WO2013118638A1 - ポリオレフィン微多孔フィルムの製造方法及び積層多孔フィルム - Google Patents
ポリオレフィン微多孔フィルムの製造方法及び積層多孔フィルム Download PDFInfo
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- WO2013118638A1 WO2013118638A1 PCT/JP2013/052228 JP2013052228W WO2013118638A1 WO 2013118638 A1 WO2013118638 A1 WO 2013118638A1 JP 2013052228 W JP2013052228 W JP 2013052228W WO 2013118638 A1 WO2013118638 A1 WO 2013118638A1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
- B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
- B29C55/04—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets uniaxial, e.g. oblique
- B29C55/06—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets uniaxial, e.g. oblique parallel with the direction of feed
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
- B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
- B29C55/04—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets uniaxial, e.g. oblique
- B29C55/08—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets uniaxial, e.g. oblique transverse to the direction of feed
- B29C55/085—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets uniaxial, e.g. oblique transverse to the direction of feed in several stretching steps
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/18—Manufacture of films or sheets
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
- H01M50/451—Separators, membranes or diaphragms characterised by the material having a layered structure comprising layers of only organic material and layers containing inorganic material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
- H01M50/457—Separators, membranes or diaphragms characterised by the material having a layered structure comprising three or more layers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M50/491—Porosity
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2023/00—Use of polyalkenes or derivatives thereof as moulding material
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2023/00—Use of polyalkenes or derivatives thereof as moulding material
- B29K2023/04—Polymers of ethylene
- B29K2023/06—PE, i.e. polyethylene
- B29K2023/0658—PE, i.e. polyethylene characterised by its molecular weight
- B29K2023/0683—UHMWPE, i.e. ultra high molecular weight polyethylene
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
- B29K2105/04—Condition, form or state of moulded material or of the material to be shaped cellular or porous
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
- B29K2105/04—Condition, form or state of moulded material or of the material to be shaped cellular or porous
- B29K2105/041—Microporous
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
- B29K2105/25—Solid
- B29K2105/253—Preform
- B29K2105/256—Sheets, plates, blanks or films
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2995/00—Properties of moulding materials, reinforcements, fillers, preformed parts or moulds
- B29K2995/0012—Properties of moulding materials, reinforcements, fillers, preformed parts or moulds having particular thermal properties
- B29K2995/0016—Non-flammable or resistant to heat
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2995/00—Properties of moulding materials, reinforcements, fillers, preformed parts or moulds
- B29K2995/0037—Other properties
- B29K2995/0088—Molecular weight
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
- B29L2031/00—Other particular articles
- B29L2031/34—Electrical apparatus, e.g. sparking plugs or parts thereof
- B29L2031/3468—Batteries, accumulators or fuel cells
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
- C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
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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
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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
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T156/00—Adhesive bonding and miscellaneous chemical manufacture
- Y10T156/10—Methods of surface bonding and/or assembly therefor
- Y10T156/1002—Methods of surface bonding and/or assembly therefor with permanent bending or reshaping or surface deformation of self sustaining lamina
- Y10T156/1007—Running or continuous length work
- Y10T156/1008—Longitudinal bending
- Y10T156/101—Prior to or during assembly with additional lamina
Definitions
- the present invention relates to a method for producing a polyolefin microporous film. More specifically, the present invention relates to a method for producing a polyolefin microporous film suitable as a constituent member of a nonaqueous electrolyte secondary battery separator.
- Non-aqueous electrolyte secondary batteries especially lithium secondary batteries, are widely used as batteries for personal computers, mobile phones, personal digital assistants, etc. due to their high energy density, and recently developed as in-vehicle batteries. It is coming.
- a microporous film mainly composed of polyolefin or a laminated porous film in which other functional layers are laminated using the microporous film as a base material are used.
- Such a microporous film has a structure having pores connected to the inside thereof, and a liquid containing ions can be transmitted from one surface to the other surface through the connected pores. Therefore, it is suitable as a battery separator member that exchanges ions between the positive electrode and the negative electrode.
- the microporous film preferably has a high porosity from the viewpoint of improving ion permeability.
- the pore diameter of the pores in the microporous film is too large, when the microporous film is used as a battery separator, the dendrite produced in the negative electrode reaches the positive electrode and is likely to cause a short circuit. Therefore, the pore diameter of the microporous film is preferably as small as possible.
- Examples of a method for controlling the pore structure of the microporous film include a method of uniaxially or biaxially stretching a resin sheet as a raw material.
- Patent Document 1 discloses a method for producing a microporous film in which the pore structure is controlled by changing the strain rate from the initial stage to the final stage of stretching while stretching the temperature constant.
- Patent Document 2 discloses a method of performing heat setting by changing the temperature in the upstream and downstream stages of stretching.
- Patent Document 3 discloses a method for producing a thermoplastic resin film in which the temperature of the stretching step is lower than the temperature of the preheating step in the simultaneous biaxial tenter stretching method.
- an object of the present invention is to provide a method for producing a polyolefin microporous film having a porosity and a pore diameter suitable for a separator for a non-aqueous electrolyte secondary battery with high reproducibility and high efficiency.
- the present invention provides the following. ⁇ 1> A method for producing a microporous polyolefin film having a film stretching step in which a raw polyolefin sheet having fine pores is conveyed into a furnace of a tenter-type stretching machine and tenter-stretched in a plurality of stretching regions in the furnace.
- the plurality of stretching regions have at least two stretching regions having different film widening speeds, and the temperature of the stretching region having a large film widening speed in the at least two stretching regions is lower than the stretching region having a small film widening speed, And the manufacturing method of the polyolefin microporous film in which the extending
- ⁇ 6> The polyolefin microporous film according to any one of ⁇ 1> to ⁇ 5>, wherein the raw material polyolefin sheet comprises an ultrahigh molecular weight polyolefin having a weight average molecular weight of 500,000 or more and a polyolefin wax having a weight average molecular weight of 2000 or less.
- ⁇ 7> The method for producing a polyolefin microporous film according to any one of ⁇ 1> to ⁇ 6>, wherein the porosity of the raw material polyolefin sheet is 30 to 50% by volume.
- a porous layer comprising a fine particle as a main component and the fine particles bonded together with a binder polymer is laminated on the polyolefin microporous film obtained by the production method according to any one of ⁇ 1> to ⁇ 7>.
- a laminated porous film is laminated on the polyolefin microporous film obtained by the production method according to any one of ⁇ 1> to ⁇ 7>.
- an ordinary tenter stretching apparatus is used, and the film is stretched without significantly clogging the pores of the polyolefin film only by appropriately combining the temperature in the stretching process and the film widening speed. be able to. Therefore, the polyolefin microporous film suitable for the base material porous film of the separator can be produced with high productivity.
- FIG. 1 It is a schematic diagram of a uniaxial tenter type stretching machine. It is a figure (plan view) for demonstrating the film extending process by a uniaxial tenter type extending machine. It is a figure (sectional drawing) for demonstrating the film extending process by a uniaxial type tenter type extending machine. It is a figure for demonstrating the film widening speed S prescribed
- the method for producing a polyolefin microporous film according to the present invention includes a film stretching step in which a raw polyolefin sheet having fine pores is conveyed into a furnace of a tenter-type stretching machine and tenter-stretched in a plurality of stretching regions in the furnace.
- a method for producing a polyolefin microporous film, wherein the plurality of stretching regions have at least two stretching regions having different film widening speeds, and the temperature of the stretching region having a large film widening speed in the at least two stretching regions is The stretching region having a lower film widening speed and the largest film widening speed is located in the preceding stage than the stretching region having the smallest film widening speed.
- a sheet-like polyolefin as a raw material is referred to as a “raw material polyolefin sheet”, and the one obtained by stretching the sheet is referred to as a film, and the preceding stage refers to the raw material polyolefin sheet or the film transport direction.
- the front side refers to the reference, and the rear stage refers to the transport direction.
- a polyolefin microporous film (hereinafter sometimes simply referred to as “microporous film”) is a so-called multi-stage process in which a raw material polyolefin sheet conveyed in a furnace of a tenter-type stretching machine is tenter-stretched in a plurality of stretching regions. It can be obtained by a formula tenter stretching method.
- the tenter type stretching machine means that a plurality of portions called chucks that grip both ends of the film move on a predetermined tenter rail continuously from the entrance to the exit of the stretching machine, and are uniaxially or biaxially.
- the tenter type stretching machine in the present invention has a plurality of stretching regions divided into two or more and adjusts the tenter rail angle for each stretching region.
- the stretching ratio and the film widening speed can be arbitrarily adjusted, and the temperature can be set for each stretching region.
- the tenter stretching machine may be uniaxial stretching or biaxial stretching, but a uniaxial stretching machine having a simple apparatus configuration is preferable.
- FIG. 1 is a schematic diagram conceptually showing a uniaxial tenter type stretching machine.
- a chuck C is a jig for sandwiching the polyolefin microporous film 11 and is disposed on the tenter rail R at a constant interval.
- the tenter rail R is a portion where the chuck C moves, and the film 11 can be stretched by forming the tenter rail R into a target shape.
- the film stretching step is a step of obtaining the polyolefin microporous film 11 by stretching the raw polyolefin sheet 10 in the lateral direction (film width direction).
- the raw polyolefin sheet 10 is stretched laterally by a tenter stretching method.
- a heating furnace 20 used for film stretching includes a preheating region 21, stretching regions 22 and 23, and a heat fixing region 24.
- the temperature of each region in the heating furnace 20 can be adjusted independently, and the temperature can be appropriately set according to the type of raw material polyolefin and the film stretching conditions. For example, when the raw material polyolefin sheet 10 is made of a polyethylene resin, the temperature is set in a temperature range of about 80 to 170 ° C.
- the raw material polyolefin sheet 10 having the width F 1 is fixed by the chuck C in the tenter rail R.
- the raw material polyolefin sheet 10 is introduced into the preheating region 21 as the chuck C moves from the front stage to the rear stage (in the direction of the arrow) on the tenter rail R.
- the raw material polyolefin sheet 10 moves as the chuck C moves while being heated in the preheating region 21.
- the conveyance speed of the raw polyolefin sheet 10 is usually about 1 to 100 m / min, preferably 3 to 40 m / min.
- the raw polyolefin sheet 10 is heated to a temperature sufficient to stretch the raw polyolefin sheet 10.
- the preheating temperature in the preheating region 21 is preferably (Tg ⁇ 20) to (Tg + 30) ° C.
- Tg is the glass-transition temperature.
- the temperature is preferably (Tm ⁇ 40) to (Tm + 20) ° C.
- Tm is the melting point.
- the preheating temperature in this specification means the temperature of the atmosphere in the preheating area
- the preheated raw material polyolefin sheet 10 moves from the preheating region 21 to the stretching regions 22 and 23 in the subsequent stage.
- seat 10 is extended
- regions 22 and 23 is set so that the said conditions may be satisfy
- the raw material polyolefin sheet 10 When the raw material polyolefin sheet 10 is made of a polyethylene resin, the raw material polyolefin sheet 10 can be stretched more uniformly by laterally stretching the preheated raw material polyolefin sheet 10 at a temperature lower than the preheating temperature. As a result, a stretched film having excellent thickness and retardation uniformity can be obtained.
- the temperature of the atmosphere in the stretching regions 22 and 23 is preferably 5 to 30 ° C lower than the temperature of the preheating region 21 and more preferably 10 to 25 ° C.
- the transverse stretching of the raw polyolefin sheet 10 in the stretching regions 22 and 23 is performed by expanding the chuck C that fixes the raw polyolefin sheet 10 in the width direction (direction perpendicular to the film transport method). That is, the raw material polyolefin sheet 10 is stretched in the width direction by extending in the width direction in the stretching regions 22 and 23 while the chuck C moves in the arrow direction (film transport method). Finally, the raw polyolefin sheet 10 is laterally stretched from the width F 1 to the width F 2 .
- the raw material polyolefin sheet 10 is stretched in the stretching regions 22 and 23 and then moved to the subsequent heat setting region 24.
- the heat setting temperature (the temperature of the atmosphere of the heat setting region 24) may be the same as or different from that of the previous drawing region 23. However, if a temperature far exceeding the temperature applied to the film is applied, a stretched film is applied. Therefore, the heat setting temperature is preferably in the temperature range from the same temperature as the stretching temperature in the stretching region 23 to a temperature 30 ° C. higher than the stretching temperature.
- the stretched film 11 is discharged from the heating furnace 20 after passing through the heat setting region 24. Thereby, the stretched film 11 stretched in the lateral direction (film width direction) can be obtained.
- the film widening speed of at least two stretching regions is different, and the temperature of the stretching region where the film widening speed is large in the at least two stretching regions is the film.
- the stretching region that is set lower than the stretching region where the widening speed is small and has the largest film widening speed is located in the preceding stage than the stretching region where the film widening speed is the smallest. That is, as shown in FIG. 2 and FIG. 3, when the stretching region where tenter stretching is performed is two regions, the film widening speed of the preceding stretching region 22 is larger than the film widening speed of the subsequent stretching region 23, In addition, the former drawing region 22 has a lower temperature than the latter drawing region 23.
- the stretching region having the largest film widening speed located in the previous stage is set at a lower temperature than the stretching area located in the latter stage having the smallest film widening speed.
- FIGS 2 and 3 show an example in which two stretching regions are subjected to tenter stretching.
- at least two of the stretching regions are the production method of the present invention. It is sufficient to satisfy the conditions. Therefore, there may be regions of different film widening speeds at the same temperature and regions of the same film widening speed at different temperatures.
- the width draw ratio (F 2 / F 1 ratio in FIG. 2) of the raw material polyolefin sheet is preferably 2 to 10 times. From the viewpoint of further improving the uniformity of the thickness and retardation of the obtained stretched film, the width stretch ratio is more preferably 4 to 8 times.
- the clogging of the pores during the film stretching described above tends to occur particularly when the thickness of the film is reduced. Therefore, when the raw material polyolefin sheet is supplied to the stretching region having the smallest film widening speed, the raw material polyolefin sheet is stretched to a thickness of 5% to 40% (preferably 10% to 30%) of the initial value. Is preferred. By stretching the film under such conditions, the pores are blocked from being blocked during the film stretching, and a film having an appropriate porosity and pore diameter can be obtained.
- velocity is 10 degreeC or more.
- 15 ° C. or higher is more preferable, and 20 ° C. or higher is more preferable.
- the film widening speed is a speed at which the film is spread in the width direction (direction orthogonal to the film transport direction) per unit time.
- the film widening speed S is expressed by the following formula: It can be defined as (1).
- Film widening speed S V ⁇ W / L (1)
- L is the distance in the film conveying direction in each stretching region
- W is the difference in the distance between the line perpendicular to the film conveying direction in each stretching region and the tenter rail
- V is the stretching of the film in each stretching region. (It represents the speed of passing through the area in the transport direction.)
- FIG. 4 is a diagram for explaining the film widening speed S when the film stretching method is uniaxial stretching.
- FIG. 4 for ease of explanation, only one tenter rail R is shown, and the other tenter rail and components other than the tenter rail are not shown.
- L is the distance in the film conveyance direction in each stretching region, and corresponds to the length of each stretching region. Therefore, L depends on the structure of the tenter stretching machine to be used. Let L in the stretching regions A, B, and C be L A , L B , and L C , respectively.
- W is the difference in the distance formed by the intersection of the tenter rail R and the line orthogonal to the film conveying direction in each stretching region. That is, it defines the amount that the film is stretched in the width direction.
- W in the stretching regions A, B, and C be W A , W B , and W C , respectively.
- V is a speed at which the film passes through each stretching region in the transport direction, that is, a so-called film transport speed.
- V in the stretching regions A, B, and C be V A , V B , and V C , respectively.
- the angles of the tenter rails R in the stretching regions A, B, and C with respect to the film conveying direction are ⁇ A , ⁇ B , and ⁇ C , respectively.
- S defined by the expression (1) in the stretched regions A, B, and C is S A , S B , and S C , respectively.
- the temperatures in the stretching regions A, B, and C are T A , T B , and T C , respectively.
- the film widening speed is a speed at which the film spreads in the lateral direction (width direction) per unit time. Since the interval between the chucks C on the tenter rail R is constant, when the tenter rail R takes an angle ⁇ with respect to the film transport direction, the film widening speed S is proportional to the film transport speed V, and the film transport speed. The film widening speed S increases as V increases. In addition, the tenter rail R steeply moves away from the film center as the angle ⁇ increases, so the film widening speed S increases as the angle ⁇ increases.
- Equation (1) W / L corresponds to tan ⁇ , and therefore, as shown in Equation (1), S, which is the product of W / L and the velocity V in each stretching region, is per unit time. This corresponds to the speed at which the film spreads in the lateral direction (width direction), that is, the film widening speed.
- S which is the product of W / L and the velocity V in each stretching region
- S is per unit time. This corresponds to the speed at which the film spreads in the lateral direction (width direction), that is, the film widening speed.
- S in the formula (1) When the film widening speed is defined by S in the formula (1), it can be applied even when (i) L is different, that is, when the widths of the respective stretching regions are different, (ii) W is different. In other words, it can be applied even when the stretching amount in the width direction of each stretching region is different.
- ⁇ that is, when the angle formed by the tenter rail R with respect to the film transport direction is different.
- regulated by Formula (1) is applicable also when a tenter extending
- film stretching when the tenter stretching method is simultaneous biaxial stretching will be described with reference to FIG. In FIG. 5, for the sake of simplicity of explanation, the stretching region is described with two stretching regions A and B.
- the simultaneous biaxial stretching method is a method in which the film is stretched not only in the width direction but also in the film transport direction (longitudinal direction) in each stretching region, and the film transport speeds V A and V B are in the stretching regions A and B.
- the film conveyance speed V in the simultaneous biaxial stretching method means an average conveyance speed in each stretching region.
- the film widening speed S A in the stretching region A is preferably at least twice the film widening speed S B in the stretching region B, and more preferably four times or more. Preferably, it is 5 times or more.
- the absolute value of the film widening speed S defined by the above formula (1) is appropriately determined in consideration of the film material, the necessary draw ratio, and the like, but is usually 0.1 to 50 m / min. It is preferably 3 to 20 m / min.
- the polyolefin in the raw material polyolefin sheet include high molecular weight homopolymers or copolymers obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and the like.
- an ultrahigh molecular weight polyolefin having a weight average molecular weight of 500,000 or more is preferable, and a high molecular weight polyethylene mainly having ethylene and having a weight average molecular weight of 1,000,000 or more is preferable.
- the ratio of the polyolefin component in the raw material polyolefin sheet is required to be 50% by weight or more of the total weight of the raw material polyolefin sheet, preferably 90% by weight or more, and more preferably 95% by weight or more.
- the polyolefin component of the raw material polyolefin sheet preferably contains a high molecular weight polyolefin component having a weight average molecular weight of 5 ⁇ 10 5 to 150 ⁇ 10 5 .
- a polyolefin component having a weight average molecular weight of 1,000,000 or more is contained as a polyolefin component, the strength of the polyolefin microporous film (after stretching the raw material polyolefin sheet) tends to be improved.
- the polyolefin component of the raw polyolefin sheet preferably contains a polyolefin wax having a weight average molecular weight of 2000 or less together with a high molecular weight polyolefin component having a weight average molecular weight of 5 ⁇ 10 5 to 150 ⁇ 10 5 .
- a polyolefin wax acts as a plasticizer when processing the high-molecular-weight polyolefin, whereby the high-molecular-weight polyolefin component becomes easy to move and promotes the crystallization of the high-molecular-weight polyolefin, thereby increasing the strength of the entire film.
- the porosity of the raw material polyolefin sheet is preferably 30 to 50% by volume. If the porosity of the raw material polyolefin sheet is smaller than 30% by volume, it is difficult to increase the porosity of the microporous film after stretching. In some cases, the strength of the porous film cannot be sufficiently maintained.
- a raw material polyolefin sheet manufacturing method which is a raw material of a polyolefin microporous film, for example, in order to have a void (fine pores) in the raw material polyolefin, the resin composition comprising polyolefin is filled with an extractable filler, A method of extracting and removing the filler after forming into a predetermined thickness is mentioned.
- the pore size of the voids (fine pores) of the raw polyolefin sheet is determined by the particle size of the filler.
- the polyolefin microporous film obtained by the production method of the present invention has a structure having pores connected to the inside thereof, and is a microporous film mainly composed of polyolefin, and has one surface through the connected pores. Gas or liquid can pass through the other surface.
- the film thickness of the microporous film is preferably 4 to 40 ⁇ m, more preferably 7 to 30 ⁇ m. If the film thickness is less than 4 ⁇ m, the handling property may be inferior, and when used as a battery separator, the positive and negative electrodes may not be insulated. On the other hand, if the film thickness exceeds 40 ⁇ m, the battery capacity may be reduced when used as a battery separator.
- the basis weight of the microporous film is usually 4 to 20 g / m 2 and preferably 5 to 12 g / m 2 . If the basis weight is less than 4 g / m 2 , the strength and handling properties of the microporous film may be inferior, or insulation between the positive and negative electrodes may not be maintained when used as a battery separator. On the other hand, if the weight per unit area exceeds 20 g / m 2 , the weight energy density becomes small, and there is a risk of insufficient capacity when used as a battery separator.
- the ion permeability of the microporous film can be evaluated by Gurley air permeability.
- the air permeability of the microporous film is a Gurley value of 250 seconds / 100 cc or less, preferably 220 seconds / 100 cc or less, more preferably 200 seconds / 100 cc or less.
- the air permeability is in the above range, ion permeability required when used as a separator for a high-power secondary battery such as an in-vehicle secondary battery can be exhibited.
- the air permeability is preferably 30 seconds / 100 cc or more, more preferably 50 seconds / 100 cc or more.
- the porosity of a microporous film is 43 volume% or more, Preferably it is 45 volume% or more, More preferably, it is 47 volume% or more.
- the porosity of the microporous film is preferably 80% by volume or less, more preferably 75% by volume or less, from the viewpoint that the shutdown function can be reliably obtained.
- the pore diameter of the microporous film is 0.073 ⁇ m in that it can prevent the positive electrode and negative electrode particles from entering when it is used as a battery separator and can prevent a short circuit caused by dendrite generated in the negative electrode.
- the following is preferable, more preferably 0.071 ⁇ m or less, and particularly preferably 0.069 ⁇ m or less.
- the ratio of the average pore diameter and the porosity of the microporous film is preferably 0.1 to 0.16, more preferably 0.12 to 0.15. If it is such a range, it will be easy to suppress generation
- the microporous film has pores having ion permeability, but is melted to become nonporous by overheating, and thus can be used as a battery separator having a shutdown function.
- the laminated porous film of the present invention has a heat resistant layer laminated on one side or both sides of the above-mentioned polyolefin microporous film (hereinafter sometimes referred to as “substrate porous film” in the explanation of the laminated porous film). Become.
- the laminated porous film of the present invention is suitable as a battery separator. When excessive heat generation occurs in the battery, the porous substrate film melts and becomes nonporous, thereby exhibiting a shutdown function and heat resistance.
- the layer exhibits functions of heat resistance and dimensional stability against high temperatures during excessive heat generation.
- the substrate porous film is a substrate of a laminated porous film, and uses the polyolefin microporous film produced according to the present invention described above, so the description is omitted here.
- the heat-resistant layer is a porous layer composed mainly of fine particles and bonded to each other by a binder polymer, and is laminated on the surface of the substrate porous film.
- the heat-resistant layer is not particularly limited as long as it has functions of heat resistance against high temperatures and excessive dimensional heat and dimensional stability, and a nitrogen-containing aromatic polymer such as polyamide or polyimide can be used.
- a porous layer having a main component and fine particles bonded with a binder polymer is preferably used.
- heat-resistant layer which is a porous layer mainly composed of fine particles and in which the fine particles are bonded to each other with a binder polymer (the heat-resistant layer may be hereinafter referred to as a “heat-resistant porous layer”). This will be described in detail.
- inorganic fine particles generally called a filler
- a filler calcium carbonate, talc, clay, kaolin, silica, hydrotalcite, diatomaceous earth, magnesium carbonate, barium carbonate, calcium sulfate, magnesium sulfate, barium sulfate, aluminum hydroxide, magnesium hydroxide, calcium oxide, magnesium oxide
- examples thereof include fine particles made of inorganic substances such as titanium oxide, alumina, mica, zeolite, and glass.
- the fine particles are preferably inorganic oxides, more preferably magnesium oxide, titanium oxide, and alumina, and particularly preferably alumina. These fine particles can be used alone or in admixture of two or more.
- the average particle size of the fine particles is preferably 3 ⁇ m or less, more preferably 1 ⁇ m.
- Examples of the shape of the fine particles include a spherical shape and a bowl shape.
- the average particle size of the fine particles was determined by arbitrarily extracting 25 particles with a scanning electron microscope (SEM) and measuring the particle size (diameter) of each particle. And a method of calculating an average particle diameter by measuring a BET specific surface area and approximating a sphere.
- SEM scanning electron microscope
- the average particle size by measuring a BET specific surface area and approximating a sphere When calculating the average particle size by SEM, if the shape of the fine particles is other than spherical, the length in the direction showing the maximum length of the particles is taken as the particle size. Also, two or more kinds of fine particles having different particle diameters and / or specific surface areas can be mixed.
- the binder polymer used for forming the heat resistant porous layer has a role of binding fine particles constituting the porous layer, and the fine particles to the polyolefin porous film.
- a binder polymer is preferably a polymer that is insoluble in the electrolyte of the battery and is electrochemically stable within the range of use of the battery.
- polyolefins such as polyethylene and polypropylene
- fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene
- fluorine-containing resins such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer
- Rubbers such as rubber, styrene-butadiene copolymer and its hydride, methacrylate ester copolymer, acrylonitrile-acrylate copolymer, styrene-acrylate copolymer, ethylene propylene rubber, polyvinyl acetate, Melting point and glass transition of polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyetheramide, polyamide, polyester, etc.
- Water-soluble polymers such as polymethacrylic acid.
- water-soluble polymers such as cellulose ether, sodium alginate, and polyacrylic acid can use water as a solvent, and are preferable in terms of process and environmental load.
- cellulose ether is preferably used.
- the cellulose ether include carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), carboxyethyl cellulose, methyl cellulose, ethyl cellulose, cyanethyl cellulose, oxyethyl cellulose, and the like, and CMC and HEC excellent in chemical stability are particularly preferable. preferable.
- resins having a melting point or glass transition temperature of 180 ° C. or higher such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyetheramide, and polyester, have high heat resistance, and are not suitable for laminated porous films. This is preferable because the heating shape retention rate is improved.
- the heat resistant resins polyetherimide, polyamideimide, polyetheramide, and polyamide are more preferable, and polyamide is more preferable.
- the film thickness of the heat resistant porous layer is determined within a range in which the ion permeability is not hindered and the functions of heat resistance and dimensional stability against high temperatures can be secured. If the heat-resistant porous layer is too thick, the load characteristics of the non-aqueous electrolyte secondary battery may decrease when used as a separator. If it is too thin, the battery will generate heat due to an accident or the like. Occasionally, the separator may shrink without being able to resist the heat shrinkage of the polyolefin porous film.
- the specific film thickness of the heat resistant porous layer depends on the number of laminated layers in the laminated porous film, but when the heat resistant porous layer is formed on one side or both sides of the substrate porous film, it is usually 0. 1 ⁇ m or more and 20 ⁇ m or less, preferably 2 ⁇ m or more and 15 ⁇ m or less (in the case of both surfaces, the total value is represented).
- the porosity of the heat resistant porous layer is preferably 20 to 85% by volume, more preferably 40 to 75% by volume. If the porosity of the heat-resistant porous layer is too low, the ion permeability may be deteriorated. If the porosity is too high, the strength of the heat-resistant porous layer will be low, and when the battery is heated due to an accident or the like, the polyolefin porous film There is a possibility that the separator shrinks without being able to resist the heat shrinkage.
- the average pore size of the heat resistant porous layer is preferably 0.005 to 0.3 ⁇ m, more preferably 0.01 to 0.2 ⁇ m. If the average pore diameter is too small, the ion permeability may be deteriorated, and if it is too large, a short circuit is likely to occur due to the dendrites formed by the electrodes.
- a coating liquid containing fine particles, a binder polymer and a solvent (dispersion medium) is directly coated on the substrate porous film to remove the solvent (dispersion medium).
- Method Method of coating the coating liquid on a suitable support, removing the solvent (dispersion medium) and then pressing the porous layer formed on the substrate porous film and then peeling off the support; coating A method of removing the solvent (dispersion medium) after coating the liquid on a suitable support and then pressing it against the base porous film and removing it from the support; dipping the base porous film in the coating liquid And a method of removing the solvent (dispersion medium) after performing dip coding.
- a resin film, a metal belt, a drum, or the like can be used as the support.
- a sequential lamination method of laminating a heat-resistant porous layer on the other side after forming a heat-resistant porous layer on one side A simultaneous lamination method in which a heat-resistant porous layer is simultaneously formed on both surfaces of a porous film.
- the solvent (dispersion medium) for dispersing the fine particles and the binder polymer may be any solvent (dispersion medium) that can uniformly and stably dissolve or disperse the fine particles and the binder polymer.
- solvents such as methanol, ethanol and isopropanol, toluene, xylene, hexane, N-methylpyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide and the like.
- any method can be used as long as the dispersion characteristics necessary for forming a desired heat-resistant porous layer can be obtained. Examples thereof include a dispersion method, a high pressure dispersion method, and a media dispersion method.
- the coating liquid may contain a dispersant, a plasticizer, a pH adjuster and the like as components other than the fine particles and the binder polymer as long as the object of the present invention is not impaired.
- the method for applying the coating liquid to the substrate porous film or the support is not particularly limited as long as it can achieve the required basis weight and coating area, and a conventionally known method can be adopted. it can.
- gravure coater method small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor blade coater method, blade coater method, rod coater method, squeeze coater method
- Examples thereof include a cast coater method, a die coater method, a screen printing method, and a spray coating method.
- the method for removing the solvent (dispersion medium) is not particularly limited, but a drying method is generally used.
- a drying method any method such as natural drying, air drying, heat drying, and vacuum drying may be used.
- a drying operation may be performed after replacing the solvent (dispersion medium) of the coating liquid with another solvent.
- the following method can be exemplified.
- solvent X another solvent that dissolves in the solvent (dispersion medium) used in the preparation of the coating liquid and is easy to evaporate without dissolving the binder polymer contained in the coating liquid.
- the substrate porous film or support coated with the coating solution is immersed in the solvent, and the solvent (dispersion medium) is used from the film-like coating solution on the substrate porous film or support. ) Is replaced with the solvent X, and then the solvent X is evaporated.
- the solvent (dispersion medium) can be efficiently removed.
- heating is performed when removing the solvent (dispersion medium) or the solvent X of the coating liquid from the substrate porous film to which the coating liquid has been applied, It is necessary to avoid shrinkage and decrease in air permeability.
- the physical properties of the films of Examples and Comparative Examples were measured by the following methods.
- Thickness measurement (unit: ⁇ m) The thickness of the film was measured in accordance with JIS standards (K7130-1992).
- Gurley air permeability (unit: sec / 100cc) The air permeability of the film was measured with a digital timer type Gurley type densometer manufactured by Toyo Seiki Seisakusho, based on JIS P8117.
- Porosity (% by volume) 100 ⁇ [ ⁇ (W1 / true specific gravity 1) + (W2 / true specific gravity 2) + ⁇ + (Wn / true specific gravity n) ⁇ / (10 ⁇ 10 ⁇ D)] ⁇ 100 (4) Average pore diameter Based on JISK3832, the average pore diameter was determined using Automated Capillary Flow Porometer (manufactured by POROUS MATERIALS INC.) As the impregnating solution with Fluorinert FC-40 (manufactured by Sumitomo 3M Limited).
- antioxidant Irg1010, manufactured by Ciba Specialty Chemicals
- antioxidant antioxidant
- P168 manufactured by Cib
- polyolefin resin composition was rolled with a pair of rolls having a surface temperature of 150 ° C. to produce a sheet.
- This sheet was immersed in an aqueous hydrochloric acid solution (hydrochloric acid 4 mol / L, nonionic surfactant 0.5% by weight) to dissolve and remove calcium carbonate to obtain a raw material polyolefin sheet.
- hydrochloric acid solution hydrochloric acid 4 mol / L, nonionic surfactant 0.5% by weight
- a tenter type stretching machine As a tenter type stretching machine, a uniaxial stretching type tenter type stretching machine manufactured by Ichikin Kogyo Co., Ltd. was used. The stretching region of the tenter type stretching machine was divided into two regions, a stretching region A and a stretching region B, from the previous stage, and the stretching operation was performed by changing the film widening speed and temperature in each stretching region.
- the tenter rail in each stretched region was set to be a straight line.
- the three patterns shown in the table below were set as rail patterns.
- L, W, and V in Table 1 below indicate the distance in the film transport direction of each stretched region, L, and the difference in position between the film transport direction and the vertical direction where the tenter rail passes through the inlet and outlet of each region.
- V is the speed at which the film passes through each region in the transport direction.
- Reference example 1 As a standard film manufacturing method, a film was manufactured under stretching conditions in which the film widening speed S and the film stretching temperature were constant. First, the rail pattern of the stretching machine is set to the pattern 2 having the same film widening speed S, the temperatures of the stretching region A and the stretching region B are set to 105 ° C., and the temperatures of the preheating region and the heat setting region are set to 120 ° C., respectively. Then, the raw material polyolefin sheet was stretched to obtain a polyolefin microporous film of Reference Example 1.
- Example 1 The rail pattern is set to pattern 1, the temperature of the stretching region A is set to 95 ° C., the temperature of the stretching region B is set to 115 ° C., and the temperatures of the preheating region and the heat setting region are each set to 120 ° C. A polyolefin microporous film of Example 1 was obtained.
- Example 2 The rail pattern is set to pattern 1, the temperature of the stretching region A is set to 100 ° C., the temperature of the stretching region B is set to 110 ° C., and the temperatures of the preheating region and the heat setting region are each set to 120 ° C. A polyolefin microporous film of Example 2 was obtained.
- Comparative Example 1 The rail pattern is set to Pattern 1, the temperature of the stretching region A and the stretching region B is set to 105 ° C., the temperature of the preheating region and the heat setting region is set to 120 ° C., respectively, and the raw material polyolefin sheet is stretched. A polyolefin microporous film was obtained.
- Comparative Example 2 The rail pattern is set to Pattern 1, the temperature of the stretching region A is set to 115 ° C., the temperature of the stretching region B is set to 95 ° C., and the temperatures of the preheating region and the heat setting region are each set to 120 ° C. A polyolefin microporous film of Comparative Example 2 was obtained.
- Comparative Example 3 The rail pattern is set to pattern 2, the temperature of the stretching region A is set to 95 ° C., the temperature of the stretching region B is set to 115 ° C., and the temperatures of the preheating region and the heat setting region are set to 120 ° C. A polyolefin microporous film of Comparative Example 3 was obtained.
- Comparative Example 4 The rail pattern is set to Pattern 2, the temperature of the stretching region A is set to 115 ° C., the temperature of the stretching region B is set to 95 ° C., the temperatures of the preheating region and the heat setting region are set to 120 ° C., respectively, and the raw material polyolefin sheet is stretched. A polyolefin microporous film of Comparative Example 4 was obtained.
- Comparative Example 5 The rail pattern is set to pattern 3, the temperature of the stretching region A is set to 95 ° C., the temperature of the stretching region B is set to 115 ° C., and the temperatures of the preheating region and the heat setting region are set to 120 ° C. A polyolefin microporous film of Comparative Example 5 was obtained.
- Comparative Example 6 The rail pattern is set to pattern 3, the temperature of the stretching region A is set to 115 ° C., the temperature of the stretching region B is set to 95 ° C., and the temperatures of the preheating region and the heat setting region are each set to 120 ° C. A polyolefin microporous film of Comparative Example 6 was obtained.
- Table 2 summarizes the film thickness and porosity of the raw material sheet, the film stretching conditions, and the physical properties of the obtained polyolefin microporous film.
- Example 1 Compared to Reference Example 1 in which the film widening speed and temperature in the stretching region A and the stretching region B are constant, the film widening speed of the stretching region A in the preceding stage is larger than the stretching region B, and the stretching region A is the stretching region.
- Examples 1 and 2 which are lower in temperature than B, the Gurley air permeability is clearly smaller, and the ratio of the average pore diameter / void ratio is smaller than that in Reference Example 1. From this, it can be seen that Example 1 and Example 2 have a structure that easily suppresses the occurrence of short circuits due to dendrites while ensuring ion permeability.
- the Gurley air permeability is higher than that of Reference Example 1 in Comparative Example 5 and Comparative Example 6 in which the film widening speed of the stretching region A in the preceding stage is smaller than that of the stretching region B. From the above results, the temperature of the stretching region where the film widening speed is large is lower than the stretching region where the film widening speed is small, and the stretching region where the film widening speed is large is more than the stretching region where the film widening speed is small, It was found that the Gurley air permeability was small, that is, the ion permeability could be increased while maintaining the predetermined porosity and average pore diameter when positioned in the previous stage.
- Example 1 and Example 2 when Example 1 and Example 2 are compared, it is suggested that the one where the temperature difference of the extending
- the coating liquid 1 is produced in the following procedures. First, carboxymethyl cellulose (CMC, Serogen 3H, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) is dissolved in a 20 wt% aqueous ethanol solution as a medium to obtain a CMC solution (CMC concentration: 0.70 wt% vs. CMC solution). Next, 3500 parts by weight of alumina (AKP3000, manufactured by Sumitomo Chemical Co., Ltd.) is added to and mixed with 100 parts by weight of the CMC solution in terms of CMC, and the mixture is mixed under high pressure dispersion conditions (60 MPa) using a gorin homogenizer. The coating liquid 1 is prepared by performing the treatment once.
- CMC carboxymethyl cellulose
- Serogen 3H manufactured by Daiichi Kogyo Seiyaku Co., Ltd.
- the coating liquid 2 is produced in the following procedures.
- Poly (paraphenylene terephthalamide) is produced using a 3 liter separable flask having a stirring blade, a thermometer, a nitrogen inlet pipe and a powder addition port.
- the flask is sufficiently dried, charged with 2200 g of N-methyl-2-pyrrolidone (NMP), added with 151.07 g of calcium chloride powder vacuum-dried at 200 ° C. for 2 hours, heated to 100 ° C. and completely dissolved. After returning to room temperature, 68.23 g of paraphenylenediamine is added and completely dissolved. While maintaining this solution at 20 ° C.
- NMP N-methyl-2-pyrrolidone
- 124.97 g of terephthalic acid dichloride is added in 10 divided portions every about 5 minutes. Thereafter, with stirring, the solution is aged for 1 hour while maintaining the temperature at 20 ° C. ⁇ 2 ° C. Filter through a 1500 mesh stainless steel wire mesh. The resulting solution has a para-aramid concentration of about 6%.
- alumina C manufactured by Nippon Aerosil Co., Ltd.
- 6 g of advanced alumina AA-03 manufactured by Sumitomo Chemical Co., Ltd.
- the obtained solution is filtered through a 1000-mesh wire mesh, 0.73 g of calcium oxide is added, and the mixture is neutralized by stirring for 240 minutes, and defoamed under reduced pressure to obtain a slurry-like coating liquid 2.
- a separator that is not easily short-circuited and has high ion permeability, which is suitable as a separator for an in-vehicle secondary battery.
- a desired separator can be obtained only by appropriately combining the temperature in the stretching process without requiring a special apparatus, and the manufacturing cost can be reduced.
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Abstract
Description
このような微多孔フィルムは、その内部に連結した細孔を有す構造を有し、連結した細孔を介して一方の面から他方の面にイオンを含む液体が透過可能である。そのため、正極-負極間でイオンのやり取りを行う電池用セパレータ部材として好適である。
例えば、特許文献1では、延伸温度を一定としつつ、延伸の初期段階から最終段階において歪速度を変えて延伸することで細孔構造を制御した微多孔フィルムを製造する方法が開示されている。また、特許文献2では、延伸の上流段階と下流段階で温度を変えて、熱セットする方法が開示されている。また、特許文献3では、同時二軸型テンター延伸法において、延伸工程の温度を予熱工程の温度に対して低温にする熱可塑性樹脂フィルムの製造方法が開示されている。
<1> 微細空孔を有する原料ポリオレフィンシートをテンター式延伸機の炉内に搬送し、前記炉内の複数の延伸領域にてテンター延伸する、フィルム延伸工程を有するポリオレフィン微多孔フィルムの製造方法であって、
前記複数の延伸領域は、フィルム拡幅速度の異なる少なくとも2つの延伸領域を有し、当該少なくとも2つの延伸領域におけるフィルム拡幅速度が大きい延伸領域の温度が、フィルム拡幅速度が小さい延伸領域より低く、
且つ、最もフィルム拡幅速度が大きい延伸領域が、最もフィルム拡幅速度が小さい延伸領域より、前段に位置するポリオレフィン微多孔フィルムの製造方法。
<2> 前記最もフィルム拡幅速度が小さい延伸領域に供給される際に、原料ポリオレフィンシートが、初期値の5%以上40%以下の厚みまで延伸される<1>記載のポリオレフィン微多孔フィルムの製造方法。
<3> 前記最もフィルム拡幅速度が大きい延伸領域と、前記最もフィルム拡幅速度が小さい延伸領域との温度差が10℃以上である<1>または<2>に記載のポリオレフィン微多孔フィルムの製造方法。
<4> 下記式(1)で規定されるSにおいて、
前記最もフィルム拡幅速度が大きい延伸領域でのフィルム拡幅速度(SA)が、前記最もフィルム拡幅速度が小さい延伸領域での拡幅速度(SB)の2倍以上である<1>から<3>のいずれかに記載のポリオレフィン微多孔フィルムの製造方法。
フィルム拡幅速度S=V×W/L (1)
(式(1)中、Lは各延伸領域におけるフィルム搬送方向の距離、Wは各延伸領域におけるフィルム搬送方向と直交する線とテンターレールとの交点がなす距離の差、Vはフィルムが各延伸領域を搬送方向へ通過する速度を表す。)
<5> 前記テンター延伸が一軸延伸である<1>から<4>のいずれかに記載のポリオレフィン微多孔フィルムの製造方法。
<6> 前記原料ポリオレフィンシートが、重量平均分子量50万以上の超高分子量ポリオレフィンと重量平均分子量2000以下のポリオレフィンワックスとからなる<1>から<5>のいずれかに記載のポリオレフィン微多孔フィルムの製造方法。
<7> 前記原料ポリオレフィンシートの空隙率が、30~50体積%である<1>から<6>のいずれかに記載のポリオレフィン微多孔フィルムの製造方法。
<8> <1>から<7>のいずれかに記載の製造方法により得られるポリオレフィン微多孔フィルムに、微粒子を主成分とし、該微粒子同士がバインダー高分子により接着されてなる多孔質層が積層されてなる積層多孔フィルム。
10 原料ポリオレフィンシート
11 ポリオレフィン微多孔フィルム(延伸フィルム)
20 加熱炉
21 予熱領域
22 延伸領域(延伸領域A)
23 延伸領域(延伸領域B)
24 熱固定領域
C チャック
R テンターレール
F1 原料ポリオレフィンシートの幅
F2 ポリオレフィン微多孔フィルム(延伸フィルム)の幅
LA,LB,LC 延伸領域A,B,Cそれぞれにおけるフィルム搬送方向の移動距離(延伸領域A,B,Cの長さ)
WA,WB,WC 延伸領域A,B,Cそれぞれにおけるフィルム搬送方向と直交する線とテンターレールとの交点がなす距離の差
VA,VB,VC フィルムが延伸領域A,B,Cそれぞれを搬送方向へ通過する速度
SA,SB,SC 延伸領域A,B,Cそれぞれでのフィルム拡幅速度
TA、TB、TC 延伸領域A,B,Cそれぞれの温度
なお、本発明において、原料となるシート状のポリオレフィンを「原料ポリオレフィンシート」と称し、該シートを延伸してものをフィルムと呼び、また、前段とは、原料ポリオレフィンシート乃至はフィルムの搬送方向を基準に手前側を指し、後段とは搬送方向を指す。
ここで、テンター式延伸機とは、フィルムの両端を掴む複数のチャックと呼ばれる部分が延伸機の入口から出口に向かって連続的にある定められたテンターレール上を動き、一軸、または二軸にフィルムを連続的に延伸する機構を有するものであり、特に本発明におけるテンター式延伸機は、2つ以上に区切られた複数の延伸領域を有し、延伸領域ごとにテンターレール角度を調整することで延伸倍率やフィルム拡幅速度を任意に調整することができ、かつ、延伸領域ごとに温度を設定することができるものである。
本発明の製造方法において、テンター延伸機は、一軸延伸でも二軸延伸でもよいが、装置構成がシンプルな一軸延伸機が好ましい。図1に一軸式のテンター式延伸機を概念的に示した模式図を示す。図1においてチャックCは、ポリオレフィン微多孔フィルム11を挟む治具であり、テンターレールRに一定の間隔で配置されている。テンターレールRはチャックCが動く部分であり、テンターレールRを目的とする形状とすることによって、フィルム11を延伸することができる。
加熱炉20におけるそれぞれの領域は、温度を独立に調節することができ、原料ポリオレフィンの種類やフィルム延伸条件に合わせて適宜温度を設定することができる。例えば、原料ポリオレフィンシート10がポリエチレン系樹脂からなる場合、80~170℃程度の温度範囲で設定される。
予熱領域21における予熱温度は、原料ポリオレフィンシート10に含まれる熱可塑性樹脂が非晶性樹脂の場合、(Tg-20)~(Tg+30)℃とすることが好ましい。Tgはガラス転移点(glass-transition temperature)である。
一方、原料ポリオレフィンシート10に含まれる熱可塑性樹脂が結晶性樹脂の場合、(Tm-40)~(Tm+20)℃とすることが好ましい。Tmは融点(melting point)である。なお、本明細書における予熱温度とは、加熱炉20の予熱領域21内の雰囲気の温度をいう。
すなわち、図2及び図3に示すように、テンター延伸が行われる延伸領域が2領域の場合には、前段の延伸領域22のフィルム拡幅速度が、後段の延伸領域23のフィルム拡幅速度より大きく、かつ、前段の延伸領域22の方が後段の延伸領域23より低温である。
上述したフィルム延伸の際の細孔の閉塞は、特にフィルムの厚みが小さくなった場合に起こりやすい。そのため、前記最もフィルム拡幅速度が小さい延伸領域に供給される際に、原料ポリオレフィンシートが、初期値の5%以上40%以下(好ましくは、10%以上30%以下)の厚みまで延伸されることが好ましい。このような条件で延伸を行うことで、フィルム延伸の際の細孔の閉塞がより抑制され、適度な空隙率と細孔径を有するフィルムを得ることができる。
このように温度差を付けることにより、フィルムの膜質を高め、フィルムのイオン透過性を向上させることができる。
フィルム拡幅速度S=V×W/L (1)
(式(1)中、Lは各延伸領域におけるフィルム搬送方向の距離、Wは各延伸領域におけるフィルム搬送方向と直交する線とテンターレールとの交点がなす距離の差、Vはフィルムが各延伸領域を搬送方向へ通過する速度を表す。)
また、フィルム搬送方向に対する延伸領域A,B,CにおけるテンターレールRの角度を、それぞれθA,θB,θCとする。
なお、フィルム拡幅速度を、式(1)のSで規定すると、(i)Lが異なる場合、すなわち、それぞれの延伸領域の幅が異なる場合においても適用することができる、(ii)Wが異なる場合、すなわち、それぞれの延伸領域の幅方向の延伸量が異なる場合においても適用することができる、(iii)θが異なる場合、すなわち、テンターレールRがフィルム搬送方向に対してなす角度が異なる場合においても適用できる、等の利点がある。
なお、図4において、SA>Sc>SBの関係であるため、Sが最大である延伸領域Aの温度TAが、Sが最小である延伸領域Bの温度TBより、低温であれば、上述した本発明の製造方法の要件を満たす。
以下、図5に基づいて、テンター延伸方式が、同時二軸延伸の場合のフィルム延伸について説明する。なお、図5では、説明を簡単にするために、延伸領域は、2つの延伸領域A,Bで説明する。
同時二軸延伸方式の場合には、一軸延伸方式と同様に、テンターレールRは角度θが大きいほど急峻にフィルム中心から遠ざかるが、フィルム搬送速度Vによってフィルム拡幅速度Sは、大小関係が変化することになる。例えば、図5でθA=θBのである場合も、VA<VBならば、SA<SBとなる
原料ポリオレフィンシートにおけるポリオレフィンとしては、例えば、エチレン、プロピレン、1-ブテン、4-メチル-1-ペンテン、1-ヘキセンなどを重合した高分子量の単独重合体又は共重合体が挙げられる。これらの中でも重量平均分子量50万以上の超高分子量ポリオレフィンが好ましく、特にエチレンを主体とする重量平均分子量100万以上の高分子量ポリエチレンが好ましい。
原料ポリオレフィンシートにおけるポリオレフィン成分の割合は、該原料ポリオレフィンシート全重量の50重量%以上であることを必須とし、90重量%以上であることが好ましく、95重量%以上であることがより好ましい。
このようなポリオレフィンワックスは、高分子量ポリオレフィンを加工する際に可塑剤として作用することで高分子量ポリオレフィン成分が動きやすくなり、高分子量ポリオレフィンの結晶化を促進するため、膜全体の強度が高くなる。
本発明の製造方法により得られるポリオレフィン微多孔フィルムは、その内部に連結した細孔を有する構造を有し、ポリオレフィンを主成分とする微多孔フィルムであり、連結した細孔を介して一方の面から他方の面に気体や液体が透過可能である。
微多孔フィルムの透気度は、ガーレ値で250秒/100cc以下、好ましくは220秒/100cc以下であり、より好ましくは200秒/100cc以下である。上記範囲の透気度を有すると、車載用二次電池等の高出力二次電池用セパレータとして用いた際に必要となるイオン透過性を発揮することができる。
一方、正負極間の絶縁を保つという観点からは、透気度は30秒/100cc以上が好ましく、より好ましくは50秒/100cc以上である。
一方、確実にシャットダウン機能を得ることができる点で、微多孔フィルムの空隙率は80体積%以下が好ましく、75体積%以下がより好ましい。
本発明の積層多孔質フィルムは、電池用セパレータとして適しており、電池に過剰発熱が生じた場合、基材多孔質フィルムが溶融して無孔化することにより、シャットダウン機能を発揮し、また耐熱層は過剰発熱時の高温に対する耐熱性と寸法安定性の機能を発揮する。
基材多孔質フィルムは、積層多孔質フィルムの基材であり、上述した本発明により製造されるポリオレフィン微多孔フィルムを使用するため、ここでは説明を省略する。
耐熱層は、微粒子を主成分とし、微粒子同士がバインダー高分子により接着されてなる多孔質層であり、基材多孔質フィルムの表面に積層される。
耐熱層としては、過剰発熱時の高温に対する耐熱性と寸法安定性の機能を有するものであれば特に制限はなく、ポリアミド、ポリイミド等の含窒素芳香族重合体を用いることもできるが、微粒子を主成分とし、微粒子同士がバインダー高分子により接着されてなる多孔質層が好ましく用いられる。
以下、好適な耐熱層である、微粒子を主成分とし、微粒子同士がバインダー高分子により接着されてなる多孔質層(当該耐熱層を以下、「耐熱多孔質層」と称す場合がある)についてより詳細に説明する。
また、粒径、および/または比表面積が異なる2種類以上の微粒子を混用することもできる。
例えば、ポリエチレンやポリプロピレンなどのポリオレフィン、ポリフッ化ビニリデンやポリテトラフルオロエチレンなどの含フッ素樹脂、フッ化ビニリデン-ヘキサフルオロプロピレン-テトラフルオロエチレン共重合体やエチレン-テトラフルオロエチレン共重合体などの含フッ素ゴム、スチレン-ブタジエン共重合体およびその水素化物、メタクリル酸エステル共重合体、アクリロニトリル-アクリル酸エステル共重合体、スチレン-アクリル酸エステル共重合体、エチレンプロピレンラバー、ポリ酢酸ビニルなどのゴム類、ポリフェニレンエーテル、ポリスルホン、ポリエーテルスルホン、ポリフェニレンスルフィド、ポリエーテルイミド、ポリアミドイミド、ポリエーテルアミド、ポリアミド、ポリエステルなどの融点やガラス転移温度が180℃以上の樹脂、ポリビニルアルコール、ポリエチレングリコール、セルロースエーテル、アルギン酸ナトリウム、ポリアクリル酸、ポリアクリルアミド、ポリメタクリル酸等の水溶性ポリマーが挙げられる。
これらの中でも、セルロースエーテル、アルギン酸ナトリウム、ポリアクリル酸等の水溶性ポリマーは、溶媒として水を用いることができ、プロセスや環境負荷の点で好ましい。水溶性ポリマーの中でもセルロースエーテルが好ましく用いられる。
セルロースエーテルとして具体的には、カルボキシメチルセルロース(CMC)、ヒドロキシエチルセルロース(HEC)、カルボキシエチルセルロース、メチルセルロース、エチルセルロース、シアンエチルセルロース、オキシエチルセルロース等が挙げられ、化学的な安定性に優れたCMC、HECが特に好ましい。
また、ポリフェニレンエーテル、ポリスルホン、ポリエーテルスルホン、ポリフェニレンスルフィド、ポリエーテルイミド、ポリアミドイミド、ポリエーテルアミド、ポリエステルなどの融点やガラス転移温度が180℃以上の樹脂は、耐熱性が高く、積層多孔フィルムの加熱形状維持率を向上させるため好ましい。耐熱性樹脂の中でもポリエーテルイミド、ポリアミドイミド、ポリエーテルアミド、ポリアミドがより好ましく、ポリアミドがさらに好ましい。
具体的な耐熱多孔質層の膜厚は、積層多孔質フィルムにおける積層数にもよるが、基材多孔質フィルムの片面あるいは両面に耐熱多孔質層を形成する場合においては、通常、通常0.1μm以上20μm以下であり、好ましくは2μm以上15μm以下の範囲である(両面の場合は合計値を表す)。
また、基材多孔質フィルムの両面に耐熱多孔質層を積層する場合においては、一方に耐熱多孔質層を形成させた後に他面に耐熱多孔質層を積層する逐次積層方法や、基材多孔質フィルムの両面に同時に耐熱多孔質層を形成させる同時積層方法が挙げられる。
乾燥方法としては、自然乾燥、送風乾燥、加熱乾燥、減圧乾燥などいかなる方法でもよい。また、塗工液の溶媒(分散媒)を他の溶媒に置換した後、乾燥操作を行ってもよい。
好適には以下の方法を例示することができる。
塗工液の調製に使用された溶媒(分散媒)に溶解し、かつ、塗工液に含まれるバインダー高分子を溶解することなく、蒸発し易い他の溶媒(以下、溶媒X)を用意し、該溶媒中に、塗工液が塗工された基材多孔質フィルムあるいは支持体を浸漬し、基材多孔質フィルムあるいは支持体の上の膜状の塗工液から前記使用溶媒(分散媒)を溶媒Xで置換した後に、溶媒Xを蒸発させる方法が挙げられる。この方法では、効率よく溶媒(分散媒)を除去することができる。
なお、塗工液が塗工された基材多孔質フィルムから、塗工液の溶媒(分散媒)あるいは溶媒Xを除去する際に加熱を行う場合には、基材多孔質フィルムの細孔が収縮して透気度が低下することを回避する必要がある。
(1)厚み測定(単位:μm)
フィルムの厚みは、JIS規格(K7130-1992)に従い、測定した。
(2)ガーレー透気度(単位:sec/100cc)
フィルムの透気度は、JIS P8117に基づいて、株式会社東洋精機製作所製のデジタルタイマー式ガーレー式デンソメータで測定した。
フィルムを一辺の長さ10cmの正方形に切り取り、重量:W(g)と厚み:D(cm)を測定した。サンプル中の材質の重量を計算で割りだし、それぞれの材質の重量:Wi(g)を真比重で割り、それぞれの材質の体積を算出して、次式より空隙率(体積%)を求めた。
空隙率(体積%)=100-[{(W1/真比重1)+(W2/真比重2)+・・+(Wn/真比重n)}/(10×10×D)]×100
(4)平均孔径
JISK3832の規定に基づいて、Automated Capillary Flow Porometer(POROUS MATERIALS INC社製)を用い、含浸液をフロリナートFC-40(住友スリーエム株式会社製)として平均孔径を求めた。
超高分子量ポリエチレン粉末(340M、三井化学社製、分子量320万)を70重量%および重量平均分子量1000のポリエチレンワックス(FNP-0115、日本精鑞社製)30重量%と、該超高分子量ポリエチレンとポリエチレンワックスとの合計量100重量部に対して、酸化防止剤(Irg1010、チバ・スペシャリティ・ケミカルズ社製)を0.4重量%と、酸化防止剤(P168、チバ・スペシャリティ・ケミカルズ社製)を0.1重量%と、ステアリン酸ナトリウムを1.3重量%とを加え、更に全体積に対して38体積%となるように平均粒径0.1μmの炭酸カルシウム(丸尾カルシウム社製)を加え、これらを粉末のままヘンシェルミキサーで混合した後、二軸混練機で溶融混練してポリオレフィン樹脂組成物とした。該ポリオレフィン樹脂組成物を表面温度が150℃の一対のロールにて圧延しシートを作製した。このシートを塩酸水溶液(塩酸4mol/L、非イオン系界面活性剤0.5重量%)に浸漬し、炭酸カルシウムを溶解、除去し、原料ポリオレフィンシートを得た。
該テンター式延伸機の延伸領域を、前段から延伸領域A、延伸領域Bの2領域に分けて、それぞれの延伸領域でフィルム拡幅速度、温度を変更して延伸操作を行なった。各延伸領域のテンターレールは直線となるように設定した。
レールパターンとして下表の3パターンを設定した。下記表1のL、W、Vは、それぞれ各延伸領域のフィルム搬送方向の距離をL、テンターレールが各領域の入口および出口を通過する位置のフィルム搬送方向と垂直方向における位置の差をW、フィルムが各領域を搬送方向へ通過する速度をVとする。各領域のフィルム拡幅速度SはS=V×W/Lより計算された値である。
基準になるフィルム製造方法として、フィルム拡幅速度S及びフィルム延伸温度が一定の延伸条件にて、フィルム製造を行った。
まず、延伸機のレールパターンをフィルム拡幅速度Sが同一速度のパターン2に設定し、延伸領域A及び延伸領域Bの温度をそれぞれ105℃、予熱領域及び熱固定領域の温度をそれぞれ120℃に設定して原料ポリオレフィンシートを延伸し、参考例1のポリオレフィン微多孔フィルムを得た。
レールパターンをパターン1に設定し、延伸領域Aの温度を95℃、延伸領域Bの温度を115℃、予熱領域及び熱固定領域の温度をそれぞれ120℃に設定して原料ポリオレフィンシートを延伸し、実施例1のポリオレフィン微多孔フィルムを得た。
レールパターンをパターン1に設定し、延伸領域Aの温度を100℃、延伸領域Bの温度を110℃、予熱領域及び熱固定領域の温度をそれぞれ120℃に設定して原料ポリオレフィンシートを延伸し、実施例2のポリオレフィン微多孔フィルムを得た。
レールパターンをパターン1に設定し、延伸領域A及び延伸領域Bの温度をそれぞれ105℃、予熱領域及び熱固定領域の温度をそれぞれ120℃に設定して原料ポリオレフィンシートを延伸し、比較例1のポリオレフィン微多孔フィルムを得た。
レールパターンをパターン1に設定し、延伸領域Aの温度を115℃、延伸領域Bの温度を95℃、予熱領域及び熱固定領域の温度をそれぞれ120℃に設定して原料ポリオレフィンシートを延伸し、比較例2のポリオレフィン微多孔フィルムを得た。
レールパターンをパターン2に設定し、延伸領域Aの温度を95℃、延伸領域Bの温度を115℃、予熱領域及び熱固定領域の温度をそれぞれ120℃に設定して原料ポリオレフィンシートを延伸し、比較例3のポリオレフィン微多孔フィルムを得た。
レールパターンをパターン2に設定し、延伸領域Aの温度を115℃、延伸領域Bの温度を95℃、予熱領域及び熱固定領域の温度をそれぞれ120℃に設定して原料ポリオレフィンシートを延伸し、比較例4のポリオレフィン微多孔フィルムを得た。
レールパターンをパターン3に設定し、延伸領域Aの温度を95℃、延伸領域Bの温度を115℃、予熱領域及び熱固定領域の温度をそれぞれ120℃に設定して原料ポリオレフィンシートを延伸し、比較例5のポリオレフィン微多孔フィルムを得た。
レールパターンをパターン3に設定し、延伸領域Aの温度を115℃、延伸領域Bの温度を95℃、予熱領域及び熱固定領域の温度をそれぞれ120℃に設定して原料ポリオレフィンシートを延伸し、比較例6のポリオレフィン微多孔フィルムを得た。
一方、実施例1と同じパターン1で、温度条件が実施例1と異なる比較例1及び比較例3では明らかにガーレー透気度が明らかに大きくなっていることがわかる。
また、一方、延伸速度が一定(パターン2)で、実施例1と同じ温度条件の比較例3ではガーレー透気度が参考例1とほぼ同じであり、前段の延伸領域Aが延伸領域Bより高温であるが比較例4では、ガーレー透気度が参考例1より大きくなっている。
また、実施例1と反対に、前段にある延伸領域Aのフィルム拡幅速度が延伸領域Bより小さい、比較例5及び比較例6においてもガーレー透気度が参考例1より大きくなっている。
以上の結果から、フィルム拡幅速度が大きい延伸領域の温度が、フィルム拡幅速度が小さい延伸領域より低温であり、且つ、前記フィルム拡幅速度が大きい延伸領域が、前記フィルム拡幅速度が小さい延伸領域より、前段に位置すると、所定の空隙率、平均孔径を保ちながら、ガーレー透気度が小さく、すなわち、イオン透過度を大きくすることができることがわかった。
(1)塗工液1の調製
塗工液1を以下の手順で作製する。
まず、媒体として、20重量%エタノール水溶液にカルボキシメチルセルロース(CMC、第一工業製薬株式会社製セロゲン3H)を溶解させてCMC溶液を得る(CMC濃度:0.70重量%対CMC溶液)。
次いで、CMC換算で100重量部のCMC溶液に対して、アルミナ(AKP3000、住友化学株式会社製)を3500重量部、添加、混合して、ゴーリンホモジナイザーを用いた高圧分散条件(60MPa)にて3回処理することにより、塗工液1を調製する。
上記で得られた多孔質フィルムの両面に、グラビア塗工機を用いて、塗工液1を塗工、乾燥し、基材多孔質フィルムと耐熱層とからなる積層多孔質フィルムを作製する。得られる積層多孔質フィルムは良好なイオン透過性を示し、高温で基材多孔質フィルムがシャットダウンしたときも、耐熱層の働きで形状を保持する。
(1)塗工液2の調製
塗工液2を以下の手順で作製する。
攪拌翼、温度計、窒素流入管及び粉体添加口を有する、3リットルのセパラブルフラスコを使用して、ポリ(パラフェニレンテレフタルアミド)の製造を行う。フラスコを十分乾燥し、N-メチル-2-ピロリドン(NMP)2200gを仕込み、200℃で2時間真空乾燥した塩化カルシウム粉末151.07gを添加し、100℃に昇温して完全に溶解させる。室温に戻して、パラフェニレンジアミン、68.23gを添加し完全に溶解させる。この溶液を20℃±2℃に保ったまま、テレフタル酸ジクロライド、124.97gを10分割して約5分おきに添加する。その後も攪拌しながら、溶液を20℃±2℃に保ったまま1時間熟成する。1500メッシュのステンレス金網でろ過する。得られた溶液は、パラアラミド濃度約6%である。
上記多孔質フィルムの片面に、バー塗工機を用いて、塗工液2を塗工、乾燥し、ポリオレフィン層と耐熱層とからなる積層多孔質フィルムを作製する。得られる積層多孔質フィルムは良好なイオン透過性を示し、高温で基材多孔質フィルムがシャットダウンしたときも、耐熱層の働きで形状を保持する。
Claims (8)
- 微細空孔を有する原料ポリオレフィンシートをテンター式延伸機の炉内に搬送し、前記炉内の複数の延伸領域にてテンター延伸する、フィルム延伸工程を有するポリオレフィン微多孔フィルムの製造方法であって、
前記複数の延伸領域は、フィルム拡幅速度の異なる少なくとも2つの延伸領域を有し、当該少なくとも2つの延伸領域におけるフィルム拡幅速度が大きい延伸領域の温度が、フィルム拡幅速度が小さい延伸領域より低く、
且つ、最もフィルム拡幅速度が大きい延伸領域が、最もフィルム拡幅速度が小さい延伸領域より、前段に位置するポリオレフィン微多孔フィルムの製造方法。 - 前記最もフィルム拡幅速度が小さい延伸領域に供給される際に、原料ポリオレフィンシートが、初期値の5%以上40%以下の厚みまで延伸される請求項1記載のポリオレフィン微多孔フィルムの製造方法。
- 前記最もフィルム拡幅速度が大きい延伸領域と、前記最もフィルム拡幅速度が小さい延伸領域との温度差が10℃以上である請求項1または2に記載のポリオレフィン微多孔フィルムの製造方法。
- 前記フィルム拡幅速度を、下記式(1)で表されるSと規定した場合において、
前記最もフィルム拡幅速度が大きい延伸領域でのフィルム拡幅速度(SA)が、前記最もフィルム拡幅速度が小さい延伸領域での拡幅速度(SB)の2倍以上である請求項1から3のいずれかに記載のポリオレフィン微多孔フィルムの製造方法。
フィルム拡幅速度S=V×W/L (1)
(式(1)中、Lは各延伸領域におけるフィルム搬送方向の距離、Wは各延伸領域におけるフィルム搬送方向と直交する線とテンターレールとの交点がなす距離の差、Vはフィルムが各延伸領域を搬送方向へ通過する速度を表す。) - 前記テンター延伸が一軸延伸である請求項1から4のいずれかに記載のポリオレフィン微多孔フィルムの製造方法。
- 前記原料ポリオレフィンシートが、重量平均分子量50万以上の超高分子量ポリオレフィンと重量平均分子量2000以下のポリオレフィンワックスとからなる請求項1から5のいずれかに記載のポリオレフィン微多孔フィルムの製造方法。
- 前記原料ポリオレフィンシートの空隙率が、30~50体積%である請求項1から6のいずれかに記載のポリオレフィン微多孔フィルムの製造方法。
- 請求項1から7のいずれかに記載の製造方法により得られるポリオレフィン微多孔フィルムに、耐熱層が積層されてなる積層多孔フィルム。
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