JP2017132925A - Heat-resistant synthetic resin microporous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-resistant synthetic resin microporous film excellent in both heat resistance and melt-down resistance.SOLUTION: A heat-resistant synthetic resin microporous film has a film melting temperature in TMA measurement of 180°C or higher and a tensile strength at break of 40 MPa or more, preferably, has the maximum heat shrinkage ratio in TMA measurement of 20% or less and accordingly is excellent in heat resistance and melt down resistance and is suitably used as a separator for a nonaqueous electrolyte solution secondary battery.SELECTED DRAWING: None

Description

  The present invention relates to a heat resistant synthetic resin microporous film.

  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 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 synthetic resin microporous film processed by electron beam irradiation and having a thermomechanical analysis (TMA) value at 100 ° C. of 0% to −1% as a separator for a lithium ion secondary battery. ing.

JP 2003-22793 A

  However, the heat resistance of the synthetic resin microporous film is insufficient only by the treatment by electron beam irradiation, and when the inside of the battery becomes high temperature, the synthetic resin microporous film melts by heat and penetrates into the electrode, Short circuit between the positive electrode and the negative electrode cannot be prevented, and the safety of the lithium ion secondary battery may be lowered. Therefore, there is a need for a separator that is excellent in heat resistance and that is not easily melted even at an abnormally high temperature and has excellent melt-down resistance.

  Then, this invention provides the heat resistant synthetic resin microporous film excellent in heat resistance and meltdown resistance.

The heat-resistant synthetic resin microporous film of the present invention is
The film fusing temperature in TMA measurement is 180 ° C. or higher, and the tensile strength at break is 40 MPa or higher.

  ADVANTAGE OF THE INVENTION According to this invention, the heat resistant synthetic resin microporous film excellent in heat resistance and meltdown resistance can be provided.

  The heat-resistant synthetic resin microporous film of the present invention is characterized in that the film fusing temperature in TMA measurement is 180 ° C. or more and the tensile strength at break is 40 MPa or more.

  In the heat-resistant synthetic resin microporous film, the film fusing temperature in TMA measurement is 180 ° C. or higher, preferably 190 ° C. or higher, more preferably 200 ° C. or higher, particularly preferably 200 to 240 ° C., and 220 to 240 ° C. Most preferred. When the film fusing temperature is within the above range, the shape stability at high temperature is improved, and the film does not melt even under abnormal heat generation in the battery, and a heat-resistant synthetic resin microporous film that suppresses short circuit between the electrodes is obtained. be able to. In the present invention, the film fusing temperature in the TMA measurement may be such that either the MD direction or the TD direction is within the above range, and both the MD direction and the TD direction are preferably within the above range.

In the heat resistant synthetic resin microporous film, the film fusing temperature in the TMA measurement is measured as follows. First, a flat rectangular test piece (width 3 mm × length 30 mm) is obtained by cutting the heat-resistant synthetic resin microporous film. The both ends of the length direction of a test piece are gripped with a gripper, and attached to a TMA measuring apparatus (for example, 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. And each temperature which heats a test piece from 25 degreeC to 250 degreeC with the temperature increase rate of 5 degree-C / min in the state which added the tension | tensile_strength of 19.6mN (2gf) to the length direction to the test piece. The distance L (mm) between the gripping tools is measured and the heat shrinkage rate is calculated based on the following formula.
Thermal contraction rate (%) = 100 × (10−L) / 10

  When the test piece contracts as the temperature rises, the thermal contraction rate increases. However, when the test piece is heated above a certain temperature, the test piece starts to soften and expands due to tension. That is, the thermal contraction rate decreases and eventually blows and the TMA measurement ends. When the thermal contraction rate exceeds 0% at the end of the TMA measurement, the temperature at the end of the TMA measurement is set as the film fusing temperature. On the other hand, when the heat shrinkage rate is 0% or less at the time when the TMA measurement is completed, the temperature at the time when the heat shrinkage rate becomes 0% is set as the film fusing temperature.

  The tensile break strength of the heat-resistant synthetic resin microporous film is 40 MPa or more, and if the tensile break strength of the heat-resistant synthetic resin microporous film is within the above range, the heat-resistant synthetic resin microporous film is damaged by dendrites or foreign substances. It is possible to suppress the short circuit between the electrodes effectively. In addition, the tensile fracture strength of a heat resistant synthetic resin microporous film is a value calculated based on an SS curve measured according to JIS K 7127.

  The maximum heat shrinkage in the TMA measurement of the heat resistant synthetic resin microporous film is preferably 20% or less.

In addition, the measurement of the maximum heat shrinkage rate in TMA measurement of a heat resistant synthetic resin microporous film can be performed as follows. First, a flat rectangular test piece (width 3 mm × length 30 mm) is obtained by cutting the heat-resistant synthetic resin microporous film. The both ends of the length direction of a test piece are gripped with a gripper, and attached to a TMA measuring apparatus (for example, 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 in air from 25 ° C. to 250 ° C. at a heating rate of 5 ° C./min with a tension of 19.6 mN (2 gf) in the length direction. The distance L (mm) between the grippers is measured for each interval, the heat shrinkage rate is calculated based on the following formula, and the maximum value is set as the maximum heat shrinkage rate.
Thermal contraction rate (%) = 100 × (10−L) / 10

  Although the air permeability of a heat resistant synthetic resin microporous film is not specifically limited, 50-600 sec / 100 mL is preferable and 100-300 sec / 100 mL is more preferable.

  In addition, the air permeability of the heat-resistant synthetic resin microporous film should be measured at any 10 locations in an atmosphere of a temperature of 23 ° C. and a relative humidity of 65% in accordance with JIS P8117, and the arithmetic mean value thereof should be calculated. The value obtained by

  The heat-resistant synthetic resin microporous film has a synthetic resin microporous film and a coating layer formed on at least a part of the surface of the synthetic resin microporous film and containing a polymer of a polymerizable compound. Is preferred.

(Synthetic resin microporous film)
The synthetic resin microporous film can be used without particular limitation as long as it is a microporous film used as a separator in a conventional secondary battery such as a lithium ion secondary battery. As the synthetic resin microporous film, an olefin resin microporous film is preferable.

  The olefin resin microporous film preferably contains an olefin resin. As the olefin resin, ethylene resin and propylene resin are preferable, and ethylene resin is more preferable. In addition, an olefin resin may be used independently or 2 or more types may be used together.

  Examples of the propylene-based resin include homopolypropylene and copolymers of propylene and other olefins. When a synthetic resin microporous film is produced by the stretching method, homopolypropylene is preferable. Propylene-type resin may be used independently, or 2 or more types may be used together. The copolymer of propylene and another olefin may be a block copolymer or a random copolymer. The content of the propylene component in the propylene-based resin is preferably 50% by mass or more, and more preferably 80% by mass or more.

  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.

  Examples of the ethylene-based resin include ultra-low density polyethylene, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high density polyethylene, and an ethylene-propylene copolymer. Further, the ethylene-based resin microporous film may contain other olefin-based resin as long as it contains an ethylene-based resin. The content of the ethylene component in the ethylene-based resin is preferably more than 50% by mass, more preferably 80% by mass or more. The ethylene-based resin preferably contains ultra high molecular weight polyethylene. The ultrahigh molecular weight polyethylene may be a homopolymer of ethylene or a copolymer of ethylene and an α-olefin other than ethylene. In addition, as an alpha olefin, propylene, 1-butene, 1-pentene, 1-octene etc. are mentioned, for example. The weight average molecular weight of the ultrahigh molecular weight polyethylene is preferably 700,000 or more, more preferably 700,000 to 15 million.

  The weight average molecular weight of the olefin resin is preferably 30,000 to 500,000, and more preferably 50,000 to 480,000. The weight average molecular weight of the propylene-based resin is preferably 250,000 to 500,000, and more preferably 280,000 to 480,000. The weight average molecular weight of the ethylene-based resin is preferably 30,000 to 450,000, and more preferably 50,000 to 400,000. As the ethylene-based resin, ultrahigh molecular weight polyethylene having a weight average molecular weight of 300,000 to 7,000,000, more preferably 400,000 to 3,000,000 can be used. According to the olefin resin having a weight average molecular weight within the above range, it is possible to provide a heat-resistant synthetic 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 5.0 to 30, and more preferably 7.5 to 25. The molecular weight distribution of the propylene-based resin is preferably 7.5 to 12, and more preferably 8 to 11. The molecular weight distribution of the ethylene-based resin is preferably 5.0 to 30, and more preferably 8.0 to 27. According to the olefin resin having a molecular weight distribution within the above range, a heat-resistant synthetic resin microporous film having a high porosity can be provided.

  Here, the weight average molecular weight and number average molecular weight of the olefin resin are polystyrene-converted values measured by a GPC (gel permeation chromatography) method. Specifically, 6 to 7 mg of an olefin resin is sampled, the collected olefin resin is supplied to a test tube, and 0.05% by mass of BHT (dibutylhydroxytoluene) is contained in the test tube. 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
TSKguardcolumn-HHR (30) HT x 1
Mobile phase: o-DCB 1.0 mL / min
Sample concentration: 1 mg / mL
Detector: Bryce refractometer
Reference material: Polystyrene (Molecular weight: 500-8420000, manufactured by TOSOH)
Elution conditions: 145 ° C
SEC temperature: 145 ° C

  130-170 degreeC is preferable and, as for melting | fusing point of olefin resin, 133-165 degreeC is more preferable. 160-170 degreeC is preferable and, as for melting | fusing point of propylene-type resin, 160-165 degreeC is more preferable. The melting point of the ethylene resin is preferably 130 to 140 ° C, more preferably 133 to 139 ° C. According to the olefin resin having a melting point within the above range, an olefin resin microporous film excellent in meltdown resistance can be provided.

  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 synthetic resin microporous film includes micropores. It is preferable that the micropore part penetrates in the film thickness direction, and this can impart excellent air permeability to the heat resistant synthetic resin microporous film. Such a heat-resistant synthetic resin microporous film can transmit ions such as lithium ions in the thickness direction.

  The air permeability of the synthetic resin microporous film is preferably 50 to 600 sec / 100 mL, and more preferably 100 to 300 sec / 100 mL. According to the synthetic resin microporous film having an air permeability within the above range, a heat-resistant synthetic resin microporous film having excellent ion permeability can be provided.

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

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

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

  The method for producing the synthetic resin microporous film is not particularly limited and may be either a dry method or a wet method, but a wet method is preferable because of excellent heat resistance.

As a method for producing a synthetic resin microporous film by a dry method, specifically,
(1) A step of obtaining a synthetic resin film by extruding a synthetic resin, a step of generating and growing a lamellar crystal in the synthetic resin film, and a micropore by stretching the synthetic resin film and separating the lamellar crystals And (2) a step of obtaining a synthetic resin film by extruding a synthetic resin composition containing a synthetic resin and a filler; and And a method of obtaining a synthetic resin microporous film in which micropores are formed by uniaxially stretching or biaxially stretching a synthetic resin film to peel off the interface between the synthetic resin and the filler.

As a method for producing a synthetic resin microporous film by a wet method, specifically,
(1) After adding a film-forming solvent to the synthetic resin, the synthetic resin is melt-kneaded using a known kneading apparatus such as an extruder to produce a synthetic resin solution, and the synthetic resin solution is formed into a film and cooled. A film forming process for forming a gel-like film, and a washing process for producing a synthetic resin microporous film by removing the solvent for film formation in the gel-like film to form a microporous portion and then drying the film. Is mentioned.

  You may have the extending | stretching process of extending | stretching the gel-like film manufactured at the film formation process between the film formation process and the washing | cleaning process. By performing the stretching step, the mechanical strength of the resulting heat-resistant synthetic resin microporous film is improved, and micropores can be sufficiently formed inside the film, and the heat-resistant synthetic resin is excellent in ion permeability. A microporous film can be obtained. The stretching may be uniaxial stretching or biaxial stretching. However, the film strength is not anisotropic and a heat-resistant synthetic resin microporous film having excellent ion permeability can be obtained. Biaxial stretching is preferred. The biaxial stretching may be simultaneous biaxial stretching, sequential biaxial stretching or multistage stretching, but simultaneous biaxial stretching is preferred.

  The film forming solvent is not particularly limited, and examples thereof include aliphatic or cyclic hydrocarbons such as paraffin oil such as nonane, decane, decalin, and liquid paraffin, and phthalic acid esters such as dibutyl phthalate and dioctyl phthalate.

  In the film forming step, the film is preferably cooled at a cooling rate of 50 ° C./min or more until at least the gelation temperature. By cooling the film in this way, it is possible to form a structure in which the synthetic resin and the film-forming solvent are microscopically separated. The film is preferably cooled to 25 ° C. or lower.

  In the washing step, the solvent for film formation in the gel-like film is removed using a washing solvent to form micropores inside the film. In the gel film, since the synthetic resin is phase-separated from the film-forming solvent, micropores can be formed inside the film by removing the cleaning solvent. Examples of the washing solvent include saturated hydrocarbons such as pentane and hexane, and methylene chloride.

  The method for drying the gel-like film in which the micropores are formed is not particularly limited, and examples thereof include a method for heating and drying the film and a method for blowing a drying air onto the film.

  The obtained synthetic resin microporous film may be stretched in at least a uniaxial direction within a range not impairing the effects of the present invention. The synthetic resin microporous film may be stretched using a known stretching method such as a tenter stretching method while heating the synthetic resin microporous film.

(Coating layer)
The heat-resistant synthetic resin microporous film preferably has a film layer containing a polymer of a polymerizable compound formed on at least a part of the surface of the synthetic resin microporous film.

  In the heat-resistant synthetic resin microporous film, a coating layer containing a polymer of a polymerizable compound having two or more radically polymerizable functional groups in one molecule is formed on at least a part of the surface of the synthetic resin microporous film. More preferably.

  By forming a coating layer on at least a part of the surface of the synthetic resin microporous film, a heat-resistant synthetic resin microporous film having further excellent heat resistance and meltdown resistance and excellent mechanical strength can be formed. .

  Furthermore, a coating layer can be formed on the wall surface of the microporous part (inside the synthetic resin microporous film) through the microporous part of the synthetic resin microporous film, and the heat resistant synthetic resin microporous film is generally excellent. Heat resistance and meltdown resistance.

  The coating layer contains a polymer of a polymerizable compound. The coating layer containing such a polymer has high hardness and moderate elasticity and elongation. Therefore, a heat-resistant synthetic resin microporous film excellent in both heat resistance and melt-down resistance can be provided by using a coating layer containing the polymer.

  The coating layer may be formed on at least a part of the surface of the synthetic resin microporous film, but is preferably formed on the entire surface of the synthetic resin microporous film, and the surface of the synthetic resin microporous film, and It is more preferable to form also on the wall surface of the micropore part which continues from the surface of a synthetic resin microporous film.

  Further, by using a polymerizable compound, a coating layer can be formed on the surface of the synthetic resin microporous film so as not to block the micropores of the synthetic resin microporous film. Thereby, it is possible to provide a heat-resistant synthetic resin microporous film in which excellent air permeability and ion permeability are ensured.

  The polymerizable compound preferably 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, and urethane (meth) acrylate oligomer having two or more (meth) acryloyl groups 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 more preferable.

As a polyfunctional acrylic monomer,
Bifunctional polyfunctional acrylic monomers such as 1,9-nonanediol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol 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 polyfunctional acrylic monomer such as acrylate can be exemplified.

  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 such as a poly (1,2-butadiene) oligomer and a poly (1,3-butadiene) oligomer.

  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.

  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.

  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.

  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 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.

  In the present invention, among the polymerizable compounds described above, a polyfunctional acrylic monomer is preferable, and trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol. Hexa (meth) acrylate and ditrimethylolpropane tetra (meth) acrylate are preferred. According to these, excellent heat resistance and meltdown resistance can be imparted to the heat resistant synthetic resin microporous film.

  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 mass or more, more preferably 80% by mass or more, and particularly preferably 100% by mass. preferable. By using a polymerizable compound containing 30% by mass or more of a polyfunctional acrylic monomer, the resulting heat resistant synthetic resin microporous film has excellent heat resistance and meltdown resistance without reducing air permeability. Can be granted.

  In the present invention, as the polymerizable compound, only one kind of the above-described polymerizable compounds may be used, or two or more kinds of polymerizable compounds may be used in combination.

  The coating layer preferably contains a polymer of the above-described polymerizable compound. This polymer is preferably a polymer obtained by polymerizing a polymerizable compound by irradiation with active energy rays. That is, the polymer is preferably a polymer of a polymerizable compound by irradiation with active energy rays. The coating layer containing such a polymer has a high hardness, thereby reducing the heat shrinkage of the heat-resistant synthetic resin microporous film at a high temperature and improving the heat resistance.

  The active energy ray is not particularly limited, and examples thereof include an electron beam, plasma, ultraviolet rays, α rays, β rays, and γ rays. Of these, electron beams and ultraviolet rays are preferable, and electron beams are more preferable.

  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. By using a coating layer containing such a polymer, as described above, heat shrinkage at high temperatures is reduced, heat resistance is reduced, and heat resistance synthetic resin microporous material having excellent meltdown resistance A film can be provided. The chemical bond is not particularly limited, and examples thereof include a covalent bond, an ionic bond, and an intermolecular bond.

  The content of the coating layer in the heat-resistant synthetic resin microporous film is preferably 5 to 80 parts by mass, more preferably 5 to 60 parts by mass, and 10 to 40 parts by mass with respect to 100 parts by mass of the synthetic resin microporous film. Is particularly preferred. By setting the content of the coating layer within the above range, the coating layer can be uniformly formed without blocking the micropores on the surface of the synthetic resin microporous film. Thereby, the heat resistant synthetic resin microporous film with improved heat resistance and meltdown resistance can be provided without reducing air permeability.

  The thickness of the coating layer is not particularly limited, but is preferably 1 to 100 nm, and more preferably 5 to 50 nm. By setting the thickness of the coating layer within the above range, the coating layer can be formed uniformly without blocking the micropores on the surface of the synthetic resin microporous film. Thereby, the heat resistant synthetic resin microporous film with improved heat resistance and meltdown resistance can be provided without reducing air permeability.

Even if the heat resistant synthetic resin microporous film does not contain inorganic particles, the heat resistance and meltdown resistance of the heat resistant synthetic resin microporous film can be improved. Therefore, it is preferable that the heat resistant synthetic resin microporous film does not contain inorganic particles. However, the heat-resistant synthetic resin microporous film may contain inorganic particles as necessary. Examples of the inorganic particles include inorganic particles generally used for heat resistant porous layers. Examples of the material constituting the inorganic particles include Al ₂ O ₃ , SiO ₂ , TiO ₂ , and MgO.

(Method for producing heat-resistant synthetic resin microporous film)
As a manufacturing method of a heat resistant synthetic resin microporous film, the method of manufacturing a heat resistant synthetic resin microporous film by forming a film layer in at least one part of the surface of a synthetic resin microporous film is mentioned, for example.

The manufacturing method of the heat-resistant synthetic resin microporous film is not particularly limited, but the following steps,
An application step of applying a polymerizable compound to at least a part of the surface of the synthetic resin microporous film;
An irradiation step of irradiating the synthetic resin microporous film coated with the polymerizable compound with active energy rays in an atmosphere having an oxygen concentration of 10 ppm or less,
It is preferable to have.
It is more preferable to have a heating process of heat-treating the synthetic resin microporous film irradiated with the active energy rays in an atmosphere having an oxygen concentration of 10 ppm or less after the irradiation process.

(Coating process)
First, an application step of applying a polymerizable compound to at least a part of the surface of the synthetic resin microporous film is performed.

  By applying the polymerizable compound to the surface of the synthetic resin microporous film, the polymerizable compound can be attached to the surface of the synthetic resin microporous film. At this time, the polymerizable compound may be directly applied to the surface of the synthetic resin microporous film. However, it is preferable to disperse or dissolve the polymerizable compound in a solvent to obtain a coating solution, and to apply this coating solution to the surface of the synthetic resin microporous film. By using the polymerizable compound as the coating liquid in this way, the polymerizable compound can be uniformly attached to the surface of the synthetic resin microporous film while reducing the blockage of the micropores. This makes it possible to produce a heat-resistant synthetic resin microporous film having a uniform coating layer and improved heat resistance and melt-down resistance without reducing air permeability.

  Furthermore, the coating liquid can smoothly flow on the wall surface of the microporous part in the synthetic resin microporous film, thereby not only the surface of the synthetic resin microporous film but also the open end of the microporous part continuous to this surface. A coating layer can also be formed on the wall surface of the part. Thereby, a membrane | film | coat layer can be firmly integrated with the surface of a synthetic resin microporous film.

  In addition, when the polymerizable compound is a polymerizable compound having a radical polymerizable functional group having two or more functional groups, the polymerizable compound is excellent in compatibility with the synthetic resin microporous film. The polymerizable compound can be applied without blocking the micropores. 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 heat-resistant synthetic resin microporous film having improved heat resistance and meltdown resistance without reducing air permeability.

  The solvent used in the coating solution is not particularly limited as long as the polymerizable compound can be dissolved or dispersed. For example, alcohols such as methanol, ethanol, propanol, isopropyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, and the like. Examples include ketones, ethers such as tetrahydrofuran and dioxane, ethyl acetate, and chloroform. 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.

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

  The method for applying the polymerizable compound to the surface of the synthetic resin microporous film is not particularly limited. For example, (1) a method of applying the polymerizable compound to the surface of the synthetic resin microporous film; 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 of heating the synthetic resin microporous film after coating on the surface of the synthetic resin microporous film and removing the solvent; and (4) preparing a coating solution by dissolving or dispersing the polymerizable compound in the solvent. A method of immersing the synthetic resin microporous film in the coating solution and applying the coating solution in the synthetic resin microporous film is followed by heating the synthetic resin microporous film to remove the solvent. Of these, the methods (3) and (4) are preferred. According to these methods, the polymerizable compound can be uniformly applied to the surface of the synthetic resin microporous film.

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

  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 above-mentioned, a polymeric compound can be made to adhere to a synthetic resin microporous film surface by apply | coating a polymeric compound or a coating liquid to the synthetic resin microporous film surface.

(Irradiation process)
Next, the irradiation process which irradiates an active energy ray to the said synthetic resin microporous film which apply | coated the polymeric compound is implemented. Thereby, the polymerizable compound is polymerized, and the coating layer containing the polymer of the polymerizable compound can be integrally formed on at least a part of the surface of the synthetic resin microporous film, preferably the entire surface.

  By irradiating the active energy ray, a part of the synthetic resin contained in the synthetic resin microporous film may be decomposed, and the meltdown resistance of the synthetic resin microporous film may be lowered. However, according to the coating layer containing the polymer of the polymerizable compound, as described above, the decrease in the meltdown resistance of the synthetic resin microporous film can be compensated for, thereby improving both the heat resistance and the meltdown resistance. It is possible to provide an excellent heat-resistant synthetic resin microporous film.

  When the synthetic resin microporous film contains an ethylene-based resin, irradiation with active energy rays causes the ethylene-based resin to crosslink and mechanical strength, heat resistance, and meltdown resistance of the entire synthetic resin microporous film. Therefore, the resulting heat-resistant synthetic resin microporous film has excellent mechanical strength, heat resistance and meltdown resistance.

  And even if the synthetic resin microporous film is given a cross-linked structure, and the inside of the battery becomes a high temperature and becomes higher than the melting point of the ethylene-based resin, the synthetic resin microporous film has a cross-linked structure. The film shape is maintained, and an electrical short circuit between the positive and negative electrodes is effectively prevented.

  Moreover, when the synthetic resin microporous film contains an ethylene resin, a part of the synthetic resin microporous film starts to melt, and the micropores are blocked at the initial stage of abnormal temperature rise in the battery. Therefore, the secondary battery excellent in safety can be constructed by exhibiting an excellent shutdown effect, preventing the passage of ions and stopping the discharge of the secondary battery to prevent the temperature rise in the battery.

  When the synthetic resin microporous film contains a propylene-based resin, the active energy ray irradiation dose for the synthetic resin microporous film is preferably 50 to 100 kGy, more preferably 40 to 180 kGy, and particularly preferably 80 to 120 kGy. Moreover, when a synthetic resin microporous film contains ethylene-type resin, 20-200 kGy is preferable, 40-150 kGy is more preferable, and 60-110 kGy is especially preferable. By setting the irradiation dose of the active energy ray within the above range, the polymerizable compound can be polymerized while reducing the deterioration of the synthetic resin in the synthetic resin microporous film, thereby improving the heat resistance and the meltdown resistance. A heat-resistant synthetic resin microporous film excellent in both can be provided.

  The active energy ray is not particularly limited, and examples thereof include an electron beam, plasma, ultraviolet rays, α rays, β rays, and γ rays. Of these, electron beams and ultraviolet rays are preferable, and electron beams are more preferable.

  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 not particularly limited, but is preferably 50 to 300 kV, and more preferably 100 to 250 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 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 using a plasma as the active energy rays, plasma energy density to a synthetic resin microporous film is not particularly limited, but is preferably 5~50J / cm ^2, more preferably ^{10~45J / cm 2, 20~45J / cm} 2 Is particularly preferred.

  In the irradiation step, it is preferable to irradiate an active energy ray to the synthetic resin microporous film coated with the polymerizable compound in an atmosphere having an oxygen concentration of 10 ppm or less. The oxygen concentration in the atmosphere in the irradiation step is preferably 10 ppm or less, more preferably 8 to 0 ppm, and particularly preferably 5 to 0 ppm. By carrying out the irradiation step in an atmosphere having such an oxygen concentration, the oxidation deterioration of the synthetic resin contained in the synthetic resin microporous film can be reduced in the irradiation step, and the crosslinking density of the coating layer can be reduced. Can be high. Thereby, the heat resistance and meltdown resistance of a heat resistant synthetic resin microporous film can be improved.

  The irradiation step is preferably performed in an inert gas atmosphere. Thereby, the oxygen concentration in the atmosphere in the irradiation process can be easily adjusted. The inert gas is not particularly limited, and examples thereof include nitrogen, helium, neon, argon, krypton, xenon, radon, and a mixed gas thereof.

(Heating process)
Next, the heating process which heat-processes the synthetic resin microporous film which irradiated the active energy ray is implemented. According to the heating step, the polymerization of the polymerizable compound can be promoted based on the residual radical remaining in the irradiation step described above, and the remaining radical can be deactivated also by the acceleration of the polymerization of the polymerizable compound. it can. Thereby, the heat resistance and meltdown resistance of the heat resistant synthetic resin microporous film can be improved.

  In the heating step, the synthetic resin microporous film irradiated with active energy rays is preferably subjected to heat treatment at 90 to 150 ° C, more preferably 110 to 150 ° C, and particularly preferably 115 to 150 ° C. By setting the heat treatment temperature of the synthetic resin microporous film within the above range, the polymerization of the polymerizable compound based on the residual radical remaining in the irradiation step is promoted, and the synthetic resin in the synthetic resin microporous film is deteriorated. Remaining radicals can also be deactivated by promoting the polymerization of the polymerizable compound while reducing the above.

  In the heating step, the heat treatment time of the synthetic resin microporous film irradiated with active energy rays is preferably 2 minutes to 3 hours, and more preferably 20 minutes to 3 hours. By setting the heat treatment time of the synthetic resin microporous film within the above range, the polymerization of the polymerizable compound based on the residual radical remaining in the irradiation step is promoted, and the synthetic resin in the synthetic resin microporous film is deteriorated. Remaining radicals can also be deactivated by promoting the polymerization of the polymerizable compound while reducing the above.

  In the heating step, the oxygen concentration is not particularly limited, but it is preferable to heat-treat the synthetic resin microporous film irradiated with active energy rays in an atmosphere having an oxygen concentration of 10 ppm or less. Although the oxygen concentration in the atmosphere in a heating process is not specifically limited, 10 ppm or less is preferable, 8-0 ppm is more preferable, 5-0 ppm is especially preferable. By carrying out the heating step in such an oxygen concentration atmosphere, the oxidation degradation of the synthetic resin contained in the synthetic resin microporous film can be reduced in the heating step, and the crosslinking density of the coating layer can be reduced. Can be high. Thereby, the heat resistance and meltdown resistance of a heat resistant synthetic resin microporous film can be improved.

  The heating step is preferably performed in an inert gas atmosphere. Thereby, the oxygen concentration in the atmosphere in the heating process can be easily adjusted. The inert gas is not particularly limited, and examples thereof include nitrogen, helium, neon, argon, krypton, xenon, radon, and a mixed gas thereof.

  In the method for producing a heat-resistant synthetic resin microporous film described above, in the irradiation step, the polymerizable compound was polymerized by irradiation with active energy rays, but there is no particular limitation as long as the polymerizable compound can be polymerized. The polymerizable compound may be polymerized by a method other than irradiation with energy rays, for example, heating.

(Second manufacturing method of heat-resistant synthetic resin microporous film)
Another method for producing a heat-resistant synthetic resin microporous film is a method for producing a heat-resistant synthetic resin microporous film without forming a coating layer on the synthetic resin microporous film. In particular,
The second production method of the heat-resistant synthetic resin microporous film of the present invention includes the following steps:
An irradiation step of irradiating the synthetic resin microporous film with active energy rays;
A heating step of heat-treating the synthetic resin microporous film irradiated with the active energy ray;
It is characterized by having.

(Irradiation process)
In the method of the present invention, an irradiation step of irradiating the synthetic resin microporous film with active energy rays is performed. Thereby, especially when the synthetic resin microporous film contains an ethylene-based resin, the crosslink density of the synthetic resin microporous film increases, thereby improving the heat resistance and meltdown resistance of the heat resistant synthetic resin microporous film. be able to.

  When the synthetic resin microporous film contains an ethylene-based resin, the irradiation dose of active energy rays for the synthetic resin microporous film is preferably 30 to 200 kGy, more preferably 50 to 150 kGy, and still more preferably 90 to 120 kGy. By setting the irradiation dose of active energy rays within the above range, a heat-resistant synthetic resin microporous film excellent in both heat resistance and meltdown resistance can be provided.

  The active energy ray is not particularly limited, and examples thereof include an electron beam, plasma, ultraviolet rays, α rays, β rays, and γ rays. Of these, electron beams and ultraviolet rays are preferable, and electron beams are more preferable.

  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 not particularly limited, but is preferably 50 to 300 kV, and more preferably 100 to 250 kV. By setting the acceleration voltage of the electron beam within the above range, a heat-resistant synthetic resin microporous film excellent in both heat resistance and meltdown resistance can be provided.

  In the irradiation step, the oxygen concentration is not particularly limited, but it is preferable to irradiate the synthetic resin microporous film with active energy rays in an atmosphere of 10 ppm or less. The oxygen concentration in the atmosphere in the irradiation step is preferably 10 ppm or less, more preferably 8 to 0 ppm, and particularly preferably 5 to 0 ppm. By performing the irradiation step in an atmosphere having such an oxygen concentration, oxidative degradation of the synthetic resin contained in the synthetic resin microporous film can be reduced in the irradiation step. Thereby, the heat resistance and meltdown resistance of a heat resistant synthetic resin microporous film can be improved.

  The irradiation step is preferably performed in an inert gas atmosphere. Thereby, the oxygen concentration in the atmosphere in the irradiation process can be easily adjusted. The inert gas is not particularly limited, and examples thereof include nitrogen, helium, neon, argon, krypton, xenon, radon, and a mixed gas thereof.

(Heating process)
Next, in the method of the present invention, a heating step of heat-treating the synthetic resin microporous film irradiated with active energy rays is performed. According to the heating step, residual radicals remaining in the irradiation step described above can be deactivated. Thereby, the heat resistance and meltdown resistance of the heat resistant synthetic resin microporous film can be improved.

  In the heating step, the synthetic resin microporous film irradiated with active energy rays is preferably heat-treated at 90 to 150 ° C, more preferably 110 to 150 ° C, and particularly preferably 115 to 125 ° C. By setting the heat treatment temperature of the synthetic resin microporous film within the above range, the remaining radicals can be deactivated while reducing the deterioration of the synthetic resin in the synthetic resin microporous film.

  In the heating step, the heat treatment time of the synthetic resin microporous film irradiated with active energy rays is preferably 2 minutes to 3 hours, and more preferably 5 minutes to 15 minutes. By setting the heat treatment time of the synthetic resin microporous film within the above range, the remaining radicals can be deactivated.

  In the heating step, the oxygen concentration is not particularly limited, but it is preferable to heat-treat the synthetic resin microporous film irradiated with active energy rays in an atmosphere of 200 ppm or less. The oxygen concentration in the atmosphere in the heating step is preferably 200 ppm or less, more preferably 150 to 0 ppm, and particularly preferably 100 to 0 ppm. By carrying out the heating step in such an oxygen concentration atmosphere, it is possible to reduce the oxidative deterioration of the synthetic resin contained in the synthetic resin microporous film in the heating step. Thereby, the heat resistance and meltdown resistance of a heat resistant synthetic resin microporous film can be improved.

  The heating step is preferably performed in an inert gas atmosphere. Thereby, the oxygen concentration in the atmosphere in the heating process can be easily adjusted. The inert gas is not particularly limited, and examples thereof include nitrogen, helium, neon, argon, krypton, xenon, radon, and a mixed gas thereof.

  The heat resistant synthetic resin microporous film is suitably used as a separator for a non-aqueous electrolyte secondary battery. Examples of the non-aqueous electrolyte secondary battery include a lithium ion secondary battery. Since the heat-resistant synthetic resin microporous film is excellent in heat resistance and meltdown resistance, by using such a heat-resistant synthetic resin microporous film, the inside of the battery is, for example, 100 to 150 ° C., particularly 130 to Even in the case of a high temperature of 150 ° C., an electrical short circuit between the electrodes due to shrinkage and melting of the heat-resistant synthetic resin microporous film can be reduced.

  The non-aqueous electrolyte secondary battery is not particularly limited as long as it includes the heat-resistant synthetic resin microporous film as a separator, and includes a positive electrode, a negative electrode, a separator including the heat-resistant synthetic resin microporous film, and non-aqueous electrolysis. Contains liquid. The heat-resistant synthetic resin microporous film is disposed between the positive electrode and the negative electrode, thereby preventing an electrical short circuit between the electrodes. In addition, the nonaqueous electrolytic solution is filled at least in the micropores of the heat-resistant synthetic resin 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 .

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

[Examples 1 and 2]
(Extrusion process)
25 parts by mass of a polyethylene mixture composed of 30% by mass of ultra high molecular weight polyethylene (weight average molecular weight: 2.5 × 10 ⁶ ) and 70% by mass of high density polyethylene (weight average molecular weight: 2.8 × 10 ⁵ ) and 75 parts by mass of liquid paraffin The part is supplied to a twin screw extruder using a side feeder, melt kneaded at a resin temperature of 170 ° C., extruded from a die attached to the tip of the extruder into a film shape, and a cooling roll set at a surface temperature of 25 ° C. To obtain a cooled gel film.

(Stretching process)
The obtained gel-like film was simultaneously biaxially stretched at 116 ° C. in each of the MD direction and the TD direction at a stretch ratio of 5 times.

(Washing process)
The gel-like film was immersed and washed in methylene chloride maintained at 25 ° C., and liquid paraffin was removed to form micropores in the gel-like film. The washed gel film was air-dried at 25 ° C.

(Annealing process)
The gel-like film was heat set at 127 ° C. for 10 minutes to obtain a synthetic resin microporous film having a thickness of 20 μm.

(Coating process)
A coating solution containing ethyl acetate as a solvent and trimethylolpropane triacrylate (TMPTA, trade name “Light Acrylate TMP-A” manufactured by Kyoei Chemical Co., Ltd.) as a polymerizable compound was prepared. Next, after coating the coating liquid on the surface of the synthetic resin microporous film, the solvent was removed by heating the synthetic resin microporous film at 80 ° C. for 2 minutes. Thereby, the polymerizable compound was adhered to the entire surface of the synthetic resin microporous film.

(Irradiation process)
The synthetic resin microporous film was irradiated with an electron beam at an acceleration voltage of 110 kV and an irradiation dose shown in Table 1 in a nitrogen atmosphere (oxygen concentration: 10 ppm or less). Thus, the polymerizable compound was polymerized to integrally form a coating layer containing a polymer of the polymerizable compound on the entire surface of the synthetic resin microporous film.

(Heating process)
Subsequently, the synthetic resin microporous film was transported to a 120 ° C. constant temperature bath (oxygen concentration: 10 ppm or less) continuous with the irradiation step so that the heating time was 2 minutes. As a result, a heat-resistant synthetic resin microporous film in which a coating layer containing a polymer of a polymerizable compound is formed on the surface of the synthetic resin microporous film and the wall surface of the open end of the micropore continuous with the surface is obtained. It was.

[Example 3]
The synthetic resin microporous film produced through the extrusion process, stretching process, washing process and annealing process of Example 1 was subjected to an acceleration voltage of 110 kV and an irradiation dose shown in Table 1 under a nitrogen atmosphere (oxygen concentration: 10 ppm or less). The sample was irradiated with an electron beam (irradiation process). Subsequently, the synthetic resin microporous film was conveyed to a 120 ° C. constant temperature bath (oxygen concentration: 10 ppm or less) continuous with the irradiation step so that the heating time was 2 minutes (heating step). Thereby, a heat resistant synthetic resin microporous film was obtained.

[Comparative Example 1]
The synthetic resin microporous film produced through the extrusion process, stretching process, washing process and annealing process of Example 1 was used.

  About the heat-resistant synthetic resin microporous film obtained in each Example and the synthetic resin microporous film of Comparative Example 1 (hereinafter sometimes simply referred to as “microporous film”), the film fusing temperature in the TMA measurement, the MD direction, and The tensile breaking strength, the maximum heat shrinkage rate, and the air permeability in the TD direction were measured as described above, and the results are shown in Table 1.

  Regarding the heat-resistant synthetic resin microporous film obtained in each Example and the synthetic resin microporous film of Comparative Example 1, the shrinkage start temperature, the puncture strength, and the tensile breaking elongation in the MD direction and the TD direction are shown below. The measurement was performed as described above, and the results are shown in Table 1.

(Shrinkage start temperature)
By cutting the microporous film, a flat rectangular test piece (width 3 mm × length 30 mm) was obtained. At this time, the length direction (extrusion direction) of the microporous film and the length direction of the test piece were made parallel. Both ends in the length direction of the test piece were held by a gripper and attached to a TMA measuring apparatus (trade name “TMA-SS6000” manufactured by Seiko Instruments Inc.). At this time, the distance between the gripping tools was set to 10 mm, and the gripping tools were allowed to move along with the thermal contraction of the test piece. The test piece was heated in air from 25 ° C. to 250 ° C. at a heating rate of 5 ° C./min in a state where a tension of 19.6 mN (2 gf) was applied to the test piece in the length direction. The temperature at which shrinkage started was measured, and this temperature was taken as the shrinkage start temperature.

(Puncture strength)
The puncture strength of the microporous film was measured using a universal tensile tester (trade name “RTC-1310A” manufactured by Orientic). The measurement conditions were as follows: the hole was measured with a φ1 mm needle at a tensile speed of 50 mm / min.

(Tensile elongation at break)
The tensile breaking elongation of the microporous film was measured based on JIS K7127, and calculated based on the SS curve.

  The heat-resistant synthetic resin microporous film of the present invention is excellent in both heat resistance and meltdown resistance. Therefore, this heat-resistant synthetic resin microporous film is suitably used as a separator for non-aqueous electrolyte secondary batteries.

Claims (6)

  A heat-resistant synthetic resin microporous film having a film fusing temperature in TMA measurement of 180 ° C or higher and a tensile breaking strength of 40 MPa or higher.   2. The heat-resistant synthetic resin microporous film according to claim 1, wherein the maximum heat shrinkage rate in TMA measurement is 20% or less. A synthetic resin microporous film;
The heat-resistant synthesis according to claim 1 or 2, further comprising a coating layer formed on at least a part of the surface of the synthetic resin microporous film and containing a polymer of a polymerizable compound. Resin microporous film.   The heat-resistant synthetic resin microporous film according to claim 3, wherein the coating layer contains a polymer of a polymerizable compound having two or more radically polymerizable functional groups in one molecule.   The heat-resistant synthetic resin microporous film according to any one of claims 1 to 4, wherein the synthetic resin microporous film contains an olefin resin.   6. The heat resistant synthetic resin microporous film according to claim 5, wherein the olefin resin contains an ethylene resin.