JP5354735B2 - Multilayer porous membrane - Google Patents

Description

  The present invention relates to a multilayer porous membrane suitably used for separation and purification of various substances and a membrane disposed between a positive electrode and a negative electrode in a battery and a method for producing the same. Furthermore, it is related with the separator for non-aqueous electrolyte batteries using the same, and a non-aqueous electrolyte battery.

Polyolefin porous membranes are widely used as separators in batteries and capacitors because they exhibit excellent electrical insulation and ion permeability. In particular, in recent years, with the increase in functionality and weight of portable devices, lithium ion secondary batteries with high output density and high capacity density have been used as power sources. Polyolefin porous membranes are mainly used in such battery separators. Is used.
Lithium ion secondary batteries have high output density and capacity density, but because the electrolyte uses an organic solvent, the electrolyte decomposes due to heat generated by abnormal situations such as short circuit and overcharge. May cause fire. In order to prevent such a situation, some safety functions are incorporated in the lithium ion secondary battery, and one of them is a separator shutdown function. The shutdown function is a function that stops the progress of the electrochemical reaction by suppressing the ionic conduction in the electrolytic solution by blocking the micropores of the separator due to heat melting or the like when the battery generates abnormal heat. Generally, the lower the shutdown temperature, the higher the safety. One of the reasons why polyethylene is used as a component of the separator is that it has an appropriate shutdown temperature.
However, in batteries with high energy, the temperature inside the battery continues to rise even if the electrochemical reaction is stopped by shutting down. As a result, the separator contracts due to heat shrinkage, and both electrodes are short-circuited. Problem may occur.

  For the purpose of producing a highly safe battery, Patent Document 1 describes a technique for forming a separator by laminating a heat-resistant layer on a first porous layer mainly composed of a thermoplastic resin. .

Japanese Patent No. 3756815

In recent years, however, the capacity of batteries has been increasing. In such a high-capacity battery, the amount of heat generated during abnormal heat generation is large, and a higher temperature environment is likely to occur. Although the separator described in Patent Document 1 is considered to be improved in safety as compared with a normal separator having no heat-resistant layer, it suppresses the thermal contraction of the separator even in a high temperature environment, and the separator breaks the membrane. From the viewpoint of reducing the possibility of short circuiting, there is still room for improvement.
An object of the present invention is to provide a multilayer porous membrane in which thermal shrinkage is suppressed even under a high temperature environment.

As a result of intensive studies to solve the above problems, the present inventors have maintained a high permeability by forming an inorganic particle layer using a specific binder in a polyolefin porous film in which an inorganic particle-containing layer is laminated. However, the present inventors have found that a multilayer porous membrane in which thermal shrinkage at high temperatures is suppressed can be realized, and the present invention has been achieved.
That is, the present invention is as follows.
[1] A multilayer porous membrane comprising a porous layer containing inorganic particles and a resin binder on at least one surface of a porous membrane containing polyolefin resin as a main component, and a proportion of the inorganic particles in the porous layer ( % By mass) is 70% or more and 99.99% or less, and the resinous binder is one or more monomers selected from (meth) acrylic acid ester monomers and unsaturated carboxylic acid monomers. When a copolymer containing crosslinking monomers as a raw material unit, wherein among the monomer composition state, and are the proportion of the unsaturated carboxylic acid monomer is more than 1.0 mass%, the crosslinking The monomer is a monomer having two or more radical polymerizable double bonds, an epoxy group-containing vinyl monomer, a methylol group-containing monomer, an alkoxymethyl group-containing monomer, and a hydrolyzable silyl group. Selected from the group consisting of vinyl monomers Multilayer porous membrane which is a one even without.
[2] The multilayer porous membrane according to [1], wherein the copolymer further contains a hydroxyl group-containing vinyl monomer as a raw material unit.
[3] The multilayer porous membrane according to [1] or [2], wherein the inorganic particles are at least one selected from the group consisting of an aluminum silicate compound, aluminum hydroxide oxide, and calcium carbonate.
[4] The multilayer porous membrane according to any one of [1] to [3], wherein the polyolefin resin contains polypropylene.
[5] The multilayer porous membrane according to [4], wherein the proportion of the polypropylene in the polyolefin resin is 1 to 35% by mass.
[6] A separator for a non-aqueous electrolyte battery comprising the multilayer porous membrane according to any one of [1] to [5].
[7] A non-aqueous electrolyte battery comprising the separator for a non-aqueous electrolyte battery according to [6], a positive electrode, a negative electrode, and an electrolytic solution.
[8] A method for producing a multilayer porous membrane according to any one of [1] to [5], wherein the following steps (A) to (B):
(A) at least a monomer composition containing at least one monomer selected from (meth) acrylic acid ester monomers, an unsaturated carboxylic acid monomer, and a crosslinkable monomer; A dispersion in which a monomer composition having an unsaturated carboxylic acid monomer ratio of 1.0% by mass or more is subjected to emulsion polymerization to form a dispersion in which polymer particles are dispersed in a solvent. Body formation process,
(B) a coating step of coating a coating liquid containing the dispersion and inorganic particles on at least one surface of a porous film mainly composed of a polyolefin resin;
The manufacturing method characterized by including.
[9] The production method according to [8], wherein the monomer composition further contains a hydroxyl group-containing vinyl monomer.
[10]
A coating liquid for forming a multilayer porous film having a porous film comprising a polyolefin resin as a main component and a porous layer comprising inorganic particles and a resin binder laminated on at least one surface of the porous film, The proportion (mass%) of the inorganic particles in the porous layer is 70% or more and 99.99% or less, and the resin binder is one or more types selected from (meth) acrylic acid ester monomers. It is a copolymer containing a monomer, an unsaturated carboxylic acid monomer, and a crosslinkable monomer as raw material units, and the ratio of the unsaturated carboxylic acid monomer in the monomer composition is 1. 0% by mass or more, and as the crosslinkable monomer, a monomer having two or more radical polymerizable double bonds, an epoxy group-containing vinyl monomer, a methylol group-containing monomer, an alkoxy Methyl group-containing monomer and hydrolyzable Coating solution is characterized in that at least one selected from the group consisting of vinyl monomers having a drill group.

  ADVANTAGE OF THE INVENTION According to this invention, the multilayer porous membrane by which heat shrinkage was suppressed also in the high temperature environment, its manufacturing method, the separator for nonaqueous electrolyte batteries using the same, and a nonaqueous electrolyte battery can be provided.

  Hereinafter, modes for carrying out the present invention (hereinafter abbreviated as “embodiments”) 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.

  The multilayer porous membrane of the present embodiment has a porous membrane containing a polyolefin resin as a main component, and a porous layer including inorganic particles and a resin binder laminated on at least one surface of the porous membrane.

  The resinous binder includes one or more monomers selected from (meth) acrylic acid ester monomers (in this application, acrylic acid and methacrylic acid are combined and expressed as (meth) acrylic acid), It is a copolymer containing a saturated carboxylic acid monomer and a crosslinkable monomer as raw material units.

  Examples of the (meth) acrylic acid ester monomer include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, and 2-ethylhexyl acrylate. , Lauryl acrylate, benzyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl acrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, benzyl Meta relay , And phenyl methacrylate, and the like. Preferred are butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, butyl methacrylate, and cyclohexyl methacrylate.

  Examples of the unsaturated carboxylic acid monomer include monocarboxylic acid acrylic acid, methacrylic acid, itaconic acid half ester, maleic acid half ester, fumaric acid half ester, and dicarboxylic acid as itacone. An acid, fumaric acid, maleic acid, etc. are mentioned. Acrylic acid, methacrylic acid and itaconic acid are preferred, and acrylic acid and methacrylic acid are more preferred.

Examples of the crosslinkable monomer include monomers having two or more radically polymerizable double bonds, and monomers having a functional group that gives a self-crosslinking structure during or after polymerization. Can be mentioned.
Examples of the monomer having two or more radical polymerizable double bonds include divinylbenzene, polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, polyoxypropylene diacrylate, polyoxypropylene dimethacrylate, Neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate and the like can be mentioned.
Examples of monomers having a functional group that gives a self-crosslinking structure during or after polymerization include, for example, epoxy group-containing vinyl monomers, methylol group-containing monomers, alkoxymethyl group-containing monomers, hydrolyzable Examples thereof include a vinyl monomer having a silyl group.

Examples of the epoxy group-containing vinyl monomer include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, methyl glycidyl acrylate, and methyl glycidyl methacrylate. Glycidyl methacrylate is preferred.
Examples of the methylol group-containing vinyl monomer include N-methylol acrylamide, N-methylol methacrylamide, dimethylol acrylamide, and dimethylol methacrylamide.
Examples of the alkoxymethyl group-containing vinyl monomer include N-methoxymethyl acrylamide, N-methoxymethyl methacrylamide, N-butoxymethyl acrylamide, N-butoxymethyl methacrylamide, etc. Vinyl having a hydrolyzable silyl group Examples of the monomer include vinyl silane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, and the like.

The copolymer preferably further contains a hydroxyl group-containing vinyl monomer as a raw material unit.
Examples of the hydroxyl group-containing vinyl monomer include hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, polyethylene glycol acrylate, and polyethylene glycol methacrylate. Preferred are hydroxyethyl acrylate and hydroxyethyl methacrylate.

In addition to these monomers, monomer components other than those described above can be further used in order to improve various qualities and physical properties. Examples of the monomers other than the above include amide group-containing vinyl monomers, cyano group-containing vinyl monomers, aromatic vinyl monomers, and other ethylenically unsaturated monomers.
Examples of the amide group-containing vinyl monomer include acrylamide, methacrylamide, N, N-methylenebisacrylamide, diacetone acrylamide, diacetone methacrylamide, maleic amide, maleimide and the like. Preferred are acrylamide and methacrylamide.
Examples of the cyano group-containing vinyl monomer include acrylonitrile and methacrylonitrile.
Examples of the aromatic vinyl monomer include styrene, vinyl toluene, and α-methyl styrene. Styrene is preferred.

  Other ethylenically unsaturated monomers include various vinyl monomers having functional groups such as amino groups, sulfonic acid groups, and phosphoric acid groups, as well as vinyl acetate, vinyl propionate, vinyl versatate, and vinyl. Pyrrolidone, methyl vinyl ketone, butadiene, ethylene, propylene, vinyl chloride, vinylidene chloride and the like can be used as necessary.

The proportion of the unsaturated carboxylic acid monomer contained in the monomer composition is 1.0% by mass or more, preferably 1 to 10% by mass (more preferably 1 to 5% by mass),
The ratio of the (meth) acrylic acid ester monomer is preferably 30 to 98.5% by mass (more preferably 40 to 98.5% by mass, still more preferably 50 to 98.0% by mass),
The proportion of the crosslinkable monomer is preferably 0.5 to 10% by mass (more preferably 1 to 5% by mass),
The proportion of the hydroxyl group-containing vinyl monomer is preferably 0 to 10% by mass (more preferably 0.5 to 5% by mass),
The proportion of other monomers is preferably 0 to 50% by mass.

  The copolymer can be obtained, for example, by an ordinary emulsion polymerization method. There is no restriction | limiting in particular regarding the method of emulsion polymerization, A conventionally well-known method can be used. For example, in a dispersion system containing the above-mentioned monomer composition, surfactant, radical polymerization initiator, and other additive components used as necessary in an aqueous medium as a basic composition component, the monomer composition A copolymer is obtained by polymerizing the product. In the polymerization, the composition of the monomer composition to be supplied is made constant throughout the entire polymerization process, or the morphological composition of the particles of the resin dispersion produced by changing the polymerization process sequentially or continuously. Various methods can be used as required, such as a method of giving change.

A surfactant refers to a compound having at least one hydrophilic group and one or more lipophilic groups in one molecule. Examples of the surfactant include non-reactive alkyl sulfate, polyoxyethylene alkyl ether sulfate, alkylbenzene sulfonate, alkyl naphthalene sulfonate, alkyl sulfosuccinate, alkyl diphenyl ether disulfonate, naphthalene sulfonate. Anionic surface activity such as formalin condensate, polyoxyethylene polycyclic phenyl ether sulfate, polyoxyethylene distyrenated phenyl ether sulfate, fatty acid salt, alkyl phosphate, polyoxyethylene alkylphenyl ether sulfate Non-reactive polyoxyethylene alkyl ether, polyoxyalkylene alkyl ether, polyoxyethylene polycyclic phenyl ether, polyoxyethylene Distyrenated phenyl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, alkylalkanolamide, polyoxyethylene alkylphenyl ether, etc. Nonionic surfactants.
In addition to these, a so-called reactive surfactant in which an ethylenic double bond is introduced into the chemical structural formula of a surfactant having a hydrophilic group and a lipophilic group may be used.

  Among the reactive surfactants, the anionic surfactant is, for example, an ethylenically unsaturated monomer having a sulfonic acid group, a sulfonate group or a sulfate ester group and a salt thereof, a sulfonic acid group, or an ammonium thereof. A compound having a group (ammonium sulfonate group or alkali metal sulfonate group) which is a salt or an alkali metal salt is preferable. For example, alkylallylsulfosuccinate (for example, Sanyo Kasei Co., Ltd., Eleminol (trademark) JS-20, for example, Laumul (trademark) S-120, S-180A, S-180, etc. manufactured by Kao Corp.), for example, poly Oxyethylene alkyl propenyl phenyl ether sulfate ester salt (for example, Aqualon (trademark) HS-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), for example, α- [1-[(allyloxy) methyl] -2- (nonylphenoxy) ) Ethyl] -ω-polyoxyethylene sulfate ester salt (for example, Adeka Soap (trademark) SE-10N manufactured by ADEKA Co., Ltd.), for example, ammonium = α-sulfonato-ω-1- (allyloxymethyl) Alkyloxypolyoxyethylene (for example, Aqualon KH-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) For example, styrene sulfonate (for example, Spinomer (trademark) NaSS manufactured by Tosoh Organic Chemical Co., Ltd.), for example, α- [2-[(allyloxy) -1- (alkyloxymethyl) ethyl]- ω-Polyoxyethylene sulfate ester salt (for example, Adeka Soap (trademark) SR-10 manufactured by ADEKA Corporation), for example, sulfate of polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) ether Examples thereof include salts (for example, LATEMUL (trademark) PD-104 manufactured by Kao Corporation) and the like.

  Examples of the reactive surfactant and nonionic surfactant include α- [1-[(allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-hydroxypolyoxyethylene (for example, ADEKA Corporation). Adekaria soap NE-20, NE-30, NE-40, etc., such as polyoxyethylene alkylpropenyl phenyl ether (for example, Aqualon RN-10, RN-20, RN- manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 30, RN-50 etc.), for example, α- [2-[(allyloxy) -1- (alkyloxymethyl) ethyl] -ω-hydroxypolyoxyethylene (for example, Adeka Soap manufactured by ADEKA Corporation (trademark) ER-10 etc.), for example, polyoxyethylene polyoxybutylene (3-methyl-3-buteni ) Ether (e.g. Kao Corp. LATEMUL (trademark) PD-420 and the like) and the like.

  As the amount of the surfactant, 0.1 to 5 parts by mass of an anionic surfactant and 0.1 to 5 parts by mass of a nonionic surfactant can be used with respect to 100 parts by mass of the monomer composition.

The radical polymerization initiator is one that initiates the addition polymerization of the monomer by radical decomposition with heat or a reducing substance, and both inorganic and organic initiators can be used. As such, water-soluble and oil-soluble polymerization initiators can be used. Examples of water-soluble polymerization initiators include peroxodisulfates, peroxides, water-soluble azobis compounds, peroxide-reducing agent redox systems, and the like. Peroxodisulfates include, for example, potassium peroxodisulfate ( KPS), sodium peroxodisulfate (NPS), ammonium peroxodisulfate (APS) and the like. Examples of peroxides include hydrogen peroxide, t-butyl hydroperoxide, t-butyl peroxymaleic acid, and succinic acid peroxide. Examples of water-soluble azobis compounds include 2,2-azobis (N-hydroxyethylisobutyramide), 2,2-azobis (2-amidinopropane) dihydrochloride, 4,4- Azobis (4-cyanopentanoic acid) and the like. Examples of the dox system include sodium sulfooxylate formaldehyde, sodium bisulfite, sodium thiosulfate, sodium hydroxymethanesulfinate, L-ascorbic acid, and salts thereof, cuprous salts and ferrous salts. A reducing agent such as can also be used in combination with the polymerization initiator.
As a quantity of a radical polymerization initiator, 0.05-2 mass parts of radical polymerization initiators can be used with respect to 100 mass parts of monomer compositions.

In addition, emulsion polymerization of a monomer composition containing one or more monomers selected from (meth) acrylic acid ester monomers, an unsaturated carboxylic acid monomer, and a crosslinkable monomer, When forming a dispersion in which polymer particles are dispersed in a solvent, the solid content of the obtained dispersion is preferably 30% by mass to 70% by mass.
The dispersion is preferably adjusted to a pH range of 5 to 12 using amines such as ammonia, sodium hydroxide, potassium hydroxide and dimethylaminoethanol in order to maintain long-term dispersion stability.

  The average particle diameter of the polymer particles is preferably 70 to 250 nm, more preferably 75 to 230 nm, and still more preferably 80 to 220 nm. An average particle size of 70 nm or more is preferable from the viewpoint of sufficiently exhibiting heat resistance when used as a binder for a porous layer. Moreover, it is preferable that an average particle diameter shall be 250 nm or less from a viewpoint of expressing the favorable coating layer intensity | strength which does not drop | omit of the inorganic particle from a porous layer.

  The inorganic particles used in the porous layer are preferably those having a melting point of 200 ° C. or higher, high electrical insulation, and electrochemical stability within the range of use of the lithium ion secondary battery.

  For example, oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, nitride ceramics such as silicon nitride, titanium nitride, boron nitride, silicon carbide, calcium carbonate, sulfuric acid Magnesium, aluminum sulfate, aluminum hydroxide, aluminum hydroxide oxide, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amicite, bentonite, asbestos, zeolite, silica Examples thereof include ceramics such as calcium acid, magnesium silicate, diatomaceous earth, and silica sand, and glass fibers. These may be used alone or in combination.

  From the viewpoint of electrochemical stability and heat resistance characteristics of multilayer porous membranes, it has ion exchange ability such as aluminum oxide compounds such as alumina and aluminum hydroxide oxide, or kaolinite, dickite, nacrite, halloysite, and pyrophyllite. No aluminum silicate compound or calcium carbonate is preferred. As the aluminum oxide compound, aluminum hydroxide oxide is particularly preferable. As the aluminum silicate compound having no ion exchange ability, kaolin mainly composed of kaolin mineral is more preferable because it is inexpensive and easily available. Kaolin includes wet kaolin and calcined kaolin, which is calcined. However, calcined kaolin releases crystal water during the calcining process and removes impurities, so that it is electrochemically stable. Particularly preferred. As the calcium carbonate, columnar, needle-shaped or spindle-shaped light calcium carbonate is particularly preferable.

  The average particle size of the inorganic particles is preferably larger than 0.1 μm and not larger than 4.0 μm, more preferably larger than 0.2 μm and not larger than 3.5 μm, and larger than 0.4 μm and not larger than 3.0 μm. It is particularly preferred. Such an average particle diameter is preferable from the viewpoint of suppressing thermal shrinkage at high temperatures even when the thickness of the porous layer is thin (for example, 7 μm or less).

In the inorganic particles, the proportion of the particles having a particle size larger than 0.2 μm and not larger than 1.4 μm in the whole inorganic particles is preferably 2% by volume or more, more preferably 3% by volume or more, and further preferably 5% by volume. % Or more, preferably 90% by volume or less, more preferably 80% by volume or less.
In the inorganic particles, the proportion of the particles having a particle size larger than 0.2 μm and not larger than 1.0 μm in the entire inorganic particles is preferably 1% by volume or more, more preferably 2% by volume or more, preferably 80%. Volume% or less, More preferably, it is 70 volume% or less.
In the inorganic particles, the proportion of the particles having a particle size larger than 0.5 μm and not larger than 2.0 μm in the entire inorganic particles is preferably 8% by volume or more, more preferably 10% or more, preferably 60 volume% or less, More preferably, it is 50 volume% or less.
Furthermore, in the inorganic particles, the proportion of the particles having a particle size larger than 0.6 μm and smaller than 1.4 μm in the whole inorganic particles is preferably 1% by volume or more, more preferably 3% by volume or more, preferably Is 40% by volume or less, more preferably 30% by volume or less.
Such a particle size distribution is preferable from the viewpoint of suppressing thermal shrinkage at a high temperature even when the porous layer is thin (for example, 7 μm or less).
Examples of a method for adjusting such a ratio include a method of pulverizing inorganic particles using a ball mill, a bead mill, a jet mill or the like to reduce the particle size.

  The proportion (% by mass) of the inorganic particles in the porous layer can be appropriately determined from the viewpoint of the binding properties of the inorganic particles, the permeability and heat resistance of the multilayer porous membrane, and the like, but 50% or more It is preferably less than 100%, more preferably 70% or more and 99.99% or less, further preferably 80% or more and 99.9% or less, and particularly preferably 90% or more and 99% or less.

  The layer thickness of the porous layer is preferably 1 μm or more from the viewpoint of heat resistance of the multilayer porous film, and preferably 50 μm or less from the viewpoint of increasing the capacity and permeability of the battery. More preferably, they are 1.5 micrometers or more and 20 micrometers or less, More preferably, they are 2 micrometers or more and 10 micrometers or less, Especially preferably, they are 3 micrometers or more and 10 micrometers or less, Most preferably, they are 3 micrometers or more and 7 micrometers or less.

Examples of the method for forming the porous layer include a method in which a porous layer is formed by applying a coating liquid containing inorganic particles and a resin binder on at least one surface of a porous film mainly composed of a polyolefin resin. .
As the solvent of the coating solution, those capable of uniformly and stably dispersing or dissolving the inorganic particles and the resin binder are preferable. For example, N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, Water, ethanol, toluene, hot xylene, methylene chloride, hexane and the like can be mentioned.

  Various additives such as surfactants, thickeners, wetting agents, antifoaming agents, PH preparations containing acids and alkalis are added to the coating solution in order to stabilize dispersion and improve coating properties. May be added. These additives are preferably those that can be removed when the solvent is removed, but are porous if they are electrochemically stable in the range of use of the lithium ion secondary battery, do not inhibit the battery reaction, and are stable up to about 200 ° C. It may remain in the layer.

  The method for dissolving or dispersing the inorganic particles and the polymer particles in the solvent of the coating solution is not particularly limited as long as it can achieve the dissolution or dispersion characteristics of the coating solution necessary for the coating step. Examples thereof include a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid 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.

  The method for applying the coating solution to the porous film is not particularly limited as long as it can achieve the required layer thickness and coating area. For example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast Examples include a coater method, a die coater method, a screen printing method, and a spray coating method.

  Furthermore, it is preferable to perform a surface treatment on the surface of the porous film prior to coating, since it becomes easy to apply the coating liquid and the adhesion between the inorganic particle-containing porous layer after coating and the surface of the porous film is improved. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the porous film. For example, corona discharge treatment method, mechanical surface roughening method, solvent treatment method, acid treatment method, ultraviolet oxidation method Etc.

  The method for removing the solvent from the coating film after coating is not particularly limited as long as it does not adversely affect the porous film. For example, a method of drying at a temperature below the melting point while fixing the porous membrane, a method of drying under reduced pressure at a low temperature, a method of immersing in a poor solvent for a resin binder to solidify the resin binder and simultaneously extracting the solvent, etc. Is mentioned.

Next, the porous film which has polyolefin resin as a main component is demonstrated.
The porous film containing a polyolefin resin as a main component means that the polyolefin resin occupies 50% or more and 100% or less of the mass fraction of the resin component constituting the porous film from the viewpoint of shutdown performance when used as a battery separator. A porous film formed of a polyolefin resin composition is preferred. The proportion of the polyolefin resin is more preferably 60% or more and 100% or less, and most preferably 70% or more and 100% or less.

  The polyolefin resin refers to a polyolefin resin used for normal extrusion, injection, inflation, blow molding and the like, such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. Homopolymers and copolymers, multistage polymers, and the like can be used. In addition, polyolefins selected from the group of these homopolymers, copolymers, and multistage polymers can be used alone or in combination. Representative examples of the polymer include low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultrahigh molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene random copolymer, polybutene. And ethylene propylene rubber.

When the multilayer porous membrane is used as a battery separator, it is preferable to use a resin mainly composed of high-density polyethylene because of its low melting point and high strength required performance.
From the viewpoint of improving the heat resistance of the porous film and the heat resistance of the multilayer porous film, it is more preferable to use a porous film made of polypropylene and a resin composition containing a polyolefin resin other than polypropylene.

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

The ratio of polypropylene to the total polyolefin in the polyolefin resin composition is preferably 1 to 35% by mass, more preferably 3 to 20% by mass, and still more preferably from the viewpoint of achieving both heat resistance and a good shutdown function. It is 4-10 mass%.
In this case, the polyolefin resin other than polypropylene is not limited, and examples thereof include homopolymers or copolymers of olefin hydrocarbons such as ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. Can be mentioned. Specific examples include polyethylene, polybutene, and ethylene-propylene random copolymer.

When the pores are required to shut down due to thermal melting, such as when used as a battery separator, as polyolefin resins other than polypropylene, low density polyethylene, linear low density polyethylene, medium density polyethylene, high It is preferable to use polyethylene such as density polyethylene and ultrahigh molecular weight polyethylene. Among these, from the viewpoint of strength, it is more preferable to use polyethylene having a density measured according to JIS K 7112 of 0.93 g / cm ³ or more.

  The viscosity average molecular weight of the polyolefin resin is preferably from 30,000 to 12 million, more preferably from 50,000 to less than 2 million, and still more preferably from 100,000 to less than 1 million. A viscosity average molecular weight of 30,000 or more is preferable because the melt tension at the time of melt molding becomes large and the moldability becomes good and the strength becomes high due to the entanglement of the polymers. On the other hand, a viscosity average molecular weight of 12 million or less is preferable because uniform melt kneading is facilitated, and sheet formability, particularly thickness stability, is excellent. Furthermore, when the multilayer porous membrane of the present embodiment is used as a battery separator, it is preferable that the viscosity average molecular weight is less than 1 million because a good shutdown function can be obtained because the pores are easily closed when the temperature rises. For example, instead of using a polyolefin having a viscosity average molecular weight of less than 1 million alone, a mixture of a polyolefin having a viscosity average molecular weight of 2 million and a polyolefin having a viscosity average molecular weight of 270,000 may be used, and the viscosity average molecular weight of the mixture may be less than 1 million. Good.

Arbitrary additives can be contained in the polyolefin resin composition. Examples of such additives include polymers other than polyolefins; inorganic fillers; phenol-based, phosphorus-based and sulfur-based antioxidants; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; Stabilizers; antistatic agents; antifogging agents; colored pigments and the like.
The total amount of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and still more preferably 5 parts by mass or less with respect to 100 parts by mass of the polyolefin resin composition.

  There is no limitation on the average pore diameter of the porous membrane, and it can be determined appropriately according to the application. However, when the multilayer porous membrane is used as a battery separator, the pore diameter is preferably 0.001 to 10 μm, more preferably 0.01 to 1 μm. It is.

  There is no restriction | limiting in the method of manufacturing the said porous film, A well-known manufacturing method is employable. For example, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded and formed into a sheet shape, optionally stretched and then made porous by extracting the plasticizer, and a polyolefin resin composition is melt-kneaded to obtain a high draw rate. After extruding at a ratio, the polyolefin crystal interface is peeled off by heat treatment and stretching, the polyolefin resin composition and the inorganic filler are melt-kneaded and molded on a sheet, and then the polyolefin and inorganic filler are stretched And a method of making the structure porous by removing the solvent at the same time as solidifying the polyolefin by dissolving it in a poor solvent for the polyolefin after dissolving the polyolefin resin composition.

Hereinafter, as an example of a method for producing a porous film, a method for extracting a plasticizer after melting and kneading a polyolefin resin composition and a plasticizer to form a sheet will be described.
First, a polyolefin resin composition and a plasticizer are melt-kneaded. As the melt-kneading method, for example, polyolefin resin and other additives as required may be added to a resin kneading apparatus such as an extruder, kneader, lab plast mill, kneading roll, Banbury mixer, etc. A method of introducing a plasticizer at a ratio of kneading and kneading. At this time, it is preferable that the polyolefin resin, other additives, and the plasticizer are pre-kneaded in advance at a predetermined ratio using a Henschel mixer or the like before being added to the resin kneading apparatus. More preferably, only a part of the plasticizer is added in the pre-kneading, and the remaining plasticizer is kneaded while side-feeding the resin kneading apparatus. By doing so, the dispersibility of the plasticizer is increased, and when stretching a sheet-like molded product of the melt-kneaded mixture of the resin composition and the plasticizer in the subsequent step, the film is stretched at a high magnification without breaking. can do.

  As the plasticizer, a non-volatile solvent capable of forming a uniform solution at a melting point or higher of the polyolefin can be used. Specific examples of such a non-volatile solvent include hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; higher alcohols such as oleyl alcohol and stearyl alcohol.

  Among these, liquid paraffin is preferable because it has high compatibility with polyethylene and polypropylene, and even when the melt-kneaded product is stretched, the interface peeling between the resin and the plasticizer hardly occurs.

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

  Next, the melt-kneaded product is formed into a sheet shape. As a method for producing a sheet-like molded product, for example, a melt-kneaded product is extruded into a sheet shape via a T-die or the like, and brought into contact with a heat conductor to cool to a temperature sufficiently lower than the crystallization temperature of the resin component. And then solidify. As the heat conductor used for cooling and solidification, metal, water, air, plasticizer itself, or the like can be used. However, a metal roll is preferable because of high heat conduction efficiency. At this time, it is more preferable that the metal roll is sandwiched between the rolls, since the efficiency of heat conduction is further increased, the sheet is oriented and the film strength is increased, and the surface smoothness of the sheet is also improved. The die lip interval when extruding into a sheet form from a T die is preferably 400 μm or more and 3000 μm or less, and more preferably 500 μm or more and 2500 μm or less. When the die lip interval is 400 μm or more, the mess and the like are reduced, and there is little influence on the film quality such as streaks and defects, and film breakage and the like can be prevented in the subsequent stretching process. On the other hand, when the die lip interval is 3000 μm or less, the cooling rate is high and uneven cooling can be prevented and the thickness stability of the sheet can be maintained.

  It is preferable to stretch the sheet-like molded body thus obtained. As the stretching treatment, either uniaxial stretching or biaxial stretching can be suitably used, but biaxial stretching is preferred from the viewpoint of the strength of the porous film to be obtained. When the sheet-like molded body is stretched at a high magnification in the biaxial direction, the molecules are oriented in the plane direction, and the finally obtained porous film is not easily torn and has a high puncture strength. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multi-stage stretching, multiple stretching, and the like, and simultaneous biaxial from the viewpoint of improvement of puncture strength, uniformity of stretching, and shutdown property Stretching is preferred.

  Here, simultaneous biaxial stretching means stretching in which stretching in the MD direction (machine direction of the microporous membrane) and stretching in the TD direction (direction crossing the MD of the microporous membrane at an angle of 90 °) are performed simultaneously. It refers to a method, and the draw ratio in each direction may be different. Sequential biaxial stretching refers to a stretching method in which stretching in the MD direction or TD direction is independently performed. When stretching is performed in the MD direction or TD direction, the other direction is unconstrained or constant length. It is assumed that it is fixed to

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

  Moreover, you may roll a sheet-like molded object. Rolling can be performed, for example, by a pressing method using a double belt press or the like. Rolling can particularly increase the orientation of the surface layer portion. The rolling surface magnification is preferably greater than 1 and 3 or less, more preferably greater than 1 and 2 or less. When the rolling ratio is larger than 1, the plane orientation increases and the film strength of the finally obtained porous film increases. On the other hand, a rolling ratio of 3 times or less is preferable because the orientation difference between the surface layer portion and the center is small, and a uniform porous structure can be formed in the thickness direction of the film.

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

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

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

Next, the case where the multilayer porous membrane of this Embodiment is used as a battery separator is demonstrated.
The multilayer porous membrane of the present embodiment is excellent in heat resistance and has a shutdown function, and is therefore suitable for a battery separator that separates a positive electrode and a negative electrode in a battery.
In particular, the multilayer porous membrane of the present embodiment is not easily short-circuited even at high temperatures, and can be used safely as a separator for a high electromotive force battery.

  As such a high electromotive force battery, for example, a non-aqueous electrolyte battery can be cited, and the multilayer porous film of the present embodiment is disposed between the positive electrode and the negative electrode to hold the non-aqueous electrolyte, thereby A water electrolyte battery can be manufactured.

There is no limitation in a positive electrode, a negative electrode, and a non-aqueous electrolyte, A well-known thing can be used.
Examples of the positive electrode material include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel type LiMnO ₄ , and olivine type LiFePO ₄ , and examples of the negative electrode material include graphite, non-graphitizable carbonaceous, and easy graphite. Carbonaceous materials such as carbonaceous carbonaceous and composite carbon bodies; silicon, tin, metallic lithium, various alloy materials, and the like.

As the non-aqueous electrolyte, an electrolyte in which an electrolyte is dissolved in an organic solvent can be used. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples thereof include lithium salts such as LiClO ₄ , LiBF ₄ , and LiPF ₆ .

  When the multilayer porous membrane is used as a battery separator, the air permeability of the multilayer porous membrane 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. More preferably, it is 30 seconds / 100 cc or more and 450 seconds / 100 cc or less, and particularly preferably 50 seconds / 100 cc or more and 400 seconds / 100 cc or less. When the air permeability is 10 seconds / 100 cc or more, there is little self-discharge when used as a battery separator, and when it is 650 seconds / 100 cc or less, good charge / discharge characteristics are obtained.

  The rate of increase in the air permeability of the multilayer porous membrane due to the formation of the porous layer is preferably 0% or more and 200% or less, more preferably 0% or more and 100% or less, and more preferably 0% or more and 50%. It is particularly preferable that the ratio is 0% or more and 30% or less. However, when the air permeability of the porous film is less than 100 seconds / 100 cc, the increase in the air permeability of the multilayer porous film after forming the porous layer can be preferably used if it is 0% or more and 500% or less.

The final film thickness of the multilayer porous membrane is preferably 2 μm to 200 μm, more preferably 5 μm to 100 μm, and even more preferably 7 μm to 30 μm.
If the film thickness is 2 μm or more, the mechanical strength is sufficient, and if it is 200 μm or less, the occupied volume of the separator is reduced, which is advantageous in terms of increasing the battery capacity.

  The thermal shrinkage rate of the multilayer porous film at 150 ° C. is preferably 0% or more and 15% or less in both the MD direction and the TD direction, more preferably 0% or more and 10% or less, and further preferably 0% or more and 5% or less. It is. When the thermal shrinkage rate is 15% or less in both the MD direction and the TD direction, it is preferable because the multilayer porous film is prevented from being broken during abnormal heat generation of the battery and short-circuiting hardly occurs.

  The shutdown temperature of the multilayer porous membrane is preferably 120 ° C. or higher and 160 ° C. or lower, more preferably 120 ° C. or higher and 150 ° C. or lower. It is preferable that the shutdown temperature is 160 ° C. or lower because 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 is 120 ° C. or higher because the battery can be used at around 100 ° C.

  The short-circuit temperature of the multilayer porous membrane is preferably 180 ° C. or higher and 1000 ° C. or lower, more preferably 200 ° C. or higher and 1000 ° C. or lower. When the short-circuit temperature is 180 ° C. or higher, even if abnormal heat generation occurs in the battery, a short circuit does not occur immediately, so heat can be dissipated during that time, and better safety performance can be obtained.

The short temperature can be controlled to a desired value by adjusting the content of polypropylene, the type of polyolefin other than polypropylene, the type of inorganic particles, the thickness of the inorganic particle-containing layer, and the like.
In addition, about the various parameters mentioned above, unless otherwise indicated, it measures according to the measuring method in the Example mentioned later.

  Next, the present embodiment will be described more specifically with reference to examples and comparative examples. However, the present embodiment 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.

(1) Average particle diameter of polymer particles The volume average particle diameter (nm) was measured using a particle diameter measuring device (LECR & NORTHRUP MICROTRACTMUPA150) by a light scattering method to obtain an average particle diameter.
(2) Polyolefin viscosity average molecular weight (Mv)
Based on ASTM-D4020, the intrinsic viscosity [η] (dl / g) at 135 ° C. in a decalin solvent was determined.
About polyethylene, it computed by the following formula.
[Η] = 6.77 × 10 ⁻⁴ Mv ^0.67
For polypropylene, Mv was calculated by the following formula.
[Η] = 1.10 × 10 ⁻⁴ Mv ^0.80

(3) Thickness of porous film, layer thickness of porous layer A sample of MD 10 mm x TD 10 mm is cut out from the porous film and multilayer porous film, and nine locations (3 points x 3 points) are selected in a lattice shape, and the film thickness is dial gauge (PEACOCK No. 25 (registered trademark) manufactured by Ozaki Mfg. Co., Ltd.) was used, and the average value of the measurement values at nine locations was defined as the film thickness (μm) of the porous film and multilayer porous film. Further, the difference in film thickness between the multilayer porous film and the porous film thus measured was defined as the layer thickness (μm) of the porous layer of the porous layer.

(4) Average particle size of inorganic particles (μm)
After adding inorganic particles to distilled water and adding a small amount of sodium hexametaphosphate aqueous solution and dispersing for 1 minute with an ultrasonic homogenizer, the particle size is measured using a laser particle size distribution analyzer (Microtrac MT3300EX manufactured by Nikkiso Co., Ltd.). Distribution was measured. The particle size at which the cumulative frequency was 50% was taken as the average particle size.

(5) Air permeability (second / 100cc), air permeability increase (rise) rate (%)
Using a JIS P-8117 compliant Gurley type air permeability meter (G-B2 (trademark) manufactured by Toyo Seiki, inner cylinder mass: 567 g), with respect to a measurement target membrane having an area of 645 mm ² (circle having a diameter of 28.6 mm) Then, the time (seconds) through which 100 cc of air passes was measured and defined as the air permeability.
The rate of increase in air permeability due to the formation of the porous layer was calculated by the following formula.
Permeability increase rate (%) = {(Air permeability of multilayer porous membrane−Air permeability of porous membrane) / Air permeability of porous membrane} × 100

(6) 150 ° C. thermal shrinkage (%)
The separator is 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 is sandwiched between two sheets of paper so that the hot air does not directly hit the sample. After the sample is taken out from the oven and cooled, the length (mm) is measured, and the thermal contraction rate of MD and TD is calculated by the following formula.
MD thermal shrinkage (%) = (100−MD length after heating) / 100 × 100
TD heat shrinkage rate (%) = (100−length of TD after heating) / 100 × 100

(7) Shutdown temperature and short-circuit temperature of the multilayer porous film a. Production of positive electrode 92.2 parts by mass of lithium cobalt composite oxide (LiCoO ₂ ) as the positive electrode active material, 2.3 parts by mass of flake graphite and acetylene black as the conductive material, and polyvinylidene fluoride (PVDF) as the resin binder 3.2 parts by mass were prepared, and these were dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. This slurry was applied to one side of a 20 μm-thick aluminum foil serving as a positive electrode current collector using a die coater so that the positive electrode active material application amount was 250 g / m ² . After drying at 130 ° C. for 3 minutes, using a roll press machine, compression molding was performed so that the bulk density of the positive electrode active material was 3.00 g / cm ³ to obtain a positive electrode.
b. Preparation of Negative Electrode 96.6 parts by mass of artificial graphite as a negative electrode active material, 1.4 parts by mass of ammonium salt of carboxymethyl cellulose and 1.7 parts by mass of styrene-butadiene copolymer latex as a resin binder were prepared and purified. A slurry was prepared by dispersing in water. This slurry was applied to one side of a 12 μm-thick copper foil serving as a negative electrode current collector using a die coater so that the negative electrode active material application amount was 106 g / m ² . After drying at 120 ° C. for 3 minutes, using a roll press machine, the negative electrode active material was compression-molded so that the bulk density of the negative electrode active material was 1.35 g / cm ³ to obtain a negative electrode.
c. Preparation of Nonaqueous Electrolytic Solution LiBF ₄ as a solute was dissolved in a mixed solvent of propylene carbonate: ethylene carbonate: γ-butyllactone = 1: 1: 2 (volume ratio) to a concentration of 1.0 mol / L, A water electrolyte was prepared.
d. Measurement of shutdown temperature and short-circuit temperature A negative electrode cut into 65 mm × 20 mm and immersed in a non-aqueous electrolyte for 1 minute or longer, 9 μm (thickness) × 50 mm × 50 mm aramid film with a 16 mm diameter hole in the center, 65 mm × A multilayer porous membrane or porous membrane cut into 20 mm and immersed in a non-aqueous electrolyte for 1 hour or more, a positive electrode cut into 65 mm × 20 mm and immersed in a non-aqueous electrolyte for 1 minute or more, a Kapton film, and a silicon rubber with a thickness of about 4 mm It was prepared and laminated in this order on a ceramic plate to which a thermocouple was connected. This laminate is set on a hot plate, heated at a rate of 15 ° C./min with a pressure of 4.1 MPa applied by a hydraulic press, and the impedance change between the positive and negative electrodes is 1 V AC and 1 kHz. The measurement was performed up to 200 ° C.
The temperature at the time when the impedance reached 1000Ω was taken as the shutdown temperature, and the temperature at which the impedance again fell below 1000Ω after the shutdown was taken as the short-circuit temperature.

(8) Evaluation of battery separator suitability a. Production of Positive Electrode A positive electrode produced in the same manner as (7) a was punched into a circle having an area of 2.00 cm ² .
b. Production of Negative Electrode A negative electrode produced in the same manner as b in (7) was punched into a circle having an area of 2.05 cm ² .
c. Nonaqueous Electrolytic Solution Prepared by dissolving LiPF ₆ as a solute in a mixed solvent of ethylene carbonate: ethyl methyl carbonate = 1: 2 (volume ratio) to a concentration of 1.0 ml / L.
d. Battery assembly The negative electrode, the multilayer porous film, and the positive electrode were stacked in this order from the bottom so that the active material surfaces of the positive electrode and the negative electrode faced each other. The laminate was stored in a stainless steel container with a lid in which the container main body and the lid were insulated so that the copper foil of the negative electrode and the aluminum foil of the positive electrode were in contact with the container main body and the lid, respectively. A non-aqueous electrolyte was poured into the container and sealed.
e. Evaluation (rate characteristics)
d. The simple battery assembled in step 1 is charged to a battery voltage of 4.2 V at a current value of 3 mA (about 0.5 C) at 25 ° C., and the current value starts to be reduced from 3 mA so as to hold 4.2 V. The first charge after battery preparation was performed for a total of about 6 hours, and then discharged to a battery voltage of 3.0 V at a current value of 3 mA.
Next, at 25 ° C., the battery is charged to a battery voltage of 4.2 V at a current value of 6 mA (about 1.0 C), and the current value starts to be reduced from 6 mA so as to hold 4.2 V. The battery was charged for a period of time and then discharged at a current value of 6 mA to a battery voltage of 3.0 V, and the discharge capacity at that time was set to 1 C discharge capacity (mAh).
Next, at 25 ° C., the battery is charged to a battery voltage of 4.2 V at a current value of 6 mA (about 1.0 C), and the current value starts to be reduced from 6 mA so as to hold 4.2 V. The battery was charged for a period of time and then discharged at a current value of 12 mA (about 2.0 C) to a battery voltage of 3.0 V, and the discharge capacity at that time was set to 2 C discharge capacity (mAh).
The ratio of the 2C discharge capacity to the 1C discharge capacity was calculated, and this value was used as the rate characteristic.
Rate characteristic (%) = (2C discharge capacity / 1C discharge capacity) × 100
(Cycle characteristics)
A simple battery that has been evaluated for rate characteristics is charged to a battery voltage of 4.2 V at a current value of 6 mA (about 1.0 C) at 60 ° C., and then the current value starts to be reduced from 6 mA so as to maintain 4.2 V. In this method, a cycle of charging for about 3 hours in total and discharging to a battery voltage of 3.0 V at a current value of 6 mA was repeated 100 times, and the discharge capacities (mAh) of the first cycle and the 100th cycle were measured.
The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first time was calculated, and this value was used as the cycle characteristics.
Cycle characteristics (%) = (100th discharge capacity / first discharge capacity) × 100

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

[Synthesis Example 1]
In a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank and a thermometer, 74 parts by mass 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 65 parts by mass of water are 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, filtration was performed with 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 40%. The average particle diameter of the obtained latex 1 was 90 nm.

[Synthesis Examples 2 to 5 and 9, 10]
Latexes 2 to 5, 9, and 10 were obtained in the same manner as in Synthesis Example 1 except that the monomer composition ratio was changed to the composition ratio shown in Table 1.

[Synthesis Example 6]
Latex 6 was obtained in the same manner as in Synthesis Example 1 except that the amount of Aqualon KH10 used for initial charging was changed to 0.03 parts by mass and the amount of Aqualon KH10 in the emulsion was changed to 1.0 parts by mass. It was.

[Synthesis Example 7]
PD104 (polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) ether sulfate ammonium salt: 20% solids / Kao instead of Aqualon KH10 (0.5 parts by mass) used for initial preparation 4.0 parts by mass (as a 20% product), 70.5 parts by mass of water initially charged, PD104, 7 instead of Aqualon KH10 (1.5 parts by mass) used in the emulsion Latex 7 was obtained in the same manner as in Synthesis Example 1 except that 0.5 part by mass (as a 20% product) and water in the emulsion were changed to 59 parts by mass.

[Synthesis Example 8]
1.25 parts by mass of G15 (sodium dodecylbenzenesulfonate: 16% solids / manufactured by Kao Corporation) instead of Aqualon KH10 (0.5 parts by mass) used for the initial preparation, 2. Perex SSL (sodium alkyldiphenyl ether disulfonate: 50% solids / manufactured by Kao Corp.) instead of Aqualon KH10 (1.5 parts by mass) using 73 parts by mass of initially charged water for the emulsion. Latex 8 was obtained in the same manner as in Synthesis Example 1 except that 0 part by mass (as a 50% product) and water in the emulsion were changed to 63.5 parts by mass.
The monomer composition ratios of Synthesis Examples 1 to 10 and the physical properties of the obtained latexes 1 to 10 are shown in Table 1.

[Example 1]
47 parts by mass of polyethylene having an Mv of 700,000, 46 parts by mass of polyethylene having an Mv of 250,000, and 7 parts by mass of polypropylene having an Mv of 400,000 were dry blended using a tumbler blender. 1% by mass of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant is added to 99% by mass of the obtained pure polymer mixture, and again A mixture such as a polymer was obtained by dry blending using a tumbler blender. The obtained mixture of polymers and the like was substituted with nitrogen and then fed to the twin-screw extruder with a feeder under a nitrogen atmosphere. Further, liquid paraffin (kinematic viscosity at 37.78 ° C .: 7.59 × 10 ⁻⁵ m ² / s) was injected as a plasticizer into the extruder cylinder by a plunger pump. The feeder and pump were adjusted so that the liquid paraffin content ratio in the total mixture melt-kneaded and extruded was 65% by mass. The melt-kneading conditions were set at a preset temperature of 200 ° C., a screw rotation speed of 240 rpm, and a discharge rate of 12 kg / h.
Subsequently, the melt-kneaded material was extruded and cast on a cooling roll controlled at a surface temperature of 25 ° C. through a T-die to obtain a sheet-like polyolefin composition having a thickness of 2000 μm.
Next, it led to the simultaneous biaxial tenter stretching machine, and simultaneous biaxial stretching was performed 7 times in the MD direction and 7 times in the TD direction. At this time, the setting temperature of the simultaneous biaxial tenter was 125 ° C. Next, the solution was introduced into a methyl ethyl ketone tank, and liquid paraffin was extracted and removed, and then methyl ethyl ketone was removed by drying.
Furthermore, it was led to a TD tenter heat fixing machine and heat fixed. The heat setting temperature was 133 ° C. and the TD relaxation rate was 0.80. As a result, a polyolefin resin porous film having a film thickness of 16 μm, a porosity of 40%, and an air permeability of 160 seconds / 100 cc was obtained.
Next, 90.6 masses of calcined kaolin 1 (wet kaolin containing kaolinite (Al ₂ Si ₂ O ₅ (OH) ₄ ) as a main component and calcined at high temperature, average particle size 1.89 μm) as inorganic particles. Part and 9.4 parts by weight of latex 1 as a resin binder were uniformly dispersed in 150 parts by weight of water to prepare a coating solution, which was applied to the surface of the polyolefin resin porous film using a microgravure coater. . Water was removed by drying at 60 ° C. to obtain a multilayer porous film in which a porous layer having a thickness of 5 μm (a binder ratio in the porous layer of 4.0%) was formed on the polyolefin resin porous film.

[Example 2]
95.1 parts by mass of spindle-shaped light calcium carbonate 1 (average particle size 0.98 μm) as inorganic particles and 4.9 parts by mass of latex 1 as a resin binder are uniformly dispersed in 150 parts by mass of water. A coating solution was prepared in the same manner as in Example 1 except that a porous layer having a thickness of 3 μm (a binder ratio of 2.0% in the porous layer) was formed on the polyolefin resin porous membrane. .

[Example 3]
92.8 parts by mass of aluminum hydroxide oxide 1 (average particle size 1.0 μm) as inorganic particles and 7.2 parts by mass of latex 1 as a resin binder are uniformly dispersed in 150 parts by mass of water and applied. A multilayer porous membrane was obtained in the same manner as in Example 1 except that a liquid was prepared and a porous layer having a thickness of 4 μm (binder ratio in the porous layer: 3.0%) was formed on the polyolefin resin porous membrane.

[Example 4]
A multilayer porous membrane was obtained in the same manner as in Example 1 except that latex 2 was used as the resin binder.

[Example 5]
A multilayer porous membrane was obtained in the same manner as in Example 4 except that aluminum hydroxide oxide 1 was used as inorganic particles and a porous layer having a thickness of 4 μm was formed on the polyolefin resin porous membrane.

[Example 6]
A multilayer porous membrane was obtained in the same manner as in Example 1 except that latex 3 was used as the resin binder and a porous layer having a thickness of 6 μm was formed on the polyolefin resin porous membrane.

[Example 7]
A multilayer porous membrane was obtained in the same manner as in Example 1 except that latex 4 was used as the resin binder.

[Example 8]
Except that a polyolefin resin porous film thickness was 12 μm, porosity was 40%, air permeability was 120 sec / 100 cc, and a porous layer having a thickness of 4 μm was formed on the polyolefin resin porous film, the same as in Example 7. A multilayer porous membrane was obtained.

[Example 9]
A multilayer porous membrane was obtained in the same manner as in Example 3 except that the thickness of the polyolefin resin porous membrane was 12 μm, the porosity was 40%, and the air permeability was 120 seconds / 100 cc.

[Example 10]
A multilayer was formed in the same manner as in Example 2 except that the porous film had a thickness of 20 μm, the porosity was 40%, the air permeability was 280 seconds / 100 cc, and a porous layer having a thickness of 5 μm was formed on the polyolefin resin porous film. A porous membrane was obtained.

[Example 11]
A multilayer porous membrane was obtained in the same manner as in Example 6 except that latex 5 was used as the resin binder.

[Example 12]
A multilayer porous membrane was obtained in the same manner as in Example 1 except that latex 6 was used as the resin binder.

[Example 13]
A multilayer porous membrane was obtained in the same manner as in Example 8 except that latex 6 was used as the resin binder.

[Example 14]
(Manufacture of porous membrane)
47.5 parts by mass of Mv 700,000 homopolymer polyethylene, 47.5 parts by mass of Mv 250,000 homopolymer polyethylene, and 5 parts by mass of Mv 400,000 homopolymer polypropylene were dry blended using a tumbler blender. 1% by mass of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant is added to 99% by mass of the obtained pure polymer mixture, and again A mixture such as a polymer was obtained by dry blending using a tumbler blender. The obtained mixture of polymers and the like was substituted with nitrogen and then fed to the twin-screw extruder with a feeder under a nitrogen atmosphere. Further, liquid paraffin (kinematic viscosity at 37.78 ° C .: 7.59 × 10 ⁻⁵ m ² / s) was injected as a plasticizer into the extruder cylinder by a plunger pump. The feeder and pump were adjusted so that the liquid paraffin content ratio in the total mixture melt-kneaded and extruded was 65% by mass. The melt-kneading conditions were set at a preset temperature of 200 ° C., a screw rotation speed of 240 rpm, and a discharge rate of 12 kg / h.
Subsequently, the melt-kneaded material was extruded and cast on a cooling roll controlled at a surface temperature of 25 ° C. through a T-die to obtain a sheet-like polyolefin composition having a thickness of 1300 μm.
Next, it led to the simultaneous biaxial tenter stretching machine, and simultaneous biaxial stretching was performed 7 times in the MD direction and 6.4 times in the TD direction. At this time, the set temperature of the simultaneous biaxial tenter was 118 ° C. Next, the solution was introduced into a methyl ethyl ketone tank, and liquid paraffin was extracted and removed, and then methyl ethyl ketone was removed by drying.
Furthermore, it was led to a TD tenter heat fixing machine and heat fixed. The heat setting temperature was 122 ° C. and the TD relaxation rate was 0.80. As a result, a polyolefin resin porous film having a film thickness of 16 μm, a porosity of 49%, and an air permeability of 155 seconds / 100 cc was obtained.
A multilayer porous membrane was obtained in the same manner as in Example 1 except that the polyolefin resin porous membrane was used.

[Example 15]
A multilayer porous membrane was obtained in the same manner as in Example 3 except that calcium carbonate 1 was used as the inorganic particles, and a porous layer having a thickness of 3 μm was formed on the polyolefin resin porous membrane.

[Example 16]
A multilayer porous membrane was obtained in the same manner as in Example 3 except that latex 6 was used as the resin binder.

[Example 17]
A coating solution is prepared by uniformly dispersing 86.2 parts by mass of calcined kaolin 1 as inorganic particles and 13.8 parts by mass of latex 7 as a resin binder in 150 parts by mass of water. A multilayer porous membrane was obtained in the same manner as in Example 1 except that a 5 μm thick porous layer (binder ratio in the porous layer was 6.0%) was formed.

[Example 18]
A multilayer porous membrane was obtained in the same manner as in Example 6 except that latex 8 was used as the resin binder.

[Comparative Example 1]
A multilayer porous membrane was obtained in the same manner as in Example 1 except that latex 9 was used as the resin binder and a porous layer having a thickness of 8 μm was formed on the polyolefin resin porous membrane.

[Comparative Example 2]
A multilayer porous membrane was obtained in the same manner as in Example 5 except that latex 9 was used as the resin binder and a porous layer having a thickness of 6 μm was formed on the polyolefin resin porous membrane.

[Comparative Example 3]
A multilayer porous membrane was obtained in the same manner as in Example 1 except that latex 10 was used as the resin binder and a 9 μm thick porous layer was formed on the polyolefin resin porous membrane.

[Comparative Example 4]
A multilayer porous membrane was obtained in the same manner as in Example 5 except that latex 10 was used as the resin binder and a porous layer having a thickness of 8 μm was formed on the polyolefin resin porous membrane.

[Comparative Example 5]
A porous membrane was obtained in the same manner as in Example 1 except that the porous layer was not formed.

[Comparative Example 6]
A porous membrane was obtained in the same manner as in Example 8 except that the porous layer was not formed.

[Comparative Example 7]
A porous membrane was obtained in the same manner as in Example 10 except that the porous layer was not formed.

[Comparative Example 8]
A porous membrane was obtained in the same manner as in Example 14 except that the porous layer was not formed.

Table 2 shows the air permeability and the air permeability increase rate, the 150 ° C. heat shrinkage rate, the shutdown temperature and the short-circuit temperature of the multilayer porous membranes prepared in Examples 1 to 18 and Comparative Examples 1 to 8.
The porous films of Comparative Examples 5 to 8 in which no porous layer was formed exhibited a very large value with a thermal shrinkage rate at 150 ° C. exceeding 50%.
On the other hand, the multilayer porous membranes of Examples 1 to 18 had a thermal shrinkage rate at 150 ° C. of 5% or less in both the MD direction and the TD direction even though the thickness of the porous layer was 2 to 6 μm. It was very small and showed good heat shrinkage characteristics.

  On the other hand, even if it is a copolymer containing one or more monomers selected from (meth) acrylic acid ester monomers, an unsaturated carboxylic acid monomer, and a crosslinkable monomer as raw material units In the monomer composition, the ratio of the unsaturated carboxylic acid monomer is less than 1.0 part by mass, and the multilayer porous membranes of Comparative Examples 1 to 4 using Latex 9 and 10 as a resin binder are: Compared with the porous membranes of Comparative Examples 5 to 8 in which no porous layer was formed, the heat shrinkage rate at 150 ° C. was suppressed, but the suppression effect was insufficient as compared with the Examples of the present application.

  The shutdown temperature of the multilayer porous film of Examples 1-18 and Comparative Examples 1-8 or a porous film is 145-148 degreeC, and had a favorable shutdown function. The porous films of Comparative Examples 5 to 8 that did not form the porous layer were short-circuited only by heating to the shutdown temperature + several degrees C., but the porous layers of Examples 1 to 18 and Comparative Examples 1 to 4 were formed. All the films did not short-circuit even when heated to 200 ° C. or higher, and were excellent in heat resistance.

  The air permeability of the multilayer porous membranes of Examples 1 to 18 was as small as about 300 seconds / 100 CC or less. In particular, compared with the porous films of Comparative Examples 5 to 8 in which no porous layer was formed, the rate of increase in air permeability could be suppressed to 25% or less.

  All of the simple batteries using the multilayer porous membranes or porous membranes of Examples 1 to 18 and Comparative Examples 5 to 8 as separators exhibited rate characteristics and cycle characteristics of 90% or more. From this, it has confirmed that the multilayer porous film or porous film manufactured in Examples 1-18 and Comparative Examples 5-8 can be used as a battery separator.

Since the multilayer porous membrane of this embodiment is excellent in heat resistance, it can be suitably used for separation and purification of various substances at high temperatures.
Moreover, since the multilayer porous film of this Embodiment has a shutdown function, it can be used especially suitably for a battery separator. In particular, it is suitable for a battery separator for a lithium ion secondary battery.

Claims (10)

A multilayer porous membrane comprising a porous layer containing inorganic particles and a resin binder on at least one surface of a porous membrane mainly composed of a polyolefin resin,
The proportion (mass%) of the inorganic particles in the porous layer is 70% or more and 99.99% or less,
A copolymer in which the resin binder includes one or more monomers selected from (meth) acrylic acid ester monomers, an unsaturated carboxylic acid monomer, and a crosslinkable monomer as raw material units. And
Among the monomer composition state, and it is percentage 1.0% by weight of the unsaturated carboxylic acid monomer,
The crosslinkable monomer is a monomer having two or more radical polymerizable double bonds, an epoxy group-containing vinyl monomer, a methylol group-containing monomer, an alkoxymethyl group-containing monomer, and a hydrolyzable A multilayer porous membrane characterized by being at least one selected from the group consisting of vinyl monomers having a silyl group .   The multilayer porous membrane according to claim 1, wherein the copolymer further contains a hydroxyl group-containing vinyl monomer as a raw material unit.   The multilayer porous membrane according to claim 1 or 2, wherein the inorganic particles are at least one selected from the group consisting of an aluminum silicate compound, aluminum hydroxide oxide, and calcium carbonate.   The multilayer porous membrane according to any one of claims 1 to 3, wherein the polyolefin resin contains polypropylene.   The multilayer porous membrane according to claim 4, wherein the proportion of the polypropylene in the polyolefin resin is 1 to 35 mass%.   The separator for nonaqueous electrolyte batteries which consists of a multilayer porous membrane in any one of Claims 1-5.   A non-aqueous electrolyte battery comprising the separator for a non-aqueous electrolyte battery according to claim 6, a positive electrode, a negative electrode, and an electrolytic solution. It is a manufacturing method of the multilayer porous membrane in any one of Claims 1-5, Comprising: Each process of the following (A)-(B),
(A) at least a monomer composition containing at least one monomer selected from (meth) acrylic acid ester monomers, an unsaturated carboxylic acid monomer, and a crosslinkable monomer; A dispersion in which a monomer composition having an unsaturated carboxylic acid monomer ratio of 1.0% by mass or more is subjected to emulsion polymerization to form a dispersion in which polymer particles are dispersed in a solvent. Body formation process,
(B) a coating step of coating a coating liquid containing the dispersion and inorganic particles on at least one surface of a porous film mainly composed of a polyolefin resin;
The manufacturing method characterized by including.   The production method according to claim 8, wherein the monomer composition further contains a hydroxyl group-containing vinyl monomer.   A coating liquid for forming a multilayer porous film having a porous film comprising a polyolefin resin as a main component and a porous layer comprising inorganic particles and a resin binder laminated on at least one surface of the porous film,
  The proportion (mass%) of the inorganic particles in the porous layer is 70% or more and 99.99% or less,
  A copolymer in which the resin binder includes one or more monomers selected from (meth) acrylic acid ester monomers, an unsaturated carboxylic acid monomer, and a crosslinkable monomer as raw material units. And
  Of the monomer composition, the proportion of unsaturated carboxylic acid monomer is 1.0 mass% or more,
  As the crosslinkable monomer, a monomer having two or more radical polymerizable double bonds, an epoxy group-containing vinyl monomer, a methylol group-containing monomer, an alkoxymethyl group-containing monomer, And at least one selected from the group consisting of vinyl monomers having hydrolyzable silyl groups.