Classifications

• • 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
  • H01M50/50—Current conducting connections for cells or batteries
  • H01M50/572—Means for preventing undesired use or discharge
  • H01M50/574—Devices or arrangements for the interruption of current
  • H01M50/581—Devices or arrangements for the interruption of current in response to temperature
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/12—Composite membranes; Ultra-thin membranes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
  • B01D71/06—Organic material
  • B01D71/26—Polyalkenes
• • 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
• • 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
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2325/00—Details relating to properties of membranes
  • B01D2325/22—Thermal or heat-resistance properties
• • 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 having excellent shutdown characteristics and high safety when used as a secondary battery separator, a secondary battery separator containing a polyolefin microporous membrane, and a secondary battery.
• Microporous membranes are used in various fields such as filters for filtration membranes and dialysis membranes, separators for secondary batteries and separators for electrolytic capacitors.
• polyolefin microporous membranes made of polyolefin as a resin material are excellent in chemical resistance, insulating property, mechanical strength, etc., and have shutdown characteristics, and are therefore widely used as separators for secondary batteries in recent years.
• Secondary batteries for example, lithium ion secondary batteries, have a high energy density and are therefore widely used as batteries used in personal computers, mobile phones, and the like. Secondary batteries are also expected to be used as power sources for driving motors of electric vehicles and hybrid vehicles, and as stationary storage batteries.
• the energy density of secondary batteries has been increasing, and the electrodes used accordingly have lower thermal stability (lower thermal runaway start temperature). Therefore, the microporous membrane used for the separator for secondary batteries shuts down at a lower temperature in the event of a short circuit or abnormal heat generation of the battery due to overcharging, and prevents thermal runaway by preventing ion movement on the positive electrode side and the negative electrode side. Is required.
• Patent Document 1 discloses a polyethylene microporous membrane in which the pore closing temperature Tf is 134 ° C. or lower and the relationship between the melting temperature Tm and Tf of the film is Tm ⁇ Tf> 0, and when used as a battery separator, it is disclosed. It is said that it can prevent a short circuit during overcharging.
• the electrolyte injection property is 20 seconds or less
• the shutdown temperature is 132 ° C. or less
• the air permeability when the film thickness is converted to 20 ⁇ m is 700 seconds / 100 cm 3 or less
• the film thickness is 20 ⁇ m.
• a polyolefin microporous film having a puncture strength of 2,000 mN or more in terms of puncture strength is disclosed. It is said that this can be achieved by a polyolefin microporous membrane containing polyethylene having a low melting point and a low molecular weight in which polypropylene is uniformly dispersed in a film.
• E'(40 ° C.) and the storage elastic modulus at the shutdown temperature is E'(SD), E'(40 ° C.) / E'(SD) is The polyolefin microporous membrane according to any one of [1] to [3], which is 300 or less.
• E'(40 ° C.) / E'(SD) is The polyolefin microporous membrane according to any one of [1] to [3], which is 300 or less.
• the present invention it is possible to provide a polyolefin microporous membrane having excellent shutdown characteristics and high safety, a separator for a secondary battery having the polyolefin microporous membrane, and a secondary battery.
• the microporous polyolefin membrane according to the embodiment of the present invention has a shutdown temperature of 135 ° C. or lower and a crystal melting rate of 50% or less at the shutdown temperature.
• the shutdown temperature is a temperature at which the porous structure is closed by melting with heat and power generation is stopped by stopping the ion movement when the battery overheats abnormally.
• the shutdown temperature of the microporous polyolefin membrane according to the embodiment of the present invention is 135 ° C. or lower. It is more preferably 132 ° C. or lower, further preferably 130 ° C. or lower, and particularly preferably 128 ° C. or lower. By controlling the shutdown temperature to 135 ° C or lower, it is excellent in safety when it is used as a separator for a secondary battery.
• the lower limit of the shutdown temperature is not particularly limited, but it is preferably 100 ° C.
• the above-mentioned shutdown temperature range can be obtained by adjusting the composition of the polyolefin raw material constituting the microporous film to the range described later and setting the film forming conditions to the range described later.
• the shutdown temperature can be measured by the method described later.
• the crystal melting rate of the microporous polyolefin membrane according to the embodiment of the present invention at the shutdown temperature is 50% or less. It is more preferably 45% or less, further preferably 40% or less, and particularly preferably 35% or less.
• the lower limit of the crystal melting rate at the shutdown temperature is not particularly limited, but is preferably 5% or more because the decrease in ion permeability due to pore blockage during film formation can be suppressed.
• the crystal melting rate at the shutdown temperature described above can be obtained by adjusting the composition of the polyolefin raw material constituting the microporous film to the range described later and setting the film forming conditions to the range described later.
• the crystal melting rate at the shutdown temperature of the polyolefin microporous film is calculated by the following formula by measuring the heat of crystal melting and the heat of total crystal melting below the shutdown temperature using the differential scanning calorimetry (DSC) method. Can be done.
• DSC differential scanning calorimetry
• the puncture strength per 10 ⁇ m of the polyolefin microporous membrane according to the embodiment of the present invention is preferably 2.3 N or more, more preferably 2.5 N or more, still more preferably 2.7 N or more, and particularly preferably 3.0 N or more. Is.
• the upper limit of the puncture strength per 10 ⁇ m is not particularly limited, but it is preferably 8.0 N or less because it becomes easy to control the shutdown temperature within an appropriate range.
• the puncture strength in terms of 10 ⁇ m is within the above range, the secondary battery using this as a separator suppresses the occurrence of short-circuiting of the electrodes.
• the puncture strength in terms of 10 ⁇ m can be set within the above range by adjusting the weight average molecular weight (Mw) of the raw material resin, stretching conditions, and the like when producing the polyolefin microporous film.
• the film thickness of the polyolefin microporous membrane according to the embodiment of the present invention is preferably 20 ⁇ m or less, more preferably 13 ⁇ m or less, still more preferably 10 ⁇ m or less, and particularly preferably 7 ⁇ m or less.
• the lower limit of the film thickness is not particularly limited, but it is preferably 1 ⁇ m or more because the occurrence of a short circuit can be suppressed when used as a separator for a secondary battery.
• the film thickness is within the above range, the battery capacity is improved by using the polyolefin microporous membrane as a separator for a secondary battery.
• the porosity of the polyolefin microporous membrane according to the embodiment of the present invention is preferably 30% or more, more preferably 35% or more, still more preferably 40% or more.
• the upper limit of the porosity is not particularly set, but it is preferably 75% or less because the decrease in film strength can be suppressed.
• the porosity can be within the above range by adjusting the blending ratio of the polyolefin constituents, the stretching ratio, the heat fixing conditions, and the like in the manufacturing process.
• the air permeation resistance of the polyolefin microporous membrane according to the embodiment of the present invention in terms of thickness of 10 ⁇ m is preferably 400 seconds / 100 cm 3 or less, more preferably 300 seconds / 100 cm 3 or less, and further preferably 200 seconds / 100 cm. 3 or less, particularly preferably 150 seconds / 100 cm 3 or less.
• the air permeation resistance is preferably 50 seconds / 100 cm 3 or more.
• the storage elastic modulus (E') of the polyolefin microporous membrane according to the embodiment of the present invention measured at 1 Hz the storage elastic modulus at 40 ° C. is E'(40 ° C.), and the polyolefin microporous membrane is stored at the shutdown temperature.
• E'(SD) the elastic modulus
• E'(40 ° C.) / E'(SD) is preferably 300 or less, more preferably 200 or less, still more preferably 150 or less.
• the lower limit of E'(40 ° C.) / E'(SD) is not particularly set, but it is preferably 10 or more because it can suppress the decrease in ion permeability during film formation.
• the storage elastic modulus E'(SD) of the polyolefin microporous membrane at the shutdown temperature is preferably 6 MPa or more, more preferably 7 MPa or more, still more preferably 8 MPa or more, and particularly preferably 10 MPa or more.
• E'(SD) By setting E'(SD) to 6 MPa or more, the film strength at shutdown is high, and the safety is more excellent.
• the upper limit of E'(SD) is not particularly set, but it is preferably 100 MPa or less from the viewpoint of compatibility with the shutdown temperature.
• the E'of the polyolefin microporous membrane can be measured by the method described later.
• the half width of the crystal melting peak when the temperature distribution curve of the heat of crystal melting of the polyolefin microporous film according to the embodiment of the present invention is measured by differential scanning calorimetry (DSC) is preferably 12 ° C. or lower, more preferably 10. ° C. or lower, more preferably 9 ° C. or lower.
• DSC differential scanning calorimetry
• the lower limit of the half width of the crystal melting peak is not particularly set, it is preferably 1 ° C. or higher because the decrease in film strength at shutdown can be suppressed.
• the average pore size (average flow rate pore size) of the polyolefin microporous membrane according to the embodiment of the present invention is preferably 25 nm or less, more preferably 22 nm or less, still more preferably 20 nm or less, and particularly preferably 17 nm or less.
• the lower limit of the average pore size is not particularly set, but it is preferable that the average pore size is 5 nm or more because good permeability can be easily obtained.
• the average pore size is a value measured by a method (half-dry method) based on ASTM E1294-89, and can be measured by the method described later.
• the maximum pore size of the polyolefin microporous membrane according to the embodiment of the present invention is preferably 40 nm or less, more preferably 38 nm or less, still more preferably 35 nm or less.
• the lower limit of the maximum pore diameter is not particularly set, but if it is 10 nm or more, good permeability can be easily obtained, which is preferable.
• the maximum hole diameter is a value measured by the method (bubble point method) specified in JIS K 3832 (1990), and can be measured by the method described later.
• the difference between the maximum pore size and the average pore size (maximum pore size-average pore size) of the polyolefin microporous membrane according to the embodiment of the present invention is preferably 25 nm or less, more preferably 20 nm or less, still more preferably 17 nm or less, and particularly preferably. It is 15 nm or less.
• the lower limit of the difference between the maximum pore size and the average pore size is not particularly set, but if it is 3 nm or more, the range of polyolefin raw material selection and process conditions is widened, and it is preferable because it is easy to achieve both productivity.
• the polyolefin microporous membrane according to the embodiment of the present invention contains a polyolefin resin as a main component.
• the polyolefin resin is preferably contained in an amount of 80% by mass, more preferably 90% by mass or more, based on the total mass of the microporous polyolefin membrane.
• the polyolefin resin include polyethylene-based resin and polypropylene-based resin, and it is preferable to use polyethylene as a main component from the viewpoint of functional balance such as shutdown behavior, strength, and permeability.
• polyethylene-based resin various types of polyethylene can be used, and examples thereof include ultra-high density polyethylene, high density polyethylene, medium density polyethylene, branched low density polyethylene, and linear low density polyethylene.
• the polyethylene-based resin may be an ethylene homopolymer or a copolymer of ethylene and another ⁇ -olefin. Examples of the ⁇ -olefin include propylene, butene-1, hexene-1, penten-1, 4-methylpentene-1, octene, vinyl acetate, methyl methacrylate, styrene and the like.
• the polyolefin microporous film according to the embodiment of the present invention preferably contains high-density polyethylene (density: 0.940 g / m 3 or more and 0.970 g / cm 3 or less), and ⁇ -olefin other than ethylene, for example, propylene. It is more preferable to contain high-density polyethylene copolymerized with 1-butene, 1-hexene, 1-pentene, 4-methyl-1-pentene, octene, vinyl acetate, methyl methacrylate, styrene and the like, and hexene-1 is also used.
• the polyolefin microporous film is mainly composed of a high-density polyethylene (ethylene / 1-hexene copolymer) in which 1-hexene is copolymerized.
• ethylene / 1-hexene copolymer high-density polyethylene
• 1-hexene copolymerized polyethylene
• the melt extrusion characteristics are excellent, and at the same time, the melting point and crystallinity of the polyolefin microporous film can be adjusted within an appropriate range. It is possible to achieve both low shutdown temperature and film strength at shutdown.
• the ⁇ -olefin can be confirmed by measuring with C13-NMR.
• the high-density polyethylene is preferably contained in an amount of 10% by mass or more, more preferably 20% by mass or more, still more preferably 40% by mass or more, and particularly preferably 60% by mass or more, based on the total mass of the microporous polyolefin membrane.
• the lower limit of the weight average molecular weight in the high density polyethylene is preferably 1 ⁇ 10 4 or more, more preferably 1 ⁇ 10 5 or more, further preferably 1.5 ⁇ 10 5 or more.
• the upper limit of the weight average molecular weight of high density polyethylene 1 ⁇ 10 6 or less, more preferably 8.0 ⁇ 10 5 or less, more preferably 6.0 ⁇ 10 5 or less.
• the melting point of the high-density polyethylene in the above range, it is possible to achieve both a low shutdown temperature and the permeability of the polyolefin microporous film (film).
• the polyolefin microporous film according to the embodiment of the present invention is a low-density polyethylene, a linear low-density polyethylene, an ethylene / ⁇ -olefin copolymer produced by a single-site catalyst, and a low weight average molecular weight of 1000 to 100,000.
• a molecular weight polyethylene or the like is added, a shutdown function at a low temperature is imparted, and the characteristics as a separator for a secondary battery can be improved.
• the above-mentioned low molecular weight polyethylene is added in a large proportion, coarse pores are formed in the microporous membrane in the film forming process, the shutdown temperature rises, and the film strength at the time of shutdown decreases.
• high-density polyethylene having a density as an ethylene / ⁇ -olefin copolymer exceeding 0.94 g / cm 3 , and as described above, it is necessary to improve the shutdown characteristics and achieve both film strength at shutdown. Therefore, it is more preferable to add branched high-density polyethylene containing long-chain branched.
• the molecular weight distribution of the polyolefin microporous membrane according to the embodiment of the present invention preferably has an area ratio of a component having a molecular weight of less than 10,000 in the differential molecular weight distribution curve obtained by the gel permeation chromatography (GPC) method. Is 20% or less, more preferably 15% or less, still more preferably 10% or less, and particularly preferably 5% or less.
• GPC gel permeation chromatography
• the lower limit of the area ratio of the component having a molecular weight of less than 10,000 is not particularly set, but it is preferable if it is 0.001% or more because the film forming property is good.
• a microporous polyolefin membrane according to an embodiment of the present invention it is preferable that the weight average molecular weight (Mw) containing 1 ⁇ 10 6 or more ultra-high molecular weight polyethylene.
• the ultra-high molecular weight polyethylene is preferably contained in an amount of 5% by mass or more, more preferably 20% by mass, and particularly preferably 30% by mass or more, based on the total mass of the microporous polyolefin membrane.
• the upper limit is preferably 80% by mass or less, more preferably 70% by mass or less, and particularly preferably 60% by mass or less.
• the ultra-high molecular weight polyethylene may contain at least one type, and for example, two or more types of ultra-high molecular weight polyethylene having different Mw may be mixed and used as a raw material.
• the melting point of the ultrahigh molecular weight polyethylene is preferably 132 ° C. or lower, more preferably 130 ° C. or lower, still more preferably 128 ° C. or lower. Although the lower limit is not particularly set, the decrease in ion permeability of the microporous membrane can be suppressed by setting the temperature to 115 ° C.
• the obtained microporous membrane has a uniform and fine pore structure, a low shutdown temperature when used as a separator for a secondary battery, and a crystal melting rate at the time of shutdown. It is a separator with excellent safety while achieving both reduction.
• a polypropylene resin as the polyolefin resin from the viewpoint of improving the meltdown temperature when used as a separator for a secondary battery.
• a polypropylene-based resin in addition to homopolypropylene, block copolymers and random copolymers can also be used.
• the block copolymer and the random copolymer can contain a copolymer component with ⁇ -ethylene other than propylene, and ethylene is preferable as ⁇ -ethylene.
• the amount of the polypropylene-based resin added is preferably 30% by mass or less, more preferably 20% by mass or less, based on the total mass of the microporous polyolefin membrane. By setting the content to 30% by mass or less, it is possible to suppress a decrease in strength and ion permeability in addition to an increase in shutdown temperature.
• the polyolefin microporous membrane may contain one kind of polyolefin resin, or may contain two or more different kinds of polyolefin resins.
• the polyolefin microporous membrane can contain a resin component other than the polyethylene-based resin and the polypropylene-based resin, if necessary.
• various additives such as antioxidants, heat stabilizers, antistatic agents, ultraviolet absorbers, blocking inhibitors and fillers, crystal nucleating agents, and crystallization retarders can be used as long as the effects of the present invention are not impaired. It may be contained.
• the polyolefin microporous film of the present invention may be a multilayer polyolefin microporous film in which the same or different multiple polyolefin resins are laminated in layers.
• the polyolefin microporous membrane of the present invention may be provided with one or more coating layers on at least one surface.
• the coating layer include porous layers other than polyolefin.
• the other porous layer is not particularly limited, but for example, a porous layer such as an inorganic particle layer containing a binder and inorganic particles is preferable.
• the binder component constituting the inorganic particle layer is not particularly limited, and known components can be used, for example, acrylic resin, polyvinylidene fluoride resin, polyamideimide resin, polyamide resin, aromatic polyamide resin, polyimide resin and the like. Can be used.
• the inorganic particles constituting the inorganic particle layer are not particularly limited, and known materials can be used. For example, alumina, boehmite, barium sulfate, magnesium oxide, magnesium hydroxide, magnesium carbonate, silicon and the like can be used. it can.
• Method for producing microporous polyolefin membrane Next, a method for producing a microporous polyolefin membrane according to the embodiment of the present invention will be described.
• the method for producing a polyolefin microporous film include a dry film forming method and a wet film forming method.
• a wet film forming method is preferable from the viewpoint of controlling the structure and physical properties of the membrane.
• a method for producing a microporous polyolefin membrane in a wet manner will be described. The following description is an example of a manufacturing method, and is not limited to this method.
• the method for producing the microporous polyolefin membrane in the embodiment of the present invention preferably includes the following steps (1) to (5), may further include the following steps (6), and further includes the following steps (7). ) And (8) can also be included.
• a step of melt-kneading the polyolefin resin and a film-forming solvent to prepare a polyolefin resin composition (2) A step of extruding the polyolefin resin composition and cooling it to form a gel-like sheet (3)
• the gel-like First stretching step of stretching the sheet (4) Step of removing the film-forming solvent from the stretched gel-like sheet (5) Step of drying the sheet after removing the film-forming solvent (6) After the drying Second stretching step of stretching the sheet (7) Step of heat-treating the dried sheet (8) Step of cross-linking and / or hydrophilizing the dried sheet
• the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower
• a polyolefin resin composition is prepared by heating and dissolving a polyolefin resin in a plasticizer (solvent for film formation).
• the plasticizer is not particularly limited as long as it is a solvent capable of sufficiently dissolving polyolefin, 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, and liquid paraffin, mineral oil distillates having corresponding boiling points, and dibutylphthalate.
• Examples thereof include phthalates that are liquid at room temperature, such as dioctyl phthalates.
• a non-volatile liquid solvent such as liquid paraffin.
• the blending ratio of the polyolefin resin and the plasticizer may be appropriately selected as long as the molding processability is not impaired, but the content of the polyolefin resin is 10 to 50% by mass with respect to the total mass of the polyolefin resin composition. preferable.
• the polyolefin resin is 10% by mass or more (the plasticizer is 90% by mass or less), the swell and neck-in do not become large at the outlet of the base when molding into a sheet, so that the formability and film forming property of the sheet are good. It becomes.
• the polyolefin resin is 50% by mass or less (the plasticizer is 50% by mass or more), shrinkage in the thickness direction is suppressed and the molding processability is improved.
• the uniform melt-kneading method of the polyolefin resin and the plasticizer is not particularly limited, but it is preferably performed in a twin-screw extruder.
• the lower limit of the temperature at the time of kneading is preferably 170 ° C. or higher, more preferably 175 ° C. or higher, and further preferably 180 ° C. or higher. By setting the temperature to 170 ° C. or higher, the viscosity of the molten resin can be lowered and the polyolefin resin can be uniformly dispersed.
• the upper limit is preferably 250 ° C. or lower, more preferably 220 ° C. or lower, and even more preferably 200 ° C. or lower.
• the lower limit of Q / Ns calculated from the ratio of the extrusion mass Q (kg / hr) and the screw rotation speed Ns (rpm) is preferably 0.05 or more. It is preferably 0.1 or more, more preferably 0.15 or more. As a result, it is possible to prevent a decrease in strength due to resin deterioration during kneading.
• the upper limit is preferably 3.0 or less, more preferably 2.0 or less, and particularly preferably 1.0 or less. As a result, sufficient shear can be applied to the polyolefin resin composition, and a uniform dispersed state can be obtained.
• the melt of the polyolefin resin composition is supplied from an extruder to a die and extruded into a sheet.
• the extrusion method may be either a flat die method or an inflation method.
• a plurality of polyolefin resin compositions having the same or different compositions may be supplied from a plurality of extruders to one multi-manifold type composite T-die, laminated in layers, and extruded into a sheet having a laminated structure.
• the extrusion temperature is preferably 140 to 250 ° C., and the extrusion speed is preferably 0.2 to 15 m / min.
• the resin composition melt-extruded into a sheet is cooled and solidified to become a gel sheet.
• the cooling step it is preferable to cool to 10 to 50 ° C. 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.
• the cooling rate at this time is preferably 50 ° C./min or higher, more preferably 100 ° C./min or higher, and even more preferably 150 ° C./min or higher. By setting the cooling rate to 50 ° C./min or more, an increase in crystallinity is suppressed, and it is difficult to obtain a gel-like sheet suitable for stretching.
• the obtained gel-like sheet is stretched at least in the uniaxial direction.
• the gel sheet is preferably stretched at a predetermined ratio by a tenter method, a roll method, an inflation method, or a combination thereof.
• the stretching may be uniaxial stretching or biaxial stretching, but biaxial stretching is preferable.
• biaxial stretching any of simultaneous biaxial stretching, sequential stretching and multi-stage 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 25 times or more, more preferably 36 times or more.
• the draw ratio in this step refers to the area stretch ratio of the polyolefin microporous membrane immediately before being subjected to the next step, based on the polyolefin microporous membrane immediately before this step.
• the stretching temperature in this step is preferably in the range of the crystal dispersion temperature (TCD) of the polyolefin resin to TCD + 30 ° C., more preferably in the range of TCD + 5 ° C. to TCD + 28 ° C., and in the range of TCD + 10 ° C. to TCD + 26 ° C. It is especially preferable to keep it inside.
• TCD crystal dispersion temperature
• the crystal dispersion temperature (TCD) is determined by measuring the temperature characteristics of dynamic viscoelasticity with ASTM D4065.
• the drawing temperature is 90 to 130 ° C. because the polyethylene and polyethylene resin compositions other than the ultra high molecular weight polyethylene and the ultra high molecular weight polyethylene have a crystal dispersion temperature of about 100 to 110 ° C.
• the temperature is preferably 105 to 120 ° C, more preferably 110 to 117 ° C. Due to the above stretching, cleavage occurs between the polyethylene lamellae, the polyethylene phase becomes finer, and a large number of fibrils are formed. Fibrils form a three-dimensionally irregularly connected network structure.
• the film-forming solvent is removed (cleaned) using a cleaning solvent. Since the polyolefin phase is phase-separated from the film-forming solvent phase, when the film-forming solvent is removed, it is composed of fibrils that form a fine three-dimensional network structure, and pores (voids) that communicate irregularly in three dimensions. A porous membrane having the above is obtained. Since the cleaning solvent and the method for removing the film-forming solvent using the cleaning solvent are known, the description thereof will be omitted. For example, the method disclosed in Japanese Patent No. 2132327 and Japanese Patent Application Laid-Open No. 2002-256099 can be used.
• the polyolefin 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 lower than the crystal dispersion temperature (TCD) of the polyolefin resin, and particularly preferably 5 ° C. or higher lower than the TCD.
• TCD crystal dispersion temperature
• the drying is preferably carried out until the total mass of the polyolefin microporous membrane is 100 parts by mass (dry mass) and the residual cleaning solvent is 5 parts by mass or less, and more preferably 3 parts by mass or less.
• the dried polyolefin microporous membrane may be stretched at least in the uniaxial direction.
• the microporous polyolefin membrane can be stretched by the tenter method, the roll method, the inflation 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 135 ° C., more preferably 95 to 130 ° C.
• the upper limit of the area stretching ratio in this step is preferably 16.0 times or less, more preferably 4.0 times or less, and further preferably 2.0 times or less.
• the stretching ratios in the MD direction and the TD direction may be the same or different from each other.
• the draw ratio in this step refers to the draw ratio of the polyolefin microporous membrane immediately before being subjected to the next step, based on the polyolefin microporous membrane immediately before this step.
• the dried polyolefin microporous membrane can be heat-treated.
• the heat treatment stabilizes the crystals and homogenizes the lamella.
• a heat fixing treatment and / or a heat relaxation treatment can be used.
• the heat fixing treatment is a heat treatment in which the film is heated while being held so that the dimensions of the film do not change.
• the heat relaxation treatment is a heat treatment in which the membrane is heat-shrinked in the MD direction or the TD direction during heating.
• the heat fixing treatment is preferably performed by a tenter method or a roll method.
• a heat relaxation treatment method the method disclosed in Japanese Patent Application Laid-Open No. 2002-256099 can be mentioned.
• the heat treatment temperature is preferably in the range of the TCD to the melting point of the polyolefin resin.
• the polyolefin microporous membrane after drying can be further subjected to a crosslinking treatment and a hydrophilic treatment.
• the microporous polyolefin membrane is subjected to a cross-linking treatment by irradiating it with ionizing radiation such as ⁇ -rays, ⁇ -rays, ⁇ -rays, and electron beams.
• ionizing radiation such as ⁇ -rays, ⁇ -rays, ⁇ -rays, and electron beams.
• electron beam irradiation an electron dose of 0.1 to 100 Mrad is preferable, and an accelerating voltage of 100 to 300 kV is preferable.
• the cross-linking treatment raises the meltdown temperature of the microporous polyolefin membrane.
• the hydrophilization treatment can be performed by a monomer graft, a surfactant treatment, a corona discharge or the like. The monomer graft is preferably carried out after the cross-linking treatment.
• the present invention also relates to a separator for a secondary battery containing the above-mentioned microporous polyolefin membrane, and a secondary battery including a separator for a secondary battery.
• the 10 ⁇ m equivalent puncture strength is obtained by using a force gauge (DS2-20N manufactured by Imada Co., Ltd.) with a needle having a spherical tip (radius of curvature R: 0.5 mm) and a diameter of 1 mm, and using a polyolefin microporous film in an atmosphere of 25 ° C.
• the maximum load (N) when pierced at a speed of 2 mm / sec is measured, and this is a value calculated by the following formula converted to 10 ⁇ m.
• Puncture strength (10 ⁇ m conversion) (N) maximum load (N) ⁇ 10 ( ⁇ m) / film thickness ( ⁇ m) of polyolefin microporous membrane
• Air permeation resistance For a polyolefin microporous membrane with a film thickness of T 1 ( ⁇ m), in accordance with JIS P-8117, an air permeability meter (made by Asahi Seiko Co., Ltd., EGO-1T) is used to resist air permeation under an atmosphere of 25 ° C. (Sec / 100 cm 3 ) was measured. Further, the air permeation resistance (10 ⁇ m conversion) (sec / 100 cm 3 ) when the film thickness was 10 ⁇ m was calculated by the following formula.
• Air permeation resistance (10 ⁇ m conversion) (sec / 100 cm 3 ) Air permeation resistance (sec / 100 cm 3 ) ⁇ 10 ( ⁇ m) / Film thickness of polyolefin microporous membrane T 1 ( ⁇ m)
• DSC Different Scanning Calorimetry
• Crystal melting rate The calculation of the crystal melting rate at the shutdown temperature of the polyolefin microporous film is obtained by using the polyolefin microporous film as a sample and measuring the total crystal melting heat at the first temperature rise and the shutdown temperature measurement of the polyolefin microporous film described later. It was calculated by the following formula from the amount of heat of crystal melting below the shutdown temperature.
• Crystal melting rate at shutdown temperature (%) (heat of crystal melting below shutdown temperature / heat of total crystal melting) x 100 (%) (Half width of crystal melting peak)
• the polyolefin microporous film was used as a sample, and the half-value width in the temperature distribution curve of the amount of heat of crystal melting at the first temperature rise was calculated.
• melting point of polyolefin resin As the melting point of the raw material polyolefin resin, the raw material polyolefin resin was used as a sample, and the temperature at which the peak was reached in the temperature distribution curve of the amount of heat of crystal melting in the second temperature rise was defined as the melting point (° C.).
• Weight average molecular weight of polyolefin resin, content of components with molecular weight less than 10,000 in polyolefin microporous membrane The weight average molecular weight (Mw) of the polyolefin resin and the polyolefin microporous membrane was determined by the gel permeation chromatography (GPC) method under the following conditions.
• GPC gel permeation chromatography
• the area ratio with a molecular weight of less than 10,000 was calculated from the differential molecular weight distribution curve of the obtained polyolefin microporous membrane.
• the content rate was calculated as the ratio of the peak area corresponding to the molecular weight of less than 10,000 to the entire peak area in the differential molecular weight distribution curve.
• -Measuring device GPC-150C manufactured by Waters Corporation -Column: Showa Denko Corporation Shodex UT806M ⁇ Column temperature: 135 °C -Solvent (mobile phase): o-dichlorobenzene-Solvent flow velocity: 1.0 ml / min-Sample concentration: 0.1 wt% (dissolution condition: 135 ° C./1 h) -Injection amount: 500 ⁇ l -Detector: Waters Corporation differential refractometer (RI detector) -Calibration curve: Prepared from the calibration curve obtained using a monodisperse polystyrene standard sample using a polyethylene conversion coefficient (0.46).
• the average pore size and the maximum pore size of the polyolefin microporous membrane were determined using a palm poromometer (CFP-1500A, manufactured by PMI). GALWICK (surface tension: 15.9 days / cm) was used as the impregnating liquid for the polyolefin microporous membrane, and the measurement was performed in the order of Dry-up and Wet-up.
• the average pore size (nm) is measured based on ASTM E1294-89 (1999) (half-dry method), and the dry-up measurement shows a curve showing the slope of 1/2 of the pressure and flow rate curves, and the Wet-up measurement.
• the pore diameter was converted from the pressure (KPa) at the intersection of the curves.
• KPa the maximum pore diameter
• the maximum pore diameter was calculated from the bubble point pressure (KPa) measured based on the bubble point method (JIS K 3832 (1990)).
• KPa bubble point pressure
• the following formula was used to convert the pressure and the pore diameter.
• d C ⁇ ⁇ / P (In the above formula, "d (nm)” is the average pore diameter or the maximum pore diameter of the microporous membrane, “ ⁇ (dynes / cm)” is the surface tension of the impregnated liquid, “P (KPa)” is the pressure, and "C” is. It is a constant and is set to 2860.)
• Example 1 The weight average molecular weight (Mw) of 1.5 ⁇ 10 6, ultra high molecular weight polyethylene 40 wt% and the weight average molecular weight of melting point 127 ° C. (Mw) is 3.0 ⁇ 10 5, branched high-density polyethylene 60 of melting point 133 ° C. Weight% was mixed to give this as a polyolefin mixture A.
• the polyolefin resin composition A was supplied to a T-die, extruded into a sheet, and cooled with a cooling roll adjusted to a temperature of 30 ° C. at a take-up speed of 4 m / min to form a gel-like sheet.
• the obtained gel-like sheet was cut into a quadrangle of 80 mm square, and simultaneously biaxially stretched at a stretching temperature of 110 ° C.
• the stretched membrane is washed in a methylene chloride washing tank to remove liquid paraffin, the washed membrane is dried in a drying oven adjusted to 20 ° C, and heated in an electric oven at 115 ° C for 10 minutes.
• a microporous polyolefin membrane was obtained by immobilization treatment.
• Example 2 The weight average molecular weight (Mw) of 1.5 ⁇ 10 6, ultra high molecular weight polyethylene 15 wt% of the melting point of 127 ° C., a weight average molecular weight (Mw) of 3.0 ⁇ 10 5, branched high-density polyethylene 85 of melting point 133 ° C.
• a polyolefin microporous film was obtained in the same manner as in Example 1 except that mass% was mixed to obtain a polyolefin mixture A.
• Example 3 The obtained gel-like sheet was cut into a quadrangle of 80 mm square, and simultaneously biaxially stretched at a stretching temperature of 110 ° C. and a stretching speed of 1000 mm / min so as to be 7 times in the MD direction and 7 times in the TD direction.
• a polyolefin microporous film was obtained in the same manner as in Example 1 except for the above.
• Example 4 The weight average molecular weight of 100 wt% polyolefin mixture A (Mw) is 3.0 ⁇ 10 5, it has a branched high-density polyethylene having a melting point of 133 ° C., is the polyolefin mixture A29.8 wt% and the antioxidant tetrakis [Methylene-3- (3,5-ditershire butyl-4-hydroxyphenyl) -propionate] A mixture of 0.2% by mass of methane is charged into a twin-screw extruder and flows from the side feeder of the twin-screw extruder.
• Polyolefin microporous in the same manner as in Example 1 except that 70% by mass of paraffin was supplied and melt-kneaded at 200 ° C. and 250 rpm under the conditions of Q / Ns 0.2 to prepare the polyolefin resin composition A. A membrane was obtained.
• Example 5 The weight average molecular weight (Mw) of 2.0 ⁇ 10 6, ultra high molecular weight polyethylene 40 wt% and the weight average molecular weight of melting point 133 ° C. (Mw) is 3.0 ⁇ 10 5, branched high-density polyethylene 60 of melting point 133 ° C.
• Mw weight average molecular weight of 2.0 ⁇ 10 6
• Mw weight average molecular weight of melting point 133 ° C.
• a polyolefin microporous film was obtained in the same manner as in Example 1 except that% by weight was mixed to obtain a polyolefin mixture A.
• Example 6 The weight average molecular weight (Mw) of 2.0 ⁇ 10 6, ultra high molecular weight polyethylene 40 wt% of the melting point of 133 ° C. and a weight average molecular weight (Mw) of 6.0 ⁇ 10 5, a high-density polyethylene 60 wt% of the melting point of 136 ° C. was mixed to obtain a polyolefin mixture A.
• the weight average molecular weight (Mw) of 2.0 ⁇ 10 6, ultra high molecular weight polyethylene 30 wt% and the weight average molecular weight of melting point 133 ° C. (Mw) is 6.0 ⁇ 10 5, a high density polyethylene having a melting point of 136 ° C.
• a mixture of 24.8% by mass of the above-mentioned polyolefin mixture A and 0.2% by mass of tetrakis [methylene-3- (3,5-ditercious butyl-4-hydroxyphenyl) -propionate] methane, which is an antioxidant, is biaxial.
• the polyolefin-based resin composition A and the polyolefin-based resin composition B are supplied from each twin-screw extruder to the three-layer T-die, and the polyolefin resin composition B layer / polyolefin resin composition A layer / polyolefin resin composition B layer.
• a gel-like sheet was formed by extruding into a sheet so that the lamination ratio was 1/3/1 and cooling while taking over with a cooling roll whose temperature was adjusted to 30 ° C. at a take-up speed of 4 m / min.
• the obtained gel-like sheet was cut into a quadrangle of 80 mm square, and simultaneously biaxially stretched at a stretching temperature of 110 ° C. and a stretching speed of 1000 mm / min so as to be 5 times in the MD direction and 5 times in the TD direction. It was.
• the stretched membrane is washed in a methylene chloride washing tank to remove liquid paraffin, the washed membrane is dried in a drying oven adjusted to 20 ° C, and heated in an electric oven at 115 ° C for 10 minutes.
• a microporous polyolefin membrane was obtained by immobilization treatment.
• Example 1 The weight average molecular weight (Mw) of 2.0 ⁇ 10 6, ultra high molecular weight having a melting point of 133 ° C. Polyethylene 40 wt% and the weight average molecular weight (Mw) of 6.0 ⁇ 10 5, branched high-density polyethylene 60 of melting point 136 ° C. A polyolefin microporous film was obtained in the same manner as in Example 1 except that% by weight was mixed to obtain a polyolefin mixture A.
• the weight average molecular weight (Mw) of 3.0 ⁇ 10 4 a mixture of low molecular weight polyethylene 30 wt% of the melting point of 123 ° C., which it has a polyolefin mixture a, the polyolefin mixture A29.8 wt% and the antioxidant Tetrakiss [methylene-3- (3,5-ditersary butyl-4-hydroxyphenyl) -propionate], which is a mixture of 0.2% by mass of methane, is charged into a twin-screw extruder and side of the twin-screw extruder. 70% by mass of liquid paraffin was supplied from the feeder and melt-kneaded under the conditions of 200 ° C.
• Example 2 A polyolefin microporous film was obtained in the same manner as in Example 1 except that it was stretched.
• the film strength at shutdown is high, which is excellent when used as a separator for a secondary battery. Shutdown characteristics and high safety can be imparted.
• the polyolefin microporous membranes of Comparative Examples 1 and 3 have a high crystal melting rate at the shutdown temperature, and the polyolefin microporous membrane of Comparative Example 2 has a high shutdown temperature and a high crystal melting rate at the shutdown temperature. Therefore, the safety is not sufficient.
• the shutdown temperature is low and the film strength at shutdown is excellent. Therefore, the polyolefin microporous membrane is excellent in safety especially in a secondary battery that requires a high capacity. It can be suitably used as a separator.

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• 2020
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