JP2015221889A - Production method of heat-resistant synthetic resin microporous film, heat-resistant synthetic resin microporous film, separator for nonaqueous electrolyte secondary battery and nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a heat-resistant synthetic resin microporous film.SOLUTION: A production method of a heat-resistant synthetic resin microporous film includes an extrusion step of obtaining a synthetic resin film by extruding a synthetic resin, a cure step of curing the synthetic resin film, a first drawing step of conducting uniaxial drawing of the synthetic resin film in the extrusion direction at a surface temperature of -20 to 100°C and a draw ratio of 1.05-2.0, a second drawing step of conducting uniaxial drawing of the synthetic resin film in the extrusion direction at a surface temperature of 100-150°C, a draw ratio of 2.8-4.0 and a drawing rate of 5-400%/min, an annealing step of shrinking the synthetic resin oriented film at a shrinkage ratio of 5-25% while heating to obtain a synthetic resin microporous film and an irradiation step of applying a polymerizable compound having two or more radical polymerizable functional groups in one molecule to the synthetic resin microporous film and then irradiating with active energy rays.

Description

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

  Conventionally, lithium ion batteries have been used as batteries for portable electronic devices and automobiles. This lithium-on battery generally includes a positive electrode, a negative electrode, a separator, and an electrolytic solution. The positive electrode is formed by applying lithium cobalt oxide or lithium manganate to the surface of the aluminum foil. The negative electrode is formed by applying carbon to the surface of the copper foil. And the separator is arrange | positioned so that a positive electrode and a negative electrode may be partitioned off, and the electrical short circuit between electrodes is prevented.

  When the lithium ion secondary battery is charged, lithium ions are released from the positive electrode and move into the negative electrode. On the other hand, when the lithium ion secondary battery is discharged, lithium ions are released from the negative electrode and move to the positive electrode. Therefore, the separator is required to have excellent ion permeability of lithium ions.

  As the separator, a synthetic resin microporous film is used because of its excellent 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 secondary battery separator that is processed by electron beam irradiation and has a thermomechanical analysis (TMA) value at 100 ° C. of 0% to −1%. However, the heat resistance of the lithium secondary battery separator cannot be sufficiently improved only by treatment with electron beam irradiation. In addition, only by treatment with electron beam irradiation, the synthetic resin microporous film becomes brittle and mechanical strength such as puncture strength is lowered, and is easily broken by a slight impact.

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

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

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

JP 2003-22793 A Japanese Patent Laid-Open No. 3-193125

  Then, this invention provides the manufacturing method of the heat resistant synthetic resin microporous film which is excellent in ion permeability and heat resistance. Furthermore, the present invention relates to a heat-resistant synthetic resin microporous film excellent in ion permeability and heat resistance, a non-aqueous electrolyte secondary battery separator and a non-aqueous electrolyte secondary battery using the heat-resistant synthetic resin microporous film. I will provide a.

[Method for producing heat-resistant synthetic resin microporous film]
The method for producing the heat-resistant synthetic resin microporous film of the present invention is as follows:
An extrusion step of supplying a synthetic resin to an extruder, melt-kneading, and obtaining a synthetic resin film by extruding from a T-die attached to the tip of the extruder;
A curing process for curing the synthetic resin film obtained in the extrusion process at (Tm-30) to (Tm-5) ° C.
A first stretching step in which the synthetic resin film after the curing step is uniaxially stretched in the extrusion direction to a stretching ratio of 1.05 to 2.0 times at a surface temperature of -20 to 100 ° C;
By uniaxially stretching the synthetic resin film after the first stretching step in the extrusion direction at a surface temperature of 100 to 150 ° C. at a stretching ratio of 2.8 to 4.0 times and a stretching speed of 5 to 400% / min. A second stretching step to obtain a synthetic resin stretched film;
While the surface temperature of the synthetic resin stretched film after the second stretching step is (Tm-35) ° C. or higher and below the melting point of the synthetic resin, the shrinkage is 5 to 25% in the extrusion direction. An annealing step of obtaining a synthetic resin microporous film by shrinking;
After applying the polymerizable compound having two or more radical polymerizable functional groups in one molecule on the surface of the synthetic resin microporous film after the annealing step, the synthetic resin microporous film is irradiated with active energy rays. An irradiation process to perform,
(Tm is the melting point of the synthetic resin).

(Extrusion process)
In the method of the present invention, first, an extrusion process is performed in which a synthetic resin is supplied to an extruder, melted and kneaded, and extruded from a T die attached to the tip of the extruder to obtain a synthetic resin film.

  As the synthetic resin, an olefin resin is preferable. Among the synthetic resin microporous films, the olefin-based resin microporous film is likely to melt and deform or heat shrink at high temperatures. On the other hand, according to the method of the present invention, excellent heat resistance can be imparted to the olefin resin microporous film. Therefore, the effect of this invention can be exhibited more by using an olefin resin as a synthetic resin.

  As the olefin resin, ethylene resin and propylene resin are preferable, and propylene resin is preferable.

  Examples of the propylene resin include a propylene homopolymer (homopolypropylene), a copolymer of propylene and another olefin, and the like, and a propylene homopolymer 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 propylene-based resin is preferably 250,000 to 500,000, and more preferably 280,000 to 480,000. According to the propylene-based resin having a weight average molecular weight within the above range, it is possible to provide a 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 propylene-based resin is preferably 7.5 to 12.0, and more preferably 8 to 11. According to the propylene-based resin having a molecular weight distribution within the above range, it is possible to provide a synthetic resin microporous film having a high surface opening ratio and excellent mechanical strength.

  Here, the weight average molecular weight and the number average molecular weight of the propylene-based resin are values converted by polystyrene using a GPC (gel permeation chromatography) method. Specifically, 6 to 7 mg of propylene-based resin is collected, and after the collected propylene-based resin is supplied to a test tube, the test tube contains 0.05% by weight of BHT (dibutylhydroxytoluene). A diluted solution is prepared by adding a DCB (orthodichlorobenzene) solution and diluting the propylene 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 propylene resin is dissolved in the o-DCB solution to obtain a measurement sample. Using this measurement sample, the weight average molecular weight and the number average molecular weight of the propylene-based resin can be measured by the GPC method.

The weight average molecular weight and number average molecular weight in the propylene-based resin can be measured, for example, with the following measuring apparatus and measurement conditions.
Product name “HLC-8121GPC / HT” manufactured by TOSOH
Measurement conditions Column: TSKgelGMHHR-H (20) HT x 3
TSK guard column-HHR (30) HT x 1
Mobile phase: o-DCB 1.0 mL / min
Sample concentration: 1 mg / mL
Detector: Bryce refractometer
Standard substance: Polystyrene (Molecular weight: 500-842000, manufactured by TOSOH)
Elution conditions: 145 ° C
SEC temperature: 145 ° C

  160-170 degreeC is preferable and, as for melting | fusing point of propylene-type resin, 163-170 degreeC is more preferable. According to the propylene-based resin having a melting point within the above range, it is possible to provide a synthetic resin microporous film that is excellent in film forming stability and suppressed in mechanical strength at high temperatures.

  The heat of fusion obtained by differential scanning calorimetry (DSC) in the propylene-based resin is preferably 85 mJ / mg or more, and more preferably 90 mJ / mg or more. According to the propylene resin having the heat of fusion within the above range, the orientation of the propylene resin can be improved, and uniform micropores can be formed in the synthetic resin microporous film.

  The melting point of the propylene-based resin and the heat of fusion obtained by DSC are values measured in the following manner. First, 10 mg of propylene-based resin is collected. Next, the propylene-based resin is heated from 0 ° C. to 250 ° C. at a heating rate of 10 ° C./min, and held at 250 ° C. for 3 minutes. Next, the propylene-based resin is cooled from 250 ° C. to 0 ° C. at a temperature decrease rate of 10 ° C./min and held at 0 ° C. for 3 minutes. Subsequently, the propylene-based resin is reheated from 0 ° C. to 250 ° C. at a heating rate of 10 ° C./min, the melting peak top temperature in this reheating step is taken as the melting point, and the total area of the melting peak is calculated to calculate the heat of fusion. And The DSC of the propylene-based resin can be performed using, for example, DSC220C manufactured by Seiko Instruments Inc.

  The temperature of the synthetic resin when melt-kneading the synthetic resin with an extruder is preferably (Tm + 20) to (Tm + 100) ° C., more preferably (Tm + 25) to (Tm + 80) ° C., and (Tm + 25) to (Tm + 60) ° C. Particularly preferred. By setting the temperature of the synthetic resin during melt kneading to (Tm + 20) ° C. or higher, a synthetic resin film having a uniform thickness can be obtained. In addition, by setting the temperature of the synthetic resin at the time of melt kneading to (Tm + 100) ° C. or less, the orientation of the synthetic resin can be improved and the generation of lamellae can be promoted.

  50-300 are preferable and, as for the draw ratio at the time of extruding a synthetic resin into a film form from an extruder, 70-230 are more preferable. By setting the draw ratio to 50 or more, the tension applied to the synthetic resin can be improved. This makes it possible to sufficiently orient the synthetic resin and promote the production of lamellae. Moreover, the film-forming stability of a synthetic resin film can be improved by making a draw ratio 300 or less. This makes it possible to obtain a synthetic resin film having a uniform thickness and width.

  The draw ratio is a value obtained by dividing the clearance of the lip of the T die by the thickness of the synthetic 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. In addition, the thickness of the synthetic resin film extruded from the T-die was measured by measuring the thickness of the synthetic resin film extruded from the T-die at 10 or more locations using a dial gauge (eg, Signal ABS Digimatic Indicator manufactured by Mitutoyo Corporation). , By calculating the arithmetic mean value.

  Furthermore, the film formation rate of the synthetic resin film is preferably 10 to 300 m / min, more preferably 15 to 250 m / min, and particularly preferably 15 to 200 m / min. The tension | tensile_strength added to a synthetic resin can be improved by making the film-forming speed | rate of a synthetic resin film into 10 m / min or more. This makes it possible to sufficiently align the synthetic resin molecules and promote the generation of lamellae. Moreover, the film-forming stability of a synthetic resin film can be improved by making the film-forming speed | rate of a synthetic resin film into 300 m / min or less. This makes it possible to obtain a synthetic resin film having a uniform thickness and width.

  And the synthetic resin which comprises the synthetic resin film crystallizes by cooling the synthetic resin film extruded from T-die until the surface temperature becomes (Tm-100) degrees C or less, and produces | generates a lamella. In the present invention, the synthetic resin is oriented by extruding the melt-kneaded synthetic resin to pre-orient the synthetic resin molecules constituting the synthetic resin film and then cooling the synthetic resin film. The part can promote the production of lamellae.

  The surface temperature of the cooled synthetic resin film is preferably (Tm-100) ° C. or less, more preferably (Tm-140) to (Tm-110) ° C., and (Tm-135) to (Tm-120) ° C. Particularly preferred. By cooling the surface temperature of the synthetic resin film to the above range, the synthetic resin can be crystallized to highly generate lamellae.

(Curing process)
Next, in the method of the present invention, the synthetic resin film obtained by the extrusion process described above is cured. This curing process is performed in order to grow the lamella formed in the synthetic resin film in the extrusion process. Thereby, it is possible to promote the formation of a laminated lamella structure in which crystallized portions (lamellar) and non-crystalline portions are alternately arranged in the extrusion direction of the synthetic resin film. A crack is generated not between the lamellas but between the lamellae, and a minute through hole (microhole part) can be formed starting from this crack.

  The curing process is performed by heating the synthetic resin film obtained by the extrusion process at (Tm-30) to (Tm-5) ° C.

  The curing temperature of the synthetic resin film is (Tm-30) to (Tm-5) ° C, preferably (Tm-25) to (Tm-10) ° C. By setting the curing temperature of the synthetic resin film to (Tm-30) ° C. or higher, crystallization of the synthetic resin film can be sufficiently promoted. Moreover, collapse of the lamellar structure due to melting of the synthetic resin can be reduced by setting the curing temperature of the synthetic resin film to (Tm-5) ° C. or lower.

  The curing temperature of the synthetic resin film is the surface temperature of the synthetic resin film. However, when the surface temperature of the synthetic resin film cannot be measured, for example, when the synthetic resin film is cured in a roll shape, the curing temperature of the synthetic resin film is the ambient temperature. For example, when curing is performed in a state where a synthetic resin film is wound in a roll shape inside a heating apparatus such as a hot stove, the temperature inside the heating apparatus is set as the curing temperature.

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

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

  When curing the synthetic resin film in a roll-up state, the curing time is preferably 1 hour or longer, and more preferably 15 hours or longer. By curing in this way, the entire roll of the synthetic resin film can be uniformly cured. Thereby, the lamella in a synthetic resin film can fully be grown. Moreover, from a viewpoint of reducing the thermal deterioration of a synthetic resin film, the curing time is preferably 35 hours or less, and more preferably 30 hours or less.

  In addition, what is necessary is just to unwind a synthetic resin film from the synthetic resin film roll after a curing process, and to implement the extending | stretching process and annealing process which are mentioned later, when it is made to cure in the state wound up by the synthetic resin film.

(First stretching process)
Next, in the method of the present invention, the first stretching step in which the synthetic resin film after the curing step is uniaxially stretched in the extrusion direction to a stretching ratio of 1.05 to 2.0 times at a surface temperature of -20 to 100 ° C. To implement. In the first stretching step, the lamella in the synthetic resin film is hardly melted, and by separating the lamellae by stretching, a fine crack is efficiently generated independently in the non-crystalline part between the lamellae, Starting from this crack, a large number of micropores are reliably formed.

  In the first stretching step, the surface temperature of the synthetic resin film is -20 to 100 ° C, preferably 0 to 80 ° C, and more preferably 10 to 40 ° C. According to the synthetic resin film having a surface temperature within the above range, breakage of the synthetic resin film at the time of stretching can be reduced, and cracks can be generated in the non-crystalline portion between lamellae.

  In the first stretching step, the stretching ratio of the synthetic resin film is 1.05 to 2.0 times, preferably 1.1 to 1.8 times, and more preferably 1.2 to 1.5 times. By setting the draw ratio to 1.05 times or more, micropores can be formed in the non-crystalline part between lamellae. Moreover, the synthetic resin film can be prevented from being broken by setting the draw ratio to 2.0 times or less.

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

  The stretching speed in the first stretching step of the synthetic resin film is preferably 20% / min or more, more preferably 20 to 3000% / min, and particularly preferably 20 to 2000% / min. By setting the stretching speed to 20% / min or more, the micropores can be formed uniformly in the non-crystalline part between lamellae. By setting the stretching speed to 3000% / min or less, breakage of the synthetic resin film due to stretching can be suppressed.

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

  The method for stretching the synthetic resin film in the first stretching step is not particularly limited as long as the synthetic resin film can be uniaxially stretched. For example, the synthetic resin film is a longitudinal uniaxial stretching device using rolls having different peripheral speeds. And a method of uniaxially stretching at a predetermined temperature using

(Second stretching step)
Subsequently, the synthetic resin film after the first stretching step is uniaxially stretched at a stretching ratio of 2.8 to 4.0 times at a stretching temperature of 5 to 400% / min at a surface temperature of 100 to 150 ° C. The 2nd extending process which obtains a synthetic resin stretched film is implemented. In the second stretching step, the synthetic resin film is uniaxially stretched only in the extrusion direction. By performing such a second stretching step, a large number of micropores formed in the synthetic resin film in the first stretching step can be grown.

  In the second stretching step, the surface temperature of the synthetic resin film is 100 to 150 ° C, but preferably 110 to 140 ° C. By setting the surface temperature of the synthetic resin film to 100 ° C. or higher, the micropores formed in the synthetic resin film in the first stretching step can be highly grown. Moreover, the obstruction | occlusion of the micropore part formed in the synthetic resin film in a 1st extending | stretching process can be reduced by making the surface temperature of a synthetic resin film into 150 degrees C or less.

  In the second stretching step, the stretch ratio of the synthetic resin film is 2.8 to 4.0 times, preferably 2.9 to 3.9 times, and more preferably 3.1 to 3.9 times. By setting the stretch ratio of the synthetic resin film to 2.8 times or more, the micropores formed in the synthetic resin film during the first stretching step can be grown. Moreover, the permeability | transmittance of lithium ion can be raised by making the draw ratio of a synthetic resin film 2.8 times or more, promoting the opening of a crystal | crystallization, and increasing the number of micropores. Thereby, the heat shrink of a synthetic resin microporous film can be reduced and heat resistance can be improved. Moreover, the obstruction | occlusion of the micropore part formed in the synthetic resin film in a 1st extending | stretching process can be suppressed by making the draw ratio of a synthetic resin film 4.0 times or less. Furthermore, by setting the draw ratio of the synthetic resin film to 4.0 times or less, it is possible to reduce the orientation of the fibrillated non-crystalline part more than necessary, and thereby the heat shrinkage of the synthetic resin microporous film. Can be reduced to improve heat resistance.

  In the second stretching step, the stretching speed of the synthetic resin film is 5 to 400% / min, preferably 5 to 300% / min, and more preferably 5 to 200% / min. By setting the stretching speed to 5% / min or more, the excessive growth of the micropores can be suppressed, and thereby the excessive increase in the porosity is reduced and the synthetic resin is excellent in mechanical strength. A microporous film can be provided. Moreover, a micropore part can be uniformly formed in a synthetic resin film by making a extending | stretching speed into 400% / min or less.

  The method of stretching the synthetic resin film in the second stretching step is not particularly limited as long as the synthetic resin film can be uniaxially stretched. For example, a vertical uniaxial stretching apparatus using rolls having different peripheral speeds is used for the synthetic resin film. And a method of uniaxially stretching at a predetermined temperature.

(Annealing process)
Next, in the method of the present invention, an annealing step is performed to obtain a synthetic resin microporous film by shrinking the synthetic resin stretched film in the extrusion direction while heating the synthetic resin stretched film after the second stretching step.

  This annealing step is performed in order to relieve the residual strain generated in the stretched synthetic resin film by stretching applied in the stretching step described above and to suppress thermal shrinkage of the resulting synthetic resin microporous film. In the method of the present invention, the annealing step is performed after the synthetic resin film is stretched at a relatively high stretching ratio in the second stretching step described above. Thereby, the heat shrink under high temperature is highly reduced, and the microporous resin film excellent in heat resistance can be provided.

  The surface temperature of the synthetic resin stretched film in the annealing step is (Tm−35) ° C. or higher and not higher than the melting point of the synthetic resin, but (Tm−25) to (Tm−1) ° C. is preferable. By setting the surface temperature of the stretched synthetic resin film to (Tm−35) ° C. or higher, the strain remaining in the stretched synthetic resin film can be sufficiently relaxed. This makes it possible to improve dimensional stability during heating of the synthetic resin microporous film. Moreover, blockage | closure of the micropore part formed at the extending process can be suppressed by making the surface temperature of a synthetic resin stretched film below into the temperature of melting | fusing point of a synthetic resin.

  The shrinkage ratio of the stretched synthetic resin film in the annealing step is 5 to 25%, preferably 8 to 22%. By setting the shrinkage ratio of the synthetic resin stretched film to 5% or more, the strain remaining in the stretched synthetic resin film is sufficiently relaxed without stretching the fibrillated amorphous part more than necessary. The heat resistance of the resulting heat resistant synthetic resin microporous film can be improved. Further, by setting the shrinkage rate of the synthetic resin stretched film to 25% or less, the synthetic resin stretched film can be annealed uniformly without suppressing the blockage of the micropores.

  The shrinkage ratio of the stretched synthetic resin film refers to the shrinkage length of the stretched synthetic resin film in the extrusion direction (stretching direction) during the annealing process, and the stretched synthetic resin film in the extrusion direction (stretching direction) after the second stretching process. A value obtained by dividing by the length of 100 and multiplying by 100.

  The synthetic resin microporous film after the annealing step has a large number of micropores penetrating in the film thickness direction. Even if a coating layer is formed on at least a part of the surface of such a synthetic resin microporous film, the micropores are not easily blocked by the coating layer, and the air permeability and ion permeability of the heat resistant synthetic resin microporous film are reduced. High reduction can be achieved.

(Irradiation process)
In the method of the present invention, the synthetic resin microporous film is coated with a polymerizable compound having two or more radical polymerizable functional groups in one molecule on the surface of the synthetic resin microporous film after the annealing step. An irradiation step of irradiating active energy rays is performed.

  The polymerizable compound only needs to have two or more radical polymerizable functional groups in one molecule. Examples of the radical polymerizable functional group include a functional group containing a radical polymerizable unsaturated bond capable of radical polymerization upon irradiation with active energy rays. Although it does not specifically limit as a radically polymerizable functional group, For example, a (meth) acryloyl group, a vinyl group etc. can be illustrated, and it is preferable that it is a (meth) acryloyl group.

  As a polymerizable compound, a polyfunctional acrylic monomer, a vinyl oligomer having a vinyl group, a polyfunctional (meth) acrylate modified product, a dendritic polymer having a bifunctional or higher (meth) acryloyl group, a bifunctional or higher functional Examples include urethane (meth) acrylate oligomers having (meth) acryloyl groups, and tricyclodecane dimethanol di (meth) acrylate. In addition, a polymeric compound may use only 1 type and may use 2 or more types together.

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

  The polyfunctional acrylic monomer only needs to have two or more radical polymerizable functional groups in one molecule, but it has three or more functional groups having three or more radical polymerizable functional groups in one molecule. A polyfunctional acrylic monomer is preferable, and a trifunctional to hexafunctional polyfunctional acrylic monomer is more 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 and glycerin di (meth) acrylate;
Trifunctional polyfunctional acrylic monomers such as trimethylolpropane tri (meth) acrylate and pentaerythritol tri (meth) acrylate;
Tetrafunctional polyfunctional acrylic monomers such as pentaerythritol tetra (meth) acrylate and ditrimethylolpropane tetra (meth) acrylate;
A polyfunctional acrylic monomer having 5 or more functional groups such as dipentaerythritol poly (meth) acrylate such as dipentaerythritol penta (meth) acrylate and dipentaerythritol hexa (meth) acrylate can be exemplified.

  The vinyl-based oligomer has two or more radically polymerizable functional groups in one molecule. 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 a bifunctional or higher functional (meth) acryloyl group means a spherical macromolecule obtained by radially assembling branch molecules having (meth) acryloyl groups.

  Examples of the dendritic polymer having a (meth) acryloyl group include a dendrimer having a bifunctional or higher functional (meth) acryloyl group and a hyperbranched polymer having a bifunctional or higher functional (meth) acryloyl group.

  A dendrimer having a bifunctional or higher functional (meth) acryloyl group means a spherical polymer obtained by integrating bifunctional or higher functional (meth) acrylates into branch molecules and accumulating (meth) acrylates in a spherical shape.

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

  A hyperbranched polymer having a bi- or higher functional (meth) acryloyl group is obtained by polymerizing 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 interior of a hyperbranched structure having an irregular branched structure.

  The urethane (meth) acrylate oligomer having a bifunctional or higher functional (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.

  As a urethane (meth) acrylate oligomer having a bifunctional or higher functional (meth) acryloyl group, a commercially available product can be used. 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 and a polyfunctional (meth) acrylate modified product are preferable, a polyfunctional acrylic monomer is more preferable, and trimethylolpropane tri (meth) acrylate. , Glyceryl tri (meth) acrylate, pentaerythritol tri (meth) acrylate, tris- (2-acryloxyethyl) isocyanurate, pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, dipentaerythritol hexa ( Particularly preferred are (meth) acrylates and dipentaerythritol polyacrylates. According to these, excellent heat resistance can be imparted to the heat-resistant synthetic resin microporous film without reducing the mechanical strength.

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

  The polymerizable compound may be any bifunctional or higher polymerizable compound having two or more radical polymerizable functional groups in one molecule, but has three or more radical polymerizable functional groups in one molecule. The trifunctional or higher functional polymerizable compound is preferable, and the polymerizable compound composed substantially only of the trifunctional or higher functional polymerizable compound is more preferable. By using a trifunctional or higher functional polymerizable compound, a heat resistant synthetic resin microporous film having improved heat resistance can be obtained.

  In addition, although a bifunctional polymerizable compound having two radical polymerizable functional groups in one molecule can be desired to improve heat resistance, from the viewpoint of further improving heat resistance, When using a polymerizable compound, it is preferably used in combination with a polymerizable compound having three or more functional groups.

  Combined use of a trifunctional or higher functional polymerizable compound having three or more radical polymerizable functional groups in one molecule and a bifunctional polymerizable compound having two radical polymerizable functional groups in one molecule. In this case, it is preferable to use 1 to 150 parts by weight of bifunctional polymerizable compound, more preferably 5 to 125 parts by weight, more preferably 20 to 110 parts per 100 parts by weight of the trifunctional or higher functional polymerizable compound. It is particularly preferable to use parts by weight, and most preferably 50 to 110 parts by weight.

  By applying a polymerizable compound having two or more radical polymerizable functional groups in one molecule to the surface of the synthetic resin microporous film, two or more radical polymerizable functional groups in one molecule are applied to the synthetic resin microporous film. A polymerizable compound having a group can be attached. At this time, a polymerizable compound having two or more radically polymerizable functional groups in one molecule may be directly applied to the surface of the synthetic resin microporous film. However, after a polymerizable compound having two or more radically polymerizable functional groups in one molecule is dispersed or dissolved in a solvent to obtain a coating solution, this coating solution is applied to the surface of the synthetic resin microporous film. It is preferable to work.

  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. Therefore, the coating layer laminated and integrated on at least one surface of the synthetic resin microporous film can be firmly integrated with the surface of the synthetic resin microporous film. Such a coating layer can impart excellent heat resistance to the heat resistant synthetic resin 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.

  The solvent used in the coating solution is not particularly limited as long as it can dissolve or disperse a polymerizable compound having two or more radically polymerizable functional groups in one molecule. For example, methanol, ethanol, propanol, Examples include alcohols such as isopropyl alcohol, ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, 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 battery, and is excellent in safety.

  The content of the polymerizable compound having two or more radically polymerizable functional groups in one molecule in the coating liquid is preferably 3 to 15% by weight, and more preferably 5 to 12% by weight. By making the content of the polymerizable compound having two or more radical polymerizable functional groups in one molecule within the above range, the coating layer can be made uniform without blocking the micropores on the surface of the synthetic resin microporous film. Therefore, a heat-resistant synthetic resin microporous film with improved heat resistance can be produced without reducing air permeability.

  The method for applying a polymerizable compound having two or more radical polymerizable functional groups in one molecule to the synthetic resin microporous film is not particularly limited. For example, (1) one molecule on the surface of the synthetic resin microporous film A method of applying a polymerizable compound having two or more radically polymerizable functional groups therein; (2) a synthetic resin microporous film in a polymerizable compound having two or more radically polymerizable functional groups in one molecule; A method of immersing and applying a polymerizable compound having two or more radical polymerizable functional groups in one molecule on the surface of the synthetic resin microporous film; (3) Two or more radical polymerizable functionals in one molecule A polymerizable compound having a group is dissolved or dispersed in a solvent to prepare a coating liquid. After the coating liquid is applied to the surface of the synthetic resin microporous film, the synthetic resin microporous film is heated to remove the solvent. A method of removing; and 4) A polymerizable compound having two or more radical polymerizable functional groups in one molecule is dissolved or dispersed in a solvent to prepare a coating solution, and a synthetic resin microporous film is immersed in the coating solution. Then, after the coating liquid is applied in the synthetic resin microporous film, the synthetic resin microporous film is heated to remove the solvent. Of these, the methods (3) and (4) are preferred. According to these methods, a polymerizable compound having two or more radical polymerizable functional groups in one molecule 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 reducing heat shrinkage and blockage of the micropores of the synthetic resin microporous film.

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

  As described above, by applying a polymerizable compound or coating liquid having two or more radical polymerizable functional groups in one molecule on the surface of the synthetic resin microporous film, the surface of the synthetic resin microporous film is in one molecule. A polymerizable compound having two or more radically polymerizable functional groups can be attached to the substrate.

  The amount of the polymerizable compound having two or more radical polymerizable functional groups in one molecule to the synthetic resin microporous film is preferably 1 to 80 parts by weight with respect to 100 parts by weight of the synthetic resin microporous film, 5 to 50 parts by weight is preferable, and 10 to 40 parts by weight is more preferable. By making the amount of the polymerizable compound having two or more radical polymerizable functional groups in one molecule within the above range, the coating layer can be made uniform without blocking the micropores on the surface of the synthetic resin microporous film. Can be formed. Thereby, it becomes possible to manufacture a heat-resistant synthetic resin microporous film having improved heat resistance without reducing air permeability.

  Next, in the method of the present invention, active energy rays are irradiated to a synthetic resin microporous film coated with a polymerizable compound having two or more radical polymerizable functional groups in one molecule. Thus, a film containing a polymer of a polymerizable compound having two or more radical polymerizable functional groups in one molecule by polymerizing a polymerizable compound having two or more radical polymerizable functional groups in one molecule The layer 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, A heat-resistant synthetic resin microporous film having reduced heat shrinkage at a high temperature and having excellent heat resistance can be provided. In addition, since a polymerizable compound having two or more radical polymerizable functional groups in one molecule is excellent in compatibility with a synthetic resin microporous film, it does not block the micropores of the synthetic resin microporous film. A film layer can be formed. Therefore, according to the coating layer, excellent heat resistance can be imparted to the synthetic resin microporous film without reducing air permeability.

  Moreover, in this invention, after applying the polymeric compound which has a 2 or more radically polymerizable functional group in 1 molecule on the synthetic resin microporous film surface, an active energy ray is irradiated. At this time, since the active energy rays have high energy, the active energy rays reach the synthetic resin microporous film, and radicals can also be generated in the synthetic resin in the synthetic resin microporous film. it can. Thereby, a part of the synthetic resin and a part of the polymer of the polymerizable compound having two or more radical polymerizable functional groups in one molecule can be chemically bonded. By forming such chemical bonds, it is possible to form a coating layer that is firmly integrated with the surface of the synthetic resin microporous film. Thereby, the heat resistance of the synthetic resin microporous film can be further improved.

  Furthermore, by irradiating the synthetic resin microporous film with active energy rays, a part of the synthetic resin is decomposed to lower the molecular weight, and as a result, the stress relaxation of the synthetic resin microporous film can proceed. It is considered that such stress relaxation effectively prevents thermal shrinkage of the heat-resistant synthetic resin microporous film at high temperatures. As a synthetic resin microporous film in which such an effect is particularly obtained, a polypropylene resin microporous film can be mentioned.

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

  When an electron beam is used as the active energy ray, the absorbed dose of the electron beam with respect to the synthetic resin microporous film is not particularly limited, but is preferably 10 to 150 kGy, and more preferably 10 to 100 kGy. By setting the absorbed dose 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 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, more preferably 50 to 250 kV, and particularly preferably 50 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 ultraviolet rays as the active energy rays, the integrated quantity of ultraviolet light to the synthetic resin microporous film is not particularly limited, but 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, 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 ^{5~45J / 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 is polymerizable. Many chemical bonds can be formed with a part of the polymer of the compound.

[Heat-resistant synthetic resin microporous film]
According to the method of the present invention described above, a heat-resistant synthetic resin microporous film having excellent heat resistance can be provided. The heat-resistant synthetic resin microporous film includes a synthetic resin microporous film in which micropores are formed by uniaxially stretching a synthetic resin film containing a synthetic resin in an extrusion direction, and at least the surface of the synthetic resin microporous film. A coating layer formed in part, and the coating layer contains a polymer of a polymerizable compound having two or more radical polymerizable functional groups in one molecule, and the temperature is raised from 30 ° C. to 250 ° C. The maximum shrinkage stress in the stretching direction when heated at a rate of 5 ° C./min is 1.2 MPa or less.

(Synthetic resin microporous film)
The synthetic resin microporous film includes micropores penetrating in the film thickness direction. As described above, the micropores can be formed by uniaxially stretching a synthetic resin film containing a synthetic resin in the extrusion direction, and the synthetic resin film containing the synthetic resin is orthogonal to the extrusion direction and the extrusion direction. It can also be formed by biaxially stretching in the direction of stretching. Such micropores can impart excellent ion permeability to the heat-resistant synthetic resin microporous film. Thereby, the heat-resistant synthetic resin microporous film can transmit ions such as lithium ions in the thickness direction.

  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 maximum shrinkage stress in the extrusion direction of the synthetic resin microporous film when the synthetic resin microporous film is heated from 30 ° C. to 250 ° C. at a heating rate of 5 ° C./min is preferably 2.2 MPa or less, and 2.0 MPa or less. Is more preferable, 1.7 MPa or less is even more preferable, and 1.5 MPa or less is particularly preferable. A synthetic resin microporous film having a maximum shrinkage stress of 2.2 MPa or less is excellent in heat resistance. Therefore, by using such a synthetic resin microporous film, even if the temperature inside the non-aqueous electrolyte secondary battery becomes high, the electrical shrinkage of the synthetic resin microporous film causes electrical contact between the electrodes. It is possible to reduce the occurrence of a short circuit.

  The maximum shrinkage stress of the synthetic resin microporous film refers to the highest shrinkage stress in the surface of the synthetic resin microporous film and corresponds to the stretching direction of the synthetic resin film. The maximum shrinkage stress of the synthetic resin microporous film can be measured using a thermomechanical analyzer (for example, TMA / SS7100C manufactured by Hitachi High-Tech Science Co., Ltd.). Specifically, it is as follows. First, an arbitrary portion of the synthetic resin microporous film is cut to obtain a strip having a width of 3 mm and a length of 50 mm. At this time, the length direction of the strip is set to be the stretching direction of the synthetic resin microporous film. The both ends of the strip in the length direction are gripped by a pair of grips and attached to the thermomechanical analyzer. At this time, the distance between the grippers is 10 mm. An initial load of 0.261 MPa is applied in the length direction of the band to prevent the band from sagging between the grippers. Furthermore, the gripping tool is fixed so as not to move during the measurement. Thereafter, the strip was heated from 30 ° C. to 250 ° C. at a rate of 5 ° C./min, the shrinkage stress (MPa) at each temperature was measured, and the maximum value was taken as the maximum shrinkage stress of the synthetic resin microporous film ( MPa). When the synthetic resin microporous film is formed by biaxially stretching the synthetic resin film, the maximum shrinkage stress is measured as described above for each stretching direction of the synthetic resin microporous film, and each stretching direction is measured. Of the maximum shrinkage stresses in, the larger maximum shrinkage stress is defined as the maximum shrinkage stress (MPa) of the microporous resin film.

  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. According to the synthetic resin microporous film having a maximum long diameter of 1 μm or less at the opening end of the micropore portion, even if dendrite (dendritic crystal) grows on the electrode surface by repeatedly charging and discharging the battery, Can be reduced.

  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 in a photograph be the maximum long diameter of the opening end of the micropore part in a microporous resin film. The arithmetic mean value of the major axis of the opening end in each micropore in the photograph is taken as the average major axis of the opening end of the micropore in the microporous resin 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. According to the synthetic resin microporous film having a pore density of 15 / μm ² or more, a heat-resistant synthetic resin microporous film excellent in mechanical strength and ion permeability can be provided.

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).

  The porosity of the synthetic resin microporous film is preferably 45 to 70%, more preferably 47 to 67%. A synthetic resin microporous film having a porosity in the above range is excellent in air permeability and mechanical strength.

The porosity of the synthetic resin microporous film can be measured in the following manner. First, a test piece having a plane square shape (area: 100 cm ² ) measuring 10 cm in length and 10 cm in width is obtained by cutting the synthetic resin microporous film. Next, the weight W (g) and thickness T (cm) of the test piece are measured, and the apparent density ρ (g / cm ³ ) is calculated by the following formula (1). In addition, the thickness of a test piece measures 15 thickness of a test piece using a dial gauge (for example, signal ABS Digimatic indicator by Mitutoyo Corporation), and makes it the arithmetic mean value. Then, using this apparent density ρ (g / cm ³ ) and the density ρ ₀ (g / cm ³ ) of the synthetic resin itself, the porosity P (%) of the synthetic resin microporous film is calculated based on the following formula (2). Can be calculated.
Apparent density ρ (g / cm ³ ) = W / (100 × T) (1)
Porosity P [%] = 100 × [(ρ ₀ −ρ) / ρ ₀ ] (2)

  Although the thickness in particular of a synthetic resin microporous film is not restrict | limited, 1-100 micrometers is preferable and 1-50 micrometers is more preferable. In addition, the thickness of a synthetic resin microporous film measured 15 thickness of a synthetic resin microporous film using a dial gauge (for example, signal ABS Digimatic indicator by Mitutoyo Corporation), and made it an arithmetic mean value. .

(Coating layer)
The heat-resistant synthetic resin microporous film includes a coating layer formed on at least a part of the above-described synthetic resin microporous film surface. The coating layer contains a polymer of a polymerizable compound having two or more radical polymerizable functional groups in one molecule. By using the coating layer containing such a polymer, as described above, it is possible to provide a heat-resistant synthetic resin microporous film having reduced heat shrinkage at high temperatures and having excellent heat resistance.

Further, the coating layer can improve the heat resistance of the heat-resistant synthetic resin microporous film even if it does not contain inorganic particles, but may contain inorganic particles as necessary. The material constituting the inorganic particles is not particularly limited, and examples thereof 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.

  The content of the coating layer in the heat-resistant synthetic resin microporous film is preferably 1 to 80 parts by weight, more preferably 5 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. Is particularly preferred. By setting the content of the coating layer within the above range, excellent heat resistance can be imparted to the resulting heat-resistant synthetic resin microporous film without reducing air permeability.

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

  The maximum shrinkage stress in the stretching direction of the heat resistant synthetic resin microporous film when the heat resistant synthetic resin microporous film is heated from 30 ° C. to 250 ° C. at a heating rate of 5 ° C./min is 1.2 MPa or less. 1.1 MPa is more preferable, 1.0 MPa or less is further preferable, and 0.9 MPa or less is particularly preferable. A heat resistant synthetic resin microporous film having a maximum shrinkage stress of 1.2 MPa or less is excellent in heat resistance. Therefore, by using such a heat-resistant synthetic resin microporous film, even when the temperature inside the non-aqueous electrolyte secondary battery becomes high, the heat-resistant synthetic resin microporous film causes the electrode to contract due to heat shrinkage. It is highly possible to reduce the occurrence of an electrical short circuit.

  The maximum shrinkage stress of the heat-resistant synthetic resin microporous film can be obtained in the same manner as the above-described method for measuring the maximum shrinkage stress of the synthetic resin microporous film.

  When the heat-resistant synthetic resin microporous film is heated from 25 ° C. to 180 ° C. at a heating rate of 5 ° C./min, the maximum heat shrinkage in the stretching direction of the heat-resistant synthetic resin microporous film is 20% or less. Preferably, 17% or less is more preferable, and 5 to 17% is particularly preferable. The heat resistant synthetic resin microporous film is provided with excellent heat resistance by the coating layer. Therefore, the maximum heat shrinkage rate of the heat resistant synthetic resin microporous film can be 20% or less.

The maximum heat shrinkage rate of the heat-resistant synthetic resin 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 synthetic resin microporous film. At this time, the stretching direction of the heat-resistant synthetic resin 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. When the heat-resistant synthetic resin microporous film is formed by biaxially stretching a synthetic resin film, the maximum heat shrinkage rate is measured as described above for each stretching direction of the heat-resistant synthetic resin microporous film. Of the maximum heat shrinkage rates in each stretching direction, the larger maximum heat shrinkage rate is defined as the maximum heat shrinkage rate of the heat-resistant synthetic resin microporous film.
Thermal contraction rate (%) = 100 × (10−L) / 10

  The gel fraction of the heat resistant synthetic resin microporous film is preferably 5% or more, and more preferably 10% or more. By setting the gel fraction to 5% or more, a strong coating layer is formed, whereby the heat resistance of the heat resistant synthetic resin microporous film can be improved. Further, the gel fraction of the heat resistant synthetic resin microporous film is preferably 99% or less. By making the gel fraction 99% or less, the heat-resistant synthetic resin microporous film can be prevented from becoming brittle.

In the present invention, the gel fraction of the heat-resistant synthetic resin microporous film can be measured according to the following procedure. First, a heat resistant synthetic resin microporous film is cut to obtain about 0.1 g of a test piece. 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

  The puncture strength per 25 μm thickness of the heat resistant synthetic resin microporous film is preferably 0.5 N or more, and more preferably 0.7 N or more. The heat-resistant synthetic resin microporous film of the present invention has improved heat resistance while the reduction in mechanical strength such as puncture strength is reduced by the formation of the coating layer. Therefore, the heat-resistant synthetic resin microporous film has excellent mechanical strength, and the piercing strength can be within the above range. According to the heat-resistant synthetic resin microporous film having a puncture strength within the above range, when the heat-resistant synthetic resin microporous film is cut in the battery manufacturing process, tearing of the heat-resistant synthetic resin microporous film can be reduced. it can.

In the present invention, the puncture strength of the heat-resistant synthetic resin microporous film can be measured according to JIS Z1707 (1998). Specifically, a needle having a diameter of 1.0 mm and a tip having a semicircular shape with a radius of 0.5 mm is pierced into a heat-resistant synthetic resin microporous film at a speed of 50 mm / min, and the maximum stress until the needle penetrates is determined. The piercing strength is S ₀ [N]. On the other hand, the thickness T [μm] of the heat-resistant synthetic resin microporous film is measured. The thickness of the heat-resistant synthetic resin microporous film was determined by measuring the thickness of the heat-resistant synthetic resin microporous film at 15 locations using a dial gauge (for example, Signal ABS Digimatic Indicator manufactured by Mitutoyo Corporation). Average value. Based on the following formula, the puncture strength S [N] per 25 μm thickness of the heat-resistant synthetic resin microporous film can be calculated.
Puncture strength S [N] per 25 μm thickness of heat-resistant synthetic resin microporous film
= S ₀ [N] × 25 [μm] / T [μm]

  Although the thickness in particular of a heat resistant synthetic resin microporous film is not restrict | limited, 1-100 micrometers is preferable and 1-50 micrometers is more preferable. In addition, the thickness of a heat resistant synthetic resin microporous film can be measured according to the said procedure.

  The heat-resistant synthetic resin microporous film of the present invention described above has excellent air permeability and can smoothly and uniformly transmit lithium ions. Furthermore, the heat-resistant synthetic resin microporous film of the present invention has high heat shrinkage at high temperatures and is excellent in heat resistance. In addition, since the heat-resistant synthetic resin microporous film of the present invention does not require the use of inorganic particles in the coating layer, it is excellent in light weight and does not cause contamination of the production line due to falling off of inorganic particles during the production process. .

  Therefore, the heat-resistant synthetic resin microporous film of the present invention is suitably used as a separator for non-aqueous electrolyte secondary batteries. Examples of the non-aqueous electrolyte secondary battery include a lithium ion secondary battery. Since the heat-resistant synthetic resin microporous film of the present invention is excellent in lithium ion permeability, it is possible to charge and discharge at a high current density by using this heat-resistant synthetic resin microporous film. A water electrolyte secondary battery can be provided. Furthermore, since the heat-resistant synthetic resin microporous film of the present invention is also excellent in heat 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. Even when the temperature becomes high at ˜150 ° C., it is possible to provide a non-aqueous electrolyte secondary battery in which electrical short circuit between electrodes due to shrinkage of the heat-resistant synthetic resin microporous film is highly reduced. .

  The non-aqueous electrolyte secondary battery is not particularly limited as long as it includes the heat-resistant synthetic resin microporous film of the present invention as a separator, and includes a positive electrode, a negative electrode, a separator including a heat-resistant synthetic resin microporous film, Contains water electrolyte. 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 .

  The heat-resistant synthetic resin microporous film of the present invention has a coating layer containing a polymer of a polymerizable compound having two or more radically polymerizable functional groups in one molecule. According to this coating layer, the wettability of the heat-resistant synthetic resin microporous film with respect to the non-aqueous electrolyte can also be improved. For this reason, the heat-resistant synthetic resin microporous film allows the nonaqueous electrolytic solution to easily enter into the micropores, and can uniformly hold a large amount of the nonaqueous electrolytic solution. Therefore, by using a heat-resistant synthetic resin microporous film as a separator, it is possible to provide a non-aqueous electrolyte secondary battery that is excellent in productivity and has a high reduction in lifetime due to deterioration of the electrolyte. it can.

  According to the method of the present invention, a heat-resistant synthetic resin microporous film excellent in lithium ion permeability and heat resistance can be provided.

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

[Examples 1-7 and Comparative Examples 1-6]
1. Production of homopolypropylene microporous film (extrusion process)
Homopolypropylene (weight average molecular weight: 400,000, number average molecular weight: 37,000, molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) 10.8, melt flow rate: 3.7 g / 10 min, ¹³ C- T-die attached to the tip of the extruder by supplying an isotactic pentad fraction measured by NMR method: 97%, melting point: 163 ° C. to a single screw extruder, melt kneading at a resin temperature of 200 ° C. Extruded into a film. Next, the extruded homopolypropylene was supplied onto the outer peripheral surface of a cast roll having a surface temperature of 95 ° C., and was fed out in close contact over the lower arc length of the cast roll as the cast roll rotated. Thereafter, the fed homopolypropylene was cooled with cold air until the surface temperature reached 30 ° C. This obtained the elongate homopolypropylene film (width 200mm). The extrusion rate was 10 kg / hour, the film formation rate was 25 m / min, and the draw ratio was 85.

(Curing process)
The obtained long homopolypropylene film (length 400 m) was wound into a roll around a cylindrical core having an outer diameter of 178 mm 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, after the homopolypropylene film was unwound from the cured homopolypropylene film roll, the surface temperature of the homopolypropylene film was 23 ° C., and the draw ratio was 1.2 times at a draw rate of 240% / min. The film was uniaxially stretched only in the extrusion direction using a uniaxial stretching apparatus.

(Second stretching step)
Next, the homopolypropylene film was stretched uniaxially only in the extrusion direction at a stretching speed and a stretching ratio shown in Table 1 so that the surface temperature was 115 ° C. using a uniaxial stretching apparatus, and the homopolypropylene stretched. A film was obtained.

(Annealing process)
Then, the homopolypropylene stretched film was annealed by heating for 45 seconds at a surface temperature of 143 ° C. while preventing tension from being applied to the homopolypropylene stretched film, thereby obtaining a homopolypropylene microporous film (thickness 26 μm). . In addition, the shrinkage rate of the homopolypropylene stretched film in the annealing step was set to the value shown in Table 1.

2. Formation of film layer (irradiation process)
As a polymerizable compound having two or more radically polymerizable functional groups in one molecule, trimethylolpropane triacrylate (TMPTA), dipentaerythritol hexaacrylate (DPHA), trimethylolpropane trimethacrylate (TMPTMA), or penta A mixture (PTA) of erythritol triacrylate and pentaerythritol tetraacrylate was used as shown in Table 1, and 5 parts by weight of the polymerizable compound was dissolved in 95 parts by weight of ethyl acetate to prepare a coating solution. 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. On the homopolypropylene microporous film, the polymerizable compound was adhered in an amount shown in the column “Adhesive amount of polymerizable compound” in Table 1 with respect to 100 parts by weight of the homopolypropylene microporous film.

  A homopolypropylene microporous film was irradiated with an electron beam under an acceleration voltage of 200 kV and an absorbed dose (kGy) shown in Table 1 in a nitrogen atmosphere to polymerize the polymerizable compound. As a result, a heat-resistant homopolypropylene microporous film in which a film layer containing a polymer of a polymerizable compound is formed on the surface of the homopolypropylene microporous film and the wall surface of the opening end of the micropores continuous with the surface is obtained. It was. Table 1 shows the content (parts by weight) of the coating layer in 100 parts by weight of the homopolypropylene microporous film in the heat-resistant homopolypropylene microporous film.

[Evaluation]
About the homopolypropylene microporous film obtained in each annealing step of the examples and comparative examples, the air permeability, the surface opening ratio, the maximum long diameter and average long diameter of the opening end of the micropores, the hole density, the porosity, and the thickness Each was measured according to the procedure described above. Further, the maximum shrinkage stress in the stretching direction of the homopolypropylene microporous film when the homopolypropylene microporous film was heated from 30 ° C. to 250 ° C. at a heating rate of 5 ° C./min was measured according to the above-described procedure. These results are shown in Table 1.

  About the heat-resistant homopolypropylene microporous film obtained in the Example and the comparative example, the air permeability, the gel fraction, the puncture strength per 25 μm thickness, and the thickness were measured according to the above-described procedures. The maximum shrinkage stress in the stretching direction of the heat resistant homopolypropylene microporous film when the heat resistant homopolypropylene microporous film was heated from 30 ° C. to 250 ° C. at a heating rate of 5 ° C./min was measured according to the procedure described above. When the heat-resistant homopolypropylene microporous film was heated from 25 ° C. to 180 ° C. at a rate of temperature increase of 5 ° C./min, the maximum heat shrinkage rate in the stretching direction of the heat-resistant homopolypropylene microporous film was measured according to the procedure described above. did. These results are shown in Table 1.

(Tensile fracture stress)
The tensile fracture stress in the extrusion direction of the heat-resistant homopolypropylene microporous film obtained in the examples and comparative examples was measured according to JISK7127 / 2/300. During the measurement, the distance between the gripping tools was 50 mm, and the tensile speed was 300 mm / min. The sample piece had a width of 10 mm and a length of 150 mm.

(Nail penetration test)
The heat-resistant homopolypropylene microporous film obtained in Examples and Comparative Examples was subjected to a nail penetration test according to the following procedure. The results are shown in Table 1.

  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 homopolypropylene microporous film was punched out to obtain a planar rectangular shape of 52 mm long × 124 mm wide.

Next, a laminated body was obtained by laminating 10 positive electrode layers and 11 negative electrode layers alternately through a heat-resistant homopolypropylene 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 performed 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 Table 1, “excellent” and “inferior” are as follows.
Excellent: Smoke and fire did not occur in the laminate element after the test.
Inferior: At least one of smoke and ignition occurred in the laminate element after the test.

Claims (18)

An extrusion step of supplying a synthetic resin to an extruder, melt-kneading, and obtaining a synthetic resin film by extruding from a T-die attached to the tip of the extruder;
A curing process for curing the synthetic resin film obtained in the extrusion process at (Tm-30) to (Tm-5) ° C.
A first stretching step in which the synthetic resin film after the curing step is uniaxially stretched in the extrusion direction to a stretching ratio of 1.05 to 2.0 times at a surface temperature of -20 to 100 ° C;
By uniaxially stretching the synthetic resin film after the first stretching step in the extrusion direction at a surface temperature of 100 to 150 ° C. at a stretching ratio of 2.8 to 4.0 times and a stretching speed of 5 to 400% / min. A second stretching step to obtain a synthetic resin stretched film;
While the surface temperature of the synthetic resin stretched film after the second stretching step is (Tm-35) ° C. or higher and below the melting point of the synthetic resin, the shrinkage is 5 to 25% in the extrusion direction. An annealing step of obtaining a synthetic resin microporous film by shrinking;
After applying the polymerizable compound having two or more radical polymerizable functional groups in one molecule on the surface of the synthetic resin microporous film after the annealing step, the synthetic resin microporous film is irradiated with active energy rays. An irradiation process to perform,
(Wherein Tm is the melting point of the synthetic resin). A method for producing a heat-resistant synthetic resin microporous film.   The method for producing a heat-resistant synthetic resin microporous film according to claim 1, wherein the synthetic resin contains a propylene-based resin.   The propylene-based resin has a weight average molecular weight of 250,000 to 500,000, a molecular weight distribution of 7.5 to 12.0, and a melting point of 160 to 170 ° C. A method for producing a heat-resistant synthetic resin microporous film.   In the extrusion step, the synthetic resin is melt kneaded at (Tm + 20) to (Tm + 100) ° C. in an extruder (Tm is a melting point of the synthetic resin). 2. A method for producing a heat-resistant synthetic resin microporous film according to item 1.   The polymerizable compound is a polyfunctional acrylic monomer, a vinyl oligomer having a vinyl group, a polyfunctional (meth) acrylate modified product, a dendritic polymer having a bifunctional or higher (meth) acryloyl group, and a bifunctional or higher functional polymer. The heat-resistant synthetic resin microporous film according to any one of claims 1 to 4, which is at least one selected from the group consisting of urethane (meth) acrylate oligomers having a (meth) acryloyl group. Production method.   The polymerizable compound is trimethylolpropane tri (meth) acrylate, glyceryl tri (meth) acrylate, pentaerythritol tri (meth) acrylate, tris- (2-acryloxyethyl) isocyanurate, pentaerythritol tetra (meth) acrylate, ditrile. 6. The method according to claim 1, which is at least one selected from the group consisting of methylolpropane tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and dipentaerythritol polyacrylate. The manufacturing method of the heat-resistant synthetic resin microporous film of description.   The heat resistance according to any one of claims 1 to 6, wherein in the irradiation step, a coating liquid in which the polymerizable compound is dispersed or dissolved in a solvent is applied to the surface of the synthetic resin microporous film. For producing a porous synthetic resin microporous film.   In the irradiation step, before irradiating the synthetic resin microporous film with active energy rays, the synthetic resin microporous film coated with the coating liquid is heated to remove the solvent. A method for producing a heat-resistant synthetic resin microporous film.   In the irradiation step, 1 to 80 parts by weight of the polymerizable compound is attached to 100 parts by weight of the synthetic resin microporous film by applying a polymerizable compound to the surface of the synthetic resin microporous film. The manufacturing method of the heat resistant synthetic resin microporous film of any one of Claims 1-8. A synthetic resin microporous film in which micropores are formed by stretching a synthetic resin film containing a synthetic resin, and a coating layer formed on at least a part of the surface of the synthetic resin microporous film,
The coating layer contains a polymer of a polymerizable compound having two or more radically polymerizable functional groups in one molecule, and stretched when heated from 30 ° C. to 250 ° C. at a heating rate of 5 ° C./min. A heat-resistant synthetic resin microporous film having a maximum shrinkage stress in the direction of 1.2 MPa or less.   The polymerizable compound is a polyfunctional acrylic monomer, a vinyl oligomer having a vinyl group, a polyfunctional (meth) acrylate modified product, a dendritic polymer having a bifunctional or higher (meth) acryloyl group, and a bifunctional or higher functional polymer. The heat-resistant synthetic resin microporous film according to claim 10, which is at least one selected from the group consisting of urethane (meth) acrylate oligomers having a (meth) acryloyl group.   The polymerizable compound is trimethylolpropane tri (meth) acrylate, glyceryl tri (meth) acrylate, pentaerythritol tri (meth) acrylate, tris- (2-acryloxyethyl) isocyanurate, pentaerythritol tetra (meth) acrylate, ditrile. The heat-resistant synthesis according to claim 10 or 11, which is at least one selected from the group consisting of methylolpropane tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and dipentaerythritol polyacrylate. Resin microporous film.   Air permeability is 600 sec / 100mL or less, The heat-resistant synthetic resin microporous film of any one of Claims 10-12 characterized by the above-mentioned.   14. The maximum heat shrinkage rate in the stretching direction when heated from 25 ° C. to 180 ° C. at a rate of temperature increase of 5 ° C./min is 20% or less. Heat resistant synthetic resin microporous film.   The heat resistant synthetic resin microporous film according to any one of claims 10 to 14, wherein the gel fraction is 5% or more.   The heat-resistant synthetic resin microporous film according to any one of claims 10 to 15, wherein a puncture strength per thickness of 25 µm is 0.5 N or more.   A separator for a non-aqueous electrolyte secondary battery, comprising the heat-resistant synthetic resin microporous film according to any one of claims 10 to 16.   A non-aqueous electrolyte secondary battery comprising: a negative electrode; a positive electrode; a separator for a non-aqueous electrolyte secondary battery according to claim 17; and a non-aqueous electrolyte.