TWI511353B - A multilayer porous film, a method for producing the same, and a separator for a nonaqueous electrolyte battery - Google Patents

Description

Multilayer porous film, manufacturing method thereof, and separator for nonaqueous electrolyte battery

The present invention relates to a multilayer porous film, a method for producing the same, and a separator for a nonaqueous electrolyte battery.

In recent years, further efforts have been made to promote the high capacitance of batteries, and a separator having a relatively small thickness and high heat resistance is required in such a high-capacity battery, and research is being advanced. For example, Patent Document 1 discloses a separator for a battery in which a porous film containing an inorganic filler mainly composed of plate-like particles and a porous film mainly composed of polyolefin are integrated at a high temperature. It can also maintain the shutdown state.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2010-123465

However, it is considered that the battery separator described in Patent Document 1 has improved heat resistance as compared with a normal separator having no heat-resistant layer. However, if the porous film containing the inorganic filler is thinned, the desired heat resistance cannot be obtained. Sex, there is room for improvement in this regard.

The present invention has been made in view of the above problems, and an object thereof is to provide a multilayer porous film having a low heat shrinkage ratio, a method for producing the same, and a separator for a nonaqueous electrolyte battery comprising the multilayer porous film.

The inventors of the present invention have conducted intensive studies on the above problems. As a result, it has been found that the above problems can be solved by forming a specific porous layer on one or both sides of the polyolefin porous film, and the present invention has been completed.

That is, the present invention is as follows.

[1] A multilayer porous film comprising: a polyolefin porous film; and a porous layer disposed on one surface or both surfaces of the polyolefin porous film and containing an inorganic filler, a resin binder, and an ionic dissociable inorganic dispersant.

[2] The multilayer porous film according to [1] above, wherein the porous layer further contains an ionic dissociable organic dispersant.

[3] The multilayer porous film according to the above [2], wherein the content of the ionic dissociable inorganic dispersant is 20% by mass based on 100 parts by mass of the total of the ionic dissociable inorganic dispersant and the ionic dissociable organic dispersant More than 95 parts by weight.

[4] The multilayer porous film according to any one of [1] to [3] wherein the ionic dissociable inorganic dispersant comprises a condensed phosphate.

[5] The multilayer porous film according to any one of [1] to [4] wherein the above-mentioned resin binder comprises an acrylic polymer.

[6] A separator for a non-aqueous electrolyte battery, comprising the multilayer porous film according to any one of [1] to [5].

[7] A method for producing a multilayer porous film, comprising the step of coating: porous in polyolefin A dispersion containing an inorganic filler, a resin binder, and an ionic dissociable inorganic dispersant is applied to one side or both sides of the film.

[8] The method for producing a multilayer porous film according to the above [7], wherein the resin binder comprises an acrylic polymer.

[9] The method for producing a multilayer porous film according to the above [7] or [8] wherein the dispersion further contains an ionic dissociable organic dispersant.

According to the invention, it is possible to provide a multilayer porous film having a low heat shrinkage ratio, a method for producing the same, and a separator for a nonaqueous electrolyte battery comprising the multilayer porous film.

Hereinafter, the form for carrying out the invention (hereinafter simply referred to as "this embodiment") will be described in detail. The present invention is not limited to the embodiments described below, and various modifications can be made without departing from the spirit and scope of the invention.

[Multilayer porous film]

The multilayer porous film of the present embodiment has a polyolefin porous film, and a porous layer which is disposed on one surface or both surfaces of the polyolefin porous film and contains an inorganic filler, a resin binder, and an ionic dissociable inorganic dispersant (hereinafter only It is called "porous layer").

[Polyolefin porous film]

The polyolefin porous film is not particularly limited, and a porous film containing a polyolefin resin can be used. The content of the polyolefin resin in the polyolefin porous film is not particularly limited, and is preferably 50% by mass or more, more preferably 70 to 100% by mass. When the content of the polyolefin resin in the polyolefin porous film is within the above range, the shutdown performance in the case of use as a separator for a battery tends to be further improved.

The polyolefin resin is not particularly limited, and for example, a polyolefin resin which is usually used in extrusion molding, injection molding, inflation molding, blow molding, or the like can be used. Specific examples of such a polyolefin resin include homopolymers of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene, and the like. Copolymers and such multistage polymers. More specifically, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, and ultra high molecular weight polyethylene, the same row of polypropylene, atactic polypropylene, ethylene-propylene random copolymer , polybutene, and ethylene propylene rubber. In addition, the polyolefin resin may be used alone or in combination of two or more.

Among them, the polyolefin resin preferably contains polypropylene. The content of the polypropylene in the polyolefin resin is not particularly limited, but is preferably 1 to 35% by mass, more preferably 3 to 20% by mass, still more preferably 4 to 10% by mass. When the content of the polypropylene is 1% by mass or more, the heat resistance of the porous film tends to be further improved. Further, when the content of the polypropylene having a relatively high melting point is 35% by mass or less, when the multilayer porous film of the present embodiment is used as a separator for a battery, the film is thermally melted and porous at a shutdown temperature. It is easier to block (shutdown), and it tends to shut down at a lower temperature.

The viscosity average molecular weight (Mv) of the polyolefin resin is not particularly limited, and is preferably 50,000 to 3,000,000, more preferably 100,000 to 1,000,000, still more preferably 200,000 to 800,000. When the Mv of the polyolefin resin is 50,000 or more, the mechanical strength of the obtained polyolefin porous film tends to be further improved. In addition, when the Mv of the polyolefin resin is 3,000,000 or less, the moldability at the time of production tends to be further improved. Further, when Mv is 1,000,000 or less, when it is used as a separator for a battery, it is easy to close the hole when the temperature rises, and the shutdown function tends to be further improved. Further, in order to control the mechanical strength of the porous film, a mixture of two or more kinds of polyolefin resins having different Mv may be used. By. Further, the viscosity average molecular weight (Mv) of the polyolefin resin can be measured by the method described in the examples.

The polyolefin porous film may contain an antioxidant such as a phenol compound, a phosphorus compound or a sulfur compound, a metal soap such as calcium stearate or zinc stearate, a UV absorber, a light stabilizer, and an antistatic agent, as needed. , anti-fogging agents, coloring pigments and other additives.

The film thickness of the polyolefin porous film is not particularly limited, but is preferably 0.10 μm or more and 25 μm or less, more preferably 1.0 μm or more and 20 μm or less, further preferably 3.0 μm or more and 18 μm or less, and particularly preferably 5.0 μm or more. 16 μm or less. When the film thickness of the polyolefin porous film is 0.10 μm or more, the mechanical strength of the obtained multilayer porous film tends to be further improved. In addition, when the film thickness of the polyolefin porous film is 25 μm or less, the battery tends to be further increased in capacitance. Further, the film thickness of the polyolefin porous film can be measured by the method described in the examples.

The average pore diameter of the polyolefin porous film is not particularly limited, but is preferably 0.030 μm or more and 0.20 μm or less, more preferably 0.040 μm or more and 0.10 μm or less, still more preferably 0.050 μm or more and 0.090 μm or less, and particularly preferably 0.060. Μm or more and 0.090 μm or less.

The porosity of the polyolefin porous film is not particularly limited, but is preferably 25% or more and 65% or less, more preferably 30% or more and 60% or less, and still more preferably 35% or more and 55% or less. When the porosity of the polyolefin porous film is 25% or more, the increase in the air permeability after the application of the dispersion containing the inorganic filler described below can be further suppressed. Further, the porosity of the polyolefin porous film can be measured by the method described in the examples.

The maximum value of the heat shrinkage stress of the polyolefin porous film is not particularly limited, and the extraction direction (hereinafter also referred to as "MD") and the width direction (hereinafter also referred to as "TD") are preferably 10 g or less, more preferably 8 g. Hereinafter, it is more preferably 6 g or less, and particularly preferably 4 g or less. When the maximum value of the heat shrinkage stress of the polyolefin porous film is 10 g or less, both heat resistance and permeability tend to be excellent.

[Porous layer]

The multilayer porous film of the present embodiment has a porous layer which is disposed on one surface or both surfaces of the polyolefin porous film and contains an inorganic filler, a resin binder, and an ionic dissociable inorganic dispersant. By having such a porous layer, heat shrinkage of the polyolefin porous film can be suppressed at a high temperature to prevent short circuit due to breakage of the film. Hereinafter, each component will be described.

(ion dissociable inorganic dispersant)

In the multilayer porous film of the present embodiment, the ionic dissociable inorganic dispersant is contained in the porous layer, and the heat resistance is further improved. It is considered that the reason is that the ionic dissociable inorganic dispersant exhibits a strong affinity with the surface of the inorganic filler, and the affinity of the inorganic filler to the slurry solvent can be improved in the slurry used in forming the porous layer, and The dispersibility of the inorganic filler in the slurry solvent is increased by charge repulsion. Further, the reason why the heat resistance is improved is that not only the inorganic filler but also the dispersibility of the resin binder is improved by using the ionic dissociable inorganic dispersant, and aggregation of the resin binder can be suppressed. However, the reason for improving heat resistance is not limited to these.

The ionic dissociable inorganic dispersant is not particularly limited, and examples thereof include inorganic acid salts. The inorganic acid salt may, for example, be an orthophosphate or a condensed phosphate or aluminate. Among them, a condensed phosphoric acid which has a plurality of phosphate groups in one molecule and which is considered to have a strong affinity with the surface of the inorganic filler is preferable. salt. The condensed phosphate is not particularly limited, and examples thereof include polyphosphates, metaphosphates, and superphosphates. Among them, polyphosphates or metaphosphates are preferred. In general, a polyphosphate-based orthophosphoric acid has a structure in which chains are connected, and a metaphosphate salt has a structure in which it is connected in a ring shape, and a superphosphate has a structure in which a network is connected. From the viewpoint of improving the dispersibility of the inorganic filler in the porous layer, a polyphosphate or a metaphosphate is particularly preferable.

The polyphosphate salt is not particularly limited, and examples thereof include a compound represented by the formula (M _n+2 P _n O _3n+1 ). The degree of condensation n of the formula is not particularly limited, but is preferably 2 to 30, more preferably 2 to 10, still more preferably 2 to 6. Further, M is a cation. The polyphosphate salt is not particularly limited, and examples thereof include pyrophosphate, tripolyphosphate, tetrapolyphosphate, pentapolyphosphate, and hexapolyphosphate. By using such a polyphosphate, the adsorption to the inorganic filler is fast and the dispersion property can be maintained stably, and the resin binder or the like tends not to be aggregated.

The metaphosphate salt is not particularly limited, and examples thereof include a compound represented by the formula (MPO ₃ ) _n . The degree of condensation n of the formula is not particularly limited, but is preferably from 3 to 200, more preferably from 3 to 25, still more preferably from 3 to 6. Further, M is a cation. The metaphosphate salt is not particularly limited, and examples thereof include trimetaphosphate, tetrametaphosphate, penta-phosphate, and hexametaphosphate. By using such a metaphosphate, the adsorption to the inorganic filler is faster and the dispersion property can be maintained stably, and the resin binder or the like tends not to be aggregated.

The cation constituting the ionic dissociable inorganic dispersant is not particularly limited, and examples thereof include an inorganic cation or an organic cation. The inorganic cation is not particularly limited, and examples thereof include an alkali metal ion or an alkaline earth metal ion such as a potassium ion or a sodium ion. Further, the organic cation is not particularly limited, and examples thereof include an amine ion and an ammonium ion. In particular, in the case where the following acrylic polymer is used as the resin binder, the cation constituting the ionic dissociable inorganic dispersant is preferably an amine ion or an ammonium ion from the viewpoint of affinity with the resin binder. .

As the condensed phosphate, a commercially available product manufactured by Taiyo Chemical Industry Co., Ltd., manufactured by Phosphor Chemical Industry Co., Ltd., manufactured by San Nopco Co., Ltd., manufactured by Kirin Kyowa-foods Co., Ltd., or the like can be used. The ionic dissociable inorganic dispersant may be used alone or in combination of two or more.

The content of the ionic dissociable inorganic dispersant in the porous layer is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and still more preferably 0.3 parts by mass or more based on 100 parts by mass of the inorganic filler. When the content of the ionic dissociable inorganic dispersant in the porous layer is 0.05 parts by mass or more, the heat resistance of the multilayer porous film tends to be further improved. In addition, the content of the ionic dissociable inorganic dispersant in the porous layer is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and still more preferably 3 parts by mass or less based on 100 parts by mass of the inorganic filler. By the content of the ionic dissociable inorganic dispersant in the porous layer being 5 parts by mass or less, there is a further The step of suppressing the content ratio of the other components in the porous layer is small, and the effect obtained by the other components tends to be small.

In the case where the porous layer contains the following ionic dissociable organic dispersant, the ionic dissociable inorganic dispersant in the porous layer is 100 parts by mass based on the total content of the ionic dissociable inorganic dispersant and the ionic dissociable organic dispersant. The content is preferably 20 parts by mass or more and 95 parts by mass or less, more preferably 30 parts by mass or more and 93 parts by mass or less, still more preferably 50 parts by mass or more and 90 parts by mass or less. When the content of the ionic dissociable inorganic dispersant in the porous layer is within the above range, heat resistance tends to be further improved.

(inorganic filler)

Since the porous layer of the present embodiment contains an inorganic filler, the heat resistance of the multilayer porous film is improved. When the multilayer porous film is used as a separator for a non-aqueous electrolyte battery, the inorganic filler contained in the porous layer preferably has a melting point of 200 ° C or more, a high electrical insulating property, and a use condition as a separator. Under the electrochemical stability.

The inorganic filler is not particularly limited, and examples thereof include alumina, alumina hydroxide (alumina), cerium oxide, titanium oxide, zirconium oxide, magnesium oxide, cerium oxide, cerium oxide, zinc oxide, and iron oxide. Oxide ceramics and the like; hydrated ceramics such as tantalum nitride, titanium nitride, boron nitride; ceramics such as tantalum carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, barium titanate; talc, Kaolinite, dicar, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, magnesium chlorite, etc.; glass fiber. The inorganic filler may be used singly or in combination of two or more.

Among the above, alumina-based ceramics such as alumina or alumina hydroxide (aluminous alumina) and hydrates thereof are preferred; kaolinite, dickite, pearlite, halloysite, pyrophyllite, etc. do not have Layered silicate minerals with ion exchange capacity. By using such an inorganic filler, there is a tendency that the electrochemical stability and heat resistance of the multilayer porous film are further improved.

The alumina-based ceramics and the hydrates thereof are not particularly limited, and for example, more preferably It is alumina hydroxide. Further, as the layered niobate mineral having no ion exchange ability, it is more preferably a kaolin composed mainly of kaolinite in terms of being inexpensive and easily available. The wet kaolin is formed in the kaolin clay and the calcined kaolin is obtained by calcining the calcined kaolin. The calcined kaolin clay releases the crystal water during the calcination treatment, and the impurities are removed, so that the electrochemical stability is particularly preferable.

The average particle diameter of the inorganic filler is not particularly limited, but is preferably 0.10 μm or more and 3.0 μm or less, more preferably 0.20 μm or more and 2.0 μm or less, further preferably 0.50 μm or more and 1.2 μm or less, and further preferably 0.50. Μm or more and 0.80 μm or less. When the average particle diameter of the inorganic filler is 0.10 μm or more, the tendency of the short-circuit temperature in the case of being used as a separator for a battery can be further improved. Moreover, since the average particle diameter of the inorganic filler is 3.0 μm or less, the thickness of the porous layer tends to be thinner. Further, when the average particle diameter of the inorganic filler is 2.0 μm or less, the density of the porous layer becomes higher, and the effect of suppressing heat shrinkage tends to be remarkably improved. The average particle diameter of the inorganic filler can be determined by using a water as a dispersion medium and measuring the particle size distribution using a laser-type particle size distribution measuring apparatus, and obtaining the particle diameter as a cumulative particle having a cumulative frequency of 50%.

The content of the inorganic filler in the porous layer is not particularly limited, but is preferably 50% or more and less than 100%, more preferably 55% or more and 99.99% or less, further preferably 60% or more and 99.9% or less. It is 65% or more and 99% or less, and most preferably 90% or more and 99% or less. When the content of the inorganic filler in the porous layer is within the above range, heat resistance and the like tend to be further improved.

(resin adhesive)

The resin binder contained in the porous layer has a function of bonding the inorganic filler to the porous film. When the multilayer porous film is used as a separator for a lithium ion secondary battery, the resin binder contained in the porous layer is preferably insoluble for the electrolyte of the lithium ion secondary battery and secondary to the lithium ion. Electrochemically stable in the range of use of the battery.

The resin binder is not particularly limited, and examples thereof include polyethylene or a polyolefin resin such as polypropylene or α-polyolefin; a fluorine-based polymer such as polyvinylidene fluoride or polytetrafluoroethylene; and a copolymer containing the same; butadiene, isoprene and the like containing a conjugated diene as a diene polymer of a monomer unit or a copolymer comprising the same and a hydride thereof; an acrylic polymer containing acrylate, methacrylate or the like as a monomer unit or a copolymer comprising the same and a hydride thereof ; rubbers such as ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose; polyphenylene ether, polyfluorene a resin having a melting point and/or a glass transition temperature of 180 ° C or higher, such as a polyether oxime, a polyphenylene sulfide, a polyether phthalimide, a polyamidoximine, a polyamidamine or a polyester, and the like. One type of the resin binder may be used alone or two or more types may be used in combination. Among them, a fluorine-based polymer, a diene polymer, and an acrylic polymer are preferable, and an acrylic polymer is more preferable. By using such a resin binder, there is a tendency that the adhesion, heat resistance, and permeability are further improved. In particular, by using an acrylic polymer, oxidation resistance is further improved. Moreover, by using a fluorine-based polymer, the electrochemical stability tends to be further improved.

The fluorine-based polymer is not particularly limited, and examples thereof include a homopolymer of vinylidene fluoride and a copolymer of a monomer copolymerizable with vinylidene fluoride. The content of the vinylidene fluoride monomer unit in the fluorine-based polymer is not particularly limited, but is preferably 40% by mass or more, more preferably 50% by mass or more, and still more preferably 60% by mass or more.

The monomer copolymerizable with vinylidene fluoride is not particularly limited, and examples thereof include vinyl fluoride, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, hexafluoroisobutylene, perfluoroacrylic acid, and perfluoromethyl group. a fluorine-containing ethylenically unsaturated compound such as a fluoroalkyl acrylate or acrylic acid or a fluoroalkyl acrylate; a fluorine-free ethylenically unsaturated compound such as cyclohexyl vinyl ether or hydroxyethyl vinyl ether; butadiene and isoprene a fluorine-free diene compound such as an ene or a chloroprene.

The fluorine-based polymer is not particularly limited, and is preferably a homopolymer of vinylidene fluoride, a vinylidene fluoride/tetrafluoroethylene copolymer, or a vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene copolymer. Polymer, etc. Among them, a vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene copolymer is more preferred. The monomer composition of the vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene copolymer is not particularly limited, and is, for example, 30 to 90% by mass of vinylidene fluoride, 50 to 9% by mass of tetrafluoroethylene, and 20 to 1% of hexafluoropropylene. quality%. The fluorine-based polymer may be used alone or in combination of two or more.

The diene polymer is not particularly limited as long as it is a polymer containing a diene monomer unit having two double bonds as a repeating unit, and examples thereof include a homopolymer of a diene monomer, and a dimerizable polymer. a copolymer of monomers in which an olefin monomer is copolymerized. The diene monomer is not particularly limited, and examples thereof include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 2-phenyl-1. , 3-butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octane Alkene, 3-butyl-1,3-octadiene, and the like. The diene monomer may be used alone or in combination of two or more.

The content of the diene monomer unit in the diene polymer is not particularly limited, and is preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 50% by mass or more based on the total amount of the diene polymer. 60% by mass or more.

The monomer which can be copolymerized with the diene monomer is not particularly limited, and examples thereof include the following (meth) acrylate monomers or the following monomers (hereinafter also referred to as "other monomers"). The other monomer is not particularly limited, and examples thereof include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; styrene, chlorostyrene, vinyl toluene, t-butyl styrene, and ethylene; Styrene monomers such as benzoic acid, methyl benzoate, vinyl naphthalene, chloromethyl styrene, methylol styrene, α-methyl styrene, divinyl benzene, etc.; olefins such as ethylene and propylene a monomer containing a halogen atom such as vinyl chloride or vinylidene chloride; a vinyl ester such as vinyl acetate, vinyl propionate, vinyl butyrate or vinyl benzoate; methyl vinyl ether, ethyl vinyl ether, Vinyl ethers such as butyl vinyl ether; ketenes such as methyl ketene, ethyl ketene, butyl ketene, hexyl ketene, isopropenyl ketene; N-vinyl pyrrolidone, vinyl pyridine, a heterocyclic-containing vinyl compound such as vinyl imidazole; a decylamine such as acrylamide, N-methylol acrylamide or acrylamide-2-methylpropanesulfonic acid a hydroxyl group-containing vinyl monomer such as pentenol; vinylsulfonic acid, methyl vinylsulfonic acid, (meth)acrylic acid, styrenesulfonic acid, (meth)acrylic acid-2-sulfonic acid a sulfonic acid group-containing monomer such as an ester, 2-propenylamine-2-methylpropanesulfonic acid or 3-allyloxy-2-hydroxypropanesulfonic acid; an amine containing 2-aminoethyl methacrylate or the like a monomer having a cyano group such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-cyanoethyl acrylate or the like. The monomer which can be copolymerized with the diene monomer may be used alone or in combination of two or more.

The acrylic polymer is not particularly limited as long as it is a polymer containing a (meth) acrylate monomer unit, and examples thereof include a homopolymer of a (meth) acrylate monomer and a (meth)acrylic acid. A copolymer of monomers copolymerized with an ester monomer. In the present specification, the term "(meth)acrylic acid" means "acrylic acid or methacrylic acid", and the term "(meth)acrylate" means "acrylic acid ester or methacrylic acid ester". Further, the acrylic polymer is not particularly limited, and is preferably in the form of a latex.

The (meth) acrylate monomer is not particularly limited, and examples thereof include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, and (meth) acrylate. Propyl ester, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, amyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, (methyl) Octyl acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, n-tetradecyl (meth)acrylate An alkyl (meth)acrylate such as an ester or a stearyl (meth)acrylate; a hydroxyl group such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate or hydroxybutyl (meth)acrylate (Meth) acrylate; an amino group-containing (meth) acrylate such as aminoethyl (meth) acrylate; or an epoxy group-containing (meth) acrylate such as glycidyl (meth)acrylate. The (meth) acrylate monomer may be used alone or in combination of two or more.

The content of the (meth) acrylate monomer unit in the acrylic polymer is not particularly limited, and is preferably 40% by mass or more, more preferably 50% by mass or more, based on the total amount of the acrylic polymer, and further Preferably, it is 60% by mass or more.

The monomer copolymerizable with the (meth) acrylate monomer is not particularly limited, and examples thereof include other monomers exemplified in the item of the above diene polymer. The monomer which can be copolymerized with the (meth) acrylate monomer may be used alone or in combination of two or more. Among other monomers, unsaturated carboxylic acids are preferably used. The unsaturated carboxylic acid is not particularly limited, and examples thereof include a monocarboxylic acid such as acrylic acid, methacrylic acid, a half ester of itaconic acid, a half ester of maleic acid, and a half ester of fumaric acid; and itaconic acid. Dicarboxylic acid such as fumaric acid or maleic acid. Among them, acrylic acid, methacrylic acid, and itaconic acid are preferable, and acrylic acid and methacrylic acid are further preferable.

Further, when polyvinyl alcohol is used as the resin binder, the degree of saponification is preferably 85% or more and 100% or less, more preferably 90% or more and 100% or less, further preferably 95% or more and 100% or more. Hereinafter, it is particularly preferably 99% or more and 100% or less. When the saponification degree is 85% or more, when the multilayer porous film is used as a separator for a battery, the temperature (short circuit temperature) of the short circuit is increased, and the safety performance tends to be further improved.

The degree of polymerization of the polyvinyl alcohol is preferably 200 or more and 5,000 or less, more preferably 300 or more and 4,000 or less, and still more preferably 500 or more and 3,500 or less. When the degree of polymerization is 200 or more, there is a tendency that the inorganic filler can be firmly bonded by using a small amount of polyvinyl alcohol, and the mechanical strength of the porous layer can be maintained while suppressing an increase in the gas permeability of the multilayer porous film due to the formation of the porous layer. . In addition, when the degree of polymerization is 5,000 or less, it tends to prevent gelation or the like in the preparation of the dispersion.

The content of the resin binder in the porous layer is not particularly limited, and is preferably 0.5 parts by mass or more, more preferably 0.7 parts by mass or more, even more preferably 1.2 parts by mass or more, and particularly preferably 1.2 parts by mass or more based on 100 parts by mass of the inorganic filler. 1.5 parts by mass or more. When the content of the resin binder in the porous layer is 0.5 parts by mass or more, the adhesion between the resin binder and the inorganic filler tends to be further improved. Further, the content of the resin binder in the porous layer is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, still more preferably 7 parts by mass or less. When the content of the resin binder in the porous layer is 10 parts by mass or less, the ion permeability is further improved. to.

[Other additives]

The porous layer may also contain other additives than inorganic fillers, resin binders, and ionic dissociable inorganic dispersants. The other additives are not particularly limited, and examples thereof include an ionic dissociable organic dispersant.

(ion dissociable organic dispersant)

The porous layer of the present embodiment preferably contains a ionic dissociable organic dispersant from the viewpoint of heat resistance of the multilayer porous film. It is considered that the reason why the heat resistance is improved by the ionic dissociable organic dispersant is that the dispersion of the inorganic filler and the resin binder in the slurry can be further improved by using a dispersing agent other than the ionic dissociable inorganic dispersant. Sex, but there is no particular limitation.

The ionic dissociable organic dispersant is not particularly limited, and examples thereof include organic acid salts. As the organic acid salt, for example, an anionic or cationic polymer-based surfactant can be used. From the viewpoint of heat resistance, the ionic dissociable organic dispersant preferably contains a plurality of ionic dissociable acid groups (carboxyl groups, sulfonic acid groups, amino acid groups, maleic acid groups, etc.) or ionic dissociable acids. A salt group (carboxylate group, sulfonate group, maleate group, etc.). Specifically, as the ionic dissociable organic dispersant, a polycarboxylate, a polyacrylate, or a polymethacrylate is more preferred. The ionic dissociable organic dispersant may be used singly or in combination of two or more.

The content of the ionic dissociable organic dispersant in the porous layer is not particularly limited, and is preferably 20 parts by mass or more and 95 parts by mass based on 100 parts by mass of the total of the ionic dissociable inorganic dispersant and the ionic dissociable organic dispersant. In the following, it is more preferably 30 parts by mass or more and 93 parts by mass or less, and still more preferably 50 parts by mass or more and 90 parts by mass or less. When the content of the ionic dissociable inorganic dispersant in the porous layer is 20 parts by mass or more and 95 parts by mass or less, the heat resistance tends to be further improved.

(Characteristics of the porous layer, etc.)

The layer thickness of the porous layer in the present embodiment is preferably 0.1 μm or more and 10 μm or less, more preferably 0.5 μm or more and 8 μm or less, further preferably 1 μm or more and 6 μm or less, and particularly preferably 1.5 μm or more and 5 μm or less. When the thickness of the porous layer is 0.1 μm or more, the heat resistance tends to be further improved. In addition, when the thickness of the porous layer is 10 μm or less, the battery is further increased in capacitance, and the ion permeability of the separator is further improved, and the tendency of the inorganic filler to fall into powder during use is further suppressed.

In the present embodiment, the porous layer is sufficiently permeable to the extent that it does not significantly impede the permeability of the polyolefin porous film in the state of the multilayer porous film, and the porosity of the multilayer porous film due to the formation of the porous layer is sufficient. The increase rate is preferably 0% or more and 200% or less, more preferably 0% or more and 100% or less, further preferably 0% or more and 70% or less. In the case where the polyolefin porous film before the formation of the porous layer has a gas permeability of less than 100 sec/100 cc, the porosity of the multilayer porous film after the formation of the porous layer is preferably 0% or more and 500% or less.

[Physical properties of multilayer porous film]

The multilayer porous film of the present embodiment has a polyolefin porous film and a porous layer disposed on one surface or both surfaces of the polyolefin porous film. The gas permeability of the multilayer porous film of the present embodiment is not particularly limited, but is preferably 10 seconds/100 cc or more and 650 seconds/100 cc or less, more preferably 20 seconds/100 cc or more and 500 seconds/100 cc or less, and still more preferably 30%. Seconds/100 cc or more and 450 sec/100 cc or less, particularly preferably 50 seconds/100 cc or more and 400 seconds/100 cc or less. When the gas permeability of the multilayer porous film is 10 seconds/100 cc or more, the self-discharge resistance tends to be further improved. Moreover, since the gas permeability of the multilayer porous film is 650 sec/100 cc or less, the charge and discharge characteristics tend to be further improved.

The final film thickness of the multilayer porous film of the present embodiment is not particularly limited, but is preferably 2 μm or more and 20 μm or less, more preferably 5 μm or more and 19 μm or less, further preferably 7 μm or more and 18 μm or less, and particularly preferably 9 μm or more. Below 17μm. When the final film thickness of the multilayer porous film is 2 μm or more, the mechanical strength tends to be further improved. Again, by The final film thickness of the multilayer porous film is 20 μm or less, and there is a tendency that the battery is further increased in capacitance.

The heat shrinkage ratio at 150 ° C of the multilayer porous film of the present embodiment is not particularly limited, and both MD and TD are preferably 0% or more and 15% or less, more preferably 0% or more and 10% or less, and further preferably 0% or more and 5% or less. The heat shrinkage rate at 150 ° C in both directions of MD and TD is 15% or less, and the film of the separator can be prevented from being damaged even when the battery is abnormally heated, so that contact between the positive and negative electrodes can be suppressed. A tendency to have better safety performance.

The shutdown temperature of the multilayer porous film of the present embodiment is not particularly limited, but is preferably 120° C. or higher and 160° C. or lower, and more preferably 120° C. or higher and 150° C. or lower. When the shutdown temperature of the multilayer porous film is 160 ° C or lower, even when the battery is heated, the current is quickly released, and there is a tendency to obtain better safety performance. On the other hand, the shutdown temperature of the multilayer porous film is preferably 120 ° C or higher, and it is preferably used, for example, at a temperature of about 100 ° C, heat treatment, or the like.

The short-circuit temperature of the multilayer porous film of the present embodiment is not particularly limited, but is preferably 180 ° C or higher, preferably 190 ° C or higher, and more preferably 200 ° C or higher. When the short-circuit temperature of the multilayer porous film is 180 ° C or higher, the contact between the positive and negative electrodes can be suppressed before the heat is released even when the battery is abnormally heated, so that a better safety performance can be obtained.

[Method of Manufacturing Multilayer Porous Film]

The method for producing a multilayer porous film according to this embodiment includes a coating step of applying a dispersion containing an inorganic filler, a resin binder, and an ionic dissociable inorganic dispersant on one side or both sides of the polyolefin porous film. Further, the method for producing the multilayer porous film may include a step of producing a polyolefin porous film as needed.

In the production method of the present embodiment, the method for producing the polyolefin porous film is not particularly limited. For example, after the polyolefin resin and the plasticizer are melt-kneaded and formed into a sheet shape, the plasticizer is extracted. a method of making a porous; after the polyolefin resin is melt-kneaded and extruded at a high draw ratio, the polyolefin crystal interface is peeled off by heat treatment and elongation. A method of making a porous film by melt-kneading a polyolefin resin and an inorganic filler, and then forming a sheet, and then peeling the interface between the polyolefin resin and the inorganic filler by stretching, thereby making it porous In the method of dissolving a polyolefin resin, it is immersed in a poor solvent of a polyolefin resin to solidify the polyolefin resin, and at the same time, a solvent is removed to make a porous method.

The production method of the present embodiment is not particularly limited. If the surface of the polyolefin porous film is actively surface-treated before the coating step, the inorganic filler-containing resin dispersion is more easily applied and coated. The adhesion between the resin layer of the inorganic filler and the surface of the polyolefin porous film is improved, which is preferable.

The method of the surface treatment is not particularly limited as long as it does not significantly impair the porous structure of the polyolefin porous film, and examples thereof include a corona discharge treatment method, a mechanical roughening method, a solvent treatment method, an acid treatment method, and an ultraviolet oxidation method. Wait.

After the polyolefin porous film is produced, a dispersion liquid containing an inorganic filler, a resin binder, and an ionic dissociable inorganic dispersant is applied to one surface or both surfaces of the polyolefin porous film in the coating step.

In the dispersion liquid used in the production method of the present embodiment, the ionic dissociable inorganic dispersant is contained in addition to the inorganic filler and the resin binder, so that the dispersion stability of the inorganic filler in the dispersion is further improved. Since the dispersion contains a resin binder, the adhesion between the porous film and the inorganic filler and the inorganic filler is further improved.

In the production method of the present embodiment, the inorganic filler is not particularly limited, and the above may be used.

Further, in the production method of the present embodiment, the resin binder is not particularly limited, and the above may be used. In particular, in order to prevent the ion permeability from being lowered on at least one surface of the porous film, it is preferred to use an aliphatic conjugated diene monomer or an unsaturated carboxylic acid monomer, and A latex obtained by emulsion polymerization with other monomers copolymerized. Further, in terms of electrochemical stability or adhesion, the resin binder is more Preferably, it is an acrylic polymer, and particularly preferably an acrylic latex. In particular, depending on the inorganic filler to be used, aggregation may occur when the acrylic polymer is added. However, in the production method of the present embodiment, since a dispersant containing an ionic dissociable inorganic dispersant is used, resin adhesion can be suppressed. The agglomeration of the agent.

In the production method of the present embodiment, the ionic dissociable inorganic dispersant is not particularly limited, and the above may be used.

The solvent of the dispersion is not particularly limited, and examples thereof include N-methylpyrrolidone or N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, and heat. Xylene, hexane, and the like. From the viewpoint of dispersibility of the inorganic filler and the resin binder, water is preferred.

The dispersion preferably further contains an ionic dissociable organic dispersant. When the dispersion contains an ionic dissociable organic dispersant, the dispersion stability of the inorganic filler and the resin binder in the dispersion tends to be further improved. The ionic dissociable organic dispersant is not particularly limited, and the same as described above can be used. In the dispersion liquid of the production method of the present embodiment, the ionic dissociable organic dispersant functions as a dispersing agent together with the ionic dissociable inorganic dispersant.

In the case where the dispersion further contains an ionic dissociable organic dispersant, the content of the ionic dissociable inorganic dispersant in the dispersion is not particularly limited, and the total content of the ionic dissociable inorganic dispersant and the ionic dissociable organic dispersant is 100 parts by mass, preferably 20 parts by mass or more and 95 parts by mass or less, more preferably 30 parts by mass or more and 93 parts by mass or less, further preferably 50 parts by mass or more and 90 parts by mass or less. When the content of the ionic dissociable inorganic dispersant in the dispersion is 20 parts by mass or more and 95 parts by mass or less, the dispersibility of the inorganic filler and the resin binder in the slurry solvent tends to be further improved.

In the production method of the present embodiment, in order to stabilize the dispersion or to improve the coating property to the polyolefin porous film, a dispersant such as a surfactant, a thickener, a wetting agent, an antifoaming agent, or the like may be added. Various additives such as an acid or a base pH adjuster. The The additive is preferably removed when the solvent is removed or the plasticizer is removed. However, if it is electrochemically stable within the range of use of the lithium ion secondary battery and does not interfere with the battery reaction, it may remain in the battery.

In the production method of the present embodiment, the method of dissolving or dispersing the inorganic filler, the resin binder, and the ionic dissociable inorganic dispersant in a solvent is not particularly limited, and examples thereof include a ball mill, a bead mill, and a planetary ball mill. , mechanical grinding of vibrating ball mill, sand mill, colloid mill, grinder, roller mill, high speed impeller dispersion, disperser, homogenizer, high speed impact mill, ultrasonic dispersion, stirring wing, etc.

In the production method of the present embodiment, the method of applying the dispersion liquid to the polyolefin porous film is not particularly limited as long as it is a method capable of achieving a necessary layer thickness or coating area. For example, a gravure coating method, a small-diameter gravure coating method, a reverse roll coating method, a conveyance roll coating method, a contact coating method, a dip coating method, a knife coating method, an air knife coating method, Scraper coating method, bar coating method, extrusion coating method, casting coating method, die coating method, screen printing method, spray coating method, and the like. Further, depending on the application, the resin dispersion containing the inorganic filler may be applied only to one surface of the polyolefin porous film or may be applied to both surfaces.

In the production method of the present embodiment, it is preferred to remove the solvent after applying the dispersion. Examples of the method for removing the solvent include a method in which the polyolefin porous film is fixed while drying at a temperature equal to or lower than the melting point, a method of drying under reduced pressure at a low temperature, and a immersion in a poor solvent for the resin binder to cause the resin. A method in which a binder is solidified, and a solvent is simultaneously extracted.

[Separator for non-aqueous electrolyte battery]

The separator for a nonaqueous electrolyte battery of the present embodiment includes the multilayer porous film. The multilayer porous film has heat resistance and can be preferably used as a separator for a nonaqueous electrolyte battery. The multilayer porous film of the present embodiment can have both good heat resistance and ion permeability (air permeability). When such a multilayer porous film is used as a separator for a nonaqueous electrolyte battery, a nonaqueous electrolyte battery excellent in safety performance or output characteristics can be realized.

Further, the above various parameters are values measured according to the measurement methods in the following examples unless otherwise specified.

[Examples]

Hereinafter, the present invention will be specifically described by way of examples and comparative examples, but the present invention is not limited to the following examples as long as the scope of the invention is not exceeded. Further, the physical properties in the examples were measured by the following methods. Further, unless otherwise specified, various measurements and evaluations were carried out under the conditions of a room temperature of 23 ° C, an atmospheric pressure, and a relative humidity of 50%.

(1) Viscosity average molecular weight Mv of polyolefin resin

The ultimate viscosity [η] (dl/g) at 135 ° C of the decalin solvent of the polyolefin resin was determined in accordance with ASTM (American Society for Tests and Materials) - D4020.

The Mv of polyethylene was calculated by the following formula.

[η]=6.77×10-4Mv0.67

The Mv of polypropylene was calculated by the following formula.

[η]=1.10×10-4Mv0.80

(2) Film thickness (μm) of the multilayer porous film and the polyolefin porous film, and the layer thickness (μm) of the porous layer

The film thickness of the multilayer porous film and the polyolefin porous film was measured by a dial gauge (manufactured by Ozaki Seisakusho Co., Ltd., trade name "PEACOCK No. 25"). Specifically, a sample having a size of 100 mm in the MD direction × 100 mm in the TD direction was cut out, and a local film thickness of 9 places (3 points × 3 points) was measured in a lattice form, and the arithmetic mean of the partial film thicknesses obtained at 9 places was obtained. The value is taken as the film thickness. Further, the layer thickness of the porous layer was calculated from the difference between the film thickness of the multilayer porous film and the film thickness of the polyolefin porous film (measured by peeling the porous layer).

(3) Air permeability (second/100 cc) of multilayer porous film and polyolefin porous film, rate of increase in air permeability (%)

In the measurement of the gas permeability (second/100 cc) of the multilayer porous film and the polyolefin porous film, a Gurley gas permeability meter (G-B2 manufactured by Toyo Seiki Co., Ltd.) according to JIS (Japanese Industrial Standards) P-8117 was used. trademark)). The inner cylinder weight was 567 g, and the time when the air 100 mL was passed through the area of the diameter of 28.6 mm and 645 mm ² was measured as the air permeability.

On the other hand, the increase rate of the air permeability is calculated by the following formula.

Air permeability increase rate (%) = 100 × (permeability of multilayer porous film - air permeability of polyolefin porous film) / air permeability of polyolefin porous film

(4) Porosity of polyolefin porous film (%)

A sample of 10 cm × 10 cm square was cut out from the polyolefin porous film, and the volume (cm ³ ) and mass (g) thereof were determined, and the film density was set to 0.95 (g/cm ³ ), and calculation was performed using the following formula.

Porosity = (1 - mass / volume / 0.95) × 100

(5) Thermal shrinkage maximum stress of MD and TD of polyolefin porous film (g)

The measurement was carried out using TMA50 (trademark) manufactured by Shimadzu Corporation. The sample of the polyolefin porous film cut out having a width of 3 mm and having a width of 3 mm was fixed to the chuck so that the distance between the chucks became 10 mm, and was placed under a dedicated probe. The initial load was set to 1.0 g, and the temperature was raised from 30 ° C to 200 ° C at a temperature increase rate of 10 ° C / min, and the load (g) generated at this time was measured, and the maximum value thereof was defined as the maximum heat shrinkage stress (g) of MD. Further, the same operation was carried out, except that the sample of the polyolefin porous film cut out with a width of MD of 3 mm was used, and the maximum contraction heat stress (g) of TD was measured.

(6) Average particle size of inorganic filler

The average particle diameter of the inorganic filler is determined by using a water-based dispersion medium and a laser particle size distribution measuring apparatus (Microtrac MT3300EX manufactured by Nikkiso Co., Ltd.) to measure the particle size distribution, and the particle size of the cumulative frequency is 50% as the average particle size. path.

(7) 150 ° C thermal shrinkage of MD and TD of multilayer porous film

The multilayer porous film was cut into 100 mm in the MD direction, cut into 100 mm in the TD direction, and allowed to stand in an oven at 150 ° C for 1 hour. At this time, by clamping the sample to 2 sheets Between the papers, the warm wind does not directly contact the sample. The sample was taken out from the oven and cooled, and the length (mm) was measured, and the heat shrinkage ratio of MD and TD was calculated by the following formula.

MD heat shrinkage rate (%) = (100 - length of MD after heating) / 100 × 100

TD heat shrinkage rate (%) = (100 - length of TD after heating) / 100 × 100

[Example 1] (Manufacture of polyolefin porous film)

Using a roller mixer, 47 parts by mass of a polyethylene having an Mv of 700,000, 46 parts by mass of a polyethylene having an Mv of 300,000, and 7 parts by mass of a polypropylene having an Mv of 400,000 were dry-blended. Then, the mass of pentaerythritol-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]1 as an antioxidant was added to 99 parts by mass of the pure polymer mixture obtained. The mixture was adjusted to a total of 100 parts by mass, and dry blending was again performed using a tumbler mixer, whereby a mixture of a polymer or the like was obtained. After replacing the inside of the twin-screw extruder with nitrogen gas, the obtained polymer or the like was supplied to the twin-screw extruder by a feeder under a nitrogen atmosphere. Further, liquid paraffin (dynamic viscosity of 7.59 × 10 ^-5 m ² /s at 37.78 ° C) was injected into the extruder cylinder by a plunger pump.

The mixture of the polymer and the like is melt-kneaded with the liquid paraffin in a twin-screw extruder, and the feeder and the pump are adjusted so that the liquid paraffin ratio in all the extruded mixtures becomes 65 parts by mass. . As the melt kneading conditions, the set temperature was set to 200 ° C, the screw rotation speed was set to 240 rpm, and the discharge amount was set to 12 kg / h. Next, the melt kneaded product was extrusion-cast through a T die to a cooling roll whose surface temperature was controlled to 25 ° C, whereby a gel sheet having a thickness of 1600 μm was obtained.

Then, the obtained gel sheet was introduced into a simultaneous biaxial tenter stretching machine to perform biaxial stretching. The setting extension conditions were set to 7.0 times the MD magnification, 7.0 times the TD magnification, and a set temperature of 125 °C.

Then, the extended gel sheet is introduced into a methyl ethyl ketone tank, fully immersed in methyl ethyl ketone, and the liquid paraffin is extracted and removed, and then the methyl ethyl ketone is dried. except.

Then, the dried gel sheet was introduced into a TD tenter and heat-fixed. The elongation temperature and the magnification at the time of heat fixation were heat-fixed at 128 ° C and 2.0 times, and the temperature and the relaxation rate at the time of relaxation were set to 133 ° C and 0.80. As a result, a porous film having a film thickness of 12 μm, a porosity of 40% by volume, a gas permeability of 130 seconds/100 cc, an MD maximum heat shrinkage stress of 2.5 g, and a TD maximum heat shrinkage stress of 2.6 g was obtained.

(Synthesis of acrylic polymer)

In a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer, 65 parts by mass of water, Aqualon KH10 (polyoxyethylene-1-(allyloxymethyl) alkyl ether) was introduced as an initial feed. Sulfate ammonium salt: 100% solid content / manufactured by First Industrial Co., Ltd.) 0.5 parts by mass, the temperature in the reaction vessel was maintained at 80 ° C, and 1.5 parts by mass of a 10% aqueous solution of ammonium peroxodisulfate was added. After 5 minutes after the addition, it took 26.5 parts by mass of methyl methacrylate, 6 parts by mass of cyclohexyl methacrylate, 25 parts by mass of butyl acrylate, and 35 parts by mass of 2-ethylhexyl methacrylate in 150 minutes. 1 part by mass of methacrylic acid, 1.5 parts by mass of acrylic acid, 3 parts by mass of glycidyl methacrylate, 2 parts by mass of 2-hydroxyethyl methacrylate, 1.5 parts by mass of Aqualon KH10, and 10% aqueous solution of ammonium peroxydisulfate An emulsified mixed solution of 1.5 parts by mass and 55 parts by mass of water was introduced into the reaction vessel from the dropping tank. The pH of the reaction system is maintained at 4 or less. After the completion of the emulsified mixture, the temperature of the reaction vessel was maintained at 80 ° C while maintaining the original state, and stirring was continued for 120 minutes. Thereafter, it was cooled to room temperature.

After cooling, it was filtered through a 200-mesh wire net to remove aggregates and the like. After filtration, the pH was adjusted to 8 with 25% ammonia water, and then water was added so as to adjust the solid content to 45%.

(formation of porous layer)

94 parts by mass of aluminum hydroxide particles (average particle diameter: 1.0 μm) as an inorganic filler, and an acrylic polymer (solid content concentration) synthesized as a resin binder 45%) 6.0 parts by mass and 1.0 part by mass of a polyphosphoric acid amine salt (dispersant) as an ionic dissociable inorganic dispersant were uniformly dispersed in 100 parts by mass of water to prepare a dispersion for forming a porous layer. The prepared dispersion for forming a porous layer was applied onto the surface of the above polyolefin porous film by using a gravure coater. Thereafter, the mixture was dried at 60 ° C to remove water, and a multilayer porous film having a total thickness of 14 μm in which a porous layer having a thickness of 2 μm was formed on the porous film was obtained. The results are shown in Table 1. Further, as the "polyphosphoric acid", tripolyphosphoric acid was used (the same applies to the other examples).

[Embodiment 2]

The dispersant in the dispersion for forming a porous layer was set to a mixture of 0.95 parts by mass of polyphosphoric acid salt and 0.05 parts by mass of ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco) as an ionic dissociable organic dispersant, except Otherwise, a multilayer porous film was obtained in the same manner as in Example 1. The results are shown in Table 1.

[Example 3]

In the same manner as in Example 1, except that the dispersing agent in the dispersion for forming a porous layer was a mixture of 0.8 parts by mass of polyphosphoric acid salt and 0.2 parts by mass of ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco). The multilayer porous film was obtained in the same manner. The results are shown in Table 1.

[Example 4]

In the same manner as in Example 1, except that the dispersing agent in the dispersion for forming a porous layer was set to a mixture of 0.6 parts by mass of polyphosphoric acid salt and 0.4 parts by mass of ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco). The multilayer porous film was obtained in the same manner. The results are shown in Table 1.

[Example 5]

The dispersing agent in the dispersion for forming a porous layer was set to be a mixture of 0.2 parts by mass of polyphosphoric acid salt and 0.8 parts by mass of ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco), except that it was the same as in Example 1. The multilayer porous film was obtained in the same manner. Record the result It is shown in Table 1.

[Embodiment 6]

The dispersing agent in the dispersion for forming a porous layer was set to be a mixture of 0.05 parts by mass of polyphosphoric acid salt and 0.95 parts by mass of ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco), except that it was the same as in Example 1. The multilayer porous film was obtained in the same manner. The results are shown in Table 1.

[Embodiment 7]

A multilayer porous film was obtained in the same manner as in Example 3 except that the thickness of the porous layer was set to 5 μm. The results are shown in Table 1.

[Embodiment 8]

A multilayer porous film was obtained in the same manner as in Example 3 except that the thickness of the porous layer was changed to 7 μm. The results are shown in Table 1.

[Embodiment 9]

A multilayer porous film was obtained in the same manner as in Example 3 except that the thickness of the porous layer was set to 10 μm. The results are shown in Table 1.

[Embodiment 10]

The same procedure as in Example 3 except that the dispersing agent in the dispersion for forming a porous layer was set to a mixture of 0.8 parts by mass of polyphosphoric acid salt and 0.2 parts by mass of sodium polyacrylate as an ionic dissociable organic dispersing agent. A multilayer porous membrane was obtained in a manner. The results are shown in Table 1.

[Example 11]

12 parts by mass of ultrahigh molecular weight polyethylene having a viscosity average molecular weight (Mv) of 2000,000, 12 parts by mass of high density polyethylene having Mv of 280,000, 16 parts by mass of linear low density polyethylene having Mv of 150,000, and cerium oxide 17.6 parts by mass (average particle diameter: 8.3 μm) and 42.4 parts by mass of dioctyl phthalate (DOP) as a plasticizer, and then granulated by a twin-screw extruder equipped with a T-die. It was formed into a sheet having a thickness of 90 μm. from The molded product was extracted with dichloromethane to remove DOP, and extracted with sodium hydroxide to remove cerium oxide to form a porous film. The porous film was heated to 118 ° C, and in this state, it was extended 5.3 times in the longitudinal direction, and then extended 1.8 times in the transverse direction. As a result, a porous film having a film thickness of 11 μm, a porosity of 48% by volume, a gas permeability of 55 seconds/100 cc, an MD maximum heat shrinkage stress of 8.7 g, and a TD maximum heat shrinkage stress of 0.9 g was obtained.

A multilayer porous film was obtained in the same manner as in Example 3 except that the above polyolefin porous film was used for the substrate. The results are shown in Table 1.

[Embodiment 12]

A multilayer porous film was obtained in the same manner as in Example 1 except that the calcined kaolin (average particle diameter: 1.0 μm) was used as the inorganic filler in the dispersion for forming a porous layer. The results are shown in Table 1.

[Example 13]

A multilayer porous film was obtained in the same manner as in Example 1 except that alumina (average particle diameter: 1.0 μm) was used as the inorganic filler in the dispersion liquid for forming a porous layer. The results are shown in Table 1.

[Embodiment 14]

A multilayer porous film was obtained in the same manner as in Example 1 except that the ammonium polyphosphate was used as the dispersing agent in the dispersion for forming a porous layer. The results are collectively shown in Table 1.

[Example 15]

A multilayer porous film was obtained in the same manner as in Example 1 except that a sodium polyphosphate salt was used as a dispersing agent in the dispersion liquid for forming a porous layer. The results are collectively shown in Table 1.

[Example 16]

A multilayer porous film was obtained in the same manner as in Example 1 except that the dispersing agent in the dispersion for forming a porous layer was set to 0.3 parts by mass of the polyphosphoric acid salt. Record the result It is shown in Table 1.

[Example 17]

A multilayer porous film was obtained in the same manner as in Example 1 except that the dispersing agent in the dispersion for forming a porous layer was set to 2.5 parts by mass of the polyphosphoric acid salt. The results are shown in Table 1.

[Embodiment 18]

A multilayer porous film was obtained in the same manner as in Example 1 except that the amount of the inorganic filler in the dispersion for forming a porous layer was 90 parts by mass, and the resin binder was changed to 10 parts by mass. The results are shown in Table 1.

[Embodiment 19]

A multilayer porous film was obtained in the same manner as in Example 1 except that the amount of the inorganic filler in the dispersion for forming a porous layer was set to 98 parts by mass, and the resin binder was set to 2 parts by mass. The results are shown in Table 1.

[Comparative Example 1]

In the dispersion liquid for forming a porous layer, 94 parts by mass of aluminum hydroxide particles (average particle diameter: 1.0 μm) as an inorganic filler and 6 parts by mass of an acrylic polymer (solid content concentration: 45%) as a resin binder The dispersion for forming a porous layer was prepared by uniformly dispersing in 100 parts by mass of water, respectively. A multilayer porous film was obtained in the same manner as in Example 11 except that the obtained dispersion for forming a porous layer was used. The results are shown in Table 1.

[Comparative Example 2]

A multilayer porous film was obtained in the same manner as in Example 1 except that the dispersing agent in the dispersion liquid for forming a porous layer was set to 1 part by mass of ammonium polycarboxylate. The results are shown in Table 1.

[Comparative Example 3]

The dispersing agent in the dispersion for forming a porous layer is set to 1 part by mass of sodium polyacrylate, A multilayer porous film was obtained in the same manner as in Example 1 except the above. The results are shown in Table 1.

The present application is based on Japanese Patent Application No. 2012-240637, filed on Dec.

[Industrial availability]

The multilayer porous film of the present invention has industrial applicability as a separator for a battery, particularly a high-capacity battery.

Claims (9)

A multilayer porous film comprising: a polyolefin porous film; and a porous layer disposed on one surface or both surfaces of the polyolefin porous film and containing an inorganic filler, a resin binder, and an ionic dissociable inorganic dispersant. The multilayer porous film of claim 1, wherein the porous layer further contains an ionic dissociable organic dispersant. The multilayer porous film according to claim 2, wherein the content of the ionic dissociable inorganic dispersant is 20 parts by mass or more and 95% by mass based on 100 parts by mass of the total of the ionic dissociable inorganic dispersant and the ionic dissociable organic dispersant. Below the mass. The multilayer porous film according to any one of claims 1 to 3, wherein the ionic dissociable inorganic dispersant comprises a condensed phosphate. The multilayer porous film according to any one of claims 1 to 3, wherein the above-mentioned resin binder comprises an acrylic polymer. A separator for a non-aqueous electrolyte battery, comprising the multilayer porous film according to any one of claims 1 to 5. A method for producing a multilayer porous film, comprising a coating step of coating a dispersion containing an inorganic filler, a resin binder, and an ionic dissociable inorganic dispersant on one side or both sides of a polyolefin porous film. The method for producing a multilayer porous film according to claim 7, wherein the resin binder comprises an acrylic polymer. The method for producing a multilayer porous film according to claim 7 or 8, wherein the dispersion further contains an ionic dissociable organic dispersant.