Espacenet- Bibliographic data
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`Details/bibl
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`10?CC=
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`JP&NR=2016072120A&...
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`10/8/2021
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`Notice
`This translation is machine-generated. It cannot be guaranteedthatit is intelligible, accurate,
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`
`DESCRIPTION J P2016072120A
`10 Separator for power storage device
`
`[0001]
`14 The present invention relates to a separator for a power storage device. The separator of the
`present invention is particularly preferably used as a separator in a non-aqueous electrolyte
`secondary battery.
`
`[0002]
`20 Storage devices such as lithium ion secondary batteries and electric double layer capacitors
`are provided with a separator made of a microporous film between the positive and negative
`electrodes. Functions of the separator include, for example, preventing direct contact between
`the positive and negative electrodes, allowing ions to permeate, and the like. Polyolefin resin
`porous membranesare widely used as separators in power storage devices because they
`exhibit excellent electrical insulation and ion permeability. In particular, in recent years,
`lithium ion secondary batteries and the like having high output density and capacity density
`have been used as a power source for portable devices having significantly increased
`functionality and weight. As a separator for such a battery, a polyolefin resin porous
`membrane is mainly used. However, when the lithium ion secondary battery is used for
`automobile applications, the usage conditions such as temperature, charge / discharge
`current, and upper limit voltage become harsher than those for portable devices, so that the
`electrodes and separators deteriorate over time. It becomes a problem. In this regard, Patent
`Document 1 describes a battery separator in which a metal compound such as hydroxide,
`carbonate, phosphate, or sulfate is supported for the purpose of preventing deterioration of
`the electrode and the separator.
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`[0003]
`39 <patcit num="1"> <text> HRA 2009- 14661 1 542)#8 </text> </patcit>
`
`[0004]
`43 According to the technique of Patent Document 1, although oxidative deterioration of the
`separator is certainly suppressed and the battery characteristics in the cycle evaluation are
`improved, the battery cycle characteristics at high temperature (hereinafter, also referred to as
`"high temperature characteristics"). ) Is inadequate. The present invention has been made in
`view of the above situation. Therefore, an object of the present invention is to provide a
`separator for a power storage device having excellent battery cycle characteristics at high
`temperatures.
`
`[0005]
`53 The outline of the present invention is as follows.
`
`[0006]
`57[1] A separator for a power storage device having a porous base material layer (A), wherein at
`least the outermost layer on one side thereof contains a layer (C) containing a basic phosphate
`(c-1) in a part thereof. The separator for a power storage device, characterized in thatit has.
`60 [2] The area of the layer (C) containing the basic phosphate (c-1) is the surface of the surface
`having the layer (C) containing the basic phosphate (c-1) of the energy storage device
`separator. The separator for a power storage device according to [1], which is 5% or more and
`90% or less with respect to the total area.
`
`[0007]
`67 [3] The separator for a powerstorage device according to [1] or [2], wherein the layer (C)
`containing the basic phosphate (c-1) is present in a dot shape.
`69 [4] Any one of[1] to [3], wherein the basic phosphate(c-1) is at least one selected from the
`group consisting of an alkali metal salt of phosphoric acid and an alkaline earth metal salt. The
`separator for a power storage device according to item 1.
`
`[0008]
`75 [5] The energy storage device separator includes a porous layer (B) containing a resin binder
`(b-1) and an inorganic filler (b-2) on at least one side of the porous substrate layer (A), and
`The storage device according to any one of[1] to [4], wherein the surface on which the layer
`(C) containing the basic phosphate(c-1) is present is the surface of the porous layer (B).
`Separator.
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`[0009]
`83 [6] A powerstorage device comprising the separator for a power storage device according to
`any one of[1] to [5], a positive electrode, a negative electrode, and an electrolytic solution.
`85 [7] The power storage device according to [6], wherein the potential of the positive electrode is
`4.5 V or more based onlithium, and the battery is used as a non-aqueous electrolyte
`secondary battery.
`
`[0010]
`91 According to the present invention, there is provided a separator for a power storage device
`having excellent battery cycle characteristics at high temperatures.
`93 The separator of the present invention can be suitably used, for example, as a separator for a
`non-aqueous electrolyte battery.
`
`[0011]
`98 Hereinafter, a mode for carrying out the present invention (hereinafter, also referred to as "the
`present embodiment’).
`700 ) Will be described in detail.
`101 The present invention is not limited to the following embodiments, and can be variously
`modified and implemented within the scope of the gist thereof.
`
`[0012]
`106 The separator in the present embodimentis characterized in that at least the outermost layer
`on one side thereof has a layer (C) containing a basic phosphate (c-1) in a part thereof.
`108 The separator has at least a porous substrate layer (A).
`109 A porous layer (B) containing a resin binder (b-1) and an inorganic filler (b-2) may be
`provided on at least one side of the porous substrate layer(A).
`171 Whenthe separator includes the porous layer (B), the surface on which the layer (C)
`containing the basic phosphate(c-1) is present is preferably the surface of the porous layer
`(B). ..
`
`[0013]
`117 <Perforated base material layer (A)> The porous base material layer (A) in the present
`invention will be described.
`
`779 The porous base material layer (A) preferably has low electron conductivity, ionic
`conductivity, high resistance to an organic solvent, and a fine pore size.
`121 Examples of such a porous base material layer (A) include a porous film containing a
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`polyolefin resin; polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide,
`polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, and polytetra. Porous films
`containing resins such as fluoroethylene; woven polyolefin-based fibers (woven cloth); non-
`polyolefin-based fiber non-woven fabrics; paper; and aggregates of insulating substance
`particles can be mentioned.
`127 Among these, when a separator is obtained through a coating process, the coating property of
`the coating liquid is excellent, the film thickness of the separator is made thinner, and the
`ratio of active material in a power storage device such as a battery is increased to increase
`the ratio of active material per volume. From the viewpoint of increasing the capacity,it is
`also referred to as a porous membrane containing a polyolefin resin (hereinafter, also
`referred to as“ polyolefin resin porous membrane” ”
`133 ) Is preferable.
`
`[0014]
`137 From the viewpoint of improving the shutdown performance when the porous base material
`layer (A) is used as a battery separator, the porous base material layer (A) is made of a
`polyolefin resin containing 50% by mass or more and 100% by massor less of the resin
`componentconstituting the porous base material layer (A). It is preferably the porous base
`material layer (A) formed by the polyolefin resin composition occupied by.
`142 The proportion of the polyolefin resin in the polyolefin resin composition is more preferably
`60% by mass or more and 100% by massor less, and further preferably 70% by mass or
`more and 100% by massor less.
`
`[0015]
`148 The polyolefin resin contained in the polyolefin resin composition is not particularly limited,
`and for example, ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and
`the like are used as monomers. Examples thereof include the obtained homopolymer,
`copolymer, and multistage polymer.
`152 Further, these polyolefin resins may be used alone or in combination of two or more.
`153 Of these, polyethylene, polypropylene, copolymers thereof, and mixtures thereof are
`preferable as the polyolefin resin from the viewpoint of shutdown characteristics when used
`as a battery separator.
`156 Specific examples of polyethylene include low-density polyethylene, linear low-density
`polyethylene, medium-density polyethylene, high-density polyethylene, ultra-high-molecular-
`weight polyethylene, and specific examples of polypropylene include isotactic polypropylene,
`syndiotactic polypropylene, and tacticic. Specific examples of the copolymer such as
`polypropylene include ethylene-propylene random copolymer, polyethylene propylene
`rubber and the like.
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`[0016]
`165 Above all, polyethylene, particularly high-density polyethylene, is preferably used as the
`polyolefin resin from the viewpointof satisfying the required performance of low melting
`point and high strength when used as a battery separator.
`168 In the present invention, the high-density polyethylene means polyethylene having a density
`of 0.942 to 0.970 g/ cm3.
`170 In the present invention, the density of polyethylene means a value measured according to
`the D) density gradient tube method described in JIS K7112 (1999).
`
`[0017]
`175 Further, from the viewpoint of improving the heat resistance of the porous base material layer
`(A), it is preferable to use a mixture of polyethylene and polypropylene as the polyolefin
`resin.
`
`178 In this case, the ratio of polypropylene to the total polyolefin resin in the polyolefin resin
`composition is preferably 1 to 35% by mass, more preferably 3 to 20% by mass, from the
`viewpoint of achieving both heat resistance and a good shutdown function. %, More
`preferably 4 to 10% by mass.
`
`[0018]
`185 Any additive can be contained in the polyolefin resin composition.
`186 Additives include, for example, polymers other than polyolefin resins; inorganic materials;
`antioxidants such as phenol-based, phosphorus-based, and sulfur-based; metal soaps such as
`calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers. Antistatic agents;
`antifogging agents; coloring pigments and the like.
`190 The total amount of these additives added is preferably 20 parts by massor less with respect
`to 100 parts by mass of the polyolefin resin from the viewpoint of improving shutdown
`performance and the like, more preferably 10 parts by massor less, still more preferably 5
`parts by mass. It is less than a part.
`
`[0019]
`197 Since the porous base material layer (A) has a porous structure in which a large number of
`very small pores are gathered to form dense communication holes, the porous base material
`layer (A) has excellent ionic conductivity and at the same time has good withstand voltage
`characteristics. Moreover, it has a feature of high strength.
`
`[0020]
`204 The porous base material layer (A) may be a single-layer film made of the above-mentioned
`material or a laminated film.
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`206 The film thickness of the porous substrate layer (A) is preferably 0.1 uy mor more and 100
`U mor less, more preferably 1 p mor more and 50 p mor less, and further preferably 3
`UM mor more and 25 up mor less.
`209 From the viewpoint of mechanical strength, 0.1 p mor more is preferable, and from the
`viewpoint of increasing the capacity of the battery, 100 y mor less is preferable.
`211 The film thickness of the porous substrate layer (A) can be adjusted by controlling the die lip
`interval, the stretching ratio in the stretching step, and the like.
`
`[0021]
`216 The average poresize of the porous substrate layer (A) is preferably 0.03 p m or more and
`0.70 u mor less, more preferably 0.04 p m or more and 0.20 yp mor less, still more
`preferably 0.05 p mor more and 0.10 yp mor less, and particularly preferably. It is 0.06 p m
`or more and 0.09 up mor less.
`220 From the viewpoint of high ionic conductivity and withstand voltage, 0.03 yp m or more and
`0.70 uy mor less is preferable.
`222 The average poresize of the porous base material layer (A) can be measured by a measuring
`method described later.
`
`224 The average poresize can be adjusted by controlling the composition ratio, the cooling rate of
`the extruded sheet, the stretching temperature, the stretching ratio, the heat fixing
`temperature, the stretching ratio during heat fixing, and the relaxation rate during heat
`fixing, or by combining these. Can be done.
`
`[0022]
`231 The porosity of the porous substrate layer (A) is preferably 25% or more and 95% or less,
`more preferably 30% or more and 65% or less, and further preferably 35% or more and 55%
`or less.
`
`234 From the viewpoint of improving ionic conductivity, 25% or more is preferable, and from the
`viewpoint of withstand voltage characteristics, 95% or less is preferable.
`236 The porosity of the porous substrate layer (A) can be measured by a method describedlater.
`237 Whenthis is a polyolefin resin porous film, the pore ratio of the porous base material layer
`(A) is the mixing ratio of the polyolefin resin composition and the plasticizer, the stretching
`temperature, the stretching ratio, the heat fixing temperature, and the stretching ratio at the
`time of heat fixing. , It can be adjusted by controlling the relaxation rate at the time of heat
`fixation or by combining these.
`
`[0023]
`245 Whenthe porous base material layer (A) is a porous polyolefin resin film, the viscosity
`average molecular weight of the porous polyolefin resin film is preferably 30,000 or more
`and 120,000 or less, more preferably 50,000 or more.It is less than 2,000,000, more
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`preferably 100,000 or more and less than 1,000,000.
`249 Whenthe viscosity average molecular weight is 30,000 or more, the melt tension during melt
`molding is increased, the moldability is improved, and the polymer tends to be entangled
`with each other to increase the strength, which is preferable.
`252 On the other hand, when the viscosity average molecular weight is 12,000,000 or less,it
`becomes easy to uniformly melt-knead, and the formability of the sheet, particularly the
`thickness stability tends to be excellent, which is preferable.
`255 Further, when the separator for a battery is used, when the viscosity average molecular
`weightis less than 1,000,000, it is preferable that the pores are easily closed when the
`temperature rises and a good shutdown function tends to be obtained.
`258 The viscosity average molecular weight of the polyolefin resin porous membrane can be
`measured by the method described later.
`
`[0024]
`263 The methodfor producing the polyolefin resin porous film as the porous substrate layer (A) is
`not particularly limited, and a known production method can be adopted.
`265 For example; (1) A method in which a polyolefin resin composition and a pore-forming
`material are melt-kneaded, formed into a sheet, stretched as necessary, and then made
`porous by extracting the pore-forming material, (2) Polyolefin. A method in which the resin
`composition is melt-kneaded and extruded at a high draw ratio, and then the polyolefin
`crystal interface is peeled off by heat treatment and stretching to make it porous. (3) The
`polyolefin resin composition and the inorganic material are melt-kneaded and kneadedinto a
`sheet. A method of forming the polyolefin on top and then peeling the interface between the
`polyolefin and the inorganic material to make it porous. (4) After dissolving the polyolefin
`resin composition, it is immersed in a poor solvent for the polyolefin to coagulate the
`polyolefin at the same time. Examples thereof include a method of making porous by
`removing the solvent.
`
`[0025]
`279 Hereinafter, as an example of a method for producing a polyolefin resin porous film as the
`porous base material layer (A), a method in which a polyolefin resin composition and a pore-
`forming material are melt-kneaded and molded into a sheet, and then the pore-forming
`material is extracted. Will be described.
`
`[0026]
`286 First, the polyolefin resin composition and the pore-forming material described above are
`melt-kneaded.
`
`288 AS a melt-kneading method, for example, a polyolefin resin and other additives, if necessary,
`are put into a resin kneading device such as an extruder, a kneader, a lab plast mill, a
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`kneading roll, or a Banbury mixer to heat and melt the resin components. Examples thereof
`include a method of introducing a pore-forming material at an arbitrary ratio and kneading.
`
`[0027]
`295 Examples of the pore-forming material include a plasticizer, an inorganic material, or a
`combination thereof.
`
`[0028]
`300 The plasticizer is not particularly limited, but it is preferable to use a non-volatile solvent
`capable of forming a uniform solution above the melting point of polyolefin.
`302 Specific examples of such a non-volatile solvent include hydrocarbons such as liquid paraffin
`and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; higher alcohols such
`as oleyl alcohol and steary! alcohol. ..
`305 After extraction, these plasticizers may be recovered and reused by an operation such as
`distillation.
`
`307 Further, preferably, the polyolefin resin, other additives and the plasticizer are pre-kneaded at
`a predetermined ratio using a Henschel mixer or the like before being put into the resin
`kneading apparatus.
`3170 More preferably, in the pre-kneading, only a part of the plasticizer is added, and the
`remaining plasticizer is kneaded while being appropriately heated in a resin kneading device
`and side-fed.
`
`373 By using such a kneading method, the dispersibility of the plasticizer is enhanced, and when
`the sheet-shaped molded product of the melt-kneaded product of the resin composition and
`the plasticizer is stretched in a later step, the film is not broken and the magnification is high.
`It tends to be able to be stretched with.
`
`[0029]
`320 Among the plasticizers, liquid paraffin has high compatibility with polyethylene or
`polypropylene whenthe polyolefin resin is polyethylene or polypropylene, and even if the
`melt-kneaded productis stretched, interfacial peeling between the resin and the plasticizer is
`unlikely to occur, and uniform stretching is performed. Is preferable because it tends to be
`easier to carry out.
`
`[0030]
`328 The ratio of the polyolefin resin composition and the plasticizer is not particularly limited as
`long as they can be uniformly melt-kneaded and molded into a sheet.
`330 For example, the massfraction of the plasticizer in the composition composedof the
`polyolefin resin composition and the plasticizer is preferably 20 to 90% by mass, more
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`preferably 30 to 80% by mass.
`333 Whenthe massfraction of the plasticizer is 90% by massor less, the melt tension at the time
`of melt molding tends to be sufficient for improving the moldability.
`335 On the other hand, whenthe massfraction of the plasticizer is 20% by mass or more, the
`polyolefin molecular chain is not broken even whenthe mixture of the polyolefin resin
`composition and the plasticizer is stretched at a high magnification, and a uniform and fine
`pore structure is formed. Is easy to form, and the strength is also easy to increase.
`
`[0031]
`342 The non-equipmentis not particularly limited, and for example, oxide-based ceramics such as
`alumina, silica (silicon oxide), titania, zirconia, magnesia, ceria, itria, zinc oxide, iron oxide;
`silicon nitride, titanium nitride, nitrided. Nitride ceramics such as boron; silicon carbide,
`calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin
`clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite.,
`Asbestos, zeolite, calcium silicate, magnesium silicate, kaolin, silica sand and other ceramics;
`glass fiber.
`349 These may be used alone or in combination of two or more.
`350 Among these,silica, alumina, and titania are preferable from the viewpoint of electrochemical
`stability, and silica is particularly preferable from the viewpoint of easy extraction.
`
`[0032]
`355 The ratio of the polyolefin resin composition to the inorganic material is preferably 5% by
`mass or more, more preferably 10% by mass or more, and higher than the total mass of
`these, from the viewpoint of obtaining good isolation properties. From the viewpoint of
`ensuring strength, it is preferably 99% by massor less, and more preferably 95% by mass or
`less.
`
`[0033]
`363 Next, the melt-kneaded product is formed into a sheet.
`364 AS a method for producing a sheet-shaped molded product, for example, the melt-kneaded
`product is extruded into a sheet shape via a T-die or the like, brought into contact with a heat
`conductor, and cooled to a temperaturesufficiently lower than the crystallization
`temperature of the resin component. There is a methodofsolidifying.
`368 Examples of the heat conductor used for cooling solidification include metal, water, air, and a
`plasticizer.
`370 Among these,it is preferable to use a metal roll because of its high heat conduction efficiency.
`371 Further, when the extruded kneaded product is brought into contact with the metal roll,
`sandwiching it betweenthe rolls further enhances the efficiency of heat conduction, and the
`sheet is oriented to increase the film strength and the surface smoothnessof the sheet.It is
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`morepreferable because it tends to be.
`375 The die lip interval when extruding the melt-kneaded product from the T die into a sheetis
`preferably 200 p mor more and 3,000 p mor less, and more preferably 500 p mor more
`and 2,500 u mor less.
`378 Whenthe die lip interval is 200 p mor more, the shavings and the like are reduced, the
`influence on the film quality such as streaks and defects is small, and the risk of film
`breakage and the like can be reduced in the subsequent stretching step.
`381 On the other hand, whenthe die lip interval is 3,000 pp mor less, the cooling rate is high,
`cooling unevenness can be prevented, and the thicknessstability of the sheet can be
`maintained.
`
`[0034]
`387 Further, the sheet-shaped molded product maybe rolled.
`388 Rolling can be carried out by, for example, a pressing method using a double belt press
`machine or the like.
`
`390 By rolling, the orientation of the surface layer portion can be increased in particular.
`391 The rolled surface magnification is preferably more than 1 time and 3 times or less, and more
`preferably more than 1 time and 2 timesor less.
`393 Whenthe rolling ratio exceeds 1 times, the plane orientation tends to increase and the film
`strength of the finally obtained porous base material layer (A) tends to increase.
`395 On the other hand, whenthe rolling ratio is 3 times or less, the orientation difference between
`the surface layer portion and the inside of the center is small, and there is a tendency that a
`uniform porous structure can be formed in the thickness direction of the film.
`
`[0035]
`401 Next, the pore-forming material is removed from the sheet-shaped molded product to obtain a
`porous base material layer (A).
`403 Examples of the method for removing the pore-forming material include a method in which a
`sheet-shaped molded product is immersed in an extraction solvent to extract the pore-
`forming material and sufficiently dried.
`406 The methodfor extracting the pore-forming material may be either a batch method or a
`continuous method.
`
`408 In order to suppress the shrinkage of the porous base material layer(A), it is preferable to
`restrain the end portion of the sheet-shaped molded product during a series of steps of
`dipping and drying.
`411 Further, the residual amount of the pore-forming material in the porous base material layer
`(A) is preferably less than 1% by masswith respect to the total mass of the porous base
`material layer (A).
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`[0036]
`417 Whenthe porous base material layer (A) is a polyolefin resin, the extraction solvent used
`when extracting the pore-forming material is a poor solvent for the polyolefin resin and a
`good solvent for the pore-forming material. It is preferable to use one having a boiling point
`lower than the melting point of the polyolefin resin.
`421 Examples of such an extraction solvent include hydrocarbons such as n-hexane and
`cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-
`trichloroethane; non-chlorine type such as hydrofluoroether and hydrofluorocarbon.
`Halogenation solvents; alcohols such as ethanol and isopropanol; ethers such as diethyl ether
`and tetrahydrofuran; ketones such as acetone and methyl ethyl ketone.
`426 These extraction solvents may be recovered and reused by an operation such as distillation.
`427 Whenan inorganic material is used as the pore-forming material, an aqueous solution of
`sodium hydroxide, potassium hydroxide or the like can be used as the extraction solvent.
`
`[0037]
`432 Further, it is preferable to stretch the sheet-shaped molded product or the porous base
`material layer (A).
`434 Stretching may be performed before extracting the pore-forming material from the sheet-
`shaped molded product.
`436 Further, it may be applied to the porous base material layer (A) from which the pore-forming
`material is extracted from the sheet-shaped molded product.
`438 Further, it may be performed before and after extracting the pore-forming material from the
`sheet-shaped molded product.
`440 As the stretching treatment, either uniaxial stretching or biaxial stretching can be preferably
`used, but biaxial stretching is preferable from the viewpoint of improving the film strength of
`the obtained porous substrate layer (A).
`443 Whenthe sheet-shaped molded bodyis stretched at a high magnification in the biaxial
`direction, the molecules are oriented in the plane direction, the finally obtained porous base
`material layer (A) is less likely to tear, and the sheet-like molded body has high puncture
`strength.
`447 Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial
`stretching, multi-stage stretching, and multiple stretching.
`449 Simultaneous biaxial stretching is preferable from the viewpoint of improving puncture
`strength, stretching uniformity, and shutdown property.
`451 Further, from the viewpoint of ease of controlling the plane orientation, successive biaxial
`stretching is preferable.
`
`[0038]
`456 Here, the simultaneous biaxial stretching means stretching in the MD (mechanical direction
`(length method) when continuously molding the porous substrate layer (A)) and TD (MD of
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`.A stretching method in which stretching is performed
`the porous substrate layer (A) at 90 °
`at the same time (in the direction of crossing at the angle of), and the stretching ratio in each
`direction may be different.
`461 Sequential biaxial stretching refers to a stretching method in which MD and TD are stretched
`independently, and when MD or TD is stretched, the other direction is fixed in an
`unconstrained state or a fixed length. Make it a state.
`
`[0039]
`467 The draw ratio is preferably in the range of 20 times or more and 100 times or less in terms
`of surface magnification, and more preferably in the range of 25 times or more and 70 times
`or less.
`
`470 The stretching ratio in each axial direction is preferably in the range of 4 times or more and
`10 times or less for MD and 4 times or more and 10 times or less for TD, 5 times or more
`and 8 times or less for MD, and 5 times or more and 8 timesor less for TD. It is more
`preferable that the rangeis.
`474 Whenthe total area magnification is 20 times or more, sufficient strength tends to be
`imparted to the obtained porous base material layer (A), while when the total area
`magnification is 100 times or less, film breakage in the stretching step tends to occur.It
`tends to prevent and obtain high productivity.
`
`[0040]
`481 In order to suppress the shrinkage of the porous base material layer (A), heat treatment may
`be performed for the purpose of heatfixation after the stretching step or after the formation
`of the porous base material layer (A).
`484 Further, the porous base material layer (A) may be subjected to post-treatment such as a
`hydrophilic treatment with a surfactant or the like, a cross-linking treatment with an ionizing
`radiation or the like.
`
`[0041]
`490 The porous base material layer (A) is preferably heat-treated for the purpose of heatfixation
`from the viewpoint of suppressing shrinkage.
`492 The heat treatment method includes a stretching operation performed at a predetermined
`temperature atmosphere and a predeterminedstretching rate for the purpose of adjusting
`physical properties, and / or relaxation performed at a predetermined temperature
`atmosphere and a predeterminedrelaxation rate for the purpose of reducing stretching
`stress. The operation can be mentioned.
`497 The relaxation operation may be performedafter the stretching operation.
`498 These heat treatments can be performed using a tenter or a roll stretching machine.
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`[0042]
`502 In the stretching operation, the MD and / or TD of the membrane is stretched 1.1 times or
`more, more preferably 1.2 times or more to obtain a porous base material layer (A) having
`higher strength and high porosity. It is preferable from the viewpoint of
`505 The relaxation operation is a reduction operation of the membrane to MD and/or TD.
`506 The relaxation rate is a value obtained by dividing the size of the film after the relaxation
`operation by the size of the film before the relaxation operation.
`508 When both MD and TD are relaxed,it is a value obtained by multiplying the relaxation rate of
`MD and the relaxation rate of TD.
`
`5170 The relaxation rate is preferably 1.0 or less, more preferably 0.97 or less, and even more
`preferably 0.95 or less.
`512 The relaxation rate is preferably 0.5 or more from the viewpointoffilm quality.
`5173 The relaxation operation may be performed in both MD and TD directions, but only one of
`MD or TD may be performed.
`
`[0043]
`5178 The stretching and relaxation operations after the plasticizer extraction is preferably
`performed in TD.
`520 The temperature in the stretching and relaxation operations is also referred to as the melting
`point of the polyolefin resin (hereinafter, also referred to as“ Tm” ).
`522), And more preferably 1° C.to25° C. lower than Tm.
`523 Whenthe temperaturein the stretching and relaxation operations is in the above range,it is
`preferable from the viewpoint of the balance between the reduction of the heat shrinkage
`rate and the porosity.
`
`[0044]
`529 <Perforated layer (B)> The separator in the present invention is a porous layer (b-2)
`containing a resin binder (b-1) and an inorganic filler (b-2) on at least one side of the porous
`base material layer (A) as described above. B) may be provided.
`532 The inorganic filler (b-2) used for the porous layer (B) is not particularly limited, but has high
`heat resistance and electrical insulation, and is electrochemically stable within the range of
`use of the lithium ion secondary battery. Some are preferred.
`535 Examples of the inorganic filler (b-2) include aluminum compounds, magnesium compounds,
`and other compounds.
`
`[0045]
`540 Examples of the aluminum compound include aluminum oxide, aluminum silicate, aluminum
`hydroxide, aluminum hydroxide oxide, sodium aluminate, aluminum sulfate, aluminum
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`phosphate, hydrotalcite and the like.
`543 Examples of the magnesium compound include magnesium sulfate and magnesium hydroxide.
`544 Other compoundsinclude oxide-based ceramics, nitride-based ceramics, clay minerals, silicon
`carbide, calcium carbonate, barium titanate, asbestos, zeolite, calcium silicate, magnesium
`silicate, diatomaceous earth, silica sand, glass fiber, etc. Can be mentioned.