WO2013183666A1 - ポリオレフィン系樹脂多孔性フィルム - Google Patents
ポリオレフィン系樹脂多孔性フィルム Download PDFInfo
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- WO2013183666A1 WO2013183666A1 PCT/JP2013/065573 JP2013065573W WO2013183666A1 WO 2013183666 A1 WO2013183666 A1 WO 2013183666A1 JP 2013065573 W JP2013065573 W JP 2013065573W WO 2013183666 A1 WO2013183666 A1 WO 2013183666A1
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- porous film
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- polyolefin resin
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- resin porous
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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
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/18—Manufacture of films or sheets
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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
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/20—Manufacture of shaped structures of ion-exchange resins
- C08J5/22—Films, membranes or diaphragms
- C08J5/2206—Films, membranes or diaphragms based on organic and/or inorganic macromolecular compounds
- C08J5/2218—Synthetic macromolecular compounds
- C08J5/2231—Synthetic macromolecular compounds based on macromolecular compounds obtained by reactions involving unsaturated carbon-to-carbon bonds
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
- B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
- B29C55/10—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial
- B29C55/12—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial
- B29C55/14—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial successively
- B29C55/143—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial successively firstly parallel to the direction of feed and then transversely thereto
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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
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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
- H01M50/411—Organic 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
- H01M50/411—Organic material
- H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
- H01M50/417—Polyolefins
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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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- 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
- H01M50/457—Separators, membranes or diaphragms characterised by the material having a layered structure comprising three or more layers
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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
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
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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
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M50/491—Porosity
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2023/00—Use of polyalkenes or derivatives thereof as moulding material
- B29K2023/10—Polymers of propylene
- B29K2023/12—PP, i.e. polypropylene
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
- B29K2105/04—Condition, form or state of moulded material or of the material to be shaped cellular or porous
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
- B29L2031/00—Other particular articles
- B29L2031/34—Electrical apparatus, e.g. sparking plugs or parts thereof
- B29L2031/3468—Batteries, accumulators or fuel cells
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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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- 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
- C08J2323/10—Homopolymers or copolymers of propene
- C08J2323/12—Polypropene
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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
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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
- H01M50/406—Moulding; Embossing; Cutting
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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
Definitions
- the present invention relates to a polyolefin resin 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 coating type lithium ion It can be suitably used as a battery separator.
- lithium-ion secondary batteries are being expanded to large batteries related to environmental issues such as electric vehicles and emergency power applications. Yes.
- Patent Document 1 proposes a separator coated with a heat resistant resin as a heat resistant porous layer.
- Patent Document 2 proposes a separator in which a filler is provided as a heat-resistant layer on the surface of the separator has been proposed.
- the heat-resistant layer is usually formed by applying a heat-resistant resin imparting heat resistance or a mixed solution containing a filler, a resin binder, and a solvent to the separator surface, and then removing the solvent through a drying process to form the heat-resistant layer.
- the separator obtained by the manufacturing method described in Patent Document 3 has a high porosity, the separator is insufficient in rigidity. For example, there is a problem that wrinkles are more easily generated with a slight tension in the transport process. Therefore, when the heat resistant layer is provided by coating, it is difficult to form the heat resistant layer with a uniform thickness. Even when a heat resistant layer is not provided on the surface of the porous film as a coating, wrinkles are likely to occur when forming a raw roll product by winding a thin porous film with high porosity and pulling it. There is a problem that tends to decrease. In Patent Document 4, the elastic modulus (rigidity) at room temperature is improved.
- the resin softens in a high-temperature atmosphere, the elastic modulus is lowered. Is easier, and problems arise when a coating layer is provided and in the process of winding on a roll. In addition, since the transverse draw ratio is reduced, it is difficult to increase the porosity, the transmission characteristics of the resulting porous film are lowered, and there is a problem that sufficient battery performance is difficult to be exhibited.
- the present invention has been made in view of the above problems, and has a high shrinkage stress, so that it is difficult for wrinkles to occur in a transport process in a high-temperature environment, and a process of providing a heat-resistant layer with a coating on the surface of a porous film and / or a roll It is an object of the present invention to provide a polyolefin-based resin porous film that does not generate wrinkles in the winding process, has good air permeability and maintains air permeability, and can be suitably used particularly as a battery separator.
- the present invention provides a polyolefin resin porous material characterized by having a 1% modulus in the flow direction at 90 ° C. of 4.5 MPa or more and an air permeability of 800 seconds / 100 ml or less.
- a sex film We provide a sex film.
- the shrinkage stress in the flow direction at 90 ° C. is preferably 1.5 MPa or more.
- the polyolefin resin is preferably a polypropylene resin as a main component.
- the present invention preferably has ⁇ crystal activity.
- the present invention it is preferable to stretch in the flow direction after biaxial stretching. Specifically, longitudinal stretching is performed at a stretching temperature of 20 to 130 ° C. and a stretching ratio of 3.0 to 8.0 in the flow direction (longitudinal direction). Next, transverse stretching is performed at a stretching temperature of 100 to 160 ° C. and a stretching ratio of 1.1 to 6.0 times in a direction perpendicular to the flow direction (lateral direction). Next, a relaxation treatment of 1 to 20% is performed at 130 ° C. or higher in the direction perpendicular to the flow direction (lateral direction), Then, it is preferable to perform re-longitudinal stretching at a draw ratio of 1.1 times or more in the flow direction (longitudinal direction).
- At least one surface is coated with a heat-resistant layer.
- the polyolefin resin porous film according to the present invention has a 1% modulus in the flow direction at 90 ° C. of 4.5 MPa or more, wrinkles are hardly generated during transportation. Therefore, when applying a tension to the porous film and coating the surface with a heat-resistant layer, it can be applied with a uniform thickness, and when wound on a roll while applying tension to the porous film, It can wind up without generating and can raise the precision of a product. Furthermore, since the air permeability is 800 sec / 100 ml or less, the permeation characteristics are not deteriorated and sufficient battery performance can be exhibited.
- 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.
- the flow direction of the membrane and porous film is “longitudinal direction”, the direction perpendicular to the flow direction is “lateral direction”, the stretching in the flow direction is “longitudinal stretching”, and the direction perpendicular to the flow direction is This stretching may be referred to as “lateral stretching”.
- polyolefin resin Specific examples of the polyolefin resin include a polyethylene resin and a polypropylene resin. Among these, a polypropylene resin is 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 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 porous 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. According 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 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 less than 0.5 g / 10 min, the resin has a high melt viscosity at the time of molding and the productivity is lowered. On the other hand, if it exceeds 15 g / 10 minutes, the mechanical strength of the resulting porous film is insufficient, and problems are likely to occur in practice. MFR is measured according to JIS K7210 under conditions of a temperature of 230 ° C. and a load of 2.16 kg.
- 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” “Tufselen” (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” Commercially available products such as “Inspire” (manufactured by Dow Chemical Company) can be used.
- the production method of the polypropylene-based 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-based 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-based catalyst.
- a polymerization method using a single site catalyst for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene-based catalyst.
- the 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 are formed by subsequent stretching, so that a porous film having air permeability can be obtained. Presence / absence of the “ ⁇ crystal activity” is determined by the case where the crystal melting peak temperature derived from the ⁇ crystal is detected by a differential scanning calorimeter described later and / or by measurement using an X-ray analyzer described later. When a diffraction peak derived from the ⁇ crystal is detected, it is judged to have “ ⁇ crystal activity”.
- the porous film is heated from a temperature of 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min for 1 minute with a differential scanning calorimeter (DSC), and then cooled from 240 ° C. to 25 ° C. for 10 minutes.
- the crystal melting peak temperature (Tm ⁇ ) derived from the ⁇ -crystal of the polypropylene-based resin is maintained when the temperature is lowered for 1 minute after the temperature is lowered for 1 minute, and further heated again from 25 ° C to 240 ° C at a heating rate of 10 ° C / minute. If detected, it is judged to have ⁇ crystal activity.
- the ⁇ crystal activity of the porous film is calculated by the following formula 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 ⁇ film has a higher ⁇ crystal activity, and the ⁇ crystal activity is preferably 20% or more. More preferably, it is 40% or more, and particularly preferably 60% or more. If the porous film has a ⁇ crystal activity of 20% or more, it indicates that a large amount of ⁇ crystals of polypropylene resin can be produced even in a film-like material before stretching, and fine and uniform pores are formed by stretching. A porous film having a large number of formed and excellent permeation characteristics 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 of the entire porous film, regardless of whether the porous film of the present invention has a single layer structure or other porous layers are laminated. it can.
- a method for obtaining the ⁇ crystal activity of the porous layer described above a method that does not add a substance that promotes the formation of ⁇ crystal of a polypropylene-based resin, or a peroxide radical is generated as described in Japanese Patent No. 3739481. Examples thereof include a method of adding a treated polypropylene resin and a method of adding a ⁇ crystal nucleating agent to the composition.
- ⁇ 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 Commercially available products of ⁇ crystal nucleating agent include ⁇ crystal nucleating agent “NJESTER NU-100” manufactured by Shin Nippon Rika Co., Ltd.
- polypropylene resins to which ⁇ crystal nucleating agent is added include polypropylene manufactured by Aristech Examples include “Bepol® B-022SP”, polypropylene “Beta ( ⁇ ) -PP® BE60-7032” manufactured by Borealis, and polypropylene “BNX BETAPP-LN” manufactured by Mayzo.
- the ⁇ crystal nucleating agent is preferably blended with a polypropylene resin.
- 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. 0.0001 to 5.0 parts by mass of the agent is preferred. 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.
- 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 include recycling resin, silica, talc, kaolin, calcium carbonate, and the like, which are added for the purpose of improving and adjusting molding processability, productivity, and various physical properties of the porous film.
- Inorganic particles such as, pigments such as titanium oxide and carbon black, flame retardants, weathering stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers, crosslinking agents, lubricants, nucleating agents, plasticizers, anti-aging agents, Examples thereof include additives such as antioxidants, light stabilizers, ultraviolet absorbers, neutralizers, antifogging agents, antiblocking agents, slip agents, and coloring agents.
- the porous film may be a single layer or a laminate.
- the layer structure of the porous film is not particularly limited as long as at least one layer containing a polyolefin resin (hereinafter referred to as “A layer”) is present.
- other layers hereinafter referred to as “B layer”.
- a layer a polyolefin resin
- B layer other layers
- a low melting point resin layer that closes the hole in a high temperature atmosphere as described in JP-A No. 04-181651 and ensures the safety of the battery.
- Specific examples include a two-layer structure in which an A layer / B layer is laminated, a three-layer structure in which an A layer / B layer / A layer, or a B layer / A layer / B layer are laminated.
- the physical properties of the porous film of the present invention can be freely adjusted by the layer constitution, the lamination ratio, the composition of each layer, and the production method.
- a coating layer (hereinafter abbreviated as a coating layer) may be laminated on at least one surface of the polyolefin resin porous film.
- the coat layer is preferably a heat-resistant layer containing a filler and a resin binder.
- the case where the polyolefin resin porous film of the present invention is not provided by coating the heat-resistant layer is included.
- Filler examples of the filler that can be used in the present invention include an inorganic filler and an organic filler, 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.
- barium sulfate and aluminum oxide are preferable.
- 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. Among these, cross-linked polystyrene and the like are particularly preferable.
- the average particle size of the filler is preferably 0.1 ⁇ m or more, more preferably 0.2 ⁇ m or more, still more preferably 0.3 ⁇ m or more, and the upper limit is preferably 3.0 ⁇ m or less, more preferably 1.5 ⁇ m or less. It is. Sufficient heat resistance can be exhibited when the average particle diameter is within the specified range. Further, from the viewpoint of dispersibility of the filler in the coat layer, the average particle size is more preferably 1.5 ⁇ m or less.
- the “average particle diameter of the filler” is a value measured according to a method using SEM.
- the content of the filler is preferably 100% by mass or more, and more preferably 200% by mass or more with respect to 100% by mass of the resin binder.
- about an upper limit 1500 mass% or less is more preferable, and 800 mass% or less is still more preferable. If the content of the filler is 100% by mass or more with respect to 100% by mass of the resin binder, it is preferable because a porous film having communication can be produced and excellent air permeability can be exhibited.
- the content rate of the said filler is 1500 mass% or less, it is preferable from generation
- the filler and the polyolefin-based resin porous film can be favorably bonded, are electrochemically stable, and the laminated porous film is non-aqueous electrolyte secondary.
- the non-aqueous electrolyte there is no particular limitation as long as it is stable with respect to the non-aqueous electrolyte.
- 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, etc.
- fluorinated rubber styrene-butadiene rubber (SBR), nitrile butadiene rubber (NBR), polybutadiene rubber (BR), polyacrylonitrile (PAN), polyacrylic acid (PAA), carboxymethyl cellulose (CMC) ), Hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), poly N-vinylacetamide, crosslinked acrylic resin, polyurethane, epoxy resin and the like.
- organic binders may be used alone or in combination of two or more.
- polyvinyl alcohol polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose, and polyacrylic acid are preferable, and polyvinyl alcohol is more preferable from the viewpoint of heat resistance and stretchability.
- the coating layer is coated on the surface of the polyolefin resin porous film by applying a dispersion obtained by dissolving or dispersing the filler and the resin binder in a solvent to at least one surface of the polyolefin resin porous film. Can be produced.
- the solvent it is preferable to use a solvent in which the filler and the resin binder can be dissolved or dispersed uniformly and stably.
- a solvent include N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, water, ethanol, toluene, hot xylene, and hexane.
- the dispersion may include a dispersant such as a surfactant, a thickener, a wetting agent, a disinfectant.
- Various additives such as foaming agents, pH adjusting agents including acids and alkalis 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 a method for dissolving or dispersing the filler and the resin binder 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, a disperser, a homogenizer, and a high-speed Examples thereof include an impact mill, ultrasonic dispersion, a mechanical stirring method using stirring blades, and the like.
- the dispersion may be applied to the surface of the polyolefin resin porous film after the extrusion molding, after the longitudinal stretching step, or after the transverse stretching step. May be.
- the extrusion process or the longitudinal stretching process is preferable in that the drying process and the stretching process can be performed simultaneously.
- the application method in the application step is not particularly limited as long as it can realize a required layer thickness and application area.
- coating methods include gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod Examples include a 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 solvent is preferably a solvent that can be removed from the dispersion applied to the polyolefin resin porous film.
- a method for removing the solvent any method that does not adversely affect the polyolefin resin porous film can be adopted without any particular limitation.
- a method for removing the solvent for example, a method of drying at a temperature below the melting point while fixing the polyolefin resin porous film, a method of drying under reduced pressure at a low temperature, a resin binder immersed in a poor solvent for the resin binder And a method of extracting the solvent at the same time as coagulating.
- the polyolefin resin porous film of the present invention it is important that the 1% modulus in the flow direction at 90 ° C., that is, the vertical direction, is 4.5 MPa or more. Furthermore, 5.5 MPa or more is preferable, 6.0 MPa or more is more preferable, and 7.0 MPa or more is particularly preferable. Normally, due to the rigidity of the resin, the polyolefin resin porous film has an antagonistic force against the tension due to conveyance, and is difficult to stretch.
- the drying temperature is higher than that of the organic solvent, which is very severe from the viewpoint of the rigidity of the porous film. It will be exposed to. Therefore, in a high temperature environment, the polyolefin resin is softened and the antagonistic force is reduced.
- the rigidity of the porous film is extended against the tension due to the conveyance, the shrinkage occurs in the direction perpendicular to the flow direction of the porous film, that is, in the lateral direction. At this time, if the shrinkage rate in the lateral direction is large, wrinkles appear. As a result, many wrinkles are generated in parallel with the vertical direction, resulting in poor coating.
- the thickness of the coat layer is not uniform, and the heat resistance is lowered, which is not preferable.
- the stretching ratio of longitudinal stretching or re-longitudinal stretching is increased, or the stretching ratio of transverse stretching is decreased. This can be achieved.
- the shrinkage stress in the flow direction at 90 ° C. is preferably 1.5 MPa or more, more preferably 2.0 MPa or more, and further preferably 3.0 MPa or more.
- the shrinkage stress in the flow direction at 90 ° C. is 1.5 MPa or more
- the elastic modulus in the longitudinal direction is improved as an antagonistic force against the tension due to the conveyance.
- the shrinkage stress acts in the longitudinal direction in the temperature range of the coating layer drying process, the elongation in the longitudinal direction is suppressed even in a high temperature environment, and wrinkles in the drying process of the coating layer are suppressed. Expression can be prevented.
- the shrinkage stress is 1.5 MPa or more because the porous film is hardly stretched by the shrinkage stress even if the elastic modulus of the porous film in a high temperature environment is lowered.
- the shrinkage stress is 10 MPa or less, the shrinkage in the flow direction at room temperature can be sufficiently suppressed.
- the means for improving the shrinkage stress in the flow direction at 90 ° C. can be achieved by increasing the stretching ratio of longitudinal stretching or the stretching ratio of re-longitudinal stretching, or decreasing the stretching ratio of transverse stretching.
- the air permeability of the polyolefin resin porous film of the present invention is 800 seconds / 100 ml or less. Further, 10 to 600 seconds / 100 ml is preferable, and 50 to 400 seconds / 100 ml is more preferable.
- the air permeability represents the difficulty in passing through the air in the thickness direction of the porous film, and is specifically expressed in the number of seconds required 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 more difficult it is to pass. That is, the smaller the value means that the connectivity in the thickness direction of the porous film is better, and the larger the value means that the connectivity in the thickness direction of the film is worse.
- the term “communication” refers to the degree of connection of pores in the thickness direction of the porous film. If the air permeability of the polyolefin resin 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. If the air permeability is 800 seconds / 100 ml or less, it indicates that the porous film has communication properties, suggesting excellent air permeability. Means for improving the air permeability can be achieved by increasing the stretching ratio of transverse stretching or decreasing the stretching ratio of re-longitudinal stretching.
- the method for producing the film-like material 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. It is done. Moreover, the method of cutting open the film-like thing manufactured by the tubular method and making it planar is also applicable.
- the stretching method of the film-like material there are methods 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 for uniaxial stretching or biaxial stretching. Do.
- a mixed resin composition containing a polyolefin resin and, if necessary, a thermoplastic resin and additives is prepared.
- polypropylene resin, ⁇ crystal nucleating agent, and additives, etc. if necessary, preferably using a Henschel mixer, super mixer, tumbler mixer, etc., or all components in a bag and mixing by hand blending
- a kneader or the like preferably a twin-screw extruder
- 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 based on the finally required porous film thickness, stretching conditions, draft rate, various conditions, etc., but is generally about 0.1 to 3.0 mm, preferably 0.5 to 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 temperature is set to 350 ° C. or lower, it is possible to suppress the deterioration of the resin composition, and hence the mechanical strength of the resulting polyolefin resin porous film.
- 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.
- the temperature is preferable because troubles such as the extruded molten resin sticking to and wound around the cast roll hardly occur and the film can be efficiently formed into a film.
- the ⁇ crystal ratio can be sufficiently increased and a sufficient porosity can be obtained.
- 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 porous film having good air permeability can be obtained because it is easily made porous by a subsequent stretching operation.
- the ⁇ crystal ratio of 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 flow direction (longitudinal direction) or in the direction perpendicular to the flow direction (transverse direction), or biaxial or more stretching may be performed.
- it is preferable to stretch in the flow direction after biaxial stretching hereinafter abbreviated as “re-longitudinal stretching”. It is more preferable to carry out re-longitudinal stretching after sequential biaxial stretching in the above order.
- re-longitudinal stretching it is more preferable to carry out re-longitudinal stretching after sequential biaxial stretching in the above order.
- molecules are oriented in the longitudinal direction by the first longitudinal stretching and the elastic modulus in the longitudinal direction is improved, but the molecular orientation in the longitudinal direction is reduced by the subsequent transverse stretching.
- the molecular orientation in the longitudinal direction is improved again, the elastic modulus can be improved, and shrinkage stress can be expressed in a high temperature environment.
- an antagonistic force against the tension due to the conveyance is obtained in the drying process of the coat layer, so that deformation of the porous film and expression of wrinkles can be suppressed, and coating defects are reduced.
- the stretching temperature must be appropriately selected depending on the composition of the resin composition to be used, the crystal melting peak temperature of the thermoplastic resin, the crystallinity of the polyolefin resin, etc. It is preferable to select.
- the stretching temperature for the first longitudinal stretching is preferably controlled at 20 to 130 ° C, more preferably 40 to 120 ° C, and even more preferably 60 to 110 ° C.
- a stretching temperature in the longitudinal stretching of 20 ° C. or higher is preferable because breakage during the longitudinal stretching hardly occurs and a void starting point is formed.
- the stretching temperature in the longitudinal stretching is 130 ° C. or lower, void formation occurs in the polyolefin-based resin, so that appropriate void formation can be performed.
- the draw ratio of the first longitudinal stretching is preferably 3.0 to 8.0 times, and more preferably 4.0 to 7.0 times.
- the stretching ratio of the longitudinal stretching By setting the stretching ratio of the longitudinal stretching to 3.0 times or more, sufficient pore starting points can be formed, and the molecular orientation in the longitudinal direction is increased, so that the elastic modulus in the longitudinal direction can be improved. . Moreover, the fracture frequency at the time of extending
- the stretching temperature for transverse stretching is preferably 100 ° C. to 160 ° C., more preferably 110 ° C. to 150 ° C., and still more preferably 120 ° C. to 145 ° C. If the stretching temperature in the transverse stretching is within the above range, the fracture at the transverse stretching due to the softening of the polyolefin-based resin hardly occurs, and the void starting points formed by the longitudinal stretching are easily opened. As a result, a porous film having a high porosity can be obtained. Further, the draw ratio of the transverse drawing is preferably 1.1 to 6.0 times, more preferably 1.1 to 4.0 times, and still more preferably 1.1 to 2.0 times.
- the pore starting point formed by the longitudinal drawing can be expanded to an appropriate size, and a biaxially stretched film having a dense porous structure can be obtained.
- the breaking frequency during drawing can be reduced.
- moderate pore expansion is performed while maintaining the molecular orientation generated by the longitudinal stretching, so that a separator having excellent transmission characteristics can be obtained.
- the stretching speed of the transverse stretching is preferably 100 to 10,000% / min, more preferably 200 to 5000% / min, and further preferably 500 to 2000% / min. If it is the extending
- stretching in the flow direction after biaxial stretching is preferred.
- re-longitudinal stretching By performing re-longitudinal stretching, the expression of wrinkles can be sufficiently suppressed in the coating layer drying step.
- 80 degreeC or more is preferable as a minimum, 90 degreeC or more is more preferable, and 100 degreeC or more is still more preferable.
- 160 degrees C or less is preferable, 150 degrees C or less is more preferable, and 140 degrees C or less is still more preferable.
- the stretching temperature of re-longitudinal stretching is in the above range, the desired porous film can be obtained because breakage during stretching is suppressed by softening the polypropylene resin and sufficient shrinkage stress is obtained in a high temperature environment. Can do.
- 1.1 times or more is preferable as a minimum about the draw ratio of re-longitudinal stretching, and 1.2 times or more is more preferable.
- the upper limit is preferably 3.0 times, more preferably 2.5 times or less, and still more preferably 2.0 times or less.
- the porous film thus obtained is preferably subjected to heat treatment for the purpose of reducing thermal shrinkage.
- heat processing temperature 130 degreeC or more is preferable, 135 degreeC or more is more preferable, and 140 degreeC or more is still more preferable.
- the heat treatment temperature is 130 ° C. or higher, the crystallization of the polypropylene resin is promoted, and the residual strain of the porous film generated by stretching can be reduced. Therefore, heat treatment has an effect of reducing thermal shrinkage, and deterioration of air permeability in a high temperature environment can be suppressed.
- the upper limit of the heat treatment temperature is preferably 160 ° C. or lower, and more preferably 155 ° C. or lower.
- the heat treatment temperature is 160 ° C. or lower because the polypropylene resin does not melt or soften more than necessary and the porous structure of the porous film can be maintained.
- a relaxation treatment of 1 to 20% may be performed as necessary, or the relaxation treatment may be performed after the heat treatment is performed in a restrained state to promote crystallization.
- the porous film of the present invention can be obtained by uniformly cooling slowly.
- the stretching and relaxation treatment are preferably performed under the following conditions.
- the stretching temperature is preferably 20 to 130 ° C, more preferably 60 ° C to 110 ° C, still more preferably 100 to 110 ° C, and the stretching ratio is preferably 3.0 to 8.0 times.
- longitudinal stretching is performed at 4.0 to 7.0 times, more preferably 4.5 to 6.0 times,
- the stretching temperature is preferably 100 to 160 ° C., more preferably 110 to 150 ° C.
- the stretching ratio is preferably 1.1 to 6.0 times, more preferably Perform transverse stretching at 1.1 to 4.0 times, Then, a relaxation treatment is preferably performed in a direction perpendicular to the flow direction (lateral direction), preferably 1 to 20% at 130 ° C. or more, more preferably 3 to 12% at 135 to 160 ° C., Thereafter, re-longitudinal stretching is performed at a draw ratio of preferably 1.1 times or more, more preferably 1.1 to 3.0 times in the flow direction.
- a nonaqueous electrolyte battery (lithium ion battery) containing the polyolefin resin porous film of the present invention as a separator for a nonaqueous electrolyte secondary battery
- 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 battery separator 10 has a thickness of 5 to 40 ⁇ m, particularly preferably 5 to 30 ⁇ m. When the thickness is 5 ⁇ m or more, the battery separator is difficult to break, and when the thickness is 40 ⁇ m or less, the battery area can be increased when wound in a predetermined battery can and thus the battery capacity is increased. Can do.
- the wound body integrally wound with the positive electrode plate 21, the battery separator 10 and the negative electrode plate 22 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 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 size of 10 ⁇ m is mixed with a solution in which vinylidene fluoride is dissolved in N-methylpyrrolidone to form a slurry, and this negative electrode mixture slurry is passed through a 70-mesh net. After removing the large particles, uniformly apply to both sides of a 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, and strip-shaped negative electrode plate What is used.
- 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.
- the 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 and dried. After compression molding, it is cut into a strip-like positive electrode plate.
- ⁇ crystal activity was evaluated as follows. (6) Differential scanning calorimetry (DSC) The polyolefin resin 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 Perkin Elmer, and then held for 240 minutes. The temperature was lowered from 0 ° C. to 25 ° C. at a scanning rate of 10 ° C./min and held for 1 minute, and then heated again from 25 ° C. to 240 ° C. at a scanning rate of 10 ° C./min.
- DSC-7 differential scanning calorimeter
- 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
- ⁇ When Tm ⁇ is detected within the range of 145 ° C to 160 ° C (with ⁇ crystal activity)
- ⁇ When Tm ⁇ was not detected within the range of 145 ° C. to 160 ° C. (no ⁇ crystal activity) Note that the ⁇ crystal activity was measured with a sample amount of 10 mg in a nitrogen atmosphere.
- XRD Wide angle X-ray diffraction measurement
- a polyolefin-based resin porous film was cut into a 60 mm length and a 60 mm square, and an aluminum plate (material: JIS A5052, size: It was sandwiched between two sheets (length 60 mm, width 60 mm, thickness 1 mm), and the periphery was fixed with clips as shown in FIG.
- a sample in which the polyolefin resin porous film was constrained to two aluminum plates was placed in a constant temperature oven (Yamato Scientific Co., Ltd., model: DKN602) having a set temperature of 180 ° C. and a display temperature of 180 ° C. and held for 3 minutes.
- the set temperature was changed to 100 ° C., and gradually cooled to 100 ° C. over 10 minutes or more.
- the display temperature reached 100 ° C.
- the sample was taken out and cooled in an atmosphere of 25 ° C. for 5 minutes while being restrained by two aluminum plates.
- a wide-angle X-ray diffraction measurement was performed on a circular portion of 40 mm ⁇ .
- -Wide-angle X-ray diffraction measurement device manufactured by Mac Science, 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
- ⁇ -crystal of polypropylene resin 300
- the presence or absence of ⁇ crystal activity was evaluated from the peak derived from the surface as follows.
- a sample may be prepared by adjusting the porous film to be installed in a circular hole of 40 mm ⁇ in the center.
- the molten resin sheet extruded from a T-die is shown in Table 1.
- the film was taken up with a cast roll at a temperature and cooled and solidified to obtain a film-like product having a width of 300 mm and a thickness of 80 ⁇ m. At this time, the contact time between the molten resin sheet and the cast roll was 15 seconds.
- the obtained film-like material was stretched in the machine direction between rolls at the stretching temperature and the stretching ratio shown in Table 1 using a roll longitudinal stretching machine.
- the film was stretched in the transverse direction at the stretching temperature and stretch ratio shown in Table 1, and then sufficiently heat-set, and then in the transverse direction as shown in Table 1.
- Thermal relaxation was performed at the relaxation temperature and relaxation rate to obtain a porous film.
- the obtained porous film was stretched in the longitudinal direction at a stretching temperature and a stretching ratio between rolls using a roll longitudinal stretching machine, and then heated in a longitudinal direction of 3% at 120 ° C. with a heat treatment roll. Relaxing was performed to obtain the final porous film.
- the obtained physical properties are shown in Table 1.
- the polyolefin-based resin porous film subjected to re-longitudinal stretching as in Examples 1 to 3 has a 1% modulus in the flow direction at 90 ° C. of 4.5 MPa or more, and a shrinkage stress in the flow direction at 90 ° C. of 1.5 MPa or more. Therefore, it became the polyolefin resin porous film which was excellent in the conveyance property, ie, the wrinkle expression in the drying process of a coat layer.
- the polyolefin resin porous film subjected to re-longitudinal stretching as in Comparative Example 1 does not satisfy the specified range of 1% modulus in the flow direction at 90 ° C. and the shrinkage stress in the flow direction at 90 ° C. Insufficient transportability, that is, a polyolefin-based resin porous film in which wrinkles are easily expressed in the coating layer drying process.
- the porous film of the present invention has excellent air permeability and elastic modulus, it can be used as a porous film in various fields.
- Nonaqueous Electrolyte Secondary Battery Separator 20
- Nonaqueous Electrolyte Secondary Battery 21
- Positive Electrode Plate 22
- Negative Electrode Plate 31
- Aluminum Plate 32
- Porous Film 33 Clip 34 Film Vertical Direction 35 Film Horizontal Direction
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Abstract
Description
また、特許文献4では、常温での弾性率(剛性)を改善しているが、高温雰囲気下では樹脂が軟質化するために弾性率が低下し、前記特許文献3と同様に搬送工程でシワがよりやすく、コーティング層を設ける場合およびロールに巻き取る工程で問題が生じる。かつ、横延伸倍率を低減させるため、空孔率を高めることが困難となり、得られる多孔性フィルムの透過特性が低下し、十分な電池性能を発現し難い問題もある。
具体的には、流れ方向(縦方向)に延伸温度が20~130℃で、延伸倍率が3.0~8.0倍で縦延伸を行い、
ついで、流れ方向に対して垂直方向(横方向)に延伸温度が100~160℃、延伸倍率が1.1~6.0倍で横延伸を行い、
ついで、流れ方向に対して垂直方向(横方向)に130℃以上で1~20%の弛緩処理を行い、
その後、流れ方向(縦方向)に延伸倍率が1.1倍以上で再縦延伸を行うことが好ましい。
さらに、透気度が800秒/100ml以下としているため、透過特性が低下せず、十分な電池性能を発現できる。
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。
また、膜状物及び多孔性フィルムの流れ方向を「縦方向」、流れ方向に対して垂直方向を「横方向」、流れ方向への延伸を「縦延伸」、流れ方向に対して垂直方向への延伸を「横延伸」と称することもある。
ポリオレフィン系樹脂として、具体的にはポリエチレン系樹脂、ポリプロピレン系樹脂などが挙げられる。中でも、ポリプロピ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、多孔性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(Macromolecules 8,687,(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、その後延伸を施すことで微細孔が形成されるため、透気特性を有する多孔性フィルムを得ることができる。
前記の「β晶活性」の有無は、後述する示差走査型熱量計によりβ晶に由来する結晶融解ピーク温度が検出された場合か、及び/又は後述するX線解析装置を用いた測定により、β晶に由来する回析ピークが検出された場合、「β晶活性」を有すると判断している。
具体的には、示差走査型熱量計(DSC)で多孔性フィルムを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。
β晶活性度の上限値は特に限定されないが、β晶活性度が高いほど前記効果がより有効に得られるので100%に近いほど好ましい。
詳細には、ポリプロピレン系樹脂(ホモプロピレン)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・成長させた多孔性フィルムについて広角X線回折測定を行い、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線回折測定に関する詳細は、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線回折測定を用いた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。
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樹脂層以外に、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、生産性および多孔性フィルムの諸物性を改良・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。
本発明において、多孔性フィルムは、単層でも積層でも構わない。多孔性フィルムの層構成は、ポリオレフィ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、多孔性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。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)などを積層させた構成が挙げられる。例えば、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化で孔閉塞し、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。
本発明では、ポリオレフィン系樹脂多孔性フィルムの少なくとも片面にコーティング層(以下、コート層と略称する)を積層させても良い。該コート層はフィラーと樹脂バインダーとが含まれている耐熱層とすることが好ましい。
なお、本発明のポリオレフィン系樹脂多孔性フィルムは前記耐熱層をコーティングして設けない場合も含まれる。
本発明に用いることができるフィラーとして、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。
なお、本実施の形態において「フィラーの平均粒径」とは、SEMを用いる方法に準じて測定される値である。
本発明のコート層として用いることができる樹脂バインダーとして、前記フィラー、および前記ポリオレフィン系樹脂多孔性フィルムを良好に接着でき、電気化学的に安定で、かつ積層多孔性フィルムを非水電解液二次電池として使用する場合には、非水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。これらの有機バインダーは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く、耐熱性と延伸性の観点からポリビニルアルコールがより好ましい。
前記コート層について、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、前記ポリオレフィン系樹脂多孔性フィルムの少なくとも片面に塗布することによって、ポリオレフィン系樹脂多孔性フィルム表面にコート層を形成して製造することができる。
本発明のポリオレフィン系樹脂多孔性フィルムにおいては、90℃における流れ方向、つまり縦方向の1%モジュラスが4.5MPa以上であることが重要である。さらに、5.5MPa以上が好ましく、6.0MPa以上がより好ましく、7.0MPa以上が特に好ましい。
通常では、樹脂の剛性によって、ポリオレフィン系樹脂多孔性フィルムは搬送による張力に対する拮抗力を持っており、伸び難いものである。しかし、コート層の乾燥工程において、乾燥時間、材料にもよるが、分散液に水系溶媒を用いる場合、乾燥温度は有機溶剤に比べて高く、多孔性フィルムの剛性の観点からは非常に厳しい状態に晒されることになる。よって、高温環境下では、ポリオレフィン系樹脂が軟化して拮抗力が低下する。多孔性フィルムの剛性が搬送による張力に負けて伸ばされるとき、多孔性フィルムの流れ方向に対して垂直方向、つまり横方向に縮みが発生する。この際、横方向の収縮率が大きいとシワが発現する。その結果、縦方向と平行にシワが多数発生するために、コーティング不良となる。この場合、コート層の厚さは不均一となり、耐熱性は低下するために好ましくない。
90℃における流れ方向の1%モジュラスを4.5MPa以上にする手段としては、後述するように縦延伸の延伸倍率または再縦延伸の延伸倍率を高くしたり、横延伸の延伸倍率を低くしたりすることで達成できる。
更に、前記収縮応力が1.5MPa以上あることで、高温環境下での多孔性フィルムの弾性率が低下しても、収縮応力によって多孔性フィルムが伸びにくくなるため好ましい。 90℃における流れ方向の収縮応力は高ければ高いほうが望ましいが、上限として10MPa以下が好ましい。前記収縮応力が10MPa以下であることによって、常温における流れ方向の収縮も十分に抑制できる点で好ましい。90℃における流れ方向の収縮応力を向上させる手段としては、縦延伸の延伸倍率または再縦延伸の延伸倍率を高くしたり、横延伸の延伸倍率を低くしたりすることで達成できる。
透気度は多孔性フィルムの厚さ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秒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多孔性フィルムの厚さ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当該フィルムの厚さ方向の連通性が悪いことを意味する。連通性とは多孔性フィルムの厚さ方向の孔のつながり度合いである。本発明のポリオレフィン系樹脂多孔性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。例えば非水電解質二次電池用セパレータとして使用した場合、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。透気度が800秒/100ml以下であれば、前記多孔性フィルムに連通性があることを示し、優れた透気特性を示唆している。透気特性を向上させる手段としては、横延伸の延伸倍率を大きくしたり、再縦延伸の延伸倍率を低くしたりすることで達成できる。
次に、本発明のポリオレフィン系樹脂多孔性フィルムの製造方法について説明する。
なお、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性フィルムのみに限定されるものではない。
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、あるいは二軸以上の延伸を行う。
まずポリオレフィン系樹脂と、必要であれば熱可塑性樹脂、添加剤を含有する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、および所望により添加物等を、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、最終的に必要な多孔性フィルムの厚さ、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。規定した温度範囲にすることによって、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。また、β晶活性を有する膜状物において、β晶の比率を十分に増加させることができ、十分な空孔率を得ることができるために好ましい。
延伸前の膜状物のβ晶比率は、示差走査型熱量計を用いて、当該膜状物を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
通常、逐次二軸延伸を行う場合、最初の縦延伸により縦方向に分子が配向し、縦方向の弾性率が向上するが、その後の横延伸で縦方向の分子配向は低減する。逐次二軸延伸の後、再縦延伸を行うことで縦方向への分子配向は再度向上し、弾性率を向上させるとともに、高温環境下で収縮応力を発現させることができる。その結果、コート層の乾燥工程で搬送による張力に対する拮抗力が得られので、多孔性フィルムの変形、シワの発現を抑制させることができ、コーティング不良は低減される。
また、最初の縦延伸の延伸倍率は3.0~8.0倍が好ましく、4.0~7.0倍より好ましい。前記縦延伸の延伸倍率が3.0倍以上とすることによって、十分な空孔起点を形成することができるとともに、縦方向の分子配向が増すため、縦方向の弾性率を向上させることができる。また前記縦延伸の延伸倍率が8.0倍以下とすることで、延伸時の破断頻度を低減させることができる。なお、空孔起点の形成と熱的安定性の観点から、前記縦延伸の延伸倍率は5.0~6.0倍であることが更に好ましい。
また、横延伸の延伸倍率は好ましくは1.1~6.0倍、より好ましくは1.1~4.0倍、更に好ましくは1.1~2.0倍である。横延伸の延伸倍率を1.1倍以上にすることで、縦延伸により形成された空孔起点を適度なサイズに拡大させ、緻密な多孔構造を有する二軸延伸フィルムを得ることができる。横延伸倍率を6.0倍以下とすることで、延伸時の破断頻度を低減させることができる。この際、横延伸倍率が低くすることで、縦延伸にて生じた分子配向を維持しつつ適度な空孔拡大が行われるため、透過特性に優れたセパレータを得ることができる。
再縦延伸の延伸温度について、下限としては80℃以上が好ましく、90℃以上がより好ましく、100℃以上が更に好ましい。一方、上限としては160℃以下が好ましく、150℃以下がより好ましく、140℃以下が更に好ましい。再縦延伸の延伸温度が前記範囲であれば、延伸時の破断がポリプロピレン系樹脂の軟質化によって抑制され、また高温環境下において十分な収縮応力が得られるため、所望の多孔性フィルムを得ることができる。
また、再縦延伸の延伸倍率について、下限として1.1倍以上が好ましく、1.2倍以上がより好ましい。一方、上限としては3.0倍が好ましく、2.5倍以下がより好ましく、2.0倍以下が更に好ましい。再縦延伸の延伸倍率を1.1倍以上とすることによって、高温環境下において十分な収縮応力を有する多孔性フィルムを得ることができる。また、再縦延伸の延伸倍率を3.0倍以下とすることによって、延伸時における破断を抑制させることができる。
一方、熱処理温度の上限として、160℃以下が好ましく、155℃以下がより好ましい。熱処理温度が160℃以下であることによって、ポリプロピレン系樹脂の必要以上の融解・軟質化が起こらず、多孔性フィルムの多孔構造が維持できるため好ましい。
熱処理において、必要に応じて1~20%の弛緩処理を施しても良いし、拘束状態で熱処理を行い結晶化促進させた後に、弛緩処理を施しても良い。熱処理後、均一に徐冷していくことで本発明の多孔性フィルムが得られる。
流れ方向(縦方向)に延伸温度が好ましくは20~130℃、より好ましくは60℃~110℃、更に好ましくは100~110℃で、延伸倍率が好ましくは3.0~8.0倍、より好ましくは4.0~7.0倍、更に好ましくは4.5~6.0倍で縦延伸を行い、
ついで、流れ方向に対して垂直方向(横方向)に延伸温度が好ましくは100~160℃、より好ましくは110~150℃で、延伸倍率が好ましくは1.1~6.0倍、より好ましくは1.1~4.0倍で横延伸を行い、
ついで、流れ方向に対して垂直方向(横方向)に好ましくは130℃以上で1~20%、より好ましくは135~160℃で3~12%の弛緩処理を行い、
その後、流れ方向に延伸倍率が好ましくは1.1倍以上、より好ましくは1.1~3.0倍で再縦延伸を行う。
次に、本発明のポリオレフィン系樹脂多孔性フィルムを非水電解液二次電池用セパレータとして収容している非水電解液電池(リチウムイオン電池)について、図1を参照して説明する。
正極板21、負極板22の両極は前記電池用セパレータ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。この渦巻き状に巻回する際、電池用セパレータ10は厚さが5~40μmであることがなかでも好ましく、5~30μmであることが特に好ましい。厚さを5μm以上とすることにより電池用セパレータが破れにくくなり、40μm以下にすることにより所定の電池缶に捲回して収納する際電池面積を大きくとることができ、ひいては電池容量を大きくすることができる。
なかでも、エチレンカーボネート1質量部に対してメチルエチルカーボネートを2質量部混合した溶媒中に六フッ化リン酸リチウム(LiPF6)を1.0mol/Lの割合で溶解した電解質が好ましい。
負極に炭素材料を用いる場合、炭素材料としてはリチウムイオンをドープ、脱ドープできるものであればよく、例えば黒鉛、熱分解炭素類、コークス類、ガラス状炭素類、有機高分子化合物の焼成体、メソカーボンマイクロビーズ、炭素繊維、活性炭などを用いることができる。
得られたポリオレフィン系樹脂多孔性フィルムは、以下のようにして各種特性の測定および評価を行い、その結果を表1にまとめた。
1/1000mmのダイアルゲージにて、面内を不特定に10箇所測定し、その平均を厚さとした。
JIS P8117に準拠して、20℃環境下で透気度(秒/100ml)を測定した。
JIS K7127に準じて、90℃における流れ方向の1%伸張時の張力の測定を行い、以下の式に基づいて90℃における流れ方向の1%モジュラスを算出した。また、下記の基準で評価した結果も併記した。
(1%モジュラス)=(1%伸長時の張力)/(伸張前のフィルム断面積)
○:90℃における流れ方向のモジュラスが4.5MPa以上
×:90℃における流れ方向のモジュラスが4.5MPa未満
熱応力歪測定装置(TMA/SS150、セイコー電子工業株式会社製)により測定を行い、90℃における流れ方向の収縮応力を得た。測定条件はサンプル幅3mm、チャック間隔5mm、昇温スピード3℃/分、荷重9.8kN/m2で行った。また、下記の基準で評価した結果も併記した。
○:90℃における流れ方向の収縮応力が1.5MPa以上
×:90℃における流れ方向の収縮応力が1.5MPa未満
得られたポリオレフィン系樹脂多孔性フィルムのフィルムロールをスリット設備にて幅200mmにスリットし、巻取張力は10Nで、1000m長のスリットロールを得た。得られたスリットロールをコーター設備にて、10分間搬送させて、出口のシワの状態を確認して、下記の基準で評価した。なお、搬送条件として、オーブン温度は90℃、オーブン内搬送張力は30N、走行速度は40m/分であった。
○:シワが発現しなかったもの
×:シワが発現したもの
(6)示差走査型熱量測定(DSC)
ポリオレフィン系樹脂多孔性フィルムをパーキンエルマー社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。
サンプルとして、ポリオレフィン系樹脂多孔性フィルムを縦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。
ポリオレフィン系樹脂多孔性フィルムをアルミ板2枚に拘束した状態のサンプルを設定温度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℃になった時点でサンプルを取り出し、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前記フィルムについて、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:マックサイエンス社製、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°/分
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、前記フィルム片が縦60mm、横60mm角に切り出せない場合は、中央部に40mmφの円状の穴に前記多孔性フィルムが設置されるように調整し、サンプルを作成しても構わない。
ポリプロピレン系樹脂としてプライムPP F300SV(プライムポリマー社製、MFR:3.0g/10分)を100質量部に対して、β晶核剤として3,9-ビス[4-(N-シクロヘキシルカルバモイル)フェニル]-2,4,8,10-テトラオキサスピロ[5.5]ウンデカンを0.1質量部添加した後、2軸押出機(東芝機械株式会社製、口径:40mmφ、L/D=32)に投入し、設定温度270℃で溶融混合後、24℃の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てペレットを作製した。
次いで、単軸押出機(三菱重工株式会社製、口径:40mmφ、L/D=32)を用いて、設定温度200℃で溶融混合した後、Tダイより押出した溶融樹脂シートを表1記載の温度のキャストロールで引き取り、冷却固化させて、幅300mm、厚さ80μmの膜状物を得た。この際、溶融樹脂シートとキャストロールの接触時間は15秒であった。
得られた膜状物は、ロール縦延伸機を用い、ロール間で表1に記載の延伸温度および延伸倍率で縦方向に延伸を行った。次いでフィルムテンター設備(京都機械社製)にて、表1に記載の延伸温度および延伸倍率で横方向に延伸を行った後、熱固定を十分に施した後、横方向に表1に記載の弛緩温度および弛緩率で熱弛緩を行い、多孔性フィルムを得た。
次いで、得られた多孔性フィルムは、ロール縦延伸機を用い、ロール間で延伸温度、延伸倍率で縦方向に延伸を行った後、熱処理ロールにて120℃にて3%の縦方向に熱弛緩を行い、最終的な多孔性フィルムを得た。得られた物性を表1に示す。
一方、比較例1のように再縦延伸を行ったポリオレフィン系樹脂多孔性フィルムは、90℃における流れ方向の1%モジュラス、90℃における流れ方向の収縮応力が規定された範囲を満たさないため、不十分な搬送性、すなわちコート層の乾燥工程においてシワが発現しやすいポリオレフィン系樹脂多孔性フィルムとなった。
20 非水電解液二次電池
21 正極板
22 負極板
31 アルミ板
32 多孔性フィルム
33 クリップ
34 フィルム縦方向
35 フィルム横方向
Claims (9)
- 90℃における流れ方向の1%モジュラスが4.5MPa以上であり、かつ、透気度が800秒/100ml以下であることを特徴とするポリオレフィン系樹脂多孔性フィルム。
- 90℃における流れ方向の収縮応力が1.5MPa以上である請求項1に記載のポリオレフィン系樹脂多孔性フィルム。
- 前記ポリオレフィン系樹脂について、ポリプロピレン系樹脂が主成分である請求項1または請求項2に記載のポリオレフィン系樹脂多孔性フィルム。
- β晶活性を有する請求項1乃至請求項3のいずれか1項に記載のポリオレフィン系樹脂多孔性フィルム。
- 二軸延伸の後に流れ方向に延伸する請求項1乃至請求項4のいずれか1項に記載のポリオレフィン系樹脂多孔性フィルム。
- 少なくとも片面にコート層を積層させる請求項1乃至請求項5のいずれか1項に記載のポリオレフィン系樹脂多孔性フィルム。
- 請求項1乃至請求項6のいずれか1項に記載のポリオレフィン系樹脂多孔性フィルムからなる非水電解質二次電池用セパレータ。
- 請求項7に記載の非水電解質二次電池用セパレータを有する非水電解質二次電池。
- 請求項5に記載のポリオレフィン系樹脂多孔性フィルムの形成方法であって、
前記二軸延伸は、
流れ方向(縦方向)に延伸温度が20~130℃で、延伸倍率が3.0~8.0倍で縦延伸を行い、ついで、流れ方向に対して垂直方向(横方向)に延伸温度が100~160℃、延伸倍率が1.1~6.0倍で横延伸を行い、
ついで、流れ方向に対して垂直方向(横方向)に130℃以上で1~20%の弛緩処理を行い、
その後、流れ方向(縦方向)に延伸倍率が1.1倍以上で再縦延伸を行うポリオレフィン系樹脂多孔性フィルムの形成方法。
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- 2013-06-05 KR KR1020147034056A patent/KR102089256B1/ko active IP Right Grant
- 2013-06-05 WO PCT/JP2013/065573 patent/WO2013183666A1/ja active Application Filing
- 2013-06-05 JP JP2014520026A patent/JP6222087B2/ja active Active
- 2013-06-05 US US14/406,011 patent/US20150125734A1/en not_active Abandoned
- 2013-06-05 EP EP13801339.6A patent/EP2860216A4/en not_active Withdrawn
- 2013-06-05 CN CN201380029263.9A patent/CN104334619B/zh active Active
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WO2014103713A1 (ja) * | 2012-12-26 | 2014-07-03 | 東レ株式会社 | 多孔性ポリオレフィンフィルムおよびその製造方法、ならびにそれを用いてなる蓄電デバイス用セパレータ |
JP2018159080A (ja) * | 2013-06-21 | 2018-10-11 | 住友化学株式会社 | 積層多孔質フィルムの製造方法 |
WO2016157656A1 (ja) * | 2015-03-31 | 2016-10-06 | 帝人株式会社 | 複合膜の製造方法 |
JPWO2016157656A1 (ja) * | 2015-03-31 | 2017-04-27 | 帝人株式会社 | 複合膜の製造方法 |
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WO2020129411A1 (ja) | 2018-12-18 | 2020-06-25 | 日本碍子株式会社 | リチウム二次電池 |
CN112542653A (zh) * | 2019-09-05 | 2021-03-23 | 深圳市拓邦锂电池有限公司 | 锂电池的抗褶皱隔膜及其制备方法 |
Also Published As
Publication number | Publication date |
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KR20150020548A (ko) | 2015-02-26 |
CN104334619B (zh) | 2018-07-10 |
JPWO2013183666A1 (ja) | 2016-02-01 |
EP2860216A4 (en) | 2015-11-25 |
EP2860216A1 (en) | 2015-04-15 |
KR102089256B1 (ko) | 2020-03-16 |
US20150125734A1 (en) | 2015-05-07 |
CN104334619A (zh) | 2015-02-04 |
JP6222087B2 (ja) | 2017-11-01 |
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