JP2015212322A - Manufacturing method of heat resistant microporous film, heat resistant microporous film, separator for nonaqueous electrolyte secondary cell and nonaqueous electrolyte secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a heat resistant microporous film excellent in ion permeability as well as having enhanced heat resistance without reducing mechanical strength.SOLUTION: There is provided a manufacturing method of a heat resistant microporous film by applying a polymerizable compound having two or more radical polymerizable functional group in a molecule on a surface of a synthetic resin microporous film containing a synthetic resin and a crystal nucleus, adhering 5 to 80 pts.wt. of the polymerizable compound to 100 pts.wt. of the synthetic resin microporous film and then irradiating active energy ray to the synthetic resin microporous film.

Description

  The present invention relates to a method for producing a heat-resistant microporous film, a heat-resistant microporous film, a separator for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery.

  Conventionally, lithium ion secondary batteries have been used as batteries 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 into the positive electrode. Therefore, the separator is required to have excellent ion permeability such as lithium ions.

  As the separator, a synthetic resin microporous film is used because it is excellent in insulation and cost. The synthetic resin microporous film contains a synthetic resin such as a propylene resin.

  And the synthetic resin microporous film is manufactured by extending | stretching a synthetic resin film. The synthetic resin microporous film produced by the stretching method generates high residual stress due to stretching. Therefore, it has been pointed out that such a synthetic resin microporous film thermally contracts at a high temperature, and as a result, the positive electrode and the negative electrode may be short-circuited. Therefore, it is desired to ensure the safety of the lithium ion secondary battery by improving the heat resistance of the synthetic resin microporous film.

  Patent Document 1 discloses a lithium ion 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 ion secondary battery separator is insufficient only by the treatment by electron beam irradiation. Furthermore, the lithium ion secondary battery separator becomes brittle and the mechanical strength of the lithium ion secondary battery separator decreases only by treatment with electron beam irradiation. When the mechanical strength is lowered, the lithium ion secondary battery separator is easily broken in the process of producing the lithium ion secondary battery, and the productivity of the lithium ion secondary battery is lowered.

JP 2003-22793 A

  Therefore, the present invention provides a method for producing a heat-resistant microporous film having excellent ion permeability and improved heat resistance without reducing mechanical strength. Furthermore, the present invention provides a heat-resistant microporous film having excellent ion permeability and improved heat resistance without reducing mechanical strength, and a non-aqueous electrolyte secondary solution using the heat-resistant microporous film. A battery separator and a non-aqueous electrolyte secondary battery are provided.

[Method for producing heat-resistant microporous film]
In the method for producing a heat-resistant microporous film of the present invention, a polymerizable compound having two or more radically polymerizable functional groups in one molecule is applied to the surface of a synthetic resin microporous film containing a synthetic resin and a crystal nucleating agent. And after attaching 5 to 80 parts by weight of the polymerizable compound to 100 parts by weight of the synthetic resin microporous film, the synthetic resin microporous film is irradiated with active energy rays.

(Synthetic resin microporous film)
The synthetic resin microporous film contains a synthetic resin and a crystal nucleating agent. According to the crystal nucleating agent, the crystal structure in the resultant synthetic resin microporous film can be refined, and the crystallinity can be increased. Thereby, the amorphous part which is easy to deteriorate by irradiation of active energy rays can be reduced, thereby providing a heat-resistant microporous film with improved heat resistance while suppressing a decrease in mechanical strength. .

  As the synthetic resin, an olefin resin is preferable. Therefore, the olefin resin microporous film is preferable as the synthetic resin microporous film. 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 in an olefin resin microporous film.

  Furthermore, the olefin-based resin microporous film that does not contain a crystal nucleating agent is easily embrittled by irradiation with active energy rays, and its mechanical strength is likely to decrease. On the other hand, in the present invention, by using a crystal nucleating agent, it is possible to suppress a decrease in mechanical strength of the olefin-based resin microporous film due to irradiation with active energy rays.

  Examples of olefin resins include ethylene resins and propylene resins. Especially, since it is excellent in heat resistance, a propylene-type resin is preferable. Olefinic resins may be used alone or in combination of two or more.

  Examples of the propylene-based resin include homopolypropylene (propylene homopolymer), copolymers of propylene and other olefins, and the like. 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. Further, 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 5.5 to 12, more preferably 7.5 to 12, and particularly preferably 8 to 11. According to the olefin resin having a molecular weight distribution within the above range, it is possible to provide an olefin resin microporous film having a high surface opening ratio and excellent mechanical strength.

  Here, the weight average molecular weight and number average molecular weight of the olefin resin are polystyrene-converted values measured by a GPC (gel permeation chromatography) method. Specifically, after collecting 6 to 7 mg of olefin resin, supplying the collected olefin resin to a test tube, the test tube contains 0.05 wt% BHT (dibutylhydroxytoluene). A diluted solution is prepared by adding a DCB (orthodichlorobenzene) solution and diluting the olefin-based resin concentration to 1 mg / mL.

  The dilution liquid 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 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: 500-842000, 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.

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

  The crystal nucleating agent is not particularly limited, and an inorganic crystal nucleating agent and an organic crystal nucleating agent can be used. Examples of the inorganic crystal nucleating agent include talc. Examples of the organic crystal nucleating agent include an α-type crystal nucleating agent and a β-type crystal nucleating agent. The α-type crystal nucleating agent means a nucleating agent having an effect of promoting the formation of an α-type crystal that is a monoclinic crystal that forms a cross-hatch structure in which a daughter lamella grows in a direction substantially perpendicular to the parent lamella. The β-type crystal nucleating agent means a nucleating agent having an effect of preferentially promoting the formation of a β-type crystal that is a hexagonal crystal having a lamellar structure that does not have a cross hatch structure different from the α-type crystal nucleating agent. A crystal nucleating agent may be used independently or 2 or more types may be used together.

  Examples of the α-type crystal nucleating agent include dibenzylidene sorbitol-based crystal nucleating agents such as dibenzylidene sorbitol derivatives, 2-hydroxy-2-oxo-4,6,10,12-tetra-tert-butyl-1,3,2- Phosphate crystal nucleating agents such as sodium salt of dibenzo [d, g] perhydrodioxaphospharosin, sorbitol crystal nucleating agents such as bis (p-methylbenzylidene) sorbitol, N, N ′, N ″ -Non-acetal crystal nucleating agents such as tris (2-methylcyclohexane-1-yl) propane-1,2,3-triylcarboxamide, rosin crystal nucleating agents, and aluminum benzoate crystal nucleating agents. .

  Examples of commercially available dibenzylidene sorbitol crystal nucleating agents include “Rike Master PN-10R”, “Rike Master FC-1”, and “Rike Master SN-003P” manufactured by Riken Vitamin Co., Ltd.

  Commercially available phosphate ester crystal nucleating agents include product names “ADK STAB NA-11”, “ADK STAB NA-27”, “ADK STAB NA-902”, “ADK STAB NA-21”, and “ADK STAB NA-21” manufactured by Adeka Corporation. 71 ”,“ ADK STAB NA-05 ”, product name“ IRGASTAB NA11 ”manufactured by BASF Japan Ltd., and the like.

  As commercial products of sorbitol-based crystal nucleating agents, product names “Gelall MD-LM30G”, “Gelall D”, “Gelall M”, “Gelall MD”, “Gelall E-200”, “RiKAFAST AC” manufactured by Shin Nippon Rika Co., Ltd. "RiKAFAST P1", Mitsui Chemicals product name "NC-4", BASF Japan product name "IRGACURE D", "IRGACURE DM" and the like.

  Examples of commercially available non-acetal crystal nucleating agents include “Rika Clear PC-1”, “Rika Clear PC-25-HA”, and “Rika Clear PC-25-RZ” manufactured by Shin Nippon Rika Co., Ltd.

  Examples of the β-type crystal nucleating agent include aromatic carboxylic acid amide, γ-quinacridone, carboxylate, calcium pimelate and the like. As a commercial product of the β-type crystal nucleating agent, a product name “NU-100” manufactured by Shin Nippon Rika Co., Ltd. can be mentioned.

  The crystal nucleating agent can also be used as a masterbatch. Commercially available masterbatches containing crystal nucleating agents include product names “PP-RM M105”, “PP-RM M102”, “PP-RM M301” manufactured by Dainichi Seika Co., Ltd., “PPM ST” manufactured by Tokyo Ink Co., Ltd. -0024 "and the like.

  0.05-20 weight part is preferable with respect to 100 weight part of synthetic resin microporous films, and, as for content of the crystal nucleating agent in a synthetic resin microporous film, 0.5-5 weight part is preferable. By setting the content of the crystal nucleating agent within the above range, it is possible to efficiently suppress a decrease in mechanical strength of the synthetic resin microporous film due to irradiation with active energy rays.

  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. 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 in the olefin resin microporous film manufactured by the extending | stretching method.

  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 an olefin resin containing a crystal nucleating agent, and this olefin resin film A method having a step of generating and growing a lamellar crystal therein, and a step of obtaining an olefin resin microporous film in which micropores are formed by stretching the olefin resin film and separating the lamella crystals. And (2) a step of obtaining an olefinic resin film by extruding an olefinic resin containing a crystal nucleating agent and a filler, and filling the olefinic resin with the olefinic resin film by uniaxial stretching or biaxial stretching. An olefin resin microporous film in which micropores are formed by peeling the interface with the material A method and a step, and the like. 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:
Extrusion to obtain an olefin resin film by melting and kneading an olefin resin and a crystal nucleating agent at (Tm + 20) to (Tm + 100) ° C. with an extruder and extruding from a T die attached to the tip of the extruder. Process,
A curing step of curing the olefin-based resin film after the extrusion step at (Tm-30) to (Tm-1) ° C;
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;
Annealing step of annealing the olefin resin film that has been stretched in the second stretching step,
("Tm" means the melting point of the olefin resin).

  According to the said method, the olefin resin microporous film in which many micropores penetrated in the film thickness direction can be obtained. According to such an olefin-based resin microporous film, it is possible to provide a heat-resistant microporous film having excellent air permeability and capable of smoothly and uniformly transmitting ions such as lithium ions. it can.

(Extrusion process)
In the method of the present invention, first, an olefinic resin film and a crystal nucleating agent are supplied to an extruder, melt-kneaded, and then extruded from a T-die attached to the tip of the extruder to obtain an olefinic resin film. Perform the process.

  The temperature of the olefin resin when melt-kneading the olefin resin and the crystal nucleating agent with an extruder is preferably (Tm + 20) to (Tm + 100) ° C., more preferably (Tm + 25) to (Tm + 80) ° C., and (Tm + 25). ~ (Tm + 50) ° C is particularly preferred. By setting the temperature of the olefin resin at the time of melt kneading to (Tm + 20) ° C. or more, an olefin resin 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 promoted by setting the temperature of the olefin resin at the time of melt-kneading to (Tm + 100) degree C or less.

  50-300 are preferable, as for the draw ratio at the time of extruding an olefin resin and a crystal nucleating agent into a film form from an extruder, 65-250 are more preferable, and 70-250 are especially preferable. By setting the draw ratio to 50 or more, the tension applied to the 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 resin 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. Further, 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.

  Furthermore, 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 resin film having a uniform thickness and width.

  And the olefin resin which comprises the olefin resin film crystallizes by cooling the olefin resin film extruded from the T-die until the surface temperature becomes (Tm-100) ° C. or less. Generate. In the present invention, the olefin resin is cooled by extruding the melt-kneaded olefin resin to orient the olefin resin molecules constituting the olefin resin film in advance and then cooling the olefin resin film. The portion where the is oriented can promote the formation of lamellae.

  The surface temperature of the cooled olefin resin film is preferably (Tm-100) ° C. or less, more preferably (Tm-140) to (Tm-110) ° C., and (Tm-135) to (Tm-120) ° C. Is particularly preferred. 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)
Next, a curing process for curing the olefin resin film obtained by the extrusion process described above is performed. The curing process of the olefin resin is performed to grow the lamella formed in the olefin resin film in the extrusion process. This can promote 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 (Tm-30) to (Tm-1) ° C.

  The curing temperature of the olefin resin film is preferably (Tm-30) to (Tm-1) ° C, more preferably (Tm-30) to (Tm-5) ° C, and (Tm-25) to (Tm-10). ) ° C. is particularly preferred. By setting the curing temperature of the olefin resin film to (Tm-30) ° C. or higher, 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 into (Tm-1) degree C or less.

  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 resin film is wound up in a roll inside a heating apparatus such as a hot stove, the temperature inside the heating apparatus is set as the curing temperature.

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

  When the olefin resin film is cured while running on 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. According to the olefin resin film having a surface temperature within the above range, breakage of the olefin resin film at the time of stretching can be reduced, and a crack can be generated at an amorphous portion between lamellae.

  In the first stretching step, the stretching ratio of the olefin resin film is preferably 1.2 to 1.6 times, and particularly 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 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 due to stretching.

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

  The method for stretching the olefinic resin film in the first stretching step is not particularly limited as long as the olefinic resin film can be uniaxially stretched. For example, the olefinic resin film is brought to a predetermined temperature using a uniaxial stretching device. And a uniaxial stretching method.

(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 treatment at a surface temperature of 100 to 150 ° C. and a stretching ratio of 1.2 to 2.2 times. Also in the second stretching step, the olefin resin film is preferably uniaxially stretched only in the extrusion direction. By performing the stretching treatment in such a first 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 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. 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 within the above range, micropores can be uniformly formed in the olefin-based resin film.

  The method for stretching the olefinic resin film in the second stretching step is not particularly limited as long as the olefinic resin film can be uniaxially stretched. For example, the olefinic resin film is brought to a predetermined temperature using a uniaxial stretching device. And a uniaxial stretching method.

(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 in order to relieve residual strain generated in the olefin resin film due to stretching applied in the above-described stretching step, and to suppress thermal shrinkage from occurring in the resulting olefin resin microporous film.

  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 not more than (Tm-10) ° C. 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 film. Moreover, obstruction | occlusion of the micropore part formed at the extending process can be suppressed by making the surface temperature of an olefin resin film into (Tm-10) degree C or less.

  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.

  The synthetic resin microporous film includes micropores penetrating in the film thickness direction. The fine pores can impart excellent ion permeability to the heat-resistant microporous film. Thereby, the heat-resistant microporous film can transmit ions such as lithium ions in the thickness direction.

  The air permeability of the synthetic resin microporous film is preferably 300 sec / 100 mL or less, more preferably 100 to 300 sec / 100 mL, still more preferably 100 to 250 sec / 100 mL, and particularly preferably 100 to 200 sec / 100 mL. 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 locations at 10 cm intervals in the length direction of the synthetic resin microporous film in an atmosphere of a temperature of 23 ° C. and a relative humidity of 65% according to JIS P8117. The value obtained by calculating the arithmetic mean value.

  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. The rectangle is adjusted so that both the long side and the short side have the minimum dimension. Let the area of the said rectangle be an opening area of each micropore part. The total opening area S (μm ² ) of the micropores is calculated by summing the opening areas of the micropores. This is the total opening area S of the minute hole ([mu] m ²⁾ of 122.88μm ² (9.6μm × 12.8μm) surface porosity values multiplied by 100 and divided by the (%). In addition, about the micropore part which exists over the measurement part and the part which is not a measurement part, only the part which exists in the measurement part in the micropore part is made into 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 900 nm. A synthetic resin microporous film having a maximum major axis at the opening end of the micropores of 1 μm or less is excellent in mechanical strength. 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 10 nm to 400 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. 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. And let the largest long diameter among the long diameters of the opening end in the micropore part which has appeared in the photograph be the maximum long diameter of the opening end of the micropore part in the synthetic resin microporous film. The arithmetic mean value of the major axis of the opening end in each micropore portion appearing in the photograph is taken as the average major axis of the opening end of the micropore portion in the synthetic resin microporous film.

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 times. Then, the number of micropores is measured in the measurement part, and the pore density can be calculated by dividing this number by 122.88 μm ² (9.6 μm × 12.8 μm).

  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.

(Coating process)
Next, in the method of the present invention, 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 containing the above-described synthetic resin and crystal nucleating agent. Then, a coating process is carried out for adhering 5 to 80 parts by weight of the polymerizable compound to 100 parts by weight of the synthetic resin microporous film.

  The polymerizable compound has two or more radically polymerizable functional groups in one molecule. The radical polymerizable functional group is a functional group containing a radical polymerizable unsaturated bond that can be radically polymerized by irradiation with active energy rays. 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.

  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, pentaerythritol tri (meth) acrylate, ethoxylated isocyanuric acid tri (meth) acrylate, ε-caprolactone modified tris- (2-acryloxyethyl) isocyanurate, and ethoxylated glycerol tri (meth) ) A trifunctional or higher functional acrylic monomer such as 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, a polyfunctional acrylic monomer, a polyfunctional (meth) acrylate modified product, a dendritic polymer having a (meth) acryloyl group, and a urethane having a (meth) acryloyl group (Meth) acrylate oligomers are preferred. Further, as the polymerizable compound, a polyfunctional acrylic monomer and a polyfunctional (meth) acrylate modified product are more preferable, a polyfunctional acrylic monomer is particularly preferable, and trimethylolpropane tri (meth) acrylate, glyceryl tri ( Most preferred are meth) acrylate, pentaerythritol tri (meth) acrylate, tris- (2-acryloxyethyl) isocyanurate, pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, and dipentaerythritol polyacrylate. . According to these polymerizable compounds, it is possible to form a coating layer having high hardness and appropriate elasticity and elongation. Thereby, the outstanding heat resistance can be provided to a heat-resistant microporous film, without reducing mechanical strength. In addition, a polymeric compound may be used independently and may use 2 or more types together.

  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.

  By applying a polymerizable compound to the surface of the synthetic resin microporous film, the polymerizable compound can be attached to 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 that the polymerizable compound is dispersed or dissolved in a solvent to obtain a coating solution, and then this coating solution is applied to the surface of the synthetic resin microporous film.

  The coating liquid can be adjusted to a low viscosity. Therefore, when the coating liquid is applied to the surface of the synthetic resin microporous film, the coating liquid can smoothly flow to the wall surfaces of the micropores in the synthetic resin microporous film. A coating layer can be formed not only on the surface of the porous film, but also on the wall surface of the open end of the micropores continuous with the surface. Thus, the coating layer portion extending on the wall surface of the opening end portion of the minute hole portion can play a role of an anchor effect. Thereby, a membrane | film | coat layer can be firmly integrated with the surface of a synthetic resin microporous film. With such a coating layer, excellent heat resistance can be imparted to the heat-resistant microporous film. As a result, even when the heat-resistant microporous film is unexpectedly exposed to a heating condition, the synthetic resin microporous film can be highly unlikely to shrink or melt due to the coating layer.

  When the coating liquid is applied to the upper surface of the synthetic resin microporous film, the coating liquid can pass through the micropores and reach the lower surface of the synthetic resin microporous film, thereby making the synthetic resin microporous film A film layer can be formed not only on the upper surface but also on the lower surface of the porous film.

  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, etc. 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 solution is preferably 3 to 20% by weight, more preferably 3 to 15% by weight, and particularly preferably 5 to 12% by weight. By setting the content of the bifunctional or higher 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. A heat-resistant microporous film with improved heat resistance can be produced without reducing it.

  The method for applying the polymerizable compound to 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 in which a synthetic resin microporous film is immersed and a polymerizable compound is applied to the surface of the synthetic resin microporous film; (3) A coating solution is prepared by dissolving or dispersing the polymerizable compound in a solvent. A method in which the working 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. There is a method in which a synthetic resin microporous film is immersed in this coating liquid, and after the coating liquid is applied in the synthetic resin microporous film, the solvent is removed by heating the synthetic resin microporous film. Can be mentioned. Of these, the methods (3) and (4) are preferred. According to these methods, the polymerizable compound can be uniformly applied and adhered 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 further reducing thermal 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 5 to 80 parts by weight, preferably 7 to 50 parts by weight, and 10 to 40 parts by weight with respect to 100 parts by weight of the synthetic resin microporous film. More preferred. 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 microporous film with improved heat resistance without reducing air permeability.

(Irradiation process)
Next, in the method of the present invention, an irradiation step of irradiating an active energy ray to a synthetic resin microporous film coated with a polymerizable compound having two or more radical polymerizable functional groups in one molecule is performed. By the irradiation step, 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 on the entire surface. .

  As described above, the coating layer contains a polymer of a polymerizable compound having two or more radically polymerizable functional groups in one molecule, and by using the coating layer containing such a polymer, heat resistance is improved. The heat shrinkage of the porous microporous film at high temperatures can be reduced to improve the heat resistance.

  Moreover, by irradiating the synthetic resin microporous film with active energy rays, a part of the synthetic resin is decomposed, and mechanical strength such as tear strength of the synthetic resin microporous film may be lowered. However, since the synthetic resin microporous film of the present invention contains a crystal nucleating agent, decomposition of the synthetic resin microporous film by active energy rays is suppressed. Therefore, it is possible to suppress a decrease in the mechanical strength of the synthetic resin microporous film, thereby providing a heat-resistant microporous film having an improved heat resistance while being highly reduced in mechanical strength.

  Furthermore, since a polymerizable compound having two or more radically polymerizable functional groups is excellent in compatibility with the synthetic resin microporous film, the polymerizable compound can be applied without blocking the micropores of the synthetic resin microporous film. Can be crafted. Thereby, the membrane | film | coat layer which has the through-hole penetrated in the thickness direction can be formed in the location corresponding to the micropore part of a synthetic resin microporous film. Therefore, according to such a coating layer, it is possible to provide a synthetic resin microporous film having improved heat resistance without reducing air permeability.

  The active energy ray is not particularly limited, and examples thereof include ultraviolet rays, electron beams, α rays, β rays, γ rays, and plasma.

When using ultraviolet rays as the active energy ray, the accumulated light quantity of ultraviolet to the synthetic resin microporous film is preferably 1000~5000mJ / cm ^2, more preferably ^{1000~4000mJ / cm 2, 1500~3700mJ / cm} 2 is particularly preferred. In addition, when using an ultraviolet-ray as an active energy ray, it is preferable that the photoinitiator is contained in the said coating liquid. Examples of the photopolymerization initiator include benzophenone, benzyl, methyl-o-benzoylbenzoate, and anthraquinone.

  When an electron beam is used as the active energy ray, the irradiation dose of the electron beam to the synthetic resin microporous film is preferably 10 to 150 kGy, and more preferably 10 to 100 kGy. By setting the electron beam irradiation dose within the above range, the coating layer can be formed while reducing deterioration of the synthetic resin in the synthetic resin microporous film.

  When an electron beam is used as the active energy ray, the acceleration voltage of the electron beam with respect to the synthetic resin microporous film is preferably 50 to 300 kV, more preferably 50 to 250 kV, and particularly preferably 100 to 200 kV. By setting the acceleration voltage of the electron beam within the above range, the coating layer can be formed while reducing deterioration of the synthetic resin in the synthetic resin microporous film.

When using a plasma as an active energy ray, plasma energy density to a synthetic resin microporous film is preferably 5~50J / cm ^2, more preferably ^{5~50J / cm 2, 10~45J / cm} 2 is particularly preferred.

  As the active energy rays, ultraviolet rays, electron beams and plasma are preferable, and electron beams are particularly preferable. According to the electron beam, since it has a moderately high energy, sufficient radicals are also generated in the synthetic resin in the synthetic resin microporous film by irradiation of the electron beam, and a part of the synthetic resin and the polymerizable compound Many chemical bonds can be formed with a part of the polymer.

[Heat-resistant microporous film]
According to the method of the present invention described above, a heat-resistant microporous film having excellent mechanical strength and heat resistance can be provided. Such heat-resistant microporous film is
100 parts by weight of a synthetic resin microporous film containing a synthetic resin and a crystal nucleating agent;
Including 5 to 80 parts by weight of a coating layer formed on at least part of the surface of the synthetic resin microporous film,
The coating layer includes a polymer of a polymerizable compound having two or more radical polymerizable functional groups in one molecule.

  The coating layer contains a polymer of a polymerizable compound having two or more radically polymerizable functional groups. By using a coating layer containing such a polymer, it is possible to provide a heat-resistant microporous film having a high heat shrinkage at a high temperature and having excellent heat resistance.

Moreover, even if the coating layer does not contain inorganic particles, the heat resistance of the heat-resistant microporous film can be improved. If necessary, the coating layer may contain inorganic particles. Examples of the material constituting the inorganic particles include Al ₂ O ₃ , SiO ₂ , TiO ₂ , and MgO.

  It is preferable that a part of the polymer in the coating layer and a part of the synthetic resin in the synthetic resin microporous film are chemically bonded. Such chemical bonds are not particularly limited, and examples thereof include covalent bonds, ionic bonds, and intermolecular bonds.

  The content of the coating layer in the heat-resistant microporous film is preferably 5 to 80 parts by weight, more preferably 5 to 50 parts by weight, and particularly preferably 10 to 40 parts by weight with respect to 100 parts by weight of the synthetic resin microporous film. preferable. By setting the content of the coating layer within the above range, excellent heat resistance can be imparted to the obtained heat-resistant microporous film without reducing the air permeability.

  The air permeability of the heat-resistant 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 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 microporous film of the present invention can be within the above range. The air permeability of the heat-resistant 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.

  The gel fraction of the heat resistant 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 microporous film can be reduced to a high level. Further, the gel fraction of the heat-resistant microporous film is preferably 99% or less, and more preferably 60% or less. By making the gel fraction 99% or less, the heat-resistant microporous film can be prevented from becoming brittle.

In the present invention, the gel fraction of the heat-resistant microporous film can be measured according to the following procedure. First, about 0.1 g of a test piece is obtained by cutting the heat-resistant microporous film. After weighing the weight [W ₁ (g)] of the test piece, the test piece is 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 [W ₀ (g)] of the mesh cage 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 weighed. Then, the gel fraction is calculated according to the following formula.
Gel fraction [%] = 100 × (W ₂ −W ₀ ) / W ₁

  When the heat-resistant 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 microporous film is preferably 25% or less, more preferably 20% or less. Preferably, 5 to 17% is particularly preferable. The heat resistant microporous film is provided with excellent heat resistance by the coating layer. Therefore, the heat-resistant microporous film can have a maximum heat shrinkage of 25% or less.

The maximum heat shrinkage rate of the heat-resistant microporous film can be measured as follows. First, a plane rectangular test piece (width 3 mm × length 30 mm) is cut out by cutting an arbitrary portion of the heat-resistant microporous film. At this time, the extrusion direction of the heat-resistant microporous film is made parallel to the length direction of the test piece. The both ends of the test piece in the length direction are gripped 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 gripping tools is set to 10 mm, and the gripping tools can be moved along with the thermal contraction of the test piece. The test piece was heated from 25 ° C. to 180 ° C. at a heating rate of 5 ° C./min with a tension of 19.6 mN (2 gf) applied to the test piece in the length direction. The distance L (mm) between them is measured, the heat shrinkage rate is calculated based on the following formula, and the maximum value is taken as the maximum heat shrinkage rate.
Thermal contraction rate (%) = 100 × (10−L) / 10

  The piercing strength of the heat resistant microporous film is preferably 0.5 N / 25 μm or more, and more preferably 0.7 N / 25 μm or more. According to the heat-resistant microporous film having a puncture strength of 0.5 N / 25 μm or more, tearing of the heat-resistant microporous film can be reduced when the heat-resistant microporous film is cut in the battery manufacturing process.

  The maintenance rate of the puncture strength of the heat-resistant microporous film before and after irradiation with ionizing radiation at an acceleration voltage of 200 kV and an absorbed dose of 35 kGy is preferably 50% or more, and more preferably 55% or more. According to the heat resistant microporous film having a puncture strength maintenance rate within the above range, it is possible to reduce tearing of the heat resistant microporous film when the heat resistant microporous film is cut in the battery manufacturing process.

In the present invention, the puncture strength of the heat-resistant microporous film can be measured according to JIS Z1707 (1998). Specifically, a needle having a diameter of 1.0 mm and a semicircular tip having a radius of 0.5 mm is pierced into a heat-resistant microporous film at a speed of 50 mm / min, and the maximum stress until the needle penetrates is determined as the puncture strength. To do. The puncture strength S ₁ [N / 25 μm] of the heat-resistant microporous film before irradiation with ionizing radiation and the heat-resistant microporous film after irradiation with ionizing radiation at an acceleration voltage of 200 kV and an absorbed dose of 35 kGy The puncture strength S ₂ [N / 25 μm] is measured according to the above-described procedure, and the puncture strength maintenance rate [%] can be calculated by the following formula.
Puncture strength maintenance rate [%] = 100 × S ₂ / S ₁

  The heat-resistant microporous film of the present invention is suitably used as a separator for nonaqueous electrolyte secondary batteries. Examples of the non-aqueous electrolyte secondary battery include a lithium ion secondary battery. Since the heat-resistant microporous film of the present invention has excellent mechanical strength, the film is split when the heat-resistant microporous film is cut in the process of producing a non-aqueous electrolyte secondary battery. And the productivity of the non-aqueous electrolyte secondary battery can be improved.

  Moreover, since the heat resistant microporous film of the present invention is excellent in ion permeability, the internal resistance of the secondary battery can be reduced by using such a heat resistant microporous film as a separator. Such a non-aqueous electrolyte secondary battery can be charged and discharged at a high current density even in high output applications such as vehicles such as electric vehicles. Furthermore, since the heat-resistant microporous film of the present invention is also excellent in heat resistance, even when the internal temperature of the secondary battery becomes high due to occurrence of an abnormal situation such as overcharge or internal short circuit, The electrical short circuit between the electrodes can be highly suppressed by the conductive microporous film, and the excellent safety of the non-aqueous electrolyte secondary battery can be ensured.

  The non-aqueous electrolyte secondary battery is not particularly limited as long as it includes the heat-resistant microporous film of the present invention as a separator, and includes a positive electrode, a negative electrode, a separator including a heat-resistant microporous film, and a non-aqueous electrolyte. Is included. A heat-resistant microporous film is arrange | positioned between a positive electrode and a negative electrode, and can prevent the electrical short circuit between electrodes by this. Further, the non-aqueous electrolyte is at least filled in the micropores of the heat-resistant microporous film, so that lithium ions can move between the electrodes during charging and discharging.

  The positive electrode is not particularly limited, but preferably includes a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector. The positive electrode active material layer preferably includes a positive electrode active material and voids formed between the positive electrode active materials. When the positive electrode active material layer includes voids, the voids are also filled with the non-aqueous electrolyte. The positive electrode active material is a material capable of occluding and releasing lithium ions, and examples of the positive electrode active material include lithium cobaltate and lithium manganate. Examples of the current collector used for the positive electrode include aluminum foil, nickel foil, and stainless steel foil. The positive electrode active material layer may further contain a binder, a conductive auxiliary agent, and the like.

  The negative electrode is not particularly limited, but preferably includes a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector. The negative electrode active material layer preferably includes a negative electrode active material and voids formed between the negative electrode active materials. When the negative electrode active material layer contains voids, the voids are also filled with the non-aqueous electrolyte. The negative electrode active material is a material capable of occluding and releasing lithium ions. Examples of the negative electrode active material include graphite, carbon black, acetylene black, and ketjen black. Examples of the current collector used for the negative electrode include copper foil, nickel foil, and stainless steel foil. The negative electrode active material layer may further contain a binder, a conductive auxiliary agent, and the like.

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. According to this coating layer, the wettability of the heat-resistant microporous film with respect to the non-aqueous electrolyte can also be improved. For this reason, the heat-resistant microporous film easily allows the nonaqueous electrolyte to enter into the micropores, and can uniformly hold a large amount of the nonaqueous electrolyte. Therefore, by using a heat-resistant microporous film as a separator, it is possible to provide a non-aqueous electrolyte secondary battery that is excellent in productivity and highly reduced in life due to deterioration of the electrolyte.

  According to the method of the present invention, it is possible to provide a heat-resistant microporous film having excellent ion permeability and improved heat resistance without reducing mechanical strength.

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

[Examples 1 to 3, Comparative Examples 1 to 7]
1. Production of homopolypropylene microporous film (extrusion process)
Homopolypropylene A (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), homopolypropylene B (weight average molecular weight: 410,000, number average molecular weight: 72000, melt flow rate: 3.0 g / 10 min, isotactic pentad fraction measured by ¹³ C-NMR method: 98%, Melting point: 166 ° C.), crystal nucleating agent A (dibenzylidene sorbitol-based crystal nucleating agent, “Rike Master SN-003P” manufactured by Riken Vitamin Co., Ltd.), and crystal nucleating agent B (“NS-01” manufactured by Shachihata) A T-die that is supplied to a single screw extruder at a compounding amount as shown in Tables 1 and 2 and melt-kneaded at a resin temperature of 200 ° C. and attached to the tip of the extruder Extruded onto a casting roll of al 95 ° C., the surface temperature by applying cold air was cooled until 30 ° C.. This obtained the elongate homopolypropylene film (200 mm in width) containing the homopolypropylene A, the homopolypropylene B, and the crystal nucleating agent. The extrusion rate was 10 kg / hour, the film formation rate was 22 m / min, and the draw ratio was 83.

(Curing process)
Next, the homopolypropylene film (length: 50 m) was wound into a roll around a cylindrical core having an outer diameter of 3 inches 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 was continuously unwound from the roll at an unwinding speed of 1.5 m / min, and the homopolypropylene film was stretched at a stretching speed of 50% / min after setting the surface temperature to 20 ° C. Uniaxial stretching was performed only in the extrusion direction at a magnification of 1.4.

(Second stretching step)
Next, the homopolypropylene film fed from the second stretching roll is supplied into a heating furnace, the surface temperature of the homopolypropylene film is set to 120 ° C., and a stretching ratio of 2 at a stretching rate of 42% / min. It was uniaxially stretched only in the extrusion direction by a factor of 0.0.

(Annealing process)
Next, the homopolypropylene film is fed into the hot stove and conveyed in the hot stove for 4 minutes so that the surface temperature of the homopolypropylene film is 155 ° C. and no tension is applied to the homopolypropylene film. Thus, the homopolypropylene film was annealed 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)
To a predetermined amount of ethyl acetate shown in Tables 1 and 2, trimethylolpropane triacrylate (TMPTA), 1,9-nonanediol dimethacrylate (NDDM), or divinylbenzene (DVB) is used as a polymerizable compound. And it was made to melt | dissolve in the quantity shown in 2, and the coating liquid was produced. This coating solution was applied to the surface of a homopolypropylene microporous film.

  Thereafter, the homopolypropylene microporous film was heated at 80 ° C. for 2 minutes to evaporate and remove ethyl acetate. In the homopolypropylene microporous film, the polymerizable compound was attached in an amount shown in Tables 1 and 2 with respect to 100 parts by weight of the homopolypropylene microporous film.

(Irradiation process)
The homopolypropylene microporous film was irradiated with an electron beam in an nitrogen atmosphere with an acceleration voltage of 200 kV and the absorbed dose shown in Tables 1 and 2. As a result, the polymerizable compound was polymerized to integrally form a film layer containing a polymer of the radical polymerizable compound on the entire surface of the homopolypropylene microporous film. Moreover, a part of homopolypropylene contained in the homopolypropylene microporous film and a part of the polymer contained in the coating layer were chemically bonded. The heat resistant microporous film had the thicknesses shown in Tables 1 and 2. Tables 1 and 2 show the content (parts by weight) of the coating layer in 100 parts by weight of the homopolypropylene microporous film in the heat-resistant microporous film. In Comparative Example 1, only the homopolypropylene microporous film was obtained without performing the coating process and the irradiation process.

[Evaluation]
About the heat-resistant microporous film obtained in Examples 1-3 and Comparative Examples 2-7, and the homopolypropylene microporous film obtained in Comparative Example 1, the air permeability and the gel fraction were measured according to the above-described procedure. . These results are shown in Tables 1 and 2. In addition, the gel fraction of the homopolypropylene microporous film obtained in Comparative Example 1 was measured using the same method as the measurement method described above for the gel fraction of the heat-resistant microporous film.

Further, in each of the Examples and Comparative Examples, the homopolypropylene microporous film coated with the coating liquid after the coating process is irradiated with ionizing radiation at an acceleration voltage of 200 kV and an absorbed dose of 35 kGy, and the ionizing radiation is irradiated. The puncture strength of the homopolypropylene microporous film to which the coating liquid before and after was applied was measured according to JIS Z1707 (1998). Specifically, a needle having a diameter of 1.0 mm and a semicircular tip having a radius of 0.5 mm is pierced into a homopolypropylene microporous film coated with a coating liquid at a speed of 50 mm / min until the needle penetrates. The maximum stress was defined as the piercing strength. And after irradiating the puncture strength S ′ ₁ [N / 25 μm] of the homopolypropylene microporous film to which the coating liquid before irradiating the ionizing radiation is applied, and the ionizing radiation at an acceleration voltage of 200 kV and an absorbed dose of 35 kGy The puncture strength S ′ ₂ [N / 25 μm] of the homopolypropylene microporous film coated with the coating solution was measured according to the above-described procedure, and the puncture strength maintenance rate [%] was calculated according to the following formula. The results are shown in Tables 1 and 2. In Tables 1 and 2, “◯” means the case where the puncture strength maintenance rate was 50% or more, and “X” means the case where the puncture strength maintenance rate was less than 50%.
Puncture strength maintenance rate [%] = 100 × S ′ ₂ / S ′ ₁

(Tensile fracture stress)
The tensile fracture stress of the heat-resistant microporous film obtained in Examples 1 to 3 and Comparative Examples 2 to 7 and the homopolypropylene microporous film obtained in Comparative Example 1 was measured according to the following procedure.

  With respect to the heat-resistant microporous film or the homopolypropylene microporous film, the tensile fracture stress in the extrusion direction was measured according to JIS K7127 / 2/300. At the time of measurement, the sample piece had a width of 10 mm and a length of 150 mm.

(Nail penetration test)
About the heat-resistant microporous film obtained in Examples 1-3 and Comparative Examples 2-7, the nail penetration test was implemented in the following way. In addition, the homopolypropylene microporous film obtained in Comparative Example 1 was subjected to a nail penetration test in the same manner as described below except that the homopolypropylene microporous film was used instead of the heat-resistant microporous film. These results are shown in Tables 1 and 2.

  A composition for forming a positive electrode containing nickel-cobalt-lithium manganate (1: 1: 1) as a positive electrode active material was prepared. This positive electrode forming composition was applied to one surface of an aluminum foil as a positive electrode current collector and dried to prepare a positive electrode active material layer. Thereafter, a positive electrode current collector having a positive electrode active material layer formed on one surface was punched out to obtain a positive electrode having a plane rectangular shape of 48 mm long × 117 mm wide.

  Next, a negative electrode forming composition containing natural graphite as a negative electrode active material was prepared. This negative electrode forming composition was applied to one surface of an aluminum foil as a negative electrode current collector and dried to prepare a negative electrode active material layer. Thereafter, a negative electrode current collector in which the negative electrode active material layer was formed on one surface was punched out to obtain a flat rectangular negative electrode having a length of 50 mm and a width of 121 mm.

  Then, a heat-resistant microporous film was punched out to obtain a planar rectangular shape of 52 mm long × 124 mm wide.

Next, a laminate was obtained by laminating 10 positive electrode layers and 11 negative electrode layers alternately through a heat-resistant microporous film. Thereafter, a tab lead was joined to each electrode by ultrasonic welding. After storing the laminate in an exterior material made of aluminum laminate foil, the exterior material was heat sealed to obtain a laminate element. A surface pressure of 1 kgf / cm ² was applied to the obtained laminate element, and it was confirmed by resistance measurement that there was no short circuit.

Next, after drying a laminated body element at 80 degreeC under pressure reduction for 24 hours, electrolyte solution was inject | poured under normal temperature normal pressure in the dry box (50 degreeC or less of dew points). As the electrolytic solution, a LiPF ₆ solution (1 mol / L) containing ethylene carbonate and dimethyl carbonate in a volume ratio of 3: 7 was used as a solvent. After the electrolyte solution was injected into the laminated body element, aging, vacuum impregnation, and temporary vacuum sealing were performed.

  Next, the laminate element after the temporary vacuum seal was stored at 20 ° C. for 24 hours, and then charged 0.2 CA, constant current constant voltage (CC-CV), 4.2 V, 12 Initial charging was performed under the condition of time cut-off.

Next, the laminated body element was degassed under reduced pressure and sealed, and then aged for one week in a charged state (SOC 100%). Subsequently, the multilayer element was subjected to initial discharge at 0.2 CA, 2nd charge / discharge at 0.2 CA, and a 5-cycle capacity confirmation test at 1 CA. Subsequently, AC resistance (ACR) and DC resistance (DCR) were measured under the following conditions for each cell.
ACR (SOC 50% 1kHz), DCR (SOC 50% 1CA, 2CA, 3CA x 10 seconds discharge)

Then, the multilayer element is charged until it becomes a fully charged state (SOC 100%) under the conditions of 0.2 CA, low current low voltage (CC-CV), 4.2 V, and 10 hours cutoff. did. Thereafter, a nail penetration test was conducted in which a nail having a thickness of 3φ mm and a tip angle of 60 ° was pierced at a piercing speed of 10 mm / sec. In Tables 1 and 2, “◯” and “x” are as follows.
○: Smoke and ignition did not occur in the laminate element after the test.
X: At least one of smoke and ignition occurred in the laminate element after the test.

Claims (13)

  A polymerizable compound having two or more radical polymerizable functional groups in one molecule is applied to the surface of a synthetic resin microporous film containing a synthetic resin and a crystal nucleating agent, and 100 parts by weight of the synthetic resin microporous film is added. A method for producing a heat-resistant microporous film, comprising attaching 5 to 80 parts by weight of the polymerizable compound and then irradiating the synthetic resin microporous film with active energy rays.   The method for producing a heat-resistant microporous film according to claim 1, wherein the synthetic resin is a propylene-based resin.   The method for producing a heat-resistant microporous film according to claim 1 or 2, wherein the synthetic resin is homopolypropylene having an isotactic pentad fraction of 90% or more.   A polymerizable compound is a polyfunctional acrylic monomer having two or more radical polymerizable functional groups in one molecule, a polyfunctional (meth) acrylate modified product having two or more (meth) acryloyl groups in one molecule, It is at least one selected from the group consisting of dendritic polymers having two or more (meth) acryloyl groups in one molecule and urethane (meth) acrylate oligomers having two or more (meth) acryloyl groups in one molecule. The manufacturing method of the heat resistant microporous film of any one of Claims 1-3 characterized by the above-mentioned.   The heat-resistant fine powder according to any one of claims 1 to 4, wherein a coating liquid in which a polymerizable compound is dispersed or dissolved in a solvent is applied to the surface of a synthetic resin microporous film. A method for producing a porous film.   6. The heat-resistant microporous film according to claim 5, wherein the solvent is removed by heating the synthetic resin microporous film coated with the coating liquid before irradiating the synthetic resin microporous film with active energy rays. A method for producing a film. 100 parts by weight of a synthetic resin microporous film containing a synthetic resin and a crystal nucleating agent;
Including 5 to 80 parts by weight of a coating layer formed on at least part of the surface of the synthetic resin microporous film,
The heat-resistant microporous film, wherein the coating layer contains a polymer of a polymerizable compound having two or more radically polymerizable functional groups in one molecule.   A polymerizable compound is a polyfunctional acrylic monomer having two or more radical polymerizable functional groups in one molecule, a polyfunctional (meth) acrylate modified product having two or more (meth) acryloyl groups in one molecule, It is at least one selected from the group consisting of dendritic polymers having two or more (meth) acryloyl groups in one molecule and urethane (meth) acrylate oligomers having two or more (meth) acryloyl groups in one molecule. The heat-resistant microporous film according to claim 7.   The heat-resistant microporous film according to claim 7 or 8, wherein the air permeability is 50 to 600 sec / 100 mL.   The heat-resistant microporous film according to any one of claims 7 to 9, wherein the gel fraction is 5% or more.   The heat resistance according to any one of claims 7 to 10, wherein a maximum heat shrinkage rate when heated from 25 ° C to 180 ° C at a heating rate of 5 ° C / min is 25% or less. Microporous film.   A separator for a nonaqueous electrolyte secondary battery comprising the heat-resistant microporous film according to any one of claims 7 to 11.   A nonaqueous electrolyte secondary battery comprising the separator for a nonaqueous electrolyte secondary battery according to claim 12.