Polyester film and method for producing the same

Abstract

To provide a polyester film having excellent puncture resistance.SOLUTION: A polyester film contains polybutylene terephthalate and polyethylene terephthalate, where an absolute value of a difference between a transverse orientation degree (Δnv) and a longitudinal orientation degree (Δnp) of the polyester film is 57 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a shaping polyester film, a method for producing the same, and a laminate and an exterior material comprising the shaping polyester film. [Background technology]

[0002] Conventionally, polyester films, particularly polyethylene terephthalate films and polyethylene naphthalate films, have excellent mechanical properties, heat resistance, and chemical resistance, and have been used in a variety of applications, including packaging, electronic components, electrical insulation, metal lamination, optical applications such as display components for foldable displays, bendable displays, and rollable displays, touch panels, anti-reflection applications, and glass shatter prevention applications (see, for example, Patent Documents 1 and 2).

[0003] In many of these applications, polyester film is not used as is, but rather is molded and processed, and in these cases, many products place emphasis on mechanical properties. As a result, polyester film alone cannot meet the required quality, and many products are compounded with other layers (such as resin layers or metal layers). For example, in lithium ion batteries, exterior materials are used as packaging materials to seal electrodes, electrolytes, etc. Conventionally, metal exterior materials have been widely used. Meanwhile, in recent years, with the increasing performance of electric vehicles, hybrid electric vehicles, personal computers, cameras, mobile phones, etc., lithium-ion batteries are being required to have a variety of shapes as well as to be thinner and lighter. However, the metal exterior materials that have been widely used up until now have difficulty keeping up with the diversification of shapes, and there are also problems with limitations to how much weight can be reduced.

[0004] For this reason, in recent years, bags (pouches) made of a laminate in which a plastic film is laminated on a metal foil such as aluminum foil have come into use as packaging materials that can be easily processed into a variety of shapes and can be made thinner and lighter. In pouch-shaped packaging materials, a recess is generally formed by cold-forming the laminate, and electricity storage device elements such as electrodes and electrolyte are placed in the space formed by the recess, and the laminates are heat-sealed to obtain a lithium-ion battery or the like in which the electricity storage device elements are housed inside the packaging material.

[0005] Polyamide is widely used as the substrate of the laminate because of its excellent formability. In addition to formability, moisture resistance, sealing properties, and chemical resistance may be required, and a structure consisting of a polyester film / polyamide film / metal foil / sealant film in this order from the outer layer is also being considered.

[0006] In addition, in recent years, electronic devices have been required to be smaller and thinner, and sharper corners of pouches have been considered to efficiently install lithium-ion batteries together with printed circuit boards and other components. Furthermore, in order to further increase the capacity and energy density of batteries per unit volume by increasing the content volume per pouch, there has been increasing emphasis in recent years on the development of pouch films with excellent formability that allow for the formation of deeper recesses during cold forming, such as deep drawing. For example, Patent Documents 3 and 4 discuss the use of polyester films primarily composed of polybutylene terephthalate, which has good formability, as battery exterior materials. Patent Documents 5 to 7 also discuss the use of polyester films containing polybutylene terephthalate as battery exterior materials. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-341546 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-122767 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-077292 [Patent Document 4] WO2014 / 017457 [Patent Document 5] Japanese Patent Application Publication No. 2017-177412 [Patent Document 6] Japanese Patent Publication No. 2022-056851 [Patent Document 7] WO2017 / 057773 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the polyester films described in Patent Documents 1 and 2 are not intended for use as battery exterior packaging. The polybutylene terephthalate disclosed in Patent Document 5 is a polyester-based elastomer, which may result in insufficient mechanical properties. When an exterior packaging material is produced using a laminate containing a polyester film primarily composed of polybutylene terephthalate as disclosed in Patent Documents 3, 4, and 6, the laminate exhibits excellent elongation and moldability, but suffers from poor puncture resistance. Specifically, the film exhibits large variations in displacement upon puncture and puncture strength, making it unsuitable for use as an exterior packaging material. Furthermore, Patent Document 7 also fails to adequately prevent such variations, potentially resulting in insufficient improvement in mechanical strength, such as puncture resistance.

[0009] Therefore, an object of the present invention is to provide a polyester film for forming that has good puncture resistance. [Means for solving the problem]

[0010] After extensive research, the inventors discovered that the above problem can be solved by incorporating polyethylene terephthalate and polybutylene terephthalate into a polyester film for molding and by setting the absolute value of the difference between the degree of horizontal orientation (Δnv) and the degree of vertical orientation (Δnp) of the polyester film to a certain value or less, and thus completed the present invention described below. That is, the present invention provides the following [1] to

[22] .

[0011] [1] A shaping polyester film containing polybutylene terephthalate and polyethylene terephthalate, A polyester film for molding, wherein the absolute value of the difference between the degree of transverse orientation (Δnv) and the degree of longitudinal orientation (Δnp) of the polyester film is 57 or less. [2] The polyester film for extrusion molding according to the above [1], wherein the ratio of the content of polyethylene terephthalate to that of polybutylene terephthalate (PET / PBT) is 55 / 45 or more and 95 / 5 or less by mass ratio. [3] The polyester film for extrusion molding according to [1] or [2] above, having a puncture strength of 480 N / mm or more. [4] The polyester film for extrusion molding according to any one of the above [1] to [3], which has a displacement of 4 mm or more when pierced. [5] The polyester film for extrusion molding according to any one of the above [1] to [4], which has a puncture strength variation of 0.036 or less. [6] The polyester film for extrusion molding according to any one of the above [1] to [5], wherein the variation in displacement upon piercing is 0.034 or less. [7] The polyester film for molding according to any one of the above [1] to [6], which has a degree of planar orientation of 100 or more and 200 or less. [8] A polyester film for molding according to any one of [1] to [7] above, in which, after heat treatment at 160°C for 15 minutes, the heat shrinkage rate in one of the longitudinal and transverse directions of the polyester film is less than 5%, and the heat shrinkage rate in the other direction is more than 2%. [9] The polyester film for extrusion molding according to any one of the above [1] to [8], which has a haze of 10% or less.

[10] The polyester film for extrusion molding according to any one of the above [1] to [9], which has a melting point (1st run) of 230°C or higher.

[11] The polyester film for extrusion molding according to any one of the above [1] to

[10] , wherein the intrinsic viscosity of the polyester film is 0.6 dL / g or more and 0.85 dL / g or less.

[12] The polyester film for extrusion molding according to any one of the above [1] to

[11] , which is a biaxially stretched polyester film.

[13] A method for producing the shaping polyester film according to any one of [1] to

[12] above, Stretching in the machine direction and the transverse direction, A method for producing a formable polyester film, in which the preheating temperature during transverse stretching is 60°C or higher and 90°C or lower, and the stretching temperature is 70°C or higher and 120°C or lower.

[14] The method for producing a shaped polyester film according to the above

[13] , wherein the heat setting temperature after the stretching is 190°C or higher.

[15] A method for producing a moldable polyester film according to the above

[13] or

[14] , wherein the ratio of the transverse stretching ratio to the longitudinal stretching ratio (TD / MD) is 1 or more and 1.7 or less.

[16] The method for producing a moldable polyester film according to any one of the above

[13] to

[15] , wherein the stretching temperature during longitudinal stretching is 50°C or higher and 85°C or lower.

[17] The method for producing a moldable polyester film according to any one of the above

[13] to

[16] , wherein the longitudinal stretching ratio is 2.5 times or more and 4.5 times or less.

[18] The method for producing a moldable polyester film according to any one of the above

[13] to

[17] , wherein the transverse stretching ratio is 3.5 times or more and 5.5 times or less.

[19] A laminate comprising the polyester film for extrusion molding according to any one of the above [1] to

[12] and at least one of a resin layer and a metal layer.

[20] An exterior packaging material comprising the polyester film according to any one of [1] to

[12] above or the laminate according to

[19] above.

[21] The packaging material according to

[20] above, which is a packaging material for a battery.

[22] A battery comprising the packaging material according to

[20] or

[21] above. [Effects of the Invention]

[0012] According to the present invention, a polyester film for extrusion molding having good puncture resistance can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Polyester film for extrusion molding] The shaping polyester film of the present invention (hereinafter sometimes simply referred to as "the polyester film") contains polybutylene terephthalate (hereinafter sometimes referred to as "PBT") and polyethylene terephthalate (hereinafter sometimes referred to as "PET").

[0014] (PBT) The PBT constituting the polyester film is a polycondensate of a dicarboxylic acid component and a diol component, and is a polyester containing terephthalic acid as the dicarboxylic acid component and 1,4-butanediol as the diol component. PBT is primarily composed of terephthalic acid and 1,4-butanediol, and preferably contains 50 mol% or more of terephthalic acid as the dicarboxylic acid component and 50 mol% or more of 1,4-butanediol (BDO) as the diol component. The proportion of terephthalic acid in the dicarboxylic acid component of PBT is more preferably 70 mol% or more, even more preferably 90 mol% or more, and most preferably 100 mol%. Also, the proportion of 1,4-butanediol in the diol component of PBT is more preferably 70 mol% or more, even more preferably 90 mol% or more, and most preferably 100 mol%. Therefore, homo-PBT is most preferred as PBT. By increasing the proportion of terephthalic acid and BDO in PBT, the crystallinity of the polyester film is increased, and the degree of planar orientation is easily increased.

[0015] In PBT, the dicarboxylic acid other than terephthalic acid is not particularly limited, and examples thereof include aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 4,4'-benzophenonedicarboxylic acid, 4,4'-diphenoxyethanedicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid, alicyclic dicarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid, and aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. These dicarboxylic acid components other than terephthalic acid may be used alone or in combination of two or more.

[0016] In the present invention, the diol component other than BDO is not particularly limited, and examples thereof include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, and dibutylene glycol; alicyclic diols such as 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,1-cyclohexanedimethylol, and 1,4-cyclohexanedimethylol; and aromatic diols such as xylylene glycol, 4,4'-dihydroxybiphenyl, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone. These diol components other than BDO may be used alone or in combination of two or more.

[0017] Furthermore, in PBT, one or more of the following copolymerization components can be used: hydroxycarboxylic acids such as lactic acid, glycolic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, 6-hydroxy-2-naphthalenecarboxylic acid, and p-β-hydroxyethoxybenzoic acid; monofunctional components such as alkoxycarboxylic acids, stearyl alcohol, benzyl alcohol, stearic acid, benzoic acid, t-butylbenzoic acid, and benzoylbenzoic acid; and trifunctional or higher polyfunctional components such as tricarballylic acid, trimellitic acid, trimesic acid, pyromellitic acid, gallic acid, trimethylolethane, trimethylolpropane, glycerol, and pentaerythritol.

[0018] The intrinsic viscosity of PBT is not particularly limited, but is preferably 0.7 dL / g to 1.4 dL / g, more preferably 0.73 dL / g to 1.37 dL / g, even more preferably 0.77 dL / g to 1.33 dL / g, and even more preferably 0.8 dL / g to 1.3 dL / g. Setting the intrinsic viscosity of PBT within the above range facilitates improving the heat resistance, productivity, and film-forming properties of the polyester film. The intrinsic viscosity of PBT can be appropriately set within the above range, and may be, for example, but not limited to, 0.8 dL / g to 1.2 dL / g, 0.8 dL / g to 1.1 dL / g, or 0.8 dL / g to 1 dL / g.

[0019] When two or more types of PBT or the like with different intrinsic viscosities are used, the intrinsic viscosity refers to the intrinsic viscosity of the mixed polyester. The intrinsic viscosity can be measured by a conventional method, for example, using an Uperohde viscometer with a phenol:tetrachloroethane=1:1 solvent at 30°C.

[0020] (PET) The PET constituting this film is a polycondensate of a dicarboxylic acid component and a diol component, and is a polyester containing terephthalic acid as the dicarboxylic acid component and ethylene glycol as the diol component. PET is primarily composed of terephthalic acid and ethylene glycol, and preferably contains 50 mol% or more of terephthalic acid as the dicarboxylic acid component and 50 mol% or more of ethylene glycol as the diol component. The proportion of terephthalic acid in the dicarboxylic acid component of PET is more preferably 70 mol% or more, even more preferably 90 mol% or more, and most preferably 100 mol%. The proportion of ethylene glycol in the diol component is more preferably 70 mol% or more, even more preferably 90 mol% or more, and most preferably 100 mol%. Therefore, homo-PET is the most preferred PET. Increasing the proportion of terephthalic acid and ethylene glycol in PET increases the crystallinity of the polyester film, making it easier to increase the degree of planar orientation, etc. It also makes it easier to impart a certain level of mechanical strength, making it easier to increase puncture resistance, Martens hardness, indentation hardness, elastic deformation power, etc.

[0021] In PET, there are no particular limitations on the dicarboxylic acid other than terephthalic acid, and examples of dicarboxylic acids other than terephthalic acid are as listed for PBT above. In PET, the dicarboxylic acid other than terephthalic acid may be used alone or in combination of two or more. In addition, there are no particular limitations on the diol component other than ethylene glycol, and specific examples include 1,4-butanediol and the diols other than ethylene glycol listed for PBT above. Furthermore, in PET, one or more of hydroxycarboxylic acids, monofunctional components, trifunctional or higher polyfunctional components, etc. may be used as copolymer components, and specific examples of these are as described for PBT.

[0022] The intrinsic viscosity of PET is not particularly limited, but is preferably 0.5 dL / g to 1 dL / g, more preferably 0.53 dL / g to 0.96 dL / g, even more preferably 0.57 dL / g to 0.93 dL / g, and even more preferably 0.6 dL / g to 0.9 dL / g. Setting the intrinsic viscosity of PET within the above ranges facilitates improving the heat resistance, productivity, and film-forming properties of the polyester film. The intrinsic viscosity of PET can be appropriately set within the above ranges, and may be, for example, but not limited to, 0.6 dL / g to 0.8 dL / g or 0.6 dL / g to 0.75 dL / g.

[0023] (mass ratio of PBT to PET) In the present polyester film, the ratio of the polyethylene terephthalate content to the polybutylene terephthalate content (PET / PBT) is preferably 55 / 45 or more and 95 / 5 or less by mass. By setting the mass ratio at 55 / 45 or more, the mechanical strength of the present polyester film is increased, and the puncture resistance is further improved. Furthermore, the heat resistance is also easily improved. Furthermore, by setting the mass ratio at 95 / 5 or less, it is easy to ensure elongation and to increase the amount of displacement during puncture, as described below. The mass ratio is more preferably 60 / 40 or more, even more preferably 63 / 37 or more, even more preferably 65 / 35 or more, and particularly preferably 72 / 28 or more, and is more preferably 90 / 10 or less, even more preferably 85 / 15 or less, and even more preferably 82 / 18 or less.

[0024] The polyester film may contain a resin other than the above-mentioned PET and PBT, provided that the effects of the present invention are not impaired. Examples of the resin other than the above-mentioned PET and PBT include polyester resins other than PET and PBT and resins other than polyester resins. Examples of resins other than polyester resins include polystyrene-based resins, polyvinyl chloride-based resins, polyvinylidene chloride-based resins, chlorinated polyethylene-based resins, polycarbonate-based resins, polyamide-based resins, polyacetal-based resins, acrylic-based resins, ethylene-vinyl acetate copolymers, polymethylpentene-based resins, polyvinyl alcohol-based resins, cyclic olefin-based resins, polylactic acid-based resins, polybutylene succinate-based resins, polyacrylonitrile-based resins, polyethylene oxide-based resins, cellulose-based resins, polyimide-based resins, polyurethane-based resins, polyphenylene sulfide-based resins, polyphenylene ether-based resins, polyvinyl acetal-based resins, polybutadiene-based resins, polybutene-based resins, polyamide-imide-based resins, polyamide bismaleimide-based resins, polyetherimide-based resins, polyether ether ketone-based resins, polyether ketone-based resins, polyethersulfone-based resins, polyketone-based resins, polysulfone-based resins, aramid-based resins, and fluorine-based resins.

[0025] In the present polyester film, PBT and PET are preferably the main components, and specifically, the total amount of PBT and PET is preferably 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the total amount of the present polyester film. There is no particular upper limit to the total amount of PBT and PET, as long as it is 100% by mass or less, but from the viewpoint of blending additives, etc., it is preferable that the total amount is less than 100% by mass based on the total amount of the present polyester film.

[0026] The thickness of the polyester film is not particularly limited as long as it can be formed into a film, but is, for example, in the range of 6 μm to 90 μm, preferably 8 μm to 70 μm, more preferably 9 μm to 50 μm, and even more preferably 10 μm to 40 μm. The polyester film is preferably a biaxially stretched polyester film. By using a biaxially stretched polyester film, it becomes easier to achieve a certain degree of planar orientation, as described below, and it also becomes easier to adjust |Δnv−Δnp| within a desired range.

[0027] The polyester film may have a single layer structure (single layer film) or a multilayer structure (multilayer film) having two or more layers. In the case of a multilayer structure, it may have a surface layer and a core layer. The surface layer is a layer that constitutes one surface of the polyester film, and the core layer is a layer that is disposed inside the surface layer. The polyester film may have a surface layer that constitutes the other surface of the polyester film, in addition to the surface layer and core layer that constitute one surface. In the case of a multilayer structure, the polyester film may have a two-layer structure of surface layer / core layer, a three-layer structure of surface layer / core layer / surface layer, or a layer structure of four or more layers, but preferably has a three-layer structure of surface layer / core layer / surface layer. In a layer structure of four or more layers, it is preferable that the core layer has two or more layers.

[0028] In the case of a multilayer structure, each layer may contain PET and PBT, and the ratio of PET to PBT in each layer may be as described above. Furthermore, the ratio of PET to PBT in some of the layers may be as described above, or the ratio of PET to PBT in all of the layers may be as described above. Furthermore, the ratio of PET to PBT in the entire multilayer structure may be as described above. Furthermore, each layer may contain a resin other than PET and PBT as described above, and the total content of PET and PBT in each layer may be as described above based on each layer, instead of the total content based on the polyester film.

[0029] However, as will be described later, for example, the core layer may contain PET and PBT, while the surface layer may contain PET but not PBT. Furthermore, in the case of a multilayer structure, the material composition (e.g., resin composition) constituting one surface layer may be different from the material composition constituting at least one of the other layers, for example, the material composition constituting the surface layer may be different from the material composition constituting the core layer. Specifically, the contents of PET and PBT in each layer may be adjusted so that the contents at the surface and the central part in the thickness direction of the film are as shown in a preferred embodiment described below. Furthermore, for example, it is preferable that the PET content in at least one surface layer is greater than the PBT content in at least one of the other layers, based on the content ratio, and in particular, it is preferable that the PET content in at least one surface layer (hereinafter, content (A1)) is greater than the PET content (A2) in the core layer. "Different material compositions" means that the material compositions are not the same or are not substantially the same. "Not substantially the same" means that when comparing the components that make up each material, the difference in the content of each component exceeds ±1% by mass, and / or, if different components are contained, the total content of the different components is 2% by mass or more of the entire material.

[0030] The thickness of the surface layer is preferably smaller than that of the core layer. The thickness of each surface layer is preferably 1% to 20% of the total thickness of the polyester film, more preferably 2% to 15%, and even more preferably 4% to 12%. When the thickness of the surface layer is within this range, if the surface layer contains particles as described below, the particles can impart lubricity without impairing transparency, and problems such as particle shedding are less likely to occur. From the same viewpoint, the thickness of each surface layer is preferably 0.2 μm or more and 10 μm or less, more preferably 0.4 μm or more and 7.5 μm or less, even more preferably 0.8 μm or more and 6 μm or less, and even more preferably 1 μm or more and 4 μm or less.

[0031] The core layer is preferably a layer that constitutes the central portion of the polyester film in the thickness direction, and the thickness of the core layer is preferably 65% ​​to 98% of the total thickness of the polyester film, more preferably 70% to 96%, and even more preferably 75% to 94%. The thickness of the core layer is preferably 7 μm or more and 88 μm or less, more preferably 10 μm or more and 70 μm or less, and even more preferably 15 μm or more and 55 μm or less. The thickness ratio of each surface layer to the core layer is, for example, 1 / 99 to 40 / 60, preferably 2 / 98 to 35 / 65, more preferably 4 / 96 to 30 / 70, and even more preferably 6 / 94 to 25 / 75. Furthermore, when the polyester film has a three-layer structure of a surface layer, a core layer, and a surface layer, the thickness ratio (thickness of the surface layer:thickness of the core layer:thickness of the surface layer) is preferably 1-20:65-98:1-20, more preferably 2-15:70-96:2-15, and even more preferably 3-12.5:75-94:3-12.5. The thickness of the core layer referred to here is the total thickness of the core layers when there are two or more core layers.

[0032] [Content of each resin on the film surface and center] A preferred embodiment of the content of each resin on the film surface and in the central region is described below. In a preferred embodiment, the PET content (hereinafter also referred to as "content (A1)") on at least one surface of the polyester film is greater than the PET content (hereinafter also referred to as "content (A2)") in the central region of the film thickness, based on a mass ratio. When the polyester film contains both PBT and PET and the PET content (A1) on the surface is increased, the puncture strength, Martens hardness, indentation hardness, etc. are increased, resulting in excellent pinhole resistance and resistance to fracture when subjected to external force. When used as a battery exterior material, the battery is less likely to break even if damaged due to an accident or other reasons. Furthermore, the high Martens hardness and indentation hardness reduce swelling of the battery when heated, preventing contact with the battery casing, for example, beyond the battery exterior material. Furthermore, when the polyester film contains both PBT and PET and the PET content (A1) on the surface is greater than the content (A2), the elastic deformation power can also be increased. A high value of the elastic deformation power means that a molded article can easily return to its original shape even if it is deformed. This makes it easier for the molded article to maintain its shape during molding, resulting in molded articles with excellent design and shape recovery, and reducing molding defects. Furthermore, even when an external force such as a puncture is applied, the molded article can easily return to its original shape when the external force is released, more effectively suppressing deformation of the molded article. The present polyester film may have a PET content (A1) on one surface that is greater than the PET content (A2) in the center of the film, but it is preferable that the PET content (A1) on both surfaces be greater than the PET content (A2).

[0033] In a preferred embodiment, the PET content (A1) on at least one surface of the polyester film is, for example, 70% by mass or more, preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 89% by mass or more, and even more preferably 92% by mass or more. The PET content (A1) may be 100% by mass or less. However, when PBT is incorporated into one surface, for example, it is preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 97% by mass or less. The PET content (A1) on the surface with a higher PET content than the above-mentioned content (A2) may be at least the lower limit and at most the upper limit as described above. However, it is preferred that the PET content (A1) on both surfaces be at least the lower limit and at most the upper limit as described above. In a preferred embodiment, the PET content (A2) in the central portion of the polyester film in the thickness direction may be, for example, 50% by mass or more, but is preferably 55% by mass or more, more preferably 60% by mass or more, even more preferably 63% by mass or more, still more preferably 65% ​​by mass or more, and particularly preferably 72% by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, and still more preferably 82% by mass or less.

[0034] In a preferred embodiment, the PET content (A1) on at least one surface is greater than the PET content (A2) in the central region, but the difference (A1-A2) between the PET content (A1) and the PET content (A2) is preferably within a certain range, specifically, 3% to 35% by mass. By maintaining this difference within a certain range, the mechanical strength of the polyester film is improved, and the puncture resistance, Martens hardness, indentation hardness, and elastic deformation power are likely to be further improved. The difference (A1-A2) is more preferably 5% by mass or more, even more preferably 8% by mass or more, even more preferably 10% by mass or more, and more preferably 30% by mass or less, even more preferably 25% by mass or less, and even more preferably 22% by mass or less.

[0035] In a preferred embodiment, the ratio (B1 / A1) of the PBT content (B1) to the PET content (A1) on at least one surface of the polyester film is preferably 20 / 80 or less, more preferably 15 / 85 or less, even more preferably 10 / 90 or less, and even more preferably 8 / 92 or less, by mass. By keeping the content ratio (B1 / A1) at or below the above-mentioned certain value, the Martens hardness, indentation hardness, elastic deformation power, etc. can be easily increased. The polyester film may not contain PBT on at least one surface, and therefore the content ratio (B1 / A1) may be 0 / 100 or more. However, the polyester film may contain PBT on at least one surface, and in that case, the content ratio (B1 / A1) is preferably 1 / 99 or more, more preferably 2 / 98 or more, and even more preferably 3 / 97 or more, by mass. The content ratio (B1 / A1) may be equal to or less than the upper limit value and equal to or more than the lower limit value on the surface where the content (A1) is greater than the content (A2), but it is preferable that the content ratio (B1 / A1) on both surfaces is equal to or less than the upper limit value and equal to or more than the lower limit value.

[0036] In a preferred embodiment, the polyester film has a mass ratio (B2 / A2) of the PBT content (B2) to the PET content (A2) at the center of the film thickness direction, of 5 / 95 or more and 45 / 55 or less. A mass ratio of 45 / 55 or less enhances the mechanical strength of the polyester film, making it easier to improve pinhole resistance, breaking strength, and other properties, and also to improve heat resistance. Furthermore, a mass ratio of 5 / 95 or more improves elongation and shape recovery, among other properties. The ratio (B2 / A2) is more preferably 40 / 60 or less, even more preferably 35 / 65 or less, even more preferably 30 / 70 or less, and is more preferably 10 / 90 or more, even more preferably 15 / 85 or more, and even more preferably 18 / 82 or more.

[0037] In this specification, the PET content (A1) and the PBT content (B1) on one surface refer to the PET and PBT contents in the surface layer of a multilayer film. However, in the present polyester film, even within the same layer, as in the monolayer film having a concentration gradient described below, the blending may vary along the thickness direction near the surface, resulting in changes in the PET content and PBT content. When the PET content varies near the surface in this way, the PET content and PBT content in the region from the film surface to 5% of the total thickness may be taken as the content (A1) and the content (B1), respectively. Furthermore, the PET content (A2) and PBT content (B2) in the central portion in the thickness direction may be the PET content and PBT content, respectively, in the core layer of a multilayer film. However, when the PET content and PBT content in the core layer or the central portion in the thickness direction of the film vary in the thickness direction, such as when the composition of the core layer in a multilayer film varies in the thickness direction or when the composition of a monolayer film varies in the thickness direction, the PET content (A2) and PBT content (B2) are defined as the PET content and PBT content, respectively, in a region of 10% of the total thickness centered on the center in the thickness direction of the film.

[0038] When the present film is, for example, a monolayer film, the PET and PBT may have a concentration gradient in the thickness direction, and by providing a concentration gradient, the PET contents (A1), (A2) and the PBT contents (B1), (B2) may be adjusted to fall within the ranges specified in the above preferred embodiment. Specifically, the PET content may have a concentration gradient that decreases from one surface of the film toward the center in the thickness direction. Preferably, the PET content decreases from one surface of the film toward the center in the thickness direction, and then increases again toward the other surface. That is, it is sufficient for the PET content to have a region with a high content (first region) and a region with a low content (second region) from one surface to the other, but it is preferable for the region with a high content (first region), a region with a low content (second region), and a region with a high content (first region) to be provided in this order. On the other hand, the PBT content may have a concentration gradient that increases from one surface of the film toward the center in the thickness direction. It is also preferable that the PBT content increases from one surface toward the center of the film, and then increases again toward the other surface. That is, for PBT, a region with a low content (first region) and a region with a high content (second region) may be provided from one surface toward the other, but it is preferable that the region with a low content (first region), a region with a high content (second region), and a region with a low content (first region) are provided in this order. It should be noted that the low PBT content region is a concept that also encompasses regions that do not contain PBT.

[0039] (particle) The polyester film may contain particles. The inclusion of particles in the polyester film can impart properties such as easy slippage and improve the film's handleability. Examples of particles include, but are not limited to, inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, and titanium oxide; crosslinked polymers such as crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, and crosslinked polyester particles; and organic particles such as calcium oxalate and ion exchange resins. Among these, silica and aluminum oxide are preferred, with silica being more preferred.

[0040] Considering both the transparency and ease of handling of the film, the average particle size of the particles is usually in the range of 0.05 μm to 10 μm, preferably 0.1 μm to 6 μm, more preferably 0.3 μm to 5 μm, and even more preferably 0.6 μm to 4.5 μm. The average particle size of the particles is the particle size at an integrated volume fraction of 50% (d50) in the equivalent sphericity distribution measured using a centrifugal sedimentation particle size distribution analyzer.

[0041] The particles may be contained throughout the entire polyester film, but are preferably contained on at least one surface of the polyester film. Therefore, in the multilayer structure described above, it is sufficient to contain particles in at least one surface layer, but when the film has surface layers on both sides, it is more preferable to contain particles in both surface layers. The particle content is not particularly limited, but is usually less than 5% by mass, preferably 0.0003% to 3% by mass, more preferably 0.001% to 2.5% by mass, and even more preferably 0.01% to 1% by mass. When particles are not contained or when the particle content is low, the film has excellent transparency. On the other hand, when particles are contained within the above range, the slipperiness can be improved and the handling can be improved. Even when particles are contained, the transparency of the film can be sufficiently ensured as long as the particle content is less than 5% by mass. The particle content should be within the above range at least in a region from the surface of the film to a depth of 1 μm in the thickness direction. When the film has a multilayer structure, the particle content in the surface layer should be within the above range. When the film has a single-layer structure, the particle content relative to the entire film should be within the above range. Furthermore, when the film has a multilayer structure, the particle content relative to the entire film is preferably 0.0001% by mass or more and 2% by mass or less, more preferably 0.0005% by mass or more and 1.5% by mass or less, even more preferably 0.001% by mass or more and 1% by mass or less, and even more preferably 0.005% by mass or more and 0.7% by mass or less. When particles are present on the surface of the present polyester film, the amount of particles present is not particularly limited, but is preferably about 3 mg / m 2More preferably, 4 mg / m 2 More than 15mg / m 2 or less, more preferably 5 mg / m 2 More than 14mg / m 2 The particles present on the surface of the polyester film may be particles exuded from the resin constituting the polyester film, or particles coated on the surface of the polyester film.

[0042] In addition to the above-mentioned particles, the polyester film may contain conventionally known antioxidants, ultraviolet absorbers, antistatic agents, heat stabilizers, lubricants, colorants such as dyes and pigments, etc., as needed.

[0043] One or both surfaces of the present polyester film may be appropriately surface-treated. The surface treatment may be a known modification treatment performed on the surface of a resin film, such as a corona treatment or a plasma treatment. The functional layer described below may be formed on the surface of the present polyester film that has been surface-treated, or on the surface of the present polyester film that has not been surface-treated. However, the surface treatment is preferably performed on the surface on which the functional layer is not to be formed. For example, it is also preferable that the present polyester film has a functional layer on one surface and a corona-treated surface on the other surface on which no functional layer is to be formed.

[0044] <Functional layer> The polyester film may have a functional layer such as an easy-adhesion layer, a release layer, an antistatic layer, a coating layer such as an antiblocking layer, a hard coat layer, an inorganic vapor deposition layer, or a printed layer on at least one surface, as long as the effects of the present invention are not impaired. Among these, a coating layer is preferred, and an easy-adhesion layer is more preferred. The easy-adhesion layer is a layer provided to adhere other layers or films to the polyester film, and is preferably formed from a resin such as a polyurethane resin, a vinyl resin, a polyamide resin, a polyester resin, an acrylic resin, or a polyvinyl acetal resin. The resin in the easy-adhesion layer may be appropriately blended with additives such as various crosslinking agents and particles. When the polyester film has a functional layer such as functional layer X, the various physical properties of the polyester film described below can be determined by measuring the polyester film having the functional layer.

[0045] The functional layer has a mass per unit area of ​​1 mg / m 2 More than 1000mg / m 2 When the mass per unit area is within the above range, the functional layer does not become thicker than necessary, and when it is made into the functional layer X described below, the surface free energy and / or the water droplet contact angle can be easily adjusted to the desired values. The mass per unit area of ​​the functional layer is 5 mg / m 2 More than 500mg / m 2 Less than 10 mg / m is more preferable. 2 More than 300mg / m 2 More preferably, 15 mg / m 2 More than 150mg / m 2 Even more preferred are the following: The mass per unit area of ​​the functional layer can be determined from the amount of nonvolatile components applied when forming the resin composition for forming the functional layer, and when drying and stretching are performed, it is the mass per unit area of ​​the functional layer after drying and stretching. Furthermore, when functional layers are provided on both sides of the present film, the mass per unit area of ​​the functional layer is the mass per unit area of ​​the functional layer provided on each surface of the present film.

[0046] The thickness of the functional layer is, for example, 0.001 μm to 1 μm, preferably 0.005 μm to 0.5 μm, 0.01 μm to 0.4 μm, preferably 0.01 μm to 0.3 μm, and more preferably 0.01 μm to 0.2 μm. In order to improve the slip property, the above-mentioned particles or the like may be contained as necessary.

[0047] (Function layer X) In one embodiment of the present invention, the functional layer preferably has a surface free energy of 49 mN / m or less or a water droplet contact angle of 63° or more. For example, during extrusion molding to form an exterior material such as a pouch, polyester films can have insufficient releasability from a mold such as a die, resulting in deformation of the molded product (battery exterior material) obtained upon release, and thickness unevenness. When the surface free energy of the functional layer is below a certain value or the water droplet contact angle is above a certain value, the coefficient of friction (dynamic friction coefficient and static friction coefficient) is reduced. Therefore, when the polyester film is placed in a mold such as a die, the film slides appropriately, making it easier to follow the mold. Furthermore, uniform pressure is easily applied during extrusion molding, making it easier for the entire film to stretch uniformly. This reduces deformation of the molded product and makes it easier to obtain molded products with minimal thickness variation.

[0048] A functional layer having the above-described surface free energy and / or water droplet contact angle is generally also called a release layer. Note that, hereinafter, the functional layer having the above-described surface free energy and / or water droplet contact angle will be referred to as functional layer X. From the viewpoint of reliably reducing the coefficient of friction, it is more preferable that the surface of the functional layer X has a surface free energy of 49 mN / m or less and a water droplet contact angle of 63° or more.

[0049] From the viewpoint of reducing the coefficient of friction, the surface free energy of the surface of the functional layer X is more preferably 40 mN / m or less, even more preferably 30 mN / m or less, and even more preferably 27 mN / m or less. In addition, the surface free energy of the surface of the functional layer X is not particularly limited in terms of its lower limit, but from the viewpoint of ease of obtaining it by adjusting the composition of the functional layer X, it is, for example, 5 mN / m or more, preferably 10 mN / m or more, more preferably 15 mN / m or more. Furthermore, from the viewpoint of reducing the coefficient of friction, the water droplet contact angle on the surface of the functional layer X is more preferably 75° or more, even more preferably 90° or more, and even more preferably 100° or more. Furthermore, the upper limit of the surface free energy of the surface of the functional layer X is not particularly limited and is, for example, 140° or less, but from the viewpoint of ease of obtaining it by adjusting the composition of the functional layer X, it is preferably 130° or less, more preferably 120° or less.

[0050] In the present invention, the water droplet contact angle and surface free energy are measured as follows. [Method for measuring water droplet contact angle] The contact angle is measured using a contact angle meter when 1 μL of pure water is dropped onto the surface of the functional layer of a film that has been conditioned for at least 24 hours in an environment of 23°C and 50% RH. The contact angle is measured 60 seconds after the drop onto the film. For example, a contact angle meter (DMo-501 model) manufactured by Kyowa Interface Science Co., Ltd. may be used.

[0051] [Method for measuring surface free energy] Using a contact angle meter, 1 μL of pure water and methylene iodide are dropped onto the functional layer surface of a film that has been conditioned for at least 24 hours at 23°C and 50% RH. The contact angle is measured 60 seconds after each liquid is dropped onto the film. For contact angle measurements, a Kyowa Interface Science contact angle meter (DMo-501 model) can be used. Using the obtained contact angles and the surface tension component values ​​for each liquid listed in Table 1 below, the surface free energy of the functional layer surface of the film is calculated using the Owens-Wendt-Rable-Kaelble (OWRK) theoretical formula.

[0052] [Table 1]

[0053] Surface free energy is composed of the sum of the components of intermolecular forces. Intermolecular forces are classified into dispersion forces, orientation forces, induction forces, and hydrogen bonding forces, which respectively make up the surface free energy as a dispersion component (Dispersion), polar component (Polar), induction component (Induction), and hydrogen bonding component (Hydrogen). Of these components, the induction component is very weak and can be ignored, and the hydrogen bonding component can be lumped together with the polar component.

[0054] In this specification, the surface free energy γ SV Each component (variance component γ SV d and polar component γ SV p ) is a value determined by the following measurement and calculation methods. LV1 , γ LV1 d and γ LV1 p The contact angle (θ1) between the first liquid and the surface to be measured is known, and the following γ LV2 , γ LV2 d and γ LV2 p The contact angle (θ2) between the second liquid, whose angle is known, and the surface to be measured is measured. Next, these values ​​are substituted into the following equations (I-1) and (I-2), and the surface free energy γ of the functional layer surface to be measured is calculated from the simultaneous equations (I-1) and (I-2) below. SV The variance component of γ SV d and the polar component γ SV p The units are mN / m.

[0055] (γ SV d γ LV1 d ) 1 / 2 +(γ SVp γ LV1 p ) 1 / 2 =γ LV1 (1+cosθ1) / 2 (I-1) (γ SV d γ LV2 d ) 1 / 2 +(γ SV p γ LV2 p ) 1 / 2 =γ LV2 (1+cosθ2) / 2 (I-2)

[0056] gamma SV d : Surface free energy γ of the surface to be measured SV Variance component of gamma SV p : Surface free energy γ of the surface to be measured SV Polar component of gamma LV1 : surface tension of the first liquid gamma LV2 : surface tension of the second liquid θ1: contact angle of the first liquid θ2: contact angle of the second liquid gamma LV1 d : Dispersion component of the surface tension of the first liquid gamma LV1 p : Polar component of the surface tension of the first liquid gamma LV2 d : the dispersive component of the surface tension of the second liquid gamma LV2 p : the polar component of the surface tension of the second liquid

[0057] The above formulas (I-1) and (I-2) are derived from the following Owens-Wendt-Rable-Kaelble (OWRK) theoretical formula and the following Young's formula. Theoretical formula of OWRK: gamma SL =γ SV +γLV -2(γ SV d γ LV d ) 1 / 2 -2(γ SV p γ LV p ) 1 / 2 Young's formula: gamma SV =γ SL +γ LV cosθ (where, γ SL is the interfacial tension between the surface being measured and the liquid.)

[0058] There are no particular limitations on the method for adjusting the surface free energy and water droplet contact angle of the surface of the functional layer X within the above ranges. For example, adjusting the composition and thickness of the functional layer X is effective. In adjusting the composition of the functional layer X, it is effective to appropriately adjust the types and content ratios of commonly used release agents, crosslinking agents, binder resins, etc. Selecting the type of release agent and crosslinking agent and adjusting their content ratios is particularly effective. Furthermore, the presence of hydrophilic groups that form weak bonds with water molecules, such as hydroxyl groups, carboxyl groups, amide groups, and thiol groups, tends to increase the surface free energy or decrease the water droplet contact angle. Therefore, appropriately adjusting the content ratio of such hydrophilic groups also makes it easier to adjust the surface free energy or water droplet contact angle within the desired range. Other methods include a method of adjusting by physically changing the surface microstructure, a method of adjusting by introducing functional groups onto the surface through physicochemical treatment such as heat, light, electromagnetic treatment, oxidation, reduction, etc., and a method of adjusting by chemical treatment using a surface treatment agent such as a surfactant, a coupling agent, etc.

[0059] When the functional layer X is provided, the functional layer X may be provided on one surface or both surfaces of the present polyester film, but from the viewpoint of more appropriately exerting the effect of providing the functional layer X, it is preferable that the functional layer X is provided on at least one surface where the content (A1) is higher than the content (A2). As described above, the surface of the polyester film having the functional layer X has a low coefficient of friction due to the surface free energy being below a certain value and / or the water droplet contact angle being above a certain value. The dynamic friction coefficient of the surface of the polyester film having the functional layer X is, for example, 0.3 or less, preferably 0.25 or less, more preferably 0.2 or less, and even more preferably 0.18 or less. The lower limit of the dynamic friction coefficient is not particularly limited, but may be 0.05, 0.08, or 0.1 to prevent the polyester film from slipping too much when placed in a mold or other form, thereby reducing the film's handleability. The static friction coefficient of the surface of the polyester film having the functional layer X is, for example, 0.32 or less, preferably 0.28 or less, more preferably 0.25 or less, and even more preferably 0.23 or less. The lower limit of the static friction coefficient is not particularly limited, but may be 0.05, 0.1, or 0.12 to prevent the polyester film from slipping too much when placed in a mold or other form, thereby reducing the film's handleability.

[0060] The static friction coefficient can be measured, for example, using a parallel displacement friction tester (MCS-300) manufactured by Yokohama Systems Research Institute under the following measurement conditions. A test piece measuring 15 x 160 mm is cut from this polyester film, and the static friction coefficient between one side of the test piece and the other side is measured. Specifically, one side of the test piece is held in contact with the other side for 15 seconds before the start of the test, and then measurement is performed in the machine direction (MD) under the following conditions. The sample is humidified for at least 6 hours before measurement. The static friction coefficient can then be measured under the following measurement conditions. The kinetic friction coefficient can also be measured in the same way as the static friction coefficient. Slider: Total mass 104g (contact area 12mm square) Test speed: 20mm / min ·Temperature: 23℃±2℃ Relative humidity: 50%±10% Test score: n=12, average of 10 points after dividing the maximum and minimum values

[0061] The functional layer X may contain a component used as a so-called release agent. Specific examples include long-chain alkyl group-containing compounds, waxes, fluorine compounds, silicone compounds, etc. These release agents may be used alone or in combination.

[0062] Among the above-mentioned release agents, compounds containing a long-chain alkyl group are preferred from the viewpoint of making it difficult for the release agent to transfer to a mold such as a die during molding, while easily adjusting the surface free energy and / or water droplet contact angle to the specified values ​​described above. Furthermore, it is preferable to use a compound having a long-chain alkyl group as the main component in the functional layer X. When the release agent contains a long-chain alkyl group, it has good compatibility with components other than the release agent in the functional layer, and can exhibit good release properties even with a small amount. Here, the main component refers to the component with the highest content among the release agents. Furthermore, in the functional layer X, in addition to the long-chain alkyl group-containing compound, wax, fluorine compounds, silicone compounds, etc. may also be used in combination as a release agent.

[0063] (Compounds with long-chain alkyl groups) A compound having a long-chain alkyl group refers to a compound having a linear or branched alkyl group having 4 or more carbon atoms. The alkyl group preferably has 9 or more carbon atoms, more preferably 12 or more carbon atoms, even more preferably 15 or more carbon atoms, and particularly preferably 18 or more carbon atoms. Increasing the number of carbon atoms in the alkyl group as described above can impart appropriate mold releasability to the functional layer X, lower the surface free energy of the functional layer X, and / or increase the water droplet contact angle. There is no particular upper limit on the number of carbon atoms in the alkyl group, and it is usually about 30, but preferably 25. Having the number of carbon atoms in the alkyl group of 25 or less is preferred from the viewpoint of solubility in a solvent when preparing a coating liquid, which will be described later. Examples of the linear or branched alkyl group having 4 or more carbon atoms include n-butyl, isobutyl, sec-butyl, t-butyl, pentyl, neopentyl, isoamyl, hexyl, heptyl, 2-ethylhexyl, octyl, isooctyl, nonyl, isononyl, decyl, isodecyl, undecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, stearyl, and various octadecyl groups such as isostearyl; and behenyl groups. Examples of compounds having a long-chain alkyl group include various long-chain alkyl group-containing polymer compounds, long-chain alkyl group-containing amine compounds, long-chain alkyl group-containing ether compounds, long-chain alkyl group-containing quaternary ammonium salts, etc. From the viewpoint of exhibiting good mold releasability, long-chain alkyl group-containing polymer compounds are preferred.

[0064] The long-chain alkyl group-containing polymer compound is preferably a polymer compound having a long-chain alkyl group on the side chain, and the method for producing the polymer compound is as follows: (1) A method of polymerizing a monomer having a long-chain alkyl group, or copolymerizing a monomer having a long-chain alkyl group with a monomer copolymerizable with said monomer; (2) A method of reacting a polymer having a reactive group with a compound having a long-chain alkyl group that can react with the reactive group. The compound having a long-chain alkyl group can be preferably produced by the above method (2).

[0065] In the above method (1), the monomer having a long-chain alkyl group is preferably a (meth)acrylic monomer, for example, a (meth)acrylic acid ester having an alkyl group having 4 to 30 carbon atoms is preferred. More specifically, examples thereof include (meth)acrylic acid esters such as isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-heptyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and various octadecyl (meth)acrylates such as isostearyl (meth)acrylate, and behenyl (meth)acrylate. In this case, as above, the number of carbon atoms in the alkyl group is preferably 9 or more, more preferably 12 or more, even more preferably 15 or more, and particularly preferably 18 or more. The long-chain alkyl group-containing polymer compound obtained by the above method (1) is preferably a (meth)acrylic acid ester (co)polymer, and the content of the structural unit derived from the monomer having the long-chain alkyl group is preferably in the range of 10% by mass to 100% by mass, more preferably in the range of 20% by mass to 80% by mass, and even more preferably in the range of 30% by mass to 60% by mass.

[0066] On the other hand, the monomer copolymerizable with the monomer having a long-chain alkyl group is not particularly limited, but (meth)acrylic monomers, vinyl group-containing monomers, and the like are preferred. Examples of the (meth)acrylic monomer include hydroxyl group-containing monomers such as hydroxyalkyl (meth)acrylates, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate; carboxy group-containing monomers such as (meth)acrylic acid, itaconic acid, carboxyethyl acrylate, mono(2-acryloyloxyethyl) succinate, ω-carboxy-dicarolactone monoacrylate, and monohydroxyethyl acrylate phthalate; and alkyl (meth)acrylates having less than 4 carbon atoms other than the compounds having the long-chain alkyl group, such as methyl (meth)acrylate, ethyl (meth)acrylate, and n-propyl (meth)acrylate. Examples of vinyl group-containing monomers include styrene, vinyl acetate, vinyl propionate, and divinylbenzene. Among these, the copolymerizable monomer preferably includes a monomer containing a functional group such as a hydroxyl group-containing monomer or a carboxy group-containing monomer, from the viewpoint of contributing to the reaction with the crosslinking agent described later, and more preferably includes a carboxy group-containing monomer such as (meth)acrylic acid. In this specification, (meth)acrylic means acrylic or methacrylic.

[0067] In the above method (2), examples of the reactive group of the polymer having a reactive group include a hydroxyl group, an amino group, a carboxy group, an acid anhydride, etc. Specific examples of the polymer having a reactive group include polyvinyl alcohol, polyethyleneimine, polyethyleneamine, a polyester resin containing a reactive group, a poly(meth)acrylic resin containing a reactive group, etc. Among these, from the viewpoints of releasability and ease of handling, polyvinyl alcohol and a poly(meth)acrylic resin containing a reactive group are preferred, and polyvinyl alcohol is more preferred.

[0068] In order to exhibit good water solubility of the long-chain alkyl group-containing compound, the reactive group may be neutralized. To neutralize the reactive group, a stabilizer may be used. For example, basic stabilizers include inorganic basic compounds such as calcium hydroxide, magnesium hydroxide, lithium hydroxide, potassium hydroxide, and sodium hydroxide, and amine compounds such as ammonia, trimethylamine, triethylamine, diethylamine, and dimethylaminoethanol. Among these, it is preferable to use inorganic basic compounds, and specifically, calcium hydroxide, magnesium hydroxide, and lithium hydroxide are preferred.

[0069] Examples of compounds having a long-chain alkyl group capable of reacting with the above-mentioned reactive group include long-chain alkyl group-containing isocyanates such as various octadecyl isocyanates such as octyl isocyanate, decyl isocyanate, lauryl isocyanate, isostearyl isocyanate, and stearyl isocyanate, and behenyl isocyanate; long-chain alkyl group-containing acid chlorides such as hexanoyl chloride, octanoyl chloride, decanoyl chloride, lauroyl chloride, octadecanoyl chloride, and behenoyl chloride; long-chain alkyl group-containing amines; long-chain alkyl group-containing alcohols, etc. Among these, from the viewpoints of mold releasability and ease of handling, long-chain alkyl group-containing isocyanates are preferred, and stearyl isocyanate is particularly preferred.

[0070] The number-average molecular weight (Mn) of the long-chain alkyl group-containing polymer compound obtained by the above methods (1) and (2) is preferably 1,000 to 100,000, more preferably 2,000 to 80,000. When these number-average molecular weights are equal to or greater than the lower limit, the low-molecular-weight components in the functional layer X can be reduced, allowing the long-chain alkyl group moiety to be efficiently localized on the surface of the functional layer, thereby achieving sufficient releasability. On the other hand, when the number-average molecular weight is equal to or less than the upper limit, the functional layer resin composition is easily dissolved in a solvent contained in a coating liquid, which is a preferred form of the functional layer resin composition, and is easily applied to a polyester film. The melting point of the long-chain alkyl group-containing compound is preferably 0°C or higher and 100°C or lower, more preferably 10°C or higher and 100°C or lower, and even more preferably 20°C or higher and 90°C or lower.

[0071] (wax) Examples of waxes include natural waxes, synthetic waxes, and waxes made by combining these. Natural waxes include vegetable waxes, animal waxes, mineral waxes, and petroleum waxes. Vegetable waxes include candelilla wax, carnauba wax, rice wax, Japan wax, and jojoba oil. Animal waxes include beeswax, lanolin, and spermaceti wax. Mineral waxes include montan wax, ozokerite, and ceresin. Petroleum waxes include paraffin wax, microcrystalline wax, and petrolatum.

[0072] Examples of synthetic waxes include synthetic hydrocarbons, modified waxes, hydrogenated waxes, fatty acids, fatty acid amides, amines, imides, ester waxes, and ketones. Synthetic hydrocarbons include Fischer-Tropsch wax (Sazol wax), polyethylene wax, oxidized polyethylene wax, oxidized polypropylene wax, etc. Also included are low molecular weight polymers (number average molecular weight 500-20,000), such as polypropylene, ethylene-acrylic acid copolymer, polyethylene glycol, polypropylene glycol, and block or graft conjugates of polyethylene glycol and polypropylene glycol. Examples of modified waxes include montan wax derivatives, paraffin wax derivatives, and microcrystalline wax derivatives. The derivatives herein refer to compounds obtained by any of the following treatments: purification, oxidation, esterification, and saponification, or a combination thereof. Hydrogenated waxes include hydrogenated castor oil and hydrogenated castor oil derivatives.

[0073] Among these waxes, synthetic waxes are preferred from the viewpoint of excellent release performance and easy availability, synthetic hydrocarbons are more preferred, and oxidized polyethylene wax and oxidized polypropylene wax are even more preferred. Note that, from the viewpoint of efficiently distributing the long-chain alkyl group moiety on the surface of the functional layer X by reducing the low molecular weight components in the functional layer X, the number average molecular weight (Mn) of the wax is preferably in the range of 1,000 to 100,000, and the weight average molecular weight (Mw) is preferably in the range of 2,000 to 80,000.

[0074] The melting point or softening point of the wax is preferably 80° C. or higher, more preferably 110° C. or higher, taking into consideration durability against heat treatment during use, and is preferably 200° C. or lower, more preferably 170° C. or lower, and even more preferably 150° C. or lower, from the viewpoint of controlling release performance after heat treatment. The melting point or softening point of the wax can be measured by a differential scanning calorimeter (DSC).

[0075] (Fluorine compounds) The fluorine compound may be any polymeric compound containing a fluorine atom in the molecule, such as a perfluoroalkyl group-containing polymeric compound, a polymer of an olefin compound containing a fluorine atom, etc. From the viewpoint of being able to exhibit releasability with a small content, a perfluoroalkyl group-containing polymeric compound is preferred. As the monomer for forming the perfluoroalkyl group-containing polymer compound, a perfluoroalkyl group-containing (meth)acrylate, a perfluoroalkyl group-containing vinyl ether, or the like is preferred.

[0076] Examples of perfluoroalkyl group-containing (meth)acrylates include perfluoroalkyl (meth)acrylate, perfluoroalkylmethyl (meth)acrylate, 2-perfluoroalkylethyl (meth)acrylate, 3-perfluoroalkylpropyl (meth)acrylate, 3-perfluoroalkyl-1-methylpropyl (meth)acrylate, and 3-perfluoroalkyl-2-propenyl (meth)acrylate. Examples of perfluoroalkyl group-containing vinyl ethers include perfluoroalkylmethyl vinyl ether, 2-perfluoroalkylethyl vinyl ether, 3-perfluoropropyl vinyl ether, 3-perfluoroalkyl-1-methylpropyl vinyl ether, and 3-perfluoroalkyl-2-propenyl vinyl ether. These may be polymerized singly or in combination of two or more. From the viewpoint of exhibiting releasability with a small content, the perfluoroalkyl group preferably has 3 to 11 carbon atoms. In addition, from the viewpoint of efficiently distributing the long-chain alkyl group portion on the surface of the functional layer X by reducing the low molecular weight components in the functional layer X, the number average molecular weight (Mn) of the fluorine compound (polymer compound) is preferably in the range of 1,000 or more and 100,000 or less, and the weight average molecular weight (Mw) is preferably in the range of 2,000 or more and 80,000 or less.

[0077] (silicone compounds) The silicone compound is a compound having a siloxane bond (—Si—O—) in the molecule, and examples thereof include silicone emulsion, acrylic-grafted silicone, silicone-grafted acrylic, amino-modified silicone, perfluoroalkyl-modified silicone, alkyl-modified silicone, etc. From the viewpoints of releasability, heat resistance, etc., curable silicone resins are preferred. The types of curable silicone resins include addition type, condensation type, ultraviolet curable type, and electron beam curable type, and any of the curable types can be used. In addition, from the viewpoint of efficiently distributing the long-chain alkyl group portion on the surface of the functional layer X by reducing the low molecular weight components in the functional layer X, the number average molecular weight (Mn) of the silicone compound is preferably in the range of 100 or more and 100,000 or less, and the weight average molecular weight (Mw) is preferably in the range of 200 or more and 80,000 or less.

[0078] (Crosslinking agent) The functional layer X, i.e., the resin composition for the functional layer described below, preferably further contains a crosslinking agent. Examples of crosslinking agents include melamine compounds, oxazoline compounds, epoxy compounds, isocyanate compounds, carbodiimide compounds, and silane coupling agents. Among these crosslinking agents, melamine compounds are preferred because they have high crosslink density and elastic modulus while providing good releasability. Therefore, the functional layer X, i.e., the resin composition for the functional layer described below, preferably contains a long-chain alkyl group-containing compound and a crosslinking agent, and more preferably contains a long-chain alkyl group-containing compound and a melamine compound.

[0079] The crosslinking agent reacts with a release agent such as a long-chain alkyl group-containing compound to improve the performance of the release layer. Therefore, it is preferable that the crosslinking agent reacts with the long-chain alkyl group-containing compound, which is the release agent, in the functional layer X. The use of a crosslinking agent effectively distributes the release agent, such as a long-chain alkyl group-containing compound, unevenly on the surface of the functional layer X, thereby making it easier to lower the surface free energy and increase the water droplet contact angle. However, it is believed that the crosslinking agent exists in the functional layer X in the form of both an unreacted compound and a reacted compound.

[0080] The melamine compound is a compound having a melamine skeleton within the compound. Examples of suitable melamine compounds include alkylolated melamine derivatives, compounds obtained by reacting alkylolated melamine derivatives with alcohols to partially or completely etherify them, and mixtures thereof. Suitable alcohols for etherification include methanol, ethanol, isopropyl alcohol, n-butanol, and isobutanol. The melamine compound may be a monomer or a dimer or higher polymer, or a mixture thereof. Furthermore, melamine may be partially co-condensed with urea or the like, and a catalyst may be used to increase the reactivity of the melamine compound.

[0081] Examples of alkylolation include methylolation, ethylolation, isopropylolation, n-butylolation, and isobutyrolation. Among these, methylolation is preferred from the viewpoint of reactivity. From the viewpoint of improving the coating film strength and improving the adhesion between the functional layer X and the polyester film, the melamine compound is preferably a partially etherified alkylolated melamine derivative, more preferably an alkylol etherified with methanol. Therefore, a more preferred form is a partially etherified melamine having a methylol group and a methoxy group. The amount of etherified alkylol groups relative to the amount of unetherified alkylol groups is preferably 0.5 to 5 equivalents, more preferably 0.7 to 3 equivalents, and even more preferably 1.2 to 2.8 equivalents. The melamine compound may be a monomer or a dimer or higher polymer, or a mixture thereof. Furthermore, melamine may be partially co-condensed with urea or the like, and a catalyst may be used to increase the reactivity of the melamine compound.

[0082] The oxazoline compound is a compound having an oxazoline group in the molecule, and a polymer containing an oxazoline group is particularly preferred. The polymer containing an oxazoline group can be synthesized by polymerizing an oxazoline group-containing monomer alone or with other monomers. Examples of the oxazoline group-containing monomer include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.

[0083] Epoxy compounds are compounds having an epoxy group in the molecule, and examples thereof include condensation products of epichlorohydrin with a hydroxyl group or an amino group of ethylene glycol, polyethylene glycol, glycerin, polyglycerin, bisphenol A, etc., polyepoxy compounds, diepoxy compounds, monoepoxy compounds, glycidylamine compounds, etc.

[0084] Examples of isocyanate compounds include tolylene diisocyanate compounds such as 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate; xylylene diisocyanate compounds such as 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate and tetramethylxylylene diisocyanate; aromatic isocyanate compounds such as 1,5-naphthalene diisocyanate and triphenylmethane triisocyanate; hexamethylene diisocyanate, isophorone diisocyanate, and adducts of these isocyanate compounds with polyol compounds such as trimethylolpropane; and biuret compounds and isocyanurates of these polyisocyanate compounds.

[0085] Examples of carbodiimide compounds include monocarbodiimide compounds such as dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, diphenylcarbodiimide, di-t-butylcarbodiimide, and di-β-naphthylcarbodiimide; and isocyanate-terminated polycarbodiimides obtained by condensation reaction of diisocyanate accompanied by decarbonation.

[0086] Examples of the silane coupling agent include γ-mercaptopropyltrimethoxysilane, γ-isocyanatepropyltriethoxysilane, γ-isocyanatepropyltrimethoxysilane, and N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine.

[0087] As described above, the functional layer X preferably contains a long-chain alkyl group-containing compound and a crosslinking agent. In this case, it is preferable that the content of the long-chain alkyl group-containing compound is 5% by mass or more and 95% by mass or less, and the content of the crosslinking agent is 5% by mass or more and 95% by mass or less, based on the total nonvolatile components of the functional layer X (the resin composition for the functional layer). When the content of the long-chain alkyl group-containing compound is 5% by mass or more, appropriate releasability can be imparted to the functional layer X, the surface free energy of the functional layer surface can be kept below a certain level, and the water droplet contact angle can be easily adjusted to a predetermined value or higher. When the content is 95% by mass or less, it becomes easier to incorporate appropriate amounts of components other than the long-chain alkyl group-containing compound, such as crosslinking agents, into the functional layer X. The content of the long-chain alkyl group-containing compound is more preferably 15% by mass or more and 80% by mass or less, even more preferably 30% by mass or more and 70% by mass or less, and even more preferably 40% by mass or more and 65% by mass or less. Furthermore, when the content of the crosslinking agent is 5% by mass or more, the crosslinking agent can appropriately crosslink the functional layer X, improving the performance of the functional layer X and making it easier to adjust the surface free energy and water droplet contact angle of the functional layer surface to desired values. Furthermore, when the content is 95% by mass or less, it is easier to incorporate appropriate amounts of components other than the crosslinking agent, such as long-chain alkyl group-containing compounds, into the functional layer X. The content of the crosslinking agent is more preferably 10% by mass or more and 80% by mass or less, even more preferably 20% by mass or more and 70% by mass or less, and even more preferably 30% by mass or more and 50% by mass or less.

[0088] The functional layer X, i.e., the resin composition for the functional layer, may contain components other than the release agent and the crosslinking agent, such as a binder resin. The binder resin makes it easier to impart film-forming properties to the functional layer X. The binder resin is not particularly limited, and conventionally known binder resins such as polyester resin, (meth)acrylic resin, polyurethane resin, polyvinyl resin (polyvinyl alcohol, vinyl chloride vinyl acetate copolymer, etc.), polyalkylene glycol, polyalkyleneimine, methyl cellulose, hydroxycellulose, starch, etc., can be used. Among them, from the viewpoint of film-forming properties and adhesion to polyester film, at least one selected from polyester resin, (meth)acrylic resin, and polyurethane resin is preferred. One type of binder resin may be used alone, or two or more types may be used in combination.

[0089] (additives) In addition to the above components, the functional layer X, i.e., the resin composition for the functional layer, may further contain particles and additives. The particles are added to improve blocking properties and slippage, and their type, shape, average particle size, and content are the same as those of the particles that may be incorporated into the polyester film described above. Examples of additives include antistatic agents, UV absorbers, antioxidants, antifoaming agents, lubricants, foaming agents, dyes, and pigments.

[0090] The functional layer X is formed on at least one side of the polyester film using a resin composition for the functional layer. The resin composition for the functional layer preferably contains a release agent such as a compound having a long-chain alkyl group, and further contains a crosslinking agent. The resin composition for the functional layer may further contain a binder resin, particles, other additives, and a solvent, as necessary. The resin composition for the functional layer is preferably in the form of a coating liquid containing a solvent. When used as a coating liquid, the solid content of the composition is preferably 0.1% by mass to 50% by mass, more preferably 0.5% by mass to 40% by mass, and even more preferably 1% by mass to 30% by mass.

[0091] The functional layer resin composition preferably contains a solvent to form a liquid coating solution, which is then applied to the surface of a polyester film, dried, and cured as necessary to form the functional layer X. In the coating solution, each component forming the functional layer X may be dissolved in the solvent or may be dispersed in the solvent. In addition, in the functional layer resin composition, the solvent is a volatile component. The solvent may be either water or an organic solvent, or a mixture of water and an organic solvent. Examples of the organic solvent include aromatic hydrocarbons such as toluene; aliphatic hydrocarbons such as hexane, heptane, and isooctane; esters such as ethyl acetate and butyl acetate; ketones such as ethyl methyl ketone and isobutyl methyl ketone; alcohols such as ethanol and 2-propanol; and ethers such as diisopropyl ether and dibutyl ether. The organic solvent may be used alone or in combination of two or more.

[0092] (Surface roughness (Ra)) The surface roughness (Ra) of the functional layer X is not particularly limited, but is, for example, 1 nm to 100 nm, preferably 5 nm to 50 nm, and more preferably 10 nm to 30 nm. When the surface roughness (Ra) of the surface of the functional layer X is within the above range, the polyester film has good sliding processability when placed in a mold or other form, and also has good sliding properties when unwinding the film for lamination with other films, etc., and the film tends to be easy to handle. Surface roughness (Ra) is the arithmetic mean roughness, one of the line roughness parameters (JIS B0601:1994), and represents the average difference in height from the average surface. That is, when a portion of reference length L is sampled and the average line of this sampled portion is represented as the x-axis and the direction of longitudinal magnification as the y-axis, and the roughness curve is expressed as y = Z(x), it can be calculated from the following formula.

number

[0093] <Orientation degree> This polyester film has an absolute value (|Δnv - Δnp|) of the difference between the transverse orientation degree (Δnv) and the longitudinal orientation degree (Δnp) of 57 or less. As described above, this polyester film contains PBT and PET, and by setting |Δnv - Δnp| to 57 or less, it can have excellent puncture resistance. Specifically, the variation in displacement and puncture strength upon puncture is small, and the elongation in the thickness direction is more uniform, making it more suitable for use as an exterior material. Although the principle is not clear, it is presumed that a lower |Δnv-Δnp| reduces the difference in crystallinity between the horizontal and vertical directions, suppressing the anisotropy of the film, thereby bringing out the advantages of both PET and PBT and achieving excellent puncture resistance. Specifically, when a puncture force from a needle or the like is applied to the film, the film stretches and deforms in the thickness direction as if it were being wrapped around the needle, and it is presumed that this degree of stretching of the film (the degree to which the film is wrapped around the needle) tends to be similar in both the vertical and horizontal directions of the film, reducing the variation in puncture displacement and puncture strength depending on the puncture position. In this way, by using a film with small variations in puncture displacement and puncture strength, it is possible to obtain a practical product with superior puncture resistance. From the viewpoint of puncture resistance, |Δnv−Δnp| is preferably 50 or less, more preferably 45 or less, and even more preferably 40 or less. Furthermore, |Δnv−Δnp| is not particularly limited as long as it is 0 or more, but in practice it is sufficient if it is 5 or more, preferably 10 or more, and more preferably 15 or more.

[0094] The polyester film preferably has a planar orientation degree (ΔP) of 100 or more, more preferably 120 or more, even more preferably 140 or more, and even more preferably 150 or more. When the polyester film has a planar orientation degree of a certain value or more, the crystallinity of the film is enhanced, and the puncture strength is easily increased. The planar orientation degree is not particularly limited, but is preferably 200 or less, more preferably 180 or less, and even more preferably 170 or less.

[0095] Furthermore, the present polyester film typically has a transverse orientation degree (Δnv) greater than a longitudinal orientation degree (Δnp). The transverse orientation degree (Δnv) is not particularly limited, but is, for example, 50 to 130, preferably 60 to 120, more preferably 70 to 110, and even more preferably 75 to 105. The longitudinal orientation degree (Δnp) is also not particularly limited, but is, for example, 20 to 100, preferably 30 to 90, more preferably 40 to 80, and even more preferably 45 to 70.

[0096] The |Δnv-Δnp|, transverse orientation (Δnv), longitudinal orientation (Δnp), and planar orientation (ΔP) of the present polyester film can be adjusted to the above ranges by adjusting the stretching ratio, stretching temperature, preheating temperature and time of the present polyester film, heat setting temperature and time, etc. during the process of producing the present polyester film.

[0097] The planar orientation degree (ΔP), longitudinal orientation degree (Δnp), and transverse orientation degree (Δnv) of the present polyester film can be determined as follows. The refractive index of the polyester film in the longitudinal direction (nx), transverse direction (ny), and thickness direction (nz) was measured using an Abbe refractometer with sodium D line as a light source according to JIS K 7142:2014 5.1 (Method A). The measurement results were applied to the following equations to calculate the degree of planar orientation (also called the planar orientation coefficient; ΔP), the degree of longitudinal orientation (also called the longitudinal plane orientation coefficient; Δnp), and the degree of transverse orientation (also called the transverse plane orientation coefficient; Δnv). ΔP=((nx+ny) / 2-nz)×1000 Δnp=(nx-(ny+nz) / 2)×1000 Δnv=(ny-(nx+nz) / 2)×1000

[0098] The machine direction (MD) of the film refers to the direction in which the film advances during the film manufacturing process, i.e., the winding direction of the film roll. The transverse direction (TD) of the film refers to the direction parallel to the film surface and perpendicular to the machine direction, i.e., the direction parallel to the central axis of the roll when the film is rolled.

[0099] <Puncture strength> The present polyester film preferably has a puncture strength of 480 N / mm or more. A puncture strength of 480 N / mm or more provides high puncture resistance, making it suitable for use as an exterior material, such as an exterior material for a battery. The puncture strength is more preferably 490 N / mm or more, even more preferably 500 N / mm or more, even more preferably 510 N / mm or more, even more preferably 520 N / mm or more, and even more preferably 530 N / mm or more. The puncture strength is not particularly limited, but is, for example, 1000 N / mm or less, preferably 800 N / mm, more preferably 700 N / mm or less, even more preferably 650 N / mm or less, even more preferably 590 N / mm or less, even more preferably 585 N / mm or less, even more preferably 580 N / mm or less, and even more preferably 575 N / mm or less. A puncture strength of less than the above upper limit facilitates the extensibility of the present polyester film to be improved. Furthermore, by setting the puncture strength to be equal to or less than the above upper limit, when the film is made into an actual product such as a battery exterior material by, for example, extrusion molding, the restoring force of the film trying to return to its original shape is kept low, and the shape retention of the actual product tends to be improved. For example, in the case of a battery exterior material, deformation of the exterior material due to post-processing such as heat fusion or heat generation from an electricity storage device element housed inside can be more effectively suppressed.

[0100] <Displacement when piercing> Furthermore, the present polyester film preferably has a displacement amount at the time of piercing of 4 mm or more. When the displacement amount at the time of piercing is 4 mm or more, the film has good extensibility, and is sufficiently stretched during shaping, making it easier to increase the molding depth, etc. The displacement amount at the time of piercing is more preferably 4.2 mm or more, and even more preferably 4.3 mm or more. The displacement amount at the time of piercing is not particularly limited, but may be, for example, 8 mm or less, 6 mm or less, or 5 mm or less.

[0101] <Variation in puncture strength> The present polyester film preferably has a coefficient of variation in puncture strength of 0.036 or less, more preferably 0.034 or less, even more preferably 0.032 or less, even more preferably 0.03 or less, even more preferably 0.028 or less, even more preferably 0.026 or less, even more preferably 0.024 or less, even more preferably 0.022 or less, and even more preferably 0.02 or less. A smaller coefficient of variation reduces the variation in puncture strength of the present polyester film, resulting in uniform elongation in the thickness direction, making it suitable for use as an exterior packaging material. The lower the coefficient of variation in puncture strength, the better, but for practical purposes, it is preferably 0.001 or more, more preferably 0.005 or more, and even more preferably 0.01 or more. The coefficient of variation of puncture strength indicates the variation in puncture strength and is calculated by dividing the standard deviation by the mean value. The mean value and standard deviation are the mean and standard deviation of measurements (puncture strength) at 12 points on a sample of this polyester film. The coefficient of variation of displacement upon puncture, which will be described later, indicates the variation in displacement upon puncture and can be calculated in the same way, except that the measured value is replaced by the displacement upon puncture.

[0102] <Variation in displacement during piercing> The present polyester film preferably has a coefficient of variation of displacement upon piercing of 0.034 or less, more preferably 0.03 or less, even more preferably 0.027 or less, even more preferably 0.025 or less, even more preferably 0.023 or less, even more preferably 0.021 or less, and even more preferably 0.019 or less. The reduced coefficient of variation of displacement upon piercing reduces the variation in displacement, resulting in uniform elongation in the thickness direction, making the film suitable for use as an exterior packaging material. Furthermore, the film tends to stretch uniformly during shaping, resulting in good formability. The lower the coefficient of variation of displacement upon piercing, the better, but for practical purposes, it is preferably 0.001 or more, more preferably 0.005 or more, and even more preferably 0.01 or more.

[0103] <Martens hardness> This polyester film has a Martens hardness of 132N / mm 2 It is preferable that the resistance is 135N / mm or more. 2 More preferably, it is 138N / mm 2 If the Martens hardness is at least a certain level, pinhole resistance, breaking strength, etc. tend to be high. The upper limit of the Martens hardness is not particularly limited, but may be, for example, 300 N / mm 2 may be 200N / mm 2 may be.

[0104] <Indentation hardness> This polyester film has an indentation hardness of 200N / mm 2 It is preferable that the resistance is 210N / mm or more. 2 More preferably, it is 215N / mm 2 If the indentation hardness is at least a certain level, pinhole resistance and breaking strength tend to be high. The upper limit of the indentation hardness is not particularly limited, but is, for example, 400 N / mm 2 may be 300N / mm 2 may be.

[0105] <Elastic deformation power> The elastic deformation power of the polyester film is preferably 42% or more, more preferably 43% or more, and even more preferably 44% or more. Having a certain level of elastic deformation power or higher makes it easier to obtain molded articles with excellent design and shape recovery. The upper limit of the elastic deformation power of the polyester film is not particularly limited, but may be, for example, 60%, 57%, 53%, or 50%.

[0106] The Martens hardness, indentation hardness, and elastic deformation power measured on at least one surface of the polyester film should be equal to or greater than the lower limit. Specifically, the values ​​measured on the surface of the polyester film where the PET content (A1) is greater than the PET content (A2) in the central portion of the film should be equal to or greater than the lower limit. However, it is preferable that the values ​​measured on both surfaces are equal to or greater than the lower limit. The Martens hardness, indentation hardness, and elastic deformation power can be measured by a load-unload test in which an indenter is pressed against the surface of the polyester film with a force of 20 mN using microhardness measurement. Specifically, they can be measured by the method described in the Examples below.

[0107] <Haze> The haze of the polyester film is preferably 10% or less, more preferably 8% or less, even more preferably 5% or less, and particularly preferably 3% or less. By setting the haze to the above lower limit or less, sufficient transparency is obtained. The haze is not particularly limited, and may be, for example, 0.01% or more, 0.1% or more, or 0.7% or more.

[0108] <Heat shrinkage rate> After heat treatment at 160°C for 15 minutes, the polyester film preferably has a heat shrinkage rate of less than 5% in either the longitudinal or transverse direction of the polyester film and a heat shrinkage rate of more than 2% in the other direction. When one of the heat shrinkage rates of the polyester film is less than 5%, the polyester film has excellent heat resistance. Therefore, when the polyester film is laminated onto other films by lamination, dimensional deformation is reduced, making it easier to laminate onto other films. Furthermore, when the polyester film is laminated onto other films to form a laminate, shrinkage stress is less likely to remain, and secondary processability is improved without shrinkage during secondary processing into battery exterior materials, etc. Furthermore, when the polyester film is used as a battery exterior material, deterioration of the exterior material is more likely to be prevented even if the battery radiates heat and the exterior material is heated. On the other hand, if the other heat shrinkage rate exceeds 2%, the film will shrink by a certain amount or more during thermal lamination, resulting in good adhesion to the metal layer or other films.

[0109] From the viewpoint of improving heat resistance, the one heat shrinkage rate is preferably 4.5% or less, more preferably 4% or less, even more preferably 3.5% or less, and even more preferably 3% or less. From the viewpoint of heat resistance, the lower the one heat shrinkage rate, the better, but from the viewpoint of improving adhesion to a metal layer or other films during thermal lamination, it is better that the one heat shrinkage rate is at least a certain value, for example, 0.1% or more, preferably 0.5% or more, more preferably 0.8% or more, even more preferably 1% or more, and even more preferably 1.3% or more. Furthermore, from the viewpoint of improving adhesion to a metal layer or other films, the heat shrinkage rate of the other film is preferably 2.3% or more, more preferably 2.5% or more, even more preferably 3% or more, even more preferably 3.5% or more, and even more preferably 3.7% or more. The heat shrinkage rate of the other film is preferably 9% or less, more preferably 8% or less, even more preferably 7% or less, even more preferably 6% or less, and even more preferably 5.5% or less. In addition to the heat shrinkage rate of one film, if the heat shrinkage rate of the other film is set to a certain value or less, the heat resistance of the film is further improved. This makes it easier to laminate onto other films by lamination processing, and also improves secondary processability. The ratio of the thermal shrinkage rate in the longitudinal direction to the thermal shrinkage rate in the transverse direction is not particularly limited, but is, for example, 0.4 or more and 10 or less, preferably 0.6 or more and 8 or less, more preferably 0.8 or more and 6 or less, even more preferably 1 or more and 4 or less, and also more preferably 0.7 or more and 2 or less. The heat shrinkage rate can be adjusted appropriately by adjusting the stretching conditions of the polyester film, the heat setting temperature, etc., which will be described later.

[0110] <Melting point> The melting point (Tm) of the first run of the polyester film measured by differential scanning calorimetry is not particularly limited, but is preferably 230°C or higher. A melting point (Tm) of the first run of 230°C or higher provides good heat resistance and facilitates low thermal shrinkage. The melting point (Tm) of the first run of the polyester film is preferably 235°C or higher, more preferably 240°C or higher. Furthermore, from the viewpoint of making it easier to exert the effects of using PBT, the melting point (Tm) of the first run of the polyester film is preferably 260°C or lower, more preferably 255°C or lower, even more preferably 252°C or lower, and even more preferably 250°C or lower.

[0111] The melting point (Tm) of the second run of the polyester film measured by differential scanning calorimetry is not particularly limited, but is preferably 223°C or higher. A melting point (Tm) of the second run of 223°C or higher results in good heat resistance and facilitates low thermal shrinkage. The melting point (Tm) of the second run of the polyester film is preferably 228°C or higher, more preferably 233°C or higher. Furthermore, from the viewpoint of easily achieving the effects of using PBT, the melting point (Tm) of the second run of the polyester film is preferably 255°C or lower, more preferably 250°C or lower, even more preferably 247°C or lower, and even more preferably 243°C or lower.

[0112] Furthermore, the present polyester film preferably exhibits a single endothermic peak during temperature rise in differential scanning calorimetry, and more preferably a single melting peak in both the first and second runs. Having a single endothermic peak reduces the risk of softening at low temperatures. Therefore, when used as a battery exterior material, deterioration of the exterior material is more likely to be prevented even if the battery heats up and heats the exterior material. Furthermore, when performing secondary processing such as molding, if two endothermic peaks are present, the processing temperature can be adjusted to match either the lower peak or the higher peak. However, adjusting the processing temperature to the lower peak results in molding being performed while the resin at the higher peak is not yet melted, resulting in reduced moldability. Conversely, adjusting the processing temperature to the higher peak can result in dimensional changes due to the resin at the lower peak before the processing temperature is reached, potentially resulting in problems such as wrinkles due to shrinkage. Therefore, forming the present polyester film so that it has a single endothermic peak also has the advantage of more easily improving secondary processability, such as moldability. Furthermore, the manufacturing method described below allows stable film formation even at high heat setting temperatures, making it easier to adjust the heat shrinkage rate. By making PBT and PET compatible, polyester film can be adjusted to have a single endothermic peak. The single endothermic peak may have a shoulder at its base, excluding cases where two or more endothermic peaks originating from PBT and PET are clearly observed. The melting point (Tm) is measured in accordance with JIS K7121:2012 at a temperature of -70 to 280°C, a heating rate of 10°C / min, and a cooling rate of 600°C / min. The value at the top of the endothermic peak observed during the first heating is taken as the melting point of the first run, and the value at the top of the endothermic peak observed during the second heating (reheating) is taken as the melting point of the second run.

[0113] <Glass transition temperature (Tg)> The glass temperature (Tg) of the polyester film measured by differential scanning calorimetry is not particularly limited, but is preferably 50°C or higher, more preferably 55°C or higher, and even more preferably 60°C or higher. When the glass transition temperature (Tg) is a certain value or higher, the heat resistance is good and the heat shrinkage rate and other properties tend to be low. The glass temperature (Tg) of the polyester film is not particularly limited, but is preferably 80°C or higher, more preferably 75°C or lower, and even more preferably 70°C or lower. The glass transition temperature (Tg) is measured in accordance with JIS K7121:2012 at −70 to 280° C., at a heating rate of 10° C. / min and a cooling rate of 600° C. / min, and the midpoint glass transition temperature upon reheating is used.

[0114] <Intrinsic viscosity> The intrinsic viscosity of the polyester film is preferably 0.6 dL / g or more and 0.85 dL / g or less. Setting the intrinsic viscosity of the polyester film within the above range facilitates improving the productivity and film-forming properties of the polyester film. The intrinsic viscosity of the polyester film is more preferably 0.62 dL / g or more and 0.8 dL / g or less, even more preferably 0.63 dL / g or more and 0.78 dL / g or less, and even more preferably 0.64 dL / g or more and 0.75 dL / g or less.

[0115] [Polyester film manufacturing method] Next, the method for producing the present polyester film (hereinafter, sometimes simply referred to as "the present production method") will be described using the case where the present polyester film is a biaxially stretched polyester film as an example. When the present polyester film is a biaxially stretched polyester film, it is preferable to first produce an unstretched sheet, and then stretch it in two directions to obtain a biaxially stretched polyester film.

[0116] The unstretched sheet is preferably obtained by feeding the aforementioned PET and PBT, and optionally other resins, particles, and other additives, into an extruder, mixing them appropriately, extruding the mixture as a molten sheet from a die using the extruder, and cooling and solidifying it on a cooling roll. In this case, it is preferable to increase the adhesion between the sheet and the cooling roll to improve the flatness of the sheet, and an electrostatic application adhesion method and / or a liquid application adhesion method are preferably used. In addition, the PET and PBT are preferably mixed in the extruder so that they are compatible with each other, specifically, kneaded at a temperature of 270 to 300°C, preferably 275 to 295°C, and more preferably 280 to 290°C. Furthermore, compatibility may be improved by blending a compatibilizer, which may be appropriately selected from those commonly used for PBT and PET.

[0117] When kneading using an extruder, it is sufficient to knead the PBT and PET sufficiently to achieve compatibility. Among these, a method using an extruder in which the ratio of screw length L (mm) to screw diameter D (mm) (L / D) is preferably 15 or more, more preferably 20 or more, and preferably 50 or less, more preferably 40 or less, can be used. The use of such an extruder facilitates further improvement of the compatibility between PBT and PET, and prevents the resin residence time from becoming too long or the resin temperature from becoming too high, making it easier to suppress film discoloration due to thermal degradation, outgassing during film formation, and the generation of gel-like foreign matter. Regarding the screw configuration of the extruder, a structure having a kneading unit, particularly a spiral kneading unit, is preferred for improving kneading performance. One or two kneading units are preferred. It is also effective to use as the kneader a continuous kneader in which a plurality of rotating blades are provided on a screw rotatably mounted in the cylinder of an extruder, and a fixed blade is further provided in the cylinder and inserted between the plurality of rotating blades.

[0118] It is also effective to adjust the ratio Q / N of the discharge rate Q (kg / hr) to the screw rotation speed N (rpm) during melt-kneading. Q / N is preferably 0.1 or more, more preferably 0.2 or more, and is preferably 10 or less, more preferably 6 or less, and even more preferably 4 or less. By setting Q / N within the above range, discoloration of the film and generation of foreign matter caused by excessively high resin temperature or excessively long residence time can be suppressed, while making it easy to achieve sufficient compatibility between PBT and PET.

[0119] Furthermore, it is also effective to make the melt viscosity of PBT and that of PET similar to each other. The melt viscosity can be controlled by the molecular weight and branching structure.

[0120] The temperature of the cooling roll is preferably 10 to 40° C., more preferably 15 to 35° C., and even more preferably 20 to 30° C. In order to improve the flatness of the sheet, it is preferable to increase the adhesion between the sheet and the rotating cooling drum, and as described above, preferably, an electrostatic application adhesion method or a liquid application adhesion method can be appropriately adopted.

[0121] When the polyester film has a multilayer structure, multiple layers may be coextruded to form an unstretched sheet having a multilayer structure. The polyester raw material may be fed to the extruder as pellets, appropriately dried, or the like. Particles and other additives may be incorporated into the pellets.

[0122] When the polyester film is a monolayer film, the PET and PBT contained in the monolayer film may have a concentration gradient along the thickness direction. To obtain such a monolayer film, the PET and PBT in the resin composition for forming the monolayer film may be adjusted to be unevenly distributed using a known method. Specifically, this can be achieved by appropriately adjusting the conditions during the production of the monolayer film. For example, the temperature when melt-kneading the resin composition and extruding it into a film may be set low, or the degree of kneading may be reduced by appropriately adjusting the screw rotation speed, etc., to avoid promoting the reaction between PET and PBT to an appropriate degree, thereby utilizing the difference in surface free energy between the two to adjust the concentration gradient. In addition, in this production method, particles may also have a concentration gradient.

[0123] The unstretched sheet obtained as described above is stretched in the machine direction and the cross direction. The stretching method is not particularly limited, but it is preferable to stretch using a roll or tenter type stretching machine. Furthermore, it is preferable to stretch in the machine direction and then in the cross direction, but the reverse is also possible. Here, the stretching temperature during longitudinal stretching is preferably 50°C or higher and 85°C or lower, more preferably 58°C or higher and 75°C or lower, even more preferably 60°C or higher and 74°C or lower, and even more preferably 62°C or higher and 73°C or lower, and the longitudinal stretching ratio is preferably 2.5 times or higher and 4.5 times or lower, more preferably 2.8 times or higher and 4.2 times or lower, even more preferably 3 times or higher and 4 times or lower, and even more preferably 3.2 times or higher and 3.8 times or lower. Furthermore, when stretching transversely, it is preferable to preheat the polyester film before stretching, and the preheating temperature is preferably 60°C to 110°C, more preferably 62°C to 100°C, even more preferably 64°C to 90°C, and even more preferably 65°C to 85°C. Furthermore, the stretching temperature during transverse stretching is preferably 70°C to 120°C, more preferably 74°C to 110°C, even more preferably 77°C to 100°C, and still more preferably 80°C to 95°C. Furthermore, the transverse stretching ratio during transverse stretching is, for example, 3.5 to 6 times, preferably 3.5 to 5.5 times, more preferably 4 to 5.5 times, and even more preferably 4.5 to 5.2 times. The above transverse stretching ratios are relatively low, even though PBT is used. The polyester film is generally produced as a raw film having a length in the TD direction (film width) of a certain size or more during production, but by keeping the transverse stretching ratio relatively low as described above, it is possible to keep various physical properties within desired ranges and to suppress variations in various physical properties (e.g., degree of orientation, puncture strength, amount of displacement upon puncture, etc.) between the center and the edge portions in the TD direction of the raw film.

[0124] Furthermore, after stretching the polyester film in the longitudinal and transverse directions, it is preferable to subsequently heat-set the film at a heat-setting temperature of 180°C or higher to obtain a biaxially stretched polyester film. The heat-setting is preferably performed at the heat-setting temperature under tension or with a relaxation of 30% or less, preferably 10% or less, and more preferably 7% or less. The heat-setting temperature is preferably 190°C or higher, more preferably over 190°C, even more preferably 195°C or higher, and even more preferably 200°C or higher. The heat-setting temperature is not particularly limited, but is preferably 240°C or lower, more preferably 230°C or lower, even more preferably 225°C or lower, and even more preferably 220°C or lower. The heat-setting time is preferably 3 to 15 seconds, more preferably 4 to 14 seconds, and even more preferably 5 to 13 seconds. After the heat setting step, the film may be cooled in a cooling zone under a relaxation of 0 to 20%, 0.5 to 15%, preferably 1 to 10%, and more preferably 1.5 to 7%. The cooling temperature is, for example, preferably about 120 to 160°C, and more preferably about 130 to 150°C.

[0125] In this production method, the ratio of the transverse stretching ratio to the longitudinal stretching ratio (TD / MD) is preferably 1 or more and 1.7 or less. By maintaining the ratio of the transverse stretching ratio to the longitudinal stretching ratio within a certain range, preheating as described above, maintaining the stretching temperature during transverse stretching within a certain range, and setting the heat setting temperature after stretching to a certain temperature or higher, the degree of orientation (planar orientation) of the entire polyester film can be increased while keeping the difference between the transverse orientation degree (Δnv) and the longitudinal orientation degree (Δnp) below a certain level. The ratio of the transverse stretching ratio to the longitudinal stretching ratio (TD / MD) is more preferably 1.1 or more and 1.7 or less, and even more preferably 1.2 or more and 1.7 or less. Furthermore, the ratio of the transverse stretching ratio to the longitudinal stretching ratio (TD / MD) is more preferably 1.1 or more and 1.6 or less, and even more preferably 1.2 or more and 1.5 or less. Furthermore, in this manufacturing method, as described above, by keeping the stretching temperature during longitudinal stretching, as well as the transverse stretching ratio and longitudinal stretching ratio, within a certain range, it becomes easier to increase the degree of planar orientation while further reducing the difference between the transverse orientation degree (Δnv) and the longitudinal orientation degree (Δnp). In addition, in this production method, the heat shrinkage can be easily adjusted to a desired range by stretching the film under the above-mentioned stretching conditions and setting the heat setting temperature within a certain range. In particular, it is effective to set the preheating temperature, stretching temperature, and stretch ratio conditions slightly lower than usual, and to set the heat setting temperature slightly higher than usual.

[0126] In addition, in the present production method, the product of the transverse stretching ratio and the longitudinal stretching ratio is preferably 14 or more, more preferably 15 or more, and even more preferably more than 15.5, and is preferably 25 or less, more preferably 20 or less, and even more preferably 18 or less. In addition, in the present production method, the difference between the transverse stretching ratio and the longitudinal stretching ratio is preferably 0.3 times or more, more preferably 0.5 times or more, and even more preferably 0.7 times or more, and is, for example, 2.4 times or less, preferably 2 times or less, more preferably 1.8 times or less, and even more preferably 1.6 times or less. By adjusting the transverse and longitudinal stretching ratios of the present polyester film within a certain range as described above, it is possible to improve various physical properties while suppressing variations in various physical properties (e.g., degree of orientation, puncture strength, amount of displacement upon puncture, etc.) between the center and the end portions in the TD direction of the raw film. The stretching ratio is determined, for example, from the ratio of the film transport speed before stretching to the film transport speed after stretching in the longitudinal direction, and from the ratio of the film width before stretching to the film width after stretching in the transverse direction.

[0127] When the polyester film has a functional layer such as a functional layer X or an easy-adhesion layer, the method for forming the functional layer such as the easy-adhesion layer is not particularly limited, but examples include in-line coating and offline coating. In-line coating is a method of coating within the polyester film production process, and more specifically, it is preferable to coat the polyester after melt extrusion and longitudinal stretching, but before transverse stretching. Meanwhile, offline coating is a method of providing an easy-adhesion layer using a coating device in a separate process after polyester film production.

[0128] <Laminate> The present polyester film is used, for example, in a laminate. The present polyester film is preferably used as a laminate for a battery exterior packaging material. The laminate of the present invention includes the present polyester film. The laminate of the present invention may include, in addition to the polyester film, at least one of a resin layer, a metal layer, and a sealant layer, and preferably includes at least one of a resin layer and a metal layer. The metal layer is a layer formed of a metal, a metal oxide, or a mixture of a metal and a metal oxide. Among these, the metal layer is preferably formed from a metal, such as aluminum, nickel, titanium, or alloys thereof, or steel materials such as stainless steel and titanium steel. Among these, an aluminum alloy is more preferable. The metal layer may be formed from a metal foil or by metal vapor deposition, but is preferably formed from a metal foil. From the viewpoint of preventing the occurrence of wrinkles and pinholes, the metal layer is more preferably formed from a soft aluminum alloy foil such as annealed aluminum (JIS H4160:1994 A8021H-O, JIS H4160:1994 A8079H-O, JIS H4000:2014 A8021P-O, JIS H4000:2014 A8079P-O).

[0129] The metal layer may be a single layer or a laminate of two or more layers. The thickness of the metal layer is not particularly limited as long as it exhibits a barrier function against water vapor, etc., but from the viewpoint of reducing the thickness of the pouch, the thickness is preferably about 100 μm or less, more preferably 3 μm to 100 μm, even more preferably 3 μm to 80 μm, still more preferably 6 μm to 60 μm, and even more preferably 10 μm to 40 μm.

[0130] Furthermore, from the viewpoints of stabilizing adhesion, preventing dissolution and corrosion, etc., the metal layer is preferably chemically treated on at least one surface, more preferably on both surfaces. Here, chemical treatment is a treatment for forming an acid-resistant coating on the surface of the metal layer, and the metal layer may be provided with an acid-resistant coating on one surface, may be provided with acid-resistant coatings on both surfaces, or may not be provided with an acid-resistant coating. The thickness of the acid-resistant coating is not particularly limited, but from the viewpoint of the cohesive strength of the coating and the adhesive strength with the metal layer and the heat-sealable resin layer, it is preferably from 1 to 1000 nm, more preferably from 3 to 100 nm, and even more preferably from 5 to 50 nm. The thickness of the acid-resistant coating can be measured by observation with a transmission electron microscope, or by a combination of observation with a transmission electron microscope and energy dispersive X-ray spectroscopy or electron energy loss spectroscopy.

[0131] The chemical conversion treatment is preferably carried out by applying a solution containing a compound used to form the acid-resistant coating to the surface of the metal layer by bar coating, roll coating, gravure coating, immersion, or the like, and then heating the metal layer so that the temperature thereof becomes, for example, from 70° C. to 200° C. Before the chemical conversion treatment is carried out on the metal layer, the metal layer may be subjected to a degreasing treatment by alkali immersion, electrolytic cleaning, acid cleaning, electrolytic acid cleaning, or the like.

[0132] Examples of resins constituting the resin layer include polyester resins, polyamide resins, polyolefin resins, epoxy resins, acrylic resins, fluororesins, polyurethane resins, silicone resins, and phenolic resins, and mixtures of these resins may also be used. Among these, polyester resins and polyamide resins are preferred, with polyamide resins being particularly preferred. Examples of polyamide resins include, but are not limited to, aliphatic polyamides such as polyamide 6, polyamide 66, polyamide 510, polyamide 12, polyamide 46, and copolymers of polyamide 6 and polyamide 66; hexamethylenediamine-isophthalic acid-terephthalic acid copolymer polyamides such as polyamide 6I, polyamide 6T, polyamide 6IT, and polyamide 6I6T (where I represents isophthalic acid and T represents terephthalic acid) containing structural units derived from terephthalic acid and / or isophthalic acid; and aromatic polyamides such as polymetaxylylene adipamide (MXD6); alicyclic polyamides such as polyaminomethylcyclohexyl adipamide (PACM6); polyamides copolymerized with a lactam component or an isocyanate component such as 4,4'-diphenylmethane diisocyanate; polyesteramide copolymers and polyetheresteramide copolymers, which are copolymers of copolymerized polyamides with polyesters or polyalkylene ether glycols; and copolymers thereof. These may be used alone or in combination of two or more.

[0133] Furthermore, a resin film may be used as the resin layer, and a stretched film is preferred from the viewpoint of mechanical strength, etc. The stretched film may be a uniaxially stretched film or a biaxially stretched film. Therefore, the resin layer is preferably composed of a polyamide film, and more preferably composed of a stretched polyamide film. The stretched polyamide film can be produced by a conventionally known method. For example, examples of stretching methods for forming a biaxially stretched polyamide film include a sequential biaxial stretching method, an inflation method, and a simultaneous biaxial stretching method, and the sequential biaxial stretching method is preferred.

[0134] The resin layer may be a single layer or a laminate of two or more layers. The thickness of the resin layer is, for example, in the range of 5 μm to 80 μm, preferably 8 μm to 60 μm, and more preferably 10 μm to 40 μm.

[0135] The thickness ratio of the present polyester film to the metal layer (present polyester film layer:metal layer) is preferably in the range of 1:1 to 1:5, more preferably 1:1.1 to 1:4, and even more preferably 1:1.2 to 1:3.

[0136] The laminate may also include a sealant layer. By having the sealant layer, the laminate can be adhered to another member by heat fusing with a sealant layer provided on another member. Therefore, by having the sealant layer, the laminate can easily form an exterior material by lamination. Note that the laminate of the present invention may be adhered to another laminate of the present invention via a sealant layer, but the laminate of the present invention may also be adhered to a member other than the laminate of the present invention via a sealant layer. The sealant layer may be formed from a heat-sealable resin material, and examples of resins constituting the sealant layer include polyolefins, cyclic polyolefins, carboxylic acid-modified polyolefins, and carboxylic acid-modified cyclic polyolefins. Of these, carboxylic acid-modified polyolefins are preferred, and carboxylic acid-modified polypropylene is more preferred.

[0137] Specific examples of polyolefins include polyethylenes such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene; polypropylenes such as homopolypropylene, block copolymers of polypropylene (e.g., block copolymers of propylene and ethylene), and random copolymers of polypropylene (e.g., random copolymers of propylene and ethylene); and ethylene-butene-propylene terpolymers. Among these, polyethylene and polypropylene are preferred, and polypropylene is more preferred.

[0138] The cyclic polyolefin is a copolymer of an olefin and a cyclic monomer, and examples of the olefin constituting the cyclic polyolefin include ethylene, propylene, 4-methyl-1-pentene, butadiene, and isoprene. Examples of the cyclic monomer constituting the cyclic polyolefin include cyclic alkenes such as norbornene; specifically, cyclic dienes such as cyclopentadiene, dicyclopentadiene, cyclohexadiene, and norbornadiene. Among these, cyclic alkenes are preferred, and norbornene is more preferred. Styrene can also be used as a constituting monomer.

[0139] The carboxylic acid-modified polyolefin is a polymer obtained by modifying the polyolefin by block polymerization or graft polymerization with a carboxylic acid. Examples of the carboxylic acid used for modification include maleic acid, acrylic acid, itaconic acid, crotonic acid, maleic anhydride, and itaconic anhydride.

[0140] The sealant layer has a thickness of, for example, about 10 μm or more and 100 μm or less, preferably about 15 μm or more and 80 μm or less, and more preferably about 20 μm or more and 60 μm or less.

[0141] An adhesive layer may be present between each layer (e.g., between a resin layer and the polyester film, between a resin layer and a metal layer, between the polyester film and a metal layer, etc.), and each layer may be bonded via the adhesive layer. The adhesive layer is not particularly limited, but may be composed of a known adhesive such as a polyether adhesive, a polyester adhesive, a polyurethane adhesive, an epoxy adhesive, a phenolic resin adhesive, a polyamide adhesive, a polyolefin adhesive, a polyacrylic adhesive, an amino resin adhesive, a rubber adhesive, or a silicone adhesive. Furthermore, each layer may be bonded by a known lamination method such as a dry lamination method, but is not particularly limited.

[0142] The laminate of the present invention preferably has at least a metal layer, which improves the strength of the laminate and functions as a barrier layer that prevents the transmission of water, steam, oxygen, light, etc., making the laminate suitable for use as an exterior packaging material, particularly an exterior packaging material for batteries. When the laminate has a metal layer, the metal layer may be provided on one side of the polyester film, and the metal layer may be bonded to the polyester film via an adhesive layer. When the laminate of the present invention has a metal layer, a resin layer may be further provided between the metal layer and the polyester film. In this case, it is preferable that an adhesive layer is further provided between the polyester film and the resin layer or between the resin layer and the metal layer, and that the layers are bonded by the adhesive layer.

[0143] The present polyester film is preferably disposed as the outermost layer of a laminate. In particular, the present polyester film is preferably used as the outermost layer of a battery exterior material. The outermost layer of a laminate is easily damaged by external forces during molding or use, but the present polyester film, as described above, has good puncture resistance. Furthermore, the Martens hardness and indentation hardness can be increased, resulting in excellent pinhole resistance and breaking strength. Therefore, using the present polyester film as the outermost layer of a laminate makes it easier to appropriately prevent damage to the laminate during molding and to the battery exterior material containing the laminate. From the same perspective, when the present polyester film has a surface where the content (A1) is higher than the content (A2), it is preferable that the surface where the content (A1) is higher than the content (A2) be disposed on the outermost surface of the laminate. Furthermore, when the polyester film has a functional layer X, the functional layer X is preferably disposed at a position where it contacts the mold as described above. Therefore, the functional layer X is preferably disposed on the outermost surface of the laminate. That is, it is also preferable that the surface of the polyester film having the functional layer X and having a content (A1) higher than the content (A2) is disposed on the outermost surface of the laminate.

[0144] Preferred lamination structures of the laminate of the present invention include the present polyester film / adhesive layer / metal layer, and the present polyester film / adhesive layer / resin layer / adhesive layer / metal layer. The laminate of the present invention also preferably has a laminate structure having a sealant layer in addition to the metal layer. Preferred laminate structures when the metal layer and sealant layer are present include the present polyester film / adhesive layer / metal layer / sealant layer and the present polyester film / adhesive layer / resin layer / adhesive layer / metal layer / sealant layer. The sealant layer may be bonded to the metal layer directly or via an adhesive layer. Furthermore, the resin constituting the resin layer is preferably a polyamide resin, and therefore the resin layer in each of the above laminate structures is preferably a polyamide resin layer, and particularly preferably a stretched polyamide film.

[0145] <Application> The polyester film is used for forming. The polyester film is usually formed into the laminate described above, but may also be formed as a single layer. By forming the polyester film, for example, a recess can be formed, and components constituting a battery, such as an electricity storage device element, can be housed inside the recess. The extrusion molding is a method of molding a polyester film or a laminate using a mold to form it into a desired shape. The extrusion molding is not particularly limited, and may be performed by any molding method such as vacuum forming, pressure forming, or press forming. The extrusion molding is preferably cold forming. Furthermore, the extrusion molding is preferably deep drawing. Since the polyester film of the present invention has good extensibility, it can be appropriately molded without causing breakage, even when molded by extrusion molding, particularly deep drawing, etc.

[0146] The polyester film is preferably used in molded articles. The polyester film is preferably used as an exterior material for housing and protecting a specified component. In particular, the polyester film has excellent puncture resistance and is expected to also have polyester chemical resistance. Therefore, it can be suitably used as a battery exterior material for packaging battery cells in various batteries, such as lithium ion batteries, lithium ion polymer batteries, lead-acid batteries, nickel-metal hydride batteries, nickel-cadmium batteries, nickel-iron batteries, nickel-zinc batteries, silver oxide-zinc batteries, metal-air batteries, and polyvalent cation batteries. It is particularly suitable for use as an exterior material for lithium batteries, particularly for automotive lithium batteries. When the polyester film is used as an exterior material, the exterior material may have any configuration as long as it contains the polyester film or the laminate, but it is preferable that the exterior material contain the laminate. That is, the present invention also provides a battery exterior material comprising the polyester film or laminate described above, and a battery comprising the battery exterior material.

[0147] When the laminate of the present invention is used as an exterior packaging material and a predetermined component such as a battery cell is packaged inside, the polyester film may be disposed on the outside, preferably as the outermost layer, and the metal layer may be disposed on the inside in each of the above-mentioned laminate structures. That is, when the polyester film is used as a battery exterior packaging material, it is preferably used as the outermost layer of the battery exterior packaging material. The polyester film has high chemical resistance, and when placed on the outer surface (preferably the outermost layer) of an exterior packaging material, it can adequately protect the components inside the exterior packaging material. Furthermore, when used as an exterior packaging material for a battery, it can adequately prevent delamination caused by leakage of electrolyte. Furthermore, when the laminate of the present invention is used as an exterior packaging material, it is preferable to sandwich a predetermined component (for example, a battery cell such as an electricity storage device element) between a pair of laminates, and then heat-seal the peripheral edges of the laminates together via a sealant layer by lamination or the like, thereby sealing the component such as the battery cell inside the exterior packaging material. Furthermore, it is preferable to form a recess in the laminate of the present invention by molding, store a component such as a battery cell in the recess, and heat-seal the laminates having the recess together via a sealant layer, and then seal the component such as the battery cell inside the exterior packaging material.

[0148] <<Explanation of terms>> In the present invention, the term "film" includes the term "sheet", and the term "sheet" includes the term "film". In the present invention, when it is stated that "X to Y" (X and Y are any numbers), unless otherwise specified, it means "X or more and Y or less", and also means "preferably larger than X" or "preferably smaller than Y". Furthermore, when it is stated that the amount is "X or more" (X is any number), it also means that the amount is "preferably greater than X" unless otherwise specified, and when it is stated that the amount is "Y or less" (Y is any number), it also means that the amount is "preferably smaller than Y" unless otherwise specified. [Example]

[0149] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

[0150] <Evaluation method> (1) Measurement of intrinsic viscosity (dl / g) of polyester and film 1 g of polyester was precisely weighed, dissolved in 100 ml of a mixed solvent of phenol / tetrachloroethane = 50 / 50 (mass ratio), and measured at 30° C. When particles were blended, the particles were removed and 1 g of polyester was precisely weighed to measure the intrinsic viscosity.

[0151] (2) Lateral orientation (Δnv), longitudinal orientation (Δnp), and planar orientation (ΔP) The degree of transverse orientation (Δnv), the degree of longitudinal orientation (Δnp), and the degree of planar orientation (ΔP) were measured by the methods described in the specification.

[0152] (3-1) Piercing strength (N / mm) and displacement (mm) when measuring piercing strength The puncture strength (N) was measured in accordance with JIS Z1707:2019, and the value per unit thickness obtained by dividing the puncture strength (N) by the film thickness was taken as the puncture strength (N / mm). The amount of displacement when measuring the puncture strength was taken as the amount of displacement at the time of puncture. The average value of 12 points was used for the measurement. Specifically, a 210 mm x 297 mm sample was cut from the center of a film roll obtained using the method described below, with the short side aligned horizontally across the film. Measurements were then conducted at 12 randomly selected points evenly spaced on the cut sample, and the average of these measured values ​​was used.

[0153] (3-2) Variation in piercing strength and displacement during piercing Using the measured values ​​of the puncture strength and the displacement at the time of puncture obtained above at 12 points, the variation in the puncture strength and the variation in the displacement at the time of puncture were evaluated using the coefficient of variation calculated using the following formula (1). A smaller value indicates a smaller variation. Formula (1) = Standard deviation / Average value

[0154] (4) Glass transition temperature (Tg), number of endothermic peaks, and melting point (Tm) Using a differential scanning calorimeter (PerkinElmer Japan, "Diamond DSC"), the sample was heated from -70°C to 280°C at a heating rate of 10°C / min, held at that temperature for 10 minutes, then cooled to -70°C at a cooling rate of 600°C / min, and heated again at a heating rate of 10°C / min. The change in specific heat due to the transition from the glassy state to the rubbery state during the second heating run was measured to determine the Tg (glass transition temperature). The midpoint glass transition temperature was used as the Tg (glass transition temperature). The melting points were determined by measuring the peak top temperatures of the endothermic peaks observed during the first heating run (1st run) and the second heating run (2nd run), as shown in Table 2. When two or more peak tops were observed, all values ​​were reported. Therefore, one value in the melting point column indicates one endothermic peak, and two values ​​in the melting point column indicate two endothermic peaks. If two or more endothermic peaks are observed, the melting point is the temperature at the top of the maximum peak.

[0155] (5) Heat shrinkage rate A 15 mm x 150 mm sample of the polyester film obtained in the Examples and Comparative Examples was heat-treated for 15 minutes in an oven maintained at 160°C in an untensioned state, and the length of the sample before and after treatment was measured, and the heat shrinkage rate in each of the machine direction (MD) and transverse direction (TD) of the film was calculated using the following formula. Heat shrinkage rate (%) = {(L0-L1) / L0} x 100 (In the above formula, L0 is the sample length before heat treatment, and L1 is the sample length after heat treatment) Measurements were taken at five points in each of the machine direction (MD) and the transverse direction (TD) of the film, and the average value was calculated for each.

[0156] (6) Haze Measurement was carried out in accordance with JIS K 7136:2000 using a haze meter NDH-2000 manufactured by Nippon Denshoku Industries Co., Ltd.

[0157] (7) Martens hardness, indentation hardness and elastic deformation power Approximately 2 to 8 mg of Aron Alpha (registered trademark) (general-purpose, manufactured by Toa Gosei Chemical Industry Co., Ltd.) was dropped onto a glass slide (S1112, manufactured by Matsunami Glass Industry Co., Ltd.). One side (the side opposite to the surface to be measured) of a polyester film (1.5 cm x 1.5 cm) was placed on top of it as an adhesive surface and allowed to harden. The slide glass with the polyester film was then fixed to the sample stage of a hardness tester (dynamic ultra-micro hardness tester (DUH-211S, manufactured by Shimadzu Corporation)), and a load-unload test was performed on the surface of the polyester film, and the elastic deformation power (η it ) was measured, and the Martens hardness and indentation hardness were also measured. Each value was calculated as the average of 10 measurements (n=11) excluding the first one. Wtotal = Wplast + Welast (N m) (Wtotal = total deformation work (N·m), Wplast = plastic deformation work (N·m), Welast = elastic deformation work (N·m)) η it = (Welast / Wtotal) x 100 (%) (Measurement conditions) Indenter used: Diamond regular triangular pyramid indenter (edge ​​angle: 115) Measurement mode: Load-unload test Test force: 20.00mN Minimum test force: 0.20 mN Load speed: 0.1464mN / sec Load holding time: 2sec Unloading holding time: 0sec Measurement atmosphere: 23±2°C, relative humidity 50±5% Number of measurements: 11

[0158] <Materials used> [Polyester raw materials] (PBT) PBT-A: Homobutylene terephthalate (intrinsic viscosity = 0.85 dL / g) PBT-B: Homobutylene terephthalate (intrinsic viscosity = 1.26 dL / g) (PET) PET-A: homopolyethylene terephthalate (intrinsic viscosity = 0.64 dL / g) PET-B: homopolyethylene terephthalate (intrinsic viscosity = 0.85 dL / g) PET-C: Masterbatch of homopolyethylene terephthalate containing 0.55% by mass of silica particles with an average particle size of 3.1 μm (intrinsic viscosity = 0.61 dl / g)

[0159] Example 1 As shown in Table 2, PBT-A, PET-A, and PET-C were dry-blended in a mass ratio of 20:70:10 to form the surface layer raw materials, and PBT-A and PET-A were dry-blended in a mass ratio of 20:80 to form the core layer raw materials. The mixed raw materials for the surface layer and core layer were each fed into separate twin-screw extruders, kneaded at 280°C, and co-extruded at 280°C. The materials were then cooled and solidified on a cooling roll set at 25°C using an electrostatic adhesion method, yielding an unstretched film with two types and three layers (surface layer / core layer / surface layer). The unstretched film was then stretched 3.5 times in the machine direction (MD) at 73°C using a roll stretching machine. It was then introduced into a tenter stretching machine, preheated at 75°C for 6 seconds, and then stretched 4.5 times in the transverse direction (TD) at 85°C. After stretching, the film was subsequently heat-set at 210°C for 8 seconds and cooled to 140°C with 2% relaxation in the transverse direction (TD) to obtain a biaxially stretched polyester film with a thickness of 25 μm (skin layers: 2.5 μm, core layer: 20 μm). The biaxially stretched polyester film was wound into a film roll. The resulting polyester film was evaluated. The evaluation results are shown in Table 2. The PET / PBT mass ratio shown in Table 2 is the mass ratio of PET and PBT contained in the entire three-layer biaxially oriented polyester film. Specifically, the PET / PBT mass ratio in the entire polyester film is calculated from the blending ratio of PET and PBT in each layer and the ratio of the thickness of each layer, and the mass ratio is rounded to one decimal place.

[0160] (Examples 2 to 4, 6, and 7, and Comparative Examples 1 and 2) The same procedure as in Example 1 was carried out, except that the compositions of the surface layer and core layer and the film production conditions were changed as shown in Table 2. For Example 8, the Martens hardness, indentation hardness, and elastic deformation power of the obtained polyester film were measured, and the Martens hardness was 140 N / mm 2 , indentation hardness is 220N / mm 2 , and the elastic deformation power was 45%.

[0161] Example 5 The compositions of the surface layer and core layer and the film production conditions were changed as shown in Table 2. The preheating time after longitudinal stretching was changed to 7 seconds, the heat setting time was changed to 10 seconds, and by in-line coating, a coating solution for an easy-adhesion layer having the following composition was applied to one side of the polyester film after longitudinal stretching and before transverse stretching, so that the coating amount of the coating solution (after drying and stretching) on ​​one side of the polyester film was 0.05 g / m 2 The same procedure as in Example 1 was carried out, except that the adhesive layer was formed by coating the mixture so that the adhesive layer was formed as follows: (Formulation of coating solution for easy adhesion layer) Polyester resin water dispersion 90% by mass Monomer composition: (acid component) terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid / / (diol component) ethylene glycol / 1,4-butanediol / diethylene glycol = 56 / 40 / 4 / / 70 / 20 / 10 (mol%) polyester resin copolymerized Melamine compound: hexamethoxymethylol melamine 9% by mass 1% by mass of silica particles with an average particle size of 0.07 μm

[0162] Example 8 The same procedure as in Example 1 was carried out except that the composition of the surface layer and core layer and the film production conditions were changed as shown in Table 2, the preheating time after longitudinal stretching was changed to 7 seconds, and the heat setting treatment time was changed to 10 seconds.

[0163] [Table 2]

[0164] The polyester films of the above examples contained both PBT and PET, and the absolute value of the difference between the horizontal orientation degree (Δnv) and the vertical orientation degree (Δnp) was 57 or less. Therefore, they had high puncture strength, large displacement upon puncture, and small variation in displacement and strength upon puncture, resulting in excellent puncture resistance. In contrast, the polyester films of Comparative Examples 1 and 2 contained both PBT and PET, but the absolute value of the difference between the transverse orientation degree (Δnv) and the longitudinal orientation degree (Δnp) was greater than 57, resulting in large variations in the amount of displacement or strength upon puncture, and the films were unable to achieve excellent puncture resistance. The polyester film of Example 8 contained both PBT and PET, and the PET content (A1) at the surface was higher than the PET content (A2) at the center (core layer) in the thickness direction, so the puncture strength, Martens hardness, indentation hardness, and elastic deformation power were all high. Therefore, it can be seen that the polyester film of Example 8 has excellent pinhole resistance, is less likely to break when external force is applied, and also has excellent design and shape recovery properties, making it particularly suitable for battery exterior materials.

Claims

1. A polyester film containing polybutylene terephthalate and polyethylene terephthalate, The polyester film has an absolute value of the difference between the transverse orientation degree (Δnv) and the longitudinal orientation degree (Δnp) of the polyester film of 57 or less.

2. 2. The polyester film according to claim 1, wherein the ratio of the content of polyethylene terephthalate to the content of polybutylene terephthalate (PET / PBT) is 55 / 45 or more and 95 / 5 or less in mass ratio.

3. 2. The polyester film according to claim 1, which has a puncture strength of 480 N / mm or more.

4. 2. The polyester film according to claim 1, which has a displacement of 4 mm or more when pierced.

5. 2. The polyester film according to claim 1, wherein the puncture strength variation is 0.036 or less.

6. 2. The polyester film according to claim 1, wherein the variation in displacement upon piercing is 0.034 or less.

7. 2. The polyester film according to claim 1, wherein the degree of planar orientation is 100 or more and 200 or less.

8. 2. The polyester film according to claim 1, wherein after heat treatment at 160°C for 15 minutes, the polyester film has a heat shrinkage rate of less than 5% in one of the longitudinal and transverse directions and a heat shrinkage rate of more than 2% in the other direction.

9. 2. The polyester film according to claim 1, having a haze of 10% or less.

10. The polyester film according to claim 1, having a melting point (1st run) of 230°C or higher.

11. 2. The polyester film according to claim 1, wherein the intrinsic viscosity of the polyester film is 0.6 dL / g or more and 0.85 dL / g or less.

12. 10. The polyester film of claim 1, which is a biaxially oriented polyester film.

13. A method for producing a polyester film according to any one of claims 1 to 12, comprising: Stretching in the machine direction and the transverse direction, A method for producing a polyester film, wherein the preheating temperature during transverse stretching is 60°C or higher and 90°C or lower, and the stretching temperature is 70°C or higher and 120°C or lower.

14. The method for producing a polyester film according to claim 13, wherein the heat setting temperature after the stretching is 190°C or higher.

15. The method for producing a polyester film according to claim 13, wherein the ratio of the transverse stretching ratio to the longitudinal stretching ratio (TD / MD) is 1 or more and 1.7 or less.

16. The method for producing a polyester film according to claim 13, wherein the stretching temperature during longitudinal stretching is 50°C or higher and 85°C or lower.

17. The method for producing a polyester film according to claim 13, wherein the longitudinal stretching ratio is 2.5 times or more and 4.5 times or less.

18. The method for producing a polyester film according to claim 13, wherein the transverse stretching ratio is 3.5 times or more and 5.5 times or less.

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