WO2014192860A1 - ポリオレフィン多層微多孔膜およびその製造方法 - Google Patents
ポリオレフィン多層微多孔膜およびその製造方法 Download PDFInfo
- Publication number
- WO2014192860A1 WO2014192860A1 PCT/JP2014/064246 JP2014064246W WO2014192860A1 WO 2014192860 A1 WO2014192860 A1 WO 2014192860A1 JP 2014064246 W JP2014064246 W JP 2014064246W WO 2014192860 A1 WO2014192860 A1 WO 2014192860A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- polyolefin
- weight
- less
- molecular weight
- microporous membrane
- Prior art date
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Images
Classifications
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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 multilayer microporous membrane and a method for producing the same, and more particularly to a polyolefin multilayer microporous membrane useful as a battery separator and a method for producing the same.
- Polyolefin multilayer microporous membranes are used in various applications such as battery separators, electrolytic capacitor membranes, various filters, moisture permeable and waterproof clothing, reverse osmosis filtration membranes, ultrafiltration membranes, and microfiltration membranes.
- a battery separator particularly a lithium ion battery separator
- its performance is closely related to battery characteristics, battery productivity, and battery safety. Therefore, excellent permeability, mechanical characteristics, heat shrinkage resistance, shutdown characteristics, meltdown characteristics, etc. are required.
- the voltage of the battery may decrease due to a short circuit of the electrodes.
- lithium ion batteries are known to deteriorate battery performance if they continue to be used while being charged almost fully charged, and oxidative degradation of the separators contributes to this, so improvements in separators are required. I came.
- Patent Document 1 Japanese Patent Laid-Open No. 11-269290
- Patent Document 2 Japanese Patent Application Laid-Open No.
- a polyolefin multilayer microporous film suitable as a separator capable of achieving both oxidation resistance and cycle characteristics 5 to 50% by weight of a polypropylene component and 50 to 50% of a polyethylene component are used. 95% by weight, the polyethylene component includes ultra high molecular weight polyethylene, and the temperature difference between the melting point Tme of the polyethylene component and the melting point Tmp of the polypropylene component is ⁇ 20 ° C. ⁇ Tmp ⁇ Tme ⁇ 23 ° C. And a polyolefin multilayer microporous membrane having a bubble point of 400 to 600 kPa.
- Patent Document 3 Japanese Patent Application Laid-Open No. 2004-152614
- a polyolefin such as specific polypropylene
- the polyolefin is segregated on the surface, and the polyethylene content in the vicinity of the surface may decrease.
- This microporous membrane is a single layer containing 50% by weight or more of polyethylene, and the polyethylene content in the vicinity of the surface of at least one side of the membrane is less than the average value of the entire membrane, and the viscosity average molecular weight is 200,000 or more.
- the problem to be solved by the present invention is to provide a polyolefin multilayer microporous membrane having excellent oxidation resistance and electrolyte solution pouring property, and excellent permeability and strength balance.
- the polyolefin multilayer microporous membrane of the present invention has the following configuration. That is, A first microporous layer containing polypropylene, an electrolyte solution pouring property of 20 seconds or less, at least one surface layer being the first microporous layer, and a polypropylene distribution of the first microporous layer; A polyolefin multilayer microporous membrane having a uniform (hereinafter, PP distribution) in the in-plane direction.
- the method for producing a polyolefin multilayer microporous membrane of the present invention has the following configuration. That is, (A) a step of melt-kneading a polyolefin resin and a film-forming solvent to prepare a polyolefin solution, (A-1) a first polyolefin resin comprising polyethylene having a weight average molecular weight of less than 1.0 ⁇ 10 6 and polypropylene having a weight average molecular weight of greater than 6.0 ⁇ 10 4 and less than 3.0 ⁇ 10 5 ; A step of preparing a first polyolefin solution by melt-kneading a film-forming solvent; and And (a-2) the weight average molecular weight of the second polyolefin resin and membrane-forming solvent comprising an ultra high molecular weight polyethylene polyethylene and the weight average molecular weight of less than 1.0 ⁇ 10 6 is at 1.0 ⁇ 10 6 or more A step including a step of
- the polyolefin multilayer microporous membrane of the present invention has an average value of normalized polypropylene / polyethylene ratio (hereinafter referred to as normalized PP / PE ratio) of 0.5 or more, as measured by Raman spectroscopy of the first microporous layer.
- the standard deviation of the normalized PP / PE ratio is preferably 0.2 or less, and the kurtosis of the normalized PP / PE ratio is preferably ⁇ 1.0 or more and 1.0 or less.
- the polypropylene has a weight average molecular weight of more than 6.0 ⁇ 10 4 and less than 3.0 ⁇ 10 5
- the first microporous layer includes the first
- the total weight of the polyolefin resin of the microporous layer is preferably 0.5% by weight or more and less than 5% by weight based on 100% by weight.
- the piercing strength (Punc 1 ) of the first microporous layer is 4500 mN / 20 ⁇ m or more and 7000 mN / 20 ⁇ m or less, and the porosity (Po) of the first microporous layer is 1 ) is preferably 40% or more and 50% or less.
- the puncture strength (Punc 1 ) of the first microporous layer and the porosity (Po 1 ) of the first microporous layer satisfy the relationship of the following formula (A): It is preferable.
- the first microporous layer is made of a first polyolefin resin
- the first polyolefin resin is a polyethylene having a weight average molecular weight of less than 1.0 ⁇ 10 6 , a weight average It is preferable to comprise ultrahigh molecular weight polyethylene having a molecular weight of 1.0 ⁇ 10 6 or more and polypropylene having a weight average molecular weight of more than 6.0 ⁇ 10 4 and less than 3.0 ⁇ 10 5 .
- the first polyolefin resin is a high-density polyethylene having a weight average molecular weight of 5.0 ⁇ 10 4 or more and less than 5.0 ⁇ 10 5 (the total weight of the first polyolefin resin is Ultra-high molecular weight polyethylene having a weight average molecular weight of 1.0 ⁇ 10 6 or more and less than 3.0 ⁇ 10 6 (first polyolefin resin).
- the polyolefin multilayer microporous membrane of the present invention preferably includes a second microporous layer made of a second polyolefin resin disposed between both surface layers.
- the second polyolefin resin is a high-density polyethylene having a weight average molecular weight of 5.0 ⁇ 10 4 or more and less than 5.0 ⁇ 10 5 (the total weight of the second polyolefin resin is Ultra-high molecular weight polyethylene having a weight average molecular weight of 1.0 ⁇ 10 6 or more and less than 3.0 ⁇ 10 6 (second polyolefin resin). It is preferable that the total weight is 100% by weight and the amount is 1.0% by weight or more and 50.0% by weight or less, and that polypropylene is not included.
- the polyolefin multilayer microporous membrane of the present invention preferably has a three-layer structure in which the second microporous layer is disposed between both surface layers composed of the first microporous layer.
- the polyolefin multilayer microporous membrane of the present invention is a polyolefin multilayer microporous membrane containing polypropylene (PP), and has a first microporous layer containing polypropylene, and at least one surface layer is the first microporous layer.
- PP polypropylene
- the PP distribution of the first microporous layer is uniform in the in-plane direction, and the electrolyte solution pouring property is 20 seconds or less, so that it has excellent oxidation resistance and electrolyte solution pouring property, and permeability. ⁇ Excellent strength balance.
- the polyolefin multilayer microporous membrane When a polyolefin multilayer microporous membrane is used as a battery separator, the polyolefin multilayer microporous membrane may deteriorate during charging / discharging of the battery if there is a part with a high polyethylene concentration in the polyolefin multilayer microporous membrane. There is.
- the polyolefin multilayer microporous membrane of the present invention is used as a battery separator, it is possible to suppress deterioration that occurs during charging and discharging of the battery, and to extend the life of the battery.
- the polyolefin multilayer microporous membrane of the present invention is a polyolefin resin of the first microporous layer having a weight average molecular weight of greater than 6.0 ⁇ 10 4 and less than 3.0 ⁇ 10 5 in the first microporous layer.
- the total weight is preferably 100% by weight and preferably 0.5% by weight or more and less than 5% by weight. This is because it has an excellent balance between air permeability and strength, and has an electrolyte solution pouring property equivalent to that of a polyethylene multilayer microporous membrane.
- the content of the specific polypropylene is less than 5% by weight, the film thickness distribution becomes uniform, which is preferable.
- the polyolefin multilayer microporous membrane of the present invention is used as a battery separator, the productivity of the battery is improved, and the battery can be extended in life due to excellent oxidation resistance.
- the piercing strength (Punc 1 ) of the first microporous layer is 4500 mN / 20 ⁇ m or more and 7000 mN / 20 ⁇ m or less, and the porosity (Po 1 ) of the first microporous layer. Is preferably 40% or more and 50% or less.
- the polyolefin multilayer microporous membrane of the present invention is used as a battery separator, the deterioration of the separator is suppressed even when full charge is continued, and the battery life can be extended.
- the puncture strength (Punc 1 ) of the first microporous layer and the porosity (Po 1 ) of the first microporous layer satisfy the relationship of the following formula (A): preferable. It is because it is more excellent in oxidation resistance and can extend the life of the battery. 110 ⁇ Po 1 + 0.01275 ⁇ Punc 1 ⁇ 122 Formula (A) Po 1 : porosity (%) of the first microporous layer, Punc 1 : Puncture strength (mN / 20 ⁇ m) when the thickness of the first microporous layer is converted to 20 ⁇ m
- the method for producing a polyolefin multilayer microporous membrane of the present invention (A) melt-kneading a polyolefin resin and a film-forming solvent to prepare a polyolefin solution; (However, the polyolefin resin has polyethylene as a main component and 1 to 50% by weight of 100% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 1.0 ⁇ 10 6 or more, and a weight average molecular weight of 6.0 ⁇ 10 to 4 and less than 3.0 ⁇ 10 5 polypropylene, including 0.5 wt% or more and less than 5 wt%).
- the polyolefin multilayer microporous membrane of the present invention has two or more layers, preferably three layers, and has at least one first microporous layer.
- the first microporous layer is composed of a polyolefin resin (first polyolefin resin) containing polyethylene as a main component and containing polypropylene.
- the first microporous layer is at least one surface layer of the polyolefin multilayer microporous membrane of the present invention.
- the layer other than the first microporous layer may be a second microporous layer made of the second polyolefin resin.
- the polyolefin multilayer microporous membrane of the present invention has a three-layer structure in which both surface layers (skin layers) are first microporous layers and a second microporous layer is disposed between both surface layers (core layers). Is preferred.
- the first and second polyolefin resins constituting the polyolefin multilayer microporous membrane of the present invention are mainly composed of polyethylene (PE), and the entire polyolefin resin is 100% by weight, and the ratio of polyethylene is preferably 80% by weight or more, More preferably, it contains 90% by weight or more.
- the first and second polyolefin resins may be compositions containing resins other than polyolefins. Therefore, the term “polyolefin resin” may include not only polyolefin but also resin other than polyolefin.
- the first microporous layer is composed of a first polyolefin resin.
- the first polyolefin resin contains polypropylene in addition to polyethylene. Details of each component are shown below.
- Polyethylene polyethylene has (a) Mw (weight average molecular weight) less than 1.0 ⁇ 10 6 polyethylene (hereinafter “PE (A)”) or (b) PE (A) and Mw is 1.0 ⁇ .
- PE (A) weight average molecular weight polyethylene
- PE composition (B) ultrahigh molecular weight polyethylene
- the ratio Mw / Mn (molecular weight distribution) of Mw and number average molecular weight (Mn) of PE (A) and PE composition (B) is not limited, but is preferably in the range of 5 to 300. Is more preferable, and a range of 5 to 25 is particularly preferable.
- Mw / Mn is within the above preferred range, the polyethylene solution can be easily extruded, and the resulting polyolefin multilayer microporous membrane is excellent in strength.
- PE (A) may be any of high density polyethylene (HDPE), medium density polyethylene (MDPE), and low density polyethylene (LDPE), but HDPE is preferred.
- PE (A) may be not only a homopolymer of ethylene but also a copolymer containing a small amount of other ⁇ -olefin. Examples of ⁇ -olefins other than ethylene include propylene, butene-1, hexene-1, pentene-1, 4-methylpentene-1, octene, vinyl acetate, methyl methacrylate, styrene, and the like.
- PE (A) has a weight average molecular weight (Mw) of less than 1.0 ⁇ 10 6 , for example in the range of about 2.0 ⁇ 10 5 to about 0.9 ⁇ 10 6 , about 2.0 to 50.0.
- Mw weight average molecular weight
- a molecular weight distribution within the range (MWD, defined as Mw divided by number average molecular weight Mn) and polyethylene having less than 0.20 terminal unsaturated groups per 10,000 carbon atoms may be used.
- the Mw of PE (A) is preferably 1.0 ⁇ 10 4 or more and less than 5.0 ⁇ 10 5 .
- the Mw of HDPE is more preferably 5.0 ⁇ 10 4 or more and less than 4.0 ⁇ 10 5 .
- PE (A) may be made of two or more types having different Mw or densities.
- PE (A) has a terminal unsaturation of less than or equal to 0.14 per 10,000 carbon atoms, or less than or equal to 0.12, for example in the range of 0.05 to 0.14 (
- PE composition (B) When polyethylene is the PE composition (B), the upper limit of PE (A) is preferably 98.5% by weight, more preferably 94.0%, based on 100% by weight of the entire first polyolefin resin. % By weight.
- the lower limit of PE (A) is preferably 45.0% by weight, more preferably 46.5% by weight.
- the content of UHMwPE is preferably 55.0% by weight or less based on 100% by weight of the entire first polyolefin resin. Especially preferably, it is 45.0 weight% or less. When the content is within the above preferable range, the pressure does not increase during molding, and the productivity is good.
- the lower limit of the content is not particularly limited, but is more preferably 1.5% by weight and particularly preferably 30.0% by weight from the viewpoint of maintaining mechanical strength and maintaining a high meltdown temperature.
- the Mw of UHMwPE is preferably in the range of 1.0 ⁇ 10 6 to 3.0 ⁇ 10 6 . By making the Mw of UHMwPE to be 3.0 ⁇ 10 6 or less, melt extrusion can be facilitated.
- UHMwPE is not limited to a homopolymer of ethylene but may be a copolymer containing a small amount of other ⁇ -olefin. Other ⁇ -olefins other than ethylene may be the same as described above.
- PE composition (B) polybutene-1 of the Mw as optional ingredients 1.0 ⁇ 10 4 ⁇ 4.0 ⁇ 10 6 , and Mw of 1.0 ⁇ 10 4 ⁇ 4.0 ⁇ 10 6 ethylene / Any of ⁇ -olefin copolymers may be included. These optional components are preferably contained in an amount of 40% by weight or less based on 100% by weight of the entire first polyolefin resin.
- the content of the polypropylene the polypropylene is preferably a weight of the entire first polyolefin resin is less than 5.0 wt% 100 wt%.
- the upper limit of the polypropylene content is preferably 3.5% by weight.
- the lower limit of the polypropylene content is preferably 0.5% by weight, more preferably 1% by weight.
- the Mw of polypropylene is preferably larger than 6.0 ⁇ 10 4 and smaller than 3.0 ⁇ 10 5, more preferably larger than 6.0 ⁇ 10 4 and smaller than 1.5 ⁇ 10 5 .
- the molecular weight distribution (Mw / Mn) of polypropylene is preferably 1.01 to 100, and more preferably 1.1 to 50.
- the polypropylene may be a single material or a composition containing two or more types of polypropylene.
- the melting point of polypropylene is preferably 150 to 175 ° C., more preferably 150 to 160 ° C.
- polypropylene not only a homopolymer but also a block copolymer and / or a random copolymer containing other ⁇ -olefin or diolefin may be used.
- Other olefins are preferably ethylene or ⁇ -olefins having 4 to 8 carbon atoms. Examples of the ⁇ -olefin having 4 to 8 carbon atoms include 1-butene, 1-hexene, 4-methyl-1-pentene and the like.
- the diolefin preferably has 4 to 14 carbon atoms.
- diolefin having 4 to 14 carbon atoms examples include butadiene, 1,5-hexadiene, 1,7-octadiene, 1,9-decadiene, and the like.
- the content of other olefins or diolefins is preferably less than 10 mol% with respect to 100 mol% of the propylene copolymer.
- the second polyolefin resin includes polyethylene.
- the polyethylene the polyethylene described in the first polyolefin resin can be used. That is, polyethylene has (a) Mw (weight average molecular weight) less than 1.0 ⁇ 10 6 polyethylene (PE (A)) or (b) PE (A), and Mw is 1.0 ⁇ 10 6 or more. It is preferable that it is a composition (PE composition (B)) consisting of the ultra high molecular weight polyethylene (UHMwPE).
- the second polyolefin resin preferably does not contain polypropylene.
- the upper limit of PE (A) is preferably 99.0% by weight, more preferably 95.0%, with the total weight of the second polyolefin resin being 100% by weight. % By weight.
- the lower limit of PE (A) is preferably 50.0% by weight, more preferably 80.0% by weight.
- the UHMwPE content is preferably 50.0% by weight or less, with the total weight of the second polyolefin resin being 100% by weight. Especially preferably, it is 20.0 weight% or less. This is because when the content is within the above range, an increase in pressure is suppressed even during molding, and productivity is improved.
- the lower limit of the content is not particularly limited, but is more preferably 1.0% by weight and particularly preferably 5.0% by weight from the viewpoint of maintaining mechanical strength and maintaining a high meltdown temperature.
- PE composition (B) polybutene-1 of the Mw as optional ingredients 1.0 ⁇ 10 4 ⁇ 4.0 ⁇ 10 6 , and Mw of 1.0 ⁇ 10 4 ⁇ 4.0 ⁇ 10 6 ethylene / Any of the ⁇ -olefin copolymers may be added. These addition amounts are preferably 40% by weight or less, based on 100% by weight of the entire second polyolefin resin.
- the first and second polyolefin resins may be polyolefins other than polyethylene and polypropylene, or compositions containing resins other than polyolefins.
- polyolefins other than polyethylene and polypropylene include homopolymers and copolymers such as polybutene-1, pentene-1, hexene-1, 4-methylpentene-1, and octene.
- the melt-down temperature is improved when the polyolefin multilayer microporous membrane is used as a battery separator, so that the high temperature storage characteristics of the battery are further improved.
- the heat resistant resin those described in International Publication WO2006 / 137540 can be used.
- the addition amount of the heat resistant resin is preferably 3 to 20% by weight, more preferably 3 to 15% by weight, based on 100% by weight of the whole polyolefin resin.
- mechanical strength such as puncture strength and tensile rupture strength is excellent.
- the polyolefin multilayer microporous film of the present invention may include a third microporous layer or more microporous layers.
- the third microporous layer is located on the surface layer opposite to the first microporous layer.
- the resin constituting the third microporous layer is not particularly limited, but may be composed of the first polyolefin resin or the second polyolefin resin, but preferably does not contain polypropylene.
- the method for producing a polyolefin multilayer microporous membrane of the present invention includes: (A) a step of melt-kneading a polyolefin resin and a film-forming solvent to prepare a polyolefin solution, (A-1) a first polyolefin resin comprising polyethylene having a weight average molecular weight of less than 1.0 ⁇ 10 6 and polypropylene having a weight average molecular weight of greater than 6.0 ⁇ 10 4 and less than 3.0 ⁇ 10 5 ; A step of preparing a first polyolefin solution by melt-kneading a film-forming solvent; and And (a-2) the weight average molecular weight of the second polyolefin resin and membrane-forming solvent comprising an ultra high molecular weight polyethylene polyethylene and the weight average molecular weight of less than 1.0 ⁇ 10 6 is at 1.0 ⁇ 10 6 or more A step including a step of preparing a second polyolefin solution by melt-kn
- a first production method for producing a polyolefin multilayer microporous membrane of the present invention comprises: (i) first kneading a first polyolefin resin and a film-forming solvent by first kneading; Preparing a polyolefin solution; (ii) preparing a second polyolefin solution by melt-kneading the second polyolefin resin and a film-forming solvent; and (iii) combining the first and second polyolefin solutions from one die.
- the obtained extruded product is cooled to form a gel-like sheet.
- a step of creating a stretched product by stretching the gel-like sheet at least in a uniaxial direction first stretching step
- a step of removing (washing) the film-forming solvent from the stretched product and
- cleaning is included.
- the method may further include (viii) a step of stretching the dried film at least in a uniaxial direction (second stretching step), and (ix) a step of heat treatment.
- any one of the heat setting treatment step, the heat roll treatment step, and the heat solvent treatment step may be provided before the film forming solvent removal step (vi). Further, after the steps (i) to (ix), a drying step, a heat treatment step, a crosslinking treatment step by ionizing radiation, a hydrophilization treatment step, a surface coating treatment step, and the like may be provided. Further, (v) a step of heat-treating the stretched product may be provided after the first stretching step.
- first polyolefin solution The first polyolefin resin and a film-forming solvent are melt-kneaded to prepare a first polyolefin solution.
- a suitable film forming solvent is blended with the first polyolefin resin described above, and then melt-kneaded to prepare a polyolefin resin solution.
- a melt-kneading method for example, a method using a twin-screw extruder described in the specifications of Japanese Patent Nos. 2132327 and 3347835 can be used. Since the melt-kneading method is well-known, description is abbreviate
- the polyolefin resin concentration of the polyolefin resin solution is 20 to 50% by weight, preferably 25 to 45% by weight of the polyolefin resin, where the total of the polyolefin resin and the solvent for film formation is 100% by weight.
- the polyolefin resin concentration of the polyolefin resin solution is within the above range, a decrease in productivity and a decrease in moldability of the gel-like sheet are prevented.
- first polyolefin resin those described above can be used.
- Second polyolefin solution A second polyolefin resin and a film-forming solvent are melt-kneaded to prepare a second polyolefin solution.
- the film forming solvent used for the second polyolefin solution may be the same as or different from the film forming solvent used for the first polyolefin solution, but is preferably the same.
- the other preparation methods may be the same as in the preparation of the first polyolefin solution.
- the second polyolefin resin those described above can be used.
- the first and second polyolefin solutions are each fed from an extruder to a die where they are combined in layers and extruded into sheets.
- the first polyolefin solution forms at least one surface layer (first microporous layer)
- the second polyolefin solution is at least between both surface layers. Both solutions are combined in layers and extruded into sheets to form a single layer (second microporous layer) (preferably in contact with one or both of the surface layers).
- the extrusion method may be either a flat die method or an inflation method. In either method, the solution is supplied to separate manifolds and stacked in layers at the lip inlet of a multilayer die (multiple manifold method), or the solution is supplied to the die in a layered flow in advance (block method) Can be used. Since the multi-manifold method and the block method itself are known, a detailed description thereof will be omitted.
- the gap of the multilayer flat die is preferably 0.1 to 5 mm.
- the extrusion temperature is preferably 140 to 250 ° C., and the extrusion speed is preferably 0.2 to 15 m / min.
- the screw length (L) to diameter (D) ratio (L / D) of the twin screw extruder is preferably in the range of 20-100.
- the inner diameter of the twin screw extruder is preferably 40 to 200 mm.
- the ratio Q / Ns of the amount Q (kg / h) of the polyolefin resin solution to the screw rotation speed Ns (rpm) is set to 0.1 to 0.55 kg / h / rpm. Is preferred.
- the screw rotation speed Ns is preferably 180 rpm or more.
- the upper limit of the screw rotation speed Ns is not particularly limited, but 500 rpm is preferable.
- a polyolefin containing the first polyolefin resin solution is used.
- the shear rate of the resin solution from the die is 60 / sec or more.
- the shear rate from the die is more preferably 150 / sec or more.
- the extruded product obtained by the formation (iii) of the gel-like sheet is cooled to form a gel-like sheet.
- a method for forming a gel-like sheet for example, methods disclosed in Japanese Patent Nos. 2132327 and 3347835 can be used. Cooling is preferably performed until the extruded product reaches 40 ° C. or lower. By cooling, the polyolefin microphase separated by the film-forming solvent can be immobilized.
- a method of contacting with a refrigerant such as cold air or cooling water, a method of contacting with a cooling roll, or the like can be used.
- the cooling rate of the extruded product of the polyolefin resin solution containing the first polyolefin resin solution is 30 ° C./sec or more.
- shear rate from the die and the cooling rate are appropriately controlled, it is easy to make the distribution of polypropylene uniform in the gel sheet, and the oxidation resistance and the electrolyte solution pouring property become good.
- (V) First stretching step The obtained gel-like sheet is stretched in at least a uniaxial direction.
- the first stretching causes cleavage between the polyethylene crystal lamella layers, the polyethylene phase is refined, and a large number of fibrils are formed.
- the obtained fibrils form a three-dimensional network structure (a network structure that is irregularly connected three-dimensionally). Since the gel-like sheet contains a film-forming solvent, it can be stretched uniformly.
- the first stretching can be performed at a predetermined magnification by heating the gel-like sheet and then using a normal tenter method, roll method, inflation method, rolling method, or a combination of these methods.
- the first stretching may be uniaxial stretching or biaxial stretching, but biaxial stretching is preferred. In the case of biaxial stretching, either simultaneous biaxial stretching or sequential stretching may be performed.
- the draw ratio varies depending on the thickness of the gel-like sheet, but it is preferably 2 times or more, more preferably 3 to 30 times in uniaxial stretching.
- biaxial stretching it is preferable to make at least 3 times or more in any direction, that is, 9 times or more in area magnification. This improves the piercing strength of the obtained polyolefin multilayer microporous film, and increases the elasticity and strength. Is possible.
- area magnification is in the above preferable range, there are no restrictions in terms of stretching apparatus, stretching operation, and the like.
- the magnification in both directions is preferably set to the same magnification.
- the first stretching temperature is preferably not more than about 10 ° C. above the melting point of polyethylene used for preparing the polyolefin solution.
- the stretching temperature may be in the range of more than Tcd to less than Tme.
- Tme and Tcd are the melting point and crystal dispersion temperature of all polyethylene used for preparing the polyolefin solution, respectively.
- Tme + 10 ° C. or lower the orientation of the molecular chains of the polyolefin in the gel sheet tends to be promoted during stretching.
- the stretching temperature is Tcd or more, film breakage due to stretching is suppressed, and stretching at a high magnification becomes possible.
- the stretching temperature is from about 90 ° C to about 140 ° C, or from about 100 ° C to about 130 ° C.
- the stretching temperature is usually in the range of 90 to 130 ° C, preferably in the range of 100 to 125 ° C, more preferably in the range of 105 to 120 ° C.
- the Tme of PE (A), ultra high molecular weight polyethylene (UHMwPE), or polyethylene composition (PE composition (B)) is generally about 130 ° C. to about 140 ° C., and Tcd is about 90 ° C. to about 100 ° C. It is. Tcd can be determined from the temperature characteristics of dynamic viscoelasticity according to ASTM D 4065.
- the first stretching may be performed in multiple stages at different temperatures, and the stretching temperature and the final stretching ratio in the former stage and the latter stage are within the above ranges, respectively.
- the film may be stretched by providing a temperature distribution in the film thickness direction, whereby a polyolefin multilayer microporous film having further excellent mechanical strength can be obtained.
- the method for example, the method disclosed in Japanese Patent No. 3347854 can be used.
- (Vii) Membrane drying step The polyolefin multilayer microporous membrane obtained by removing the film-forming solvent is dried by a heat drying method, an air drying method or the like.
- Second stretching step Furthermore, the dried film may be stretched again in at least a uniaxial direction.
- the second stretching can be performed by a tenter method or the like, similar to the first stretching, while heating the film.
- the second stretching may be uniaxial stretching or biaxial stretching.
- the second stretching temperature may be substantially the same or lower than the melting point Tme of all polyethylene used for preparing the polyolefin solution. In one embodiment, the second stretching temperature is from about Tcd to about Tme. When the second stretching temperature is Tme or less, the resulting polyolefin multilayer microporous membrane has appropriate permeability and tends to suppress variations in physical properties such as permeability in the lateral direction (width direction: TD direction). On the other hand, when the second stretching temperature is Tcd or higher, film breakage due to stretching is suppressed, and uniform stretching can be achieved. When the polyolefin resin is made of polyethylene, the stretching temperature is usually in the range of 90 to 140 ° C, preferably in the range of 100 to 140 ° C.
- the magnification in the uniaxial direction of the second stretching is preferably 1.1 to 1.8 times.
- the MD direction referred to as the film production direction, also referred to as the machine direction or the longitudinal direction
- the TD direction referred to as the same direction as the longitudinal direction and perpendicular to the transverse direction
- 1 to 1.8 times in the case of biaxial stretching, it is 1.1 to 1.8 times in the MD direction and TD direction, respectively.
- each stretching ratio in the MD direction and TD direction may be different from each other as long as it is 1.1 to 1.8 times.
- the resulting polyolefin multilayer microporous membrane had a tendency to improve the permeability, heat shrinkage resistance, electrolyte solution absorbability, and compression resistance.
- the magnification of the second stretching is more preferably 1.2 to 1.6 times.
- the second stretching speed is preferably 3% / second or more in the stretching axis direction.
- the stretching speed (% / second) in the stretching axis direction is the ratio of the length stretched per second with the length in the stretching axis direction before re-stretching being 100% in the region where the film (sheet) is re-stretched. Represents.
- the stretching speed is 3% / second or more
- the permeability of the resulting polyolefin multilayer microporous membrane becomes appropriate, and there is a tendency that variations in physical properties such as permeability in the sheet width direction are suppressed.
- the speed of the second stretching is preferably 5% / second or more, and more preferably 10% / second or more.
- each stretching speed in the MD direction and the TD direction may be different from each other in the MD direction and the TD direction as long as it is 3% / second or more, but is preferably the same.
- stretching It is preferable that it is 50% / second or less from a viewpoint of fracture
- the film after the second stretching may be heat treated.
- a polyolefin multi-layer microporous membrane that retains a network composed of fibrils formed by the second stretching, has a large pore diameter, and is excellent in strength can be produced.
- heat setting treatment and / or heat relaxation treatment can be used.
- the heat setting treatment is a heat treatment in which heating is performed while keeping the dimensions of the film unchanged.
- the thermal relaxation treatment is a heat treatment that heat-shrinks the film in the MD direction or the TD direction during heating. In particular, the crystal of the film is stabilized by the heat setting treatment.
- the heat treatment can be performed by a conventional method such as a tenter method, a roll method, or a rolling method.
- a thermal relaxation treatment method a method disclosed in Japanese Patent Application Laid-Open No. 2002-256099 can be given.
- the heat treatment is performed within a temperature range from the crystal dispersion temperature to the melting point of all polyolefin resins constituting the polyolefin multilayer microporous film.
- the heat setting treatment temperature is preferably within the range of the second stretching temperature ⁇ 5 ° C., thereby stabilizing the physical properties. This temperature is more preferably within the range of the second stretching temperature ⁇ 3 ° C.
- an in-line method in which the first stretching, solvent removal for film formation, drying, second stretching and heat treatment are continuously performed on a series of lines.
- an off-line system in which the dried film is wound once and then unwound to perform second stretching and heat treatment may be adopted.
- any of a heat setting treatment step, a heat roll treatment step and a heat solvent treatment step may be provided. Moreover, you may provide the process which heat-sets with respect to the film
- the method for heat-setting the stretched gel-like sheet before and / or after washing and the film during the second stretching step may be the same as described above.
- the second method for manufacturing a polyolefin multilayer microporous membrane is as follows: (i) preparing a first polyolefin solution by melting and kneading a first polyolefin resin and a film-forming solvent. And (ii) preparing a second polyolefin solution by melting and kneading the second polyolefin resin and a film-forming solvent, and (iii-2) extruding the first and second polyolefin solutions from separate dies. Immediately after lamination, (iv) the obtained extruded product (laminated product) is cooled to form a gel-like sheet.
- the first manufacturing method forms an extruded body by laminating a polyolefin solution in one die
- the second manufacturing method is a method in which the solution is laminated immediately after being extruded from a separate die.
- the following steps can employ the same method as the first manufacturing method.
- step (iii-2) the first and second polyolefin solutions are extruded into sheets from adjacent dies connected to each of the plurality of extruders, and the temperature of each solution is high (eg, 100 ° C. or higher). Laminate immediately to obtain a laminated extruded product.
- the other steps may be the same as in the first manufacturing method.
- a third production method for producing a polyolefin multilayer microporous membrane is as follows: (i) a first polyolefin resin and a film-forming solvent are melt-kneaded to obtain a first polyolefin solution. (Ii) a second polyolefin resin and a film-forming solvent are melt-kneaded to prepare a second polyolefin solution, and (iii-3-1) the first polyolefin solution is extruded from one die.
- first extrudate Forming a first extrudate, and (iii-3-2) extruding the second polyolefin solution from another die to form a second extrudate, and (iv-3) the resulting first and The second extrudates were cooled to form first and second gel sheets, respectively (v-3) the first and second gel sheets were stretched, and (xi-3) stretched Laminating the first and second stretched materials, (vi )
- the film-forming solvent is removed from the obtained stretched product. That is, it is performed separately until the gel-like sheet is stretched and then laminated.
- the following steps can employ the same method as the first manufacturing method. Between the steps (vi-3) and (vii-3), (viii-3) a step of stretching the gel-like laminated sheet may be provided.
- Steps (iii-3-1) and (iii-3-2) differ from step (iii) in the first production method only in that the first and second polyolefin solutions are not combined in layers.
- the die used is the same as the die used in step (iii-2) in the second manufacturing method.
- Step (iv-3) differs from step (iv) in the first production method only in that the first and second extrudates are separately cooled.
- Step (v-3) differs from step (v) in the first production method only in that the first and second gel sheets are each stretched.
- the step (xi-3) is a step that is not in the first and second production methods of laminating the first and second stretched products, but a known method may be used for laminating the stretched products. .
- a fourth production method for producing a polyolefin multilayer microporous membrane is as follows: (i) a first polyolefin resin and a film-forming solvent are melt-kneaded to obtain a first polyolefin solution.
- the process is performed separately until the porous film is formed, and then laminated to form a multilayer microporous film.
- a heat treatment step may be performed on each of the first and second polyolefin microporous membranes (ix-4) between steps (vii) and (viii-4).
- the following processes can take the same method as a 1st manufacturing method.
- step (v-4) can be performed in the same manner as in the third manufacturing method.
- Step (vi-4) differs from step (vi) in the first and third production methods only in that the film-forming solvent is removed from the first and second stretched materials, respectively.
- Step (vii-4) is different from step (vii) in the first and third production methods only in that the first and second films are dried.
- step (viii-4) is not necessarily required in the first to third production methods, but in the fourth production method, at least the second polyolefin microporous membrane is regenerated in this step (viii-4).
- the stretching temperature is preferably below the melting point, more preferably from the crystal dispersion temperature to the melting point. If necessary, the first polyolefin microporous membrane may also be stretched.
- the stretching temperature is preferably below the melting point, more preferably from the crystal dispersion temperature to the melting point. In either case of stretching the first and second polyolefin microporous membranes, the stretch ratio may be the same as in the first production method except that the non-laminated polyolefin microporous membrane is stretched.
- the step (xi-4) is a step that is not in the first to third manufacturing methods of laminating the first and second films, but the laminating of the film is a known method as in the case of laminating the stretched product. May be used.
- Step (a) corresponds to steps (i) and (ii) of the first to fourth manufacturing methods.
- the step (b) includes the step (iii) of the first manufacturing method, the step (iii-2) of the second manufacturing method, the step (iii-3-1) of the third manufacturing method, and the fourth manufacturing. This corresponds to step (iii-4-1) of the method.
- Step (c) includes steps (iv) of the first manufacturing method, steps (iv-2) of the second manufacturing method, steps (iv-3) of the third manufacturing method, and steps of the fourth manufacturing method. This corresponds to the step (iv-4).
- Step (d) corresponds to step (v) of the first and second manufacturing methods, step (v-3) of the third manufacturing method, and step (v-4) of the fourth manufacturing method.
- Step (e) corresponds to step (vi) of the first to third manufacturing methods and step (vi-4) of the fourth manufacturing method.
- polyolefin multilayer microporous membrane according to a preferred embodiment of the present invention has the following physical properties.
- the structure, physical properties, and measurement methods thereof will be described.
- the polyolefin multilayer microporous membrane of the present invention has a structure in which the PP distribution of the first microporous layer is uniform in the in-plane direction.
- the uniformity of the PP distribution the relative value when the maximum PP / PE ratio on the film surface is 1 with respect to the peak intensity ratio (PP / PE ratio) of PP and PE obtained by microscopic Raman spectroscopy.
- PP / PE ratio peak intensity ratio
- the normalized PP / PE ratio has an average value of 0.5 or more, a standard deviation of 0.2 or less, and a kurtosis that is a parameter indicating a distribution shape of 1.0 or less. It preferably has a structure of ⁇ 1.0 or more. Furthermore, the polyolefin multilayer microporous membrane of the present invention may have a structure with an average value of 0.68 or more, a standard deviation of 0.1 or less, and a kurtosis of 0.3 or less in the normalized PP / PE ratio. More preferred.
- a method for measuring the PP / PE ratio on the film surface by micro-Raman spectroscopy will be described below.
- area analysis was performed with a 1 micron spot diameter in a depth direction of 1 to 2 microns and a 20 ⁇ 20 micron field using a wavelength of 532 nm laser, and a total of 400 points of frequency 807 cm ⁇ 1 (PP), The peak intensity ratio of 1127 cm ⁇ 1 (PE) is measured.
- the relative value when the maximum value of the intensity ratio in the 20 ⁇ 20 micron visual field is 1 is defined as “standardized PP / PE ratio”.
- the polyolefin multilayer microporous membrane of the present invention has excellent oxidation resistance because it has a uniform PP distribution in the in-plane direction as described above in the first microporous layer. Furthermore, when the content of polypropylene is as low as less than 5% by weight, it is preferable because deterioration of physical properties due to polypropylene is suppressed and the permeability, strength, and electrolyte absorption are excellent. Therefore, when used as a separator for a lithium ion battery, excellent battery productivity, safety, and battery cycle characteristics can be realized.
- the air permeability (Gurley value) of the polyolefin multilayer microporous membrane of the present invention converted to a thickness of 20 ⁇ m is preferably 20 to 600 seconds / 100 cm 3 , more preferably 100 to 500 seconds / 100 cm 3 .
- the air permeability is in this range, when the polyolefin multilayer microporous membrane is used as a battery separator, the battery capacity is large, the battery cycle characteristics are good, and the shutdown is sufficiently performed when the temperature inside the battery rises, When used in a battery, the resistance value is unlikely to increase during charging and discharging, and the average electrochemical stability is good.
- the air permeability is a value obtained by measuring according to JIS P 8117 and converting the film thickness to 20 ⁇ m.
- the porosity of the first microporous layer is determined so that the gel sheet corresponding to the first microporous layer (surface layer) is singly used when the gel sheets of the surface layer and the intermediate layer are prepared to be multilayered.
- the film is formed under the same molding conditions, and the porosity is measured in the same manner.
- the porosity is measured in the same manner.
- the puncture strength is a value obtained by measuring the maximum load value when a polyolefin multilayer microporous membrane is pierced at a speed of 2 mm / sec using a needle having a diameter of 1 mm (0.5 mmR) and converting the film thickness to 20 ⁇ m. It is.
- the puncture strength when the film thickness of the polyolefin multilayer microporous membrane of the present invention is converted to 20 ⁇ m is preferably 2,000 mN or more, preferably 2,500 mN or more, more preferably 4,000 mN or more. When the puncture strength is 2,000 mN / 20 ⁇ m or more, short-circuiting of electrodes can be effectively suppressed when a polyolefin multilayer microporous membrane is incorporated in a battery as a battery separator.
- the puncture strength of the first microporous layer is the same as that of the gel sheet corresponding to the first microporous layer (surface layer) when the surface layer and the intermediate layer are each formed into a multilayered sheet.
- a film is formed under the molding conditions, and the puncture strength is measured in the same manner.
- the puncture strength of the first microporous layer is preferably 4500 mN / 20 ⁇ m or more and 7000 mN / 20 ⁇ m or less, more preferably 4900 mN / 20 ⁇ m or more and 6400 mN / 20 ⁇ m or less.
- the porosity of the first microporous layer is preferably 40% or more and 50% or less.
- the polyolefin multilayer microporous membrane of the present invention having these physical properties is used as a battery separator, the shape of the separator in contact is maintained even when the electrode expands at full charge, and the separator can follow the deformation of the electrode.
- the electrolyte layer present at the electrode interface is maintained. Therefore, even if the battery is fully charged, deterioration of the separator is suppressed, and the battery can be extended in life.
- the strength and porosity of the first microporous layer are the resin composition, resin concentration, gel formation conditions (temperature, shear rate during extrusion, cooling rate) of the first microporous layer, and first / second It can be controlled by stretching conditions (temperature, magnification) and the like.
- the 20 ⁇ m equivalent puncture strength (Punc 1 ) and porosity (Po 1 ) of the first microporous layer satisfy the relationship of the formula (A). 110.8 ⁇ Po 1 + 0.125 ⁇ Punc 1 ⁇ 122 (A) Po 1 : porosity (%) of the first microporous layer, Punc 1 : Puncture strength (mN / 20 ⁇ m) when the thickness of the first microporous layer is converted to 20 ⁇ m
- the polyolefin multilayer microporous membrane of the present invention can suppress performance deterioration during charging and discharging of the battery when the puncture strength and porosity of the first microporous layer satisfy the relationship of the formula (A). This is because even when the strength is small, it is possible to prevent deterioration of the wettability of the electrolytic solution by adhering to the electrode when a part of the separator is deformed. This is thought to be because the decrease in ion permeability can be prevented.
- the tensile breaking strength of the polyolefin multilayer microporous membrane of the present invention is 60,000 kPa or more, more preferably 80,000 kPa or more, and further preferably 100,000 kPa or more in both the MD direction and the TD direction.
- the tensile breaking strength is 60,000 kPa or more, it is easy to prevent film breakage during battery production.
- the tensile strength at break is a value measured by ASTM D882 using a strip-shaped test piece having a width of 10 mm.
- the tensile fracture elongation of the polyolefin multilayer microporous membrane of the present invention is preferably 80% or more, more preferably 100% or more in both the MD direction and the TD direction. Thereby, it is easy to prevent film breakage during battery production.
- the tensile elongation at break is a value measured by ASTM D882 using a strip-shaped test piece having a width of 10 mm.
- Thermal shrinkage (%) The thermal shrinkage after exposure for 8 hours at 105 ° C. of the polyolefin multilayer microporous membrane of the present invention is preferably 10% or less in both the MD and TD directions, more preferably 8% or less, and even more preferably 6%. It is as follows. When the heat shrinkage rate is 10% or less, when the polyolefin multilayer microporous membrane is used as a lithium battery separator, the end of the separator shrinks during heat generation, and the possibility of short-circuiting of the electrode is reduced.
- the thermal shrinkage is a value obtained by measuring the thermal shrinkage in the MD and TD directions three times each when the polyolefin multilayer microporous membrane is exposed at 105 ° C. for 8 hours, and calculating the average value. .
- the polyolefin multilayer microporous membrane of the present invention preferably has a shutdown temperature of 137 ° C or lower, more preferably 135 ° C or lower.
- the shutdown temperature is measured by the method disclosed in International Publication No. 2007/052663. According to this method, the polyolefin multilayer microporous membrane is exposed to an atmosphere of 30 ° C. and heated at 5 ° C./minute, during which the air permeability of the membrane is measured.
- the shutdown temperature of the polyolefin multilayer microporous membrane was defined as the temperature at which the air permeability (Gurley value) of the polyolefin multilayer microporous membrane initially exceeded 100,000 seconds / 100 cm 3 .
- the air permeability of the polyolefin multilayer microporous membrane is measured according to JIS P 8117 using an air permeability meter (AGO Seiko Co., Ltd., EGO-1T).
- Electrolyte injection property of the polyolefin multilayer microporous membrane of the present invention is 20 seconds or less.
- the electrolyte solution pouring property was evaluated by the penetration time of propylene carbonate.
- a sample of 50 mm ⁇ 50 mm is placed on a glass plate, 0.5 ml of propylene carbonate is dropped from about 2 cm above the sample, and time measurement is started from the end of dropping.
- propylene carbonate rises on the film due to surface tension, but the dropped propylene carbonate penetrates with the passage of time.
- the time measurement is stopped and the permeation time is taken. Penetration time of 20 seconds or less is good, 20 seconds or more and 50 seconds or less are good, and those exceeding 50 seconds are unsuitable.
- a film having a length of 70 mm (MD) and a width of 60 mm (TD) is placed between a negative electrode and a positive electrode having the same area as the film.
- the negative electrode is made of natural graphite
- the positive electrode is made of LiCoO 2 .
- the electrolyte is prepared by dissolving LiPF 6 as a 1M solution in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (3/7, V / V). An electrolyte is impregnated in the film in the region between the negative electrode and the positive electrode to complete the battery.
- electrochemical stability is defined as the integrated current (mAh) flowing between the voltage source and the battery over 28 days. Electrochemical stability is measured on three batteries under the same conditions (three batteries of the same condition are made from three film samples of the same condition). The average electrochemical stability (leakage current value) is the average (arithmetic average) of the measured electrochemical stability values of the three batteries.
- Electrochemical stability is a film property related to the oxidation resistance of the film when the film is used as a separator in a battery that is exposed to relatively high temperatures during storage or use. Electrochemical stability is in mAh, and generally lower values are desirable (representing less total charge loss during storage or overcharge at high temperatures). Batteries for automobiles, such as batteries used for starting or feeding power to electric vehicles and hybrid electric vehicles, and power tool batteries are used for relatively high output and large capacity applications. Therefore, even a slight loss of battery capacity such as a self-discharge loss due to the electrochemical instability of the battery separator is an important problem.
- the average electrochemical stability of the polyolefin multilayer microporous membrane of the present invention is preferably 45.0 mAh or less, particularly preferably 35.0 mAh or less.
- the term “high capacity” battery usually refers to a battery that can be supplied for 1 amp hour (1 Ah) or more, for example, 2.0 Ah to 3.6 Ah.
- Leakage current value increase rate (mA / h)
- the rate of increase in leakage current value (mA / h) is defined as the increment per hour of the current value from 60 hours to 100 hours from the start of the experiment in the aforementioned electrochemical stability measurement.
- a graph showing the relationship between the leakage current value and the elapsed time in the multilayer microporous membrane of Example 3 is shown in FIG. 4 as an example.
- the leakage current value increase rate is obtained by subtracting the leakage current value for 60 hours after the start of the experiment from the leakage current value for 100 hours after the start of the experiment and dividing by 40.
- the rate of increase in leakage current value represents the degree of battery capacity decrease when charging continues at full charge.
- the rate of increase in the leakage current value is preferably 22 ⁇ 10 ⁇ 3 mA / h or less, more preferably 7 ⁇ 10 ⁇ 3 mA / h or less.
- the film thickness of the polyolefin multilayer microporous film of the present invention is preferably 5 to 50 ⁇ m, more preferably 5 to 35 ⁇ m, even more preferably 10 to 25 ⁇ m, for example, when used as a battery separator.
- the method for measuring the film thickness may be a contact thickness measurement method or a non-contact thickness measurement method. For example, it can be measured with a contact-type thickness meter over a width of 10.0 cm at intervals of 1.0 cm in the vertical direction, and then the average value can be obtained to obtain the film thickness.
- a thickness gauge such as Mitutoyo Corporation Lightmatic is suitable.
- the melting point of the resin was measured by the following procedure according to JIS K7122. That is, the resin sample was left in a sample holder of a scanning differential calorimeter (Perkin Elmer, Inc., DSC-System7 type), heat-treated at 230 ° C. for 10 minutes in a nitrogen atmosphere, and heated at 10 ° C./minute for 40 minutes. After cooling to 0 ° C., it was held at 40 ° C. for 2 minutes and then heated to 230 ° C. at a rate of 10 ° C./min. The temperature at which the maximum endotherm was reached (peak temperature) was taken as the melting point.
- a scanning differential calorimeter Perkin Elmer, Inc., DSC-System7 type
- the polyolefin multilayer microporous membrane of the present invention is excellent in oxidation resistance and electrolyte solution pouring property, and is not easily blackened even after repeated charge and discharge as a battery, and has permeability. In addition, since it is excellent in strength balance, it is particularly suitable as a battery separator.
- the separator made of the polyolefin multilayer microporous membrane of the present invention can be used for batteries and electric double layer capacitors. Although there is no restriction
- a known electrode and electrolyte may be used for the lithium secondary battery / capacitor using the separator composed of the polyolefin multilayer microporous membrane of the present invention.
- a known electrode and electrolyte may be used for the lithium secondary battery / capacitor using the separator made of the polyolefin multilayer microporous membrane of the present invention.
- the structure of the lithium secondary battery / capacitor using the separator made of the polyolefin multilayer microporous membrane of the present invention may be a known one.
- Example 1 (1) Preparation of first polyolefin solution (a) 25% by weight of UHMwPE (Mw / Mn: 8.0) with Mw of 2.0 ⁇ 10 6 based on the total weight of the first polyolefin composition, (b) Mw Is 2.5 ⁇ 10 5 HDPE (Mw / Mn: 8.6) 72% by weight, (c) Mw is 9.7 ⁇ 10 4 polypropylene (Mw / Mn: 2.6, melting point 155 ° C.) 3% A first polyolefin composition containing 1% was prepared by dry blending.
- Tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane as an antioxidant is dry blended at 0.2 parts by weight per 100 parts by weight of the first polyolefin composition, A polyolefin resin was prepared.
- first polyolefin resin 20 parts by weight was supplied to the strong kneading twin-screw extruder, and 80 parts by weight of liquid paraffin (50 cSt at 40 ° C.) was supplied from the side feeder to the twin-screw extruder.
- a first polyolefin solution was prepared by melt-kneading at 210 ° C. and 200 rpm.
- the second polyolefin solution was prepared in the same manner as the preparation method of the first polyolefin solution except the following points.
- a second polyolefin composition containing 70% by weight (Mw / Mn: 8.6, terminal vinyl group concentration of 0.1 per 10000 carbon) was prepared by dry blending.
- Tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane as an antioxidant is dry blended at 0.2 parts by weight per 100 parts by weight of the second polyolefin composition
- a polyolefin resin was prepared. 28.5 parts by weight of the obtained second polyolefin composition was supplied to a strong kneading twin screw extruder, and 71.5 parts by weight of liquid paraffin (50 cst at 40 ° C.) was supplied from the side feeder to the twin screw extruder.
- a second polyolefin solution was prepared by melt-kneading at 210 ° C. and 200 rpm.
- the first and second polyolefin solutions are supplied from the respective twin-screw extruders to the three-layer T-die, and the layer constitution is first polyolefin solution / second polyolefin solution / first.
- a three-layer extruded product having a layer thickness ratio of 15/70/15 was formed from the polyolefin solution.
- the extruded product was cooled by passing through a cooling roll controlled at 20 ° C. to form a three-layer gel-like laminated sheet.
- dye of an extrusion molded object was 190 / sec
- the cooling rate with a cooling roll was 32 degrees C / sec.
- the obtained gel-like laminated sheet was subjected to simultaneous biaxial stretching (first stretching) at a stretching ratio of 5 ⁇ 5 at a temperature of 117 ° C. using a tenter stretching machine and wound up. Then, a part was taken from the wound stretched product, fixed to a frame plate [size: 20 cm ⁇ 20 cm, made of aluminum (hereinafter the same)], dipped in a methylene chloride washing tank adjusted to 25 ° C., and 100 rpm And washed with rocking for 3 minutes. The washed membrane was air dried at room temperature. The dried microporous membrane is subjected to a second stretching (restretching) at a stretching ratio of 1.5 times in the TD direction at 128 ° C.
- a polyolefin multilayer microporous film was prepared by heat-relaxing treatment and then heat-fixing treatment for 10 minutes at the temperature of re-stretching while attached to a batch stretching machine.
- Examples 2 to 8 and Comparative Examples 1 to 6 A polyolefin multilayer microporous membrane was prepared in the same manner as in Example 1 using the raw materials and conditions shown in Tables 1 and 2. Note that “ ⁇ ” in Example 7 and Comparative Example 2 in Tables 1 and 2 indicates that heat relaxation treatment was not performed. Further, “-” in Comparative Examples 1 to 4 in Table 2 indicates that PP or PE described in the table is not included.
- Tables 3 and 4 show the physical properties of the polyolefin microporous membranes of Examples 1 to 8 and Comparative Examples 1 to 6.
- “-” in Comparative Example 1 indicates that measurement was not possible because PP was not included.
- “-” In Comparative Example 4 indicates that the surface has large irregularities that can be visually judged, and measurement was not possible.
- FIG. 1 is a graph showing the distribution of the normalized PP / PE ratio of the surface layer of the polyolefin multilayer microporous membrane of Example 3, which is concentrated in a narrow range where the normalized PP / PE ratio is 0.5 or more. You can see that FIG.
- FIG. 2 shows a two-dimensional distribution diagram of the normalized PP / PE ratio of the surface layer of the polyolefin multilayer microporous membrane of Example 3, in which almost no region where the polypropylene concentration is low (the dark portion) is observed. It turns out that it exists on average.
- FIG. 3 shows a two-dimensional distribution diagram of the normalized PP / PE ratio of the surface layer of the polyolefin multilayer microporous membrane of Comparative Example 2, where there are many regions where the polypropylene concentration is low (dark portions), It turns out that it does not exist on the surface layer on average.
- the polyolefin multilayer microporous membranes of Examples 1 to 7 have excellent electrolyte solution pouring properties, excellent permeability and strength balance, and good tensile elongation at break and heat shrinkage resistance. Furthermore, since the film thickness is uniform, the oxidation reaction of the separator generated in the battery is further suppressed.
- the polyolefin multilayer microporous membranes of Examples 3 to 7 have a surface piercing strength of 4500 mN / 20 ⁇ m and 7000 mN and a porosity of 40% to 50%, making them more permeable and resistant to oxidation. Excellent and suppresses deterioration of battery performance.
- the surface layer 20 ⁇ m-equivalent puncture strength (Punc 1 ) and porosity (Po 1 ) satisfy the relationship of the formula (A), and more oxidation resistance and Deterioration of battery performance is suppressed.
- the polyolefin multilayer microporous film of Comparative Example 1 does not contain polypropylene
- the polyolefin multilayer microporous film of Comparative Example 2 contains polypropylene having a weight average molecular weight of 3.0 ⁇ 105 or more, The balance of physical properties is poor, such as deterioration of battery performance and oxidation resistance and deterioration of the battery.
- the polyolefin multilayer microporous membrane of Comparative Example 3 contains 8% by weight of the same polypropylene as that used in Examples 1 to 6 and 8. Although the porosity increased and the air permeability decreased, the strength decreased. The appearance of the film was visually indented and confirmed to be inferior in terms of general physical properties as a battery separator.
- the polyolefin multilayer microporous membrane of Comparative Example 4 contains 0.3% by weight of the same polypropylene as that used in Examples 1 to 6 and 8. Although the dispersibility (standard deviation, kurtosis) of polypropylene is good, it is considered that the polypropylene concentration in the vicinity of the surface became insufficient and the oxidation resistance was not improved.
- Comparative Example 5 the same resin composition as in Example 8 was used, and the shear rate from the T-die was reduced. As a result, permeability deteriorated and electrolyte solution pouring property and oxidation resistance deteriorated. It was.
- Comparative Example 6 the same resin composition as in Example 8 was used, and the cooling rate was reduced. As a result, the permeability deteriorated and the electrolyte solution pouring property decreased and the oxidation resistance deteriorated.
- the present invention provides a polyolefin microporous membrane excellent in oxidation resistance and electrolyte solution pouring property, and further having excellent permeability and strength balance.
- the polyolefin multilayer microporous membrane of the present invention has suitable performance as an electricity storage device for non-aqueous electrolyte solutions for capacitor use, capacitor use, battery use, etc., and contributes to improvement in safety and reliability. Can do. Among them, it can be suitably used as a battery separator, more specifically as a lithium ion battery separator. As other uses, it is also used as various separation membranes such as one component of a fuel cell, a humidification membrane, and a filtration membrane, and thus has industrial applicability in those fields.
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Abstract
Description
従って、本発明が解決しようとする課題は、耐酸化性および電解液注液性に優れ、さらに透過性および強度バランスに優れたポリオレフィン多層微多孔膜を提供することである。
ポリプロピレンを含む第1の微多孔層を有し、電解液注液性が20秒以下であり、少なくとも一方の表層が前記第1の微多孔層であり、前記第1の微多孔層のポリプロピレン分布(以下、PP分布)が面内方向で均一であるポリオレフィン多層微多孔膜、である。
(a)ポリオレフィン樹脂と成膜用溶剤とを溶融混練してポリオレフィン溶液を調製する工程であって、
(a-1)重量平均分子量が1.0×106未満のポリエチレンおよび重量平均分子量が6.0×104より大きく、3.0×105未満であるポリプロピレンを含む第1のポリオレフィン樹脂と成膜用溶剤とを溶融混練して第1のポリオレフィン溶液を調製する工程、および、
(a-2)重量平均分子量が1.0×106未満のポリエチレンおよび重量平均分子量が1.0×106以上である超高分子量ポリエチレンを含む第2のポリオレフィン樹脂と成膜用溶剤とを溶融混練して第2のポリオレフィン溶液を調製する工程を含む工程、
(b)せん断速度60/sec以上で、ポリオレフィン溶液を押し出して成形体を形成する工程、
(c)得られた押出成形体を冷却速度30℃/sec以上で冷却してゲル状シートを形成する工程、
(d)得られたゲル状シートを少なくとも一軸方向に延伸して延伸物を作成する工程、および、
(e)得られた延伸物から前記成膜用溶剤を除去する工程を含むポリオレフィン多層微多孔膜の製造方法、である。
110≦Po1+0.01275×Punc1≦122 式(A)
Po1:第1の微多孔層の空孔率(%)
Punc1:第1の微多孔層の膜厚20μm換算時の突刺強度(mN/20μm)
本発明のポリオレフィン多層微多孔膜は、前記第1の微多孔層が第1のポリオレフィン樹脂からなり、前記第1のポリオレフィン樹脂が、重量平均分子量が1.0×106未満のポリエチレン、重量平均分子量が1.0×106以上の超高分子量ポリエチレンおよび重量平均分子量が6.0×104より大きく、3.0×105未満であるポリプロピレンを含んでなることが好ましい。
本発明のポリオレフィン多層微多孔膜は、両表層間に配置された第2のポリオレフィン樹脂からなる第2の微多孔層を含むことが好ましい。
本発明のポリオレフィン多層微多孔膜は、前記第1の微多孔層からなる両表層間に前記第2の微多孔層が配置されてなる三層構造を有することが好ましい。
110≦Po1+0.01275×Punc1≦122 式(A)
Po1:第1の微多孔層の空孔率(%)、
Punc1:第1の微多孔層の膜厚20μm換算時の突刺強度(mN/20μm)
(a)ポリオレフィン樹脂と成膜用溶剤とを溶融混練してポリオレフィン溶液を調製する工程と、
(ただし、前記ポリオレフィン樹脂は、ポリエチレンを主成分とし、重量平均分子量が1.0×106以上の超高分子量ポリエチレンを100重量%として1~50重量%と、重量平均分子量が6.0×104より大きく、3.0×105未満であるポリプロピレンを0.5重量%以上、5重量%未満とを含む。)、
(b)せん断速度60/sec以上で、ポリオレフィン溶液を押し出して成形体を形成する工程、
(c)得られた押出成形体を冷却速度30℃/sec以上で冷却してゲル状シートを形成する工程、
(d)得られたゲル状シートを少なくとも一軸方向に延伸して延伸物を作成する工程、
(e)得られた延伸物から前記成膜用溶剤を除去する工程
を含むことにより、前述の特性を有するポリオレフィン多層微多孔膜を効率よく製造できる。
[ポリオレフィン樹脂]
本発明のポリオレフィン多層微多孔膜を構成する第1および第2のポリオレフィン樹脂は、ポリエチレン(PE)を主成分とし、ポリオレフィン樹脂全体を100重量%として、ポリエチレンの割合が好ましくは80重量%以上、より好ましくは90重量%以上含む。第1および第2のポリオレフィン樹脂は、ポリオレフィン以外の樹脂を含む組成物であってもよい。従って、「ポリオレフィン樹脂」という言葉は、ポリオレフィンのみならず、ポリオレフィン以外の樹脂を含むものであってもよい。
本発明のポリオレフィン多層微多孔膜において、第1の微多孔層は第1のポリオレフィン樹脂から構成される。第1のポリオレフィン樹脂はポリエチレンの他にポリプロピレンを含む。以下に各成分について詳細を示す。
ポリエチレンは、(a)Mw(重量平均分子量)が1.0×106未満のポリエチレン(以下、「PE(A)」)、又は(b)PE(A)と、Mwが1.0×106以上の超高分子量ポリエチレン(UHMwPE)とからなる組成物(以下、「PE組成物(B)」)であることが好ましい。
PE(A)は、高密度ポリエチレン(HDPE)、中密度ポリエチレン(MDPE)および低密度ポリエチレン(LDPE)のいずれでもよいが、HDPEが好ましい。PE(A)は、エチレンの単独重合体のみならず、他のα-オレフィンを少量含有する共重合体であってもよい。エチレン以外の他のα-オレフィンとしてはプロピレン、ブテン-1、ヘキセン-1、ペンテン-1、4-メチルペンテン-1、オクテン、酢酸ビニル、メタクリル酸メチル、スチレン等が挙げられる。
ポリエチレンがPE組成物(B)である場合、PE(A)の上限は、第1のポリオレフィン樹脂全体の重量を100重量%として98.5重量%であることが好ましく、より好ましくは94.0重量%である。PE(A)の下限は、45.0重量%であることが好ましく、より好ましくは46.5重量%である。
ポリプロピレンの含有量は、第1のポリオレフィン樹脂全体の重量を100重量%として5.0重量%未満であることが好ましい。ポリプロピレンの含有量の上限は好ましくは3.5重量%である。ポリプロピレンの含有量の下限は、好ましくは0.5重量%、より好ましくは1重量%である。ポリプロピレンの含有量が上記範囲内であると耐酸化性、膜厚均一性および強度が向上する。
第2の微多孔層を構成する第2のポリオレフィン樹脂の態様は以下のとおりである。
前述のとおり、第1および第2のポリオレフィン樹脂は、ポリエチレン、ポリプロピレン以外のポリオレフィンや、ポリオレフィン以外の樹脂を含む組成物であってもよい。ポリエチレン、ポリプロピレン以外のポリオレフィンとしては、ポリブテン-1、ペンテン-1、ヘキセン-1、4-メチルペンテン-1、オクテン等の単独重合体および共重合体が挙げられる。
次に、本発明のポリオレフィン多層微多孔膜の製造方法を説明する。なお、本発明のポリオレフィン多層微多孔膜の製造方法は、これに限定されるものではない。
(a)ポリオレフィン樹脂と成膜用溶剤とを溶融混練してポリオレフィン溶液を調製する工程であって、
(a-1)重量平均分子量が1.0×106未満のポリエチレンおよび重量平均分子量が6.0×104より大きく、3.0×105未満であるポリプロピレンを含む第1のポリオレフィン樹脂と成膜用溶剤とを溶融混練して第1のポリオレフィン溶液を調製する工程、および、
(a-2)重量平均分子量が1.0×106未満のポリエチレンおよび重量平均分子量が1.0×106以上である超高分子量ポリエチレンを含む第2のポリオレフィン樹脂と成膜用溶剤とを溶融混練して第2のポリオレフィン溶液を調製する工程を含む工程、
(b)せん断速度60/sec以上で、ポリオレフィン溶液を押し出して成形体を形成する工程、
(c)得られた押出成形体を冷却速度30℃/sec以上で冷却してゲル状シートを形成する工程、
(d)得られたゲル状シートを少なくとも一軸方向に延伸して延伸物を作成する工程、
(e)得られた延伸物から前記成膜用溶剤を除去する工程
を含む。
(2-1)第1の製造方法
本発明のポリオレフィン多層微多孔膜を製造する第1の製造方法は、(i)第1のポリオレフィン樹脂と成膜用溶剤とを溶融混練して第1のポリオレフィン溶液を調製し、(ii)第2のポリオレフィン樹脂と成膜用溶剤とを溶融混練して第2のポリオレフィン溶液を調製し、(iii)第1および第2のポリオレフィン溶液を1つのダイより同時に押し出し、(iv)得られた押出成形体を冷却してゲル状シートを形成する。さらに、(v)ゲル状シートを少なくとも一軸方向に延伸して延伸物を作成する工程(第1の延伸工程)、(vi)延伸物から成膜用溶剤を除去(洗浄)する工程、および(vii)洗浄後の膜を乾燥する工程を含む。(i)~(vii)の工程の後、さらに(viii)乾燥した膜を少なくとも一軸方向に再び延伸する工程(第2の延伸工程)、および(ix)熱処理する工程を含んでもよい。必要に応じて、(vi)の成膜用溶剤除去工程の前に熱固定処理工程、熱ロール処理工程および熱溶剤処理工程のいずれかを設けてもよい。さらに(i)~(ix)の工程の後、乾燥工程、熱処理工程、電離放射による架橋処理工程、親水化処理工程、表面被覆処理工程等を設けてもよい。さらに(v)第1の延伸工程の後に延伸物を熱処理する工程を設けてもよい。
第1のポリオレフィン樹脂と成膜用溶剤とを溶融混練し、第1のポリオレフィン溶液を調製する。前述した第1のポリオレフィン樹脂に適当な成膜用溶剤を配合した後、溶融混練し、ポリオレフィン樹脂溶液を調製する。溶融混練方法として、例えば特許第2132327号および特許第3347835号の明細書に記載の二軸押出機を用いる方法を利用することができる。溶融混練方法は公知であるので説明を省略する。ただしポリオレフィン樹脂溶液のポリオレフィン樹脂濃度は、ポリオレフィン樹脂と成膜用溶剤の合計を100重量%として、ポリオレフィン樹脂が20~50重量%であり、好ましくは25~45重量%である。ポリオレフィン樹脂溶液のポリオレフィン樹脂濃度が上記範囲内であると、生産性の低下や、ゲル状シートの成形性の低下が防止される。
第2のポリオレフィン樹脂と成膜用溶剤とを溶融混練し、第2のポリオレフィン溶液を調製する。第2のポリオレフィン溶液に用いる成膜用溶剤は、第1のポリオレフィン溶液に用いる成膜用溶剤と同じでもよいし、異なってもよいが、同じであることが好ましい。それ以外の調製方法は第1のポリオレフィン溶液の調製の場合と同じでよい。
第2のポリオレフィン樹脂としては、前記したとおりのものが使用可能である。
第1および第2のポリオレフィン溶液をそれぞれ押出機から1つのダイに送給し、そこで両溶液を層状に組合せ、シート状に押し出す。三層以上の構造を有するポリオレフィン多層微多孔膜を製造する場合、第1のポリオレフィン溶液が少なくとも一方の表層(第1の微多孔層)を形成し、第2のポリオレフィン溶液が両表層間の少なくとも一層(第2の微多孔層)を形成するように(好ましくは、両表層の一方又は両方に接触するように)両溶液を層状に組合せ、シート状に押し出す。
得られたゲル状シートを少なくとも一軸方向に延伸する。第1の延伸によりポリエチレン結晶ラメラ層間の開裂が起こり、ポリエチレン相が微細化し、多数のフィブリルが形成される。得られるフィブリルは三次元網目構造(三次元的に不規則に連結したネットワーク構造)を形成する。ゲル状シートは成膜用溶剤を含むので、均一に延伸できる。第1の延伸は、ゲル状シートを加熱後、通常のテンター法、ロール法、インフレーション法、圧延法又はこれらの方法の組合せにより所定の倍率で行うことができる。第1の延伸は一軸延伸でも二軸延伸でもよいが、二軸延伸が好ましい。二軸延伸の場合、同時二軸延伸又は逐次延伸のいずれを施してもよい。
次に、洗浄溶剤を用いて、延伸したゲル状シート(延伸物)中に残留する成膜用溶剤を除去する。ポリオレフィン相は成膜用溶剤と相分離しているので、成膜用溶剤を除去すると多孔質の膜が得られる。洗浄溶剤およびこれを用いた成膜用溶剤の除去方法は公知であるので説明を省略する。例えば特許第2132327号明細書や特開2002-256099号公報に開示の方法を利用することができる。
成膜用溶剤除去により得られたポリオレフィン多層微多孔膜は、加熱乾燥法、風乾法等により乾燥する。
さらに、乾燥後の膜を再び少なくとも一軸方向に延伸してもよい。第2の延伸は、膜を加熱しながら、第1の延伸と同様にテンター法等により行うことができる。第2の延伸は一軸延伸でも二軸延伸でもよい。
第2の延伸後の膜を熱処理してもよい。第2の延伸により形成されたフィブリルからなる網状組織が保持され、細孔径が大きく、強度に優れたポリオレフィン多層微多孔膜を作製できる。熱処理は、熱固定処理および/又は熱緩和処理を用いることができる。熱固定処理とは、膜の寸法が変わらないように保持しながら加熱する熱処理である。熱緩和処理とは、膜を加熱中にMD方向やTD方向に熱収縮させる熱処理である。特に熱固定処理により膜の結晶が安定化する。熱処理は、テンター方式、ロール方式又は圧延方式といった従来の方法で行うことができる。例えば、熱緩和処理方法としては特開2002-256099号公報に開示の方法があげられる。
第1の延伸を施したゲル状シートから成膜用溶剤を除去する前に、熱固定処理工程、熱ロール処理工程および熱溶剤処理工程のいずれかを設けてもよい。また洗浄後や第2の延伸工程中の膜に対して熱固定処理する工程を設けてもよい。洗浄前および/又は後の延伸ゲル状シート、並びに第2の延伸工程中の膜を熱固定処理する方法は上記と同じでよい。
ポリオレフィン多層微多孔膜を製造する第2の方法は、(i)第1のポリオレフィン樹脂と成膜用溶剤とを溶融混練して第1のポリオレフィン溶液を調製し、(ii)第2のポリオレフィン樹脂と成膜用溶剤とを溶融混練して第2のポリオレフィン溶液を調製し、(iii-2)第1および第2のポリオレフィン溶液を別個のダイより押出した直後に積層し、(iv)得られた押出成形体(積層体)を冷却してゲル状シートを形成することを特徴とする。すなわち、第1の製造方法が1つのダイの中でポリオレフィン溶液を積層して押出成形体を形成するのに対し、第2の製造方法は溶液を別個のダイより押出した直後に積層する点でのみ異なり、以下の工程は第1の製造方法と同じ方法を採用することができる。
ポリオレフィン多層微多孔膜を製造する第3の製造方法は、(i)第1のポリオレフィン樹脂と成膜用溶剤とを溶融混練して第1のポリオレフィン溶液を調製し、(ii)第2のポリオレフィン樹脂と成膜用溶剤とを溶融混練して第2のポリオレフィン溶液を調製し、(iii-3-1)第1のポリオレフィン溶液を一つのダイより押し出して第1の押出成形体を形成し、(iii-3-2)第2のポリオレフィン溶液を別のダイより押し出して第2の押出成形体を形成し、(iv-3)得られた第1および第2の押出成形体をそれぞれ冷却して第1および第2のゲル状シートを形成し、(v-3)第1および第2のゲル状シートをそれぞれ延伸し、(xi-3)延伸した第1および第2の延伸物を積層し、(vi)得られた延伸物から成膜用溶剤を除去することを特徴とする。すなわち、ゲル状シートを延伸するまでは別々に行い、その後に積層するものであって、以下の工程は第1の製造方法と同じ方法を採用することができる。工程(vi-3)と(vii-3)の間に、(viii-3)ゲル状積層シートの延伸工程等を設けてもよい。工程(iii-3-1)及び(iii-3-2)は、第1及び第2のポリオレフィン溶液を層状に組合せない点でのみ、第1の製造方法における工程(iii)と異なる。使用するダイは第2の製造方法における工程(iii-2)で使用するダイと同じである。工程(iv-3)は、第1および第2の押出成形体をそれぞれ別々に冷却する点でのみ第1の製造方法における工程(iv)と異なる。工程(v-3)は、第1および第2のゲル状シートをそれぞれ延伸する点でのみ第1の製造方法における工程(v)と異なる。一方、工程(xi-3)は、第1および第2の延伸物を積層するという第1及び第2の製造方法にはない工程であるが、延伸物の積層は公知の方法を用いればよい。
ポリオレフィン多層微多孔膜を製造する第4の製造方法は、(i)第1のポリオレフィン樹脂と成膜用溶剤とを溶融混練して第1のポリオレフィン溶液を調製し、(ii)第2のポリオレフィン樹脂と成膜用溶剤とを溶融混練して第2のポリオレフィン溶液を調製し、(iii-4-1)第1のポリオレフィン溶液を一つのダイより押し出し、(iii-4-2)第2のポリオレフィン溶液を別のダイより押し出し、(iv-4)得られた各押出成形体をそれぞれ冷却して第1および第2のゲル状シートを形成し、(v-4)第1および第2のゲル状シートをそれぞれ延伸し、(vi-4)延伸した各延伸物から成膜用溶剤を除去し、(vii-4)得られた第1および第2のポリオレフィン微多孔膜を乾燥し、(viii-4)少なくとも第2のポリオレフィン微多孔膜を延伸し、(xi-4)第1および第2のポリオレフィン微多孔膜を積層する工程を有する。すなわち、多孔膜とするまでは別々に行い、その後に積層して多層微多孔膜とするものである。必要に応じて、工程(vii)と(viii-4)の間に(ix-4)第1および第2のポリオレフィン微多孔膜のそれぞれに熱処理工程を行ってもよい。また以下の工程は第1の製造方法と同じ方法を採ることができる。
工程(b)は、第1の製造方法の工程(iii)、第2の製造方法の工程(iii-2)、第3の製造方法の工程(iii-3-1)、及び第4の製造方法の工程(iii-4-1)に該当する。
工程(c)は、第1の製造方法の工程(iv)、第2の製造方法の工程(iv-2)、第3の製造方法の工程(iv-3)、及び第4の製造方法の工程(iv-4)に該当する。
工程(d)は、第1~第2の製造方法の工程(v)、第3の製造方法の工程(v-3)、及び第4の製造方法の工程(v-4)に該当する。
工程(e)は、第1~第3の製造方法の工程(vi)、及び第4の製造方法の工程(vi-4)に該当する。
本発明の好ましい実施態様によるポリオレフィン多層微多孔膜は、次の物性を有する。以下に、構造、物性およびその測定方法を説明する。
本発明のポリオレフィン多層微多孔膜は、第1の微多孔層のPP分布が面内方向で均一な構造となっている。PP分布の均一性を表現する一例として、顕微ラマン分光法により求めたPPとPEのピーク強度比(PP/PE比率)について、膜表面の最大のPP/PE比率を1としたときの相対値を規格化PP/PE比率とすれば、規格化PP/PE比率の平均値/標準偏差/尖度が一定の値を示す構造と表現することができる。すなわち、本発明のポリオレフィン多層微多孔膜は規格化PP/PE比率が、平均値で0.5以上、標準偏差で0.2以下、分布の形状を示すパラメーターである尖度で1.0以下-1.0以上である構造を有することが好ましい。さらに、本発明のポリオレフィン多層微多孔膜は、上記規格化PP/PE比率において、平均値が0.68以上、標準偏差が0.1以下、尖度が0.3以下の構造を有することがより好ましい。
本発明のポリオレフィン多層微多孔膜の膜厚を20μmに換算した透気度(ガーレー値)は20~600秒/100cm3であることが好ましく、より好ましくは100~500秒/100cm3である。透気度がこの範囲であると、ポリオレフィン多層微多孔膜を電池セパレータとして用いた場合に電池容量が大きく、電池のサイクル特性も良好で、電池内部の温度上昇時にシャットダウンが十分に行われる一方、電池に利用した場合に充放電時に抵抗値が上がりにくく、平均電気化学的安定性は良好である。なお、透気度は、JIS P 8117により測定し、膜厚を20μmに換算することにより求めた値である。
本発明のポリオレフィン多層微多孔膜の空孔率は25~80%であることが好ましく、より好ましくは30~50%である。空孔率が上記範囲内であると、ポリオレフィン多層微多孔膜を電池セパレータとして用いた場合の透過性と強度が適正であり、電極の短絡が抑制される。空孔率は質量法により測定した値である。
空孔率(%)=100×(w2-w1)/w2
w1:微多孔膜の実重量
w2:同じ大きさおよび厚さを有する、(同じポリマーの)同等の非多孔性膜の重量
突刺強度は、直径1mm(0.5mmR)の針を用い、速度2mm/secでポリオレフィン多層微多孔膜を突刺したときの最大荷重値を測定し、膜厚を20μmに換算することにより求めた値である。本発明のポリオレフィン多層微多孔膜の膜厚を20μmに換算した突刺強度は2,000mN以上であることが好ましく、好ましくは2,500mN以上、より好ましくは4,000mN以上である。突刺強度が2,000mN/20μm以上であると、ポリオレフィン多層微多孔膜を電池用セパレータとして電池に組み込んだ場合に、電極の短絡を効果的に抑制できる。
110.8≦Po1+0.125×Punc1≦122 (A)
Po1:第1の微多孔層の空孔率(%)、
Punc1:第1の微多孔層の膜厚20μm換算時の突刺強度(mN/20μm)
115≦Po1+0.125×Punc1≦120
本発明のポリオレフィン多層微多孔膜の引張破断強度はMD方向およびTD方向のいずれにおいても60,000kPa以上、より好ましくは80,000kPa以上、さらに好ましくは100,000kPa以上である。引張破断強度が60,000kPa以上であることにより、電池製造時の破膜を防止しやすい。引張破断強度は、幅10mmの短冊状試験片を用いてASTM D882により測定した値である。
本発明のポリオレフィン多層微多孔膜の引張破断伸度はMD方向およびTD方向のいずれにおいても80%以上であることが好ましく、より好ましくは100%以上である。これにより電池製造時の破膜を防止しやすい。引張破断伸度は、幅10mmの短冊状試験片を用いてASTM D882により測定した値である。
本発明のポリオレフィン多層微多孔膜の105℃の温度で8時間暴露後の熱収縮率はMD方向およびTD方向ともに10%以下であることが好ましく、より好ましくは8%以下、さらに好ましくは6%以下である。熱収縮率が10%以下であると、ポリオレフィン多層微多孔膜をリチウム電池用セパレータとして用いた場合、発熱時にセパレータ端部が収縮し、電極の短絡が発生する可能性が低くなる。
熱収縮率(%)=100×(加熱前の長さ-加熱後の長さ)/加熱前の長さ
本発明のポリオレフィン多層微多孔膜のシャットダウン温度は137℃以下であることが好ましく、135℃以下が更に好ましい。なお、シャットダウン温度は、国際公開第2007/052663号に開示されている方法によって測定する。この方法に従い、ポリオレフィン多層微多孔膜を30℃の雰囲気中にさらして、5℃/分で昇温し、その間に膜の透気度を測定する。ポリオレフィン多層微多孔膜のシャットダウン温度は、ポリオレフィン多層微多孔膜の透気度(ガーレー値)が最初に100,000秒/100cm3を超える時の温度と定義した。ポリオレフィン多層微多孔膜の透気度は、透気度計(旭精工株式会社製、EGO-1T)を用いてJIS P 8117に従って測定する。
本発明のポリオレフィン多層微多孔膜の電解液注液性は20秒以下である。電解液注液性はプロピレンカーボネートの浸透時間にて評価した。50mm×50mmのサンプルをガラス板の上に載せ、サンプルの約2cm上からプロピレンカーボネートを0.5ml滴下し、滴下終了から時間の計測を開始する。滴下終了直後、プロピレンカーボネートは膜上に表面張力で盛り上がるが、滴下したプロピレンカーボネートは時間の経過とともに浸透する。膜上のプロピレンカーボネートが全て透過したところで時間の計測を停止し、浸透時間とする。浸透時間が20秒以下を良好、20秒より大きく50秒以下をやや良好、50秒を超えたものを不適とする。
電気化学的安定性を測定するために、70mmの長さ(MD)および60mmの幅(TD)を有する膜を膜と同じ面積を有する負極と正極の間に配置する。負極は天然黒鉛製であり、正極はLiCoO2製である。電解質は、エチレンカーボネート(EC)とジメチルカーボネート(DMC)(3/7、V/V)との混合物中にLiPF6を1M溶液として溶解させることにより調製する。負極と正極の間の領域にある膜の中に電解質を含浸させ、電池を完成させる。
漏れ電流値上昇速度(mA/h)とは、前述の電気化学的安定性の測定おける実験開始60時間から100時間までの電流値の1時間当たりの増分と定義する。計算方法を説明するために、実施例3の多層微多孔膜における漏れ電流値と経過時間の関係を表したグラフを例として図4に示す。実験開始後100時間の漏れ電流値から実験開始後60時間の漏れ電流値を引いて、40で割った値が漏れ電流値上昇速度である。漏れ電流値上昇速度は満充電時で充電を継続した場合のバッテリー容量低下の程度を表す。これは、電池の劣化による自己放電の増加を意味しており、小さいほど電池性能の劣化が小さいことを示す。漏れ電流値上昇速度は、22×10-3mA/h以下が好ましく、より好ましくは7×10-3mA/h以下である。
本発明のポリオレフィン多層微多孔膜の膜厚は、例えば電池用セパレータとして使用する場合は5~50μmが好ましく、5~35μmがより好ましく、10~25μmがさらに好ましい。膜厚の測定方法は、接触式厚さ測定方法でも非接触式厚さ測定方法でもかまわない。例えば、縦方向に1.0cm間隔で10.0cmの幅にわたって接触式厚さ計により測定することができ、次いで平均値を出して膜厚を得ることができる。接触式厚さ計としては、例えば株式会社ミツトヨ製ライトマチック等の厚さ計が好適である。
膜の外観は目視/多点膜厚測定にて評価した。目視により厚みの変動が小さいものについて「良好」とした。「良好」は、多点における膜厚測定において、膜厚変動が5ミクロン未満である場合に相当する。
樹脂の融点はJIS K 7122に準じて以下の手順で測定した。すなわち、樹脂サンプルを走査型示差熱量計(Perkin Elmer, Inc.製、DSC-System7型)のサンプルホルダー内に静置し、窒素雰囲気中、230℃で10分間熱処理し、10℃/分で40℃まで冷却した後、40℃に2分間保持し、その後10℃/分の速度で230℃まで加熱した。最大吸熱量となった温度(ピーク温度)を融点とした。
以上のように、本発明のポリオレフィン多層微多孔膜は、耐酸化性および電解液注液性に優れ、電池として充放電を繰り返した後も黒色化等が起こりにくく、透過性および強度バランスに優れるので、特に電池用セパレータとして好適である。
(1)第1のポリオレフィン溶液の調製
第1ポリオレフィン組成物の全重量に対し(a)Mwが2.0×106のUHMwPE(Mw/Mn:8.0)25重量%、(b)Mwが2.5×105のHDPE(Mw/Mn:8.6)72重量%、(c)Mwが9.7×104のポリプロピレン(Mw/Mn:2.6、融点155℃)3重量%含む第1ポリオレフィン組成物をドライブレンドにより調製した。酸化防止剤としてテトラキス[メチレン-3-(3,5-ジターシャリーブチル-4-ヒドロキシフェニル)-プロピオネート]メタンを、第1ポリオレフィン組成物100重量部当たり0.2重量部ドライブレンドし、第1ポリオレフィン樹脂を調製した。
第2のポリオレフィン溶液は、以下の点を除き第1のポリオレフィン溶液の調整方法と同様にして調製した。第2ポリオレフィン組成物の全重量に対し(a)Mwが2.0×106のUHMwPE(Mw/Mn:8.0)30重量%、(b)Mwが2.5×105のHDPE(Mw/Mn:8.6、末端ビニル基濃度0.1個/10000炭素あたり)70重量%含む第2ポリオレフィン組成物をドライブレンドにより調製した。酸化防止剤としてテトラキス[メチレン-3-(3,5-ジターシャリーブチル-4-ヒドロキシフェニル)-プロピオネート]メタンを、第2ポリオレフィン組成物100重量部当たり0.2重量部ドライブレンドし、第2ポリオレフィン樹脂を調製した。得られた第2ポリオレフィン組成物28.5重量部を強混練二軸押出機に供給し、71.5重量部の液体パラフィン(40℃で50cst)をサイドフィーダーから二軸押出機に供給した。210℃、200rpmで溶融混練して第2のポリオレフィン溶液を調製した。
第1および第2のポリオレフィン溶液をそれぞれの二軸押出機から三層Tダイへ供給して、層構成が第1のポリオレフィン溶液/第2のポリオレフィン溶液/第1のポリオレフィン溶液で、層厚み比が15/70/15の三層の押出成形体を形成した。この押出成形体を20℃に制御された冷却ロールに通して冷却して三層のゲル状積層シートを形成した。なお、押出成形体のダイ中でのせん断速度を190/sec、冷却ロールでの冷却速度を32℃/secとした。得られたゲル状積層シートに対して、テンター延伸機を用いて、117℃の温度で延伸倍率5×5倍の同時二軸延伸(第1の延伸)を施し、巻き取った。次いで巻き取った延伸物から一部を採取し、枠板[サイズ:20cm×20cm、アルミニウム製(以下同じ)]に固定し、25℃に温調した塩化メチレンの洗浄槽中に浸漬し、100rpmで3分間揺動させながら洗浄した。洗浄した膜を室温で風乾した。乾燥した微多孔膜をバッチ延伸機により128℃でTD方向に1.5倍の延伸倍率で第2の延伸(再延伸)をした後、同温度下でTD方向に延伸倍率1.3倍まで熱緩和処理し、その後バッチ延伸機に取り付けたままの状態で、再延伸の温度で10分間熱固定処理してポリオレフィン多層微多孔膜を作製した。
表1および表2に示す原料・条件にて実施例1と同様にポリオレフィン多層微多孔膜を作成した。なお、表1および表2の実施例7および比較例2の「-」は熱緩和処理を行わなかったことを示す。また表2の比較例1~4の「-」は表に記載のPP又はPEを含まないことを示す。
110≦Po1+0.01275×Punc1≦ 122 式(A)
本発明のポリオレフィン多層微多孔膜は、キャパシター用途、コンデンサー用途、電池用途等の非水系電解液の蓄電デバイスとして好適な性能を有しており、安全性、及び、信頼性の向上に貢献することができる。中でも電池用セパレータ、より具体的には、リチウムイオン電池用セパレータとして好適に利用できる。その他の用途として、燃料電池の一構成部品、加湿膜、ろ過膜等の各種分離膜としても用いられるので、それらの分野において産業上の利用可能性がある。
Claims (11)
- ポリプロピレンを含む第1の微多孔層を有し、電解液注液性が20秒以下であり、少なくとも一方の表層が前記第1の微多孔層であり、前記第1の微多孔層のポリプロピレン分布が面内方向で均一であるポリオレフィン多層微多孔膜。
- 前記第1の微多孔層のラマン分光法により測定した、規格化ポリプロピレン/ポリエチレン比率の平均値が0.5以上、規格化ポリプロピレン/ポリエチレン比率の標準偏差が0.2以下、規格化ポリプロピレン/ポリエチレン比率の尖度が-1.0以上1.0以下である請求項1に記載のポリオレフィン多層微多孔膜。
- 前記ポリプロピレンは、重量平均分子量が6.0×104より大きく、3.0×105未満であり、前記第1の微多孔層中に前記第1の微多孔層のポリオレフィン樹脂全体の重量を100重量%として0.5重量%以上、5.0重量%未満含まれる請求項1または2に記載のポリオレフィン多層微多孔膜。
- さらに、前記第1の微多孔層の突刺強度(Punc1)が4500mN/20μm以上、7000mN/20μm以下であり、前記第1の微多孔層の空孔率(Po1)が40%以上、50%以下である請求項1~3のいずれか1項に記載のポリオレフィン多層微多孔膜。
- さらに、前記第1の微多孔層の突刺強度(Punc1)と前記第1の微多孔層の空孔率(Po1)が以下の式(A)の関係を満たす請求項4に記載のポリオレフィン多層微多孔膜。
110≦Po1+0.01275×Punc1≦122 式(A)
Po1:第1の微多孔層の空孔率(%)
Punc1:第1の微多孔層の膜厚20μm換算時の突刺強度(mN/20μm) - 前記第1の微多孔層が第1のポリオレフィン樹脂からなり、前記第1のポリオレフィン樹脂が、重量平均分子量が1.0×106未満のポリエチレン、重量平均分子量が1.0×106以上の超高分子量ポリエチレンおよび重量平均分子量が6.0×104より大きく、3.0×105未満であるポリプロピレンを含んでなる請求項3~5のいずれか1項に記載のポリオレフィン多層微多孔膜。
- 前記第1のポリオレフィン樹脂が、重量平均分子量が5.0×104以上5.0×105未満の高密度ポリエチレン(第1のポリオレフィン樹脂全体の重量を100重量%として45.0重量%以上98.5重量%以下となる量)、重量平均分子量が1.0×106以上3.0×106未満の超高分子量ポリエチレン(第1のポリオレフィン樹脂全体の重量を100重量%として1.0重量%以上55.0重量%以下となる量)、および重量平均分子量が6.0×104より大きく、3.0×105未満であるポリプロピレン(第1のポリオレフィン樹脂全体の重量を100重量%として0.5重量%以上5.0重量%未満となる量)を含んでなる請求項6に記載のポリオレフィン多層微多孔膜。
- 両表層間に配置された第2のポリオレフィン樹脂からなる第2の微多孔層を含む請求項1~7のいずれか1項に記載のポリオレフィン多層微多孔膜。
- 前記第2のポリオレフィン樹脂が、重量平均分子量が5.0×104以上5.0×105未満の高密度ポリエチレン(第2のポリオレフィン樹脂全体の重量を100重量%として50.0重量%以上99.0重量%以下となる量)、重量平均分子量が1.0×106以上3.0×106未満の超高分子量ポリエチレン(第2のポリオレフィン樹脂全体の重量を100重量%として1.0重量%以上50.0重量%以下となる量)を含んでなり、ポリプロピレンを含まない請求項8に記載のポリオレフィン多層微多孔膜。
- 前記第1の微多孔層からなる両表層間に前記第2の微多孔層が配置されてなる三層構造を有する請求項8または請求項9のいずれか1項に記載のポリオレフィン多層微多孔膜。
- (a)ポリオレフィン樹脂と成膜用溶剤とを溶融混練してポリオレフィン溶液を調製する工程であって、
(a-1)重量平均分子量が1.0×106未満のポリエチレンおよび重量平均分子量が6.0×104より大きく、3.0×105未満であるポリプロピレンを含む第1のポリオレフィン樹脂と成膜用溶剤とを溶融混練して第1のポリオレフィン溶液を調製する工程、および、
(a-2)重量平均分子量が1.0×106未満のポリエチレンおよび重量平均分子量が1.0×106以上である超高分子量ポリエチレンを含む第2のポリオレフィン樹脂と成膜用溶剤とを溶融混練して第2のポリオレフィン溶液を調製する工程を含む工程、
(b)せん断速度60/sec以上で、ポリオレフィン溶液を押し出して成形体を形成する工程、
(c)得られた押出成形体を冷却速度30℃/sec以上で冷却してゲル状シートを形成する工程、
(d)得られたゲル状シートを少なくとも一軸方向に延伸して延伸物を作成する工程、および、
(e)得られた延伸物から前記成膜用溶剤を除去する工程を含むポリオレフィン多層微多孔膜の製造方法。
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US14/893,021 US10411237B2 (en) | 2013-05-31 | 2014-05-29 | Multilayer, microporous polyolefin membrane, and production method thereof |
CN201480030817.1A CN105246693B (zh) | 2013-05-31 | 2014-05-29 | 聚烯烃多层微多孔膜及其制造方法 |
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KR20190124199A (ko) * | 2017-03-08 | 2019-11-04 | 도레이 카부시키가이샤 | 폴리올레핀 미다공막 |
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JP7103715B2 (ja) * | 2018-10-26 | 2022-07-20 | 帝人株式会社 | ポリオレフィン微多孔膜、フィルター、クロマトグラフィー担体及びイムノクロマトグラフ用ストリップ |
EP3932529A4 (en) | 2019-02-28 | 2022-11-30 | Toyobo Co., Ltd. | HOLLOW FIBER MEMBRANE AND METHOD OF MAKING A HOLLOW FIBER MEMBRANE |
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KR20190124199A (ko) * | 2017-03-08 | 2019-11-04 | 도레이 카부시키가이샤 | 폴리올레핀 미다공막 |
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JP2019072901A (ja) * | 2017-10-13 | 2019-05-16 | 旭化成株式会社 | ポリオレフィン微多孔膜及びこれを用いたリチウムイオン二次電池 |
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US10411237B2 (en) | 2019-09-10 |
US20160118639A1 (en) | 2016-04-28 |
EP3006210B1 (en) | 2017-11-15 |
CN105246693B (zh) | 2018-06-29 |
HUE037883T2 (hu) | 2018-09-28 |
MY171677A (en) | 2019-10-23 |
EP3006210A1 (en) | 2016-04-13 |
JPWO2014192860A1 (ja) | 2017-02-23 |
PL3006210T3 (pl) | 2018-06-29 |
JP6394596B2 (ja) | 2018-09-26 |
EP3006210A4 (en) | 2016-11-02 |
KR102269114B1 (ko) | 2021-06-23 |
CN105246693A (zh) | 2016-01-13 |
KR20160016805A (ko) | 2016-02-15 |
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