WO2015190487A1 - ポリオレフィン微多孔フィルム、その製造方法及び電池用セパレータ - Google Patents
ポリオレフィン微多孔フィルム、その製造方法及び電池用セパレータ Download PDFInfo
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- WO2015190487A1 WO2015190487A1 PCT/JP2015/066620 JP2015066620W WO2015190487A1 WO 2015190487 A1 WO2015190487 A1 WO 2015190487A1 JP 2015066620 W JP2015066620 W JP 2015066620W WO 2015190487 A1 WO2015190487 A1 WO 2015190487A1
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- polyolefin
- film
- microporous film
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- polyolefin microporous
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
-
- 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
- H01M50/494—Tensile strength
-
- 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
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/28—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
-
- 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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M50/491—Porosity
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- 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 film.
- the present invention relates to a polyolefin microporous film and a production method suitably used as a lithium ion battery separator and the like, and a battery separator using the polyolefin microporous film.
- Polyolefin microporous films are widely used as separation membranes and separators used for the separation and selective filtration of various substances. For example, they are used as microfiltration membranes, fuel cell separators, capacitor separators, and the like. Among these, the polyolefin microporous film is particularly preferably 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 film has excellent mechanical strength and shutdown characteristics.
- the shutdown characteristic is a performance that ensures the safety of the battery by melting the polymer and closing the pores when the inside of the battery is heated in an overcharged state, thereby blocking the battery reaction.
- the separator must have a certain level of strength in order to withstand the tension during winding for battery manufacture, from the viewpoint of preventing short circuits caused by foreign matter in the battery and preventing film breakage due to impact.
- Polyolefin microporous films satisfy these requirements and have been conventionally used as separators.
- the separator has been required to have excellent heat shrinkage characteristics at high temperatures so that excellent results can be obtained in a high-temperature storage test, a high-temperature cycle test, an oven test, etc. in a battery state.
- the polyolefin microporous film has a property of shrinking due to heat, and its shrinking characteristics greatly affect the safety and performance of the battery. Therefore, a polyolefin microporous film having excellent heat shrinkage properties at high temperatures has been sought from the past, but just because it has excellent heat shrinkage properties at high temperatures, it is not necessarily excellent in short circuit prevention. I have found that there is no.
- One cause of the occurrence of a short circuit is winding deviation at the time of winding for battery production. Even if the thermal shrinkage property is excellent at high temperature, the occurrence of winding deviation is observed.
- an object of the present invention is to provide a polyolefin microporous film having excellent shutdown characteristics and mechanical strength, excellent in heat shrinkage properties at high temperatures, and further excellent in preventing short circuit in a battery.
- the present inventors have contracted the separator as a film roll and stored it in a warehouse or the like, that is, the width dimension of the separator changed even under relatively low temperature conditions as product storage conditions. This shrinkage causes winding slippage during battery production, resulting in an increased risk of short circuiting, that is, in order to prevent short circuiting in the battery, the thermal contraction characteristics of the separator at low temperatures We found out that it was important and reached the present invention.
- the present invention is a polyolefin microporous film having excellent shutdown characteristics, mechanical strength and heat shrinkage properties at high temperatures, and excellent heat shrinkage properties at low temperatures when used as a film roll, It is a polyolefin microporous film excellent in prevention of short circuit when used in a battery as a separator.
- the present invention has the following configuration. That is, (1) A microporous film comprising a polyolefin resin as a main component, and having a shrinkage in the width direction of ⁇ 0.1% to 0.4% after being treated as a film roll at 60 ° C. for 4 hours. .
- polyolefin having a weight average molecular weight of less than 1 ⁇ 10 6 and a polyolefin having a weight average molecular weight of 1 ⁇ 10 6 or more The content of polyolefin of less than the weight average molecular weight 1 ⁇ 10 6 is 50% to 99% by weight in a composition comprising a weight-average molecular weight 1 ⁇ 10 of less than 6 polyolefin and a weight average molecular weight 1 ⁇ 10 6 or more polyolefins
- a polyolefin microporous film that not only exhibits excellent heat shrinkage properties at high temperatures but also can be used as a separator excellent in mechanical strength and short circuit prevention, a manufacturing method thereof, and a battery separator. Can do.
- the polyolefin microporous film of the present invention comprises a polyolefin resin as a main component, and the polyolefin resin refers to a polyolefin and / or a polyolefin composition.
- the main component mentioned here is a component that occupies a majority of the weight of the whole film (50% by weight or more when the whole film is 100% by weight).
- the polyolefin resin used in the present invention is a polyolefin having a weight average molecular weight of 1 ⁇ 10 6 or more and / or a polyolefin composition and a polyolefin having a weight average molecular weight of less than 1 ⁇ 10 6 and / or a polyolefin when the total of the polyolefins is 100% by weight.
- the composition is preferable because stability and safety in the case of a battery are improved due to the effects of improving the puncture strength of the microporous film and reducing the through-hole diameter.
- the mixing ratio of polyolefins having different weight average molecular weights can be obtained from an integral curve of gel permeation chromatography (GPC) measurement.
- the polyolefin (ultra high molecular weight polyolefin) having a weight average molecular weight of 1 ⁇ 10 6 or more in the present invention is preferably ultra high molecular weight polyethylene or ultra high molecular weight polypropylene, and more preferably ultra high molecular weight polyethylene.
- the weight average molecular weight of the ultrahigh molecular weight polyolefin is preferably 1 ⁇ 10 6 or more and 1 ⁇ 10 7 or less. If the weight average molecular weight exceeds 1 ⁇ 10 7 , the uniformity during melt-kneading may be inferior, or the viscosity may become too high to make melt extrusion difficult.
- the mixing ratio of the ultra-high molecular weight polyolefin having a weight average molecular weight of 1 ⁇ 10 6 or more is preferably 1 to 50% by weight, more preferably 5 to 40% by weight, when the total of the polyolefins is 100% by weight.
- the mixing ratio of the ultra-high molecular weight polyolefin is less than 1% by weight, the through-hole diameter of the microporous film becomes coarse.
- the mixing ratio of the ultrahigh molecular weight polyolefin exceeds 50% by weight, the viscosity of the dissolved resin becomes too high, so that the extrusion stability is deteriorated and the heat shrinkage characteristic is deteriorated.
- the molecular weight distribution (weight average molecular weight / number average molecular weight) of polyolefin is preferably 50 or less, more preferably 1.2 to 50, from the viewpoint of moldability of the microporous film.
- the ultra high molecular weight polyethylene having a weight average molecular weight of 1 ⁇ 10 6 or more in the present invention contains 50% or more of ethylene-derived repeating units, preferably at least 85% of the repeating units are polyethylene, more preferably An ethylene homopolymer or an ethylene / ⁇ -olefin copolymer, and 5.0 mol% or less is a comonomer such as at least one ⁇ -olefin (mol% is a value when the total monomer of the copolymer is 100 mol%) .)
- the comonomer is for example selected from at least one of propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, vinyl acetate, methyl methacrylate or styrene.
- Such polymers or copolymers can be obtained using Ziegler-Natta catalysts or single site catalysts.
- fusing point is 134 degreeC or more.
- the polyolefin having a weight average molecular weight of less than 1 ⁇ 10 6 is preferably a linear polyolefin, and more preferably a linear high-density polyethylene.
- the weight average molecular weight of the polyolefin is preferably 1 ⁇ 10 5 or more and 8 ⁇ 10 5 or less, more preferably 1 ⁇ 10 5 or more and 5 ⁇ 10 5 or less.
- the strength of the polyolefin microporous film may be insufficient and the puncture strength characteristics may be inferior, or the heat resistance of the film may be inferior.
- the mixing ratio of the polyolefin having a weight average molecular weight of less than 1 ⁇ 10 6 is preferably 50 to 99 parts by weight, more preferably 60 to 95% by weight, when the total amount of polyolefins is 100% by weight.
- the mixing ratio of the polyolefin having a weight average molecular weight of less than 1 ⁇ 10 6 is less than 50% by weight, the heat shrink property of the film may be deteriorated or the thickness unevenness of the film may be increased.
- the mixing ratio of the polyolefin having a weight average molecular weight of less than 1 ⁇ 10 6 exceeds 99% by weight, the strength of the polyolefin microporous film may be insufficient and the piercing characteristics may be deteriorated, or the through-hole diameter may be increased.
- the molecular weight distribution (weight average molecular weight / number average molecular weight) of the polyolefin as the main component is in the range of 2 to 15 and 3.0 to 10.0 from the viewpoint of moldability of the microporous film. More preferred.
- the amount of unsaturated end groups of the polyolefin is preferably less than 0.20 / 1.0 ⁇ 10 4 carbon atoms, and more preferably less than 0.14 / 1.0 ⁇ 10 4 carbon atoms. More preferably, it is 0.14 / 1.0 ⁇ 10 4 carbon atoms or less, and particularly preferably 0.05 / 1.0 ⁇ 10 4 to 0.14 / 1.0 ⁇ 10 4 carbon atoms.
- the constitution of the high density polyethylene having a weight average molecular weight of less than 1 ⁇ 10 6 in the present invention includes 50% or more of repeating units derived from ethylene, preferably at least 85% of repeating units are polyethylene, more preferably At least 85% of the repeating units are polyethylene, more preferably ethylene homopolymer or ethylene / ⁇ -olefin copolymer, and 5.0 mol% or less is at least one comonomer such as ⁇ -olefin (mol% is This is a value where the monomer of the entire copolymer is 100 mol%.)
- the comonomer is, for example, selected from at least one of propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, vinyl acetate, methyl methacrylate, or styrene.
- Such polymers or copolymers can be obtained using Ziegler-Natta catalysts or single site catalysts.
- a content (additive) other than the above-described polyolefin resin for example, a filler, an antioxidant, a stabilizer, and / or a heat-resistant resin can be used as long as the characteristics of the film are not deteriorated.
- types and types of additives that are preferably used include those described in International Publication No. 2007/132294, International Publication No. 2008/016174, International Publication No. 2008/140835, and the like.
- the polyolefin microporous film of the present invention has a shrinkage in the width direction of -0.1% or more and 0.4% or less, preferably 0.0% or more and 0.0. 3% or less.
- the polyolefin microporous film is usually stored and transported in the state of a film roll.
- the shrinkage rate after treatment at 60 ° C. for 4 hours exceeds 0.4% when the film roll is used, The width of the product cannot be maintained in an environment such as during transportation in the tropics and subtropics.
- the shrinkage rate after treatment at 60 ° C. for 4 hours in the case of a film roll takes a positive value (does not expand).
- the polyolefin microporous film in the present invention preferably has a shrinkage in the width direction of ⁇ 0.1% or more and 0.4% or less after being treated at 60 ° C. for 4 hours as a film roll having a width of less than 100 mm. It is more preferably 0% or more and 0.3% or less.
- the method of setting the shrinkage ratio in the width direction after being treated at 60 ° C. for 4 hours as a film roll as the above range is, for example, to perform a slow cooling relaxation treatment after heat setting treatment in the production of a polyolefin microporous film.
- crystallization of polyolefin is mentioned.
- the shrinkage rate was measured with a film roll that was slit into a 78.0 mm width with a polyolefin microporous film having a length of 1000 m and a winding tension of 20 N / m and wound on a plastic core having an outer diameter of 90 mm. The value measured by the method.
- the thickness of the polyolefin microporous film of the present invention is 3 ⁇ m or more and 30 ⁇ m or less, preferably 5 ⁇ m or more and 25 ⁇ m or less from the viewpoint of film strength and permeability.
- the film thickness is less than 3 ⁇ m, the film strength is insufficient and the safety of the battery is impaired, or the product is liable to break during production and the productivity is lowered.
- the film thickness exceeds 30 ⁇ m, the permeability deteriorates.
- the air permeability resistance of the polyolefin microporous film of the present invention is 40 to 600 seconds / 100 cc, preferably 100 seconds / cc or more and 300 seconds / 100 cc or less.
- the air permeability resistance exceeds 600 seconds / 100 cc, the self-discharge phenomenon cannot be suppressed when used as a battery separator, the impedance tends to be too high, and the battery characteristics tend to deteriorate.
- the air permeability resistance of the microporous film is less than 40 seconds / 100 cc, the puncture strength of the film may be lowered, or dendrite growth cannot be suppressed, and a short circuit may occur easily.
- the porosity of the polyolefin microporous film of the present invention is 25 to 60%, preferably 30 to 50%.
- the porosity of the microporous film is less than 25%, the film has poor permeability and battery characteristics tend to deteriorate.
- the porosity of the microporous film exceeds 50%, the puncture strength of the film may be reduced, or dendrite growth may not be suppressed, and a short circuit may occur.
- the puncture strength of the polyolefin microporous film of the present invention is 20 gf / ⁇ m or more, preferably 25 gf / ⁇ m or more.
- the puncture strength is preferably high.
- the MD microporous film of the present invention has an MD tensile strength of 1000 kg / cm 2 or more, preferably 1200 kg / cm 2 or more. Moreover, MD tensile elongation is 180% or less, Preferably it is 160% or less. Since tension is applied in the MD direction at the time of battery production or film roll production, the higher the MD tensile strength of the film and the lower the MD tensile elongation, the less likely the film will stretch, and the TD shrinkage caused by the elongation is also suppressed. Cheap.
- the thermal shrinkage in the MD direction at 105 ° C. of the polyolefin microporous film of the present invention is 10% or less, preferably 7% or less, more preferably 6% or less.
- the thermal shrinkage in the MD direction causes the shrinkage stress in the MD direction to become strong when heat is received in a state where the MD direction of the film is fixed, for example, in the state of a cylindrical battery.
- the thermal shrinkage in the TD direction at 105 ° C. is 5% or less, preferably 4% or less. If the thermal shrinkage in the TD direction at 105 ° C. is 5% or more, a short circuit is likely to occur due to the shrinkage of the separator due to heat generation during charging and discharging.
- a mixture containing a composition of ultrahigh molecular weight polyethylene and high density polyethylene (compounding ultrahigh molecular weight polyethylene and high density polyethylene in a desired ratio) and a film-forming solvent is melt-kneaded by an extruder and extruded. Cool and solidify.
- the film-forming solvent may be of any kind as long as it is generally compatible with the polymer and can be used at the melt extrusion temperature, and a plurality of different kinds of film-forming solvents may be combined.
- the solvent for film formation include use of aliphatic hydrocarbons or cyclic hydrocarbons such as nonane, decane, decalin, paraxylene, undecane, dodecane, liquid paraffin, or mineral oil fractions having boiling points corresponding to these. it can.
- a non-volatile solvent such as liquid paraffin is preferably used.
- the viscosity of the solvent is preferably 30 to 500 cSt at 25 ° C., more preferably 50 to 200 cSt. If the viscosity of the solvent at 25 ° C. is less than 30 cSt, kneading with the polyolefin becomes difficult, and if it exceeds 500 cSt, it is difficult to remove the solvent.
- the formation (mixing) and extrusion of the polyethylene composition and the solvent for film formation are preferably performed using a twin screw extruder.
- additives such as the filler described above may be added by a side feeder.
- the above-mentioned mixture is mixed by an extruder in which the rotation speed of the mixing screw is set to 450 rpm or less, and the rotation speed of the mixing screw is preferably 430 rpm or less, more preferably 410 rpm or less, and preferably 150 rpm or more, more preferably. Is 250 rpm or more.
- the mixing temperature of the mixture of the polyethylene composition and the film-forming solvent is 140 ° C. to 260 ° C., preferably 210 ° C. to 250 ° C.
- the sheet extruded from the die is exposed to a temperature range of 15 to 80 ° C. by, for example, a cooling roll to form an unstretched sheet (gel-like sheet).
- the cooling rate of the sheet extruded from the die is not particularly critical, but is preferably less than 30 ° C./min.
- the sheet extruded from the die is cooled to near the gel temperature of the extrudate.
- the manufacturing conditions for cooling the sheet extruded from the die are disclosed in International Publication No. 2007/132294, International Publication No. 2008/016174, International Publication No. 2008/016174, International Publication No. 2008/140835. What is described can be applied.
- the cooled unstretched sheet is stretched at least uniaxially, and preferably stretched in the biaxial direction of the longitudinal (MD) direction and the width (TD) direction. Such stretching causes orientation in the polymer in the mixture.
- the stretching method of the unstretched sheet is not particularly limited.
- a tenter grips both ends in the width direction of the film with clips, and a clip that is adjacent in the width direction distance and / or the longitudinal direction of the clips facing in the width direction.
- the tenter stretching method that stretches by extending the longitudinal distance of the film, the roll stretching method that stretches by adjusting the speed difference between multiple rolls, the inflation method that stretches the film by the pressure of air, or a combination thereof Can be used. These methods are described in, for example, International Publication No. 2008/016174.
- the stretching is preferably biaxial stretching. In biaxial stretching, simultaneous biaxial stretching, sequential stretching, multi-stage stretching, combinations thereof, and the like can be used.
- the draw ratio of the unstretched sheet is preferably 4 to 50 times, more preferably 9 to 49 times.
- the stretching temperature is preferably between the crystal dispersion temperature (Tcd) of polyethylene and the melting point (Tm) of polyethylene.
- Tcd and Tm are values of polyethylene having the lowest melting point among polyethylenes mixed in an amount of 5% by weight or more used for extrudates.
- the crystal dispersion temperature is measured as the temperature of the dynamic viscoelasticity measurement characteristic described in ASTM D4065.
- the stretching temperature depends on the polyolefin resin to be used, in the present invention, it is preferably 90 ° C. to 100 ° C., more preferably 100 ° C. to 125 ° C., and most preferably 105 ° C. to 125 ° C.
- the dried stretched film can be restretched.
- Re-stretching may be performed in one direction or both directions in the longitudinal direction and / or the width direction.
- the stretching ratio at the time of re-stretching is preferably 1.1 to 1.6 times, more preferably 1.1 to 1.5 times in the longitudinal direction.
- the width direction is preferably 1.0 to 1.6 times, more preferably 1.2 to 1.4 times.
- the longitudinal direction and the width direction may be stretched simultaneously or separately.
- stretching separately either the longitudinal direction or the width direction may be stretched first.
- the temperature at the time of redrawing the temperature is preferably Tm or less, for example, Tcd-30 ° C.
- Tm and Tcd are values of polyethylene having the lowest melting point among polyethylenes of 5% by weight or more used in the extrudate.
- the re-stretching temperature is preferably in the range of 70 ° C to 135 ° C, more preferably 120 ° C to 132 ° C, and particularly preferably 128 ° C to 132 ° C.
- the temperature in the heat setting step is preferably between Tcd and Tm, more preferably (Tm-25) ° C. or higher and (Tm-5) ° C. or lower.
- the heat setting temperature is 105 ° C to 135 ° C, more preferably 120 ° C to 132 ° C, and more preferably 122 ° C to 130 ° C.
- heat setting requires sufficient time to form a uniform lamella in the film and to eliminate the stress strain remaining in the film by thermal relaxation.
- the treatment time for the fixing treatment is preferably in the range of 1 to 300 seconds, and more preferably in the range of 1 to 120 seconds.
- the polyethylene crystal can be further stabilized by performing a slow cooling relaxation treatment after the heat setting treatment and before returning to room temperature. Further, the crystal can be further stabilized by performing relaxation (relaxation) during the slow cooling relaxation treatment.
- the slow cooling rate of the slow cooling relaxation treatment is preferably 5 ° C./min to 400 ° C./min.
- the ultimate temperature of the slow cooling relaxation treatment a process of relaxing between the heat fixing treatment temperature and a temperature higher than room temperature (hereinafter referred to as “the ultimate temperature of the slow cooling relaxation treatment”) after the heat fixing treatment is effective.
- the ultimate temperature of the slow cooling treatment is preferably (room temperature + 50) ° C.
- the ultimate temperature of the slow cooling relaxation treatment is 95 ° C. to 125 ° C., more preferably 100 ° C. to 120 ° C.
- the relaxation during the slow cooling step is performed during the slow cooling step after the heat setting treatment.
- the ultimate temperature of the slow cooling relaxation treatment is too low, the relaxation may not be sufficiently performed.
- the ultimate temperature of the slow cooling relaxation treatment is preferably 95 ° C. or higher.
- the relaxation rate (relaxation rate) in the slow cooling relaxation treatment is preferably 0.1% to 20%, and more preferably 0.1% to 10%.
- the relaxation rate here is based on the width dimension after heat setting, and the shrinkage ratio of the width dimension when the slow cooling relaxation process is completed ⁇ ((width dimension after heat setting)-(after the slow cooling relaxation process is completed). (Width dimension)) ⁇ (width dimension after heat setting) ⁇ 100 ⁇ .
- the relaxation rate is less than 0.1%, the effect of promoting crystal stabilization is difficult to obtain, and the shrinkage in a state where tension is applied increases.
- the stepwise slow cooling step after the heat setting treatment is intended to prevent rapid cooling, and the treatment time (slow cooling relaxation time) is preferably in the range of 1 to 200 seconds, more preferably 3 to 100 seconds. Range.
- the treatment time of the slow cooling relaxation treatment is preferably 1 second or longer, and 200 seconds or shorter is preferable in view of productivity. .
- “average slow cooling rate during relaxation” means the temperature of the film before performing such slow cooling relaxation treatment, the temperature that the film reaches after performing slow cooling relaxation treatment, and the slow cooling
- the value obtained by the time required for the relaxation treatment ⁇ ((film arrival temperature) ⁇ (temperature of the film before the slow cooling relaxation treatment)) ⁇ (time required for the slow cooling relaxation treatment) ⁇ is expressed as an absolute value.
- a tenter is used, and after heat fixing in a state where both ends of the film in the width direction are held by clips, the slow cooling process is continuously performed in the tenter. This can be done by reducing the distance in the width direction of the clips facing each other in the width direction of the film. Therefore, in the slow cooling process, the film in which both ends in the width direction are gripped by the clips are not naturally contracted in the heating atmosphere, but the dimensions in the width direction are regulated by the clips facing each other in the film width direction. The dimension is narrowed.
- the winding tension is preferably 1 to 20 N / m, more preferably 2 to 15 N / m, and it is desirable to obtain a master roll.
- the winding tension exceeds 20 N / m, the internal stress of the film increases during winding, and the dimensional change is likely to occur.
- the winding tension is lower than 1 N / m, deviation occurs during winding, and the film is tightened by tightening the film. Wrinkles may occur in the inner layer of the roll.
- the wound-up master roll is preferably subjected to an annealing treatment in order to release the remaining distortion inside the film.
- the temperature at the time of annealing is preferably 40 to 80 ° C., more preferably 50 to 70 ° C., from the viewpoint of preventing deterioration of the master roll shape.
- the treatment time is preferably 10 to 50 hours, more preferably 20 to 40 hours.
- the core is not particularly limited. However, when the annealing process is performed, the core may buckle by tightening and the film may be wrinkled. Therefore, the outer diameter of the core is preferably 100 mm or more.
- the obtained master roll is cut into a desired width in a slitting process, wound up, and becomes a film roll.
- the width and length of the microporous polyolefin film are not particularly limited, but when used as a battery separator, the width is 30 to 1000 mm, more preferably 50 to 800 mm, and the length is 300 to 3000 m. Preferably, it is 500 to 2000 m.
- the winding tension is preferably 5 N / m to 80 N / m.
- the core for winding the polyolefin microporous film is not particularly limited, but preferably has an outer diameter of 50 mm or more in order to prevent buckling.
- the polyolefin microporous film of the present invention can be suitably used as a separator for batteries, particularly for nonaqueous electrolyte secondary batteries. Moreover, since the polyolefin microporous film of the present invention is excellent in heat shrink characteristics at high and low temperatures, it can also be suitably used as a coated separator.
- Puncture strength The maximum load when a polyolefin microporous film was punctured at a speed of 2 mm / second was measured with a needle having a spherical tip (curvature radius R: 0.5 mm) and a diameter of 1 mm.
- Thermal Shrinkage Rate at 105 ° C. The thermal shrinkage rate at 105 ° C. in the width direction and longitudinal direction of the polyolefin microporous film was measured as follows. (I) The film was unwound by 5 m from the polyolefin microporous film roll, cut out, and a square part having a longitudinal direction of 50 mm and a width direction of 50 mm was cut out from the cut film as a reference and used as a measurement sample. The dimensions of this sample at 23 ° C. were measured (width direction, longitudinal direction). Three samples for such measurement were prepared. (Ii) Next, this sample was exposed to conditions of 105 ° C. for 8 hours without load, and then cooled to 23 ° C.
- Air permeability resistance The air resistance (second / 100 cc) was measured according to JIS P8117 (2009) item 6 Oken tester method.
- the width shrinkage of the polyolefin microporous film at 60 ° C. was measured as follows.
- the polyolefin microporous film roll is a film roll that is slit from a master roll obtained by film formation to a width of 78 mm and a length of 1000 m, and wound around a plastic core having a tension of 20 N / m and an outer diameter of 90 mm.
- sample of (ii) was cut into a length of 1 m, and three width direction dimensions were measured within 30 minutes, and the average value was determined as the width direction dimension after shrinkage. did.
- the measurement position was set to a line passing through the center of the 1 m sample.
- the width heat shrinkage rate of the polyolefin microporous film at 60 ° C. is obtained by dividing the size of (iii) by the size of (i) and subtracting that value from 1 as a percentage ⁇ (1-((iii) Dimension) ⁇ (dimension of (i)))) ⁇ 100 ⁇ .
- the strip-shaped positive electrode body, the separator, and the strip-shaped positive electrode body are stacked in this order, and the electrode plate laminate is formed using a winder (KMW-2BY) manufactured by Minato Seisakusho. Winding and winding evaluation were performed.
- the positive electrode body or the negative electrode body that protrudes 0.5 mm or more in the width direction with respect to the separator is regarded as a winding deviation, and the same sample is evaluated 10 times, and the occurrence rate of the winding deviation is less than 20%. Were evaluated as “ ⁇ (good)” and 20% or more as “ ⁇ (impossible)”.
- Example 1 (1) Preparation of a mixture of a polymer and a solvent for film formation A weight average molecular weight of 2.5 ⁇ 10 6 , an ultrahigh molecular weight polyethylene resin having a melting point of 136 ° C., 18 parts by weight, a weight average molecular weight of 3.5 ⁇ 10 5 , With 82 parts by weight of a linear high-density polyethylene resin having a melting point of 135 ° C., a weight average molecular weight / number average molecular weight of 4.05 and an unsaturated terminal group weight of 0.14 / 1.0 ⁇ 10 4 carbon atoms The mixture was put into a twin screw extruder, and liquid paraffin (135 cSt / 25 ° C.) was injected from the side feeder of the twin screw extruder by a pump.
- liquid paraffin (135 cSt / 25 ° C.
- the amount of liquid paraffin injected was adjusted so that the amount of the polyethylene resin mixture was 30% by weight when the total of the polyethylene resin composition and liquid paraffin was 100% by weight. After injecting the mixture into a twin screw extruder, the mixture was dissolved and kneaded to obtain a mixed solution of a polyethylene resin mixture and liquid paraffin (film-forming solvent).
- the unstretched sheet was simultaneously biaxially stretched by a first tenter at a stretching ratio of 5 times in both the width direction and the longitudinal direction at 115.1 ° C., and then the stretched gel sheet was immersed in methylene chloride at 25 ° C. to flow.
- the paraffin was removed and dried by blowing air at room temperature to obtain a polyethylene microporous film.
- the both ends of the obtained polyethylene microporous film were guided to a second tenter while being held with clips, and stretched 1.4 times in the width direction while being heat-set at 130.2 ° C. Further, a slow cooling relaxation treatment was performed in which the relaxation was 3.0% in the width direction at 110 ° C.
- the heat setting treatment and the slow cooling relaxation treatment are the same with a plurality of zones in which the temperature can be adjusted for each zone. It is processed continuously in the tenter and is not exposed to room temperature.) Therefore, the microporous film is relaxed while being gradually cooled from 130.2 ° C. to 110 ° C. Thereafter, a master roll having a winding length of 1050 m was obtained at a tension of 5 N / m.
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Abstract
Description
本発明者らは、セパレータはフィルムロールとされ倉庫等で保管されている間にも収縮が発生しており、つまり、製品保管条件である比較的低温の条件でもセパレータの幅寸法が変化しており、この収縮により電池作製のための捲回時の巻きずれが生じ、結果として短絡の危険性が高まること、すなわち、電池での短絡防止のためにはセパレータの低温下での熱収縮特性も重要であることを見出し、本発明に到達した。
(1)主成分がポリオレフィン樹脂からなる微多孔フィルムであって、フィルムロールとして60℃4時間処理した後の幅方向の収縮率が-0.1%~0.4%であるポリオレフィン微多孔フィルム。
重量平均分子量1×106未満のポリオレフィン及び重量平均分子量1×106以上のポリオレフィンからなる組成物における前記重量平均分子量1×106未満のポリオレフィンの含有量が50重量%~99重量%である前記(1)記載のポリオレフィン微多孔フィルム。
本発明のポリオレフィン微多孔フィルムは、主成分としてポリオレフィン樹脂からなるが、ポリオレフィン樹脂とはポリオレフィンおよび/又はポリオレフィン組成物をいう。ここで言う主成分とは、フィルム全体の重量の過半(フィルム全体を100重量%とした時に50重量%以上)を占める成分のことである。
本発明におけるポリオレフィン微多孔フィルムは、フィルムロールとして60℃4時間処理した後での幅方向の収縮率が-0.1%以上0.4%以下であり、好ましくは0.0%以上0.3%以下である。ポリオレフィン微多孔フィルムは通常、フィルムロールとした状態で保管・搬送されるが、フィルムロールとした場合の60℃4時間処理後の収縮率が0.4%を超える場合、例えば夏期の搬送時や熱帯・亜熱帯地方での搬送時などの環境下では製品の幅寸法を保つことができない。また、フィルムロールとした場合の60℃4時間処理後の収縮率が0.4%を超える場合、通常の室温よりも温度が高い倉庫での長期間保管時、例えば30℃を超える温度下での長期間の保管時において、製品の幅寸法を規格範囲内に保つことができず、このような条件での保管を経た後に電池用セパレータとして使用された場合、電池製造時の捲回時に巻きズレが起こりやすく、巻きズレ起因による短絡発生リスクが生じる。また、60℃4時間処理後の収縮量が-0.1%よりも小さい場合は、フィルムロールとして拘束された状態で幅方向に大きな膨張が発生するということであり、皺が発生しやすくなり、やはり短絡発生リスクが生じる。従って、フィルムロールとした場合の60℃4時間処理後の収縮率は正の値を取る(膨張しない)ことが好ましい。
本発明におけるポリオレフィン微多孔フィルムは、幅100mm未満のフィルムロールとして60℃4時間処理した後での幅方向の収縮率が-0.1%以上0.4%以下であることが好ましく、0.0%以上0.3%以下がより好ましい。
なお、上記の収縮率は、ポリオレフィン微多孔フィルムを長さ1000m、巻取張力を20N/mとして78.0mm幅でスリットし、外径90mmのプラスチックコアに捲回したフィルムロールで、後述する測定法で測定した値をいう。
次に本発明のポリオレフィン微多孔フィルムの製造方法について、ポリオレフィン樹脂をポリエチレン(特に、超高分子量ポリエチレンと高密度ポリエチレンとの組成物)とした場合を例にとって説明するが、これに限定されるものではない。
超高分子量ポリエチレンと高密度ポリエチレンの組成物(超高分子量ポリエチレンと高密度ポリエチレンとを所望の割合で配合する。)と製膜用溶剤とを含有する混合物を押出機によって溶融混練して押出し、冷却、固化させる。製膜用溶剤は一般的にポリマーと相溶性があり溶融押出温度にて使用可能なものであれば、如何なる種類のものでも良く、また種類の異なる製膜用溶剤を複数組み合わせてもよい。製膜用溶剤の具体例として、ノナン、デカン、デカリン、パラキシレン、ウンデカン、ドデカン、流動パラフィン等の脂肪族炭化水素若しくは環状炭化水素、又は沸点がこれらに対応する鉱油留分等を用いることができる。溶媒含有量が安定な溶融混合物を得るためには、流動パラフィンのような不揮発性の溶剤を用いることが好ましい。また、溶剤の粘度は25℃において30~500cStであることが好ましく、さらには50~200cStである。25℃における溶剤の粘度が30cSt未満では、ポリオレフィンとの混練が困難となり、500cStを超えると溶剤除去が困難となる。
ポリエチレン組成物と製膜用溶剤の混合物は、異物を取り除くためのろ過工程を経た後に、ダイから押出され押出物を形成する。押出物は後の工程のために好ましい厚さで調整され、延伸後の最終的な膜の所望の厚さを得ることができるように調整される。好ましい製造条件は国際公開公報第2008/016174号に記載の条件を適用することができる。
冷却された未延伸シートは少なくとも一軸に延伸され、好ましくは長手(MD)方向、幅(TD)方向の二軸方向に延伸される。このような延伸は混合物中のポリマー中に配向を生じさせる。未延伸シートの延伸方法としては、特には限定されないが、例えばテンターによりフィルムの幅方向両端部をクリップにより把持し、幅方向に対向するクリップの幅方向距離および/又は長手方向に隣接するクリップとの長手方向距離を広げることで延伸するテンター延伸法や複数のロール間の速度差を調整することで延伸を行うロール延伸法や、エアーの圧力によりフィルムを延伸するインフレーション法、若しくはこれらの組み合わせを用いることができる。これらの方法については、例えば、国際公開公報第2008/016174号に記載されている。延伸は二軸延伸であることが好ましい。二軸延伸では、同時二軸延伸、逐次延伸、多段延伸、それらの組合せなどを用いることが可能である。
次に、製膜用溶剤を除去するために易揮発性洗浄溶剤にて洗浄する。易揮発性洗浄溶剤としては、ペンタン、ヘキサン、へプタン等の炭化水素、塩化メチレン、四塩化炭素等の塩素化炭化水素、三フッ化エタン等のフッ化水素、ジエチルエーテル、ジオキサン等のエーテル等を用いることができる。これらの溶剤は、ポリオレフィンの溶解に用いた製膜用溶剤に応じて適宜選択可能であり、単独もしくは混合して用いることができる。洗浄の具体的な方法については、例えば、国際公開公報第2008/016174号に記載された方法を用いることができる。次に残留した易揮発性洗浄溶剤を、例えば熱乾燥、風乾燥などにより除去し、乾燥フィルムとする。具体的な方法としては、例えば、国際公開公報2008/016174号に記載の方法を用いることができる。
必要に応じて、乾燥された延伸フィルムを再延伸することができる。再延伸は、長手方向及び/又は幅方向において1方向で実施しても、両方向で実施してもよい。再延伸時の延伸倍率は長手方向には1.1~1.6倍が好ましく、さらに好ましくは1.1~1.5倍である。また、幅方向については1.0~1.6倍好ましく、さらに好ましくは1.2~1.4倍である。また、二軸方向に再延伸する場合には、長手方向と幅方向を同時に延伸しても、別々に延伸してもよい。また別々に延伸する場合は長手方向と幅方向のどちらを先に延伸してもよい。再延伸時の温度については、Tm以下の温度、例えばTcd-30℃~Tmの範囲で行われることが好ましい。なお、ここでのTm、Tcdは押出物に用いられる5重量%以上混合されているポリエチレンの中で融点が最も低いポリエチレンでの値である。再延伸時の温度は、具体的には70℃~135℃の範囲が好ましく、さらには120℃~132℃、特に128℃~132℃が好ましい。また、再延伸は後述する熱固定処理工程と同時に行ってもよい。
次に、ポリエチレンの結晶を安定化させ、膜中に均一なラメラを形成させると共に熱緩和させることでフィルム中に残存している応力歪を解消するために熱固定処理を行う。熱固定工程における温度は、Tcd~Tmの間が好ましく、さらには(Tm-25)℃以上(Tm-5)℃以下が特に好ましい。具体的には、熱固定温度は、105℃~135℃、さらに好ましくは120℃~132℃、より好ましくは122℃~130である。また、一般的に熱固定は膜中に均一なラメラを形成し熱緩和により膜中に残存している応力歪を解消できるのに十分な時間があればよく、生産性の観点も考慮した熱固定処理の処理時間としては1~300秒の範囲が好ましく、より好ましくは1~120秒の範囲である。
さらに、ポリエチレンの結晶を安定化させ、膜中に均一なラメラを形成させる処置で、熱固定処理後から室温に戻す前に徐冷緩和処理を行うことでよりポリエチレンの結晶を安定化させられる。また、徐冷緩和処理時に弛緩(緩和)を行うことで、より結晶を安定化させられる。徐冷緩和処理の徐冷速度は5℃/分~400℃/分が好ましい。徐冷緩和を行う方法は熱固定処理後に熱固定処理温度と室温よりも高い温度(以下「徐冷緩和処理の到達温度」と言う)との間で緩和させる工程が有効である。徐冷緩和処理の到達温度は(室温+50)℃以上(熱固定処理温度-3)℃以下の温度が好ましい。具体的には徐冷緩和処理の到達温度は95℃~125℃、さらに好ましくは100℃~120℃が好ましい。本発明のポリオレフィン微多孔フィルムの製造においては、徐冷緩和処理が完了するまではフィルムを室温に晒すことなく連続して、段階的に温度を低下させることが肝要である。従って、徐冷緩和処理と当該徐冷緩和処理の前に行われる熱固定処理とは、共通のテンターを用いて(同一テンター内にて)行うことが好ましい。徐冷工程中の弛緩は熱固定処理後の徐冷工程中に弛緩を行う。ただし、徐冷緩和処理の到達温度が低すぎる場合には十分に弛緩を行えない場合があるため、徐冷緩和処理の到達温度は95℃以上で行うことが好ましい。徐冷緩和処理における弛緩率(緩和率)は0.1%~20%が好ましく、さらには0.1%~10%が好ましい。ここでいう弛緩率とは熱固定後の幅寸法を基準として、徐冷緩和処理が完了した時の幅寸法の収縮率{((熱固定後の幅寸法)-(徐冷緩和処理完了後の幅寸法))÷(熱固定後の幅寸法)×100}である。この弛緩率が0.1%未満の場合は結晶安定化の促進効果が得られにくく張力が掛かった状態での収縮が大きくなる。また、熱固定処理後の段階的な徐冷工程は急冷を防止させることが目的であり、処理時間(徐冷弛緩時間)としては1~200秒の範囲が好ましく、より好ましくは3~100秒の範囲である。透過性及び強度を維持したまま低温領域の収縮を抑制させるためには、徐冷緩和処理の処理時間が1秒以上であることが好ましく、生産性の観点も考慮した場合は200秒以下が好ましい。後述の実施例における「弛緩時の平均徐冷速度」とは、このような徐冷緩和処理を行う前のフィルムの温度、徐冷緩和処理を行った後にフィルムが到達する温度、及び当該徐冷緩和処理に要する時間により求められる値{((フィルムの到達温度)-(徐冷緩和処理前のフィルムの温度))÷(徐冷緩和処理に要する時間)}を絶対値で示したものである。
徐冷工程中の弛緩はテンターを使用し、フィルムの幅方向両端部をクリップにより把持した状態で熱固定を実施後に、テンター内にて連続して徐冷工程を実施し、徐冷工程中にフィルムの幅方向において互いに対向するクリップの幅方向距離を狭めることで行うことができる。従って、徐冷工程では、幅方向両端部をクリップにより把持されたフィルムは、加熱雰囲気において自然に収縮するのではなく、フィルムの幅方向において互いに対向するクリップにより幅方向における寸法を規制された状態で当該寸法が狭められる。
徐冷緩和処理ポリオレフィン微多孔フィルムを巻き取る。製膜工程後の最初の巻き取りは巻取張力を1~20N/mとすることが好ましく、より好ましくは2~15N/mとしてマスターロールを得ることが望ましい。巻取張力が20N/mを超えるとフィルムの内部応力が巻き取り時に増大し、寸法変化が発生しやすく、1N/mより低い場合は巻き取り時にずれが生じたり、フィルムの巻締りにより、マスターロールの内層にシワが発生したりすることがある。巻き取られたマスターロールは、さらに残留しているフィルム内部の歪を解放するために、アニール処理を行うことが望ましい。アニール時の温度については、マスターロール形状の悪化を防止する観点から、40~80℃が好ましく、より好ましくは50~70℃である。また、処理時間としては10~50時間、さらには20~40時間が好ましい。コアについては特に限定しないが、アニール処理を行った場合に巻き締りでコアが座屈し、フィルムに皺が入る可能性があるため、コアの外径は100mm以上が好ましい。
得られたマスターロールは、スリット工程にて所望の幅に切断し、巻き取られ、フィルムロールとなる。ここでのポリオレフィン微多孔フィルムの幅・長さは特には限定されないが、電池用セパレータとして用いる場合は、幅については30~1000mm、より好ましくは50~800mm、長さについては300~3000m、より好ましくは500~2000mである。巻き取り張力は5N/m~80N/mが好ましい。ポリオレフィン微多孔フィルムを巻き取るコアについては特に限定しないが、座屈を防ぐために外径50mm以上が好ましい。
本発明のポリオレフィン微多孔フィルムは、電池用、特に非水電解質二次電池用のセパレータとして好適に使用することができる。
また、本発明のポリオレフィン微多孔フィルムは、高温及び低温での熱収縮特性に優れることから、コーティングを施したコーティングセパレータとしても好適に使用することができる。
1.厚さ
ポリオレフィン微多孔フィルムの任意の位置から5cm×5cmの正方形状に切り出し、切り出されたポリオレフィン微多孔フィルムの5点(四隅及び中央部)の膜厚を接触厚さ計により測定し、平均することにより求めた。膜厚測定機はミツトヨ(Mitutoyo)製ライトマチックVL-50Aを用いた。
先端が球面(曲率半径R:0.5mm)の直径1mmの針で、ポリオレフィン微多孔フィルムを2mm/秒の速度で突刺したときの最大荷重を測定した。
微多孔フィルムの空孔率はポリオレフィン微多孔フィルムの質量w1とそれと等価な空孔の無いポリマーの質量w2(幅、長さ、組成の同じポリマーについての)との比較によって測定した。空孔率は以下の式によって決定した。
空孔率(%)=(1-w1/w2)×100
ポリオレフィン微多孔フィルムの幅方向、長手方向における105℃での熱収縮率は以下の様に測定した。
(i)ポリオレフィン微多孔フィルムロールからフィルムを5m分巻き出して切り取り、この切り取ったフィルムにおける幅方向中心位置を基準として長手方向50mm、幅方向50mmの正方形の部分を切り出し測定用試料とした。この試料の23℃での寸法を測定(幅方向、長手方向)した。このような測定用試料を3サンプル準備した。
(ii)次に、この試料を無荷重にて105℃8時間の条件に晒し、その後23℃に冷却した。
(iii)冷却後、測定用試料の幅方向、長手方向の寸法を測定した。
幅方向と長手方向の熱収縮率は(iii)の寸法を(i)の寸法で割り、その値を1から引いたものをパーセントで表したもの{(1-((iii)の寸法)÷((i)の寸法)))×100}である。3つのサンプルについて同様の測定を行い、その平均値を熱収縮率とした。
JIS P8117(2009)6項の王研試験機法に準拠して、透気抵抗度(秒/100cc)を測定した。
ポリオレフィン微多孔フィルムの60℃における幅収縮率は以下の様に測定した。なお、ポリオレフィン微多孔フィルムロールは、製膜により得られたマスターロールから幅78mm、長さ1000mにスリットし、張力20N/mで外径90mmのプラスチックのコアに捲回したフィルムロールである。
(i)まず、ポリオレフィン微多孔フィルムロールからフィルムを5m巻き出して切り取り、この切り取ったフィルムを更に1mの長さに3つ切り出し、収縮前(23℃)の測定試料とした。試料を1mに切り出してから30分以内に幅方向寸法を3サンプル測定し、平均値を収縮前の幅方向の寸法とした。測定位置は1m試料の中心部を通るラインに設定した。
(ii)次に、収縮前測定試料切り出し後のポリオレフィン微多孔フィルムロールを無荷重にて60℃4時間の条件に晒し、その後23℃にまで冷却した。冷却後に微多孔フィルムロールからフィルムを5m巻き出して切り取り、この切り取ったフィルムを更に1mの長さに3つ切り出し、収縮後の測定試料とした。
(iii)23℃に冷却後の試料((ii)の試料)を1mの長さに切り出してから30分以内に幅方向寸法を3サンプル測定し、平均値を収縮後の幅方向の寸法とした。測定位置は1m試料の中心部を通るラインに設定した。
ポリオレフィン微多孔フィルムの60℃における幅熱収縮率は(iii)の寸法を(i)の寸法で割り、その値を1から引いたものをパーセントで表したもの{(1-((iii)の寸法)÷((i)の寸法)))×100}である。
JIS K7127に準拠し、長手方向と幅方向の両方においてASTM D-882の10mm幅の試験片を用いてMD及びTD方向の引張強度及び引張伸度の測定を測定した。
8.電極板積層体の巻取評価
電極板積層体の巻取評価として、厚さ20μmのアルミニウム箔を帯状正極体とし、厚さ10μmの銅箔を帯状負極体として用いた。帯状正極体及び帯状負極体は長さ60cm、幅77.5mmを使用した。次に60℃4時間処理させた後のセパレータを用いて、帯状正極体、セパレータ、帯状正極体の順に重ね、皆藤製作所(株)の巻取機(KMW-2BY)にて電極板積層体を巻き取り、巻取評価を行った。得られた電極板積層体で正極体又は負極体がセパレータに対し幅方向において0.5mm以上はみ出したものを巻きズレとし、同一サンプルについて10回評価を行い、巻きズレの発生率が20%未満のものを「○(良)」、20%以上のものを「×(不可)」とし、評価した。
(1)ポリマーと製膜用溶剤の混合物の調製
重量平均分子量が2.5×106、融点が136℃の超高分子量ポリエチレン樹脂18重量部と、重量平均分子量が3.5×105、融点が135℃、重量平均分子量/数平均分子量が4.05、不飽和末端基量が0.14/1.0×104炭素原子である直鎖状の高密度ポリエチレン樹脂82重量部との混合物を二軸押出機に投入し、二軸押出機のサイドフィーダーから流動パラフィン(135cSt/25℃)をポンプによって注入した。流動パラフィンの注入量はポリエチレン樹脂組成と流動パラフィンの合計を100重量%とした時に、ポリエチレン樹脂混合物の量が30重量%となるように調整した。二軸押出機に混合物を注入後に溶解混練し、ポリエチレン樹脂混合物と流動パラフィン(製膜用溶剤)の混合溶液を得た。
得られたポリエチレン樹脂混合物と流動パラフィン(製膜用溶剤)の混合溶液を一軸押出機に投入し、温度210℃にて溶解押出を行った。ステンレス鋼繊維を焼結圧縮した平均目開き20μmのフィルターで混合溶液を濾過したのちに、T字型ダイからシート状に押出し、温度が20℃に設定された冷却ロールにて冷却しゲル状の未延伸シートを得た。未延伸シートを115.1℃にて幅方向、長手方向ともに延伸倍率5倍で第一のテンターによって同時二軸延伸した後に、延伸されたゲル状シートを25℃の塩化メチレンに浸漬して流動パラフィンを除去、室温の送風にて乾燥しポリエチレン微多孔フィルムを得た。得られたポリエチレン微多孔フィルムの両端をクリップで保持しながら第2のテンターに導き、130.2℃にて熱固定を実施しながら幅方向に1.4倍延伸を実施した。さらに同テンター内にて110℃にて幅方向に3.0%の弛緩を行う徐冷緩和処理を行った(熱固定処理と徐冷緩和処理はゾーンごとに温調できる複数のゾーンを有する同一のテンター内で連続して処理されており、途中室温には晒されていない。)。従って、微多孔フィルムは130.2℃から110℃まで徐冷されながら緩和されている。その後、張力5N/mにて巻き長1050mのマスターロールを得た。
得られたマスターロールを巻き張力20N/mにて78.0mmにスリットし、外径90mmのプラスチックコアに捲回することでフィルムロールを得た。
表1で示された条件以外は実施例1と同様にしてポリオレフィン微多孔フィルムを製造し、さらにポリオレフィン微多孔フィルムロールを得た。これらのフィルム製造条件を表1に併せて示し、評価結果については、表2に示す。
Claims (7)
- 主成分がポリオレフィン樹脂からなる微多孔フィルムであって、フィルムロールとして60℃4時間処理した後の幅方向の収縮率が-0.1%~0.4%であるポリオレフィン微多孔フィルム。
- 重量平均分子量1×106未満のポリオレフィン及び重量平均分子量1×106以上のポリオレフィンからなり、
重量平均分子量1×106未満のポリオレフィン及び重量平均分子量1×106以上のポリオレフィンからなる組成物における前記重量平均分子量1×106未満のポリオレフィンの含有量が50重量%~99重量%である請求項1に記載のポリオレフィン微多孔フィルム。 - 突刺強度が20gf/μm以上である請求項1または2に記載のポリオレフィン微多孔フィルム。
- MD引張強度1000kg/cm2以上、MD引張伸度170%以下、105℃におけるMD方向の熱収縮が10%以下である請求項1~3のいずれかに記載のポリオレフィン微多孔フィルム。
- 請求項1~4のいずれかに記載のポリオレフィン微多孔フィルムの製造方法であって、ポリオレフィンと製膜用溶剤を溶融混練し、ダイから押出して形成したシートを延伸し、製膜用溶剤を除去、乾燥後、熱固定処理を行い、その後に連続して100℃以上かつ該熱固定処理の温度未満の温度で徐冷緩和処理を行うポリオレフィン微多孔フィルムの製造方法。
- 徐冷緩和処理時に幅方向に0.1%~20%の弛緩を行う工程を有する請求項5に記載のポリオレフィン微多孔フィルムの製造方法。
- 請求項1~4のいずれかに記載のポリオレフィン微多孔フィルムを用いた電池用セパレータ。
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