WO2016104792A1 - ポリオレフィン微多孔膜、その製造方法および電池用セパレータ - Google Patents
ポリオレフィン微多孔膜、その製造方法および電池用セパレータ Download PDFInfo
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- WO2016104792A1 WO2016104792A1 PCT/JP2015/086418 JP2015086418W WO2016104792A1 WO 2016104792 A1 WO2016104792 A1 WO 2016104792A1 JP 2015086418 W JP2015086418 W JP 2015086418W WO 2016104792 A1 WO2016104792 A1 WO 2016104792A1
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- Prior art keywords
- microporous membrane
- polyolefin microporous
- polyolefin
- film
- resin
- Prior art date
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Classifications
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- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
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- C08J5/18—Manufacture of films or sheets
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01D71/06—Organic material
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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
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F10/00—Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F10/04—Monomers containing three or four carbon atoms
- C08F10/06—Propene
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- C—CHEMISTRY; METALLURGY
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- 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
- C08J9/28—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
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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
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- 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
-
- 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
- B29K2105/041—Microporous
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F2500/00—Characteristics or properties of obtained polyolefins; Use thereof
- C08F2500/12—Melt flow index or melt flow ratio
-
- 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
- C08J2201/00—Foams characterised by the foaming process
- C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
- C08J2201/054—Precipitating the polymer by adding a non-solvent or a different solvent
- C08J2201/0542—Precipitating the polymer by adding a non-solvent or a different solvent from an organic solvent-based polymer composition
- C08J2201/0543—Precipitating the polymer by adding a non-solvent or a different solvent from an organic solvent-based polymer composition the non-solvent being organic
-
- 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
-
- 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
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- 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
-
- 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 microporous membrane, a method for producing the same, and a battery separator, and more specifically, a polyolefin microporous film that is excellent in mechanical strength such as oxidation resistance, meltdown temperature, and toughness, and can be suitably used for a battery separator.
- the present invention relates to a membrane, a manufacturing method thereof, and a battery separator.
- JP-A-5-222237 discloses a gel composition by cooling a nucleating agent, a mixed solvent of a good solvent for polyolefin and a solvent excellent in dispersibility of the nucleating agent, and a polyolefin solution obtained by melting and mixing the polyolefin.
- a polyolefin microporous membrane produced by forming a product, heating and stretching the gel composition, and then removing the remaining solvent is described. Since such a polyolefin microporous membrane uses a mixed solvent, the solvent is not uniformly dispersed in the polyolefin solution, and the maximum pore size and average flow pore size of the resulting polyolefin microporous membrane due to the porometer increase. The air resistance is also very low. For this reason, when using it as a separator film of a battery, further improvement was required in withstand voltage characteristics and mechanical strength.
- JP 2010-215901 A and JP-T 2009-527633 A disclose a polypropylene porous film produced by a production method known as a dry method. Specifically, it is a method of forming a void by adopting a low-temperature extrusion and a high draft ratio at the time of melt extrusion, controlling a lamella structure in a film before stretching and stretching it.
- a production method known as a dry method.
- the pore structure tends to be non-uniform, and there is a concern that a structure containing voids locally occurs.
- the pore diameter on the surface of the microporous membrane increases and the distribution thereof becomes non-uniform, resulting in poor withstand voltage characteristics, extremely low mechanical strength of the microporous membrane in a specific direction, and poor toughness. There was a problem such as.
- JP-A No. 2014-141644 describes a biaxially oriented porous polypropylene film having a ratio of tensile strength between MD direction and TD direction of 0.9 or more and less than 1.5.
- the polypropylene film is produced by a dry method, the air resistance is low, and further improvement in tensile elongation and toughness is required.
- JP-A-6-223802 describes a microporous membrane formed from a mixture of high molecular weight polyethylene and high molecular weight polypropylene. However, since such a microporous membrane is mostly composed of polyethylene, further improvement in oxidation resistance is required.
- An object of the present invention is to provide a polyolefin microporous membrane mainly composed of polypropylene having excellent oxidation resistance and toughness, and a battery separator.
- 1st aspect of this invention consists of polyolefin resin which contains 90 mass% or more of polypropylene resins, MD direction tensile strength is 25 Mpa or more, TD direction tensile strength is 25 Mpa or more, MD direction and TD direction Tensile strength ratio (MD / TD) is 0.4 or more and 2.0 or less, MD direction tensile elongation is 80% or more, and MD direction and TD direction tensile elongation ratio (MD / TD) is A polyolefin microporous film characterized by being from 0.6 to 1.7.
- the polyolefin microporous membrane preferably has a meltdown temperature of 160 ° C. or higher, and preferably has a gas permeability resistance of 300 sec / 100 cc or higher when the film thickness is 20 ⁇ m, and has an average flow pore diameter of 25 by a porometer. It is preferably 0.0 nm or less.
- the film thickness of the polyolefin microporous membrane is preferably 1 ⁇ m or more and 12 ⁇ m or less.
- the weight average molecular weight of the polypropylene resin is preferably 1 ⁇ 10 5 or more and 1 ⁇ 10 8 or less.
- the second aspect of the present invention is a battery separator comprising the polyolefin microporous membrane
- the third aspect of the present invention is a secondary battery using the separator.
- a fourth aspect of the present invention includes the following steps (1) to (5), wherein the MD direction tensile strength is 25 MPa or more, the TD direction tensile strength is 25 MPa or more, and the MD direction:
- the ratio of the tensile strength in the TD direction (MD / TD) is 0.4 or more and 2.0 or less, the MD direction tensile elongation is 80% or more, and the ratio of the MD and TD direction tensile elongation (MD / This is a method for producing a polyolefin microporous membrane having a (TD) of 0.6 or more and 1.7 or less.
- the polyolefin microporous membrane of the present invention is mainly composed of polypropylene, and has low mechanical strength such as oxidation resistance, meltdown temperature and toughness because of its small anisotropy in tensile properties in the MD and TD directions. .
- the method for producing a microporous polyolefin membrane of the present invention can efficiently produce a microporous polyolefin membrane having mechanical strength such as excellent oxidation resistance, meltdown temperature and toughness.
- the battery separator of the present invention comprises a polyolefin microporous film having excellent mechanical properties such as oxidation resistance, meltdown temperature and toughness, so that when used in a battery such as a lithium ion secondary battery, It can be expected to provide a longer life, improved charge / discharge cycle characteristics and improved safety.
- polyolefin microporous membrane of the present invention comprises a polyolefin resin.
- the present invention will be described for each item.
- Polyolefin resin has a polypropylene resin as a main component.
- the content of the polypropylene resin in the polyolefin resin is preferably 90% by mass or more, more preferably 95% by mass or more, and most preferably 100% by mass.
- the content of the polypropylene resin in the polyolefin resin is less than the above range, the oxidation resistance of the polyolefin microporous membrane of the present invention is deteriorated.
- the polypropylene resin preferably has a weight average molecular weight of 1 ⁇ 10 5 or more and 1 ⁇ 10 8 or less, and more preferably 1 ⁇ 10 6 or more and 1 ⁇ 10 8 or less.
- the molecular weight distribution of the polypropylene resin is preferably about 5 or more and 10 or less.
- the melting point of the polypropylene resin is not particularly limited, but is preferably 180 ° C. or lower.
- the polypropylene resin may be a copolymer with another olefin, but is preferably a homopolymer.
- Examples of the copolymer of polypropylene and other olefins include a propylene-ethylene copolymer, a propylene-butene copolymer, and a propylene-hexene copolymer.
- polyolefin resin other than polypropylene may contain a small amount of polyolefin other than polypropylene, such as polyethylene and polybutene, as the polyolefin resin.
- polystyrene resin examples include polyethylene, polypropylene, polyethylene, polyethylene, polypropylene, polyethylene, polyethylene, polypropylene, polyethylene, polyethylene, polypropylene, polyethylene, polypropylene, polyethylene, polypropylene, polyethylene, polypropylene, polyethylene, polypropylene, polyethylene, polypropylene, polyethylene, polypropylene, polyethylene, polypropylene, polyethylene, polypropylene, polystyrene-1, polystyrene-1, polystylene waxes having Mw of 1 ⁇ 10 3 to 1 ⁇ 10 4 may be used.
- the content of the polyolefin other than the polypropylene resin in the polyolefin resin can be appropriately adjusted within a range not impairing the effects of the present invention, but is preferably 10% by mass or less, more preferably 5% by mass or less in the polyolefin resin. More preferred is mass%.
- the said polyolefin resin can contain other resin components other than the said polyolefin resin as needed.
- the other resin component is preferably a heat-resistant resin, and examples of the heat-resistant resin include crystalline resins having a melting point of 150 ° C. or higher (including partially crystalline resins) and / or glass.
- An amorphous resin having a point transfer (Tg) of 150 ° C. or higher is exemplified.
- Tg is a value measured according to JIS K7121.
- resin components include polyester, polymethylpentene [PMP or TPX (transparent polymer X), melting point: 230 to 245 ° C.], polyamide (PA, melting point: 215 to 265 ° C.), polyarylene sulfide ( Fluorine-containing resin such as PAS, polyvinylidene fluoride homopolymers such as polyvinylidene fluoride (PVDF), fluorinated olefins such as polytetrafluoroethylene (PTFE), and copolymers thereof; polystyrene (PS, melting point: 230 ° C.) ), Polyvinyl alcohol (PVA, melting point: 220-240 ° C.), polyimide (PI, Tg: 280 ° C.
- the resin component is not limited to one composed of a single resin component, and may be composed of a plurality of resin components.
- the preferred Mw of other resin components varies depending on the type of resin, but is generally 1 ⁇ 10 3 to 1 ⁇ 10 6 , more preferably 1 ⁇ 10 4 to 7 ⁇ 10 5 .
- the content of other resin components in the polyolefin resin is appropriately adjusted within a range not departing from the gist of the present invention, but is contained in the polyolefin resin in a range of 20% by mass or less, preferably 5 It is less than mass%, more preferably 0 mass%.
- Crystallization control agent is an additive that promotes or suppresses crystallization of polyolefin resin by blending with polyolefin resin, and includes nucleating agent, clarifying agent, crystallization retarding agent, etc. can give. Of these, nucleating agents and crystallization retarders are preferred. By blending the crystallization control agent, it can be expected that the pore structure of the polyolefin microporous membrane of the present invention becomes uniform and fine.
- nucleating agent As the nucleating agent, a nucleating agent for polypropylene resin can be suitably used, and carboxylic acid metal salts such as aromatic phosphate metal salt nucleating agents and benzoic acid metal salt nucleating agents. Those commonly used as polyolefin resin nucleating agents such as nucleating agents, sorbitol nucleating agents, and mixtures thereof can be used. Among them, from the viewpoint of dispersibility in a polyolefin resin solution described later, a carboxylic acid metal salt system such as an aromatic phosphate metal salt nucleating agent or a benzoic acid metal salt nucleating agent that basically does not contain a hydrosilyl group. A nucleating agent and a mixture thereof are preferred. In addition, as a nucleating agent for polypropylene resins, a commercially available nucleating agent master batch composed of a plurality of components may be used.
- nucleating agent for polypropylene resin examples include an ⁇ crystal nucleating agent, a ⁇ crystal nucleating agent, and a ⁇ crystal nucleating agent, but the ⁇ crystal nucleating agent has a tendency to produce fine crystals. It is preferable that When a ⁇ crystal nucleating agent is used, coarse needle crystals may be formed.
- aromatic phosphate metal salt nucleating agents examples include sodium bis (4-tert-butylphenyl) phosphate, sodium 2,2′-methylenebis (4,6-di-tert-butylphenyl) phosphate, and the like. Can be mentioned.
- carboxylic acid metal salt nucleating agent examples include lithium benzoate, sodium benzoate, aluminum 4-tert-butylbenzoate, and sodium adipate.
- sorbitol nucleating agent examples include dibenzylidene sorbitol, bis (4-methylbenzylidene) sorbitol, bis (3,4-dimethylbenzylidene) sorbitol, and the like.
- the compounding amount of the nucleating agent is generally 0.01 to 5.00 parts by mass, more preferably 0.05 to 3.00 parts by mass with respect to 100 parts by mass of the polyolefin resin, but is not particularly limited. .
- the nucleating agent may be blended directly with the polyolefin resin, or may be blended with the polyolefin resin as a master batch in which the polyolefin resin and the nucleating agent are mixed in advance.
- Crystallization retarder As the crystallization retarder for polyolefin resin, amorphous polyolefin resin, low crystalline polyolefin resin, and the like can be used, and among them, low crystalline polypropylene resin and the like can be suitably used.
- examples of the amorphous polyolefin resin include polystyrene and polycarbonate
- examples of the low crystalline polyolefin resin include random copolymers such as ethylene-propylene and ethylene-butene, and atactic polypropylene. Examples include low stereoregular polyolefins.
- the compounding amount of the crystallization retarder is generally 0.01 to 5.00 parts by mass, more preferably 0.05 to 3.00 parts by mass with respect to 100 parts by mass of the polyolefin resin, but it is particularly limited. Not.
- the polyolefin microporous membrane of the present invention has an MD direction tensile strength of 25 MPa or more, a TD direction tensile strength of 25 MPa or more, and a ratio of the tensile strength in the MD direction to the TD direction of 0. .4 or more and 2.0 or less, MD direction tensile elongation is 80% or more, and the ratio of MD direction and TD direction tensile elongation is 0.6 or more and 1.7 or less.
- MD direction tensile strength of 25 MPa or more
- TD direction tensile strength of 25 MPa or more
- a ratio of the tensile strength in the MD direction to the TD direction of 0. .4 or more and 2.0 or less
- MD direction tensile elongation is 80% or more
- the ratio of MD direction and TD direction tensile elongation is 0.6 or more and 1.7 or less.
- the lower limit of the tensile strength in the MD direction (length direction of the membrane surface, machine direction) of the polyolefin microporous membrane of the present invention is 25 MPa, preferably 40 MPa, more preferably 50 MPa.
- the lower limit of the tensile strength in the TD direction is 25 MPa, preferably 40 MPa, and more preferably 50 MPa.
- the upper limit of the tensile strength in the MD direction and the TD direction of the polyolefin microporous membrane of the present invention is not particularly limited, but is generally preferably 400 MPa, and more preferably 300 MPa.
- the lower limit of the tensile elongation in the MD direction of the polyolefin microporous membrane of the present invention is 80%, preferably 90%, more preferably 100%.
- the lower limit of the tensile elongation in the TD direction of the polyolefin microporous membrane of the present invention is not particularly limited, but is preferably 70%, more preferably 80%.
- the upper limit of the tensile elongation in the MD direction and the TD direction of the polyolefin microporous membrane of the present invention is not particularly limited, but is generally preferably 500%, and more preferably 300%.
- the polyolefin microporous membrane of the present invention When the tensile strength and tensile elongation of the polyolefin microporous membrane of the present invention are within the above range, the polyolefin microporous membrane has excellent mechanical strength and flexibility, and when used as a battery separator, handling work during battery production This is because it is excellent in performance and can be expected to increase the safety and life of the battery.
- (Ii) Ratio of tensile properties in MD direction and TD direction The lower limit of the ratio of MD direction to TD direction (MD / TD) of the tensile strength of the polyolefin microporous membrane of the present invention is 0.4, preferably 0.8. 45, more preferably 0.5, and the upper limit thereof is 2.0, preferably 1.5, and more preferably 1.3.
- the lower limit of the ratio of MD / TD tensile elongation (MD / TD) of the microporous polyolefin membrane of the present invention is 0.6, preferably 0.7, more preferably 0.8.
- the upper limit is 1.7, preferably 1.6, and more preferably 1.5.
- the strength of the polyolefin microporous membrane of the present invention is within the above range, the strength of the polyolefin microporous membrane has no direction dependency. This is because when the film is stressed, it has excellent toughness and does not tear in a specific direction, and even if foreign matter penetrates the microporous film, expansion of the through hole can be avoided.
- the maximum pore diameter of the polyolefin microporous membrane of the present invention is preferably 39.0 nm or less, more preferably 37.0 nm or less.
- the “maximum pore size” indicates the maximum pore size among all the through-holes distributed in the polyolefin microporous membrane, and can be measured by a bubble point method using a porometer.
- the average flow pore size of the polyolefin microporous membrane of the present invention is preferably 25.0 nm or less, more preferably 20.0 nm or less, and further preferably 19 nm or less.
- the lower limit of the average flow hole diameter is not particularly limited, but may be less than the measurement range limit of the porometer.
- the “average flow pore size” indicates the average flow pore size of all through holes distributed in the polyolefin microporous membrane, and can be measured with a porometer.
- the polyolefin microporous membrane of the present invention When used as a separator, it has a uniform and fine pore structure, so it has excellent mechanical strength such as tensile elongation and toughness and withstand voltage performance. ) Is expected to extend the life of the battery.
- a crystallization control agent is blended in a polyolefin resin, and the stretching temperature during film formation ranges from the crystal dispersion temperature (Tcd) of the polyolefin resin to Tcd + 30 ° C.
- Tcd crystal dispersion temperature
- the stretching stress at the time of stretching acts uniformly on the structure constituting the membrane by the above means, and the pore structure of the microporous membrane can be controlled.
- the lower limit of the dielectric breakdown voltage is preferably 0.10 kV / ⁇ m, more preferably 0.14 kV / ⁇ m, and 0.17 kV / ⁇ m. It is particularly preferred.
- the upper limit of the dielectric breakdown voltage is not particularly limited, but is generally preferably kV / ⁇ m. This is because when the dielectric breakdown voltage of the polyolefin microporous membrane is within the above range, the battery can be expected to have good durability and withstand voltage performance when used as a battery separator.
- the dielectric breakdown voltage of the polyolefin microporous membrane of the present invention can be measured in accordance with, for example, a method defined in JIS C2110 or ASTM D149.
- the porosity of the microporous polyolefin membrane of the present invention is preferably 20 to 80%. It is preferable for the porosity to be in the above range since the mechanical strength of the microporous membrane is improved.
- the porosity is more preferably 30 to 65%, and particularly preferably 40 to 45%.
- the lower limit of the air resistance when the film thickness is 20 ⁇ m is preferably 300 sec / 100 cc, and more preferably 400 sec / 100 cc.
- the upper limit of the air permeability resistance is preferably 5000 sec / 100 cc, more preferably 4000 sec / 100 cc, and particularly preferably 3500 sec / 100 cc.
- the oxidation resistance of the polyolefin microporous membrane of the present invention can be evaluated by the degree of blackening of the separator.
- the blackening of the battery separator is considered to be caused by the polyeneization of the polymer due to the radical chain oxidation reaction of the polymer that occurs in parallel with the reduction of cobalt of the positive electrode in the battery. As the blackening progresses, the film strength deteriorates and a short circuit occurs.
- Polyethylene undergoes an oxidation reaction in a chain from the molecular structure, whereas polypropylene has the property of stopping the chain reaction and can be expected to prevent blackening (oxidation) from proceeding.
- the polyolefin microporous film of the present invention has a heat of crystal melting derived from ⁇ crystal of polypropylene resin in a differential thermal analysis using a differential scanning calorimeter. Does not have a peak.
- the “crystal melting heat peak” indicates a curve having a maximum value obtained by a differential scanning calorimeter.
- the maximum pore size and average flow pore size of the polyolefin microporous membrane are coarsened, or the microporous membrane is stretched. This is because the degree may decrease.
- the crystal melting heat peak derived from the ⁇ crystal of the polypropylene resin is observed on the low temperature side of the crystal melting heat peak derived from the ⁇ crystal of the polypropylene resin.
- the crystal melting heat peak derived from the ⁇ crystal of the polypropylene resin is observed on the low temperature side of the crystal melting heat peak derived from the ⁇ crystal of the polypropylene resin.
- a polypropylene homopolymer it is observed at 140 ° C. or more and less than 160 ° C.
- a random propylene ethylene copolymer copolymerized with 1 to 4 mol% of ethylene it is in the range of 120 ° C. or more and less than 140 ° C. Is recognized. A specific measurement method will be described later.
- the film thickness can be up to 12 ⁇ m or less. It has been found that it can be thinned.
- the lower limit of the thickness of the microporous membrane is preferably 1 ⁇ m, more preferably 3 ⁇ m, the upper limit is more preferably 10 ⁇ m, and further preferably 9 ⁇ m. Thinning of the polyolefin microporous membrane of the present invention can be achieved by appropriately adjusting the polyolefin solution preparation conditions, gel sheet formation conditions and stretching conditions described below.
- the lower limit of the meltdown temperature of the polyolefin microporous membrane of the present invention is preferably 160 ° C, more preferably 170 ° C, from the viewpoint of heat resistance.
- the upper limit of the meltdown temperature is not particularly limited, but is generally 190 ° C. in the case of a polyolefin microporous film mainly composed of a polypropylene resin.
- the production method of the polyolefin microporous membrane of the present invention is not particularly limited as long as the polyolefin microporous membrane having the above-described characteristics can be produced, and a conventionally known method can be used.
- a conventionally known method can be used.
- methods described in Japanese Patent No. 2132327, Japanese Patent No. 3347835, International Publication No. 2006/137540, and the like can be used.
- the following steps (1) to (5) are preferably included, the following step (6) may be further included, and the following step (7) may be further included.
- a step of melt-kneading the polyolefin resin, a crystallization control agent and a film-forming solvent to prepare a polyolefin solution (2) A step of extruding the polyolefin solution and cooling to form a gel-like sheet (3) The gel (4) Step of removing the film-forming solvent from the stretched gel-like sheet (5) Step of drying the sheet after removal of the film-forming solvent (6) Drying Second Stretching Step for Stretching Later Sheet (7) Step for Heat-treating Sheet After Drying
- a step of melt-kneading the polyolefin resin, a crystallization control agent and a film-forming solvent to prepare a polyolefin solution
- a step of extruding the polyolefin solution and cooling to form a gel-like sheet (3)
- the gel (4) Step of removing the film-forming solvent from the stretched gel-like sheet (5) Step of drying the sheet after removal of the film-forming solvent (6) Drying Second Stretching Step for Stretching Later Sheet (7)
- melt-kneading After blending a polyolefin resin with a crystallization control agent and a suitable film-forming solvent, melt-kneading to prepare a polyolefin solution.
- a melt-kneading method for example, a method using a twin-screw extruder described in Japanese Patent No. 2132327 and Japanese Patent No. 3347835 can be used. Since the melt-kneading method is known, the description thereof is omitted.
- the blending ratio of the polyolefin resin and the film forming solvent in the polyolefin solution is not particularly limited, but is preferably 50 to 80 parts by weight of the film forming solvent with respect to 20 to 50 parts by weight of the polyolefin resin.
- the film forming solvent is preferably 55 to 70 parts by mass with respect to 45 parts by mass.
- a crystallization control agent such as a nucleating agent or a crystallization retarder is added to the polyolefin solution.
- the blending amount is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 3 parts by mass with respect to 100 parts by mass of the polyolefin resin.
- a polyolefin solution is fed from an extruder to a die and extruded into a sheet.
- a plurality of polyolefin solutions having the same or different compositions may be fed from an extruder to a single die, where they are laminated in layers and extruded into sheets.
- the extrusion method may be either a flat die method or an inflation method, but the flat die method is preferred from the viewpoint of control accuracy such as film thickness and film flatness.
- the extrusion temperature is preferably 140 to 250 ° C., and the extrusion speed is preferably 0.2 to 15 m / min.
- the film thickness can be adjusted by adjusting each extrusion amount of the polyolefin solution.
- a gel-like sheet is formed by cooling the obtained extrusion-molded body.
- a method for forming the gel-like sheet for example, methods disclosed in Japanese Patent No. 2132327 and Japanese Patent No. 3347835 can be used. Cooling is preferably performed at a rate of 50 ° C./min or more at least up to the gelation temperature. Cooling is preferably performed to 25 ° C. or lower. (3) 1st extending
- the gel-like sheet is preferably stretched at a predetermined ratio after heating by a tenter method, a roll method, an inflation method, or a combination thereof.
- the tenter method is preferable from the viewpoint of control accuracy such as film thickness and film flatness.
- the stretching may be uniaxial stretching or biaxial stretching, but biaxial stretching is preferred.
- biaxial stretching any of simultaneous biaxial stretching, sequential stretching and multistage stretching (for example, a combination of simultaneous biaxial stretching and sequential stretching) may be used.
- the stretching ratio (area stretching ratio) in this step is preferably 2 times or more, more preferably 3 to 30 times in the case of uniaxial stretching. In the case of biaxial stretching, 9 times or more is preferable, 16 times or more is more preferable, and 25 times or more is particularly preferable. Further, it is preferably 3 times or more in both the longitudinal direction and the transverse direction (MD and TD directions), and the draw ratios in the MD direction and the TD direction may be the same or different. When the draw ratio is 9 times or more, improvement of puncture strength can be expected.
- the draw ratio in this process means the area draw ratio of the microporous film immediately before being used for the next process on the basis of the microporous film immediately before this process.
- the stretching temperature in this step is preferably in the range of the crystal dispersion temperature (Tcd) to Tcd + 30 ° C. of the polyolefin resin, and in the range of crystal dispersion temperature (Tcd) + 5 ° C. to crystal dispersion temperature (Tcd) + 25 ° C. It is more preferable that the temperature be within the range of Tcd + 10 ° C. to Tcd + 20 ° C.
- the stretching temperature is within the above range, membrane breakage due to stretching of the polyolefin resin is suppressed, stretching at a high magnification can be performed, and the pore structure of the resulting polyolefin microporous membrane is refined and homogenized.
- the crystal dispersion temperature (Tcd) is determined by measuring the dynamic viscoelastic temperature characteristics according to ASTM D4065. Since the polyolefin resin of the present invention has a crystal dispersion temperature of about 110 to 130 ° C., the stretching temperature is preferably 110 to 160 ° C., more preferably 115 to 155 ° C., and further preferably 120 to 150 ° C. It is.
- Fibrils form a very fine network structure that is irregularly connected three-dimensionally.
- the film may be stretched by providing a temperature distribution in the film thickness direction, whereby a microporous film having further excellent mechanical strength can be obtained. Details of the method are described in Japanese Patent No. 3347854.
- the film-forming solvent is removed (washed) using a cleaning solvent. Since the polyolefin phase is phase-separated from the film-forming solvent phase, removing the film-forming solvent consists of fibrils that form a fine three-dimensional network structure, and pores (voids) that communicate irregularly in three dimensions. A porous membrane having the following is obtained. Since the cleaning solvent and the method for removing the film-forming solvent using the same are known, the description thereof is omitted. For example, the methods disclosed in Japanese Patent No. 2132327 and Japanese Patent Application Laid-Open No. 2002-256099 can be used.
- the microporous film from which the film-forming solvent has been removed is dried by a heat drying method or an air drying method.
- the drying temperature is preferably not higher than the crystal dispersion temperature (Tcd) of the polyolefin resin, and particularly preferably 5 ° C. or more lower than Tcd. Drying is preferably performed until the residual cleaning solvent is 5% by mass or less, more preferably 3% by mass or less, with the microporous membrane being 100% by mass (dry weight).
- the dried microporous membrane may be stretched in at least a uniaxial direction.
- the microporous membrane can be stretched by the tenter method or the like in the same manner as described above while heating.
- the stretching may be uniaxial stretching or biaxial stretching. In the case of biaxial stretching, either simultaneous biaxial stretching or sequential stretching may be used.
- the stretching temperature in this step is not particularly limited, but is usually 90 to 150 ° C, more preferably 95 to 145 ° C.
- the lower limit of the stretching ratio (area stretching ratio) in the uniaxial direction of stretching of the microporous membrane in this step is preferably 1.0 or more, more preferably 1.1 or more, and still more preferably 1.2. It is more than double.
- the upper limit is preferably 1.8 times or less. In the case of uniaxial stretching, it is 1.0 to 2.0 times in the MD direction or TD direction.
- the lower limit of the area stretching ratio is preferably 1.0 times or more, more preferably 1.1 times or more, and still more preferably 1.2 times or more.
- the upper limit is preferably 3.5 times or less, and 1.0 to 2.0 times in each of the MD direction and the TD direction, and the draw ratios in the MD direction and the TD direction may be the same or different.
- the draw ratio in this process means the draw ratio of the microporous film just before being provided to the next process on the basis of the microporous film immediately before this process.
- the microporous film after drying can be heat-treated.
- the crystal is stabilized by heat treatment, and the lamella is made uniform.
- heat setting treatment and / or heat relaxation treatment can be used.
- the heat setting treatment is a heat treatment in which heating is performed while keeping the dimensions of the film unchanged.
- the thermal relaxation treatment is a heat treatment that heat-shrinks the film in the MD direction or the TD direction during heating.
- the heat setting treatment is preferably performed by a tenter method or a roll method.
- a thermal relaxation treatment method a method disclosed in Japanese Patent Application Laid-Open No. 2002-256099 can be given.
- the heat treatment temperature is preferably within the range of Tcd to Tm of the polyolefin resin, more preferably within the range of the stretching temperature ⁇ 5 ° C. of the microporous membrane, and particularly preferably within the range of the second stretching temperature ⁇ 3 ° C. of the microporous membrane.
- a porous layer may be provided on at least one surface of the polyolefin microporous membrane to form a laminated porous membrane.
- the porous layer formed using the filler containing resin solution and heat resistant resin solution containing a filler and a resin binder can be mentioned, for example.
- the filler examples include inorganic fillers such as alumina, silica, titania and zirconia; and organic fillers such as fluororesin particles and cross-linked polymer fillers, which have a melting point of 200 ° C. or higher, high electrical insulation, and lithium. Those that are electrochemically stable within the range of use of the ion secondary battery are preferred. These can be used alone or in combination of two or more.
- the average particle diameter of the filler is not particularly limited, but is preferably 0.1 ⁇ m or more and 3.0 ⁇ m or less, for example.
- the proportion (mass fraction) of the filler in the porous layer is preferably 50% or more and 99.99% or less from the viewpoint of heat resistance.
- polyolefins and heat resistant resins described in the section of other resin components contained in the above-described polyolefin resin can be suitably used.
- the proportion of the resin binder in the total amount of the filler and the resin binder is preferably 0.5% or more and 8% or less in terms of volume fraction from the viewpoint of the binding property of both.
- heat resistant resin those similar to the heat resistant resin described in the section of other resin components contained in the polyolefin resin can be suitably used.
- the method for applying the filler-containing resin solution or the heat-resistant resin solution to the surface of the polyolefin microporous membrane is not particularly limited as long as it can achieve the required layer thickness and application area, such as a gravure coater method.
- the solvent for the filler-containing solution and the heat-resistant resin solution is preferably a solvent that can be removed from the solution applied to the polyolefin microporous membrane, and is not particularly limited. Specific examples include N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride and hexane.
- the method for removing the solvent is not particularly limited as long as it does not adversely affect the polyolefin microporous membrane. Specifically, for example, a method of drying a polyolefin microporous film while fixing it at a temperature below its melting point, a method of drying under a reduced pressure, a resin binder and a poor solvent such as a heat-resistant resin, and simultaneously solidifying the resin The method of extracting is mentioned.
- the thickness of the porous layer is preferably from 0.5 ⁇ m to 100 ⁇ m from the viewpoint of improving heat resistance.
- the ratio of the thickness of the porous layer to the thickness of the laminated porous membrane can be appropriately adjusted according to the purpose. Specifically, for example, it is preferably 15% or more and 80% or less, and more preferably 20% or more and 75% or less.
- porous layer may be formed on one surface of the laminated porous film or on both surfaces.
- the polyolefin microporous membrane of the present invention can be suitably used for both a battery using an aqueous electrolyte and a battery using a non-aqueous electrolyte. Specifically, it can be preferably used as a separator for secondary batteries such as nickel-hydrogen batteries, nickel-cadmium batteries, nickel-zinc batteries, silver-zinc batteries, lithium secondary batteries, and lithium polymer secondary batteries. Especially, it is preferable to use as a separator of a lithium ion secondary battery using a non-aqueous electrolyte.
- a positive electrode and a negative electrode are laminated via a separator, and the separator contains an electrolytic solution (electrolyte).
- the structure of the electrode is not particularly limited, and a conventionally known structure can be used.
- an electrode structure coin type in which a disk-shaped positive electrode and a negative electrode are opposed to each other, a plate-shaped positive electrode and a negative electrode
- An electrode structure laminate type in which layers are stacked alternately, an electrode structure in which laminated strip-like positive and negative electrodes are wound (winding type), and the like can be used.
- the current collector, the positive electrode, the positive electrode active material, the negative electrode, the negative electrode active material, and the electrolyte used for the lithium ion secondary battery are not particularly limited, and conventionally known materials can be used in appropriate combination.
- this invention is not limited to said embodiment, It can implement in various deformation
- Porosity (%) (w 2 ⁇ w 1 ) / w 2 ⁇ 100
- Air permeability resistance (sec / 100cc)
- d C ⁇ ⁇ / P (In the above formula, “d ( ⁇ m)” is the pore diameter of the microporous membrane, “ ⁇ (mN / m)” is the surface tension of the liquid, “P (Pa)” is the pressure, and “C” is a constant.
- Weight average molecular weight (Mw) Mw of PP, UHMWPE and HDPE was determined by gel permeation chromatography (GPC) method under the following conditions.
- GPC gel permeation chromatography
- ⁇ Measurement device GPC-150C manufactured by Waters Corporation Column: Shodex UT806M manufactured by Showa Denko KK -Column temperature: 135 ° C
- Injection volume 500 ⁇ l
- Detector Differential refractometer (RI detector) manufactured by Waters Corporation -Calibration curve: Prepared from a calibration curve obtained using a monodisperse polystyrene standard sample, using a predetermined conversion constant.
- Oxidation resistance In order to evaluate the oxidation resistance of the polyolefin microporous membrane, an accelerated overcharge test was conducted by incorporating it as a separator in a battery chemical cell comprising an anode, a cathode, a separator and an electrolyte.
- An anode in which natural graphite having a density of 1.65 g / cm 3 was laminated on a 10 ⁇ m thick copper film substrate at a unit area mass of 5.5 mg / cm 2 was used. The anode and cathode were used after drying in a 120 ° C. vacuum oven.
- a polyolefin microporous film having a length of 50 mm and a width of 60 mm was dried in a vacuum oven at 50 ° C. and used.
- the electrolyte was prepared by dissolving 1M LiPF 6 in a mixture of ethylene carbonate and ethyl methyl carbonate (3/7, V / V).
- An anode, a separator, and a cathode were stacked, the separator was impregnated with an electrolyte, and the obtained laminate was vacuum-sealed and sealed in an aluminum laminate to produce an electrochemical cell.
- the prepared electrochemical cell was charged with a constant current to a voltage of 4.3 V at a current of 0.5 C, and then charged with a constant voltage of 4.3 V at a temperature of 60 ° C. for 200 hours.
- the separator was taken out and washed with diethyl carbonate, ethanol, N-methylpyrrolidone and 1N hydrochloric acid for 1 hour each to remove deposits. Then, it dried in the air, the discoloration in the cathode (positive electrode) contact surface of a separator was visually confirmed, and oxidation resistance evaluation was performed. The evaluation was made by the ratio of the area of the discolored portion per the entire area of the separator. The evaluation results are shown as follows. Less than 5%: ⁇ 5% to less than 10%: ⁇ 10% to 20%: ⁇ 20% or more: ⁇
- the crystal melting heat peak derived from the ⁇ crystal of the polyolefin microporous film is obtained by heating the polyolefin microporous film from 25 ° C. to 240 ° C. at a scanning temperature of 10 ° C./min with a differential scanning calorimeter. Hold for 1 minute, then lower the temperature from 240 ° C. to 25 ° C. at a scanning rate of 10 ° C./minute, hold for 1 minute, and further raise the temperature from 25 ° C. to 240 ° C. at a scanning rate of 10 ° C./minute. The change over time in the amount of heat with respect to the temperature was recorded and measured. The case where the crystal melting heat peak derived from the ⁇ crystal was observed on the low temperature side of the crystal melting heat peak derived from the ⁇ crystal was evaluated as “Yes”, and the case where it was not recognized was evaluated as “None”.
- a 50 mm square microporous membrane is sandwiched between metal block frames having a 12 mm diameter hole, and a tungsten carbide 10 mm diameter sphere is placed on the microporous membrane.
- the microporous membrane is installed so as to have a flat surface in the horizontal direction. Start from 30 ° C and raise the temperature at 5 ° C / min. The temperature at which the microporous membrane was broken by the sphere was measured and used as the meltdown temperature.
- Toughness evaluation (through hole observation results) A microporous membrane fixed with a 1 mm diameter needle having a spherical tip (curvature radius R: 0.5 mm) at the tip was pierced at 2 mm / second, and the shape of the through hole diameter was visually observed, and at the same time, the through hole diameter was measured. The test was repeated three times, and the through-hole diameter was evaluated by an average value of three measurement values. The evaluation results are shown as follows.
- Example 1 24.75 parts by weight of ultra high molecular weight polypropylene (UHMWPP) having a weight average molecular weight (Mw) of 2.6 ⁇ 10 6 and a molecular weight distribution (Mw / Mn) of 6.2, and a nucleating agent NA-11 (A DEKA Co., Ltd .: aromatic phosphate ester metal salt nucleating agent) 0.25 part by mass is charged into a twin screw extruder, and 75.00 parts by mass of liquid paraffin is supplied from the side feeder of the twin screw extruder.
- a polypropylene resin solution was prepared in a twin screw extruder by melt-kneading under the conditions of 200 ° C. and 200 ° C.
- the polypropylene resin solution was extruded from a sheet forming die installed at the tip of the twin-screw extruder, and a gel-like sheet was formed while taking the obtained sheet-like extrudate with a 25 ° C. cooling roll.
- the gel-like sheet was biaxially stretched at 120 ° C. to 5 ⁇ 5 times, then immersed in methylene chloride at 25 ° C. to remove liquid paraffin, air-dried at room temperature, and then heat-treated at 125 ° C. for 10 minutes.
- a polypropylene microporous membrane was prepared. The characteristics of the obtained microporous membrane are shown in Table 1.
- Example 2 A polypropylene microporous membrane was obtained in the same manner as in Example 1 except that the temperatures during simultaneous biaxial stretching were 130 ° C, 140 ° C, and 145 ° C, respectively. The characteristics of the obtained microporous membrane are shown in Table 1.
- the weight average molecular weight (Mw) is 2.60 ⁇ 10 6
- the molecular weight distribution (Mw / Mn) is 6.2
- the ultrahigh molecular weight polypropylene (UHMWPP) is 23.50 parts by mass
- the weight average molecular weight (Mw) is 5.72.
- a molecular weight distribution (Mw / Mn) of high density polyethylene (HDPE) 1.25 parts by mass is 4.81, and, (manufactured by ADEKA Corporation) nucleating agent NA-11
- a polyolefin microporous membrane was obtained in the same manner as in Example 1 except that 0.25 part by mass was charged into a twin screw extruder and 75 parts by mass of liquid paraffin was supplied from the side feeder of the twin screw extruder. The characteristics of the obtained microporous membrane are shown in Table 1.
- Example 6 Weight average molecular weight (Mw) 2.60 ⁇ 10 6 , molecular weight distribution (Mw / Mn) 6.2 ultrahigh molecular weight polypropylene (UHMWPP) 24.25 parts by mass, and El Modu (Idemitsu Kosan Co., Ltd.) as a crystallization retarder 0.75 part by mass was charged into a twin screw extruder, 75 parts by mass of liquid paraffin was supplied from the side feeder of the twin screw extruder, and the stretching temperature was 130 ° C. Similarly, a polyolefin microporous membrane was obtained. The characteristics of the obtained microporous membrane are shown in Table 2.
- Example 7 A polyolefin microporous membrane was obtained in the same manner as in Example 6 except that the stretching temperature was 140 ° C. The characteristics of the obtained microporous membrane are shown in Table 2.
- the average flow pore size of the microporous membranes obtained in Examples 1, 2, 3, 5, 6, 7, and 9 was less than the measurement limit (14.2 nm) of the porometer. In Table 1 and Table 2, it was described as 14.2 nm or less.
- [Comparative Example 2] 30.00 parts by weight of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight Mw of 2.89 ⁇ 10 6 and a molecular weight distribution Mw / Mn of 5.28, and a weight average molecular weight Mw of 5.72 ⁇ 10 5
- UHMWPE ultra high molecular weight polyethylene
- HDPE high-density polyethylene
- a microporous polyolefin membrane was obtained in the same manner as in Example 1 except that 70.00 parts by mass of liquid paraffin was supplied from the side feeder and the stretching temperature was 115 ° C.
- the characteristics of the obtained microporous membrane are shown in Table 2.
- a polyolefin microporous membrane was obtained in the same manner as in Example 1 except that it was put into a twin screw extruder and 75.00 parts by mass of liquid paraffin was supplied from the side feeder of the twin screw extruder. The characteristics of the obtained microporous membrane are shown in Table 2.
- Example 8 A polyolefin microporous membrane was obtained in the same manner as in Example 3 except that the gel sheet was stretched 5 times in the MD direction at 140 ° C. and then stretched 5 times in the TD direction. The properties of the resulting polyolefin microporous membrane are shown in Table 3.
- Example 9 Polyolefin resin solution using 39.75 parts by mass of ultra high molecular weight polypropylene (UHMWPP) having a weight average molecular weight (Mw) of 2.6 ⁇ 10 6 and a molecular weight distribution (Mw / Mn) of 6.2 and 60 parts by mass of liquid paraffin
- UHMWPP ultra high molecular weight polypropylene
- Mw weight average molecular weight
- Mw / Mn molecular weight distribution
- the polyolefin microporous membrane according to the present invention is excellent in mechanical strength such as oxidation resistance, meltdown temperature and toughness, it is particularly like a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery. It can be suitably used for a secondary battery.
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Abstract
Description
(1)ポリプロピレン樹脂を90質量%以上含んでなるポリオレフィン樹脂、結晶化制御剤および成膜用溶剤を溶融混練し、ポリオレフィン溶液を調製する工程
(2)前記ポリオレフィン溶液を押出し、冷却しゲル状シートを形成する工程
(3)前記ゲル状シートを延伸する延伸工程
(4)前記延伸後のゲル状シートから成膜用溶剤を除去する工程
(5)前記成膜用溶剤除去後のシートを乾燥する工程
本発明のポリオレフィン微多孔膜は、ポリオレフィン樹脂からなる。
以下、本発明について、各項目毎に説明する。
ポリオレフィン樹脂は、ポリプロピレン樹脂を主成分とする。ポリオレフィン樹脂中のポリプロピレン樹脂の含有量は、90質量%以上であることが好ましく、より好ましくは95質量%以上、最も好ましくは100質量%である。ポリオレフィン樹脂中のポリプロピレン樹脂の含有量が上記範囲未満であると本発明のポリオレフィン微多孔膜の耐酸化性が悪化する。
ポリプロピレン樹脂としては、その重量平均分子量が1×105以上1×108以下であることが好ましく、1×106以上1×108以下であることがさらに好ましい。ポリプロピレン樹脂の分子量分布は5以上10以下程度であることが好ましい。ポリオレフィン樹脂の重量平均分子量が上記範囲内であると、成膜用溶剤と溶融混練して押出す工程での取り扱い作業性が向上する。
本発明のポリオレフィン微多孔膜はポリオレフィン樹脂として、ポリエチレン、ポリブテン等のポリプロピレン以外のポリオレフィンを少量含んでもよい。このようなポリオレフィンとしては、Mwが1×104~1×106のポリエチレン、Mwが1×106~5×106の超高分子量ポリエチレン、Mwが1×104~4×106のポリブテン-1ポリブテン-1、ポリペンテン-1、ポリヘキセン-1、ポリオクテン-1およびMwが1×103~1×104のポリエチレンワックスからなる群から選ばれた少なくとも一種を用いてもよい。
前記ポリオレフィン樹脂は、必要に応じて、前記ポリオレフィン樹脂以外のその他の樹脂成分を含むことができる。その他の樹脂成分としては、耐熱性樹脂であることが好ましく、耐熱性樹脂としては、例えば、融点が150℃以上の結晶性樹脂(部分的に結晶性である樹脂を含む)、および/又はガラス点移転(Tg)が150℃以上の非晶性樹脂が挙げられる。ここでTgはJIS K7121に準拠して測定した値である。
結晶化制御剤とは、ポリオレフィン樹脂に配合することでポリオレフィン樹脂の結晶化を促進または抑制する添加剤であり、造核剤、透明化剤、結晶化遅延剤等があげられる。中でも造核剤および結晶化遅延剤が好ましい。結晶化制御剤の配合により、本発明のポリオレフィン微多孔膜の細孔構造が均一に微細になることが期待できる。
造核剤としては、ポリプロピレン樹脂用造核剤が好適に使用でき、芳香族リン酸エステル金属塩系造核剤、安息香酸金属塩系造核剤等のカルボン酸金属塩系造核剤、ソルビトール系造核剤およびこれらの混合物などポリオレフィン樹脂用造核剤として一般的に使用されるものが使用できる。中でも、後述するポリオレフィン樹脂溶液への分散性の観点から、基本的にヒドロシリル基を含有しない芳香族リン酸エステル金属塩系造核剤、安息香酸金属塩系造核剤等のカルボン酸金属塩系造核剤およびこれらの混合物であることが好ましい。なお、ポリプロピレン樹脂用造核剤としては市販の複数成分からなる造核剤マスターバッチを用いてもよい。
ポリオレフィン樹脂の結晶化遅延剤としては、非晶性ポリオレフィン樹脂、低結晶性ポリオレフィン樹脂などが使用でき、中でも低結晶性ポリプロピレン樹脂などが好適に使用できる。
本発明のポリオレフィン微多孔膜は、MD方向引張強度が25MPa以上であり、TD方向引張強度が25MPa以上であり、MD方向とTD方向の引張強度の比が0.4以上2.0以下であり、MD方向引張伸度が80%以上であり、MD方向とTD方向の引張伸度の比が0.6以上1.7以下であるため、機械的強度の等方性に優れ、電池用セパレータとして使用した場合、電池の生産性に優れ、得られた電池に高い安全性と長寿命化を付与できる。
本発明のポリオレフィン微多孔膜のMD方向(膜表面の長さ方向、機械方向)の引張強度の下限は25MPaであり、好ましくは40MPaあり、より好ましくは50MPaであり、TD方向(MD方向と垂直の膜表面幅方向)の引張強度の下限は25MPaであり、好ましくは40MPaであり、より好ましくは50MPaである。本発明のポリオレフィン微多孔膜のMD方向およびTD方向の引張強度の上限は特に限定されないが、一般的に400MPaであることが好ましく、300MPaであることがより好ましい。
本発明のポリオレフィン微多孔膜の引張強度のMD方向とTD方向の比(MD/TD)の下限は、0.4であり、好ましくは0.45であり、より好ましくは0.5であり、その上限は2.0であり、好ましくは1.5であり、より好ましくは1.3である。
本発明のポリオレフィン微多孔膜の最大孔径は、39.0nm以下であることが好ましく、より好ましくは37.0nm以下である。本明細書において、「最大孔径」とは、ポリオレフィン微多孔膜中に分布する全貫通孔の中で最大の孔径を示すものであり、ポロメータを用いたバブルポイント法により測定できる。
本発明のポリオレフィン微多孔膜は、絶縁破壊電圧の下限が0.10kV/μmであることが好ましく、0.14kV/μmであることがより好ましく、0.17kV/μmであることが特に好ましい。絶縁破壊電圧の上限は特に限定されないが、一般的にkV/μmであることが好ましい。ポリオレフィン微多孔膜の絶縁破壊電圧が上記範囲内であると、バッテリーセパレータとして使用した際、電池の耐久性、耐電圧性能が良好になることが期待できるからである。
本発明のポリオレフィン微多孔膜の空孔率は20~80%であることが好ましい。空孔率が上記範囲内であると、微多孔膜の機械的強度が良好になるので好ましい。空孔率は30~65%であることがより好ましく、40~45%であることが特に好ましい。
本発明のポリオレフィン微多孔膜は、膜厚を20μmとしたときの透気抵抗度の下限が300sec/100ccが好ましく、400sec/100ccがより好ましい。透気抵抗度の上限は5000sec/100ccが好ましく、4000sec/100ccがより好ましく、3500sec/100ccが特に好ましい。ここで、膜厚を20μmとしたときの透気抵抗度とは、膜厚T1(μm)の微多孔膜において、JIS P 8117(2009)に準拠して測定した透気抵抗度をP1するとき、式:P2=(P1×20)/T1によって算出される透気抵抗度P2のことを指す。ポリオレフィン微多孔膜の透気抵抗度が上記範囲内であると、機械的強度や靱性の観点から有利である。
本発明のポリオレフィン微多孔膜の耐酸化性は、セパレータの黒色化の程度により評価できる。電池用セパレータの黒色化は電池内の正極のコバルトの還元と並行して発生するポリマーのラジカル連鎖的酸化反応に起因するポリマーのポリエン化が原因と考えられている。黒色化が進行すると膜強度の劣化、短絡が引き起こされる。ポリエチレンは分子構造から連鎖的に酸化反応が進行するのに対し、ポリプロピレンは、連鎖反応を止める性質を持ち黒色化(酸化)の進行を防ぐ効果が期待できる。
本発明のポリオレフィン微多孔膜は、好ましくは、示差走査型熱量計を用いた示差熱分析においてポリプロピレン樹脂のβ晶に由来する結晶融解熱ピークを有さない。本明細書において、「結晶融解熱ピーク」とは、示差走査型熱量計で得られる極大値を有する曲線を示す。一般にβ晶造核剤を配合すると、ポリプロピレン樹脂のβ晶由来結晶融解熱ピークが検出されるが、 その場合、ポリオレフィン微多孔膜の最大孔径や平均流量孔径が粗大化したり、微多孔膜の伸度が低下したりする場合があるからである。
本発明のポリオレフィン微多孔膜のメルトダウン温度の下限は、耐熱性の観点から、好ましくは、160℃であり、より好ましくは、170℃である。メルトダウン温度の上限は特に限定されないが、ポリプロピレン樹脂を主成分とするポリオレフィン微多孔膜の場合は、一般的に、190℃である。
本発明のポリオレフィン微多孔膜の製造方法としては、上述した特性を有するポリオレフィン微多孔膜が製造できれば、特に限定されず、従来公知の方法を用いることができる。例えば、日本国特許第2132327号および日本国特許第3347835号公報、国際公開2006/137540号等に記載された方法を用いることができる。具体的には、下記の工程(1)~(5)を含むことが好ましく、下記の工程(6)をさらに含んでもよく、さらに下記の工程(7)を含むこともできる。
(1)前記ポリオレフィン樹脂、結晶化制御剤および成膜用溶剤を溶融混練し、ポリオレフィン溶液を調製する工程
(2)前記ポリオレフィン溶液を押出し、冷却しゲル状シートを形成する工程
(3)前記ゲル状シートを延伸する第1の延伸工程
(4)前記延伸後のゲル状シートから成膜用溶剤を除去する工程
(5)前記成膜用溶剤除去後のシートを乾燥する工程
(6)前記乾燥後のシートを延伸する第2の延伸工程
(7)前記乾燥後のシートを熱処理する工程
以下、各工程についてそれぞれ説明する。
ポリオレフィン樹脂に、結晶化制御剤および適当な成膜用溶剤を配合した後、溶融混練し、ポリオレフィン溶液を調製する。溶融混練方法として、例えば日本国特許第2132327号および日本国特許第3347835号公報に記載の二軸押出機を用いる方法を利用することができる。溶融混練方法は公知であるので説明を省略する。
ポリオレフィン溶液を押出機からダイに送給し、シート状に押し出す。同一または異なる組成の複数のポリオレフィン溶液を、押出機から一つのダイに送給し、そこで層状に積層し、シート状に押出してもよい。
(3)第1の延伸工程
次に、得られたゲル状シートを少なくとも一軸方向に延伸する。ゲル状シートは、結晶化制御剤および成膜用溶剤を含むので、均一に延伸できる。ゲル状シートは、加熱後、テンター法、ロール法、インフレーション法、又はこれらの組合せにより所定の倍率で延伸するのが好ましい。中でも、膜厚や膜の平面性等の制御の精度の観点から、テンター法が好ましい。延伸は一軸延伸でも二軸延伸でもよいが、二軸延伸が好ましい。二軸延伸の場合、同時二軸延伸、逐次延伸および多段延伸(例えば同時二軸延伸および逐次延伸の組合せ)のいずれでもよい。
洗浄溶媒を用いて、成膜用溶剤の除去(洗浄)を行う。ポリオレフィン相は成膜用溶剤相と相分離しているので、成膜用溶剤を除去すると、微細な三次元網目構造を形成するフィブリルからなり、三次元的に不規則に連通する孔(空隙)を有する多孔質の膜が得られる。洗浄溶媒およびこれを用いた成膜用溶剤の除去方法は公知であるので説明を省略する。例えば日本国特許第2132327号公報や特開2002-256099号公報に開示の方法を利用することができる。
成膜用溶剤を除去した微多孔膜を、加熱乾燥法又は風乾法により乾燥する。乾燥温度はポリオレフィン樹脂の結晶分散温度(Tcd)以下であるのが好ましく、特にTcdより5℃以上低いことが好ましい。乾燥は、微多孔膜を100質量%(乾燥重量)として、残存洗浄溶媒が5質量%以下になるまで行うのが好ましく、3質量%以下になるまで行うのがより好ましい
必要に応じて、乾燥後の微多孔膜を、少なくとも一軸方向に延伸してもよい。微多孔膜の延伸は、加熱しながら上記と同様にテンター法等により行うことができる。延伸は一軸延伸でも二軸延伸でもよい。二軸延伸の場合、同時二軸延伸および逐次延伸のいずれでもよい。
また、乾燥後の微多孔膜は、熱処理を行うことができる。熱処理によって結晶が安定化し、ラメラが均一化される。熱処理方法としては、熱固定処理および/又は熱緩和処理を用いることができる。熱固定処理とは、膜の寸法が変わらないように保持しながら加熱する熱処理である。熱緩和処理とは、膜を加熱中にMD方向やTD方向に熱収縮させる熱処理である。熱固定処理は、テンター方式又はロール方式により行うのが好ましい。例えば、熱緩和処理方法としては特開2002-256099号公報に開示の方法があげられる。熱処理温度はポリオレフィン樹脂のTcd~Tmの範囲内が好ましく、微多孔膜の延伸温度±5℃の範囲内がより好ましく、微多孔膜の第2の延伸温度±3℃の範囲内が特に好ましい。
また、前記ポリオレフィン微多孔膜の少なくとも一方の表面に、多孔層を設け、積層多孔膜としてもよい。多孔層としては、例えば、フィラーと樹脂バインダとを含むフィラー含有樹脂溶液や耐熱性樹脂溶液を用いて形成される多孔層を挙げることができる。
本発明のポリオレフィン微多孔膜は、水系電解液を使用する電池、非水系電解質を使用する電池のいずれにも好適に使用できる。具体的には、ニッケル-水素電池、ニッケル-カドミウム電池、ニッケル-亜鉛電池、銀-亜鉛電池、リチウム二次電池、リチウムポリマー二次電池等の二次電池のセパレータとして好ましく用いることができる。中でも、非水系電解質を使用するリチウムイオン二次電池のセパレータとして用いることが好ましい。
(1)膜厚(μm)
微多孔膜の95mm×95mmの範囲内における5点の膜厚を接触厚み計(株式会社ミツトヨ製ライトマチック)により測定し、膜厚の平均値を求めた。
微多孔膜の重量w1とそれと等価な空孔のないポリマーの重量w2(幅、長さ、組成の同じポリマー)とを比較した、以下の式によって、空孔率を測定した。
空孔率(%)=(w2-w1)/w2×100
膜厚T1の微多孔膜に対して透気度計(旭精工株式会社製、EGO-1T)で透気抵抗度P1を測定した。また、式:P2=(P1×20)/T1により、膜厚を20μmとしたときの透気抵抗度P2を算出した。
パームポロメータ(PMI社製、CFP-1500A)を用いて、Dry-up、Wet-upの順で、最大孔径および平均流量孔径を測定した。Wet-upには表面張力が既知のPMI社製Galwick(商品名)で十分に浸した微多孔膜に圧力をかけ、空気が貫通し始める圧力から換算される孔径を最大孔径とした。
平均流量孔径については、Dry-up測定で圧力、流量曲線の1/2の傾きを示す曲線と、Wet-up測定の曲線が交わる点の圧力から孔径を換算した。圧力と孔径の換算は下記の数式を用いた。
d=C・γ/P
(上記式中、「d(μm)」は微多孔膜の孔径、「γ(mN/m)」は液体の表面張力、「P(Pa)」は圧力、「C」は定数とした。
PP、UHMWPEおよびHDPEのMwは以下の条件でゲルパーミエーションクロマトグラフィー(GPC)法により求めた。
・測定装置:Waters Corporation製GPC-150C
・カラム:昭和電工株式会社製Shodex UT806M
・カラム温度:135℃
・溶媒(移動相):o-ジクロルベンゼン
・溶媒流速:1.0 ml/分
・試料濃度:0.1 wt%(溶解条件:135℃/1h)
・インジェクション量:500μl
・検出器:Waters Corporation製ディファレンシャルリフラクトメーター(RI検出器)
・検量線:単分散ポリスチレン標準試料を用いて得られた検量線から、所定の換算定数を用いて作成した。
一辺150mmの正方形のアルミニウム板上に、直径60mmの円状に切り出した膜厚T1の微多孔膜を置き、その上に真鍮製の直径50mm、高さ30mm、重さ500gの円柱電極を置いて、菊水電子工業製TOS5051A耐絶縁破壊特性試験器を接続した。0.2kV/秒の昇圧速度で電圧を加え、絶縁破壊したときの値V1を読み取った。絶縁破壊電圧の測定はそれぞれ15回行い平均値を求めた。
ポリオレフィン微多孔膜の耐酸化性を評価するために、アノード、カソード、セパレータおよび電解質からなる電池化学セルにセパレータとして組み込んで、加速過充電試験を行った。
5%未満:◎
5%~10%未満:○
10%~20%:△
20%以上:×
ポリオレフィン微多孔膜のβ晶由来の結晶融解熱ピークは、示差走査型熱量計でポリオレフィン微多孔膜を25℃から240℃まで走査温度10℃/分で昇温後1分間保持し、次に240℃から25℃まで走査速度10℃/分で降温後1分間保持し、更に25℃から240℃まで走査速度10℃/分で再昇温させ、再昇温の際の温度に対する熱量の時間変化を記録して測定した。α晶由来の結晶融解熱ピークの低温側にβ晶由来の結晶融解熱ピークが認められた場合を“あり”、認められなった場合を“なし”と評価した。
各方向に対応する引張強度および引張伸度については、幅10mmの短冊状試験片を用いて、ASTM D882に準拠した方法により測定した。
50mm角の微多孔膜を直径12mmの穴を有する金属製のブロック枠を用いて挟み、タングステンカーバイド製の直径10mmの球を微多孔膜上に設置する。微多孔膜は水平方向に平面を有するように設置される。30℃からスタートし、5℃/分で昇温する。微多孔膜が球によって破膜されたときの温度を測定し、メルトダウン温度とした。
先端が球面(曲率半径R:0.5mm)の直径1mmの針で固定した微多孔膜を2mm/秒で突刺し、貫通孔径の形状を目視で観察すると同時に貫通孔径を測定した。試験は3回繰り返し、貫通孔径は3回の測定値の平均値で評価した。評価結果は下記の通りに表記した。
貫通孔が直径1mm以下の円形または長径1mm以下のだ円形:◎
貫通孔が直径1.7mm未満の円形または長径1.7mm未満のだ円形:○
貫通孔の直径または長径が1.7mmを超えた場合、または、貫通孔周囲に裂けが認められた場合:×
重量平均分子量(Mw)が2.6×106、分子量分布(Mw/Mn)が6.2の超高分子量ポリプロピレン(UHMWPP)24.75質量部、および、造核剤NA-11(A
DEKA社製:芳香族リン酸エステル金属塩系造核剤) 0.25質量部を二軸押出機に投入し、二軸押出機のサイドフィーダーから流動パラフィン75.00質量部を供給し、180℃、200rpmの条件で溶融混練して、ポリプロピレン樹脂溶液を二軸押出機中で調製した。続いて、ポリプロピレン樹脂溶液を、二軸押出機の先端に設置されたシート形成ダイから押し出し、得られたシート状押出物を25℃の冷却ロールで引き取りながら、ゲル状シートを形成した。次いで、ゲル状シートを120℃で5×5倍になるように二軸延伸した後、25℃の塩化メチレンに浸漬して流動パラフィンを除去し、室温で風乾後、125℃で10分間熱処理してポリプロピレン微多孔膜を調整した。得られた微多孔膜の特性を表1に示した。
同時二軸延伸時の温度をそれぞれ130℃、140℃、145℃としたこと以外は、実施例1と同様にしてポリプロピレン微多孔膜を得た。得られた微多孔膜の特性を表1に示した。
重量平均分子量(Mw)が2.60×106、分子量分布(Mw/Mn)が6.2の超高分子量ポリプロピレン(UHMWPP)23.50質量部、および重量平均分子量(Mw)が5.72×105であり、分子量分布(Mw/Mn)が4.81である高密度ポリエチレン(HDPE)1.25質量部、および、造核剤NA-11(ADEKA社製)
0.25質量部を二軸押出機に投入し、二軸押出機のサイドフィーダーから流動パラフィン75質量部を供給したこと以外は実施例1と同様にしてポリオレフィン微多孔膜を得た。得られた微多孔膜の特性を表1に示した。
重量平均分子量(Mw)が2.60×106、分子量分布(Mw/Mn)6.2の超高分子量ポリプロピレン(UHMWPP)24.25質量部、および、結晶化遅延剤としてエルモーデュ(出光興産社製)0.75質量部を二軸押出機に投入し、二軸押出機のサイドフィーダーから流動パラフィン75質量部を供給したこと、および、延伸温度を130℃としたこと以外は実施例1と同様にしてポリオレフィン微多孔膜を得た。得られた微多孔膜の特性を表2に示した。
延伸温度を140℃としたこと以外は実施例6と同様にしてポリオレフィン微多孔膜を得た。得られた微多孔膜の特性を表2に示した。
乾式一軸延伸法により製造されたポリプロピレン製単層微多孔膜を評価し、その特性を表2に示した。
重量平均分子量Mwが2.89×106であり、分子量分布Mw/Mnが5.28である超高分子量ポリエチレン(UHMWPE)30.00質量部 と、重量平均分子量Mwが5.72×105であり、分子量分布Mw/Mnが4.81である高密度ポリエチレン(HDPE)70.00質量部とからなるポリエチレン樹脂組成物30.00質量部を二軸押出機に投入し、二軸押出機のサイドフィーダーから流動パラフィン70.00質量部を供給したこと、および、延伸温度を115℃としたこと以外は実施例1と同様にしてポリオレフィン微多孔膜を得た。得られた微多孔膜の特性を表2に示した。
重量平均分子量(Mw)が2.60×106、分子量分布(Mw/Mn)が6.2の超高分子量ポリプロピレン(UHMWPP)17.33質量部、および重量平均分子量(Mw)が5.72×105であり、分子量分布(Mw/Mn)が4.81である高密度ポリエチレン(HDPE)7.42質量部、および、造核剤NA-11(ADEKA社製)0.25質量部を二軸押出機に投入し、二軸押出機のサイドフィーダーから流動パラフィン75.00質量部を供給したこと以外は実施例1と同様にしてポリオレフィン微多孔膜を得た。得られた微多孔膜の特性を表2に示した。
ゲル状シートを140℃でMD方向に5倍延伸した後、TD方向に5倍延伸した以外は実施例3と同様にしてポリオレフィン微多孔膜を得た。得られたポリオレフィン微多孔膜の特性を表3に示した。
重量平均分子量(Mw)が2.6×106、分子量分布(Mw/Mn)が6.2の超高分子量ポリプロピレン(UHMWPP)39.75質量部と流動パラフィン60質量部を用いてポリオレフィン樹脂溶液を調製し、ポリオレフィン微多孔膜の膜厚を5.5μmとした以外は実施例1と同様にしてポリオレフィン微多孔膜を得た。得られた微多孔膜の特性を表3に示した。
Claims (15)
- ポリプロピレン樹脂を90質量%以上含んでなるポリオレフィン樹脂からなり、MD方向引張強度が25MPa以上であり、TD方向引張強度が25MPa以上であり、MD方向とTD方向の引張強度の比(MD/TD)が0.4以上2.0以下であり、MD方向引張伸度が80%以上であり、MD方向とTD方向の引張伸度の比(MD/TD)が0.6以上1.7以下であることを特徴とするポリオレフィン微多孔膜。
- 前記ポリオレフィン微多孔膜の示差走査型熱量計を用いたβ晶由来の結晶融解熱ピークが認められないことを特徴とする請求項1に記載のポリオレフィン微多孔膜。
- 前記ポリオレフィン微多孔膜のメルトダウン温度が160℃以上であることを特徴とする請求項1または請求項2に記載のポリオレフィン微多孔膜。
- 前記ポリオレフィン微多孔膜の膜厚を20μmとした時の透気抵抗度が300sec/100cc以上であることを特徴とする請求項1~3いずれか一項に記載のポリオレフィン微多孔膜。
- 前記ポリオレフィン微多孔膜のポロメータによる平均流量孔径が25.0nm以下であることを特徴とする請求項1~4いずれか一項に記載のポリオレフィン微多孔膜。
- 前記ポリオレフィン微多孔膜の膜厚が1μm以上12μm以下であるであることを特徴とする請求項1~5いずれか一項に記載のポリオレフィン微多孔膜。
- 前記ポリプロピレン樹脂の重量平均分子量が1×105以上1×108以下であることを特徴とする請求項1~6のいずれか一項に記載のポリオレフィン微多孔膜
- 請求項1~7のいずれか一項に記載のポリオレフィン微多孔膜からなる電池用セパレータ。
- 非水電解液系二次電池用であることを特徴とする請求項8に記載の電池用セパレータ。
- 請求項8に記載の電池用セパレータを用いた二次電池。
- 下記(1)~(5)の工程を含むことを特徴とする、MD方向引張強度が25MPa以上であり、TD方向引張強度が25MPa以上であり、MD方向とTD方向の引張強度の比が0.4以上2.0以下であり、MD方向引張伸度が80%以上であり、MD方向とTD方向の引張伸度の比が0.6以上1.7以下のポリオレフィン微多孔膜の製造方法。
(1)ポリプロピレン樹脂を90質量%以上含んでなるポリオレフィン樹脂、結晶化制御剤および成膜用溶剤を溶融混練し、ポリオレフィン溶液を調製する工程
(2)前記ポリオレフィン溶液を押出し、冷却しゲル状シートを形成する工程
(3)前記ゲル状シートを延伸する延伸工程
(4)前記延伸後のゲル状シートから成膜用溶剤を除去する工程
(5)前記成膜用溶剤除去後のシートを乾燥する工程 - 使用される結晶化制御剤が造核剤または結晶化遅延剤であることを特徴とする請求項11に記載のポリオレフィン微多孔膜の製造方法。
- ポリオレフィン微多孔膜の微多孔膜の示差走査型熱量計を用いたβ晶由来の結晶融解熱ピークが認められないことを特徴とする請求項11または請求項12に記載のポリオレフィン微多孔膜の製造方法。
- 110℃~160℃でゲル状シートを延伸することを特徴とする請求項11~13のいずれか一項に記載のポリオレフィン微多孔膜の製造方法。
- さらに、下記工程を含むことを特徴とすることを特徴とする請求項11~14のいずれか一項に記載のポリオレフィン微多孔膜の製造方法。
(7)120℃~130℃でポリオレフィン微多孔膜を熱処理する工程
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