat resistance can be provided. Such a heat-resistant synthetic resin microporous film is formed integrally with a synthetic resin microporous film containing a synthetic resin and at least a part of the surface of the synthetic resin microporous film, and in one molecule. And a film layer containing a polymer of a polymerizable compound having two or more radically polymerizable functional groups.

  The coating layer contains a polymer of a polymerizable compound having two or more radically polymerizable functional groups in one molecule. And it is preferable that a part of polymer in a membrane | film | coat layer and a part of synthetic resin in a synthetic resin microporous film have couple | bonded chemically. By using a coating layer containing such a polymer, it is possible to provide a heat-resistant synthetic resin microporous film having reduced heat shrinkage at high temperatures and having excellent heat resistance.

The coating layer can improve the heat resistance of the heat-resistant synthetic resin microporous film without using inorganic particles. Therefore, the coating layer can exhibit high heat resistance even when it does not contain inorganic particles, but it can also contain inorganic particles as necessary. 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 polymerizable compound having two or more radical polymerizable functional groups in one molecule, a coating layer can be formed without blocking the micropores of the synthetic resin microporous film. The formation of the layer reduces the decrease in air permeability of the heat-resistant synthetic resin microporous film.

  The gel fraction of the heat resistant synthetic resin microporous film is preferably 5% or more, and more preferably 10% or more. By setting the gel fraction to 5% or more, a strong coating layer is formed, and thereby the heat shrinkage of the heat-resistant synthetic resin microporous film can be highly reduced. Further, the gel fraction of the heat resistant synthetic resin microporous film is preferably 99% or less. By making the gel fraction 99% or less, it is possible to reduce the brittleness of the heat-resistant synthetic resin microporous film.

In the present invention, the gel fraction of the heat-resistant synthetic resin microporous film can be measured according to the following procedure. First, a heat-resistant synthetic resin microporous film is cut to obtain 0.1 g of a test piece, and this test piece [W ₁ (g)] is weighed and filled into a test tube. Next, 20 ml of xylene is poured into the test tube, and the entire test piece is immersed in xylene. The test tube is covered with an aluminum lid and immersed in an oil bath heated to 130 ° C. for 24 hours. The contents in the test tube taken out from the oil bath are immediately opened in a stainless steel mesh basket (# 200) before the temperature drops, and insoluble matter is filtered. The weight of the mesh cage [W ₀ (g)] is weighed in advance. The mesh basket and the filtrate are dried under reduced pressure at 80 ° C. for 7 hours, and then the weight [W ₂ (g)] of the mesh basket and the filtrate is measured. Then, the gel fraction is calculated according to the following formula.
Gel fraction [%] = 100 × (W ₂ −W ₀ ) / W ₁

  The air permeability of the heat-resistant synthetic resin microporous film is not particularly limited, but is preferably 50 to 600 sec / 100 mL, and more preferably 100 to 300 sec / 100 mL. As described above, the heat-resistant synthetic resin microporous film of the present invention has a high reduction in air permeability due to the formation of the coating layer. Therefore, the air permeability of the heat resistant synthetic resin microporous film of the present invention can be within the above range. The air permeability of the heat-resistant synthetic resin microporous film can be measured by the same method as the method for measuring the air permeability of the synthetic resin microporous film described above.

  When the heat-resistant synthetic resin microporous film is heated from 25 ° C. to 180 ° C. at a heating rate of 5 ° C./min, the maximum heat shrinkage rate of the heat-resistant synthetic resin microporous film is preferably 25% or less, 20% The following is more preferable, and 5 to 17% is particularly preferable. The heat resistant synthetic resin microporous film is provided with excellent heat resistance by the coating layer. In addition, the maximum heat shrinkage rate of a heat resistant synthetic resin microporous film can be measured by the method as described in the Example mentioned later.

  The puncture strength of the heat resistant synthetic resin microporous film is preferably 0.5 N / μm or more, more preferably 0.7 N / μm or more, and particularly preferably 1.0 N / μm or more. According to the heat-resistant synthetic resin microporous film having a puncture strength within the above range, when the heat-resistant synthetic resin microporous film is cut in the battery production line suitability, the tear of the heat-resistant synthetic resin microporous film is reduced. Can do.

  In the present invention, the puncture strength of the heat-resistant synthetic resin microporous film can be measured according to JIS Z1707 (1998). Specifically, a needle having a diameter of 1.0 mm and a tip having a semicircular shape with a radius of 0.5 mm is pierced into a heat-resistant synthetic resin microporous film at a speed of 50 mm / min, and the maximum stress until the needle penetrates is determined. The piercing strength.

  The heat-resistant synthetic resin microporous film of the present invention is suitably used as a separator for non-aqueous electrolyte secondary batteries. Examples of the non-aqueous electrolyte secondary battery include a lithium ion secondary battery. Since the heat-resistant synthetic resin microporous film of the present invention is excellent in heat resistance, even when the inside of the battery becomes high temperature by using such a heat-resistant synthetic resin microporous film as a separator, It is possible to provide a non-aqueous electrolyte secondary battery in which an electrical short circuit between 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 coating layer containing a polymer of a polymerizable compound having two or more radically polymerizable functional groups in one molecule. According to this coating layer, the wettability of the heat-resistant synthetic resin microporous film with respect to the non-aqueous electrolyte can also be improved. For this reason, the heat-resistant synthetic resin microporous film allows the nonaqueous electrolytic solution to easily enter into the micropores, and can uniformly hold a large amount of the nonaqueous electrolytic solution. Therefore, by using a heat-resistant synthetic 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. it can.

  According to the method for producing a synthetic resin microporous film of the present invention, as described above, it is possible to produce a heat-resistant synthetic resin microporous film having improved heat resistance without reducing ion permeability such as lithium ions. it can. Therefore, according to such a heat-resistant synthetic resin microporous film, it is possible to provide a non-aqueous electrolyte secondary battery that can charge and discharge at a high current density while reducing 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 synthetic resin microporous film produced by the method for producing a synthetic resin microporous film of the present invention does not require the use of a porous coating layer containing inorganic particles, and thus has excellent lightweight properties and a production process. There is no contamination of the production line due to the dropping of inorganic particles.

It is a schematic diagram which shows the remote type plasma processing apparatus used suitably with the method of this invention.

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

[Examples 1 to 9, Comparative Example 1]
1. Production of homopolypropylene microporous film (extrusion process)
Homopolypropylene (weight average molecular weight: 400,000, number average molecular weight: 37000, melt flow rate: 3.7 g / 10 min, isotactic pentad fraction measured by ¹³ C-NMR method: 97%, melting point: 165 ° C. ) Was fed to a single screw extruder and melt kneaded at a resin temperature of 200 ° C. Next, the melt-kneaded homopolypropylene was extruded from a T die attached to the tip of a single-screw extruder onto a cast roll at 95 ° C., and cooled to a surface temperature of 30 ° C. by applying cold air. This obtained the homopolypropylene film (width 200mm) which has the thickness shown in Table 1 of the elongate shape. The extrusion rate was 10 kg / hour, the film formation rate was 22 m / min, and the draw ratio was 83.

(Curing process)
The obtained long homopolypropylene film 50 m was wound around a cylindrical core having an outer diameter of 3 inches in a roll shape to obtain a homopolypropylene film roll. The homopolypropylene film roll was allowed to cure for 24 hours in a hot air oven where the atmospheric temperature of the place where the 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 of the roll to the inside.

(First stretching process)
Next, the homopolypropylene film is continuously unwound from the roll, and after the surface temperature of the homopolypropylene film is set to 20 ° C., the homopolypropylene film is sequentially passed over the first stretching roll and the second stretching roll, and the peripheral speed of the second stretching roll Was rotated so as to be larger than the peripheral speed of the first stretching roll, so that the homopolypropylene film was uniaxially stretched only in the transport direction (extrusion direction) at a stretching ratio of 1.4 times at a stretching speed of 50% / min. .

(Second stretching step)
Next, the homopolypropylene film fed from the second stretching roll is supplied into the heating furnace, the surface temperature of the homopolypropylene film is set to 120 ° C., and there is a predetermined interval in the vertical direction in the heating furnace and The homopolypropylene film is hung up and down in a zigzag manner in each of the seven stretching rolls arranged in a staggered manner in the transport direction of the homopolypropylene film, and the respective peripheral speeds of the stretching roll are homogenized. The homopolypropylene film was uniaxially stretched only in the transport direction at a stretch ratio of 2.0 times at a stretch rate of 42% / min by rotating the polypropylene film so as to increase gradually in the transport direction.

(Annealing process)
Next, the homopolypropylene film is sequentially supplied to the first roll and the second roll that are arranged above and below in the hot air furnace so that the surface temperature of the homopolypropylene film becomes 155 ° C. and tension is applied to the homopolypropylene film. As a result, the homopolypropylene film was annealed by being conveyed in a hot air oven for 4 minutes to obtain a homopolypropylene microporous film (thickness: 25 μm, basis weight: 11 g / m ² ). The shrinkage ratio of the homopolypropylene film in the annealing process was 5%.

The resulting homopolypropylene microporous film has an air permeability of 190 sec / 100 mL, a surface opening ratio of 30%, a maximum major axis of the open end of the microporous part is 530 nm, an average major axis of the open end of the microporous part is 320 nm, The pore density was 20 / μm ² .

2. Formation of coating layer (Coating process)
1) Impregnation of a polymerizable compound into a homopolypropylene microporous film Table 1 shows a polymerizable compound having two or more radically polymerizable functional groups in one molecule in a predetermined amount of ethyl acetate shown in Table 1 as a solvent. A predetermined amount of trimethylolpropane triacrylate (TMPTA), ditrimethylolpropane tetraacrylate (DPTA), and pentaerythritol triacrylate (PETIA) were dissolved to prepare a coating solution. This coating solution was applied to the surface of a homopolypropylene microporous film to obtain a synthetic resin microporous film coated with a polymerizable compound.

  Thereafter, the homopolypropylene microporous film was heated at 80 ° C. for 2 minutes to evaporate and remove ethyl acetate. In the homopolypropylene microporous film, the polymerizable compound was attached in an amount shown in Table 1 with respect to the homopolypropylene microporous film.

(Plasma treatment process)
Plasma processing was performed using the remote plasma processing apparatus (1) shown in FIG. More specifically, a synthetic resin microporous film coated with a polymerizable compound is subjected to remote plasma treatment under the conditions (total irradiation energy, transport speed) shown in Table 1 under a nitrogen atmosphere. Examples and Comparative Examples A heat-resistant homopolypropylene microporous film was prepared. During the plasma treatment, the distance (WD) between the opening end of the blowout port (15) and the synthetic resin microporous film (A) coated with the polymerizable compound was set to 4 mm.

<Voltage application conditions>
Glow discharge Pulse width: 9μsec
Rise time: 5 μs
Fall time: 5μs
Discharge frequency: 15 kHz
Dead time: 2.0 sec
DC voltage: 420V
Current value: 2.2A
Input power: 0.92kW

  By the above-mentioned plasma treatment, the polymerizable compound is polymerized, and the coating layer containing the polymer of the polymerizable compound is integrated on the entire surface of the homopolypropylene microporous film and the wall surface of the opening end of the micropore continuous with the surface. Formed. The heat-resistant homopolypropylene microporous film had the air permeability, puncture strength and maximum heat shrinkage shown in Table 1. The air permeability and piercing strength were measured by the above-described methods, and the maximum heat shrinkage rate was measured by the following methods.

(Maximum heat shrinkage)
By cutting the heat-resistant homopolypropylene microporous film, a flat rectangular test piece having a width of 3 mm and a length of 30 mm was obtained. At this time, the length direction (extrusion direction) of the heat-resistant homopolypropylene microporous film was made parallel to the length direction of the test piece. Both ends in the length direction of the test piece were held by a gripper and attached to a TMA measuring apparatus (trade name “TMA-SS6000” manufactured by Seiko Instruments Inc.). At this time, the distance between the grips was set to 10 mm, and a tension of 19.6 mN (2 gf) was applied to the test piece in the length direction. Then, the test piece is heated from 25 ° C. to 180 ° C. at a rate of 5 ° C./min, the distance L (mm) between the gripping tools is measured at each temperature, and the heat shrinkage rate is calculated based on the following formula. did. Table 1 shows the maximum thermal shrinkage in the measurement range from 25 ° C to 180 ° C.
Thermal contraction rate (%) = 100 × (10−L) / 10

DESCRIPTION OF SYMBOLS 1 Remote type plasma processing apparatus 10 Processing head 11 Electrode 12 Power supply 13 Gas supply source 14 for plasma generation Electric field interruption member 15 Air outlet 16 Mobile sample stand 17 Discharge space

Claims (13)

  After coating a polymerizable compound having two or more radical polymerizable functional groups in one molecule on at least the surface of the synthetic resin microporous film, the synthetic resin microporous film is subjected to plasma treatment by a remote plasma processing apparatus. A method for producing a heat-resistant synthetic resin microporous film.   2. The heat-resistant synthetic resin microporous film according to claim 1, wherein the polymerizable compound having two or more radically polymerizable functional groups in one molecule contains a trifunctional or higher polyfunctional acrylic monomer. Production method.   2. A coating solution in which a polymerizable compound having two or more radically polymerizable functional groups in one molecule is dispersed or dissolved in a solvent is applied to the surface of a synthetic resin microporous film. Or the manufacturing method of the heat resistant synthetic resin microporous film of 2.   The heat-resistant synthetic resin fine film according to claim 3, wherein the solvent is removed by heating the synthetic resin microporous film coated with the coating liquid before the plasma treatment is performed on the synthetic resin microporous film. A method for producing a porous film.   By applying a polymerizable compound having two or more radical polymerizable functional groups in one molecule on the surface of the synthetic resin microporous film, radical polymerization in one molecule is performed on 100 parts by weight of the synthetic resin microporous film. The method for producing a heat-resistant synthetic resin microporous film according to any one of claims 1 to 4, wherein 5 to 80 parts by weight of a polymerizable compound having two or more functional groups are attached. The plasma is applied to the synthetic resin microporous film, the distance between the tip of the outlet and the film is within 10 mm, and the energy density is irradiated at 5 to 300 J / cm ^2. The manufacturing method of the heat-resistant synthetic resin microporous film of description. A synthetic resin microporous film containing a synthetic resin;
A film layer that is integrally formed on at least a part of the surface of the synthetic resin microporous film and includes a polymer of a polymerizable compound having two or more radically polymerizable functional groups in one molecule. A heat-resistant synthetic resin microporous film.   The heat resistant synthetic resin microporous film according to claim 7, wherein the gel fraction is 5% or more.   The heat-resistant synthetic resin microporous film according to claim 7, wherein the puncture strength is 0.5 N or more.   The heat-resistant synthetic resin microporous film according to claim 7 or 8, wherein the air permeability is 50 to 600 sec / 100 mL.   When the heat-resistant synthetic resin microporous film is heated from 25 ° C. to 180 ° C. at a heating rate of 5 ° C./min, the maximum heat shrinkage rate of the heat-resistant synthetic resin microporous film is 20% or less. The heat-resistant synthetic resin microporous film according to any one of claims 7 to 10.   A separator for a non-aqueous electrolyte secondary battery comprising the heat-resistant synthetic resin microporous film according to any one of claims 7 to 10.   A non-aqueous electrolyte secondary battery using the separator for a non-aqueous electrolyte secondary battery according to claim 12.

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