JP6147088B2 - Battery exterior laminated film - Google Patents

Description

  The present invention relates to a laminated film for battery exterior, and more specifically, for a battery exterior used for a lithium battery, to provide a laminated film having favorable thickness deflection and moldability, which are contradictory properties.

  A lithium battery is also called a lithium secondary battery, which has a liquid, gel-like polymer, solid polymer, polymer electrolyte, etc., and generates current by the movement of lithium ions. Including those made of polymers.

  The configuration of the lithium secondary battery is as follows: positive electrode current collector (aluminum, nickel) / positive electrode active material layer (polymer positive electrode material such as metal oxide, carbon black, metal sulfide, electrolyte, polyacrylonitrile) / electrolyte layer ( Carbonate electrolytes such as propylene carbonate, ethylene carbonate, dimethyl carbonate, ethylene methyl carbonate, inorganic solid electrolytes made of lithium salts, gel electrolytes) / negative electrode active material layers (lithium metals, alloys, carbon, electrolytes, polyacrylonitrile, etc. Polymer negative electrode material) / negative electrode current collector (copper, nickel, stainless steel) and an outer package for packaging them.

  In recent years, attention has been focused on its high volumetric efficiency and light weight, and it has been attracting attention as various small and large-capacity power supplies such as personal computers, mobile phones, PDAs, video cameras, electric vehicles, and storage batteries for energy storage. Is in a situation.

  As a lithium battery outer package, a metal can obtained by pressing a metal into a cylindrical or cuboid container, or a multilayer film composed of an outermost layer / aluminum / sealant layer in a bag shape is generally used. It is. However, because the outer wall of the container is rigid, the shape of the battery itself is fixed and the hardware side is designed to match the battery, so the dimensions of the hardware that uses the battery are determined by the battery. There were restrictions on the degree of freedom. Therefore, there exists a tendency for the bag-shaped exterior body comprised from a multilayer film with a higher freedom degree of design design to be liked.

  On the other hand, the required physical properties of the lithium battery outer package include moisture resistance, content resistance (resistance to compounds such as electrolytes used as contents), moldability, etc., but film materials that satisfy these required characteristics at the same time. Examples of the thermoplastic resin film include a polyamide film and a polyester film. (For example, refer to Patent Document 1).

  However, when the thermoplastic resin film is used, delamination may occur between the film layer and the aluminum layer during battery sealing (see, for example, Patent Document 2).

  As one of the delamination generation factors, when the film thickness fluctuation is large, it may be difficult to obtain uniform adhesion with the metal foil to be bonded.

JP 2006-331897 A Japanese Patent Laid-Open No. 2004-362953

  The present invention has been made in view of the above circumstances, and provides a laminated film that has good thickness deflection and good moldability and is less prone to delamination, which are contradictory properties, particularly for lithium battery exteriors. It is a problem to be solved.

  In order to complete the present invention, the present inventors have found that the above problems can be easily solved by using a polyester film having a specific configuration as a constituent member as a result of intensive studies in view of the above-described actual situation. It came.

  That is, the gist of the present invention is that a film elastic modulus E ′ at 120 ° C. is 20 MPa or less, a film elastic modulus E ′ at 180 ° C. is 5 MPa or less, and a polyester film having a thickness of 6 to 50 μm on one side of the metal foil. It exists in the laminated film for battery exteriors characterized by being laminated | stacked.

  Since the laminated film of the present invention has good thickness deflection and moldability, which are contradictory properties, particularly for battery exterior use, lithium batteries using the laminated film are personal computers, tablets, smartphones, digital It can be used as various small-capacity power supplies such as cameras, and its industrial value is high.

  The polyester film in the present invention may be a single layer or a laminate, and in the case of a laminate configuration, it may have a two-layer configuration. As long as it has three or more layers, it is not particularly limited.

  The polyester used for the polyester film in the present invention may be a homopolyester or a copolyester. In the case of a homopolyester, those obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol are preferred. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyester includes polyethylene terephthalate (PET) and the like. On the other hand, examples of the dicarboxylic acid component of the copolyester include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid (eg, P-oxybenzoic acid). 1 type or 2 types or more are mentioned, As a glycol component, 1 type or 2 types or more, such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1, 4- cyclohexane dimethanol, neopentyl glycol, is mentioned. In any case, the polyester referred to in the present invention refers to a polyester that is usually 60 mol% or more, preferably 80 mol% or more of polyethylene terephthalate or the like which is an ethylene terephthalate unit.

  In the present invention, it is preferable to blend particles in the polyester layer mainly for the purpose of imparting slipperiness. The kind of the particle to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness. Specific examples thereof include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and magnesium phosphate. , Particles of kaolin, aluminum oxide, titanium oxide and the like. Further, the heat-resistant organic particles described in JP-B-59-5216, JP-A-59-217755 and the like may be used. Examples of other heat-resistant organic particles include thermosetting urea resins, thermosetting phenol resins, thermosetting epoxy resins, benzoguanamine resins, and the like. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

  On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more as required.

  Moreover, the average particle diameter of the particle | grains to be used is 0.01-3 micrometers normally, Preferably it is the range of 0.01-1 micrometer. When the average particle diameter is less than 0.01 μm, the particles are likely to aggregate and dispersibility may be insufficient. On the other hand, when the average particle diameter exceeds 3 μm, the surface roughness of the film becomes too rough and There may be a problem when a release layer is applied in the process.

Furthermore, the particle content in the polyester layer is usually in the range of 0.001 to 5% by weight, preferably 0.005 to 3% by weight. When the particle content is less than 0.001% by weight,
In some cases, the slipperiness of the film is insufficient. On the other hand, when the amount exceeds 5% by weight, the transparency of the film may be insufficient.

  The method for adding particles to the polyester layer is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage for producing the polyester constituting each layer, but the polycondensation reaction may proceed preferably after the esterification stage or after the transesterification reaction.

  Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a blending of dried particles and a polyester raw material using a kneading extruder. It is done by methods.

  Conventionally known antioxidants, antistatic agents, thermal stabilizers, lubricants, dyes, pigments and the like can be added to the polyester film in the present invention, if necessary, in addition to the above-mentioned particles.

  The thickness of the polyester film of the present invention is not particularly limited as long as it can be formed as a film, but is usually in the range of 6 to 50 μm, preferably 6 to 25 μm. When thickness is less than 6 micrometers, there exists a tendency for continuous film forming property to be inferior. On the other hand, if it exceeds 50 μm, it may be difficult to follow the deformation of the metal foil.

  Next, although the manufacture example of the polyester film in this invention is demonstrated concretely, it is not limited to the following manufacture examples at all.

  First, a method of using the polyester raw material described above and cooling and solidifying a molten sheet extruded from a plurality of dies with a cooling roll to obtain an unstretched sheet is preferable. In this case, in order to improve the flatness of the sheet, it is necessary to improve the adhesion between the sheet and the rotary cooling drum, and an electrostatic application adhesion method and / or a liquid application adhesion method are preferably employed. Next, the obtained unstretched sheet is stretched in the biaxial direction. In that case, first, the unstretched sheet is stretched in one direction by a roll or a tenter type stretching machine. The stretching temperature is usually 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Subsequently, the extending | stretching temperature orthogonal to the 1st step | paragraph extending | stretching direction is 70-170 degreeC normally, and a draw ratio is 3.0-7 times normally, Preferably it is 3.5-6 times. Subsequently, heat treatment is performed at a temperature of 180 to 270 ° C. under tension or under relaxation within 30% to obtain a biaxially oriented film. In the above-described stretching, a method in which stretching in one direction is performed in two or more stages can be employed. In that case, it is preferable to carry out so that the draw ratios in the two directions finally fall within the above ranges.

  The simultaneous biaxial stretching method can also be adopted for the production of the polyester film in the present invention. The simultaneous biaxial stretching method is a method in which the unstretched sheet is usually stretched and oriented in the machine direction and the width direction at 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is as follows: The area magnification is 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times. Subsequently, heat treatment is performed at a temperature of 170 to 250 ° C. under tension or under relaxation within 30% to obtain a stretched oriented film. With respect to the simultaneous biaxial stretching apparatus that employs the above-described stretching method, a conventionally known stretching method such as a screw method, a pantograph method, or a linear driving method can be employed.

  Furthermore, a so-called coating stretching method (in-line coating) in which the film surface is treated during the above-described polyester film stretching step can be applied. When a coating layer is provided on a polyester film by a coating stretching method, coating can be performed simultaneously with stretching and the thickness of the coating layer can be reduced according to the stretching ratio, producing a film suitable as a polyester film. it can.

  The polyester film used in the present invention needs to have an elastic modulus E ′ ′ at 120 ° C. of 20 MPa or less, preferably 15 MPa or less, more preferably 10 MPa or less. When the elastic modulus exceeds 20 MPa, the moldability is poor and problems such as partial tearing occur. Furthermore, the polyester film of the present invention needs to have an elastic modulus E ′ at 180 ° C. of 5 MPa or less, preferably 3 MPa or less. If the elastic modulus exceeds 5 MPa, the moldability is inferior, and the film cannot follow the metal foil and partial tearing easily occurs.

  The plane orientation degree (ΔP) of the film used in the present invention is preferably 0.030 or more and 0.080 or less, and more preferably 0.030 or more and 0.050 or less. When ΔP is less than 0.030, the moldability is good, but the thickness fluctuation tends to increase. On the other hand, when it exceeds 0.080, the moldability tends to decrease.

  In the polyester film used in the present invention, either a single layer structure or a laminated structure may be used. However, when viewed in terms of the total film layer, the polyester raw material satisfies the above film elastic modulus (E ′) range. The CHDM unit is preferably 29 mol% or more and 32 mol% or less. When the CHDM unit in terms of all layers is less than 29 mol%, the moldability after bonding the metal foil and the polyester film is inferior, and the film cannot follow the metal foil and partial tearing tends to occur. On the other hand, when the CHDM unit in terms of all layers exceeds 32 mol%, the film thickness fluctuation increases and the processability tends to be impaired.

  In this invention, it is preferable that the CHDM unit of the outermost layer of a polyester film is 29 mol% or more and 32 mol% or less. When the CHDM unit in the outermost layer of the film exceeds 32 mol%, when the film is formed by the tenter method, the film may be fused to the clip and breakage may occur frequently. On the other hand, when the CHDM unit in the outermost layer of the film is less than 29 mol%, the moldability is poor, and the film may not follow the metal foil and partial tearing may occur easily.

  The thickness fluctuation of the polyester film in the present invention is preferably 10% or less, more preferably 5% or less, from the viewpoint of productivity or prevention of delamination after metal foil bonding. When the thickness deviation exceeds 10%, there may be a problem that productivity is lowered or delamination occurs.

  The metal foil used for the battery exterior of the present invention is preferably selected from either an aluminum foil or a stainless steel foil. Regarding the thickness of the metal foil, the thickness is preferably 10 μm or more and 50 μm or less in consideration of strength and formability. More preferably, the range of 10-40 micrometers is good. When the thickness is less than 10 μm, after injection of the electrolytic solution, problems such as deterioration of gas barrier properties may occur. On the other hand, when the thickness exceeds 50 μm, the moldability is lowered, and it may be difficult to obtain a battery exterior body having a desired shape.

  An example of the metal foil will be described using an aluminum foil, but is not limited at all. As a material of the aluminum foil, for example, a pure aluminum-based or aluminum-iron-based alloy material can be used. By making the thickness of the aluminum foil in the above range, it becomes possible to achieve both molding followability and oxygen and moisture barrier properties.

  Further, the aluminum foil may be subjected to a pretreatment such as an undercoat such as a silane coupling agent or a titanium coupling agent, or a corona discharge treatment for the purpose of improving the adhesion performance of the laminate.

  The method for laminating the battery exterior polyester film and the aluminum foil is not particularly limited, but dry lamination using an adhesive is preferably used from the viewpoint of adhesion. The adhesive used may be a thermosetting type or a thermoplastic type, but a thermosetting type is preferred. For example, polyurethane resins, polyester resins, polyvinyl chloride resins, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, methyl methacrylate-butadiene copolymers, rubber resins such as chloroprene and polybutadiene, poly From acrylic ester resins, polyvinylidene chloride resins, polybutadiene, or carboxyl modified products of these resins, epoxy resins, cellulose derivatives, ethylene vinyl acetate copolymers, polyethylene oxide, acrylic resins, lignin derivatives, etc. The adhesive which becomes is mentioned. From the viewpoint of adhesion between the polyester film and the polyolefin film, an adhesive composed of a polyurethane resin or a polyester resin is preferable.

  The laminated film for battery exterior in the present invention preferably further comprises a sealant film laminated on the aluminum foil. Examples of sealant films include low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, ethylene resins such as ethylene-butene copolymer, homopolypropylene, ethylene-propylene copolymer, ethylene-propylene-butene. A simple substance or a mixture of propylene resins such as a copolymer can be appropriately selected and used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. The measuring method used in the present invention is as follows.

(1) Measurement of intrinsic viscosity of polyester 1 g of polyester from which other polymer components and pigments incompatible with polyester have been removed are precisely weighed, and 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) is added. It was dissolved and measured at 30 ° C.

(2) Measurement of average particle diameter (d ₅₀ : μm) Integration (weight basis) 50% in equivalent spherical distribution measured using centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type manufactured by Shimadzu Corporation) Was the average particle size.

(3) Measurement of film elastic modulus (E ′) A dynamic viscoelasticity measuring apparatus (DVA-200 type) manufactured by IT Measurement Control was used. A film having a width of 5 mm was set in a measuring apparatus so that the distance between chucks was 20 mm, and the temperature was changed from 0 ° C. to 300 ° C. at 10 ° C./min. The transition of viscoelasticity was measured at a frequency of 10 Hz while raising the temperature at a rate of. The storage elastic modulus (E ′) at 120, 150, and 180 ° C. was determined from this measurement result.

(4) Thickness Fluctuation For a polyester film having a width of 1 m, 20 points were measured evenly in the width direction with a JIS class 1 micrometer, and the maximum thickness (μm) −minimum thickness (μm) was defined as the thickness fluctuation.

(5) Productivity Using the number of breaks (film breaks) that occurred when producing a polyester film, productivity was determined according to the following criteria.
(Criteria)
○: 0 times per 8 hours Δ: 1-2 times per 8 hours ×: 3 times or more per 8 hours

(6) Film Lamination Thickness It was performed by observing a film cross section with a transmission electron microscope (TEM). That is, a small piece of a film sample was embedded in a resin in which an epoxy resin was mixed with a curing agent and an accelerator, and a section having a thickness of 200 nm was prepared with an ultramicrotome to obtain an observation sample. The obtained sample was observed with a transmission electron microscope (H-9000) manufactured by Hitachi, Ltd. In the cross section, the interface is observed by light and darkness almost parallel to the film surface. The distance from the interface to the film surface was averaged for one transmission electron micrograph to determine the surface layer thickness. However, the acceleration voltage was set to 300 kV, and the magnification was set in the range of 1 to 100,000 times according to the surface layer thickness. At least 50 photographs were taken, and 10 points were deleted from the thicker measurement value, 10 points were deleted from the thinner one, and 30 points were averaged to obtain a measurement value.

(7) Measurement of degree of plane orientation (ΔP) An Atago Abbe refractometer was used. Methylene iodide is mounted, the sample film is closely attached to the prism so that the measurement surface is face down, and the refractive index in the longitudinal direction, the width direction, and the thickness direction (nX, respectively) using a monochromatic light sodium D line (589 nm) as a light source nY, nZ) were measured. From the obtained value, the plane orientation degree ΔP of each layer was determined by the following formula. The measurement sample was collected from the center part of the product master roll.
ΔP = (nX + nY) / 2−nZ

(8) Formability of laminated body for battery exterior A two-layer coextruded film (malein) obtained by coextruding maleic acid-modified polypropylene resin and polypropylene as a sealant on the aluminum foil of a polyester film / aluminum foil laminated film for battery exterior. The acid-modified polypropylene resin layer: 15 μm and the polypropylene resin layer: 30 μm are placed so that the maleic acid-modified polypropylene resin layer is positioned on the aluminum foil side, and thermocompression-bonded using a laminator (measurement temperature: 120 ° C., measurement pressure: 0.00). 3 MPa, line speed: 2 m / min) to form a laminated body for battery exterior. The obtained laminate was cut into a size of 200 mm × 200 mm, and a gold consisting of a 150 mm × 150 mm rectangular male mold (R: 2 mm) and a female mold (R: 2 mm) with a clearance of 0.5 mm between the male mold. Using the mold, the laminate for battery exterior was set on the female mold so that the sealant side was on the male mold side, and press molding (pressurization: 0.1 MPa) was performed to obtain a molded body for battery exterior. About the obtained molded object for battery exterior, it determined by the following criteria.
(Criteria)
◎: Moldable at 10mm or more (no damage)
○: Breakage occurred at 7 m or more and less than 10 mm Δ: Breakage occurred at 5 mm or more and less than 7 mm ×: Breakage occurred at less than 5 mm

(9) Delamination resistance of battery exterior laminate Two battery exterior molded bodies obtained in the same manner as in (8) were prepared, and the respective sealant sides were overlapped, and thermocompression bonding using a laminator (set temperature: 200 ° C., set pressure: 0.3 MPa, line speed: 2 m / min). The thermocompression bonding was performed so that the end portion where the molding of each molded article for battery exterior rises was sealed. In the molded article for battery exterior after sealing, visual determination was made as to whether or not delamination occurred between the polyester film and the aluminum foil.
(Criteria)
○: No delamination occurred ×: Delamination occurred

The polyester used in the examples and comparative examples was prepared as follows.
<Manufacture of polyester>

Production Example 1 <Polyester 1>
Using terephthalic acid as the dicarboxylic acid component and ethylene glycol as the polyhydric alcohol component, a polyester chip containing no lubricant particles having an intrinsic viscosity of 0.66 dl / g by a conventional melt polymerization method was produced.

Production Example 2 <Polyester 2>
Using terephthalic acid as the dicarboxylic acid component and ethylene glycol as the polyhydric alcohol component, 0.20% by weight of amorphous silica having an intrinsic viscosity of 0.66 dl / g and an average particle size of 3.1 μm by a conventional melt polymerization method A polyester chip containing was produced.

Production Example 3 <Polyester 3>
Using terephthalic acid as the dicarboxylic acid component and 1,4-cyclohexanedimethanol and ethylene glycol as the diol component, raw material chips polymerized by a conventional melt polycondensation method were produced. The 1,4-cyclohexanedimethanol unit in the diol component of this raw material was 33 mol%.

Example 1:
Raw materials blended with polyesters 1, 2, and 3 in proportions of 6%, 4%, and 90%, respectively, as surface layer materials, and blended materials of polyesters 1, 3 in proportions of 5% and 95%, respectively, as intermediate layer materials Supply to two extruders with vents, supply to vented extruders, melt extrusion at 290 ° C, then cool and solidify on cooling roll set to 35 ° C using electrostatic adhesion method Thus, an amorphous film having a thickness of about 180 μm was obtained. First, the obtained unstretched sheet is stretched 3.2 times in the MD direction at 80 ° C., led to a tenter, and successively biaxially stretched 4.0 times in the TD direction to achieve 5% relaxation. However, it was heat-set at 175 ° C. for 3 seconds to obtain a 12 μm thick polyester film having a layer structure of 2/8/2 (μm).
Next, the obtained polyester film and aluminum foil (manufactured by Sumikin Light Metal Industry: thickness 40 μm) are urethane adhesives (manufactured by Toyo Morton, AD-502, CAT10L, ethyl acetate 15: 1.5: 25 (mass). The laminate film for battery exterior was produced by dry lamination using a conventional method.

Examples 2-8:
In Example 1, a laminated film for battery exterior was obtained in the same manner as in Example 1 except that the polyester film was changed to the polyester film shown in Table 1 below.

Comparative Examples 1-4:
In Example 1, a laminated film for battery exterior was obtained in the same manner as in Example 1 except that the polyester film was changed to the polyester film shown in Table 1 below.

  Tables 1 and 2 show the characteristics of the films obtained in the above Examples and Comparative Examples. In addition, CHDM in each table | surface means 1, 4- cyclohexane dimethanol.

  The laminated film of the present invention can be suitably used particularly for battery exteriors used for lithium batteries.

Claims (1)

A film elastic modulus E ′ at 120 ° C. is 20 MPa or less, a film elastic modulus E ′ at 180 ° C. is 5 MPa or less, and a polyester film having a thickness of 6 to 50 μm is laminated on one side of a metal foil. Laminated film for battery exterior.