Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/26—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a solid phase from a macromolecular composition or article, e.g. leaching out
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
  • B32B5/18—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by features of a layer of foamed material
• • 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
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
  • C08J7/04—Coating
• • 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
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/04—Homopolymers or copolymers of ethene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/10—Homopolymers or copolymers of propene
• • 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
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
• • 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
• • 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
• • 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
  • C08J2323/04—Homopolymers or copolymers of ethene
• • 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
  • C08J2323/04—Homopolymers or copolymers of ethene
  • C08J2323/06—Polyethene
• • 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
• • 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
  • C08J2423/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
  • C08J2423/02—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
  • C08J2423/04—Homopolymers or copolymers of ethene
  • C08J2423/06—Polyethene
• • 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
  • C08J2423/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
  • C08J2423/02—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
  • C08J2423/10—Homopolymers or copolymers of propene
  • C08J2423/12—Polypropene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/04—Oxygen-containing compounds
  • C08K5/13—Phenols; Phenolates
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/04—Oxygen-containing compounds
  • C08K5/13—Phenols; Phenolates
  • C08K5/134—Phenols containing ester groups
  • C08K5/1345—Carboxylic esters of phenolcarboxylic acids
• • 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 laminate, and a battery using the same, which are excellent in safety and output characteristics when used as a battery separator.
• Polyolefin microporous membranes are used as filters, fuel cell separators, condenser separators, etc. In particular, it is suitably used as a separator for lithium-ion batteries widely used in notebook personal computers, mobile phones, digital cameras, and the like. The reason is that the polyolefin microporous membrane has excellent mechanical strength and shutdown characteristics of the membrane.
• lithium-ion secondary batteries have been developed with the aim of increasing energy density, capacity, and output, mainly for in-vehicle applications, and along with this, the required characteristics for safety of separators are even higher. It is becoming a thing.
• the separator needs to have a function (shutdown function) of melting and clogging the holes to cut off the current in order to prevent accidents such as ignition when the inside of the battery is overheated in an overcharged state. It is preferable that the temperature at which the shutdown function is exhibited (shutdown temperature) is low. In addition, the temperature inside the battery continues to rise momentarily even after shutdown. Therefore, it is necessary to maintain the shape of the separator itself and prevent short-circuiting of the electrodes at a temperature equal to or higher than the shutdown temperature, and it is preferable that the break film temperature (meltdown temperature) of the separator is high.
• the thickness of the separator tends to become thinner, and it is required to increase the strength of the separator in order to prevent short circuits due to foreign matter in the battery or when winding.
• a method of controlling the crystal orientation of polyolefin by stretching at a high magnification and a method of increasing the molecular weight of the raw material can be mentioned.
• the melting point becomes high and the shutdown temperature also becomes high, so there is a trade-off between high strength and low shutdown temperature.
• Patent Document 1 and Patent Document 2 describe a technique for achieving both low shutdown and high meltdown by laminating a layer for lowering the shutdown rate and a layer for increasing the temperature of the meltdown. There is.
• Patent Document 3 exemplifies a single-layer thin film microporous membrane, but it has been difficult to achieve both low shutdown and high meltdown.
• An object of the present invention is to solve the above-mentioned problems. That is, it is an object of the present invention to provide a polyolefin microporous membrane having excellent safety and output characteristics when used as a battery separator.
• the present invention has the following configurations.
• It is a single-layer polyolefin microporous membrane containing polyethylene (A) and polyolefin (B) other than polyethylene, has a film thickness of 8 ⁇ m or less, a shutdown temperature of 135 ° C. or less, and a meltdown temperature of 160 ° C. or more.
• Polyolefin microporous membrane [2] The polyolefin microporous membrane according to [1], wherein the M TD is 50 MPa or more when the tensile strength in the TD direction is M TD.
• the polyolefin microporous membrane of the present invention is a thin film, it has excellent strength, low shutdown characteristics and high meltdown characteristics, and therefore is excellent in safety and output characteristics when used as a battery separator. Therefore, it can be suitably used as a battery separator or a laminate for a battery such as an electric vehicle that requires high energy density, high capacity, and high output, and a secondary battery.
• the polyolefin microporous membrane according to the embodiment of the present invention is a single-layer polyolefin microporous membrane containing polyethylene (A) and a polyolefin (B) other than polyethylene, has a film thickness of 8 ⁇ m or less, and has a shutdown temperature of 135 ° C.
• the meltdown temperature is 160 ° C. or higher.
• the polyolefin microporous membrane according to the embodiment of the present invention (hereinafter, may be simply referred to as “microporous membrane”) has a film thickness of 8 ⁇ m or less. It is more preferably 7 ⁇ m or less, further preferably 6 ⁇ m or less, and most preferably 5 ⁇ m or less. If the film thickness exceeds 8 ⁇ m, sufficient output characteristics and energy density may not be obtained when used as a separator for future high-capacity batteries. From the above viewpoint, a thin film thickness is preferable, but the lower limit of the film thickness is preferably 2 ⁇ m or more because safety may be lowered and handling may be difficult.
• the film thickness can be adjusted by adjusting the discharge amount of the extruder, the film forming speed, the stretching ratio, the stretching temperature, and the like within a range that does not deteriorate other physical properties.
• the microporous polyolefin membrane in the embodiment of the present invention is composed of a single layer containing polyethylene (A) and a polyolefin (B) other than polyethylene.
• the single layer referred to here is a structure in which layers having different compositions, raw materials used, and physical properties are not arranged in the film thickness direction of the polyolefin microporous film.
• the polyolefin microporous film is a single layer, it is manufactured as compared with a laminated structure in which two or more layers having different compositions, raw materials used, and physical properties are arranged in the film thickness direction of the polyolefin microporous film.
• a single layer is preferable because it not only simplifies the process but also enables thinning.
• the microporous polyolefin membrane of the present invention has a shutdown temperature of 135 ° C or lower. It is more preferably 134 ° C. or lower, further preferably 133 ° C. or lower, and most preferably 132 ° C. or lower.
• the shutdown temperature is 135 ° C. or lower, safety is improved when used as a battery separator for a secondary battery that requires high energy density, high capacity, and high output for electric vehicles and the like. From the viewpoint of safety, the lower the shutdown temperature is, the more preferable it is. However, if the shutdown temperature is 80 ° C or lower, the holes will close even under normal operating environment and the battery characteristics will deteriorate. Therefore, the shutdown temperature should be about 80 ° C. It is the lower limit. In order to set the shutdown temperature in the above range, it is preferable that the raw material composition of the film is in the range described later, and the stretching conditions and heat fixing conditions at the time of film formation are in the range described later.
• the polyolefin microporous membrane of the present invention has a meltdown temperature of 160 ° C. or higher. It is more preferably 162 ° C. or higher, further preferably 165 ° C. or higher, and most preferably 168 ° C. or higher.
• the meltdown temperature is 160 ° C. or higher, safety is improved when used as a battery separator for a secondary battery that requires high energy density, high capacity, and high output in an electric vehicle or the like.
• the raw material composition of the film is in the range described later, and the stretching conditions and heat fixing conditions at the time of film formation are in the range described later.
• the polyolefin microporous membrane of the present application is a thin film of 8 ⁇ m or less, but has both excellent shutdown characteristics and meltdown characteristics.
• a method of laminating a layer for lowering the shutdown temperature and a layer for increasing the temperature of the meltdown has been common.
• the film thickness of each layer becomes too thin when laminated, so that it is difficult to express the characteristics of each layer, and uneven thickness and uneven lamination become large. In some cases, the variation in physical properties became large.
• Microporous polyolefin membrane of the present invention when the tensile strength in a longitudinal direction of the film M MD, the tensile strength in the width direction was set to M TD, it is preferable M TD is not less than 50 MPa.
• M TD is more preferably 80MPa or more, more preferably more than 100 MPa, most preferably above 120 MPa.
• Tensile the intensity M TD is less than 50 MPa, the handling property tends wrinkles in the film during processing is lowered after such coating when the thin, short circuit due to such wound or when foreign matter in the battery occurs It becomes easier and the safety of the battery may decrease.
• the raw material composition of the film is in the range described later, and the stretching conditions at the time of film formation are in the range described later.
• the direction parallel to the film forming direction of the film is referred to as the film forming direction, the longitudinal direction, or the MD direction, and the direction orthogonal to the film forming direction in the film surface is referred to as the width direction or the TD direction. ..
• Microporous polyolefin membrane of the present invention it is preferable tensile strength M MD is not less than 80 MPa.
• Tensile strength M MD is more preferably 100MPa or more, more preferably 120MPa or more, and most preferably at least 160 MPa. If the tensile strength is less than 80 MPa, a short circuit is likely to occur during winding or due to foreign matter in the battery when the thin film is formed, which may reduce the safety of the battery. From the viewpoint of improving safety, the higher the tensile strength is, the more preferable it is, but lowering the shutdown temperature and improving the tensile strength are often trade-offs, and the upper limit is about 200 MPa.
• the raw material composition of the film is in the range described later, and the stretching conditions at the time of film formation are in the range described later.
• the polyolefin microporous membrane of the present invention preferably has an M MD / M TD value of 0.5 to 2.0.
• the value of M MD / M TD is more preferably 0.7 to 1.8, still more preferably 0.8 to 1.6, and most preferably 1.0 to 1.6. If the value of M MD / M TD is less than 0.5 or more than 2.0, the anisotropy of the film becomes too large, and the film may be easily avoided when it is made into a thin film, and the handleability may be deteriorated.
• the raw material composition of the film is in the range described later and the stretching conditions at the time of film formation are in the range described later.
• the tensile elongation (tensile breaking elongation) of the polyolefin microporous membrane in the MD direction is not particularly limited, but is preferably 40% or more and 300% or less, and more preferably 60% or more and 200% or less. Further, it is preferably 70% or more and 150% or less.
• breaking elongation in the MD direction is within the above range, it is less likely to be deformed and wrinkled even when a high tension is applied during coating, so that the occurrence of coating defects is suppressed and the flatness of the coating surface is flat. Is preferable because it is good.
• the tensile elongation (tensile breaking elongation) of the polyolefin microporous membrane in the TD direction is preferably 60% or more, and more preferably 70% or more.
• breaking elongation in the TD direction is within the above range, it has excellent collision resistance that can be evaluated by an impact test or the like, and when a polyolefin microporous film is used as a separator, the unevenness of the electrode, the deformation of the battery, and the heat generation of the battery are generated. This is preferable because the separator can follow the generation of internal stress due to the above.
• the MD tensile elongation and the TD tensile elongation are values measured by a method based on ASTM D882.
• the polyolefin microporous film of the present invention preferably has a film puncture strength of 1.0 N or more in terms of a thickness of 5 ⁇ m. It is more preferably 1.2 N or more, further preferably 1.4 N or more, and most preferably 1.6 N or more.
• the puncture strength is 1.0 N or more, even if it is used as a thin film separator, short circuits are less likely to occur during winding or due to foreign matter in the battery, and the safety of the battery can be improved.
• 5N is the upper limit.
• the raw material composition of the film is in the range described later and the stretching conditions at the time of film formation are in the range described later, and generally, the stretching ratio is increased to increase the stretching ratio. It is possible to increase the strength.
• the air permeation resistance of the film converted to a thickness of 5 ⁇ m is preferably 50 seconds / 100 cm 3 or more and 1000 seconds / 100 cm 3 or less. More preferably 50 seconds / 100 cm 3 or more and 300 seconds / 100 cm 3 or less, further preferably 50 seconds / 100 cm 3 or more and 200 seconds / 100 cm 3 or less, and most preferably 70 seconds / 100 cm 3 or more and 200 seconds / 100 cm 3 or less.
• the air permeation resistance When the air permeation resistance is 50 seconds / 100 cm 3 or more, the film strength is excellent and the handleability is good when used as a thin film separator, and when used as a separator for a high output battery, a slight short circuit due to dendrite is performed. Is less likely to occur. When the air permeation resistance is 1000 seconds / 100 cm 3 or less, when used as a battery separator, the ion permeability becomes sufficient and the output characteristics of the battery are excellent. In order to set the air permeation resistance within the above range, it is preferable that the raw material composition of the film is within the range described later, and the stretching conditions during film formation are within the range described later.
• the polyolefin microporous membrane of the present invention preferably has an average pore diameter of 50 nm or less. It is more preferably 40 nm or less, further preferably 30 nm or less, and most preferably 25 nm or less.
• the average pore diameter is 50 nm or less, a slight short circuit due to dendrite is unlikely to occur when used as a thin film separator for a high-power battery. From the above viewpoint, the smaller the average pore diameter is, the more preferable it is. However, if it is too small, the ion permeability may be insufficient and the output characteristics of the battery may be deteriorated. Therefore, the lower limit is about 10 nm.
• the raw material composition of the film is in the range described later and the stretching conditions at the time of film formation are in the range described later.
• the polyolefin microporous membrane of the present invention preferably has an average pore diameter to maximum pore diameter ratio (average pore diameter / maximum pore diameter) of 0.56 to 1.0. It is more preferably 0.60 to 1.0, still more preferably 0.65 to 1.0, and most preferably 0.68 to 1.0.
• average pore diameter / maximum pore diameter 0.56 or more, the uniformity of the pore diameter is high, so that it is possible to suppress a slight short circuit due to dendrite even when used as a thin film separator for a high-power battery.
• the upper limit is 1.0 in principle of measurement. In order to set (average pore size / maximum pore size) in the above range, it is preferable that the raw material composition of the film is in the range described later and the stretching conditions at the time of film formation are in the range described later.
• the polyolefin microporous membrane of the present invention preferably has peaks at less than 150 ° C. and 150 ° C. or higher, respectively, when heated by a differential scanning calorimeter (DSC) based on JIS K7121. Having a peak here means that the result obtained by DSC has a maximum value when the horizontal axis is temperature and the vertical axis is heat flow, and the polyolefin microporous membrane in the present invention has the maximum value. It is preferable that the temperature is less than 150 ° C. and 150 ° C. or higher.
• the maximum temperature of the peak below 150 ° C. is preferably 135 ° C. or lower.
• the lower limit is 120 ° C., preferably 123 ° C. or higher.
• the shutdown may become hot when used as a battery separator. Further, when the maximum temperature of the peak below 150 ° C. is lower than the above range, the shrinkage rate at high temperature becomes high, and the electrodes may come into contact with each other in the battery to cause a short circuit.
• the half width of the peak below 150 ° C. is preferably 10.0 ° C. or lower, more preferably 9.5 ° C. or lower, still more preferably 9.3 ° C. or lower, and more. More preferably, it is 9.1 ° C. or lower, and most preferably 9.0 ° C. or lower.
• the smaller the full width at half maximum the easier it is for the resin to melt at once when the temperature reaches a certain level when the polyolefin microporous membrane is used as a battery separator, which increases the shutdown speed and improves battery safety. It is preferable because it connects.
• the half width of the peak referred to here is the temperature at which the calorific value Q 1/2 is 0.5 times the maximum calorific value Q in the region below 150 ° C., respectively, T 1 and T 2 (T 1 ⁇ T 2). ) as meaning the value of T 2 -T 1 in the case of. If there are two or more maximum values in the region below 150 ° C and three or more temperatures that are Q 1/2 , the minimum temperature of the corresponding temperature is T 1 and the maximum temperature is T 2. Calculate the price range. In order to set the full width at half maximum in the above range, it is preferable that the raw material composition of the film is in the range described later, and the stretching conditions and heat fixing conditions at the time of film formation are in the range described later.
• the porosity of the microporous polyolefin membrane of the present invention is preferably 30% or more, more preferably 35% or more, and further preferably 40% or more.
• the upper limit is preferably 70% or less, more preferably 65% or less, and even more preferably 60% or less.
• the porosity is lower than the above range, the ion permeability becomes insufficient when used as a battery separator, and the output characteristics of the battery deteriorate. Therefore, it is preferably 30% or more. If it is higher than the above range, the strength is lowered and a short circuit is likely to occur during winding or due to a foreign substance in the battery, so that it is preferably 70% or less.
• the raw material composition of the film is within the range described later, and the stretching conditions and heat fixing conditions at the time of film formation are within the range described later.
• the polyolefin microporous film according to the embodiment of the present invention is a film containing a polyolefin resin as a main component.
• the "main component” means that the ratio of the specific component to all the components is 50% by mass or more, more preferably 90% by mass or more, still more preferably 95. By mass or more, most preferably 99% by mass or more.
• the polyolefin resin used in the embodiment of the present invention is preferably a polyolefin-based resin, and may be a polyolefin composition.
• the polyolefin-based resin include polyethylene-based resin and polypropylene-based resin, and two or more kinds of these may be blended and used.
• the polyolefin microporous membrane according to the embodiment of the present invention preferably contains a polyethylene resin as a main component.
• the polyolefin microporous membrane according to the embodiment of the present invention contains polyethylene (A) and polyolefin (B) other than polyethylene.
• polyethylene (A) will be described.
• Polyethylene (A) contains a polyethylene-based resin.
• the polyethylene-based resin various types of polyethylene can be used, and examples thereof include ultra-high density polyethylene, high density polyethylene, medium density polyethylene, and low density polyethylene.
• the polyethylene (A) used for the microporous polyolefin membrane according to the embodiment of the present invention is excellent in melt extrusion characteristics and uniform stretching processing characteristics, and therefore is a high-density polyethylene (density: 0.920 g / cm 3 or more and 0.970 g). / Cm 3 or less) is preferably used.
• Such a polyethylene-based resin is preferably a copolymer containing not only an ethylene homopolymer but also another ⁇ -olefin in order to lower the melting point and crystallinity of the raw material.
• the ⁇ -olefin include propylene, butene-1, hexene-1, pentene-1, 4-methylpentene-1, octene, vinyl acetate, methyl methacrylate, styrene and the like.
• copolymer containing ⁇ -olefin ethylene / ⁇ -olefin copolymer
• a copolymer containing hexene-1 is preferable, and polyethylene (A) contains an ethylene / 1-hexene copolymer as a main component. It is more preferable to do so.
• the ⁇ -olefin can be confirmed by measuring with C 13-NMR.
• the high-density polyethylene it is preferable to include branched high-density polyethylene (branched HDPE).
• branched high-density polyethylene is more preferable because the in-plane crystal orientation does not easily proceed, changes in the crystal structure can be suppressed, and the shutdown temperature can be lowered. Furthermore, even if the draw ratio is increased, the crystal orientation does not easily proceed, and the formation of the high melting point component can be suppressed, so that the increase in the half width of the peak in DSC can also be suppressed. As a result, it is possible to achieve high strength and thin film by high-magnification stretching while maintaining the shutdown speed.
• the weight average molecular weight of high density polyethylene (Mw) of preferably at 1.0 ⁇ 10 4 or more 1.0 ⁇ 10 6 or less, more not less 3.5 ⁇ 10 5 or less 5.0 ⁇ 10 4 or more preferably, 8.0 ⁇ more preferably 10 4 or more 2.5 ⁇ 10 5 or less, particularly preferably 1.5 ⁇ 10 5 or more 2.0 ⁇ 10 5 or less.
• Mw high density polyethylene
• the melting point of the high-density polyethylene is preferably 130 ° C. or higher, and preferably 135 ° C. or lower.
• the melting point is 130 ° C. or higher, the decrease in the porosity can be suppressed, and when the melting point is 135 ° C. or lower, the increase in the shutdown temperature can be suppressed.
• Mw of 1.0 ⁇ 10 5 ⁇ 1.0 ⁇ 10 6 and polyethylene having a melting point of 130 ⁇ 135 ° C. of the raw materials used in the main raw material or the purpose of reducing the shutdown temperature in the embodiment of the present invention It is preferable that this polyethylene is contained in an amount of 50% by mass or more when the total amount of the polyolefin resin is 100% by mass.
• low molecular weight polyethylene such as low density polyethylene, linear low density polyethylene, ethylene / ⁇ -olefin copolymer produced by a single site catalyst, and low molecular weight polyethylene having a weight average molecular weight of 1000 to 100,000 is added to polyethylene (A).
• polyethylene (A) When added, a shutdown function at a low temperature is imparted, and the characteristics as a battery separator can be improved.
• the content ratio of the above-mentioned low molecular weight polyethylene is high in the polyethylene (A), the porosity of the microporous membrane is lowered in the film forming process, so that the content ratio of the low molecular weight polyethylene is ethylene / ⁇ -.
• the density as an olefin copolymer it is preferable to adjust the density as an olefin copolymer to be a high-density polyethylene exceeding 0.94 g / cm 3, and it is more preferable to add a branched high-density polyethylene having a long-chain branched component to adjust the density. ..
• the molecular weight distribution of the polymer constituting the polyolefin microporous membrane according to the embodiment of the present invention preferably contains less than 20% of components having a molecular weight of less than 40,000. More preferably, the amount of components having a molecular weight of less than 20,000 is less than 20%, and even more preferably, the amount of components having a molecular weight of less than 10,000 is less than 20%.
• the shutdown temperature can be lowered without significantly lowering the molecular weight, and as a result, compatibility with other physical properties such as strength and porosity can be achieved.
• the weight average molecular weight it is preferred to use 1.0 ⁇ 10 6 or more 4.0 ⁇ 10 under 6 ultra high molecular weight polyethylene .
• the ultra-high molecular weight polyethylene may be a copolymer containing a small amount of other ⁇ -olefins as well as a homopolymer of ethylene.
• Other ⁇ -olefins other than ethylene may be the same as above.
• the swell and neck are large at the outlet of the base when molding into a sheet, and the formability of the sheet deteriorates. Tend to do.
• ultra-high molecular weight polyethylene because the viscosity and strength of the sheet are increased and the process stability is increased by adding ultra high molecular weight polyethylene as an auxiliary material.
• the proportion of ultra-high molecular weight polyethylene is 50% by mass or more, the extrusion load increases and the extrusion moldability deteriorates. Therefore, the amount of ultra-high molecular weight polyethylene added is less than 50% by mass with respect to the total amount of polyethylene (A). Is preferable.
• the polyolefin microporous membrane according to the embodiment of the present invention contains a polyolefin (B) other than polyethylene for the purpose of improving the meltdown characteristics.
• the polyolefin (B) is not particularly limited, and polypropylene-based resin, polymethylpentene-based resin, polybutene-based resin, polyacetal-based resin, styrene-based resin, polyphenylene ether-based resin, and the like can be used.
• a polypropylene resin is preferable from the viewpoint of electrical stability when used as a separator.
• As the type of polypropylene-based resin a block copolymer or a random copolymer can be used in addition to the propylene homopolymer.
• the block copolymer and the random copolymer can contain a copolymer component with ⁇ -ethylene other than propylene, and ethylene is preferable as the other ⁇ -ethylene.
• the polyolefin (B) and polyethylene (A) are different resins.
• the upper limit of the content of polyolefin (B) in the polyolefin microporous membrane is preferably 40% by mass or less, more preferably 35% by mass or less, based on the total mass of the polyolefin microporous membrane.
• the lower limit of the amount of the polyolefin (B) added is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 15% by mass or more, and 20% by mass or more. Most preferably.
• the polyolefin (B) is 40% by mass or less, the pore size of the microporous membrane becomes large, sufficient permeability can be obtained, the strength is excellent, and the rise in shutdown temperature can be suppressed. Further, when it is 5% by mass or more, it has a co-continuous structure with the polyolefin resin which is the main component, and the effect of improving the meltdown temperature by adding the polyolefin (B) is likely to be exhibited.
• the melting point of the polyolefin (B) to be added is preferably 150 ° C. or higher, more preferably 155 ° C. or higher, and even more preferably 160 ° C. or higher.
• Further molecular weight of the polyolefin (B) is preferably a weight average molecular weight 5.0 ⁇ 10 5 or more, more preferably 10 ⁇ 10 5 or more, further preferably 15 ⁇ 10 5 or more. Also preferably the upper limit of the weight average molecular weight is 10 ⁇ 10 6 or less, more preferably 8.0 ⁇ 10 6 or less, further preferably 5.0 ⁇ 10 6 or less, and most preferably 3 .0 is ⁇ 10 6 or less. When the molecular weight is in the above range, the strength of the obtained polyolefin microporous film is sufficient, which is preferable.
• the molecular weight is 10 ⁇ 106 or less, it is preferable during melt-kneading in the process of producing the polyolefin microporous film described later. It is preferable that the viscosity does not become too high and the kneading can be performed uniformly.
• the blending ratio of the polyolefin resin and the plasticizer may be 100% by mass based on the total of the polyolefin resin and the plasticizer, and the content of the polyolefin resin may be appropriately selected within a range that does not impair the moldability, but is 10 to 50 mass. %.
• the polyolefin resin is less than 10% by mass (when the plasticizer is 90% by mass or more)
• the amount of the polyolefin resin exceeds 50% by mass (when the amount of the plasticizer is 50% by mass or less)
• the shrinkage in the film thickness direction becomes large and the molding processability also deteriorates.
• the polyolefin microporous membrane according to the embodiment of the present invention includes antioxidants, heat stabilizers and antistatic agents, ultraviolet absorbers, and further blocking inhibitors and fillers as long as the effects of the present invention are not impaired.
• Various additives such as the above may be contained.
• an antioxidant for the purpose of suppressing oxidative deterioration due to the thermal history of the polyethylene resin.
• examples of the antioxidant include 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4) and 1,3,5-trimethyl-2,4,6-tris (3,5-di).
• Benzene for example, BASF "Irganox” (registered trademark) 1330: molecular weight 775.2), tetrakis [methylene-3- (3,5-di-t-butyl-4-) It is preferable to use one or more selected from [hydroxyphenyl) propionate] methane (for example, "Irganox” (registered trademark) 1010: molecular weight 1177.7 manufactured by BASF).
• Appropriate selection of the type and amount of antioxidant and heat stabilizer is important for adjusting or enhancing the characteristics of the microporous membrane.
• the polyolefin microporous membrane according to the embodiment of the present invention can be obtained by biaxial stretching using the above-mentioned raw materials.
• the biaxial stretching method can be obtained by any of the inflation method, the simultaneous biaxial stretching method, and the sequential biaxial stretching method. Among them, film forming stability, thickness uniformity, high rigidity and dimensional stability of the film are obtained. It is preferable to adopt the simultaneous biaxial stretching method or the sequential biaxial stretching method in terms of controlling the above.
• the method for producing a microporous polyolefin membrane according to the embodiment of the present invention comprises the following steps (a) to (e).
• a polymer material containing a single polyolefin, a polyolefin mixture, a polyolefin solvent (plasticizer) mixture, an additive, and a polyolefin kneaded product is kneaded and dissolved to prepare a polyolefin solution.
• B The dissolved product is extruded into a sheet. Molding, cooling and solidification (c) The obtained sheet is stretched by a roll method or a tenter method (d) Then, a plasticizer is extracted from the obtained stretched film and the film is dried (e), followed by heat treatment / Re-stretch / heat-fix.
• a polyolefin resin solution is prepared by heating and dissolving the polyolefin resin used in the embodiment of the present invention in a plasticizer.
• the plasticizer is not particularly limited as long as it is a solvent capable of sufficiently dissolving the polyolefin resin, but the solvent is preferably a liquid at room temperature in order to enable stretching at a relatively high magnification.
• Solvents include aliphatic, cyclic aliphatic or aromatic hydrocarbons such as nonane, decane, decalin, paraxylene, undecane, dodecane, liquid paraffin, mineral oil distillates having corresponding boiling points, and dibutylphthalates.
• Examples thereof include phthalates that are liquid at room temperature, such as dioctyl phthalates.
• a non-volatile liquid solvent such as liquid paraffin.
• a solid solvent may be mixed with the liquid solvent.
• examples of such a solid solvent include stearyl alcohol, ceryl alcohol, paraffin wax and the like. However, if only a solid solvent is used, uneven stretching may occur.
• the viscosity of the liquid solvent is preferably 20 to 200 cSt at 40 ° C.
• the viscosity at 40 ° C. is 20 cSt or more, the sheet obtained by extruding the polyolefin resin solution from the die is unlikely to become non-uniform.
• the liquid solvent can be easily removed.
• the viscosity of the liquid solvent is the viscosity measured at 40 ° C. using an Ubbelohde viscometer.
• the uniform melt-kneading of the polyolefin-based resin solution is not particularly limited, but when it is desired to prepare a high-concentration polyolefin-based resin solution, it can be performed in a twin-screw extruder. preferable. If necessary, various additives such as antioxidants may be added as long as the effects of the present invention are not impaired. In particular, it is preferable to add an antioxidant in order to prevent oxidation of the polyolefin resin.
• the polyolefin microporous membrane according to the embodiment of the present invention is a single membrane microporous membrane containing polyethylene (A) and polyolefin (B) other than polyethylene, it is necessary to uniformly knead and extrude a plurality of raw materials having different melting points. is there. If the kneaded state is not uniform, the strength and meltdown temperature of the microporous membrane may decrease, and the pore size may vary widely.
• the first half of the extruder is set to Tm1 + 30 ° C or lower when the melting point of the raw material with the lowest melting point among the polyethylene (A) and polyolefin (B) used is Tm1, and before the raw material melts. It is preferable to mix uniformly in the state of.
• the polyolefin-based resin solution is uniformly mixed at a temperature at which the polyethylene (A) and the polyolefin (B) are completely melted.
• the melt-kneading temperature is preferably (Tm2-10 ° C.) to (Tm2 + 120 ° C.) when the melting point of the raw material having the highest melting point among the polyethylene (A) and polyolefin (B) used is Tm2. More preferably, it is (Tm2 + 20 ° C.) to (Tm2 + 100 ° C.).
• the melting point means a value measured by DSC based on JIS K7121 (1987) (hereinafter, the same applies).
• the melt-kneading temperature is preferably in the range of 160 ° C. or lower in the first half of the extruder and 150 to 280 ° C. in the latter half.
• the melt-kneading temperature is low from the viewpoint of suppressing the deterioration of the resin, but if it is lower than the above-mentioned temperature, unmelted matter is generated in the extruded product extruded from the die, causing film rupture or the like in the subsequent stretching step. If the temperature is higher than the above-mentioned temperature, the thermal decomposition of the polyolefin resin becomes intense, and the physical properties of the obtained microporous film, for example, strength and porosity may be inferior. In addition, the decomposed product precipitates on a chill roll or a roll in the stretching process and adheres to the sheet, which leads to deterioration of the appearance. Therefore, it is preferable to knead within the above range.
• a gel-like sheet is obtained by cooling the obtained extruded product, and the microphase of the polyolefin-based resin separated by the solvent can be immobilized by cooling. It is preferable to cool to 10 to 50 ° C. in the cooling step. This is because the final cooling temperature is preferably set to be equal to or lower than the crystallization end temperature, and by making the higher-order structure finer, uniform stretching can be easily performed in the subsequent stretching. Therefore, cooling is preferably performed at a rate of 30 ° C./min or higher at least up to the gelation temperature or lower. If the cooling rate is less than 30 ° C./min, the crystallinity increases and it is difficult to obtain a gel-like sheet suitable for stretching.
• cooling method there are a method of directly contacting with cold air, cooling water, and other cooling media, a method of contacting with a roll cooled with a refrigerant, a method of using a casting drum, and the like.
• the obtained gel-like (including laminated sheet) sheet is stretched.
• the stretching method used includes uniaxial stretching in the sheet transport method (MD direction) by a roll stretching machine, uniaxial stretching in the sheet width direction (TD direction) by a tenter, a roll stretching machine and a tenter, or a combination of a tenter and a tenter. Sequential biaxial stretching by, simultaneous biaxial stretching by simultaneous biaxial tenter, and the like.
• the stretching ratio varies depending on the thickness of the gel-like sheet from the viewpoint of uniformity of film thickness, but it is preferable to stretch 5 times or more in any direction.
• the area magnification is preferably 25 times or more, more preferably 36 times or more, even more preferably 49 times, and most preferably 64 times or more.
• the area magnification is preferably 100 times or less.
• the area magnification is increased, tearing is likely to occur frequently during the production of the microporous film, the productivity is lowered, and when the orientation is advanced and the crystallinity is high, the melting point and strength of the microporous film are improved.
• the higher crystallinity means that the amorphous part is reduced, and the melting point and shutdown temperature of the film are raised.
• the stretching temperature is preferably in the range of (melting point of the gel sheet + 10 ° C. or lower) to (crystal dispersion temperature Tcd of the polyolefin resin) to (melting point of the gel sheet + 5 ° C.).
• the stretching temperature is preferably 90 to 125 ° C., more preferably 90 to 120 ° C.
• the crystal dispersion temperature Tcd is obtained from the temperature characteristics of dynamic viscoelasticity measured according to ASTM D 4065. Alternatively, it may be obtained from NMR.
• the temperature is lower than 90 ° C., the pores are insufficiently opened due to low temperature stretching, it is difficult to obtain uniformity in film thickness, and the pore ratio is also low. If the temperature is higher than 125 ° C., the sheet melts and the pores are likely to be closed.
• Cleavage occurs in the higher-order structure formed on the gel sheet by the above stretching, the crystal phase becomes finer, and a large number of fibrils are formed. Fibrils form a three-dimensionally irregularly connected network structure. Stretching improves the mechanical strength and expands the pores, making it suitable as a battery separator. Further, by stretching before removing the plasticizer, the polyolefin-based resin is in a state of being sufficiently plasticized and softened, so that the higher-order structure is smoothly cleaved and the crystal phase is uniformly refined. Can be done. Further, since the cleavage is easy, strain at the time of stretching is less likely to remain, and the heat shrinkage rate can be lowered as compared with the case of stretching after removing the plasticizer.
• plasticizer extraction (cleaning) / drying step Next, the plasticizer (solvent) remaining in the gel sheet is removed using a cleaning solvent. Since the polyolefin-based resin phase and the solvent phase are separated, a microporous film can be obtained by removing the solvent.
• the cleaning solvent include saturated hydrocarbons such as pentane, hexane and heptane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, ethers such as diethyl ether and dioxane, ketones such as methyl ethyl ketone, and ethane trifluoride. Chain fluorocarbon and the like can be mentioned.
• These cleaning solvents have low surface tension (eg, 24 mN / m or less at 25 ° C.). By using a cleaning solvent with a low surface tension, in a network structure that forms microporous, shrinkage due to surface tension at the gas-liquid interface is suppressed during drying after cleaning, and microporous with good porosity and permeability. A film is obtained.
• These cleaning solvents are appropriately selected according to the plasticizer and used alone or in combination.
• the cleaning method can be performed by immersing the gel-like sheet in a cleaning solvent and extracting it, showering the gel-like sheet with the cleaning solvent, or a method using a combination thereof.
• the amount of the cleaning solvent used varies depending on the cleaning method, but is generally preferably 300 parts by mass or more with respect to 100 parts by mass of the gel sheet.
• the washing temperature may be 15 to 30 ° C., and if necessary, heat to 80 ° C. or lower.
• the mechanical and electrical properties of the polyolefin microporous film are examined.
• the longer the gel sheet is immersed in the cleaning solvent the better.
• the above-mentioned washing is preferably carried out until the residual solvent in the gel-like sheet after washing, that is, the polyolefin microporous membrane becomes less than 1% by mass.
• the solvent in the polyolefin microporous membrane is dried and removed in the drying step.
• the drying method is not particularly limited, and a method using a metal heating roll, a method using hot air, or the like can be selected.
• the drying temperature is preferably 40 to 100 ° C, more preferably 40 to 80 ° C. If the drying is insufficient, the porosity of the polyolefin microporous membrane will decrease in the subsequent heat treatment, and the permeability will deteriorate.
• the dried polyolefin microporous film may be stretched (re-stretched) in at least the uniaxial direction.
• the re-stretching can be performed by the tenter method or the like in the same manner as the above-mentioned stretching while heating the microporous membrane.
• the re-stretching may be uniaxial stretching or biaxial stretching. In the case of multi-stage stretching, simultaneous biaxial and / and sequential stretching are combined.
• the temperature of re-stretching is preferably equal to or lower than the melting point of the polyolefin-based composition, and more preferably within the range of (Tcd-20 ° C.) to the melting point. Specifically, 70 to 135 ° C. is preferable, and 110 to 132 ° C. is more preferable. Most preferably, it is 120 to 130 ° C.
• the re-stretching ratio is preferably 1.01 to 1.6 times, particularly preferably 1.1 to 1.6 times in the TD direction, and more preferably 1.2 to 1.4 times.
• the ratio is 1.01 to 1.6 times in the MD direction and the TD direction, respectively.
• the re-stretching magnification may be different in the MD direction and the TD direction.
• the relaxation rate from the maximum re-stretching ratio is preferably 0.9 or less, and more preferably 0.8 or less.
• the re-stretched film is heat-fixed by fixing the width of the film to a constant level.
• the heat fixing temperature is preferably 70 to 135 ° C, more preferably 110 to 132 ° C. Most preferably, it is 115 to 130 ° C.
• the heat fixing time is not particularly limited, but is about 1 second to 10 minutes.
• the microporous membrane can be hydrophilized.
• the hydrophilization treatment can be performed by monomer grafting, surfactant treatment, corona discharge, or the like.
• the monomer graft is preferably carried out after the cross-linking treatment.
• the microporous polyolefin membrane is crosslinked by irradiation with ionizing radiation such as ⁇ -ray, ⁇ -ray, ⁇ -ray, and electron beam.
• ionizing radiation such as ⁇ -ray, ⁇ -ray, ⁇ -ray, and electron beam.
• electron beam irradiation an electron dose of 0.1 to 100 Mrad is preferable, and an acceleration voltage of 100 to 300 kV is preferable.
• the cross-linking treatment raises the meltdown temperature of the microporous polyolefin membrane.
• any of nonionic surfactant, cationic surfactant, anionic surfactant or amphoteric surfactant can be used, but nonionic surfactant is preferable.
• the microporous membrane is immersed in water or a solution prepared by dissolving a surfactant in a lower alcohol such as methanol, ethanol, or isopropyl alcohol, or the solution is applied to the microporous membrane by the doctor blade method.
• the polyolefin microporous film is made of a fluororesin porous body such as polyvinylidene fluoride or polytetrafluoroethylene, or a polyimide or polyphenylene sulfide for the purpose of improving meltdown characteristics and heat resistance when used as a battery separator.
• a surface coating such as a porous body or an inorganic coating such as ceramic may be applied.
• the polyolefin microporous film according to the embodiment of the present invention is a laminate having a coat layer on at least one side.
• the polyolefin microporous film obtained as described above can be used for various purposes such as filters, fuel cell separators, and condenser separators. Especially when used as a battery separator, it has low shutdown characteristics and high melt. Not only does it have down characteristics, but it also has high strength despite being a thin film, which makes it possible to achieve both high energy density, high capacity, and high output for electric vehicles, etc. It can be preferably used as a battery separator for a required secondary battery.
• the present invention also relates to a battery using the polyolefin microporous membrane or laminate according to the embodiment of the present invention.
• Mw (PE conversion) Mw (PS conversion measurement value) x 0.468
• Mn (PE conversion) Mn (PS conversion measurement value) x 0.468
• the thickness of the microporous membrane was randomly selected using a contact thickness gauge and Mitutoyo Co., Ltd.
• Lightmatic VL-50 (10.5 mm ⁇ cemented carbide spherical stylus, measuring load 0.01 N). Measured at position. Measurements were made at points along the TD (width) of the membrane over a distance of 30 cm at 5 mm intervals. Then, the measurement along the above TD was performed 5 times, and the arithmetic mean thereof was taken as the sample thickness.
• the puncture strength L2 (N) was calculated when the film thickness was 5 ⁇ m.
• Tensile strength, tensile elongation Tensile strength M MD and tensile strength M TD , and tensile elongation in the MD direction and tensile elongation in the TD direction are 100 mm in accordance with ASTM D882 using a strip-shaped test piece with a width of 10 mm. Measured at a speed of / min.
• the above-mentioned air permeability resistance is measured while raising the temperature from room temperature at 5 ° C / min, and the temperature when the air permeability resistance reaches 100,000 seconds / 100 cm 3 is the shutdown temperature (SD temperature) (° C). And said.
• the measurement cell was composed of an aluminum block and had a structure having a thermocouple directly under the microporous polyolefin membrane. The sample was cut into 5 cm ⁇ 5 cm squares, and the temperature was measured while fixing the periphery with an ⁇ ring.
• a microporous membrane having a meltdown temperature of 50 mm square is sandwiched between a pair of metal block frames having holes with a diameter of 12 mm, and a tungsten carbide sphere with a diameter of 10 mm is placed on the microporous membrane.
• the microporous membrane is installed so as to have a horizontal plane. Start from 30 ° C and raise the temperature at 5 ° C / min. The temperature at which the microporous membrane was ruptured by the sphere was measured and used as the meltdown temperature (MD temperature).
• DSC measurement Melting point and full width at half maximum are determined by differential scanning calorimetry (DSC). This DSC was carried out using TA Instruments MDSC2920 or Q1000Tzero-DSC, and the temperature was raised from 30 ° C. to 230 ° C. at a rate of 10 ° C./min based on JISK7121 to obtain the maximum temperature (peak) of the melting peak. Temperature) was evaluated. The peak temperature in the region below 150 ° C. was defined as P1, and the peak temperature in the region above 150 ° C. was defined as P2.
• the full width at half maximum is T when the temperature at which the calorific value Q 1/2 is 0.5 times the maximum calorific value Q in the region below 150 ° C. is T 1 and T 2 (T 1 ⁇ T 2 ), respectively.
• the value of 2- T 1 was calculated. If there are two or more maximum values in the region below 150 ° C and three or more temperatures that are Q 1/2 , the minimum temperature of the corresponding temperature is T 1 and the maximum temperature is T 2.
• the price range was calculated.
• d ( ⁇ m) is the pore size of the porous polyolefin film
• ⁇ (mN / m) is the surface tension of the liquid
• P (Pa) is the pressure
• C is the wetting tension of the immersion liquid.
• Example 1 The weight average molecular weight (Mw) of 1.8 ⁇ 10 5, 54.6 parts by weight of branched high-density polyethylene (branch HDPE) having a melting point of 133 ° C., ultra high molecular weight polyethylene (UHPE) (Mw2.0 ⁇ 10 6 , melting point 133 ° C.) 23.4 parts by mass of polypropylene (PP) (Mw1.1 ⁇ 10 6 , melting point 165 ° C.) 22.0 parts by mass, were mixed respectively to give the polyolefin composition.
• WPE branched high-density polyethylene
• UHPE ultra high molecular weight polyethylene
• PP polypropylene
• the obtained polyethylene resin solution is put into a twin-screw extruder, kneaded at 150 ° C in the first half of the extruder and 180 ° C in the second half, and supplied to a T-die so that the thickness of the microporous membrane is finally 5 ⁇ m. After extruding into a sheet, the extrude was cooled with a cooling roll controlled at 15 ° C. to form a gel sheet.
• the obtained gel-like sheet was clipped on four sides with a film stretcher, stretched 7 times in the longitudinal direction at 115 ° C., stretched 7 times in the width direction (sequential stretching (surface magnification 49 times)), and as it was.
• the sheet width was fixed in a film stretcher, held at a temperature of 115 ° C. for 10 seconds, and taken out.
• the stretched gel-like sheet was fixed to a gold frame, immersed in a methylene chloride bath in a washing tank, and dried after removing liquid paraffin to obtain a polyolefin microporous film.
• microporous polyolefin membrane fixed to the metal frame was introduced into a hot air oven, and heat fixing treatment was performed at 120 ° C. for 10 minutes.
• Table 1 shows the raw material characteristics of the polyolefin microporous membrane, the film forming conditions, and the evaluation results for the microporous membrane.
• Examples 2 to 3 Comparative Examples 1 to 4
• a polyolefin laminated microporous film was prepared in the same manner as in Example 1 except that the raw material composition and the film forming conditions were changed as shown in Tables 1 and 2.
• the raw material characteristics of the polyolefin microporous membrane, the film forming conditions, and the evaluation results of the obtained polyolefin microporous membrane are as shown in Tables 1 and 2.
• linear HDPE linear high-density polyethylene
• Example 4 The weight average molecular weight (Mw) of 9.0 ⁇ 10 4, 20 parts by weight of branched high-density polyethylene (branch HDPE) having a melting point of 131 ° C., ultra high molecular weight polyethylene (UHPE) (mp 136 °C, Mw1.0 ⁇ 10 6 70 parts by mass), polypropylene (PP) (Mw1.1 ⁇ 10 6 ) 10.0 parts by mass, were mixed respectively to give the polyolefin composition.
• WPE branched high-density polyethylene
• UHPE ultra high molecular weight polyethylene
• PP polypropylene
• the obtained polyethylene resin solution is put into a twin-screw extruder, kneaded at 150 ° C. in the first half of the extruder and 180 ° C. in the second half, and supplied to a T-die so that the thickness of the microporous membrane is finally 6 ⁇ m. After extruding into a sheet, the extrude was cooled with a cooling roll controlled at 15 ° C. to form a gel sheet.
• the obtained gel-like sheet is clipped on four sides by a film stretcher and stretched 5 times in the longitudinal direction and the width direction at 115 ° C. (simultaneous stretching (surface magnification 25 times)) in the film stretcher as it is.
• the sheet width was fixed with, held at a temperature of 115 ° C. for 10 seconds, and taken out.
• the stretched gel-like sheet was fixed to a gold frame, immersed in a methylene chloride bath in a washing tank, and dried after removing liquid paraffin to obtain a polyolefin microporous film.
• microporous polyolefin membrane fixed to the gold frame was introduced into a hot air oven, and heat fixing treatment was performed at 130 ° C. for 10 minutes.
• Table 1 shows the raw material characteristics of the polyolefin microporous membrane, the film forming conditions, and the evaluation results for the microporous membrane.
• Example 5 The stretching ratio by the film stretcher was set to 7 times stretching in the longitudinal direction and the width direction (simultaneous stretching (surface magnification 49 times)), and a porous film having a thickness of 6 ⁇ m was obtained by the same method as in Example 4 except for the stretching ratio.
• Table 1 shows the raw material characteristics of the polyolefin microporous membrane, the film forming conditions, and the evaluation results for the microporous membrane.
• the polyolefin microporous membrane of the present invention is a thin film, it has excellent strength, low shutdown characteristics and high meltdown characteristics, and therefore is excellent in safety and output characteristics when used as a battery separator. Therefore, it can be suitably used as a battery separator or a laminate for a battery such as an electric vehicle that requires high energy density, high capacity, and high output, and a secondary battery.

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• 2020
  • 2020-08-19 KR KR1020227004158A patent/KR20220051166A/ko active Pending
  • 2020-08-19 WO PCT/JP2020/031349 patent/WO2021033733A1/ja not_active Ceased
  • 2020-08-19 JP JP2020545382A patent/JP7683215B2/ja active Active
  • 2020-08-19 CN CN202080056541.XA patent/CN114207003A/zh active Pending

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