JP2014233950A - Biaxially-oriented polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially-oriented polyester film which can be used suitably as an exterior of a battery, particularly as a deep-drawn exterior of a lithium ion secondary battery having an electrolyte (of a solid or liquid state) and can cope with various shapes and consequently used suitably as a package of a medical product.SOLUTION: The biaxially-oriented polyester film comprises a polyester film obtained by stacking an A layer, which comprises polyester A, and a B layer, which comprises polyester B, alternately in the thickness direction by 50 or more layers. The crystal melting calorie of the polyester A is equal to or higher than 20 J/g or lower than 60 J/g when DSC measurement thereof is performed and the temperature rising rate is 20°C/minute. The polyester B has 1.5 or higher tensile stress ratio A (σ1/σ2), the tensile stress σ2 being lower than 100 MPa and the elastic modulus being lower than 4,000 MPa when a stress-elongation curve is obtained in a tensile test thereof and the tensile stress is defined as σ1 when the elongation rate becomes 50% and that is defined as σ2 at the yield point.

Description

  The present invention relates to a biaxially oriented polyester film that can be suitably used particularly for battery outer packaging and pharmaceutical packaging.

  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 widely used because of their high volumetric efficiency and weight efficiency. PCs, mobile terminal devices (cell phones, PDAs, etc.), video cameras, electric vehicles, energy storage batteries, robots, satellites It is used as a small and large capacity power source.

  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, that is, stability to contents), moldability, etc. For example, a polyamide film is used as a film material that satisfies the above requirements (see, for example, Patent Document 1). However, the polyamide film has insufficient moisture resistance and acid resistance (resistance to an acid solution generated by electrolyte deterioration and hydrolysis), and improvement has been demanded. Moreover, examination using the polyester film which is excellent in moisture resistance and acid resistance is also performed (for example, refer patent document 2). However, the polyester film proposed here does not necessarily have sufficient moldability, and it has been difficult to cope with deep drawing. In addition, a polyester film that has improved deep drawability by increasing the draw ratio of the film has also been proposed (see, for example, Patent Document 3). However, the polyester film proposed here has a problem that the molded body warps to the polyester film side after forming a laminated body laminated with a metal foil. In addition, an example in which formability is improved by using a polybutylene terephthalate (hereinafter referred to as PBT) film having excellent pinhole resistance and impact resistance is disclosed (for example, see Patent Document 4). However, the PBT film proposed here is produced by the tubular method for suppressing the crystallization of PBT, the moldability is still insufficient, and the quality deterioration due to the thickness nonuniformity is also caused. I was invited. In addition, a method of obtaining a biaxially stretched film by a T-die method by multilayerly laminating PET and PBT in the thickness direction is disclosed (for example, see Patent Document 5). However, the film obtained by the method proposed here has a stress ratio A (σ1 / σ2) which is a ratio of the tensile stress σ1 when the elongation reaches 50% and the tensile stress σ2 at the yield point. Is less than 1.5, and delamination occurs between the PET and PBT layers under more severe molding conditions. Moreover, although the film which bonds a polyamide film and a polyester film is also examined, the process of bonding is needed and has caused the increase in production cost.

  In addition, for pharmaceutical packaging, in order to prevent the deterioration of the contents, there is an increasing need for packaging forms having metal foils such as aluminum, and there is a demand for improved moldability of the metal foils according to the shape of the contents. Yes.

JP 2006-236938 A Japanese Patent Laid-Open No. 2004-362953 JP 2011-204673 A JP 2012-172091 A JP 2004-122664 A

  The biaxially oriented polyester film of the present invention provides a laminate having excellent moldability, warpage resistance, and acid resistance, and having no delamination during molding, for battery outer packaging and pharmaceutical packaging.

  In order to solve the above problems, the present invention has the following configuration.

A polyester film in which 50 layers or more of A layers made of polyester A and B layers made of polyester B are alternately laminated in the thickness direction, and polyester A has a heating rate of 20 ° C./min in DSC measurement. The heat of crystal fusion of 20 J / g or more and less than 60 J / g, and polyester B has either (I) or (II) characteristics and a lamination ratio, and the elongation rate in the stress-elongation curve in the tensile test The stress ratio A (σ1 / σ2), which is the ratio of the tensile stress σ1 at the time of 50% to the tensile stress σ2 at the yield point, is 1.5 or more, the tensile stress σ2 is less than 100 MPa, and the elasticity A biaxially oriented polyester film characterized in that the rate is less than 4000 MPa.
(I) In DSC measurement, the amount of heat of crystal melting when the rate of temperature rise is 20 ° C./min is less than 0.01 J / g, and the stacking ratio of each layer thickness of A layer / B layer is in the range of 1-6. .
(II) In DSC measurement, the amount of heat of crystal melting when the rate of temperature rise is 20 ° C./min is 20 J / g or more and less than 60 J / g, the glass transition temperature is 60 ° C. or less, and each layer of A layer / B layer The lamination ratio of thickness is in the range of 0.3-5.

  The biaxially oriented polyester film of the present invention has improved moldability and warpage of the molded product. It can be suitably used for a battery exterior construction body and a pharmaceutical packaging construction body that support high capacity.

It is a figure of the stress-elongation curve obtained by the tensile test of a film. It is the figure which looked at the structure which was fabricated in evaluation of molding followability from right above.

  Hereinafter, embodiments of the present invention will be described in detail.

  The biaxially oriented polyester film of the present invention requires that 50 layers or more of polyester A and polyester B are alternately laminated in the thickness direction. The number of stacked layers in the thickness direction is preferably 100 layers or more, more preferably 200 layers or more, and still more preferably 400 layers or more. By increasing the number of layers in this way, the number of interface between layers increases, pinhole resistance and impact resistance are improved, and formability is improved. Even when the polyester used is a resin having a very high crystallization speed such as PBT, the crystallization is suppressed and the unstretched film maintains an extremely low crystal state. Sexually improves. When the number of laminated layers is less than 50, not only the crystallinity of the obtained unstretched film becomes high and the stretchability is lowered, but in an extreme case, stretch breakage may occur.

  In the laminated film of the present invention, the laminated structure is not particularly limited. For example, it is possible to select an arbitrary laminated configuration such as laminating only the same kind of resin, laminating two kinds of resins randomly, and laminating three or more kinds of resins alternately. As a specific laminated structure, for example, a case of three types of resin layers may be used. For example, it may be completely random, or A (BCA) n, A (BCBA) n, A (BABCBA) n (here And n may be a regular permutation such as a natural number). More preferably, they are laminated in a regular order.

  In this invention, it is preferable that the thickness of the main layer which comprises a laminated | multilayer film is 200 nm or less. Here, the thickness of the main layer constituting the laminated film being 200 nm or less means a state in which a portion having an area ratio of about 70% or more is composed of a layer having a layer thickness of 200 nm or less in the film cross section. By setting the thickness of each main layer to 200 nm or less, the ratio of the interface portion occupying one layer increases, and the physical properties of the layer interface appear as a whole laminated film, improving the gas barrier properties, impact resistance, and pinhole resistance. To do. Moreover, since crystal growth due to heating is suppressed, stretchability is significantly improved.

  In the present invention, polyesters A and B have various additives such as an antioxidant, an ultraviolet absorber, an antistatic agent, a crystal nucleating agent, a flame retardant, an inert substance, as long as the effects of the present invention are not hindered. Inorganic particles, organic particles, thickeners, heat stabilizers, lubricants, infrared absorbers and the like may be added. Here, when particles are added, these particles preferably have an average particle diameter of about 1 to 50 times the thickness of the main layer in order not to disturb the lamination interface of the laminated film. It is also possible to provide a layer having these functions on the surface layer of the laminated film.

  The biaxially oriented polyester film of the present invention has a stress ratio A (the ratio of the tensile stress σ1 when the elongation becomes 50% and the tensile stress σ2 at the yield point in the stress-elongation curve in the tensile test. (σ1 / σ2) is 1.5 or more, the tensile stress σ2 is less than 100 MPa, and the elastic modulus is less than 4000 MPa.

  Biaxial orientation is a structure in which the main chain of the constituent polymer is oriented and arranged in the biaxial direction of the longitudinal direction and the width direction, and is different from the polar figure or the in-plane distribution of refractive index by wide-angle X-ray diffraction. Judgment from the direction.

  By adopting such a configuration, it has excellent moldability, strength and warpage resistance, and can exhibit these characteristics particularly during cold forming. In the present invention, cold forming refers to forming performed in a temperature atmosphere less than the glass transition point (Tg) of the resin. Such cold forming is preferably performed by using a cold forming machine used for forming a metal layer such as an aluminum foil and pressing the sheet material into the female mold with a male mold and pressing the sheet material at a high speed. According to the inter-forming, plastic deformation such as molding, bending, shearing and drawing can be generated without heating.

  In the present invention, the elongation rate, the stress ratio A, and the elastic modulus of the film are obtained by carrying out a tensile test (sample width 10 mm, tensile distance 50 mm, tensile speed 300 mm / min), and the stress-strain curve obtained thereby. Ask based.

  Here, as a stress-elongation curve obtained by the said tension test, what is shown, for example in FIG. 1 is mentioned.

  In FIG. 1, the vertical axis indicates the tensile stress σ (MPa) of the biaxially oriented polyester film, and the horizontal axis indicates the elongation (%) of the biaxially oriented polyester film. When a tensile test of a biaxially oriented polyester film is performed, the tensile stress σ increases in a substantially linear function as the elongation increases, and the increasing tendency of the tensile stress σ greatly changes at a predetermined elongation. In the present invention, this point is defined as the yield point. When the elongation further increases and reaches a predetermined strain, the film reaches the breaking point. In the thus obtained stress-elongation curve shown in FIG. 1, the stress ratio A (σ1 / σ2), which is the ratio between the tensile stress σ1 when the elongation becomes 50% and the tensile stress σ2 at the yield point, is , 1.5 or more is necessary. Preferably it is 1.7 or more, More preferably, it is 2.0 or more. If the stress ratio A (σ1 / σ2) is less than 1.5, the moldability is drastically lowered, which is not preferable. Although this mechanism has not been clearly clarified, the present inventors presume as follows. When a film is formed together with a metal layer such as an aluminum foil, the metal layer is originally a material that is not easily deformed. Therefore, the film is deformed following the film, but there is a clear yield point when the film is deformed. If the inclination of the stress is small, the metal layer cannot follow the change in the stress and easily breaks. For this reason, when the stress ratio A is 1.5 or more, it is estimated that the metal layer can be deformed following the deformation of the film.

  Further, the tensile stress σ2 needs to be less than 100 MPa. More preferably, it is less than 80 MPa. The elastic modulus needs to be less than 4000 MPa. More preferably, it is less than 3800 MPa. When the tensile stress σ2 is 100 MPa or more or 4000 MPa or more, a strong forming force is required, so that the formed metal layer is easily thinned and the formability is lowered. Moreover, since the film shrinkage force after shaping | molding becomes high and curvature also becomes large, it is unpreferable.

  In order to set the stress ratio A (σ1 / σ2) to 1.5 or more, it is necessary to increase the orientation of the molecular chain. The stretching ratio in the stretching direction is 3 in each of the longitudinal direction and the width direction. Stretching is performed at a rate of 0.5 to 4.5 times, preferably 3.6 to 4.2 times, more preferably 3.7 to 4 times. On the other hand, when the orientation is increased, σ2 and the elastic modulus are also increased. Therefore, it is very difficult to satisfy the above-described values of the stress ratio A, σ2, and the elastic modulus in a single polyester film.

  Therefore, in the present invention, in order to satisfy the above-described physical properties, polyester A has a so-called crystalline property in which DSC measurement has a crystal melting heat amount of 20 J / g or more and less than 60 J / g when the rate of temperature rise is 20 ° C./min. It needs to be a resin. When the heat of crystal fusion of polyester A is less than 20 J / g, it is difficult to achieve a stress ratio A (σ1 / σ2) of 1.5 or more because the crystal orientation of the molecular chain is hindered, and the acid resistance of the film Inferior properties.

The lamination ratio of polyester B and layer thickness (A layer thickness / B layer thickness) needs to be either of the following.
(I) In DSC measurement, it is a so-called amorphous resin having a heat of crystal fusion of less than 0.01 J / g when the rate of temperature rise is 20 ° C./min, and the lamination ratio of each layer thickness of A layer / B layer Is in the range of 1-6.
(II) In DSC measurement, it is a so-called crystalline resin having a heat of crystal fusion of 20 J / g or more and less than 60 J / g when the rate of temperature rise is 20 ° C./min.
The glass transition temperature is 60 ° C. or lower, and the lamination ratio of the thicknesses of the A layer / B layer is in the range of 0.3 to 5.

  By adopting such a configuration, it is possible to reduce σ2 and the elastic modulus while increasing the stress ratio A (σ1 / σ2). In particular, the configuration of (II) is preferable in order that the stress ratio A (σ1 / σ2) is 1.7 or more, σ2 is 80 MPa or less, and the elastic modulus is 3800 MPa or less.

  Moreover, the lamination ratio shown here is the ratio (A layer thickness / B layer thickness) of each layer thickness obtained from the TEM photograph of a film cross section.

  The crystalline polyester A used in the present invention desirably has a structure obtained by polycondensation of a dicarboxylic acid component and a diol component because of its simple synthesis. Here, polyester A is crystalline means that the heat of crystal melting is 20 J / g or more in differential calorimetry (DSC) at a rate of temperature increase of 20 ° C./min. Typical examples include terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, poly-1,4-cyclohexanedimethylene terephthalate, and polyethylene diphenylate. These copolymers and blends are typical examples. It doesn't matter. In particular, polyethylene terephthalate is preferable because it is inexpensive and can be used in a wide variety of applications.

  The amorphous polyester B used in the present invention is desirable because it is easy to synthesize. Like the polyester A, the amorphous polyester B desirably has a structure obtained by polycondensation of a dicarboxylic acid component and a diol component. Here, that the polyester B is non-crystalline means that the heat of crystal melting is 0.01 J / g or less in the temperature increase rate of 20 ° C./min in the differential calorimetry (DSC). Preferred amorphous polyesters have, for example, a structure obtained by polycondensation of the following dicarboxylic acid component and diol component. Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, Examples include 4'-diphenylsulfone dicarboxylic acid, adipic acid, sebacic acid, dimer acid, cyclohexanedicarboxylic acid and ester-forming derivatives thereof. Examples of the glycol component include ethylene glycol, 1,2-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentadiol, diethylene glycol, polyalkylene glycol, and 2,2-bis (4 ′ -Β-hydroxyethoxyphenyl) propane, isosorbate, 1,4-cyclohexanedimethanol, spiroglycol, and ester-forming derivatives thereof. Particularly preferred amorphous polyester B is preferably polyethylene terephthalate copolymerized with 15 to 40% of isophthalic acid or 1,4-cyclohexanedimethanol. As long as the amorphous polyester B used for the B layer is amorphous, a mixture of two or more polyester resins may be used.

The crystalline polyester B having a glass transition temperature of 60 ° C. or less used in the present invention is composed of 90 mol% or more of glycol units, 1,2-propanediol, 1,3-butanediol, 1,4-butanediol. 1,5-pentadiol-derived structural units, and 90 mol% or more of the dicarboxylic acid units are preferably terephthalic acid-derived structural units.

The biaxially oriented polyester film of the present invention preferably has an interlayer adhesion strength of polyester A (A layer) and polyester B (B layer) of 0.4 N / mm or more. When the interlayer adhesion strength is 0.4 N / mm or more, it is possible to suppress delamination due to shrinkage during molding or thermal processing. In order to set the interlayer adhesion strength to 0.4 N / mm or more, it is important to increase the affinity between the polyester A (A layer) and the polyester B (B layer). A layer and a layer made of polyester B are B layers, and each of the A layers contains more than 50% by mass of polyester A, and B layer contains more than 50% by mass of polyester B. It is preferable to add polyester B to B or polyester A to layer B in the range of 5 to 25% by mass. If the amount is less than 5% by mass, the effect of improving the interlayer adhesion is not observed, and if added more than 25% by mass, the crystal orientation of the molecular chain is hindered. Therefore, a more preferable stress ratio A (σ1 / σ2) of 1.7 or more is required. It can be difficult to achieve.

  The polyester in the present invention includes a polyester resin that is a polycondensate of a dicarboxylic acid derivative and a diol derivative. Examples of glycols or derivatives thereof that give the polyester used in the present invention include 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1, other than ethylene glycol. Aliphatic dihydroxy compounds such as 5-pentanediol, 1,6-hexanediol and neopentyl glycol, polyoxyalkylene glycols such as diethylene glycol, polyethylene glycol, polypropylene glycol and polytetramethylene glycol, 1,4-cyclohexanedimethanol, spiro Examples thereof include alicyclic dihydroxy compounds such as glycol, aromatic dihydroxy compounds such as bisphenol A and bisphenol S, and derivatives thereof. In addition to terephthalic acid, the dicarboxylic acid or derivative thereof that provides the polyester used in the present invention includes isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfone dicarboxylic acid, diphenoxyethanedicarboxylic acid. Acids, aromatic dicarboxylic acids such as 5-sodiumsulfone dicarboxylic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, fumaric acid and other aliphatic dicarboxylic acids, 1,4-cyclohexanedicarboxylic acid, etc. Alicyclic dicarboxylic acids, oxycarboxylic acids such as paraoxybenzoic acid, and derivatives thereof. Examples of dicarboxylic acid derivatives include dimethyl terephthalate, diethyl terephthalate, 2-hydroxyethyl methyl terephthalate, dimethyl 2,6-naphthalenedicarboxylate, dimethyl isophthalate, dimethyl adipate, diethyl maleate, and dimethyl dimer. An esterified product can be mentioned.

  The polyester of the present invention may be a homo resin, copolymer or blend, but at least one of polyester A and polyester B is preferably a homo resin. If both resins are copolymerized or blended, it may be difficult to achieve a stress ratio A (σ1 / σ2) of 1.5 or more. Examples of dicarboxylic acid components that can be copolymerized with polyester include isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 4,4′-diphenyldicarboxylic acid. Examples include acids, 4,4′-diphenylsulfone dicarboxylic acid, sebacic acid, and dimer acid. Examples of the copolymerizable glycol component include 1,2-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentadiol, diethylene glycol, polyalkylene glycol, and sandimethanol. .

  When polyesters are blended, the resins are compatibilized and the molecular orientation of the molecular chain is inhibited, so that the stress ratio A (σ1 / σ2), which is a more preferable characteristic, is 1.7 or more. It can be difficult to achieve. Therefore, in order to suppress the compatibilization of the polyesters, it is preferable to use a catalyst in which the catalyst contained in at least one of the polyester A and polyester B resins is deactivated. The deactivation here means that the transesterification ability of the catalyst contained in the polyester is inactivated. The catalyst having the highest deactivation effect is a germanium dioxide catalyst, which is deactivated by contact with hot water for 10 minutes to 120 minutes. Examples of PET resin having a germanium dioxide catalyst include Mitsui PET manufactured by Mitsui Chemicals.

In particular, the polyester A is preferably polyethylene terephthalate which is inexpensive and has an appropriate crystal stretchability. In the case of the amorphous resin (I), the polyester B is preferably polyethylene terephthalate copolymerized with 15 to 40% of isophthalic acid or 1,4-cyclohexanedimethanol. When polyester B is a crystalline resin of (II), 90 mol% or more of the glycol units of polyester B are structural units derived from 1,4-butanediol, and 90 mol% or more of dicarboxylic acid units are terephthalic acid. It is preferably a structural unit derived from.
By adopting such a configuration and performing appropriate stretching, the stress ratio, the tensile stress σ2, and the elastic modulus can be set within a preferable range.

  In addition, when 90 mol% or more of the glycol unit of polyester B is a structural unit derived from 1,4-butanediol, crystallization by stretching is large, and in order to increase the surface magnification to 12.3 times or more, layer B Is preferably suppressed as much as possible, and the preheating temperature until reaching the stretching section is preferably in the range of −10 to + 20 ° C. from the glass transition temperature of polyester B (hereinafter referred to as Tg). If the temperature is lower than Tg-10 ° C, the film thickness is likely to fluctuate due to insufficient heat. If the amount of heat required for the stretching of the polyester A is insufficient by setting the preheating temperature low, it is compensated by increasing the heating capacity of the radiation in the stretching section.

  In addition, since crystallization proceeds quickly at the edge part where the film thickness is thick, and tearing at the edge part often becomes a problem, trimming the edge part before adjusting the thickness of the base and entering the tenter, It is preferable to adjust so that the value of (edge thickness / film thickness) is 5 or less, preferably 4 or less.

  From the viewpoint of heat resistance, the biaxially oriented polyester film of the present invention preferably has a thermal shrinkage rate of 5% or less when held in a 190 ° C. atmosphere for 10 minutes. The biaxially oriented polyester film of the present invention is often used in the configuration of polyester film / aluminum foil / sealant film when used for battery exterior and medicine packaging, but when heat-sealing the sealant film and battery There may be a need for heat resistance in the temperature-decreasing environment after the product is manufactured. When the thermal shrinkage rate at 190 ° C. is 5% or less, curling as a constituent can be suppressed, and peeling between the polyester film and the aluminum foil due to shrinkage when exposed to a temperature-decreasing environment is also suppressed. be able to.

  In order to set the heat shrinkage rate of the biaxially oriented polyester film of the present invention to 5% or less when held in a 190 ° C. atmosphere for 10 minutes, for example, a method of adjusting the heat treatment conditions of the film after biaxial stretching can be mentioned. . From the viewpoint of heat resistance and film quality, the heat treatment conditions after biaxial stretching are preferably 200 ° C to 240 ° C, more preferably 210 ° C to 230 ° C. The heat treatment time is preferably 10 to 60 seconds, more preferably 15 to 30 seconds. Further, the heat treatment may be performed by relaxing the film in the longitudinal direction and / or the width direction. Furthermore, it is preferable to perform the heat treatment while relaxing in the longitudinal direction and / or the width direction because the heat shrinkage rate can be reduced. A preferable relaxation rate (relaxation rate) at the time of heat treatment is 3% or more. From the viewpoint of dimensional stability and productivity, 3% to 10% is preferable, and 3% to 5% is most preferable. preferable.

  Also, a method of heat treatment under two or more conditions is very preferable. After heat treatment at a high temperature of 200 ° C. to 240 ° C., the heat shrinkage rate can be further reduced by performing heat treatment at a temperature lower than the heat treatment temperature while relaxing in the longitudinal direction and / or the width direction. The heat treatment temperature in the second stage at this time is preferably 120 ° C. to 180 ° C., more preferably 150 ° C. to 180 ° C.

  The polyester film used in the present invention has a thickness of preferably 12 μm or more and 40 μm, more preferably 16 μm or more and 38 μm or less, and more preferably 18 μm or more and 30 μm, from the viewpoint of molding followability after metal foil lamination and warping resistance after molding. The following is most preferable.

  The biaxially oriented polyester film of the present invention is preferably used for battery exteriors. In order to maintain battery performance, the battery exterior has a water vapor barrier that prevents the ingress of water vapor, an electrolytic solution that does not swell with electrolyte, a deep drawability that meets the needs for higher capacity, Warpage resistance with little warping is required. By laminating the biaxially oriented polyester film of the present invention with a metal foil, it has a water vapor barrier property (hereinafter referred to as a laminated film), and the laminated film has good molding followability. In addition, since the warpage resistance after molding is compatible, it can be applied to battery exterior applications and can cope with higher capacities, and an excellent laminate for battery exteriors can be obtained. Is possible.

  The biaxially oriented polyester film of the present invention is also preferably used for pharmaceutical packaging applications. The medical packaging needs gas barrier properties and water vapor barrier properties in order to prevent deterioration of the contents, and printability is required so that it can meet the specifications for printing. In addition, there is a growing need for deep drawability that can accommodate contents of various shapes. The laminated film has good molding followability and also has both warping resistance after molding, so it can be applied to pharmaceutical packaging applications and can be used for various forms of drugs. It is possible to obtain a laminate for a pharmaceutical packaging and further a constituent.

  When the biaxially oriented polyester film of the present invention is used for battery exterior or pharmaceutical packaging applications, lamination with a metal foil that is a barrier layer for preventing deterioration of the contents is indispensable. By providing a polyester film on one side of the metal foil as the outermost layer, moisture resistance and stability to the contents can be ensured when used for battery exteriors and the like. As a metal constituting the metal foil, aluminum, stainless steel, copper, nickel, titanium, tin, silver, gold, zinc, iron or the like can be used according to the purpose. Especially, it is preferable that it is a layer containing aluminum from a viewpoint of a moldability, gas barrier property, water vapor | steam barrier property, intensity | strength, and economical efficiency. The metal foil may be aluminum alone or an aluminum alloy to which copper, zinc, manganese, magnesium, silicon, lithium, iron or the like is added. The aluminum content with respect to the metal foil is preferably 95% by mass or more, and a pure aluminum system or an aluminum / iron alloy is preferably used. The thickness is preferably a metal foil having a thickness of 10 μm or more and 100 μm or less. If the thickness is less than 10 μm, the formability by cold pressing or the like is inferior. On the other hand, when the thickness exceeds 100 μm, improvement in characteristics cannot be expected and the cost is inferior.

  The method for laminating the biaxially oriented polyester film of the present invention and the metal 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 metal foil, an adhesive made of a polyurethane resin or a polyester resin is preferable.

  The biaxially oriented polyester film used in the present invention is preferably subjected to corona treatment, plasma treatment, ozone treatment, and easy adhesion treatment on the surface in order to improve the adhesion to the metal foil.

  Moreover, a laminated film may laminate | stack a sealant film further on metal foil. Examples of the sealant film 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. -Propylene resin such as butene copolymer, polyolefin resin such as methylpentene resin and cyclic olefin resin, polyvinyl chloride, ethylene copolymerizable with vinyl chloride monomer, propylene, vinyl acetate, allyl chloride, allyl glycidyl Vinyl chloride resins such as ethers, acrylic acid esters, methacrylic acid esters, vinyl ether copolymers with vinyl chloride, and mixtures thereof are preferably used.

  In order to improve the adhesion between the metal foil and the sealant film, a method in which a modified polyolefin resin is interposed between the metal foil and the sealant film is also preferably used. Here, the modified polyolefin resin refers to a polyolefin resin containing one or more polar groups at least one of one end, both ends, and the inside of the polyolefin resin. Here, the polar group is a functional group containing an atom having a large electronegativity such as an oxygen atom or a nitrogen atom. Specifically, a functional group such as an amide group, a carboxyl group, or a hydroxyl group, and these functional groups It is a substituent containing.

  Such a modified polyolefin resin is preferably a polyolefin resin modified with an unsaturated dicarboxylic acid or modified by oxidative decomposition of the resin, and more preferably a modified polyolefin resin modified with an unsaturated dicarboxylic acid. Specifically, low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, ethylene-α / olefin copolymer polymerized using metallocene catalyst, polypropylene, ethylene-propylene copolymer, methylpentene A modified polyolefin resin obtained by modifying a polyolefin resin such as a random copolymer or block copolymer composed of a polymer or other α-olefin monomer with an unsaturated dicarboxylic acid such as acrylic acid, methacrylic acid, maleic anhydride, or fumaric acid. It is preferable from the point of interlayer adhesion with a polyester film. As the unsaturated dicarboxylic acid, maleic anhydride is particularly preferable, that is, a modified polyolefin resin obtained by modifying a polyolefin resin with maleic anhydride is particularly preferable.

  Examples of such modified polyolefin resin with unsaturated dicarboxylic acid include “Yomex” manufactured by Sanyo Kasei, “Admer” manufactured by Mitsui Chemicals, “Modic” manufactured by Mitsubishi Chemical, “Orebak” manufactured by Arkema, “Rotada”, Toyo Kasei. Various resins such as “Toyo Tac” manufactured by Toyo Ink are listed. Examples of the modified polyolefin resin modified by oxidative decomposition of the resin include “Biscol” and “Sun Wax” manufactured by Sanyo Chemical.

  Next, the preferable manufacturing method of the biaxially-oriented polyester film of this invention is demonstrated below.

  First, for the polyesters A and B used in the film of the present invention, commercially available polyethylene terephthalate resin or polybutylene terephthalate resin can be purchased and blended into a desired composition. When using a terephthalate resin, it can superpose | polymerize as follows.

  Magnesium acetate and antimony trioxide are added to a mixture of dimethyl terephthalate and ethylene glycol, the temperature is gradually raised, and finally the ester exchange reaction is performed while distilling methanol at 220 ° C. Next, an 85% aqueous solution of phosphoric acid is added to the transesterification reaction product, and then transferred to a polycondensation reaction kettle. The reaction system is gradually depressurized while being heated in the polymerization kettle, and a polycondensation reaction is performed at 290 ° C. under a reduced pressure of 1 hPa to obtain a polyethylene terephthalate resin having a desired intrinsic viscosity. In the case of adding particles, it is preferable to carry out polymerization by adding a slurry in which particles are dispersed in ethylene glycol to a polymerization reaction kettle so as to have a predetermined particle concentration.

  The production of polybutylene terephthalate resin that can be used for polyester B can be performed, for example, as follows. A mixture of terephthalic acid and 1,4-butanediol was heated to 140 ° C. under a nitrogen atmosphere to obtain a homogeneous solution, and then tetra-n-butyl orthotitanate and monohydroxybutyltin oxide were added to esterify the mixture. Perform the reaction. Subsequently, tetra-n-butyl orthotitanate is added and a polycondensation reaction is carried out under reduced pressure to obtain a polybutylene terephthalate resin having a desired intrinsic viscosity.

  A preferred method for producing the film of the present invention using the polyesters A and B obtained as described above will be specifically described. First, when mixing the polyester resin to be used, it measures and mixes so that it may become a predetermined | prescribed ratio. Next, drying is performed, for example, at 150 ° C. for 5 hours in a nitrogen atmosphere, a vacuum atmosphere, or the like, and the moisture content in the polyester resin is preferably 50 ppm or less.

  It is also preferable to use a germanium compound as a polycondensation catalyst instead of antimony trioxide. This is because the germanium compound has a high deactivation effect by the deactivation treatment described below. Preferable germanium compounds include compounds such as amorphous germanium dioxide, crystalline germanium dioxide, germanium tetroxide, germanium hydroxide, germanium tetraethoxide and the like. When a germanium compound is used, the amount of germanium remaining in the produced polymer is preferably 6 to 70 ppm.

  As a deactivation method, a method of immersing the obtained polyester chip in hot water at 50 to 100 ° C. for 10 to 60 minutes is common.

  Next, polyesters A and B are fed to separate extruders. In the extruder, the resin melted by heating to a temperature equal to or higher than the melting point is made uniform in the amount of resin extruded by a gear pump or the like, and foreign matter or denatured resin is removed through a filter or the like.

  Polyesters A and B sent out from different flow paths using these two or more extruders are then fed into the multilayer laminating apparatus. As the multilayer stacking apparatus, a multi-manifold die or a field block can be used. Moreover, you may combine these arbitrarily. The structure of the feed block has at least one member in a comb-shaped slit plate having a large number of fine slits, and polyester A and polyester B extruded from two extruders pass through each manifold, Introduced into the slit plate. Here, since the resin A and the resin B selectively flow alternately into the slit through the introduction plate, finally, a multilayer film such as A / B / A / B / A... Can be formed. . In addition, the number of layers can be increased by further overlapping the slit plates. Further, when the resin C is provided on both surface layers, the resin C is introduced from the third extruder to the surface layer side of the three-layer composite device (feed block), and the multilayer film is introduced to the center layer, thereby providing C A multilayer film such as / A / B / A... A / B / A / C can be formed.

  The melt thus multilayered is discharged in the form of a sheet from the T die onto the cooling drum. In that case, for example, a method of applying static electricity using a wire-like electrode or a tape-like electrode, a casting method in which a water film is provided between a casting drum and an extruded polymer sheet, and a casting drum temperature from a glass transition point of a polyester resin to ( A sheet-like polymer is brought into close contact with the casting drum by a method of sticking the extruded polymer at a glass transition point of -20 ° C or a combination of these methods, and solidified by cooling to obtain an unstretched film. Among these casting methods, when using polyester, a method of applying an electrostatic force is preferably used from the viewpoint of productivity and flatness.

  Subsequently, the unstretched film is stretched in the longitudinal direction and then stretched in the width direction, or the stretched film is stretched in the width direction and then stretched in the longitudinal direction, or the longitudinal direction and the width direction of the film. The film is stretched by a simultaneous biaxial stretching method or the like that stretches almost simultaneously.

  As a draw ratio in such a drawing method, preferably 3.5 to 4.5 times, more preferably 3.6 to 4.2 times, and particularly preferably 3.7 to 4 times in each direction. The The stretching speed is desirably 1,000 to 200,000% / min. Moreover, the temperature of the glass transition point (glass transition point +20 degreeC)-(glass transition point +70 degreeC) of polyester B is employ | adopted for extending | stretching temperature. Preferably, the stretching temperature in the longitudinal direction is preferably 55 to 95 ° C, and the stretching temperature in the width direction is preferably 60 to 85 ° C. Further, the stretching may be performed a plurality of times in 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 200 to 240 ° C. From the viewpoint of transparency and dimensional stability of the film, it is more preferably 210 to 235 ° 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. Further, before the transverse stretching step, at least one surface can be subjected to corona treatment or a coating layer can be provided in order to improve the adhesive force with the ink printing layer, the adhesive, and the vapor deposition layer. The coating liquid at this time is applied to the transparent substrate using a known coating means such as a roll coater, a gravure coater, a micro gravure coater, a bar coater, a die coater, or a dip coater.

  Next, the case of simultaneous biaxial stretching will be described. In the case of simultaneous biaxial stretching, the resulting cast film is subjected to surface treatment such as corona treatment, flame treatment, and plasma treatment as necessary, and then, such as slipperiness, easy adhesion, antistatic properties, etc. The function may be imparted by in-line coating.

  Next, the cast film is guided to a simultaneous biaxial tenter, and conveyed while holding both ends of the film with clips, and stretched in the longitudinal direction and the width direction simultaneously and / or stepwise. As simultaneous biaxial stretching machines, there are pantograph method, screw method, drive motor method, linear motor method, but it is possible to change the stretching ratio arbitrarily and drive motor method that can perform relaxation treatment at any place or A linear motor system is preferred. Although the stretching magnification varies depending on the type of resin, it is usually preferably 9 to 30 times as the area magnification. When polyethylene terephthalate is used as one of the resins constituting the laminated film of the present invention, the area magnification is 12 as the area magnification. .3 to 20.5 times is particularly preferably used. In particular, in the case of simultaneous biaxial stretching, it is preferable to make the stretching ratios in the longitudinal direction and the width direction the same and to make the stretching speeds substantially equal in order to suppress the in-plane orientation difference. Moreover, as extending | stretching temperature, the glass transition temperature of the resin which comprises a laminated film-glass transition temperature +60 degreeC is preferable.

  In order to impart flatness and dimensional stability, the biaxially stretched film is preferably subsequently subjected to a heat treatment not less than the stretching temperature and not more than the melting point in the tenter. In order to suppress the distribution of the main alignment axis in the width direction during this heat treatment, it is preferable to perform a relaxation treatment in the longitudinal direction immediately before and / or immediately after entering the heat treatment zone. After being heat-treated in this way, it is gradually cooled down uniformly, then cooled to room temperature and wound up. Moreover, you may perform a relaxation | loosening process in a longitudinal direction and / or the width direction at the time of annealing from heat processing as needed. Immediately before and / or immediately after entering the heat treatment zone, relaxation treatment is performed in the longitudinal direction.

  Further, the obtained polyester film can be subjected to a surface treatment such as corona as necessary to adhere a metal foil. Although not particularly limited, it is preferable to use a dry laminating method for adhesion. The adhesive may be urethane, acrylic, ether or epoxy. After bonding, an aging treatment may be performed as necessary for the purpose of improving the adhesive strength.

  An evaluation method of physical property values used in the present invention will be described. In the biaxially oriented polyester film of the present invention, the moldability, warpage resistance, and acid resistance after laminating the aluminum foil are important characteristics for increasing the capacity.

(1) Film thickness, layer thickness, lamination ratio When measuring the thickness of the entire film, using a dial gauge, cut the film into 200 mm x 300 mm, and measure the thickness of five arbitrary locations of each sample, Obtained on average. Moreover, about each layer thickness, a film is embedded in an epoxy resin, a film cross section is cut out with a microtome, the cross section of this film is 40000 using the transmission electron microscope HU-12 type (made by Hitachi, Ltd.). A cross-sectional photograph was taken by magnifying the image twice. The embodiment of the present invention was not carried out because a sufficient contrast was obtained, but the contrast may be increased by using a known dyeing technique using RuO ₄ or OsO ₄ depending on the combination of thermoplastic resins used. The lamination ratio of A layer / B layer was computed from the obtained thickness of each layer.

(2) Breaking elongation of polyester film, stress, stress ratio, elastic modulus The film was cut into a rectangular shape having a length of 150 mm and a width of 10 mm in the longitudinal direction and the width direction, and used as a sample (where the longitudinal direction is the direction in which the film flows ( (Winding direction) and the width direction is the direction perpendicular to the longitudinal direction). Using a tensile tester (Orientec Tensilon UCT-100) under the conditions of 25 ° C. and 63% Rh, the film was stretched in the longitudinal direction and width direction of the film with a crosshead speed of 300 mm / min, a width of 10 mm, and a sample length of 50 mm. A test was performed to obtain a stress-strain curve. From the obtained stress-strain curve, elastic modulus, elongation at break, yield point stress (σ1), and 50% elongation stress (σ2) were determined. Each measurement was performed 5 times each in the longitudinal direction and the width direction, and all average values of the values measured in the longitudinal direction and the width direction were used.

(3) Interlayer adhesion strength of polyester A (A layer) and polyester B (B layer) Interlayer adhesion strength was determined by a T-peel test. The T-peeling test was performed with reference to the T-peeling method among those specified in JIS K-6854. Corona treatment was performed on both sides of the sample film, and an adhesive was applied. The corona treatment method and the adhesive were selected so that the adhesive strength of the adhesive would be 0.5 N / mm or more. Specifically, when the surface layer of the sample film contains 75 mol% or more of polyethylene terephthalate, it is subjected to corona treatment in the atmosphere, and adhesive Takelac A610, curing agent Takenate A50, and ethyl acetate manufactured by Mitsui Takeda Chemical Co., Ltd. 36: The adhesive mixed at 4:60 was applied using a metabar so as to have a coating thickness of 3 μm. To this, a PET film “Lumirror” T60 (thickness: 100 μm) manufactured by Toray Industries, Inc., one side of which was corona-treated, was bonded to both sides and cured at 40 ° C. for 96 hours. At this time, as a portion to be grasped by the chuck, the PET film as the adherend was protruded by 50 mm or more from the sample film only on one side. However, when pasting together using other adhesives, the curing temperature and the curing time are performed under the condition that sufficient adhesive strength can be obtained with the adhesive. In the case of bonding using another adhesive, the adhesive is selected so that the characteristics of the sample film are not changed in the bonding process. Next, cut out so that the width is 25 ± 0.2 mm, the adhesive part is 125 mm or more, and the part to be gripped with the chuck is 50 mm, and the tensile tester made by Toyo Seiki Seisakusho Co., Ltd. The load when the sample film was peeled by moving the chuck at 100 ± 5 mm / min was measured. For the adhesion strength value, the cross section of the film after the test was observed with a TEM, the sample peeled between the A and B layers was selected, and the peeling of the test where the sample film was peeled without tearing the adherend A value obtained by dividing the average value of loads from the start 25 mm to 125 mm by the width of the test piece (25 ± 0.2 mm) was used. Moreover, when it peeled in the adhesive part or the tear had arisen in the film, the test was repeated again. Peeling at the adhesive part was judged by whether the peeled and / or cleaved part was wiped off with ethyl acetate and the adhesive was wiped off. Seven samples were measured for one sample, and the average value of the remaining five values excluding the maximum and minimum values is shown in Table 1.

(4) Heat Shrinkage The film was sampled to a width of 10 mm and a length of 150 mm, and marked lines with an interval of about 100 mm were marked on the sample, and then the distance between the marked lines was accurately measured using a universal projector. Next, the film sample was suspended in the length direction, a load of 3 g was applied in the length direction, and the film sample was heated in a hot air oven maintained at 190 ° C. for 30 minutes. The distance between the marked lines after heating was measured, and the amount of shrinkage of the film was expressed as a percentage with respect to the original dimension.

(5) Preparation method of constituent film Polyester film of the present invention and aluminum foil (Fukuda Metal Foil Mining Co., Ltd .: thickness 40 μm) urethane adhesive (Toyo Morton, AD-502, CAT10L, ethyl acetate) 15: 1.5: 25 (mass ratio)) and dry laminated by a conventional method to prepare a laminate for battery exterior. Further, a two-layer co-extruded film (maleic acid-modified polypropylene resin layer: 15 μm, polypropylene resin layer: 30 μm) obtained by co-extrusion of maleic acid-modified polypropylene resin and polypropylene as a sealant on an aluminum foil, and a maleic acid-modified polypropylene resin layer Was placed on the aluminum foil side and laminated by thermocompression bonding (120 ° C., 0.3 MPa, 2 m / min) using a laminator to form a battery exterior constituent film.

(6) Formability of constituent film The constituent film obtained in (5) is cut out to a size of 100 mm x 100 mm, and is a 50 mm x 30 mm rectangular male mold (a corner portion in the mold (R and square of depth)) R: 2 mm) and a female mold having a clearance of 0.5 mm between the male mold (R: 2 mm of a corner portion (R of the depth and square) R: 2 mm) Set the composition film on the female mold so that the center and the center of the male mold are aligned and the sealant side is on the male mold side, press molding (pressurization: 0.1 MPa), pinholes, cracks, etc. The maximum molding depth at which no defects occur was evaluated at a pitch of 0.5 mm. The maximum molding depth that can be practically used in battery exterior applications is 4 mm or more, and the larger the maximum molding depth, the better the moldability. On the other hand, if it is less than 3 mm, there are many molding breaks and it cannot be used for battery exterior use.

(7) Warping resistance of the constituent film The constituent film which has been formed without being damaged in the moldability evaluation of (6) is placed on a graph paper so that the sealant surface is on top. When viewed from directly above, as shown in FIG. 2, the constituent film is warped to the biaxially stretched film surface side by molding, and the projected image is smaller than the film area before molding (FIG. 23). Using a camera CV-H035 manufactured by Keyence Corporation, the film area after molding (FIG. 22) seen in a state observed from directly above is obtained by profile measurement, and the warpage frequency is obtained by the following equation. Evaluation was performed according to the following criteria. In battery exterior applications, warpage frequencies ◎ to □ are acceptable, and Δ to × cannot be used due to large warpage.
Degree of warpage = film area after molding / film area before molding × 100
◎: Warpage frequency is 90 or more ○: Warpage frequency is 89-80 □: Warpage frequency is 79-75 △: Warpage frequency is 74-70 x: Warpage frequency is less than 69 What is.

(8) Delamination resistance The film that was formed without being damaged in the molding followability evaluation of (6) was 168 using a pressure cooker manufactured by Tabai Espec Co., Ltd. at a temperature of 60 ° C. and a relative humidity of 90% RH. Time treatment is performed, and then the occurrence of delamination between the polyester film and the aluminum foil is confirmed. The state is visually confirmed, and it is determined that the case where the delamination is clearly generated is defective. If it cannot be judged visually, the cross section of any five irregularities made by molding is observed with SEM (500 times), depending on whether there is a place where the distance between the polyester film (B) / aluminum foil is 100 μm or more. Judged as follows. Moreover, even if the judgment is “good”, it is judged as “triangle” when peeling occurs between the layers of the film.
○: There is no part separated by 100 μm or more ×: One part is separated by 100 μm or more Δ: Peeling occurs between the layers of the film (9) Acid resistance Biaxially oriented polyester surface of the obtained constituent film 0.05 ml of concentrated hydrochloric acid was added dropwise and left at room temperature for 1 hour. After standing, the dropped acid was wiped off, and the state of the film was determined as follows.
○: No change Δ: Whitening is observed ×: The film surface is melted to form a dent mark (10) Glass transition temperature, crystal melting temperature, crystal melting heat quantity Differential calorimetry (DSC) “DSC-RDC220” (Seiko) Measured and calculated according to JIS-K-7122 (1987). Immediately after melting and discharging, a resin sample cooled with cold water of 10 ° C. or less was heated from 25 ° C. to 290 ° C. at a rate of 20 ° C./min. At this time, the inflection point before the crystallization peak was seen was the glass transition temperature, the peak top at the time of crystal melting was the crystal melting temperature, and the integrated value from the baseline was the heat of crystal melting. Moreover, when there were two peak tops, the integrated value from the baseline of each peak top was calculated, and the sum was used as the amount of heat of crystal melting.

Example 1
Polyester A is polyethylene terephthalate (indicated in the table as PET1) [Toray F20S] having an intrinsic viscosity of 0.65 and a melting point of 255 ° C., and polyester B is polybutylene terephthalate (hereinafter also referred to as PBT). (Registered trademark) [manufactured by Toray] After drying, each was supplied to a separate extruder.

  Polyester resin A and polyester resin B are each melted at 270 ° C. with an extruder, passed through 5 sheets of FSS type leaf disk filters, and the discharge ratio is polyester resin A / polyester resin B = 1 with a gear pump. While being measured so as to be 5/1, polyester A and polyester B were alternately laminated by a feed block to obtain a laminate of 51 layers. A layer made of polyester resin A supplied to the manifold die and further supplied from another extruder is formed on the surface layer, formed into a sheet shape, and then on a casting drum maintained at a surface temperature of 25 ° C. by electrostatic application. It quickly solidified. Further, by adjusting the gap between the base lips, the value of (edge thickness / film center thickness) was set to 3.5. The cast film at this time was slightly whitened by crystallization of the PBT layer.

  The obtained cast film was heated by a roll group set at 60 ° C., and then rapidly heated by a radiation heater from both sides of the stretch section length of 100 mm while being stretched at a stretching temperature of 85 ° C. in the longitudinal direction 3.5 times. The film was stretched and then cooled once. Next, this uniaxially stretched film was guided to a tenter, preheated with hot air of 85 ° C., and then stretched 3.5 times in the transverse direction at a temperature of 95 ° C. The stretched film is heat-treated with hot air of 210 ° C in a tenter, and then relaxed by 5% in the width direction in the section set at 190 ° C, followed by 5% relaxation treatment in the width direction at the same temperature. Applied, gradually cooled to room temperature, and wound up. The thickness of the obtained film was 25 μm (in addition, the stretching ratio of the longitudinal magnification and the lateral magnification was the limit, and when the stretching ratio was further increased, the tenter was broken).

  Table 1 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. It was confirmed that the moldability and warpage resistance were all excellent. Slight delamination was observed in the delamination resistance test.

(Example 2)
A biaxially oriented polyester film having a film thickness of 25 μm was obtained in the same manner as in Example 1 except that the number of slits was changed to a 201-layer feed block. Since the crystallization of the PBT layer was suppressed, the cast film became almost transparent, and the draw ratio in the longitudinal direction and the transverse direction could be increased up to 3.6 times respectively. )

  Table 1 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. It was confirmed that the moldability was improved as compared with Example 1.

Example 3
A biaxially oriented polyester film having a film thickness of 25 μm was obtained in the same manner as in Example 1 except that the number of slits was changed to a 491-layer feed block. Since the crystallization of the PBT layer was suppressed, the cast film became transparent, and the stretching ratio in the longitudinal direction and the transverse direction could be increased up to 3.8 times, respectively. ).

  Table 1 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. It was confirmed that the moldability was improved as compared with Example 2.

Example 4
A biaxially oriented polyester film having a film thickness of 25 μm was obtained in the same manner as in Example 3 except that the lamination ratio was 0.8. Table 1 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. It was confirmed that the formability and warpage resistance were improved by lowering σ1.

(Example 5)
Polyester A was mixed with 20 wt% PBT with respect to PET. Moreover, after heating the obtained cast film with the roll group set to 50 degreeC, it is 3 mm in a longitudinal direction at the extending | stretching temperature of 74 degreeC, rapidly heating with a radiation heater from both sides of a film between 100 mm of extending area length. The film was stretched 8 times and then cooled once. Next, this uniaxially stretched film was guided to a tenter, preheated with hot air at 75 ° C., and then stretched 3.8 times in the transverse direction at a temperature of 85 ° C. Otherwise in the same manner as in Example 4, a biaxially oriented polyester film having a film thickness of 25 μm was obtained. Table 1 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. It was confirmed that the delamination resistance was improved due to the significant improvement in interlayer adhesion. On the other hand, by combining polyesters having different A layers, the orientation of the molecular chain is hindered, the stress ratio is lowered, the moldability is lowered as compared with Example 3, and the acid resistance is also slightly deteriorated. It was.

(Example 6)
A biaxially oriented polyester film having a film thickness of 25 μm was obtained in the same manner as in Example 5 except that the lamination ratio was set to 0.8. Table 1 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. It was confirmed that the formability was improved by lowering σ1.

(Example 7)
A biaxially oriented polyester film with a film thickness of 25 μm was obtained in the same manner except that the polyester A PET used in Example 6 was changed to PET (J125, manufactured by Mitsui Chemicals) which had been deactivated. Table 1 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. Compared to Example 6, it was confirmed that the moldability and acid resistance were improved.

(Example 8)
The PBT of polyester B used in Example 3 was changed to PET (represented as PET / I in the table) in which 17.5 mol% of isophthalic acid having an intrinsic viscosity of 0.7 was copolymerized. Moreover, after heating the obtained cast film by the roll group set to 70 degreeC, while extending rapidly by the radiation heater from the both surfaces of a film between 100 mm of extending | stretching area length, it is 4.degree. The film was stretched twice and then cooled once. Next, this uniaxially stretched film was guided to a tenter, preheated with hot air of 95 ° C., and then stretched 4.2 times in the transverse direction at a temperature of 105 ° C. Otherwise in the same manner as in Example 3, a biaxially oriented polyester film having a film thickness of 25 μm was obtained. The stretched film is heat-treated in a tenter with hot air of 235 ° C., and then relaxed by 5% in the width direction in the section set at 210 ° C., followed by 5% relaxation treatment in the width direction at the same temperature. Applied, gradually cooled to room temperature, and wound up. The thickness of the obtained film was 25 μm. Table 1 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. It was confirmed that the warpage resistance was improved by performing a heat treatment at a temperature equal to or higher than the melting point of the B layer.

Example 9
Polyester B used in Example 8 was changed to a mixture of GN001 (manufactured by Eastman Chemical, hereinafter also referred to as PETG) and PET1 at a weight ratio of 82/18, the heat treatment temperature in the tenter was 230 ° C., and the relaxation temperature was A biaxially oriented polyester film having a film thickness of 25 μm was obtained in the same manner as in Example 8 except that the temperature was set to 210 ° C. Table 1 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. It was confirmed that the delamination resistance was improved due to the significant improvement in interlayer adhesion.

(Examples 10 to 11)
Biaxial orientation with a film thickness of 25 μm was performed in the same manner as in Example 9 except that the lamination ratio of Example 9 was changed to the values shown in the table and the draw ratio in the longitudinal direction and the transverse direction was 3.8 times. A polyester film was obtained. Table 1 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior.

(Comparative Example 1)
A biaxially oriented polyester film having a film thickness of 25 μm was obtained in the same manner as in Example 10 except that the polyester B was changed to PET1 (substantially a single film of PET1). Table 2 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. While the moldability was excellent, the warpage resistance was very poor.

(Comparative Example 2)
After drying pellets of nylon 6 (product number: Amilan 1021T, Ny6) manufactured by Toray, the pellets were melted at 270 ° C. in an extruder, passed through a filter and a gear pump, removed foreign matter, and the amount of extrusion was leveled. The sheet was discharged from a die onto a cooling drum whose temperature was controlled at 4 ° C. to obtain an unstretched film. Next, simultaneous biaxial stretching in the MD direction and the TD direction was performed by a tenter method. The draw ratio was 3.0 times in the MD direction and 3.2 times in the TD direction. This stretched film was subsequently heat-set at 195 ° C. with a tenter to obtain a film having a thickness of 25 μm. Table 2 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. While excellent in moldability and warpage resistance, it was inferior in chemical resistance.

(Comparative Example 3)
Toray PBT pellets (product number: Toraycon 1200S) were dried in a hot air dryer at 140 ° C for 5 hours, melted at 270 ° C in an extruder, passed through a filter and gear pump, removed for foreign matter, and leveled. After performing this, it was extruded as a cylindrical film with an annular die and quenched with cold water to produce a raw film. Subsequently, the gas was sealed in, expanded, heated at a temperature of 60 ° C., and subjected to simultaneous biaxial stretching in the MD direction and the TD direction by a tubular method. The magnification at the time of stretching was 3.0 times in the MD direction and 3.0 times in the TD direction (in addition, the stretching ratio of the longitudinal magnification and the lateral magnification is the limit, and if the stretching ratio is further increased, The tenter broke.) The stretched film was subsequently heat-set at 210 ° C. with a tenter to obtain a film having a thickness of 25 μm. Table 2 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. Due to the lack of molecular orientation, the moldability was poor.

(Comparative Example 4)
The same resin as in Example 1 was used. Each was melted at 270 ° C. by an extruder, passed through a gear pump and a filter, and then joined by a feed block. The merged polyesters A and B were supplied to a static mixer and had a structure in which polyester A was laminated alternately in the thickness direction consisting of 9 layers and 8 layers of polyester B. At this time, the flow channel shape was square. As a specific laminating method, it was designed to be 519 layers using a square mixer after laminating 9 layers with a fee block. Polyester A was both surface layers, and the total lamination thickness ratio was adjusted by the discharge amount so that A / B = 1. The laminate comprising 519 layers thus obtained was supplied to a T-die and formed into a sheet, and then rapidly cooled and solidified on a casting drum maintained at a surface temperature of 20 ° C. while applying electrostatic force.

  The obtained cast film was heated in a roll group set at 90 ° C., stretched 3.0 times in the longitudinal direction, led to a tenter, preheated with hot air at 100 ° C., and stretched 3.3 times in the lateral direction ( When the draw ratio was further increased, tearing occurred in the tenter). The stretched film was directly heat-treated in a tenter with hot air at 190 ° C., gradually cooled to room temperature, and wound up. The thickness of the obtained laminated film was 25 μm. Table 2 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. Due to the lack of molecular orientation, the moldability was poor.

(Comparative Example 5)
Using the same apparatus as in Comparative Example 4, it was designed to have 33 layers using a square mixer. The raw materials and conditions used were the same as in Example 1. The cast film at this time was particularly whitened at the edge portion for crystallization of the PBT layer, and the magnification in the longitudinal direction and the width direction could not be increased by 3.1 times or more. Occurred). The thickness of the obtained laminated film was 25 μm. Table 2 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. Due to the lack of molecular orientation, the moldability was poor.

(Comparative Example 6)
A biaxially oriented polyester film having a film thickness of 25 μm was obtained in the same manner as in Example 9 except that the draw ratio in the longitudinal direction and the transverse direction was changed to 3.3 times. Table 2 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. Due to the lack of molecular orientation, the moldability was poor.

(Comparative Example 7)
A biaxially oriented polyester film having a film thickness of 25 μm was obtained in the same manner as in Example 11 except that the draw ratio in the longitudinal direction and the transverse direction was 4.0 times. Table 2 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. Warpage resistance was poor because the molecular orientation was too high.

(Comparative Example 8)
A biaxially oriented polyester film having a film thickness of 25 μm was obtained in the same manner as in Example 3 except that PBT of polyester B was changed to PET (represented as PET / A in the table) in which 20 mol% of adipic acid was copolymerized. . Table 2 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. Due to the lack of molecular orientation, the moldability was poor.

(Comparative Example 9)
A biaxially oriented polyester film having a film thickness of 25 μm was obtained in the same manner as in Example 3 except that the polyester A was changed to PET in which 20 mol% of adipic acid was copolymerized (represented as PET / A in the table). At this time, the cast film had a flow pattern, and the magnification in the longitudinal direction and the width direction could not be increased by 3.1 times or more (breaking occurred in the tenter when the stretching ratio was further increased). Table 2 shows the evaluation results of the obtained biaxially oriented polyester film and the constituent film for battery exterior. Since the orientation of the molecules is insufficient, the moldability is inferior, and since the polyester A has low crystallinity, the acid resistance is inferior.

1 Film area after molding 2 Molded part (concave)
3 Film area before molding

  The biaxially oriented polyester film of the present invention is excellent in moldability and warping resistance after molding by adjusting the mechanical strength of the polyester, so it can be used for battery exterior components and various shapes. It can be suitably used for a medical packaging composition.

Claims (6)

A polyester film in which 50 layers or more of A layers made of polyester A and B layers made of polyester B are alternately laminated in the thickness direction, and polyester A has a heating rate of 20 ° C./min in DSC measurement. The heat of crystal fusion of 20 J / g or more and less than 60 J / g, and polyester B has either (I) or (II) characteristics and a lamination ratio, and the elongation rate in the stress-elongation curve in the tensile test The stress ratio A (σ1 / σ2), which is the ratio of the tensile stress σ1 at the time of 50% to the tensile stress σ2 at the yield point, is 1.5 or more, the tensile stress σ2 is less than 100 MPa, and the elasticity A biaxially oriented polyester film characterized in that the rate is less than 4000 MPa.
(I) In DSC measurement, the amount of heat of crystal melting when the rate of temperature rise is 20 ° C./min is less than 0.01 J / g, and the stacking ratio of each layer thickness of A layer / B layer is in the range of 1-6. .
(II) In DSC measurement, the amount of heat of crystal melting when the rate of temperature rise is 20 ° C./min is 20 J / g or more and less than 60 J / g, the glass transition temperature is 60 ° C. or less, and each layer of A layer / B layer The lamination ratio of thickness is in the range of 0.3-5.   The biaxially oriented polyester film according to claim 1, wherein the interlayer adhesion strength between the A layer and the B layer is 0.4 N / mm or more.   90.% or more of the glycol unit of polyester B is a structural unit derived from 1,4-butanediol, and 90 mol% or more of the dicarboxylic acid unit is a structural unit derived from terephthalic acid. Or the biaxially oriented polyester film of 2.   The biaxially oriented polyester film according to any one of claims 1 to 3, wherein the thermal shrinkage rate when held in a 190 ° C atmosphere for 10 minutes is 5% or less. The biaxially oriented polyester film according to any one of claims 1 to 4, which is used for battery exterior. The biaxially oriented polyester film according to any one of claims 1 to 4, which is used for pharmaceutical packaging.

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