WO2012165580A1 - 積層多孔フィルム、電池用セパレータおよび電池 - Google Patents
積層多孔フィルム、電池用セパレータおよび電池 Download PDFInfo
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- WO2012165580A1 WO2012165580A1 PCT/JP2012/064168 JP2012064168W WO2012165580A1 WO 2012165580 A1 WO2012165580 A1 WO 2012165580A1 JP 2012064168 W JP2012064168 W JP 2012064168W WO 2012165580 A1 WO2012165580 A1 WO 2012165580A1
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- porous film
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
- B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
- B32B5/18—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by features of a layer of foamed material
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
- C08J7/04—Coating
- C08J7/042—Coating with two or more layers, where at least one layer of a composition contains a polymer binder
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
- C08J7/04—Coating
- C08J7/043—Improving the adhesiveness of the coatings per se, e.g. forming primers
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/36—After-treatment
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L69/00—Compositions of polycarbonates; Compositions of derivatives of polycarbonates
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/431—Inorganic material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
- C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/249921—Web or sheet containing structurally defined element or component
- Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/249921—Web or sheet containing structurally defined element or component
- Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
- Y10T428/249981—Plural void-containing components
Definitions
- the present invention relates to a laminated porous film, and can be used as a packaging, sanitary, livestock, agricultural, architectural, medical, separation membrane, light diffusion plate, battery separator, and in particular, a lithium ion of a non-aqueous electrolytic battery. It can be suitably used as a secondary battery separator.
- the polymer porous body with many fine communication holes is used for separation membranes used for the production of ultrapure water, purification of chemicals, water treatment, waterproof and moisture-permeable films used for clothing and sanitary materials, and batteries. It is used in various fields such as battery separators.
- secondary batteries are widely used as power sources for portable devices such as OA, FA, household appliances or communication devices.
- portable devices using lithium ion secondary batteries are increasing because they have a high volumetric efficiency when mounted on devices, leading to a reduction in size and weight of the devices.
- large-sized secondary batteries are being researched and developed in many fields related to energy / environmental issues, including road leveling, UPS, and electric vehicles, and are excellent in large capacity, high output, high voltage, and long-term storage. Therefore, the use of lithium ion secondary batteries, which are a kind of non-aqueous electrolyte secondary battery, is expanding.
- the working voltage of a lithium ion secondary battery is usually designed with an upper limit of 4.1V to 4.2V.
- the aqueous solution causes electrolysis and cannot be used as an electrolyte. Therefore, so-called non-aqueous electrolytes using organic solvents are used as electrolytes that can withstand high voltages.
- the solvent for the non-aqueous electrolyte a high dielectric constant organic solvent capable of allowing more lithium ions to be present is used, and organic carbonate compounds such as propylene carbonate and ethylene carbonate are mainly used as the high dielectric constant organic solvent. in use.
- a highly reactive electrolyte such as lithium hexafluorophosphate is dissolved in the solvent and used.
- a separator is interposed between the positive electrode and the negative electrode from the viewpoint of preventing an internal short circuit.
- the separator is required to have insulating properties due to its role.
- a porous film is used as a separator.
- SD characteristic As a characteristic that contributes to the safety of the battery separator, there is a shutdown characteristic (hereinafter referred to as “SD characteristic”).
- This SD characteristic is a function that can prevent a subsequent increase in temperature inside the battery because the micropores are closed when the temperature is about 100 to 150 ° C., and as a result, ion conduction inside the battery is blocked.
- the lowest temperature among the temperatures at which the micropores of the laminated porous film are blocked is referred to as a shutdown temperature (hereinafter referred to as “SD temperature”).
- SD temperature shutdown temperature
- Patent Documents 1, 2, and 3 propose a multilayer porous film having a porous layer containing a filler and a resin binder on at least one surface of a polyolefin resin porous film.
- a coating layer that is highly filled with a filler such as inorganic on a porous film abnormal heat generation occurs, the SD temperature is exceeded, and even when the temperature continues to rise, short-circuiting of both electrodes is performed. It can be prevented and is considered a very safe method.
- Patent Documents 1 to 3 in order to ensure high air permeability, it is necessary to reduce the content of the resin binder and increase the particle size of the filler. However, when a filler having a large particle size is used, there is a problem in that the binding force between the fillers is reduced and powder falling easily occurs.
- the object of the present invention is to solve the above-mentioned problems, so that the binding property between fillers is high, the heat resistance is excellent, and when used as a separator for a non-aqueous electrolyte secondary battery, excellent SD characteristics can be exhibited. It is an object to provide a laminated porous film.
- the present invention is a laminated porous film in which a coating layer containing a filler and a resin binder is laminated on at least one surface of a polyolefin-based resin porous film to be a base material layer, Within 25% of the thickness of the coating layer from the interface between the average particle diameter (Du) of the filler within 25% of the thickness of the coating layer from the surface of the coating layer that is the surface of the laminated porous film and the base material layer
- the ratio (Du / Db) to the average particle size (Db) of the filler is 1.2 to 10, and the average particle size (Du) of the filler on the surface side of the coating layer is 0.05 ⁇ m or less.
- a laminated porous film is provided.
- the average particle size of the filler contained in the entire layer thickness of the coating layer is 0.1 ⁇ m or more and 3.0 ⁇ m or less.
- the average particle diameter (Du) of the filler is 0.05 ⁇ m to 0.5 ⁇ m
- the average particle diameter (Db) of the filler is 0.1 ⁇ m to 3.0 ⁇ m or more
- the thickness is 25% from the surface of the coating layer.
- the average particle diameter of the filler in the intermediate portion in the thickness direction of the coating layer between the interface between the substrate layer and the base material layer is 25% of the thickness of the coating layer is between (Du) and (Db).
- the coating layer has a gradient in which the average particle diameter increases from the surface side to the interface side with the base material layer. *
- the density of the filler (a) is twice or more the density of the resin binder (b).
- the polyolefin resin porous film of the base material layer includes at least one layer mainly composed of a polypropylene resin.
- the polyolefin resin porous film serving as the base layer is composed of a layer mainly composed of a polypropylene resin (A layer) and another polyolefin resin porous layer (B layer) such as polyethylene or / and a resin porous material other than a polyolefin resin.
- a layer may be laminated, and the coating layer may be laminated on the surface of the laminated polyolefin resin porous layer.
- the polyolefin resin porous film of the base material layer has ⁇ crystal activity.
- the peeling strength between the base material layer and the coating layer is 3 N / 15 mm or more.
- stacked the base material layer of this invention and the said coating layer is less than 25%.
- this invention provides the separator for nonaqueous electrolyte secondary batteries which consists of the said laminated porous film. Furthermore, this invention provides the non-aqueous electrolyte secondary battery using the said separator for non-aqueous electrolyte secondary batteries.
- a dispersion obtained by dissolving or dispersing the filler and the resin binder in a solvent is applied to at least one surface of the polyolefin resin porous film of the base material layer.
- a dispersion having different average particle diameters of the filler is applied to at least one surface of the polyolefin resin porous film of the base layer in multiple times.
- the dispersion is applied from a dispersion having a large average particle size of the filler, and then sequentially applied by dispersing the dispersion having a small average particle size, and the base material layer is formed from the surface side in the thickness direction of the coating layer.
- a method for producing a laminated porous film having an average particle size of the filler on the side having a gradient of (Du / Db) 1.2-10.
- a laminated porous film having a gradient in which the average particle diameter of the filler is in the thickness direction from the surface of the coating layer toward the base layer and the (Du / Db) is 1.2 to 10.
- a manufacturing method is provided.
- heat treatment is performed at 100 ° C. or more and 170 ° C. or less, and a relaxation treatment of 1 to 20% is performed during the heat treatment so that the shrinkage rate at 150 ° C. Is preferably less than 25%.
- the coating layer laminated on the surface of the polyolefin resin porous film to be the base material layer has a gradient that makes the average particle size of the filler smaller and larger from the interface side to the surface with the base material layer. ing.
- the average particle size of the filler on the surface side of the coating layer is small and has a fine structure, so that the binding force between the fillers on the surface side becomes strong and large fillers can be prevented from falling off from the base material layer side. it can.
- the average particle diameter of the filler is large on the base material layer side of the coating layer, a structure with high air permeability is obtained, and deterioration of air permeability can be suppressed.
- the laminated porous film of the present invention has excellent heat shrinkage resistance, a heat shrinkage rate as low as less than 25%, and has excellent SD characteristics. In this way, by providing a gradient in the average particle diameter of the filler in the thickness direction of the coating layer, it is possible to suppress the dropout of the filler of the coating layer and ensure high adhesion between the coating layer and the base material layer.
- a laminated porous film having excellent characteristics can be obtained.
- the expression “main component” includes the intention to allow other components to be contained within a range that does not interfere with the function of the main component, unless otherwise specified.
- the content ratio of the components is not specified, but the main component includes 50% by mass or more, preferably 70% by mass or more, particularly preferably 90% by mass or more (including 100%) in the composition. It is.
- “X to Y” (X and Y are arbitrary numbers) is described, it means “preferably greater than X” and “preferably smaller than Y” with the meaning of “X to Y” unless otherwise specified. Is included.
- Polyolefin resin porous film to be the base material layer (I layer) examples include homopolymers or copolymers obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexane and the like. Among these, a polypropylene resin and a polyethylene resin are preferable.
- Polypropylene resins include homopropylene (propylene homopolymer), or propylene and ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, etc. Random copolymers or block copolymers with ⁇ -olefins may be mentioned. Among these, homopolypropylene is more preferably used from the viewpoint of maintaining the mechanical strength and heat resistance of the laminated porous film.
- the polypropylene resin preferably has an isotactic pentad fraction (mmmm fraction) exhibiting stereoregularity of 80 to 99%. More preferably 83 to 98%, and still more preferably 85 to 97%. If the isotactic pentad fraction is too low, the mechanical strength of the film may be reduced.
- the upper limit of the isotactic pentad fraction is defined by the upper limit that can be obtained industrially at the present time, but this is not the case when a more regular resin is developed in the industrial level in the future. is not.
- the isotactic pentad fraction (mmmm fraction) is the same direction for all five methyl groups that are side chains with respect to the main chain of carbon-carbon bonds composed of any five consecutive propylene units. Means the three-dimensional structure located at or its proportion. Signal assignment of the methyl group region is as follows. It conformed to Zambelli et al (Macromolecules 8, 687, (1975)).
- Mw / Mn which is a parameter indicating a molecular weight distribution
- Mw / Mn is 2.0 to 10.0. More preferred is 2.0 to 8.0, and still more preferred is 2.0 to 6.0. This means that the smaller the Mw / Mn is, the narrower the molecular weight distribution is.
- Mw / Mn is less than 2.0, problems such as a decrease in extrusion moldability occur, and it is difficult to produce industrially.
- Mw / Mn exceeds 10.0, low molecular weight components increase, and the mechanical strength of the laminated porous film tends to decrease.
- Mw / Mn is obtained by GPC (gel permeation chromatography) method.
- the melt flow rate (MFR) of the polypropylene resin is not particularly limited, but usually the MFR is preferably 0.5 to 15 g / 10 minutes, and 1.0 to 10 g / 10 minutes. It is more preferable. When the MFR is 0.5 g / 10 min or more, the resin has a high melt viscosity at the time of molding, and sufficient productivity can be ensured. On the other hand, the mechanical strength of the obtained laminated porous film can be sufficiently maintained by setting it to 15 g / 10 min or less. MFR is measured according to JIS K7210 under conditions of a temperature of 230 ° C. and a load of 2.16 kg.
- the method for producing the polypropylene resin is not particularly limited, and a known polymerization method using a known polymerization catalyst, for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene catalyst. And a polymerization method using a single site catalyst.
- a known polymerization method using a known polymerization catalyst for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene catalyst.
- a polymerization method using a single site catalyst for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene catalyst.
- polypropylene resins examples include trade names “Novatec PP” “WINTEC” (manufactured by Nippon Polypro), “Notio” “Toughmer XR” (manufactured by Mitsui Chemicals), “Zeras” “Thermolan” (manufactured by Mitsubishi Chemical) , “Sumitomo Noblen”, “Tuff Selenium” (manufactured by Sumitomo Chemical Co., Ltd.), “Prime TPO” (manufactured by Prime Polymer Co., Ltd.), “Adflex”, “Adsyl”, “HMS-PP (PF814)” (manufactured by Sun Allomer Co., Ltd.), “Versify” "Inspire” (manufactured by Dow Chemical Co.) can be used.
- the laminated porous film of the present invention preferably has ⁇ crystal activity.
- the ⁇ crystal activity can be regarded as an index indicating that the polypropylene resin produced ⁇ crystals in the film-like material before stretching. If the polypropylene resin in the film-like material before stretching produces ⁇ crystals, fine pores can be easily formed by stretching even when additives such as fillers are not used. A laminated porous film having characteristics can be obtained.
- the presence or absence of “ ⁇ crystal activity” is determined when the crystal melting peak temperature derived from the ⁇ crystal is detected by a differential scanning calorimeter described later and / or the X-ray diffractometer described later.
- a diffraction peak derived from the ⁇ crystal is detected by measurement using, it is determined that the crystal has “ ⁇ crystal activity”.
- the laminated porous film is heated from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min for 1 minute with a differential scanning calorimeter, and then cooled from 240 ° C. to 25 ° C. at a cooling rate of 10 ° C./min.
- Tm ⁇ crystal melting peak temperature
- the ⁇ crystal activity of the laminated porous film is calculated by the following equation using the heat of crystal melting derived from the ⁇ crystal of the polypropylene resin ( ⁇ Hm ⁇ ) and the heat of crystal melting derived from the ⁇ crystal ( ⁇ Hm ⁇ ).
- ⁇ crystal activity (%) [ ⁇ Hm ⁇ / ( ⁇ Hm ⁇ + ⁇ Hm ⁇ )] ⁇ 100
- the amount of heat of crystal melting derived from the ⁇ crystal ( ⁇ Hm ⁇ ) detected mainly in the range of 145 ° C. or higher and lower than 160 ° C., and mainly detected at 160 ° C. or higher and 170 ° C. or lower.
- the amount of heat of crystal melting ( ⁇ Hm ⁇ ) derived from the ⁇ crystal detected mainly in the range of 120 ° C. or more and less than 140 ° C. It can be calculated from the crystal melting calorie ( ⁇ Hm ⁇ ) derived from the ⁇ crystal detected in the range of from 0 ° C. to 165 ° C.
- the ⁇ -crystal activity of the laminated porous film is preferably large, and the ⁇ -crystal activity is preferably 20% or more. More preferably, it is 40% or more, and particularly preferably 60% or more. If the laminated porous film has a ⁇ crystal activity of 20% or more, it indicates that a large number of ⁇ crystals of polypropylene resin can be produced in the film-like material before stretching, and fine and uniform pores are formed by stretching. As a result, a separator for a non-aqueous electrolyte secondary battery having high mechanical strength and excellent air permeability can be obtained.
- the upper limit value of the ⁇ crystal activity is not particularly limited, but the higher the ⁇ crystal activity, the more effective the effect is obtained, so the closer it is to 100%, the better.
- the ⁇ crystal activity can be measured in the state where the laminated porous film of the present invention is in the entire laminated porous film. Further, if a layer containing a polypropylene resin other than the layer made of polypropylene resin is laminated, it is preferable that both layers have ⁇ crystal activity.
- ⁇ crystal nucleating agent examples include those shown below, but are not particularly limited as long as they increase the formation and growth of ⁇ crystals of polypropylene resin, and two or more types are mixed. May be used.
- examples of the ⁇ crystal nucleating agent include amide compounds; tetraoxaspiro compounds; quinacridones; iron oxides having a nanoscale size; potassium 1,2-hydroxystearate, magnesium benzoate or magnesium succinate, magnesium phthalate, etc.
- Alkali or alkaline earth metal salts of carboxylic acids represented by: aromatic sulfonic acid compounds represented by sodium benzenesulfonate or sodium naphthalenesulfonate; di- or triesters of dibasic or tribasic carboxylic acids; phthalocyanine blue Phthalocyanine pigments typified by: a two-component compound comprising component A which is an organic dibasic acid and a component B which is an oxide, hydroxide or salt of a Group IIA metal of the periodic table; a cyclic phosphorus compound; Made of magnesium compound Such as the formation thereof.
- specific types of nucleating agents are described in JP-A No. 2003-306585, JP-A No. 06-289656, and JP-A No. 09-194650.
- ⁇ crystal nucleating agent As a commercial product of ⁇ crystal nucleating agent, ⁇ crystal nucleating agent “NJESTER NU-100” manufactured by Shin Nippon Rika Co., Ltd.
- polypropylene resin to which ⁇ crystal nucleating agent is added polypropylene manufactured by Aristech “Bepol B” -022SP ", Borealis Polypropylene” Beta ( ⁇ ) -PP BE60-7032 ", Mayzo Polypropylene” BNX BETAPP-LN "and the like.
- the ratio of the ⁇ -crystal nucleating agent added to the polypropylene resin needs to be appropriately adjusted depending on the type of the ⁇ -crystal nucleating agent or the composition of the polypropylene-based resin.
- the agent is preferably 0.0001 to 5.0 parts by mass. 0.001 to 3.0 parts by mass is more preferable, and 0.01 to 1.0 part by mass is still more preferable. If it is 0.0001 part by mass or more, ⁇ -crystals of polypropylene resin can be sufficiently produced and grown during production, and sufficient ⁇ -crystal activity can be secured even when used as a separator, and desired air permeability performance. Is obtained.
- Addition of 5.0 parts by mass or less is preferable because it is economically advantageous and there is no bleeding of the ⁇ crystal nucleating agent on the surface of the laminated porous film.
- the amount of ⁇ crystal nucleating agent added to each layer may be the same or different.
- the porous structure of each layer can be appropriately adjusted by changing the addition amount of the ⁇ crystal nucleating agent.
- additives generally added to the resin composition can be added as appropriate within a range that does not significantly impair the effects of the present invention.
- the additive is added for the purpose of improving and adjusting the molding processability, productivity and various physical properties of the polyolefin resin porous film (I layer), recycled resin generated from trimming loss such as ears, silica, Inorganic particles such as talc, kaolin and calcium carbonate, pigments such as titanium oxide and carbon black, flame retardants, weathering stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers, crosslinkers, lubricants, nucleating agents, plastics Additives such as an agent, an anti-aging agent, an antioxidant, a light stabilizer, an ultraviolet absorber, a neutralizing agent, an antifogging agent, an antiblocking agent, a slipping agent or a coloring agent.
- polyethylene resin Specific examples of the polyethylene resin include ultra low density polyethylene, low density polyethylene, high density polyethylene, linear low density polyethylene, and homopolymer polyethylene such as ultra high molecular weight polyethylene characterized by molecular weight, as well as ethylene propylene.
- a copolymer or a copolymer polyethylene of a polyethylene resin and another polyolefin resin may be mentioned.
- homopolymer polyethylene or copolymer polyethylene having an ⁇ -olefin comonomer content of 2 mol% or less is preferable, and homopolymer polyethylene is more preferable.
- the density of the polyethylene resin is preferably 0.910 to 0.970 g / cm 3 , more preferably 0.930 to 0.970 g / cm 3 , and 0.940 to 0.970 g / cm 3. 3 is more preferable.
- a density of 0.910 g / cm 3 or more is preferable because it can have appropriate SD characteristics.
- 0.970 g / cm 3 or less is preferable in that it can have an appropriate SD characteristic and can maintain stretchability.
- the density can be measured according to JIS K7112 using a density gradient tube method.
- the melt flow rate (MFR) of the polyethylene resin is not particularly limited, but usually the MFR is preferably 0.03 to 30 g / 10 minutes, and preferably 0.3 to 10 g / 10 minutes. It is more preferable. If the MFR is 0.03 g / 10 min or more, the melt viscosity of the resin during the molding process is sufficiently low, which is excellent in productivity and preferable. On the other hand, if it is 30 g / 10 minutes or less, since sufficient mechanical strength can be obtained, it is preferable. MFR is measured in accordance with JIS K7210 under conditions of a temperature of 190 ° C. and a load of 2.16 kg.
- the polymerization catalyst for the polyethylene resin is not particularly limited, and may be any one such as a Ziegler type catalyst, a Philips type catalyst, or a Kaminsky type catalyst.
- a polymerization method of the polyethylene resin there are a one-stage polymerization, a two-stage polymerization, or a multistage polymerization more than that, and any method of the polyethylene resin can be used.
- the porosity promoting compound X is not limited, but specific examples thereof include a porosity promoting compound X selected from a modified polyolefin resin, an alicyclic saturated hydrocarbon resin or a modified product thereof, an ethylene copolymer, or a wax. It is more preferable that at least one of them is included. Among these, an alicyclic saturated hydrocarbon resin or a modified product thereof, an ethylene copolymer, or a wax, which is more effective when made porous, is more preferable, and a wax is more preferable from the viewpoint of moldability.
- Examples of alicyclic saturated hydrocarbon resins and modified products thereof include petroleum resins, rosin resins, terpene resins, coumarone resins, indene resins, coumarone-indene resins, and modified products thereof.
- the petroleum resin in the present invention is a C4 to C10 aliphatic olefin or diolefin obtained from a by-product such as by thermal decomposition of naphtha, or a C8 or more aromatic compound having an olefinically unsaturated bond.
- An aliphatic, aromatic, and copolymerized petroleum resin obtained by singly or copolymerizing one or more of the compounds contained in the above.
- Examples of petroleum resins include aliphatic petroleum resins mainly containing C5 fraction, aromatic petroleum resins mainly containing C9 fraction, copolymer petroleum resins thereof, and alicyclic petroleum resins.
- Examples of the terpene resin include terpene resins and terpene-phenol resins from ⁇ -pinene
- examples of the rosin resin include rosin resins such as gum rosin and utudrodin, and esterified rosin resins modified with glycerin and pentaerythritol.
- the alicyclic saturated hydrocarbon resin and the modified product thereof have relatively good compatibility when mixed with a polyethylene resin, but a petroleum resin is more preferable in terms of color tone and thermal stability, and a hydrogenated petroleum resin is used. More preferably.
- Hydrogenated petroleum resin is obtained by hydrogenating petroleum resin by a conventional method.
- Examples thereof include hydrogenated aliphatic petroleum resins, hydrogenated aromatic petroleum resins, hydrogenated copolymer petroleum resins and hydrogenated alicyclic petroleum resins, and hydrogenated terpene resins.
- hydrogenated petroleum resins hydrogenated alicyclic petroleum resins obtained by copolymerizing and hydrogenating a cyclopentadiene compound and an aromatic vinyl compound are particularly preferable.
- Examples of commercially available hydrogenated petroleum resins include “ALCON” (manufactured by Arakawa Chemical Industries).
- the ethylene copolymer in the present invention is a compound obtained by copolymerizing ethylene and one or more of vinyl acetate, unsaturated carboxylic acid, unsaturated carboxylic acid anhydride, or carboxylic acid ester. It is.
- the ethylene copolymer preferably has an ethylene monomer unit content of 50% by mass or more, more preferably 60% by mass or more, and still more preferably 65% by mass or more.
- the content of ethylene monomer units is preferably 95% by mass or less, more preferably 90% by mass or less, and further preferably 85% by mass or less. If the content of the ethylene monomer unit is within a predetermined range, a porous structure can be formed more efficiently.
- ethylene copolymer those having an MFR (JIS K7210, temperature: 190 ° C., load: 2.16 kg) of 0.1 g / 10 min to 10 g / 10 min are preferably used.
- MFR JIS K7210, temperature: 190 ° C., load: 2.16 kg
- the MFR is 0.1 g / 10 min or more, the extrudability can be maintained satisfactorily.
- the MFR is 10 g / 10 min or less, the strength of the film is hardly lowered, which is preferable.
- the ethylene-based copolymers are “EVAFLEX” (Mitsui / DuPont Polychemical Co., Ltd.), “Novatech EVA” (Nippon Polyethylene Co., Ltd.) as an ethylene-vinyl acetate copolymer, and “NUC” as an ethylene-acrylic acid copolymer.
- the wax in the present invention is an organic compound that satisfies the following properties (a) and (b).
- the melting point is 40 ° C to 200 ° C.
- the melt viscosity at a temperature 10 ° C. higher than the melting point is 50 Pa ⁇ s or less.
- ⁇ For wax including polar or nonpolar wax, polypropylene wax, polyethylene wax and wax modifier.
- paraffin wax, polyethylene wax, and microcrystalline wax are preferable from the viewpoint of efficiently forming a porous structure, and microcrystalline wax that can further reduce the pore diameter is more preferable from the viewpoint of SD characteristics.
- examples of commercially available polyethylene wax include “FT-115” (manufactured by Nippon Seiwa), and examples of microcrystalline wax include “Hi-Mic” (manufactured by Nippon Seiwa).
- the blending amount of the porosity promoting compound X is set as a lower limit with respect to 100 parts by mass of the polyethylene resin contained in one layer when peeling the interface between the polyethylene resin and the porosity promoting compound X to form micropores. 1 part by mass or more is preferable, 5 parts by mass or more is more preferable, and 10 parts by mass or more is still more preferable.
- the upper limit is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and still more preferably 30 parts by mass or less.
- thermoplastic resin may be used as long as the thermal characteristics of the porous film, specifically, the porosity is not impaired.
- thermoplastic resins include styrene resins such as styrene, AS resin, and ABS resin: polyvinyl chloride, fluorine resin, polyethylene terephthalate, polybutylene terephthalate, and polycarbonate.
- ester resins such as polyarylate
- Ether resins such as polyacetal, polyphenylene ether, polysulfone, polyethersulfone, polyetheretherketone or polyphenylene sulfide
- polyamides such as 6 nylon, 6-6 nylon, 6-12 nylon
- thermoplastic resins such as resins.
- thermoplastic elastomer examples include styrene / butadiene, polyolefin, urethane, polyester, polyamide, 1,2-polybutadiene, polyvinyl chloride, and ionomer.
- additives or other components that are generally blended in the resin composition may be included.
- the additive is added for the purpose of improving and adjusting the molding processability, productivity and various physical properties of the polyolefin resin porous film (I layer), recycled resin generated from trimming loss such as ears, silica, Inorganic particles such as talc, kaolin and calcium carbonate, pigments such as titanium oxide and carbon black, flame retardants, weathering stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers, crosslinkers, lubricants, nucleating agents, plastics Additives such as an agent, an anti-aging agent, an antioxidant, a light stabilizer, an ultraviolet absorber, a neutralizing agent, an antifogging agent, an antiblocking agent, a slipping agent or a coloring agent.
- the nucleating agent is preferable because it has an effect of controlling the crystal structure of the polyethylene resin and reducing the porous structure at the time of stretching and opening.
- “Gelall D” manufactured by Shin Nippon Chemical Co., Ltd.
- “Adeka Stub” manufactured by Asahi Denka Kogyo Co., Ltd.
- “Hyperform” manufactured by Milliken Chemical Co., Ltd.
- “IRGACLEAR D” Ciba Special Chemicals
- the polyolefin resin porous film (I layer) may be a single layer or a laminate, but is preferably laminated in two or more layers. Especially, what laminated
- the layer structure of the polyolefin resin porous film is not particularly limited as long as at least one layer containing a polypropylene resin (hereinafter referred to as “A layer”) is present.
- other layers hereinafter referred to as “B layer” can be laminated as long as they do not interfere with the function of the polyolefin resin porous film.
- the layer B to be laminated with the layer A is not limited to the polyolefin resin, and the layer A is provided with functions such as a strength retention layer, a heat-resistant layer (high melting temperature resin layer), a shutdown layer (low melting temperature resin layer). It is preferable to make it the structure which laminates. For example, when used as a separator for a lithium ion battery, a low melting point resin layer that ensures the safety of the battery is laminated by closing the hole in a high temperature atmosphere as described in JP-A No. 04-181651. Is preferred.
- Specific examples include a two-layer structure in which A layers / B layers are stacked, a three-layer structure in which A layers / B layers / A layers, or B layers / A layers / B layers are stacked.
- the order of stacking with layers having other functions is not particularly limited. Further, the number of layers may be increased as necessary to 4 layers, 5 layers, 6 layers, and 7 layers.
- the physical properties of the polyolefin resin porous film of the present invention can be freely adjusted by the layer constitution, lamination ratio, composition of each layer, and production method.
- the method for producing the non-porous film is not particularly limited, and a known method may be used. For example, a method of melting a thermoplastic resin composition using an extruder, extruding from a T die, and cooling and solidifying with a cast roll. Is mentioned. Moreover, the method of cutting open the film-like thing manufactured by the tubular method and making it planar is also applicable.
- There are methods for stretching the nonporous film-like material such as a roll stretching method, a rolling method, a tenter stretching method, and a simultaneous biaxial stretching method, and these methods are used alone or in combination of two or more to perform uniaxial stretching or biaxial stretching. . Among these, sequential biaxial stretching is preferable from the viewpoint of controlling the porous structure.
- a manufacturing method is divided roughly into the following four according to the order of porous formation and lamination.
- (I) A method of laminating each layer constituting the polyolefin-based resin porous film after laminating, and laminating each porous layer or bonding with an adhesive or the like.
- (II) A method of laminating each layer to produce a laminated nonporous film-like material, and then making the nonporous film-like material porous.
- III A method in which one of the layers is made porous and then laminated with another layer of a nonporous film to make it porous.
- (IV) A method of forming a laminated porous film by preparing a porous layer and then applying a coating such as inorganic / organic particles or depositing metal particles.
- a coating such as inorganic / organic particles or depositing metal particles.
- a method of forming a porous layer after preparing is particularly preferable.
- a mixed resin composition of a polypropylene resin and, if necessary, a thermoplastic resin and additives is prepared.
- raw materials such as polypropylene resin, ⁇ crystal nucleating agent, and other additives as required, preferably using a Henschel mixer, super mixer, tumbler type mixer, etc., or by hand-blending all ingredients in a bag
- the mixture is melt-kneaded with a single-screw or twin-screw extruder, a kneader or the like, preferably a twin-screw extruder, and then cut to obtain pellets.
- the pellets are put into an extruder and extruded from a T-die extrusion die to form a film.
- the type of T die is not particularly limited.
- the T die may be a multi-manifold type for two types and three layers or a feed block type for two types and three layers.
- the gap of the T die to be used is determined from the final required film thickness, stretching conditions, draft ratio, various conditions, etc., but is generally about 0.1 to 3.0 mm, preferably 0.5. -1.0 mm. If it is less than 0.1 mm, it is not preferable from the viewpoint of production speed, and if it is more than 3.0 mm, it is not preferable from the viewpoint of production stability because the draft rate increases.
- the extrusion temperature is appropriately adjusted depending on the flow characteristics and moldability of the resin composition, but is generally preferably 180 to 350 ° C, more preferably 200 to 330 ° C, and further preferably 220 to 300 ° C.
- a temperature of 180 ° C. or higher is preferable because the viscosity of the molten resin is sufficiently low and the moldability is excellent and the productivity is improved.
- the cooling and solidification temperature by the cast roll is very important in the present invention, and the ratio of the ⁇ crystal of the polypropylene resin in the film can be adjusted.
- the cooling and solidifying temperature of the cast roll is preferably 80 to 150 ° C, more preferably 90 to 140 ° C, and still more preferably 100 to 130 ° C. It is preferable to set the cooling and solidification temperature to 80 ° C. or higher because the ratio of ⁇ crystals in the film can be sufficiently increased. Further, it is preferable to set the temperature to 150 ° C. or lower because troubles such as the extruded molten resin sticking to and wrapping around the cast roll hardly occur and the film can be efficiently formed into a film.
- the ⁇ crystal ratio of the polypropylene resin of the film-like material before stretching is adjusted to 30 to 100% by setting a cast roll in the temperature range. More preferably, it is 40 to 100%, more preferably 50 to 100%, and most preferably 60 to 100%.
- a polyolefin-based resin porous film having good gas permeability can be obtained because it is easily made porous by the subsequent stretching operation.
- the ⁇ crystal ratio in the film before stretching is detected when the film is heated from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min using a differential scanning calorimeter.
- uniaxial stretching may be performed in the longitudinal direction or the transverse direction, or biaxial stretching may be performed.
- biaxial stretching simultaneous biaxial stretching may be sufficient and sequential biaxial stretching may be sufficient.
- sequential biaxial stretching is more preferable because the stretching conditions can be selected in each stretching step and the porous structure can be easily controlled.
- Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching, but the stretching conditions (magnification, temperature) can be easily selected in each stretching step, and the porous structure can be easily controlled. Biaxial stretching is more preferable.
- the longitudinal direction of the film and the film is referred to as “longitudinal direction”, and the direction perpendicular to the longitudinal direction is referred to as “lateral direction”.
- stretching in the longitudinal direction is referred to as “longitudinal stretching”
- stretching in the direction perpendicular to the longitudinal direction is referred to as “lateral stretching”.
- the stretching temperature needs to be appropriately selected depending on the composition of the resin composition to be used and the crystallization state, but it is preferable to select within the range of the following conditions.
- the stretching temperature needs to be changed appropriately depending on the composition of the resin composition to be used, the crystal melting peak temperature, the crystallinity, etc., but the stretching temperature in the longitudinal stretching is preferably about 0 to 130 ° C., More preferably, it is controlled in the range of 10 to 120 ° C., more preferably 20 to 110 ° C. Further, it is preferably 2 to 10 times, more preferably 3 to 8 times, still more preferably 4 to 7 times.
- the stretching temperature in transverse stretching is generally from 100 to 160 ° C., preferably from 110 to 150 ° C., more preferably from 120 to 140 ° C.
- the preferred longitudinal draw ratio is preferably 1.2 to 10 times, more preferably 1.5 to 8 times, still more preferably 2 to 7 times.
- the stretching speed in the stretching step is preferably 500 to 12000% / min, more preferably 1500 to 10,000% / min, and further preferably 2500 to 8000% / min.
- the laminated porous film thus obtained is preferably subjected to heat treatment for the purpose of improving dimensional stability.
- the effect of dimensional stability can be expected by setting the temperature to preferably 100 ° C. or higher, more preferably 120 ° C. or higher, and still more preferably 140 ° C. or higher.
- the heat treatment temperature is preferably 170 ° C. or lower, more preferably 165 ° C. or lower, and further preferably 160 ° C. or lower.
- a heat treatment temperature of 170 ° C. or lower is preferable because the polypropylene resin hardly melts by the heat treatment and can maintain a porous structure.
- a relaxation treatment of 1 to 20% may be performed as necessary.
- a laminated porous film is obtained by cooling uniformly and winding up after heat processing.
- a coating layer (II layer) containing a filler (a) and a resin binder (b) is laminated on at least one side of a polyolefin resin porous film to be a base material layer (I layer).
- the base material layer may be a single polyolefin-based resin porous film or a polyolefin-based resin porous film in which multiple layers are laminated.
- a coating layer (II layer) is laminated on the surface of at least one surface of the single-layer or multi-layer polyolefin resin porous film.
- Filler (a) examples of the filler (a) used in the coating layer include inorganic fillers and organic fillers, but are not particularly limited.
- inorganic fillers include carbonates such as calcium carbonate, magnesium carbonate and barium carbonate; sulfates such as calcium sulfate, magnesium sulfate and barium sulfate; chlorides such as sodium chloride, calcium chloride and magnesium chloride, aluminum oxide and oxidation
- oxides such as calcium, magnesium oxide, zinc oxide, titanium oxide, and silica
- silicates such as talc, clay, and mica can be used.
- the laminated porous film is used as a separator for a non-aqueous electrolyte secondary battery, it is barium sulfate, aluminum oxide from the viewpoint of being chemically inert when incorporated in a non-aqueous electrolyte secondary battery. Is preferred.
- organic fillers include ultra high molecular weight polyethylene, polystyrene, polymethyl methacrylate, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polytetrafluoroethylene, polyimide, polyether.
- examples thereof include thermoplastic resins such as imide, melamine, and benzoguanamine, and thermosetting resins.
- crosslinked polystyrene and the like are preferable from the viewpoint of resistance to electrolytic solution swelling.
- the coating layer (II layer) it is important for the coating layer (II layer) to have a particle size gradient of the filler (a) in the thickness direction.
- the “average particle diameter of the filler” is a value measured according to a method using SEM.
- the coating layer (II layer) The average particle size (Db) of the filler (a) within 25% of the layer thickness is made different from the average particle size (Du) of the filler (a) on the laminated porous film surface side, and the opposite side in the thickness direction.
- the average particle size (Db) of the filler (a) on the interface side of the base material layer (I layer) with the polyolefin resin porous film is increased, and the average particle size of the filler (a) is gradually increased.
- the average particle size of the filler (a) is different in the thickness direction of the coating layer (II layer), so that the air permeability is increased in the coating layer (II layer) on the interface side of the base material layer (I layer). It is possible to construct both a high rough structure and a fine structure excellent in heat-shrinkage suppression of the filler (a) on the surface side and to exhibit the effect.
- the average particle size ratio (Du / Db) of the filler (a) is 1.2 to 10.
- the lower limit of (Du / Db) is preferably 1.2 or more, and more preferably 1.5 or more. When the lower limit is 1.2 or more, it is possible to suppress the filler from falling off and to have sufficient heat shrinkage.
- the upper limit of (Du / Db) is preferably 10 or less, and more preferably 5 or less. When the (Du / Db) is 10 or less, it is possible to suppress the deterioration of air permeability caused by the fine filler blocking the gaps between coarse fillers.
- the average particle diameter (Du) of the filler (a) on the surface side is 0.5 ⁇ m or less, preferably 0.3 ⁇ m or less, and more preferably 0.25 ⁇ m or less. It is preferable that the average particle diameter (Du) is 0.5 ⁇ m or less because the dropout of the filler (a) can be sufficiently suppressed.
- the lower limit of the average particle diameter (Du) of the filler (a) on the interface side with the polyolefin resin porous film is not particularly limited, but is preferably 0.05 ⁇ m or more.
- the average particle diameter (Db) is preferably 0.1 ⁇ m or more, and more preferably 0.3 ⁇ m or more.
- the average particle diameter (Db) is 0.1 ⁇ m or more, it is preferable because high air permeability can be secured.
- the upper limit of the average particle diameter (Db) is not particularly limited, but is preferably 3.0 ⁇ m or less.
- the density of the filler (a) in the coating layer (II layer) is preferably at least twice the density of the resin binder (b) described later. More preferably 2.5 times or more, still more preferably 3 times or more. Since the density of the filler (a) is at least twice that of the resin binder (b), the coating layer (II layer) is formed by applying a dispersion of the filler (a) and the resin binder (b). In doing so, it is preferable for the sedimentation of the filler to proceed rapidly after coating.
- the resin binder (b) that can be used in the present invention can adhere the filler and the polyolefin-based resin porous film well, is electrochemically stable, and is organic when a laminated porous film is used as a battery. If it is stable with respect to electrolyte solution, there will be no restriction
- ethylene-acrylic acid copolymer such as ethylene-vinyl acetate copolymer (EVA, whose structural unit derived from vinyl acetate is 20 to 35 mol%), ethylene-ethyl acrylate copolymer, fluorine, etc.
- Resins [polyvinylidene fluoride (PVDF), etc.], fluorinated rubber, styrene-butadiene rubber (SBR), nitrile butadiene rubber (NBR), polybutadiene rubber (BR), polyacrylonitrile (PAN), polyacrylic acid (PAA), carboxy Examples thereof include methyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), poly N-vinylacetamide, cross-linked acrylic resin, polyurethane, and epoxy resin.
- These resin binders (b) may be used individually by 1 type, and may use 2 or more types together. Among these resin binders (b), polyvinyl alcohol, polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose, and polyacrylic acid are preferable.
- the content of the filler (a) in the total amount of the filler (a) and the resin binder (b) is preferably 92% by mass or more, and more preferably 95% by mass or more. 98 mass% or more is more preferable. If the content of the filler (a) is 92% by mass or more, it is possible to produce a laminated porous film having communication properties, not only exhibiting excellent air permeability, but also imparting heat shrinkage resistance. preferable.
- the laminated porous film of the present invention at least a dispersion obtained by dissolving or dispersing the filler (a) and the resin binder (b) in a solvent becomes the laminated porous film surface of the polyolefin resin porous film (I layer). It can be manufactured by forming a coating layer (II layer) on the surface of the polyolefin resin porous film (I layer) by applying to one side and allowing the filler (a) to settle before or during the solvent removal step. it can. In addition, you may apply
- the solvent it is preferable to use a solvent in which the filler (a) and the resin binder (b) can be dissolved or dispersed in an appropriately uniform and stable manner.
- a solvent include N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, water, ethanol, toluene, hot xylene, and hexane.
- the dispersion includes a dispersant such as a surfactant, a thickener, a wetting agent, an antifoaming agent.
- additives such as an agent, a pH adjuster including an acid and an alkali may be added.
- the additive is preferably one that can be removed upon solvent removal or plasticizer extraction, but is electrochemically stable in the range of use of the nonaqueous electrolyte secondary battery, does not inhibit the battery reaction, and is about 200 ° C. If it is stable, it may remain in the battery (in the laminated porous film).
- Examples of the method for dissolving or dispersing the filler (a) and the resin binder (b) in a solvent include, for example, 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, and a disperser. And a mechanical stirring method using a mixer, a homogenizer, a high-speed impact mill, ultrasonic dispersion, a stirring blade, and the like.
- the method of applying the dispersion to the surface of the polyolefin resin porous film (I layer) may be after the extrusion molding, after the longitudinal stretching step, or in the transverse stretching step. It may be later.
- the application method in the application step is not particularly limited as long as the required layer thickness and application area can be realized.
- coating methods include gravure coater method, small diameter gravure coater method, bar coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade Examples include a coater method, a rod coater method, a squeeze coater method, a cast coater method, a die coater method, a screen printing method, and a spray coating method.
- the said dispersion liquid may be apply
- the filler (a) in the coating process, a method in which the coated surface faces the upper surface until the drying process is finished is preferable.
- the filler (a) can be precipitated, and the coating layer (II layer) can have a particle size gradient of the filler (a), and the average particle size ratio of the filler (a) ( Du / Db) can satisfy a predetermined range.
- the sedimentation method of the filler (a) after the coating step is not particularly limited as long as it can develop a required particle size gradient in the thickness direction.
- a sedimentation method include a natural sedimentation method, a centrifugal sedimentation method, a precipitation agent addition method, and the like.
- the natural sedimentation method is preferable from the viewpoint that it is simple and can be used in combination with a drying step.
- the solvent is preferably a solvent that can be removed from the dispersion applied to the polyolefin resin porous film (I layer).
- a method for removing the solvent any method that does not adversely affect the polyolefin resin porous film (I layer) can be employed without any particular limitation.
- a method for removing the solvent for example, a method of drying the polyolefin-based resin porous film (I layer) at a temperature below its melting point, a method of drying at a low temperature under reduced pressure, a poor solvent for the resin binder (b) And a method of extracting the solvent simultaneously with solidifying the resin binder (b).
- dispersions having different average particle diameters of the filler (a) may be applied to the polyolefin resin porous film (I layer) in a plurality of times.
- the solvent is dried, and sequentially applying to the dispersion liquid containing the filler (a) having a smaller average particle diameter. Dry the solvent.
- the coating layer (II layer) can have a particle size gradient of the filler (a), and the average particle size ratio (Du / Db) of the filler (a) satisfies a predetermined range. be able to.
- the total thickness of the laminated porous film in which the coating layer is provided on the surface of the base material layer made of the polyolefin resin porous film of the present invention is preferably 5 to 100 ⁇ m. More preferably, it is 8 to 50 ⁇ m, and still more preferably 10 to 30 ⁇ m.
- a separator for a non-aqueous electrolyte secondary battery if it is 5 ⁇ m or more, substantially necessary electrical insulation can be obtained. For example, even when a large force is applied to the protruding portion of the electrode, Breaks through the separator for the electrolyte secondary battery and is not easily short-circuited.
- thickness is 100 micrometers or less, since the electrical resistance of a lamination
- the thickness of the coating layer (II layer) is preferably 0.5 ⁇ m or more, more preferably 2 ⁇ m or more, still more preferably 3 ⁇ m or more, and particularly preferably 4 ⁇ m or more from the viewpoint of heat resistance.
- the upper limit is preferably 90 ⁇ m or less, more preferably 50 ⁇ m or less, still more preferably 30 ⁇ m or less, and particularly preferably 10 ⁇ m or less from the viewpoint of communication.
- the porosity is preferably 30% or more, more preferably 35% or more, and further preferably 40% or more. If the porosity is 30% or more, it is possible to obtain a laminated porous film that ensures communication and has excellent air permeability.
- the upper limit is preferably 70% or less, more preferably 65% or less, and still more preferably 60% or less. If the porosity is 70% or less, the strength of the laminated porous film is hardly lowered, which is preferable from the viewpoint of handling. The porosity is measured by the method described in the examples.
- the air permeability of the laminated porous film in which the substrate layer and the coating layer of the present invention are laminated is preferably 2000 seconds / 100 ml or less, more preferably 10 to 1000 seconds / 100 ml, and further preferably 50 to 800 seconds / 100 ml.
- An air permeability of 2000 seconds / 100 ml or less is preferable because it indicates that the laminated porous film has communication properties and can exhibit excellent air permeability.
- the air permeability represents the difficulty in passing through the air in the film thickness direction, and is specifically expressed by the number necessary for 100 ml of air to pass through the film. Therefore, it means that the smaller the numerical value is, the easier it is to pass through, and the higher numerical value is, the easier it is to pass.
- the air permeability of the laminated porous film of the present invention is low, it can be used for various applications. For example, when used as a separator for a non-aqueous electrolyte secondary battery, a low air permeability means that lithium ions can be easily transferred, which is preferable because battery performance is excellent.
- the laminated porous film of the present invention has excellent SD characteristics when used as a separator for a non-aqueous electrolyte secondary battery.
- the air permeability after heating at 135 ° C. for 5 seconds is preferably 10,000 seconds / 100 ml or more, more preferably 25000 seconds / 100 ml or more, and further preferably 50000 seconds / 100 ml or more.
- the shrinkage rate at 150 ° C. of the laminated porous film in which the base material layer and the coating layer of the present invention are laminated is preferably less than 25%, more preferably less than 15%, and still more preferably less than 10%. If the shrinkage rate at 150 ° C. is less than 25%, even when abnormal heat is generated above the SD temperature, it is suggested that it has good dimensional stability and heat resistance, preventing film breakage, and internal short circuit. The temperature can be improved. Although it does not specifically limit as a minimum, 0% or more is more preferable.
- the peel strength between the polyolefin resin porous film (I layer) and the coating layer (II layer) of the laminated porous film in which the base material layer and the coating layer of the present invention are laminated is preferably 1 N / 15 mm or more, More preferably, it is 3N / 15 mm or more.
- the peel strength of 1 N / 15 mm or more is preferable because the possibility of the filler (a) dropping off can be greatly reduced.
- a nonaqueous electrolyte secondary battery containing the laminated porous film of the present invention as a battery separator will be described with reference to FIG.
- Both electrodes of the positive electrode plate 21 and the negative electrode plate 22 are wound in a spiral shape so as to overlap each other via the battery separator 10, and the outside is stopped with a winding tape to form a wound body.
- the winding process will be described in detail.
- One end of the battery separator is passed between the slit portions 1 of the pin (FIG. 2), and the pin is slightly rotated to wind one end of the battery separator around the pin. At this time, the surface of the pin is in contact with the coating layer of the battery separator.
- the positive electrode and the negative electrode are arranged so as to sandwich the battery separator, and the pins are rotated by a winding machine to wind the positive and negative electrodes and the battery separator. After winding, the pin is pulled out of the wound object.
- the wound body in which the positive electrode plate 21, the battery separator 10 and the negative electrode plate 22 are integrally wound is accommodated in a bottomed cylindrical battery case and welded to the positive and negative electrode lead bodies 24 and 25.
- the electrolyte is injected into the battery can, and after the electrolyte has sufficiently penetrated into the battery separator 10 or the like, the positive electrode lid 27 is sealed around the opening periphery of the battery can via the gasket 26, and precharging and aging are performed.
- a cylindrical non-aqueous electrolyte secondary battery is manufactured.
- an electrolytic solution in which a lithium salt is used as an electrolytic solution and is dissolved in an organic solvent is used.
- the organic solvent is not particularly limited.
- esters such as propylene carbonate, ethylene carbonate, butylene carbonate, ⁇ -butyrolactone, ⁇ -valerolactone, dimethyl carbonate, methyl propionate or butyl acetate, and nitriles such as acetonitrile.
- ethers such as tetrahydrofuran, 2-methyltetrahydrofuran or 4-methyl-1,3-dioxolane, or sulfolane.
- LiPF 6 lithium hexafluorophosphate
- an alkali metal or a compound containing an alkali metal integrated with a current collecting material such as a stainless steel net is used.
- the alkali metal include lithium, sodium, and potassium.
- the compound containing an alkali metal include an alloy of an alkali metal and aluminum, lead, indium, potassium, cadmium, tin or magnesium, a compound of an alkali metal and a carbon material, a low potential alkali metal and a metal oxide, and the like. Or a compound with a sulfide or the like.
- the carbon material may be any material that can be doped and dedoped with lithium ions, such as graphite, pyrolytic carbons, cokes, glassy carbons, a fired body of an organic polymer compound, Mesocarbon microbeads, carbon fibers, activated carbon and the like can be used.
- a carbon material having an average particle diameter of 10 ⁇ m is mixed with a solution in which polyvinylidene fluoride is dissolved in N-methylpyrrolidone to form a slurry, and this negative electrode mixture slurry is passed through a mesh of 70 mesh. After removing the large particles, uniformly apply to both sides of the negative electrode current collector made of a strip-shaped copper foil having a thickness of 18 ⁇ m and dry, and then compression-molded with a roll press machine, cut, strip-shaped negative electrode plate and We use what we did.
- lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, manganese dioxide, metal oxide such as vanadium pentoxide or chromium oxide, metal sulfide such as molybdenum disulfide, etc. are used as active materials.
- These positive electrode active materials are combined with conductive additives and binders such as polytetrafluoroethylene as appropriate, and finished with a current collector material such as a stainless steel mesh as a core material. It is done.
- a strip-like positive electrode plate produced as follows is used as the positive electrode. That is, lithium graphite oxide (LiCoO 2 ) is added with phosphorous graphite as a conductive additive at a mass ratio of 90: 5 (lithium cobalt oxide: phosphorous graphite) and mixed, and this mixture and polyvinylidene fluoride are mixed with N Mix with a solution in methylpyrrolidone to make a slurry.
- This positive electrode mixture slurry is passed through a 70-mesh net to remove large particles, and then uniformly applied to both sides of a positive electrode current collector made of an aluminum foil having a thickness of 20 ⁇ m, dried, and then compressed by a roll press. After forming, it is cut into a strip-like positive electrode plate.
- the longitudinal direction of the laminated porous film is referred to as “longitudinal direction”, and the direction perpendicular to the longitudinal direction is referred to as “lateral direction”.
- Solid content rate was made into the ratio with respect to 100 mass% of dispersion liquids of the total amount of a filler (a) and a resin binder (b).
- Air permeability (Gurley value) The air permeability (second / 100 ml) was measured according to JIS P8117.
- Average particle size ratio Db / Du
- Binding property was evaluated according to the following evaluation criteria. ⁇ : The peel strength is 3 N / 15 mm or more. ⁇ : The peel strength is 1 N / 15 mm or more and less than 3 N / 15 mm. X: The peel strength is less than 1 N / 15 mm.
- Coating property was evaluated according to the following evaluation criteria. ⁇ : Coating is possible. Forms a good coating film without particle aggregation during visual observation. ⁇ : Coating is possible. In visual observation, particle aggregation can be confirmed. X: Many particles are aggregated and coating is difficult.
- DSC Differential scanning calorimetry
- the obtained laminated porous film was heated from 25 ° C. to 240 ° C. at a scanning speed of 10 ° C./min for 1 minute using a differential scanning calorimeter (DSC-7) manufactured by PerkinElmer Co., Ltd.
- the temperature was lowered from 240 ° C. to 25 ° C. at a scanning rate of 10 ° C./min and held for 1 minute, and then the temperature was raised again from 25 ° C. to 240 ° C. at a scanning rate of 10 ° C./min.
- the presence or absence of ⁇ -crystal activity was evaluated according to the following criteria depending on whether or not a peak was detected at 145 to 160 ° C., which is the crystal melting peak temperature (Tm ⁇ ) derived from ⁇ -crystal of the polypropylene resin at the time of re-heating. .
- Tm ⁇ crystal melting peak temperature
- X When Tm ⁇ is not detected within the range of 145 ° C to 160 ° C (no ⁇ crystal activity) The ⁇ crystal activity was measured with a sample amount of 10 mg in a nitrogen atmosphere.
- -Wide-angle X-ray diffraction measurement device manufactured by Mac Science Co., Ltd., model number: XMP18A X-ray source: CuK ⁇ ray, output: 40 kV, 200 mA Scanning method: 2 ⁇ / ⁇ scan, 2 ⁇ range: 5 ° to 25 °, scanning interval: 0.05 °, scanning speed: 5 ° / min
- the presence or absence of ⁇ crystal activity was evaluated as follows from the peak derived from the (300) plane of ⁇ crystal of the polypropylene resin.
- Polyolefin resin film Polypropylene resin (Prime Polymer Co., Ltd., Prime Polypro F300SV, density: 0.90 g / cm 3 , MFR: 3.0 g / 10 min) as layer A, and N, N′-dicyclohexyl as ⁇ crystal nucleating agent -2,6-Naphthalenedicarboxylic acid amide was prepared. Each raw material is blended at a ratio of 0.2 part by mass of ⁇ -crystal nucleating agent with respect to 100 parts by mass of this polypropylene resin, and the same direction twin screw extruder manufactured by Toshiba Machine Co., Ltd.
- the ⁇ -crystal activity of the polypropylene resin composition was 80%.
- a mixed resin composition constituting the B layer 100 parts by mass of high density polyethylene (Nippon Polyethylene Co., Ltd., Novatec HD HF560, density: 0.963 g / cm 3 , MFR: 7.0 g / 10 min) Add 0.04 parts by mass of glycerin monoester and 10 parts by mass of microcrystalline wax (Nippon Seiwa Co., Ltd., Hi-Mic 1080), and melt knead at 220 ° C. using the same type of twin-screw extruder. Thus, a resin composition processed into a pellet was obtained.
- a heat treatment / relaxation treatment is carried out, so that two layers and three layers, A layer / B layer / A layer, and a polyolefin resin having a total thickness of 20 ⁇ m
- the base material layer which consists of a porous film (I layer) was obtained.
- Example 1 19.7 parts by mass of alumina (Sumitomo Chemical Co., Ltd., Sumiko Random AA-03, average particle size: 0.3 ⁇ m, density: 3.9 g / cm 3 ), polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA124, degree of saponification: 98.0 to 99.0, average polymerization degree: 2400, density: 1.3 g / cm 3 ) A dispersion having 0.3 parts by mass dispersed in 80.0 parts by mass of water was obtained. At this time, the solid content in the dispersion was 20% by mass with respect to 100% by mass of the dispersion.
- alumina Suditomo Chemical Co., Ltd., Sumiko Random AA-03, average particle size: 0.3 ⁇ m, density: 3.9 g / cm 3
- polyvinyl alcohol manufactured by Kuraray Co., Ltd., PVA124, degree of saponification: 98.0 to 99.0, average polymerization degree: 2400
- the obtained dispersion was applied to one surface of a polyolefin-based resin porous film (I layer) of two types and three layers as the A layer / B layer / A layer using a bar coater having a basis weight of # 20. Then, the filler was allowed to settle while drying at 20 ° C. for 30 minutes to form a coating layer (II layer), and a laminated porous film composed of a polyolefin-based resin porous film (I layer) -covering layer (II layer) was prepared. . The overall thickness of the laminated porous film was 25 ⁇ m. The physical properties of the obtained laminated porous film were evaluated, and the results are summarized in Table 1.
- Example 2 19.7 parts by mass of alumina (manufactured by Nippon Light Metal Co., Ltd., low soda alumina LS-235C, average particle size: 0.5 ⁇ m, density: 3.9 g / cm 3 ), polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA124, degree of saponification) : 98.0 to 99.0, average polymerization degree: 2400, density: 1.3 g / cm 3 ) Dispersion X in which 0.3 part by mass was dispersed in 80.0 parts by mass of water was obtained.
- alumina manufactured by Nippon Light Metal Co., Ltd., low soda alumina LS-235C, average particle size: 0.5 ⁇ m, density: 3.9 g / cm 3
- polyvinyl alcohol manufactured by Kuraray Co., Ltd., PVA124, degree of saponification
- Dispersion X in which 0.3 part by mass was dispersed in 80.0 parts by mass of water was obtained
- dispersion liquid Y dispersed in was obtained.
- the solid content in each of the dispersions X and Y was 20% by mass with respect to 100% by mass of the dispersion.
- Hydrochloric acid was added to the obtained dispersion X so as to be 0.7% by mass, and the resulting liquid was used as the above-mentioned A layer / B layer / A layer.
- the obtained dispersion liquid was made into the same A layer / B layer / A layer as in Example 1 with a basis weight amount of # 10 on one side surface of a polyolefin resin porous film (I layer) serving as a base material layer of two types and three layers. After applying using a bar coater, it was dried at 60 ° C. for 2 minutes to obtain a laminated porous film having an overall thickness of 27 ⁇ m. The physical properties of the obtained laminated porous film were evaluated, and the results are summarized in Table 1.
- the laminated porous films obtained in Example 1 and Example 2 have high air permeability because the filler (a) in the coating layer (II layer) has a predetermined particle size gradient on the surface of the base material layer. Excellent heat resistance while maintaining That is, because fine particles form a dense structure on the surface, it has excellent binding properties and excellent heat resistance, while the inside of the coating layer (II layer) has a rough structure. High breathability could be maintained.
- the laminated porous film obtained in Comparative Example 1 does not have a predetermined particle size gradient despite the fact that the composition of the solid content of the coating liquid is the same as that of Example 1, so that the result is Wearability and heat resistance were insufficient. Moreover, since the polyolefin resin porous film of the comparative example 2 was not laminated
- the laminated porous film of the present invention can be applied to various uses that require air permeability.
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Abstract
Description
前記積層多孔フィルムの表面となる前記被覆層の表面から該被覆層の厚さ25%内におけるフィラーの平均粒径(Du)と前記基材層との界面から該被覆層の厚さ25%内におけるフィラーの平均粒径(Db)との比(Du/Db)が1.2~10であり、かつ、前記被覆層の表面側のフィラーの平均粒径(Du)が0.05μm以下であることを特徴とする積層多孔フィルムを提供している。
前記基材層となるポリオレフィン系樹脂多孔フィルムは、ポリプロピレン系樹脂を主成分とする層(A層)とポリエチレン等の他のポリオレフィン系樹脂多孔層(B層)または/およびポリオレフィン系以外の樹脂多孔層とを積層し、該積層の前記ポリオレフィン系樹脂多孔層の表面に前記被覆層を積層してもよい。
さらにまた、本発明は前記非水電解液二次電池用セパレータを用いた非水電解液二次電池を提供している。
前記溶媒の除去工程前または除去工程中に前記フィラーを前記基材層に向けて沈降させ、前記被覆層の厚み方向で前記表面側から基材層側にフィラーの平均粒径が、前記(Du/Db)=1.2~10となる勾配をつけている積層多孔フィルムの製造方法を提供している。
また、前記本発明の積層多孔フィルムの他の製造方法として、前記基材層のポリオレフィン系樹脂多孔フィルムの少なくとも片面の表面に、前記フィラーの平均粒径が異なる分散液を複数回にわけて塗布し、該分散液の塗布はフィラーの平均粒径が大きな分散液から塗布して、順次平均粒径が小さい分散液を重ねて塗布し、前記被覆層の厚み方向で前記表面側から基材層側にフィラーの平均粒径が、前記(Du/Db)=1.2~10となる勾配をつけている積層多孔フィルムの製造方法を提供している。前記被覆層の表面から厚み方向で前記基材層に近接する方向に向けてフィラーの平均粒径が、前記(Du/Db)が1.2~10となる勾配をつけている積層多孔フィルムの製造方法を提供している。
なお、本発明において、「主成分」と表現した場合には、特に記載しない限り、当該主成分の機能を妨げない範囲で他の成分を含有することを許容する意を包含し、特に当該主成分の含有割合を特定するものではないが、主成分は組成物中の50質量%以上、好ましくは70質量%以上、特に好ましくは90質量%以上(100%含む)を占める意を包含するものである。
また、「X~Y」(X,Yは任意の数字)と記載した場合、特にことわらない限り「X以上Y以下」の意と共に、「好ましくはXより大きい」及び「好ましくはYより小さい」の意を包含するものである。
ポリオレフィン系樹脂多孔フィルムで用いるポリオレフィン系樹脂として、エチレン、プロピレン、1-ブテン、4-メチル-1-ペンテン、1-ヘキサンなどを重合した単独重合体または共重合体が挙げられる。この中でも、ポリプロピレン系樹脂、ポリエチレン系樹脂が好ましい。
ポリプロピレン系樹脂としては、ホモプロピレン(プロピレン単独重合体)、またはプロピレンとエチレン、1-ブテン、1-ペンテン、1-へキセン、1-へプテン、1-オクテン、1-ノネンもしくは1-デセンなどα-オレフィンとのランダム共重合体またはブロック共重合体などが挙げられる。この中でも、積層多孔フィルムの機械的強度、耐熱性などを維持する観点から、ホモポリプロピレンがより好適に使用される。
アイソタクチックペンタッド分率(mmmm分率)とは、任意の連続する5つのプロピレン単位で構成される炭素-炭素結合による主鎖に対して側鎖である5つのメチル基がいずれも同方向に位置する立体構造あるいはその割合を意味する。メチル基領域のシグナルの帰属は、A.Zambelli et al(Macromolecules8,687,(1975))に準拠した。
β晶活性は、延伸前の膜状物においてポリプロピレン系樹脂がβ晶を生成していたことを示す一指標と捉えることができる。延伸前の膜状物中のポリプロピレン系樹脂がβ晶を生成していれば、フィラー等の添加剤を使用しない場合においても、延伸を施すことで微細孔が容易に形成されるため、透気特性を有する積層多孔フィルムを得ることができる。
具体的には、示差走査型熱量計で積層多孔フィルムを25℃から240℃まで加熱速度10℃/分で昇温後1分間保持し、次に240℃から25℃まで冷却速度10℃/分で降温後1分間保持し、更に25℃から240℃まで加熱速度10℃/分で再昇温させた際に、ポリプロピレン系樹脂のβ晶に由来する結晶融解ピーク温度(Tmβ)が検出された場合、β晶活性を有すると判断している。
β晶活性度(%)=〔ΔHmβ/(ΔHmβ+ΔHmα)〕×100
例えば、ポリプロピレン系樹脂がホモポリプロピレンの場合は、主に145℃以上160℃未満の範囲で検出されるβ晶由来の結晶融解熱量(ΔHmβ)と、主に160℃以上170℃以下に検出されるα晶由来の結晶融解熱量(ΔHmα)から計算することができる。また、例えばエチレンが1~4モル%共重合されているランダムポリプロピレンの場合は、主に120℃以上140℃未満の範囲で検出されるβ晶由来の結晶融解熱量(ΔHmβ)と、主に140℃以上165℃以下の範囲に検出されるα晶由来の結晶融解熱量(ΔHmα)から計算することができる。
詳細には、ポリプロピレン系樹脂の融点を超える温度である170℃~190℃の熱処理を施し、徐冷してβ晶を生成・成長させた積層多孔フィルムについて広角X線測定を行い、ポリプロピレン系樹脂のβ晶の(300)面に由来する回折ピークが2θ=16.0°~16.5°の範囲に検出された場合、β晶活性が有ると判断している。
ポリプロピレン系樹脂のβ晶構造と広角X線回折に関する詳細は、Macromol.Chem.187,643-652(1986)、Prog.Polym.Sci.Vol.16,361-404(1991)、Macromol.Symp.89,499-511(1995)、Macromol.Chem.75,134(1964)、及びこれらの文献中に挙げられた参考文献を参照することができる。広角X線回折を用いたβ晶活性の詳細な評価方法については、後述の実施例にて示す。
また、仮に、ポリプロピレン系樹脂からなる層以外に、ポリプロピレン系樹脂を含有する層などを積層させる場合には、両層ともにβ晶活性を有することが好ましい。
本発明で用いるβ晶核剤としては以下に示すものが挙げられるが、ポリプロピレン系樹脂のβ晶の生成・成長を増加させるものであれば特に限定される訳ではなく、また2種類以上を混合して用いても良い。
β晶核剤としては、例えば、アミド化合物;テトラオキサスピロ化合物;キナクリドン類;ナノスケールのサイズを有する酸化鉄;1,2-ヒドロキシステアリン酸カリウム、安息香酸マグネシウムもしくはコハク酸マグネシウム、フタル酸マグネシウムなどに代表されるカルボン酸のアルカリもしくはアルカリ土類金属塩;ベンゼンスルホン酸ナトリウムもしくはナフタレンスルホン酸ナトリウムなどに代表される芳香族スルホン酸化合物;二もしくは三塩基カルボン酸のジもしくはトリエステル類;フタロシアニンブルーなどに代表されるフタロシアニン系顔料;有機二塩基酸である成分Aと周期律表第IIA族金属の酸化物、水酸化物もしくは塩である成分Bとからなる二成分系化合物;環状リン化合物とマグネシウム化合物からなる組成物などが挙げられる。そのほか核剤の具体的な種類については、特開2003-306585号公報、特開平06-289566号公報、特開平09-194650号公報に記載されている。
また、仮にポリプロピレン系樹脂からなる層以外に、ポリプロピレン系樹脂を含有する層などを積層させる場合には、各層のβ晶核剤の添加量は同じであっても、異なっていても良い。β晶核剤の添加量を変更することで各層の多孔構造を適宜調整することができる。
本発明においては、前述した成分のほか、本発明の効果を著しく阻害しない範囲内で、一般に樹脂組成物に配合される添加剤を適宜添加できる。前記添加剤としては、成形加工性、生産性およびポリオレフィン系樹脂多孔フィルム(I層)の諸物性を改良・調整する目的で添加される、耳などのトリミングロス等から発生するリサイクル樹脂やシリカ、タルク、カオリン、炭酸カルシウム等の無機粒子、酸化チタン、カーボンブラック等の顔料、難燃剤、耐候性安定剤、耐熱安定剤、帯電防止剤、溶融粘度改良剤、架橋剤、滑剤、核剤、可塑剤、老化防止剤、酸化防止剤、光安定剤、紫外線吸収剤、中和剤、防曇剤、アンチブロッキング剤、スリップ剤または着色剤などの添加剤が挙げられる。
ポリエチレン系樹脂としては、具体的に超低密度ポリエチレン、低密度ポリエチレン、高密度ポリエチレン、線状低密度ポリエチレン、また分子量に特徴のある超高分子量ポリエチレンのようなホモポリマーポリエチレンだけでなく、エチレンプロピレン共重合体、またはポリエチレン系樹脂と他のポリオレフィン系樹脂とのコポリマーポリエチレンが挙げられる。中でも、ホモポリマーポリエチレン、或いはα-オレフィンコモノマー含量が2モル%以下のコポリマーポリエチレンが好ましく、ホモポリマーポリエチレンであることが更に好ましい。α-オレフィンコモノマーの種類については特に制限はない。
密度の測定は密度勾配管法を用いてJIS K7112に準じて測定することができる。
MFRはJIS K7210に従い、温度190℃、荷重2.16kgの条件で測定している。
ポリエチレン系樹脂に、多孔化を促進させる多孔化促進化合物Xを添加することが好ましい。前記多孔化促進化合物Xを添加することにより、より効率的に多孔構造を得ることができ、孔の形状や孔径を制御しやすくなる。
前記多孔化促進化合物Xは限定しないが、具体的に例示すると、変性ポリオレフィン樹脂、脂環族飽和炭化水素樹脂若しくはその変性体、エチレン系共重合体、またはワックスから選ばれる多孔化促進化合物Xのうち少なくとも1種が含まれていることがより好ましい。中でも、多孔化でより効果の大きい脂環族飽和炭化水素樹脂若しくはその変性体、エチレン系共重合体、またはワックスがより好ましく、成形性の観点からワックスが更に好ましい。
(ア)融点が40℃~200℃である。
(イ)融点より10℃高い温度での溶融粘度が50Pa・s以下である。
中でも、核剤はポリエチレン系樹脂の結晶構造を制御し、延伸開孔時の多孔構造を細かくするという効果があるため好ましい。市販されているものとして、「ゲルオールD」(新日本理化社製)、「アデカ スタブ」(旭電化工業社製)、「Hyperform」(ミリケンケミカル社製)、または「IRGACLEAR D」(チバ スペシャルケミカルズ社製)等が挙げられる。また、核剤の添加されたポリエチレン系樹脂の具体例としては、「リケマスター」(理研ビタミン社製)等が商業的に入手できる。
本発明において、ポリオレフィン系樹脂多孔フィルム(I層)は、単層でも積層でも構わないが、2層以上に積層させることが好ましい。中でも、ポリプロピレン系樹脂を含有する層とポリエチレン系樹脂を含有する層とを積層したものがより好ましい。
ポリオレフィン系樹脂多孔フィルムの層構成は、ポリプロピレン系樹脂を含有する層(以降「A層」と称す)を少なくとも1層存在すれば特に限定されるものではない。また、ポリオレフィン系樹脂多孔フィルムの機能を妨げない範囲で他の層(以降「B層」と称す)を積層することもできる。前記A層と積層するB層はポリオレフィン系樹脂に限定されず、強度保持層、耐熱層(高融解温度樹脂層)、シャットダウン層(低融解温度樹脂層)などの機能を持たせて前記A層と積層させる構成とすることが好ましい。例えば、リチウムイオン電池用セパレータとして用いる際には、特開平04-181651号公報に記載されているような高温雰囲気下で孔閉塞し、電池の安全性を確保する低融点樹脂層を積層させることが好ましい。
具体的にはA層/B層を積層した2層構造、A層/B層/A層、若しくは、B層/A層/B層として積層した3層構造などが例示できる。また、他の機能を持つ層と組み合わせて3種3層の様な形態も可能である。この場合、他の機能を持つ層との積層順序は特に問わない。更に層数としては4層、5層、6層、7層と必要に応じて増やしても良い。
次に、ポリオレフィン系樹脂多孔フィルムからなる基材層(I層)の製造方法について説明するが、本発明はかかる製造方法により製造されるポリオレフィン系樹脂多孔フィルム(I層)のみに限定されるものではない。
無孔膜状物の延伸方法については、ロール延伸法、圧延法、テンター延伸法、同時二軸延伸法などの手法があり、これらを単独あるいは2つ以上組み合わせて一軸延伸あるいは二軸延伸を行う。中でも、多孔構造制御の観点から逐次二軸延伸が好ましい。
(I)前記ポリオレフィン系樹脂多孔フィルムを構成する各層を多孔化したのち、多孔化された各層をラミネートしたり接着剤等で接着したりして積層する方法。
(II)各層を積層して積層無孔膜状物を作製し、ついで当該無孔膜状物を多孔化する方法。
(III)各層のうちいずれか1層を多孔化したのち、もう1層の無孔膜状物と積層し、多孔化する方法。
(IV)多孔層を作製した後、無機・有機粒子などのコーティング塗布や、金属粒子の蒸着などを行うことにより積層多孔フィルムとする方法。
本発明においては、その工程の簡略さ、生産性の観点から(II)の方法を用いることが好ましく、なかでも2層の層間接着性を確保するために、共押出で積層無孔膜状物を作製した後、多孔化する方法が特に好ましい。
まず、ポリプロピレン系樹脂と、必要であれば熱可塑性樹脂、添加剤の混合樹脂組成物を作製する。例えば、ポリプロピレン系樹脂、β晶核剤、および所望によりその他添加物等の原材料を、好ましくはヘンシェルミキサー、スーパーミキサー、タンブラー型ミキサー等を用いて、または袋の中に全成分を入れてハンドブレンドにて混合した後、一軸あるいは二軸押出機、ニーダー等、好ましくは二軸押出機で溶融混練後、カッティングしてペレットを得る。
使用するTダイのギャップは、最終的に必要なフィルムの厚み、延伸条件、ドラフト率、各種条件等から決定されるが、一般的には0.1~3.0mm程度、好ましくは0.5~1.0mmである。0.1mm未満では生産速度という観点から好ましくなく、また3.0mmより大きければ、ドラフト率が大きくなるので生産安定性の観点から好ましくない。
キャストロールによる冷却固化温度は本発明において非常に重要であり、膜状物中のポリプロピレン系樹脂のβ晶の比率を調整することができる。キャストロールの冷却固化温度は好ましくは80~150℃、より好ましくは90~140℃、更に好ましくは100~130℃である。冷却固化温度を80℃以上とすることで、膜状物中のβ晶の比率を十分に増加させることができるために好ましい。また、150℃以下とすることで押出された溶融樹脂がキャストロールへ粘着し巻き付いてしまうなどのトラブルが起こりにくく、効率よく膜状物化することが可能であるので好ましい。
延伸前の膜状物中のβ晶比率は、示差走査型熱量計を用いて、該膜状物を25℃から240℃まで加熱速度10℃/分で昇温させた際に、検出されるポリプロピレン系樹脂(A)のα晶由来の結晶融解熱量(ΔHmα)とβ晶由来の結晶融解熱量(ΔHmβ)を用いて下記式で計算される。
β晶比率(%)=〔ΔHmβ/(ΔHmβ+ΔHmα)〕×100
ついで、得られた無孔膜状物を少なくとも二軸延伸することがより好ましい。二軸延伸は同時二軸延伸であってもよいし、逐次二軸延伸であってもよいが、各延伸工程で延伸条件(倍率、温度)を簡便に選択でき、多孔構造を制御し易い逐次二軸延伸がより好ましい。なお、膜状物及びフィルムの長手方向を「縦方向」、長手方向に対して垂直方向を「横方向」と称する。また、長手方向への延伸を「縦延伸」、長手方向に対して垂直方向への延伸を「横延伸」と称する。
一方、横延伸での延伸温度は概ね100~160℃、好ましくは110~150℃、更に好ましくは120~140℃である。また、好ましい縦延伸倍率は1.2~10倍が好ましく、より好ましくは1.5~8倍、更に好ましくは2~7倍である。前記範囲内で横延伸することで、縦延伸により形成された空孔起点を適度に拡大させ、微細な多孔構造を発現させることができる。
前記延伸工程の延伸速度としては、500~12000%/分が好ましく、1500~10000%/分がさらに好ましく、2500~8000%/分であることが更に好ましい。
本発明は、基材層(I層)となるポリオレフィン系樹脂多孔フィルムの少なくとも片面に、フィラー(a)、樹脂バインダー(b)を含む被覆層(II層)を積層させている。具体的には、前記基材層は1層のポリオレフィン系樹脂多孔フィルムでも良いし、複層を積層したポリオレフィン系樹脂多孔フィルムでもよい。前記単層または複層のポリオレフィン系樹脂多孔フィルムの少なくとも片面の表面に被覆層(II層)を積層している。基材層(I層)がA層とB層の積層である場合、A層とB層の界面には被覆層(II層)は介在させていない。
前記被覆層で用いるフィラー(a)として、無機フィラー、有機フィラーなどが挙げられるが、特に制約されるものではない。
このように、被覆層(II層)の厚さ方向でフィラー(a)の平均粒径が異なることによって、基材層(I層)の界面側の被覆層(II層)中に通気性の高い粗雑な構造と、表面側にフィラー(a)の脱落抑制、および耐熱収縮性に優れる微細な構造と、の両方を構築し、その効果を発現することができる。
本発明に用いることができる樹脂バインダー(b)は、前記フィラー、前記ポリオレフィン系樹脂多孔フィルムを良好に接着でき、電気化学的に安定で、かつ積層多孔フィルムを電池として使用する場合には、有機電解液に対して安定であれば特に制限はない。具体的には、エチレン-酢酸ビニル共重合体(EVA、酢酸ビニル由来の構造単位が20~35モル%のもの)、エチレン-エチルアクリレート共重合体などのエチレン-アクリル酸、共重合体、フッ素樹脂[ポリフッ化ビニリデン(PVDF)など]、フッ素系ゴム、スチレン-ブタジエンゴム(SBR)、ニトリルブタジエンゴム(NBR)、ポリブタジエンゴム(BR)、ポリアクリロニトリル(PAN)、ポリアクリル酸(PAA)、カルボキシメチルセルロース(CMC)、ヒドロキシエチルセルロース(HEC)、ポリビニルアルコール(PVA)、ポリビニルブチラール(PVB)、ポリビニルピロリドン(PVP)、ポリN-ビニルアセトアミド、架橋アクリル樹脂、ポリウレタン、エポキシ樹脂などが挙げられる。これらの樹脂バインダー(b)は1種単独で使用してもよく、2種以上を併用しても構わない。これらの樹脂バインダー(b)の中でもポリビニルアルコール、ポリフッ化ビニリデン、スチレン-ブタジエンゴム、カルボキシメチルセルロース、ポリアクリル酸が好ましい。
本発明の積層多孔フィルムは、前記フィラー(a)と前記樹脂バインダー(b)を溶媒に溶解または分散させた分散液を、前記ポリオレフィン系樹脂多孔フィルム(I層)の積層多孔フィルム表面となる少なくとも片面に塗布し、溶媒の除去工程前あるいは除去工程中においてフィラー(a)を沈降せしめることによって、ポリオレフィン系樹脂多孔フィルム(I層)表面に被覆層(II層)を形成して製造することができる。なお、必要に応じて、前記ポリオレフィン系樹脂多孔フィルム(I層)の両側表面に塗布して被覆層を形成してもよい。
中でも、塗布工程において、塗布面が乾燥工程を終わるまで上面を向いている方式が好ましい。前記方式を用いることでフィラー(a)を沈降させることができ、前記被覆層(II層)において、フィラー(a)の粒径勾配を有することができ、フィラー(a)の平均粒径比(Du/Db)が所定の範囲を満たすことができる。
本発明のポリオレフィン系樹脂多孔フィルムからなる基材層の表面に被覆層を設けた積層多孔フィルムの全体厚みは5~100μmが好ましい。より好ましくは8~50μm、更に好ましくは10~30μmである。非水電解液二次電池用セパレータとして使用する場合、5μm以上であれば、実質的に必要な電気絶縁性を得ることができ、例えば電極の突起部分に大きな力がかかった場合でも、非水電解液二次電池用セパレータを突き破って短絡しにくく安全性に優れる。また、厚みが100μm以下であれば、積層多孔フィルムの電気抵抗を小さくすることができるので、電池の性能が十分に確保することができる。
一方、上限については70%以下が好ましく、65%以下がより好ましく、60%以下が更に好ましい。空孔率が70%以下であれば、積層多孔フィルムの強度が低下しにくく、ハンドリングの観点からも好ましい。なお、空孔率は実施例に記載の方法で測定している。
透気度はフィルム厚み方向の空気の通り抜け難さを表し、具体的には100mlの空気が当該フィルムを通過するのに必要な数で表現されている。そのため、数値が小さい方が通り抜け易く、数値が大きい方が通り抜け難いことを意味する。すなわち、その数値が小さい方がフィルムの厚み方向の連通性が良いことを意味し、その数値が大きい方がフィルム厚み方向の連通性が悪いことを意味する。連通性とはフィルム厚み方向の孔のつながり度合いである。本発明の積層多孔フィルムの透気度が低ければ様々な用途に使用することができる。例えば非水電解液二次電池用セパレータとして使用する場合、透気度が低いということはリチウムイオンの移動が容易であることを意味し、電池性能に優れるため好ましい。
続いて、本発明の前記積層多孔フィルムを電池用セパレータとして収容している非水電解液二次電池について、図1に参照して説明する。
正極板21、負極板22の両極は電池用セパレータ10を介して互いに重なるようにして渦巻き状に捲回し、巻き止めテープで外側を止めて捲回体としている。
前記捲回工程について詳しく説明する。電池用セパレータの片端をピン(図2)のスリット部1の間に通し、ピンを少しだけ回転させて電池用セパレータの一端をピンに巻きつけておく。この時、ピンの表面と電池用セパレータの被覆層とが接触している。その後、電池用セパレータを間に挟むようにして正極と負極を配置し、捲回機によってピンを回転させて、正負極と電池用セパレータを捲回する。捲回後、ピンは捲回物から引き抜かれる。
分散液中のフィラー(a)と樹脂バインダー(b)との総量に占めるフィラー(a)の割合をフィラー(a)の含有率とした。
固形分率は、フィラー(a)と樹脂バインダ(b)の総量の、分散液100質量%に対する比率とした。
1/1000mmのダイアルゲージにて、面内を不特定に5箇所測定し、その平均値を積層多孔フィルムの厚みとした。
JIS P8117に準拠して透気度(秒/100ml)を測定した。
SEMを用いる方法により、積層多孔フィルム表面から被覆層(II層)の層厚25%内におけるフィラー(a)の平均粒径(Du)と、ポリオレフィン系樹脂多孔フィルム(I層)界面から被覆層(II層)の層厚25%内におけるフィラー(a)の平均粒径(Db)を測定し、以下の式により平均粒径比を算出した。
平均粒径比 = Db / Du
JIS Z0237に準拠して、ポリオレフィン系樹脂多孔フィルム(I層)と被覆層(II層)との引き剥がし強度を測定した。まず、サンプルとして、積層多孔フィルムを横50mm×縦150mmに切り出し、当該サンプルの縦方向にテープ43として、セロハンテープ(ニチバン株式会社製、JIS Z1522)を貼付け、当該テープ背面が重なるように180°に折り返し、当該サンプルから25mm剥がした。次に、引張試験機(株式会社インテスコ製、インテスコIM-20ST)の下部チャックに剥がした部分のサンプルの片端を固定し、上部チャックにテープを固定し、試験速度300mm/分にて引き剥がし強度を測定した(図2)。測定後、最初の25mmの長さの測定値は無視し、試験片から引き剥がされた50mmの長さの引き剥がし強度測定値を平均し、引き剥がし強度とした。
結着性は、以下の評価基準によって評価した。
○:引き剥がし強度が3N/15mm以上。
△:引き剥がし強度が1N/15mm以上、3N/15mm未満。
×:引き剥がし強度が1N/15mm未満。
塗工性は、以下の評価基準によって評価した。
○:塗工が可能。可視観察において、粒子の凝集がなく良好な被覆膜を形成。
△:塗工が可能。可視観察において、粒子の凝集が確認できる。
×:粒子の凝集が多く、塗工困難。
積層多孔フィルムを150×10mm四方に切り出したサンプルをチャック間100mmとなるように印を入れ、150℃に設定したオーブン(タバイエスペック株式会社製、タバイギヤオーブンGPH200)に該サンプルを入れ、1時間静置した。該サンプルをオーブンから取り出し冷却した後、長さを測定し、以下の式にて収縮率をそれぞれ算出した。
収縮率(%)={(100-加熱後の長さ)/100}×100
以上の測定は、積層多孔フィルムの縦方向、横方向について行った。
耐熱性は、以下の評価基準において評価した。
○:150℃における収縮率が、縦方向、横方向いずれも10%未満
△:150℃における収縮率が、縦方向もしくは横方向で10%以上25%未満
×:150℃における収縮率が、縦方向もしくは横方向で25%以上
得られた積層多孔フィルムを株式会社パーキンエルマー製の示差走査型熱量計(DSC-7)を用いて、25℃から240℃まで走査速度10℃/分で昇温後1分間保持し、次に240℃~25℃まで走査速度10℃/分で降温後1分間保持し、次に25℃から240℃まで走査速度10℃/分で再昇温させた。この再昇温時にポリプロピレン系樹脂のβ晶に由来する結晶融解ピーク温度(Tmβ)である145~160℃にピークが検出されるか否かによりβ晶活性の有無を以下の基準にて評価した。
○:Tmβが145℃~160℃の範囲内に検出された場合(β晶活性あり)
×:Tmβが145℃~160℃の範囲内に検出されなかった場合(β晶活性なし)
なお、β晶活性の測定は、試料量10mgで、窒素雰囲気下にて行った。
積層多孔フィルムを縦60mm、横60mm角に切り出し、図2(A)に示すように中央部が40mmφの円状に穴の空いたアルミ板(材質:JIS A5052、サイズ:縦60mm、横60mm、厚さ1mm)2枚の間にはさみ、図2(B)に示すように周囲をクリップで固定した。
積層多孔フィルムをアルミ板2枚に拘束した状態で設定温度180℃、表示温度180℃である送風定温恒温器(ヤマト科学株式会社製、型式:DKN602)に入れ3分間保持した後、設定温度を100℃に変更し、10分以上の時間をかけて100℃まで徐冷を行った。表示温度が100℃になった時点で取り出し、アルミ板2枚に拘束した状態のまま25℃の雰囲気下で5分間冷却して得られたものについて、以下の測定条件で、中央部の40mmφの円状の部分について広角X線回折測定を行った。
・広角X線回折測定装置:株式会社マックサイエンス製、型番:XMP18A
・X線源:CuKα線、出力:40kV、200mA
・走査方法:2θ/θスキャン、2θ範囲:5°~25°、走査間隔:0.05°、走査速度:5°/min
得られた回折プロファイルについて、ポリプロピレン系樹脂のβ晶の(300)面に由来するピークより、β晶活性の有無を以下のように評価した。
○:ピークが2θ=16.0~16.5°の範囲に検出された場合(β晶活性あり)
×:ピークが2θ=16.0~16.5°の範囲に検出されなかった場合(β晶活性なし)
なお、積層多孔フィルム片が縦60mm、横60mm角に切り出せない場合は、中央部に40mmφの円状の穴に積層多孔フィルムが設置されるように調整しても構わない。
A層として、ポリプロピレン系樹脂(株式会社プライムポリマー製、プライムポリプロ F300SV、密度:0.90g/cm3、MFR:3.0g/10分)と、β晶核剤として、N,N’-ジシクロヘキシル-2,6-ナフタレンジカルボン酸アミドを準備した。このポリプロピレン系樹脂100質量部に対して、β晶核剤を0.2質量部の割合で各原材料をブレンドし、東芝機械株式会社製の同方向二軸押出機(口径:40mmφ、L/D:32)に投入し、設定温度300℃で溶融混合後、水槽にてストランドを冷却固化し、ペレタイザーにてストランドをカットし、ポリプロピレン系樹脂のペレットを作製した。ポリプロピレン系樹脂組成物のβ晶活性は80%であった。
前記積層膜状物を、縦延伸機を用いて縦方向に4.6倍延伸し、コロナ表面処理を施した。その後、横延伸機にて100℃で横方向に2倍延伸後、熱固定/弛緩処理を行うことで、A層/B層/A層とした2種3層で全体厚み20μmのポリオレフィン系樹脂多孔フィルム(I層)からなる基材層を得た。
アルミナ(住友化学株式会社製、スミコランダムAA-03、平均粒径:0.3μm、密度:3.9g/cm3)19.7質量部、ポリビニルアルコール(株式会社クラレ製、PVA124、鹸化度:98.0~99.0、平均重合度:2400、密度:1.3g/cm3)0.3質量部を水80.0質量部に分散させた分散液を得た。この時、分散液中の固形分率は、分散液100質量%に対し20質量%であった。
得られた分散液を前記A層/B層/A層とした2種3層の基材層のポリオレフィン系樹脂多孔フィルム(I層)の片側表面に目付量#20のバーコーターを用いて塗布した後、20℃で30分間乾燥させながらフィラーを沈降せしめて、被覆層(II層)を形成、ポリオレフィン系樹脂多孔フィルム(I層)-被覆層(II層)からなる積層多孔フィルムを作成した。該積層多孔フィルムの全体厚みは25μmであった。得られた積層多孔フィルムの物性評価を行い、その結果を表1にまとめた。
アルミナ(日本軽金属株式会社製、低ソーダアルミナLS-235C、平均粒径:0.5μm、密度:3.9g/cm3)19.7質量部、ポリビニルアルコール(株式会社クラレ製、PVA124、鹸化度:98.0~99.0、平均重合度:2400、密度:1.3g/cm3)0.3質量部を水80.0質量部に分散させた分散液Xを得た。続いて、アルミナを電気化学工業株式会社製、球状アルミナASFP-20(平均粒径0.2μm、密度:3.9g/cm3)に替えた以外は、分散液Xと同様にポリビニルアルコールと水に分散させた分散液Yを得た。この時、分散液XおよびY中の固形分率は、いずれも分散液100質量%に対し20質量%であった。
得られた分散液Xに、塩酸を0.7質量%となるよう加え、当該液を前記A層/B層/A層とした2種3層の基材層のポリオレフィン系樹脂多孔フィルム(I層)の片側表面に目付量#10のバーコーターを用いて塗布した後、60℃で2分間乾燥させた。続いて分散液Yを当該面に目付け量#10のバーコーターを用いて塗布した後、60℃で2分間乾燥させることで、被覆層(II層)を形成、ポリオレフィン系樹脂多孔フィルム(I層)-被覆層(II層)からなる積層多孔フィルムを作成した。該積層多孔フィルムの全体厚みは26μmであった。得られた積層多孔フィルムの物性評価を行い、その結果を表1にまとめた。
アルミナ(住友化学株式会社製、スミコランダムAA-03、平均粒径:0.3μm、密度:3.9g/cm3)39.4質量部、ポリビニルアルコール(株式会社クラレ製、PVA124、鹸化度:98.0~99.0、平均重合度:2400、密度:1.3g/cm3)0.6質量部を水60.0質量部に分散させた分散液を得た。この時、分散液中の固形分率は、分散液100質量%に対し40質量%であった。
得られた分散液を前記実施例1と同じA層/B層/A層とした2種3層の基材層となるポリオレフィン系樹脂多孔フィルム(I層)の片側表面に目付量#10のバーコーターを用いて塗布した後、60℃で2分間乾燥させ、全体厚みが27μmの積層多孔フィルムを得た。
得られた積層多孔フィルムの物性評価を行い、その結果を表1にまとめた。
前記ポリオレフィン系樹脂多孔フィルムの物性評価を行い、その結果を表1にまとめた。
一方、比較例1で得た積層多孔フィルムは、塗液の固形分の組成が実施例1のものと同じものであるにもかかわらず、所定の粒径勾配を有していないために、結着性、耐熱性が不十分であった。
また、比較例2のポリオレフィン系樹脂多孔フィルムは、被覆層が積層されていないため、耐熱性が不十分であった。
21 正極板
22 負極板
24 正極リード体
25 負極リード体
26 ガスケット
27 正極蓋
31 アルミ板
32 多孔フィルム
33 クリップ
34 多孔フィルム縦方向
35 多孔フィルム横方向
41 サンプル
42 テープ
43 滑り止め
44 上部チャック
45 下部チャック
Claims (14)
- 基材層となるポリオレフィン系樹脂多孔フィルムの少なくとも片面に、フィラーと樹脂バインダーを含む被覆層を積層している積層多孔フィルムであり、
前記積層多孔フィルムの表面となる前記被覆層の表面から該被覆層の厚さ25%内におけるフィラーの平均粒径(Du)と前記基材層との界面から該被覆層の厚さ25%内におけるフィラーの平均粒径(Db)との比(Du/Db)が1.2~10であり、かつ、前記被覆層の表面側のフィラーの平均粒径(Du)が0.05μm以下であることを特徴とする積層多孔フィルム。 - 前記フィラーの平均粒径が、0.1μm以上3.0μm以下である請求項1に記載の積層多孔フィルム。
- 前記フィラーの平均粒径(Du)は0.05μm~0.5μm、フィラーの平均粒径(Db)は0.1μm~3.0μm以上であり、前記被覆層の表面から厚さ25%と前記基材層との界面から該被覆層の厚さ25%の間の前記被覆層の厚さ方向の中間部の前記フィラーの平均粒径は前記(Du)と(Db)の間であり、前記被覆層の表面側から前記基材層との界面側へ平均粒子径が大径化する勾配を有する請求項1または請求項2に記載の積層多孔フィルム。
- 前記フィラーの密度が、前記樹脂バインダーの密度の2倍以上である請求項1乃至請求項3のいずれか1項に記載の積層多孔フィルム。
- 前記基材層となるポリオレフィン系樹脂多孔フィルムが、ポリプロピレン系樹脂を主成分とする層を少なくとも1層備えている請求項1乃至請求項4のいずれかに1項に記載の積層多孔フィルム。
- 前記基材層となるポリオレフィン系樹脂多孔フィルムは、ポリプロピレン系樹脂を主成分とする層(A層)と他のポリオレフィン系樹脂層(B層)または/およびポリオレフィン系樹脂以外の樹脂層とを積層した積層フィルムであり、該積層フィルムからなる前記基材層の表面に前記被覆層を積層している請求項1乃至請求項4のいずれか1項に記載の積層多孔フィルム。
- 前記基材層のポリオレフィン系樹脂多孔フィルムが、β晶活性を有する請求項1乃至6のいずれか1項に記載の積層多孔フィルム。
- 前記基材層と前記被覆層との引き剥がし強度が3N/15mm以上である請求項1乃至請求項7いずれかに1項に記載の積層多孔フィルム。
- 150℃における収縮率が25%未満である請求項1乃至請求項8のいずれか1項に記載の積層多孔フィルム。
- 請求項1乃至請求項9のいずれか1項に記載の積層多孔フィルムからなる非水電解液二次電池用セパレータ。
- 請求項10に記載の非水電解液二次電池用セパレータを用いた非水電解液二次電池。
- 請求項1乃至請求項9のいずれか1項に記載の積層多孔フィルムの製造方法であって、
前記基材層のポリオレフィン系樹脂多孔フィルムの少なくとも片面の表面に、前記フィラーと前記樹脂バインダーとを溶媒に溶解または分散させた分散液を塗布して前記被覆層を形成し、
前記溶媒の除去工程前または除去工程中に前記フィラーを前記基材層に向けて沈降させ、前記被覆層の厚み方向で表面側から基材層側にフィラーの平均粒径が、前記(Du/Db)=1.2~10となる勾配をつけている積層多孔フィルムの製造方法。 - 請求項1乃至請求項9のいずれか1項に記載の積層多孔フィルムの製造方法であって、前記基材層のポリオレフィン系樹脂多孔フィルムの少なくとも片面の表面に、前記フィラーの平均粒径が異なる分散液を複数回にわけて塗布し、該分散液の塗布はフィラーの平均粒径が大きな分散液から塗布して、順次平均粒径が小さい分散液を重ねて塗布し、前記被覆層の厚み方向で前記表面側から基材層側にフィラーの平均粒径が、前記(Du/Db)=1.2~10となる勾配をつけている積層多孔フィルムの製造方法。
- 前記基材層に前記分散液を塗布する前または前記被覆層を形成後に、100℃以上170℃以下で熱処理するとともに、該熱処理中に1~20%の弛緩処理を施し、150℃における収縮率を25%未満としている請求項11または請求項12に記載の積層多孔フィルムの製造方法。
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WO2010008003A1 (ja) * | 2008-07-16 | 2010-01-21 | 東レ株式会社 | 蓄電デバイス用セパレータ |
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JP2014208780A (ja) * | 2013-03-27 | 2014-11-06 | 三菱樹脂株式会社 | 塗工液の製造方法、積層多孔フィルム、非水電解液二次電池用セパレータ、及び非水電解液二次電池 |
JP2015115266A (ja) * | 2013-12-13 | 2015-06-22 | 三星エスディアイ株式会社Samsung SDI Co.,Ltd. | 非水電解質二次電池用電極巻回素子、それを用いた非水電解質二次電池、及び非水電解質二次電池用電極巻回素子の製造方法 |
US10944088B2 (en) | 2014-04-09 | 2021-03-09 | Sumitomo Chemical Company, Limited | Layered porous film, and non-aqueous electrolyte secondary battery |
JP2015225791A (ja) * | 2014-05-28 | 2015-12-14 | 東レバッテリーセパレータフィルム株式会社 | 電池用セパレータ及びその製造方法 |
JP2016040354A (ja) * | 2014-08-12 | 2016-03-24 | 三菱樹脂株式会社 | 積層多孔フィルムの製造方法 |
WO2017073598A1 (ja) * | 2015-10-30 | 2017-05-04 | Jnc株式会社 | 平滑性に優れた有機・無機複合膜及びこれを用いた多層耐熱セパレータ材 |
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US20140099530A1 (en) | 2014-04-10 |
JP5298247B2 (ja) | 2013-09-25 |
KR101316995B1 (ko) | 2013-10-11 |
CN102917876A (zh) | 2013-02-06 |
KR20130014052A (ko) | 2013-02-06 |
CN102917876B (zh) | 2014-06-11 |
JPWO2012165580A1 (ja) | 2015-02-23 |
US8785032B2 (en) | 2014-07-22 |
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