JP5803147B2 - Battery exterior polyester film and battery exterior structure - Google Patents

Description

  The present invention relates to a polyester film, and relates to a polyester film for battery exterior that can be suitably used for battery exterior use, particularly for lithium ion secondary batteries having an electrolyte (solid, liquid) because of high puncture strength and large puncture displacement. .

  A lithium battery, also called a lithium secondary battery, is a battery that has a liquid, gel-like polymer, solid polymer, polymer electrolyte, etc., and generates current by the movement of lithium ions. Including those consisting of molecules. 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, lithium batteries have been used for various purposes and are used as small and large capacity power sources for personal computers, portable terminal devices (cell phones, PDAs, etc.), video cameras, electric vehicles, energy storage batteries, robots, satellites, etc. Yes.

  As the exterior body of a lithium battery, a metal can obtained by pressing a metal into a cylindrical or rectangular parallelepiped container or a multilayer film composed of an outermost layer / aluminum / sealant layer in a bag shape is used. ing. However, since the outer wall of the container in a metal can is rigid, the shape of the battery itself is determined, and the hardware side using the battery is determined by the battery in order to design the hardware side to match the battery. As a result, there is a problem that the design can be restricted, for example, so that a bag-like exterior body made of a multilayer film has been favored. Physical properties and functions required for the exterior of lithium batteries include moisture resistance, content resistance (resistance to compounds such as electrolytes used as contents), moldability, etc. As what is used, for example, polyamide film / polyester film bonding is used (see Patent Document 1). However, with this configuration, the process becomes complicated, which is insufficient in terms of economy, moisture resistance, and resistance to physical properties during processing. Moreover, the film excellent in the moldability as a polyester film single-piece | unit is proposed (refer patent document 2). However, as the demand for deep drawing for battery exteriors has increased, further improvements in aluminum followability and moldability have been desired.

  These problems are particularly noticeable in lithium battery packaging materials that involve drawing with a mold as a processing step.

Japanese Patent Laid-Open No. 9-115428 Japanese Patent Laid-Open No. 2004-362953

  An object of the present invention is to eliminate the above-described problems. That is, an object of the present invention is to provide a lithium battery exterior polyester film having excellent formability and high strength in a lithium battery packaging material that involves drawing with a mold as a processing step.

  The present invention for solving the above problems has the following configuration.

(1) The piercing load of the film at 25 ° C. is a linear distance in which the tip of the needle moves until it breaks after performing a puncture test with a needle of 0.5 mmφ on the film surface at a speed of 5 mm / min. piercing displacement is 2.5～7Mm, the thickness of the film is Ri 10~40μm der a 100-250% elongation at break at 25 ° C. in the longitudinal direction of the film and the transverse direction, 190 ° C., for 10 minutes heat treatment film longitudinal direction and the width direction of the heat shrinkage rate after a 0 to 4% thermal history peak temperature (T-meta) is 190 ℃ ~234 ℃ der Ru battery to be observed by differential scanning calorimetry (DSC) Polyester film for exterior.

  (2) The polyester film for battery exterior according to the above (1), wherein the breaking strength in the film longitudinal direction and the width direction at 25 ° C. is 200 to 400 MPa.

  (3) The elongation at break at 25 ° C. in the longitudinal direction and the width direction of the film is 100 to 250%, and the stress (F-5 value) / breaking strength value when stretched by 5% is 0.5 or less The polyester film for battery exterior according to the above (1) or (2).

  (4) The polyester film for battery exterior according to any one of (1) to (3), wherein the plane orientation coefficient is 0.161 or more.

  (5) The polyester film for battery exterior according to any one of (1) to (4), wherein the absolute value of the birefringence index (Δn) is less than 10.

  (6) The polyester film for battery exterior according to any one of (1) to (5), wherein the intrinsic viscosity of the film is 0.65 to 0.80.

  (7) The polyester film for battery exterior according to any one of the above (1) to (6), wherein the film has a thermal shrinkage of 0 to 6% after heat treatment at 190 ° C. for 10 minutes in at least one direction.

  (8) The polyester for battery exterior according to any one of (1) to (7), wherein the thermal history peak temperature (T-meta) observed by differential scanning calorimetry (DSC) is 190 ° C to 250 ° C. the film.

  (9) The polyester film for battery exterior according to any one of (1) to (8), wherein an easy-adhesion layer is laminated on at least one surface.

  (10) A battery exterior structure obtained by laminating a metal layer on at least one surface of the battery exterior polyester film according to any one of (1) to (9).

  The polyester film for battery exterior of the present invention can be suitably used as a film for battery exterior. In particular, since the piercing strength and the piercing displacement are large, a member excellent in workability can be produced.

  The polyester constituting the polyester film for battery exterior of the present invention is a general term for polymers in which the main bond in the main chain, the covalent bond that bonds the monomer residue and the monomer residue is an ester bond, Usually, it can be obtained by polycondensation reaction of a dicarboxylic acid compound and a glycol component, or a dicarboxylic acid ester compound and a glycol component.

  Here, examples of the dicarboxylic acid compound include terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-sodium sulfoterephthalic acid, and phthalic acid. Aromatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, fumaric acid and other aliphatic dicarboxylic acids, cyclohexanedicarboxylic acid and other alicyclic dicarboxylic acids, paraoxybenzoic acid, etc. An oxycarboxylic acid etc. can be mentioned. Examples of the dicarboxylic acid ester compounds include esterified products of the above dicarboxylic acid compounds, such as dimethyl terephthalate, diethyl terephthalate, 2-hydroxyethyl methyl terephthalate, dimethyl 2,6-naphthalenedicarboxylate, dimethyl isophthalate, and dimethyl adipate. , Diethyl maleate, dimethyl dimer, and the like.

  On the other hand, as the glycol component, for example, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6 -Aliphatic dihydroxy compounds such as hexanediol and neopentyl glycol, polyoxyalkylene glycols such as diethylene glycol, polyethylene glycol, polypropylene glycol and polytetramethylene glycol, alicyclic dihydroxy compounds such as cyclohexanedimethanol, bisphenol A, bisphenol S, etc. And aromatic dihydroxy compounds. Among these, terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid or their dimethyl ester compounds are used as the dicarboxylic acid compound, and ethylene glycol, 1,3-propanediol, 1,4-butane is used as the glycol component. Diol, polytetramethylene glycol and the like can be preferably used.

  In producing the polyester used in the present invention, conventionally known reaction catalysts and anti-coloring agents can be used. Examples of the reaction catalyst include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, and germanium compounds. Phosphorus compounds and the like can be used, but the present invention is not particularly limited to these.

  Usually, it is preferable to add an antimony compound, a germanium compound and / or a titanium compound as a polymerization catalyst at an arbitrary stage before the production of the polyester is completed. As such a method, for example, taking a germanium compound as an example, a method of adding germanium compound powder as it is, or a glycol which is a starting material of polyester as described in Japanese Patent Publication No. 54-22234 A method in which a germanium compound is dissolved in a component and added can be used.

  Examples of the germanium compound include germanium dioxide, germanium hydroxide hydrate or germanium tetramethoxide, germanium alkoxide compounds such as germanium ethyleneglycoxide, phosphoric acid containing germanium phenoxide compounds, germanium phosphate, germanium phosphite, and the like. A germanium compound, germanium acetate, or the like can be used. Of these, germanium dioxide is preferably used.

  The antimony compound is not particularly limited, and for example, oxides such as antimony trioxide, antimony acetate, and the like can be used. Further, the titanium compound is not particularly limited, but titanium tetraalkoxide such as titanium tetraethoxide and titanium tetrabutoxide can be preferably used.

  As described above, the polyester used in the present invention is produced, and will be described using a specific example. For example, when producing antimony trioxide as a catalyst in the production of polyethylene terephthalate, 67 parts by mass of ethylene glycol, which is a glycol component, is added to 100 parts by mass of dimethyl terephthalate, which is a dicarboxylic acid ester compound, and then transesterified. 0.06 parts by mass of magnesium acetate is added as a catalyst, and transesterification is performed by a conventional method. Next, 0.02 part by mass of 85% phosphoric acid aqueous solution and 0.03 part by mass of antimony trioxide are added, and the temperature is gradually raised and reduced. Finally, the temperature is raised to 290 ° C. and 0.5 mmHg, and the pressure is reduced. A polyester resin can be obtained by performing a polycondensation reaction until the intrinsic viscosity is reached.

  The polyester film for battery exterior of the present invention has a piercing load in a piercing test at 25 ° C. of the polyester film of 5N to 15N. When the piercing load is within this range, the moldability is improved. When the piercing load is less than 5N, the strength of the film is low, and the film may be broken due to friction with the base material during molding or a pinhole may be vacant. Further, if the piercing load of the film exceeds 15N, it may not be possible to mold into a predetermined shape. A more preferable piercing load of the film is 5 to 14N, and more preferably 6 to 13N. Although it does not specifically limit as a method made into the range which applies a piercing load, It is preferable to make the plane orientation coefficient of a film into 0.161 or more. By setting the plane orientation coefficient in the above range, the piercing load can be set in the range of 5N to 15N. From the viewpoint of piercing load and film forming property, the plane orientation coefficient is more preferably 0.162 to 0.175, and even more preferably 0.164 to 0.174. Here, in the present invention, the plane orientation coefficient is obtained as follows.

Using sodium D-line (wavelength 589 nm) as a light source, methylene iodide as a mounting solution, and using an Abbe refractometer at 25 ° C., MD (film formation direction, longitudinal direction), TD (direction perpendicular to MD, width direction) ) And the refractive index in the thickness direction (n _MD , n _TD , and n _ZD , respectively). A plane orientation coefficient (fn) is calculated from the obtained refractive index by the following formula.

fn = (n _MD + n _TD ) / 2-n _ZD
As a method of setting the plane orientation coefficient of the film to 0.161 or more, when a polyester film is produced, particularly when a sequential biaxial stretching method is adopted, first, an unstretched film is stretched in the longitudinal direction, and then the width direction. The film is stretched by a sequential biaxial stretching method in which the film is stretched in the width direction and then stretched in the longitudinal direction, or by a simultaneous biaxial stretching method in which the longitudinal direction and the width direction of the film are stretched almost simultaneously. It can be obtained by doing.

  As a draw ratio in such a drawing method, preferably 3.3 to 5 times, more preferably 3.4 to 4.8 times, and particularly preferably 3.5 to 4.5 times in each direction. The The stretching speed is desirably 1,000 to 200,000% / min. The stretching temperature is preferably 70 to 130 ° C, more preferably 85 to 110 ° C in the longitudinal direction and 80 to 105 ° C in the width direction. Moreover, you may perform extending | stretching in multiple times with respect to each direction.

  Furthermore, the film is heat-treated after biaxial stretching. The heat treatment can be performed by any conventionally known method such as in an oven or on a heated roll. This heat treatment is carried out at a temperature of 120 ° C. or higher and below the melting point of the polyester, but is preferably a heat treatment temperature of 190 to 230 ° C. The heat treatment time can be arbitrarily set within a range not deteriorating the characteristics, and is preferably 1 to 60 seconds, more preferably 1 to 30 seconds. Further, the heat treatment may be performed by relaxing the film in the longitudinal direction and / or the width direction.

  Moreover, although the above-mentioned polyester resin can be used arbitrarily as a method of making it the range which applies a piercing load, it consists of a polyester resin which has a polyethylene terephthalate as a main component. Here, the polyester resin whose main component is polyethylene terephthalate is a polyester in which 95 mol% or more of the dicarboxylic acid component constituting the polyester is a terephthalic acid component and 95 mol% or more of the glycol component is an ethylene glycol component. It means resin. Residue components other than terephthalic acid and ethylene glycol may be contained as a dicarboxylic acid component and a glycol component in a range of 5 mol% or less, and as a manner of inclusion, copolymerized polyethylene terephthalate may be used. Although a polyester resin may be blended and used, it is preferable to use a polyethylene terephthalate resin itself that is not copolymerized or blended.

  In the present invention, when a film is formed using polyethylene terephthalate, the amount of ethylene glycol (EG) is preferably 97 mol% or more and the amount of terephthalic acid (TPA) is preferably 97 mol% or more. Most preferably, the amount of EG) is 98 mol% or more and the amount of terephthalic acid (TPA) is 98 mol% or more.

  In the polyester resin, in order not to impair the effect of the present invention, in order to improve the handleability and processability, 0.01 to 1 internal particles, inorganic particles or organic particles having an average particle diameter of 0.01 to 5 μm are contained. The average particle diameter of the particles to be used is preferably 0.01 to 3 μm, and more preferably 0.01 to 0.2 μm, in order to achieve the above-described piercing load. Moreover, in order to make slipperiness and piercing property compatible, 0.05-2.5 micrometers is preferable and 0.1-2 micrometers is more preferable. In order to achieve both slipperiness and piercing property, the particle concentration in the film is preferably 0.001 to 0.06% by mass, and more preferably 0.003 to 0.04% by mass. .

  Examples of the internal particle precipitation method include the techniques described in JP-A-48-61556, JP-A-51-12860, JP-A-53-41355, JP-A-54-90397, and the like. Can be adopted. In addition, other particles such as JP-B-55-20496 and JP-A-59-204617 can be used in combination. Examples of inorganic particles that can be used include wet and dry silica, colloidal silica, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, aluminum oxide, mica, kaolin, and clay. Moreover, as organic particles, particles containing styrene, silicone, acrylic acids, methacrylic acids, polyesters, divinyl compounds and the like as constituent components can be used. Among them, it is preferable to use inorganic particles such as wet and dry silica and alumina, and particles containing styrene, silicone, acrylic acid, methacrylic acid, polyester, divinylbenzene and the like as constituent components. Furthermore, these internal particles, inorganic particles, and organic particles may be used in combination of two or more.

  The polyester film of the present invention may be a single layer film or a laminated film having two or more layers of A / B. In the case of a three-layer configuration of A / B / C, it is preferable that the polyester constituting the C layer is the same as the polyester constituting the A layer from the viewpoint of economy and productivity (that is, A / B / A configuration). Furthermore, in order to improve economy and productivity, it is preferable to make the laminated thickness of the A layer and the C layer equal. Further, in order to reduce the particle concentration in the film and keep the cost low, it is preferable to have two or more layers and to add the particles only to at least one layer.

  Moreover, in order to reduce the particle | grain density | concentration in a film, the method of making particle | grains contain in a coating layer is also applicable. In the case of the present invention, the coating layer has a method of coating on a biaxially stretched film after completion of crystal orientation or a method of stretching after coating on a film before completion of crystal orientation, in order to express the effects of the present invention more remarkably. The latter method is particularly preferred. The method of applying is not particularly limited, but it is preferable to apply using a roll coater, gravure coater, reverse coater, kiss coater, bar coater or the like. Moreover, you may corona-discharge-process in the air | atmosphere other various atmosphere before application | coating as needed before apply | coating.

  The polyester film for battery exterior of the present invention has a film stab displacement at 2.5 ° C. of 2.5 mm to 7 mm. When the piercing displacement is within this range, excellent moldability can be exhibited. If the piercing displacement is less than 2.5 mm, the film may be broken during molding. Further, from the viewpoint of economy, productivity, moldability, etc., the piercing displacement of the film is preferably 2.5 mm to 6.5 mm, and most preferably 2.5 mm to 6 mm. The piercing displacement here is a value obtained by performing a piercing test with a 0.5 mmφ needle on the film surface at a speed of 5 mm / min and obtaining a linear distance that the tip of the needle has moved until it breaks.

  As a method for adjusting the stab displacement, it is preferable that the intrinsic viscosity of the film is 0.61 to 0.80 dl / g. If the intrinsic viscosity is less than 0.61 dl / g, the piercing displacement may be lowered, and if it exceeds 0.80 dl / g, the productivity of the film tends to be lowered. The intrinsic viscosity of the film is preferably 0.63 to 0.80 dl / g, and more preferably 0.65 to 0.80 dl / g. In order to set the intrinsic viscosity of the polyester film to 0.61 to 0.80 dl / g, the intrinsic viscosity of the polyester resin used is preferably 0.65 to 0.90 dl / g. If the intrinsic viscosity of the polyester resin is less than 0.65 dl / g, the intrinsic viscosity of the film after extrusion may be less than 0.61 dl / g. Also, when the intrinsic viscosity of the polyester resin exceeds 0.90 dl / g, the extrusion amount of the polyester resin may have to be limited due to an increase in the filtration pressure of the extruder and an increase in the current value, resulting in a decrease in productivity. There is. The intrinsic viscosity of the polyester resin is more preferably 0.70 to 0.90 dl / g, and even more preferably 0.75 to 0.85 dl / g. When particularly severe moldability is required, it is preferable to increase the stab displacement, the intrinsic viscosity of the polyester film is preferably greater than 0.65 dl / g, and the intrinsic viscosity of the polyester resin used is 0.75 dl / g. It is preferable to make it larger than g. On the other hand, in order to achieve moldability with respect to a commonly used shape, the intrinsic viscosity of the film can be achieved even at 0.61 to 0.65 dl / g, and the intrinsic viscosity of the polyester resin used is 0.65 to 0. Preferably it is .75 dl / g. In this case, productivity is good. From the viewpoints of productivity and moldability, the intrinsic viscosity of the polyester film can be appropriately selected.

  The polyester used in the present invention is produced by the above-described method. In order to obtain a polyester raw material having a large molecular weight and a high intrinsic viscosity, a method of further increasing the degree of polymerization by performing solid phase polymerization is preferably used. The method of solid phase polymerization is not particularly limited, but the solid phase polymerization of polyester is usually carried out under reduced pressure or in a nitrogen atmosphere, but any method may be used. The solid state polymerization temperature is preferably 180 ° C. or higher and 240 ° C. or lower, more preferably 190 ° C. or higher and 230 ° C. or lower. When the polymerization temperature is less than 180 ° C., the reaction rate is slow and the productivity is very poor. On the other hand, when the temperature exceeds 240 ° C., not only the fusion between the polyester chips occurs, but also the voids of the chips formed by the heat treatment in the solvent disappear, and the polymerization rate decreases. The solid-phase polymerization temperature can be arbitrarily set within the above range, but as a general tendency, when polymerized at a low temperature, the reaction rate decreases and the time required to increase to the expected intrinsic viscosity becomes longer. However, the highest intrinsic viscosity increases. Conversely, when the polymerization temperature is increased, the reaction rate increases, but at the same time, the degradation reaction also proceeds, so that the maximum intrinsic viscosity decreases. In the actual process, the reaction temperature may be set in consideration of the intrinsic viscosity and reaction time expected in the solid phase polymerization temperature range.

  Further, as a method of setting the range in which the intrinsic viscosity of the film is applied, when the polyester resin is supplied to the extruder and melted, the inside of the supply unit is supplied in an inert gas, preferably a flowing nitrogen atmosphere, and the oxygen inside the supply unit is set. The concentration is preferably 0.1 to 0.7% by volume. In order to make the oxygen concentration less than 0.1% by volume, it is economically undesirable, and when the oxygen concentration exceeds 0.7% by volume, the polyester resin may be oxidatively decomposed to lower the intrinsic viscosity. Preferably, it is 0.1 volume%-0.5 volume%.

  Furthermore, the temperature at which the polyester resin is supplied to the extruder and melted is preferably the melting point + 10 to melting point + 35 ° C. of the polyester resin used. If the temperature is lower than the melting point + 10 ° C., it may not be melted in the extruder and an unmelted product may be generated. Moreover, when it exceeds melting | fusing point +35 degreeC, the temperature concerning a polyester resin will become excessive, will cause thermal decomposition, and an intrinsic viscosity may fall. More preferably, the melting point of the polyester resin is +15 to + 30 ° C.

  As a method for producing a polyester film for battery exterior, for example, the polyester to be used is dried at 150 ° C. for 5 hours in a nitrogen atmosphere, a reduced pressure atmosphere, etc., supplied to an extruder, and melted. The supply is preferably performed under a flowing nitrogen atmosphere. At this time, when using a vent type twin screw extruder, the drying step may be omitted. The resin melted in the extruder is subjected to removal of foreign matters and leveling of the amount of extrusion through a filter and a gear pump, and discharged and extruded in a sheet form from a T-die onto a cooling drum to obtain an unstretched sheet. At that time, a wire electrode, a tape-like electrode or a needle-like electrode is used to apply static electricity and adhere to the cooling drum, a casting method in which a water film is provided between the cooling drum and the extruded polymer sheet, and the cooling drum temperature. An unstretched film is obtained by adhering a polymer extruded from the glass transition point of polyester to (glass transition point -20 ° C), or by adhering a sheet polymer to a cooling drum by a combination of these methods. obtain. Among these casting methods, a method of applying an electrostatic force is preferably used from the viewpoint of productivity flatness. The unstretched film obtained here can be further stretched to obtain a biaxially stretched polyester film.

  The thickness of the polyester film for battery exterior of the present invention is 10 to 40 μm from the viewpoints of economy, productivity, moldability and the like. If the thickness is less than 10 μm, the strength is low, and there is a risk of tearing or breaking during molding. Further, when the thickness is 40 μm or more, the strength of the film is high, and the adhesiveness to the metal layer and the molding followability may be deteriorated and breakage may occur. More preferably, it is 15-30 micrometers.

  The polyester film for battery exterior of the present invention preferably has a breaking strength at 25 ° C. of 200 to 400 MPa in the longitudinal direction and the width direction of the film from the viewpoint of adhesion to the metal layer and followability. If the breaking strength is less than 200 MPa, the followability with the metal layer at the time of forming may be inferior and may break. On the other hand, when it is going to obtain the intensity | strength exceeding 400 MPa, the stress at the time of shaping | molding will become high and it may be unable to shape | mold. If it is 200-350 Mpa, it is still more preferable, and if it is 200-300 Mpa, it is still more preferable. As a method of setting the range to take the breaking strength, when adopting a sequential biaxial stretching method, particularly when a polyester film is manufactured, first, an unstretched film is stretched in the longitudinal direction and then stretched in the width direction, or It is obtained by stretching in the width direction and then by a sequential biaxial stretching method in which the film is stretched in the longitudinal direction, or by a simultaneous biaxial stretching method in which the longitudinal direction and the width direction of the film are stretched almost simultaneously. Can do.

  As a draw ratio in such a drawing method, preferably 3.3 to 5 times, more preferably 3.4 to 4.8 times, and particularly preferably 3.5 to 4.5 times in each direction. The The stretching speed is desirably 1,000 to 200,000% / min. The stretching temperature is preferably 70 to 130 ° C., more preferably 85 to 95 ° C. in the longitudinal direction and 85 to 105 ° C. in the width direction. Moreover, you may perform extending | stretching in multiple times with respect to each direction.

  Furthermore, the film is heat-treated after biaxial stretching. The heat treatment can be performed by any conventionally known method such as in an oven or on a heated roll. This heat treatment is carried out at a temperature of 120 ° C. or higher and below the melting point of the polyester, but is preferably a heat treatment temperature of 190 to 230 ° C. The heat treatment time can be arbitrarily set within a range not deteriorating the characteristics, and is preferably 1 to 60 seconds, more preferably 1 to 30 seconds. Further, the heat treatment may be performed by relaxing the film in the longitudinal direction and / or the width direction.

  From the viewpoint of moldability, the polyester film for battery exterior of the present invention preferably has a breaking elongation at 25 ° C. in the longitudinal direction and the width direction of 100 to 250%. If the elongation at break is less than 100%, it may break during molding. On the other hand, if an elongation exceeding 250% is to be obtained, the strength of the film may decrease. The breaking elongation at 25 ° C is more preferably 100 to 230%, and even more preferably 100 to 220%. The film forming method and the stretching method described above can be employed as a method for setting the range of breaking elongation.

  The stress (F-5 value) / breaking strength applied when the polyester film for battery exterior of the present invention is stretched by 5% is preferably 0.5 or less. If the F-5 value / breaking strength exceeds 0.5, there is a risk of peeling off from the metal layer or rupturing of the film during molding after bonding with aluminum. As a method of setting the F-5 value / breaking strength to 0.5 or less, it is preferable to adjust the amount of diethylene glycol (DEG) in the film using polyethylene terephthalate to 0.01 to 2.5% by mass. Although diethylene glycol is generally produced as a by-product during the production of polyester, if the amount of diethylene glycol is less than 0.01% by mass, the polymerization process becomes complicated, which may increase the cost. On the other hand, when the amount of diethylene glycol exceeds 2.5% by mass, it is difficult to orient during stretching, and the F-5 value / breaking strength may exceed 0.5. The smaller the amount of diethylene glycol, the lower the F-5 value / breaking strength and the better the film-forming property, so that 0.02 to 2.0% by mass, more preferably 0.05 to 1.5% by mass. % Is desirable. Moreover, when comprising the film of this application as a laminated | multilayer film, it is preferable that the DEG amount of the layer which uses a polyethylene terephthalate is 0.05-1.0 mass%. Here, the layer made of polyethylene terephthalate is a polyester resin in which 95 mol% or more of the dicarboxylic acid component constituting the polyester is a terephthalic acid component, and 95 mol% or more of the glycol component is an ethylene glycol component. It means the layer used. To reduce the amount of diethylene glycol, shorten the polymerization time, limit the amount of antimony compound, germanium compound, titanium compound, etc. used as a polymerization catalyst, combine liquid layer polymerization and solid layer polymerization, alkaline components And the like.

  The polyester film for battery exterior of the present invention preferably has an absolute value of birefringence (Δn) of less than 10. Thereby, a film excellent in piercing strength can be obtained. Here, the birefringence is obtained by multiplying the difference between the refractive index of MD of the film and the refractive index of TD by 1,000. When the absolute value of the birefringence exceeds 10, anisotropy appears in the plane of the film, so that the puncture strength tends to decrease. From the viewpoint of piercing strength, it is more preferable that the absolute value of birefringence is less than 9. An absolute value of birefringence of less than 8 is particularly preferable because the film has excellent puncture strength because of excellent alignment balance.

  As a method for setting the absolute value of birefringence to less than 10, when a polyester film is manufactured, particularly when a sequential biaxial stretching method is adopted, first, an unstretched film is stretched in the longitudinal direction and then stretched in the width direction. Or stretching by the sequential biaxial stretching method of stretching in the longitudinal direction after stretching in the width direction or the simultaneous biaxial stretching method of stretching the longitudinal direction and the width direction of the film almost simultaneously. Can be obtained at

The stretching ratio in such a stretching method is not particularly limited, but in the case of adopting the above-described film forming method such as the sequential biaxial stretching method, the longitudinal direction and the width direction are preferably stretched at the same ratio.
Here, in the present invention, the refractive index and the plane orientation coefficient are obtained as follows.

Using a sodium D line (wavelength 589 nm) as a light source, using methylene iodide as a mounting liquid, and using an Abbe refractometer at 25 ° C., MD, TD, and refractive index in the thickness direction (n _MD , n _TD , n _ZD , respectively) ) Birefringence (Δn) is calculated from the obtained refractive index according to the following formula.

Δn = (| n _MD −n _TD |) × 1,000.

  The polyester film for battery exterior of the present invention preferably has an easy-adhesion layer laminated on at least one side in order to improve the adhesion to the metal layer. Thereby, the improvement of the outstanding adhesiveness and adhesive strength can be aimed at. The method for providing the coating layer is not particularly limited, but as the method for forming the easy-adhesion layer, a resin is coated on the film surface (composite melt extrusion method, hot melt coating method, solvent other than water, water-soluble and / or water). For example, an in-line or off-line coating method from a dispersible resin, and a surface lamination method of the same composition or a blended product thereof. In particular, an in-line coating method in which orientation crystallization is completed by applying a coating agent on one surface of the film before completion of orientation crystallization, stretching in at least one direction, and heat-treating to complete orientation crystallization. Industrially preferable. Moreover, when providing an easily bonding layer by coating, as resin which provides easy adhesiveness, it is not specifically limited, For example, acrylic resin, urethane resin, polyester resin, olefin resin, fluorine type Resins, vinyl resins, chlorine resins, styrene resins, various graft resins, epoxy resins, silicone resins, and the like can be used, and mixtures of these resins can also be used. From the viewpoint of adhesion, it is preferable to use a polyester resin or an acrylic resin. When the polyester resin is used as an aqueous coating liquid, a water-soluble or water-dispersible polyester resin is used. For such water-solubilization or water-dispersion, a compound containing a sulfonate group or a carboxyl group is used. It is preferable to copolymerize a compound containing an acid base. When an acrylic resin is used as an aqueous coating liquid, it needs to be dissolved or dispersed in water, and as an emulsifier, a surfactant (for example, a polyether compound, etc. can be mentioned, but it is not limited. Not.) May be used.

  Moreover, in the easy-adhesion layer used for this invention, in order to improve adhesiveness, various crosslinking agents can be used together with resin.

  As the crosslinking agent resin, melamine-based, epoxy-based, and oxazoline-based resins are generally used. Examples of the particles contained in the easy-adhesion layer of the present invention include inorganic particles and organic particles. However, since the slipperiness and blocking resistance are improved, inorganic particles are more preferable. As the inorganic particles, silica, alumina, kaolin, talc, mica, calcium carbonate, titanium and the like can be used.

  The intrinsic viscosity of the polyester film for battery exterior of the present invention is preferably 0.65 to 0.80 dl / g. When the intrinsic viscosity of the film is less than 0.65 dl / g, the electrolytic solution resistance of the film may be lowered, and when it exceeds 0.80 dl / g, the film forming property tends to be lowered. More preferably, it is 0.68-0.78 dl / g, More preferably, it is 0.70-0.75 dl / g. The intrinsic viscosity here is the same as the value obtained by dissolving the resin in 100 ml of orthochlorophenol (solution concentration C = 1.2 g / ml) and measuring the viscosity of the solution at 25 ° C. using an Ostwald viscometer. The value obtained as [η] in the following formula using the value obtained by measuring the viscosity of the solvent.

ηsp / C = [η] + K [η] ² · C
(Where ηsp = (solution viscosity / solvent viscosity) −1, K is a Huggins constant (assuming 0.343)) In order to set the intrinsic viscosity of the polyester film to 0.65 to 0.80 dl / g The polyester resin used preferably has an intrinsic viscosity of 0.75 to 0.90 dl / g.

  If the polyester raw material contains organic fine particles, inorganic fine particles, metals, metal salts, and other additives that are insoluble in the solvent, the insoluble components are removed by filtration with a filter or centrifugation. Is the value (η) measured after adjusting the solution. If the polyester resin may contain additives such as plasticizers, surfactants, dyes, etc., after removing insoluble components, reprecipitation method, recrystallization method, chromatography method, extraction method, etc. Is the value (η) measured after adjusting the solution again.

  When the intrinsic viscosity is larger than the above range, the sheet is less likely to be deformed during shaping and may not be molded. Moreover, even if it can shape | mold, it exists in the tendency for a shaping speed to be slow, or for a residual stress to remain in a molded article and for shape stability to fall. Therefore, it is necessary to increase the load to increase the press pressure, or to increase the pressurization time, but it is not efficient. Further, when the load is increased, the load on the mold is increased, and the repeated use durability may be lowered. In addition, when η is less than the above range, the resistance to electric field liquid may decrease, the mechanical strength of the molded product may decrease, or the film may break during molding.

  The polyester used in the present invention is produced by the above-described method. In order to obtain a polyester raw material having a large molecular weight and a high intrinsic viscosity, a method of further increasing the degree of polymerization by performing solid phase polymerization is preferably used. The method for solid phase polymerization is as described above.

  The polyester film for battery exterior according to the present invention preferably has a thermal shrinkage of 0 to 6% after heat treatment at 190 ° C. for 10 minutes in at least one direction. When the heat shrinkage rate exceeds 6%, wrinkles may occur when laminating with other materials or metal foils in the processing step. More preferably, it is 0 to 5%, and particularly preferably 0 to 4%.

  Furthermore, from the viewpoint of twist curl properties, it is preferable that the heat shrinkage rate in one direction and the direction perpendicular to the direction is 0 to 4%.

  A method for setting the heat shrinkage rate in the above-described range is not particularly limited, but a method for increasing the heat treatment temperature of the film after biaxial stretching is effective. By performing the heat treatment at such a high temperature, distortion in the film is alleviated, so that the thermal shrinkage rate can be lowered. A preferable heat treatment temperature is 190 ° C. or higher and a film melting point or lower. If the heat treatment temperature is lower than 190 ° C, the distortion in the film is not relaxed, and the thermal shrinkage at 190 ° C may not be lowered. If the heat treatment temperature exceeds the film melting point, the film may be melted during the heat treatment. More preferably, it is 220 degreeC-melting | fusing point -5 degreeC, and if it is 225 degreeC-melting | fusing point -10 degreeC, it is especially preferable. Further, a method in which the film is relaxed in the longitudinal direction or the width direction during the heat treatment is also preferably used. By relaxing at the time of the heat treatment, the residual strain in the film is released, so the thermal shrinkage rate is lowered. A preferred relaxation rate (relaxation rate) during the heat treatment is preferably 3% or more and 7% or less. If it is less than 3%, the thermal shrinkage rate may increase, and if it exceeds 7%, the quality of the film may deteriorate. From the viewpoint of quality and dimensional stability, it is more preferably 3% or more and 6% or less, and particularly preferably 3% or more and 5% or less. In addition, a method of relaxing after the heat treatment at a temperature lower than the temperature of the heat treatment is also preferable.

  The polyester film for battery exterior of the present invention preferably has a thermal history peak temperature (T-meta) observed by differential scanning calorimetry (DSC) of 190 ° C to 250 ° C. If the thermal history peak temperature is less than 190 ° C., the thermal shrinkage at 190 ° C. may not be lowered. Moreover, when the thermal history peak temperature exceeds 250 ° C., the crystal orientation of the film is relaxed, and the piercing load and piercing displacement may be reduced. The thermal history peak temperature (T-meta) is 220 ° C. to 245 ° C., and most preferably 225 ° C. to 245 ° C.

  The method for setting the heat history peak temperature of the polyester film for battery exterior of the present invention in such a range is not particularly limited, but it is preferable to heat-treat the film after biaxially stretching the unstretched sheet. This heat treatment can be performed by any method such as in an oven or on a heated roll. The heat treatment temperature is preferably 190 ° C to 235 ° C, particularly preferably 190 ° C to 230 ° C. The heat treatment temperature can be any time, but it is preferably 1 to 60 seconds. Such heat treatment may be performed while relaxing the film in the longitudinal direction or the width direction. Further, re-stretching may be performed once or more in each direction, and then heat treatment may be performed. Moreover, it is preferable to heat-treat the film by providing two or more multi-stage heat treatment zones from the viewpoint of improving heat shrinkability. For example, although not particularly limited, in the case where good heat shrinkability at 190 ° C. is required, the first stage heat treatment zone preferably has an arbitrary temperature of 190 ° C. to 250 ° C. More preferably, it is 220 degreeC-245 degreeC, and if it is 225 degreeC-240 degreeC, it is especially preferable. Further, the second stage heat treatment zone is preferably in the same temperature range as or lower than the first stage.

  The polyester film for battery exterior of the present invention can be suitably used as a battery exterior member formed by laminating a metal layer on at least one surface. The metal layer to be laminated is not particularly limited, but aluminum is preferably used as the metal layer because it has excellent moldability and moisture resistance. The thickness of the aluminum layer is preferably 10 μm to 60 μm. If the thickness is 10 μm or less, it may not be able to withstand the pressure during molding and may break, and if it is 60 μm or more, molding may not be possible. More preferably, it is 12 micrometers-48 micrometers, and if it is 15 micrometers-45 micrometers, it is especially preferable.

(1) Puncture load, puncture displacement The film was cut into a square having a length of 50 mm and a width of 50 mm in the longitudinal direction and the width direction to obtain a sample. Using a tensile tester (Orientec Tensilon UCT-100), a piercing test was performed at a crosshead speed of 5 mm / min, and the piercing load and piercing displacement were measured. Each measurement was made 5 times, and the average was used. The room temperature was controlled at 25 ° C. and 63% Rh.

(2) Melting point, thermal history peak temperature (T-meta)
It measured using the differential scanning calorimeter (Seiko Denshi Kogyo make, RDC220). Using 5 mg of the film as a sample, the endothermic peak temperature when the temperature is raised from 25 ° C. to 300 ° C. at 20 ° C. is defined as the melting point, and the endothermic peak at the higher temperature side than the glass transition temperature (Tg) and lower than the melting point is T−. meta. When there are a plurality of endothermic peaks, the peak temperature of the endothermic peak on the highest temperature side was the melting point, and the endothermic peak on the lowest temperature side was T-meta.

(3) Intrinsic viscosity of polyester The intrinsic viscosity of the polyester resin and the film was measured at 25 ° C. using an Ostwald viscometer after dissolving the polyester in orthochlorophenol.

(4) Composition of polyester The polyester resin and film were dissolved in hexafluoroisopropanol (HFIP), and the content of each monomer residue and by-product diethylene glycol was quantified using ¹ H-NMR and ¹³ C-NMR.

(5) Breaking elongation, breaking strength, F-5 value, F-5 value / breaking strength A film was cut into a rectangle 150 mm long × 10 mm wide in the longitudinal direction and the width direction to obtain a sample. Using a tensile tester (Orientec Tensilon UCT-100), measuring the breaking elongation, breaking strength and F-5 value in the longitudinal and width directions of the film as a crosshead speed of 300 mm / min, a width of 10 mm, and a sample length of 50 mm. did. In the evaluation, the breaking elongation, breaking strength and F-5 value in each of the longitudinal direction and the width direction were measured 5 times each, and the average was used. Moreover, using the value obtained by further averaging the average value of the obtained F-5 values in each direction and the value obtained by further averaging the average value of the obtained breaking strength in each direction, F-5 / breaking strength The value was calculated. In all cases, the measurement was performed by controlling the room temperature to 25 ° C. and 63% Rh.

(6) Electrolytic solution resistance A biaxially oriented polyester film (PET) film was cut into a size of 50 mm × 50 mm to prepare a sample. In an equal volume mixed solvent of propylene carbonate and dimethyl carbonate as an electrolytic solution, 100 ml of LiPF ₆ dissolved at a rate of 1 mol / L was placed in a beaker, and a biaxially stretched polyester film was immersed for 24 hours. Thereafter, visual evaluation was performed according to the following criteria.

○: No discoloration Δ: Some discoloration ×: Discoloration occurred or dissolved.

(7) Aluminum followability Polyester film and aluminum foil (thickness 40 μm) are used urethane adhesive (Toyo Morton, AD-502, CAT10L, ethyl acetate 15: 1.5: 25 (mass ratio)). Then, it was dry laminated by a conventional method to prepare a multilayer structure. The resulting structure was drawn with a mold so that the polyester film was on the outside. The size of the molding is 10mm x 100mm (the shape of the convex part of the mold), and the molding is performed by increasing the drawing depth at 1mm to 1mm at the time of molding. Evaluation was performed in depth.

  ○: Molding was possible at 7 mm (no breakage).

Δ: Damaged at 4 mm or more and less than 7 mm ×: Damaged at less than 4 mm

(8) Birefringence (Δn), plane orientation coefficient (fn)
Using a sodium D line (wavelength 589 nm) as a light source, using methylene iodide as a mounting liquid, and using an Abbe refractometer at 25 ° C., MD, TD, and refractive index in the thickness direction (n _MD , n _TD , n _ZD , respectively) ) The birefringence (Δn) and the plane orientation coefficient are calculated from the obtained refractive index by the following formula.

Δn = (| n _MD −n _TD |) × 1,000.

fn = ( _nMD + _nTD ) / 2- _nZD .

  The specific example of manufacture of the polyester film for battery exteriors of this invention is described below.

(Manufacture of polyester)
The polyester resin used for film formation was prepared as follows.

(9) Productivity Productivity at the time of forming a polyester film was evaluated according to the following criteria. If it is ○ and △, it can be judged that productivity is good.

○: At the time of resin discharge, discharge was possible at 80 or more of the extruder output. Δ: At the time of resin discharge, discharge was possible at 60% to less than 80% of the extruder output. % Could not be discharged.

(10) Thermal shrinkage The polyester film is cut into strips each having a width of 10 mm and a length of 150 mm in the longitudinal direction and the width direction, and a line parallel to the width direction is drawn 25 mm inside from both ends in the length direction. The distance L0 between the lines was accurately measured. Subsequently, the strip-shaped sample was heat-treated in a hot air oven at 190 ° C. for 10 minutes, and after cooling, the distance L1 between two parallel lines was measured. A universal projector (V-16A (manufactured by Nikon)) was used for the measurement, and the measurement was made to a unit of 1 μm. The shrinkage percentage (%) was calculated from the dimensions before heat treatment and the dimensions after heat treatment by the following formula.

Thermal contraction rate (%) = ((L0−L1) / L0) × 100
In addition, 10 samples were measured for each of the longitudinal direction and the width direction, and the average value of each was used as the heat shrinkage rate in that direction.

(11) Twist curl Polyester film and aluminum foil (thickness 40 μm) using urethane adhesive (Toyo Morton, AD-502, CAT10L, ethyl acetate 15: 1.5: 25 (mass ratio)) Then, thermocompression bonding (80 ° C., 0.1 MPa, 3 m / min) was performed with a laminator to prepare a multilayer structure. The obtained structure was cut into a size of 10 mm × 100 mm. Next, the cut out sample was placed in a flat plate shape, the distortion height at each corner was measured, and the determination was made according to the following criteria.

○: No distortion Δ: Strain height of less than 5 mm ×: Strain height of 5 mm or more

(PET-1)
To a mixture of 100 parts by weight of dimethyl terephthalate and 70 parts by weight of ethylene glycol, 0.09 parts by weight of magnesium acetate and 0.03 parts by weight of antimony trioxide are added, the temperature is gradually raised, and finally Conducted transesterification while distilling methanol at 220 ° C. Subsequently, 0.020 parts by mass of an aqueous solution of 85% by mass of phosphoric acid was added to the transesterification reaction product, and then transferred to a polycondensation reaction kettle. The reaction system is gradually depressurized while heating in the polymerization kettle, and a polycondensation reaction is performed at 290 ° C. under a reduced pressure of 1 hPa. The inherent viscosity is 0.65, and by-product diethylene glycol is copolymerized by 0.9 mol%. A polyethylene terephthalate resin was obtained.

(PET-2)
To a mixture of 100 parts by weight of dimethyl terephthalate and 70 parts by weight of ethylene glycol, 0.09 parts by weight of magnesium acetate and 0.03 parts by weight of antimony trioxide are added, the temperature is gradually raised, and finally Conducted transesterification while distilling methanol at 220 ° C. Subsequently, 0.020 parts by mass of an aqueous solution of 85% by mass of phosphoric acid was added to the transesterification reaction product, and then transferred to a polycondensation reaction kettle. The reaction system is gradually depressurized while heating in the polymerization kettle, and a polycondensation reaction is performed at 290 ° C. under a reduced pressure of 1 hPa. The inherent viscosity is 0.65, and by-product diethylene glycol is copolymerized by 0.9 mol%. A polyethylene terephthalate resin was obtained. The polyethylene terephthalate resin obtained above was supplied to a rotary evaporator, and the pressure inside the apparatus was reduced to 50 Pa, followed by solid phase polymerization at 220 ° C. for 10 hours, an intrinsic viscosity of 0.85, and by-produced diethylene glycol was 0.9 mol. % Copolymerized polyethylene terephthalate resin was obtained.

(PET-3)
To a mixture of 100 parts by weight of dimethyl terephthalate and 70 parts by weight of ethylene glycol, 0.09 parts by weight of magnesium acetate and 0.03 parts by weight of antimony trioxide are added, the temperature is gradually raised, and finally Conducted transesterification while distilling methanol at 220 ° C. Subsequently, 0.020 parts by mass of an aqueous solution of 85% by mass of phosphoric acid was added to the transesterification reaction product, and then transferred to a polycondensation reaction kettle. The reaction system is gradually depressurized while heating in the polymerization kettle, and a polycondensation reaction is performed at 290 ° C. under a reduced pressure of 1 hPa. The inherent viscosity is 0.65, and by-product diethylene glycol is copolymerized by 0.9 mol%. A polyethylene terephthalate resin was obtained. The polyethylene terephthalate resin obtained above is supplied to a rotary evaporator, and after reducing the pressure in the apparatus to 50 Pa, solid phase polymerization is performed at 220 ° C. for 12 hours, and an intrinsic viscosity of 0.90 and by-produced diethylene glycol is 0.9 mol. % Copolymerized polyethylene terephthalate resin was obtained.

(PET-4)
To a mixture of 100 parts by weight of dimethyl terephthalate and 70 parts by weight of ethylene glycol, 0.09 parts by weight of magnesium acetate and 0.03 parts by weight of antimony trioxide are added, the temperature is gradually raised, and finally Conducted transesterification while distilling methanol at 220 ° C. Subsequently, 0.020 parts by mass of an aqueous solution of 85% by mass of phosphoric acid was added to the transesterification reaction product, and then transferred to a polycondensation reaction kettle. The reaction system is gradually depressurized while heating in the polymerization kettle, and a polycondensation reaction is performed at 290 ° C. under a reduced pressure of 1 hPa. The inherent viscosity is 0.65, and by-product diethylene glycol is copolymerized by 0.9 mol%. A polyethylene terephthalate resin was obtained. The polyethylene terephthalate resin obtained above is supplied to a rotary evaporator, the pressure inside the apparatus is reduced to 50 Pa, solid phase polymerization is performed at 220 ° C. for 8 hours, an intrinsic viscosity of 0.75, and by-produced diethylene glycol is 0.9 mol. % Copolymerized polyethylene terephthalate resin was obtained.

(Particle master) * Indicated below and in the table as particle M When producing the above polyethylene terephthalate, polycondensation reaction is carried out after adding an ethylene glycol slurry of agglomerated silica particles having an average particle diameter of 1.6 μm after the transesterification reaction. A particle master having a particle concentration of 2% by mass in the polymer was prepared.

(PET-G)
0.04 parts by mass of manganese acetate is added to a mixture of 100 parts by mass of dimethyl terephthalate, 60 parts by mass of ethylene glycol, and 20 parts by mass of 1,4-cyclohexanedimethanol, and the temperature is gradually raised. Transesterification was carried out while distilling methanol at 0 ° C. Next, 0.045 parts by mass of 85% phosphoric acid aqueous solution and 0.01 parts by mass of germanium dioxide were added, and the temperature was gradually raised and reduced. Finally, the temperature was raised to 275 ° C. and 1 hPa, and the intrinsic viscosity was reduced. The polycondensation reaction was carried out until 0.67, then discharged into a strand, cooled, and cut to copolymerize 8 mol% of 1,4-cyclohexanedimethanol and 2.0 mol% of diethylene glycol as a by-product. A polyethylene terephthalate resin was obtained. The polymer was cut into cubes having a diameter of 3 mm, and solid phase polymerization was performed using a rotary vacuum polymerization apparatus under a reduced pressure of 1 hPa at 225 ° C. until the intrinsic viscosity was 0.8.

(PBT)
A mixture of 100 parts by mass of terephthalic acid and 110 parts by mass of 1,4-butanediol was heated to 140 ° C. under a nitrogen atmosphere to obtain a homogeneous solution, and then 0.054 parts by mass of tetra-n-butyl orthotitanate. Then, 0.054 parts by mass of monohydroxybutyltin oxide was added to carry out an esterification reaction. Next, 0.066 parts by mass of tetra-n-butyl orthotitanate was added and a polycondensation reaction was performed under reduced pressure to prepare a polybutylene terephthalate resin having an intrinsic viscosity of 0.88. Thereafter, crystallization was performed at 140 ° C. in a nitrogen atmosphere, followed by solid phase polymerization at 200 ° C. for 6 hours in a nitrogen atmosphere to obtain a polybutylene terephthalate resin having an intrinsic viscosity of 1.22.

( Reference Example 1)
It was set as the single layer film. PET-2 was used as a constituent polyester. After the polyester resin is dried at 180 ° C. for 4 hours in a vacuum dryer and moisture is sufficiently removed, it is supplied to a single screw extruder under a nitrogen atmosphere, melted at 280 ° C., passed through a filter and a gear pump, to remove foreign matters. After the amount of extrusion was leveled, the sheet was discharged from a T-die onto a cooling drum whose temperature was controlled at 25 ° C. At that time, a wire-like electrode having a diameter of 0.1 mm was applied electrostatically and adhered to the cooling drum to obtain an unstretched film.

  Next, before stretching in the longitudinal direction, the film temperature is raised with a heated roll, the preheating temperature is 90 ° C., the stretching temperature is 95 ° C. and the film is stretched 4 times in the longitudinal direction, and immediately controlled at 40 ° C. Cooled down. This uniaxially stretched film is subjected to corona discharge treatment in air, and the following coating agents A, B, C, and D are mixed as an easy-adhesion layer on the treated surface while ultrasonically dispersing, and uniform with a # 4 metering bar. It was applied to.

Coating agent A: Water-dispersed acrylic resin (solid concentration 25% by mass), 20% by mass
Coating agent B: 79.4% by mass of methylolated melamine (diluent: isopropanol / water)
Coating agent C: colloidal silica (average particle size: 80 nm) 0.2% by mass
Coating D: Fluorine-based surfactant (diluent: water) 0.4% by mass
Next, the film was stretched 4.0 times in the width direction at a preheating temperature of 90 ° C. and a stretching temperature of 95 ° C. with a tenter-type transverse stretching machine, and the temperature was kept at 220 ° C. for 5 seconds while relaxing 4% in the width direction. Heat treatment was performed to obtain a biaxially oriented polyester film having a film thickness of 25 μm.

( Reference Example 2)
A / B two-layer laminated film was obtained. As polyester which comprises A layer, PET-2 and particle | grains M were mixed and used by mass ratio 97: 3. PET-2 was used as the polyester constituting the B layer. Thereafter, the polyester resin is dried at 180 ° C. for 4 hours in a vacuum dryer, and after sufficiently removing moisture, it is supplied to a separate single-screw extruder under a nitrogen atmosphere, melted at 280 ° C., and separated in a separate route. After removing foreign substances and leveling the extrusion amount through a filter and gear pump, the layers were laminated so as to have an A layer / B layer (lamination ratio 2: 8) in a feed block installed on the top of the T die. Thereafter, the sheet was discharged from a T die onto a cooling drum whose temperature was controlled at 25 ° C. At that time, a wire-like electrode having a diameter of 0.1 mm was applied electrostatically and adhered to the cooling drum to obtain an unstretched film. Then, the biaxially oriented polyester film which laminated | stacked the 36-micrometer-thick easy-adhesion layer was obtained like the reference example 1 except the point which does not apply | coat an easy-adhesion layer.

The film was slightly reduced in piercing load and piercing displacement .

( Reference Example 3)
It was set as the single layer film. As polyester which comprises, PET-2 and particle | grains M were mixed and used by mass ratio 97: 3. Thereafter, a biaxially oriented polyester film having a thickness of 30 μm was obtained in the same manner as in Reference Example 1. Since the film had a high particle concentration, the aluminum followability deteriorated .

( Reference Example 4)
A three-layer film of A / B / A was obtained. As polyester which comprises B layer, PET-2 and PET-G were mixed and used by mass ratio 95: 5. As polyester constituting the A layer, PET-2, PET-G and particles M were mixed and used at 94.2: 5: 0.8 (mass ratio).

Thereafter, the film thickness was 15 μm (lamination ratio 1: 1: 5) in the same manner as in Reference Example 2 except that the preheating temperature in the longitudinal direction was 95 ° C., the draw ratio was 4.1 times, and the draw ratio in the width direction was 4.1 times. A biaxially oriented polyester film of 8: 1) was obtained.

Since the film was thin, the piercing load was slightly reduced .

( Reference Example 5)
It was set as the single layer film. PET-1 was used as a constituent polyester. Thereafter, a biaxially oriented polyester film having a thickness of 35 μm was obtained in the same manner as in Reference Example 1. Since the intrinsic viscosity of the film was low, the aluminum followability and the electrolytic solution resistance were lowered .

( Reference Example 6)
It was set as the single layer film. PET-1 was used as a constituent polyester. A biaxially oriented polyester film having a thickness of 35 μm was obtained in the same manner as in Reference Example 1 except that the relaxation in the width direction was 7% and the heat treatment temperature was 250 ° C. Since the film had a low intrinsic viscosity, the heat shrinkage rate was high, and the aluminum following ability and the electrolytic solution resistance were lowered .

( Reference Example 7)
It was set as the single layer film. PET-3 was used as a constituent polyester. A biaxially oriented polyester film having a thickness of 28 μm was obtained in the same manner as in Reference Example 1 except that the relaxation in the width direction was 5% and the heat treatment temperature was 225 ° C. The film had high intrinsic viscosity and deteriorated productivity .

(Example 8)
It was set as the single layer film. PET-3 was used as a constituent polyester. The thickness is 28 μm as in Reference Example 1 except that the draw ratio in the longitudinal direction is 4.1 times, the draw ratio in the width direction is 4.2 times, the relaxation in the width direction is 5%, and the heat treatment temperature is 230 ° C. A biaxially oriented polyester film was obtained. The film exhibited excellent properties as a battery exterior polyester film.

Example 9
It was set as the single layer film. As polyester which comprises, PET-1 and particle | grains M were mixed and used by mass ratio 98.5: 1.5. The thickness is 25 μm as in Reference Example 1 except that the draw ratio in the longitudinal direction is 4.2 times, the draw ratio in the width direction is 4.3 times, the relaxation in the width direction is 6%, and the heat treatment temperature is 225 ° C. A biaxially oriented polyester film was obtained. Although the resistance to electrolytic solution was lowered, the film showed a satisfactory characteristic as a film for battery exterior.

(Example 10)
It was set as the single layer film. PET-1 was used as a constituent polyester. The thickness is 20 μm in the same manner as in Reference Example 1 except that the stretching ratio in the longitudinal direction is 4.2 times, the stretching ratio in the width direction is 4.4 times, the relaxation in the width direction is 5%, and the heat treatment temperature is 235 ° C. A biaxially oriented polyester film was obtained. The film exhibited excellent properties as a battery exterior polyester film.

(Comparative Example 1)
A three-layer film of A / B / A was obtained. As polyester which comprises B layer, PET-1 and PBT were mixed and used by mass ratio 70:30. As polyester which comprises A layer, PET-1, PBT, and particle | grains M were mixed and used by mass ratio 69: 30: 1. Thereafter, in the same manner as in Reference Example 2, a biaxially oriented polyester film having a film thickness of 25 μm (lamination ratio 1: 8: 1) was obtained.

  The film had a low piercing load, poor aluminum followability, and could not be used as a battery exterior polyester film.

(Comparative Example 2)
A three-layer film of A / B / A was obtained. As polyester which comprises B layer, PET-1 and PET-G were mixed and used by mass ratio 50:50. As polyester which comprises A layer, PET-1, PET-G, and particle | grains M were mixed and used by mass ratio 49: 50: 1. Thereafter, in the same manner as in Reference Example 4, a biaxially oriented polyester film having a film thickness of 20 μm (lamination ratio 1: 8: 1) was obtained.

  The film had a small stab displacement, poor aluminum followability and electrolytic solution resistance, and could not be used as a polyester film for battery exterior.

(Comparative Example 3)
It was set as the single layer film. PET-1 was used as a constituent polyester. Thereafter, in the same manner as in Reference Example 1, a biaxially oriented polyester film having a film thickness of 20 μm was obtained. Since the film had a low intrinsic viscosity of the film, the piercing load and piercing displacement were low, the aluminum followability was inferior, and the film could not be used as a polyester film for battery exterior.

(Comparative Example 4)
It was set as the single layer film. As polyester which comprises, PET-1 and particle | grains M were mixed and used by mass ratio 80:20.

Thereafter, in the same manner as in Reference Example 2, a biaxially oriented polyester film having a film thickness of 15 μm was obtained. The film was too high in particle concentration in the film so that the piercing load and piercing displacement were low, and the aluminum followability was extremely inferior, so that it could not be used as a polyester film for battery exterior.

(Comparative Example 5)
It was set as the single layer film. PET-2 was used as a constituent polyester. The polyester resin is dried at 180 ° C for 4 hours in a vacuum dryer, and after sufficiently removing moisture, it is supplied to a single screw extruder, melted at 280 ° C, passed through a filter and a gear pump, removed foreign matter, and the amount of extrusion is leveled. After the formation, the sheet was discharged from a T die onto a cooling drum whose temperature was controlled at 25 ° C. At that time, a wire-like electrode having a diameter of 0.1 mm was applied electrostatically and adhered to the cooling drum to obtain an unstretched film.

Thereafter, a biaxially oriented polyester film having a film thickness of 25 μm was obtained in the same manner as in Reference Example 1 except that the stretching ratio in the longitudinal direction was 3.2 times and the stretching ratio in the width direction was 3.0 times. Since the film was not supplied under a nitrogen atmosphere, the film had a low intrinsic viscosity, low piercing load and piercing displacement, and extremely poor aluminum followability, and could not be used as a polyester film for battery exteriors. It was.

(Comparative Example 6)
It was set as the single layer film. PET-2 was used as a constituent polyester. The polyester resin is dried at 180 ° C for 4 hours in a vacuum dryer, and after sufficiently removing moisture, it is supplied to a single screw extruder, melted at 280 ° C, passed through a filter and a gear pump, removed foreign matter, and the amount of extrusion is leveled. After the formation, the sheet was discharged from a T die onto a cooling drum whose temperature was controlled at 25 ° C. At that time, a wire-like electrode having a diameter of 0.1 mm was applied electrostatically and adhered to the cooling drum to obtain an unstretched film.

  Thereafter, a biaxially oriented polyester film having a film thickness of 25 μm was obtained in the same manner as in Comparative Example 5, except that the heat treatment temperature after stretching in the width direction was 185 ° C.

  The present invention relates to a polyester film, and particularly to a polyester film for battery exterior that can be suitably used for battery exteriors, particularly lithium ion secondary batteries having an electrolyte (solid or liquid) because of high puncture strength and large puncture displacement. is there.

Claims (8)

The piercing load is 5N to 15N at 25 ° C., and a puncture displacement is a linear distance in which the tip of the needle moves until it breaks by performing a puncture test with a 0.5 mmφ needle on the film surface at a speed of 5 mm / min. a 2.5～7Mm, the thickness of the film is Ri 10~40μm der a 100-250% elongation at break at 25 ° C. in the longitudinal direction of the film and the transverse direction, the film at 190 ° C., after 10 minutes heat treatment longitudinal direction and the width direction of the heat shrinkage 0-4% thermal history peak temperature observed by differential scanning calorimetry (DSC) (T-meta) is 190 ℃ ~234 ℃ der Ru cell exterior polyester the film. The polyester film for battery exteriors of Claim 1 whose breaking strength of the film longitudinal direction in 25 degreeC and the width direction is 200-400 MPa. The polyester film for battery exterior according to claim 1 or 2, wherein a stress (F-5 value) / breaking strength applied when stretched by 5 % is 0.5 or less. The polyester film for battery exterior according to any one of claims 1 to 3, wherein the plane orientation coefficient is 0.161 or more. The polyester film for battery exterior according to any one of claims 1 to 4, wherein the absolute value of the birefringence (Δn) is less than 10. The polyester film for battery exterior according to any one of claims 1 to 5, wherein the intrinsic viscosity of the film is 0.65 to 0.80. The polyester film for battery exterior according to any one of claims 1 to 6 , wherein an easily adhesive layer is laminated on at least one surface. At least one surface formed by laminating a metal layer to the battery exterior structure of the battery exterior polyester film according to any one of claims 1-7.