WO2014069410A1

WO2014069410A1 - Multilayer porous film and method for manufacturing same, and separator for non-aqueous electrolyte cell

Info

Publication number: WO2014069410A1
Application number: PCT/JP2013/079155
Authority: WO
Inventors: 健片桐; 主隼熊添
Original assignee: 旭化成イーマテリアルズ株式会社
Priority date: 2012-10-31
Filing date: 2013-10-28
Publication date: 2014-05-08
Also published as: KR20170073712A; JPWO2014069410A1; TWI511353B; JP6279479B2; KR102053259B1; KR20150063119A; CN104812579A; TW201431158A; CN104812579B

Abstract

The purpose of this invention is to provide a multilayer porous film having a low heat shrinkage rate and a method for manufacturing same, and a separator for a non-aqueous electrolyte cell provided with the multilayer porous film. A multilayer porous film having: a polyolefin porous film; and a porous layer containing an inorganic filler, a resin binder, and an ion dissociative inorganic dispersant, the porous layer being provided on one or both sides of the polyolefin porous film.

Description

Multilayer porous membrane, method for producing the same, and separator for non-aqueous electrolyte battery

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

In recent years, the capacity of batteries has been further increased, and in such high capacity batteries, a separator having a thin thickness and high heat resistance has been demanded, and studies thereof are being conducted. For example, Patent Document 1 discloses 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 so that a shutdown state can be maintained even at high temperatures. A separator for use is disclosed.

JP 2010-123465 A

However, although the battery separator described in Patent Document 1 is considered to have improved heat resistance as compared with a normal separator having no heat-resistant layer, it is desirable that the porous film containing the inorganic filler is made thinner. However, there is still room for improvement from the viewpoint of not being able to obtain the heat resistance.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a multilayer porous membrane having a low thermal shrinkage rate, a method for producing the same, and a separator for a nonaqueous electrolyte battery including the multilayer porous membrane. And

The present inventors diligently studied the above problems. As a result, it has been found that the above-mentioned problems can be solved by forming a predetermined porous layer on one or both surfaces of the polyolefin porous membrane, and the present invention has been completed.

That is, the present invention is as follows.
[1]
A polyolefin porous membrane,
A porous layer containing an inorganic filler, a resin binder, and an ion dissociable inorganic dispersant, disposed on one or both sides of the polyolefin porous membrane;
A multilayer porous membrane.
[2]
The multilayer porous membrane according to [1] above, wherein the porous layer further contains an ion dissociative organic dispersant.
[3]
The content of the ionic dissociable inorganic dispersant is 20 parts by mass or more and 95 parts by mass or less with respect to 100 parts by mass of the total content of the ionic dissociative inorganic dispersant and the ionic dissociative organic dispersant. The multilayer porous membrane according to [2].
[4]
The multilayer porous membrane according to any one of [1] to [3], wherein the ion dissociable inorganic dispersant contains a condensed phosphate.
[5]
The multilayer porous membrane according to any one of [1] to [4], wherein the resin binder includes 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] above.
[7]
The manufacturing method of a multilayer porous membrane which has the application | coating process which apply | coats the dispersion liquid containing an inorganic filler, a resin binder, and an ion dissociative inorganic dispersing agent to the single side | surface or both surfaces of a polyolefin porous membrane.
[8]
The method for producing a multilayer porous membrane according to [7] above, wherein the resin binder contains an acrylic polymer.
[9]
The method for producing a multilayer porous membrane according to [7] or [8] above, wherein the dispersion further contains an ion dissociative organic dispersant.

According to the present invention, it is possible to provide a multilayer porous membrane having a low thermal shrinkage rate, a method for producing the same, and a separator for a nonaqueous electrolyte battery provided with the multilayer porous membrane.

Hereinafter, a mode for carrying out the present invention (hereinafter abbreviated as “the present embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

[Multilayer porous membrane]
The multilayer porous membrane of this embodiment is
A polyolefin porous membrane,
It has a porous layer (hereinafter also simply referred to as “porous layer”) containing an inorganic filler, a resin binder, and an ion dissociating inorganic dispersant, which is disposed on one or both surfaces of the polyolefin porous membrane.

[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 membrane is not particularly limited, but is preferably 50% by mass or more, and more preferably 70 to 100% by mass. When the content of the polyolefin resin in the polyolefin porous membrane is within the above range, the shutdown performance when used as a battery separator tends to be further improved.

The polyolefin resin is not particularly limited, and for example, a polyolefin resin used for normal extrusion, injection, inflation, blow molding and the like can be used. Specific examples of such polyolefin resins include homopolymers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene, copolymers thereof, and these And a multistage polymer. More specifically, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, and ultrahigh molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene random copolymer, polybutene, and Examples include ethylene propylene rubber. In addition, polyolefin resin may be used individually by 1 type, or may use 2 or more types together.

Among these, the polyolefin resin preferably contains polypropylene. The content of polypropylene in the polyolefin resin is not particularly limited, but is preferably 1 to 35% by mass, more preferably 3 to 20% by mass, and further preferably 4 to 10% by mass. When the content of polypropylene is 1% by mass or more, the heat resistance of the porous membrane tends to be further improved. In addition, since the content of polypropylene having a relatively high melting point is 35% by mass or less, when the multilayer porous membrane of this embodiment is used as a battery separator, the membrane is more thermally melted at the shutdown temperature. It tends to block (shutdown property) and tends to cause shutdown at a lower temperature.

The viscosity average molecular weight (Mv) of the polyolefin resin is not particularly limited, but 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 resulting polyolefin porous film tends to be further improved. Moreover, when the Mv of the polyolefin resin is 3,000,000 or less, the moldability during production tends to be further improved. Furthermore, when Mv is 1,000,000 or less, when used as a battery separator, the hole tends to be blocked when the temperature rises, and the shutdown function tends to be further improved. In order to control the mechanical strength of the porous film, a mixture of two or more polyolefin resins having different Mvs may be used. In addition, the viscosity average molecular weight (Mv) of polyolefin resin can be measured by the method as described in an Example.

Polyolefin porous membranes are made of antioxidants such as phenolic compounds, phosphorus compounds, or sulfur compounds, metal soaps such as calcium stearate and zinc stearate, UV absorbers, light stabilizers, and antistatics as necessary. An additive such as an agent, an antifogging agent, and a color pigment may be included.

The film thickness of the polyolefin porous membrane 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. Is 5.0 μm or more and 16 μm or less. When the film thickness of the polyolefin porous membrane is 0.10 μm or more, the mechanical strength of the resulting multilayer porous membrane tends to be further improved. Moreover, when the film thickness of the polyolefin porous membrane is 25 μm or less, the battery tends to have a higher capacity. In addition, the film thickness of a polyolefin porous membrane can be measured by the method as described in an Example.

The average pore diameter of the polyolefin porous membrane 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, and further preferably 0.050 μm or more and 0.090 μm or less. Or less, and particularly preferably 0.060 μm or more and 0.090 μm or less.

The porosity of the polyolefin porous membrane is not particularly limited, but is preferably 25% or more and 65% or less, more preferably 30% or more and 60% or less, and further preferably 35% or more and 55% or less. When the porosity of the polyolefin porous membrane is 25% or more, an increase in the air permeability after applying the inorganic filler-containing dispersion described later tends to be further suppressed. In addition, the porosity of a polyolefin porous membrane can be measured by the method as described in an Example.

The maximum value of the heat shrinkage stress of the polyolefin porous film is not particularly limited, but is preferably 10 g or less in both the drawing direction (hereinafter also referred to as “MD”) and the width direction (hereinafter also referred to as “TD”). More preferably, it is 8 g or less, More preferably, it is 6 g or less, Especially preferably, it is 4 g or less. When the maximum value of the heat shrinkage stress of the polyolefin porous membrane is 10 g or less, both heat resistance and permeability tend to be excellent.

(Porous layer)
The multilayer porous membrane of this embodiment has a porous layer containing an inorganic filler, a resin binder, and an ion dissociative inorganic dispersant, which are disposed on one or both sides of a polyolefin porous membrane. By having such a porous layer, thermal shrinkage of the polyolefin porous membrane can be suppressed even at high temperatures, and a short circuit due to a membrane breakage can be prevented. Hereinafter, each component will be described.

(Ion dissociative inorganic dispersant)
When the multilayer porous membrane of this embodiment contains an ion dissociable inorganic dispersant in the porous layer, the heat resistance is further improved. The reason for this is that the ion dissociable inorganic dispersant has a strong affinity with the surface of the inorganic filler, and in the slurry used when forming the porous layer, the affinity of the inorganic filler to the slurry solvent can be increased, and charge repulsion can be achieved. This is considered to be because the dispersibility of the inorganic filler in the slurry solvent can be improved. Further, by using an ion dissociable inorganic dispersant, not only the inorganic filler but also the dispersibility of the resin binder is improved, and the fact that the aggregation of the resin binder can be suppressed is also a reason for improving the heat resistance. However, the reason why the heat resistance is improved is not limited to these.

The ion dissociable inorganic dispersant is not particularly limited, and examples thereof include inorganic acid salts. Examples of inorganic acid salts include orthophosphates, condensed phosphates, and aluminates. Among them, it has multiple phosphate groups in one molecule and is considered to exhibit strong affinity with the inorganic filler surface. A condensed phosphate is preferred. The condensed phosphate is not particularly limited, and examples thereof include polyphosphate, metaphosphate, and ultraphosphate. Among these, polyphosphate and metaphosphate are preferable. In general, polyphosphate has a structure in which orthophosphoric acid is linked in a chain, metaphosphate has a structure linked in a ring, and ultraphosphate has a structure linked in a network. From the viewpoint of improving the dispersibility of the inorganic filler in the porous layer, polyphosphate and metaphosphate are particularly preferable.

The polyphosphates are not particularly limited, for example, a compound represented by the formula _{_{_{(M n + 2 P n O}}} 3n + 1) and the like. The degree of condensation n in the formula is not particularly limited, but is preferably 2 to 30, more preferably 2 to 10, and further preferably 2 to 6. M is a cation. The polyphosphate 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 stable dispersibility can be maintained, and aggregation of the resin binder and the like tends not to occur.

The metaphosphate is not particularly limited, for example, a compound represented by the formula (MPO ₃₎ _n and the like. The degree of condensation n in the formula is not particularly limited, but is preferably 3 to 200, more preferably 3 to 25, and further preferably 3 to 6. M is a cation. Although it does not specifically limit as a metaphosphate, For example, a trimetaphosphate, a tetrametaphosphate, a pentametaphosphate, and a hexametaphosphate are mentioned. By using such a metaphosphate, adsorption to the inorganic filler becomes faster, stable dispersibility can be maintained, and aggregation of a resin binder or the like tends not to occur.

Although it does not specifically limit as a cation which comprises an ion dissociable inorganic dispersing agent, For example, an inorganic cation or an organic cation is mentioned. The inorganic cation is not particularly limited, and examples thereof include alkali metal ions or alkaline earth metal ions such as potassium ions and sodium ions. Moreover, it does not specifically limit as an organic cation, For example, an amine ion, an ammonium ion, etc. are mentioned. Among these, in particular, when an acrylic polymer described later is used as the resin binder, the cation constituting the ion 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, commercially available products such as those manufactured by Taiyo Chemical Industry Co., Ltd., phosphorus chemical industry Co., Ltd., San Nopco Co., Ltd., and Kirin Kyowa Foods Co., Ltd. can be used. An ion dissociative inorganic dispersing agent may be used individually by 1 type, and may use 2 or more types together.

The content of the ion 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, further preferably 100 parts by mass of the inorganic filler. 0.3 parts by mass or more. When the content of the ion dissociable inorganic dispersant in the porous layer is 0.05 parts by mass or more, the heat resistance of the multilayer porous membrane tends to be further improved. Further, the content of the ion dissociable inorganic dispersant in the porous layer is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and further preferably 3 parts by mass with respect to 100 parts by mass of the inorganic filler. Or less. When the content of the ion dissociable inorganic dispersant in the porous layer is 5 parts by mass or less, the content ratio of the other components in the porous layer is reduced, and the effect of the other components is further suppressed from being reduced. There is a tendency.

Further, when the porous layer contains an ion dissociable organic dispersant described later, the content of the ion dissociable inorganic dispersant in the porous layer is the total content of the ion dissociable inorganic dispersant and the ion dissociable organic dispersant. Preferably it is 20 to 95 mass parts with respect to 100 mass parts, More preferably, it is 30 to 93 mass parts, More preferably, it is 50 to 90 mass parts. When the content of the ion dissociable inorganic dispersant in the porous layer is within the above range, the heat resistance tends to be further improved.

(Inorganic filler)
When the porous layer of this embodiment contains an inorganic filler, the heat resistance of a multilayer porous membrane improves. When the multilayer porous membrane is used as a separator for a non-aqueous electrolyte battery, the inorganic filler contained in the porous layer has a melting point of 200 ° C. or higher, high electrical insulation, and under the conditions for use as a separator. Those that are electrochemically stable are preferred.

The inorganic filler is not particularly limited. For example, alumina, aluminum hydroxide oxide (boehmite), silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, and other oxide ceramics and hydration thereof. Nitride ceramics such as silicon nitride, titanium nitride, boron nitride; ceramics such as silicon carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, barium titanate; talc, kaolinite, dickite, nacrite, halloysite, pyrophyll Layered silicate minerals such as light, montmorillonite, sericite, mica, and amesite; glass fibers and the like. An inorganic filler may be used individually by 1 type, and may use 2 or more types together.

Among these, aluminum oxide ceramics such as alumina and aluminum hydroxide oxide (boehmite) and hydrates thereof; layered silicates having no ion exchange ability such as kaolinite, dickite, nacrite, halloysite, and pyrophyllite Minerals are preferred. By using such an inorganic filler, the electrochemical stability and heat resistance characteristics of the multilayer porous membrane tend to be further improved.

The aluminum oxide ceramics and their hydrates are not particularly limited, but for example, aluminum hydroxide oxide is more preferable. Moreover, as a layered silicate mineral which does not have ion exchange ability, since it is cheap and easy to obtain, kaolin mainly composed of kaolinite is more preferable. Kaolin includes wet kaolin and calcined kaolin, which is calcined. However, calcined kaolin releases crystal water during the calcining process and removes impurities. Particularly preferred.

The average particle size of the inorganic filler is not particularly limited, but is preferably from 0.10 μm to 3.0 μm, more preferably from 0.20 μm to 2.0 μm, still more preferably from 0.50 μm to 1. It is 2 μm or less, more preferably 0.50 μm or more and 0.80 μm or less. When the average particle size of the inorganic filler is 0.10 μm or more, the short temperature when used as a battery separator tends to be higher. Moreover, it exists in the tendency which can make the thickness of a porous layer thinner because the average particle diameter of an inorganic filler is 3.0 micrometers or less. Furthermore, 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 thermal shrinkage tends to be remarkably improved. The average particle size of the inorganic filler can be obtained as a value of a particle size at which the cumulative frequency of the number of particles is 50% by measuring the particle size distribution using water as a dispersion medium and using a laser particle size distribution measuring device.

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, and further preferably 60% or more and 99.9%. % Or less, particularly preferably 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, the heat resistance and the like tend to be further improved.

(Resin binder)
The resin binder contained in the porous layer has a function for binding the inorganic filler onto the porous film. When the multilayer porous membrane is used as a separator for a lithium ion secondary battery, the resin binder contained in the porous layer is insoluble in the electrolyte solution of the lithium ion secondary battery, and the use of the lithium ion secondary battery It is preferable to use one that is electrochemically stable within a range.

Such a resin binder is not particularly limited, but examples thereof include polyolefin resins such as polyethylene, polypropylene, and α-polyolefin; fluorine-based polymers such as polyvinylidene fluoride and polytetrafluoroethylene and copolymers containing them; butadiene, isoprene, and the like A diene polymer containing a conjugated diene as a monomer unit or a copolymer thereof and a hydride thereof; an acrylic polymer containing an acrylate ester, a methacrylic acid ester or the like as a monomer unit or a copolymer containing the same and a hydride thereof; ethylene propylene Rubbers such as rubber, polyvinyl alcohol and polyvinyl acetate; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose and carboxymethyl cellulose ; Polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, melting point and / or glass transition temperature is above 180 ° C. resins and mixtures thereof, such as polyester. A resin binder may be used individually by 1 type, or may use 2 or more types together. Among these, a fluorine polymer, a diene polymer, and an acrylic polymer are preferable, and an acrylic polymer is more preferable. By using such a resin binder, the binding property, heat resistance, and permeability tend to be further improved. In particular, oxidation resistance tends to be further improved by using an acrylic polymer. In addition, electrochemical stability tends to be improved by using a fluorine-based polymer.

The fluorine-based polymer is not particularly limited, and examples thereof include a homopolymer of vinylidene fluoride and a copolymer with a monomer copolymerizable with vinylidene fluoride. The content of the vinylidene fluoride monomer unit in the fluoropolymer is not particularly limited, but is preferably 40% by mass or more, more preferably 50% by mass or more, and further preferably 60% by mass 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 and hydroxyethyl vinyl ether; fluorine-free diene compounds such as butadiene, isoprene and chloroprene Can be mentioned.

The fluorine-based polymer is not particularly limited, but a homopolymer of vinylidene fluoride, a vinylidene fluoride / tetrafluoroethylene copolymer, a vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer, or the like is preferable. Among these, a vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer is more preferable. The monomer composition of the vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer is not particularly limited. For example, 30 to 90% by mass of vinylidene fluoride, 50 to 9% by mass of tetrafluoroethylene, and 20 to 1% by mass of hexafluoropropylene. It is. A fluorine-type polymer may be used individually by 1 type, or may use 2 or more types together.

The diene polymer is not particularly limited as long as it contains a diene monomer unit having two double bonds as a repeating unit. For example, a diene monomer homopolymer or a copolymer of a diene monomer and a copolymerizable monomer can be used. Can be mentioned. The diene monomer is not particularly limited, and examples thereof include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 1,3-pentadiene, 2- Examples include methyl-1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octadiene, and 3-butyl-1,3-octadiene. A diene monomer may be used individually by 1 type, or may use 2 or more types together.

The content of the diene monomer unit in the diene 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% with respect to the total amount of the diene polymer. It is at least mass%.

The monomer copolymerizable with the diene monomer is not particularly limited, and examples thereof include a (meth) acrylate monomer described below and the following monomers (hereinafter also referred to as “other monomers”). Other monomers are 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, vinyl benzoic acid, and vinyl benzoic acid. Styrene monomers such as methyl, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, α-methylstyrene, divinylbenzene; olefins such as ethylene and propylene; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl acetate, propion Vinyl esters such as vinyl acid vinyl, vinyl butyrate, vinyl benzoate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether; methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hex Vinyl ketones such as ruvinyl ketone and isopropenyl vinyl ketone; heterocycle-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine and vinyl imidazole; amide monomers such as acrylamide, N-methylol acrylamide and acrylamide-2-methylpropane sulfonic acid; Hydroxy group-containing vinyl monomers such as penteneol; vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) acryl sulfonic acid, styrene sulfonic acid, ethyl (meth) acrylic acid-2-sulfonate, 2-acrylamido-2-methylpropane Sulfonic acid group-containing monomers such as sulfonic acid and 3-allyloxy-2-hydroxypropanesulfonic acid; Amino group-containing monomers such as 2-aminoethyl methacrylate; Acrylonitrile, methacrylonitrile, α Chloroacrylonitrile, a cyano group-containing monomers such as α- cyanoethyl acrylate. The monomer copolymerizable 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 copolymer of a monomer copolymerizable with a (meth) acrylate monomer. In the present specification, “(meth) acrylic acid” means “acrylic acid or methacrylic acid”, and “(meth) acrylate” means “acrylate or methacrylate”. The acrylic polymer is not particularly limited, but is preferably latex.

The (meth) acrylate monomer is not particularly limited. For example, 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, stearyl (meth) acrylate; hydroxyethyl (meth) acrylate, hydroxypropyl (meth) ) Acrylate, hydroxy group-containing (meth) acrylate such as hydroxybutyl (meth) acrylate; amino group-containing (meth) acrylate such as aminoethyl (meth) acrylate; epoxy group-containing (meth) acrylate such as glycidyl (meth) acrylate Can be mentioned. (Meth) acrylate monomers 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, but is preferably 40% by mass or more, more preferably 50% by mass or more, based on the total amount of the acrylic polymer. Preferably it is 60 mass% or more.

The monomer copolymerizable with the (meth) acrylate monomer is not particularly limited, and examples thereof include other monomers listed in the item of the diene polymer. The monomer copolymerizable with the (meth) acrylate monomer may be used alone or in combination of two or more. Among other monomers, it is preferable to use unsaturated carboxylic acids. Unsaturated carboxylic acids are not particularly limited. For example, monocarboxylic acids such as acrylic acid, methacrylic acid, itaconic acid half ester, maleic acid half ester, fumaric acid half ester; itaconic acid, fumaric acid, maleic acid. And dicarboxylic acids such as acids. Of these, acrylic acid, methacrylic acid and itaconic acid are preferred, and acrylic acid and methacrylic acid are more preferred.

When polyvinyl alcohol is used as the resin binder, the saponification degree is preferably 85% or more and 100% or less, more preferably 90% or more and 100% or less, and further preferably 95% or more and 100%. Or less, particularly preferably 99% 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 temperature) is improved, and the safety performance tends to be further improved.

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 particularly preferably 500 or more and 3500 or less. When the polymerization degree is 200 or more, the inorganic filler can be firmly bound with a small amount of polyvinyl alcohol, and the increase in the air permeability of the multilayer porous film due to the formation of the porous layer can be suppressed while maintaining the mechanical strength of the porous layer. It tends to be possible. Moreover, it exists in the tendency which can prevent the gelatinization at the time of preparing a dispersion liquid by having a polymerization degree of 5000 or less.

Although content of the resin binder in a porous layer is not specifically limited, Preferably it is 0.5 mass part or more with respect to 100 mass parts of inorganic fillers, More preferably, it is 0.7 mass part or more, More preferably Is 1.2 parts by mass or more, particularly preferably 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 binding property between the resin binder and the inorganic filler tends to be further improved. 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, and further 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 tends to be further improved.

[Other additives]
The porous layer may contain other additives other than the inorganic filler, the resin binder, and the ion dissociable inorganic dispersant. Other additives are not particularly limited, and examples thereof include ion dissociable organic dispersants.

(Ion dissociative organic dispersant)
In the porous layer of the present embodiment, it is preferable that the porous layer further contains an ion dissociative organic dispersant from the viewpoint of heat resistance of the multilayer porous membrane. The reason why heat resistance is improved by including an ion dissociable organic dispersant is that the dispersion stability of the inorganic filler and resin binder in the slurry is further improved by using a dispersant other than the ion dissociable inorganic dispersant. Although it is thought that it is because it can be made, it is not specifically limited.

Although it does not specifically limit as an ion dissociative organic dispersing agent, Organic acid salt can be mentioned. As the organic acid salt, for example, various anionic or cationic polymer surfactants can be used. From the viewpoint of heat resistance, the ion dissociable organic dispersant is an ion dissociable acid group (carboxyl group, sulfonic acid group, amino acid group, maleic acid group, etc.) or ion dissociable acid base (carboxylic acid group, sulfonic acid). Those containing a plurality of bases, maleate bases, etc.) are preferred. Specifically, as the ion dissociable organic dispersant, polycarboxylate, polyacrylate, and polymethacrylate are more preferable. An ion dissociative organic dispersing agent may be used individually by 1 type, and may use 2 or more types together.

The content of the ion dissociable organic dispersant in the porous layer is not particularly limited, but is preferably 20 parts by mass or more with respect to 100 parts by mass of the total content of the ion dissociable inorganic dispersant and the ion dissociable organic dispersant. 95 parts by mass or less, more preferably 30 parts by mass or more and 93 parts by mass or less, and further preferably 50 parts by mass or more and 90 parts by mass or less. When the content of the ion 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 etc. of porous layer)
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. It is 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. Moreover, when the layer thickness of the porous layer is 10 μm or less, the battery has a higher capacity, the ion permeability of the separator is further improved, and the powder of the inorganic filler during use tends to be further suppressed.

In the present embodiment, it is sufficient that the porous layer has a permeability that does not significantly impair the permeability of the polyolefin porous membrane in the state of the multilayer porous membrane, but the air permeability of the multilayer porous membrane due to the formation of the porous layer is sufficient. The rate of increase in the degree is preferably 0% or more and 200% or less, more preferably 0% or more and 100% or less, and further preferably 0% or more and 70% or less. When the air permeability of the polyolefin porous membrane before forming the porous layer is less than 100 seconds / 100 cc, the rate of increase in the air permeability of the multilayer porous membrane after forming the porous layer is preferably 0% or more and 500% or less. is there.

[Physical properties of multilayer porous membrane]
The multilayer porous membrane of this embodiment has a polyolefin porous membrane and a porous layer disposed on one side or both sides of the polyolefin porous membrane. The air permeability of the multilayer porous membrane of the present embodiment is not particularly limited, but is preferably 10 seconds / 100 cc to 650 seconds / 100 cc, more preferably 20 seconds / 100 cc to 500 seconds / 100 cc, It is preferably 30 seconds / 100 cc or more and 450 seconds / 100 cc or less, particularly preferably 50 seconds / 100 cc or more and 400 seconds / 100 cc or less. When the air permeability of the multilayer porous membrane is 10 seconds / 100 cc or more, the self-discharge resistance tends to be further improved. Moreover, when the air permeability of the multilayer porous membrane is 650 seconds / 100 cc or less, the charge / discharge characteristics tend to be further improved.

The final film thickness of the multilayer porous membrane 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, and further preferably 7 μm or more and 18 μm or less. Preferably they are 9 micrometers or more and 17 micrometers or less. When the final film thickness of the multilayer porous membrane is 2 μm or more, the mechanical strength tends to be further improved. Moreover, when the final film thickness of the multilayer porous membrane is 20 μm or less, the battery tends to have a higher capacity.

The heat shrinkage rate at 150 ° C. of the multilayer porous membrane of the present embodiment is not particularly limited, but both MD and TD are preferably 0% or more and 15% or less, more preferably 0% or more and 10% or less, More preferably, it is 0% or more and 5% or less. Since the thermal contraction rate at 150 ° C. in both the MD and TD directions is 15% or less, it is possible to prevent the separator from being broken even when the battery is abnormally heated. Good safety performance tends to be obtained.

The shutdown temperature of the multilayer porous membrane of this embodiment is not particularly limited, but is preferably 120 ° C. or higher and 160 ° C. or lower, more preferably 120 ° C. or higher and 150 ° C. or lower. When the shutdown temperature of the multilayer porous membrane is 160 ° C. or lower, even when the battery generates heat, current interruption is promptly promoted, and better safety performance tends to be obtained. On the other hand, it is preferable that the shutdown temperature of the multilayer porous membrane is 120 ° C. or higher because, for example, use of a high temperature around 100 ° C., heat treatment, etc. can be carried out.

The short-circuit temperature of the multilayer porous membrane 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 multilayer porous membrane has a short-circuit temperature of 180 ° C. or higher, contact between the positive and negative electrodes can be suppressed until heat is dissipated even in abnormal battery heat generation, and thus better safety performance tends to be obtained.

[Method for producing multilayer porous membrane]
The manufacturing method of the multilayer porous membrane of this embodiment has the application | coating process which apply | coats the dispersion liquid containing an inorganic filler, a resin binder, and an ion dissociative inorganic dispersing agent to the single side | surface or both surfaces of a polyolefin porous membrane. Moreover, the manufacturing method of a multilayer porous membrane may have the process of manufacturing a polyolefin porous membrane as needed.

In the production method of the present embodiment, the production method of the polyolefin porous film is not particularly limited. For example, the polyolefin resin and the plasticizer are melt-kneaded and formed into a sheet shape, and then the porous film is extracted by extracting the plasticizer. Method: Polyolefin resin is melt-kneaded and extruded at a high draw ratio, then the polyolefin crystal interface is peeled off by heat treatment and stretching, and polyolefin resin and inorganic filler are melt-kneaded and molded on a sheet After that, by making the interface by peeling the interface between the polyolefin resin and the inorganic filler by stretching, the polyolefin resin is dissolved and then immersed in a poor solvent for the polyolefin resin to solidify the polyolefin resin and simultaneously remove the solvent. Well-known methods, such as a method of making it porous, can be mentioned.

In the production method of the present embodiment, although not particularly limited, if the surface of the polyolefin porous membrane is positively treated prior to the coating step, the inorganic filler-containing resin dispersion can be more uniformly applied and moreover, after the coating. Since the adhesiveness of an inorganic filler containing resin layer and the polyolefin porous membrane surface improves, it is preferable.

The surface treatment method is not particularly limited as long as the porous structure of the polyolefin porous membrane is not significantly impaired, and examples thereof include a corona discharge treatment method, a mechanical surface roughening method, a solvent treatment method, an acid treatment method, and an ultraviolet oxidation method. Can be mentioned.

After producing the polyolefin porous membrane, in the coating step, a dispersion containing an inorganic filler, a resin binder, and an ion dissociating inorganic dispersant is applied to one or both sides of the polyolefin porous membrane.

Since the dispersion used in the production method of the present embodiment contains an ion dissociable inorganic dispersant in addition to the inorganic filler and the resin binder, the dispersion stability of the inorganic filler in the dispersion is further improved. Since the dispersion contains a resin binder, the binding property between the porous film, the inorganic filler, and the inorganic filler is further improved.

In the manufacturing method of the present embodiment, the inorganic filler is not particularly limited, and those described above can be used.

Further, in the manufacturing method of the present embodiment, the resin binder is not particularly limited, and the above-mentioned ones can be used. Of these, aliphatic conjugated diene monomers and unsaturated carboxylic acid monomers and their copolymerization are possible because the ion permeability is less likely to decrease when the porous layer is laminated on at least one side of the porous membrane. It is preferable to use a latex obtained by emulsion polymerization of other monomers. Furthermore, from the viewpoint of electrochemical stability and binding properties, the resin binder is preferably an acrylic polymer, particularly an acrylic latex. In particular, depending on the inorganic filler used, aggregation is likely to occur when an acrylic polymer is added. However, in the manufacturing method of this embodiment, since a dispersant containing an ion dissociable inorganic dispersant is used, the aggregation of the resin binder is suppressed. Can do.

In the production method of the present embodiment, the ion dissociable inorganic dispersant is not particularly limited, and those described above can be used.

The solvent of the dispersion is not particularly limited, and examples thereof include N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, water, ethanol, toluene, hot xylene, and hexane. Water is preferable from the viewpoint of dispersibility of the inorganic filler and the resin binder.

The dispersion preferably further contains an ion dissociable organic dispersant. When the dispersion contains the ion dissociable organic dispersant, the dispersion stability of the inorganic filler and the resin binder in the dispersion tends to be further improved. It does not specifically limit as an ion dissociative organic dispersing agent, The same thing as the above can be used. The ion dissociable organic dispersant, together with the ion dissociable inorganic dispersant, serves as a dispersant in the dispersion of the production method of the present embodiment.

In the case where the dispersion further contains an ion dissociable organic dispersant, the content of the ion dissociable inorganic dispersant in the dispersion is not particularly limited, but is the total of the ion dissociable inorganic dispersant and the ion dissociable organic dispersant. Preferably it is 20 mass parts or more and 95 mass parts or less with respect to 100 mass parts of content, More preferably, they are 30 mass parts or more and 93 mass parts or less, More preferably, they are 50 mass parts or more and 90 mass parts or less. When the content of the ion 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 this embodiment, in order to stabilize the dispersion or improve the coating property to the polyolefin porous membrane, a dispersant such as a surfactant, a thickener, a wetting agent, an antifoaming agent, Various additives such as pH adjusting agents including acids and alkalis may be added. These additives are preferably those that can be removed upon solvent removal or plasticizer extraction. However, if they are electrochemically stable in the range of use of the lithium ion secondary battery and do not inhibit the battery reaction, May remain.

In the production method of the present embodiment, a method for dissolving or dispersing the inorganic filler, the resin binder, and the ion dissociable inorganic dispersant in a solvent is not particularly limited. For example, a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid Examples thereof include a mill, an attritor, a roll mill, a high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and mechanical stirring using a stirring blade.

In the production method of the present embodiment, the method for applying the dispersion to the polyolefin porous film is not particularly limited as long as it can realize the required 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, Examples thereof include a cast coater method, a die coater method, a screen printing method, and a spray coating method. Moreover, according to a use, an inorganic filler containing resin dispersion liquid may be apply | coated only to the single side | surface of a polyolefin porous membrane, and may be apply | coated to both surfaces.

In the manufacturing method of this embodiment, it is preferable to remove the solvent after applying the dispersion. As a method for removing the solvent, for example, a method of drying at a temperature below the melting point while fixing the polyolefin porous film, a method of drying under reduced pressure at a low temperature, and immersing in a poor solvent for the resin binder to solidify the resin binder The method of extracting a solvent simultaneously is mentioned.

[Separator for non-aqueous electrolyte battery]
The separator for nonaqueous electrolyte batteries of this embodiment includes the multilayer porous film. The multilayer porous membrane has heat resistance and can be suitably used as a separator for nonaqueous electrolyte batteries. The multilayer porous membrane of this embodiment can achieve both good heat resistance and ion permeability (air permeability). When such a multilayer porous membrane is used as a separator for a non-aqueous electrolyte battery, a non-aqueous electrolyte battery excellent in safety performance and output characteristics can be realized.

The various parameters described above are values measured according to the measurement methods in the examples described later unless otherwise specified.

Next, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist. In addition, the physical property in an Example was measured with the following method. Unless otherwise stated, various measurements and evaluations were performed under conditions of room temperature 23 ° C., 1 atm, and relative humidity 50%.

(1) Viscosity average molecular weight Mv of polyolefin resin
Based on ASTM-D4020, the intrinsic viscosity [η] (dl / g) of a polyolefin resin decalin solvent at 135 ° C. was determined.
Mv of polyethylene was calculated by the following formula.
[Η] = 6.77 × 10 −4 Mv 0.67
Mv of polypropylene was calculated by the following formula.
[Η] = 1.10 × 10 −4 Mv 0.80

(2) Thickness (μm) of multilayer porous membrane and polyolefin porous membrane, and layer thickness (μm) of porous layer
The film thicknesses of the multilayer porous membrane and the polyolefin porous membrane were measured with a dial gauge (manufactured by Ozaki Seisakusho, trade name “PEACOCK No. 25”). Specifically, a sample having a dimension of 100 mm in the MD direction × 100 mm in the TD direction was cut out, and the local film thicknesses at 9 locations (3 points × 3 points) were measured in a lattice shape. The arithmetic average value was defined as the film thickness. The thickness of the porous layer was calculated from the difference between the thickness of the multilayer porous membrane and the thickness of the polyolefin porous membrane (measured by peeling the porous layer).

(3) Air permeability (second / 100 cc), rate of increase in air permeability (%) of multilayer porous membrane and polyolefin porous membrane
For measurement of the air permeability (second / 100 cc) of the multilayer porous membrane and the polyolefin porous membrane, a Gurley type air permeability meter (G-B2 (trademark) manufactured by Toyo Seiki Co.) conforming to JIS P-8117 was used. The inner cylinder weight was 567 g, and the time required for 100 mL of air to pass through an area of 28.6 mm in diameter and 645 mm ² was measured as the air permeability.
On the other hand, the air permeability increase rate was calculated by the following formula.
Permeability increase rate (%) = 100 × (air permeability of multilayer porous membrane−air permeability of polyolefin porous membrane) / air permeability of polyolefin porous membrane

(4) Porosity of polyolefin porous membrane (%)
A 10 cm × 10 cm square sample was cut from the polyolefin porous membrane, its volume (cm ³ ) and mass (g) were determined, and the membrane density was calculated as 0.95 (g / cm ³ ) using the following formula.
Porosity = (1−mass / volume / 0.95) × 100

(5) Maximum thermal shrinkage stress (g) of MD and TD of polyolefin porous membrane
It measured using Shimadzu Corporation TMA50 (trademark). A polyolefin porous membrane sample cut out with a TD width of 3 mm was fixed to a chuck such that the distance between chucks was 10 mm, and set on a dedicated probe. The initial load is 1.0 g, the sample is heated from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min, the load (g) generated at that time is measured, and the maximum value is the maximum heat shrinkage stress (g) of MD It was. Moreover, except having used the sample of the polyolefin porous membrane cut out by making MD width 3mm, the same operation was performed and the heat-shrinkage maximum stress (g) of TD was measured.

(6) Average particle size of inorganic filler The average particle size of the inorganic filler is measured by measuring the particle size distribution using a laser particle size distribution measuring device (Microtrack MT3300EX manufactured by Nikkiso Co., Ltd.) using water as a dispersion medium, and the cumulative frequency. Was the average particle size.

(7) Thermal shrinkage ratio of MD and TD of multilayer porous membrane at 150 ° C. The multilayer porous membrane was cut to 100 mm in the MD direction and 100 mm in the TD direction, and left in an oven at 150 ° C. for 1 hour. At this time, the sample was sandwiched between two sheets of paper so that the hot air was not directly applied to the sample. After the sample was taken out of the oven and cooled, the length (mm) was measured, and the thermal contraction rate of MD and TD was calculated by the following formula.
MD thermal shrinkage (%) = (100−MD length after heating) / 100 × 100
TD heat shrinkage (%) = (100−length of TD after heating) / 100 × 100

[Example 1]
(Manufacture of polyolefin porous membrane)
47 parts by mass of polyethylene having an Mv of 700,000, 46 parts by mass of polyethylene having an Mv of 300,000, and 7 parts by mass of polypropylene having an Mv of 400,000 were dry blended using a tumbler blender. Next, 1 part by mass of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant was added to 99 parts by mass of the obtained pure polymer mixture. Then, the mixture was made into 100 parts by mass in total, and dry blended again using a tumbler blender to obtain a polymer mixture. After substituting the inside of the twin screw extruder with nitrogen, the obtained mixture such as polymer was fed to the twin screw extruder by a feeder under a nitrogen atmosphere. Further, 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.

A mixture such as a polymer and liquid paraffin were melt-kneaded in a twin-screw extruder, and the feeder and pump were adjusted so that the liquid paraffin content ratio in the total mixture to be extruded was 65 parts by mass. The melt kneading conditions were a set temperature of 200 ° C., a screw rotation speed of 240 rpm, and a discharge rate of 12 kg / h. Subsequently, the melt-kneaded product was extruded and cast on a cooling roll controlled at a surface temperature of 25 ° C. through a T-die to obtain a gel sheet having a thickness of 1600 μm.
Next, the obtained gel sheet was guided to a simultaneous biaxial tenter stretching machine, and biaxial stretching was performed. The set stretching conditions were an MD magnification of 7.0 times, a TD magnification of 7.0 times, and a preset temperature of 125 ° C.
Next, the stretched gel sheet was introduced into a methyl ethyl ketone bath and sufficiently immersed in methyl ethyl ketone to extract and remove liquid paraffin, and then methyl ethyl ketone was removed by drying.
Next, the dried gel sheet was guided to a TD tenter and heat fixed. The stretching temperature and magnification during heat setting were 128 ° C. and 2.0 times, and the temperature and relaxation rate during subsequent relaxation were 133 ° C. and 0.80. As a result, a porous film having a film thickness of 12 μm, a porosity of 40 vol%, an air 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)
Into a reaction vessel equipped with a stirrer, reflux condenser, dripping tank and thermometer, 65 parts by weight of water as an initial charge, Aqualon KH10 (polyoxyethylene-1- (allyloxymethyl) alkyl ether sulfate ammonium salt: 100% solids 0.5 parts by weight per minute / Daiichi Kogyo Seiyaku Co., Ltd. was added, the temperature in the reaction vessel was kept at 80 ° C., and 1.5 parts by weight of a 10% aqueous solution of ammonium peroxodisulfate was added. 5 minutes after the addition, methyl methacrylate 26.5 parts by mass, cyclohexyl methacrylate 6 parts by mass, butyl acrylate 25 parts by mass, 2-ethylhexyl methacrylate 35 parts by mass, methacrylic acid 1 part by mass, acrylic acid 1.5 parts by mass, glycidyl methacrylate 3 parts by mass, 2 parts by mass of 2-hydroxyethyl methacrylate, 1.5 parts by mass of Aqualon KH10, 1.5 parts by mass of 10% aqueous solution of ammonium peroxodisulfate, and 55 parts by mass of water were added dropwise over 150 minutes. The reaction vessel was charged from the tank. The pH of the reaction system was maintained at 4 or lower. After the addition of the emulsified liquid mixture was completed, the temperature of the reaction vessel was kept at 80 ° C. and stirring was continued for 120 minutes. Then, it 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% aqueous ammonia, and then water was added to adjust the solid content to 45%.

(Formation of porous layer)
94 parts by mass of aluminum hydroxide oxide particles (average particle size: 1.0 μm) as inorganic filler, 6.0 parts by mass of acrylic polymer (solid content concentration: 45%) as resin binder, and ion dissociable inorganic dispersant Then, 1.0 part by mass of polyphosphate amine salt (dispersant) was 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 to the surface of the polyolefin porous film using a gravure coater. Then, it dried at 60 degreeC and water was removed, and the multilayer porous film with a total film thickness of 14 micrometers which formed the porous layer with a thickness of 2 micrometers on the porous film was obtained. The results are listed in Table 1. In addition, tripolyphosphoric acid was used as “polyphosphoric acid” (the same applies to other examples).

[Example 2]
The dispersant in the dispersion for forming the porous layer is 0.95 part by mass of polyphosphate amine salt, 0.05 part by mass of ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco) that is an ion dissociative organic dispersant, A multilayer porous membrane was obtained in the same manner as in Example 1 except that the mixture was used. The results are listed in Table 1.

[Example 3]
Example 1 except that the dispersant in the porous layer-forming dispersion was a mixture of 0.8 parts by mass of polyphosphate amine salt and 0.2 parts by mass of ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco). In the same manner, a multilayer porous membrane was obtained. The results are listed in Table 1.

[Example 4]
Example 1 except that the dispersant in the porous layer-forming dispersion was a mixture of 0.6 parts by mass of polyphosphate amine salt and 0.4 parts by mass of ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco). In the same manner, a multilayer porous membrane was obtained. The results are listed in Table 1.

[Example 5]
Example 1 except that the dispersant in the dispersion for forming the porous layer was a mixture of 0.2 parts by mass of polyphosphate amine salt and 0.8 parts by mass of ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco). In the same manner, a multilayer porous membrane was obtained. The results are listed in Table 1.

[Example 6]
Example 1 except that the dispersant in the dispersion for forming a porous layer was a mixture of 0.05 part by mass of a polyphosphate amine salt and 0.95 part by mass of ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco). In the same manner, a multilayer porous membrane was obtained. The results are listed in Table 1.

[Example 7]
A multilayer porous membrane was obtained in the same manner as in Example 3 except that the thickness of the porous layer was 5 μm. The results are listed in Table 1.

[Example 8]
A multilayer porous membrane was obtained in the same manner as in Example 3 except that the thickness of the porous layer was 7 μm. The results are listed in Table 1.

[Example 9]
A multilayer porous membrane was obtained in the same manner as in Example 3 except that the thickness of the porous layer was 10 μm. The results are listed in Table 1.

[Example 10]
Example except that the dispersant in the dispersion for forming the porous layer was a mixture of 0.8 parts by mass of polyphosphate amine salt and 0.2 parts by mass of sodium polyacrylate which is an ionic dissociative organic dispersant. In the same manner as in Example 3, a multilayer porous membrane was obtained. The results are listed in Table 1.

[Example 11]
Viscosity average molecular weight (Mv) 2000,000 ultra high molecular weight polyethylene 12 parts by mass, Mv280,000 high density polyethylene 12 parts by mass, Mv150,000 linear low density polyethylene 16 parts by mass and silica (average particle size 8. (3 μm) After 17.6 parts by mass and 42.4 parts by mass of dioctyl phthalate (DOP) as a plasticizer are mixed and granulated, they are kneaded and extruded by a twin screw extruder equipped with a T-die, and the thickness is 90 μm. Molded into a sheet. The molded product was subjected to extraction removal of DOP with methylene chloride and silica with sodium hydroxide to form a porous film. The porous membrane was heated to 118 ° C. and stretched 5.3 times in the longitudinal direction and then 1.8 times in the transverse direction. As a result, a porous film having a film thickness of 11 μm, porosity of 48 volume%, air permeability of 55 seconds / 100 cc, MD maximum heat shrinkage stress of 8.7 g, and TD maximum heat shrinkage stress of 0.9 g was obtained.

A multilayer porous membrane was obtained in the same manner as in Example 3 except that the polyolefin porous membrane was used as a substrate. The results are listed in Table 1.

[Example 12]
A multilayer porous membrane was obtained in the same manner as in Example 1 except that calcined kaolin (average particle size: 1.0 μm) was used as the inorganic filler in the porous layer forming dispersion. The results are listed in Table 1.

[Example 13]
A multilayer porous membrane was obtained in the same manner as in Example 1 except that alumina (average particle size: 1.0 μm) was used as the inorganic filler in the dispersion for forming the porous layer. The results are listed in Table 1.

[Example 14]
A multilayer porous membrane was obtained in the same manner as in Example 1 except that ammonium polyphosphate was used as the dispersant in the dispersion for forming the porous layer. The results are also shown in Table 1.

[Example 15]
A multilayer porous membrane was obtained in the same manner as in Example 1 except that sodium polyphosphate was used as the dispersant in the dispersion for forming the porous layer. The results are also shown in Table 1.

[Example 16]
A multilayer porous membrane was obtained in the same manner as in Example 1 except that the dispersant in the dispersion for forming the porous layer was changed to 0.3 parts by mass of polyphosphate amine salt. The results are listed in Table 1.

[Example 17]
A multilayer porous membrane was obtained in the same manner as in Example 1 except that the dispersant in the dispersion for forming a porous layer was changed to 2.5 parts by mass of polyphosphate amine salt. The results are listed in Table 1.

[Example 18]
A multilayer porous membrane was obtained in the same manner as in Example 1 except that 90 parts by mass of the inorganic filler and 10 parts by mass of the resin binder in the dispersion for forming the porous layer were used. The results are listed in Table 1.

[Example 19]
A multilayer porous membrane was obtained in the same manner as in Example 1 except that 98 parts by mass of the inorganic filler in the dispersion for forming the porous layer and 2 parts by mass of the resin binder were used. The results are listed in Table 1.

[Comparative Example 1]
100 parts by mass of 94 parts by mass of an aluminum hydroxide oxide particle (average particle size 1.0 μm) as an inorganic filler and 6 parts by mass of an acrylic polymer (solid content concentration 45%) as a resin binder are added to the dispersion for forming a porous layer. A dispersion for forming a porous layer was prepared by uniformly dispersing each in a portion of water. A multilayer porous membrane 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 listed in Table 1.

[Comparative Example 2]
A multilayer porous membrane was obtained in the same manner as in Example 1 except that the dispersant in the dispersion for forming the porous layer was 1 part by mass of ammonium polycarboxylate. The results are listed in Table 1.

[Comparative Example 3]
A multilayer porous membrane was obtained in the same manner as in Example 1 except that the dispersant in the dispersion for forming the porous layer was 1 part by mass of sodium polyacrylate. The results are listed in Table 1.

This application is based on a Japanese patent application (Japanese Patent Application No. 2012-240637) filed with the Japan Patent Office on October 31, 2012, the contents of which are incorporated herein by reference.

The multilayer porous membrane of the present invention has industrial applicability as a separator for batteries, particularly high capacity batteries.

Claims

A polyolefin porous membrane,
A porous layer containing an inorganic filler, a resin binder, and an ion dissociable inorganic dispersant, disposed on one or both sides of the polyolefin porous membrane;
A multilayer porous membrane.
The multilayer porous membrane according to claim 1, wherein the porous layer further contains an ion dissociable organic dispersant.
The content of the ion dissociable inorganic dispersant is 20 parts by mass or more and 95 parts by mass or less with respect to 100 parts by mass of the total content of the ion dissociable inorganic dispersant and the ion dissociable organic dispersant. Item 3. The multilayer porous membrane according to Item 2.
The multilayer porous membrane according to any one of claims 1 to 3, wherein the ion dissociable inorganic dispersant contains a condensed phosphate.
The multilayer porous membrane according to any one of claims 1 to 4, wherein the resin binder contains an acrylic polymer.
A non-aqueous electrolyte battery separator comprising the multilayer porous membrane according to any one of claims 1 to 5.
The manufacturing method of a multilayer porous membrane which has the application | coating process which apply | coats the dispersion liquid containing an inorganic filler, a resin binder, and an ion dissociative inorganic dispersing agent to the single side | surface or both surfaces of a polyolefin porous membrane.
The method for producing a multilayer porous membrane according to claim 7, wherein the resin binder contains an acrylic polymer.
The method for producing a multilayer porous membrane according to claim 7 or 8, wherein the dispersion further contains an ion dissociative organic dispersant.