JP7615593B2 - Polyester Film - Google Patents

Description

The present invention relates to a polyester film that can be suitably used for battery exterior packaging and pharmaceutical packaging.

Lithium batteries, also known as lithium secondary batteries, are batteries that have liquid, gel-like polymers, solid polymers, or polymer electrolytes, and generate current by the movement of lithium ions, including those with polymeric positive and negative active materials. Lithium secondary batteries are composed of a positive electrode current collector (aluminum, nickel), a positive electrode active material layer (polymeric positive electrode materials such as metal oxides, carbon black, metal sulfides, electrolyte, polyacrylonitrile, etc.), an electrolyte layer (carbonate-based electrolytes such as propylene carbonate, ethylene carbonate, dimethyl carbonate, ethylene methyl carbonate, etc., inorganic solid electrolytes made of lithium salts, gel electrolytes), a negative electrode active material layer (polymeric negative electrode materials such as lithium metal, alloys, carbon, electrolyte, polyacrylonitrile, etc.), a negative electrode current collector (copper, nickel, stainless steel), and an exterior body that wraps them. In recent years, lithium batteries have come to be used in a wide range of fields due to their high volumetric and weight efficiency, and are used as small, high-capacity power sources in personal computers, mobile terminal devices (smartphones, etc.), video cameras, electric vehicles, energy storage batteries, robots, satellites, etc.

A typical exterior body for a lithium battery is a metal can made by pressing metal into a cylindrical or rectangular container. However, when a metal can is used, the shape of the battery itself is determined because the outer wall of the container is rigid, and the hardware side must be designed to match the battery, and the dimensions of the hardware that uses the battery are determined by the battery, resulting in problems such as design restrictions. Therefore, exterior bodies in which two molded bodies formed by drawing and molding a structure composed of a resin layer/aluminum/sealant layer into a rectangular shape and laminating them with heat sealing have become popular. In the structure, the sealant layer is responsible for heat sealing properties, the aluminum is responsible for barrier properties, and the resin layer is responsible for deep drawing properties. Recently, in the battery manufacturing process, a decrease in yield due to deterioration of the resin layer that constitutes the structure due to leakage of electrolyte, etc. has become a problem, and the resin layer is required to have electrolyte resistance in addition to deep drawing properties.

Until now, for example, polyamide film has been used as the resin layer (see Patent Document 1, for example). However, polyamide film is not sufficiently moisture-proof and stable against electrolyte, and may deteriorate when electrolyte is attached during the battery manufacturing process, so improvements have been required. Also, in order to prevent deterioration of the polyamide film when electrolyte is attached during the battery manufacturing process, a configuration has been proposed in which polyester is provided on the outermost exterior (see Patent Documents 2 and 3). Although the formability is sufficient, there is an issue that productivity is poor because an extra process is required to bond the polyester film and polyamide.

Polyester film alone has also been investigated (see, for example, Patent Documents 4 and 5).

JP 2006-236938 A JP 2000-334891 A Patent No. 6476679 JP 2011-204674 A Patent No. 6177475

However, although the use of the above polyester film improves deep drawability and electrolyte resistance, the deep drawability is insufficient compared to a configuration using a polyester film and a polyamide film. The present invention aims to provide a polyester film with improved deep drawability compared to conventional polyester film alone.

In order to solve the above problems, the polyester film of the present invention has the following configuration.
(1) The work-hardening index in both the longitudinal and transverse directions is 1.6 to 3.0, and the difference between the work-hardening indexes in the longitudinal and transverse directions is 0.5 or less, the intrinsic viscosity is 0.66 to 0.95, and the rigid amorphous amount is 28% to 60%.
(2) The melting point is 248°C or higher.
(3) The crystallinity is 25% or more and 40% or less.
(4) The breaking elongation in both the longitudinal and transverse directions is 100% or more.
(5) Used for battery exteriors.
(6) Used for pharmaceutical packaging.

The polyester film of the present invention has excellent electrolyte resistance due to the use of polyester resin, and by setting the work hardening index, intrinsic viscosity, and rigid amorphous amount within specific ranges, it is possible to achieve deep draw formability comparable to that of structures using polyamide, despite being polyester, and it can be suitably used for battery exterior components that support high capacity and packaging components that can be adapted to various shapes.

FIG. 2 is a schematic side view of a base consisting of a rectangular male mold and a rectangular female mold. FIG. 2 is a top view of a molded component in an evaluation of molding followability.

The polyester film of the present invention has a work hardening index in both the longitudinal direction and the width direction of 1.6 to 3.0. The work hardening index is a value calculated from the stress at 5% elongation and the stress at 60% elongation obtained from a tensile test defined in the evaluation method (11) Work Hardening Index described later. The laminate material used for the battery exterior is typically configured by laminating the outermost exterior film, metal foil, and sealant layer in this order, and in many cases the outermost exterior film is a single layer or composite structure of about 25 μm, the metal foil is 40 μm, and the sealant layer is about 80 μm, with the outermost exterior film being the thinnest. After extensive research, the inventors have clarified that when drawing is performed with this structure, the neutral axis of the stress applied in the thickness direction is determined according to the work hardening state of each layer, and the position in the thickness direction at which the stress is concentrated is determined. If the work-hardening state of the outermost film, i.e., the work-hardening index, is less than 1.6, the neutral axis is biased toward the metal foil and sealant layer, and the metal foil is likely to be subjected to uneven stress, resulting in breakage or pinholes in the metal foil during drawing. For this reason, the polyester film of the present invention must have a work-hardening index of at least 1.6. In order to prevent the neutral axis from being biased toward the outermost film, the work-hardening index must be 3.0 or less in both the longitudinal and transverse directions. It is preferably 2.0 or more and 2.6 or less.

In order to make the work hardening index of the polyester film in both the longitudinal and width directions 1.6 to 3.0, it is preferable to make the breaking strength in the longitudinal and width directions 200 MPa or more. In this case, the longitudinal and width directions of the film are measured by measuring the breaking strength in any one direction of the film (0°) and in directions 15°, 30°, 45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°, and 165° from that direction, and the direction with the highest breaking strength is the width direction, and the direction perpendicular to the width direction is the longitudinal direction. In order to make the polyester film breaking strength 200 MPa or more, it is recommended to stretch it at a high ratio. Specifically, it is most preferable to stretch it biaxially, and it is recommended to stretch it by a known method at an areal stretching ratio of 11.0 times or more sequentially or simultaneously. If the work hardening index is less than 1.6, the drawing formability is poor. In addition, the higher the work hardening index, the greater the elastic deformation caused by bending during drawing, which tends to result in greater warpage after forming. For this reason, it is important to keep the work hardening index to a minimum according to the required degree of warpage.

In the present invention, from the viewpoint of in-plane uniformity, the difference in work hardening index between the longitudinal direction and the width direction is 0.5 or less. If the difference in work hardening index between the longitudinal direction and the width direction exceeds 0.5, the in-plane uniformity is low, and the load is applied unevenly during drawing, causing localized deformation and resulting in poor draw formability. The difference in work hardening index is preferably 0.3 or less.

In the present invention, it is preferable that the breaking elongation in both the longitudinal and width directions is 100% or more. One of the deformation behaviors of materials in drawing is elongation. The greater the elongation of the film, the greater the element of deformation behavior that can be stretched, and the better the drawing processability. For this reason, it is preferable that the breaking elongation in both the longitudinal and width directions is 100% or more. To make the breaking elongation in the longitudinal and width directions 100% or more, it is possible to adjust the stretching ratio in both directions to 4.0 times or less. If there is a direction in which the stretching ratio exceeds 4.0 times, it is advantageous in increasing the work hardening index, but the breaking elongation in that stretching direction will be 100% or less, and the drawing formability may decrease.

The polyester film of the present invention has a rigid amorphous amount of 28% or more and 60% or less relative to the entire film. Here, the rigid amorphous amount is a value measured by the method described in (9) Rigid Amorphous Amount below. When the rigid amorphous amount is in this range, it is possible to obtain a particularly remarkable characteristic in the thickness direction, which is piercing resistance. The drawing process that is often performed in battery exterior laminate materials is a process in which the four corners are fixed with a mold and the film is drawn in the thickness direction. By controlling the rigid amorphous amount relative to the entire film within this range, excellent drawing characteristics are exhibited in the above-mentioned drawing process. When the rigid amorphous amount exceeds 60%, the amorphous component occupies the majority of the film bulk composition, and the dimensional stability of the film is significantly reduced. On the other hand, when the rigid amorphous amount is less than 28%, the piercing resistance, which is a characteristic in the thickness direction, is poor. The film bulk state is determined by the crystallinity of the raw material used as well as the film-forming conditions. For example, when polyethylene terephthalate is used, in order to make the rigid amorphous amount 28% or more, it is important to make the plane orientation coefficient fn of the film at least 0.165 or more. Here, the plane orientation coefficient of the film is measured by the method described in Evaluation Method (5) Planar Orientation Coefficient fn of Polyester Film, which will be described later. In order to make the plane orientation coefficient of the film 0.165 or more, a method of setting the areal stretch ratio during biaxial stretching to 12.25 times or more can be mentioned. In addition, it is preferable to control the rigid amorphous by the heat treatment temperature after sequential biaxial stretching, and it is important to set the highest temperature (heat treatment temperature) applied during film formation to 200 ° C or less. On the other hand, even if the heat treatment temperature is set to 230 ° C or more, the rigid amorphous amount tends to increase due to the initiation of melting of the resin, but since this promotes crystallization of the film by heat, the crystallization degree described later increases, and the crystallization degree of the film bulk composition is higher than that of the rigid amorphous. For this reason, it is important to set the heat treatment temperature to 200 ° C or less. If the heat treatment temperature of the film is more than 200 ° C and less than 230 ° C, the rigid amorphous amount may be less than 28%.

The polyester film of the present invention preferably has a crystallinity of 25% or more and 40% or less. The crystallinity can increase the mechanical strength of the film by orientation crystallization due to stretching or crystallization due to heat. If the crystallinity is less than 25%, the film plane orientation may be insufficient and the work hardening index may not be controlled within the range of the present invention, and if the crystallinity is more than 35%, the rigid amorphous amount may not be within the range of the present invention. To achieve a crystallinity of 25% or more and 40% or less, for example, a homopolyester resin is used, the plane orientation coefficient of the film is set to 0.165 or more and 0.170 or less, and the heat treatment temperature is set to 150°C or more and 200°C or less, but other resins may also be mixed.

The polyester film of the present invention has an intrinsic viscosity of 0.66 or more and 0.95 or less. Here, the intrinsic viscosity is a value measured by the method described in (4) Intrinsic Viscosity described later. When the intrinsic viscosity is in this range, the entanglement of molecular chains increases, and deformation in the thickness direction, particularly puncture resistance, can be obtained. If the intrinsic viscosity is less than 0.66, the entanglement of molecular chains is insufficient, and sufficient drawing processability cannot be obtained. On the other hand, if the intrinsic viscosity exceeds 0.95, the filtration pressure during melt film formation increases, and the discharge amount must be reduced, resulting in poor productivity. The intrinsic viscosity can be adjusted by the raw materials used in melt film formation, and if it is desired to increase the intrinsic viscosity of the film, it is preferable to increase the intrinsic viscosity of the raw materials used during film formation. Considering both the molecular chain entanglement effect and productivity, the intrinsic viscosity is preferably 0.69 or more and 0.88 or less.

The polyester film of the present invention preferably has a 150°C heat shrinkage rate of 3.5% or more and 14.0% or less in both the longitudinal and transverse directions. When using the polyester film of the present invention for secondary processing involving heating, such as a lamination process in which molten resin is directly laminated to a film and heat of about 150°C is applied, the 150°C heat shrinkage rate is preferably 3.5% or more in order to suppress wrinkles during extrusion lamination. On the other hand, if the heat shrinkage rate of the temperature applied during lamination exceeds 14%, the film may deform too much during lamination due to heat shrinkage during lamination, causing problems. From the viewpoint of achieving both wrinkles and thermal deformation during lamination, the polyester film of the present invention preferably has a 150°C heat shrinkage rate of 10% or less in the longitudinal and transverse directions. In order to control the 150°C heat shrinkage rate in the longitudinal and transverse directions to 3.5% or more and 14.0% or less, the film area magnification should be set to 12.25 times or more, and the heat treatment temperature should be set to 160°C or more and 200°C or less.

The polyester film of the present invention preferably has a melting point (melting endothermic peak temperature (Tm)) of 248°C or higher as determined by a differential scanning calorimeter. When the polyester film of the present invention is used as an exterior material for a battery, the sealant layers are heat-sealed together to form a container. For this reason, it is necessary to suppress melting of the exterior film by the heat of heat sealing. If the melting endothermic peak temperature Tm is less than 248°C, the heating temperature during heat sealing must be lowered, and the time required to form a container by heat sealing increases, which may result in poor mass productivity. To achieve a melting endothermic peak temperature Tm of 248°C or higher, it is most preferable to use a homopolyester. From the viewpoint of processability, it is preferable that the temperature is 320°C or lower.

The polyester film of the present invention is mainly composed of polyester. Polyester is a general term for polymeric compounds in which the main bond in the main chain is an ester bond. Polyester can usually be obtained by polycondensation reaction of dicarboxylic acid or its derivative with diol or its derivative, and electrolyte resistance can be obtained by using polyester as the main component. In the present invention, "mainly composed" refers to a ratio of 60% by mass to 100% by mass of the entire object, and here refers to the ratio to the polyester film. Here, dicarboxylic acid unit (structural unit) or diol unit (structural unit) means a divalent organic group excluding the portion removed by polycondensation, and is represented by the following general formula.

Dicarboxylic acid unit (structural unit): -CO-R-CO-
Diol unit (structural unit): -O-R'-O-
(Here, R and R' are divalent organic groups. R and R' may be the same or different.)
Examples of diols or derivatives thereof which give the polyester used in the present invention include, in addition to ethylene glycol, aliphatic dihydroxy compounds such as 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, and neopentyl glycol; polyoxyalkylene glycols such as diethylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; alicyclic dihydroxy compounds such as 1,4-cyclohexanedimethanol and spiroglycol; aromatic dihydroxy compounds such as bisphenol A and bisphenol S; and derivatives thereof.
Examples of dicarboxylic acids or derivatives thereof that provide the polyester used in the present invention include, in addition to terephthalic acid, aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, and 5-sodiumsulfonedicarboxylic acid, aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, and fumaric acid, alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, and oxycarboxylic acids such as paraoxybenzoic acid, as well as derivatives thereof. Examples of dicarboxylic acid derivatives include esters of dimethyl terephthalate, diethyl terephthalate, 2-hydroxyethyl methyl terephthalate, dimethyl 2,6-naphthalenedicarboxylate, dimethyl isophthalate, dimethyl adipate, diethyl maleate, and dimethyl dimerate.

The polyester film of the present invention may have a single layer structure or a multi-layer structure of two or more layers. In the case of a multi-layer structure, a symmetrical structure with a central layer as the base point, such as B layer/A layer/B layer, is preferable from the viewpoint of suppressing warpage after film formation. If warpage occurs after film formation, the handling property may deteriorate in the subsequent battery manufacturing process. In addition, in the present invention, a five-layer structure such as B/A/B/A/B may be used. In the case of a multi-layer structure, a three-layer laminate structure of B/A/B is preferable from the viewpoint of warpage after film formation. In the present invention, if the film has a two-layer structure such as A layer/B layer with different molecular orientations, warpage may occur immediately after film formation. However, as long as the effect of the present invention is not hindered, an asymmetric structure such as a two-layer structure of A/B may be used.
In order to improve the drawing property, the polyester film of the present invention preferably has a dynamic friction coefficient μd of 0.3 or less on the contact surface with the die. By setting the dynamic friction coefficient in the above range, the deformation resistance during drawing is reduced, and the processability is improved. There is no particular limitation on the dynamic friction coefficient of 0.3 or less, but for example, it is preferable that the outermost layer has a layer containing 0.3 mass% or more and 5 mass% or less of inorganic particles and/or organic particles with an average particle size of 0.005 μm to 10 μm. More preferably, it is 0.5 mass% to 3 mass%. However, if too many particles are added, the breaking elongation of the composite may be reduced. For this reason, it is important to add particles within a range that does not impede the present invention. In the present invention, particles having an average primary particle size of 0.005 μm or more are used. The particle size referred to here refers to the number average particle size, and means the particle size observed in the cross section of the film. If the shape is not a perfect circle, the value converted to a perfect circle with the same area is taken as the particle size. Here, the number average particle size Dn can be obtained by the following steps (1) to (4).
(1) First, a cross section of the film is cut in the thickness direction using a microtome without crushing it, and a magnified observation image is obtained using a scanning electron microscope. At this time, the cut is made in a direction parallel to the TD direction (transverse direction) of the film.
(2) Next, for each particle observed in the cross section of the image, its cross-sectional area S is calculated, and its particle diameter d is calculated using the following formula.

d=2×(S/π) ^1/2
(3) Using the obtained particle diameter d and the number n of resin particles, Dn is calculated according to the following formula.

Dn = Σd/n
where Σd is the sum of the particle diameters in the observation area, and n is the total number of particles in the observation area.
(4) The above (1) to (3) are carried out at five different locations, and the average value is the number-average particle size of the particles. The above evaluation is carried out on an area of 2500 μm2 ^or more for each observation point.

As inorganic particles, for example, wet and dry silica, colloidal silica, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, aluminum oxide, mica, kaolin, clay, etc. can be used. As organic particles, particles containing styrene, silicone, acrylic acids, methacrylic acids, polyesters, divinyl compounds, etc. can be used. Among them, it is preferable to use inorganic particles such as wet and dry silica, alumina, calcium carbonate, and particles containing styrene, silicone, acrylic acid, methacrylic acid, polyester, divinylbenzene, etc. as components. Furthermore, two or more of these inorganic particles and organic particles may be used in combination. It is also preferable to apply uneven processing such as embossing and sandblasting to the film surface in order to control the maximum surface height.

The thickness of the polyester film of the present invention is preferably 9 μm or more and 30 μm or less from the viewpoint of molding followability when made into a structure and warping after molding. It is most preferably 12 μm or more and 28 μm or less. Although it depends on the required drawing depth, if it is less than 9 μm, moldability may be poor, and if it is 30 μm or more, rigidity is high and warping may occur after molding.

In order to improve the adhesion to the adhesive layer, the polyester film used in the present invention may be subjected to a surface treatment such as corona treatment, plasma treatment, ozone treatment, or provision of an anchor coat layer. Examples of methods for forming an anchor coat layer include coating a resin on the film surface (composite melt extrusion method, hot melt coating method, in-line coating method using a solvent other than water, water-soluble and/or water-dispersible resin, offline coating method, etc.). Among these, the in-line coating method in which a coating agent is applied to one side of the film before the orientation crystallization is completed, stretched in at least one direction, and heat-treated to complete the orientation crystallization is preferred in terms of uniform coating formation and productivity. In addition, when an anchor coat layer is provided, the resin is not particularly limited, but for example, acrylic resin, urethane resin, polyester resin, olefin resin, fluorine resin, vinyl resin, chlorine resin, styrene resin, various graft resins, epoxy resin, silicone resin, etc. can be used, and a mixture of these resins can also be used. From the viewpoint of adhesion, it is preferable to use a polyester resin, an acrylic resin, or a urethane resin. When a polyester resin is used as a water-based coating liquid, a water-soluble or water-dispersible polyester resin is used, and in order to make it water-soluble or water-dispersible, it is preferable to copolymerize a compound containing a sulfonate group or a compound containing a carboxylate group. When an acrylic resin is used as a water-based coating liquid, it is necessary to make it dissolved or dispersed in water, and a surfactant (such as, but not limited to, a polyether compound) may be used as an emulsifier. In addition, in the anchor coat layer used in the present invention, various crosslinking agents can be used in combination with the resin to further improve adhesion. As the crosslinking agent resin, a melamine-based, epoxy-based, or oxazoline-based resin is generally used.
The polyester film of the present invention can be used in combination with various materials. For example, as the metal foil, aluminum, stainless steel, copper, nickel, titanium, tin, silver, gold, zinc, iron, etc. can be used according to the purpose. Among them, a layer containing aluminum is preferable from the viewpoint of formability, gas barrier property, water vapor barrier property, strength, and economical efficiency. The metal foil may be aluminum alone, or may be an aluminum alloy to which copper, zinc, manganese, magnesium, silicon, lithium, iron, etc. are added. The aluminum content of the metal foil is preferably 95 mass% or more, and pure aluminum or aluminum/iron alloy is preferably used.

The method of compounding the polyester film of the present invention with various materials is not particularly limited, but dry lamination, in which an adhesive layer made of an adhesive is provided and bonded, is preferably used from the viewpoint of adhesion. The adhesive used may be of the thermosetting type or the thermoplastic type, but the thermosetting type is preferable. For example, adhesives made of polyurethane resin, polyester resin, polyvinyl chloride resin, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, methyl methacrylate-butadiene copolymer, chloroprene, rubber resin such as polybutadiene, polyacrylic acid ester resin, polyvinylidene chloride resin, polybutadiene, or carboxyl modified products of these resins, epoxy resin, cellulose derivative, ethylene vinyl acetate copolymer, polyethylene oxide, acrylic resin, lignin derivative, etc. are listed. From the viewpoint of adhesion between the surface treatment surface of the polyester film and the metal foil, adhesives made of polyurethane resin and polyester resin are preferable.

In the present invention, the composite can be used as a structure in which a sealant layer is further provided on the composite from the viewpoint of improving heat sealability and barrier properties, and in which the structure is arranged in the order of polyester film/adhesive layer/metal foil/sealant layer. By using the above structure for battery exteriors, a battery packaging material with excellent electrolyte resistance and squeeze formability can be obtained. Examples of the sealant layer include ethylene-based resins such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, and ethylene-butene copolymers; propylene-based resins such as homopolypropylene, ethylene-propylene copolymer, and ethylene-propylene-butene copolymers; polyolefin resins such as methylpentene resins and cyclic olefin resins; polyvinyl chloride; copolymers of ethylene, propylene, vinyl acetate, allyl chloride, allyl glycidyl ether, acrylic acid esters, methacrylic acid esters, vinyl ethers, etc., which can be copolymerized with vinyl chloride monomers, and mixtures thereof.

The polyester film of the present invention is preferably used for battery exteriors. In order to maintain battery performance, battery exteriors require water vapor barrier properties to prevent the intrusion of water vapor, electrolyte resistance to prevent swelling with electrolyte and deterioration of the outermost exterior due to electrolyte leakage during the manufacturing process, and deep drawability to meet the need for higher capacity. By using the polyester film of the present invention, it has excellent deep drawability comparable to that of a polyamide structure, and by applying it to battery exterior applications, it has excellent productivity without process defects and can meet the needs for higher capacity.

The polyester film of the present invention is also preferably used for pharmaceutical packaging. Pharmaceutical packaging requires gas barrier properties and water vapor barrier properties to prevent deterioration of the contents, and is required to be printable so that it can accommodate printing specifications. Furthermore, there is an increasing need for deep draw formability to accommodate contents of various shapes. In order to achieve high gas barrier properties and water vapor barrier properties, it is preferable to have metal foil, but since deep draw forming is difficult for metal foil, it is necessary to laminate a film and form it following the film. By using the polyester film of the present invention, the deep draw formability of the composite formed by laminating various materials is good, and by applying it to pharmaceutical packaging applications, it can be applied to pharmaceuticals corresponding to various shapes.

The polyester film manufacturing method of the present invention will be illustrated. First, a polyester film is formed. To this end, the above-mentioned polyester raw material is melt-extruded by a known method and adhered to a casting drum adjusted to about 10°C to 35°C so that the polyester does not crystallize, to obtain a cast sheet. The adhesion method may be a known method such as an electrostatic application method or an air knife method. Next, the obtained cast sheet is biaxially stretched and oriented by a known method. The biaxial stretching may be a known method such as a sequential biaxial, simultaneous biaxial, or tubular method. During stretching, an anchor coat layer may be coated after uniaxial stretching in some cases. Here, it is important to set the stretch area ratio, which is the product of the stretch ratios of the first axis and the second axis, to 12.25 times or more in order to make the average work hardening index in the longitudinal direction and width direction of the polyester film 1.6 or more. For the same reason, the stretching temperature is preferably set to be equal to or higher than the glass transition temperature of the resin and equal to or lower than the glass transition temperature + 15°C. However, this is not limited as long as the effect of the present invention can be obtained. After biaxial stretching, it is preferable to perform heat treatment from the viewpoint of dimensional stability, etc. The heat treatment temperature is important in controlling the amount of rigid amorphous matter, and it is important to keep it at 200°C or less. From the viewpoint of dimensional stability, the heat treatment temperature is preferably 150°C or more. In this case, the heat treatment time is preferably in the range of 1 to 120 seconds or less. After the heat treatment, a surface treatment such as corona treatment is performed as necessary to improve adhesion to various materials, etc., to obtain a polyester film.

In the following, Examples 7, 8, and 12 shall be read as Reference Examples 7, 8, and 12.
(Evaluation Method)
Polyester films, composites and structures were produced and evaluated by the following methods.

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

(2) Film Thickness and Layer Thickness When measuring the thickness of the entire film, the film was cut into 200 mm x 300 mm pieces using a dial gauge, and the thickness was measured at five arbitrary locations on each sample, and the average was calculated. The thickness of each layer of the film, composite, and construct was determined by embedding the sample in epoxy resin, cutting out the film cross section with a microtome, and observing the cross section with a transmission electron microscope (TEM H7100, manufactured by Hitachi, Ltd.) at a magnification of 5000 times.

(3) Longitudinal and transverse directions of polyester film In the present invention, the breaking strength was measured in any one direction (0°) of the film and in directions at 15°, 30°, 45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°, and 165° from the arbitrary direction, and the direction with the highest breaking strength was defined as the transverse direction, and the direction perpendicular to the transverse direction was defined as the longitudinal direction. The breaking strength can be obtained by the method described in (8) Breaking strength of polyester film.

(4) Intrinsic Viscosity The solution viscosity of the polyester film of the present invention was measured in orthochlorophenol at 25° C. using an Ostwald viscometer, and the intrinsic viscosity was calculated from the solution viscosity. The unit of intrinsic viscosity is [dl/g]. The number of n was 3, and the average value was used.

(5) Planar orientation coefficient fn of polyester film
The layer for which the plane orientation coefficient was to be measured (hereinafter referred to as the measurement layer) was adhered to a glass surface using an Abbe refractometer, and the refractive indices (Nx, Ny, Nz) in the a direction, b direction, and thickness direction were measured using sodium D line as a light source, and the plane orientation coefficient fn of the measurement layer was calculated using the following formula.
Plane orientation coefficient fn = (Nx + Ny) / 2 - Nz
(6) Breaking elongation The film and the composite were cut into a rectangular sample of 150 mm long x 10 mm wide in the longitudinal and transverse directions. A tensile test was performed in the longitudinal and transverse directions of the film under conditions of 25°C and 63% Rh, with a crosshead speed of 300 mm/min, a width of 10 mm, and a sample length of 50 mm, using a tensile tester ("Tensilon AMF/RTA-100", an automatic film strength and elongation measuring device manufactured by Orientec Co., Ltd.), and the elongation at break was measured and the breaking elongation was determined as the value. The measurement was performed five times, and the average was used.

(7) Crystallinity: According to JIS K7122 (1999), a differential scanning calorimeter ROBOT DSC-RDC220 manufactured by Seiko Denshi Kogyo Co., Ltd. and a "Disk Session" SSC/5200 were used for data analysis, and 5 mg of a film sample was heated on an aluminum tray from room temperature to 300°C at a heating rate of 20°C/min, and held at 300°C for 5 minutes. The crystallinity was calculated from the endothermic peak heat ΔHm, cold crystallization heat ΔHc, and melting heat ΔHm0 (140.1 J/g) of perfectly crystalline PET obtained by the measurement according to the following formula.
Crystallinity (%) = (ΔHm-ΔHc)/ΔHm0x100
(8) Rigid Amorphous Amount The rigid amorphous amount was calculated from the mobile amorphous amount and crystallinity obtained by measurement according to the following formula.
Rigid amorphous amount (%) = 100 - (movable amorphous amount + crystallinity).
Theoretical specific heat difference of completely amorphous polyethylene terephthalate = 0.4052 J / (g ° C.)
In the present invention, the theoretical value of the specific heat difference of a completely amorphous material of polyethylene terephthalate was referred to.

The mobile amorphous amount was measured as follows.
Using a temperature modulated DSC manufactured by TA Instruments, 5 mg of a sample was measured in a nitrogen atmosphere at a temperature rise rate of 2° C./min from 0° C. to 150° C., with a temperature modulation amplitude of ±1° C. and a temperature modulation period of 60 seconds. The specific heat difference at the glass transition temperature obtained by the measurement was determined and calculated according to the following formula.
Mobile amorphous amount (%) = (specific heat difference) / (theoretical specific heat difference of completely amorphous polyester) x 100
Theoretical specific heat difference of completely amorphous polyethylene terephthalate = 0.4052 J / (g ° C.)
In the present invention, for those containing 70 mol % or more of polyethylene terephthalate units, the theoretical value of the specific heat difference of a completely amorphous material of polyethylene terephthalate was referenced.

(9) Glass transition temperature Tg, melting point (melting endothermic peak temperature Tm)
In accordance with JIS 7122 (1999), a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments) was used to heat 3 mg of resin in a nitrogen atmosphere from 30° C. to 300° C. at a rate of 20° C./min. The resin was then held at 300° C. for 5 minutes, and then cooled to 30° C. at a rate of 40° C./min. The resin was then held at 30° C. for 5 minutes, and then heated from 30° C. to 300° C. at a rate of 20° C./min. The glass transition temperature obtained during this temperature rise was calculated by the following formula (i).
Glass transition temperature=(extrapolated glass transition onset temperature+extrapolated glass transition end temperature)/2 (i)
Here, the extrapolated glass transition onset temperature is the temperature at the intersection of a straight line extending the low-temperature side baseline to the high-temperature side and a tangent drawn at the point where the gradient of the curve of the stepwise change in the glass transition is maximum.The extrapolated glass transition end temperature is the temperature at the intersection of a straight line extending the high-temperature side baseline to the low-temperature side and a tangent drawn at the point where the gradient of the curve of the stepwise change in the glass transition is maximum.The peak top of the endothermic peak associated with the crystal melting of the resin is taken as the melting point (melting endothermic peak temperature Tm).

(10) Work Hardening Index A film was cut into a rectangular sample having a length of 150 mm and a width of 10 mm in the longitudinal and transverse directions. A tensile test was performed in the longitudinal and transverse directions of the film under conditions of 25°C and 63% Rh using a tensile tester (Orientec Co., Ltd.'s automatic film strength and elongation measuring device "Tensilon AMF/RTA-100") with a crosshead speed of 300 mm/min, a width of 10 mm, and a sample length of 50 mm. When the initial length is ^L0 (mm), the length at 5% elongation is ^L1 (mm), the nominal stress at 5% elongation is ^P1 (MPa), the length at 60% elongation ^{is L2} (mm), and the nominal stress at 60% elongation is ^P2 (MPa), the true strain at 5% elongation is calculated from equation (1), the true strain at 60% elongation is calculated from equation (2), the true stress at 5% elongation is calculated from equation (3), and the true stress at 60% elongation is calculated from equation (4). From the values obtained from (1) to (4), the slope obtained from the equation when the X axis is the true strain and the Y axis is the true stress was taken as the work hardening index. This was measured five times in each of the longitudinal direction and the width direction, and the average value was used.

True strain at 5% elongation=Ln(L ¹ /L ⁰ ) (1)
True strain at 60% elongation = Ln ( ^L2 / ^L1 ) (2)
True stress at 5% elongation=P ¹ (1+Ln(L ¹ /L ⁰ )) (3)
True stress at 60% elongation=P ² (1+Ln(L ² /L ¹ )) (4)
*Ln: natural logarithm (11) Polyester film 150°C heat shrinkage in the width direction and longitudinal direction The film was cut into a rectangle of 150 mm length x 10 mm width in the longitudinal direction and width direction to prepare a sample. Marked lines were drawn on the sample at intervals of 100 mm, and a 3 g weight was hung and placed in a hot air oven heated to 150°C for 30 minutes to perform heat treatment. The distance between the marks after heat treatment was measured, and the heat shrinkage was calculated from the change in the distance between the marks before and after heating, which was taken as the heat shrinkage. Measurements were performed on five samples in the longitudinal direction and width direction, and the average value was used for evaluation.

(12) Dynamic friction coefficient of polyester film Using a slip tester manufactured by Toyo Seiki Co., Ltd., the stable region of the resistance value after the initial rise when both sides of the film were rubbed together was measured according to JIS-K7125 (1999), and the dynamic friction coefficient μd was obtained. The sample was a rectangle with a width of 80 mm and a length of 200 mm, and three sets (6 sheets) were cut out from the roll in the longitudinal direction of the rectangle. The measurement was performed three times, and the average value was calculated.

(13) Squeeze formability (a) Method of making a construct The construct is obtained by adhering the polyester film or polyamide film of the present invention (here, Bonyl RX25μm made by Kohjin was used) and metal foil via an adhesive layer. In addition, as the adhesive constituting the adhesive layer, Toyo Ink's "AD502" which is a urethane adhesive is used as the main agent, and the company's CAT10L is used as the crosslinking agent, and AD502, CAT10L, and ethyl acetate are mixed in a mass ratio of 15:1.5:25 to obtain a coating agent, which is applied to the surface-treated surface of the polyester film or polyamide film uniformly to 5g/m ² by dry lamination method, and the surface of the metal foil that has not been subjected to chemical conversion treatment and the adhesive-coated surface of the polyester film or polyamide film are pressed against a roll heated to 80°C at 0.5MPa while being heated and pressed, and then wound up. After that, the composition is aged at 60°C for 7 days to obtain a construct.

(b) Preparation of Composite A two-layer co-extruded film (maleic acid-modified polypropylene resin layer: 20 μm, polypropylene resin layer: 60 μm) in which maleic acid-modified polypropylene resin and polypropylene were co-extruded as a sealant layer was placed on the composite metal foil prepared in (a) so that the maleic acid-modified polypropylene resin layer was adhered to the metal foil side that had been subjected to chemical conversion treatment, and a laminator was used to heat-press the composite described in the Examples and Comparative Examples and the metal foil side to prepare a composite of polyester film or polyamide film/adhesive layer/metal foil/sealant layer.

The component obtained in (b) was cut into a size of 100 mm x 100 mm, and a mold consisting of a rectangular male mold of 50 mm x 30 mm (corner R between the surface in contact with the component and the side: 2 mm, FIG. 1) and a female mold with a clearance of 0.5 mm from the male mold (corner R between the surface in contact with the component and the side: 2 mm, FIG. 1) was used to set the component on the female mold so that the sealant side was on the male mold side, and press molding (pressure: 0.1 MPa, one shot 10 seconds) was performed, and the evaluation was performed according to the following criteria. Note that if pinholes or tears occurred in the laminate material after deep drawing, it was considered that deep drawing could not be performed.
S: Deep drawing was possible by 1 mm or more compared to the polyamide structure.
A: Deep drawing equivalent to that of a polyamide structure was possible. B: The drawing depth was within 1 mm lower than that of the A rating.
C: The drawing depth was within 1 mm lower than the B grade.
D: Poorer deep drawing formability than C grade.

(14) Wrinkles during extrusion lamination (13) Draw formability (b) A 60,000 ^mm2 piece cut out from a composite obtained by the method described in the composite production method was visually inspected and judged as follows.
A: No wrinkles were observed on the entire film.
Δ: Wrinkles of 5 mm or more were observed.

(Production of polyester film)
The resin constituting the polyester film used for film formation was a mixture of main raw materials, auxiliary raw materials, and particle masters in the types and ratios shown in Table 1 for each Example and Comparative Example. The main raw materials, auxiliary raw materials, and particle masters used in each Example and Comparative Example were prepared as follows.
Polyester A
A polyethylene terephthalate resin (intrinsic viscosity 0.72) containing 100 mol % of terephthalic acid as the dicarboxylic acid component and 100 mol % of ethylene glycol as the glycol component.
Polyester B
A polyethylene terephthalate resin (intrinsic viscosity 0.82) containing 100 mol % of a terephthalic acid component as a dicarboxylic acid component and 100 mol % of an ethylene glycol component as a glycol component.
Polyester C
A polyethylene terephthalate resin (intrinsic viscosity 0.92) containing 100 mol % of terephthalic acid as the dicarboxylic acid component and 100 mol % of ethylene glycol as the glycol component.
Polyester D
A polybutylene terephthalate resin (intrinsic viscosity 1.2) containing 100 mol % of terephthalic acid as the dicarboxylic acid component and 100 mol % of 1-4 butanediol as the glycol component.
Polyester E
A polyethylene terephthalate resin (intrinsic viscosity 0.65) containing 100 mol % of terephthalic acid as the dicarboxylic acid component and 100 mol % of ethylene glycol as the glycol component.
・Particle Master A
Polyethylene terephthalate particle master containing aggregated silica particles having an average particle size of 1.2 μm in polyester A at a particle concentration of 2% by mass.
・Particle Master B
Polybutylene terephthalate particle master containing aggregated silica particles having an average particle size of 1.2 μm in polyester D at a particle concentration of 2% by mass.

(Coating Agent A) Examples 1 to 11, Comparative Examples 1 to 3
Acrylic resin having a copolymer composition of methyl methacrylate / ethyl acrylate / acrylic acid / N-methylolacrylamide = 63 / 35 / 1 / 1 mass %: 3.00 mass %
Melamine crosslinking agent: 0.75% by mass
Colloidal silica particles (average particle size: 80 nm): 0.15% by mass
Hexanol: 0.26% by mass
Butyl cellosolve: 0.18% by mass
・Water: 95.66% by mass
(Metal foil)
The metal foil used in the present invention is as follows:
Metal foil A
The metal foil was made of aluminum "8021" manufactured by Nippon Foil Co., Ltd., and had a thickness of 40 μm, and was treated with chromate acid on both sides as a chemical conversion treatment.

(Examples 1 to 12, Comparative Examples 1 and 2)
Using an extruder, the polyester species and particle master listed in Table 1 were each dried in a vacuum dryer at 180°C for 4 hours to thoroughly remove moisture, and then the main raw materials, auxiliary raw materials, and particle master were charged into the extruder as listed in Table 1 and melted at 280°C. The resin melt-extruded from the extruder and discharged from the die were cooled and solidified on a cast drum cooled to 25°C to obtain an unstretched sheet. At that time, the distance between the lip of the T-die and the cooling drum was set to 35 mm, and a wire electrode with a diameter of 0.1 mm was used to apply electrostatic voltage of 14 kV to the sheet, thereby causing it to adhere to the cooling drum. The speed at which the unstretched sheet passed through the cooling drum was 25 m/min, and the contact length of the unstretched sheet with the cooling drum was 2.5 m.

The unstretched sheet was then preheated with a group of rolls heated to the temperatures shown in Table 2, and then stretched in the longitudinal direction (machine direction) to the ratios shown in Table 2 using heated rolls controlled to the temperatures shown in Table 2, and cooled with a group of rolls at a temperature of 25°C to obtain a uniaxially stretched film.

This uniaxially stretched film was subjected to a corona discharge treatment in air, and coating agent A was mixed as an anchor coat layer on the treated surface while being ultrasonically dispersed, and the surface was uniformly applied to the surface bonded to the cast using a #4 metaling bar for surface treatment. Next, while holding both ends of the uniaxially stretched film with clips, it was introduced into a preheating zone in a tenter controlled to the temperature shown in Table 2, and then continuously stretched in a heating zone maintained at the temperature shown in Table 2 in a direction perpendicular to the longitudinal direction (width direction) to the ratio shown in Table 2. Further, in the heat treatment zone in the tenter, heat treatment was performed for 20 seconds at the heat treatment temperature shown in Table 2, and further relaxation treatment was performed at the relaxation temperature shown in Table 2 with the relaxation ratio shown in Table 2. Next, it was uniformly cooled slowly to obtain a polyester film with the thickness shown in Table 1. The properties of the polyester film are as shown in Table 3.

The surface-treated side of the obtained polyester film was bonded to the metal foil A by dry lamination using a coating material made by mixing a urethane adhesive, Toyo Ink's "AD502", CAT10L, and ethyl acetate in a ratio of 25:15:2, as an adhesive layer. Here, the amount of adhesive applied was 5 g/ ^m2 as a solid content on the surface-treated side of the polyester film, and after bonding, the composite was subjected to aging treatment at 60°C for 144 hours to obtain a composite. The properties of the composite are as shown in Table 3.

A two-layer co-extruded film (maleic acid-modified polypropylene resin layer: 20 μm, polypropylene resin layer: 60 μm) made by co-extrusion of maleic acid-modified polypropylene resin and polypropylene as a sealant was laminated on the metal foil A of the obtained composite by heat-pressing (160°C, 0.3 MPa, 2 m/min) using a laminator, so that the maleic acid-modified polypropylene resin layer was positioned on the metal foil side, and a structure of polyester film/adhesive layer/aluminum foil/sealant was produced. The evaluation results of the obtained structure are shown in Table 3, and it was confirmed that Examples 1 to 12 had excellent draw formability.

The polyester film of the present invention exhibits draw formability equal to or greater than that of structures using polyamides by setting the work hardening index, intrinsic viscosity, and rigid amorphous content within specific ranges, and can be suitably used for battery exterior structures that support high capacity and pharmaceutical packaging structures that can be adapted to various shapes.

1 Component 2 Male mold 3 Female mold 4 Molded body

Claims (6)

A polyester film having a work-hardening index in both the longitudinal and transverse directions of 1.6 to 3.0, a difference between the work-hardening indexes in the longitudinal and transverse directions of 0.5 or less, an intrinsic viscosity of 0.66 to 0.95, a rigid amorphous amount of 28% to 60% , and a 150°C heat shrinkage rate in both the longitudinal and transverse directions of 3.5% to 10% (however, this does not include a polyester film having an elastic modulus in each of four directions, namely, 45°, 90°, and 135° clockwise from an arbitrary direction on the film surface being taken as 0°, within a range of 2.0 to 3.5 MPa in each direction) . The polyester film according to claim 1, having a melting point of 248°C or higher. The polyester film according to claim 1 or 2, having a crystallinity of 25% or more and 40% or less. A polyester film according to any one of claims 1 to 3, in which the breaking elongation in both the longitudinal and transverse directions is 100% or more. The polyester film according to any one of claims 1 to 4 is used for battery exterior packaging. The polyester film according to any one of claims 1 to 4, which is used for pharmaceutical packaging.

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