JP6698326B2 - Multilayer porous film and separator for electricity storage device - Google Patents

Description

  The present invention relates to a multilayer porous film and a power storage device separator using the same.

  In recent years, non-aqueous electrolyte batteries represented by lithium-ion batteries have been actively developed. Usually, in a non-aqueous electrolyte battery, a microporous membrane (separator) is provided between the positive and negative electrodes. Such a separator has a function of preventing direct contact between the positive and negative electrodes and a function of allowing ions to permeate through the electrolytic solution held in the micropores.

  In order to improve the cycle characteristics or safety of non-aqueous electrolyte batteries, improvement of separators has been studied. For example, in Patent Document 1, for the purpose of providing a secondary battery having excellent discharge characteristics and safety, an adhesive-carrying porous film obtained by coating a porous polymer with a reactive polymer and drying the polymer. Has been proposed.

  In recent years, as portable devices have become smaller and thinner, power storage devices such as lithium-ion secondary batteries have also been required to be smaller and thinner. On the other hand, in order to make it possible to carry a portable device for a long time, the capacity of an electricity storage device has been increased by improving the volume energy density.

  Here, in the separator, there is a characteristic that the battery reaction is quickly stopped when abnormally heated (fuse characteristic), and there is a dangerous situation that the positive electrode material and the negative electrode material directly react while maintaining the shape even at high temperature. In addition to performance related to safety that has been conventionally required such as prevention performance (short-circuit property), improvement in adhesiveness with electrodes is required from the viewpoint of uniform charging/discharging current and suppression of lithium dendrite.

  By improving the close contact between the separator and the battery electrode, nonuniform charge/discharge current is less likely to occur, and lithium dendrite is less likely to deposit, resulting in a longer charge/discharge cycle life. Become.

  Under these circumstances, attempts have been made to coat the polyolefin microporous film with an adhesive polymer as an attempt to impart adhesiveness to the separator (see, for example, Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 11-0260341 JP, 2007-059271, A JP, 2011-054502, A International Publication No. 03/012896 Japanese Patent Publication No. 2006-525624 Special table 2011-512005 gazette International Publication No. 2014/017651 International Publication No. 2011/0405062

  In the separator of Patent Document 1, it is proposed that a porous film be coated with a crosslinked polymer to exhibit adhesiveness with an electrode.

  However, although the thickness of the adhesive layer is increased in order to improve the adhesiveness, the stickiness deteriorates and a problem occurs during handling. When the thickness of the adhesive layer is reduced, the handling property is improved, but the required adhesive strength cannot be obtained.

  In the separator of Patent Document 2, after coating a reactive cross-linked polymer on the separator and attaching it to the electrode to assemble a battery, a cross-linking initiator is added to the electrolytic solution to advance the cross-linking reaction of the polymer. It has been proposed to increase the adhesiveness.

  However, the adhesiveness between the reactive polymer and the porous film is not sufficient, and the adhesiveness required during battery assembly may be insufficient, causing a problem in assembly. Further, it is difficult to uniformly carry out the reaction of the cross-linking agent added to the electrolytic solution, and there is a possibility that a portion having insufficient adhesiveness may occur in the battery.

  In the separator of Patent Document 3, it is described that a polymer having a heat-sensitive adhesive property is applied to a porous film so that it is not sticky during handling before sticking, and high adhesiveness is obtained during heat bonding.

  However, when the separator is abnormally heated, it has a characteristic that the shape of the separator changes and the battery function is stopped, so heating the separator in the assembly process may deteriorate the quality. is there.

  All of the microporous membranes described in Patent Documents 1 to 3 are not compatible with handling property or adhesiveness when winding a battery, and have room for improvement.

  Patent Document 4 proposes that a polymer dispersion liquid in which a polymer is not dissolved is applied onto a porous film so that an adhesive layer partially exists on the porous film. Patent Document 5 proposes that a gravure printing roll be used to allow the adhesive-coated portion and the adhesive-uncoated portion to exist in a regular shape. Patent Document 6 proposes coating an adhesive layer having a prescribed dot pattern on the surface of an inorganic film on a porous film. By using the techniques described in Patent Documents 4 to 6, it is possible to achieve both handling properties and adhesiveness when winding the battery.

  Patent Document 7 proposes that the adhesive resin layer on the porous film has two glass transition temperature peaks of 20° C. or higher and lower than 20° C. and has a dot-pattern sea-island structure. In Patent Document 8, polymer particles A having a number average particle size of 0.4 μm or more and less than 10 μm and a glass transition point of 65° C. or more, and a number average particle size of 0.04 μm or more and less than 0.3 μm and a glass transition A porous film for a secondary battery containing polymer particles B having a point of 15° C. or lower is disclosed.

  However, in the separator using the adhesive layer described in Patent Documents 4 to 8, the lithium ion permeability of the resin-coated portion is significantly reduced, and the charge/discharge performance of the battery is reduced.

  Therefore, the present invention provides a multilayer porous film having excellent lithium ion permeability while achieving both handleability and adhesiveness during winding of a battery, a power storage device separator comprising the multilayer porous film, and the power storage device separator. An object of the present invention is to provide a power storage device using the.

As a result of intensive studies to achieve the above-mentioned object, the present inventors have made a granular thermoplastic polymer having an average particle size of 500 nm or more and 2000 nm or less dispersed and present on at least one outermost surface of a polyolefin microporous film. Then, it was found that the above problem can be solved by providing a thermoplastic polymer coating layer having a sea-island structure.
That is, the present invention is as follows.
[1] A multilayer porous membrane having a polyolefin microporous membrane and a thermoplastic polymer coating layer coating at least a part of at least one outermost surface of the polyolefin microporous membrane,
In the thermoplastic polymer coating layer, a granular thermoplastic polymer having an average particle size of 500 nm or more and 2000 nm or less is dispersed and present,
On the outermost surface, a sea-island structure including a portion containing the granular thermoplastic polymer and a portion not containing the granular thermoplastic polymer is formed,
Multilayer porous membrane.
[2] The multilayer porous membrane according to [1], wherein the granular thermoplastic polymer is obtained by further carrying out seed polymerization after the production of seed particles.
[3] The multilayer porous membrane according to [1] or [2], wherein the average particle diameter of the granular thermoplastic polymer is 1000 nm or more and 2000 nm or less.
[4] The multilayer porous membrane according to any one of [1] to [3], wherein the glass transition temperature (Tg) of the granular thermoplastic polymer is 20°C or lower.
[5] The following formula (1):
{In the formula, "Voronoi polygon area" is the area of each polygon obtained by subjecting the granular thermoplastic polymer to Voronoi division in the visual field of the multilayer porous membrane, and "Voronoi polygon in visual field". "Average area value" is the average value of all Voronoi polygon areas obtained in the field of view. }
The minimum value of the standardized area represented by is 0.3 or more, The multilayer porous membrane as described in any one of [1]-[4].
[6] The peel strength after pressing the aluminum foil on the outermost surface of the multilayer porous film at a temperature of 25° C. and a pressure of 5 MPa for 3 minutes is 8 gf/cm or less, [1] to [5] The multilayer porous membrane according to any one of 1.
[7] The peel strength after pressing the aluminum foil on the outermost surface of the multilayer porous film at a temperature of 80° C. and a pressure of 10 MPa for 3 minutes is 10 gf/cm or more, [1] to [5] The multilayer porous membrane according to any one of 1.
[8] The multilayer porous film according to any one of [1] to [7], wherein the 90° peel strength between the polyolefin microporous film and the thermoplastic polymer coating layer is 6 gf/mm or more.
[9] The area ratio of the polyolefin microporous membrane covered with the thermoplastic polymer coating layer is 95% or less based on 100% of the total surface area of the polyolefin microporous membrane, [1] to [8]. The multilayer porous membrane according to any one of 1.
[10] The area ratio of the polyolefin microporous membrane covered with the thermoplastic polymer coating layer is 50% or less with respect to 100% of the total surface area of the polyolefin microporous membrane, [1] to [9]. The multilayer porous membrane according to any one of 1.
[11] A separator for an electricity storage device, which comprises the multilayer porous film according to any one of [1] to [10].
[12] A laminate in which the separator for an electricity storage device according to [11] and an electrode are laminated.

  According to the present invention, a multilayer porous film having both excellent adhesiveness with an electrode and handleability, and excellent cycle and/or rate characteristics of an electricity storage device when used as a separator for an electricity storage device to form an electricity storage device. It is possible to provide a power storage device separator comprising the multilayer porous film, and a power storage device using the power storage device separator.

FIG. 1 shows an example of a photograph of the surface of the polymer layer. FIG. 2 shows an example of the result of automatically specifying the thermoplastic polymer contained in the observation visual field of FIG. 1 by using image processing software. FIG. 3 shows an example of a result obtained by subjecting the plurality of particles specified in FIG. 2 to Voronoi division to obtain a Voronoi polygon.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist thereof.

[Multilayer porous film]
The multilayer porous membrane according to the present embodiment includes a polyolefin microporous membrane and a thermoplastic polymer coating layer that coats at least a part of at least one outermost surface of the polyolefin porous membrane. If desired, the multilayer porous membrane may further have a filler porous layer.

  In the multilayer porous membrane according to the present embodiment, the granular thermoplastic polymer having an average particle diameter of 500 nm or more and 2000 nm or less is dispersed and present in the thermoplastic polymer coating layer.

  In the multilayer porous membrane according to this embodiment, a sea-island structure including a portion containing a granular thermoplastic polymer and a portion not containing a granular thermoplastic polymer is formed on at least one outermost surface of the polyolefin porous membrane. Since the multilayer porous membrane has a sea-island structure on at least one outermost surface, it tends to be excellent in handleability, adhesiveness or lithium ion permeability.

  The thermoplastic polymer coating layer, the polyolefin microporous membrane and the filler porous layer will be described below.

[Thermoplastic polymer coating layer]
The multilayer porous membrane according to the present embodiment has a thermoplastic polymer coating layer that coats at least a part of at least one outermost surface of the polyolefin microporous membrane, particularly at least a portion of one side or both sides of the polyolefin microporous membrane. ..

(Structure of thermoplastic polymer coating layer)
The thermoplastic polymer coating layer is a layer in which a granular thermoplastic polymer having an average particle diameter of 500 nm or more and 2000 nm or less is uniformly dispersed and present on at least a part of at least one outermost surface of the polyolefin microporous film.

(Content of thermoplastic polymer)
The content of the thermoplastic polymer in the present embodiment, while improving the adhesive force with the polyolefin microporous membrane, from the viewpoint of suppressing the deterioration of cycle characteristics (permeability) due to the clogging of the pores of the polyolefin microporous membrane, 0.05 g / ^{m 2} or more 1.0 g / ^{m 2} or less, more preferably 0.07 g / ^{m 2} or more 0.8 g / ^{m 2} or less, more preferably 0.1 g / ^{m 2} or more 0.7g /M ² or less. The content of the thermoplastic polymer can be adjusted by changing the polymer concentration of the coating liquid or the coating amount of the polymer solution.

The thermoplastic polymer preferably has two or more glass transition temperatures. For example, it can be achieved by a method of blending two or more kinds of thermoplastic polymers or a method of using a thermoplastic polymer having a core-shell structure, but is not limited to these methods. The core-shell structure is a polymer having a double structure in which the polymer belonging to the central part and the polymer belonging to the outer part have different compositions.
In particular, the polymer blend and the core-shell structure can control the glass transition temperature of the entire thermoplastic polymer by combining a polymer having a high glass transition temperature and a polymer having a low glass transition temperature. Moreover, a plurality of functions can be imparted to the whole thermoplastic polymer. For example, in the case of blending, in particular, by blending two or more kinds of polymers having a glass transition temperature in the range of 20°C or higher and a polymer having a glass transition temperature in the range of lower than 20°C, stickiness resistance and polyolefin microporosity The adhesion to the film can be compatible. As a mixing ratio in the case of blending, the ratio of the polymer having a glass transition temperature in the region of 20° C. or more to the polymer having a glass transition temperature in the region of less than 20° C. is 0.1:99.9 to 99.9: It is preferably in the range of 0.1, more preferably 5:95 to 95:5, still more preferably 50:50 to 95:5, and even more preferably 60:40 to 90:10. is there. In the case of the core-shell structure, the adhesiveness and compatibility with other materials such as the polyolefin microporous membrane can be adjusted by changing the outer shell polymer, and by adjusting the polymer belonging to the central part, for example, the electrode after hot pressing It is possible to adjust the polymer to have improved adhesiveness to. Further, viscoelasticity can be controlled by combining a polymer having high viscosity and a polymer having high elasticity.

  In the present embodiment, at least one of the glass transition temperatures of the thermoplastic polymer used is in the region of 20° C. or higher, so that the adhesiveness and the handling property between the separator and the electrode are excellent. At least one of the glass transition temperatures of the thermoplastic polymer used is preferably in the range of 20°C or higher and 120°C or lower, and more preferably 50°C or higher and 120°C or lower. When the glass transition temperature is within the above range, good handleability can be imparted. Further, it is possible to enhance the adhesiveness between the electrode and the separator, which is manifested by the pressure applied during the production of the battery.

  In the present embodiment, at least one of the glass transition temperatures of the thermoplastic polymer used is in the region of less than 20° C., so that the adhesiveness to the microporous film is excellent, and as a result, the adhesiveness to the separator and the electrode is improved. Has the effect of being excellent. At least one of the glass transition temperatures of the thermoplastic polymer used is preferably in the region of 15°C or lower, more preferably in the region of -30°C or higher and 15°C or lower.

(Granular thermoplastic polymer)
As the structure of the thermoplastic polymer in the present embodiment, granular particles are preferable from the viewpoint of handleability, adhesiveness and lithium ion permeability of the multilayer porous film.
Among the granular thermoplastic polymers, the granular thermoplastic polymer having a core-shell structure is more preferable. The shell-side polymer and the core-side polymer are not particularly limited, but the glass transition temperature of the shell-side polymer is lower than the glass transition temperature of the core-side polymer, and more preferably 20° C. or lower. The glass transition temperature of the shell-side polymer is more preferably -30°C or higher and 15°C or lower.
Further, when blending two or more kinds of thermoplastic polymers, a granular thermoplastic polymer having a shell-side glass transition temperature of 20° C. or higher may be used.
Here, the term “granular” of the thermoplastic polymer refers to a state in which each thermoplastic polymer has a contour in measurement by a scanning electron microscope (SEM), and for example, even if it is a flat shape, it is spherical. Or may be polygonal or the like.

(Average particle size of granular thermoplastic polymer)
The average particle size of the granular thermoplastic polymer is preferably 500 nm or more and 2000 nm or less, more preferably 1000 nm or more and 2000 nm or less, from the viewpoint of handling property, adhesiveness and lithium ion permeability of the multilayer porous film.
As a method of adjusting the average particle size of the granular thermoplastic polymer to 500 nm or more, that is, a method of forming a granular thermoplastic polymer having a large particle size, for example, after the production of seed particles, particle size growth by further performing seed polymerization Is mentioned. Specifically, a monomer is dropped into an emulsion containing latex particles (seed particles) to induce polymerization of the monomer with the latex particles as a nucleus. In the seed polymerization, the polymerization reaction can be repeated (multistep polymerization can be performed), and thus latex particles having a desired large particle size can be obtained.

(Area ratio of granular thermoplastic polymer)
In the present embodiment, the area ratio of the granular thermoplastic polymer to the total area of the thermoplastic polymer present on the outermost surface of the multilayer porous film is not particularly limited, but is 95% or less, 90% or less, 85% or less, 80% or less. , Or 75% or less, and the area ratio is preferably 10% or more, 15% or more, or 20% or more. More preferably, the area ratio is 10% or more and 95% or less. The area ratio S of the granular thermoplastic polymer to the total area of the thermoplastic polymer existing on the outermost surface of the multilayer porous membrane is expressed by the following formula:
S (%)=area of granular thermoplastic polymer/total area of thermoplastic polymer present on the outermost surface of the multilayer porous membrane.
Here, the total area of the thermoplastic polymer existing on the outermost surface of the multilayer porous membrane and the area of the granular thermoplastic polymer are as described later in Examples, and the outermost surface of the multilayer porous membrane is observed by SEM (magnification: 30,000 times). It is measured by

(Standardized area of granular thermoplastic polymer)
In this embodiment, in order to evaluate the degree of aggregation of the granular thermoplastic polymer, the following formula (1):
{In the formula, "Voronoi polygonal area" is the area of each polygon obtained by subjecting the granular thermoplastic polymer to Voronoi division in the field of view of the multilayer porous film, and "the Voronoi polygonal area in the field of view". "Average value" is the average value of all Voronoi polygonal areas obtained in the field of view. }
The normalized area represented by can be calculated.
In the multilayer porous membrane according to the present embodiment, the minimum normalized area is 0.3 or more, 0.4 or more from the viewpoint of peel strength between the multilayer porous membrane and the electrode and cycle characteristics of the battery including the porous membrane. , Or 0.5 or more is preferable. The Voronoi polygon area in Formula (1), the average value of the Voronoi polygon areas in the visual field, and the normalized area are calculated by subjecting a specific visual field of the multilayer porous membrane to Voronoi division, as described later in Examples. You can

[Thermoplastic polymer]
The thermoplastic polymer used in the present embodiment is not particularly limited, but is, for example, a polyolefin resin such as polyethylene, polypropylene or α-polyolefin; a fluoropolymer such as polyvinylidene fluoride or polytetrafluoroethylene, or a copolymer containing these; A diene polymer containing a conjugated diene such as butadiene or isoprene as a monomer unit, or a copolymer containing the same, and a hydride thereof; an acrylic polymer containing an acrylic ester, a methacrylic acid ester, or the like as a monomer unit, or a copolymer containing these and a hydrogen thereof Compounds; rubbers such as ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose; polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide, Examples thereof include resins having a melting point and/or glass transition temperature of 180° C. or higher such as polyamide and polyester: and mixtures thereof.

  Among the above-mentioned thermoplastic polymers, a diene-based polymer, an acrylic-based polymer or a fluorine-based polymer is preferable because it is excellent in binding property with an electrode active material, strength and flexibility.

(Diene polymer)
The diene polymer is not particularly limited, but is a polymer containing a monomer unit obtained by polymerizing a conjugated diene monomer having two conjugated double bonds, such as butadiene and isoprene.

  The conjugated diene monomer is not particularly limited, but for example, 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 1,3-pentadiene, 2 -Methyl-1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octadiene, 3-butyl-1,3-octadiene and the like. These may be polymerized alone or may be copolymerized.

  The proportion of monomer units obtained by polymerizing the conjugated diene in the diene-based polymer is not particularly limited, but for example, based on the weight of the total diene-based polymer, preferably 40% by mass or more, more preferably 50% by mass. Or more, More preferably, it is 60 mass% or more.

  The diene-based polymer is not particularly limited, and examples thereof include homopolymers of conjugated dienes such as polybutadiene and polyisoprene, and copolymers of the conjugated diene and a copolymerizable monomer.

  The monomer copolymerizable with the conjugated diene is not particularly limited, but examples thereof include the below-mentioned (meth)acrylate monomer, and the following monomers (hereinafter, also referred to as “other monomers”).

"Other monomers"
Other monomers are not particularly limited, and examples thereof include α,β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; styrene and chloro. Styrene monomers such as styrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, α-methylstyrene and divinylbenzene; olefins such as ethylene and propylene. Halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; Vinyl acetates such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, butyl beer ether; methyl vinyl ketone, Vinyl ketones such as ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; heterocyclic ring-containing vinyl compounds such as N-vinylpyrrolidone, vinyl pyridine and vinyl imidazole; acrylic acid esters such as methyl acrylate and methyl methacrylate; / Or methacrylic acid ester compound; hydroxyalkyl group-containing compounds such as β-hydroxyethyl acrylate and β-hydroxyethyl methacrylate; amide monomers such as acrylamide, N-methylol acrylamide, and acrylamido-2-methylpropanesulfonic acid. ..
One of these may be used, or two or more thereof may be used in combination.

(Acrylic polymer)
The acrylic polymer is not particularly limited, but is preferably a polymer containing a monomer unit obtained by polymerizing a (meth)acrylate monomer.
In addition, in this specification, "(meth)acrylic acid" shows "acrylic acid or methacrylic acid", and "(meth)acrylate" shows "acrylate or methacrylate."

  The (meth)acrylate monomer is not particularly limited, and examples thereof include methyl(meth)acrylate, ethyl(meth)acrylate, n-propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, t. -Butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate Alkyl (meth)acrylates such as lauryl (meth)acrylate, n-tetradecyl (meth)acrylate and stearyl (meth)acrylate; hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate and the like. Examples thereof include hydroxy group-containing (meth)acrylates; amino group-containing (meth)acrylates such as aminoethyl (meth)acrylate; and epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate.

  The ratio of the monomer units obtained by polymerizing the (meth)acrylate monomer is not particularly limited, but is, for example, 40 mass% or more, preferably 50 mass% or more, more preferably 60 mass% based on the total mass of the acrylic polymer. It is at least mass%.

  Examples of the acrylic polymer include homopolymers of (meth)acrylate monomers, and copolymers of (meth)acrylate monomers and monomers copolymerizable with the (meth)acrylate monomers.

  Examples of the monomer copolymerizable with the (meth)acrylate monomer include the "other monomers" listed in the item of the diene polymer, and one kind or a combination of two or more kinds thereof may be used.

(Fluorine-based polymer)
The fluorine-based polymer is not particularly limited, but examples thereof include a homopolymer of vinylidene fluoride and a copolymer of vinylidene fluoride and a copolymerizable monomer. Fluorine-based polymers are preferable from the viewpoint of electrochemical stability.

  The proportion of the monomer units obtained by polymerizing vinylidene fluoride is not particularly limited, but is, for example, 40 mass% or more, preferably 50 mass% or more, more preferably 60 mass% based on the total mass of the fluoropolymer. % Or more.

  The monomer copolymerizable with vinylidene fluoride is not particularly limited, for example, vinyl fluoride, tetrafluoroethylene, trifluorochloroethylene, hexafluoropropylene, hexafluoroisobutylene, perfluoroacrylic acid, perfluoromethacrylic acid, Fluorine-containing ethylenically unsaturated compounds such as fluoroalkyl esters of acrylic acid or methacrylic acid; fluorine-free ethylenically unsaturated compounds such as cyclohexyl vinyl ether, hydroxyethyl vinyl ether; fluorine-free diene compounds such as butadiene, isoprene, chloroprene, etc. Can be mentioned.

  Among the fluorine-based polymers, vinylidene fluoride homopolymers, vinylidene fluoride/tetrafluoroethylene copolymers, vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene copolymers, and the like are preferable. A more preferable fluorine-based polymer is vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene copolymer, and its monomer composition is usually 30 to 90% by mass of vinylidene fluoride, 50 to 9% by mass of tetrafluoroethylene, and hexafluoro. Propylene is 20 to 1 mass %.

  The fluoropolymer may be in the form of particles. In that case, the fluororesin particles may be used alone or in combination of two or more kinds.

(Synthesis of thermoplastic polymer)
As a monomer used when synthesizing a thermoplastic polymer, a monomer having at least one group selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, a sulfonic acid group, an amide group and a cyano group can be used. Good.

  The hydroxyl group-containing monomer is not particularly limited, and examples thereof include vinyl monomers such as pentenol.

  The monomer having a carboxyl group is not particularly limited, and examples thereof include unsaturated carboxylic acids having an ethylenic double bond such as (meth)acrylic acid and itaconic acid, and vinyl monomers such as pentenoic acid.

  The monomer having an amino group is not particularly limited, and examples thereof include 2-aminoethyl methacrylate.

  The monomer having a sulfonic acid group is not particularly limited, and examples thereof include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) alice sulfonic acid, styrene sulfonic acid, (meth) acrylic acid-2-ethyl sulfonate, 2- Examples thereof include acrylamido-2-methylpropanesulfonic acid and 3-allyloxy-2-hydroxypropanesulfonic acid.

  The amide group-containing monomer is not particularly limited, and examples thereof include acrylamide, methacrylamide, N-methylol acrylamide, and N-methylol methacrylamide.

  The monomer having a cyano group is not particularly limited, and examples thereof include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-cyanoethyl acrylate, and the like.

  The thermoplastic polymer used in the present embodiment may be used alone or as a mixture of two or more kinds, but it is preferable to include two or more kinds of polymers.

(Glass transition point of thermoplastic polymer)
The thermoplastic polymer used in the present embodiment preferably has the thermal property that at least one glass transition temperature is in the region of less than 20° C. from the viewpoint of adhesiveness between the separator and the electrode. Here, the glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC). In this specification, the glass transition temperature may be expressed as "Tg".

  Specifically, Tg is determined by the intersection of a straight line obtained by extending the low temperature side baseline in the DSC curve to the high temperature side and a tangent line at the inflection point of the stepwise change portion of the glass transition. For more details, reference can be made to the methods described in the examples.

  Here, the "glass transition" refers to a change in the amount of heat caused by a change in the state of a polymer, which is a test piece, on the endothermic side in DSC. Such a heat quantity change is observed in the DSC curve as a stepwise change shape or a shape in which a stepwise change and a peak are combined.

  The "step change" refers to a portion of the DSC curve from the baseline until the curve transitions to a new baseline. Note that the step change also includes a combination of a peak and a step change.

  The "inflection point" refers to a point at which the gradient of the DSC curve of the stepwise change portion becomes maximum. It can also be expressed as a point at which a curve that is convex upward changes to a curve that is convex downward in the stepwise changing portion.

  “Peak” refers to a portion of the DSC curve from the time when the curve leaves the baseline to the time when the curve returns to the baseline again.

  The “baseline” refers to a DSC curve in a temperature range in which the test piece does not undergo transition and reaction.

  In the present embodiment, since at least one of the glass transition temperatures of the thermoplastic polymer used is in the region of less than 20° C., the effect of excellent adhesiveness between the separator and the electrode is exerted. At least one of the glass transition temperatures of the thermoplastic polymer used is preferably in the range of 15°C or lower, more preferably in the range of -30°C or higher and 15°C or lower.

  In the present embodiment, the glass transition temperature (Tg) of the thermoplastic polymer can be appropriately adjusted by, for example, changing the monomer component used for producing the thermoplastic polymer and the input ratio of each monomer. That is, for each monomer used in the production of the thermoplastic polymer, the Tg of the corresponding homopolymer generally shown (for example, the Tg described in "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)) and each monomer are described. The Tg of the thermoplastic polymer can be roughly estimated from the blending ratio.

  For example, a copolymer having a high proportion of monomers such as styrene, methyl methacrylate, and acrylonitrile that gives a polymer with a Tg of about 100° C. can have a high Tg. For example, copolymers in which a high proportion of monomers such as butadiene, which gives a polymer with a Tg of about -80°C, n-butyl acrylate and 2-ethylhexyl acrylate, which gives a polymer with a Tg of about -50°C, are blended at a low ratio. It can have a Tg.

Further, in general, the Tg of a polymer is expressed by the FOX formula (the following formula (2)):
1/Tg=W ₁ /Tg ₁ +W ₂ /Tg ₂ +... +W _i /Tg _i +... W _n /Tg _n (2)
Where Tg(K) is the glass transition temperature (Tg) of the copolymer, Tg _i (K) is the Tg of the homopolymer of each monomer i, and W _i is the mass fraction of each monomer. Is}
It can be estimated more. However, since the Tg obtained by the FOX equation is only an approximate value, the Tg of the thermoplastic polymer used herein is the Tg measured by the method using the DSC, unless otherwise specified.

(Swelling degree of thermoplastic polymer in electrolyte)
From the viewpoint of battery characteristics such as cycle characteristics, the thermoplastic polymer in the present embodiment preferably has a swelling property in an electrolytic solution. The degree of swelling of the thermoplastic polymer with respect to the electrolytic solution is preferably 5 times or less, more preferably 4.5 times or less, and further preferably 4 times or less. The degree of swelling is preferably 1 time or more, more preferably 2 times or more. The degree of swelling of the thermoplastic polymer with respect to the electrolytic solution is measured by the method described later in Examples.

  The degree of swelling of the thermoplastic polymer in the present embodiment with respect to the electrolytic solution can be adjusted, for example, by changing the monomer component to be polymerized and the input ratio of each monomer.

(Gel fraction of thermoplastic polymer)
In the present embodiment, the gel fraction of the thermoplastic polymer is not particularly limited, but is preferably 80% or more, more preferably from the viewpoint of suppressing dissolution in the electrolytic solution and maintaining the strength of the thermoplastic polymer inside the battery. It is 85% or more, more preferably 90% or more. Here, the gel fraction is obtained by measuring the toluene insoluble content, as described later in the examples.

  The gel fraction can be adjusted by changing the monomer component to be polymerized, the input ratio of each monomer, and the polymerization conditions.

[Polyolefin microporous membrane]
The microporous polyolefin membrane in the present embodiment is not particularly limited, but includes, for example, a porous membrane composed of a polyolefin resin composition containing a polyolefin, and a porous membrane containing a polyolefin resin as a main component is preferable. .. The content of the polyolefin resin in the polyolefin microporous membrane in the present embodiment is not particularly limited, but from the viewpoint of shutdown performance when used as a separator for an electricity storage device, the mass fraction of all components constituting the porous membrane is 50%. It is preferable that the porous film is made of a polyolefin resin composition in which the polyolefin resin occupies 100% or more and 100% or less. The proportion of the polyolefin resin is more preferably 60% or more and 100% or less, and further preferably 70% or more and 100% or less.

  The polyolefin resin is not particularly limited, but may be a polyolefin resin used for ordinary extrusion, injection, inflation, blow molding, etc., such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and Homopolymers and copolymers such as 1-octene, multistage polymers and the like can be used. Further, a polyolefin selected from the group consisting of these homopolymers and copolymers and multistage polymers can be used alone or in combination.

  Representative examples of the polyolefin resin are not particularly limited, but include, for example, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene. Random copolymers, polybutene, ethylene propylene rubber and the like can be mentioned.

  When the multilayer porous membrane of this embodiment is used as a separator for an electricity storage device, it is particularly preferable to use a resin containing high-density polyethylene as a main component because it has a low melting point and high strength.

  Further, in order to improve the heat resistance of the polyolefin microporous film, it is more preferable to use a porous film made of a resin composition containing polypropylene and a polyolefin resin other than polypropylene.

  Here, the three-dimensional structure of polypropylene is not limited, and may be any of isotactic polypropylene, syndiotactic polypropylene and atactic polypropylene.

  The ratio of polypropylene to the total polyolefin in the polyolefin resin composition is not particularly limited, but from the viewpoint of achieving both heat resistance and a good shutdown function, it is preferably 1 to 35% by mass, more preferably 3 to 20% by mass. %, and more preferably 4 to 10% by mass.

  In this case, the polyolefin resin other than polypropylene is not limited, for example, ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, homopolymers of olefin hydrocarbons such as 1-octene or the like. Mention may be made of copolymers. Specifically, examples of the polyolefin resin other than polypropylene include polyethylene, polybutene, and ethylene-propylene random copolymer.

From the viewpoint of the shutdown property in which the pores of the microporous polyolefin membrane are closed by heat melting, as the polyolefin resin other than polypropylene, polyethylene such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high-molecular-weight polyethylene is used. Is preferably used. Among these, from the viewpoint of strength, it is more preferable to use polyethylene having a density of 0.93 g/cm ³ or more measured according to JIS K7112.

The viscosity average molecular weight of the polyolefin resin constituting the polyolefin microporous film is not particularly limited, but is preferably 30,000 or more and 12 million or less, more preferably 50,000 or more and less than 2 million, and further preferably 100,000 or more. It is less than one million. When the viscosity average molecular weight is 30,000 or more, the melt tension at the time of melt molding becomes large, the moldability becomes good, and the entanglement of the polymers tends to increase the strength, which is preferable. On the other hand, when the viscosity average molecular weight is 12 million or less, uniform melt-kneading becomes easy, and the moldability of the sheet, particularly the thickness stability tends to be excellent, which is preferable. Furthermore, when the viscosity average molecular weight is less than 1,000,000, the pores are likely to be clogged when the temperature rises, and a good shutdown function tends to be obtained, which is preferable.
For example, instead of using a polyolefin having a viscosity average molecular weight of less than 1,000,000 alone, a mixture of a polyolefin having a viscosity average molecular weight of 2,000,000 and a polyolefin having a viscosity average molecular weight of 270,000, the mixture having a viscosity average molecular weight of less than 1,000,000 is used. You may use.

  The polyolefin microporous membrane in the present embodiment can contain any additive. Such additives are not particularly limited and include, for example, polymers other than polyolefin; inorganic particles; phenol-based, phosphorus-based, sulfur-based, etc. antioxidants; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorption. Agents; light stabilizers; antistatic agents; antifogging agents; coloring pigments and the like.

  The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 5 parts by mass or less with respect to 100 parts by mass of the polyolefin resin composition.

(Physical properties of polyolefin microporous membrane)
The puncture strength of the microporous polyolefin membrane in the present embodiment is not particularly limited, but is preferably 200 g/20 μm or more, more preferably 300 g/20 μm or more, preferably 2000 g/20 μm or less, more preferably 1000 g/20 μm or less. is there. It is preferable that the puncture strength is 200 g/20 μm or more from the viewpoints of suppressing the membrane rupture due to the active material that has fallen off during winding of the battery and suppressing the risk of short-circuiting due to expansion and contraction of the electrodes due to charge and discharge. .. On the other hand, the puncture strength of 2000 g/20 μm or less is preferable from the viewpoint of reducing the width shrinkage due to the orientation relaxation during heating. Here, the puncture strength is measured by the method described in Examples below.
The puncture strength can be adjusted by adjusting the stretching ratio and/or the stretching temperature of the polyolefin microporous membrane.

The porosity of the microporous polyolefin membrane in the present embodiment is not particularly limited, but is preferably 20% or more, more preferably 35% or more, preferably 90% or less, preferably 80% or less. The porosity of 20% or more is preferable from the viewpoint of ensuring the permeability of the separator. On the other hand, the porosity of 90% or less is preferable from the viewpoint of ensuring the puncture strength. Here, the porosity is measured by the method described in Examples below.
The porosity can be adjusted by changing the stretching ratio of the microporous polyolefin membrane.

  The film thickness of the polyolefin microporous film in the present embodiment is not particularly limited, but is preferably 2 μm or more, more preferably 5 μm or more, preferably 100 μm or less, more preferably 60 μm or less, further preferably 50 μm or less. The thickness of 2 μm or more is preferable from the viewpoint of improving the mechanical strength. On the other hand, it is preferable to set the film thickness to 100 μm or less, because the volume occupied by the separator in the battery is reduced, which tends to be advantageous in terms of increasing the capacity of the battery.

The air permeability of the microporous polyolefin membrane in the present embodiment is not particularly limited, but is preferably 10 sec/100 cc or more, more preferably 50 sec/100 cc or more, preferably 1000 sec/100 cc or less, more preferably 500 sec/100 cc or less. Is. The air permeability of 10 sec/100 cc or more is preferable from the viewpoint of suppressing self-discharge of the electricity storage device. On the other hand, the air permeability of 1000 sec/100 cc or less is preferable from the viewpoint of obtaining good charge/discharge characteristics. Here, the air permeability is measured by the method described in Examples below.
The air permeability can be adjusted by changing the stretching temperature and/or the stretching ratio of the microporous polyolefin membrane.

  The average pore size of the polyolefin microporous membrane in the present embodiment is preferably 0.15 μm or less, more preferably 0.1 μm or less, and the lower limit is preferably 0.01 μm or more. When the average pore diameter is 0.15 μm or less, it is preferable from the viewpoint of suppressing self-discharge of the electricity storage device and suppressing a decrease in capacity when the electricity storage device separator is used. The average pore diameter can be adjusted by, for example, changing the draw ratio when producing the polyolefin microporous membrane.

  The short-circuit temperature, which is an index of heat resistance of the microporous polyolefin membrane in the present embodiment, is preferably 140°C or higher, more preferably 150°C or higher, and further preferably 160°C or higher. Setting the short-circuit temperature to 140° C. or higher is preferable from the viewpoint of the safety of the electricity storage device when it is used as an electricity storage device separator.

  The area ratio of the polyolefin microporous membrane covered with the thermoplastic polymer coating layer is 95% or less, 85% or less, 80% or less, 70% or less, 60% or less with respect to 100% of the total surface area of the polyolefin microporous membrane. Or 50% or less, and this area ratio is preferably 2% or more, 5% or more, 10% or more, 15% or more, or 20% or more. This area ratio is measured by observing the outermost surface of the multilayer porous membrane with SEM (magnification: 30,000 times).

(Production method of polyolefin microporous membrane)
The method for producing the polyolefin microporous membrane in the present embodiment is not particularly limited, and a known production method can be adopted. For example, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded to form a sheet, and optionally stretched, and then the plasticizer is extracted to make it porous, and the polyolefin resin composition is melt-kneaded to form a high draw. After extruding in a ratio, a method of making porous by peeling the polyolefin crystal interface by heat treatment and stretching, a polyolefin resin composition and an inorganic filler are melt-kneaded and molded on a sheet, and then the polyolefin and the inorganic filler are stretched. And the like, and a method of dissolving the polyolefin resin composition and then immersing it in a poor solvent for the polyolefin to coagulate the polyolefin and at the same time remove the solvent to make it porous.

  Hereinafter, as an example of a method for producing a microporous membrane, a method of melting and kneading a polyolefin resin composition and a plasticizer to form a sheet and then extracting the plasticizer will be described.

  First, the polyolefin resin composition and the plasticizer are melt-kneaded. As the melt-kneading method, for example, a polyolefin resin and optionally other additives are charged into a resin kneading device such as an extruder, a kneader, a Labo Plastomill, a kneading roll, or a Banbury mixer, and the resin components are heated and melted optionally. A method of introducing a plasticizer at a ratio of and kneading. At this time, it is preferable to pre-knead the polyolefin resin, other additives and the plasticizer at a predetermined ratio using a Henschel mixer or the like before introducing them into the resin kneading device. More preferably, in the pre-kneading, only a part of the plasticizer is added and the remaining plasticizer is kneaded while side feeding the resin kneading device. By doing so, the dispersibility of the plasticizer is enhanced, and when the sheet-shaped molded product of the melt-kneaded mixture of the resin composition and the plasticizer is stretched in a later step, it is stretched at a high magnification without breaking the film. can do.

  As the plasticizer, a non-volatile solvent capable of forming a uniform solution at a temperature equal to or higher than the melting point of polyolefin can be used. Specific examples of such a non-volatile solvent include hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; and higher alcohols such as oleyl alcohol and stearyl alcohol. Among these, liquid paraffin has high compatibility with polyethylene and polypropylene, and even if the melt-kneaded product is stretched, interfacial peeling between the resin and the plasticizer is unlikely to occur, so that uniform stretching tends to be performed easily. Therefore, it is preferable.

  The ratio of the polyolefin resin composition and the plasticizer is not particularly limited as long as they can be uniformly melt-kneaded and molded into a sheet. For example, the mass fraction of the plasticizer in the composition comprising the polyolefin resin composition and the plasticizer is preferably 30 to 80 mass%, more preferably 40 to 70 mass%. When the mass fraction of the plasticizer is 80% by mass or less, melt tension during melt molding is less likely to be insufficient, and moldability tends to be improved. On the other hand, when the mass fraction is 30% by mass or more, the polyolefin chain is not broken even when the mixture of the polyolefin resin composition and the plasticizer is stretched at a high ratio, and a uniform and fine pore structure is formed and strength is also increased. Easy to increase.

  Next, the melt-kneaded product is formed into a sheet. As a method for producing a sheet-shaped molded product, for example, a melt-kneaded product is extruded into a sheet form through a T-die or the like, brought into contact with a heat conductor and cooled to a temperature sufficiently lower than the crystallization temperature of the resin component. There is a method of solidifying. As the heat conductor used for cooling and solidification, metal, water, air, or the plasticizer itself can be used, but a metal roll is preferable because of high heat conduction efficiency. At this time, it is more preferable that the rolls are sandwiched between the rolls when they are brought into contact with each other, because the heat conduction efficiency is further increased, the sheets are oriented and the film strength is increased, and the surface smoothness of the sheets is also improved. The die lip interval when extruded into a sheet from the T-die is preferably 400 μm or more and 3000 μm or less, and more preferably 500 μm or more and 2500 μm or less. When the die lip interval is 400 μm or more, dents and the like are reduced, the film quality such as streaks and defects is less affected, and film breakage or the like tends to be prevented in the subsequent stretching step. On the other hand, when the die lip interval is 3000 μm or less, the cooling rate is high and uneven cooling can be prevented, and the thickness stability of the sheet tends to be maintained.

It is preferable to stretch the sheet-shaped molded product thus obtained. As the stretching treatment, either uniaxial stretching or biaxial stretching can be preferably used, but biaxial stretching is preferable from the viewpoint of the strength of the resulting porous membrane. When the sheet-shaped molded product is biaxially stretched at a high ratio, the molecules are oriented in the plane direction, the porous film finally obtained is less likely to tear, and has high puncture strength. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multi-stage stretching, and multi-stretching. Simultaneous biaxial stretching from the viewpoint of puncture strength improvement, stretching uniformity, and shutdown property. Stretching is preferred.
Here, the simultaneous biaxial stretching is a stretching in which the MD direction (machine direction of the microporous membrane) and the TD direction (direction crossing MD of the microporous membrane at an angle of 90°) are simultaneously performed. Method, and the draw ratio in each direction may be different. Sequential biaxial stretching refers to a stretching method in which stretching in the MD direction or the TD direction is performed independently, and when stretching is performed in the MD direction or the TD direction, the other direction is unrestrained or has a constant length. It is fixed to.

  The stretch ratio is preferably in the range of 20 times or more and 100 times or less, and more preferably in the range of 25 times or more and 50 times or less in terms of surface magnification. The draw ratio in each axial direction is preferably 4 times or more and 10 times or less in the MD direction, 4 times or more and 10 times or less in the TD direction, and 5 times or more and 8 times or less in the MD direction and 5 times in the TD direction. More preferably, the range is 8 times or less. When the total area ratio is 20 times or more, sufficient strength tends to be imparted to the obtained porous film, while when the total area ratio is 100 times or less, film breakage in the stretching step is prevented and high productivity is obtained. It tends to be obtained.

  Further, the sheet-shaped compact may be rolled. The rolling can be carried out by a pressing method using, for example, a double belt press. Rolling can especially increase the orientation of the surface layer portion. The rolling surface magnification is preferably more than 1 time and not more than 3 times, more preferably more than 1 time and not more than 2 times. If the rolling ratio is larger than 1, the plane orientation tends to increase and the film strength of the finally obtained porous film tends to increase. On the other hand, when the rolling ratio is 3 times or less, the difference in orientation between the surface layer portion and the center is small, and a uniform porous structure tends to be formed in the film thickness direction, which is preferable.

  Next, the plasticizer is removed from the sheet-shaped molded body to form a porous film. As a method of removing the plasticizer, for example, a method of immersing the sheet-shaped molded article in an extraction solvent to extract the plasticizer and sufficiently drying it can be mentioned. The method for extracting the plasticizer may be a batch method or a continuous method. In order to suppress the shrinkage of the porous film, it is preferable to restrain the end portion of the sheet-shaped molded product during a series of steps of immersion and drying. The residual amount of plasticizer in the porous film is preferably less than 1% by mass.

  As the extraction solvent, it is preferable to use a solvent that is a poor solvent for the polyolefin resin and a good solvent for the plasticizer and has a boiling point lower than the melting point of the polyolefin resin. Examples of such an extraction solvent include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorine-based solvents such as hydrofluoroether and hydrofluorocarbon. Examples thereof include halogenated solvents; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; ketones such as acetone and methyl ethyl ketone. In addition, these extraction solvents may be recovered and reused by an operation such as distillation.

  In order to suppress the shrinkage of the porous film, heat treatment such as heat fixation or thermal relaxation can be performed after the stretching step or after the formation of the porous film. Further, the porous membrane may be subjected to a post-treatment such as a hydrophilic treatment with a surfactant or the like and a crosslinking treatment with an ionizing radiation or the like.

[Filler porous layer]
The multilayer porous membrane according to this embodiment may further include a filler porous layer containing an inorganic filler and a resin binder. The position where the multilayer porous membrane is provided with the porous filler layer may be on one side or both sides of the polyolefin microporous membrane.

(Inorganic filler)
The inorganic filler used for the filler porous layer is not particularly limited, but one having a melting point of 200° C. or higher, high electric insulation, and electrochemically stable in the range of use of the lithium ion secondary battery. preferable.

  The inorganic filler is not particularly limited, but examples thereof include oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; nitrides such as silicon nitride, titanium nitride, and boron nitride. Ceramics; silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide oxide, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, Amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, ceramics such as silica sand, glass fibers and the like, these may be used alone or in combination. Good.

  Among the above, from the viewpoint of improving the electrochemical stability and heat resistance of the multilayer porous film, alumina, aluminum oxide compounds such as aluminum hydroxide oxide, and kaolinite, dikite, nacrite, halloysite, pyrophyllite and other ions. Aluminum silicate compounds having no exchange ability are preferred. Aluminum hydroxide oxide is particularly preferable as the aluminum oxide compound. As the aluminum silicate compound having no ion exchange ability, kaolin mainly composed of kaolin minerals is more preferable because it is inexpensive and easily available. There are two types of kaolin, wet kaolin and calcined kaolin obtained by calcining it. Calcined kaolin not only releases crystal water during the calcining process but also removes impurities. Particularly preferred.

  The average particle size of the inorganic filler is preferably more than 0.1 μm and 4.0 μm or less, more preferably more than 0.2 μm and 3.5 μm or less, and more than 0.4 μm and 3. It is more preferably 0 μm or less. It is preferable to adjust the average particle diameter of the inorganic filler within the above range from the viewpoint of suppressing thermal contraction at high temperature even when the thickness of the filler porous layer is thin (for example, 7 μm or less).

  In the inorganic filler, the proportion of particles having a particle size of more than 0.2 μm and 1.4 μm or less in the whole inorganic filler is preferably 2% by volume or more, more preferably 3% by volume or more, and further preferably 5%. It is at least vol%, and the upper limit is preferably at most 90 vol%, more preferably at most 80 vol%.

  In the inorganic filler, the proportion of particles having a particle size of more than 0.2 μm and 1.0 μm or less in the whole inorganic filler is preferably 1% by volume or more, more preferably 2% by volume or more, and as an upper limit, Is preferably 80% by volume or less, more preferably 70% by volume or less.

  In the above inorganic filler, the proportion of particles having a particle size of more than 0.5 μm and not more than 2.0 μm in the whole inorganic filler is preferably 8% by volume or more, more preferably 10% by volume or more, and the upper limit. Is preferably 60% by volume or less, more preferably 50% by volume or less.

  Further, in the inorganic filler, the proportion of particles having a particle size of more than 0.6 μm and 1.4 μm or less in the whole inorganic filler is preferably 1% by volume or more, more preferably 3% by volume or more, The upper limit is preferably 40% by volume or less, more preferably 30% by volume or less.

  It is preferable to adjust the particle size distribution of the inorganic filler within the above range from the viewpoint of suppressing thermal contraction at high temperature even when the thickness of the filler porous layer is thin (for example, 7 μm or less). As a method of adjusting the particle size ratio of the inorganic filler, for example, a method of reducing the particle size by pulverizing the inorganic filler using a ball mill, bead mill, jet mill or the like can be mentioned.

  Examples of the shape of the inorganic filler include a plate shape, a scale shape, a needle shape, a column shape, a spherical shape, a polyhedral shape, and a lump shape, and a plurality of types of the inorganic filler having the above shape may be used in combination. The shape of the inorganic filler is not particularly limited as long as the heat shrinkage at 150° C. described below can be suppressed to 10% or less in the case of a multilayer porous film, but it has a plurality of surfaces from the viewpoint of improving the permeability. Polyhedral shape, columnar shape, and spindle shape are preferable.

  The ratio of the inorganic filler in the porous filler layer can be appropriately determined from the viewpoints of the binding property of the inorganic filler, the permeability of the multilayer porous membrane, the heat resistance, etc., but 50% by mass or more and 100% by mass or more. %, preferably 70% by mass to 99.99% by mass, more preferably 80% by mass to 99.9% by mass, and particularly preferably 90% by mass to 99% by mass.

(Resin binder)
The type of the resin binder is not particularly limited, when the multilayer porous film in the present embodiment is used as a lithium ion secondary battery separator, it is insoluble in the electrolyte solution of the lithium ion secondary battery, and It is preferable to use a lithium ion secondary battery that is electrochemically stable in the range of use.

  Specific examples of the resin binder include polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoro. Fluorine-containing rubber such as ethylene copolymer; styrene-butadiene copolymer and hydride thereof, acrylonitrile-butadiene copolymer and hydride thereof, acrylonitrile-butadiene-styrene copolymer and hydride thereof, methacrylic acid ester-acryl Rubbers such as acid ester copolymers, styrene-acrylic acid ester copolymers, acrylonitrile-acrylic acid ester copolymers, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate, etc.; ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, etc. Cellulose derivatives: Polyphenylene ethers, polysulfones, polyether sulfones, polyphenylene sulfides, polyetherimides, polyamideimides, polyamides, polyesters, and other resins having a melting point and/or a glass transition temperature of 180° C. or higher.

  When polyvinyl alcohol is used as the resin binder, the saponification degree is preferably 85% or more and 100% or less. When the saponification degree is 85% or more, when the multilayer porous membrane is used as a battery separator, the temperature at which a short circuit occurs (short circuit temperature) is improved, and better safety performance tends to be obtained, which is preferable. The saponification degree is more preferably 90% or more and 100% or less, further preferably 95% or more and 100% or less, and particularly preferably 99% or more and 100% or less. The polymerization degree of polyvinyl alcohol is preferably 200 or more and 5000 or less, more preferably 300 or more and 4000 or less, and further preferably 500 or more and 3500 or less. When the degree of polymerization is 200 or more, the inorganic filler such as calcined kaolin can be firmly bound to the porous film with a small amount of polyvinyl alcohol, and the multilayer porous film formed by forming the filler porous layer while maintaining the mechanical strength of the filler porous layer. It is preferable because it tends to suppress an increase in air permeability. A degree of polymerization of 5000 or less is preferable because it tends to prevent gelation and the like when preparing a coating solution.

  A resin latex binder is preferable as the resin binder. When using a resin latex binder, when a filler porous layer containing an inorganic filler and a binder is laminated on at least one side of a polyolefin porous film, after dissolving a part or all of the resin binder in a solvent, the obtained solution Is laminated on at least one side of a polyolefin porous membrane, and compared with the case where the resin binder is bound to the porous membrane by removing the solvent by dipping in a poor solvent or drying, the ion permeability is unlikely to decrease and high output characteristics are high. It tends to be easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, smooth shutdown characteristics are exhibited, and high safety tends to be obtained.

  As the resin latex binder, from the viewpoint of improving electrochemical stability and binding property, an aliphatic conjugated diene-based monomer or an unsaturated carboxylic acid monomer, and another monomer copolymerizable therewith What is obtained by emulsion-polymerizing is preferable. The emulsion polymerization method is not particularly limited, and a conventionally known method can be used. The addition method of the monomer and other components is not particularly limited, and any one of a batch addition method, a divided addition method, and a continuous addition method can be adopted, and one-step polymerization, two-step polymerization or multi-step polymerization can be adopted. Any of step polymerization and the like can be adopted.

  The aliphatic conjugated diene-based monomer is not particularly limited, and examples thereof include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3 butadiene and 2-chloro-1. , 3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like, and these may be used alone or in combination of two or more. Among the above, 1,3-butadiene is particularly preferable.

  The unsaturated carboxylic acid monomer is not particularly limited, and examples thereof include mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. May be used alone or in combination of two or more. Among the above, acrylic acid and methacrylic acid are particularly preferable.

Other monomers copolymerizable with these are not particularly limited, and examples thereof include aromatic vinyl-based monomers, vinyl cyanide-based monomers, unsaturated carboxylic acid alkyl ester monomers, and hydroxyalkyl groups. Examples thereof include unsaturated monomers and unsaturated carboxylic acid amide monomers. These may be used alone or in combination of two or more. Among the above, an unsaturated carboxylic acid alkyl ester monomer is particularly preferable. The unsaturated carboxylic acid alkyl ester monomer is not particularly limited, and examples thereof include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl. Examples thereof include maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, and 2-ethylhexyl acrylate. These may be used alone or in combination of two or more. Among the above, methyl methacrylate is particularly preferable.
In addition to these monomers, in order to improve various quality and physical properties, monomer components other than the above may be further used.

  The average particle size of the resin binder is preferably 50 to 500 nm, more preferably 60 to 460 nm, and further preferably 80 to 250 nm. When the average particle size of the resin binder is 50 nm or more, when a filler porous layer containing an inorganic filler and a binder is laminated on at least one surface of the polyolefin porous film, ion permeability is unlikely to decrease and high output characteristics are easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, smooth shutdown characteristics are exhibited, and high safety is easily obtained. When the average particle size of the resin binder is 500 nm or less, good binding properties are exhibited, and when a multilayer porous film is formed, heat shrinkage tends to be good and safety tends to be excellent.

  The average particle size of the resin binder can be controlled by adjusting the polymerization time, the polymerization temperature, the raw material composition ratio, the raw material charging order, the pH, and the like.

  The layer thickness of the filler porous layer is preferably 1 μm or more from the viewpoint of improving heat resistance and insulating properties, and is preferably 50 μm or less from the viewpoint of improving battery capacity and permeability. The layer thickness of the filler porous layer is more preferably 1.5 μm or more and 20 μm or less, further preferably 2 μm or more and 10 μm or less, still more preferably 3 μm or more and 10 μm or less, and particularly preferably 3 μm or more and 7 μm or less.

Layer density of the filler porous layer is preferably from 0.5 to 2.0 g / cm ^3, more preferably 0.7~1.5cm ^3. When the layer density of the filler porous layer is 0.5 g/cm ³ or more, the heat shrinkage ratio at high temperature tends to be good, and when it is 2.0 g/cm ³ or less, the air permeability tends to decrease. It is in.

  Examples of the method for forming the filler porous layer include a method for forming a filler porous layer by applying a coating liquid containing an inorganic filler and a resin binder on at least one surface of a porous film containing a polyolefin resin as a main component. it can.

  The solvent of the coating liquid is preferably one that can uniformly and stably disperse the inorganic filler and the resin binder, and examples thereof include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water and ethanol. , Toluene, hot xylene, methylene chloride, hexane and the like.

  In the coating liquid, various additives such as a dispersant such as a surfactant, a thickener, a wetting agent, an antifoaming agent, a pH adjusting agent containing an acid or an alkali, for the purpose of stabilizing dispersion and improving coatability. May be added. These additives are preferably those which can be removed at the time of removing the solvent, but if they are electrochemically stable in the range of use of the lithium ion secondary battery, do not hinder the battery reaction, and are stable up to about 200° C., they are fillers. It may remain in the porous layer.

  The method of dispersing the inorganic filler and the resin binder in the solvent of the coating liquid is not particularly limited as long as it can realize the dispersion characteristics of the coating liquid necessary for the coating step. Examples thereof include ball mills, bead mills, planetary ball mills, vibrating ball mills, sand mills, colloid mills, attritors, roll mills, high speed impeller dispersions, dispersers, homogenizers, high speed impact mills, ultrasonic dispersions, mechanical stirring with stirring blades and the like.

  The method of applying the coating liquid to the porous film is not particularly limited as long as it can realize the required layer thickness and coating area, and examples thereof include a gravure coater method, a small diameter gravure coater method, a reverse roll coater method, and a transfer roll. The coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast coater method, die coater method, screen printing method, spray coating method, etc. ..

  Further, it is preferable to perform a surface treatment on the surface of the porous membrane prior to coating the coating liquid, because the coating liquid can be easily coated and the adhesion between the inorganic filler-containing filler porous layer and the porous membrane surface after coating is improved. .. The method of surface treatment is not particularly limited as long as it does not significantly impair the porous structure of the porous film, and examples thereof include corona discharge treatment method, mechanical roughening method, solvent treatment method, acid treatment method, and ultraviolet oxidation method. Etc.

  The method of removing the solvent from the coating film after coating is not particularly limited as long as it does not adversely affect the porous film, for example, a method of drying at a temperature below its melting point while fixing the porous film, at low temperature. Examples thereof include a method of drying under reduced pressure. From the viewpoint of controlling the shrinkage stress in the MD direction of the porous film and the multilayer porous film, it is preferable to appropriately adjust the drying temperature, the winding tension, and the like.

[Separator]
The separator of the present embodiment is a thermoplastic polymer coating having a specific sea-island structure on at least a part of at least one surface of the multilayer microporous film composed of the multilayer porous film or the polyolefin microporous film and the filler porous layer. With layers. The separator is preferably used to form an electricity storage device.

(Peel strength of multilayer porous film or separator)
Peel strength after pressing aluminum foil (positive electrode current collector, etc.) for 3 minutes at a temperature of 25° C. and a pressure of 5 MPa on the outermost surface of the multilayer porous film or the separator for an electricity storage device on which the thermoplastic polymer coating layer is present. (Hereinafter, also referred to as “cold strength at room temperature”) is preferably 8 gf/cm or less, more preferably 7 gf/cm or less, and further preferably 6 gf/cm or less. When the room temperature peel strength is higher than 8 gf/cm, stickiness is observed, and the slit property or winding property of the separator is impaired. The room temperature peel strength can be measured by the method described in the examples.

  Peel strength after pressing an aluminum foil (positive electrode current collector, etc.) for 3 minutes at a temperature of 80° C. and a pressure of 10 MPa for the outermost surface of the multilayer porous film having a thermoplastic polymer coating layer or the separator for an electricity storage device (Hereinafter, also referred to as “heat peel strength”) is preferably 10 gf/cm or more, more preferably 15 gf/cm or more, and further preferably 20 gf/cm or more. When the heat peeling strength is less than 10 gf/cm, peeling between the electrode and the separator is observed during the assembly process or use of the separator, which causes a decrease in the performance of the electric device. The heat peel strength can be measured by the method described in Examples.

  A separator having a heat peeling strength within the above range is preferable because it is excellent in adhesiveness between an electrode and a separator when applied to an electric storage device described later.

  Further, when the separator and the negative electrode are laminated in the presence of the electrolytic solution and the separator and the negative electrode are peeled off after being pressed at 80° C. and a pressure of 10 MPa for 2 minutes, the active material on the separator is the laminated area of the separator. Based on the above, it is preferable that 10% or more is attached.

  In the multilayer porous film or the separator for an electricity storage device according to the present embodiment, the 90° peel strength between the polyolefin microporous film and the thermoplastic polymer coating layer is preferably 6 gf/mm or more, more preferably 7 gf/mm or more, and 8 gf/mm. mm or more is more preferable. When the 90° peel strength between the polyolefin microporous film and the thermoplastic polymer coating layer is 6 gf/mm or more, the adhesive property between the thermoplastic polymer and the polyolefin microporous film tends to be more excellent, and as a result, the thermoplastic polymer layer Of the separator is suppressed, or the adhesiveness between the separator and the electrode tends to be excellent.

(Other physical properties of the separator)
The lower limit of the film thickness of the electricity storage device separator is preferably 2 μm or more, more preferably 5 μm or more, and the upper limit is preferably 100 μm or less, more preferably 50 μm or less, further preferably 30 μm or less. The film thickness of 2 μm or more is suitable from the viewpoint of ensuring the strength of the electricity storage device separator. On the other hand, setting the film thickness to 100 μm or less is preferable from the viewpoint of obtaining good charge and discharge characteristics.

  The air permeability of the electricity storage device separator according to the present embodiment has a lower limit of preferably 10 sec/100 cc or more, more preferably 50 sec/100 cc or more, and an upper limit of preferably 10,000 sec/100 cc or less, and further preferably 1,000 sec. /100 cc or less. The air permeability of 10 sec/100 cc or more is suitable from the viewpoint of further suppressing self-discharge of the electricity storage device when the electricity storage device separator is used. On the other hand, it is preferable that the air permeability is 10,000 sec/100 cc or less from the viewpoint of obtaining good charge/discharge characteristics. The air permeability of the separator for an electricity storage device can be adjusted by the stretching temperature, the stretching ratio, the area ratio of the thermoplastic polymer, the existing form, etc. during the production of the polyolefin microporous film.

  The short-circuit temperature, which is an index of heat resistance, of the electricity storage device separator is preferably 140° C. or higher, more preferably 150° C. or higher, and further preferably 160° C. or higher. When the short-circuit temperature is 160° C. or higher, it is preferable from the viewpoint of safety of the electricity storage device when it is used as an electricity storage device separator.

(Manufacturing method of separator for electricity storage device)
On the polyolefin microporous film, or on the multilayer microporous film consisting of the polyolefin microporous film and the filler porous layer, as a method for forming a thermoplastic polymer, is not particularly limited, for example, a coating solution containing a thermoplastic polymer Examples thereof include a method of applying to a polyolefin microporous film or a multi-layer microporous film.

  The method of applying the coating solution containing the thermoplastic polymer to the polyolefin microporous film or the multilayer microporous film is not particularly limited as long as it can achieve the required sea-island structure, layer thickness and application area. For example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast Examples thereof include a coater method, a die coater method, a screen printing method, a spray coating method, an inkjet coating method and the like. Among these, the gravure coater method or the spray coating method is preferable from the viewpoints that the degree of freedom of the coating shape of the thermoplastic polymer is high and a preferable area ratio can be easily obtained.

  When a thermoplastic polymer is applied to the multilayer microporous film, if the coating solution enters the inside of the multilayer microporous film, the adhesive resin fills the surface and the inside of the pores and the permeability decreases. .. Therefore, a poor solvent for the thermoplastic polymer is preferable as the medium for the coating liquid. When using a poor solvent of the thermoplastic polymer as the medium of the coating liquid, the coating liquid does not enter the inside of the multilayer microporous film, because the adhesive polymer is mainly present on the surface of the multilayer microporous film, It is preferable from the viewpoint of suppressing a decrease in permeability. Water is preferred as such a medium. The medium that can be used in combination with water is not particularly limited, and examples thereof include ethanol and methanol.

  Further, it is preferable to perform surface treatment on the surface of the multi-layer, microporous membrane prior to coating, because the coating solution can be easily coated and the adhesion between the multi-layer, microporous membrane and the adhesive polymer is improved. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the multi-layer, microporous membrane, and examples thereof include corona discharge treatment method, plasma treatment method, mechanical surface roughening method, solvent treatment method, and acid. Treatment methods, ultraviolet oxidation methods and the like can be mentioned.

  The method of removing the solvent from the coating film after coating is not particularly limited as long as it does not adversely affect the polyolefin microporous film or the multilayer microporous film. For example, a method of drying the multilayer microporous membrane at a temperature below its melting point while fixing it, a method of drying under reduced pressure at a low temperature, a method of immersing in a poor solvent for the adhesive polymer to coagulate the adhesive polymer and simultaneously extract the solvent Methods and the like.

  The electricity storage device separator is excellent in handleability during winding and rate characteristics of the electricity storage device, and is also excellent in adhesiveness and permeability between the thermoplastic polymer and the microporous polyolefin membrane. Therefore, the use of the electricity storage device separator is not particularly limited, but examples thereof include production of batteries such as non-aqueous electrolyte secondary batteries, and electricity storage devices such as capacitors and capacitors. The separator according to this embodiment can also be suitably used for separating substances and the like.

[Laminate]
By adhering the separator according to the present embodiment to the electrode, it is possible to obtain a laminated body in which the separator and the electrode are laminated. Here, "adhesion with electrodes" means that the heat peeling strength between the separator and the electrodes is preferably 10 gf/cm or more, more preferably 15 gf/cm or more, further assuming that the electrodes are aluminum foil. It is preferably 20 gf/cm or more.

  The laminate has excellent handleability during winding and rate characteristics of the electricity storage device, and also has excellent adhesiveness and permeability between the thermoplastic polymer and the polyolefin microporous membrane. Therefore, the use of the laminated body is not particularly limited, but the laminated body can be suitably used for, for example, batteries such as non-aqueous electrolyte secondary batteries, and electricity storage devices such as capacitors and capacitors.

  As the electrode used in the laminated body of the present embodiment, the electrode described in the item of the electricity storage device described later can be used.

  The method for producing a laminate using the separator of the present embodiment is not particularly limited, but for example, it can be produced by stacking the separator of the present embodiment and the electrode, and heating and/or pressing as necessary. . The heating and/or pressing can be performed when the electrode and the separator are stacked. It can also be manufactured by heating and/or pressing a wound body obtained by winding the electrode and the separator in a circular or flat spiral shape after stacking them.

  In addition, the laminated body can be manufactured by laminating a positive electrode-separator-negative electrode-separator or a negative electrode-separator-positive electrode-separator in the order of a flat plate, and pressurizing and auxiliary heating if necessary.

  More specifically, the separator of the present embodiment is prepared as a vertically elongated separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m), and the separator is It can also be manufactured by stacking in the order of positive electrode-separator-negative electrode-separator, or negative electrode-separator-positive electrode-separator, and pressurizing and optionally auxiliary heating.

  The pressure at the time of pressurization is preferably 1 MPa to 30 MPa. The pressing time is preferably 5 seconds to 30 minutes. The heating temperature is preferably 40°C to 120°C. The heating time is preferably 5 seconds to 30 minutes. Further, the order of pressurization and heating may be such that heating is followed by pressurization, pressurization and then heating, or pressurization and heating are carried out simultaneously. Among these, it is preferable to apply pressure and heat at the same time.

[Power storage device]
The separator of the present embodiment can be used for manufacturing batteries, capacitors, capacitors, etc., separating substances, and the like. In particular, when used as a separator for a non-aqueous electrolyte battery, it is possible to impart adhesiveness to an electrode and excellent battery performance.
Hereinafter, a preferred mode in which the electricity storage device is a non-aqueous electrolyte secondary battery will be described.

  When a non-aqueous electrolyte secondary battery is manufactured using the separator of this embodiment, the positive electrode, the negative electrode, and the non-aqueous electrolyte are not limited, and known ones can be used.

The positive electrode material is not particularly limited, but examples thereof include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel type LiMnO ₄ , and olivine type LiFePO ₄ .

  The negative electrode material is not particularly limited, but examples thereof include carbon materials such as graphite, non-graphitizable carbonaceous material, easily graphitizable carbonaceous material, and composite carbon body; silicon, tin, metallic lithium, various alloy materials, and the like.

The non-aqueous electrolytic solution is not particularly limited, but an electrolytic solution in which an electrolyte is dissolved in an organic solvent can be used. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and the like. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiBF ₄ , and LiPF ₆ .

  The method of manufacturing an electricity storage device using the separator of the present embodiment is not particularly limited, but when the electricity storage device is a secondary battery, for example, the separator of the present embodiment is provided with a width of 10 to 500 mm (preferably 80 to 500 mm). Prepared as a vertically long separator having a length of 200 to 4000 m (preferably 1000 to 4000 m), and the separators are stacked in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator to form a circle or a flat surface. It can be manufactured by winding in a spiral shape to obtain a wound body, housing the wound body in a battery can, and further injecting an electrolytic solution. At this time, the above-mentioned laminated body may be formed by heating and/or pressurizing the wound body. It is also possible to manufacture the above-mentioned wound body by using the above-mentioned laminated body wound in a circular or flat spiral shape. Further, the electricity storage device is obtained by laminating a positive electrode-separator-negative electrode-separator or a negative electrode-separator-positive electrode-separator in the order of a flat plate, or by laminating the above-mentioned laminate with a bag-shaped film and injecting an electrolytic solution. It can also be manufactured through steps and, if desired, steps of heating and/or pressurizing. The above heating and/or pressurizing step can be performed before and/or after the step of injecting the electrolytic solution.

  The above-mentioned measured values of various physical properties are values measured according to the measuring methods in Examples described later, unless otherwise specified.

  Hereinafter, the present invention will be described in detail based on examples, but the present invention is not limited to the examples. The methods for measuring and evaluating various physical properties used in the following Production Examples, Examples and Comparative Examples are as follows. Unless otherwise stated, various measurements and evaluations were performed under the conditions of room temperature of 23° C., 1 atmospheric pressure and relative humidity of 50%.

[Measuring method]
(1) Viscosity average molecular weight (hereinafter, also referred to as “Mv”)
Based on ASRM-D4020, the intrinsic viscosity [η] at 135°C in a decalin solvent was determined, and the Mv of polyethylene was calculated by the following formula.
[Η]=0.00068×Mv ^0.67
The Mv of polypropylene was calculated by the following formula.
[Η]=1.10× 10 ⁻⁴ × Mv ^0.80

(2) Unit weight of polyolefin microporous membrane A 10 cm×10 cm square sample was cut from the polyolefin microporous membrane, and the weight thereof was measured using an electronic balance AEL-200 manufactured by Shimadzu Corporation. Is multiplied by the obtained weight 100 at 1 m ² per layer of basis weight (g / ^{m 2)} was calculated.

(3) Film thickness (μm) of polyolefin microporous film, multilayer microporous film, and separator for electricity storage device
A 10 cm×10 cm sample was cut out from each of the polyolefin microporous film, the multilayer microporous film, and the electricity storage device separator, and nine locations (3 points×3 points) were selected in a grid pattern to measure the film thickness with a micro thickness gauge ( It was measured at room temperature of 23±2° C. using Toyo Seiki Seisakusho Ltd. type KBM. The average value of the measured values at 9 points was taken as the film thickness (μm) of the polyolefin microporous film, the multilayer porous film and the electricity storage device separator.

(4) Porosity of polyolefin microporous membrane (%)
A 10 cm×10 cm square sample was cut out from the polyolefin microporous membrane, its volume (cm ³ ) and mass (g) were determined, and the membrane density was set to 0.95 (g/cm ³ ) and calculated using the following equation.
Porosity=(volume-mass/film density)/volume×100

(5) Air permeability (sec/100cc)
Based on JIS P-8117, the air permeability resistance was measured by a Gurley type air permeability meter G-B2 (trademark) manufactured by Toyo Seiki Co., Ltd.

(6) Puncture strength of polyolefin microporous membrane (g)
Using a handy compression tester KES-G5 (trademark) manufactured by KATO TECH, the polyolefin microporous membrane was fixed by a sample holder having an opening with a diameter of 11.3 mm. Next, the center of the fixed microporous polyolefin membrane was subjected to a puncture test in an atmosphere of 25°C under a condition that the curvature radius of the needle tip was 0.5 mm and the puncture speed was 2 mm/sec. The puncture strength (g) was obtained as

(7) Average pore diameter (μm) of polyolefin microporous membrane
It is known that the fluid inside the capillary follows the Knudsen flow when the mean free path of the fluid is larger than the pore size of the capillary, and follows the Poiseuille flow when it is small. Therefore, it is assumed that the air flow in the permeability measurement of the microporous membrane follows the Knudsen flow, and the water flow in the permeability measurement of the microporous membrane follows the Poiseuille flow.
The average pore diameter d (μm) is defined by the air permeation rate constant R _gas (m ³ /(m ² ·sec·Pa)), the water permeation rate constant R _liq (m ³ /(m ² ·sec·Pa)), Calculated from the molecular velocity ν (m/sec) of air, the viscosity η (Pa·sec) of water, the standard pressure Ps (=101325 Pa), the porosity ε (%), and the film thickness L (μm) using the following formula. It was
d=2ν×(R _liq /R _gas )×(16η/3Ps)×10 ⁶
Here, R _gas is calculated from the air permeability (sec) using the following equation.
R _gas =0.0001/(air permeability×(6.424×10 ⁻⁴ )×(0.01276×101325))
Further, R _liq is obtained from the water permeability (cm ³ /(cm ² ·sec·Pa)) using the following equation.
R _liq =water permeability/100
The water permeability is calculated as follows. A microporous membrane preliminarily dipped in ethanol was set in a 41 mm diameter stainless-steel permeable cell, and after the ethanol in the membrane was washed with water, water was allowed to permeate at a differential pressure of about 50,000 Pa for 120 seconds. The amount of water permeation (cm ³ ) at that time was used to calculate the amount of water permeation per unit time, unit pressure, and unit area, which was taken as the water permeability.
Further, ν is calculated from the gas constant R (=8.314), the absolute temperature T(K), the circular constant π, and the average molecular weight M of air (=2.896×10 ⁻² kg/mol) using the following formula. Desired.
ν=((8R×T)/(π×M)) ^1/2

(8) Glass transition temperature of thermoplastic polymer An appropriate amount of the coating liquid (nonvolatile content=38 to 42%, pH=9.0) of the thermoplastic polymer is placed in an aluminum dish and dried with a hot air dryer at 130° C. for 30 minutes. did. About 17 mg of the dried film after drying was packed in an aluminum container for measurement, and a DSC curve and a DDSC curve under a nitrogen atmosphere were obtained with a DSC measuring device (manufactured by Shimadzu Corporation, DSC6220). The measurement conditions were as follows.
(1st stage heating program)
Start at 70°C and raise the temperature at a rate of 15°C per minute. Hold for 5 minutes after reaching 110°C.
(2nd stage cooling program)
The temperature drops from 110℃ to 40℃ per minute. Hold for 5 minutes after reaching -50°C.
(3rd stage heating program)
The temperature is raised from -50°C to 130°C at a rate of 15°C per minute. Data of DSC and DDSC were acquired when the temperature was raised in the third step.
The intersection of the baseline (a straight line obtained by extending the baseline in the obtained DSC curve to the high temperature side) and the tangent at the inflection point (the point where the upward convex curve changes to the downward convex curve) is taken to be the glass transition temperature ( Tg).

(9) Gel fraction of thermoplastic polymer (toluene insoluble matter)
On a Teflon (registered trademark) plate, a coating solution of a thermoplastic polymer (nonvolatile content=38 to 42%, pH=9.0) was dropped with a dropper (diameter 5 mm or less), and it was heated with a hot air dryer at 130° C. to 30 Dry for minutes. After drying, about 0.5 g of the dried film was precisely weighed (a), taken into a 50 mL polyethylene container, and 30 mL of toluene was poured therein and shaken at room temperature for 3 hours. Then, the content was filtered through 325 mesh, and the toluene-insoluble matter remaining on the mesh was dried together with the mesh for 1 hour in a hot air dryer at 130°C. The dry weight of the 325 mesh used here was measured in advance.

After the toluene was volatilized, the dry weight of the insoluble portion of 325 mesh was subtracted from the dry weight of the toluene insoluble portion and the weight of 325 mesh to obtain the dry weight (b) of the toluene insoluble portion. The gel fraction (toluene-insoluble matter) was calculated by the following formula.
Gel fraction of thermoplastic polymer (toluene insoluble matter)=(b)/(a)×100 [%]

(10) Swelling degree of the thermoplastic polymer with respect to the electrolytic solution (swelling degree of the electrolyte solvent) (fold)
After leaving the thermoplastic polymer or the solution in which the thermoplastic polymer is dispersed in an oven at 130° C. for 1 hour, the dried thermoplastic polymer is cut into 0.5 g, and ethylene carbonate:ethyl methyl carbonate=1 : 2 (volume ratio) together with 10 g of mixed solvent was placed in a 50 mL vial and allowed to infiltrate for 3 hours, then a sample was taken out, washed with the above mixed solvent, and the weight (Wa) was measured. Then, after standing still in an oven at 150° C. for 1 hour, the weight (Wb) was measured, and the swelling degree of the thermoplastic polymer with respect to the electrolytic solution was measured by the following formula.
Swelling degree (times) of the thermoplastic polymer with respect to the electrolytic solution=(Wa-Wb)/(Wb)

(11) Average particle size (μm) of granular thermoplastic polymer
The average particle diameter of the granular thermoplastic polymer was determined by using an osmium vapor-deposited electricity storage device separator with a scanning electron microscope (SEM) “Model S-4800, manufactured by HITACHI” at an acceleration voltage of 1.0 kV and 30,000 times. It was measured by observing. The part of the granular thermoplastic polymer having the largest diameter was defined as the particle size, and the average value of 20 particles was defined as the average particle size.

(12) Area ratio of granular thermoplastic polymer (surface particle area ratio)
The area ratio (S) of the granular thermoplastic polymer to the thermoplastic polymer existing on the outermost surface of the electricity storage device separator was calculated by the following formula.
S (%)=area of granular thermoplastic polymer/total area of thermoplastic polymer present on outermost surface of separator×100
The area of the granular thermoplastic polymer was measured using a scanning electron microscope (SEM) "Model S-4800, manufactured by HITACHI". It was measured by osmium vapor deposition of a separator for an electricity storage device and observing at an acceleration voltage of 1.0 kV and 30,000 times.

(13) Ratio of each area of Voronoi polygon/average area of Voronoi polygon (normalized area)
Voronoi division means dividing a plurality of points (generic points) placed at arbitrary positions in a certain metric space into areas according to which other points in the same space are closer to the generatrix. .. A diagram including the regions thus obtained is called a Voronoi diagram. Generally, in a Voronoi diagram, the boundaries of a plurality of regions are part of the bisector of each generatrix, and each region forms a polygon.

  When observing the surface of the separator in a specific visual field, one thermoplastic polymer particle is regarded as one circle having an average diameter (l) in the observation visual field, and between the adjacent thermoplastic polymer particles. A vertical bisector is drawn, and a polygon surrounded by the vertical bisector for each particle is called a "Voronoi polygon".

  When Voronoi division is performed in the observation visual field, an unclosed region is not to be calculated by the above formula. Examples of the unclosed region include a region obtained by performing Voronoi division on a particle when the particle is present at the boundary of the observation visual field and the entire particle is not observed.

  Therefore, in an image obtained by photographing at least a part of the surface of the separator, it is preferable to confirm whether or not all the particles are observed with respect to the particles located at the edge of the image.

  The confirmation method varies depending on the object to be verified, but as an example, the dispersibility of the thermoplastic polymer particles is evaluated in a visual field larger than 10 μm×10 μm. Also, the number of images to be picked up cannot be unconditionally specified depending on the object, but it is considered necessary to test at least 10 fields of view randomly selected.

  The Voronoi partitioning defined above can be performed on the thermoplastic polymer particles specified in a specific viewing field of the separator surface. Specifically, the surface of the organic coating film after coating the separator surface with the thermoplastic polymer is photographed to obtain an image. By considering the thermoplastic polymer particles specified in the obtained image as a circle having an average diameter (l) and performing Voronoi division, a Voronoi polygon can be drawn. For example, the Voronoi polygon may be drawn manually or by using image processing software, and the area of the drawn Voronoi polygon may be calculated.

  For example, FIG. 2 is an example of a result obtained by performing Voronoi division on the plurality of thermoplastic polymer particles specified in FIG. 1 to obtain a Voronoi polygon. Among the Voronoi polygons shown in FIG. 2, the number and area of Voronoi polygons corresponding to the closed regions are automatically calculated using image processing software (FIG. 3).

  By the above observation method and image processing method, the projected area of the observation visual field is determined, and the total number of the thermoplastic polymer particles, the projected area and the area of the Voronoi polygon are obtained. Also, the area of the Voronoi polygon can be calculated for the thermoplastic polymer particles according to the above definition. Further, by averaging the areas of the Voronoi polygons in the visual field, the area occupied by the particles when the particles are ideally and uniformly arranged can be obtained. The degree of particle aggregation can be evaluated by dividing the area of each Voronoi polygon by the average area of the Voronoi polygons in the field of view. It can be evaluated that the Voronoi polygonal portion having a normalized area smaller than 1 has dense particles, and the portion having a normalized area larger than 1 has coarse particles.

(14) Adhesive force between the thermoplastic polymer coating layer and the polyolefin microporous film (adhesiveness with the substrate)
A tape (made by 3M) having a width of 12 mm and a length of 100 mm was attached to the thermoplastic polymer coating layer of the separator. The force when peeling the tape from the sample at a speed of 50 mm/min was measured using a 90° peel strength measuring device (manufactured by IMADA, product name IP-5N). Based on the obtained measurement results, the adhesive strength was evaluated according to the following evaluation criteria.
A: 6 gf/mm or more C: less than 6 gf/mm

(15) Heat peeling strength and stickiness (peeling strength of separator)
A separator and a positive electrode current collector (Aluminum foil 20 μm manufactured by Fuji Paper Co., Ltd.) as an adherend were cut into 30 mm×150 mm pieces, respectively, and laminated to obtain a laminated body, and the laminated body was Teflon (registered trademark). ) Sheets (Nichias Corp. Naflon PTFE sheet TOMBO-No. 9000). A test sample was obtained by pressing each laminate under the following conditions.
Condition 1) Pressurized at a temperature of 25° C. and a pressure of 5 MPa for 3 minutes Condition 2) Pressed at a temperature of 40° C. and a pressure of 5 MPa for 3 minutes Condition 3) Pressurized at a temperature of 80° C. and a pressure of 10 MPa for 3 minutes The peel strength was measured at a tensile speed of 200 mm/min in accordance with JIS K6854-2 using an autograph AG-IS type (trademark) manufactured by Shimadzu Corporation. Based on the obtained results, the peel strength of the separator was evaluated according to the following evaluation criteria.
Sticking property (separator handling property) evaluation standard: Condition 1) Evaluation standard of peel strength after pressing S: Peel strength is 4 gf/cm or less A: Peel strength is more than 4 gf/cm and 6 gf/cm or less B: Peel strength is more than 6 gf/cm and 8 gf/cm or less C: Peel strength is more than 8 gf/cm Sticking property (separator handling property) evaluation criterion: Condition 2) Peel strength after pressing evaluation standard S: Peel strength Is 4 gf/cm or less A: Peel strength is more than 4 gf/cm and 6 gf/cm or less B: Peel strength is more than 6 gf/cm and 8 gf/cm or less C: Peel strength is more than 8 gf/cm Heat peel strength evaluation criteria : Evaluation criteria for peel strength after pressing under condition 3) A: Peel strength is 10 gf/cm or more C: Peel strength is less than 10 gf/cm

(16) Adhesion between separator and electrode (adhesion (counter electrode))
The adhesiveness between the separator and the electrode was evaluated by the following procedure.

(Preparation of positive electrode)
92.2% by mass of lithium cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material, 2.3% by mass of scaly graphite and acetylene black as conductive materials, and 3.2% by mass of polyvinylidene fluoride (PVDF) as a binder. % Was dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. This slurry was applied onto one surface of an aluminum foil having a thickness of 20 μm to be a positive electrode current collector with a die coater, dried at 130° C. for 3 minutes, and then compression-molded with a roll press. At this time, the amount of active material applied to the positive electrode was 250 g/m ² , and the bulk density of the active material was 3.00 g/cm ³ .

(Preparation of negative electrode)
96.9% by mass of artificial graphite as a negative electrode active material, 1.4% by mass of ammonium salt of carboxymethyl cellulose as a binder and 1.7% by mass of styrene-butadiene copolymer latex were dispersed in purified water to prepare a slurry. This slurry was applied to one surface of a copper foil having a thickness of 12 μm to be a negative electrode current collector with a die coater, dried at 120° C. for 3 minutes, and then compression-molded with a roll press. At this time, the amount of active material applied to the negative electrode was 106 g/m ² and the bulk density of the active material was 1.35 g/cm ³ .

(Adhesion test)
The negative electrode obtained by the above method was cut into a width of 20 mm and a length of 40 mm. An electrolytic solution (manufactured by Toyama Yakuhin Kogyo Co., Ltd.) in which ethylene carbonate and diethyl carbonate were mixed at a ratio of 2:3 (volume ratio) was placed on the electrode to such an extent that the negative electrode was immersed therein, and a separator was placed thereon. This laminate was placed in an aluminum zip and pressed at 80° C. and 10 MPa for 2 minutes, then the laminate was taken out and the separator was peeled off from the negative electrode.
(Evaluation criteria)
S: When the negative electrode active material adheres to 30% or more of the area of the separator.
A: When the negative electrode active material adheres to an area of 10% or more and less than 30% of the separator.
C: When the negative electrode active material adheres to an area of less than 10% of the separator.

(17) Windability and battery cycle characteristics (17-1) Preparation of evaluation sample <Electrode>
A positive electrode and a negative electrode were prepared in the same manner as in item (17) “Adhesiveness between separator and electrode”. An electrode for evaluation was prepared by cutting the positive electrode into a width of about 57 mm and the negative electrode into a width of about 58 mm to form a strip.

<Preparation of non-aqueous electrolyte>
The non-aqueous electrolytic solution was prepared by dissolving LiPF ₆ as a solute to a concentration of 1.0 mol/L in a mixed solvent of ethylene carbonate/ethyl methyl carbonate=1/2 (volume ratio).

<Separator>
The separators obtained in Examples and Comparative Examples were slit to 60 mm to form a strip, and thus an evaluation separator was produced.

(17-2) Evaluation of winding property The negative electrode, the separator, the positive electrode, and the separator obtained in the above are stacked in this order, and are spirally wound multiple times with a winding tension of 250 gf to produce an electrode laminate. did. The presence or absence of twists and wrinkles of the separator in the 10 electrode laminates produced was visually observed and evaluated according to the following evaluation criteria.
(Evaluation criteria)
S: No appearance defect such as twisting or wrinkling occurred.
A: One appearance defect such as twist or wrinkle occurred.
C: Two or more appearance defects such as twists and wrinkles occurred.

(17-3) Evaluation of battery cycle characteristics <Battery assembly>
The negative electrode, the separator, the positive electrode, and the separator obtained in the above were stacked in this order, and the winding tension was 250 gf and the winding speed was 45 mm/sec. .. This electrode laminate was housed in a stainless steel container having an outer diameter of 18 mm and a height of 65 mm, an aluminum tab drawn from the positive electrode current collector was used as a container lid terminal, and a nickel tab drawn from the negative electrode current collector was used. Welded to the vessel wall. Then, it was dried under vacuum at 80° C. for 12 hours. The non-aqueous electrolyte solution was injected into the assembled battery container in an argon box and sealed.

<Pretreatment>
The assembled battery was charged with a constant current of 1/3C to a voltage of 4.2V, and then charged with a constant voltage of 4.2V for 8 hours, and then discharged to a final voltage of 3.0V with a current of 1/3C. went. Next, constant voltage charging was performed at a current value of 1 C to a voltage of 4.2 V, constant voltage charging at 4.2 V was performed for 3 hours, and then discharging was performed at a current of 1 C to a final voltage of 3.0 V. Finally, constant current charging was performed at a current value of 1 C to 4.2 V, and then constant voltage charging at 4.2 V was performed for 3 hours to complete the pretreatment. In addition, 1 C represents a current value for discharging the reference capacity of the battery in 1 hour.

<Cycle test>
The pretreated battery was discharged at a discharge current of 1 A to a discharge end voltage of 3 V at a temperature of 25° C., and then at a charge current of 1 A to a charge end voltage of 4.2 V. This was set as one cycle, charging and discharging were repeated, and the cycle retention was evaluated based on the following criteria using the capacity retention rate after 1000 cycles with respect to the initial capacity.
(Evaluation criteria)
S: Capacity retention rate of 95% to 100% A: Capacity retention rate of 90% to less than 95% C: Capacity retention rate of less than 90%

[Production Example 1-1] (Production of polyolefin microporous film 1)
Mv is 700,000, homopolymer high-density polyethylene 45 parts by mass, Mv is 300,000, homopolymer high-density polyethylene 45 parts by mass, homopolymer polypropylene and Mv with Mv 400,000. Was mixed with 10 parts by mass of a homopolymer of polypropylene having a ratio of 150,000 (mass ratio=4:3) by dry blending using a tumbler blender. To 99 parts by mass of the obtained polyolefin mixture, 1 part by mass of tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane was added as an antioxidant, and the tumbler blender was added again. A mixture was obtained by dry blending with. The resulting mixture was fed by a feeder into a twin-screw extruder under a nitrogen atmosphere. Liquid paraffin (kinematic viscosity at 37.78° C. 7.59×10 ⁻⁵ m ² /s) was injected into the extruder cylinder by a plunger pump. The operating conditions of the feeder and the pump were adjusted so that the ratio of liquid paraffin in the entire mixture extruded was 65 parts by mass, that is, the polymer concentration was 35 parts by mass.

  Then, they are melt-kneaded in a twin-screw extruder while being heated to 230° C., and the obtained melt-kneaded product is extruded through a T-die onto a cooling roll whose surface temperature is controlled to 80° C., and the extruded product is extruded. A sheet-like molded article was obtained by bringing the sheet into contact with a cooling roll and casting to solidify by cooling. This sheet was stretched by a simultaneous biaxial stretching machine at a magnification of 7×6.4 times at a temperature of 112° C., immersed in methylene chloride to extract and remove liquid paraffin, and then dried. The film was stretched 2 times in the transverse direction at 0°C. Then, this stretched sheet was relaxed by about 10% in the width direction and heat-treated to obtain a polyolefin microporous film 1 shown in Table 1.

  The physical properties of the obtained polyolefin microporous film 1 were measured by the methods described above. The obtained polyolefin microporous membrane was used as a separator as it was and evaluated by the above method. The results obtained are shown in Table 1.

[Production Example 1-2] (Production of polyolefin microporous membrane 2)
96.0 parts by mass of aluminum hydroxide oxide (average particle size 1.0 μm) and 4.0 parts by mass of acrylic latex (solid content concentration 40%, average particle size 145 nm, minimum film forming temperature 0° C. or lower), polycarboxylic acid A coating solution was prepared by uniformly dispersing 1.0 part by mass of an ammonium aqueous solution (SN Dispersant 5468 manufactured by San Nopco Co., Ltd.) in 100 parts by mass of water, and coating the surface of the polyolefin microporous film 1 with a microgravure coater. .. Water was removed by drying at 60° C., a filler porous layer was formed to a thickness of 2 μm, and a polyolefin microporous film 2 was obtained. The obtained polyolefin microporous film 2 was evaluated by the above method in the same manner as in Production Example 1-1. The results obtained are shown in Table 1.

[Production Example 1-3] (Production of polyolefin microporous membrane 3)
95.0 parts by weight of calcined kaolin (high-temperature calcined wet kaolin containing kaolinite (Al ₂ Si ₂ O ₅ (OH) ₄ ) as the main component, average particle diameter of 1.8 μm) and acrylic latex (solid content) A concentration of 40%, an average particle size of 220 nm, a minimum film formation temperature of 0° C. or lower) 5.0 parts by mass, and an ammonium polycarboxylate aqueous solution (SN Dispersant 5468 manufactured by San Nopco Ltd.) 0.5 parts by mass are uniformly added to 180 parts by mass of water. To prepare a coating solution, which was coated on the surface of the polyolefin microporous film 1 using a microgravure coater. Water was removed by drying at 60° C., a filler porous layer was formed to a thickness of 6 μm, and a polyolefin microporous film 3 was obtained. The obtained polyolefin microporous film 3 was evaluated by the above method in the same manner as in Production Example 1-1. The results obtained are shown in Table 1.

[Production Example 1-4] (Production of polyolefin microporous film 4)
94 parts by mass of aluminum hydroxide particles (average particle size 1.0 μm), 6.0 parts by mass of acrylic latex (solid content concentration 45%, average particle size 145 nm, minimum film forming temperature of 0° C. or less) and amine salt of polyphosphate (dispersion) Agent) An aqueous solution obtained by uniformly dispersing 1.0 parts by mass of water in 100 parts by mass of water was applied to the surface of the polyolefin microporous film 1 using a gravure coater. Water was removed by drying at 60° C., and a porous filler layer was formed to a thickness of 2 μm to obtain a polyolefin microporous film 4. The obtained polyolefin microporous film 4 was evaluated by the above method in the same manner as in Production Example 1-1. The results obtained are shown in Table 1.

[Production Example 2-1A]
(Production of Raw Polymer 1A for Thermoplastic Polymer Coating Layer)
In a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank and a thermometer, 70.4 parts by mass of ion-exchanged water and "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) were used. 5 parts by mass and 0.5 parts by mass of "Adecaria Soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd.) were charged, the temperature inside the reaction vessel was raised to 80°C, and the temperature of 80°C was reached. While maintaining the above, 7.5 parts by mass of ammonium persulfate (2% aqueous solution) was added.

  Five minutes after adding the ammonium persulfate aqueous solution, 38.5 parts by mass of methyl methacrylate, 19.6 parts by mass of n-butyl acrylate, 31.9 parts by mass of 2-ethylhexyl acrylate, 0.1 parts by mass of methacrylic acid, and acrylic Acid 0.1 part by mass, 2-hydroxyethyl methacrylate 2 parts by mass, acrylamide 5 parts by mass, glycidyl methacrylate 2.8 parts by mass, trimethylolpropane triacrylate (A-TMPT, manufactured by Shin-Nakamura Chemical Co., Ltd.) 0 0.7 parts by mass, "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 3 parts by mass, "Adecaria Soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA CORPORATION) 3 parts by mass, A mixture of 0.05 parts by mass of sodium p-styrenesulfonate, 7.5 parts by mass of ammonium persulfate (2% aqueous solution), 0.3 parts by mass of γ-methacryloxypropyltrimethoxysilane, and 52 parts by mass of ion-exchanged water, The mixture was mixed with a homomixer for 5 minutes to prepare an emulsion. The obtained emulsion was dropped from the dropping tank into the reaction vessel over 150 minutes.

  After the completion of dropping the emulsion, the temperature inside the reaction vessel was maintained at 80° C. for 90 minutes, and then cooled to room temperature. The obtained emulsion was adjusted to pH=9.0 with an aqueous ammonium hydroxide solution (25% aqueous solution) to obtain an acrylic copolymer latex having a concentration of 40% (raw polymer 1A). The obtained raw material polymer 1A was evaluated by the above method. The results obtained are shown in Table 2.

[Production Example 2-2A, 2-3A]
(Raw polymer 2A, 3A for thermoplastic polymer coating layer)
An acrylic copolymer latex was obtained in the same manner as in the production of the raw material polymer 1A, except that the compositions of the monomers and other raw materials used were changed as shown in Table 2 (raw material polymers 2A and 3A). The obtained raw material polymers 2A and 3A were evaluated by the above method. The obtained results are shown in Table 2.

  The Tg values of the raw material polymers 1A, 2A and 3A shown in Table 2 are all approximate values based on the FOX equation.

(Note) Raw material names in Table 2 or 3 MMA: methyl methacrylate BA: n-butyl acrylate CHMA: cyclohexyl methacrylate EHA: 2-ethylhexyl acrylate MAA: methacrylic acid AA: acrylic acid HEMA: methacrylic acid 2-hydroxy Ethyl AM: Acrylamide GMA: Glycidyl Methacrylate NaSS: Sodium p-styrenesulfonate A-TMPT: Trimethylolpropane triacrylate (Shin-Nakamura Chemical Co., Ltd.)
KH1025: Aqualon KH1025 (registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)
SR1025: ADEKA rear soap SR1025 (registered trademark, manufactured by ADEKA Corporation)
APS: Ammonium persulfate

(Method for producing granular particles)
(Raw material polymers 1A2-a to 1A6, 2A2 to 2A5, 3A2 to 3A6)
Granular particles were prepared by subjecting the raw material polymers shown in Table 2 to multistage polymerization. Specifically, according to the blending amount (mass basis) shown in Table 3, a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank and a thermometer was charged with ion-exchanged water, a seed polymer, and an emulsifier as an initial charge. Then, the temperature in the reaction vessel was maintained at 30° C., and a 2% aqueous solution of an initiator was added.

  Five minutes after the addition, according to the blending amount (mass basis) shown in Table 3, an emulsified mixed solution consisting of a monomer, a functional group-containing monomer, an emulsifier, a cross-linking agent, an initiator, and ion-exchanged water is taken for 150 minutes. Was charged into the reaction vessel from the dropping tank. In this state, stirring was continued for another 30 minutes to allow the seed particles to absorb the monomer. Next, while maintaining the pH of the reaction system at 4 or less, the temperature of the reaction vessel was raised to 80° C., stirring was continued for 120 minutes, and then cooled to room temperature.

  After cooling, filtration was performed with a 200-mesh wire net to remove aggregates and the like, to obtain a granular polymer. When the granular polymer is further subjected to seed polymerization to increase the particle size, it is carried out from the beginning. On the other hand, when using this granular polymer as a resin binder as it was, after filtration, the pH was adjusted to 8 with 25% ammonia water, and then water was added to adjust the solid content to 50%.

  The physical properties of the obtained raw material polymers 1A2-a to 1A6, 2A2 to 2A5, and 3A2 to 3A6 were evaluated by the methods described above. The evaluation results are shown in Table 3. The Tg of the thermoplastic polymer (raw material polymer) in Table 3 is a value measured by the method described in (8) above.

[Examples 1 to 33 (however, Examples 1 to 8, 12 to 14C, 18 to 20, 24 to 33 are reference examples) , Comparative Examples 1 to 15]
A separator for an electricity storage device was produced according to the combination of the microporous membrane and the raw material polymer shown in Tables 4 to 9. Specifically, the raw material polymers shown in Tables 4 to 9 were uniformly dispersed in water at the concentrations shown in Tables 4 to 9 to prepare coating solutions containing a thermoplastic polymer. Next, the coating liquid is applied to one surface of the microporous polyolefin membrane described in Tables 4 to 9 by the coating method (spray or gravure) described in Tables 4 to 9 and dried at 60° C. to apply the coating. The liquid water was removed. Further, the coating liquid was similarly applied to the other surface of the polyolefin microporous film and dried again to prepare a separator for an electricity storage device including a thermoplastic polymer on both surfaces of the polyolefin microporous film. The physical properties and evaluation results of the obtained separator are shown in Tables 4-9.

Claims (9)

A multilayer porous membrane having a polyolefin microporous membrane and a thermoplastic polymer coating layer coating at least a part of at least one outermost surface of the polyolefin microporous membrane,
In the thermoplastic polymer coating layer, a granular thermoplastic polymer having an average particle size of 1280 nm or more and 2000 nm or less is dispersed and present,
The glass transition temperature (Tg) of the granular thermoplastic polymer is 120° C. or lower,
The outermost surface has a sea-island structure including a portion containing the granular thermoplastic polymer and a portion not containing the granular thermoplastic polymer , and
Formula (1) below:
{In the formula, "Voronoi polygon area" is the area of each polygon obtained by subjecting the granular thermoplastic polymer to Voronoi division in the field of view of the multilayer porous film, and "Voronoi polygon in field of view""Average area value" is the average value of all Voronoi polygon areas obtained in the field of view. }
A multilayer porous membrane having a standardized area represented by the minimum value of 0.3 or more .   The multilayer porous membrane according to claim 1, wherein the granular thermoplastic polymer is obtained by further performing seed polymerization after the production of seed particles. The multilayer porous structure according to claim 1 or 2 , wherein the aluminum foil has a peel strength of 8 gf/cm or less after pressing the aluminum foil on the outermost surface of the multilayer porous film at a temperature of 25°C and a pressure of 5 MPa for 3 minutes. film. The multi-layered porous structure according to claim 1 or 2 , wherein the aluminum foil has a peel strength of 10 gf/cm or more after being pressed against the outermost surface of the multi-layered porous film at a temperature of 80°C and a pressure of 10 MPa for 3 minutes. film. The 90 ° peel strength between the polyolefin microporous membrane and the thermoplastic polymer coating layer, is 6 gf / mm or more, the multilayer porous membrane according to any one of claims 1-4. Area ratio of the polyolefin microporous membrane is covered by the thermoplastic polymer coating layer, the total surface area of 100% of the polyolefin microporous film is 95% or less, any one of claims 1 to 5 The multi-layered porous membrane according to 1. Area ratio of the polyolefin microporous membrane is covered by the thermoplastic polymer coating layer, the total surface area of 100% of the polyolefin microporous film is 50% or less, any one of claims 1 to 6 The multilayer porous membrane according to. Electric storage device separator comprising a multilayer porous membrane according to any one of claims 1-7. A laminated body in which the separator for an electricity storage device according to claim 8 and an electrode are laminated.